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  • 101.
    Asarar, Kate
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics, Vehicle Dynamics.
    Predicting comfort in autonomous driving from vibration measurements using machine learning models2021Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Highly automated driving is approaching reality at a high speed. BMW is planningto put its first autonomous driving vehicle on the road already by 2021. The path torealising this new technology is however, full of challenges. Not only the transverseand longitudinal dynamic vehicle motion play an important role in experiencedcomfort but also the requirements and expectations of the occupants regarding thevertical dynamic vibration behaviour. Especially during long trips on the motorwaywhere the so far active driver becomes the chauffeured passenger, who reads, worksor sleeps in his newly gained time. These new use-cases create new requirements forthe future design of driving comfort which are yet to be fully discovered.This work was carried out at the BMW headquarters and had the aim to usedifferent machine learning models to investigate and identify patterns between thesubjective comfort values reported by participants in a study, on a comfort scale of 1-7 and the mechanical vibrations that they experienced, measured inm/s2. The datawas collected in a previous independent study and statistical methods were used toinsure the quality of the data. A comparison of the ISO 2631-1 comfort ratings andthe study’s findings is done to understand the need for a more sophisticated model to predict comfort in autonomous driving. The work continued by investigating different dimensionality reduction methods and their influence on the performance of the models. The process used to build, optimise and validate neural networks and other models is included in the method chapter and the results are presented. The work ends with a discussion of both the prediction results and the modelsre-usability. The machine learning models investigated in this thesis have shown great po-tential for detecting complex pattern that link feelings and thoughts to mechanical variables. The models were able to predict the correct level of comfort with up to50% precision when trying to predict 6 or 7 levels of comfort. When divided into high versus low discomfort, i.e. predicting one of two comfort levels, the models were able to achieve a precision of up to 75.4%.Excluded from this thesis is the study of differences in attentive vs inattentive state when being driven in an autonomous driving vehicle. It became clear shortly before the start of this work, that the experiment that yielded the data used for it failed to find a statistically significant difference between the two states.

     

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  • 102.
    Asbjörnsson, Sverrir
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics, Solid Mechanics.
    The Sacrificial Casing Project: Optimization and Design of a Fastening Mechanism2019Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Power companies in the geothermal industry face well-known challenges when exploiting high temperature geothermal reservoirs. To extract the geothermal energy from the reservoirs, geothermal wells are drilled to retrieve the geothermal steam to produce both electricity and hot water for district heating. The geothermal steam can be both highly corrosive and cause high thermal expansions in the steel casings which can result in high repair costs. The Icelandic R&D company Gerosion is developing a protective casing for high temperature wells, called the Sacrificial Casing. The product is a multi-layered design and can protect the other casing strings from corrosion and high thermal expansions. This thesis project aims to design and optimize a new fastening mechanism for the Sacrificial Casing, a so called slip mechanism. The material selection and geometrical dimensions of the mechanism are explored based on computational results. The most feasible design for installation of the mechanism is then used to construct both 2D and 3D FE-models where the mechanism is subjected to high temperatures and pressure and the load-carrying capabilities of the design analyzed. The results indicate that thermal expansions cause extremely high stresses in the mechanism and as a result the S960 high strength steel grade does not offer sufficient strength to withstand the combined loading the mechanism is subjected to.

  • 103.
    Asp, Leif E.
    et al.
    Department of Industrial and Materials Science, Chalmers University of Technology, Gothenburg, SE-412 96, Sweden.
    Bouton, Karl
    Carlstedt, David
    Department of Industrial and Materials Science, Chalmers University of Technology, Gothenburg, SE-412 96, Sweden.
    Duan, Shanghong
    Department of Industrial and Materials Science, Chalmers University of Technology, Gothenburg, SE-412 96, Sweden.
    Harnden, Ross
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics.
    Johannisson, Wilhelm
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics.
    Johansen, Marcus
    Department of Industrial and Materials Science, Chalmers University of Technology, Gothenburg, SE-412 96, Sweden.
    Johansson, Mats
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Fibre- and Polymer Technology, Coating Technology.
    Lindbergh, Göran
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Chemical Engineering, Applied Electrochemistry.
    Liu, Fang
    Department of Industrial and Materials Science, Chalmers University of Technology, Gothenburg, SE-412 96, Sweden.
    Peuvot, Kevin
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Chemical Engineering, Applied Electrochemistry.
    Schneider, Lynn Maria
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics.
    Xu, Johanna
    Department of Industrial and Materials Science, Chalmers University of Technology, Gothenburg, SE-412 96, Sweden.
    Zenkert, Dan
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics.
    A Structural Battery and its Multifunctional Performance2021In: Advanced Energy and Sustainability Research, E-ISSN 2699-9412, Vol. 2, no 3, article id 2000093Article in journal (Refereed)
    Abstract [en]

    Engineering materials that can store electrical energy in structural load paths can revolutionize lightweight design across transport modes. Stiff and strong batteries that use solid-state electrolytes and resilient electrodes and separators are generally lacking. Herein, a structural battery composite with unprecedented multifunctional performance is demonstrated, featuring an energy density of 24 Wh kg−1 and an elastic modulus of 25 GPa and tensile strength exceeding 300 MPa. The structural battery is made from multifunctional constituents, where reinforcing carbon fibers (CFs) act as electrode and current collector. A structural electrolyte is used for load transfer and ion transport and a glass fiber fabric separates the CF electrode from an aluminum foil-supported lithium–iron–phosphate positive electrode. Equipped with these materials, lighter electrical cars, aircraft, and consumer goods can be pursued.

  • 104. Asp, Leif E
    et al.
    Johansson, Mats
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Fibre- and Polymer Technology.
    Lindbergh, Göran
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Chemical Engineering, Applied Electrochemistry.
    Xu, Johanna
    Chalmers tekniska högskola.
    Zenkert, Dan
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics.
    Carbon Fibre Composite Structural Batteries: A Review2019In: Functional Composites and Structures, ISSN 2631-6331, article id 042001Article in journal (Refereed)
    Abstract [en]

    This paper presents a comprehensive review of the state-of-the-art in structural battery composites research. Structural battery composites are a class of structural power composites aimed to provide mass-less energy storage for electrically powered structural systems. Structural battery composites are made from carbon fibres in a structural electrolyte matrix material. Neat carbon fibres are used as a structural negative electrode, exploiting their high mechanical properties, excellent lithium insertion capacity and high electrical conductivity. Lithium iron phosphate coated carbon fibres are used as the structural positive electrode. Here, the lithium iron phosphate is the electrochemically active substance and the fibres carry mechanical loads and conduct electrons. The surrounding structural electrolyte is lithium ion conductive and transfers mechanical loads between fibres. With these constituents, structural battery half-cells and full-cells are realised with a variety in device architecture. The paper also presents an overview of material modelling and characterisation performed to date. Particular reference is given to work performed in national and European research projects under the leadership of the authors, who are able to provide a unique insight into this emerging and exciting field of research.

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  • 105.
    Assenai, Tagiadin
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics, Technical Acoustics.
    Epidemiological survey of moderators moderators for railway noise annoyance2023Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    The disturbance caused by railway noise has been investigated in this paper. A total of 127residents living near the Västra Stambanan were interviewed, and the noise levels from NordiskaBeräkningsmodellen were compared with the perceived disturbance. The results of the studyindicate a correlation between indoor noise levels and disturbance. The activities that peoplereported as being affected were meals, relaxation, sleep, and conversations in decreasing order.

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  • 106.
    Asta, Nadia
    et al.
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Fibre- and Polymer Technology, Fibre Technology.
    Kaplan, Magdalena
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics, Solid Mechanics.
    Kulachenko, Artem
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics, Solid Mechanics.
    Östlund, Sören
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics, Solid Mechanics.
    Wågberg, Lars
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Fibre- and Polymer Technology, Fibre Technology.
    Influence of density and chemical additives on paper mechanical propertiesManuscript (preprint) (Other academic)
  • 107.
    Atif, Abdul-Raouf
    et al.
    Uppsala Univ, Dept Mat Sci & Engn, S-75122 Uppsala, Sweden..
    Lacis, Ugis
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Engqvist, Håkan
    Uppsala Univ, Dept Mat Sci & Engn, S-75122 Uppsala, Sweden..
    Tenje, Maria
    Uppsala Univ, Dept Mat Sci & Engn, S-75122 Uppsala, Sweden.;Uppsala Univ, Sci Life Lab, S-75122 Uppsala, Sweden..
    Bagheri, Shervin
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Mestres, Gemma
    Uppsala Univ, Dept Mat Sci & Engn, S-75122 Uppsala, Sweden.;Uppsala Univ, Sci Life Lab, S-75122 Uppsala, Sweden..
    Experimental Characterization and Mathematical Modeling of the Adsorption of Proteins and Cells on Biomimetic Hydroxyapatite2022In: ACS Omega, E-ISSN 2470-1343, Vol. 7, no 1, p. 908-920Article in journal (Refereed)
    Abstract [en]

    Biomaterial development is a long process consisting of multiple stages of design and evaluation within the context of both in vitro and in vivo testing. To streamline this process, mathematical and computational modeling displays potential as a tool for rapid biomaterial characterization, enabling the prediction of optimal physicochemical parameters. In this work, a Langmuir isotherm-based model was used to describe protein and cell adhesion on a biomimetic hydroxyapatite surface, both independently and in a one-way coupled system. The results indicated that increased protein surface coverage leads to improved cell adhesion and spread, with maximal protein coverage occurring within 48 h. In addition, the Langmuir model displayed a good fit with the experimental data. Overall, computational modeling is an exciting avenue that may lead to savings in terms of time and cost during the biomaterial development process.

