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  • 1.
    Abburu, Sai Kausik
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics, Vehicle Dynamics.
    Modelling Advanced Air Suspension with Electronic Level Control in ADAMS/Car2020Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Multi-body simulations are given more emphasis over physical tests owing toenvironmental, financial, and time requirements in the competitive automotive industry. Thus,it is imperative to develop models to accurately predict and analyse the system's behaviour.This thesis focuses on developing an air suspension model with Electronic Level Control thathas the ability to communicate with other air springs in a pneumatic circuit thus replicating thepneumatic connection in actual truck and regulate the ride height of the vehicle.To accomplish this, a comprehensive literature study is performed to identify an effectivecontrol variable to manipulate the air springs. This is done by understanding the working andthermodynamic principles of air suspension, understanding various Scania pneumaticconfigurations, and decrypting the working of the Electronic Level Control.Different methods for implementing the model through the identified control variable arediscussed. A brief explanation of the necessary physical tests performed to validate the modelis given. An extensive description of implementation of the static and dynamic model inADAMS through command batch script coding is provided.The developed static model is validated by comparing the results from simulations and the testdata. The axle weights have an error of maximum 6% and the pressure in the air springs havean error of maximum 9% which can be owed to neglection of hysteresis in the air springcharacteristics and using mean values to compare the data. The dynamic model is validated byaltering the ride height level and observing the response of the model. The results obtainedindicate the developed Electronic Level Control is able to regulate the ride height at the desiredlevel.The robustness of the model is validated by modifying the developed model for longitudinalpneumatic connection and for a truck with trailer model. The results indicate the developedmodel is capable to perform satisfactorily and conform to the Scania tolerance limits.Thus, an appropriate control variable for the air springs model is identified. Static and dynamicmodel to identify the suitable pressure in the air springs and thus, the force in the air springs isdeveloped which helped in drastically reducing the manual iterative work that was required.

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    fulltext
  • 2.
    Abburu, Sai Kausik
    KTH, School of Engineering Sciences (SCI), Centres, VinnExcellence Center for ECO2 Vehicle design. KTH, School of Engineering Sciences (SCI), Engineering Mechanics.
    Vehicle Conceptualisation, Compactness, and Subsystem Interaction: A network approach to design and analyse the complex interdependencies in vehicles2023Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    The conventional approach to vehicle design is restrictive, limited, andbiased. This often leads to sub-optimal utilisation of vehicle capabilities and allocated resources and ultimately entails the repercussions of designing andlater on an using an inefficient vehicle. To overcome these limitations, it is important to gain a deeper understanding of the interaction effects at component,subsystem, and system level. In this thesis, the research is focused on identifying appropriate methods and developing robust models to facilitate the interaction analysis.

    To scrutinise and identify appropriate methods, criteria were developed.Initially, the Design Structure Matrix (DSM) and its variations were examined.While DSM proved to be fundamental for capturing interaction effects,it lacked the ability to answer questions about the structure and behaviour ofinteractions and to predict unintended effects. Therefore, network theory wasexplored as a complementary method to DSM which was capable of providing insights into interaction structures and identifying influential variables.

    Subsequently, two criteria were established to identify subsystems significant to interaction analysis: high connectivity to other subsystems and multidisciplinary composition. The traction motor was observed to satisfyboth criteria as it had higher connectivity with other subsystems and was composed of multiple disciplines. Therefore, a detailed model of an induction motor was developed to enable the interaction analysis.

    The induction motor model was integrated into a cross-scalar design tool.The tool employed a two-step process: translating operational parametersto motor inputs using Newtonian equations and deriving physical attributes,performance characteristics, and performance attributes of the motor. Comparing the obtained performance characteristics curve against existing studiesvalidated the model’s reliability and capabilities. The design tool demonstrated adaptability to different drive cycles and the ability to modify motor performance without affecting operational parameters. Thus validating the capability of the design tool to capture cross-scalar and intra-subsystem interaction effects. To examine inter-subsystem interaction, a thermal model of an inverter was developed, capturing temperature variations in the power electronics based on motor inputs. The design tool successfully captured interaction effects between motor and inverter designs, highlighting the interplay with operational parameters.

    Thus, this thesis identifies methods for interaction analysis and develops robust subsystem models. The integrated design tool effectively captures intra-subsystem, inter-subsystem, and cross-scalar interaction effects. The research presented contributes to the overarching project goal of developing methods and models that capture interaction effects and in turn serve as a guiding tool for designers to understand the consequences of their design choices.

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    vccsi_sai_licentiate
  • 3.
    Abburu, Sai Kausik
    et al.
    KTH, School of Engineering Sciences (SCI), Centres, VinnExcellence Center for ECO2 Vehicle design. KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics.
    Casanueva, Carlos
    KTH, School of Engineering Sciences (SCI), Centres, VinnExcellence Center for ECO2 Vehicle design. KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics.
    O'Reilly, Ciarán J.
    KTH, School of Engineering Sciences (SCI), Centres, VinnExcellence Center for ECO2 Vehicle design. KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics.
    A Holistic Design Approach to the Mathematical Modelling of Induction Motors for Vehicle Design2023In: Procedia CIRP, 2023, Vol. 119, p. 1246-1251Conference paper (Refereed)
    Abstract [en]

    In early-stage vehicle design, there is a significant lack of knowledge about the impact of design requirements on the design of subsystems, theresulting knock-on effects between subsystems and the vehicle’s overall performance. This leads to a sub-optimal vehicle design with increaseddesign iterations. To mitigate this lack of knowledge, a cross-scalar design tool consisting of an induction motor model is presented in this paper.The tool calculates the motor’s attributes, namely its volume, mass, and the performance it can deliver to satisfy a given drive cycle’s requirements.This is achieved by breaking down the drive cycle requirements into motor parameters from which the various power losses are derived. Thesekey losses are then utilised to develop the torque/speed curve. Furthermore, it is proposed that the motor’s attributes can be used to design othersubsystems and consequently analyse their interaction effects. For example, the motor’s attributes can be used to design regenerative brakes andconsequently analyse their influence on brake wear, lifetime, and energy savings. Thus, the design tool enables the design of efficient vehicles withminimised design iterations by analysing the influence of design requirements on the subsystem’s design and the consequent interaction effectsamong the subsystems and on the vehicle’s overall performance.

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    math_model_motor_vehicle
  • 4.
    Abburu, Sai Kausik
    et al.
    KTH, School of Engineering Sciences (SCI), Centres, VinnExcellence Center for ECO2 Vehicle design. KTH, School of Engineering Sciences (SCI), Engineering Mechanics.
    Casanueva, Carlos
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics. KTH, School of Engineering Sciences (SCI), Centres, VinnExcellence Center for ECO2 Vehicle design.
    O'Reilly, Ciarán J.
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics. KTH, School of Engineering Sciences (SCI), Centres, VinnExcellence Center for ECO2 Vehicle design.
    Analyzing interaction effects in a vehicle model using network theory2021In: Resource Efficient Vehicles Conference, rev2021, 2021Conference paper (Other academic)
    Abstract [en]

    The vehicle industry is moving towards developing more sustainable and efficient solutions. This movement towards sustainable and efficient solutions brings up the need to develop and integrate new subsystem technologies that are beneficial for the overall vehicle system. However, introducing new technology into an existing vehicle architecture may have knock-on effects on the dependent subsystems. Furthermore, there can be a bias towards the existing technological solutions as a large part of the architecture is developed pertaining to the established solutions. Therefore, sufficient knowledge is required to understand the level of impact the interdependencies, both direct and indirect, can have at a subsystem level and at the overall vehicle system level. To address and assess these interdependencies that arise during the conceptual design phase, a bottom-up design model is proposed. The model, utilizing network theory could represent each subsystem as nodes and their interaction effects on each other as edges. Thus, the interaction effects between different subsystems and their complex influence on the overall vehicle system are considered. This model could serve to evaluate an optimal solution in terms of functional density and economic benefits thus providing the opportunity to avoid any unintended negative indirect effects. Furthermore, it could help in identifying the technological limits in the current vehicle system and thus, identifying the areas that can be developed to further enhance the vehicle system performance. The method of implementation, its advantages, disadvantages, applications, and challenges in implementation are discussed.

  • 5.
    Abburu, Sai Kausik
    et al.
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle engineering and technical acoustics. KTH, School of Engineering Sciences (SCI), Centres, VinnExcellence Center for ECO2 Vehicle design.
    Casanueva, Carlos
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics. KTH, School of Engineering Sciences (SCI), Centres, VinnExcellence Center for ECO2 Vehicle design.
    O'Reilly, Ciarán J.
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics. KTH, School of Engineering Sciences (SCI), Centres, VinnExcellence Center for ECO2 Vehicle design.
    Network Theory Approach to Analysing Knock-On Effects in Rail Vehicle Design2024In: The Sixth International Conference on Railway Technology: Research, Development and Maintenance, 2024Conference paper (Refereed)
    Abstract [en]

    Rail vehicle models have become increasingly complex, posing challenges in extracting insights using traditional model representations as they require numerous iterations to achieve a satisfactory solution. This complexity leads to high computational and time costs and possibly resulting in inefficient vehicle design. To alleviate these limitations, network models are proposed as an alternative representation in this paper. These models enable the analysis of structure, behaviour, and patterns of interactions, facilitating an understanding of knock-on effects across disciplines and subsystems. The terminology, benefits, and capabilities of network theory in early-stage vehicle design are presented in this paper, along with the aspects to consider and methods for developing network models. The applicability of network theory metrics and algorithms is demonstrated using a railway traction system example. Results indicate that the proposed representations can capture complex system knock-on effects across disciplines and subsystems.

  • 6.
    Abdulla, Hind
    et al.
    Khalifa Univ Sci & Technol, Engn Syst & Management, POB 127788, Abu Dhabi, U Arab Emirates.;Khalifa Univ Sci & Technol, Adv Digital & Addit Mfg Ctr, POB 127788, Abu Dhabi, U Arab Emirates..
    An, Heungjo
    Kumoh Natl Inst Technol, Sch Ind Engn, Gumi 39177, South Korea..
    Barsoum, Imad
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics. Khalifa Univ Sci & Technol, Adv Digital & Addit Mfg Ctr, POB 127788, Abu Dhabi, U Arab Emirates.;Khalifa Univ Sci & Technol, Mech Engn, POB 127788, Abu Dhabi, U Arab Emirates..
    Maalouf, Maher
    Khalifa Univ Sci & Technol, Engn Syst & Management, POB 127788, Abu Dhabi, U Arab Emirates.;Khalifa Univ Sci & Technol, Res Ctr Digital Supply Chain & Operat, POB 127788, Abu Dhabi, U Arab Emirates..
    Mathematical Modeling of Multi-Performance Metrics and Process Parameter Optimization in Laser Powder Bed Fusion2022In: Metals, ISSN 2075-4701, Vol. 12, no 12, article id 2098Article in journal (Refereed)
    Abstract [en]

    This study aims to develop mathematical models to improve multi-performance metrics, such as relative density and operating costs, in laser powder bed fusion (LPBF), also known as selective laser melting, a metallic additive manufacturing technique, by optimizing the printing process parameters. The work develops a data-driven model for relative density based on measurements and an analytical model for operating costs related to the process parameters. Optimization models are formulated to maximize relative density or minimize operating costs by determining the optimal set of process parameters, while meeting a target level of the other performance metrics (i.e., relative density or operating costs). Furthermore, new metrics are devised to test the sensitivity of the optimization solutions, which are used in a novel robust optimization model to acquire less sensitive process parameters. The sensitivity analysis examines the effect of varying some parameters on the relative density of the fabricated specimens. Samples with a relative density greater than 99% and a machine operating cost of USD 1.00 per sample can be produced, utilizing a combination of low laser power (100 W), high scan speed (444 mm/s), moderate layer thickness (0.11 mm), and large hatch distance (0.4 mm). This is the first work to investigate the relationship between the quality of the fabricated samples and operating cost in the LPBF process. The formulated robust optimization model achieved less sensitive parameter values that may be more suitable for real operations. The equations used in the models are verified via 10-fold cross-validation, and the predicted results are further verified by comparing them with the experimental data in the literature. The multi-performance optimization models and framework presented in this study can pave the way for other additive manufacturing techniques and material grades for successful industrial-level implementation.

