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  • 301.
    Ceccato, Chiara
    et al.
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics, Solid Mechanics.
    Kulachenko, Artem
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.).
    Barbier, C.
    BillerudKorsnäs, Grums, Värmland County, Sweden.
    Investigation of rolling contact between metal and rubber-covered cylinders governing the paper compaction process2019In: International Journal of Mechanical Sciences, ISSN 0020-7403, E-ISSN 1879-2162, Vol. 163, article id 105156Article in journal (Refereed)
    Abstract [en]

    With the goal of partial or complete replacement of plastic components with paper-based products, 3D paper structures have seen a growing interest in industrial applications: from packaging to more complex daily life objects. However, the extensibility of paper has become a key issue within this context and is the main factor determining the formability of these products and determining the depth of the achievable shapes. The most effective way to increase paper's stretch potential is by subjecting the moist paper web to a compaction process, which can be achieved through an extensible unit that is located in the drying section of a paper machine, where the network experiences in-plane compression in the machine direction (MD), under out-of-plane lateral constraints. The objective of this work is to clarify the mechanisms governing the compression process and to evaluate the influence of various parameters on the final material properties to optimize the industrial production of extensible paper. The system operation has been simulated realistically and shows that paper experiences a compressive state passing through the nip, with plastic strains in MD direction being of the same order of the applied speed difference, which was expected experimentally in optimal conditions of compaction. Starting from an initial reference case, a sensitivity study has been performed to identify and address the following factors that may affect the compression state: (a) friction coefficients; (b) indentation level; (c) speed difference; and (d) rubber properties. The analysis of the numerical results gives an insight into the mechanisms governing the compaction operations and allows a better comprehension of the features controlling the process outcome.

  • 302.
    Cederqvist, Hugo
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics, Väg- och spårfordon samt konceptuell fordonsdesign.
    Development of validation tool for antenna positioners on vehicles in motion2023Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Artificial satellites play a vital role throughout the world today. They providea broad range of services ranging from navigation to communication and reconnaissance. As antenna technology is evolving and ground based antennas are getting smaller and smaller, the demand for on-the-move solutions is growing.These antennas can be used whilst mounted on for example, a moving vehicle,where the mechanical performance of the antenna must be sufficient for thecurrent conditions. During this project, a computer based tool that can helpengineers when iterating and optimizing a two-axis gimbal type antenna designwas created. The tool uses simulated and recorded data from road vehicles andboats to calculate the required torque on the two axes necessary to sustain communication with a geostationary satellite. When completed, the tool was easy to use and configure whilst not requiring much computational power.

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  • 303.
    Cenni, Francesco
    et al.
    Univ Jyvaskyla, Fac Sport & Hlth Sci, Jyvaskyla, Finland.;Univ Jyvaskyla, Fac Sport & Hlth Sci, Rautpohjankatu 8, Jyvaskyla 40700, Finland..
    Alexander, Nathalie
    Childrens Hosp Eastern Switzerland, Lab Mot Anal, St Gallen, Switzerland..
    Sukanen, Maria
    Univ Jyvaskyla, Fac Sport & Hlth Sci, Jyvaskyla, Finland..
    Mustafaoglu, Afet
    Univ Jyvaskyla, Fac Sport & Hlth Sci, Jyvaskyla, Finland..
    Wang, Zhongzheng
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics. KTH MoveAbility.
    Wang, Ruoli
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics. KTH MoveAbility.
    Finni, Taija
    Univ Jyvaskyla, Fac Sport & Hlth Sci, Jyvaskyla, Finland..
    ISB clinical biomechanics award winner 2023: Medial gastrocnemius muscle and Achilles tendon interplay during gait in cerebral palsy2024In: Clinical Biomechanics, ISSN 0268-0033, E-ISSN 1879-1271, Vol. 111, article id 106158Article in journal (Refereed)
    Abstract [en]

    Background: The interplay between the medial gastrocnemius muscle and the Achilles tendon is crucial for efficient walking. In cerebral palsy, muscle and tendon remodelling alters the role of contractile and elastic components. The aim was to investigate the length changes of medial gastrocnemius belly and fascicles, and Achilles tendon to understand their interplay to gait propulsion in individuals with cerebral palsy.Methods: Twelve young individuals with cerebral palsy and 12 typically developed peers were assessed during multiple gait cycles using 3D gait analysis combined with a portable ultrasound device. By mapping ultrasound image locations into the shank reference frame, the medial gastrocnemius belly, fascicle, and Achilles tendon lengths were estimated throughout the gait cycle. Participants with cerebral palsy were classified into equinus and non-equinus groups based on their sagittal ankle kinematics.Findings: In typically developed participants, the Achilles tendon undertook most of the muscle-tendon unit lengthening during stance, whereas in individuals with cerebral palsy, this lengthening was shared between the medial gastrocnemius belly and Achilles tendon, which was more evident in the equinus group. The lengthening behaviour of the medial gastrocnemius fascicles resembled that of the Achilles tendon in cerebral palsy. Interpretation: The findings revealed similar length changes of the medial gastrocnemius fascicles and Achilles tendon, highlighting the enhanced role of the muscle in absorbing energy during stance in cerebral palsy. These results, together with the current knowledge of increased intramuscular stiffness, suggest the exploitation of intramuscular passive forces for such energy absorption.

  • 304. Chan, C. , I
    et al.
    Örlü, Ramis
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics.
    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.
    Chin, R. C.
    Univ Adelaide, Sch Mech Engn, Adelaide, SA 5005, Australia..
    Large-scale and small-scale contribution to the skin friction reduction in a modified turbulent boundary layer by a large-eddy break-up device2022In: Physical Review Fluids, E-ISSN 2469-990X, Vol. 7, no 3, article id 034601Article in journal (Refereed)
    Abstract [en]

    The role of streamwise length scales (lambda x) in turbulent skin friction generation is investigated using a direct numerical simulation data set of an incompressible zero pressure gradient turbulent boundary layer and the spectral analysis based on the FukagataL73 (2002)]. The total skin friction generation associated with motions scaled with local boundary layer thickness delta of lambda x 3 delta and lambda x 3 delta) contribute to a significant portion of turbulent skin friction. However, it is found that the large-scale ejection and sweep events with streamwise length scales at lambda x 3 delta are equally important. The turbulent skin friction reduction associated with the modification of largeand small-scale quadrant events is studied, using well-resolved simulation data sets of a large-eddy break-up (LEBU) device in a turbulent boundary layer. The results reveal that LEBUs modify both the large- and small-scale ejection and sweep events, yielding a substantial turbulent skin friction reduction.

  • 305.
    Chan, I. C.
    et al.
    Univ Adelaide, Sch Mech Engn, Adelaide, SA 5005, Australia..
    Örlü, Ramis
    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.
    Chin, R. C.
    Univ Adelaide, Sch Mech Engn, Adelaide, SA 5005, Australia..
    The skin-friction coefficient of a turbulent boundary layer modified by a large-eddy break-up device2021In: Physics of fluids, ISSN 1070-6631, E-ISSN 1089-7666, Vol. 33, no 3, article id 035153Article in journal (Refereed)
    Abstract [en]

    A computational study based on well-resolved large-eddy simulations is performed to study the skin friction modification by a large-eddy breakup device (LEBU) in a zero-pressure-gradient turbulent boundary layer. The LEBU was modeled using an immersed boundary method. It is observed that the presence of the device leads to the generation of wake vortices, which propagate downstream from the LEBU and toward the wall. A skin friction decomposition procedure is utilized to study different physical mechanisms of the observed skin friction reduction. From the skin friction decomposition, it is found that the skin friction reduction can be characterized by three universal regions of different changes for the skin friction contributions. The first region is predominantly associated with the formation of the wake vortices and the reduction of Reynolds shear stress. In the second region, the mean streamwise velocity fields show that a region of velocity deficit formed downstream of the LEBU propagates toward the wall and leads to turbulence reduction due to wake wall interactions, which also induces a local maximum skin friction reduction. In the third region, the dissipation of wake vortices leads to the regeneration of Reynolds shear stress. A quadrant analysis of the Reynolds shear stress contribution reveals that the LEBU increases the Q2 and Q4 contributions and attenuates the Q1 and Q3 contributions in the first region, followed by an onset of Reynolds shear stress further downstream.

  • 306.
    Chaparian, Emad
    et al.
    KTH, Centres, SeRC - Swedish e-Science Research Centre. KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics.
    Izbassarov, Daulet
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics. KTH, Centres, SeRC - Swedish e-Science Research Centre.
    De Vita, Francesco
    KTH, Centres, SeRC - Swedish e-Science Research Centre. KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics. Royal Inst Technol KTH, Mech Dept, SERC, Stockholm, Sweden..
    Brandt, Luca
    KTH, Centres, SeRC - Swedish e-Science Research Centre. KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics. Royal Inst Technol KTH, Mech Dept, SERC, Stockholm, Sweden..
    Tammisola, Outi
    KTH, Centres, SeRC - Swedish e-Science Research Centre. KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics.
    Yield-stress fluids in porous media: a comparison of viscoplastic and elastoviscoplastic flows2020In: Meccanica (Milano. Print), ISSN 0025-6455, E-ISSN 1572-9648, Vol. 55, no 2, p. 331-342Article in journal (Refereed)
    Abstract [en]

    A numerical and theoretical study of yield-stress fluid flows in two types of model porous media is presented. We focus on viscoplastic and elastoviscoplastic flows to reveal some differences and similarities between these two classes of flows. Small elastic effects increase the pressure drop and also the size of unyielded regions in the flow which is the consequence of different stress solutions compare to viscoplastic flows. Yet, the velocity fields in the viscoplastic and elastoviscoplastic flows are comparable for small elastic effects. By increasing the yield stress, the difference in the pressure drops between the two classes of flows becomes smaller and smaller for both considered geometries. When the elastic effects increase, the elastoviscoplastic flow becomes time-dependent and some oscillations in the flow can be observed. Focusing on the regime of very large yield stress effects in the viscoplastic flow, we address in detail the interesting limit of 'flow/no flow': yield-stress fluids can resist small imposed pressure gradients and remain quiescent. The critical pressure gradient which should be exceeded to guarantee a continuous flow in the porous media will be reported. Finally, we propose a theoretical framework for studying the 'yield limit' in the porous media.