  • 108.
    Atoufi, Zhaleh
    et al.
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Fibre- and Polymer Technology, Fibre Technology.
    Gordeyeva, Korneliya
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Fibre- and Polymer Technology, Fiberprocesser.
    Cortes Ruiz, Maria F.
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Fibre- and Polymer Technology, Fibre Technology.
    Hall, Stephen A
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics, Solid Mechanics.
    Larsson, Per A.
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Fibre- and Polymer Technology, Fibre Technology.
    Wågberg, Lars
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Fibre- and Polymer Technology, Fibre Technology.
    Wet-resilient foams based on heat-treated β-lactoglobulin and cellulose nanofibrilsManuscript (preprint) (Other academic)
  • 109.
    Attarzadeh, Reza
    et al.
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Chemical Engineering.
    Rovira, Marc
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics.
    Duwig, Christophe
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Chemical Engineering, Process Technology.
    Design analysis of the "Schwartz D" based heat exchanger: A numerical study2021In: International Journal of Heat and Mass Transfer, ISSN 0017-9310, E-ISSN 1879-2189, Vol. 177, article id 121415Article in journal (Refereed)
    Abstract [en]

    Triply Periodic Minimal Surfaces (TPMS) have promising thermophysical properties, which makes them a suitable candidate in the production of low-temperature waste heat recovery systems. A TPMS thermal performance is connected to the complex flow patterns inside the pores and their interactions with the walls. Unfortunately, the experimental study's design analysis and optimization of TPMS heat exchangers are complicated due to the flow pattern complexity and visual limitations inside the TPMS. In this study, three-dimensional steady-state, conjugate heat transfer (CHT) simulations for laminar incompressible flow were carried out to quantify the performance of a TPMS based heat exchanger. TPMS Lattices based on Schwartz D architecture was modeled to elucidate the design parameters and establishing relationships between gas velocity, heat transfer, and thermal performance of TPMS at different wall thicknesses. In this study, four types of lattices from the same architectures with varying wall thickness were examined for a range of the gas velocity, with one design found to be the optimized lattice providing the highest thermal performance. The results and methodology presented here can facilitate improvements in TPMSheat exchangers' fabrication for recycling the waste heat in low pitch thermal systems.

  • 110. Atzori, M.
    et al.
    Vinuesa, Ricardo
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics.
    Schlatter, Philipp
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics.
    Control effects on coherent structures in a non-uniform adverse-pressure-gradient boundary layer2022In: International Journal of Heat and Fluid Flow, ISSN 0142-727X, E-ISSN 1879-2278, Vol. 97, article id 109036Article in journal (Refereed)
    Abstract [en]

    We examine the effects of three basic but effective control strategies, namely uniform blowing, uniform suction, and body-force damping, on the intense Reynolds-stress events in the turbulent boundary layer (TBL) developing on the suction side of a NACA4412 airfoil. This flow is subjected to a non-uniform adverse pressure gradient (APG), which substantially modifies its turbulence statistics with respect to a zero-pressure-gradient (ZPG) boundary layer, and it also changes how control strategies affect the flow. The strong APG results in intense events that are shorter and more often detached from the wall than in ZPG TBLs. In a quadrant analysis, ejections remain the most relevant structures, but sweeps become more important than in ZPG TBLs, a fact that results in a lower contribution to the wall-normal velocity from intense Reynolds-stress events. Control effects are relatively less important on intense events than on the turbulent statistics. Uniform blowing has an impact similar to that of an even more intense APG, while uniform suction has more complex effects, most likely due to the particular behavior of the wall-normal velocity component near the wall. Body-force damping also reduces the probability of occurrence of very-large attached structures and that of intense events in the proximity of the actuation region. Our results show that intense Reynolds-stress events are robust features of the flow. If control strategies do not target directly these structures, their effects on the strong events is less pronounced than the effects on the mean flow. 

  • 111.
    Atzori, Marco
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics.
    Coherent structures and control in wall-bounded turbulent flows2021Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    This thesis is concerned with two distinct topics related to the study of wall-bounded turbulence: the connection between instantaneous three-dimensional coherent structures and mean-flow properties, and the development and analysis of pre-determined control techniques for adverse-pressure-gradient boundary layers.

    We examined regions with intense velocity fluctuations in various flowcases. In turbulent ducts, we found that, on the one hand, the specific geometry of the domain has measurable effects on the shape and dimensions of these structures. On the other hand, however, their contribution to the mean secondary flow, which is the main distinguishing feature of turbulent ducts, is not particularly significant. Intense events contribute to the mean velocity in a similar way as in periodic channels, where the secondary flow is not present. Studying adverse- and zero-pressure-gradient turbulent boundary layers, we found that there are qualitative differences in how intense-fluctuation events affect the mean properties of these two flows. Our results suggest that coherent structures may help to explain history effects and development of the outer peak in wall-tangential fluctuations. An efficient algorithm for percolation analysis and an in-situ adaptor for the simulation code Nek5000 and the visualization software Paraview have also been developed as part of this effort.

    We also created a new dataset including various combinations of uniform blowing and suction applied to a NACA4412 airfoil, employing high-fidelity numerical simulations and turbulence models. There are significant discrepancies between how the control interacts with turbulence under different pressure-gradient conditions, which illustrates the need of considering test cases as similar as possible to operative conditions in control studies. We also found that the most promising control configuration for a wide range of Reynolds numbers is uniform blowing applied to the airfoil pressure side. In particular, it reduces both pressure and skin-friction drag, resulting in higher aerodynamic efficiency and potential net-energy saving when the actuation cost is included.

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  • 112.
    Atzori, Marco
    et al.
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics. Department of Particulate Flow Modelling, Johannes Kepler University, Linz, Austria.
    Chibbaro, Sergio
    Sorbonne Université, CNRS, UMR 7190, Institut Jean Le Rond d’Alembert, F-75005 Paris, France.
    Duwig, Christophe
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Chemical Engineering, Process Technology.
    Brandt, Luca
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics. Department of Energy and Process Engineering, Norwegian University of Science and Technology (NTNU), Trondheim, Norway.
    LES and RANS calculations of particle dispersion behind a wall-mounted cubic obstacle2022In: International Journal of Multiphase Flow, ISSN 0301-9322, E-ISSN 1879-3533, Vol. 151, p. 104037-, article id 104037Article in journal (Refereed)
    Abstract [en]

    In the present paper, we evaluate the performances of three stochastic models for particle dispersion in the case of a three-dimensional turbulent flow. We consider the flow in a channel with a cubic wall-mounted obstacle, and perform large-eddy simulations (LESs) including passive particles injected behind the obstacle, for cases of low and strong inertial effects. We also perform Reynolds-averaged simulations of the same case, using standard turbulence models, and employ the two discrete stochastic models for particle dispersion implemented in the open-source code OpenFOAM and the continuous Lagrangian stochastic model proposed by Minier et al. (2004). The Lagrangian model is consistent with a Probability Density Function (PDF) model of the exact particle equations, and is based on the modelling of the fluid velocity seen by particles. This approach allows a consistent formulation which eliminates the spurious drifts flawing discrete models and to have the drag force in a closed form. The LES results are used as reference data both for the fluid RANS simulations and particle simulations with dispersion models. The present test case allows to evaluate the performance of dispersion models in highly non-homogeneous flow, and it used in this context for the first time. The continuous stochastic model generally shows a better agreement with the LES than the discrete stochastic models, in particular in the case of particles with higher inertia. 

  • 113.
    Atzori, Marco
    et al.
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics.
    Köpp, Wiebke
    KTH, School of Electrical Engineering and Computer Science (EECS), Computer Science, Computational Science and Technology (CST).
    Chien, Wei Der
    KTH, School of Electrical Engineering and Computer Science (EECS), Computer Science, Computational Science and Technology (CST).
    Massaro, Daniele
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics.
    Mallor, Fermin
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics.
    Peplinski, Adam
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics.
    Rezaei, Mohamad
    PDC Center for High Performance Computing, KTH Royal Institute of Technology.
    Jansson, Niclas
    KTH, School of Electrical Engineering and Computer Science (EECS), Computer Science, Computational Science and Technology (CST).
    Markidis, Stefano
    KTH, School of Electrical Engineering and Computer Science (EECS), Computer Science, Computational Science and Technology (CST).
    Vinuesa, Ricardo
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics.
    Laure, Erwin
    KTH, School of Electrical Engineering and Computer Science (EECS), Computer Science, Computational Science and Technology (CST).
    Schlatter, Philipp
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics.
    Weinkauf, Tino
    KTH, School of Electrical Engineering and Computer Science (EECS), Computer Science, Computational Science and Technology (CST).
    In-situ visualization of large-scale turbulence simulations in Nek5000 with ParaView Catalyst2021Report (Other academic)
    Abstract [en]

    In-situ visualization on HPC systems allows us to analyze simulation results that would otherwise be impossible, given the size of the simulation data sets and offline post-processing execution time. We design and develop in-situ visualization with Paraview Catalyst in Nek5000, a massively parallel Fortran and C code for computational fluid dynamics applications. We perform strong scalability tests up to 2,048 cores on KTH's Beskow Cray XC40 supercomputer and assess in-situ visualization's impact on the Nek5000 performance. In our study case, a high-fidelity simulation of turbulent flow, we observe that in-situ operations significantly limit the strong scalability of the code, reducing the relative parallel efficiency to only ~21\% on 2,048 cores (the relative efficiency of Nek5000 without in-situ operations is ~99\%). Through profiling with Arm MAP, we identified a bottleneck in the image composition step (that uses Radix-kr algorithm) where a majority of the time is spent on MPI communication. We also identified an imbalance of in-situ processing time between rank 0 and all other ranks. Better scaling and load-balancing in the parallel image composition would considerably improve the performance and scalability of Nek5000 with in-situ capabilities in large-scale simulation.

