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  • 2201.
    Zhu, Jinchao
    et al.
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics, Lightweight Structures.
    Barsoum, Zuheir
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics, Lightweight Structures.
    Mansour, Rami
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics, Solid Mechanics.
    Numerical study of the influence of weld geometry variations on fatigue life using the notch stress analysis2022Conference paper (Refereed)
    Abstract [en]

    Idealized geometry is typically used in standards for the fatigue life assessment of welded joints. In the presence of stochastic geometrical variations along the weld, the choice of the idealized geometry is however ambiguous. In the notch stress (NS) method with a fictitious notch radius rref = 1 mm, the FAT 225 curve is derived for welds with relatively good quality in toe profiles. In the NS method with rref = ractual + 1 mm, a lower FAT 200 curve is recommended. Both approaches neglect the stochastic variability in toe radius, toe angle and leg length along the weld. The aim of this paper is two-fold. First, a numerical comparison between both approaches in terms of their predicted fatigue life is performed for a non-load carrying fillet cruciform joints. The results show that the NS method with rref = 1 mm and FAT 225 is substantially more conservative. Second, these methods are enhanced by replacing the deterministic stress concentration factor by a probability distribution computed using Monte Carlo simulation. It is shown that NS with rref = 1 mm and FAT 225 does not predict any substantial influence of the stochastic variability in process parameters since the actual toe radius is not included in the analysis. However, the NS method with rref = ractual + 1 mm and FAT 200 predicts a decrease in fatigue life when uncertainties in geometrical parameters is included. This numerical study paves the way for an experimental validation of the predicted influence of stochastic variability of geometrical parameters based on the stochastic notch stress analysis.

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  • 2202.
    Zhu, Jinchao
    et al.
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics, Solid Mechanics.
    Khurshid, Mansoor
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics. Cargotec Sweden AB Bromma Conquip, Kronborgsgrand 23, S-16446 Kista, Sweden..
    Barsoum, Imad
    Khalifa Univ, Dept Mech Engn, POB 2533, Abu Dhabi, U Arab Emirates..
    Barsoum, Zuheir
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics.
    Computational weld-mechanics assessment of welding distortions in a large beam structure2021In: Engineering structures, ISSN 0141-0296, E-ISSN 1873-7323, Vol. 236, article id 112055Article in journal (Refereed)
    Abstract [en]

    Unwanted distortions are typically observed in components after the welding process. Physical trial tests and extra post-treatments are being widely utilized in industries to minimize and correct the out of tolerance distortions. These methods are time-consuming and costly. There has been growing interest in digital tools which have great potential to minimize the physical test loops and corrections. In this study welding distortions analysis has been carried out on a large beam structure experimentally and numerically using computational welding mechanics (CWM) techniques such as the inherent strain (local?global) method and the shrinkage method, together with the lumping approach. The estimated distortions from the shrinkage together with lumping approaches were in good agreement with the experimental measurements and the computational time affordable. The inherent strain (local?global) method captured the trend of distortion with an underestimation of distortions. The accuracy of the estimated residuals stresses from the inherent strain (local?global) approach is higher than the one from shrinkage together with lumping approaches. Moreover, the effects of various welding process parameters (i.e. welding sequence, fixture, and weld pool size) on welding distortions were investigated. It is found that following the proper welding sequence could minimize the welding distortion of the beam structure. Increasing the constraints of fixtures can prevent welding distortion effectively and reducing weld pool size results in less welding distortions of the beam structure.

  • 2203.
    Zhu, Lailai
    et al.
    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.
    Stone, Howard A.
    Princeton Univ, Dept Mech & Aerosp Engn, Princeton, NJ 08544 USA..
    Harnessing elasticity to generate self-oscillation via an electrohydrodynamic instability2020In: Journal of Fluid Mechanics, ISSN 0022-1120, E-ISSN 1469-7645, Vol. 888, article id A31Article in journal (Refereed)
    Abstract [en]

    Under a steady DC electric field of sufficient strength, a weakly conducting dielectric sphere in a dielectric solvent with higher conductivity can undergo spontaneous spinning (Quincke rotation) through a pitchfork bifurcation. We design an object composed of a dielectric sphere and an elastic filament. By solving an elasto-electro-hydrodynamic (EEH) problem numerically, we uncover an EEH instability exhibiting diverse dynamic responses. Varying the bending stiffness of the filament, the composite object displays three behaviours: a stationary state, undulatory swimming and steady spinning, where the swimming results from a self-oscillatory instability through a Hopf bifurcation. By conducting a linear stability analysis incorporating an elastohydrodynamic model, we theoretically predict the growth rates and critical conditions, which agree well with the numerical counterparts. We also propose a reduced model system consisting of a minimal elastic structure which reproduces the EEH instability. The elasto-viscous response of the composite structure is able to transform the pitchfork bifurcation into a Hopf bifurcation, leading to self-oscillation. Our results imply a new way of harnessing elastic media to engineer self-oscillations, and more generally, to manipulate and diversify the bifurcations and the corresponding instabilities. These ideas will be useful in designing soft, environmentally adaptive machines.