  • 307.
    Chaparian, Emad
    et al.
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Engineering Sciences (SCI), Engineering Mechanics.
    Niazi Ardekani, Mehdi
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Brandt, Luca
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Engineering Sciences (SCI), Engineering Mechanics.
    Tammisola, Outi
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Engineering Sciences (SCI), Engineering Mechanics.
    Particle migration in channel flow of an elastoviscoplastic fluid2020In: Journal of Non-Newtonian Fluid Mechanics, ISSN 0377-0257, E-ISSN 1873-2631, Vol. 284, article id 104376Article in journal (Refereed)
    Abstract [en]

    We study the dynamics of a neutrally buoyant rigid sphere carried by an elastoviscoplastic fluid in a pressure-driven channel flow numerically. The yielding to flow is marked by the yield stress which splits the flow into two main regions: the core unyielded region and two sheared yielded regions close to the walls. The particles which are initially in the plug region are observed to translate with the same velocity as the plug without any rotation/migration. Keeping the Reynolds number fixed, we study the effect of elasticity (Weissenberg number) and plasticity (Bingham number) of the fluid on the particle migration inside the sheared regions. In the viscoelastic limit, in the range of studied parameters (low elasticity), inertia is dominant and the particle finds its equilibrium position between the centreline and the wall. The same happens in the viscoplastic limit, yet the yield surface plays the role of centreline. However, the combination of elasticity and plasticity of the suspending fluid (elastoviscoplasticity) trigger particle-focusing: in the elastoviscoplastic flow, for a certain range of Weissenberg numbers (≈0.5), isolated particles migrate all the way to the centreline by entering into the core plug region. This behaviour suggests a particle-focusing process for inertial regimes which was not previously found in a viscoelastic or viscoplastic carrying fluid. 

  • 308.
    Chaparian, Emad
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics. 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.
    Tammisola, Outi
    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.
    An adaptive finite element method for elastoviscoplastic fluid flows2019In: Journal of Non-Newtonian Fluid Mechanics, ISSN 0377-0257, E-ISSN 1873-2631, Vol. 271, p. 104148-Article in journal (Refereed)
    Abstract [en]

    Elastoviscoplastic fluids are a class of yield-stress fluids that behave like neoHookean (or viscoelastic) solids when the imposed stress is less than the yield stress whereas after yielding, their behaviour is described by a viscoplastic fluid with an additional elastic history. This exceptional behaviour has been recently observed by many yield stress fluids in rheometric tests such as waxy crude oil, Carbopol gel, etc. Moreover, interesting phenomena have been evidenced experimentally such as the presence of a negative wake and a loss of fore-aft symmetry about a settling particle which are predominantly related to the elastic behaviour of yield-stress fluids (i.e., coupling of elasticity and plasticity). Here, we present a numerical scheme based on the so-called augmented Lagrangian method for numerical simulation of elastoviscoplastic fluid flows. The method is benchmarked by two rheometric flows: Poiseuille and circular Couette flows for which analytical solutions are derived. Moreover, anisotropic adaptive mesh procedure (which was previously introduced for viscoplastic fluid flows by Saramito and Roquet, Comput. Meth. Appl. Mech. Eng., vol. 190, 2001, pp. 5391-5412) is coupled to obtain a fine resolution of the yield surfaces. Finally, the presented method is applied to study more complex flows: elastoviscoplastic fluid flow in a wavy channel.

  • 309.
    Chatelais, Léa
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics, Väg- och spårfordon samt konceptuell fordonsdesign.
    Vehicle dynamics modelling of electromagnetic suspensions for MAGLEV applications2024Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    MAGnetic LEVitation Guidance System (MAGLEV) technology was commercially introduced relatively recently in the guided transport field. It is based on removing the wheels and rails of classic railway systems and supporting and guiding the train with magnets and magnetic forces instead. But, as for conventional railways, those trains need to fulfil dynamic requirements in order to make trains safe and comfortable. The dynamics of a train being mainly influenced by its suspensions characteristics, the magnetic forces generated in MAGLEV systems are of prime importance. Having a model of those systems allows to check the requirements of a certain design, and to consider the influence of different parameters on their fulfilment. This thesis leans on research work on MAGLEV vehicle modelling to model and implement magnetic levitation components in a quarter-car model in order to study the fulfilment of vehicle dynamics requirements. Specifically, the modelled vehicles are based on Electro- Magnetic Suspension (EMS) and Electro-Dynamic Suspension (EDS) (Inductrack) technologies, for which the modelling equations are analysed to study the magnetic force dependencies with physical and operational parameters. Finally, the dynamic requirements are checked in response to a set of track irregularities amplitudes, anda parametric study is carried out to verify the fulfilment of those requirements for other design cases. The results show that it is possible to model and implement simple MAGLEV MBS models for dynamic studies, although it is challenging to model and simulate specific MAGLEV components because of the lack of component specifications or experimental data on track irregularities.

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  • 310.
    Chatterjee, Abhiroop
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics, Solid Mechanics.
    Approximating Damping Coefficient of Bolted Joints using the Finite Element Method2023Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Bolted joints are important due to their energy dissipation property in structures,but the damping mechanism is also highly nonlinear and localized. The goal ofthis thesis is to develop an accurate method for modeling bolted joint dampingin large structures using finite element (FE) software. To model bolted jointdamping, the first step is to study the mechanism and define the terms like slip,micro-slip, and macro-slip. An extensive literature review identified the necessarymethods: detailed contact model, thin-layer elements, and connector elements.These methods are compared based on parameters such as computation time,modeling time, etc. The thin-layer method was used for modeling bolted jointdamping in large structures.

    To evaluate parameters for thin-layer element modeling, a local joint model wasbuilt using contact formulation of an engine housing and ladder frame assembly.The computed parameters include normal stiffness, tangential stiffness, and lossfactor. Analysis reveals that the loss factor depends on pre-load and amplitudeload. The micro-slip is the region of interest where the loss factor was computed. Using curve-fitting, a range of amplitude-dependent loss factors was calculated.

    Finally, the thin-layer elements are used in the engine housing and ladder frameassembly to model bolted joint damping. The parameters estimated using the localjoint model are used to define the properties of the thin-layer elements such thatthe elements are a phenomenological representation of bolted joint. A mode-basedsteady-state analysis has been performed to estimate the loss factor on a systemlevel. The frequency response of such an analysis accurately captures the frequencyresponse curves of structures with bolted joints. The two important behaviors thathave been captured are the shifting of the resonance peak to a lower value and thewidening of the frequency response curve as the applied load increases. However,the resonance frequency shifting to a lower frequency (softening) has not beencaptured due to modeling limitations in the FE software. A substructure couplingmodel using the Craig-Bampton formulation of the engine housing and ladderframe assembly has been analyzed using a constant loss factor. The frequencyresponse of such a system appears to give an approximate behavior of a structurewith bolted joint damping.

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  • 311.
    Chauvat, Guillaume
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics.
    Receptivity, Stability and Sensitivity analysis of two- and three-dimensional flows2020Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    This work deals with various aspects of boundary-layer stability. Modal and non-modal approaches are first used in the study of the global stability of a jet in crossflow. This flow case presents a global instability in some regimes which results from a Hopf bifurcation from a steady wake to a limit cycle consisting of a shedding of hairpin vortices. The effects of non-normality are studied in relation with transient growth and numerical accuracy. It is shown that the equations must be solved to a very high accuracy in order to properly capture the spectrum and that the computational domain must be very long due to the elongated core of the instability. Non-modal techniques do not suffer from such issues. The so-called acoustic receptivity of a flat plate with a leading-edge is analysed using a global modes approach. This leads to a spatio-temporal analysis in which the modes must be corrected for the imaginary part of the eigenvalues. This correction involves the Parabolised Stability Equations (PSE). This work confirms results previously obtained through different methods. The stability of two- and three-dimensional boundary-layer flows in the presence of surface irregularities such as steps, gaps or humps is also studied using Direct Numerical Simulation (DNS). It is found that all the surface irregularities have a destabilising effect on stability of two-dimensional boundary layers, with the rectangular hump case being the most dangerous one.  In the case of three-dimensional boundary layers the effects are more complex. Our results accurately reproduce the steady flows, caused by small  forward-facing steps, from an experimental setup, and the interaction of saturated crossflow vortices with unsteady noise is discussed. This work also describes a new method related to modal decomposition of compressible flows with shocks. Traditional linear techniques such as the Proper Orthogonal Decomposition (POD) struggle to capture strong nonlinear phenomena such as shock motion.  The proposed shock-fitting approach tackles this issue by interpolating data onto a grid following the discontinuities. This requires detecting and parametrising the shocks, then mapping the original flow fields onto a reference mesh. A method to generate this mapping in two-dimensional domains is presented. Then the method is applied to two two-dimensional cases in ascending complexity. In addition to faster decay of the singular values, the modes obtained are cleaner and devoid of oscillations around the shocks.

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  • 312.
    Chauvat, Guillaume
    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.
    Paredes, Pedro
    Leading-edge acoustic receptivity investigation through global modes analysis2020Report (Other academic)
    Abstract [en]

    The acoustic receptivity of the boundary-layer flow on a flat plate with an elliptic leading edge is determined using a global eigenmode analysis. Proper boundary conditions yielding physically relevant eigenmodes are fundamental to this approach. A branch of modes consisting of the incompressible limit of a plane acoustic wave interacting with the leading edge to form TS waves in the boundary-layer of the flat plate is found. The damping of this branch is sensitive to numerical details, and the modes can be interpreted as pseudoeigenvalues rather than pure eigenvalues of the system. The receptivity coefficient extracted from the spatial structure of eigenvectors has been corrected for the imaginary part of the eigenvalues in order to determine the response to a time-periodic perturbation. This correction is based on solving the parabolised stability equations (PSE) between the leading edge, the lower branch of neutral stabilityof the TS mode, and the outflow. The results are found to be in good agreement with recent direct numerical simulations (Shahriari et al. 2016). We have also obtained results for lower frequencies than those reported there.