  • 114.
    Atzori, Marco
    et al.
    KTH, Centres, SeRC - Swedish e-Science Research Centre. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Köpp, Wiebke
    KTH, School of Electrical Engineering and Computer Science (EECS), Computer Science, Computational Science and Technology (CST).
    Chien, Wei Der
    KTH, School of Electrical Engineering and Computer Science (EECS), Computer Science, Theoretical Computer Science, TCS. KTH, School of Electrical Engineering and Computer Science (EECS), Computer Science, Computational Science and Technology (CST).
    Massaro, Daniele
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics.
    Mallor, Fermin
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Peplinski, Adam
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, Centres, SeRC - Swedish e-Science Research Centre.
    Rezaei, Mohammadtaghi
    KTH, School of Electrical Engineering and Computer Science (EECS), Centres, Centre for High Performance Computing, PDC.
    Jansson, Niclas
    KTH, School of Electrical Engineering and Computer Science (EECS), Computer Science, Computational Science and Technology (CST).
    Markidis, Stefano
    KTH, School of Electrical Engineering and Computer Science (EECS), Computer Science, Computational Science and Technology (CST).
    Vinuesa, Ricardo
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Laure, E.
    Schlatter, Philipp
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Weinkauf, Tino
    KTH, School of Electrical Engineering and Computer Science (EECS), Computer Science, Computational Science and Technology (CST).
    In situ visualization of large-scale turbulence simulations in Nek5000 with ParaView Catalyst2022In: Journal of Supercomputing, ISSN 0920-8542, E-ISSN 1573-0484, Vol. 78, no 3, p. 3605-3620Article in journal (Refereed)
    Abstract [en]

    In situ visualization on high-performance computing systems allows us to analyze simulation results that would otherwise be impossible, given the size of the simulation data sets and offline post-processing execution time. We develop an in situ adaptor for Paraview Catalyst and Nek5000, a massively parallel Fortran and C code for computational fluid dynamics. We perform a strong scalability test up to 2048 cores on KTH’s Beskow Cray XC40 supercomputer and assess in situ visualization’s impact on the Nek5000 performance. In our study case, a high-fidelity simulation of turbulent flow, we observe that in situ operations significantly limit the strong scalability of the code, reducing the relative parallel efficiency to only ≈ 21 % on 2048 cores (the relative efficiency of Nek5000 without in situ operations is ≈ 99 %). Through profiling with Arm MAP, we identified a bottleneck in the image composition step (that uses the Radix-kr algorithm) where a majority of the time is spent on MPI communication. We also identified an imbalance of in situ processing time between rank 0 and all other ranks. In our case, better scaling and load-balancing in the parallel image composition would considerably improve the performance of Nek5000 with in situ capabilities. In general, the result of this study highlights the technical challenges posed by the integration of high-performance simulation codes and data-analysis libraries and their practical use in complex cases, even when efficient algorithms already exist for a certain application scenario.

  • 115.
    Atzori, Marco
    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, Fluid Mechanics and Engineering Acoustics.
    Mallor, Fermin
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics.
    Pozuelo, Ramon
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics.
    Fukagata, Koji
    Department of Mechanical Engineering, Keio University, 223-8522 Yokohama, Japan.
    Vinuesa, Ricardo
    KTH, Centres, SeRC - Swedish e-Science Research Centre. KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics.
    Schlatter, Philipp
    KTH, Centres, SeRC - Swedish e-Science Research Centre. KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics.
    A new perspective on skin-friction contributions in adverse-pressure-gradient turbulent boundary layersManuscript (preprint) (Other academic)
    Abstract [en]

    For adverse-pressure-gradient turbulent boundary layers, the study of integral skin-friction contributions still poses significant challenges. Beyond questions related to the integration boundaries and the derivation procedure, which have been thoroughly investigated in the literature, an important issue is how different terms should be aggregated. The nature of these flows, which exhibit significant in-homogeneity in the streamwise direction, usually results in cancellation between several contributions with high absolute values. We propose a formulation of the identity derived by Fukagata, Iwamoto \& Kasagi (Phys. Fluids, vol. 14, 2002, pp. 73--76), which we obtained from the convective form of the governing equations. A new skin-friction contribution is defined, considering wall-tangential convection and pressure gradient together. This contribution is related to the evolution of the dynamic pressure in the mean flow. The results of the decomposition are examined for a broad range of pressure-gradient conditions and different flow-control strategies. We found that the new formulation of the identity allows to readily identify the different regimes of near-equilibrium conditions and approaching separation. It also provides a more effective description of control effects. A similar aggregation between convection and pressure-gradient terms is also possible for any other decomposition where in-homogeneity contributions are considered explicitly. 

  • 116.
    Atzori, Marco
    et al.
    Johannes Kepler Univ Linz, Dept Particulate Flow Modelling, A-4040 Linz, Austria..
    Mallor, Fermin
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics.
    Pozuelo, Ramon
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Fukagata, Koji
    Keio Univ, Dept Mech Engn, Yokohama 2238522, Japan..
    Vinuesa, Ricardo
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics.
    Schlatter, Philipp
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics.
    A new perspective on skin-friction contributions in adverse-pressure-gradient turbulent boundary layers2023In: International Journal of Heat and Fluid Flow, ISSN 0142-727X, E-ISSN 1879-2278, Vol. 101, article id 109117Article in journal (Refereed)
    Abstract [en]

    For adverse-pressure-gradient turbulent boundary layers, the study of integral skin-friction contributions still poses significant challenges. Beyond questions related to the integration boundaries and the derivation procedure, which have been thoroughly investigated in the literature, an important issue is how different terms should be aggregated. The nature of these flows, which exhibit significant in-homogeneity in the streamwise direction, usually results in cancellation between several contributions with high absolute values. We propose a formulation of the identity derived by Fukagata et al. (2002), which we obtained from the convective form of the governing equations. A new skin-friction contribution is defined, considering wall-tangential convection and pressure gradient together. This contribution is related to the evolution of the dynamic pressure in the mean flow. The results of the decomposition are examined for a broad range of pressure-gradient conditions and different flow-control strategies. We found that the new formulation of the identity allows to readily identify the different regimes of near-equilibrium conditions and approaching separation. It also provides a more effective description of control effects. A similar aggregation between convection and pressure-gradient terms is also possible for any other decomposition where in-homogeneity contributions are considered explicitly.

  • 117.
    Atzori, Marco
    et al.
    Department of Particulate Flow Modelling Johannes Kepler University 4040 Linz, Austria.
    Stroh, Alexander
    Institute of Fluid Mechanics (ISTM) Karlsruhe Institute of Technology 76131 Karlsruhe, Germany.
    Gatti, Davide
    Institute of Fluid Mechanics (ISTM) Karlsruhe Institute of Technology 76131 Karlsruhe, Germany.
    Fukagata, Koji
    Department of Mechanical Engineering Keio University 223-8522 Yokohama, Japan.
    Vinuesa, Ricardo
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Engineering Sciences (SCI), Engineering Mechanics.
    Schlatter, Philipp
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Engineering Sciences (SCI), Engineering Mechanics.
    A New Point of View On Skin-Friction Contributions ni Adverse-Pressure-Gradient Turbulent Boundary Layers2022In: 12th International Symposium on Turbulence and Shear Flow Phenomena, TSFP 2022, International Symposium on Turbulence and Shear Flow Phenomena, TSFP , 2022Conference paper (Refereed)
    Abstract [en]

    Skin-friction decompositions such as the so-called FIK identity (Fukagata et al., 2002) are useful tools in identifying relevant contributions to the friction, but may also lead to results difficult to interpret when the total friction is recovered from cancellation of multiple terms with large values. We propose a new formulation of the FIK contributions related to streamwise inhomogeneity, which is derived from the convective form of the momentum equation and using the concept of dynamic pressure. We examine turbulent boundary layers subjected to various pressure-gradient conditions, including cases with drag-reducing control. The new formulation distinguishes more precisely the roles of the free-stream pressure distribution, wall-normal convection, and turbulent fluctuations. Our results allow to identify different regimes in adverse-pressure-gradient turbulent boundary layers, corresponding to different proportions of the various contributions, and suggest a possible direction towards studying the onset of mean separation.

  • 118.
    Atzori, Marco
    et al.
    Johannes Kepler Univ Linz, Dept Particulate Flow Modelling, A-4040 Linz, Austria..
    Torres, Pablo
    Univ Politecn Valencia, Inst Univ Matemat Pura & Aplicada, Valencia 46022, Spain..
    Vidal, Alvaro
    Parallel Works, Chicago, IL 60654 USA..
    Le Clainche, Soledad
    Univ Politecn Madrid, Sch Aerosp Engn, Madrid 28040, Spain..
    Hoyas, Sergio
    Univ Politecn Valencia, Inst Univ Matemat Pura & Aplicada, Valencia 46022, Spain..
    Vinuesa, Ricardo
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics.
    High-resolution simulations of a turbulent boundary layer impacting two obstacles in tandem2023In: Physical Review Fluids, E-ISSN 2469-990X, Vol. 8, no 6, article id 063801Article in journal (Refereed)
    Abstract [en]

    High-fidelity large-eddy simulations of the flow around two rectangular obstacles are carried out at a Reynolds number of 10 000 based on the freestream velocity and the obstacle height. The incoming flow is a developed turbulent boundary layer. Mean-velocity components, turbulence fluctuations, and the terms of the turbulent-kinetic-energy budget are analyzed for three flow regimes: skimming flow, wake interference, and isolated roughness. Three regions are identified where the flow undergoes the most significant changes: the first obstacle's wake, the region in front of the second obstacle, and the region around the second obstacle. In the skimming-flow case, turbulence activity in the cavity between the obstacles is limited and mainly occurs in a small region in front of the second obstacle. In the wake-interference case, there is a strong interaction between the freestream flow that penetrates the cavity and the wake of the first obstacle. This interaction results in more intense turbulent fluctuations between the obstacles. In the isolated-roughness case, the wake of the first obstacle is in good agreement with that of an isolated obstacle. Separation bubbles with strong turbulent fluctuations appear around the second obstacle.