  • 2204.
    Zieliński, Tomasz G.
    et al.
    Institute of Fundamental Technological Research, Polish Academy of Sciences, ul. Pawińskiego 5B, 02-106 Warsaw, Poland.
    Opiela, Kamil C.
    Institute of Fundamental Technological Research, Polish Academy of Sciences, ul. Pawińskiego 5B, 02-106 Warsaw, Poland.
    Pawłowski, Piotr
    Institute of Fundamental Technological Research, Polish Academy of Sciences, ul. Pawińskiego 5B, 02-106 Warsaw, Poland.
    Dauchez, Nicolas
    Université de Technologie de Compiègne, Alliance Sorbonne Université, CNRS FRE 2012, Laboratoire Roberval, Centre de recherche Royallieu, CS 60319, 60203 Compiègne CEDEX, France.
    Boutin, Thomas
    Université de Technologie de Compiègne, Alliance Sorbonne Université, CNRS FRE 2012, Laboratoire Roberval, Centre de recherche Royallieu, CS 60319, 60203 Compiègne CEDEX, France.
    Kennedy, John
    Trinity College Dublin, Department of Mechanical & Manufacturing Engineering, Dublin 2, Ireland.
    Trimble, Daniel
    Trinity College Dublin, Department of Mechanical & Manufacturing Engineering, Dublin 2, Ireland.
    Rice, Henry
    Trinity College Dublin, Department of Mechanical & Manufacturing Engineering, Dublin 2, Ireland.
    Van Damme, Bart
    Swiss Federal Laboratories for Materials Science and Technology, Laboratory for Acoustics/Noise Control, Überlandstrasse 129, 8600 Dübendorf, Switzerland.
    Hannema, Gwenael
    Swiss Federal Laboratories for Materials Science and Technology, Laboratory for Acoustics/Noise Control, Überlandstrasse 129, 8600 Dübendorf, Switzerland.
    Wróbel, Rafal
    Swiss Federal Laboratories for Materials Science and Technology, Advanced Materials Processing, Überlandstrasse 129, 8600 Dübendorf, Switzerland.
    Kim, Seok
    Massachusetts Institute of Technology, Department of Mechanical Engineering, 77 Massachusetts Avenue, Cambridge, MA, USA.
    Ghaffari Mosanenzadeh, Shahrazd
    Massachusetts Institute of Technology, Department of Mechanical Engineering, 77 Massachusetts Avenue, Cambridge, MA, USA.
    Fang, Nicolas X.
    Massachusetts Institute of Technology, Department of Mechanical Engineering, 77 Massachusetts Avenue, Cambridge, MA, USA.
    Yang, Jieun
    Eindhoven University of Technology, Department of the Built Environment, P.O. Box 513, 5600 MB Eindhoven, The Netherlands.
    Briere de La Hosseraye, Baltazar
    Eindhoven University of Technology, Department of the Built Environment, P.O. Box 513, 5600 MB Eindhoven, The Netherlands.
    Hornikx, Maarten C. J.
    Eindhoven University of Technology, Department of the Built Environment, P.O. Box 513, 5600 MB Eindhoven, The Netherlands.
    Salze, Eduoard
    Ecole Centrale de Lyon, Université de Lyon, CNRS UMR 5509, Laboratoire de Mécanique des Fluides et d’Acoustique, 36 avenue Guy de Collongue, 69134 Écully CEDEX, France.
    Galland, Marie-Annick
    Ecole Centrale de Lyon, Université de Lyon, CNRS UMR 5509, Laboratoire de Mécanique des Fluides et d’Acoustique, 36 avenue Guy de Collongue, 69134 Écully CEDEX, France.
    Boonen, Rene
    KU Leuven, Department of Mechanical Engineering, Celestijnenlaan 300B box 2420, 3001 Heverlee, Belgium.
    Carvalho de Sousa, Augusto
    KU Leuven, Department of Mechanical Engineering, Celestijnenlaan 300B box 2420, 3001 Heverlee, Belgium.
    Deckers, Elke
    KU Leuven, Department of Mechanical Engineering, Celestijnenlaan 300B box 2420, 3001 Heverlee, Belgium.
    Gaborit, Mathieu
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics, Marcus Wallenberg Laboratory MWL.
    Groby, Jean-Philippe
    Laboratoire d’Acoustique de l’Université du Mans (LAUM), UMR CNRS 6613, Institut d’Acoustique – Graduate School (IA-GS), CNRS, Le Mans Université, France.
    Reproducibility of sound-absorbing periodic porous materials using additive manufacturing technologies: Round robin study2020In: Additive Manufacturing, ISSN 2214-8604, E-ISSN 2214-7810, Vol. 36, article id 101564Article in journal (Refereed)
    Abstract [en]