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  • 313.
    Chauvat, Guillaume
    et al.
    KTH, Centres, SeRC - Swedish e-Science Research Centre. KTH, School of Engineering Sciences (SCI).
    Peplinski, Adam
    KTH, Centres, SeRC - Swedish e-Science Research Centre. KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics.
    Henningson, Dan S.
    KTH, School of Engineering Sciences (SCI). KTH, Centres, SeRC - Swedish e-Science Research Centre.
    Hanifi, Ardeshir
    KTH, School of Engineering Sciences (SCI). KTH, Centres, SeRC - Swedish e-Science Research Centre.
    Global linear analysis of a jet in cross-flow at low velocity ratios2020In: Journal of Fluid Mechanics, ISSN 0022-1120, E-ISSN 1469-7645, Vol. 889, article id A12Article in journal (Refereed)
    Abstract [en]

    The stability of the jet in cross-flow is investigated using a complete set-up including the flow inside the pipe. First, direct simulations were performed to find the critical velocity ratio as a function of the Reynolds number, keeping the boundary-layer displacement thickness fixed. At all Reynolds numbers investigated, there exists a steady regime at low velocity ratios. As the velocity ratio is increased, a bifurcation to a limit cycle composed of hairpin vortices is observed. The critical bulk velocity ratio is found at approximately for the Reynolds number , above which a global mode of the system becomes unstable. An impulse response analysis was performed and characteristics of the generated wave packets were analysed, which confirmed results of our global mode analysis. In order to study the sensitivity of this flow, we performed transient growth computations and also computed the optimal periodic forcing and its response. Even well below this stability limit, at , large transient growth ( in energy amplification) is possible and the resolvent norm of the linearized Navier-Stokes operator peaks above . This is accompanied with an extreme sensitivity of the spectrum to numerical details, making the computation of a few tens of eigenvalues close to the limit of what can be achieved with double precision arithmetic. We demonstrate that including the meshing of the jet pipe in the simulations does not change qualitatively the dynamics of the flow when compared to the simple Dirichlet boundary condition representing the jet velocity profile. This is in agreement with the recent experimental results of Klotz et al. (J. Fluid Mech., vol. 863, 2019, pp. 386-406) and in contrast to previous studies of Cambonie & Aider (Phys. Fluids, vol. 26, 2014, 084101). Our simulations also show that a small amount of noise at subcritical velocity ratios may trigger the shedding of hairpin vortices.

  • 314.
    Chauvat, Guillaume
    et al.
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics.
    Schmid, Peter J.
    Hanifi, Ardeshir
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics.
    Mode decomposition of flows with shocks2020Report (Other academic)
    Abstract [en]

    We introduce a modification of the Proper Orthogonal Decomposition (POD) to allow the decomposition of data containing moving discontinuities without the typical drawbacks of POD such as the appearance of Gibbs' phenomena near the interface. We use a shock-fitting approach and interpolate the data onto a grid following the discontinuities.  Solutions of a model problem based on the Burgers' equation and unsteady supersonic flow around a cylinder are used to illustrate the new method. The advantages of the shock-fitting approach over the standard POD are demonstrated by a faster decay of singular values and sharper discontinuities in the identified modes. The Gibbs' phenomenon has been largely eliminated.

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  • 315.
    Chauvat, Guillaume
    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.
    Tocci, Francesco
    Rius-Vidales, Alberto
    Kotsonis, Marios
    Hein, Stefan
    Hanifi, Ardeshir
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics.
    Direct numerical simulations of the effects of a forward-facing step on the instability of crossflow vortices2020Report (Refereed)
    Abstract [en]

    We reproduce three variants of an experimental setup consisting of a swept wing in a wind tunnel through direct numerical simulation (DNS). The effect of a forward-facing step of two different heights at location $x/c_x = 0.2$ on a steady crossflow instability is analysed. The effect of discrete roughness elements used to condition the instability modes in the experiments is accurately reproduced via perturbations computed through nonlinear parabolised stability equations. Our results demonstrate that the setup can be reproduced accurately numerically as far as the steady flows are concerned, with a good agreement between the experimental and numerical profiles upstream and downstream of the step. Our results shed light on the flow structure in the vicinity of the step.

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  • 316.
    Cheemakurthy, Harsha
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics, Naval Systems.
    Efficient commuter craft for urban waterborne public transportation2021Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    There has been a recent surge in interest in waterborne public transportation (WPT). Publictransport providers (PTP) are seeing its potential in complementing the existing transportnetwork and alleviating urban traffic congestion and pollution. But the adoption of WPTtoday is challenging due to a series of technical and implementation challenges. Thesechallenges include ferry procurement practices, local legislation and policies andenvironmental factors like winter ice. Several of these challenges can be alleviated if efficientferries can be made accessible off-the-shelf with a low manufacturing time and cost. Thethesis focuses on developing such a ferry concept based on modular design whose overalldimensions are standardized and internal arrangement is customizable towards operationalrequirements, with a focus towards sustainable and safe operations in ice.Starting with the characterization of WPT, ferry routes are broadly classified into three types.These routes are described with an operational requirements framework considering allrelevant stakeholder expectations. Then, overall dimensions of vessels representative ofWPT are deduced. Using these dimensions to standardize the overall dimensions, a modularferry concept is developed as an assembly of modules and submodules. The modules arepresented as standardized units having fixed dimensions and interfaces whose internalarrangements can be tailored to meet operational requirements. Design standardizationlowers costs and manufacturing time while internal customization favours tailoring the ferryconcept. One challenge associated with this for the PTP is the difficulty in choosingappropriate modules among multiple alternatives. This is overcome through thedevelopment of a ranking and selection method which benchmarks competing designs andhelps in decision making.In terms of technical challenges for the developed ferry concept, cities like Stockholmexperience freezing of water bodies during winter months. For reliable year-roundoperations that are safe and sustainable in terms of economy and environment, there is aneed for the development of lightweight and robust ice going hulls. This thesis lays thefoundation for the development of such hulls by studying the prevalent ice data and proposesa probabilistic method for estimating the design ice pressures.One must rely on probabilistic methods since most experimental studies are based on seaice whose mechanical properties are different from freshwater ice, which is typical for WPT.Traditionally, classification society rules like the Finnish Swedish Ice Class Rules are usedfor first year light ice conditions which were developed for the Baltic Sea consideringicebreaker vessels. They work well in ensuring a safe design, but their performance forfreshwater ice, applied to commuter ferries have not been tested. Therefore, a probabilisticapproach is adopted where the unknown parameters are incorporated as random variables.The probabilistic method reduces the hull-ice interaction to a pressure and contact-arearelationship. With arctic datasets that closely match WPT conditions as the parent dataset,the probabilistic method is calibrated with exposure conditions for WPT to give the designpressure-area curve. The different uncertainties arising from operations in ice are studied using a statistical tool and the leading source of uncertainty is attributed to ice-loadprediction methods. This establishes the need for more robust methods for prediction of iceloads so that a lightweight, yet robust hull may be designed which is efficient in terms of fueleconomy and emissions.WPT presents a tremendous opportunity in complementing the existing transport network.With careful design and development of the modular ferry concept and its technicalchallenges, it would be easier for PTPs to adopt WPT globally.

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  • 317.
    Cheemakurthy, Harsha
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics, Lättkonstruktioner, marina system, flyg- och rymdteknik, rörelsemekanik.
    Framework for holistic design of ferries focusing on lightweight ice going hulls.2022Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Waterborne public transportation (WPT) is slowly increasing in importance as an active component of public transportation networks in cities. City planners are looking at WPT to overcome urban congestion and pollution. However, prevalent challenges like ferry procurement, poor state of existing ferry fleets and technical challenges like the presence of ice, have created reluctance in the minds of public transport providers (PTPs).  While contemporary research shows ferries can be economical and environmentally friendly, there are some fundamental challenges that need to be addressed before PTPs can feel confident.

    In this regard, deterrents from PTP’s perspective are identified and solutions are investigated, starting with a systematic characterization of WPT. A definite structure for operational requirements is proposed in an objective manner. Using these as basis, two standard ferry sizes that could fulfil multiple WPT roles in majority of cities are introduced. For establishing city-wise tailoring, platform-architecture based modularization of ferries is proposed. The ferry modules are tailored with respect to operational requirements in a clear and objective manner through the introduction of an evaluation methodology. The method incorporates economic, social, environmental, and regulatory stakeholders. These proposed solutions are aimed at improving PTP’s confidence in WPT and provides solutions for the marine industry to produce quick, cost efficient and tailored ferries. 

    Next, the scope is focused towards investigating sustainable operations in freshwater ice conditions, typically found in the Stockholm region in Sweden. The ice going ferries today operate with ice strengthened heavy hulls. While they work well in ice, they perform poorly in comparison with non-ice going ferries during ice free months. Correspondingly, solutions towards lightweight ice going hulls are investigated. 

    This investigation starts with understanding ice-hull interaction mechanisms. Then, techniques to estimate the ice loads are investigated. We adopt a probabilistic approach to tackle the limitations due to the stochastic nature of ice and a lack of experimental data. The resulting load cases are used for evaluating lightweight structural concepts. 

    The investigation is approached by dividing ice-hull interaction into quasi-static, dynamic and abrasive loading phases. Several candidates corresponding to the first two loading phases are investigated parametrically. The range of structural concepts include metal grillages, bio-inspired composites, and sandwich structures. Realistic loading models for quasi-static and impact mechanisms are developed and validated with experiments. The winning candidates for each loading phase are combined to propose a tri-layer lightweight structural concept. Three candidates for the concept are evaluated and compared.

    The thesis answers several questions that riddle WPT today. But at the same time, it raises new questions. Several directions for future work are identified. With continued development, it would be possible to see modularly tailored ferries operating with lightweight hulls in WPT systems around the world.

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    Kappa
  • 318.
    Cheemakurthy, Harsha
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Naval Systems. KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics, Naval Systems.
    Garme, Karl (Contributor)
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Naval Systems.
    Urban waterborne public transport systems: An overview of existing operations in world cities2017Report (Other academic)
    Abstract [en]

    This report aims to collate information on existing waterborne public transport systems in order to provide a resource for cities that may be considering implementing a water transit network. Stockholm City Council has recently expressed interest in expanding its existing inland waterway network to facilitate increased passenger transport capacity within the city and surrounding districts. This report introduces waterway public transportation systems currently operating in 23 cities around the world to provide an overview of the current state of urban water transit globally. Key operational metrics have been identified and described which have been chosen in order to be most relevant in assessing water transport options for cities. Information regarding system organization, route structure, schedules, and vessels have been compiled. In addition, operational factors contributing to the success of existing water transit systems have also been highlighted as per existing literature. Such characteristics introduced in the report overview include transport integration within the wider public transport network, public perception and feasibility of implementation, land use implications, and the role of water transport in tourism and leisure travel. Efforts toward incorporating environmental sustainability are also briefly addressed. Cities have been divided into three broad categories based on the geographic size and passenger carrying capacity of each water transit system. There were 13 cities identified as large scale, 6 as medium scale and 4 as small scale, or in nascent stages of development. Facilities on board vessels and also terminal infrastructure are compared, as well as any unique features or operating characteristics, which are highlighted. Finally, the systems are mapped a scale in order to compare route structures and scope of operation.