  • 119.
    Atzori, Marco
    et al.
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics.
    Vinuesa, Ricardo
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, Centres, SeRC - Swedish e-Science Research Centre. KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics.
    Fahland, G.
    Stroh, A.
    Gatti, D.
    Frohnapfel, B.
    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.
    Aerodynamic Effects of Uniform Blowing and Suction on a NACA4412 Airfoil2020In: Flow Turbulence and Combustion, ISSN 1386-6184, E-ISSN 1573-1987Article in journal (Refereed)
    Abstract [en]

    We carried out high-fidelity large-eddy simulations to investigate the effects of uniform blowing and uniform suction on the aerodynamic efficiency of a NACA4412 airfoil at the moderate Reynolds number based on chord length and incoming velocity of Rec= 200 , 000. We found that uniform blowing applied at the suction side reduces the aerodynamics efficiency, while uniform suction increases it. This result is due to the combined impact of blowing and suction on skin friction, pressure drag and lift. When applied to the pressure side, uniform blowing improves aerodynamic efficiency. The Reynolds-number dependence of the relative contributions of pressure and friction to the total drag for the reference case is analysed via Reynolds-averaged Navier–Stokes simulations up to Rec= 10 , 000 , 000. The results suggest that our conclusions on the control effect can tentatively be extended to a broader range of Reynolds numbers. 

  • 120.
    Atzori, Marco
    et al.
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, Centres, SeRC - Swedish e-Science Research Centre.
    Vinuesa, Ricardo
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, Centres, SeRC - Swedish e-Science Research Centre.
    Gatti, D.
    Stroh, A.
    Frohnapfel, B.
    Schlatter, Philipp
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics. KTH, Centres, SeRC - Swedish e-Science Research Centre. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Effects of Different Friction Control Techniques on Turbulence Developing Around Wings2020In: ERCOFTAC Workshop Direct and Large Eddy Simulation: Direct and Large Eddy Simulation XII, Springer, 2020, p. 305-311Chapter in book (Refereed)
    Abstract [en]

    Developing efficient flow control techniques remain a challenging task due to the complexity of turbulent flows in industrial applications, a relevant example of which are turbulent boundary layers (TBL) subjected to pressure gradients. In the present study, we employ high-fidelity numerical simulations to assess the impact of different control strategies on the flow around a NACA4412 airfoil at a Reynolds number Rec=200,000 based on the chord length c and the inflow velocity U∞. The choice of this specific study case is motivated by the relatively weak dependence of the pressure distribution around the airfoil on the Reynolds number [6], which allows distinguishing the effects of increasing Reynolds number and those of the non-uniform adverse pressure gradient (APG).

  • 121.
    Atzori, Marco
    et al.
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics.
    Vinuesa, Ricardo
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, Centres, SeRC - Swedish e-Science Research Centre. KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics.
    Lozano-Durán, A.
    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.
    Contribution of Reynolds-stress structures to the secondary flow in turbulent ducts2019In: 11th International Symposium on Turbulence and Shear Flow Phenomena, TSFP 2019, International Symposium on Turbulence and Shear Flow Phenomena, TSFP , 2019Conference paper (Refereed)
    Abstract [en]

    The present work is aimed at evaluating the contribution to the secondary flow in duct flow with square and rectangular cross section from three-dimensional coherent structures, defined as intense Reynolds-stress events. The contribution to a certain mean quantity is defined as the ensemble average over the detected coherent structures, weighted with their own occupied volume fraction. Our analysis unveils that the contribution to the cross-stream components of the mean velocity is either very similar to the same contribution in channel flow, or almost negligible in respect to the contribution from the portion of the domain not occupied by coherent structures. These results suggest that the most intense events are not directly responsible for the secondary flow.

  • 122.
    Atzori, Marco
    et al.
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics. KTH, Centres, SeRC - Swedish e-Science Research Centre. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Vinuesa, Ricardo
    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.
    Lozano-Durán, Adrián
    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.
    Coherent structures in turbulent boundary layers over an airfoil2020In: Journal of Physics: Conference Series, ISSN 1742-6588, Vol. 1522, article id 012020Article in journal (Refereed)
    Abstract [en]

    This preliminary study is concerned with the identification of three-dimensional coherent structures, defined as intense Reynolds-stress events, in the turbulent boundary layer developing over the suction side of a NACA4412 airfoil at a Reynolds number based on the chord length and the incoming velocity of $Re_c=200,000$. The scientific interest for such flows originates from the non-uniform adverse pressure gradient that affects the boundary-layer development. Firstly, we assess different methods to identify the turbulent-non-turbulent interface, in order to exclude the irrotational region from the analysis. Secondly, we evaluate the contribution of the considered coherent structures to the enhanced wall-normal velocity, characteristic of adverse pressure gradients. Our results show that it is necessary to limit the detection of coherent structures to the turbulent region of the domain, and that the structures reveal qualitative differences between the contributions of intense events to the wall-normal velocity in adverse-pressure-gradient and zero-pressure-gradient turbulent boundary layers.

  • 123.
    Atzori, Marco
    et al.
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics. KTH, Centres, SeRC - Swedish e-Science Research Centre. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Vinuesa, Ricardo
    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.
    Lozano-Durán, Adrián
    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.
    Intense Reynolds-stress events in turbulent ducts2021In: International Journal of Heat and Fluid Flow, ISSN 0142-727X, E-ISSN 1879-2278, Vol. 89, article id 108802Article in journal (Refereed)
    Abstract [en]

    The aim of the present work is to investigate the role of intense Reynolds shear-stress events in the generation of the secondary flow in turbulent ducts. We consider the connected regions of flow where the product of the instantaneous fluctuations of two velocity components is higher than a threshold based on the long-time turbulence statistics, in the spirit of the three-dimensional quadrant analysis proposed by Lozano-Dur\'an \textit{et al.} (\textit{J.~Fluid Mech.}, vol. 694, 2012, pp. 100--130). We examine both the geometrical properties of these structures and their contribution to the mean in-plane velocity components, and we perform a comparison with turbulent channel flow at similar Reynolds number. The contribution to a certain mean quantity is defined as the ensemble average over the detected coherent structures, weighted with their own occupied volume fraction. In the core region of the duct, the contribution of intense events to the wall-normal component of the mean velocity is in very good agreement with that in the channel, despite the presence of the secondary flow in the former. Additionally, the shapes of the three-dimensional objects do not differ significantly in both flows. In the corner region of the duct, the proximity of the walls affects both the geometrical properties of the coherent structures and the contribution to the mean component of the vertical velocity. However, such contribution is less relevant than that of the complementary portion of the flow not included in such objects. Our results show that strong Reynolds shear-stress events are affected by the presence of a corner but, despite the important role of these structures in the dynamics of wall-bounded turbulent flows, their contribution to the secondary flow is relatively low, both in the core and in the corner.

  • 124.
    Atzori, Marco
    et al.
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics. KTH, Centres, SeRC - Swedish e-Science Research Centre.
    Vinuesa, Ricardo
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics. KTH, Centres, SeRC - Swedish e-Science Research Centre.
    Schlatter, Philipp
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics. KTH, Centres, SeRC - Swedish e-Science Research Centre.
    Control effects on coherent structures in a non-uniform adverse-pressure-gradient boundary layer2021Report (Other academic)
    Abstract [en]

    In the present report, we examine the effects of three control strategies, namely uniform blowing, uniform suction, and body-force damping, on the intense Reynolds-stress events in the turbulent boundary layer (TBL) developing on the suction side of a NACA4412 airfoil. This flow is subjected to a non-uniform adverse pressure gradient (APG), which substantially modifies its turbulence statistics with respect to a zero-pressure-gradient (ZPG) boundary layer, and it also changes how control strategies affect the flow. We found that the strong APG results in intense events that are shorter and more often detached from the wall than in ZPG TBLs, and it also modified the contributions of different quadrants. Ejections remain the most relevant structures, but sweeps become more important than in ZPG TBLs, a fact that results in a lower contribution to the wall-normal vertical velocity from intense events. We found that control effects are relatively less important on intense events than on the turbulent statistics. Uniform blowing has an impact similar to that of an even more intense APG, while uniform suction has more complex effects, most likely due to the particular behavior of the wall-normal velocity component near the wall. Body-force damping also reduces the probability of occurrence of very-large attached structures and, not surprisingly, that of intense events in the proximity of the actuation region. 

  • 125.
    Atzori, Marco
    et al.
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics.
    Vinuesa, Ricardo
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics.
    Stroh, Alexander
    Institute of Fluid Mechanics, Karlsruhe Institute of Technology (KIT), Karlsruhe, Germany.
    Gatti, Davide
    Institute of Fluid Mechanics, Karlsruhe Institute of Technology (KIT), Karlsruhe, Germany.
    Frohnapfel, Bettina
    Institute of Fluid Mechanics, Karlsruhe Institute of Technology (KIT), Karlsruhe, Germany.
    Schlatter, Philipp
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics.
    Blowing and suction applied to non-uniform adverse-pressure-gradient boundary layers2021Report (Other academic)
    Abstract [en]

    An extensive parametric study of turbulent boundary layer control on airfoils via uniform blowing or suction is presented. The control is applied on either suction or pressure side of several 4-digit NACA-series airfoils. The considered parameter variations include angle of attack, Reynolds number, control intensity, airfoil camber and airfoil thickness. Two comprehensive metrics, designed to account for the additional energy required by the control, are introduced to evaluate the net aerodynamic performance enhancements. The study confirms previous findings for suction side boundary layer control and demonstrates the interesting potential of blowing on the pressure side under various conditions, which achieves a maximum total net drag saving of 14% within the considered parameter space. The broad parameter space covered by the presented Reynolds-average Navier-Stokes (RANS) simulations allows for more general conclusions than previous studies and can thus provide guidelines for the design of future detailed experimental or numerical studies on similar boundary layer control schemes.