    The purpose of this work is to check if additive manufacturing technologies are suitable for reproducing porous samples designed for sound absorption. The work is an inter-laboratory test, in which the production of samples and their acoustic measurements are carried out independently by different laboratories, sharing only the same geometry codes describing agreed periodic cellular designs. Different additive manufacturing technologies and equipment are used to make samples. Although most of the results obtained from measurements performed on samples with the same cellular design are very close, it is shown that some discrepancies are due to shape and surface imperfections, or microporosity, induced by the manufacturing process. The proposed periodic cellular designs can be easily reproduced and are suitable for further benchmarking of additive manufacturing techniques for rapid prototyping of acoustic materials and metamaterials.

  • 2205.
    Zschäpitz, David
    et al.
    Department for Vascular and Endovascular Surgery, Klinikum rechts der Isar, Technical University Munich, Munich, Germany.
    Bohmann, Bianca
    Department for Vascular and Endovascular Surgery, Klinikum rechts der Isar, Technical University Munich, Munich, Germany.
    Lutz, Brigitta
    Division of Vascular and Endovascular Surgery, Department for Visceral-, Thoracic and Vascular Surgery, Medical Faculty Carl Gustav Carus and University Hospital, Technische Universitat Dresden, Dresden, Germany.
    Eckstein, Hans Henning
    Department for Vascular and Endovascular Surgery, Klinikum rechts der Isar, Technical University Munich, Munich, Germany.
    Reeps, Christian
    Division of Vascular and Endovascular Surgery, Department for Visceral-, Thoracic and Vascular Surgery, Medical Faculty Carl Gustav Carus and University Hospital, Technische Universitat Dresden, Dresden, Germany.
    Maegdefessel, Lars
    Department for Vascular and Endovascular Surgery, Klinikum rechts der Isar, Technical University Munich, Munich, Germany.
    Gasser, Christian
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics, Solid Mechanics.
    Busch, Albert
    Department for Vascular and Endovascular Surgery, Klinikum rechts der Isar, Technical University Munich, Munich, Germany; Division of Vascular and Endovascular Surgery, Department for Visceral-, Thoracic and Vascular Surgery, Medical Faculty Carl Gustav Carus and University Hospital, Technische Universitat Dresden, Dresden, Germany.
    Rupture risk parameters upon biomechanical analysis independently change from vessel geometry during abdominal aortic aneurysm growth2023In: JVS-Vascular Science, E-ISSN 2666-3503, Vol. 4, article id 100093Article in journal (Refereed)
    Abstract [en]

    Objective: The indication for abdominal aortic aneurysm (AAA) repair is based on a diameter threshold. However, mechanical properties, such as peak wall stress (PWS) and peak wall rupture index (PWRI), influence the individual rupture risk. This study aims to correlate biomechanical and geometrical AAA characteristics during aneurysm growth applying a new linear transformation-based comparison of sequential imaging. Methods: Patients with AAA with two sequential computed tomography angiographies (CTA) were identified from a single-center aortic database. Patient characteristics included age, gender, and comorbidities. Semiautomated segmentation of CTAs was performed using Endosize (Therenva) for geometric variables (diameter, neck configuration, α/β angle, and vessel tortuosity) and for finite element method A4 Clinics Research Edition (Vascops) for additional variables (intraluminal thrombus [ILT]), vessel volume, PWS, PWRI). Maximum point coordinates from at least one CTA 6 to 24 months before their final were predicted for the final preoperative CTA using linear transformation along fix and validation points to estimate spatial motion. Pearson's correlation and the t test were used for comparison. Results: Thirty-two eligible patients (median age, 70 years) were included. The annual AAA growth rate was 3.7 mm (interquartile range [IQR], 2.25-5.44; P <.001) between CTs. AAA (+17%; P <.001) and ILT (+43%; P <.001) volume, maximum ILT thickness (+35%; P <.001), β angle (+1.96°; P =.017) and iliac tortuosity (+0.009; P =.012) increased significantly. PWS (+12%; P =.0029) and PWRI (+16%; P <.001) differed significantly between both CTAs. Both mechanical parameters correlated most significantly with the AAA volume increase (r = 0.68 [P <.001] and r = 0.6 [P <.001]). Changes in PWS correlated best with the aneurysm neck configuration. The spatial motion of maximum ILT thickness was 14.4 mm (IQR, 7.3-37.2), for PWS 8.4 mm (IQR, 3.8-17.3), and 11.5 mm (IQR, 5.9-31.9) for PWRI. Here, no significant correlation with any of the aforementioned parameters, patient age, or time interval between CTs were observed. Conclusions: PWS correlates highly significant with vessel volume and aneurysm neck configuration. Spatial motion of maximum ILT thickness, PWS, and PWRI is detectable and predictable and might expose different aneurysm wall segments to maximum stress throughout aneurysm growth. Linear transformation could thus add to patient-specific rupture risk analysis. Clinical Relevance: Abdominal aortic aneurysm rupture risk assessment is a key feature in future individualized therapy approaches for patients, since more and more data are obtained concluding a heterogeneous disease entity that might not be addressed ideally looking only at diameter enlargement. The approach presented in this pilot study demonstrates the feasibility and importance of measuring peak wall stress and rupture risk indices based on predicted and actual position of maximum stress points including intraluminal thrombus.