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  • 319.
    Cheemakurthy, Harsha
    et al.
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics, Lättkonstruktioner, marina system, flyg- och rymdteknik, rörelsemekanik.
    Barsoum, Zuheir
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics. KTH, School of Engineering Sciences (SCI), Centres, VinnExcellence Center for ECO2 Vehicle design.
    Burman, Magnus
    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.
    A lightweight ice going hull concept for freshwater ice operationsManuscript (preprint) (Other academic)
    Abstract [en]

    A fundamental challenge in ice-prone waterborne public transportation systems is the need for ice-strengthening while being fuel efficient during ice-free periods. To achieve this, the use of lightweight hull structures is explored in the current study by starting with introducing a tri-layer structural concept for an ice going hull. The three layers correspond to abrasion loads, impact loads and pressure loads experienced during a typical ice-hull interaction. Several structural concepts suited towards these respective loading mechanisms are considered. Most favorable parametric variants are identified and assembled as contenders in the tri-layer concept. The assembly is tested against experimentally validated ice impact models in FEA as well as a realistic quasi-static pressure representation. Three different lightweight structural concepts including aluminum grillage, stiffened sandwich structure and metal-FRP stiffened sandwich structure are compared and discussed. It is found that the latter of the three concepts is suited best towards both quasi-static and impact loading. Ice going ferries built with ice strengthened lightweight hulls can reduce emissions, fuel consumption as well as increase the payload capacity. Such a ferry would be competitive with non-ice going ferries during ice free periods.

  • 320.
    Cheemakurthy, Harsha
    et al.
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics, Lättkonstruktioner, marina system, flyg- och rymdteknik, rörelsemekanik.
    Barsoum, Zuheir
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics.
    Burman, Magnus
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics.
    Garme, Karl
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics.
    Comparison of Lightweight Structures in Bearing Impact Loads during Ice–Hull Interaction2022In: Journal of Marine Science and Engineering, E-ISSN 2077-1312, Vol. 10, no 6, p. 794-, article id 794Article in journal (Refereed)
    Abstract [en]

    The current study focuses on the impact loading phase characteristic of thin first year ice in inland waterways. We investigate metal grillages, fibre reinforced plastic (FRP) composites and nature-inspired composites using LS Dyna. The impact mode is modelled as (a) simplified impact model with a rigid-body impactor and (b) an experimentally validated ice model represented by cohesive zone elements. The structural concepts are investigated parametrically for strength and stiffness using the simplified model, and an aluminium alloy grillage is analysed with the ice model. The metal–FRP composite was found to be the most favourable concept that offered impact protection as well as being light weight. By weight, FRP composites with a Bouligand ply arrangement were the most favourable but prone to impact damage. Further, aluminium grillage was found to be a significant contender for a range of ice impact velocities. While the ice model is experimentally validated, a drawback of the simplified model is the lack of experimental data. We overcame this by limiting the scope to low velocity impact and investigating only relative structural performance. By doing so, the study identifies significant parameters and parametric trends along with material differences for all structural concepts. The outcomes result in the creation of a viable pool of lightweight variants that fulfil the impact loading phase. Together with outcomes from quasi-static loading phase, it is possible to develop a lightweight ice-going hull concept.

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  • 321.
    Cheemakurthy, Harsha
    et al.
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics, Lättkonstruktioner, marina system, flyg- och rymdteknik, rörelsemekanik.
    Barsoum, Zuheir
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics.
    Burman, Magnus
    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.
    Lightweight Structural Concepts in Bearing Quasi-Static Ice Hull Interaction Loads2022In: Journal of Marine Science and Engineering, E-ISSN 2077-1312, Vol. 10, no 3, p. 416-416Article in journal (Refereed)
    Abstract [en]

    Lightweight ice-class vessels offer the possibility of increasing the payload capacity while making them comparable in energy consumption with non-ice-class vessels during ice-free periods. We approach the development of a lightweight hull by dividing ice–hull interactions into quasi-static loading and impact loading phases. Then, investigative outcomes of lightweight concepts for each loading phase may be combined to develop a lightweight ice-going hull. In this study, we focus on the quasi-static loading phase characteristic of thin first-year ice in inland waterways. We investigate metal grillages, sandwich structures and stiffened sandwich structures parametrically using the finite element method. The model is validated using previous experimental studies. In total over 2000 cases are investigated for strength and stiffness with respect to mass. The stiffened sandwich was found to be the most favorable concept that offered both a light weight as well as high gross tonnage. Further, significant parameters and their interactions and material differences for the three structural concepts were investigated and their trends discussed. The outcomes result in the creation of a viable pool of lightweight variants that fulfill the quasi-static loading phase. Together with outcomes from the impact loading phase, a lightweight ice-going hull may be developed.

  • 322.
    Cheemakurthy, Harsha
    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.
    A modularly tailored commuter ferry platform2022In: International Shipbuilding Progress, ISSN 0020-868X, E-ISSN 1566-2829, Vol. 69, p. 1-35, article id ISP-210016Article in journal (Refereed)
    Abstract [en]

    Among the challenges for implementation of Waterborne public transportation (WPT) are the difficulties in procuring efficient ferries tailored towards local requirements. Fundamental questions on the ferry’s environmental impact, speed and procurement costs linger in the public transport (PTP) mind. In this paper, a methodology for adopting a platform architecture for ferries is illustrated by a modular design approach. For this, WPT operational profiles are categorized by three route types in a structure for operational requirements including sustainability performance. Generic parameters for size and speed of WPT ferries are defined. Using these parameters as a skeletal structure, a modular commuter ferry concept is proposed as a set of basic modules. As a combination of these functionally independent modules, a ferry can be tailored to fit the operational requirements. The paper proposes standard sizes for waterborne commuter craft and shows that ferries are compatible with land-based public transport in terms of energy efficiency and speed. Suitable speed ranges for mono hulls and catamarans are investigated and the idea of modular design for rational procurement is explored and illustrated for the three type routes. The proposed concepts can make WPT more attractive for PTPs as a sustainable option to complement the existing network.

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  • 323.
    Cheemakurthy, Harsha
    et al.
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics, Naval Systems.
    Garme, Karl
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics, Naval Systems.
    Design Performance Index for evaluating ferries and its application for configuring modular ferries.Manuscript (preprint) (Other academic)
  • 324.
    Cheemakurthy, Harsha
    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.
    Fuzzy AHP-Based Design Performance Index for Evaluation of Ferries2022In: Sustainability, E-ISSN 2071-1050, Vol. 14, no 6, p. 3680-3680Article in journal (Refereed)
    Abstract [en]

    Within waterborne public transportation (WPT), one often observes a mismatch between the operational requirements and ferry characteristics. A method to holistically evaluate ferries with respect to local requirements could lead to tailored procurement and targeted refurbishment of existing fleet. In this study, we develop a structure for operational requirements and use it as a basis for a ferry evaluation methodology. The requirements’ structure follows a three-level hierarchy starting from broad vessel design to mandatory requirements to performance requirements. The performance requirements are based on the three pillars of sustainability, aided by commuter surveys carried out in Stockholm ferries, interviews with public transport providers (PTP) and previous literature. The evaluation of the ferry is performed using analytic hierarchic process (AHP) to convert the PTP’s subjective preferences and ferry performance into a single dimensionless index. Rules for quantification of performance metrics including social performance are proposed. The uncertainties associated with AHP are addressed by employing fuzzy AHP based on extent analysis and fuzzy AHP in combination with particle swarm optimization. Two applications including performance assessment of existing ferries and assembly of a modular ferry are discussed. The method can lead to objective decision making in ferry evaluation, potentially leading to a more efficient WPT.

  • 325.
    Cheemakurthy, Harsha
    et al.
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics, Naval Systems.
    Garme, Karl
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics, Naval Systems.
    Standardized Commuter Vessel Design for a Worldwide Waterborne Public Transport ApplicationManuscript (preprint) (Other academic)
  • 326.
    Chellapurath, Mrudul
    et al.
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics.
    Astolfi, Anna
    organization=The BioRobotics Institute, Scuola Superiore Sant'Anna, addressline=Viale Rinaldo Piaggio, 34, city=Pontedera, postcode=56025, country=Italy, Viale Rinaldo Piaggio, 34; organization=The Department of Excellence in Robotics and AI, Scuola Superiore Sant'Anna, addressline=Piazza Martiri della Libertà, 33, city=Pisa, postcode=56127, country=Italy, Piazza Martiri della Libertà, 33.
    Yokoyama, Yuki
    organization=Department of Engineering Science and Mechanics, Shibaura Institute of Technology, addressline=3 Chome-7-5 Toyosu, city=Tokyo, postcode=135-8548, country=Japan, 3 Chome-7-5 Toyosu.
    Maeda, Shingo
    organization=Department of Mechanical Engineering, Tokyo Institute of Technology, addressline=2 Chome-12-1 Ookayama, city=Tokyo, postcode=152-8550, country=Japan, 2 Chome-12-1 Ookayama; o=Living Systems Materialogy (LiSM) Research Group, International Research Frontiers Initiative (IRFI),Tokyo Institute of Technology, a=4259, Nagatsuta-cho, Midori-ku, c=Yokohama, p=226-8501, cy=Japan, 4259, Nagatsuta-cho, Midori-ku.
    Calisti, Marcello
    organization=The Lincoln Institute for Agri-food technology, University of Lincoln, addressline=Riseholme Park, city=Lincoln, postcode=LN2 2LG, country=UK, Riseholme Park.
    USLIP dynamics emerges in underwater legged robot with foot kinematics of punting crabs2024In: Mechatronics (Oxford), ISSN 0957-4158, E-ISSN 1873-4006, Vol. 99, article id 103142Article in journal (Refereed)
    Abstract [en]

    This article investigates bioinspired solutions for achieving stable dynamic gaits in legged robots through leg coordination and foot trajectories. In this study, we recorded the kinematics of underwater running of the crab, Pachygrapsus marmoratus, and implemented the parameterized foot trajectories and inter-leg coordination on an underwater legged robot, SILVER 2.0. The robot's design parameters like legs’ stiffness, leg length, and body mass are based on the Underwater Spring Loaded Inverted Pendulum (USLIP), a model that describes underwater running in animals. With this implementation, we observed the spontaneous emergence of USLIP dynamics in 20% of the strides in the robot. This approach allowed SILVER 2.0 to leverage the advantages of stable dynamic gaits while optimizing the foot trajectory and inter-leg coordination, resulting in improved locomotion performances. The robot achieved a forward velocity of 0.16 m/s, twice the value obtained in previous gaits. Our study presents a promising approach for improving the locomotion performance of legged robots, enabling their effective use in various field applications, and further confirms a broad embedding of controllers generating template dynamics.

