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  • 151.
    Banno, Yuki
    et al.
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics.
    Kinoshita, K.
    Ishikawa, T.
    Anami, K.
    Influence of grid blast on the fatigue strength improvement by peening2021In: Bridge Maintenance, Safety, Management, Life-Cycle Sustainability and Innovations - Proceedings of the 10th International Conference on Bridge Maintenance, Safety and Management, IABMAS 2020, CRC Press/Balkema , 2021, p. 3165-3173Conference paper (Refereed)
    Abstract [en]

    In this study, to evaluate the influence of grid blast following to the peening process on the fatigue strength improvement, residual stress measurement and fatigue tests have been conducted. Examined peening processes were UIT, PPP and HP with ICR apparatus. For the residual stress measurement, plate and on-bead specimens made of JIS-SM400, SBHS400, SBHS500 and SBHS700 were used, and X-ray diffraction method was applied to the measurement. The results concluded that the differences in the compressive residual stress distribution in the vicinity of peened area with and without blast are not so significant. For the fatigue tests, out-of-plane gusset welded joint specimens made of JIS-SM490 and SBHS500 were used. Fatigue tests were conducted under stress ratio R=0.0 and 0.5. Fatigue tests showed that fatigue strength of peened specimens with blast are almost the same as that of peened specimens without blast, and those results were observed independently of steel grade and of peening methods.

  • 152.
    Bardhi, Arbra
    et al.
    Università Di Roma “La Sapienza”, Rome, Italy.
    Martini, Francesco
    Università Di Roma “La Sapienza”, Rome, Italy.
    Ricci, Stefano
    Università Di Roma “La Sapienza”, Rome, Italy.
    Casanueva, Carlos
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics.
    Existing Studies and Information Sources on Rail High Education and Skills Development2024In: Lecture Notes in Mobility, Springer Nature , 2024, Vol. Part F2364, p. 1-11Chapter in book (Other academic)
    Abstract [en]

    This paper provides with a panorama of the review conducted on existing studies and structured information from various sources related to rail education and skills development. The purpose of this review was to gather insights from previous EU projects, research papers, web portals, and reports to better understand the current landscape and teaching approaches in rail higher education. To give a comprehensible visualization, preferably in a website format, a simple but tangible concept has been developed, facilitating a smooth connection between the concrete real-world application and more abstract fields of developments within the scope of study.

  • 153.
    Barsoum, Imad
    et al.
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics. Khalifa Univ Sci & Technol, Dept Mech Engn, POB 2533, Abu Dhabi, U Arab Emirates..
    Yurindatama, D. T.
    Khalifa Univ Sci & Technol, Dept Mech Engn, POB 2533, Abu Dhabi, U Arab Emirates..
    Collapse analysis of a large plastic pipe using cohesive zone modelling technique2020In: International Journal of Pressure Vessels and Piping, ISSN 0308-0161, E-ISSN 1879-3541, Vol. 187, article id 104155Article in journal (Refereed)
    Abstract [en]

    Polypropylene (PP) plastic pipes have recently gained widespread application in non-pressurized gravity pipes used for seawater intake lines in the petrochemical industry. These pipes consist of a solid wall base pipe, on which an outer reinforcement called the omega-profile is spirally winded and hot fusion bonded. The omega-profile is usually filled with grout to provide on-bottom stability for subsea installation. It is of high importance that the bond between the omega-profile and the base pipe has sufficient strength to provide resistance against buckling of the pipeline system. The objective of this study is to investigate the collapse behaviour of such large-diameter PP pipes subjected to a negative internal pressure. The bond is modelled with cohesive zone modelling technique with the aim to determine the failure mode that governs the collapse behaviour of the pipe, e.g. buckling or delamination. Experiments where conducted on single cantilever beam (SCB) specimens cut from the pipe to determine the cohesive bond strength between the omega-profile and base pipe. The findings from the experiments are implemented in a full pipe model, where the surface between the omega-profile and base pipe is assigned bond strength characteristics in accordance with the experimental results. The FEA results of the nonlinear collapse analysis of the full pipe model show that for the range of grout stiffness values considered (0 <= E- (g) <= 30 GPa), the governing failure mode of the pipe is initiated by buckling and proceeded by delamination. For delamination to govern the failure mode, a grout stiffness greater than 36 GPa in combination with a weaker bond strength than the experimentally measured would be required. The methodology presented in this study gives a rather accurate tool for the design and analysis of this type of structures, and can reliably assess the bond strength level required in view of the governing failure modes, e.g. buckling and delamination.

  • 154.
    Basaran, Hasan
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics, Space Technology.
    Comparison of Control Approaches for Formation Flying of Two Identical Satellites in Low Earth Orbit2020Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Formation flying of satellites describes a mission in which a set of satellites arrange their position with respect to one another. In this paper, satellite formation flying guidance and control algorithms are investigated in terms of required velocity increment Delta-v, and tracking error for a Chief/Deputy satellite system. Different control methods covering continuous and impulsive laws are implemented and tested for Low Earth Orbit (LEO). Sliding Mode, Feedback Linearization and Model Predictive Controllers are compared to an Impulsive Feedback Law which tracks the mean orbital element differences. Sliding Mode and Feedback Linearization controllers use the same dynamic model which includes Earth Oblateness perturbations. On the other hand, Model Predictive Control with Multi-Objective Cost Function is based on the Clohessy–Wiltshire equations, which do not account for any perturbation and do not cover the eccentricity of the orbit. The comparison was done for two different missions both including Earth Oblateness effects only. A relative orbit mission, which was based on the Prisma Satellite Mission and a rendezvous mission, was implemented. The reference trajectory for the controllers was generated with Yamanaka and Ankersen’s state transition matrix, while a separate method was used for the Impulsive Law. In both of the missions, it was observed that the implemented Impulsive Law outperformed in terms of Delta-v, 1.2 to 3.5 times smaller than the continuous control approaches, while the continuous controllers had a smaller tracking error, 2 to 8.3 times less, both in terms of root mean square error and maximum error in the steady state. Finally, this study shows that the tracking error and Delta-v has inversely proportional relationship.

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  • 155.
    Bashir, Zain
    et al.
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics, Lättkonstruktioner, marina system, flyg- och rymdteknik, rörelsemekanik.
    Lokat, Murtaza
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics, Lättkonstruktioner, marina system, flyg- och rymdteknik, rörelsemekanik.
    Thermal & Air management for aBus Engine Compartment: A method for determining boundary conditions for computational fluid dynamics simulation2021Independent thesis Advanced level (degree of Master of Fine Arts (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    In today's procedures of bus development in Scania CV, physical tests are the most common and reliable source of confirmation for new concepts. As of now, the majority of the physical tests are conducted in various places around the globe such as Spain, Brazil, and Sweden in order to subject the buses to various climates and environments. Naturally, these tests around the globe demand a lot of resources and are very time-consuming leading the bus development department to look for alternative ways of confirmation for these tests. An alternative to testing is in the eld of Computational Fluid Dynamics (CFD), by using 3D models to simulate in order to save resources and time. Today, the method of simulating using CFD is becoming more frequent in the development phase. However, it needs improvements. The purpose of this master's thesis is to develop a method in which the application of CFD can be successfully relied upon, by identifying a set of boundary conditions used as initial data for the CFD simulation. The boundary conditions in this project are the driving conditions and the surface temperatures of the heat sources inside the engine compartment. Initially, a physical test is conducted, in which the surface and surrounding temperatures are measured. Surrounding temperatures will act as a comparison between the physical tests and the simulations. Once the boundary conditions have been measured through physical tests, the data acquired is then used for the simulation as initial values. The goal is to achieve a maximum of10% difference between the results of the physical test and those of the simulations. From the final results, the difference between the physical tests and the simulations is 24% for one of the driving conditions which is considered the best case. However, the results are an improvement compared to the old method used currently by Scania. The method developed in this masters thesis shows an improvement of 21% compared to the old method for the same driving condition which implies a step in the right direction for reliable simulations.

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  • 156.
    Batra, Nishant
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics, Naval Systems.
    Investigation and Analysis ofAircraft System Integration2020Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Aircraft integration plays a pivotal role in the eective aggregation of varioussub-systems into a group of systems. The fundamental categorization of the aircraftintegration process points to technical and managerial aspects. The technical needsare to be managed eectively for an optimal solution. The objective of the thesiswas to investigate these two aspects as being interdependent. First, simulated theaircraft behavior at various congurations, and mapped the results with ight testdata. Subsequently, the conguration’s behavior was assessed as per certicationrequirements. Second, pre-Validation and Verication (V&V) of the Stall WarningSystem (SWS) was conducted to ensure consistent design and performance as perrequirements. Third, managed one of the FCS system’s environmental tests anddeliverables schedule for its certication maturity by utilizing the Critical PathMethod (CPM).