  • 7.
    Abdulrazaq, Muhammed
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics.
    Extensional Instability in Complex Fluids: A Computational Study2020Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    In this study, instability and failure in complex fluids (Elastoviscoplastic fluids) is explored using the classic Considère (F˙ < 0) and stress curvature (σ¨ < 0) criteria. Employing the Saramito model, numerical simulation of the extensional protocol on non-Newtonian fluids is carried out. Validation is firstly performed (with a purely viscoelastic model) and in general found to be in agreement with previous works. Parameter variation of the Bingham number (Bi), capillary number (Ca) and extension rate (ε˙) is then undertaken. It is found out that for Oldroyd-B based fluids, the stress curvature condition almost always occurs from inception of the flow for all cases. Additionally, increasing surface tension has a stabilizing effect on the extending fluid when it is below a critical value, above which it aids breakup. Increasing the yield stress, though, delays the onset of instability, but reduces the final length of the extending filament. At mild to high extension rates, the Considère criterion and the extension at the maximum stress are suit-able indicators of the final extension at strain-to-break(εST B). Furthermore, the rate of the of necking instability till final breakup varies with the εST B at moderate to high ε˙.

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  • 8. Abdulrazaq, Muhammed
    et al.
    Shahmardi, Armin
    KTH, Centres, SeRC - Swedish e-Science Research Centre. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Engineering Sciences (SCI), Engineering Mechanics.
    Edoardo Rost, Marco
    Brandt, Luca
    KTH, Centres, SeRC - Swedish e-Science Research Centre. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics. Department of Energy and Process Engineering, Norwegian University of Science and Technology (NTNU), Trondheim, Norway.
    Numerical modelling of the extensional dynamics in elastoviscoplastic fluidsManuscript (preprint) (Other academic)
    Abstract [en]

    The extensional dynamics of an elasto-viscoplastic (EVP) fluid is studied by means of numerical simulations closely modelling an experimental configuration.  Specifically, we track the interface between the EVP material and the Newtonian medium using an algebraic volume of fluid method (MTHINC-VOF) and employ a fully Eulerian immersed boundary method (IBM) to model the motion of the piston responsible of the extension of the material.

    We investigate the role of different values of the yield stress, surface tension at the interface between the EVP material and the surrounding fluid, polymer viscosity ratio, and extension rates on the necking thickness of the material, extensional viscosity, and yielding of the material. 

     The results of the simulations reveal that when the yield stress of the EVP material is much larger than the viscous stresses, the material undergoes an elastic deformation, regardless of the selected values of extension rate, interfacial forces, and viscosity ratio. Moreover, increasing the ratio of the polymeric viscosity to the total viscosity of the system accelerates the EVP rupture due to the high stress concentration in the central part of the material sample. Specific and novel to our study, we show that interfacial forces cannot be ignored when the surface tension coefficient is such that a Capillary number based on the extensional rate is order 1. For large values of the surface tension coefficient, the EVP material fails sooner, with a clear deviation from the exponential reduction in the neck thickness.

  • 9.
    Abdulrazaq, Muhammed
    et al.
    Eindhoven Univ Technol, Dept Appl Phys, Fluids & Flows Grp, POB 513, NL-5600 MB Eindhoven, Netherlands..
    Shahmardi, Armin
    KTH, Centres, SeRC - Swedish e-Science Research Centre. KTH, School of Engineering Sciences (SCI), Engineering Mechanics.
    Rosti, Marco Edoardo
    Grad Univ, Okinawa Inst Sci & Technol, Complex Fluids & Flows Unit, 1919-1 Tancha, Onna Son, Okinawa 9040495, Japan..
    Brandt, Luca
    KTH, Centres, SeRC - Swedish e-Science Research Centre. KTH, School of Engineering Sciences (SCI), Engineering Mechanics.
    Numerical modelling of the extensional dynamics in elastoviscoplastic fluids2023In: Journal of Non-Newtonian Fluid Mechanics, ISSN 0377-0257, E-ISSN 1873-2631, Vol. 318, article id 105060Article in journal (Refereed)
    Abstract [en]

    The extensional dynamics of an elasto-viscoplastic (EVP) fluid is studied by means of numerical simulations modelling an experimental configuration. Specifically, we track the interface between the EVP material and the Newtonian medium using an algebraic volume of fluid method (MTHINC-VOF) and employ a fully Eulerian immersed boundary method (IBM) to model the motion of the piston responsible for the extension of the material. We investigate the role of different values of the yield stress, surface tension at the interface between the EVP material and the surrounding fluid, polymer viscosity ratio, and extension rates on the necking thickness of the material, extensional viscosity, and yielding of the material for two sets of parameter with low and high elasticity. The results of the simulations reveal that when the yield stress of the EVP material is much larger than the viscous stresses, the material undergoes an elastic deformation, regardless of the selected values of the extension rate, interfacial forces, and viscosity ratio. Moreover, by increasing the ratio of the polymeric viscosity to the total viscosity of the system, the EVP material produces stronger strain hardening and reaches the minimum resolvable width sooner. Specific and novel to our study, we show that interfacial forces cannot be ignored when the surface tension coefficient is such that a Capillary number based on the extensional rate is of order 1. For large values of the surface tension coefficient, the EVP material fails sooner, with a clear deviation from the exponential reduction in the neck thickness. Moreover, our results suggest that the role of the yield stress value on the dynamics of the material is more pronounced at lower elasticity.

  • 10.
    Aberg, Anna Cristina
    et al.
    Uppsala Univ, Dept Publ Hlth & Caring Sci, Geriatr, BMC, Box 564, SE-75122 Uppsala, Sweden.;Dalarna Univ, Sch Hlth & Welf, SE-79188 Falun, Sweden..
    Olsson, Fredrik
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics.
    Ahman, Hanna Bozkurt
    Uppsala Univ, Dept Publ Hlth & Caring Sci, Geriatr, BMC, Box 564, SE-75122 Uppsala, Sweden..
    Tarassova, Olga
    Swedish Sch Sport & Hlth Sci, Lidingovagen 1, SE-11486 Stockholm, Sweden..
    Arndt, Anton
    Swedish Sch Sport & Hlth Sci, Lidingovagen 1, SE-11486 Stockholm, Sweden.;Karolinska Inst, SE-17177 Stockholm, Sweden..
    Giedraitis, Vilmantas
    Uppsala Univ, Dept Publ Hlth & Caring Sci, Geriatr, BMC, Box 564, SE-75122 Uppsala, Sweden.;Dalarna Univ, Sch Hlth & Welf, SE-79188 Falun, Sweden..
    Berglund, Lars
    Uppsala Univ, Dept Publ Hlth & Caring Sci, Geriatr, BMC, Box 564, SE-75122 Uppsala, Sweden.;Dalarna Univ, Sch Hlth & Welf, SE-79188 Falun, Sweden..
    Halvorsen, Kjartan
    Dalarna Univ, Sch Hlth & Welf, SE-79188 Falun, Sweden.;Tecnol Monterrey, Sch Sci & Engn, Dept Mechatron, Campus Estado Mexico, Atizapan 52926, Estado Mexico, Mexico..
    Extraction of gait parameters from marker-free video recordings of Timed Up-and-Go tests: Validity, inter- and intra-rater reliability2021In: Gait & Posture, ISSN 0966-6362, E-ISSN 1879-2219, Vol. 90, p. 489-495Article in journal (Refereed)
    Abstract [en]

    Background: We study dual-task performance with marker-free video recordings of Timed Up-and-Go tests (TUG) and TUG combined with a cognitive/verbal task (TUG dual-task, TUGdt). Research question: Can gait parameters be accurately estimated from video-recorded TUG tests by a new semiautomatic method aided by a technique for human 2D pose estimation based on deep learning? Methods: Thirty persons aged 60-85 years participated in the study, conducted in a laboratory environment. Data were collected by two synchronous video-cameras and a marker-based optoelectronic motion capture system as gold standard, to evaluate the gait parameters step length (SL), step width (SW), step duration (SD), single-stance duration (SSD) and double-stance duration (DSD). For reliability evaluations, data processing aided by a deep neural network model, involved three raters who conducted three repetitions of identifying anatomical keypoints in recordings of one randomly selected step from each of the participants. Validity was analysed using 95 % confidence intervals (CI) and p-values for method differences and Bland-Altman plots with limits of agreement. Inter- and intra-rater reliability were calculated as intraclass correlation coefficients (ICC) and standard errors of measurement. Smallest detectable change was calculated for inter-rater reliability. Results: Mean ddifferences between video and the motion capture system data for SW, DSD, and SSD were significant (p < 0.001). However, mean differences for all parameters were small (-6.4%-13.0% of motion capture system) indicating good validity. Concerning reliability, almost all 95 % CI of the ICC estimates exceeded 0.90, indicating excellent reliability. Only inter-rater reliability for SW (95 % CI = 0.892;0.973) and one rater's intrarater reliability for SSD (95 % CI = 0.793;0.951) were lower, but still showed good to excellent reliability. Significance: The presented method for extraction of gait parameters from video appears suitable for valid and reliable quantification of gait. This opens up for analyses that may contribute to the knowledge of cognitivemotor interference in dual-task testing.

  • 11.
    Abramović, Borna
    et al.
    University of Zagreb, University of Zagreb.
    Bardhi, Arbra
    Sapienza University of Rome, Sapienza University of Rome.
    Casanueva Perez, Carlos
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics.
    Dolinayová, Anna
    University of Zilina, University of Zilina.
    Domeny, Igor
    University of Zilina, University of Zilina.
    Hadeed, Reem
    Aston University, Aston University.
    Lehnert, Martin
    TH Wildau, TH Wildau.
    Marinov, Marin
    Aston University, Aston University.
    Martini, Francesco
    Sapienza University of Rome, Sapienza University of Rome.
    Osdoba, Anne Katrin
    TH Wildau.
    Ricci, Stefano
    Sapienza University of Rome, Sapienza University of Rome.
    Šipuš, Denis
    University of Zagreb, University of Zagreb.
    Rail higher education in Europe: Current situation analysis for future developments2023In: Ingegneria Ferroviaria, ISSN 0020-0956, Vol. 78, no 4, p. 331-346Article in journal (Refereed)
    Abstract [en]

    The paper aims at describing the activities developed within the project ASTONRAIL (Advanced approaches and practices for rail training and education to innovate rail study programmes & improve rail higher education provision), funded by ERASMUS+ Programme. The project target is to provide a portfolio of new rail skills development strategies, approaches and professional practices in order to strengthen and modernize Europe’s current rail higher education system.