  • 327.
    Chellapurath, Mrudul
    et al.
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics. Max Planck Institute for Intelligent Systems, Stuttgart, Germany.
    Khandelwal, Pranav C.
    Max Planck Institute for Intelligent Systems, Stuttgart, Germany; Institute of Flight Mechanics and Controls, University of Stuttgart, Stuttgart, Germany.
    Schulz, Andrew K.
    Max Planck Institute for Intelligent Systems, Stuttgart, Germany.
    Bioinspired robots can foster nature conservation2023In: Frontiers in Robotics and AI, E-ISSN 2296-9144, Vol. 10, article id 1145798Article in journal (Refereed)
    Abstract [en]

    We live in a time of unprecedented scientific and human progress while being increasingly aware of its negative impacts on our planet’s health. Aerial, terrestrial, and aquatic ecosystems have significantly declined putting us on course to a sixth mass extinction event. Nonetheless, the advances made in science, engineering, and technology have given us the opportunity to reverse some of our ecosystem damage and preserve them through conservation efforts around the world. However, current conservation efforts are primarily human led with assistance from conventional robotic systems which limit their scope and effectiveness, along with negatively impacting the surroundings. In this perspective, we present the field of bioinspired robotics to develop versatile agents for future conservation efforts that can operate in the natural environment while minimizing the disturbance/impact to its inhabitants and the environment’s natural state. We provide an operational and environmental framework that should be considered while developing bioinspired robots for conservation. These considerations go beyond addressing the challenges of human-led conservation efforts and leverage the advancements in the field of materials, intelligence, and energy harvesting, to make bioinspired robots move and sense like animals. In doing so, it makes bioinspired robots an attractive, non-invasive, sustainable, and effective conservation tool for exploration, data collection, intervention, and maintenance tasks. Finally, we discuss the development of bioinspired robots in the context of collaboration, practicality, and applicability that would ensure their further development and widespread use to protect and preserve our natural world.

  • 328.
    Chen, Jiahao
    et al.
    Chinese Acad Sci, Inst Automat, Beijing, Peoples R China..
    Su, Hang
    Univ Poitiers, HSE Dept, Politecn Milano, Poitiers, France..
    Sandoval, Juan
    Univ Poitiers, HSE Dept, Poitiers, France..
    Zhang, Longbin
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics.
    Zhong, Shanlin
    Chinese Acad Sci, Inst Automat, Beijing, Peoples R China..
    Editorial: Human inspired robotic intelligence and structure in demanding environments2022In: Frontiers in Neurorobotics, ISSN 1662-5218, Vol. 16, article id 1026917Article in journal (Other academic)
  • 329.
    Chen, Jiaxi
    et al.
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics, Väg- och spårfordon samt konceptuell fordonsdesign.
    Lennstring, Jonathan
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics, Väg- och spårfordon samt konceptuell fordonsdesign.
    Microscopic traffic simulation of free-riding cyclists in downhills2022Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    A key component of traffic models for simulating bicycle traffic focuses on capturing the interactions between cyclists and the cycling infrastructure. One of the most relevant features of the infrastructure that has a significant impact in bicycle traffic is the gradient of a bicycle path. Bicycle traffic simulations are a rather uninvestigated topic since historically, most focus on simulations has been on cars. However, bicycle simulations are an important tool to further investigate and understand cyclist’s behaviour. Therefore, the main objective of this thesis is to investigate and simulate free-riding behavior of cyclists in connection to the gradient, particularly on downhills. To do so, trajectory data of cyclists traveling on a downhill with a maximum gradient of 5.5\% are analysed to identify the impact of gradient on the speed and acceleration. The data received needed processing in order to be useful. This included filtering of the trajectories and excluding the data from cyclists which could not to be regarded as free-riding. As a result, a linear correlation is found between pedaling power and the gradient that can be used in microscopic bicycle traffic simulation. Based on this knowledge regarding this linearity, the approach used for modeling the gradient’s effect on the pedaling power is linear regression. The model can be developed in various ways, so instead of only choosing one model, several were developed and compared against each other. These models are then used for the simulation. The results indicate that the simulation captures well the impact of downhill gradients in a population of cyclists as it reproduces similar speed profiles to the ones observed. Therefore, it can be concluded that a power-based model is suitable for simulating free-riding behaviour of cyclists traveling in downhills.

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  • 330. Chen, Q.
    et al.
    Betker, Marie
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Fibre- and Polymer Technology. Deutsches Elektronen-Synchrotron DESY, Notkestraße 85, Hamburg, 22607, Germany.
    Harder, C.
    Brett, Calvin J.
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics. KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Centres, Wallenberg Wood Science Center. Deutsches Elektronen-Synchrotron DESY, Notkestraße 85, Hamburg, 22607, Germany.
    Schwartzkopf, M.
    Ulrich, N. M.
    Toimil-Molares, M. E.
    Trautmann, C.
    Söderberg, Daniel
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Fibre- and Polymer Technology, Polymer Technology. KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Centres, Wallenberg Wood Science Center.
    Weindl, C. L.
    Körstgens, V.
    Müller-Buschbaum, P.
    Ma, M.
    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, 22607, Germany.
    Biopolymer-Templated Deposition of Ordered and Polymorph Titanium Dioxide Thin Films for Improved Surface-Enhanced Raman Scattering Sensitivity2022In: Advanced Functional Materials, ISSN 1616-301X, E-ISSN 1616-3028, Vol. 32, no 6, article id 2108556Article in journal (Refereed)
    Abstract [en]

    Titanium dioxide (TiO2) is an excellent candidate material for semiconductor metal oxide-based substrates for surface-enhanced Raman scattering (SERS). Biotemplated fabrication of TiO2 thin films with a 3D network is a promising route for effectively transferring the morphology and ordering of the template into the TiO2 layer. The control over the crystallinity of TiO2 remains a challenge due to the low thermal stability of biopolymers. Here is reported a novel strategy of the cellulose nanofibril (CNF)-directed assembly of TiO2/CNF thin films with tailored morphology and crystallinity as SERS substrates. Polymorphous TiO2/CNF thin films with well-defined morphology are obtained by combining atomic layer deposition and thermal annealing. A high enhancement factor of 1.79 × 106 in terms of semiconductor metal oxide nanomaterial (SMON)-based SERS substrates is obtained from the annealed TiO2/CNF thin films with a TiO2 layer thickness of 10 nm fabricated on indium tin oxide (ITO), when probed by 4-mercaptobenzoic acid molecules. Common SERS probes down to 10 nm can be detected on these TiO2/CNF substrates, indicating superior sensitivity of TiO2/CNF thin films among SMON SERS substrates. This improvement in SERS sensitivity is realized through a cooperative modulation of the template morphology of the CNF network and the crystalline state of TiO2.

  • 331.
    Chen, Qing
    et al.
    DESY, D-22607 Hamburg, Germany.;Univ Sci & Technol China, Sch Chem & Mat Sci, Hefei 230026, Peoples R China..
    Brett, Calvin
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics. KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Centres, Wallenberg Wood Science Center. DESY, D-22607 Hamburg, Germany..
    Chumakov, Andrei
    DESY, D-22607 Hamburg, Germany..
    Gensch, Marc
    DESY, D-22607 Hamburg, Germany.;Tech Univ Munich, Phys Dept, Lehrstuhl Funkt Mat, D-85748 Garching, Germany..
    Schwartzkopf, Matthias
    DESY, D-22607 Hamburg, Germany..
    Koerstgens, Volker
    Tech Univ Munich, Phys Dept, Lehrstuhl Funkt Mat, D-85748 Garching, Germany..
    Söderberg, Daniel
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Centres, Wallenberg Wood Science Center. KTH, School of Engineering Sciences (SCI), Engineering Mechanics. KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Fibre- and Polymer Technology, Fiberprocesser.
    Plech, Anton
    Karlsruhe Inst Technol KIT, Inst Photon Sci & Synchrotron Radiat, D-76021 Karlsruhe, Germany..
    Zhang, Peng
    Sun Yat Sen Univ, Sch Mat Sci & Engn, PCFM Lab, Guangzhou 510275, Peoples R China..
    Mueller-Buschbaum, Peter
    Tech Univ Munich, Phys Dept, Lehrstuhl Funkt Mat, D-85748 Garching, Germany.;Tech Univ Munich, Heinz Maier Leibniz Zentrum MLZ, D-85748 Garching, Germany..
    Roth, Stephan V.
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Fibre- and Polymer Technology. DESY, D-22607 Hamburg, Germany..
    Layer-by-Layer Spray-Coating of Cellulose Nanofibrils and Silver Nanoparticles for Hydrophilic Interfaces2021In: ACS Applied Nano Materials, E-ISSN 2574-0970, Vol. 4, no 1, p. 503-513Article in journal (Refereed)
    Abstract [en]

    Silver nanoparticles (AgNPs) and AgNP-based composite materials have attracted growing interest due to their structure-dependent optical, electrical, catalytic, and stimuli-responsive properties. For practical applications, polymeric materials are often combined with AgNPs to provide flexibility and offer a scaffold for homogenous distribution of the AgNPs. However, the control over the assembly process of AgNPs on polymeric substrates remains a big challenge. Herein, we report the fabrication of AgNP/cellulose nanofibril (CNF) thin films via layer-by-layer (LBL) spray-coating. The morphology and self-assembly of AgNPs with increasing number of spray cycles are characterized by atomic force microscopy (AFM), grazing-incidence small-angle X-ray scattering (GISAXS), and grazing-incidence wide-angle X-ray scattering (GIWAXS). We deduce that an individual AgNP (radius = 15 +/- 3 nm) is composed of multiple nanocrystallites (diameter = 2.4 +/- 0.9 nm). Our results suggest that AgNPs are assembled into large agglomerates on SiO2 substrates during spray-coating, which is disadvantageous for AgNP functionalization. However, the incorporation of CNF substrates contributes to a more uniform distribution of AgNP agglomerates and individual AgNPs by its network structure and by absorbing the partially dissolved AgNP agglomerates. Furthermore, we demonstrate that the spray-coating of the AgNP/CNF mixture results in similar topography and agglomeration patterns of AgNPs compared to depositing AgNPs onto a precoated CNF thin film. Contact-angle measurements and UV/vis spectroscopy suggest that the deposition of AgNPs onto or within CNFs could increase the hydrophilicity of AgNP-containing surfaces and the localized surface plasmon resonance (LSPR) intensity of AgNP compared to AgNPs sprayed on SiO(2 )substrates, suggesting their potential applications in antifouling coatings or label-free biosensors. Thereby, our approach provides a platform for a facile and scalable production of AgNP/CNF films with a low agglomeration rate by two different methods as follows: (1) multistep layer-by-layer (LBL) spray-coating and (2) direct spray-coating of the AgNP/CNF mixture. We also demonstrate the ability of CNFs as a flexible framework for directing the uniform assembly of AgNPs with tailorable wettability and plasmonic properties.