  • 126.
    Atzori, Marco
    et al.
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics.
    Vinuesa, Ricardo
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics.
    Stroh, Alexander
    Karlsruhe Techonol, Inst Fluid Mech, D-76131 Karlsruhe, Germany..
    Gatti, Davide
    Karlsruhe Techonol, Inst Fluid Mech, D-76131 Karlsruhe, Germany..
    Frohnapfel, Bettina
    Karlsruhe Techonol, Inst Fluid Mech, D-76131 Karlsruhe, Germany..
    Schlatter, Philipp
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics.
    Uniform blowing and suction applied to nonuniform adverse-pressure-gradient wing boundary layers2021In: Physical Review Fluids, E-ISSN 2469-990X, Vol. 6, no 11, article id 113904Article in journal (Refereed)
    Abstract [en]

    A detailed analysis of the effects of uniform blowing, uniform suction, and body-force damping on the turbulent boundary layer developing around a NACA4412 airfoil at moderate Reynolds number is presented. The flow over the suction and the pressure sides of the airfoil is subjected to a nonuniform adverse pressure gradient and a moderate favorable pressure gradient, respectively. We find that the changes in total skin friction due to blowing and suction are not very sensitive to different pressure-gradient conditions or the Reynolds number. However, when blowing and suction are applied to an adverse-pressure-gradient (APG) boundary layer, their impact on properties such as the boundary-layer thickness, the intensity of the wall-normal convection, and turbulent fluctuations are more pronounced. We employ the Fukagata-Iwamoto-Kasagi decomposition [K. Fukagata et al., Phys. Fluids 14, 73 (2002)] and spectral analysis to study the interaction between intense adverse pressure gradient and these control strategies. We find that the control modifies skin-friction contributions differently in adverse-pressure-gradient and zero-pressure-gradient boundary layers. In particular, the control strategies modify considerably both the streamwisedevelopment and the pressure-gradient contributions, which have high magnitude when a strong adverse pressure gradient is present. Blowing and suction also impact the convection of structures in the wall-normal direction. Overall, our results suggest that it is not possible to simply separate pressure-gradient and control effects, a fact to take into account in future studies on control design in practical applications.

  • 127.
    Aulitto, Alessia
    et al.
    Eindhoven University of Technology, The Netherlands.
    Hirschberg, Avraham
    Eindhoven University of Technology, The Netherlands.
    Lopez Arteaga, Ines
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics, Marcus Wallenberg Laboratory MWL. Eindhoven University of Technology, The Netherlands.
    Saxena, Vertika
    Eindhoven University of Technology, The Netherlands.
    Experimental study of a slit in the presence of a bias flow under medium- and high-level acoustic excitations2023In: International Journal of Spray and Combustion Dynamics, ISSN 1756-8277, Vol. 15, no 2, p. 117-126Article in journal (Refereed)
    Abstract [en]

    This work presents an experimental investigation of the acoustic properties of a slit in the presence of a bias flow under moderate- and high-acoustic excitations. Impedance tube experiments are discussed for a geometry inspired by deep punching resulting in a cut in the plate. The acoustic transfer impedance of the plate is discussed for several bias flow velocities, acoustic excitation, and different frequencies. In the range considered for this study, a bias flow appears to have two main effects, globally enhancing the sound absorption of the plate and creating a protective layer downstream of the plate due to the interaction between the slits. A maximum of the enhancement factor is found at a specific ratio between the acoustic velocity and the bias flow velocity. Two simple asymptotic behaviors are found, dominated by the flow or by the acoustic excitation, respectively. The behavior of the inertance is complex. Globally the inertance decreases with decreasing flow Strouhal number while its dependency on the amplitude of the acoustic velocity is less obvious.

  • 128.
    Axelsson, Mathias
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics, Lättkonstruktioner, marina system, flyg- och rymdteknik, rörelsemekanik.
    Design of a Satellite Constellation Intended for Use with a Small User Terminal2022Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Satellite constellations intended for communications services are becoming increasingly relevant with multiple companies such as Starlink and OneWeb launching constellations consisting of hundreds or thousands of satellites. This thesis investigated how such a constellation can be designed for a small user terminal with a diameter of approximately 15 cm. Four constellations, two at 8 500 km altitude and two at 1 200 km altitude, were proposed. Methods for systematic placement of satellites in orbital planes, aspects going into the link budget, and relevant regulations on the international level were investigated. It was found that the most favourable constellation was a medium Earth orbit constellation with a minimum elevation of 30°. The primary reason for this choice was the limited budget which did not allow for a large number of satellites being launched. Finally, the concept of a hybrid constellation with both geostationary satellites and non-geostationary satellites was considered.

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  • 129.
    Axtelius, Eric
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics.
    CFD Analysis of the Flow Into a Preheater2022Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    This project has investigated and formed a basis for the thermal- and flow-induceddynamic loads in the lower parts of a preheater situated in a nuclear power plant.Special attention has been given to the bottom plate that separates the heated andnon-heated secondary steam. Using computational fluid dynamics (CFD), steady RANSsimulations were first used to investigate how the flow into the preheater was affectedby the inlet boundary conditions. From there a steady RANS conjugate heat transfer(CHT) analysis was conducted as to obtain the temperature field within the preheaterand its solid components. This also investigated different approaches in modelling theheat transfer between the primary and secondary steam. Lastly, a scale-resolving LESwas conducted as to obtain the flow-induced dynamic loads on the bottom plate.

    The results show that the modelling used in previous works gives a less uniformtemperature distribution as compared to when appropriate heat transfer coefficient(HTC) correlations are applied. Regardless of how the heat source is modelled, hot spotswith significantly larger temperatures are present in the bottom plate near the outletsof the bottom tube sections. The root mean square value, amplitude and frequencycontent of the fluctuating force acting on the bottom plate have also been obtained.The results of the analysis provide a good starting point for future work examining ifthe loads on their own or in combination may risk damaging the structure.

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  • 130.
    Babbepalli, Venkata Venu Sai Phani Ram
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics, Solid Mechanics.
    Implementation of moisturedependent constitutive model for paperboard2020Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    There has been a considerable increase in the usage of paper products due to its sustainability in the product cycle. Many environmental and process variables can affect the mechanical behavior of paper from its making to finished products. Of these variables, moisture is of particular importance and strongly influences both papermaking, converting, and end-use of the paper products.

    Experimental investigations at different humidity levels reveals that normalized in-plane constitutive parameters, such as elastic parameters and the linear hardening modulus, in both MD and CD1) follow a linear relationship with normalized moisture ratio. This relation is found to be acceptable for a wide range of commercial paperboards. To capture this observation, a novel material model with orthotropic elasticity and anisotropic hardening2 is proposed. An associative flow rule for the evolution of plastic strain is proposed. The proposed flow rule is such that all stresses contribute to plastic flow rather than an effective stress. A simple version using anisotropic linear hardening is implemented. The mechanical properties, such as elastic parameters and hardening moduli are considered functions of the moisture ratio. An implicit variant of the material model is implemented in LS-DYNA®. The simulations with the proposed material model at different humidity levels follow the experimental results well for uniaxial loading, but discrepancies are obtained for simulation of biaxial loading tests.

    The moisture is assumed constant in the proposed model since the experiments are done in a moisture-controlled environment.

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  • 131.
    Babo, Martin
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics.
    Numerical evaluation of the ground vortex2022Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    This master thesis covers the realization of a CFD calibration study regarding the numerical simulation of the ground vortex phenomenon. As part of InVIGO project (EU CleanSky2), wind tunnel test campaigns were performed using a nacelle model combined with a movable raised floor. Those tests allowed the gathering of an unprecedented amount of experimental data regarding this phenomenon, via the implementation of pressure measurements and stereo-PIV acquisition. Measured velocity fields were also post-processed to compute vortex characterization indices. In the context of this study, several Python scripts are developed to process this data through the computation of total pressure and velocity maps. A calculation matrix of 28 representative points is chosen among test cases and the corresponding nacelle geometry is prepared to generate a series of high resolution structured mesh (18.22 million cells) using an existing ICEM macro. For every case, corresponding CFD calculations are implemented on elsA using the RANS resolution method associated with the Spalart-Allmaras turbulence model. In parallel, a series of CFD post-processing scripts are developed using Cassiopée modules, in order to extract pressure/velocity maps and compute both distortion and convergence indices. Also, a Safran AE in-house script dedicated to vortex characterization is not only implemented to compute vortex indices, but also upgraded with an additional vortex profile extraction functionality. The cross-analysis of numerical and experimental data thus collected is performed, allowing the assessment of the great calculation representativeness regarding the overall inlet flow topology as well as the vortex apparition. The comparison of vortex characterization indices displays common tendencies, however disparities regarding the implemented processing methodologies along with convergence difficulties encountered for some vortex cases highlights the need to put the relevance of those results into perspective.

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  • 132.
    Backalov, Igor
    et al.
    Univ Belgrade, Belgrade, Serbia..
    Bulian, Gabriele
    Univ Trieste, Trieste, Italy..
    Cichowicz, Jakub
    Brookes Bell LLP, Glasgow, Lanark, Scotland..
    Eliopoulou, Eleftheria
    Natl Tech Univ Athens, Athens, Greece..
    Konovessis, Dimitris
    Nanyang Technol Univ, Singapore, Singapore..
    Leguen, Jean-Francois
    DGA Hydrodynam, Val De Reuil, France..
    Rosén, Anders
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics.
    Themelis, Nikolaos
    Natl Tech Univ Athens, Athens, Greece..
    Ship Stability, Dynamics and Safety: Status and Perspectives2015In: 12TH INTERNATIONAL CONFERENCE ON THE STABILITY OF SHIPS AND OCEAN VEHICLES (STAB2015), UNIV STRATHCLYDE, DEPT NAVAL ARCHITECTURE & MARINE ENGINEERING , 2015, p. 99-141Conference paper (Refereed)
    Abstract [en]

    With the aim of analysing the current status and possible future perspectives of research in the field of ship stability, dynamics and safety, this paper deals with an extensive review of the research work presented at the International Conferences on Stability of Ships and Ocean Vehicles (STAB Conferences) and the International Ship Stability Workshops (ISSW) held during the period 2009-2014. The reviewed material is organised in different sections, corresponding to a set of identified main typical focal macro-topics of research. On the basis of the reviewed material, consolidated research topics are highlighted together with emerging topics, and ideas for possible future research and its needs and focus are provided. Discussion is also provided regarding the link between research and educational aspects.