  • 12. Abreu, L. I.
    et al.
    Cavalieri, A. V. G.
    Schlatter, Philipp
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics.
    Vinuesa, Ricardo
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics.
    Henningson, Dan S.
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, Centres, SeRC - Swedish e-Science Research Centre.
    Reduced-order models to analyse coherent structures in turbulent pipe flow2019In: 11th International Symposium on Turbulence and Shear Flow Phenomena, TSFP 2019, International Symposium on Turbulence and Shear Flow Phenomena, TSFP , 2019Conference paper (Refereed)
    Abstract [en]

    Fully resolved direct numerical simulations, performed with a high-order spectral-element method, are used to study coherent structures in turbulent pipe flow at friction Reynolds numbers Reτ = 180 and 550 (El Khoury et al., 2013). The database was analysed using spectral proper orthogonal decomposition (SPOD) so as to identify dominant coherent structures, most of which are of streaky shape. As a reduced-order model for such structures, the linearised flow response to harmonic forcing was computed, and the analysed singular modes of the resolvent operator were analysed. For turbulent flows, this approach amounts to considering the non-linear terms in the Navier–Stokes system as an unknown forcing, treated convenienty as external. Resolvent analysis then allows an identification of the optimal forcing and most amplified flow response; the latter may be related to observed relevant structures obtained by SPOD, especially if the gain between forcing and response is much larger than what is found for suboptimal forcings or if the non-linear forcing is white noise. Results from SPOD and resolvent analysis were extracted for several combinations of frequencies, streamwise and azimuthal wavenumbers. For both Reynolds numbers, good agreement between SPOD and resolvent modes was observed for parameter combinations where the lift-up mechanism is present: optimal forcing from resolvent analysis represents streamwise vortices and the associated response are streaky structures.

  • 13. Abreu, Leandra, I
    et al.
    Cavalieri, Andre V. G.
    Schlatter, Philipp
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics.
    Vinuesa, Ricardo
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Henningson, Dan S.
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Resolvent modelling of near-wall coherent structures in turbulent channel flow2020In: International Journal of Heat and Fluid Flow, ISSN 0142-727X, E-ISSN 1879-2278, Vol. 85, article id 108662Article in journal (Refereed)
    Abstract [en]

    Turbulent channel flow was analysed using direct numerical simulations at friction Reynolds numbers Re-tau = 180 and 550. The databases were studied using spectral proper orthogonal decomposition (SPOD) to identify dominant near-wall coherent structures, most of which turn out to be streaks and streamwise vortices. Resolvent analysis was used as a theoretical approach to model such structures, as it allows the identification of the optimal forcing and most amplified flow response; the latter may be related to the observed relevant structures obtained by SPOD, especially if the gain between forcing and response is much larger than what is found for suboptimal forcings or if the non-linear forcing is white noise. Results from SPOD and resolvent analysis were compared for several combinations of frequencies and wavenumbers. For both Reynolds numbers, the best agreement between SPOD and resolvent modes was observed for the cases where the lift-up mechanism from resolvent analysis is present, which are also the cases where the optimal resolvent gain is dominant. These results confirm the outcomes in our previous studies (Abreu et al., 2019; Abreu et al., 2020), where we used a DNS database of a pipe flow for the same Reynolds numbers.

  • 14.
    Abreu, Leandra, I
    et al.
    Sao Paulo State Univ UNESP, Campus Sao Joao da Boa Vista, BR-13876750 Sao Joao da Boa Vista, SP, Brazil.;Inst Tecnol Aeronaut, Div Engn Aeronaut, BR-12228900 Sao Jose Dos Campos, SP, Brazil..
    Cavalieri, Andre V. G.
    Inst Tecnol Aeronaut, Div Engn Aeronaut, BR-12228900 Sao Jose Dos Campos, SP, Brazil..
    Schlatter, Philipp
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics.
    Vinuesa, Ricardo
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics.
    Henningson, Dan S.
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics, Stability, Transition and Control.
    Spectral proper orthogonal decomposition and resolvent analysis of near-wall coherent structures in turbulent pipe flows2020In: Journal of Fluid Mechanics, ISSN 0022-1120, E-ISSN 1469-7645, Vol. 900, article id A11Article in journal (Refereed)
    Abstract [en]

    Direct numerical simulations, performed with a high-order spectral-element method, are used to study coherent structures in turbulent pipe flow at friction Reynolds numbers Re-tau = 180 and 550. The database was analysed using spectral proper orthogonal decomposition (SPOD) to identify energetically dominant coherent structures, most of which turn out to be streaks and quasi-streamwise vortices. To understand how such structures can be modelled, the linear flow responses to harmonic forcing were computed using the singular value decomposition of the resolvent operator, using the mean field as a base flow. The SPOD and resolvent analysis were calculated for several combinations of frequencies and wavenumbers, allowing the mapping out of similarities between SPOD modes and optimal responses for a wide range of relevant scales in turbulent pipe flows. In order to explore physical reasons behind the agreement between both methods, an indicator of lift-up mechanism in the resolvent analysis was introduced, activated when optimal forcing is dominated by the wall-normal and azimuthal components, and associated response corresponds to streaks of streamwise velocity. Good agreement between leading SPOD and resolvent modes is observed in a large region of parameter space. In this region, a significant gain separation is found in resolvent analysis, which may be attributed to the strong amplification associated with the lift-up mechanism, here understood as nonlinear forcing terms leading to the appearance of streamwise vortices, which in turn form high-amplitude streaks. For both Reynolds numbers, the observed concordances were generally for structures with large energy in the buffer layer. The results highlight resolvent analysis as a pertinent reduced-order model for coherent structures in wall-bounded turbulence, particularly for streamwise elongated structures corresponding to near-wall streamwise vortices and streaks.

  • 15.
    Abreu, Leandra, I
    et al.
    Sao Paulo State Univ UNESP, Campus Sao Joao Boa Vista, BR-13876750 Sao Joao Da Boa Vista, SP, Brazil.;Inst Tecnol Aeronaut, Div Engn Aeronaut, BR-12228900 Sao Jose Dos Campos, SP, Brazil..
    Tanarro, Alvaro
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Cavalieri, Andre V. G.
    Inst Tecnol Aeronaut, Div Engn Aeronaut, BR-12228900 Sao Jose Dos Campos, SP, Brazil..
    Schlatter, Philipp
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics.
    Vinuesa, Ricardo
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics.
    Hanifi, Ardeshir
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics.
    Henningson, Dan S.
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics.
    Spanwise-coherent hydrodynamic waves around flat plates and airfoils2021In: Journal of Fluid Mechanics, ISSN 0022-1120, E-ISSN 1469-7645, Vol. 927, article id A1Article in journal (Refereed)
    Abstract [en]

    We investigate spanwise-coherent structures in the turbulent flow around airfoils, motivated by their connection with trailing-edge noise. We analyse well-resolved large-eddy simulations (LES) of the flow around NACA 0012 and NACA 4412 airfoils, both at a Reynolds number of 400 000 based on the chord length. Spectral proper orthogonal decomposition performed on the data reveals that the most energetic coherent structures are hydrodynamic waves, extending over the turbulent boundary layers around the airfoils with significant amplitudes near the trailing edge. Resolvent analysis was used to model such structures, using the mean field as a base flow. We then focus on evaluating the dependence of such structures on the domain size, to ensure that they are not an artefact of periodic boundary conditions in small computational boxes. To this end, we performed incompressible LES of a zero-pressure-gradient turbulent boundary layer, for three different spanwise sizes, with the momentum-thickness Reynolds number matching those near the airfoils trailing edge. The same coherent hydrodynamic waves were observed for the three domains. Such waves are accurately modelled as the most amplified flow response from resolvent analysis. The signature of such wide structures is seen in non-premultiplied spanwise wavenumber spectra, which collapse for the three computational domains. These results suggest that the spanwise-elongated structures are not domain-size dependent for the studied simulations, indicating thus the presence of very wide structures in wall-bounded turbulent flows.

  • 16.
    Abreu, Leandra I.
    et al.
    Divisão de Engenharia Aeronáutica, Instituto Tecnológico de Aeronáutica, 12228-900, São José dos Campos, SP, Brazil.
    Tanarro, Alvaro
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, Centres, SeRC - Swedish e-Science Research Centre. KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics.
    Cavalieri, André V.G.
    Divisão de Engenharia Aeronáutica, Instituto Tecnológico de Aeronáutica, 12228-900, São José dos Campos, SP, Brazil.
    Schlatter, Philipp
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, Superseded Departments (pre-2005), Mechanics. KTH, Centres, SeRC - Swedish e-Science Research Centre.
    Vinuesa, Ricardo
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, Centres, SeRC - Swedish e-Science Research Centre.
    Hanifi, Ardeshir
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, Centres, SeRC - Swedish e-Science Research Centre.
    Henningson, Dan S.
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, Superseded Departments (pre-2005), Mechanics. KTH, Centres, SeRC - Swedish e-Science Research Centre.
    Wavepackets in turbulent flows around airfoilsManuscript (preprint) (Other academic)
    Abstract [en]

    Motivated by the recent analysis by Sano et al. 2019, Phys. Rev. Fluids, vol. 4, p. 094602, of spanwise-coherent structures in the turbulent flow around airfoils and their connection to trailing-edge noise, we carry out a thorough characterisation of such structures in three simulation databases. We analyse two different numerical simulations of incompressible flow in turbulent regime, both at chord Reynolds number of 400,000: a large-eddy simulation for a NACA 0012 profile at zero angle of attack, and a direct numerical simulation for a NACA 4412 airfoil with an angle of attack of 5 degrees. Snapshots of the flow field were analysed using Spectral Proper Orthogonal Decomposition (SPOD), in order to extract the dominant coherent structures of the flow. Focus is given to  the aforementioned spanwise-coherent fluctuations, which two-dimensional disturbances in the computational domain due to the use of periodic boundary conditions. The leading SPOD modes show that the most energetic coherent structures are wavepackets, extending over the whole turbulent boundary layers around the airfoils with significant amplitudes near the trailing-edge. Higher amplitudes are observed in the region of  stronger adverse pressure gradient at the suction side of the NACA 4412 airfoil. To understand how such structures in the turbulent field can be modelled, the linear response of the flow using the singular value decomposition of the linearised resolvent operator was performed, using the mean field as a base flow and considering a locally parallel approximation. Such analysis shows that the leading SPOD modes can be associated to optimal, linearised flow responses, particularly for stations far from the trailing edge; the latter introduces a discontinuity in boundary conditions, and the locally parallel approximation becomes questionable. We then focus on evaluating the dependence of such wavepackets on the domain size, to ensure that these structures are not an artifact of the use of periodic boundary conditions in small computational boxes. To do so, we performed an incompressible LES of a zero-pressure gradient turbulent boundary layer (ZPGTBL), for three different spanwise sizes: Lz=32 δ*, Lz=64 δ* and Lz=128 δ*, where δ* is a reference displacement thickness in a region of developed turbulent flow, with Reynolds number matching the values in the airfoil simulations. The signature of such wavepackets is seen in non-premultiplied spanwise wavenumber spectra, which reaches, for the three domain sizes, a plateau for spanwise wavelengths going to infinity (or wavenumbers going to zero); this plateau is representative of the spanwise-coherent structures seen in the airfoil simulations. Similar SPOD and resolvent analyses were carried out for the zero spanwise wavenumber of the ZPGTBL, and the same coherent wavepackets were observed for the three domains, with very similar amplitudes. Such wavepackets were also accurately modelled using the optimal resolvent response. These results confirm that the spanwise-elongated structures are not domain-size dependent for the studied simulations, and are thus a feature of turbulent boundary layers.

  • 17.
    Afshari, Davood
    et al.
    Univ Zanjan, Zanjan, Iran..
    Ghaffari, Ali
    Univ Zanjan, Zanjan, Iran..
    Barsoum, Zuheir
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics.
    Optimization in the Resistant Spot-Welding Process of AZ61 Magnesium Alloy2022In: Strojniski vestnik, ISSN 0039-2480, Vol. 68, no 7-8, p. 485-492Article in journal (Refereed)
    Abstract [en]

    In this paper, an integrated artificial neural network (ANN) and multi-objective genetic algorithm (GA) are developed to optimize the resistance spot welding (RSW) of AZ61 magnesium alloy. Since the stability and strength of a welded joint are strongly dependent on the size of the nugget and the residual stresses created during the welding process, the main purpose of the optimization is to achieve the maximum size of the nugget and minimum tensile residual stress in the weld zone. It is identified that the electrical current, welding time, and electrode force are the main welding parameters affecting the weld quality. The experiments are carried out based on the full factorial design of experiments (DOE). In order to measure the residual stresses, an X-ray diffraction technique is used. Moreover, two separate ANNs are developed to predict the nugget size and the maximum tensile residual stress based on the welding parameters. The ANN is integrated with a multi-objective GA to find the optimum welding parameters. The findings show that the integrated optimization method presented in this study is effective and feasible for optimizing the RSW joints and process.