  • 2206.
    Zu, Marion
    et al.
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics.
    Garme, Karl
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics.
    Rosén, Anders
    KTH, School of Industrial Engineering and Management (ITM), Learning, Learning in Stem.
    Seakeeping criteria revisited2024In: Ocean Engineering, ISSN 0029-8018, E-ISSN 1873-5258, Vol. 297, article id 116785Article in journal (Refereed)
    Abstract [en]

    Seakeeping evaluations are important in the early design stages in order to ensure that vessels can sail the seas and execute their missions safely in the intended conditions. Such evaluations require a set of criteria that translate seakeeping design requirements into tangible measures for decision-making. Despite the availability of seakeeping criteria, certain unsuitable considerations and specifications currently in use result in challenges to crew and operations that do not become apparent until later in a vessel’s service. Though not claimed to be exhaustive, this paper catalogues and reviews the seakeeping criteria commonly used to date, guided by findings from focus group discussions and semi-structured interviews.  The paper unearths the original sources whilst discussing the scientific basis for these criteria and standards. Particular attention is given to the early design stages and opportunities for improvement and further development are highlighted. Findings from this study indicate that it is necessary to develop seakeeping criteria for certain vessel types and that there are opportunities to improve seakeeping criteria addressing crew well-being, performance and safety.

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  • 2207.
    Zu, Marion
    et al.
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics, Lättkonstruktioner, marina system, flyg- och rymdteknik, rörelsemekanik.
    Garme, Karl
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics, Lättkonstruktioner, marina system, flyg- och rymdteknik, rörelsemekanik.
    Rosén, Anders
    KTH, School of Industrial Engineering and Management (ITM), Learning, Learning in Stem.
    Costa, Nicole
    SSPA Sweden AB.
    Specifying Seakeeping Criteria for Efficient Task Performance2022In: Proceedings 15th International Symposium on Practical Design of Ships and Other Floating Structures PRADS 2022, 2022Conference paper (Refereed)
    Abstract [en]

    Determining the operability of a vessel is a critical task for the naval architect since it provides valuable information for vessel owners and operators on the vessel’s performance. This task requires a seakeeping analysis and a set of seakeeping criteria to evaluate predicted vessel motions. These seakeeping criteria link the performance and safety of the crew and vessel to operability. Existing seakeeping criteria (e.g., NORDFORSK, NATO STANAG 4154) are specified for certain vessel types and not applicable to different tasks and operational activities aboard work vessels such as pilot boats, ocean research vessels, dredgers, pipe laying crane vessels. Being relatively small in size, these work vessels are susceptible to the perils of waves, yielding motion responses that can degrade crew performance. This paper proposes a framework for specifying seakeeping criteria for efficient task performance, focusing primarily on the effects of motions on the crew and system performance. Findings from preliminary interviews with some crew at the Swedish Maritime Administration and the Swedish Sea Rescue Society align with the literature on the effects of motions on crew performance, including motion-induced interruptions, motion-induced fatigue, motion sickness, and effects on motor skills and perception. These findings from the interviews are used in a case study to demonstrate the approach of the proposed framework. The proposed framework refines further and adds to the established structure of the traditional seakeeping assessment since it captures, in addition, the effect of motions on crew performance.