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  • 157.
    Baum, Kevin
    et al.
    Deutsch Forschungszentrum Julich Kunstl Intelligen, Kaiserslautern, Germany..
    Bryson, Joanna
    Hertie Sch, Berlin, Germany..
    Dignum, Frank
    Umeå Univ, Umeå, Sweden..
    Dignum, Virginia
    Umeå Univ, Umeå, Sweden..
    Grobelnik, Marko
    OECD, Paris, France..
    Hoos, Holger
    Rhein Westfal TH Aachen, Aachen, Germany..
    Irgens, Morten
    Oslo Metropolitan Univ, CLAIRE AIorg, Oslo, Norway..
    Lukowicz, Paul
    Deutsch Forschungszentrum Julich Kunstl Intelligen, Kaiserslautern, Germany..
    Muller, Catelijne
    ALLAI, Amsterdam, Netherlands..
    Rossi, Francesca
    IBM Corp, Yorktown Hts, NY USA..
    Shawe-Taylor, John
    Int Res Inst AI, IRCAI, Ljubljana, Slovenia..
    Theodorou, Andreas
    VerAI, Umeå, Sweden..
    Vinuesa, Ricardo
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics.
    From fear to action: AI governance and opportunities for all2023In: Frontiers in Computer Science, E-ISSN 2624-9898, Vol. 5, article id 1210421Article in journal (Other academic)
  • 158.
    Baungaard, M.
    et al.
    Tech Univ Denmark, DTU Wind Energy, Riso Campus,Frederiksborgvej 399, DK-4000 Roskilde, Denmark..
    van der Laan, M. P.
    Tech Univ Denmark, DTU Wind Energy, Riso Campus,Frederiksborgvej 399, DK-4000 Roskilde, Denmark..
    Wallin, Stefan
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics.
    Abkar, M.
    Aarhus Univ, Dept Mech & Prod Engn, Katrinebjergvej 89, DK-8200 Aarhus N, Denmark..
    RANS simulation of a wind turbine wake in the neutral atmospheric pressure-driven boundary layer2023In: Proceedings 8th Wake Conference 2023 / [ed] Bottasso, C Schepers, G Larsen, G Meyers, J Uzol, O Chatelain, P Aubrun, S Leweke, T, IOP Publishing , 2023, Vol. 2505, article id 012028Conference paper (Refereed)
    Abstract [en]

    Reynolds-averaged Navier-Stokes (RANS) simulations of a single wind turbine wake in the neutral atmospheric pressure-driven boundary layer (PDBL) are conducted and compared to RANS simulations with inflow based on the more traditional log-law. The latter is valid in the neutral atmospheric surface layer (ASL), while the PDBL is a better representation of the whole atmospheric boundary layer (ABL). It is found that the wake results of the two types of simulations become more similar for increasing ABL height to rotor diameter ratio. In fact, the ASL is shown to be a special asymptotic case of the PDBL. The RANS simulations are also compared to a large-eddy simulation (LES) PDBL case, where it is found that both the ASL and PDBL RANS simulations compare well with the reference LES data in the wake region, while the RANS PDBL compares better with the data in the upper region of the domain.

  • 159.
    Baxerres, Victor
    et al.
    Illinois Tech IIT, Chicago, IL 60616 USA..
    Vinuesa, Ricardo
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Nagib, Hassan
    Illinois Tech IIT, Chicago, IL 60616 USA..
    Evidence of quasiequilibrium in pressure-gradient turbulent boundary layers2024In: Journal of Fluid Mechanics, ISSN 0022-1120, E-ISSN 1469-7645, Vol. 987, article id R8Article in journal (Refereed)
    Abstract [en]

    Two sets of measurements utilizing hot-wire anemometry and oil-film interferometry for flat-plate turbulent boundary layers, exposed to various controlled adverse and favourable pressure gradients, are used to evaluate history effects of the imposed and varying free-stream gradients. The results are from the NDF wind tunnel at Illinois Tech (IIT) and the MTL wind tunnel at KTH, over the range 800 < Re-tau <22000 (where Re-tau is the friction Reynolds number). The streamwise pressure-gradient parameter beta equivalent to (-& ell;/tau(w))& sdot;(partial derivative P-e/partial derivative x) varied between -2 < beta < 7, where & ell; is an outer length scale for boundary layers equivalent to the half-height of channel flow and the radius of pipe flow, and is estimated for each boundary-layer profile; note that tau(w) is the wall-shear stress and P-e is the free-stream static pressure. Extracting from each profile the three parameters of the overlap region, following the recent work of Monkewitz & Nagib (J. Fluid Mech., vol. 967, 2023, p. A15) that led to an overlap region of combined logarithmic and linear parts, we find minimum history effects in the overlap region. Thus, the overlap region in this range of pressure-gradient boundary layers appears to be in 'quasiequilibrium'.

  • 160.
    Bayat, Mariam
    et al.
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics, Solid Mechanics.
    Pongpairote, Nichakarn
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics, Lightweight Structures.
    Arm Injury Prediction with THUMS SAFER: Improvements of the THUMS SAFER upper extremity2020Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Globally, approximately 1.2 million people die each year due to traffic accidents. Upper extremity injuries account for 18% to 25% of all car accident injuries. In order to be able to analyze these crash-related injuries, Human body models(HBMs) are used as a complement to FE simulations. An example of a HBM is the THUMS SAFER that is based on a 50 percentile American male. The aim of this study was to improve the upper extremity of the THUMS SAFER with respect to Autoliv's requirements to better predict fractures. In addition, this was validated against the Forman experiment(Forman, et al., The journal of trauma and acute care surgery, vol. 77, 2014) where human cadavers of the upper extremity were axially impacted to replicate a car collision. This was done by generating the upper extremity geometry with segmentation of medical images of a right human hand in combination with the complete STL-geometry of the forearm from the Piper project. The STL-geometry of the segmented human hand and Piper forearm was integrated and a complete STL-geometry of the upper extremity was obtained. Based on the complete STL-geometry, the FE-arm HEX 4.0 was built with modelling of bones, ligaments, soft tissue and skin with corresponding material choice in accordance with Autoliv's requirements.

    The model HEX 4.0 was improved considering an increased mesh density from an average of 94% to 98%. HEX 4.0 was also validated against the data from the Forman experiment for experiments 5, 6 and 15. It showed a good correlation with the acceleration curves between the simulated and experimental values for the three experiments. The reaction force in the elbow was compared for experiment 15, where the simulated value 5.7 kN divided by a factor of 1.4 from 4 kN for the experiment. Furthermore, the fi rst principal strains that occurred in HEX 4.0 were analysed by 17 ms were the highest acceleration was achieved for experiments 5 and 6. Both experiments were shown to be close to the failure threshold of bones. However, the highest value e5=9.8E-03 occurred in the radius for experiment 5, while e6=9.3E-03 in a ligament for experiment 6. In addition, the failure threshold for experiment 15 exceeded 5 ms in lunate, schapoid and triquetrum. This indication of fractures is in good agreement with the experimental results where the corresponding bones resulted in fractures in experiment 15. HEX 4.0 was an improved upper extremity of the THUMS SAFER considering an increased mesh density. It is also capable of indicating fractures and corresponding positions in the form of analyzes of occurring stresses and strains. Nevertheless, improvements and further validation of HEX 4.0 has been proposed in the future work section.

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  • 161.
    Bazesefidpar, Kazem
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics.
    Numerical simulation of non-Newtonian fluids flow over surfaces2023Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Wetting of surfaces by droplets of non-Newtonian fluids is important for various industrial and natural processes such as coating and cleaning of surfaces and inkjet printing, to name a few. Viscoelastic fluids are compounds of a very small amount of polymers and solvent. They are categorized as non-Newtonian fluids, and they exhibit both elasticity and shear dependent viscosity. Despite their relevance and abundance in our environment, dynamic wetting of viscoelastic fluids has been studied much less than that of the Newtonian fluids. Furthermore, many of the viscoelastic studies make simplifying assumptions of the contact line movement, for example, a constant value of the contact angle independent of the spreading speed of the droplet.

    In this thesis work, we implement a numerical framework for dynamic contact line problems of viscoelastic fluids, taking into account contact line friction or contact line hysteresis when necessary. We solve the coupled Cahn-Hilliard, Navier-Stokes and viscoelastic constitutive models to reveal detailed information about the flow physics, such as the polymeric stress distributions inside the drops. Especially interesting is the vicinity of discontinuity regions e.g. the contact-line and liquid bridge between the coalescing drops. First, we present the idea of dual-resolution grids to address the high interfacial resolution requirements for a viscoelastic two-phase flow. In particular, a dual-resolution algorithm is presented and validated for the wetting of viscoelastic fluids. Secondly, we apply our algorithm to investigate the effect of non-Newtonian properties on jumping of two merging droplets from a superhydrophobic surface, a problem which might be of interest for self-cleaning surfaces. In the last part, the physical effects of non-Newtonian properties are investigated on both the initial wetting regime on a smooth hydrophilic surface and the pinning and depinning of a droplet in the presence of the contact angle hysteresis.

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  • 162.
    Bazesefidpar, Kazem
    et al.
    KTH, Centres, SeRC - Swedish e-Science Research Centre. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Engineering Sciences (SCI), Engineering Mechanics.
    Brandt, Luca
    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.
    Tammisola, Outi
    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.
    A dual resolution phase-field solver for wetting of viscoelastic droplets2022In: International Journal for Numerical Methods in Fluids, ISSN 0271-2091, E-ISSN 1097-0363, Vol. 94, no 9, p. 1517-1541Article in journal (Refereed)
    Abstract [en]

    We present a new and efficient phase-field solver for viscoelastic fluids with moving contact line based on a dual-resolution strategy. The interface between two immiscible fluids is tracked by using the Cahn-Hilliard phase-field model, and the viscoelasticity incorporated into the phase-field framework. The main challenge of this approach is to have enough resolution at the interface to approach the sharp-interface methods. The method presented here addresses this problem by solving the phase field variable on a mesh twice as fine as that used for the velocities, pressure, and polymer-stress constitutive equations. The method is based on second-order finite differences for the discretization of the fully coupled Navier–Stokes, polymeric constitutive, and Cahn–Hilliard equations, and it is implemented in a 2D pencil-like domain decomposition to benefit from existing highly scalable parallel algorithms. An FFT-based solver is used for the Helmholtz and Poisson equations with different global sizes. A splitting method is used to impose the dynamic contact angle boundary conditions in the case of large density and viscosity ratios. The implementation is validated against experimental data and previous numerical studies in 2D and 3D. The results indicate that the dual-resolution approach produces nearly identical results while saving computational time for both Newtonian and viscoelastic flows in 3D. 