  • 18.
    Aghaei, Shayan
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics, Vehicle Dynamics.
    Acoustic Radiation Of An Automotive Component Using Multi-Body Dynamics2020Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    An important facet of creating high-quality vehicles is to create components that are quiet and smooth under operation. In reality, however, it is challenging to measure the sound that some automotive components make under load because it requires specialist facilities and equipment which are expensive to acquire. Furthermore, the motors used in testbeds drown out the noise emitted from much quieter components, such as a Power Transfer Unit (PTU). This thesis aims to solve these issues by outlining the steps required to virtually estimate the acoustic radiation of a PTU using the Transmission Error (TE) as the input excitation via multi-body dynamics (MBD). MBD is used to estimate the housing vibrations, which can then be coupled with an acoustic tool to create a radiation analysis. Thus, creating a viable method to measure the acoustic performance without incurring significant expenses. Furthermore, it enables noise and vibration analyses to be incorporated more easily into the design stage.

    This thesis analysed the sound radiated due to gear whine which arises due to the TE and occurs at the gear mesh frequency and its multiples. The simulations highlighted that the TE can be accurately predicted using the methods outlined in this thesis. Similarly, the method can reliably obtain the vibrations of the housing. The results from this analysis show that at 2000 rpm the PTU was sensitive to vibrations at 500, 1000 and 1500 Hz, the largest amplitude being at 1000 Hz. Furthermore, the Sound Power Level (SWL) was proportional to the vibration amplitudes in the system. Analytical calculations were conducted to verify the methods and showed a strong correlation. However, it was concluded that experiments are required to further verify the findings in this thesis.

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  • 19.
    Agrawal, Vishal
    et al.
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Kulachenko, Artem
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics, Solid Mechanics.
    Scapin, Nicolo
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Tammisola, Outi
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics.
    Brandt, Luca
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. Department of Energy and Process Engineering, Norwegian University of Science and Technology, Trondheim, Norway.
    An efficient isogeometric/finite-difference immersed boundary method for the fluid–structure interactions of slender flexible structures2024In: Computer Methods in Applied Mechanics and Engineering, ISSN 0045-7825, E-ISSN 1879-2138, Vol. 418, article id 116495Article in journal (Refereed)
    Abstract [en]

    In this contribution, we present a robust and efficient computational framework capable of accurately capturing the dynamic motion and large deformation/deflection responses of highly-flexible rods interacting with an incompressible viscous flow. Within the partitioned approach, we adopt separate field solvers to compute the dynamics of the immersed structures and the evolution of the flow field over time, considering finite Reynolds numbers. We employ a geometrically exact, nonlinear Cosserat rod formulation in the context of the isogeometric analysis (IGA) technique to model the elastic responses of each rod in three dimensions (3D). The Navier–Stokes equations are resolved using a pressure projection method on a standard staggered Cartesian grid. The direct-forcing immersed boundary method is utilized for coupling the IGA-based structural solver with the finite-difference fluid solver. In order to fully exploit the accuracy of the IGA technique for FSI simulations, the proposed framework introduces a new procedure that decouples the resolution of the structural domain from the fluid grid. Uniformly distributed Lagrangian markers with density relative to the Eulerian grid are generated to communicate between Lagrangian and Eulerian grids consistently with IGA. We successfully validate the proposed computational framework against two- and three-dimensional FSI benchmarks involving flexible filaments undergoing large deflections/motions in an incompressible flow. We show that six times coarser structural mesh than the flow Eulerian grid delivers accurate results for classic benchmarks, leading to a major gain in computational efficiency. The simultaneous spatial and temporal convergence studies demonstrate the consistent performance of the proposed framework, showing that it conserves the order of the convergence, which is the same as that of the fluid solver.

  • 20.
    Ahlstrand, Felicia
    et al.
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics, Naval Systems.
    Lindbergh, Elin
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics, Naval Systems.
    Methods to Predict Hull Resistance in the Process of Designing Electric Boats2020Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Combustion engines in boats cause several environmental problems, such as greenhouse gas emissions and acidication of oceans. Most of these problems can be reduced by replacing the combustion engines with electric boats. The limited range is one of the main constraints for electric boats, and in order to decrease the energy consumption, applicable resistance prediction methods are necessary in the hull design process. X Shore, which is a start-up company in the electric boat sector, lacks a systematic way of predicting resistance in an early design phase. In this study, four well-known methods - CFD, Holtrop & Mennen, the Savitsky method and model test - have been applied in order to predict resistance for a test hull. The study is limited to bare hull resistance and calm water conditions. CFD simulations are applied using the software ANSYS FLUENT 19:0. The simulations were based on the Reynolds Average Navier-Stokes equations with SST k-ω as turbulence model together with the volume of fluid method describing the two-phased ow of both water and air surrounding the hull. The semi-empirical methods, Holtrop & Mennen and the Savitsky method, are applied through a program in Python 3, developed by the authors. The results from each method have been compared and since model tests have been conducted outside of this study, the model test results will serve as reference. To evaluate the methods, a number of evaluation criteria are identied and evaluated through a Pugh Matrix, a systems engineering tool. Holtrop & Mennen predicts the resistance with low accuracy and consistency, and the error varies between 2:2% and 70:6%. The CFD simulations result in acceptable resistance predictions with good precision for the speeds 4 - 6 knots, with an average deviation of the absolute values as12:28% which is slightly higher than the errors found in previous studies. However, the method shows inconsistency for the higher speeds where the deviation varies between 1:77% and - 43:39%. The Savitsky method predicts accurate results with good precision for planing speeds, but also for the speeds 7 and 8 knots. The method is under-predicting the resistance for all speeds except for 7 knots, where the total resistance is 10:7% higher than for model tests. In the speed range 8 - 32 knots, the average error is an under-estimation of 17:58%. Furthermore, the trim angles predicted by the Savitsky method correspond well with the trim angles from the model test. In conclusion, the recommendation to X Shore is to apply the Savitsky method when its applicability criteria are fulfilled, and CFD for the lowest speeds, where the Savitsky method is not applicable.

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  • 21.
    Ahmed, N.
    et al.
    Khalifa Univ, Adv Digital & Addit Mfg Ctr, Abu Dhabi, U Arab Emirates..
    Barsoum, Imad
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics. Khalifa Univ, Adv Digital & Addit Mfg Ctr, Abu Dhabi, U Arab Emirates.;Khalifa Univ, Dept Mech Engn, Abu Dhabi, U Arab Emirates..
    Haidemenopoulos, G.
    Univ Thessaly, Dept Mech Engn, Volos, Greece..
    Abu Al-Rub, R. K.
    Khalifa Univ, Adv Digital & Addit Mfg Ctr, Abu Dhabi, U Arab Emirates.;Khalifa Univ, Dept Mech Engn, Abu Dhabi, U Arab Emirates..
    Process parameter selection and optimization of laser powder bed fusion for 316L stainless steel: A review2022In: JOURNAL OF MANUFACTURING PROCESSES, ISSN 1526-6125, Vol. 75, p. 415-434Article, review/survey (Refereed)
    Abstract [en]

    Stainless steel 316L has been an extensively investigated metallic material for laser powder bed fusion (L-PBF) in the past few decades due to its high corrosion resistance. However, there are challenges related to producing LPBF parts with minimal defects, attaining mechanical properties comparable with traditional process and dependency on time consuming post process treatments. The selection of L-PBF process parameters is crucial to overcome these challenges. This paper reviews the research carried out on L-PBF process parameter optimization for fabrication of 316L steel components for maximizing part densifications and attaining desired microstructure morphologies in parts. A brief work on numerical simulation approach for process parameter optimization for high densifications is also included in this paper.

  • 22.
    Ahmed, Zaheer
    et al.
    Koc Univ, Dept Mech Engn, Istanbul, Turkey..
    Izbassarov, Daulet
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics. KTH, Centres, SeRC - Swedish e-Science Research Centre. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Lu, Jiacai
    Johns Hopkins Univ, Dept Mech Engn, Baltimore, MD 21218 USA..
    Tryggvason, Gretar
    Johns Hopkins Univ, Dept Mech Engn, Baltimore, MD 21218 USA..
    Muradoglu, Metin
    Koc Univ, Dept Mech Engn, Istanbul, Turkey..
    Tammisola, Outi
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, Centres, SeRC - Swedish e-Science Research Centre.
    Effects of soluble surfactant on lateral migration of a bubble in a pressure driven channel flow2020In: International Journal of Multiphase Flow, ISSN 0301-9322, E-ISSN 1879-3533, Vol. 126, article id 103251Article in journal (Refereed)
    Abstract [en]

    The effects of soluble surfactant on the lateral migration of a bubble in a pressure-driven channel flow are examined by interface-resolved numerical simulations. The interfacial and bulk surfactant concentration evolution equations are solved fully coupled with the incompressible Navier-Stokes equations. A non-linear equation of state is used to relate interfacial surface tension to surfactant concentration at the interface. Extensive computations are performed to investigate the bubble dynamics for a wide range of parameters. It is found that surfactant dramatically changes the bubble dynamics. In the clean case, the bubble position depends on its deformability, characterized by the Eotvos (Eo) and the capillary (Ca) numbers. The spherical bubble moves towards the wall, while the deformable one migrates away from it. On the other hand, in the presence of the surfactant, even the spherical bubble moves away from the wall. It is also found that the contaminated bubble stays away from the wall for Eo = 0.1 and Eo = 1.5 while it migrates towards the wall for 0.1 < Eo < 1.5. Also, at high Eo, the onset of path instability is observed for both the clean and the contaminated cases. However, adding surfactant to the system triggers the path instability earlier and amplifies the oscillations afterwards.

  • 23.
    Ahn, Myeonghwan
    et al.
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics.
    Karnam, A.
    Gutmark, E. J.
    Mihaescu, Mihai
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics.
    Flow and Near-field Pressure Fluctuations of Twin Square Jets2021In: AIAA Propulsion and Energy Forum, 2021, American Institute of Aeronautics and Astronautics Inc, AIAA , 2021Conference paper (Refereed)
    Abstract [en]

    We aim to investigate the aerodynamic and acoustics characteristics of a twin square jet using an implicit Large Eddy Simulation (ILES). A screeching cold jet condition, a nozzle pressure ratio (NPR) of 3.0, is considered to simulate a coupled twin-jet. A second-order central scheme with a modified version of Jameson’s artificial dissipation is adopted to damp numerical oscillations and to mimic the effect of small-scale turbulence without an explicit subgrid-scale (SGS) model. Numerical results show that the overall trends of time-averaged streamwise velocity profiles are similar to the experimental data, with the largest differences observed at locations associated with the presence of the shock-cell structures. A detailed investigation of the flow fluctuations in jet shear layers is performed. The amplitude of the velocity fluctuations is highly dependent on the location of the shear layers with respect to the twin-jet configuration (upper, lateral, or inner). The coupling mode of twin jets associated with the screech tone is determined as a symmetrical flapping mode be a two-points spacetime cross-correlation analysis. The overall trends of near-field pressure fluctuation spectra by LES agree well with the experimental results in both upstream and downstream regions. Near-field pressure fluctuation spectra by ILES agree well with the experimentally obtained spectra at different locations in the nozzle exit plane as well as at several downstream locations in the near-field acoustic region. The highest screech tone is observed at the inter-nozzle region where superposition of in-phase waves and standing waves are found. Fourier phase and amplitude fields at the fundamental frequency also confirm the symmetrical flapping mode of the twin jets by showing in-phase relations of hydrodynamic/acoustic waves and noise directivities. 