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  • 2208.
    Älfvåg, Hector
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics. KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Heat and Power Technology.
    Parametric Study of Separation in Outlet Diffuser of Rocket Nozzle Cooling Channel Rig: The Effect of Heat Flux and Angle of Outlet Diffuser for Rectangular-to-Circular Cross Section Transitions2021Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    The use of natural gas with high methane content as rocket fuel has gained substantial industrial attention over the past number of years. Several actors including SpaceX and Blue Origin are developing natural gas powered rocket engines. Attention is also shown from GKN Aerospace, a Sweden-based aerospace engine development company, who together with KTH Royal Institute of Technology has initiated the MERiT project. The project is intended to investigate different aspects of methane powered engines. The project is centered around a physical test rig of a rocket nozzle cooling channel along with an ANSYS CFX simulationmodel of the same rig to investigate the operation. The rig is heated from one side to simulate the boundary conditions of a real rocket nozzle. This report is a follow-up to the previous work by Pettersson (2019), which determined rig design points for two channel geometries (channel 3, channel 4) and studied the behaviours and limitations in regards to overheating, cooling and coking. The channels feature outlet diffusers transitioning from rectangular to circular cross sections. The inputs investigated were mass flow, inlet temperature, outlet pressure and heat flux. Following the discovery of flow separation occurring in the rig at certain design points, it was suggested that a parametric study of the outlet diffuser angle could investigate the effect on separation in the outlet diffuser of the rig channel geometry. This is the task at hand in this thesis, and a complementary investigation on the effect heat flux has on separation is also performed for single selected diffuser angles. To achieve this, the full rig model geometry is first reduced to its core components to reduce simulation run time, and the parametric diffuser is implemented for both channel geometries. The mesh and the model definition is then adjusted to accommodate the changes made, by for example replacing the full rig heater block with a constant heat flux boundary condition. After this, a total of 40 test cases of different diffuser angle and heat flux combinations are used to establish trends in the behaviour of the separation. The results show that separation occurs more easily for the channel 3 configuration, which sees separation occur for lower diffuser angles and heat flux settings. The separation grows diminishinly as the heat flux and diffuser angle is increased. The separation onset location is found to consistently be in the corners of the outlet diffuser, after which it expands and rotates into the symmetry plane further downstream. The channel 4 solution convergence is found to be increasingly poor for higher diffuser angles, which suggests the solutions may be transient in nature. The Reynolds and Mach number is found to be correlated to the heat flux applied but no conclusion can be made about their link to separation for the cases studied.

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  • 2209.
    Åbom, Mats
    et al.
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics, Marcus Wallenberg Laboratory MWL.
    Jacob, Stefan
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics, Marcus Wallenberg Laboratory MWL.
    A comment on the correct boundary conditions for the Cremer impedance2021In: JASA EXPRESS LETTERS, ISSN 2691-1191, Vol. 1, no 2, article id 022801Article in journal (Refereed)
    Abstract [en]

    Mode merging and the creation of exceptional points can be used to create optimum damping in a lined duct, as pointed out by Cremer [Acustica 3, 249-263 (1953)]. The effect of a mean flow has traditionally been analyzed by assuming the Ingard-Myer boundary condition at the wall. For low frequencies, however, the classical boundary condition is a better alternative. This paper shows that this choice removes two problems with the low-frequency solution: the negative real part of the optimum wall impedance and the non-valid solution for the upstream case. Theoretical derivations are complemented by numerical results to support these conclusions.

  • 2210.
    Åkesson, Anton
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics, Lättkonstruktioner, marina system, flyg- och rymdteknik, rörelsemekanik.
    Tools and Challenges in Evaluating Control Surface Airworthiness for a Blended-Wing-Body UAV2023Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    For transport aeroplanes the Blended-Wing-Body (BWB) configuration shows promise in improving aerodynamic efficiency. The Green Raven project strives to demonstrate hydrogen fuel-cell-electric propulsion on a 4 m wingspan BWB. Due to the lack of a traditional horizontal tailplane, BWBs commonly have multifunctional control surfaces that void assumptions needed for traditional sizing methods. This work endeavoured to produce a control surface configuration that would permit adequate flying qualities of the Green Raven according to the MIL-F-8785C specification, preferably while minimising cruise power draw. The open-source aerospace modelling and optimisation environment SUAVE was chosen for the task, with the intention of adding any needed functionality.SUAVE was modified to permit the definition of general-purpose control surfaces and stability derivatives to be obtained for the additional degrees of freedom they bring which was demonstrated using a SUAVE representation of the Green Raven. The precise procedure for airworthiness-constrained control surface optimisation could not be determined before cessation of work but an outline of a simplified procedure was proposed.

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  • 2211.
    Öberg, Johan
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics, Väg- och spårfordon samt konceptuell fordonsdesign.
    Track Deterioration of Ballasted Tracks – Marginal Cost Models for Different Railway Vehicles2006Independent thesis Advanced level (degree of Master of Fine Arts (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Deterioration of the railway structure of ballasted tracks is unavoidable and can result in extensive costs for the track owner. Since the railway is one of the most important infrastructures and transport systems it has to be maintained and in order to foresee the deterioration of the track; the phenomena has to be understood and described in an engineering way. Through the years a lot of research has been carried out and a lot of different models have been formulated.

    The aims of this work are to present a ‘state of the art’ overview of existing track deterioration models and their properties and, with the models as a base, put together a model that predicts average deterioration cost for different vehicle types. Relations between track-vehicle parameters on one hand and wear and rolling contact fatigue (RCF) on the other are investigated through simulations. Finally, a computer software package is designed as to implement a model proposal to track deterioration.

    For the understanding of track deterioration it is necessary to link vehicle properties – mainly forces – to the process of deterioration. Though other factors such as time and environment also affect the track construction, it is the traffic that causes much of the damage. In this report four main mechanisms are considered: (1) deterioration of the track geometric quality due to settlement; (2) component fatigue; (3) wear of rails and (4) rolling contact fatigue of rails.