  • 163.
    Bazesefidpar, Kazem
    et al.
    KTH, Centres, SeRC - Swedish e-Science Research Centre. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Engineering Sciences (SCI), Engineering Mechanics.
    Tammisola, Outi
    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.
    The effect of contact angle hysteresis on a droplet in a viscoelastic two-phase system2024In: Physics of fluids, ISSN 1070-6631, E-ISSN 1089-7666, Vol. 36, no 3, article id 033119Article in journal (Refereed)
    Abstract [en]

    We investigate the dynamic behavior of a two-dimensional droplet adhering to a wall in Poiseuille flow at low Reynolds numbers, in a system where one of the phases is viscoelastic represented by a Giesekus model. The Cahn-Hilliard Phase-Field method is used to capture the interface between the two phases. The presence of polymeric molecules alters the viscoelastic drop's deformation over time, categorizing it into two stages before contact line depinning. In the first stage, the viscoelastic droplet deforms faster, while in the second stage, the Newtonian counterpart accelerates and its deformation outpaces the viscoelastic droplet. The deformation of viscoelastic drop is retarded significantly in the second stage with increasing Deborah number De. The viscous bending of viscoelastic drop is enhanced on the receding side for small De, but it is weakened by further increase in De. On the advancing side, the viscous bending is decreased monotonically for Ca<0.25 with a non-monotonic behavior for Ca=0.25. The non-monotonic behavior on the receding side is attributed to the emergence of outward pulling stresses in the vicinity of the receding contact line and the inception of strain-hardening at higher De, while the reduction in the viscous bending at the advancing side is the result of just strain-hardening. Finally, when the medium is viscoelastic, the viscoelasticity suppresses the droplet deformation on both receding and advancing sides, and this effect becomes more pronounced with increasing De. Increasing the Giesekus mobility parameter enhances the weakening effect of viscous bending on the advancing side.

  • 164.
    Bazesefidpar, Kazem
    et al.
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Tammisola, Outi
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics.
    The effect of contact angle hysteresis on adroplet in a viscoelastic two-phase systemManuscript (preprint) (Other academic)
    Abstract [en]

    We investigate the dynamic behaviour of a two-dimensional (2D) droplet adhering to a wall in Poiseuille flow at low Reynolds numbers, in a system where either the droplet is viscoelastic (V/N) or the surrounding medium (N/V). The fluid viscoelasticity has been modeled by the Giesekus constitutive equation, and the Cahn–Hilliard Phase-Field method is used to capture the interface between two phases. The contact angle hysteresis is represented by an advancing contact angle and a receding contact angle . The results reveal that the deformation of the viscoelastic drop over time is changed due to the presence of polymeric molecules, and it can be categorized in two stages prior to depinning of the contact lines. In the first stage, the viscoelastic droplet speeds up and deforms faster, while in the second stage, the Newtonian counterpart accelerates and its deformation outpaces the viscoelastic droplet. The deformation of viscoelastic drop is retarded significantly in the second stage with increasing Deborah number De. In the V/N case, the viscous bending is enhanced on the receding side for small De, but it is weakened by further increase in De, and this non-monotonic behavior brings about an increase in the receding contact line velocity at small De and a decrease at large De. On the advancing side, the viscous bending is decreased monotonically, and hence the advancing contact line velocity is decreased with increasing De. The non-monotonic behavior on the receding side is attributed to the emergence of outward pulling stresses in the vicinity of the receding contact line and the inception of strain-hardening at higher De, while the reduction in the viscous bending at the advancing side is the result of just strain-hardening due to the presence of dominant extensional flow on the advancing side. Finally, in the N/V system, the viscoelasticity of the medium suppresses the droplet deformation on both receding and advancing sides, and this effect is more pronounced with increasing De; the weakening effect of viscous bending is enhanced significantly at the advancing side by increasing the Giesekus mobility parameter in the N/V system. These results give a thorough understanding of viscoelastic effect on both drop deformation and depinning of both contact lines over a surface with contact angle hysteresis.

  • 165.
    Becourt, Pierre-Olivier
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics, Lättkonstruktioner, marina system, flyg- och rymdteknik, rörelsemekanik.
    Design of a suction wing for wind propulsion of ships: Pre-sizing and calculations2022Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    As emissions of polluting substances due to shipping are growing, newsolutions for ship propulsion are emerging. One of them is the suctionwing, a vertical wing designed to generate lift forward, and made even moreefficient than classical wings by the suction of its boundary layer. Thisproject allowed for the participation, within a team of mechanical engineers,in the early design of a pilot model of such a system, ultimately intendedto be industrialised. The design process was followed in order to define thesolutions to match the performances of each function of the wing, basedon a set of specifications, and to verify the sustainability of those solutions.Also, a particular interest in the furniture and/or manufacturing of thosesolutions was given. For those instances, the suction system was defined withthe collaboration of manufacturers. Also, the wing orientation system wasdefined and its integration was verified with respect to the deformation ofthe components at its interfaces. Then, The flap was designed in order todefine solutions to allow mobility transmission, taking into account its stressconditions. The solution for the sealing of the system was also worked upon.Finally, the main mast of the wing was designed so to maintain its integrity,with respect to its stress charges and its strong stress concentrations.

  • 166. Benard, N.
    et al.
    Sujar Garrido, Patricia
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Bonnet, J. -P
    Moreau, E.
    Shear Layer and Shedding Modes Excitations of a Backward-Facing Step Flow by Surface Plasma Discharge2020In: Advances in Effective Flow Separation Control for Aircraft Drag Reduction, Springer, 2020, p. 55-74Chapter in book (Refereed)
    Abstract [en]

    The present experimental study interests in determining the influence of a linear plasma actuator (dielectric barrier discharge) on the development of a separated turbulent shear layer. More specifically, the plasma actuator is used to impose periodic perturbations at the step corner of a backward-facing step. Two different modes of excitation are explored. One concerns the shear layer mode of instability, a mode whose amplification leads to a minimization of the recirculation bubble. The present investigation shows how a dielectric barrier discharge plasma actuator can impose periodic perturbations that excite the shear layer mode and result in a strong regularization of the vortex street. The case of excitation at the shedding mode is also experimentally investigated using a DBD actuator. The measurements show the increase in Reynolds stress caused by this excitation as well as the specific growing mechanism of the shear layer. Indeed, phase-averaged flow measurements highlights the difference in the mechanism of development of the shear layer regarding the type of excitation used, the shear layer mode promoting a growing mechanism by fluid entrainment while the shedding mode enhancing the pairing of successive vortical flow structures.

  • 167.
    Beneitez Galan, Miguel
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Engineering Sciences (SCI), Engineering Mechanics.
    Nonlinear dynamics in transitional wall-bounded flows2021Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    This thesis focuses on numerical studies of subcritical transition to turbulence in shear flows. The thesis employs a framework based on nonlinear dynamics in the subsequent studies. The geometrical approach to subcritical transition pivots the concepts of edge manifold and edge state. Such concepts are explored in detail in the Blasius boundary layer. The identified edge trajectory is chaotic and presents a couple of high- and low-speed streaks akin to those identified in other shear flows. For long enough times the linear instability of the Blasiusboundary layer coexists with the bypass transition scenario. The edge is thus reinterpreted as a manifold separating both routes. On the edge manifold of the Blasius boundary layer, the fully localised minimal seed is identified. The minimal seed experiences a sequence of linear mechanisms: the Orr mechanism followed by the lift-up. The resulting perturbation approaches the same region in state space as identified from arbitrary perturbations.These insights from the edge trajectory identified in the Blasius boundary layer inspired a low-dimensional model. The model illustrates the e↵ect of the laminar attractor becoming linearly unstable and it agrees qualitatively withother recent studies in the literature.The edge has been identified as a hyperbolic Lagrangian coherent structure of infinite dimension. We show how two Lagrangian diagnostics can be used to locate the edge directly in state space. This allows us to revisit edge tracking as a method optimising a Lagrangian diagnostic instead of a binary algorithm.The two last studies of the thesis focus on the optimally time-dependent(OTD) modes as a basis for the linearised dynamics about a base flow with arbitrary time-dependence. The OTD modes are explored for a periodic flow in pulsating plane Poiseuille flow. The resulting OTD modes can be linked to thespectrum of the Orr-Sommerfeld operator. The results revealed perturbations which span more than one period of the base flow. Finally, the OTD frameworkis used on the edge trajectory starting from the minimal seed in the Blasiusboundary layer.

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  • 168.
    Beneitez Galan, Miguel
    et al.
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics, Stability, Transition and Control. KTH, Centres, SeRC - Swedish e-Science Research Centre.
    Duguet, Yohann
    LIMSI-CNRS, Université Paris-Saclay, P91405 Orsay, France.
    Henningson, Dan S.
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics, Stability, Transition and Control. KTH, Centres, SeRC - Swedish e-Science Research Centre.
    Modeling the collapse of the edge when two transition routes compete2020In: Physical review. E, ISSN 2470-0045, E-ISSN 2470-0053, Vol. 102, no 5, article id 053108Article in journal (Refereed)
    Abstract [en]

    The transition to turbulence in many shear flows proceeds along two competing routes, one linked with finite-amplitude disturbances and the other one originating from a linear instability, as in, e.g., boundary layer flows. The dynamical systems concept of an edge manifold has been suggested in the subcritical case to explain the partition of the state space of the system. This investigation is devoted to the evolution of the edge manifold when linear stability is added in such subcritical systems, a situation poorly studied despite its prevalence in realistic fluid flows. In particular, the fate of the edge state as a mediator of transition is unclear. A deterministic three-dimensional model is suggested, parametrized by the linear instability growth rate. The edge manifold evolves topologically, via a global saddle-loop bifurcation of the underlying invariant sets, from the separatrix between two attraction basins to the mediator between two transition routes. For larger instability rates, the stable manifold of the saddle point increases in codimension from 1 to 2 after an additional local pitchfork node bifurcation, causing the collapse of the edge manifold. As the growth rate is increased, three different regimes of this model are identified, each one associated with a flow case from the recent hydrodynamic literature. A simple nonautonomous generalization of the model is also suggested in order to capture the complexity of spatially developing flows.

  • 169.
    Beneitez Galan, Miguel
    et al.
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Engineering Sciences (SCI), Engineering Mechanics. KTH, Centres, SeRC - Swedish e-Science Research Centre.
    Duguet, Yohann
    Univ Paris Saclay, LIMSI, CNRS, P91405, Orsay, France..
    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.
    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.
    Edge manifold as a Lagrangian coherent structure in a high-dimensional state space2020In: Physical Review Research, E-ISSN 2643-1564, Vol. 2, no 3, article id 033258Article in journal (Refereed)
    Abstract [en]

    Dissipative dynamical systems characterized by two basins of attraction are found in many physical systems, notably in hydrodynamics where laminar and turbulent regimes can coexist. The state space of such systems is structured around a dividing manifold called the edge, which separates trajectories attracted by the laminar state from those reaching the turbulent state. We apply here concepts and tools from Lagrangian data analysis to investigate this edge manifold. This approach is carried out in the state space of autonomous arbitrarily high-dimensional dissipative systems, in which the edge manifold is reinterpreted as a Lagrangian coherent structure (LCS). Two different diagnostics, finite-time Lyapunov exponents and Lagrangian descriptors, are used and compared with respect to their ability to identify the edge and their scalability. Their properties are illustrated on several low-order models of subcritical transition of increasing dimension and complexity, as well on well-resolved simulations of the Navier-Stokes equations in the case of plane Couette flow. They allow for a mapping of the global structure of both the state space and the edge manifold based on quantitative information. Both diagnostics can also be used to generate efficient bisection algorithms to approach asymptotic edge states, which outperform classical edge tracking.

