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  • 1.
    Abreu, Leandra I.
    et al.
    Divisão de Engenharia Aeronáutica, Instituto Tecnológico de Aeronáutica, 12228-900, São José dos Campos, SP, Brazil.
    Tanarro, Alvaro
    KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW. KTH, Centra, SeRC - Swedish e-Science Research Centre. KTH, Skolan för teknikvetenskap (SCI), Teknisk mekanik, Strömningsmekanik och Teknisk Akustik.
    Cavalieri, André V.G.
    Divisão de Engenharia Aeronáutica, Instituto Tecnológico de Aeronáutica, 12228-900, São José dos Campos, SP, Brazil.
    Schlatter, Philipp
    KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW. KTH, Tidigare Institutioner (före 2005), Mekanik. KTH, Centra, SeRC - Swedish e-Science Research Centre.
    Vinuesa, Ricardo
    KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW. KTH, Centra, SeRC - Swedish e-Science Research Centre.
    Hanifi, Ardeshir
    KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW. KTH, Centra, SeRC - Swedish e-Science Research Centre.
    Henningson, Dan S.
    KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW. KTH, Tidigare Institutioner (före 2005), Mekanik. KTH, Centra, SeRC - Swedish e-Science Research Centre.
    Wavepackets in turbulent flows around airfoilsManuskript (preprint) (Annet vitenskapelig)
    Abstract [en]

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

  • 2.
    Alizad Banaei, Arash
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Teknisk mekanik, Strömningsmekanik och Teknisk Akustik. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW. KTH, Centra, SeRC - Swedish e-Science Research Centre.
    Rahmani, Mona
    Univ British Columbia, Dept Math, Vancouver, BC V6T 1Z2, Canada..
    Martinez, D. Mark
    Univ British Columbia, Dept Chem & Biol Engn, Vancouver, BC V6T 1Z3, Canada..
    Brandt, Luca
    KTH, Skolan för teknikvetenskap (SCI), Teknisk mekanik, Strömningsmekanik och Teknisk Akustik. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW. KTH, Centra, SeRC - Swedish e-Science Research Centre.
    Inertial settling of flexible fiber suspensions2020Inngår i: Physical Review Fluids, E-ISSN 2469-990X, Vol. 5, nr 2, artikkel-id 024301Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

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

  • 3.
    Atzori, Marco
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Teknisk mekanik, Strömningsmekanik och Teknisk Akustik.
    Vinuesa, Ricardo
    KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW. KTH, Centra, SeRC - Swedish e-Science Research Centre. KTH, Skolan för teknikvetenskap (SCI), Teknisk mekanik, Strömningsmekanik och Teknisk Akustik.
    Lozano-Durán, A.
    Schlatter, Philipp
    KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW. KTH, Centra, SeRC - Swedish e-Science Research Centre. KTH, Skolan för teknikvetenskap (SCI), Teknisk mekanik, Strömningsmekanik och Teknisk Akustik.
    Contribution of Reynolds-stress structures to the secondary flow in turbulent ducts2019Inngår i: 11th International Symposium on Turbulence and Shear Flow Phenomena, TSFP 2019, International Symposium on Turbulence and Shear Flow Phenomena, TSFP , 2019Konferansepaper (Fagfellevurdert)
    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.

  • 4.
    Banaei, Arash Alizad
    et al.
    KTH, Centra, SeRC - Swedish e-Science Research Centre. KTH, Skolan för teknikvetenskap (SCI), Teknisk mekanik, Strömningsmekanik och Teknisk Akustik.
    Rosti, Marco E.
    KTH, Centra, SeRC - Swedish e-Science Research Centre. KTH, Skolan för teknikvetenskap (SCI), Teknisk mekanik, Strömningsmekanik och Teknisk Akustik.
    Brandt, Luca
    KTH, Centra, SeRC - Swedish e-Science Research Centre. KTH, Skolan för teknikvetenskap (SCI), Teknisk mekanik, Strömningsmekanik och Teknisk Akustik.
    Numerical study of filament suspensions at finite inertia2020Inngår i: Journal of Fluid Mechanics, ISSN 0022-1120, E-ISSN 1469-7645, Vol. 882, artikkel-id A5Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 5. Benard, N.
    et al.
    Sujar Garrido, Patricia
    KTH, Skolan för teknikvetenskap (SCI), Teknisk mekanik, Strömningsmekanik och Teknisk Akustik. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Bonnet, J. -P
    Moreau, E.
    Shear Layer and Shedding Modes Excitations of a Backward-Facing Step Flow by Surface Plasma Discharge2020Inngår i: Advances in Effective Flow Separation Control for Aircraft Drag Reduction, Springer, 2020, s. 55-74Kapittel i bok, del av antologi (Fagfellevurdert)
    Abstract [en]

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

  • 6.
    Borodulin, V. I.
    et al.
    Khristianovich Institute of Theoretical and Applied Mechanics, Novosibirsk 630090, Russian Federation.
    Ivanov, A. V.
    Khristianovich Institute of Theoretical and Applied Mechanics, Novosibirsk 630090, Russian Federation.
    Kachanov, Y. S.
    Khristianovich Institute of Theoretical and Applied Mechanics, Novosibirsk 630090, Russian Federation.
    Mischenko, D. A.
    Khristianovich Institute of Theoretical and Applied Mechanics, Novosibirsk 630090, Russian Federation.
    Örlü, Ramis
    KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW. KTH, Skolan för industriell teknik och management (ITM), Centra, Competence Center for Gas Exchange (CCGEx). KTH, Centra, SeRC - Swedish e-Science Research Centre. KTH, Skolan för teknikvetenskap (SCI), Teknisk mekanik, Strömningsmekanik och Teknisk Akustik.
    Hanifi, Ardeshir
    KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW. KTH, Centra, SeRC - Swedish e-Science Research Centre.
    Hein, S.
    Institute of Aerodynamics and Flow Technology, DLR, 37073 Göttingen, Germany.
    Experimental and theoretical study of swept-wing boundary-layer instabilities. Three-dimensional Tollmien-Schlichting instability2019Inngår i: Physics of Fluids, Vol. 31, nr 11, artikkel-id 114104Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Extensive combined experimental and theoretical investigations of the linear evolution of three-dimensional (3D) Tollmien-Schlichting (TS) instability modes of 3D boundary layers developing on a swept airfoil section have been carried out. The flow under consideration is the boundary layer over an airfoil at 35° sweep and an angle of attack of +1.5°. At these conditions, TS instability is found to be the predominant one. Perturbations with different frequencies and spanwise wavenumbers are generated in a controlled way using a row of elastic membranes. All experimental results are deeply processed and compared with results of calculations based on theoretical approaches. Very good quantitative agreement of all measured and calculated stability characteristics of swept-wing boundary layers is achieved.

  • 7.
    Canton, Jacopo
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW. KTH, Skolan för teknikvetenskap (SCI), Teknisk mekanik, Strömningsmekanik och Teknisk Akustik.
    Rinaldi, Enrico
    KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW. KTH, Skolan för teknikvetenskap (SCI), Teknisk mekanik, Strömningsmekanik och Teknisk Akustik. Royal Inst Technol, Linne FLOW Ctr KTH Mech, SE-10044 Stockholm, Sweden..
    Örlü, Ramis
    KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW. KTH, Skolan för teknikvetenskap (SCI), Teknisk mekanik, Strömningsmekanik och Teknisk Akustik.
    Schlatter, Philipp
    KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW. KTH, Skolan för teknikvetenskap (SCI), Teknisk mekanik, Strömningsmekanik och Teknisk Akustik.
    Critical Point for Bifurcation Cascades and Featureless Turbulence2020Inngår i: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 124, nr 1, artikkel-id 014501Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In this Letter we show that a bifurcation cascade and fully sustained turbulence can share the phase space of a fluid flow system, resulting in the presence of competing stable attractors. We analyze the toroidal pipe flow, which undergoes subcritical transition to turbulence at low pipe curvatures (pipe-to-torus diameter ratio) and supercritical transition at high curvatures, as was previously documented. We unveil an additional step in the bifurcation cascade and provide evidence that, in a narrow range of intermediate curvatures, its dynamics competes with that of sustained turbulence emerging through subcritical transition mechanisms.

  • 8.
    Chaparian, Emad
    et al.
    KTH, Centra, SeRC - Swedish e-Science Research Centre. KTH, Skolan för teknikvetenskap (SCI), Teknisk mekanik, Strömningsmekanik och Teknisk Akustik.
    Izbassarov, Daulet
    KTH, Skolan för teknikvetenskap (SCI), Teknisk mekanik, Strömningsmekanik och Teknisk Akustik. KTH, Centra, SeRC - Swedish e-Science Research Centre.
    De Vita, Francesco
    KTH, Centra, SeRC - Swedish e-Science Research Centre. KTH, Skolan för teknikvetenskap (SCI), Teknisk mekanik, Strömningsmekanik och Teknisk Akustik. Royal Inst Technol KTH, Mech Dept, SERC, Stockholm, Sweden..
    Brandt, Luca
    KTH, Centra, SeRC - Swedish e-Science Research Centre. KTH, Skolan för teknikvetenskap (SCI), Teknisk mekanik, Strömningsmekanik och Teknisk Akustik. Royal Inst Technol KTH, Mech Dept, SERC, Stockholm, Sweden..
    Tammisola, Outi
    KTH, Centra, SeRC - Swedish e-Science Research Centre. KTH, Skolan för teknikvetenskap (SCI), Teknisk mekanik, Strömningsmekanik och Teknisk Akustik.
    Yield-stress fluids in porous media: a comparison of viscoplastic and elastoviscoplastic flows2020Inngår i: Meccanica (Milano. Print), ISSN 0025-6455, E-ISSN 1572-9648, Vol. 55, nr 2, s. 331-342Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