    The literature survey resulted in description and evaluation of a total of 21 models for track deterioration and some models for allocation of costs on vehicles for track access charging purposes. Only a few models tried to describe a more complex picture, involving several parameters and mechanisms. It is further concluded that most models dealing with settlement takes the load to a power between 1 and 5.

    Based on the literature survey a model proposal is presented that could be used to determine the cost of track deterioration for different vehicle types regarding deterioration of track geometric quality (both vertical and lateral), component fatigue, and rolling contact fatigue as well as abrasive wear of rails. The set of equations in the model is built into an Excel® environment software called DeCAyS – Deterioration Cost Associated with the Railway Superstructure. The model uses high-frequency wheel loads and wear number as main input for each vehicle type. It is proposed that track force measurements according to the UIC code 518, together with complementary data and simulations, should be used as sources for input. The high-frequency part of the wheel load is accounted for by the unsprung mass of the vehicle. It is also possible to enter measured data on high-frequency forces directly into the software.

    By assuming a traffic volume and the total cost per deteriorating mechanism, the track deterioration was determined for different vehicle types. The outcome is that there are very large differences between vehicles and their ability to cause damage to the track structure.

    An extensive series of simulations in the dynamic multibody simulation software GENSYS® have given output results on (quasi-static lateral forces, track shift forces and) approximated friction energy loss (the so-called wear number) for two different axle loads and a number of combinations of axle distance, wheel-rail friction and stiffness in wheelset guidance on 4-axle bogie vehicles. These results are examples of a set of data used as input to the deterioration model in particular regarding the friction energy loss and the associated rail wear.

  • 2212. Öhr, J.
    et al.
    Moberg, S.
    Wernholt, E.
    Hanssen, S.
    Pettersson, J.
    Persson, S.
    Tavallaey, Shiva Sander
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics, Technical Acoustics. ABB Corporate Research.
    Identification of flexibility parameters of 6-axis industrial manipulator models2006In: ISMA2006, Vol. 6, p. 3305-3313Article in journal (Refereed)
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  • 2213.
    Örlü, Ramis
    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.
    Peinke, J.
    Talamelli, A.
    Oberlack, M.
    9th iTi Conference on Turbulence, iTi 2021,  Virtual, Online2021Conference paper (Refereed)
  • 2214.
    Örlü, Ramis
    et al.
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics.
    Schlatter, Philipp
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics.
    Comment on "Evolution of wall shear stress with Reynolds number in fully developed turbulent channel flow experiments"2020In: Physical Review Fluids, E-ISSN 2469-990X, Vol. 5, no 12, article id 127601Article in journal (Other academic)
    Abstract [en]

    The recent study by Gubian et al. [Phys. Rev. Fluids 4, 074606 (2019)], based on a new wall-shear-stress sensor in a low-Reynolds-number Re turbulent channel flow, came to the surprising conclusion that the magnitude of the fluctuating wall-shear stress tau(+)(w,rms) reaches an asymptotic value of 0.44 beyond the friction Reynolds number Re-tau approximate to 600. This statement is at odds with results from well-established direct numerical simulation (DNS) results that exceed the authors' highest Reynolds number by up to a factor of 5 while exhibiting a clear Reynolds-number dependence. Furthermore, they claim that "prior estimates of these quantities did not resolve the full range of wall-shear-stress fluctuations, which extended beyond 10 standard deviations above the mean." This contradicts high-quality DNS results and calls for a more in-depth explanation, which is given in the present Comment. We shows that the measurements by Gubian et al. suffer from spatial-resolution issues among others, which when accounted for invalidate the statements made of an asymptotic state at Re-tau approximate to 600 and resurrects the Reynolds-number dependence of tau(+)(w,rms) for which DNS evidence exists exceeding Re-tau approximate to 600 by an order of magnitude.

  • 2215.
    Örlü, Ramis
    et al.
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Engineering Sciences (SCI), Engineering Mechanics.
    Tillmark, Nils
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Engineering Sciences (SCI), Engineering Mechanics.
    Alfredsson, P. Henrik
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Engineering Sciences (SCI), Engineering Mechanics.
    Measured critical size of roughness elements2021Report (Other academic)
    Abstract [en]

    This report describes wind-tunnel measurements within the RECEPT project to

    determine transition behind a single roughness element placed near the leading

    edge of a 35 degree swept airfoil at negative (-5 degrees) angle of attack with the

    rotation axis parallel to the leading edge. A negative angle of attack decreases the

    sensitivity to Tollmien-Schlichting wave-type instabilities and instead makes the

    boundary layer flow mainly sensitive to cross-flow instability disturbances.