  • 170.
    Beneitez Galan, Miguel
    et al.
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics.
    Duguet, Yohann
    Schlatter, Philipp
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics.
    Henningson, Dan S.
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics.
    Finite-time stability of an edge trajectory in the Blasius boundary layerManuscript (preprint) (Other academic)
  • 171.
    Beneitez Galan, Miguel
    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. KTH, Centres, SeRC - Swedish e-Science Research Centre.
    Duguet, Yohann
    LISN-CNRS, Campus Universitaire d'Orsay, Université Paris-Saclay, F-91400 Orsay, France.
    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.
    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.
    Instability of the optimal edge trajectory in the Blasius boundary layer2023In: Journal of Fluid Mechanics, ISSN 0022-1120, E-ISSN 1469-7645, Vol. 971, article id A42Article in journal (Refereed)
    Abstract [en]

    In the context of linear stability analysis, considering unsteady base flows is notoriously difficult. A generalisation of modal linear stability analysis, allowing for arbitrarily unsteady base flows over a finite time, is therefore required. The recently developed optimally time-dependent (OTD) modes form a projection basis for the tangent space. They capture the leading amplification directions in state space under the constraint that they form an orthonormal basis at all times. The present numerical study illustrates the possibility to describe a complex flow case using the leading OTD modes. The flow under investigation is an unsteady case of the Blasius boundary layer, featuring streamwise streaks of finite length and relevant to bypass transition. It corresponds to the state space trajectory initiated by the minimal seed; such a trajectory is unsteady, free from any spatial symmetry and shadows the laminar-turbulent separatrix for a finite time only. The finite-time instability of this unsteady base flow is investigated using the 8 leading OTD modes. The analysis includes the computation of finite-time Lyapunov exponents as well as instantaneous eigenvalues, and of the associated flow structures. The reconstructed instantaneous eigenmodes are all of outer type. They map unambiguously the spatial regions of largest instantaneous growth. Other flow structures, previously reported as secondary, are identified with this method as relevant to streak switching and to streamwise vortical ejections. The dynamics inside the tangent space features both modal and non-modal amplification. Non-normality within the reduced tangent subspace, quantified by the instantaneous numerical abscissa, emerges only as the unsteadiness of the base flow is reduced.

  • 172.
    Berggren, Filip
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics, Solid Mechanics.
    Fretting Fatigue Life Analysis of Additively Manufactured Titanium for Compressor Blades2021Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Additive manufacturing (AM) is rising in popularity as a manufacturing technique of industrial components. Compressor blades attached using dove tail joints are a common source of fretting damage and in order to evaluate AM as a manufacturing technique, its fretting fatigue behaviour must be studied. This report treats the fretting fatigue behaviour between AM electron-beam melted (EBM) titanium alloy (Ti-6Al-4V) and forged steel alloy (22NiCrMoV12-7). AM Ti-6Al-4V is compared with forged Ti-6Al-4V to analyse AMs feasibility as an optional manufacturing technique of compressor blades. Further, as AM causes the material to be anisotropic, different print orientations as well as heat-treatments are compared. Performing fretting fatigue and crack propagation experiments alongside computations, through a finite element model and the crack propagation software NASGRO, show that AM Ti-6Al-4V performs similarly to that of forged Ti-6Al-4V. The study concludes that different print orientations from manufacturing show no significant impact on fretting fatigue life. However, the non-heat-treated specimens in the experiments perform slightly better than those that were heat-treated.

  • 173.
    Bergström, Max
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics, Lättkonstruktioner, marina system, flyg- och rymdteknik, rörelsemekanik.
    Direct Remote Id based UAS Collision Avoidance System2022Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    The drone industry is growing and the need for increased autonomy will be required if large fleetof drones will be able to fly without a single pilot per drone. A useful part of automating the flighten-route can be achieved with the upcoming standard of Direct Remote Id (DRI), which signalspositional data for drones and can be used as the perceptive part in a collision avoidance systembetween drones with the advantage of limited weight penalties and minimal financial cost.Simulations were carried out to understand different kinds of evasive maneuvers and develop asimple yet effective algorithm for avoiding obstacles and continue towards the next waypoint ona mission. Positional data can be retrieved with an ESP-32 board from a flight computer withMavlink protocol, which can then be broadcasted and received to an ESP-32 board using DirectRemote Id. The distances between the nearest drones can be computed, along with the shortest al-lowable distance and closest positions of the drones, if they were to continue on a straight course. Ifthe closest passing distance turned out closer than a set safety distance, an evasive maneuver is cal-culated and executed, with preliminary work focusing on evasion maneuvers on an horizontal plane.Flight tests showed that an evasive position could be calculated, and the drone successfully di-verted to it, while continuing with the mission after the evasion was completed. These resultsshowed the potential of using Direct Remote Id as a simple close proximity detection for use withcollision avoidance

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  • 174.
    Bernabeu Peñalba, Sergio Santiago
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics, Lättkonstruktioner, marina system, flyg- och rymdteknik, rörelsemekanik.
    Development of a Level-0 Geoprocessing Platform for a Multispectral Remote Sensing Payload2022Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    This thesis presented an overview of the development of a geolocating algorithm as part of a geoprocessor for raw satellite imagery. This algorithm was devised for and limited by the specifications of a state-of-the-art multispectral telescope designed by Aistech Space, hosted onboard the Guardian spacecraft, which will observe Earth through the visible, near infrared, and thermal infrared bands of the electromagnetic spectrum. The geolocation algorithm presented here is composed of the combination of two models. The first is a physical model, which makes use of spacecraft telemetry and external satellite-tracking data to approximate the geographical center of a sensed scene. Secondly, an optical model obtains a reference Landsat image based on the timestamp and approximated location of the sensed scene and utilizes image processing techniques to pinpoint a more precise geographical location of the sensed scene within acceptable limits. This performance was achieved in 77% of the cases considered. To conclude, a roadmap of the subsequent development topics and their relevance was laid out.

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  • 175.
    Bernal, Esteban
    et al.
    Cent Queensland Univ, Ctr Railway Engn, Rockhampton, Qld, Australia..
    Spiryagin, Maksym
    Cent Queensland Univ, Ctr Railway Engn, Rockhampton, Qld, Australia..
    Stichel, Sebastian
    KTH, School of Engineering Sciences (SCI), Centres, The KTH Railway Group. KTH, School of Engineering Sciences (SCI), Engineering Mechanics.
    Bosso, Nicola
    Politecnico Torino, Dept Mech & Aerosp Engn, Turin, Italy..
    Lewis, Roger
    Univ Sheffield, Dept Mech Engn, Sheffield, S Yorkshire, England..
    Bosomworth, Christopher
    Cent Queensland Univ, Ctr Railway Engn, Rockhampton, Qld, Australia..
    Wu, Qing
    Cent Queensland Univ, Ctr Railway Engn, Rockhampton, Qld, Australia..
    Cole, Colin
    Cent Queensland Univ, Ctr Railway Engn, Rockhampton, Qld, Australia..
    Friction-Slip Curves - The Pathway From Twin-Disc Tribo Measurements To Full-Scale Locomotive Multibody Simulations2022In: PROCEEDINGS OF 2022 JOINT RAIL CONFERENCE (JRC2022), AMER SOC MECHANICAL ENGINEERS , 2022, article id V001T07A005Conference paper (Refereed)
    Abstract [en]

    Locomotive multibody simulations are commonly used as a cost-effective tool to study, energy efficiency, wheel-rail wear, rolling contact fatigue, etc. The accuracy of the wheel-rail contact forces from multibody simulations depends on the correct modelling of the friction conditions. The friction coefficient is a function of the slip velocity, and it is influenced by several tribological parameters including, for example, material mechanical properties, environmental conditions and the presence of third body layers that vary spatially and temporally along the track. In most cases, generic friction-slip curves obtained from publications and public reports are used as inputs to the wheel-rail contact model in the locomotive simulations, as direct friction measurements using full-scale experimental set-ups are generally cost-prohibitive. A pathway to produce friction-slip curves from tribo-machine friction measurements is proposed in this paper. The pathway involves manufacturing discs from actual wheel and rail material samples to measure the traction coefficient at a spectrum of slip set points using a twin-disc tribo-machine. The tribo-machine results are scaled to be used in a locomotive multibody model that uses the modified Fastsim and a traction system co-simulation approach. Two friction curves for wet and dry conditions are processed and exemplified in a dynamic model.