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

  • 9.
    Chauvat, Guillaume
    et al.
    KTH, Centra, SeRC - Swedish e-Science Research Centre. KTH, Skolan för teknikvetenskap (SCI).
    Peplinski, Adam
    KTH, Centra, SeRC - Swedish e-Science Research Centre. KTH, Skolan för teknikvetenskap (SCI), Teknisk mekanik, Strömningsmekanik och Teknisk Akustik.
    Henningson, Dan S.
    KTH, Skolan för teknikvetenskap (SCI). KTH, Centra, SeRC - Swedish e-Science Research Centre.
    Hanifi, Ardeshir
    KTH, Skolan för teknikvetenskap (SCI). KTH, Centra, SeRC - Swedish e-Science Research Centre.
    Global linear analysis of a jet in cross-flow at low velocity ratios2020Inngår i: Journal of Fluid Mechanics, ISSN 0022-1120, E-ISSN 1469-7645, Vol. 889, artikkel-id A12Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

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

  • 10.
    Chen, Song
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Teknisk mekanik, Strömningsmekanik och Teknisk Akustik.
    Gojon, Romain
    ISAE-Supaero.
    Mihaescu, Mihai
    KTH, Skolan för industriell teknik och management (ITM), Centra, Competence Center for Gas Exchange (CCGEx). KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Effect of an Adjacent Flat Plate on a Highly-Heated Rectangular Supersonic Jet2020Konferansepaper (Fagfellevurdert)
    Abstract [en]

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

  • 11.
    Costa, Pedro
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW. KTH, Centra, SeRC - Swedish e-Science Research Centre. KTH, Skolan för teknikvetenskap (SCI), Teknisk mekanik, Strömningsmekanik och Teknisk Akustik. aculty of Industrial Engineering, Mechanical Engineering and Computer Science, University of Iceland, Hjardarhagi 2-6, 107 Reykjavik, Iceland.
    Phillips, Everett
    NVIDIA Corporation, Santa Clara CA 95050, United States of America.
    Brandt, Luca
    KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW. KTH, Tidigare Institutioner (före 2005), Mekanik. KTH, Centra, SeRC - Swedish e-Science Research Centre. KTH, Skolan för teknikvetenskap (SCI), Teknisk mekanik, Strömningsmekanik och Teknisk Akustik.
    Fatica, Massimo
    NVIDIA Corporation, Santa Clara CA 95050, United States of America.
    GPU acceleration of CaNS for massively-parallel direct numerical simulations of canonical fluid flows2020Inngår i: Computers and Mathematics with ApplicationsArtikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This work presents the GPU acceleration of the open-source code CaNS for very fast massively-parallel simulations of canonical fluid flows. The distinct feature of the many-CPU Navier–Stokes solver in CaNS is its fast direct solver for the second-order finite-difference Poisson equation, based on the method of eigenfunction expansions. The solver implements all the boundary conditions valid for this type of problems in a unified framework. Here, we extend the solver for GPU-accelerated clusters using CUDA Fortran. The porting makes extensive use of CUF kernels and has been greatly simplified by the unified memory feature of CUDA Fortran, which handles the data migration between host (CPU) and device (GPU) without defining new arrays in the source code. The overall implementation has been validated against benchmark data for turbulent channel flow and its performance assessed on a NVIDIA DGX-2 system (16 T V100 32Gb, connected with NVLink via NVSwitch). The wall-clock time per time step of the GPU-accelerated implementation is impressively small when compared to its CPU implementation on state-of-the-art many-CPU clusters, as long as the domain partitioning is sufficiently small that the data resides mostly on the GPUs. The implementation has been made freely available and open source under the terms of an MIT license.

  • 12.
    De Vita, Francesco
    et al.
    KTH, Centra, SeRC - Swedish e-Science Research Centre. KTH, Skolan för teknikvetenskap (SCI), Teknisk mekanik, Strömningsmekanik och Teknisk Akustik. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Rosti, Marco E.
    KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW. KTH, Centra, SeRC - Swedish e-Science Research Centre. KTH, Skolan för teknikvetenskap (SCI), Mekanik. Okinawa Inst Sci & Technol Grad Univ, Complex Fluids & Flaws Unit, 1919-1 Tancha, Onna Son, Okinawa 9040495, Japan..
    Caserta, Sergio
    Univ Naples Federico II, Dept Chem Mat & Ind Prod Engn, Ple Tecchio 80, I-80125 Naples, Italy..
    Brandt, Luca
    KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW. KTH, Tidigare Institutioner (före 2005), Mekanik. KTH, Centra, SeRC - Swedish e-Science Research Centre.
    Numerical simulations of vorticity banding of emulsions in shear flows2020Inngår i: Soft Matter, ISSN 1744-683X, E-ISSN 1744-6848, Vol. 16, nr 11, s. 2854-2863Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Multiphase shear flows often show banded structures that affect the global behavior of complex fluids e.g. in microdevices. Here we investigate numerically the banding of emulsions, i.e. the formation of regions of high and low volume fractions, alternated in the vorticity direction and aligned with the flow (shear bands). These bands are associated with a decrease of the effective viscosity of the system. To understand the mechanism of experimentally observed banding, we have performed interface-resolved simulations of the two-fluid system. The experiments were performed starting with a random distribution of droplets, which under the applied shear, evolve in time resulting in a phase separation. To numerically reproduce this process, the banded structures are initialized in a narrow channel confined by two walls moving in opposite directions. We find that the initial banded distribution is stable when droplets are free to merge and unstable when coalescence is prevented. In this case, additionally, the effective viscosity of the system increases, resembling the rheological behavior of suspensions of deformable particles. Droplet coalescence, on the other hand, allows emulsions to reduce the total surface of the system and, hence, the energy dissipation associated with the deformation, which in turn reduces the effective viscosity.

  • 13.
    De Vita, Francesco
    et al.
    KTH, Centra, SeRC - Swedish e-Science Research Centre. KTH, Skolan för teknikvetenskap (SCI), Teknisk mekanik, Strömningsmekanik och Teknisk Akustik. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Rosti, Marco E.
    KTH, Centra, SeRC - Swedish e-Science Research Centre. KTH, Skolan för teknikvetenskap (SCI), Teknisk mekanik, Strömningsmekanik och Teknisk Akustik. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Caserta, Sergio
    Univ Naples Federico II, Dept Chem Mat & Ind Prod Engn, Piazzale V Tecchio 80, I-80125 Naples, Italy..
    Brandt, Luca
    KTH, Centra, SeRC - Swedish e-Science Research Centre. KTH, Skolan för teknikvetenskap (SCI), Teknisk mekanik, Strömningsmekanik och Teknisk Akustik. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    On the effect of coalescence on the rheology of emulsions2019Inngår i: Journal of Fluid Mechanics, ISSN 0022-1120, E-ISSN 1469-7645, Vol. 880, s. 969-991Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We present a numerical study of the rheology of a two-fluid emulsion in dilute and semidilute conditions. The analysis is performed for different capillary numbers, volume fractions and viscosity ratios under the assumption of negligible inertia and zero buoyancy force. The effective viscosity of the system increases for low values of the volume fraction and decreases for higher values, with a maximum for approximately 20% concentration of the disperse phase. When the dispersed fluid has lower viscosity, the normalised effective viscosity becomes smaller than 1 for high enough volume fractions. To single out the effect of droplet coalescence on the rheology of the emulsion we introduce an Eulerian force which prevents merging, effectively modelling the presence of surfactants in the system. When the coalescence is inhibited the effective viscosity is always greater than 1 and the curvature of the function representing the emulsion effective viscosity versus the volume fraction becomes positive, resembling the behaviour of suspensions of deformable particles. The reduction of the effective viscosity in the presence of coalescence is associated with the reduction of the total surface of the disperse phase when the droplets merge, which leads to a reduction of the interface tension contribution to the total shear stress. The probability density function of the flow topology parameter shows that the flow is mostly a shear flow in the matrix phase, with regions of extensional flow when the coalescence is prohibited. The flow in the disperse phase, instead, always shows rotational components. The first normal stress difference is positive, except for the smallest viscosity ratio considered, whereas the second normal difference is negative, with their ratio being constant with the volume fraction. Our results clearly show that the coalescence efficiency strongly affects the system rheology and that neglecting droplet merging can lead to erroneous predictions.

  • 14.
    Friederici, Anke
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Datavetenskap, Beräkningsvetenskap och beräkningsteknik (CST).
    Köpp, Wiebke
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Datavetenskap, Beräkningsvetenskap och beräkningsteknik (CST).
    Atzori, Marco
    KTH, Skolan för teknikvetenskap (SCI), Teknisk mekanik, Strömningsmekanik och Teknisk Akustik. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Vinuesa, Ricardo
    KTH, Skolan för teknikvetenskap (SCI), Teknisk mekanik, Strömningsmekanik och Teknisk Akustik. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Schlatter, Philipp
    KTH, Skolan för teknikvetenskap (SCI), Teknisk mekanik, Strömningsmekanik och Teknisk Akustik. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Weinkauf, Tino
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Datavetenskap, Beräkningsvetenskap och beräkningsteknik (CST).
    Distributed Percolation Analysis for Turbulent Flows2019Inngår i: 2019 IEEE 9th Symposium on Large Data Analysis and Visualization, LDAV 2019, Institute of Electrical and Electronics Engineers (IEEE), 2019, s. 42-51, artikkel-id 8944383Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Percolation analysis is a valuable tool to study the statistical properties of turbulent flows. It is based on computing the percolation function for a derived scalar field, thereby quantifying the relative volume of the largest connected component in a superlevel set for a decreasing threshold. We propose a novel memory-distributed parallel algorithm to finely sample the percolation function. It is based on a parallel version of the union-find algorithm interleaved with a global synchronization step for each threshold sample. The efficiency of this algorithm stems from the fact that operations in-between threshold samples can be freely reordered, are mostly local and thus require no inter-process communication. Our algorithm is significantly faster than previous algorithms for this purpose, and is neither constrained by memory size nor number of compute nodes compared to the conceptually related algorithm for extracting augmented merge trees. This makes percolation analysis much more accessible in a large range of scenarios. We explore the scaling of our algorithm for different data sizes, number of samples and number of MPI processes. We demonstrate the utility of percolation analysis using large turbulent flow data sets.