  • 133.
    Baclet, Sacha
    et al.
    KTH, School of Engineering Sciences (SCI), Centres, VinnExcellence Center for ECO2 Vehicle design. KTH, School of Engineering Sciences (SCI), Engineering Mechanics.
    Bouchouireb, Hamza
    KTH, School of Engineering Sciences (SCI), Centres, VinnExcellence Center for ECO2 Vehicle design. KTH, School of Engineering Sciences (SCI), Engineering Mechanics.
    Venkataraman, Siddharth
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics. KTH, School of Engineering Sciences (SCI), Centres, VinnExcellence Center for ECO2 Vehicle design.
    Gomez, Erik
    KTH.
    A machine learning- and compressed sensing-based approach for surrogate modelling in environmental acoustics: towards fast evaluation of building façade road traffic noise levels2022In: Internoise 2022: 51st International Congress and Exposition on Noise Control Engineering, The Institute of Noise Control Engineering of the USA, Inc. , 2022Conference paper (Refereed)
    Abstract [en]

    State-of-the-art urban road traffic noise propagation simulation methods such as the CNOSSOS-EU framework rely on ray tracing to estimate noise levels at specific locations on façades, so-called receiver points; this method is relatively computationally expensive and its cost increases with the number of receiver points, which limit the spatial resolution of such simulations in the context of real-time or near-real-time urban noise simulation applications. This contribution aims to investigate the applicability of multiple data-driven methods to the surrogate modelling of traffic noise propagation for fast façade noise calculation as an alternative to these traditional, ray-tracing-based methods. The proposed approach uses compressed sensing to select a small subset of optimal receiver points from which the dataset of the entire façade may be reconstructed, associated with either a kriging model or neural networks, used to predict noise levels for these sensors. The prediction performance of each of these steps is evaluated on an academic test case, with two levels of complexity based on the dimensionality of the problem.

  • 134.
    Baclet, Sacha
    et al.
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics, Marcus Wallenberg Laboratory MWL. KTH, School of Engineering Sciences (SCI), Centres, VinnExcellence Center for ECO2 Vehicle design. KTH Digital Futures.
    Khoshkhah, Kaveh
    ITS Lab, Institute of Computer Science, University of Tartu, Estonia.
    Pourmoradnasseri, Mozhgan
    ITS Lab, Institute of Computer Science, University of Tartu, Estonia.
    Rumpler, Romain
    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. KTH Digital Futures.
    Hadachi, Amnir
    ITS Lab, Institute of Computer Science, University of Tartu, Estonia.
    Near-real-time dynamic noise mapping and exposure assessment using calibrated microscopic traffic simulations2023In: Transportation Research Part D: Transport and Environment, ISSN 1361-9209, E-ISSN 1879-2340, Vol. 124, article id 103922Article in journal (Refereed)
    Abstract [en]

    With prospective applications ranging from improving the understanding of the daily and seasonal dynamics of noise exposure to raising public awareness of the associated health effects, dynamic noise mapping in real time is one of the next milestones in environmental acoustics. The present contribution proposes a methodology for near-real-time dynamic noise mapping, enabling the generation of dynamic noise maps and the calculation of advanced noise exposure indicators, here arbitrarily established for the previous day, on the scale of large urban areas. This methodology consists in (i) collecting live traffic counts, measured using dedicated IoT sensors, (ii) calibrating a microscopic traffic simulation using these sparsely distributed traffic counts, (iii) modelling noise emission and propagation from the microscopic traffic simulation, and finally, (iv) post-processing the noise simulation output for the calculation of a wide range of exposure indicators. The applicability of the method is demonstrated on the city of Tartu, Estonia.

  • 135.
    Baclet, Sacha
    et al.
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics, Marcus Wallenberg Laboratory MWL. KTH, School of Engineering Sciences (SCI), Centres, VinnExcellence Center for ECO2 Vehicle design.
    Venkataraman, Siddharth
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics, Marcus Wallenberg Laboratory MWL. KTH, School of Engineering Sciences (SCI), Centres, VinnExcellence Center for ECO2 Vehicle design.
    Rumpler, Romain
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics, Marcus Wallenberg Laboratory MWL. KTH, School of Engineering Sciences (SCI), Centres, VinnExcellence Center for ECO2 Vehicle design.
    A methodology to assess the impact of driving noise from individual vehicles in an urban environment2021In: "Advances in Acoustics, Noise and Vibration - 2021" Proceedings of the 27th International Congress on Sound and Vibration, ICSV 2021 / [ed] Carletti E., Crocker M., Pawelczyk M., Tuma J., 2021Conference paper (Other academic)
    Abstract [en]

    Traffic is a major source of environmental noise pollution in urban areas. The present contribution focuses on a methodology designed to assess the impact of the noise generated by individual vehicles on a city's population using NoiseModelling, an open-source library implementing the CNOSSOS-EU model, capable of producing environmental noise maps. The initial step of the proposed method consists in processing microscopic traffic data (simulated in the present contribution), where the traffic intensity is dependent on the time of day that is targeted. The micro-traffic data is subsequently used to generate background noise maps by simulating the propagation of traffic noise. Then, the impact of the noise from the vehicle of interest is simulated, based on several parameters (route followed, type of motorization: diesel or hybrid, etc.). Finally, the data is post-processed to calculate the "exceedance" (increase in ambient noise) caused by the vehicle, taking the previously calculated background noise maps as reference. The complete methodology, its underlying assumptions, and the associated criteria proposed in order to assess the impact of noise emissions from individual vehicles is demonstrated on a realistic scenario.

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  • 136.
    Baclet, Sacha
    et al.
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics, Marcus Wallenberg Laboratory MWL. KTH, School of Engineering Sciences (SCI), Centres, VinnExcellence Center for ECO2 Vehicle design.
    Venkataraman, Siddharth
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics, Marcus Wallenberg Laboratory MWL.
    Rumpler, Romain
    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.
    Billsjö, Robin
    City of Stockholm, Transport Department, Box 8311, 104 20 Stockholm, Sweden.
    Horvath, Johannes
    City of Munich, Department of Mobility, Strategy Division, Research and Innovation Unit, 80313 Munich, Germany.
    Österlund, Per Erik
    City of Stockholm, Transport Department, Box 8311, 104 20 Stockholm, Sweden.
    From strategic noise maps to receiver-centric noise exposure sensitivity mapping2022In: Transportation Research Part D: Transport and Environment, ISSN 1361-9209, E-ISSN 1879-2340, Vol. 102, p. 103114-103114, article id 103114Article in journal (Refereed)
    Abstract [en]

    Road traffic is a major source of environmental noise pollution in urban areas. While strategic noise maps are widely used to identify the critical areas and propose mitigation plans, more specific tools are needed to evaluate the impact from traffic noise such as overall population exposure or anticipated impact from specific vehicles in varying spatiotemporal traffic conditions.

    The present contribution proposes a receiver-centric mapping approach, introducing “noise-exposure sensitivity maps”, meant to assess the potential noise exposure impact from a specific vehicle in a given network, quantifying the associated exceedance over the prevailing background noise, under varying spatiotemporal traffic conditions. The resulting maps are thus focussed on a representation of the receiver exposure as opposed to considering the noise emission and propagation alone.

    The complete methodology, its underlying assumptions, and possible applications such as route optimisation are demonstrated on realistic scenarios.

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    Baclet, Venkataraman, Rumpler - sensitivity mapping
  • 137.
    Bagge, Joar
    et al.
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Numerical Analysis, NA. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, Centres, SeRC - Swedish e-Science Research Centre.
    Rosén, Tomas
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Centres, Wallenberg Wood Science Center. KTH, School of Engineering Sciences (SCI), Engineering Mechanics.
    Lundell, Fredrik
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Centres, Wallenberg Wood Science Center. KTH, School of Engineering Sciences (SCI), Engineering Mechanics.
    Tornberg, Anna-Karin
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Numerical Analysis, NA. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, Centres, SeRC - Swedish e-Science Research Centre.
    Parabolic velocity profile causes shape-selective drift of inertial ellipsoids2021In: Journal of Fluid Mechanics, ISSN 0022-1120, E-ISSN 1469-7645, Vol. 926, article id A24Article in journal (Refereed)
    Abstract [en]

    Understanding particle drift in suspension flows is of the highest importance in numerous engineering applications where particles need to be separated and filtered out from the suspending fluid. Commonly known drift mechanisms such as the Magnus force, Saffman force and Segre-Silberberg effect all arise only due to inertia of the fluid, with similar effects on all non-spherical particle shapes. In this work, we present a new shape-selective lateral drift mechanism, arising from particle inertia rather than fluid inertia, for ellipsoidal particles in a parabolic velocity profile. We show that the new drift is caused by an intermittent tumbling rotational motion in the local shear flow together with translational inertia of the particle, while rotational inertia is negligible. We find that the drift is maximal when particle inertial forces are of approximately the same order of magnitude as viscous forces, and that both extremely light and extremely heavy particles have negligible drift. Furthermore, since tumbling motion is not a stable rotational state for inertial oblate spheroids (nor for spheres), this new drift only applies to prolate spheroids or tri-axial ellipsoids. Finally, the drift is compared with the effect of gravity acting in the directions parallel and normal to the flow. The new drift mechanism is stronger than gravitational effects as long as gravity is less than a critical value. The critical gravity is highest (i.e. the new drift mechanism dominates over gravitationally induced drift mechanisms) when gravity acts parallel to the flow and the particles are small.