  • 24.
    Ahn, MyeongHwan
    et al.
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics.
    Mihaescu, Mihai
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics.
    Effects of Temperature on the Characteristics of Twin Square Jets by Large Eddy Simulations2022In: AIAA Science and Technology Forum and Exposition, AIAA SciTech Forum 2022, American Institute of Aeronautics and Astronautics (AIAA) , 2022, article id AIAA 2022-0681Conference paper (Refereed)
    Abstract [en]

    In this study, we investigate the effects of temperature on the aerodynamic and aeroacoustics characteristics of twin square jets. Implicit Large Eddy Simulations (ILES) are performed for twin jets with a fixed nozzle pressure ratio (NPR) of 3.0 and temperature ratios (TR) of 1.0, 2.0, 4.0, and 7.0. A second-order central scheme is used to resolve acoustic waves, and an artificial dissipation model is applied to capture shock waves and to suppress non-physical oscillations. In addition, the variation of a specific heat ratio as function of temperature is considered under the chemical equilibrium assumption. The numerical results show that the length of potential core is reduced with the increase of temperature due to the enhanced mixing in jet shear layers which can be estimated by turbulent kinetic energy (TKE). Meanwhile, the fluctuations of the transverse velocity show different trends between the cases within the corresponding potential core length, which can be associated with the screeching phenomena of the twin-jet. As temperature increases, the convection Mach number in the jet shear layers is also increased so that the Mach wave is generated for TR of 2.0, 4.0, and 7.0. However, a crackle noise is only observed for TR of 4.0 and 7.0, whose generation is identified by the skewness and kurtosis factors. Relatively low temperature jets (TR of 1.0 and 2.0) are screeching so that peaks are observed in the spectra obtained upstream. On the other hand, broadband component is gradually increased when the jets are heated, and the largest increase is observed at the location exposed to the Mach wave radiation.

  • 25.
    Ahn, MyeongHwan
    et al.
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Mihaescu, Mihai
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics.
    Karnam, Aatresh
    University of Cincinnati.
    Gutmark, Ephraim
    Aerospace Engineering, University of Cincinnati.
    Large-eddy simulations of flow and aeroacoustics of twin square jets including turbulence tripping2023In: Physics of fluids, ISSN 1070-6631, E-ISSN 1089-7666, Vol. 35, no 6Article in journal (Refereed)
    Abstract [en]

    In this study, we investigate the flow and aeroacoustics of twin square (i.e., aspect ratio of 1.0) jets by implicit large-eddy simulations (LESs) under a nozzle pressure ratio of 3.0 and a temperature ratio of 1.0 conditions. A second-order central scheme coupled with a modified Jameson's artificial dissipation is used to resolve acoustics as well as to capture discontinuous solutions, e.g., shock waves. The flow boundary layer inside of the nozzle is tripped, using a small step in the convergent section of the nozzle. The time-averaged axial velocity and turbulent kinetic energy of LES with boundary layer tripping approaches better to particle image velocimetry experimental data than the LES without turbulence tripping case. A two-point space–time cross-correlation analysis suggests that the twin jets are screeching and are coupled to each other in a symmetrical flapping mode. Intense pressure fluctuations and standing waves are observed between the jets. Spectral proper orthogonal decomposition (SPOD) confirms the determined mode and the relevant wave propagation. The upstream propagating mode associated with the shock-cell structures is confined inside jets. Far-field noise obtained by solving Ffowcs Williams and Hawkings equation is in good agreement with the measured acoustic data. The symmetrical flapping mode of twin jets yields different levels of the screech tone depending on observation planes. The tonalities—the fundamental tone, second and third harmonics—appear clearly in the far-field, showing different contributions at angles corresponding to the directivities revealed by SPOD.

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  • 26.
    Aihara, Aya
    et al.
    Division of Electricity, Department of Electrical Engineering, Uppsala University, Uppsala, Sweden.
    Bolin, Karl
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics, Marcus Wallenberg Laboratory MWL.
    Goude, Anders
    Division of Electricity, Department of Electrical Engineering, Uppsala University, Uppsala, Sweden.
    Bernhoff, Hans
    Division of Electricity, Department of Electrical Engineering, Uppsala University, Uppsala, Sweden.
    Aeroacoustic noise prediction of a vertical axis wind turbine using large eddy simulation2021In: International Journal of Aeroacoustics, ISSN 1475-472X, E-ISSN 2048-4003, Vol. 20, no 8, p. 959-978Article in journal (Refereed)
    Abstract [en]

    This study investigates the numerical prediction for the aerodynamic noise of the vertical axis wind turbine using large eddy simulation and the acoustic analogy. Low noise designs are required especially in residential areas, and sound level generated by the wind turbine is therefore important to estimate. In this paper, the incompressible flow field around the 12 kW straight-bladed vertical axis wind turbine with the rotor diameter of 6.5 m is solved, and the sound propagation is calculated based on the Ffowcs Williams and Hawkings acoustic analogy. The sound pressure for the turbine operating at high tip speed ratio is predicted, and it is validated by comparing with measurement. The measured spectra of the sound pressure observed at several azimuth angles show the broadband characteristics, and the prediction is able to reproduce the shape of these spectra. While previous works studying small-scaled vertical axis wind turbines found that the thickness noise is the dominant sound source, the loading noise can be considered to be a main contribution to the total sound for this turbine. The simulation also indicates that the received noise level is higher when the blade moves in the downwind than in the upwind side.

  • 27.
    Ait-Ali, Abderrahman
    et al.
    Swedish National Road and Transport Research Institute (VTI), Malvinas väg 6, 114 28, Stockholm, Sweden, Malvinas väg 6; Linköping University, Bredgatan 32, 602 21, Norrköping, Sweden, Bredgatan 32.
    Kurt, Filiz
    Deutsches Zentrum für Luft-und Raumfahrt e.V. (DLR), Lilienthalplatz 7, 38108, Braunschweig, Germany, Lilienthalplatz 7.
    Isberner, Alessa
    Deutsches Zentrum für Luft-und Raumfahrt e.V. (DLR), Lilienthalplatz 7, 38108, Braunschweig, Germany, Lilienthalplatz 7.
    Odolinski, Kristofer
    Swedish National Road and Transport Research Institute (VTI), Malvinas väg 6, 114 28, Stockholm, Sweden, Malvinas väg 6.
    Berg, Mats
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics, Väg- och spårfordon samt konceptuell fordonsdesign.
    Assessing Innovations in High-Speed Rail Infrastructure2023In: Socioeconomic Impacts of High-Speed Rail Systems - Proceedings of the 2nd International Workshop on High-Speed Rail Socioeconomic Impacts, IW-HSR 2022, Springer Nature , 2023, p. 217-233Conference paper (Refereed)
    Abstract [en]

    Innovations in high-speed rail (HSR) have had substantial effects on different stakeholders within and outside the railway system. As part of the European Shift2Rail research programme, several innovative solutions are developed for, among others, improving the HSR infrastructure. The Joint Undertaking behind this research program has set objectives for these innovations in terms of punctuality, capacity, and life cycle costs. With a focus on infrastructure-related innovations for HSR, this paper aims at assessing their impacts in relation to these targets. We review the relevant research literature about the effects of HSR innovations and their assessment. The paper presents a hybrid assessment methodology combing different approaches to assess capacity, punctuality, and cost effects. This contributes to reducing the existing gap that is found in the research literature. Based on a reference scenario for HSR line and collected data from different stakeholders, the results indicate that infrastructure innovations in HSR, being developed within the European Shift2Rail research programme, can contribute to reaching the target set for punctuality. Further innovations in HSR infrastructure and/or other railway assets may be needed to reach additional targets and for more accurate improvement values giving more insights into their impacts.

  • 28.
    Akbarpour, Sahar
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics, Lightweight Structures. KTH.
    Enhanced Composite Joint Performance through Interlacement of Metal Inserts2021Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The work in this thesis investigates bolted joints in fibre reinforced composites with particular focus on a novel insert concept. The concept is characterised by replacing all composite plies with stacked metal patches, locally around a bolt hole, so that they jointly form a solid metal reinforcement. An extensive experimental study is presented together with finite element analysis of the studied cases.

    Reinforcing bolt holes with high-strength metals improves the bearing load capacity of the composite laminates. True enhancement of the joint performance however requires that the open-hole tensile strength is improved as well. The work started with tests of pin-loaded and open-hole tensile specimens with inserts, and significant improvement of the bearing load capacity was found. The initial tests enabled more informed design, and insert configurations having sufficient open-hole tensile strength could thereby be manufactured and tested. In parallel, composite-metal joints were numerically modelled to simulate and analyse the mechanical performance of the joints and gain a better understanding of the governing damage mechanisms.

    The performance of the joints was eventually investigated by means of experiments on single-shear, single- and double-bolt specimens, with and without inserts. The allowable bolt distance and the influence from the bolt tightening torque were also examined.

    The initial samples had inserts of stainless steel. Later, specimens with titanium alloy inserts were also included in the test series. Various insert configurations were designed to study the effects of different features in the composite-metal bond lines. The numerical simulations of the composite--metal interfaces were performed with two types of models, one joining the two materials directly to each other, without modelling any adhesive film in between, and the other including an elastic representation of the adhesive layer. The experimental results were then used to support verification of the results from the simulations.

    The final assessment of the concept was performed on insert configurations designed either for pure tensile loading or for more general (bi-directional) loading conditions, and the bearing load capacity, open-hole tensile strength and the performance of bolted joints were compared for cases with different inserts. While higher bearing strength improvement was achieved when the holes were reinforced with inserts of stainless steel, reinforcement with inserts of titanium was even more successful since it improved virtually all studied aspects of the joints considerably.

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  • 29.
    Akbarpour, Sahar
    et al.
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics, Lightweight Structures.
    Hallström, Stefan
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics, Lightweight Structures.
    Enhancing the performance of bolted joints in composites by use of patched steel or titanium inserts2021In: Composite structures, ISSN 0263-8223, E-ISSN 1879-1085, Vol. 275, article id 114464Article in journal (Refereed)
    Abstract [en]

    A new insert concept that interlaces metal inserts into composite laminates has earlier been shown to improve the relatively poor bearing strength of holes in fibre reinforced polymer composites, and it is here further and more thoroughly investigated. The concept was invented to increase the efficiency of joints with mechanical fasteners in composite materials and this work presents experiments on double-bolt joints with inserts made of either stainless steel or a titanium (Ti) alloy. In particular the work compares different implementations of the insert concept by reinforcing one or two holes in double bolt joints, and the effect of using different metals in the inserts. Some complementary tests on pin-loaded specimens and open hole tensile specimens are also performed and compared, partly with results that were reported previously. Considerable improvements of the bearing load capacity are attained, i.e. 50%-60% for steel and 35%-45% for Ti, compared to references. The open-hole tensile strength is also improved considerably (almost 30%) when the holes are reinforced with Ti inserts. The fact that the inserts can improve not only the bearing strength but also the performance in open-hole tension implies that the Ti inserts bring nothing but positive effects to the strength of the joints. The test results from single-shear double-bolt specimens with inserts at one hole showed improved strengths of 30% and 20% for specimens with steel and Ti inserts, respectively. Finally, an impressive strength improvement of 40-45% is achieved for single-shear double-bolt specimens having both holes reinforced with inserts of either steel or Ti.