  • 176.
    Bernal, Esteban
    et al.
    Cent Queensland Univ, Ctr Railway Engn, Rockhampton, Australia.;CQ Univ, Ctr Railway Engn, 554-700 Yaamba Rd, Norman Gardens, Qld 4701, Australia..
    Spiryagin, Maksym
    Cent Queensland Univ, Ctr Railway Engn, Rockhampton, Australia..
    Vollebregt, Edwin
    Vtech CMCC, Rotterdam, Netherlands..
    Oldknow, Kevin
    Simon Fraser Univ, Surrey, BC, Canada..
    Stichel, Sebastian
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics. KTH, School of Engineering Sciences (SCI), Centres, The KTH Railway Group.
    Shrestha, Sundar
    Cent Queensland Univ, Ctr Railway Engn, Rockhampton, Australia..
    Ahmad, Sanjar
    Cent Queensland Univ, Ctr Railway Engn, Rockhampton, Australia..
    Wu, Qing
    Cent Queensland Univ, Ctr Railway Engn, Rockhampton, Australia..
    Sun, Yan
    Cent Queensland Univ, Ctr Railway Engn, Rockhampton, Australia..
    Cole, Colin
    Cent Queensland Univ, Ctr Railway Engn, Rockhampton, Australia..
    Prediction of rail surface damage in locomotive traction operations using laboratory-field measured and calibrated data2022In: Engineering Failure Analysis, ISSN 1350-6307, E-ISSN 1873-1961, Vol. 135, article id 106165Article in journal (Refereed)
    Abstract [en]

    Rail damage prediction is a complex task because it depends on numerous tribological parameters and the dynamic conditions produced by the vehicles operating at different speeds and configurations. Shakedown maps and Whole-Life-Rail-Model/T-Gamma have been used to predict rail damage, but they involve assumptions that may reduce their accuracy. This paper proposes a simulation modelling method to predict rail surface damage based on a locomotive digital twin, calibrated shakedown maps and friction measurements. The method improves the accuracy of rail damage predictions by including slip-dependent friction characteristics, co-simulation of locomotive traction mechatronic system and the mechanical properties of the wheel and rail materials measured through tensile tests. A set of operating conditions are simulated on a high-performance computing cluster, with stress results being post processed into calibrated shakedown heatmaps. The method clearly indicated the influences of the different operating conditions on rail damage for specific combinations of wheel-rail materials and vehicle-track configurations.

  • 177.
    Beszta-Borowski, Pawel Jan
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics, Lättkonstruktioner, marina system, flyg- och rymdteknik, rörelsemekanik.
    Motions and Hydrodynamics of a High-Speed Search and Rescue Vessel Based on a Time-Efficient Computational Fluid Dynamics Procedure2022Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

     This thesis proposes a time-effective procedure for numerical prediction of the hydrodynamic performance of a small high-speed craft (HSC) for Search and Rescue (SAR) operations. Following a naval architecture review of available SAR designs, engineering physics and numerical methods for the evaluation of resistance and seakeeping are explained. A method that utilises Reynolds-Averaged Navier Stokes equations-based Computational Fluid Dynamics theory is utilised to predict calm-water resistance and wave-induced motions of a sample SAR vessel operating in regular waves. Simulations are performed using the Orca3D Marine CFD environment, utilising the Simerics CFD package. The method is validated against experimental results found in literature. The comparative study of calm-water resistance allows for analysing the influence of the hull shape on the performance of the craft. Seakeeping analysis is performed in one wave length. Head, oblique and following seas conditions are simulated. In head and oblique seas, obtained results in the time domain present periodic motions. Non-linear pitch motions are displayed, followed by amplitudes of motions calculations. High non-linearity of roll motions in oblique seas is observed. The thesis concludes that for less demanding cases, the proposed procedure offers a time-efficient method to estimate the hydrodynamic performance of the vessel with satisfying accuracy. Further research is required to optimise the method for obtaining results in following seas in an acceptable time frame.

  • 178.
    Bettar, Michael
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics, Lättkonstruktioner, marina system, flyg- och rymdteknik, rörelsemekanik.
    Fuel Efficiency Analysis of Optimized Flights2022Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    The impact of air travel on the climate, along with its increasing share in CO2 emissions have raised the demand for sustainable air travel solutions. The current aircraft technologies have seen significant improvement throughout the years. Although, the rate at which new aircraft technologies are developed can not keep up with the increased demand for air travel. Hence, a different approach to reduce the aviation’s impact on climate can be achieved by optimizing the vertical flight path in order to reduce the fuel consumption, i.e. using dynamic programming.

    Upon departure, an optimization of the vertical flight path is initiated and an optimal flight plan is suggested to the flight crew.

     The fuel saving produced by the optimal flight plan is a potential saving that can only be fully achieved if the flight crew chose to fly according to the optimized flight path. However, restrictions from the Air Traffic Control, as well as the flight crew’s willingness to follow the optimized flight path can affect the achieved saving. Hence, a tool is developed in order to compute trip fuel consumption from post-flight data obtained from the Automatic Dependent Surveillance-Broadcast (ADS-B) surveillance technology. A method to identify the start and end positions of cruise segments is successfully implemented. Two methods of calculating the fuel are implemented and compared. The first method is based on simulating the actual flight, which uses the same performance model as for the simulation of the operational flight plan trip and optimized trip. The second method is based on utilizing the ADS-B data to obtain the aircraft speed which in return can be used as a parameter to obtain the fuel flow of the aircraft, hence the trip is not simulated. The results reveals that the simulation method produces flight trajectories that are comparable to the operational and optimized flight plans since they use the same model structure. However, using ADS-B data to obtain fuel consumption represents the actual flight trajectory more accurately.

     Furthermore, an optimization algorithm based on the onboard Flight Management Computer is implemented. According to the results, the FMC optimization offers a sufficient optimization of the cruise phase, when compared to the OFP trip, however performs worse than the dynamic programming, which provides a global optimal solution.

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  • 179.
    Bettar, Michael
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics, Lättkonstruktioner, marina system, flyg- och rymdteknik, rörelsemekanik.
    Post-Flight Analysis of Fuel Consumption2022Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    The impact of air travel on the climate, along with its increasing share in CO2 emissions haveraised the demand for sustainable air travel solutions. The current aircraft technologies haveseen significant improvement throughout the years. Although, the rate at which new aircrafttechnologies are developed can not keep up with the increased demand for air travel. Hence, adifferent approach to reduce the aviation’s impact on climate can be achieved by optimizing thevertical flight path in order to reduce the fuel consumption, i.e. using dynamic programming.Upon departure, an optimization of the vertical flight path is initiated and an optimal flight planis suggested to the flight crew.

    The fuel saving produced by the optimal flight plan is a potential saving that can only be fullyachieved if the flight crew chose to fly according to the optimized flight path. However, restrictionsfrom the Air Traffic Control, as well as the flight crew’s willingness to follow theoptimized flight path can affect the achieved saving. Hence, a tool is developed in order tocompute trip fuel consumption from post-flight data obtained from the Automatic DependentSurveillance-Broadcast (ADS-B) surveillance technology. A method to identify the start andend positions of cruise segments is successfully implemented. Two methods of calculating thefuel are implemented and compared. The first method is based on simulating the actual flight,which uses the same performance model as for the simulation of the operational flight plantrip and optimized trip. The second method is based on utilizing the ADS-B data to obtain theaircraft speed which in return can be used as a parameter to obtain the fuel flow of the aircraft,hence the trip is not simulated. The results reveals that the simulation method produces flighttrajectories that are comparable to the operational and optimized flight plans since they use thesame model structure. However, using ADS-B data to obtain fuel consumption represents theactual flight trajectory more accurately.

    Furthermore, an optimization algorithm based on the on-board Flight Management Computeris implemented. According to the results, the FMC optimization offers a sufficient optimizationof the cruise phase, when compared to the OFP trip, however performs worse than the dynamicprogramming, which provides a global optimal solution

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  • 180.
    Bezier, Antoine
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics, Lättkonstruktioner, marina system, flyg- och rymdteknik, rörelsemekanik.
    Quotation for Customer Proposal and Performance Analysis for aircraft maintenance2022Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    By working as an intern with the Quotation Officer of Sabena Technics Nîmes facility,an aircraft maintenance company, this degree project highlights the different factors totake into account in a quotation of civil planes (B737/B767/A320/A330) by analysingwork packages from airline company, applying a process to estimate the importantdata as the man hours or tools, and using my technical knowledge to understandmaintenance tasks. Management knowledge for commercial sale reviews was usefulas well, this job is in the middle of the commercial team and and the technicalteam. Finally, a critical opinion of the process has been made in order to propose animprovement of the next quotations.

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  • 181.
    Bhat, Sriharsha
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics.
    Hydrobatics: Efficient and Agile Underwater Robots2020Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    The term hydrobatics refers to the agile maneuvering of underwater vehicles. Hydrobatic capabilities in autonomous underwater vehicles (AUVs) can enable increased maneuverability without a sacrifice in efficiency and speed. This means innovative robot designs and new use case scenarios are possible. Benefits and technical challenges related to hydrobatic AUVs are explored in this thesis. The dissertation contributes to new knowledge in simulation, control and field applications, and provides a structured approach to realize hydrobatic capabilities in real world impact areas.

    Three impact areas are considered - environmental monitoring, ocean production and security. A combination of agility in maneuvering and efficiency in performance is crucial for successful AUV applications. To achieve such performance, two technical challenges must be solved. First, these AUVs have fewer control inputs than degrees of freedom, which leads to the challenge of underactuation. The challenge is described in detail and solution strategies that use optimal control and model predictive control (MPC) are highlighted. Second, the flow around an AUV during hydrobatic maneuvers transitions from laminar to turbulent flow at high angles of attack. This renders flight dynamics modelling difficult. A full 0-360 degree envelope flight dynamics model is therefore derived, which combines a multi-fidelity hydrodynamic database with a generalized component-buildup approach. Such a model enables real-time (or near real-time) simulations of hydrobatic maneuvers including loops, helices and tight turns.

    Next, a cyber-physical system (CPS) is presented -- it safely transforms capabilities derived in simulation to real-world use cases in the impact areas described. The simulator environment is closely integrated with the robotic system, enabling pre-validation of controllers and software before hardware deployment. The small and hydrobatic SAM AUV (developed in-house at KTH as part of the Swedish Maritime Robotics Center) is used as a test platform. The CPS concept is validated by using the SAM AUV for the search and detection of a submerged target in field operating conditions.

    Current research focuses on further exploring underactuated control and motion planning. This includes development of real-time nonlinear MPC implementations running on AUV hardware, as well as intelligent control through feedback motion planning, system identification and reinforcement learning. Such strategies can enable real-time robust and adaptive control of underactuated systems. These ideas will be applied to demonstrate new capabilities in the three impact areas.