    The airfoil was heated by blowing air through its hollow structure and transition

    was detected through infrared (IR) temperature measurements of the airfoil

    surface. The physical background behind the detection method is that if transition

    occurs, the flow at the wall inside the turbulent wedge behind the roughness element

    will have a larger friction than the laminar flow outside and hence a larger

    heat transfer, making the wall temperature lower in this region. To confirm the

    interpretation of the IR temperature images as well as provide measured boundary

    layer parameters additional hot-wire measurements within the boundary layer

    were performed at few of the parameters covered by the IR measurements. These

    parameters are both related to the roughness elements themselves such as their

    diameters and heights as well as free-stream velocities and turbulence levels of

    the approaching flow.

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  • 2216.
    Örlü, Ramis
    et al.
    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.
    Instantaneous wall-shear-stress measurements: advances and application to near-wall extreme events2020In: Measurement science and technology, ISSN 0957-0233, E-ISSN 1361-6501, Vol. 31, no 11, article id 112001Article, review/survey (Refereed)
    Abstract [en]

    In this article we provide an overview of widely used methods to measure the mean and fluctuating components of the wall-shear stress in wall-bounded turbulent flows. We first note that it is very important to perform direct measurements of the mean wall-shear stress, where oil-film interferometry (OFI) provides the highest accuracy with an uncertainty level of around 1%. Nonetheless, several indirect methods are commonly used due to their straightforward application and these are reviewed in the light of recent findings in wall turbulence. The focus of the review lies, however, on the fluctuating wall-shear stress, which has over the last decade received renewed interest. In this respect, it is interesting to note that one near-wall feature that has received attention is the so-called backflow event, i.e. a sudden, strong short-lived reverse-flow area, which challenges measurement techniques in terms of temporal and spatial resolution, as well as their dynamic range and multi-directional capabilities. Therefore, we provide a review on these backflow events as well as commonly used techniques for fluctuating wall-shear-stress measurements and discuss the various attempts to measure them. The review shows that further development of the accuracy and robustness of available measurement techniques is needed, so that such extreme events can be adequately measured.

  • 2217.
    Öster, Hanna
    et al.
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics, Lättkonstruktioner, marina system, flyg- och rymdteknik, rörelsemekanik.
    Isorena Guðjónsdóttir, Sara
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics, Lättkonstruktioner, marina system, flyg- och rymdteknik, rörelsemekanik.
    Incorporating Flax Fiber Composites in Hypercar Panels2023Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    This thesis investigates sound transmission loss through flat finite panels using composite materials, which incorporate both carbon and flax fibres. The study wascarried out by performing FEM simulations developed and validated in steps. Thevalidation process was time-consuming but crucial in ensuring the model’s reliability.The analysis demonstrates the relationship between the panels’ mass, stiffness, andsound reduction effectiveness by studying the sound transmission loss for a flat plate.The results show how by adjusting the plate’s stiffness, thickness, and mass one cancontrol its reaction to the incoming sound. This allows resonance frequencies to beshifted away from critical points and avoids coincidence frequencies. By understanding the acoustic behavior of composite panels, this research contributes to improvingsoundproofing properties while preserving their mechanical advantages. In an era ofgrowing demand for better acoustic performance in the automotive industry, exploring innovative methods to optimize the sound transmission loss of composite panelsis essential.

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  • 2218.
    Östlund, Sören
    et al.
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics, Solid Mechanics.
    Mäkelä, Petri
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics, Solid Mechanics.
    Fracture properties2021In: Mechanics of Paper Products, Walter de Gruyter GmbH , 2021, p. 77-103Chapter in book (Other academic)
  • 2219. Özdür, N.A.
    et al.
    Üçel, I. Buǧra
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics, Solid Mechanics. Bogazici University, Istanbul, Bebek 34342, Turkey.
    Yang, J.
    Aydıner, C. C.
    Residual Intensity as a Morphological Identifier of Twinning Fields in Microscopic Image Correlation2021In: Experimental mechanics, ISSN 0014-4851, E-ISSN 1741-2765, Vol. 61, no 3, p. 499-514Article in journal (Refereed)
    Abstract [en]

    Background: In the microscopic observation of deforming metals, it is well known that crystallite defects that accommodate strain can occasionally become visible, namely, they introduce image contrast to their locality. For microscopic digital image correlation (DIC) applications, this is typically known as a disturbance. Objective: Here, we explore a potential upside of these image-intensity offsets, to present a new mode of differential imaging that exclusively displays the underlying plasticity agents. Methods: For this, the intensity-offset signal is isolated with residual intensity, essentially the differential between reference- and deformed-configuration intensity of each material point. The premise is showcased over an autocatalytic twin band in Magnesium AZ31, with an advanced DIC instrument that utilizes bright-field optical microscopy. With robust area-scanning that utilizes in-situ corrective measures, a material field of around 5000 grains (13 μm average size) is sampled with a maximal intragranular resolution (~250 data points per grain) for this technique. For added robustness against the intensity alterations, a DIC algorithm (Augmented Lagrangian DIC) that enforces global kinematic compatibility constraints is utilized. Results: The calculated residual intensity map yields a detailed image of the twin networks that show a strong positional alignment with the strain localizations. At the band boundary, the twins (and their accompanying strain localization) protrude into the dormant material in a comb-like pattern. Conclusions: With a combination of high-resolution optics and defects that alter the surface topography, residual intensity presents a new in-situ microscopy mode that is tied to the DIC analysis. This principle also offers potential micro-deformation imaging capabilities for various other material-microscopy combinations.