  • 15.
    Gaborit, Mathieu
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Teknisk mekanik, Strömningsmekanik och Teknisk Akustik, Marcus Wallenberg Laboratoriet MWL. KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    Dazel, O.
    Göransson, Peter
    KTH, Skolan för teknikvetenskap (SCI), Teknisk mekanik, Strömningsmekanik och Teknisk Akustik, Marcus Wallenberg Laboratoriet MWL. KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    Influence of uncertain parameters on the acoustic behaviour of sound proofing laminates2019Inngår i: INTER-NOISE 2019 MADRID - 48th International Congress and Exhibition on Noise Control Engineering, SOCIEDAD ESPANOLA DE ACUSTICA - Spanish Acoustical Society, SEA , 2019Konferansepaper (Fagfellevurdert)
    Abstract [en]

    The protection against excessive noise has gathered a lot of attention along the years. Tailored solutions for specific types of noise conditions emerged and many communications on the subject are published every year. Although designing sound proofing systems is a well developed topic, building the proposed systems is still subject to many uncertainties. For instance, the very nature of the foams used in many broadband absorbers implies a degree of uncertainty on some of the most important parameters (e.g. the airflow resistivity). This phenomenon is even more noticeable in modern sound absorbing laminates in which every interface implies a barely controllable change in the continuity conditions. This effect being rarely accounted for and the interfaces' properties hard to quantify, it adds uncertainties that are widely neglected even though having a potentially strong impact. In this contribution, the effect of randomly distributed parameters on the overall acoustic response of multi-layer systems is considered. The influence of choosing specific acoustic models for each layer is emphasized and the resulting response envelope is studied.

  • 16.
    Ilkka, Karasalo
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Teknisk mekanik, Strömningsmekanik och Teknisk Akustik, Marcus Wallenberg Laboratoriet MWL.
    Tengzelius, U.
    Assessment of a simplified environmental model for aircraft noise prediction2019Inngår i: INTER-NOISE 2019 MADRID - 48th International Congress and Exhibition on Noise Control Engineering, SOCIEDAD ESPANOLA DE ACUSTICA - Spanish Acoustical Society, SEA , 2019Konferansepaper (Fagfellevurdert)
    Abstract [en]

    The environmental effects on the noise level on the ground from aircraft near the Arlanda airport are studied by numerical predictions of the acoustic transfer function from the aircraft position to the ground. Sound propagation is modelled by acoustic ray tracing using time-variable 3D atmospheric fields provided by the AROME prognosis model, combined with 2D data on ground topology and ground cover. The acoustic transfer function from selected points on the flight path to the ground is computed as function of range to the ground track at two-hour intervals during a one-year period. The results, aggregated into percentiles of the transfer function, are compared to similarly aggregated results from a simplified model of the atmosphere, the ground and the sound propagation. The simplifications are introduced to reduce the computational demands, are: (i) the ground is flat, (ii) the atmospheric parameters are functions of height only and (iii) rays are not continued beyond their first ground hit.

  • 17. Karnama, A.
    et al.
    Haghighi, E. B.
    Vinuesa, Ricardo
    KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW. KTH, Skolan för teknikvetenskap (SCI), Teknisk mekanik, Strömningsmekanik och Teknisk Akustik.
    Organic data centers: A sustainable solution for computing facilities2019Inngår i: Results in Engineering, ISSN 2590-1230, Vol. 4, artikkel-id 100063Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In the present perspective article we provide an overview of on-going work in the literature and possible future development of organic data centers (ODC). These are defined as the combined operation of a data center and a greenhouse, and given their compatible thermal and operation requirements, ODCs have the potential to provide an excellent solution in terms of sustainability. In particular, we identify possible positive impacts of ODCs on at least 5 of the 17 United Nations (UN) Sustainable Development Goals (SDGs), including SDGs 2 and 13 on zero hunger and climate change, respectively.

  • 18.
    Le Clainche, S.
    et al.
    Univ Politecn Madrid, Sch Aerosp Engn, E-28040 Madrid, Spain..
    Izbassarov, Daulet
    KTH, Skolan för teknikvetenskap (SCI), Teknisk mekanik, Strömningsmekanik och Teknisk Akustik. KTH, Centra, SeRC - Swedish e-Science Research Centre. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Rosti, Marco E.
    KTH, Skolan för teknikvetenskap (SCI), Teknisk mekanik, Strömningsmekanik och Teknisk Akustik. KTH, Centra, SeRC - Swedish e-Science Research Centre. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Brandt, Luca
    KTH, Skolan för teknikvetenskap (SCI), Teknisk mekanik, Strömningsmekanik och Teknisk Akustik. KTH, Centra, SeRC - Swedish e-Science Research Centre. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Tammisola, Outi
    KTH, Skolan för teknikvetenskap (SCI), Teknisk mekanik, Strömningsmekanik och Teknisk Akustik. KTH, Centra, SeRC - Swedish e-Science Research Centre. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Coherent structures in the turbulent channel flow of an elastoviscoplastic fluid2020Inngår i: Journal of Fluid Mechanics, ISSN 0022-1120, E-ISSN 1469-7645, Vol. 888, artikkel-id A5Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In this numerical and theoretical work, we study the turbulent channel flow of Newtonian and elastoviscoplastic fluids. The coherent structures in these flows are identified by means of higher order dynamic mode decomposition (HODMD), applied to a set of data non-equidistant in time, to reveal the role of the near-wall streaks and their breakdown, and the interplay between turbulent dynamics and non-Newtonian effects. HODMD identifies six different high-amplitude modes, which either describe the yielded flow or the yielded-unyielded flow interaction. The structure of the low- and high-frequency modes suggests that the interaction between high- and low-speed streamwise velocity structures is one of the mechanisms triggering the streak breakdown, dominant in Newtonian turbulence where we observe shorter near-wall streaks and a more chaotic dynamics. As the influence of elasticity and plasticity increases, the flow becomes more correlated in the streamwise direction, with long streaks disrupted for short times by localised perturbations, reflected in reduced drag. Finally, we present streamwise-periodic dynamic mode decomposition modes as a viable tool to describe the highly complex turbulent flows, and identify simple well-organised groups of travelling waves.

  • 19.
    Lopez Arteaga, Ines
    KTH, Skolan för teknikvetenskap (SCI), Teknisk mekanik, Strömningsmekanik och Teknisk Akustik, Marcus Wallenberg Laboratoriet MWL. Eindhoven University of Technology, Department of Mechanical Engineering, Eindhoven, Netherlands.
    Rolling noise in road and rail transportation systems2019Inngår i: INTER-NOISE 2019 MADRID - 48th International Congress and Exhibition on Noise Control Engineering, SOCIEDAD ESPANOLA DE ACUSTICA - Spanish Acoustical Society, SEA , 2019Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Long term exposure to ground transportation (road and rail traffic) noise is, after air pollution, the main environment-related health stressor in densely populated areas and compromises the quality of life and, indirectly, the life expectations of millions of people. The main source of ground transportation noise at speeds up to 130 km/h in road traffic and up to 300 km/h in rail traffic is rolling noise; noise generated due to the interaction between tyre and road (respectively wheel and rail). Although at first sight noise generation in these two transportation systems might seem unrelated, exploring the common aspects provides valuable insight in current practices for the modeling, prediction and abatement of rolling noise. In this paper the sound and vibration generation mechanisms due to tyre/road and wheel/rail interaction are discussed, focusing on the similarities and differences between the sound and vibration generation mechanisms in these two systems. This perspective is further extended to the discussion of modelling strategies and source characterization methods, with a particular emphasis on the influence of surface roughness on contact force generation. Finally, rolling noise source separation methods are touched upon, since they are a necesary tool to assess the impact of noise and vibration mitigation measures in both road and rail traffic systems.

  • 20.
    Lupi, Valerio
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Canton, J.
    Schlatter, Philipp
    KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW. KTH, Skolan för teknikvetenskap (SCI), Teknisk mekanik, Strömningsmekanik och Teknisk Akustik.
    On the onset of transition in 90°-bend pipe flow2019Inngår i: 11th International Symposium on Turbulence and Shear Flow Phenomena, TSFP 2019, International Symposium on Turbulence and Shear Flow Phenomena, TSFP , 2019Konferansepaper (Fagfellevurdert)
    Abstract [en]

    The present work deals with the global stability analysis of the flow in a 90◦-bend pipe with curvature δ = R/Rc = 0.3, being R the radius of the cross-section of the pipe and Rc the radius of curvature at the pipe centreline. Direct numerical simulations (DNS) for values of the bulk Reynolds number Reb = U-------D/v between 2000 and 3000 are performed. The bulk Reynolds number is based on the bulk velocity Ub, the pipe diameter D, and the kinematic viscosity ν. It is found that the flow is steady for Reb ≤ 2500, and two pairs of symmetric, counter-rotating vortices are observed in the section of the pipe downstream of the bend. Moreover, two recirculation regions are present inside the bend, one on the outer wall and the other on the inner one. For Reb ≥ 2550, the flow becomes periodic, oscillating with a fundamental non-dimensional frequency St = fD/Ub = 0.23. A global stability analysis reveals a pair of complex conjugate eigenvalues with positive real part. The velocity components of the unstable direct and adjoint eigenmodes are investigated, and it is observed that a large spatial separation occurs because of the non-normality of the linearised Navier–Stokes operator. Thus, an analysis of the structural sensitivity of the unstable eigenmode to spatially localised feedbacks is performed, in order to identify the core of the instability, the so-called wavemaker. It is found that the region located 15° downstream of the bend inlet, on the outer wall, is where the instability originates. Since flow separation is observed in this region, it is concluded that the instability is linked with the strong shear by the backflow phenomena.