  • 332.
    Chen, Shaoyao
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics, Rail Vehicles.
    Modified train wheel wear calculation for fast calculation2021Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    In this thesis, a modified wear calculation method is developed to calculate the train wheel wear, which can give less precise but faster results compared to the classic wear calculation method. This modified method is developed based on the classic wear calculation method developed by Jendel, which uses Hertz theory and Kalker’s simplified theory to calculate the contact variables and uses Achard theory to calculate the wear volume in an iterative manner. Compared with the classic method, this modified wear calculation method does not execute the multibody simulation (MBS) at each wear step, instead, it executes MBS by different strategies, for example, does MBS only at the first wear step or does it at every several wear steps. This way, a look-up table is utilised to store the contact variables from MBS and when no MBS is executed, the variables stored in the look-up table would be used to calculate the wear.In order to make the implementation of the modified wear calculation method possible, a contact point detection program is developed in this research. Significantly, this contact point detection program considers the material flexibility and can detect multiple contact points, which makes it very precise. It uses the pressure distribution calculated by Winkler theory as a weighting function to consider the material flexibility. In terms of multiple contact points detection, the gap between wheel and rail is regarded as a function, and the derivative relationship of the function is used to detect multiple contact points. Results from the modified wear calculation method are compared with results from the classic wear calculation method. The effects of different strategies are discussed, and the analysis of the error source is carried out in this work.This modified wear calculation method could be used for predicting the wear condition of the wheel when a quick result with only moderate precision is needed. 

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  • 333.
    Chen, Shaoyao
    et al.
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics, Rail Vehicles.
    Casanueva, Carlos
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics, Rail Vehicles.
    Hossein Nia, Saeed
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics, Rail Vehicles.
    Stichel, Sebastian
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics, Rail Vehicles.
    Modified Wear Modelling for Fast Wear Calculation2022In: IAVSD 2021: Advances in Dynamics of Vehicles on Roads and Tracks II, Springer Nature , 2022, p. 561-571Conference paper (Refereed)
    Abstract [en]

    In this paper, a modified wear calculation method is developed, which can give less precise but faster results compared to the classic wear calculation method. Besides, a precise contact point detection program is developed to cooperate with this modified method.

  • 334.
    Chen, Song
    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.
    Gojon, Romain
    ISAE-Supaero.
    Mihaescu, Mihai
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Effect of an Adjacent Flat Plate on a Highly-Heated Rectangular Supersonic Jet2020In: AIAA Scitech 2020 Forum, AIAA, 2020, article id AIAA 2020-0746Conference paper (Refereed)
    Abstract [en]

    Solid surfaces located in the vicinity of a supersonic jet may affect its flow dynamics and greatly change the aeroacoustic characteristics. Large-eddy simulations (LES) are performed to investigate the plate effects on a highly-heated rectangular supersonic jet. The rectangular nozzle has an aspect ratio of 2.0 and is operated at the over-expanded condition with a nozzle pressure ratio of 3.0 and a nozzle temperature ratio of 7.0. Four cases, JetL0 to JetL3 with a plate-to-nozzle distance ranging from 0 to 3 times of the jet equivalent nozzle diameter are investigated. The large-scale implicit LES computations are performed by a well-validated in-house finite-volume based CFD code, which uses an artificial dissipation mechanism to represent the effect of small-scale turbulence and to damp the numerical oscillation near shocks. The temperature-dependent thermal properties of air in the highly-heated jets are considered by the chemical equilibrium assumption. Numerical results show that among the four cases, JetL0 with the plate directly attached at the nozzle lip shows significant different flow and acoustic fields from the others. It exhibits a longer jet potential core length but without forming a series of well-structured shock diamonds. The other cases show similar shock/expansion wave structures as observed in the free jet but their jet plumes bend towards the plate. This bending of jet leads to JetL1 scrubs over the plate in the downstream. The scrubbing effect, together with the unaffected shock-shear layer interactions and high plate pressure loading, makes JetL1 have a stronger OASPL in the near acoustic fields than the other cases. The spectrum analysis in the nozzle upstream direction shows that the plate removes or mitigates the screech tone observed in the free jet and slightly amplifies the acoustic amplitudes in the low-frequency range.

  • 335.
    Chen, Song
    et al.
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics.
    Gojon, Romain
    ISAE-SUPAERO.
    Mihaescu, Mihai
    KTH, School of Industrial Engineering and Management (ITM), Centres, Competence Center for Gas Exchange (CCGEx). KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Flow and aeroacoustic attributes of highly-heated transitional rectangular supersonic jets2021In: Aerospace Science and Technology, ISSN 1270-9638, E-ISSN 1626-3219, Vol. 114, no 106747Article in journal (Refereed)
    Abstract [en]

    Heated transitional supersonic jets exhausting from a rectangular nozzle at over-expanded conditions are investigated by Large Eddy Simulations and Ffowcs-Williams and Hawkings acoustic analogy. Four cases with a fixed nozzle pressure ratio but different temperature ratios (TR) of 1.0, 2.0, 4.0, and 7.0 are analyzed. Numerical results show that with the increasing temperature the jet velocity significantly increases, whereas its Reynolds number decreases by about one order of magnitude, which leads to a 30% decrease in the jet potential core length and reduction in the number of shock cells. The increasing temperatures also result in supersonic shear layer convection Mach numbers and consequently Mach wave radiations in the acoustic fields. Pressure skewness and kurtosis factors indicate crackle noise and non-linear propagation effects in high temperatures. For the most heated jet TR 7.0, the Mach wave radiation is identified radiating noise at about 120 degrees, while the large turbulence structure noise at about 150 degrees. Furthermore, the vortex sheet model analysis and the LES data detect the existence of upstream-propagating neutral waves inside jet TR 7.0. The observed screech frequency falls within the range of antisymmetric mode indicating that the highly-heated jet is characterized by an antisymmetric oscillation mode at the screech frequency.

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  • 336.
    Chevallier, Yohan
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics, Solid Mechanics.
    Design of a custom motocompressor for aeronautic cooling applications2021Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    This thesis is part of a project that aims to develop a custom motocompressor for aeronautic cooling applications from an existing compressor that will no longer be manufactured. The main goals are to prevent obsolescence issues and better master all the motocompressor characteristics. In this context, various tasks are to be performed, including the design of the entire compressor froman existing model.

    Firstly, the work is to understand how the existing compressor is built and how it can be redesigned and improved. Then, the work focuses on designing the new motocompressor, and particularly the scroll section. The others main tasks are improving the existing design, in particular concerning the sealing and the balancing system, as well as checking the mechanical resistance. Finally, the 2D technical drawings are realised, a functional dimensioning is performed on all the parts drawings and discussed with the manufacturer in order toensure a proper production quality. The main results of the design process will be discussed and the remaining tasks investigated.

  • 337.
    Chicchiero, Claudio
    et al.
    Univ Pisa, Dipartimento Ingn Aerosp, I-56122 Pisa, Italy..
    Segalini, Antonio
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Camarri, Simone
    Univ Pisa, Dipartimento Ingn Aerosp, I-56122 Pisa, Italy..
    Triple-deck analysis of the steady flow over a rotating disk with surface roughness2021In: Physical Review Fluids, E-ISSN 2469-990X, Vol. 6, no 1, article id 014103Article in journal (Refereed)
    Abstract [en]

    The effect of surface roughness on the steady laminar flow induced by a rotating disk submerged by fluid otherwise at rest is investigated here theoretically and numerically. A theory is proposed where a triple-deck analysis is applied leading to a fast evaluation of the steady-flow modification due to the rough surface. The theory assumes that the roughness is much smaller than the boundary-layer height and is characterized by a significantly longer length scale (slender roughness). Only the leading-order correction is developed here, corresponding to a velocity-field correction that is linear with the roughness height. The proposed theory neglects some curvature terms (here partially accounted by means of a stretching of the radial coordinate and of a scaling of the dependent variables). Numerical simulations performed with different roughness geometries (axisymmetric roughness, radial grooves, and localized bumps) have been used to validate the theory. Results indicate that the proposed theory leads to a good quantification of the flow modifications due to surface roughness at a very low computational cost. A demonstration of the capabilities of the theory is finally proposed where the statistical effects on the flow due to a random (but statistically known) roughness distributed on the surface of a rotating disk are characterized.