  • 30.
    Akbarpour, Sahar
    et al.
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics, Lightweight Structures.
    Hallström, Stefan
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics, Lightweight Structures.
    Enhancing the performance of bolted joints in composites by use of patched steel or titanium inserts2021Report (Other academic)
    Abstract [en]

    A new insert concept that interlaces metal inserts into composite laminates has earlier been shown to improve the relatively poor bearing strength of holes in fibre reinforced polymer composites, and it is here further and more thoroughly investigated. The concept was invented to increase the efficiency of joints with mechanical fasteners in composite materials and this work presents experiments on double bolt joints with inserts made of either stainless steel or a titanium (Ti) alloy. In particular the work compares different implementations of the insert concept by reinforcing one or two holes in double bolt joints, and the effect of using different metals in the inserts. Some complementary tests on pin-loaded specimens and open hole tensile specimens are also performed and compared, also with some results reported previously.                    Considerable improvements in the bearing load capacity, i.e. 50%-60% or 35%-45%, is attained. The open-hole tensile strength is also improved considerably (almost 30%)  when the holes are reinforced with Ti inserts. The fact that the inserts can improve not only the bearing strength but also the performance in open-hole tension implies that the Ti inserts bring nothing but positive effects to the strength of the joints. The test results from single-shear double-bolt specimens with inserts at one hole showed improved strengths of 30% and 20% for specimens with steel and Ti inserts, respectively. Finally, an impressive strength improvement of 40-45% is achieved for single-shear double-bolt specimens having both holes reinforced with inserts of either steel or Ti.

  • 31.
    Akbarpour, Sahar
    et al.
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics, Lightweight Structures.
    Hallström, Stefan
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics, Lightweight Structures.
    Experimental investigation and numerical analysis of multi-material interfaces related to a composite joint concept2021Report (Other academic)
    Abstract [en]

    An insert concept for reinforcing bolt-holes with high strength metals was previously introduced by the authors, where inserts are anchored in composite laminates through interlacement of composite plies and thin metal patches. The resulting finger-joints must be strong enough to avoid composite-metal debonding happening before bearing failure at the bolt-hole. The strength of the composite-metal interfaces is thus crucial for successful implementation of the insert concept. The paper presents an experimental study investigating the strength of various interface geometries between a prepreg composite material and stainless steel or titanium alloy inserts. In addition to the experimental work, finite element simulations are performed to analyse the stresses at the interfaces. The results indicate that the stress concentrations at multi-material corner points govern the failure and that the strength can be enhanced by expedient design.

  • 32.
    Akbarpour, Sahar
    et al.
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics, Lightweight Structures.
    Hallström, Stefan
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics, Lightweight Structures.
    Strength improvement of bolted joints in composite materials by use of patched metal inserts2020In: Composite structures, ISSN 0263-8223, E-ISSN 1879-1085, Vol. 52, article id 112628Article in journal (Refereed)
    Abstract [en]

    Metal inserts are occasionally used to improve bearing load capacity of bolted joints in laminated composite materials. This paper investigates a new reinforcement concept where inserts are built by locally replacing composite plies with metal patches of various diameters, surrounding the holes. The inserts are built during composite manufacturing by alternately placing the metal patches through the thickness of the laminate at locations where holes are to be drilled after consolidation. An extensive experimental study including pin‐ loaded, open–hole tensile, and single‐shear testing of bolted specimens is presented. Considerable improve- ment of the bearing strength – 50‐60% – is attained for pin‐loaded specimens with inserts, demonstrating the potential of the reinforcement concept. The open–hole tensile tests show that the by‐pass strength can be maintained or even improved with up to 20% if the inserts are properly designed. Finally, the results from the single‐shear tests of bolted joints show more than 25% improvement in strength for reinforced single‐ and double‐bolt specimens. It is possible that the inserts would maintain clamping pressure over time, which could then almost double the imrovement (47%) for bolted joints.

  • 33.
    Alarcón, José Faúndez
    et al.
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Cavalieri, André V.G.
    Aerodynamics Department, Instituto Tecnológico de Aeronáutica, 12228-900, São José dos Campos / SP, Brazil, SP.
    Hanifi, Ardeshir
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Henningson, Dan S.
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Role of streak secondary instabilities on free-stream turbulence-induced transition2024In: Journal of Fluid Mechanics, ISSN 0022-1120, E-ISSN 1469-7645, Vol. 988, article id A6Article in journal (Refereed)
    Abstract [en]

    We study the stability of a zero-pressure gradient boundary layer subjected to free-stream disturbances by means of local stability analysis. The dataset under study corresponds to a direct numerical simulation (DNS) of a flat plate with a sharp leading edge in realistic wind tunnel conditions, with a turbulence level of 3.45 % at the leading edge. We present a method to track the convective evolution of the secondary instabilities of streaks by performing sequential stability calculations following the wave packet, connecting successive unstable eigenfunctions. A scattered nature, in time and space, of secondary instabilities is seen in the stability calculations. These instabilities can be detected before they reach finite amplitude in the DNS, preceding the nucleation of turbulent spots, and whose appearance is well correlated to the transition onset. This represents further evidence regarding the relevance of secondary instabilities of streaks in the bypass transition in realistic flow conditions. Consistent with the spatio-temporal nature of this problem, our approach allows us to integrate directly the local growth rates to obtain the spatial amplification ratio of the individual instabilities, where it is shown that instabilities reaching an -factor in the range [2.5,4] can be directly correlated to more than 65 % of the nucleation events. Interestingly, it is found that high amplification is not only attained by modes with high growth rates, but also by instabilities with sustained low growth rates for a long time.

  • 34.
    Alarcón, José Faúndez
    et al.
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Morra, Pierluigi
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Engineering Sciences (SCI), Engineering Mechanics.
    Hanifi, Ardeshir
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics.
    Henningson, Dan S.
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics.
    Disturbance growth on a NACA0008 wing subjected to free stream turbulence2022In: Journal of Fluid Mechanics, ISSN 0022-1120, E-ISSN 1469-7645, Vol. 944, article id A44Article in journal (Refereed)
    Abstract [en]

    The stability of an incompressible boundary layer flow over a wing in the presence of free stream turbulence (FST) has been investigated by means of direct numerical simulations and compared with the linearised boundary layer equations. Four different. FST conditions have been considered, which are characterised by their turbulence intensity levels and length scales. In all cases the perturbed flow develops into elongated disturbances of high and low streamwise velocity inside the boundary layer, where their spacing has been found to be strongly dependent on the scales of the incoming free stream vorticity. The breakdown of these streaks into turbulent spots from local secondary instabilities is also observed, presenting the same development as the ones reported in flat plate experiments. The disturbance growth, characterised by its root mean squares value, is found to depend not only on the turbulence level, but also on the FST length scales. Particularly, higher disturbance growth is observed for our cases with larger length scales. This behaviour is attributed to the preferred wavenumbers that can exhibit maximum transient growth. We study this boundary layer preference by projection of the flow fields at the leading edge onto optimal disturbances. Our results demonstrate that optimal disturbance growth is the main cause of growth of disturbances on the wing boundary layer.

  • 35.
    Alcantara-Avila, Francisco
    et al.
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. Univ Politecn Valencia, Inst Univ Matemat Pura & Aplicada, Valencia 46022, Spain.;KTH Royal Inst Technol, FLOW, Engn Mech, S-11428 Stockholm, Sweden..
    Garcia-Raffi, Luis Miguel
    Univ Politecn Valencia, Inst Univ Matemat Pura & Aplicada, Valencia 46022, Spain..
    Hoyas, Sergio
    Univ Politecn Valencia, Inst Univ Matemat Pura & Aplicada, Valencia 46022, Spain..
    Oberlack, Martin
    Tech Univ Darmstadt, Chair Fluid Dynam, Otto Bernd Str 2, D-64287 Darmstadt, Germany.;Tech Univ Darmstadt, Ctr Computat Engn, Dolivostr 15, D-64293 Darmstadt, Germany..
    Validation of symmetry-induced high moment velocity and temperature scaling laws in a turbulent channel flow2024In: Physical review. E, ISSN 2470-0045, E-ISSN 2470-0053, Vol. 109, no 2, article id 025104Article in journal (Refereed)
    Abstract [en]

    The symmetry -based turbulence theory has been used to derive new scaling laws for the streamwise velocity and temperature moments of arbitrary order. For this, it has been applied to an incompressible turbulent channel flow driven by a pressure gradient with a passive scalar equation coupled in. To derive the scaling laws, symmetries of the classical Navier-Stokes and the thermal energy equations have been used together with statistical symmetries, i.e., the statistical scaling and translation symmetries of the multipoint moment equations. Specifically, the multipoint moments are built on the instantaneous velocity and temperature fields other than in the classical approach, where moments are based on the fluctuations of these fields. With this instantaneous approach, a linear system of multipoint correlation equations has been obtained, which greatly simplifies the symmetry analysis. The scaling laws have been derived in the limit of zero viscosity and heat conduction, i.e., Ret -> infinity and Pr > 1, and they apply in the center of the channel, i.e., they represent a generalization of the deficit law, thus extending the work of Oberlack et al. [Phys. Rev. Lett. 128, 024502 (2022)]. The scaling laws are all power laws, with the exponent of the high moments all depending exclusively on those of the first and second moments. To validate the new scaling laws, the data from a large number of direct numerical simulations (DNS) for different Reynolds and Prandtl numbers have been used. The results show a very high accuracy of the scaling laws to represent the DNS data. The statistical scaling symmetry of the multipoint moment equations, which characterizes intermittency, has been the key to the new results since it generates a constant in the exponent of the final scaling law. Most important, since this constant is independent of the order of the moments, it clearly indicates anomalous scaling.

  • 36.
    Aldén, R.
    et al.
    SWERIM, Kista, Sweden.
    Barsoum, Zuheir
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics.
    Vouristo, T.
    SWERIM, Kista, Sweden.
    Al-Emrani, M.
    Robustness of the HFMI techniques and the effect of weld quality on the fatigue life improvement of welded joints2020In: Welding in the World, ISSN 0043-2288, E-ISSN 1878-6669, Vol. 64, no 11, p. 1947-1956Article in journal (Refereed)
    Abstract [en]

    Robustness of HFMI treatment in different weld qualities according to ISO 5817 was studied, and fatigue testing of the treated samples was carried out in order to investigate the effect of the weld quality prior treatment. The results show that HFMI-treated welds with weld quality level D shows fatigue life improvements that fall within the IIW recommendations for HFMI. No significant influence from the HFMI operator or HFMI equipment on the fatigue life was found. However, the scatter in fatigue testing results varied with HFMI operator and indicated that different HFMI operators could produce consistent treatment results. A considerable effect on fatigue life from HFMI tool radius was found, where the 2-mm tool radius showed considerably greater fatigue life compared with the 1.5-mm tool radius. According to IIW (Marquis and Barsoum 2016), for steel grade SY = 700 MPa, the fatigue strength recommendation is FAT 160 (m = 5) for transverse stiffener–welded joints with as-welded quality B according to ISO 5817 (ISO/TC 44/SC 10 2011), prior to treatment. It can be observed in the current study that fatigue-tested HFMI-treated welded joints, welded with weld quality D, are in good agreement with the IIW recommendations.

  • 37.
    Alenius, Emma
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Åbom, Mats
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Fuchs, Laszlo
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics.
    LES of acoustic-flow interaction at an orifice plate2012In: 18th AIAA/CEAS Aeroacoustics Conference (33rd AIAA Aeroacoustics Conference), American Institute of Aeronautics and Astronautics Inc. , 2012Conference paper (Refereed)
    Abstract [en]

    The scattering of plane waves by a thick orifice plate, placed in a circular or square duct with ow, is studied through Large Eddy Simulation. The scattering matrix is computed and compared to measurements, showing reasonably good agreement except around one frequency (St ≈ 0:4). Here a stronger amplification of acoustic energy is observed in the circular duct simulations than in the measurements and the square duct simulations. In order to improve the understanding of the interaction between an incoming wave, the flow, and the plate, a few frequencies are studied in more detail. A Dynamic Mode Decomposition is performed to identify flow structures at significant frequencies. This shows that the amplification of acoustic energy occurs at the frequency where the jet in the circular duct has an axisymmetric instability. Furthermore, the incoming wave slightly amplifies this instability, and suppresses background flow fiuctuations.