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  • 182.
    Bhat, Sriharsha
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics.
    Hydrobatics: Real-time Control, Simulation and Learning for Underactuated AUVs in Agile Maneuvers2023Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The term hydrobatics refers to the agile maneuvering of underwater vehicles. Underwater robots such as autonomous underwater vehicles (AUVs) and remotely operated vehicles (ROVs) are either designed as flight style, optimized for range and speed, or hover style, optimized for precise maneuverability. Hydrobatic capabilities can help balance efficiency and maneuverability in these platforms, enabling innovative robot designs for impact areas in environmental monitoring, ocean production and security. This dissertation addresses technical challenges related to hydrobatic AUVs and contributes to new knowledge in real-time control, simulation, learning and planning. 

    Hydrobatic AUVs are underactuated systems --- new strategies using nonlinear model predictive control (MPC) and behavior trees (BTs) are presented for efficient and safe real-time control of underactuated AUVs in agile maneuvers. Further, the flow around an AUV during such maneuvers transitions from laminar to turbulent flow at high angles of attack, rendering flight dynamics modelling difficult. A full 0-360 degree envelope flight dynamics model is therefore derived, which combines a multi-fidelity hydrodynamic database with a generalized component-buildup approach. Such a model enables real-time (or near real-time) simulations of hydrobatic maneuvers including loops, helices and tight turns. To increase the intelligence and robustness of such systems, data driven methods including physics-informed learning, Gaussian processes, sparse regression  and reinforcement learning are utilized to rapidly identify models of the system's dynamics and perform online adaptive control. To further enhance autonomy, informative path planning is also studied, where an adaptive sampling strategy combines AUV measurements and satellite data to track ocean fronts.

    These hydrobatic capabilities are safely brought to the real world through a cyber-physical system (CPS). Simulator environments are closely integrated with the robotic system, enabling pre-validation of controllers and software before hardware deployment. The small and hydrobatic SAM AUV (SAM: Small and Affordable Maritime robot) developed in-house at KTH as part of the Swedish Maritime Robotics Centre (SMaRC) is used as a test platform. The CPS concept is demonstrated with the SAM AUV in applications including detecting underwater targets, inspecting seaweed farm infrastructure and tracking algal blooms using the presented simulation, planning and control strategies.

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    Kappa
  • 183.
    Bhat, Sriharsha
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Davari, Mohammad Mehdi
    KTH, School of Engineering Sciences (SCI), Centres, VinnExcellence Center for ECO2 Vehicle design.
    Nybacka, Mikael
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics.
    Study on Energy Loss due to Cornering Resistance in Over-Actuated Vehicles using Optimal Control2017In: SAE INTERNATIONAL JOURNAL OF VEHICLE DYNAMICS STABILITY AND NVH, ISSN 2380-2170, Vol. 1, no 2, p. 263-269Article in journal (Refereed)
    Abstract [en]

    As vehicles become electrified and more intelligent in terms of sensing, actuation and processing; a number of interesting possibilities arise in controlling vehicle dynamics and driving behavior. Over-actuation with in-wheel motors, all wheel steering and active camber is one such possibility, which facilitate the control strategies that push boundaries in energy consumption and safety. Optimal control can be used to investigate the best combinations of control inputs to an over-actuated system. This paper shows how an optimal control problem can be formulated and solved for an over-actuated vehicle case, and highlights the translation of this optimal solution to a real-world scenario, enabling intelligent means to improve vehicle efficiency. This paper gives an insight into Dynamic Programming (DP) as an offline optimal control method that guarantees the global optimum. Therefore the optimal control allocation to minimize an objective function and simultaneously fulfill the defined constraints can be achieved. As a case study the effects of over-actuation on the cornering resistance were investigated in two different maneuvers i.e. step steer and sine with dwell, where in both cases the vehicle assumes to be in steady state situation. In this work the cornering resistance is the main objective function and maintaining the reference trajectory is the constraint which should be fulfilled. A parameter study is conducted on the benefits of over-actuation, and depending on the type of over-actuation about 15% to 50% reduction in cornering resistance were observed during step steer and sine with dwell maneuver respectively. From a second parameter study that focused on COG position from a safety perspective, it is more beneficial for the vehicle to be designed to under-steer than over-steer. Finally, a method is described to translate the offline optimal results to vehicle implementable controllers in the form of both feed-through lookup-tables and rule-based feed-forward control.

  • 184.
    Bhat, Sriharsha
    et al.
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics.
    Panteli, Chariklia
    KTH, School of Engineering Sciences (SCI).
    Stenius, Ivan
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics.
    Dimarogonas, Dimos V.
    KTH, School of Electrical Engineering and Computer Science (EECS), Intelligent systems, Decision and Control Systems (Automatic Control).
    Nonlinear model predictive control for hydrobatics: Experiments with an underactuated AUV2023In: Journal of Field Robotics, ISSN 1556-4959, E-ISSN 1556-4967, Vol. 40, no 7, p. 1840-1859Article in journal (Refereed)
    Abstract [en]

    Hydrobatic autonomous underwater vehicles (AUVs) can be efficient in range and speed, as well as agile in maneuvering. They can be beneficial in scenarios such as obstacle avoidance, inspections, docking, and under-ice operations. However, such AUVs are underactuated systems—this means exploiting the system dynamics is key to achieving elegant hydrobatic maneuvers with minimum controls. This paper explores the use of model predictive control (MPC) techniques to control underactuated AUVs in hydrobatic maneuvers and presents new simulation and experimental results with the small and hydrobatic SAM AUV. Simulations are performed using nonlinear model predictive control (NMPC) on the full AUV system to provide optimal control policies for several hydrobatic maneuvers in Matlab/Simulink. For implementation on AUV hardware in robot operating system, a linear time varying MPC (LTV-MPC) is derived from the nonlinear model to enable real-time control. In simulations, NMPC and LTV-MPC shows promising results to offer much more efficient control strategies than what can be obtained with PID and linear quadratic regulator based controllers in terms of rise-time, overshoot, steady-state error, and robustness. The LTV-MPC shows satisfactory real-time performance in experimental validation. The paper further also demonstrates experimentally that LTV-MPC can be run real-time on the AUV in performing hydrobatic maneouvers.

  • 185.
    Bhat, Sriharsha
    et al.
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics.
    Stenius, Ivan
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics.
    Controlling an Underactuated AUV as an Inverted Pendulum using Nonlinear Model Predictive Control and Behavior Trees2023In: Proceedings: IEEE International Conference on Robotics and Automation, Institute of Electrical and Electronics Engineers (IEEE) , 2023Conference paper (Refereed)
    Abstract [en]

    Agile and hydrobatic maneuvering capabilities can enhance AUV operations in increasingly challenging scenarios. In this paper, we explore the ability of an underactuated AUV to transition to and hold a pitch angle close to 90 degrees at a particular depth, like an inverted pendulum. Holding such an orientation can be valuable in observing a calving glacier, under-ice launch and recovery, underwater docking, inspecting vertical structures, and observing targets above the water surface. However, such control is challenging because of underactuation, rapid response times and varying stability in different configurations. To address this, a control policy is derived offline using nonlinear MPC in a high-fidelity simulation environment in Simulink. For real-time control, a hybrid controller using a behavior tree (BT) is developed based on the optimal MPC policy and applied on the AUV system. The BT controller considers Safety, Transit and Stabilize behaviors. The control algorithm is validated with simulations in Simulink and Stonefish-ROS as well as field experiments with the hydrobatic SAM AUV, showing repeatable performance in the inverted pendulum maneuver.

  • 186.
    Bhat, Sriharsha
    et al.
    KTH, School of Engineering Sciences (SCI).
    Stenius, Ivan
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics.
    Bore, Nils
    KTH, School of Electrical Engineering and Computer Science (EECS), Intelligent systems, Robotics, Perception and Learning, RPL.
    Severholt, Josefine
    KTH, School of Engineering Sciences (SCI).
    Ljung, Carl
    KTH, School of Engineering Sciences (SCI).
    Torroba, Ignacio
    KTH, School of Electrical Engineering and Computer Science (EECS), Intelligent systems, Robotics, Perception and Learning, RPL.
    Towards a Cyber-Physical System for  Hydrobatic AUVs2019In: OCEANS 2019 - Marseille, 2019Conference paper (Refereed)
    Abstract [en]

    Cyber-physical systems (CPSs) encompass a network of sensors and actuators that are monitored, controlled and integrated by a computing and communication core. As autonomous underwater vehicles (AUVs) become more intelligent and connected, new use cases in ocean production, security and environmental monitoring become feasible. Swarms of small, affordable and hydrobatic AUVs can be beneficial in substance cloud tracking and algae farming, and a CPS linking the AUVs with multi-fidelity simulations can improve performance while reducing risks and costs. In this paper, we present a CPS concept tightly linking the AUV network in ROS to virtual validation using Simulink and Gazebo. A robust hardware-software interface using the open-source UAVCAN-ROS bridge is described for enabling hardware-in-the-loop validation. Hardware features of the hydrobatic SAM AUV are described, with a focus on subsystem integration. Results presented include pre-tuning of controllers, validation of mission plans in simulation and real time subsystem performance in tank tests. These first results demonstrate the interconnection between different system elements and offer a proof of concept.

  • 187.
    Bhat, Sriharsha
    et al.
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics.
    Stenius, Ivan
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics.
    Miao, Tianlei
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics. RH Marine, NL-3115 Schiedam, Netherlands.;Katholieke Univ Leuven, B-3000 Leuven, Belgium..
    Real-Time Flight Simulation of Hydrobatic AUVs Over the Full 0 degrees-360 degrees Envelope2021In: IEEE Journal of Oceanic Engineering, ISSN 0364-9059, E-ISSN 1558-1691, Vol. 46, no 4, p. 1114-1131Article in journal (Refereed)
    Abstract [en]

    Hydrobatic AUVsare very agile, and can perform challenging maneuvers that encompass the full 0 degrees-360 degrees flight envelope. Such AUVs can be beneficial in novel use cases in ocean production, environmental sensing, and security, by enabling new capabilities for docking, inspection, or under-ice operations. To further explore their capabilities in such scenarios, it is crucial to be able to model their flight dynamics over the full envelope, which includes strong nonlinear effects and turbulence at high angles of attack. With accurate and efficient simulation models, new hydrobatic maneuvers can be generated and control strategies can be developed. Therefore, this article contributes with a strategy to perform efficient and accurate simulations of hydrobatic maneuvers in real time. A multifidelity hydrodynamic database is synthesized by combining analytical, semiempirical, and numerical methods, thereby capturing fluid forces and moments over the full envelope. A component buildup workflow is used to assemble a nonlinear flight dynamics model using lookup tables generated from the database. This simulation model is used to perform real-time simulations of advanced hydrobatic maneuvers. Simulation results show agreement with literature and experiment, and the simulator shows utility as a development tool in designing new maneuvers and control strategies.