  • 338.
    Chiche, Ariel
    et al.
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Chemical Engineering, Applied Electrochemistry.
    Andruetto, Claudia
    KTH, School of Industrial Engineering and Management (ITM), Centres, Integrated Transport Research Lab, ITRL.
    Lagergren, Carina
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Chemical Engineering, Applied Electrochemistry.
    Lindbergh, Göran
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Chemical Engineering, Applied Electrochemistry.
    Stenius, Ivan
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics.
    Peretti, Luca
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electric Power and Energy Systems.
    Feasibility and impact of a Swedish fuel cell-powered rescue boat2021In: Ocean Engineering, ISSN 0029-8018, E-ISSN 1873-5258, Vol. 234, p. 109259-109259, article id 109259Article in journal (Refereed)
  • 339.
    Chiche, Ariel
    et al.
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Chemical Engineering, Applied Electrochemistry.
    Lindbergh, Göran
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Chemical Engineering, Applied Electrochemistry.
    Stenius, Ivan
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics.
    Lagergren, Carina
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Chemical Engineering, Applied Electrochemistry.
    A Strategy for Sizing and Optimizing the Energy System on Long-Range AUVs2021In: IEEE Journal of Oceanic Engineering, ISSN 0364-9059, E-ISSN 1558-1691, Vol. 46, no 4, p. 1132-1143Article in journal (Refereed)
  • 340.
    Chiche, Ariel
    et al.
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Chemical Engineering, Applied Electrochemistry.
    Lindbergh, Göran
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Chemical Engineering, Applied Electrochemistry.
    Stenius, Ivan
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics.
    Lagergren, Carina
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Chemical Engineering, Applied Electrochemistry.
    Design of experiment to predict the time between hydrogen purges for an air-breathing PEM fuel cell in dead-end mode in a closed environment2021In: International journal of hydrogen energy, ISSN 0360-3199, E-ISSN 1879-3487, Vol. 46, no 26, p. 13806-13817Article in journal (Refereed)
    Abstract [en]

    Fuel cells are promising technologies for zero-emission energy conversion. They are used in several applications such as power plants, cars and even submarines. Hydrogen supply is crucial for such systems and using Proton Exchange Membrane Fuel Cell in dead-end mode is a solution to save hydrogen. Since water and impurities accumulate inside the stack, purging is necessary. However, the importance of operating parameters is not well known for fuel cells working in closed environments. A Design of Experiment approach, studying time between two purges and cell performance, was conducted on an air-breathing stack in a closed environment. The most influential parameters on the time between two purges are the relative humidity and the current load. Convection in the closed environment can decrease the stability of the fuel cell. A linear model with interactions between these last three parameters was found to accurately describe the studied responses.

  • 341.
    Chiche, Ariel
    et al.
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Chemical Engineering, Applied Electrochemistry.
    Lindbergh, Göran
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Chemical Engineering, Applied Electrochemistry.
    Stenius, Ivan
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics.
    Lagergren, Carina
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Chemical Engineering, Applied Electrochemistry.
    Including Heat Balance When Designing the Energy System of Fuel Cell-Powered AUVs2021In: Energies, E-ISSN 1996-1073, Vol. 14, no 16, p. 4920-4920, article id 4920Article in journal (Refereed)
    Abstract [en]

    Fuel cell-powered Autonomous Underwater Vehicles (AUVs) represent a growing area of research as fuel cells can increase their endurance. Fuel cells consume hydrogen and oxygen to generate electricity. Typically, the fuel cell generates as much heat as electrical energy, and heat management becomes a crucial parameter when designing AUVs. For underwater applications, there is a need to store both gases and several types of storage units with different characteristics exist which have impacts on the energy density and heat behavior. This study aims at including the heat properties of the storage units in the design process of fuel cell-powered AUVs. A heat balance over the energy system of an AUV is calculated for each combination of hydrogen and oxygen storage units. In addition, a multi-criteria decision-making analysis is conducted, considering the calculated total heat, the specific energy, the energy density and the volumetric mass of each combination of storage units as criteria, enabling a comparison and ranking them using two objective criteria weighting methods. Results show that the fuel cell is the major contributor to the heat balance, and that the combinations of liquid oxygen with liquid or compressed hydrogen can be relevant and suitable for underwater applications. 

  • 342.
    Chin, R. C.
    et al.
    Univ Adelaide, Sch Mech Engn, Adelaide, SA 5005, Australia..
    Vinuesa, Ricardo
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics. KTH, Centres, SeRC - Swedish e-Science Research Centre.
    Örlü, Ramis
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics.
    Cardesa, J. , I
    Noorani, Azad
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics. KTH, Centres, SeRC - Swedish e-Science Research Centre.
    Chong, M. S.
    Univ Melbourne, Dept Mech Engn, Melbourne, Vic 3010, Australia..
    Schlatter, Philipp
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics. KTH, Centres, SeRC - Swedish e-Science Research Centre.
    Backflow events under the effect of secondary flow of Prandtl's first kind2020In: Physical Review Fluids, E-ISSN 2469-990X, Vol. 5, no 7, article id 074606Article in journal (Refereed)
    Abstract [en]

    A study of the backflow events in the flow through a toroidal pipe at friction Reynolds number Re-tau approximate to 650 is performed and compared with the results in a straight turbulent pipe flow at Re-tau approximate to 500. The statistics and topological properties of the backflow events are analysed and discussed. Conditionally averaged flow fields in the vicinity of the backflow event are obtained, and the results for the torus show a similar streamwise wall-shear stress topology which varies considerably for the azimuthal wall-shear stress when compared to the pipe flow. In the region around the backflow events, critical points are observed. The comparison between the toroidal pipe and its straight counterpart also shows fewer backflow events and critical points in the torus. This is attributed to the secondary flow of Prandtl's first kind present in the toroidal pipe, which is responsible for the convection of momentum from the inner to the outer bend through the core of the pipe, and back from outer bend to the inner bend along the azimuthal direction. These results indicate that backflow events and critical points are genuine features of wall-bounded turbulence, and are not artefacts of specific boundary or inflow conditions in simulations and/or measurement uncertainties in experiments.

  • 343.
    Chlebek, David
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics, Solid Mechanics.
    Simulation of ultrasonic time of flight in bolted joints2021Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Ultrasonic measurements of the preload in bolted joints is a very accurate method since it does not depend on the friction and other factors which cause difficulties for common methods. The ultrasonic method works by emitting an ultrasonic pulse into the bolt which is reflected at the end and returned to the transducer, the change in the time of flight (TOF) can be related to the elongation of the bolt and therefore the preload. One must account for the acoustoelastic effect which is the change in sound speed due to an initial stress state. The goal of this thesis project was to implement a Murnaghan hyperelastic material model in order to account for the acoustoelastic effect when conducting a numerical simulation using the finite element method (FEM). An experiment was also performed to validate the numerical simulation. The DeltaTOF as a function of a tensile force was obtained for an M8 and M10 test piece from the experiment. The material model was implemented by creating a user subroutine written in Fortran for the explicit solver Radioss. Hypermesh was used to set-up the numerical simulation. The material model has shown an expected behavior with an increased sound speed with compressive stresses and a decreased speed with tensile stresses. The numerical simulation showed a good correspondence to the experimental results.

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  • 344.
    Cimarelli, Andrea
    et al.
    Dipartimento di Ingegneria Industriale, Università di Bologna, Forlì, 47121, Italy.
    de Angelis, Elisabetta
    Dipartimento di Ingegneria Industriale, Università di Bologna, Forlì, 47121, Italy.
    Schlatter, Philipp
    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.
    Brethouwer, Gert
    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), Mechanics.
    Talamelli, Alessandro
    Dipartimento di Ingegneria Industriale, Università di Bologna, Forlì, 47121, Italy.
    Casciola, Carlo Massimo
    Dipartimento di Ingegneria Meccanica e Aerospaziale, Università di Roma La Sapienza, 00185, Italy.
    Scalings of the outer energy source of wall-turbulence2020In: ETC 2013 - 14th European Turbulence Conference, Zakon Group LLC , 2020Conference paper (Refereed)
    Abstract [en]

    By means of the multidimensional description given by the Kolmogorov equation we study the energy transfer physics and the production mechanisms of wall-turbulent flows at moderately high Reynolds numbers. Two driving mechanisms are identified for the energy fluxes. The first stronger one, here called driving scale-range (DSR), belongs to the near-wall cycle. As expected, its topology remains unaltered with Reynolds number while its intensity is found to slightly increase with Re. The second mechanism, here called outer scale-range (OSR), takes place in the overlap layer and highlights different features in agreement with the attached eddies hypothesis usually considered to describe the overlap dynamics.

  • 345.
    Cisarella, Luca
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics, Väg- och spårfordon samt konceptuell fordonsdesign.
    Vehicle ride and handling optimization by development of an automation toolchain2022Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Vehicle ride and handling (R&H) characteristics are one of the key areas of the virtual development of vehicles. The number of relevant model parameters increases depending on the complexity of the model and the use-case. Due to increasing vehicle complexity and topology, it is challenging to achieve key performance indicators (KPI) via a traditional trial & error approach. Optimization tools are required to gain a better understanding of the key parameters affecting the performance and efficiently achieve targets using a structured process. 

    The master thesis describes the development of a toolchain for selected ride and handling use-cases: an automated simulation environment focused on full vehicle optimization that runs all required simulation models and tools, using remote computational resources for heavy simulation runs. The toolchain has been designed during the master thesis project in collaboration between Hyundai Motor Europe Technical Center (HMETC) chassis department, Politecnico di Torino and KTH Royal Institute of Technology. The toolchain has been implemented in MATLAB/Simulink and integrated with vehicle dynamics CAE software generally used by HMETC (based on both multi-body and functional models) and with HEEDS MDO, which provides the optimization algorithm. Finally, different R&H use-cases show the system's reached level of robustness and flexibility. 

    The resulted automated toolchain has been capable of investigating a large number of vehicle variants in different vehicle dynamics environments, while showing the key performance factors and the most influential parameters for improving the vehicle behavior. Accurate constraints and design space definitions provided feasible optimal parameters values, characterized by groups of solutions with minor differences among parameters and comparable KPIs, which help to find different development directions. Finally, the structured methodology proposed by the toolchain has effectively increased the efficiency of the virtual development process, finding optimal designs in a limited amount of time, working autonomously in the background and modifying a large number of parameters.