  • 38.
    Alex, Alvisi
    et al.
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics.
    Adalberto, Perez
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics.
    Analysis of wall-mounted hot-wire probes2020Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Flush-mounted cavity hot-wire probes have been around since two decades, but have typically not been applied as often compared to the traditional wall hot-wires mounted several wire diameters above the surface. While the latter suffer from heat conduction from the hot wire to the substrate in particular when used in air flows, the former is belived to significantly enhance the frequency response of the sensor. The recent work using a cavity hotwire by Gubian et al. (2019) came to the surprising conclusion that the magnitute of the fluctuating wall-shear stress τ+w,rms reaches an asymptotic value of 0.44 beyond the friction Reynolds number Re τ ∼ 600. In an effort to explain this result, which is at odds with the majority of the literature, the present work combines direct numerical simulations (DNS) of a turbulent channel flow with a cavity modelled using the immersed boundary method, as well as an experimental replication of the study of Gubian et al. in a turbulent boundary layer to explain how the contradicting results could have been obtained. It is shown that the measurements of the mentioned study can be replicated qualitatively as a result of measurement problems. We will present why cavity hot-wire probes should neither be used for quantitative nor qualitative measurements of wall-bounded flows, and that several experimental short-comings can interact to sometimes falsely yield seemingly correct results.

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  • 39.
    Alexakis, Alexandros Efraim
    et al.
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Fibre- and Polymer Technology, Coating Technology. KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Centres, Wallenberg Wood Science Center.
    Engström, Joakim
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Fibre- and Polymer Technology, Coating Technology. KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Centres, Wallenberg Wood Science Center.
    Stamm, Arne
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Fibre- and Polymer Technology, Coating Technology.
    Riazanova, Anastasia
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Centres, Wallenberg Wood Science Center. Wallenberg Wood Sci Ctr WWSC, Tekn Ringen 56-58, SE-10044 Stockholm, Sweden..
    Brett, Calvin
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Fibre- and Polymer Technology, Coating Technology. KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Centres, Wallenberg Wood Science Center. Deutsches Elektronen-Synchrotron (DESY), Notkestrasse 85, Hamburg, 22603, Germany.
    Roth, Stephan V.
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Fibre- and Polymer Technology, Coating Technology. Deutsches Elektronen-Synchrotron (DESY), Notkestrasse 85, Hamburg, 22603, Germany.
    Syrén, Per-Olof
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Fibre- and Polymer Technology, Coating Technology. KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Centres, Wallenberg Wood Science Center.
    Fogelström, Linda
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Fibre- and Polymer Technology, Coating Technology. KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Centres, Wallenberg Wood Science Center.
    Reid, Michael S.
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics.
    Malmström, Eva
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Fibre- and Polymer Technology, Coating Technology. KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Centres, Wallenberg Wood Science Center.
    Modification of cellulose through physisorption of cationic bio-based nanolatexes - comparing emulsion polymerization and RAFT-mediated polymerization-induced self-assembly2021In: Green Chemistry, ISSN 1463-9262, E-ISSN 1463-9270, Vol. 23, no 5, p. 2113-2122Article in journal (Refereed)
    Abstract [en]

    The polymerization of a bio-based terpene-derived monomer, sobrerol methacrylate (SobMA), was evaluated in the design of polymeric nanoparticles (nanolatexes). Their synthesis was accomplished by using emulsion polymerization, either by free-radical polymerization in the presence of a cationic surfactant or a cationic macroRAFT agent by employing RAFT-mediated polymerization-induced self-assembly (PISA). By tuning the length of the hydrophobic polymer, it was possible to control the nanoparticle size between 70 and 110 nm. The average size of the latexes in both wet and dry state were investigated by microscopy imaging and dynamic light scattering (DLS). Additionally, SobMA was successfully copolymerized with butyl methacrylate (BMA) targeting soft-core nanolatexes. The comparison of the kinetic profile of the cationically stabilized nanolatexes highlighted the differences of both processes. The SobMA-based nanolatexes yielded high T-g similar to 120 degrees C, while the copolymer sample exhibited a lower T-g similar to 50 degrees C, as assessed by Differential Scanning Calorimetry (DSC). Thereafter, the nanolatexes were adsorbed onto cellulose (filter paper), where they were annealed at elevated temperatures to result in polymeric coatings. Their morphologies were analysed by Field Emission Scanning Electron Microscopy (FE-SEM) and compared to a commercial sulfate polystyrene latex (PS latex). By microscopic investigation the film formation mechanism could be unravelled. Water contact angle (CA) measurements verified the transition from a hydrophilic to a hydrophobic surface after film formation had occured. The obtained results are promising for the toolbox of bio-based building blocks, focused on sobrerol-based monomers, to be used in emulsion polymerizations either for tailored PISA-latexes or facile conventional latex formation, in order to replace methyl methacrylate or other high T-g-monomers.

  • 40.
    Alfredsson, Bo
    et al.
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics, Solid Mechanics.
    Hazar, Selcuk
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics, Solid Mechanics.
    Lai, J.
    SKF RTD, Meidoornkade 14, NL-3992 AE Houten, Netherlands..
    Loading rate and temperature effects on the fracture toughness of a high strength bearing steel2021In: Engineering Fracture Mechanics, ISSN 0013-7944, E-ISSN 1873-7315, Vol. 245, article id 107600Article in journal (Refereed)
    Abstract [en]

    Fracture of martensitic AISI 52100 steel with 12% retained austenite was experimentally studied at temperatures below the tempering temperature by K-Ic tests and at extremely low loading rates. Depending on temperature, K-Ic and J

  • 41.
    Alfredsson, Bo
    et al.
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics, Solid Mechanics.
    Wiman, Jan
    Planning in Sweden2017In: Reshaping Regional Planning: A Northern Perspective, Taylor & Francis Group, 2017, p. 15-21Chapter in book (Other academic)
    Abstract [en]

    In principle, there is a municipal planning monopoly in Sweden, and the planning system is therefore basically designed for the municipalities. All municipalities must have a comprehensive plan that covers their entire area of responsibility. Although the plan is not binding, it must be kept up to date. The detailed development plan is a legally binding, executive planning instrument - a legal agreement between the municipality, the public and landowners - that makes it possible for the intentions of the comprehensive plan to be implemented. Special area regulations are also binding, and this form of planning is used within limited areas to guarantee compliance with certain comprehensive plan goals. A property regulation plan may be used to facilitate implementation of the detailed development plan. For the planning of matters that are of mutual interest to several municipalities, the national government may appoint a regional planning body with the task of monitoring regional questions and providing basic planning data for municipalities and Government authorities.

  • 42.
    Alfredsson, Henrik
    et al.
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics.
    Segalini, Antonio
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics.
    Örlü, Ramis
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    The Diagnostic Plot—A Tutorial with a Ten Year Perspective2021In: Progress in Turbulence IX: Proceedings of the iTi Conference in Turbulence 2021, Springer Nature , 2021, Vol. 267, p. 125-135Conference paper (Refereed)
    Abstract [en]

    The diagnostic plot was introduced in 2010 (Eur. J. Mech. B/Fluids 29: 403–406) but was used already in 2008 during a large measurement campaign as a litmus test to determine if tripped zero-pressure gradient turbulent boundary layers fulfilled basic criteria of being canonical. It used the rms-level of streamwise velocity (urms ) in the outer part of the boundary layer, a region where urms can give clear indications if insufficient or too tough tripping has been used. In standard plots one needs both the friction velocity and measurement of the full velocity and turbulence profiles. By instead plotting urms/ U∞ as a function of U/ U∞, it was found that this gives rise to a well-defined distribution that could be used as a canonical measure. It was later discovered that it is possible to extend the description to the near wall region. It has also been extended to boundary layers over rough surfaces and with pressure gradients, and some further uses. This paper aims to be both a review of the development of the method during the last 10+ years and a tutorial for those who want to employ it in their research and maybe also find new uses of the methodology.

  • 43.
    Alfredsson, P. Henrik
    et al.
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Engineering Sciences (SCI), Engineering Mechanics.
    Kato, Kentaro
    Shinshu Univ, Dept Mech Syst Engn, Nagano, Japan..
    Lingwood, Rebecca
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Engineering Sciences (SCI), Engineering Mechanics.
    Flows Over Rotating Disks and Cones2024In: Annual Review of Fluid Mechanics, ISSN 0066-4189, E-ISSN 1545-4479, Vol. 56, p. 45-68Article, review/survey (Refereed)
    Abstract [en]

    Rotating-disk flows were first considered by von Karman in a seminal paper in 1921, where boundary layers in general were discussed and, in two of the nine sections, results for the laminar and turbulent boundary layers over a rotating disk were presented. It was not until in 1955 that flow visualization discovered the existence of stationary cross-flow vortices on the disk prior to the transition to turbulence. The rotating disk can be seen as a special case of rotating cones, and recent research has shown that broad cones behave similarly to disks, whereas sharp cones are susceptible to a different type of instability. Here, we provide a review of the major developments since von Karman's work from 100 years ago, regarding instability, transition, and turbulence in the boundary layers, and we include some analysis not previously published.

  • 44.
    Alghalibi, Dhiya
    et al.
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, Centres, SeRC - Swedish e-Science Research Centre. College of Engineering, University of Kufa, Al Najaf, Iraq.
    Fornari, Walter
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, Centres, SeRC - Swedish e-Science Research Centre.
    Rosti, Marco E.
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics. KTH, Centres, SeRC - Swedish e-Science Research Centre. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. Complex Fluids and Flows Unit, Okinawa Institute of Science and Technology Graduate University, 1919-1 Tancha, Onna-son, Okinawa 904-0495, Japan.
    Brandt, Luca
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, Centres, SeRC - Swedish e-Science Research Centre.
    Sedimentation of finite-size particles in quiescent wall-bounded shear-thinning and Newtonian fluids2020In: International Journal of Multiphase Flow, ISSN 0301-9322, E-ISSN 1879-3533, Vol. 129, article id 103291Article in journal (Refereed)
    Abstract [en]

    We study the sedimentation of finite-size particles in quiescent wall-bounded Newtonian and shear-thinning fluids by interface resolved numerical simulations. The suspended phase consists of Non-Brownian rigid spherical particles with particle to fluid density ratio ρp/ρf=1.5 at three different solid volume fractions Φ=1%, 5% and 20%. Firstly, to focus on the effect of shear-thinning on the particle dynamics and interactions, the Archimedes number is increased for a single particle to have the same settling speed in the Newtonian fluid as in the shear-thinning fluid. Secondly, we consider fixed Archimedes and vary the shear-thinning properties of the fluid. Overall, we report a twofold effect of shear thinning. First and more important, the substantial increase of the particle sedimentation velocity in the shear-thinning case due to the increase of the shear rate around the particles, which reduces the local viscosity leading to a reduced particle drag. Secondly, the shear-thinning fluid reduces the level of particle interactions, causing a reduction of velocity fluctuations and resulting in particles sedimenting at approximately the same speed. Moreover, the mean settling velocities decrease with the particle concentration as a consequence of the hindering effect. Particles tend to sediment in the middle of the channel, preferentially positioning in the wake of neighbouring particles or aside them, resulting in lower levels of fluid velocity fluctuations in the gravity direction in the shear-thinning fluid.