  • 138.
    Bagheritabar, Mahmoud
    et al.
    Islamic Azad Univ, North Tehran Branch, Elect & Comp Engn Dept, Tehran, Iran..
    Bagheitabar, Hamed
    Islamic Azad Univ, Damavand Branch, Dept Elect & Energy Engn, Tehran, Iran..
    Kashani, Mohammad Mansour Riahi
    Islamic Azad Univ, North Tehran Branch, Elect & Comp Engn Dept, Tehran, Iran..
    Sayyad Khodashenas, Niloofar
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL. KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics.
    Photovoltaic Systems with Rotational Panels to Harvest Natural and Artificial Light for Electrical Production2018In: 2018 5TH INTERNATIONAL CONFERENCE ON ELECTRICAL AND ELECTRONIC ENGINEERING (ICEEE), IEEE , 2018, p. 211-214Conference paper (Refereed)
    Abstract [en]

    Regarding the fact that huge amount of non-renewable energy is extracted, distributed, converted and consumed for electrical demands in the Building-Integrated Photovoltaic systems, using the rotational photovoltaic panels as a source of energy would be more convenient. Optimization of this system which harvests outdoor natural light and indoor artificial light is an enormous need to maximize the solar panel efficiency. In this paper to achieve the main purpose, an experimental attempt has been made to model the wall and window built PV system as economical as possible. The performance of this model is carried out on the facade of buildings with a Manual switch for rotation. The result of this experiment has shown that the system is more efficient.

  • 139.
    Baghous, Nareg
    et al.
    Khalifa Univ Sci & Technol, Adv Digital & Addit Mfg ADAM Ctr, Abu Dhabi, U Arab Emirates.;Khalifa Univ Sci & Technol, Sch Engn, Dept Mech Engn, POB 127788, Abu Dhabi, U Arab Emirates..
    Barsoum, Imad
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics. Khalifa Univ Sci & Technol, Adv Digital & Addit Mfg ADAM Ctr, Abu Dhabi, U Arab Emirates.;Khalifa Univ Sci & Technol, Sch Engn, Dept Mech Engn, POB 127788, Abu Dhabi, U Arab Emirates..
    Abu Al-Rub, Rashid K.
    Khalifa Univ Sci & Technol, Adv Digital & Addit Mfg ADAM Ctr, Abu Dhabi, U Arab Emirates.;Khalifa Univ Sci & Technol, Sch Engn, Dept Mech Engn, POB 127788, Abu Dhabi, U Arab Emirates..
    Generalized yield surface for sheet-based triply periodic minimal surface lattices2023In: International Journal of Mechanical Sciences, ISSN 0020-7403, E-ISSN 1879-2162, Vol. 252, p. 108370-, article id 108370Article in journal (Refereed)
    Abstract [en]

    Triply periodic minimal surfaces (TPMS), which are a class of architected cellular materials, have attracted significant attention lately, due to their prevailing mechanical, electrical and chemical properties, to name a few, and due to the advancements in additive manufacturing technologies that make it possible to print such mate-rials. However, simulating the elastic-plastic mechanical behavior of structural systems (e.g., beams, plates, cores of sandwich panels, structural systems with various levels of geometric complexity) that are latticed with thousands of TPMS lattices are computationally expensive to model explicitly, and hence the need to develop accurate yield surfaces in order to capture their plastic behavior in a homogenized approach. In this work, a generalized initial yield criterion is proposed for sheet-based TPMS lattices, which incorporates the Lode parameter L. The initial yielding of five different sheet-based TPMS lattices are investigated in five different loading conditions. These lattices are Schoen's I-WP (IWP-s), Gyroid (GYR-s), Diamond (DIA-s), F-RD (FRD-s) and Primitive (PRIM-s). The proposed yield criterion accurately predicts the initial yielding of all these lattices in all the loading conditions considered, outperforming other yield criteria currently proposed in literature.

  • 140.
    Baghous, Nareg
    et al.
    Khalifa Univ Sci & Technol, Adv Digital & Addit Mfg ADAM Ctr, Abu Dhabi 127788, U Arab Emirates.;Khalifa Univ Sci & Technol, Sch Engn, Dept Mech Engn, POB 127788, Abu Dhabi, U Arab Emirates..
    Barsoum, Imad
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics. Khalifa Univ Sci & Technol, Adv Digital & Addit Mfg ADAM Ctr, Abu Dhabi 127788, U Arab Emirates.;Khalifa Univ Sci & Technol, Sch Engn, Dept Mech Engn, POB 127788, Abu Dhabi, U Arab Emirates..
    Al-Rub, Rashid K. Abu
    Khalifa Univ Sci & Technol, Adv Digital & Addit Mfg ADAM Ctr, Abu Dhabi 127788, U Arab Emirates.;Khalifa Univ Sci & Technol, Sch Engn, Dept Mech Engn, POB 127788, Abu Dhabi, U Arab Emirates..
    The effect of Lode parameter on the yield surface of Schoen's IWP triply periodic minimal surface lattice2022In: Mechanics of materials, ISSN 0167-6636, E-ISSN 1872-7743, Vol. 175, p. 104473-, article id 104473Article in journal (Refereed)
    Abstract [en]

    Owing to the advancements in additive manufacturing and increased applications of additively manufactured structures, it is essential to fully understand both the elastic and plastic behavior of cellular materials, which include the mathematically-driven sheet lattices based on triply periodic minimal surface (TPMS) that have received significant attention recently. The compressive elastic and plastic behaviors have been well established for many TPMS latticed structures, but not under multiaxial loading. Furthermore, TPMS lattices are compu-tationally expensive to model explicitly when used in latticing various structures for enhanced multi -functionality, and hence the need to develop accurate yield surfaces in order to capture their plastic behavior in a homogenized approach. The majority of previous yield surfaces developed for cellular materials originate from cellular foams, and limited attempts has been made to develop yield surfaces for TPMS lattices. In this study, a numerical modeling framework is proposed for developing the initial yield surface for cellular materials and is used to develop the initial yield surface for Schoen's IWP sheet-based TPMS cellular lattices. The effect of different loading conditions on the effective yield strength of the IWP sheet-based (IWP-s) TPMS lattice is numerically investigated, based on a single unit cell of IWP-s under fully periodic boundary conditions, assuming an elastic-perfectly plastic behavior of the base material, for relative densities (rho) ranging from 7% to 28%. In order to account for different loading conditions, the stress state is characterized in a generalized fashion through the Lode parameter (L). The effect of L is studied over a range of mean stress values (sigma m) to understand the effect of both L and sigma m on the effective yield strength. An initial yield surface is developed incorporating the effect of L, sigma m and rho, and is validated numerically showing rather good agreement. In the 3D principal stress space, the shape of the yield surface for the IWP-s lattice resembles the shape of a cocoa pod.

  • 141.
    Bai, X. S.
    et al.
    Lund University, Lund, Sweden.
    Haugen, N. E.L.
    SINTEF Energy Research, Trondheim, Norway.
    Fureby, C.
    Lund University, Lund, Sweden.
    Brethouwer, Gert
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics.
    Swaminathan, N.
    Engineering Department, Cambridge University, Cambridge, UK.
    Closing Remarks2022In: Advanced Turbulent Combustion Physics and Applications, Cambridge University Press , 2022, p. 460-463Chapter in book (Other academic)
  • 142.
    Baker, Dan
    et al.
    Zoox Inc.
    Sturesson, Per-Olof
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics. KTH, School of Engineering Sciences (SCI), Centres, VinnExcellence Center for ECO2 Vehicle design.
    Rajgarhia, Kushal
    Zoox Inc.
    Structure-borne Road Noise Target Allocation to Tire-Wheel Subsystem in Autonomous Vehicles2023In: Aachen Acoustics Colloquium: November 27th - 29th, 2023 / [ed] Gottfried Behler, 2023Conference paper (Refereed)
    Abstract [en]

    Personal transportation as we know it is being reimagined thanks to the introduction of autonomous electric vehicles. With autonomous vehicles (AV) on the rise, especially for Transportation Network Companies (TNC), it is expected that the experience inside of the vehicle cabin will be tailored engineered for riders, not drivers. As a result, customer-facing attributes such as noise, vibration, and harshness (NVH) will need to be considered with a new perspective. Of the many challenges in developing NVH performance of an AV, road noise and component noise have, and continue, to require the most amount of development and refinement effort. It is well known that a critical component in the chain from the tire-road interface to the occupant’s ears is the tire-wheel assembly and, therefore, allocating targets for this subsystem is essential. When in motion, the tire-wheel system possesses complex structural-acoustic properties like centrifugal, gyroscopic, fluid-structure coupling, pre-load effects, and excitation that may be described by random enforced motion at the tire contact patch and road interface. Component targets are derived by experimental and virtual methods, enabling simulation-driven product development. For tire testing and development, experimental methods are often limited by the availability of complex and expensive test infrastructure. An alternative approach is explored in order to develop tire-wheel subsystem targets using experimental tests and virtual methods applying transmissibility theory with multiple degrees of freedom based on frequency response functions derived at free-free boundary conditions.

  • 143.
    Balaji, S.
    et al.
    Department of Mechanical Engineering, Indian Institute of Technology (BHU), Varanasi, India.
    Kumar, Durgesh
    Department of Mechanical Engineering, Indian Institute of Technology (BHU), Varanasi, India.
    Parasuram, I. V. L. N.
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics.
    Sinha, Anubhav
    Department of Mechanical Engineering, Indian Institute of Technology (BHU), Varanasi, India.
    Transverse Gas Jet Injection—Effect of Density Ratio2023In: Fluid Mechanics and Fluid Power (Vol. 3)- Select Proceedings of FMFP 2021, Springer Nature , 2023, p. 245-249Conference paper (Refereed)
    Abstract [en]

    Transverse jet injection or jet in crossflow is the focus of the present study. Available literature is focused on iso-density jets; and jets with density different from crossflow are usually overlooked. However, in most practical examples, the jet and crossflow have different densities. This study attempts to investigate the effect of density ratio on jet penetration and trajectory. Gas jets with different densities are numerically simulated and their trajectories are compared. It is observed that the jet penetration is strongly dependent on the density ratio. A trajectory equation is formulated using multi-variable regression. This equation is found to match well with the available data.