  • 21.
    Manzari, Luca
    KTH, Skolan för teknikvetenskap (SCI), Teknisk mekanik, Strömningsmekanik och Teknisk Akustik.
    High-speed stereo imaging for the characterization of anisotropic viscoelastic media2020Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    This thesis proposes an experimental method for observing and characterizing the viscoelastic properties of anisotropic media using high-speed white light stereo imaging. The method uses short-time video recordings of a specimen undergoing forced harmonic motion.The three-dimensional displacement field of the specimen is then resolved using digital image correlation.Measuring for a short time has multiple advantages: it minimizes the conditioning of the specimen, and gives meaningful results when true stationary conditions are inaccessible (e.g. because of relaxation processes, or changes in the environmental conditions that cannot be accounted for).Moreover, it enables a reduction of the data storage needs and the computational costs associated with the image acquisition and processing.To overcome the intrinsic limitations of a Fourier-based approach for short time records, an optimization algorithm is used to determine the point-wise amplitude, phase and frequency of the full-field harmonic motion.This approach maximizes signal-to-noise ratio, is suitable for the identification of non-linear behaviors and tolerates data records that are non-uniformly spaced in time (e.g. because of momentary data losses and failure of the image matching algorithms).The measurement accuracy is increased by proposing a method to extract the frame of reference of the specimen on a per-frame bases, and express the measured displacement field therein.A cube of melamine foam and a pantographic sheet have been observed using the proposed method, and the measured data compared with the outcome of linear viscoelastic numerical models.The added information obtained about the melamine is believed to improve the accuracy of the characterization of its viscoelastic behavior, and the observation of the pantographic sheet represents and absolute first in the experimental studies of its dynamics.

    Fulltekst (pdf)
    fulltext
  • 22.
    Mao, Huina
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg. KTH, Skolan för teknikvetenskap (SCI), Teknisk mekanik, Strömningsmekanik och Teknisk Akustik, Marcus Wallenberg Laboratoriet MWL. KTH, Skolan för teknikvetenskap (SCI), Centra, VinnExcellence Center for ECO2 Vehicle design.
    Rumpler, Romain
    KTH, Skolan för teknikvetenskap (SCI), Centra, VinnExcellence Center for ECO2 Vehicle design. KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg. KTH, Skolan för teknikvetenskap (SCI), Teknisk mekanik, Strömningsmekanik och Teknisk Akustik, Marcus Wallenberg Laboratoriet MWL.
    Göransson, Peter
    KTH, Skolan för teknikvetenskap (SCI), Centra, VinnExcellence Center for ECO2 Vehicle design. KTH, Skolan för teknikvetenskap (SCI), Teknisk mekanik, Strömningsmekanik och Teknisk Akustik, Marcus Wallenberg Laboratoriet MWL. KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    An inverse method for characterisation of the static elastic Hooke's tensors of solid frame of anisotropic open-cell materials2020Inngår i: International Journal of Engineering Science, ISSN 0020-7225, E-ISSN 1879-2197, Vol. 147, artikkel-id 103198Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This paper proposes an inverse estimation method for the extraction of the equivalent, static elastic, Hooke's tensor. The inversion is based on a fitting of the displacements, obtained from a combination of static compression and shear traction loads, on the faces of a sample specimen. An equivalent, homogenised material model is found by varying the elastic moduli until a defined cost function, based on the error measured as the difference between the displacement fields, has reached a minimum, at which an anisotropic constitutive solid model has been identified. The method is built on a multi-level step-wise approach, both from a computational as well as an assumed constitutive model symmetry point of view. The principle of the method is validated for a target anisotropic solid material model. The proposed multi-level approach is developed and refined for a known open-cell structure based on the Kelvin cell geometry. The accuracy of the method is verified and various strategies for increasing the rate of convergence in the inversion are discussed.

  • 23.
    Mao, Huina
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Teknisk mekanik.
    Rumpler, Romain
    KTH, Skolan för teknikvetenskap (SCI), Teknisk mekanik, Strömningsmekanik och Teknisk Akustik.
    Göransson, Peter
    KTH, Tidigare Institutioner (före 2005), Farkostteknik. KTH, Skolan för teknikvetenskap (SCI), Centra, VinnExcellence Center for ECO2 Vehicle design.
    An inverse method for design and characterisation of acoustic materials2019Konferansepaper (Fagfellevurdert)
    Abstract [en]

    This paper presents applications of an inverse method for the design and characterisation of anisotropic elastic material properties of acoustic porous materials. Full field 3D displacements under static surface loads are used as targets in the inverse estimation to fit a material model of an equivalent solid to the measurement data. Test cases of artificial open-cell foams are used, and the accuracy of the results are verified. The method is shown to be able to successfully characterise both isotropic and anisotropic elastic material properties. The paper demonstrates a way to reduce costs by characterising material properties based on the design model without a need for manufacturing and additional experimental tests.

    Fulltekst (pdf)
    fulltext
  • 24.
    Mittal, Nitesh
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Teknisk mekanik, Strömningsmekanik och Teknisk Akustik, Strömningsfysik. KTH, Skolan för kemi, bioteknologi och hälsa (CBH), Centra, Wallenberg Wood Science Center. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW. Massachusetts Institute of Technology, Cambridge, MA 02142, United States.
    Benselfelt, Tobias
    KTH, Skolan för kemi, bioteknologi och hälsa (CBH), Fiber- och polymerteknologi, Fiberteknologi. KTH, Skolan för kemi, bioteknologi och hälsa (CBH), Centra, Wallenberg Wood Science Center.
    Ansari, F.
    Gordeyeva, Korneliya
    KTH, Skolan för teknikvetenskap (SCI), Teknisk mekanik, Strömningsmekanik och Teknisk Akustik. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Roth, Stephan Volkher
    KTH, Skolan för kemi, bioteknologi och hälsa (CBH), Fiber- och polymerteknologi, Ytbehandlingsteknik. DESY, D-22607 Hamburg, Germany.
    Wågberg, Lars
    KTH, Skolan för kemi, bioteknologi och hälsa (CBH), Fiber- och polymerteknologi. KTH, Skolan för kemi, bioteknologi och hälsa (CBH), Centra, Wallenberg Wood Science Center.
    Söderberg, Daniel
    KTH, Skolan för teknikvetenskap (SCI), Teknisk mekanik, Strömningsmekanik och Teknisk Akustik. KTH, Skolan för kemi, bioteknologi och hälsa (CBH), Centra, Wallenberg Wood Science Center.
    Ion-Specific Assembly of Strong, Tough, and Stiff Biofibers2019Inngår i: Angewandte Chemie International Edition, ISSN 1433-7851, E-ISSN 1521-3773, Vol. 58, nr 51, s. 18562-18569Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Designing engineering materials with high stiffness and high toughness is challenging as stiff materials tend to be brittle. Many biological materials realize this objective through multiscale (i.e., atomic- to macroscale) mechanisms that are extremely difficult to replicate in synthetic materials. Inspired from the architecture of such biological structures, we here present flow-assisted organization and assembly of renewable native cellulose nanofibrils (CNFs), which yields highly anisotropic biofibers characterized by a unique combination of high strength (1010 MPa), high toughness (62 MJ m−3) and high stiffness (57 GPa). We observed that properties of the fibers are primarily governed by specific ion characteristics such as hydration enthalpy and polarizability. A fundamental facet of this study is thus to elucidate the role of specific anion binding following the Hofmeister series on the mechanical properties of wet fibrillar networks, and link this to the differences in properties of dry nanostructured fibers. This knowledge is useful for rational design of nanomaterials and is critical for validation of specific ion effect theories. The bioinspired assembly demonstrated here is relevant example for designing high-performance materials with absolute structural control.

  • 25.
    Picano, Francesco
    et al.
    Univ Padua, Dept Ind Engn, Via Venezia 1, I-35131 Padua, Italy.;Univ Padua, Ctr Studies & Activ Space CISAS, Via Venezia 1, I-35131 Padua, Italy..
    Tammisola, Outi
    KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW. KTH, Centra, SeRC - Swedish e-Science Research Centre. KTH, Skolan för teknikvetenskap (SCI), Teknisk mekanik, Strömningsmekanik och Teknisk Akustik.
    Brandt, Luca
    KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW. KTH, Centra, SeRC - Swedish e-Science Research Centre. KTH, Skolan för teknikvetenskap (SCI), Teknisk mekanik, Strömningsmekanik och Teknisk Akustik.
    Editorial2020Inngår i: Meccanica (Milano. Print), ISSN 0025-6455, E-ISSN 1572-9648, Vol. 55, nr 2, s. 295-297Artikkel i tidsskrift (Annet vitenskapelig)
  • 26.
    Rezaeiravesh, Saleh
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Teknisk mekanik, Strömningsmekanik och Teknisk Akustik. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Vinuesa, Ricardo
    KTH, Skolan för teknikvetenskap (SCI), Teknisk mekanik, Strömningsmekanik och Teknisk Akustik. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW. KTH, Centra, SeRC - Swedish e-Science Research Centre.
    Schlatter, Philipp
    KTH, Skolan för teknikvetenskap (SCI), Teknisk mekanik, Strömningsmekanik och Teknisk Akustik. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW. KTH, Centra, SeRC - Swedish e-Science Research Centre.
    A statistics toolbox for turbulent pipe flow in Nek50002019Rapport (Annet vitenskapelig)
    Fulltekst (pdf)
    fulltext
  • 27.
    Rosti, Marco E.
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW. KTH, Centra, SeRC - Swedish e-Science Research Centre. KTH, Skolan för teknikvetenskap (SCI), Teknisk mekanik, Strömningsmekanik och Teknisk Akustik. Grad Univ, Okinawa Inst Sci & Technol, Complex Fluids & Flows Unit, 1919-1 Tancha, Onna Son, Okinawa 9040495, Japan..
    Brandt, Luca
    KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW. KTH, Centra, SeRC - Swedish e-Science Research Centre. KTH, Skolan för teknikvetenskap (SCI), Teknisk mekanik, Strömningsmekanik och Teknisk Akustik.
    Increase of turbulent drag by polymers in particle suspensions2020Inngår i: Physical Review Fluids, E-ISSN 2469-990X, Vol. 5, nr 4, artikkel-id 041301Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We study the effect of spherical particles on the turbulent flow of a viscoelastic fluid and find that the drag reducing effect of polymer additives is completely lost for semidense suspensions, with the drag increasing more than for suspensions in Newtonian fluids. This different behavior is due to three separate effects. First, polymer stretching is reduced by the presence of rigid particles, thus canceling the drag reducing benefit of the viscoelastic fluid. Second, drag increase is provided by the growth of the particle and polymeric shear stresses with the particles, due to larger shear rates in the vicinity of the particle surface. Third, particles migrate towards the wall due to the shear-thinning property of the fluid, thus enhancing the particle near-wall layer and further increasing the drag.