  • 188.
    Bhat, Sriharsha
    et al.
    KTH, School of Engineering Sciences (SCI).
    Stenius, Ivan
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics.
    Miao, Tianlei
    RH Marine.
    Real-time flight simulation of hydrobatic AUVs over the full 0 to 360 degree envelopeManuscript (preprint) (Other academic)
    Abstract [en]

    Hydrobatic AUVs are very agile, and can perform challenging maneuvers that encompass the full 0-360° flight envelope. Such AUVs can be beneficial in novel use cases in ocean production, environmental sensing and security, by enabling new capabilities for docking, inspection or under-ice operations. In order to further explore their capabilities in such scenarios, it is crucial to be able to model their flight dynamics over the full envelope, which includes strong nonlinear effects and turbulence at high angles of attack. With accurate and efficient simulation models, new hydrobatic maneuvers can be generated and control strategies can be developed. This paper therefore contributes with a strategy to perform efficient and accurate simulations of hydrobatic maneuvers in real-time. A multi-fidelity hydrodynamic database is synthesized by combining analytical, semi-empirical and numerical methods, thereby capturing fluid forces and moments over the full envelope. A component buildup workflow is used to assemble a nonlinear flight dynamics model using look-up tables generated from the database. This simulation model is used to perform real-time simulations of advanced hydrobatic maneuvers. Simulation results show agreement with literature and experiment, and the simulator shows utility as a development tool in designing new maneuvers and control strategies.

  • 189.
    Bhat, Sriharsha
    et al.
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics.
    Torroba, Ignacio
    KTH, School of Electrical Engineering and Computer Science (EECS), Intelligent systems, Robotics, Perception and Learning, RPL.
    Özkahraman, Özer
    KTH, School of Electrical Engineering and Computer Science (EECS), Intelligent systems, Robotics, Perception and Learning, RPL.
    Bore, Nils
    KTH, School of Electrical Engineering and Computer Science (EECS), Intelligent systems, Robotics, Perception and Learning, RPL.
    Sprague, Christopher
    KTH, School of Electrical Engineering and Computer Science (EECS), Intelligent systems, Robotics, Perception and Learning, RPL.
    Xie, Yiping
    KTH, School of Electrical Engineering and Computer Science (EECS), Intelligent systems, Robotics, Perception and Learning, RPL.
    Stenius, Ivan
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics.
    Severholt, Josefine
    KTH, School of Engineering Sciences (SCI).
    Ljung, Carl
    KTH, School of Engineering Sciences (SCI).
    Folkesson, John
    KTH, School of Electrical Engineering and Computer Science (EECS), Intelligent systems, Robotics, Perception and Learning, RPL.
    Ögren, Petter
    KTH, School of Electrical Engineering and Computer Science (EECS), Intelligent systems, Robotics, Perception and Learning, RPL.
    A Cyber-Physical System for Hydrobatic AUVs: System Integration and Field Demonstration2020Conference paper (Refereed)
    Abstract [en]

    Cyber-physical systems (CPSs) comprise a network of sensors and actuators that are integrated with a computing and communication core. Hydrobatic Autonomous Underwater Vehicles (AUVs) can be efficient and agile, offering new use cases in ocean production, environmental sensing and security. In this paper, a CPS concept for hydrobatic AUVs is validated in real-world field trials with the hydrobatic AUV SAM developed at the Swedish Maritime Robotics Center (SMaRC). We present system integration of hardware systems, software subsystems for mission planning using Neptus, mission execution using behavior trees, flight and trim control, navigation and dead reckoning. Together with the software systems, we show simulation environments in Simulink and Stonefish for virtual validation of the entire CPS. Extensive field validation of the different components of the CPS has been performed. Results of a field demonstration scenario involving the search and inspection of a submerged Mini Cooper using payload cameras on SAM in the Baltic Sea are presented. The full system including the mission planning interface, behavior tree, controllers, dead-reckoning and object detection algorithm is validated. The submerged target is successfully detected both in simulation and reality, and simulation tools show tight integration with target hardware.

  • 190.
    Bhat, Sriharsha
    et al.
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics.
    Troni, Giancarlo
    Monterey Bay Aquarium Research Institute (MBARI).
    Stenius, Ivan
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics.
    Online Learning for Agile Underwater Maneuvering: Gaussian Processes and Sparse Regression for Data-driven Model Predictive ControlManuscript (preprint) (Other academic)
    Abstract [en]

    Autonomous underwater vehicles (AUVs) show much promise in applications in environmental sensing, aquacultures, and security. Robust and adaptive control strategies can benefit these scenarios immensely by increasing the autonomy and en- durance. However, AUVs are nonlinear systems whose dynamics are challenging to model, and in several cases, also underactu- ated. Data-driven methods such as the Sparse Identification of Nonlinear Dynamics (SINDy), nonlinear least squares regression and Gaussian processes (GPs) can be beneficial to learn the AUV dynamics from measured data. Further, such data-driven models can be integrated into an adaptive model predictive control (MPC) scheme that drives the system to a setpoint while updating the prediction model when new measurements are available. This paper evaluates the performance of such data-driven methods for nonlinear system identification of two 6-DOF AUV systems, and implements them in an adaptive MPC scheme. Real experimental data from the SAM AUV and the MOLA AUV are used for performance evaluation. 

  • 191.
    Bhustalimath, Sangharsh
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics, Lightweight Structures.
    Development and verificationof a method to determine theshear properties of Hybrix core2020Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    This thesis helps develop a material model for a novel Fiber Core SandwichSheet construction. A test method was used to determine the mechanicalproperties of the sandwich material. Standard three point bendingtests coupled with digital image correlation was used. Results wereextracted from the digital image data. These results supplemented thedevelopment and tuning of an FE model of the sandwich material. Conclusionswere drawn about the feasibility of the method in studying sucha material.

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  • 192.
    Bici, Alfredo
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics, Lättkonstruktioner, marina system, flyg- och rymdteknik, rörelsemekanik.
    Analysis of a shape morphing structural battery: manufacturing, analytical modeling and numerical simulation2023Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    A reduction in the global use of fossil fuels is necessary when striving for a more sustainable future. One key strategy in the transition from fossil fuels is electrification. This strategy is particularly prominent within the transport sector, where more efficient ways to store electric energy are being pursued. Structural battery composites represent a promising technology. Being based on multifunctional composite materials that can carry mechanical loads and store electrical energy at the same time, they provide a ‘mass-less’ energy storage.

    This work aims to develop a shape morphing structural battery capable of bending upwards and downwards in a cantilever setup. The structural battery is made from several constituents. Two outer layers of carbon fibers act as negative electrodes and a middle layer of aluminium foil coated with NMC622 on both sides acts as the positive electrodes. Additionally, a glass veil layer and a ceramic separator separate the positive and negative electrodes. A structural battery electrolyte is used to embed the laminate in order to provide load transfer and ion transfer. From this setup, it is possible to control the lithiation/delithiation of each carbon fiber layer independently and thereby bend the laminate in the desired direction. Subsequently, the system is modeled both analytically using Matlab and numerically using Comsol Multiphysics 6.1. 

    From the models it is found that the system is in theory capable of large deformations, showing promising results. However, the experimental laminates show low capacity upon cycling which would cause near to zero deformations. The poor performance of the system could be linked to incompatibility between the structural battery electrolyte and the NMC622.

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  • 193.
    Bilandi, Rasul Niazmand
    et al.
    Estonian Maritime Academy, Tallinn University of Technology, 11712, Tallinn, Estonia.
    Tavakoli, Sasan
    Department of Infrastructure Engineering, The University of Melbourne, Parkville, 3052, VIC, Australia; Marine and Arctic Technology Group, Department of Mechanical Engineering, Aalto University, Espoo, 02150, Finland.
    Mancini, Simone
    Department of Industrial Engineering, University of Napoli ”Federico II”, 80125, Napoli, Italy.
    Dashtimanesh, Abbas
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics.
    Dynamic motion analysis of stepless and stepped planing hulls in random waves: A CFD model perspective2024In: Applied Ocean Research, ISSN 0141-1187, E-ISSN 1879-1549, Vol. 149, article id 104046Article in journal (Refereed)
    Abstract [en]

    Predicting the dynamic responses of planing hulls in real sea conditions is important for identifying how basic design factors influence their seakeeping performance. Hence, there is a pressing need to provide high-fidelity models for predicting the motions of these hulls in random waves, representing actual seas. In this article, a computational-based model for solving viscous fluid flow around the vessel is built to address this problem. Three different planing hulls, denoted as C, C1, and C2, each distinguished by the number of steps incorporated on their bottom surfaces (1 and 2 indicating the respective step count, with case C being the stepless hull), are modeled in a Computational Fluid Dynamics (CFD) tank, allowing for analysis of the effects of steps on dynamic responses of a planing surface operating in random waves. CFD data is compared against those collected in towing tank tests, revealing a satisfactory level of accuracy. Extreme value and gamma distributions are shown to give probabilities of maxima/minima of displacements and vertical acceleration at the center of gravity (CG) for all three hulls. It is shown that the stepless boat may be exposed to lower vertical acceleration at an early planing speed, but at higher planing speeds, a double-stepped design mitigates the vertical acceleration. Nevertheless, the double-stepped hull would experience more significant extreme heave responses across all speeds and may be exposed to less significant extreme pitch responses during the ride at the highest speed compared to the stepless and one-stepped hulls. The skewness of heave and pitch is evaluated, and it is found that the heave response tends to skew toward positive values (upward). This skewness becomes more noticeable with increasing speed but remains insensitive to wave steepness. Additionally, the pitch response at lower planing speeds shows a partial skew towards negative values (bow-down), but eventually, they may also be partially skewed towards positive values at higher speeds. Moreover, a correlation is observed between the kurtosis of responses of different hulls and the occurrence of the 1/100 highest responses, indicating that a kurtosis greater than 3.0 would result in more extreme responses. Overall, this analysis offers practical insights into planing hull behavior in actual sea conditions from a CFD model perspective, highlighting the potential of CFD in simulating this complex problem.