  • 144.
    Balani, Elena
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics, Flight Dynamics.
    A Safety Device for an Unmanned Aerial System2020Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Optionally piloted aircraft are conceived to operate either through manned or remote piloting. However, as long as they are under testing with remote controls, a safety pilot is usually present on board. The consequence is that the crew shall be protected from failures of the automated flight systems. For this reason, specific safety devices that serve as monitors were designed. An instance of such devices is the Fault Detection System for small rotorcrafts. The goal of this work is to adapt this monitor to a new actuation set. The existing code is adjusted to fit the updated actuators' hardware and the new code is then tested and improved based on an iterative validation process. The final outcome is a system that can successfully intervene to mitigate failures of other components in accordance with the safety requirements.

  • 145.
    Banaei, Arash Alizad
    et al.
    KTH, Centres, SeRC - Swedish e-Science Research Centre. KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics.
    Rosti, Marco E.
    KTH, Centres, SeRC - Swedish e-Science Research Centre. KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics.
    Brandt, Luca
    KTH, Centres, SeRC - Swedish e-Science Research Centre. KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics.
    Numerical study of filament suspensions at finite inertia2020In: Journal of Fluid Mechanics, ISSN 0022-1120, E-ISSN 1469-7645, Vol. 882, article id A5Article in journal (Refereed)
    Abstract [en]

    We present a numerical study on the rheology of semi-dilute and concentrated filament suspensions of different bending stiffness and Reynolds number, with the immersed boundary method used to couple the fluid and solid. The filaments are considered as one-dimensional inextensible slender bodies with fixed aspect ratio, obeying the Euler-Bernoulli beam equation. To understand the global suspension behaviour we relate it to the filament microstructure, deformation and elastic energy and examine the stress budget to quantify the effect of the elastic contribution. At fixed volume fraction, the viscosity of the suspension reduces when decreasing the bending rigidity and grows when increasing the Reynolds number. The change in the relative viscosity is stronger at finite inertia, although still in the laminar flow regime, as considered here. Moreover, we find the first normal stress difference to be positive as in polymeric fluids, and to increase with the Reynolds number; its value has a peak for an intermediate value of the filament bending stiffness. The peak value is found to be proportional to the Reynolds number, moving towards more rigid suspensions at larger inertia. Moreover, the viscosity increases when increasing the filament volume fraction, and the rate of increase of the filament stress with the bending rigidity is stronger at higher Reynolds numbers and reduces with the volume fraction. We show that this behaviour is associated with the formation of a more ordered structure in the flow, where filaments tend to be more aligned and move as a compact aggregate, thus reducing the filament-filament interactions despite their volume fraction increases.

  • 146.
    Banaei, Arash Alizad
    et al.
    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.
    Shahmardi, Armin
    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.
    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.
    Numerical study of suspensions of nucleated capsules at finite inertia2021In: Physical Review Fluids, E-ISSN 2469-990X, Vol. 6, no 4, article id 044301Article in journal (Refereed)
    Abstract [en]

    We study the rheology of suspensions of capsules with a rigid nucleus at negligible and finite flow inertia by means of numerical simulations. The capsule membrane is modeled as a thin Neo-Hookean hyperelastic material and the nucleus as a rigid particle with radius equal to half the radius of the undeformed spherical capsules. The fluid and solid motion are coupled with an immersed boundary method, validated for both the deformable membrane and the rigid nucleus. We examine the effect of the Reynolds number, capillary number, and volume fraction on the macroscopic properties of the suspensions, comparing with the case of capsules without nuclei. To explain the rheological measurables, we examine the mean capsule deformation, the mean orientation with respect to the flow direction, and the stress budget. The results indicate that the relative viscosity decreases with the capillary number, i.e., increasing deformability, and increases with inertia. The presence of a nucleus always reduces the membrane deformation. Capsules align more in the flow direction at higher capillary numbers and at higher volume fractions, where we also see a significant portion of them oriented with their longer deformed axis in the spanwise direction. When increasing inertia, the alignment with the flow decreases while more capsules orient in the spanwise direction. The first normal stress difference increases with the capillary number and it is always less for the nucleated capsules. Finally, the relative viscosity and the first normal stress difference increase with the capsule volume fraction, an effect more pronounced for the first normal stress difference.

  • 147.
    Banerjee, Indradumna
    et al.
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Protein Science, Nano Biotechnology.
    Rosti, M. E.
    Kumar, Tharagan
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Protein Science, Nano Biotechnology.
    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.
    Russom, Aman
    KTH, Centres, Science for Life Laboratory, SciLifeLab. KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Protein Science, Nano Biotechnology.
    Analogue tuning of particle focusing in elasto-inertial flow2021In: Meccanica (Milano. Print), ISSN 0025-6455, E-ISSN 1572-9648, Vol. 56, no 7, p. 1739-1749Article in journal (Refereed)
    Abstract [en]

    We report a unique tuneable analogue trend in particle focusing in the laminar and weak viscoelastic regime of elasto-inertial flows. We observe experimentally that particles in circular cross-section microchannels can be tuned to any focusing bandwidths that lie between the “Segre-Silberberg annulus” and the centre of a circular microcapillary. We use direct numerical simulations to investigate this phenomenon and to understand how minute amounts of elasticity affect the focussing of particles at increasing flow rates. An Immersed Boundary Method is used to account for the presence of the particles and a FENE-P model is used to simulate the presence of polymers in a Non-Newtonian fluid. The numerical simulations study the dynamics and stability of finite size particles and are further used to analyse the particle behaviour at Reynolds numbers higher than what is allowed by the experimental setup. In particular, we are able to report the entire migration trajectories of the particles as they reach their final focussing positions and extend our predictions to other geometries such as the square cross section. We believe complex effects originate due to a combination of inertia and elasticity in the weakly viscoelastic regime, where neither inertia nor elasticity are able to mask each other’s effect completely, leading to a number of intermediate focusing positions. The present study provides a fundamental new understanding of particle focusing in weakly elastic and strongly inertial flows, whose findings can be exploited for potentially multiple microfluidics-based biological sorting applications. 

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    fulltext
  • 148.
    Banerjee, Indradumna
    et al.
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Protein Science, Nano Biotechnology.
    Rosti, Marco E.
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Protein Science, Nano Biotechnology.
    Kumar, Tharagan
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Protein Science, Nano Biotechnology.
    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.
    Russom, Aman
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Protein Science, Nano Biotechnology.
    Particle focusing dynamics in extended elasto inertial flow2018In: 22nd International Conference on Miniaturized Systems for Chemistry and Life Sciences, MicroTAS 2018, Chemical and Biological Microsystems Society , 2018, p. 472-475Conference paper (Refereed)
    Abstract [en]

    We report the decoupled effects of inertial and viscous forces on particle focusing, the stability of particles, and particle trajectories to reach equilibrium position in an extended elasto inertial pressure driven flow, in a circular micro-capillary. We report numerically and experimentally for the first time, the existence of multiple stable equilibrium positions in the EEI regime, which was unobserved for flows previously studied at lower Reynolds number viscoelastic flows. 

  • 149.
    Banno, Yuki
    et al.
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics. Gifu University, Gifu, Japan.
    Kinoshita, K.
    Barsoum, Zuheir
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics.
    Numerical investigation of crack opening-closing behavior on pre-fatigued welded joints repaired by HFMI2022In: Welding in the World, ISSN 0043-2288, E-ISSN 1878-6669, Vol. 66, no 4, p. 767-781Article in journal (Refereed)
    Abstract [en]

    This study aims to understand crack opening-closing behavior on pre-fatigued welded joints repaired by High Frequency Mechanical Impact (HFMI). Detailed rat-hole specimen models inserting different depths of rectangle slit in the weld toes to simulate initial cracks were used in the HFMI treatment simulation. Induced compressive residual stress, change of slit geometry, and opening-closing behavior of the slit after HFMI treatment simulation were investigated numerically. The amount of induced compressive residual stress around the slit tip is reduced when slit depth becomes larger, and slit size of about 0.4 mm remains when the slit depth is 2.0 mm. The opening-closing behavior of HFMI treated slit was examined based on change of strains along the slit face. The slit is opened from the bottom side prior to its treated surface. Additionally, the crack opening-closing behavior was investigated experimentally using pre-fatigued out-of-plane gusset welded joints repaired by impact crack closure retrofit treatment. Phased array ultrasonic testing system was used to examine the change of echo height from cracks. It could be concluded that similar behavior as the numerical investigation is observed. From both investigations, experimentally and numerically, the behavior on pre-fatigue welded joints repaired by HFMI could be studied successfully. 

  • 150.
    Banno, Yuki
    et al.
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics. Department of Civil Engineering, Gifu University, Gifu, Japan.
    Kinoshita, K.
    Barsoum, Zuheir
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics.
    Numerical investigation of influence of under- and over- treatment on residual stress state induced by HFMI2021In: Welding in the World, ISSN 0043-2288, E-ISSN 1878-6669, Vol. 65, no 11, p. 2135-2146Article in journal (Refereed)
    Abstract [en]

    This study aims to investigate influence of under- and over-treatment on residual stress state induced by HFMI numerically. Finite element simulations were performed using a flat plate model considering S355 where feed rate and the number of hits were varied. To reduce computational time, the mass scaling method was adopted to the simulations. In addition, in order to survey influence of surface removal on residual stress state, electropolishing was conducted after the HFMI simulation. Additional simulations were performed on bead on plate model considering JIS-SM400 in order to investigate applicability of isotropic hardening model for residual stress estimation. From the results, the mass scaling method can result in reducing computational time more than 90% with reasonable good estimation of the residual stresses.The investigations regarding under- and over-treatment reveal that high feed rate mainly influences residual stress state on the treated surface and the number of hits is independent of amount of induced residual stress. Surface removal after the simulation can result in slightly improving the accuracy of the estimated residual stresses. The simulations to bead on plate model give reasonable results in a depth of around 0.2 mm even when the residual stresses due to welding is disregarded. 

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