  • 28.
    Rosti, Marco Edoardo
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Teknisk mekanik, Strömningsmekanik och Teknisk Akustik. KTH, Centra, SeRC - Swedish e-Science Research Centre. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Pramanik, Satyajit
    KTH, Centra, Nordic Institute for Theoretical Physics NORDITA.
    Brandt, Luca
    KTH, Skolan för teknikvetenskap (SCI), Teknisk mekanik, Strömningsmekanik och Teknisk Akustik. KTH, Centra, SeRC - Swedish e-Science Research Centre. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Mitra, Dhrubaditya
    KTH, Centra, Nordic Institute for Theoretical Physics NORDITA. Stockholm Univ, SE-10691 Stockholm, Sweden.
    The breakdown of Darcy's law in a soft porous material2020Inngår i: Soft Matter, ISSN 1744-683X, E-ISSN 1744-6848, Vol. 16, nr 4, s. 939-944Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We perform direct numerical simulations of the flow through a model of deformable porous medium. Our model is a two-dimensional hexagonal lattice, with defects, of soft elastic cylindrical pillars, with elastic shear modulus G, immersed in a liquid. We use a two-phase approach: the liquid phase is a viscous fluid and the solid phase is modeled as an incompressible viscoelastic material, whose complete nonlinear structural response is considered. We observe that the Darcy flux (q) is a nonlinear function - steeper than linear - of the pressure-difference (Delta P) across the medium. Furthermore, the flux is larger for a softer medium (smaller G). We construct a theory of this super-linear behavior by modelling the channels between the solid cylinders as elastic channels whose walls are made of material with a linear constitutive relation but can undergo large deformation. Our theory further predicts that the flow permeability is an universal function of Delta P/G, which is confirmed by the present simulations.

  • 29.
    Rumpler, Romain
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Centra, VinnExcellence Center for ECO2 Vehicle design. KTH, Skolan för teknikvetenskap (SCI), Teknisk mekanik, Strömningsmekanik och Teknisk Akustik, Marcus Wallenberg Laboratoriet MWL.
    Rodrı́guez Sánchez, Raúl
    Chair of Structural Mechanics, Technical University of Munich.
    Göransson, Peter
    KTH, Skolan för teknikvetenskap (SCI), Teknisk mekanik. KTH, Skolan för teknikvetenskap (SCI), Centra, VinnExcellence Center for ECO2 Vehicle design.
    MULTIVARIATE PADÉ APPROXIMANTS FOR FINITE ELEMENT SOLUTIONS WITH COMPLEX PARAMETRIC DEPENDENCE2019Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Most engineering applications involving solutions by numerical methods are dependent on several parameters, whose impact on the solution may significantly vary from one to the other. At times an evaluation of these multivariate solutions may be required at the expense of a prohibitively high computational cost. In the present work, a multivariate finite element approach is proposed, allowing for a fast evaluation of parametric responses. It is based on the construction of a reduced basis spanning a subspace able to capture rough variations of the response. The method consists in an extension of the Well-Conditioned Asymptotic Waveform Evaluation (WCAWE) to multivariate problems, by an appropriate choice of derivative sequences, and a selection of the most relevant basis components. It is validated and demonstrated for its potential on a semi-industrial sized 3D application involving coupled poroelasticand internal acoustic domains.

    Fulltekst (pdf)
    fulltext
  • 30. Sanmiguel Vila, C.
    et al.
    Vinuesa, Ricardo
    KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW. KTH, Centra, SeRC - Swedish e-Science Research Centre. KTH, Skolan för teknikvetenskap (SCI), Teknisk mekanik, Strömningsmekanik och Teknisk Akustik.
    Discetti, S.
    Ianiro, A.
    Schlatter, P.
    Örlü, Ramis
    KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW. KTH, Skolan för industriell teknik och management (ITM), Centra, Competence Center for Gas Exchange (CCGEx). KTH, Centra, SeRC - Swedish e-Science Research Centre. KTH, Skolan för teknikvetenskap (SCI), Teknisk mekanik, Strömningsmekanik och Teknisk Akustik.
    Large-scale energy in turbulent boundary layers: Reynolds-number and pressure-gradient effects2019Inngår i: Springer Proceedings in Physics, Springer Science and Business Media, LLC , 2019, s. 69-74Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Adverse-pressure-gradient (APG) turbulent boundary layers (TBLs) are studied using hot-wire measurements which cover a Clauser pressure-gradient-parameter range up to β ≈ 2.4. Constant and non-constant β distributions with the same upstream history are studied. The pre-multiplied power-spectral density is employed to study the differences in the large-scale energy content throughout the boundary layer. Two different large-scale phenomena are identified, the first one due to the pressure gradient and the second one due to the Reynolds number; the latter is also present in high-Re ZPG TBLs. A decomposition of the streamwise velocity fluctuations using a temporal filter shows that the small-scale velocity fluctuations do not scale in APG TBL flows since the effect of the large-scale features extends up to the near-wall region.

  • 31. Sanmiguel Vila, C.
    et al.
    Vinuesa, Ricardo
    KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW. KTH, Skolan för teknikvetenskap (SCI), Teknisk mekanik, Strömningsmekanik och Teknisk Akustik.
    Discetti, S.
    Ianiro, A.
    Schlatter, Philipp
    KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW. KTH, Skolan för teknikvetenskap (SCI), Teknisk mekanik, Strömningsmekanik och Teknisk Akustik.
    Örlü, Ramis
    KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW. KTH, Skolan för teknikvetenskap (SCI), Teknisk mekanik, Strömningsmekanik och Teknisk Akustik.
    Experimental realisation of near-equilibrium adverse-pressure-gradient turbulent boundary layers2020Inngår i: Experimental Thermal and Fluid Science, ISSN 0894-1777, E-ISSN 1879-2286, Vol. 112, artikkel-id 109975Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A new experimental database of adverse-pressure-gradient (APG) turbulent boundary layers (TBLs) obtained through hot-wire anemometry and oil-film interferometry covering a momentum–loss Reynolds number 450&lt;Reθ&lt;23450 and Clauser pressure-gradient-parameter range up to β≈2.4 is presented. Both increasing and approximately constant β distributions with the same upstream history are characterised. Turbulence statistics are compared among the different pressure-gradient distributions with additional numerical and experimental zero-pressure-gradient (ZPG) TBL data. Cases at approximately constant β, which can be considered as canonical representations of the boundary layer under a certain pressure-gradient magnitude, exhibit skin-friction and shape-factor curves consistent with the ones proposed by Vinuesa et al. (2017). These curves show a similar scaling behaviour as those proposed by Nagib et al. (2007) for ZPG TBLs. The pre-multiplied power-spectral density is employed to study the differences in the large-scale energy content throughout the boundary layer. Two different large-scale phenomena are identified, the first one related to the pressure gradient and the second one (also present in high-Re ZPG TBLs) due to the Reynolds number. Recently proposed scaling laws by Kitsios et al. (2016) and Maciel et al. (2018) are tested over a wider Reynolds-number range and for different β cases. The mean velocity and streamwise velocity fluctuation profiles are found to be dependent on the upstream development. The mean velocity profile is found to be self-similar only in the outer region, in agreement with classical theory. The mean and higher-order statistics of the new APG TBL database are made available under www.flow.kth.se.

  • 32.
    Scapin, Nicolo
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Teknisk mekanik, Strömningsmekanik och Teknisk Akustik. KTH, Centra, SeRC - Swedish e-Science Research Centre. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Costa, Pedro
    KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW. KTH, Centra, SeRC - Swedish e-Science Research Centre. KTH, Skolan för teknikvetenskap (SCI), Teknisk mekanik, Strömningsmekanik och Teknisk Akustik. Univ Iceland, Fac Ind Engn Mech Engn & Comp Sci, Hjardarhagi 2-6, IS-107 Reykjavik, Iceland..
    Brandt, Luca
    KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW. KTH, Centra, SeRC - Swedish e-Science Research Centre. KTH, Skolan för teknikvetenskap (SCI), Teknisk mekanik, Strömningsmekanik och Teknisk Akustik. KNorwegian Univ Sci & Technol NTNU, Dept Energy & Proc Engn, Trondheim, Norway..
    A volume-of-fluid method for interface-resolved simulations of phase-changing two-fluid flows2020Inngår i: Journal of Computational Physics, ISSN 0021-9991, E-ISSN 1090-2716, Vol. 407, artikkel-id 109251Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We present a numerical method for interface-resolved simulations of evaporating two-fluid flows based on the volume-of-fluid (VoF) method. The method has been implemented in an efficient EFT-based two-fluid Navier-Stokes solver, using an algebraic VoF method for the interface representation, and extended with the transport equations of thermal energy and vaporized liquid mass for the single-component evaporating liquid in an inert gas. The conservation of vaporizing liquid and computation of the interfacial mass flux are performed with the aid of a reconstructed signed-distance field, which enables the use of well-established methods for phase change solvers based on level-set methods. The interface velocity is computed with a novel approach that ensures accurate mass conservation, by constructing a divergence-free extension of the liquid velocity field onto the entire domain. The resulting approach does not depend on the type of interface reconstruction (i.e. can be employed in both algebraic and geometrical VoF methods). We extensively verified and validated the overall method against several benchmark cases, and demonstrated its excellent mass conservation and good overall performance for simulating evaporating two-fluid flows in two and three dimensions.