  • 45.
    Alhourani, A.
    et al.
    Department of Mechanical Engineering, Khalifa University of Science and Technology, Abu Dhabi 127788, United Arab Emirates.
    Sheikh-Ahmad, J.
    Department of Mechanical Engineering, Khalifa University of Science and Technology, Abu Dhabi 127788, United Arab Emirates; Department of Mechanical Engineering, Western New England University, Springfield, MA 01119, USA.
    Almaskari, F.
    Department of Aerospace Engineering, Khalifa University of Science and Technology, Abu Dhabi, 127788, United Arab Emirates.
    Khan, K.
    Department of Aerospace Engineering, Khalifa University of Science and Technology, Abu Dhabi, 127788, United Arab Emirates.
    Deveci, S.
    Borouge Pte. Ltd., Abu Dhabi, 6951, United Arab Emirates.
    Barsoum, Zuheir
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics. Department of Mechanical Engineering, Khalifa University of Science and Technology, Abu Dhabi 127788, United Arab Emirates.
    Thermal modeling of friction stir welding of thick high-density polyethylene plates2024In: Journal of Materials Research and Technology, ISSN 2238-7854, Vol. 28, p. 4186-4198Article in journal (Refereed)
    Abstract [en]

    The process temperatures in the friction stir welding of thick polymer plates play a significant role in the joint's quality since the process is characterized by mixed solid and viscous flow states. The heat generation mechanism in each state is fundamentally different, with heat being generated by friction in the solid-state and by viscous shear flow in the viscous state. In this study, the heat generation and dissipation in the friction stir welding of 14 mm thick high-density polyethylene plates were studied numerically through solving the direct heat conduction problem. Two models of heat generation were used in the numerical solution and the effect of the pin rotational speed on the process temperatures was investigated. It was shown that the utilization of a mixed heat generation model consisting of both the solid state and the viscous shear flow considerably improves the numerical model predictions. The temperature predictions were validated through welding experiments and showed a temperature difference of 3 %. Furthermore, it was found that the welding process stabilizes at rotational speeds higher than 800 rpm, where no considerable change occurs in the volume of the viscous flow region and the welding power requirement. The numerical results based on the combined solid-viscous heat model were in good agreement with the experimental thermal histories.

  • 46.
    Ali, Asad
    et al.
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics, Solid Mechanics.
    Michael, Danay
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics, Solid Mechanics.
    In-plane bi-axial testing of thin paper2022Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    During its lifetime, a beverage package is subjected to a complex loading history where the loading, in general, is multiaxial. Hence, to optimize the performance of the package, knowledge of the material’s anisotropic multi-axial deformation and subsequent failure is necessary. This report presents a way to investigate the anisotropic loading and fracture of thin paper using bi-axial testing and to analyse the bi-axial test using the Finite Element Method.

    Getting thin paper to fracture in the central region, where the deformation and loading are bi-axial, proved difficult. To overcome this challenge, a new bi-axial specimen, with a specific sample preparation technique, is proposed and implemented in this specific project. This cruciform-shaped thin paper specimen was reinforced with laminating plastic everywhere but in the central region. This was done to avoid material failure in the notched radius area or the clamps, rather to facilitate a material failure in the central region of the material specimen. In order to simulate the bi-axial test, a Hill elastic-plastic material model was calibrated, and the material parameters were obtained from uniaxial tensile tests.

    When subjected to bi-axial loading, the proposed cruciform-shaped specimen fractured systematically and repetitively for the different load cases studied. Moreover, the Hill material model captured the force vs. displacement curve from the experimental results well but overestimated its values. The overestimation was mainly due to sliding during the experimental tests.

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  • 47. Alipour, M.
    et al.
    Tavallaey, Shiva Sander
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics. ABB AB Corporate Research, Forskargränd 7, SE-721 78 Västerås, Sweden.
    Andersson, A. M.
    Brandell, D.
    Improved Battery Cycle Life Prediction Using a Hybrid Data-Driven Model Incorporating Linear Support Vector Regression and Gaussian2022In: ChemPhysChem, ISSN 1439-4235, E-ISSN 1439-7641, Vol. 23, no 7, article id e202100829Article in journal (Refereed)
    Abstract [en]

    The ability to accurately predict lithium-ion battery life-time already at an early stage of battery usage is critical for ensuring safe operation, accelerating technology development, and enabling battery second-life applications. Many models are unable to effectively predict battery life-time at early cycles due to the complex and nonlinear degrading behavior of lithium-ion batteries. In this study, two hybrid data-driven models, incorporating a traditional linear support vector regression (LSVR) and a Gaussian process regression (GPR), were developed to estimate battery life-time at an early stage, before more severe capacity fading, utilizing a data set of 124 battery cells with lifetimes ranging from 150 to 2300 cycles. Two type of hybrid models, here denoted as A and B, were proposed. For each of the models, we achieved 1.1 % (A) and 1.4 % (B) training error, and similarly, 8.3 % (A) and 8.2 % (B) test error. The two key advantages are that the error percentage is kept below 10 % and that very low error values for the training and test sets were observed when utilizing data from only the first 100 cycles.The proposed method thus appears highly promising for predicting battery life during early cycles. 

  • 48.
    Alipour, Mohammad
    et al.
    Department of Chemistry - Angstrom Laboratory, Uppsala University, 751 21 Uppsala, Sweden.
    Yin, Litao
    Department of Chemistry - Angstrom Laboratory, Uppsala University, 751 21 Uppsala, Sweden.
    Tavallaey, Shiva Sander
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics. ABB AB Corporate Research, Forskargrand 7, SE-721 78 Västerås, Sweden, Forskargränd 7.
    Andersson, Anna Mikaela
    ABB AB Corporate Research, Forskargrand 7, SE-721 78 Västerås, Sweden.
    Brandell, Daniel
    Department of Chemistry - Angstrom Laboratory, Uppsala University, 751 21 Uppsala, Sweden.
    A surrogate-assisted uncertainty quantification and sensitivity analysis on a coupled electrochemical–thermal battery aging model2023In: Journal of Power Sources, ISSN 0378-7753, E-ISSN 1873-2755, Vol. 579, article id 233273Article in journal (Refereed)
    Abstract [en]

    High-fidelity physics-based models are required to comprehend battery behavior at various operating conditions. This paper proposes an uncertainty quantification analysis on a coupled electrochemical–thermal aging model to improve the reliability of a battery model, while also investigating the impact of parametric model uncertainties on battery voltage, temperature, and aging. The coupled model's high computing cost, however, is a significant barrier to perform uncertainty quantification (UQ) and sensitivity analysis (SA). To address this problem, a surrogate model – i.e, by simulating the outcome of a quantity of interest that cannot be easily computed or measured – based on the Gaussian process regression (GPR) theory and principle component analysis (PCA) is built, using a small collection of finite element simulation results as synthetic training data. In total, 43 variable electrochemical–thermal parameters as well as 13 variable aging parameters are studied and estimated. Moreover, the trained surrogate model is also used in the parameterization of the electrochemical and thermal models. The results show that the uncertainties in the input parameters significantly affect the estimations of battery voltage, temperature, and aging. Based on this sensitivity analysis, the most influential parameters affecting the above mentioned battery outputs are reported. This approach is thereby helpful for developing robust and reliable high-fidelity battery aging models with potential applications in digital twins as well as for synthetic data generation.

  • 49.
    Alizad Banaei, Arash
    et al.
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, Centres, SeRC - Swedish e-Science Research Centre.
    Rahmani, Mona
    Univ British Columbia, Dept Math, Vancouver, BC V6T 1Z2, Canada..
    Martinez, D. Mark
    Univ British Columbia, Dept Chem & Biol Engn, Vancouver, BC V6T 1Z3, Canada..
    Brandt, Luca
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, Centres, SeRC - Swedish e-Science Research Centre.
    Inertial settling of flexible fiber suspensions2020In: Physical Review Fluids, E-ISSN 2469-990X, Vol. 5, no 2, article id 024301Article in journal (Refereed)
    Abstract [en]

    We study the inertial settling of suspensions of flexible and rigid fibers using an immersed boundary method. The fibers considered are inextensible and slender, with an aspect ratio of 20. For a single Galileo number of Ga = 160, we examine a range of dimensionless bending rigidities 0.1 < gamma < 20 and fiber concentrations 0.5 < nL(3) < 25, with n being the fiber number density and L the fiber length, that spans dilute and semidilute regimes. The settling fibers form streamers, regions where the fibers are packed and settle faster than the average settling velocity of the suspension, for nL(3) > 10. In the low-concentration regions outside the streamers, the fibers either go upward or have low settling velocities. Flexible fibers exhibit higher packing inside the streamers and smaller streamers compared to the streamers formed by the rigid fibers. Due to this higher packing, the flexible fibers settle faster compared to the rigid fibers. The formation of the streamers counterbalances the hindering of the settling velocity at higher concentrations. At higher nL(3), however, the maximum local concentration of fibers relative to a uniform distribution diminishes for both flexible and rigid fibers as the mobility of the fibers becomes limited due to the presence of other fibers in their vicinity. Due to this limited mobility, the deformation of the fibers and their settling orientation become insensitive to nL(3) for nL(3) > 7. In both the dilute and semidilute regimes, flexible fibers are more aligned with the direction perpendicular to gravity compared to rigid fibers.

  • 50.
    Alizadehgiashi, Moien
    et al.
    Univ Toronto, Dept Chem, Toronto, ON M5S 3H6, Canada..
    Nemr, Carine R.
    Univ Toronto, Dept Chem, Toronto, ON M5S 3H6, Canada..
    Chekini, Mahshid
    Univ Toronto, Dept Chem, Toronto, ON M5S 3H6, Canada..
    Ramos, Daniel Pinto
    Univ Toronto, Dept Chem, Toronto, ON M5S 3H6, Canada..
    Mittal, Nitesh
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics, Fluid Physics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Centres, Wallenberg Wood Science Center. Univ Toronto, Dept Chem, Toronto, ON M5S 3H6, Canada.
    Ahmed, Sharif U.
    Univ Toronto, Dept Pharmaceut Sci, Toronto, ON M5S 3M2, Canada..
    Khuu, Nancy
    Univ Toronto, Dept Chem, Toronto, ON M5S 3H6, Canada..
    Kelley, Shana O.
    Univ Toronto, Dept Chem, Toronto, ON M5S 3H6, Canada.;Univ Toronto, Dept Pharmaceut Sci, Toronto, ON M5S 3M2, Canada.;Univ Toronto, Inst Biomat & Biomed Engn, Toronto, ON M5S 3G9, Canada..
    Kumacheva, Eugenia
    Univ Toronto, Dept Chem, Toronto, ON M5S 3H6, Canada.;Univ Toronto, Inst Biomat & Biomed Engn, Toronto, ON M5S 3G9, Canada.;Univ Toronto, Dept Chem Engn & Appl Chem, Toronto, ON M5S 3E5, Canada..
    Multifunctional 3D-Printed Wound Dressings2021In: ACS Nano, ISSN 1936-0851, E-ISSN 1936-086X, Vol. 15, no 7, p. 12375-12387Article in journal (Refereed)
    Abstract [en]

    Personalized wound dressings provide enhanced healing for different wound types; however multicomponent wound dressings with discretely controllable delivery of different biologically active agents are yet to be developed. Here we report 3D-printed multicomponent biocomposite hydrogel wound dressings that have been selectively loaded with small molecules, metal nanoparticles, and proteins for independently controlled release at the wound site. Hydrogel wound dressings carrying antibacterial silver nanoparticles and vascular endothelial growth factor with predetermined release profiles were utilized to study the physiological response of the wound in a mouse model. Compared to controls, the application of dressings resulted in improvement in granulation tissue formation and differential levels of vascular density, dependent on the release profile of the growth factor. Our study demonstrates the versatility of the 3D-printed hydrogel dressings that can yield varied physiological responses in vivo and can further be adapted for personalized treatment of various wound types.

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