  • 2220.
    Üçel, İbrahim Buğra
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics, Solid Mechanics.
    Mechanical behavior of Lithium-ion battery electrodes – experimental and statistical finite element analyses2023Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    The applications of Li-ion batteries in the electronics and vehicle industry is increasing at a very rapid pace. This is primarily due to superior properties such as high specific energy storage and power as well as wider operation temperature ranges. Additional potential for improved properties is connected to capacity losses with time and the thereby resulting limitations of lifetime of batteries. The lifetime of a battery is strongly related to the mechanical and chemical degradation of the active material of electrodes during repeated electrochemical reactions at charging and discharging. To identify this phenomenon from a mechanical perspective, the mechanical properties of the electrode active layers should be characterized. Additionally, with the aid of mechanical properties, realistic electro-chemo-mechanical models should be developed to comprehend the mechanisms causing capacity fade.

    In the first part of this thesis, macroscopic material properties of the active layers of Li-ion battery electrodes were measured with a unique bending test technique. Contrary to methods previously used; it is capable to overcome the challenges that were encountered in other traditional testing techniques. In papers 1 and 2 this bending test technique (U-shaped bending test), is used to characterize the elastic and viscoelastic behavior of NMC cathodic and graphite anodic active layers, respectively. By using single-sided thin electrode specimens in U-shape bending tests, it was possible to distinguish tensile and compressive elastic and viscoelastic behavior of the electrode active materials. The tensile Young’s moduli of cathodic and anodic active layers are found as 0.73 GPa and 1 GPa, respectively. On the other hand, the compressive Young’s moduli show a stiffening behavior at increasing strains. Stiffnesses between 1.3 GPa and 2.8 GPa for the cathodic active layer, and between 1 GPa and 3.8 GPa for the anodic active layer were recorded. This compressive behavior of the electrode active layers is expected as a result of the porous nature of the materials. In addition, the viscoelastic behavior of the electrode active layers is expressed through Prony series. It was observed that the behavior can be described by a short term (minutes) and a long term (hours, days) relaxation.

    In paper 3, a statistical representative volume element is introduced to predict the elastic properties of a dry cathodic electrode active layer. A porous cathodic electrode active layer that is composed of NMC active particles and polymeric binder material with conductive carbon additives is modeled as a face-centered-cubic structure. Several particle-binder and particle-particle interaction conditions are repeated 50 times with random orientations. Based on the statistics for each interaction case, Young’s modulus is estimated. The results show a good agreement with the experimental findings from Paper 1. Furthermore, particle-particle and particle-binder contact force distributions are calculated for 3% of particle swelling. The characteristics of the force distributions are correlated with the typical material failures in the active layer such as particle cracking and binder debonding. The statistical data obtained here are also used to improve an analytical model that was previously derived to estimate the elastic properties of active porous layers. The analytical model, complemented by the statistical results, showed an excellent agreement with the finite element simulations.

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  • 2221.
    Stenius, Ivan (Editor)
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics. SMaRC.
    Sigray, Peter (Editor)
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics. SMaRC.
    Linn, Gunnar (Editor)
    Linnkonsult.
    SMaRC Swedish Maritime Robotics Centre: Mid-Term Evaluation Report 20202020Report (Other academic)
    Abstract [en]

    This is the midterm report of the project SMaRC (Swedish Maritime Robotics Centre), which is one of four industrial research centres (IRC) funded by the Swedish Foundation for Strategic Research (SSF). SMaRC is a unique collaborative research environment consisting of key industry, academia, and governmental partners in Sweden. The focus of the centre is to enable a transformational/disruptive shift towards the next generation of marine robots.The aim of this report is to describe how SMaRC will provide industrial outcomes that deliver into societal benefit areas, by linking user-defined scenarios with capabilities. This will strengthen the research focus as well as create a transparent mapping from scientific activities to end-user needs. The SMaRC project has now reached its midpoint and is running according to plan. The initial start-up process is now passed and key milestones of the project have been reached and demonstrated at the joint workshop and demonstration periods. SMaRC has already participated in very challenging Antarctic expeditions, developed and tested its own underwater robots, and demonstrated new capabilities for perception, navigation, endurance and autonomy in both simulator environments and in field experiments. For the upcoming second half of the project period, the focus will be on integration and demonstration to move closer to the industrial and end-user needs. The future research plan is connected to six targeted scenarios highlighting key capabilities to reach within the research projects. The demonstration of these scenarios also supports enhanced cooperation with both national and international partners.

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