  • 346.
    Clop, Julien
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics, Väg- och spårfordon samt konceptuell fordonsdesign.
    Numerical modelling of the pneumatic ejection of a projectile via Simscape2022Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Numerical modelling and simulation is a key element in the development and implementation of new equipment. This project focuses on the modelling and simulation of a pneumatic system with Matlab/Simulink and the extension Simscape. The development of such a model aims to prove that the physical system works as intended, to test the behaviour of the system under specific conditions, to have a virtual test bench of the system that is time and resource efficient, and to develop new products based on the same concept. This project concerns the creation of a model of a pneumatic circuit and a pneumatic ejection of a projectile, and of a model that simulate the trajectory of the projectile in the air accounting for various initial conditions and aerodynamic loads. The Simscape models created are then parametrised and calibrated by comparing the simulation results and experimental data of the physical system through statistical methods. The validity of the models is tested and their operating range can be evaluated. Outside of this operating range of initial conditions, the accuracy of the models decreases significantly and the latter become unable to simulate the behaviour of the real system. The obtained models at the end of the project can be used to accurately study the behaviour of the real system around its nominal operating point. Some ways of improving the models, in order to increase their validity and robustness, are discussed.

  • 347.
    Coelho Leite Fava, Thales
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics, Fluid Physics.
    Stability and transition on wind turbine blades2023Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Transition on wind turbine blades is a highly complex phenomenon due to the myriad effects influencing the process. This thesis studies some of them, namely free-stream turbulence (FST), rotation, and three-dimensionality. The investigations employ large eddy simulations (LES) with and without (implicit or wall-resolved LES) a subgrid-scale model. The role of FST in the modal and non-modal stability of the flow on the suction side of a wind turbine section at a Reynolds number 𝑅𝑒𝑐 = 100,000 is studied. This involved several simulations at varying turbulence intensity (𝑇𝐼) and primary and secondary linear stability analyses. The separated shear layers strongly govern the flow stability with the characteristic Kelvin-Helmholtz (KH) modes. Low FST levels increase the growth rates of the secondary instability of Tollmien-Schlichting (TS) and KH modes, leading to an upstream shift of transition and shrinking of the LSB. High enough 𝑇𝐼 stabilizes the flow to these modes, leading to an unexpected increase in the LSB. However, further rises in the turbulence level suppress separation. The spanwise-averaged part of the mean-flow distortion causes the stabilizing effect. The increase in the turbulence intensity also leads to a monotonic drop in the energy of coherent structures, shed from the separated shear layer, passing near the trailing edge. In the case of 𝑅𝑒𝑐 = 1,000,000, streak growth is much more intense, and even low levels of 𝑇𝐼 are enough to suppress the LSB present in the absence of FST. For 𝑇𝐼 ≤ 2.4%, transition is caused by inner modes, which in the limit of zero FST tend to TS waves. This range of 𝑇𝐼 presents linear receptivity, good agreement of the 𝑁 factor from Mack’s correlation with simulation data, and an exponential dependency of the transition location with 𝑇𝐼. For 2.4% < 𝑇𝐼 ≤ 7.0%, bypass transition occurs, characterized by the predominance of the outer varicose mode. In this regime, the transition location displays a variation ∝ 𝑇𝐼−2. A low-frequency cut-off for the free-stream turbulence is proposed to allow the computation of an effective turbulence intensity for wind turbine blades. Regarding the role of rotation, a model is developed to compute the quasi-three-dimensional base flow for stability analyses over a blade. The flow in the inboard region is highly three-dimensional and significantly affected by rotation. Highly oblique modes are the most unstable in this region, leading to a transition up to 19% earlier than the widely used two-dimensional semi-empirical 𝑒𝑁 transition model of Drela and Giles, used in the RANS simulations. A transition-prediction framework based on the boundary layer and parabolized stability equations accounting for these effects was developed. It indicates that rotation shifts transition upstream if the Reynolds number is allowed to increase with the reference velocity. Subsequent LES indicated that rotation stabilizes the flow for a fixed Reynolds number in the attached flow region and front part of the LSB for low rotation rates, delaying transition and reattachment. Even though rotation delays these phenomena, rotation may act as an adverse pressure gradient after separation occurs, leading to an increase in the growth rates of the KH modes and reverse flow. Furthermore, crossflow transition may be triggered for higher rotation rates and towards the inboard blade region, leading to an upstream shift of the transition point. Crossflow transition leads to a rise in the pressure difference between the two sides of the airfoil, generating a higher lift. In the outboard blade region, a self-excited type of instability may occur in an LSB forming near the leading edge, promoting an early transition that may cause a sudden shift of the separation line to the leading edge after a certain critical radius, as observed in experiments. Finally, a low-frequency oscillation in the normal force coefficient, with an amplitude of 10.5% around the mean, was identified in a wind turbine airfoil. The period of these oscillations was long, corresponding to several turns of a wind turbine at rated rotation speed. The occurrence of such a phenomenon in real wind turbines should be assessed and considered in the structural design of the rotor.

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  • 348.
    Coelho Leite Fava, Thales
    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.
    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.
    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.
    DIRECT NUMERICAL SIMULATIONS OF A THICK, ROTATING AIRFOIL AT A LOW REYNOLDS NUMBER2022In: 33rd Congress of the International Council of the Aeronautical Sciences, ICAS 2022, International Council of the Aeronautical Sciences , 2022, p. 3059-3072Conference paper (Refereed)
    Abstract [en]

    Direct numerical simulations of the flow around an FFA-W3 series airfoil at a chord Reynolds number of 100,000 are performed to study the effects of rotation on flow over a section of a rotating wing. In order to achieve this goal, three simulations with different rotation speeds (and corresponding angles of attack) are carried out. Three additional simulations with the same angles of attack of the former but without including Coriolis and centrifugal forces are also computed. It is shown that rotation moves the transition location upstream on the suction side for low angles of attack, and on the pressure side, due to the enhancement of the shear-layer instability and its spanwise modulation. Nevertheless, rotation delays transition on the suction side for larger angles of attack. The reason for this change is most likely the fact that the shear-layer instability is much stronger in this case, and it is not bypassed by instabilities generated by rotation such as that from the inflectional spanwise velocity profiles. However, the latter can reduce the shear in the separation bubble, mitigating the rapid growth of the former. The onset of separation is not changed by rotation, but the trailing edge of the separation bubble is displaced downstream because of an enhanced reverse flow. The lift is only significantly affected by rotation when there are large separation regions on both suction and pressure surfaces, promoting its reduction.

  • 349.
    Coelho Leite Fava, Thales
    et al.
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics, Fluid Physics.
    Henningson, Dan S.
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics, Fluid Physics.
    Hanifi, Ardeshir
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics, Fluid Physics.
    Numerical investigation of the boundary layer stability on a section of a rotating wind turbine bladeManuscript (preprint) (Other academic)
    Abstract [en]

    Wall-resolved large eddy simulations (LES) and linear stability analyses of the flow on a rotating wind turbine blade section are performed to study the effects of rotation on laminar-turbulent transition on the suction surface. A chord Reynolds number of 100,000 and angles of attack (𝐴𝑜𝐴) of 12.8, 4.2, and 1.2 are considered. For comparison, simulations with and without rotation at the same angles of attack are carried out. The rotating simulations displayed a flow toward the root outside the boundary layer. For 𝐴𝑜𝐴 = 12.8, in which the flow is subject to a strong adverse pressure gradient (APG), rotation accelerates downstream the laminar attached and weakly separated flows, stabilizing them. However, the effect is the opposite in the high reverse flow region in the LSB, where rotation leads to a reverse flow of -16% compared to -7% in the non-rotating case. Rotation fosters an oblique transition mechanism that leads to a fast breakdown to small-scale turbulence. However, the stabilization of the attached flow overcomes this effect, leading to downstream shifts of 3% in transition and 4% in reattachment. For 𝐴𝑜𝐴 = 4.2 and 𝐴𝑜𝐴 = 1.2, which are subject to a long region of favorable pressure gradient (FPG), rotation decelerates the attached flow, rendering TS waves more unstable. This effect is reversed upon separation, and rotation starts to accelerate the flow slightly. Traveling and stationary crossflow modes are triggered by the rotation-induced crossflow towards the blade tip, especially in the front part of the LSB. However, the TS/KH mode remains the most amplified mechanism, governing the stability of the separation bubble. The rolls attributed to this mode develop a steady spanwise modulation with one or two spanwise wavelengths in the non-rotating cases. Rotation is found to reduce this spanwise modulation. The transition locations are insensitive to rotation in the 𝐴𝑜𝐴 = 4.2 and 𝐴𝑜𝐴 = 1.2 cases, which may be due to the dominance of the TS/KH mode and the identified region of absolute instability in the LSB.

  • 350.
    Coelho Leite Fava, Thales
    et al.
    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, Centres, SeRC - Swedish e-Science Research Centre.
    Lobo, B A
    Kiel University of Applied Sciences, Mechanical Engineering Dept..
    Nogueira, P A S
    Monash University, Aerospace Engineering.
    Schaffarczyk, A P
    Kiel University of Applied Sciences, Mechanical Engineering Dept..
    Breuer, M
    Helmut-Schmidt-Universitat Hamburg.
    Henningson, Dan S.
    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, Fluid Physics.
    Hanifi, Ardeshir
    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, Centres, SeRC - Swedish e-Science Research Centre.
    Influence of free-stream turbulence on the boundary layer stability of a wind turbine airfoil and near wake2023In: Journal of Physics, Conference Series, ISSN 1742-6588, E-ISSN 1742-6596, Vol. 2505, no 1, p. 012002-012002Article in journal (Refereed)
    Abstract [en]

    Free-stream turbulence (FST) alters the boundary layer of wind turbine blades, changing the hydrodynamic stability and near wake. Large-eddy simulations (LES) of a blade section with a laminar separation bubble for several turbulence intensities (TI) and a Reynolds number of 100,000 are performed. The effects of boundary-layer streaks generated by FST on Tollmien-Schlichting (TS) and Kelvin-Helmholtz (KH) instabilities are analyzed with a model based on the parabolized stability equations (PSE). Two competing effects on flow stability are identified. The spanwise-averaged mean-flow distortion stabilizes primary TS/KH modes for increasing TI. However, this contribution seems dominant only for TI ≥ 8.6%. For lower TI, the spanwise-oscillating distortion caused by streaks destabilizes the flow, and the growth rates of secondary modal instabilities increase with the streak amplitude. The destabilization occurs mainly at spanwise locations with negative streaks since the inflection point shifts away from the wall, enhancing inviscid instabilities. Inflection points in the spanwise direction formed by the streaks also contribute to the destabilization. The modal structures from PSE and LES agree. Finally, the trailing-edge near-wake coherent structures are more energetic for TI ≥ 8.6% due to the partial stabilization of modal instabilities, delaying the turbulent breakdown.

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