  • 33.
    Sheng, Xia
    et al.
    KTH, Skolan för kemi, bioteknologi och hälsa (CBH), Kemi, Organisk kemi.
    Li, Yuanyuan
    KTH, Skolan för kemi, bioteknologi och hälsa (CBH), Fiber- och polymerteknologi. KTH, Skolan för kemi, bioteknologi och hälsa (CBH), Centra, Wallenberg Wood Science Center.
    Yang, T.
    Timmer, Brian
    KTH, Skolan för kemi, bioteknologi och hälsa (CBH), Kemi, Organisk kemi.
    Willhammar, T.
    Cheung, O.
    Li, L.
    Brett, Calvin
    KTH, Skolan för teknikvetenskap (SCI), Teknisk mekanik, Strömningsmekanik och Teknisk Akustik. KTH, Skolan för kemi, bioteknologi och hälsa (CBH), Centra, Wallenberg Wood Science Center.
    Roth, Stephan V.
    KTH, Skolan för kemi, bioteknologi och hälsa (CBH), Fiber- och polymerteknologi.
    Zhang, Biaobiao
    KTH, Skolan för kemi, bioteknologi och hälsa (CBH), Kemi, Organisk kemi.
    Fan, Lizhou
    KTH, Skolan för kemi, bioteknologi och hälsa (CBH), Kemi, Organisk kemi.
    Guo, Yaxiao
    KTH, Skolan för kemi, bioteknologi och hälsa (CBH), Kemi, Organisk kemi.
    Zou, Xiaodong
    Berglund, Lars
    KTH, Skolan för kemi, bioteknologi och hälsa (CBH), Fiber- och polymerteknologi, Biokompositer.
    Sun, Licheng
    KTH, Skolan för kemi, bioteknologi och hälsa (CBH), Kemi, Organisk kemi.
    Hierarchical micro-reactor as electrodes for water splitting by metal rod tipped carbon nanocapsule self-assembly in carbonized wood2020Inngår i: Applied Catalysis B: Environmental, ISSN 0926-3373, E-ISSN 1873-3883, Vol. 264, artikkel-id 118536Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Materials design of efficient electrochemical micro-reactors is challenging, although hierarchically structured, self-standing electrodes with catalyst arrays offer promise. Herein, catalyst function in compact micro-reactor electrodes is designed by nanostructural tailoring of carbonized wood for efficient water splitting. Specifically, NiFe rod tipped, N-doped graphitic carbon nanocapsule arrays are self-assembled in hierarchical wood, and the benefit of this unique presentation and its promotive effect on accessibility of the catalyst surfaces is apparent. This report also comprises the first wood based micro-reactor electrodes for electrocatalytic water oxidation demonstrating excellent performance. The overpotential for oxygen evolution reaction was as low as 180 mV for 10 mA cm−2 current density and TOFredox was high at a level of 5.8 s−1 (at 370 mV overpotential). This hierarchical electrode can also work as bifunctional catalyst (both as anodic and as cathodic electrode) for total water splitting with a cell potential of 1.49 V for 10 mA cm−2 in alkaline solution, suggestive of their potential also in other electrochemical applications.

  • 34.
    Su, Hang
    et al.
    Politecn Milan, Dept Elect Informat & Bioengn, Via Giuseppe Colombo 40, I-20133 Milan, Italy..
    Schmirander, Yunus
    Politecn Milan, Dept Elect Informat & Bioengn, Via Giuseppe Colombo 40, I-20133 Milan, Italy..
    Valderrama-Hincapie, Sarah Elena
    Politecn Milan, Dept Elect Informat & Bioengn, Via Giuseppe Colombo 40, I-20133 Milan, Italy..
    Pinedo, Jairo
    Politecn Milan, Dept Elect Informat & Bioengn, Via Giuseppe Colombo 40, I-20133 Milan, Italy..
    Zhou, Xuanyi
    Politecn Milan, Dept Elect Informat & Bioengn, Via Giuseppe Colombo 40, I-20133 Milan, Italy.;Cent South Univ, State Key Lab High Performance Complex Mfg, Changsha 410083, Peoples R China..
    Li, Jiehao
    Politecn Milan, Dept Elect Informat & Bioengn, Via Giuseppe Colombo 40, I-20133 Milan, Italy.;Beijing Inst Technol, State Key Lab Intelligent Control & Decis Complex, Beijing 100081, Peoples R China..
    Zhang, Longbin
    KTH, Skolan för teknikvetenskap (SCI), Teknisk mekanik, Strömningsmekanik och Teknisk Akustik, Biomekanik. KTH, Skolan för teknikvetenskap (SCI), Centra, BioMEx.
    Hu, Yingbai
    Tech Univ Munich, Dept Informat, D-85748 Munich, Germany..
    Ferrigno, Giancarlo
    Politecn Milan, Dept Elect Informat & Bioengn, Via Giuseppe Colombo 40, I-20133 Milan, Italy..
    De Momi, Elena
    Politecn Milan, Dept Elect Informat & Bioengn, Via Giuseppe Colombo 40, I-20133 Milan, Italy..
    Asymmetric Bimanual Control of Dual-arm Serial Manipulator for Robot-assisted Minimally Invasive Surgeries2020Inngår i: Sensors and materials, ISSN 0914-4935, Vol. 32, nr 4, s. 1223-1233Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Robotic assistance is promising for improving minimally invasive surgery (MIS). This work presents asymmetric bimanual control of a dual-arm serial robot with two remote centers of motion (RCMs) constraints for MIS. In our previous works, general null space controllers to guarantee the fixed RCM constraint have been proposed. However, an incision on a patient's abdominal wall is not fixed owing to the respiration of the patient, which generates an uncertain disturbance at the joints of robotic manipulators. To improve accuracy, a radial basis function neural network is implemented to adapt to these disturbances and control the end-effector position. Finally, the adaptive bimanual control strategy is validated through simulations based on clinical data. The proposed control shows improved accuracy in the end effector position for all the designed surgical tasks. In future works, the algorithm will be validated on an actual dual-arm serial robot making use of a body phantom.

  • 35.
    Sánchez Abad, Nour
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW. KTH, Skolan för teknikvetenskap (SCI), Mekanik.
    Vinuesa, Ricardo
    KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW. KTH, Skolan för teknikvetenskap (SCI), Teknisk mekanik, Strömningsmekanik och Teknisk Akustik.
    Schlatter, Philipp
    KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW. KTH, Skolan för teknikvetenskap (SCI), Teknisk mekanik, Strömningsmekanik och Teknisk Akustik.
    Andersson, Magnus
    Linkoping Univ, Dept Management & Engn IEI, SE-58183 Linkoping, Sweden..
    Karlsson, Matts
    Linkoping Univ, Dept Management & Engn IEI, SE-58183 Linkoping, Sweden..
    Simulation strategies for the Food and Drug Administration nozzle using Nek50002020Inngår i: AIP Advances, ISSN 2158-3226, E-ISSN 2158-3226, Vol. 10, nr 2, artikkel-id 025033Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Computational fluid dynamics (CFD) is currently a versatile tool used for flow characterization in diverse areas of industry and research; however, its application in medical devices is less developed due to high regulatory standards for safety purposes. In this context, the development of a rigorous and standardized CFD methodology is essential in order to improve the accuracy and ensure the reliability of biomedical applications. To that end, the Food and Drug Administration (FDA) proposed a benchmark model of an idealized medical device to provide a common ground for verification and validation processes. Previous studies have evaluated the potential of conventional turbulence models to predict the relevant flow features in the FDA nozzle but have also been deemed inaccurate or exhibited high dependency on the numerical scheme. Furthermore, validation of computational results relied on previous experiments performed with particle image velocimetry (PIV), which also exhibited noticeable uncertainties. Here, we perform direct numerical simulations (DNSs) of the flow through the FDA nozzle configuration, at Reynolds numbers based on the throat diameter Re-t = 500, 2000, 3500, and 5000, using the spectral-element code Nek5000. The predictive capabilities of the synthetic-eddy method and parabolic-inflow conditions at the inlet were tested, and the results were compared with PIV data. Our results highlight the very high sensitivity of this flow case to the inflow conditions and the disturbances at the throat, particularly when predicting the laminar-turbulent jet breakdown. Due to this extreme sensitivity, any benchmark data of this geometry need to include a very detailed characterization of both the conditions at the inflow and the throat, in order to enable relevant comparisons.