  • 194.
    Birgersson, F.
    et al.
    Scania Tech Ctr, SE-15148 Södertälje, Sweden..
    Elmen, P. Mikaelsson
    Scania Tech Ctr, SE-15148 Södertälje, Sweden..
    Andersson, T.
    Scania Tech Ctr, SE-15148 Södertälje, Sweden..
    Olsson, Mårten
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics, Solid Mechanics.
    Measurements and simulations of sliding wear, leakage and acoustic isolation of engine rubber gaskets2020In: International Journal of Vehicle Design. Heavy Vehicle Design, ISSN 1744-232X, E-ISSN 1741-5152, Vol. 27, no 4, p. 549-564Article in journal (Refereed)
    Abstract [en]

    Design and verification of gasket elements between engine mounted components requires computation and physical tests with respect to wear. Wear is a common problem in engines today and mainly comes from engine vibrations and thermal loading. The vibrations are due to inertial loads as well as reaction forces to gas pressure in the cylinders. Here, a new method to correctly simulate the measured wear rate of an oil pan rubber gasket is described. The engine motion is derived directly from measurements and the resulting simulation process has a high efficacy. Much work exists on investigations of gasket sealings between cylinder head and block, where the thermal loading becomes very important. The method described herein, focuses instead on other types of gaskets on the engine, where the main failure mode is due to sliding wear caused by the engine block and component vibrations.

  • 195. Bittencourt, A. C.
    et al.
    Wernholt, E.
    Tavallaey, Shiva Sander
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics, Technical Acoustics. ABB Corporate Research.
    Brogårdh, T.
    An extended friction model to capture load and temperature effects in robot joints2010In: IEEE/RSJ 2010 International Conference on Intelligent Robots and Systems, IROS 2010 - Conference Proceedings, 2010, p. 6161-6167Conference paper (Refereed)
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  • 196.
    Björkquist, Willand
    et al.
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics, Rail Vehicles.
    Janjua, Ismayil
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics, Rail Vehicles.
    Evaluation and comparison of ballastless track systems with regards to system and performance characteristics2020Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    As axle loads and speeds constantly increase in rail transport, new track systems are being developed. One such development is the ballastless track system. Today there are several types and variations of slab tracks, but how do they differ, and which one is the best? This thesis aims to answer these questions for given scenarios as each system has its unique set of strengths and therefore performs differently compared to the other systems for different projects. In this thesis, several existing ballastless track solutions have been studied. This was done viaballastless system manufacturer websites, brochures, other notable literature as well as multiple meetings with each of the system manufacturers. As a result, a descriptive list of nine different systems has been developed as well as a more detailed comparison in the shape of a table. To find out which one should be used and when, a model was developed for comparison of them. This model is based on a Multiple-criteria decision analysis (MCDA). This is a tool that can be used to compare different alternatives, based on several, often conflicting criteria. In the end, the VIKOR method was chosen. The choice was based on VIKOR’s user-friendliness, as well as implementation of auxiliary features, such as regret-value and compromise solutions. The MCDA based model was built in Excel and MATLAB and is expandable to the needs of the user. To test the model and whether it contains any bias, a sensitivity study was carried out. Ten hypothetical scenarios were set up and corresponding importance weights were assigned accordingly. The results were mixed and sparse for the different hypothetical scenarios and showed that no, or little, inherent biases were present in the model. Thus, the model proved to be successful in the end, and can therefore be a good addition to the selection process of a ballastless system alongside other studies, such as Life-cycle cost analysis (LCCA). There is however still some more development that could be done to improve the model. Finally, to demonstrate how the model is implemented for a rail project, a case study was carried out. The case study was conducted for a single hypothetical tunnel close to a city, assumed to be in Sweden. The background conditions were described, and the weighting process was illustrated and inserted to the model. For this particular case the ÖBB-Porr system from the Porr group proved to be the most suitable choice.

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  • 197.
    Björkqvist, Erik
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics, Lättkonstruktioner, marina system, flyg- och rymdteknik, rörelsemekanik.
    Continuous Fibre Reinforcements in Injection Moulded Composites2023Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    The use of continuously reinforced thermoplastics have increased in recent years andoffer some significant advantages over their thermoset counterparts. The utilizationof these materials is however still limited due to the labour intensive processingand manufacturing. In the first part of this thesis, the aim is to investigate howcontinuously reinforced thermoplastics can be used in high volume manufacturingof complex components, specifically when combined with injection moulding. Thesecond part will attempt to develop a conceptual manufacturing process and designof a demonstrator part and perform a structural analysis of the component.To answer the first question, an extensive literature study on continuous fibre materialsand thermoplastics was conducted along with research on established and newlydeveloped manufacturing methods such as automated tape laying and fibre placement,tailored fibre placement and 3D printing combined with injection overmoulding. Theconceptual manufacturing process of the demonstrator part was then based on thisresearch and the design was modeled in using finite element analysis.The results shows that continuously reinforced thermoplastics can be used forhigh volume manufacturing of complex components when combined with injectionmoulding. While some of the processing methods are still in an early developmentstage, the techniques have been tested and implemented. The structural analysis of thedemonstrator part shows that the design can withstand the maximum external loadsthus and provide proof of concept.

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  • 198.
    Blackert, Erik
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics, Naval Systems.
    Total Cost of Ownership For a Marine Fuel System2020Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    The modern marine fuel system have a vital part in preparing the fuel before it can enter theengines. Hard particles and water are removed and the viscosity needs to meet limitationsof the engines, to prevent damage. The cost for operating the fuel system and wear on theengine varies depending on how the fuel system are operated and on surrounding parameters.This thesis explains the cost impact of di erent parameters on the total cost for operating afuel system and aims to create a total cost of ownership model that also considers the costsfor systems connected to the fuel system.The total cost of ownership model includes capital expenses for the equipment and the operationalexpenses in form of; energy, service, sludge storage, water production, risk and alsoincreased costs on connected systems.The result of this total cost of ownership research shows that even if there are an increasedcost for operating the fuel system itself for highest performance will the total cost of ownershipwhen considering connected systems be lower. The user are therefore always recommendedto aim for maximum separation of hard particles to decrease the cost for enginewear and to lower the total cost of risk for a breakdown. The total energy consumption forthe fuel system can be decreased by up to 15% when variable ow control are used on thesupply pumps and meanwhile increase the separation eciency.

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  • 199. Blanco, B.
    et al.
    Gil-Negrete, N.
    Kari, Leif
    KTH, School of Engineering Sciences (SCI), Centres, VinnExcellence Center for ECO2 Vehicle design. KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics, Marcus Wallenberg Laboratory MWL.
    Alonso, A.
    On the correction of rail accelerations predicted by numerical track models based on Timoshenko beam theory2021In: Vehicle System Dynamics, ISSN 0042-3114, E-ISSN 1744-5159, p. 1-25Article in journal (Refereed)
    Abstract [en]

    Rail accelerations can be used on the defect detection and health monitoring of railway vehicle and track components; therefore, mathematical models that predict this response are of interest for reproducing its behaviour in a wide range of situations. The numerical track models based on the Timoshenko beam theory introduce a non-physical response, which is especially noticeable in the rail accelerations. It is due to the lack of dynamic convergence of the Timoshenko finite element (FE). This paper addresses this phenomenon employing an enhanced formulation of the Timoshenko FE that includes internal degrees of freedom (iDoF). The iDoF shape functions are derived from the Timoshenko beam dynamic governing equations. Firstly, the formulation is presented, and its performance is compared with a similar Timoshenko FE formulation. Secondly, the proposal is assessed in the dynamic modelling of railway track structures. The use of iDoF efficiently corrects the non-physical response of rail accelerations by improving the FE dynamic convergence. Subsequently, a filtering criterion for accelerations is proposed, which removes the remaining non-physical response while guaranteeing the conservation of coherent frequency content. Finally, practical cases are simulated for which the proposed methodology is proved to be more efficient and reliable than the standard approach.

  • 200.
    Blanco, Diego C. P.
    et al.
    Inst Tecnol Aeronaut, Div Engn Aerosp, BR-12228900 Sao Jose Dos Campos, SP, Brazil..
    Hanifi, Ardeshir
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Henningson, Dan S.
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Cavalieri, Andre V. G.
    Inst Tecnol Aeronaut, Div Engn Aerosp, BR-12228900 Sao Jose Dos Campos, SP, Brazil..
    Linear and nonlinear receptivity mechanisms in boundary layers subject to free-stream turbulence2024In: Journal of Fluid Mechanics, ISSN 0022-1120, E-ISSN 1469-7645, Vol. 979, article id A31Article in journal (Refereed)
    Abstract [en]

    Large-eddy simulations of a flat-plate boundary layer, without a leading edge, subject to multiple levels of incoming free-stream turbulence are considered in the present work. Within an input-output model, where nonlinear terms of the incompressible Navier-Stokes equations are treated as an external forcing, we manage to separate inputs related to perturbations coming through the intake of the numerical domain, whose evolution represents a linear mechanism, and the volumetric nonlinear forcing due to triadic interactions. With these, we perform the full reconstruction of the statistics of the flow, as measured in the simulations, to quantify pairs of wavenumbers and frequencies more affected by either linear or nonlinear receptivity mechanisms. Inside the boundary layer, different wavenumbers at near-zero frequency reveal streaky structures. Those that are amplified predominantly via linear interactions with the incoming vorticity occur upstream and display transient growth, while those generated by the nonlinear forcing are the most energetic and appear in more downstream positions. The latter feature vortices growing proportionally to the laminar boundary layer thickness, along with a velocity profile that agrees with the optimal amplification obtained by linear transient growth theory. The numerical approach presented is general and could potentially be extended to any simulation for which receptivity to incoming perturbations needs to be assessed.

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