  • 36.
    Tanarro, Alvaro
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW. KTH, Centra, SeRC - Swedish e-Science Research Centre.
    Mallor, Fermin
    KTH, Skolan för teknikvetenskap (SCI), Teknisk mekanik, Strömningsmekanik och Teknisk Akustik. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW. KTH, Centra, SeRC - Swedish e-Science Research Centre.
    Offermans, Nicolas
    KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Peplinski, Adam
    KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW. KTH, Centra, SeRC - Swedish e-Science Research Centre.
    Vinuesa, Ricardo
    KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW. KTH, Centra, SeRC - Swedish e-Science Research Centre.
    Schlatter, Philipp
    KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW. KTH, Centra, SeRC - Swedish e-Science Research Centre.
    Enabling adaptive mesh refinement for spectral-element simulations of turbulence around wing sectionsInngår i: Artikkel i tidsskrift (Annet vitenskapelig)
    Abstract [en]

    The implementation of adaptive mesh refinement (AMR) in the spectral-element method code Nek5000 is used for the first time on the well-resolved large-eddy  simulation (LES) of the turbulent flow over wings. In particular, the flow over a NACA4412 profile with a 5° angle of attack at chord-based Reynolds number Rec=200,000 is analysed in the present work. The mesh, starting from a coarse resolution, is progressively refined by means of AMR, which allows for high resolution near the wall and wake whereas significantly larger elements are used in the far-field. The resulting mesh is of higher resolution than those in previous conformal cases, and it allows for the use of larger computational domains, avoiding the use of precursor RANS simulations to determine the boundary conditions. All of this with, approximately, 3 times lower total number of grid points if the same spanwise length is used. Turbulence statistics obtained in the AMR simulation show good agreement with the ones obtained with the conformal mesh. Finally, using AMR on wings will enable simulations at Rec beyond 1 million, thus allowing the study of pressure-gradient effects at high Reynolds numbers relevant for practical applications.

  • 37.
    Tanarro, Alvaro
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Teknisk mekanik, Strömningsmekanik och Teknisk Akustik. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW. KTH, Centra, SeRC - Swedish e-Science Research Centre.
    Vinuesa, Ricardo
    KTH, Skolan för teknikvetenskap (SCI), Teknisk mekanik, Strömningsmekanik och Teknisk Akustik. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW. KTH, Centra, SeRC - Swedish e-Science Research Centre.
    Schlatter, Philipp
    KTH, Skolan för teknikvetenskap (SCI), Teknisk mekanik, Strömningsmekanik och Teknisk Akustik. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW. KTH, Centra, SeRC - Swedish e-Science Research Centre.
    Effect of adverse pressure gradients on turbulent wing boundary layers2020Inngår i: Journal of Fluid Mechanics, ISSN 0022-1120, E-ISSN 1469-7645, Vol. 883, nr A8, s. 1-28Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

        The characteristics of turbulent boundary layers (TBLs) subjected to adverse pressure gradients are analysed through well-resolved large-eddy simulations. The geometries under study are the NACA0012 and NACA4412 wing sections, at 0 and 5 degrees angle of attack, respectively, both of them at a Reynolds number based on inflow velocity and chord length Rec = 400,000. The turbulence statistics show that adverse pressure gradients (APGs) have a significant effect on the mean velocity, velocity fluctuations and turbulent kinetic energy budget, and this effect is more prominent on the outer region of the boundary layer. Furthermore, the effect of flow history is assessed by means of an integrated Clauser pressure-gradient parameter, β, through the study of cases with matching local values of β and the friction Reynolds number, Reτ, to isolate this effect. Our results show a noticeable effect of the flow history on the outer region, however the differences in the near-wall peak of the tangential velocity fluctuations appear to be mostly produced by the local APG magnitude. The one-dimensional power-spectral density shows energetic small scales in the outer region of APG TBLs, whereas these energetic scales do not appear in zero-pressure-gradient (ZPG) TBLs, suggesting that small scales near the wall are advected towards the outer layer by the APG. Moreover, the linear coherence spectra show that the spectral outer peak of high-Reynolds-number ZPG TBLs is highly correlated with the near-wall region , unlike APG TBLs which do not show such a correlation. This result, together with the different two-dimensional spectra of APG and high-Reynolds-number ZPG TBLs, suggests different energisation mechanisms due to APG and increase in Reynolds number. To the authors' knowledge, this is the first in-depth analysis of the TBL characteristics over wings, including detailed single-point statistics, spectra and coherence.

  • 38.
    Vinuesa, Ricardo
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Teknisk mekanik, Strömningsmekanik och Teknisk Akustik. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Azizpour, Hossein
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Intelligenta system, Robotik, perception och lärande, RPL.
    Leite, Iolanda
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Intelligenta system, Robotik, perception och lärande, RPL.
    Balaam, Madeline
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Människocentrerad teknologi, Medieteknik och interaktionsdesign, MID.
    Dignum, V.
    Domisch, S.
    Felländer, A.
    Langhans, S. D.
    Tegmark, M.
    Nerini, Francesco Fuso
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Energisystemanalys.
    The role of artificial intelligence in achieving the Sustainable Development Goals2020Inngår i: Nature Communications, ISSN 2041-1723, E-ISSN 2041-1723, Vol. 11, nr 1, artikkel-id 233Artikkel, forskningsoversikt (Fagfellevurdert)
    Abstract [en]

    The emergence of artificial intelligence (AI) and its progressively wider impact on many sectors requires an assessment of its effect on the achievement of the Sustainable Development Goals. Using a consensus-based expert elicitation process, we find that AI can enable the accomplishment of 134 targets across all the goals, but it may also inhibit 59 targets. However, current research foci overlook important aspects. The fast development of AI needs to be supported by the necessary regulatory insight and oversight for AI-based technologies to enable sustainable development. Failure to do so could result in gaps in transparency, safety, and ethical standards.

  • 39.
    Vinuesa, Ricardo
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW. KTH, Skolan för teknikvetenskap (SCI), Teknisk mekanik, Strömningsmekanik och Teknisk Akustik.
    Azizpour, Hossein
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Intelligenta system, Robotik, perception och lärande, RPL.
    Leite, Iolanda
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Intelligenta system, Robotik, perception och lärande, RPL.
    Balaam, Madeline
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Människocentrerad teknologi, Medieteknik och interaktionsdesign, MID.
    Dignum, Virginia
    Umeå Univ, Responsible AI Grp, Dept Comp Sci, SE-90358 Umeå, Sweden..
    Domisch, Sami
    Leibniz Inst Freshwater Ecol & Inland Fisheries, Muggelseedamm 310, D-12587 Berlin, Germany..
    Fellander, Anna
    AI Sustainabil Ctr, SE-11434 Stockholm, Sweden..
    Daniela Langhans, Simone
    BC3, Leioa 48940, Spain.;Univ Otago, Dept Zool, 340 Great King St, Dunedin 9016, New Zealand..
    Tegmark, Max
    MIT, Ctr Brains Minds & Machines, 77 Massachusetts Ave, Cambridge, MA 02139 USA..
    Nerini, Francesco Fuso
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Energisystemanalys. KTH Royal Inst Technol, Unit Energy Syst Anal DESA, Brinellvagen 68, SE-1004 Stockholm, Sweden..
    The role of artificial intelligence in achieving the Sustainable Development Goals2020Inngår i: Nature Communications, ISSN 2041-1723, E-ISSN 2041-1723, Vol. 11, nr 1, artikkel-id 233Artikkel, forskningsoversikt (Fagfellevurdert)
    Abstract [en]

    The emergence of artificial intelligence (AI) and its progressively wider impact on many sectors requires an assessment of its effect on the achievement of the Sustainable Development Goals. Using a consensus-based expert elicitation process, we find that AI can enable the accomplishment of 134 targets across all the goals, but it may also inhibit 59 targets. However, current research foci overlook important aspects. The fast development of AI needs to be supported by the necessary regulatory insight and oversight for AI-based technologies to enable sustainable development. Failure to do so could result in gaps in transparency, safety, and ethical standards.

  • 40.
    Vinuesa, Ricardo
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Teknisk mekanik, Strömningsmekanik och Teknisk Akustik. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW. KTH, Centra, SeRC - Swedish e-Science Research Centre.
    Peplinski, Adam
    KTH, Skolan för teknikvetenskap (SCI), Teknisk mekanik, Strömningsmekanik och Teknisk Akustik. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW. KTH, Centra, SeRC - Swedish e-Science Research Centre.
    Atzori, Marco
    KTH, Skolan för teknikvetenskap (SCI), Teknisk mekanik, Strömningsmekanik och Teknisk Akustik.
    Fick, Lambert
    MCS Division, Argonne National Laboratory, 9700 Cass Ave., Lemont, Illinois 60439, USA.
    Marin, Oana
    MCS Division, Argonne National Laboratory, 9700 Cass Ave., Lemont, Illinois 60439, USA.
    Merzari, Elia
    MCS Division, Argonne National Laboratory, 9700 Cass Ave., Lemont, Illinois 60439, USA.
    Negi, Prabal
    KTH, Skolan för teknikvetenskap (SCI), Teknisk mekanik, Strömningsmekanik och Teknisk Akustik. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW. KTH, Centra, SeRC - Swedish e-Science Research Centre.
    Tanarro, Alvaro
    Schlatter, Philipp
    KTH, Tidigare Institutioner (före 2005), Mekanik. KTH, Centra, SeRC - Swedish e-Science Research Centre. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Turbulence statistics in a spectral-element code: a toolbox for high-fidelity simulationsManuskript (preprint) (Annet vitenskapelig)
  • 41.
    Wang, Bochao
    KTH, Skolan för teknikvetenskap (SCI), Teknisk mekanik, Strömningsmekanik och Teknisk Akustik, Marcus Wallenberg Laboratoriet MWL.
    Constitutive models of magneto-sensitive rubber under a continuum mechanics basis and the application in vibration isolation2020Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    Due to its durability, stretchability, relatively low stiffness and high damping, rubber is widely used in engineering anti-vibration fields. However, a major deficiency is that once installed, the mechanical properties of traditional rubber-based devices are fixed where its adaptability to various loading conditions is poor. An alternative to traditional rubber materials is magneto-sensitive (MS) rubber. The main componentsof MS rubber are a rubber matrix and ferromagnetic particles. Under a magnetic field, the modulus of MS rubber can be altered rapidly and reversibly. Therefore, compared with conventional rubber-based devices, the stiffness of MS rubber-based devices can be adapted to various loading conditions and an enhanced vibration reduction effect can be achieved. Measurement results revealed that the mechanical behavior of MS rubber is not simple. To be specific, the dynamic modulus of MS rubber has a magnetic, frequency,amplitude and temperature dependency. In order to promote the applications of MS rubber in the anti-vibration area, models to depict the above properties are needed. The main goal of this thesis is to model the magnetic, frequency, amplitude and temperature dependence of MS rubber under a continuum mechanics basis. The research results regarding the constitutive modeling consist of three papers (Paper A, C and D). The simulation results show a good agreement with the measurement data, which proves the accuracy and feasibility of the developed model. In addition to the constitutive models of MS rubber, an investigation of MS rubber application in the vibration isolation system under harmonic and random loading cases is numerically conducted (Paper B). In order to achieve an enhanced vibration isolation effect, two control algorithms corresponding to the harmonic and random loading are developed. Numerical results verify that the vibration isolation effect ofMS rubber vibration isolator is better than the traditional rubber-based isolator. In this thesis, the model developed for MS rubber deepens the understanding of how magnetic, frequency, amplitude and temperature affect the mechanical performance of MS rubber. Moreover, the research of MS rubber application in vibration isolators and the corresponding control strategies are helpful for the design of MS rubber-based anti-vibration devices.

    Fulltekst (pdf)
    Constitutive models of magneto-sensitive rubber under a continuum mechanics basis and the application in vibration isolation
  • 42.
    Wang, Bochao
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Teknisk mekanik, Strömningsmekanik och Teknisk Akustik, Marcus Wallenberg Laboratoriet MWL.
    Kari, Leif
    KTH, Skolan för teknikvetenskap (SCI), Teknisk mekanik, Strömningsmekanik och Teknisk Akustik, Marcus Wallenberg Laboratoriet MWL.
    A visco-elastic-plastic constitutive model of isotropic magneto-sensitive rubber with amplitude, frequency and magnetic dependency2020Inngår i: International journal of plasticity, ISSN 0749-6419, E-ISSN 1879-2154Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A three-dimensional visco-elastic-plastic constitutive model of isotropic magneto-sensitive (MS) rubber with amplitude, frequency and magnetic dependency under a continuum constitutive framework is developed. MS rubber is akind of smart material mainly composed of a rubber matrix and magnetizable particles. Under a magnetic field, there is an increase of its dynamic modulus due to the interaction between the magnetic field and MS rubber, which is often referred to as the magnetic dependency of MS rubber. Experimental results reveal that besides the magnetic dependency, there is a frequency and amplitude dependency of its dynamic modulus. In specific, the modulus of MS rubber increases with increasing frequency and dereases with increasing strain amplitude. To depict the above properties and to consider the balance of energy in continuum mechanics framework, a new constitutive model consisting of a viscoelastic fractional derivative element, a bounding surface model in series with a neo-Hookean elastic model with magnetic sensitivity and a magnetic stress tensor term for MS rubber is proposed. The contribution of this constitutive model is that by using a free energy based method, with only eight material parameters, the amplitude, frequency and magnetic dependency of MS rubber can be reflected. After parameter identification, the simulationresults show a good agreement with those of measurements. Therefore, by utilizing the model proposed, the ability of approaching the dynamic behavior of MS rubber-based vibration reduction devices in the design phase is possible which contributes to the application of MS rubber in noise and vibration reduction area.

  • 43.
    Wang, Bochao
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Teknisk mekanik, Strömningsmekanik och Teknisk Akustik, Marcus Wallenberg Laboratoriet MWL.
    Kari, Leif
    KTH, Skolan för teknikvetenskap (SCI), Teknisk mekanik, Strömningsmekanik och Teknisk Akustik, Marcus Wallenberg Laboratoriet MWL.
    Constitutive model of isotropic magneto-sensitive rubber with amplitude, frequency, magnetic and temperature dependence under a continuum mechanics basis2020Inngår i: International Journal of Engineering Science, ISSN 0020-7225, E-ISSN 1879-2197Artikkel i tidsskrift (Annet vitenskapelig)
    Abstract [en]

    A three-dimensional nonlinear constitutive model of the amplitude, frequency, magnetic and temperature-dependent mechanical properties of isotropic magneto-sensitive (MS) rubber is developed. The main components of MS rubberis an elastomer matrix and magnetizable particles. When a magnetic field is applied, the modulus of MS rubber increases, which is known as the magnetic dependence of MS rubber. In addition to the magnetic dependence, there arefrequency, amplitude and temperature dependencies of MS rubber. Specifically, a higher frequency, a smaller strain amplitude and a lower temperature lead to an increased magnitude of the dynamic modulus. To represent the above properties and to stimulate the possible application of MS rubber in the anti-vibration area, a continuum mechanic framework based constitutive model consisting of a fractional standard linear solid (SLS) element, an elastoplastic element and a magnetic stress term of MS rubber is developed. The frequency and amplitude dependencies are depicted by a fractional SLS element and an elastoplastic element, respectively. A hyperbolic tangent function with a scalar product of magnetic flux density as an independent variable is introduced to consider the magnetic dependence. Furthermore, the temperature dependence is taken into account by including the William-Landel-Ferry function and the Arrhenius function to the fractional SLS element and the elastoplastic element, respectively. The technical innovation of this constitutive model is that the amplitude, frequency, magnetic and temperature dependent mechanical properties of MS rubber are incorporated into a whole constitutive model under the continuum mechanics frame and based on the free energy assumption. Comparison between the simulation and measurement results in a wide frequency range with different levels of magnetic field, strain amplitude and temperature shows that the fitting effect of the developed model is very good. Therefore, the constitutive model proposed in this paper enables the prediction ofthe mechanical properties of MS rubber under various operating conditions with high accuracy, which will drive MS rubber’s application in engineering applications, especially in the area of MS rubber-based anti-vibration devices.

  • 44.
    Wei, Jianzheng
    et al.
    Harbin Inst Technol, Natl Key Lab Sci & Technol Composites Special Env, Harbin 150080, Peoples R China..
    Yu, Jianxin
    Harbin Inst Technol, Natl Key Lab Sci & Technol Composites Special Env, Harbin 150080, Peoples R China..
    Tan, Huifeng
    Harbin Inst Technol, Natl Key Lab Sci & Technol Composites Special Env, Harbin 150080, Peoples R China..
    Wang, Weizhi
    China Aerosp Sci & Technol Corp, Beijing Inst Space Mech & Elect, Beijing 100094, Peoples R China..
    Eriksson, Anders
    KTH, Skolan för teknikvetenskap (SCI), Teknisk mekanik, Strömningsmekanik och Teknisk Akustik, Strukturmekanik.
    Design and testing of inflatable gravity-gradient booms in space2020Inngår i: CEAS Space Journal, ISSN 1868-2502, E-ISSN 1868-2510, Vol. 12, nr 1, s. 33-41Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Inflatable space structures have many advantages such as small size, high reliability, and low cost. Aiming at a gravity-gradient boom for an XY-1 satellite, New Technology Verifying Satellite-1, a slender inflatable boom with low magnetic is presented. First of all, an inflatable boom with six self-supporting thin shells made of carbon and Vectran fiber composite materials on the inner wall was designed for eliminating a magnetic dipole moment and increasing structural stiffness. A precise stowage was designed for a tip mass surrounded by a pair of lightweight honeycomb blocks added on the top of the boom. The stowed boom was tested by sine sweep vibrations with three directions on the ground to verify the reasonable design. The XY-1 satellite which carried the inflatable boom was launched into low orbit. After being stowed state in space for at least 6 months, the inflatable boom orderly unfolded a 2.0 kg tip mass to 3.0 m away in May, 2013. The inflatable boom was successfully deployed from a series of photographs received on the satellite. The results show that this kind of lightweight inflatable boom with self-supporting thin shells can orderly unfold and fulfil the function of gravity-gradient in space for a long time.

  • 45.
    $$$Yousefi, Ali
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik. KTH, Centra, SeRC - Swedish e-Science Research Centre. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Costa, Pedro
    KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW. KTH, Centra, SeRC - Swedish e-Science Research Centre. KTH, Skolan för teknikvetenskap (SCI), Teknisk mekanik, Strömningsmekanik och Teknisk Akustik. Univ Iceland, Fac Ind Engn Mech Engn & Comp Sci, Hjardarhagi 2-6, IS-107 Reykjavik, Iceland..
    Brandt, Luca
    KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW. KTH, Centra, SeRC - Swedish e-Science Research Centre. KTH, Skolan för teknikvetenskap (SCI), Teknisk mekanik, Strömningsmekanik och Teknisk Akustik.
    Single sediment dynamics in turbulent flow over a porous bed - insights from interface-resolved simulations2020Inngår i: Journal of Fluid Mechanics, ISSN 0022-1120, E-ISSN 1469-7645, Vol. 893, artikkel-id A24Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We use interface-resolved direct numerical simulations to study the dynamics of a single sediment particle in a turbulent open channel flow over a fixed porous bed. The relative strength of the gravitational acceleration, quantified by the Galileo number, is varied so as to reproduce the different modes of sediment transport - resuspension, saltation and rolling. The results show that the sediment dynamics at lower Galileo numbers (i.e. resuspension and saltation) are mainly governed by the mean flow. Here, the regime of motion can be predicted by the ratio between the gravity and the shear-induced boundary force. In these cases, the sediment particle rapidly takes off when exposed to the flow, and proceeds with an oscillatory motion. Increasing the Galileo number, the frequency of these oscillations increases and their amplitude decreases, until the transport mode switches from resuspension to saltation. In this case, the sediment travels by short successive collisions with the bed. Further increasing the Galileo number, the particle rolls without detaching from the bed. Differently from the previous modes, the motion is triggered by extreme turbulent events, and the particle response depends on the specific initial conditions, at fixed Reynolds number. The results reveal that close to the onset of sediment motion, only turbulent sweeps can effectively trigger the particle motion by increasing the stagnation pressure upstream. We show that for the parameters in this study, a criterion based on the streamwise flow-induced force can successfully predict the incipient movement.

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