scholarly journals 3D DEM simulations of monotonic interface behaviour between cohesionless sand and rigid wall of different roughness

2020 ◽  
Author(s):  
A. Grabowski ◽  
M. Nitka ◽  
J. Tejchman
Keyword(s):  
Normal Stress ◽  
Three Dimensional ◽  
Rigid Wall ◽  
Interface Roughness ◽  
Wall Friction ◽  
Dem Simulations ◽  
New Perspective ◽  
Interface Behaviour ◽  
Good Agreement ◽  
Three Dimensional Simulations

Abstract The paper deals with three-dimensional simulations of a monotonic quasi-static interface behaviour between cohesionless sand and a rigid wall of different roughness during wall friction tests in a parallelly guided direct shear test under constant normal stress. Numerical modelling was carried out by the discrete element method (DEM) using spheres with contact moments to approximately capture a non-uniform particle shape. The varying wall surface topography was simulated by a regular mesh of triangular grooves (asperities) along the wall with a different height, distance and inclination. The calculations were carried out with different initial void ratios of sand and vertical normal stress. The focus was to quantify the effect of wall roughness on the evolution of mobilized wall friction and shear localization, also to specify the ratios between slip and rotation and between shear stress/force and couple stress/moment in the sand at the wall. DEM simulations were generally in good agreement with reported experimental results for similar interface roughness. The findings presented in this paper offer a new perspective on the understanding of the wall friction phenomenon in granular bodies.

scholarly journals Comparative 3D DEM simulations of sand–structure interfaces with similarly shaped clumps versus spheres with contact moments

2021 ◽  
Author(s):  
A. Grabowski ◽  
M. Nitka ◽  
J. Tejchman
Keyword(s):  
Particle Shape ◽  
Friction Angle ◽  
Rigid Wall ◽  
Numerical Results ◽  
Contact Forces ◽  
Interface Roughness ◽  
Interface Shear ◽  
Dem Simulations ◽  
Micropolar Continua ◽  
Interface Behaviour

AbstractThree-dimensional simulations of a monotonic quasi-static interface behaviour between initially dense cohesionless sand and a rigid wall of different roughness during tests in a parallelly guided direct shear test under constant normal stress are presented. Numerical modelling was carried out by the discrete element method (DEM) using clumps in the form of convex non-symmetric irregularly shaped grains. The clumps had an aspect ratio of 1.5. A regular grid of triangular grooves (asperities) along the wall with a different height at the same distance was assumed. The numerical results with clumps were directly compared under the same conditions with our earlier DEM simulations using pure spheres with contact moments with respect to the peak and residual interface friction angle, width of the interface shear zone, ratio between grain slips and grain rotations, distribution of contact forces and stresses. The difference between the behaviour of clumps and pure spheres with contact moments proved to be noticeable in the post-peak regime due to a different particle shape. The rolling resistance model with pure spheres was proved to be limited for capturing particle shape effects. Three different boundary conditions along the interface were proposed for micropolar continua, considering grain rotations and grain slips, wall grain moments and wall grain forces, and normalized interface roughness. The numerical results in this paper offer a better understanding of the interface behaviour of granular bodies in DEM and FEM simulations.

Vortex rings impinging on walls: axisymmetric and three-dimensional simulations

1993 ◽  
Vol 256 ◽  
pp. 615-646 ◽  
Author(s):  
Paolo Orlandi ◽  
Roberto Verzicco
Keyword(s):  
Numerical Simulations ◽  
Strain Tensor ◽  
Three Dimensional ◽  
Reynolds Numbers ◽  
Vortex Rings ◽  
Compression Phase ◽  
Vortex Pairing ◽  
The Impact ◽  
Good Agreement ◽  
Three Dimensional Simulations

Accurate numerical simulations of vortex rings impinging on flat boundaries revealed the same features observed in experiments. The results for the impact with a free-slip wall compared very well with previous numerical simulations that used spectral methods, and were also in qualitative agreement with experiments. The present simulation is mainly devoted to studying the more realistic case of rings interacting with a no-slip wall, experimentally studied by Walker et al. (1987). All the Reynolds numbers studied showed a very good agreement between experiments and simulations, and, at Rev > 1000 the ejection of a new ring from the wall was seen. Axisymmetric simulations demonstrated that vortex pairing is the physical mechanism producing the ejection of the new ring. Three-dimensional simulations were also performed to investigate the effects of azimuthal instabilities. These simulations have confirmed that high-wavenumber instabilities originate in the compression phase of the secondary ring within the primary one. The large instability of the secondary ring has been explained by analysis of the rate-of-strain tensor and vorticity alignment. The differences between passive scalars and the vorticity field have been also investigated.

Numerical Investigation on Unstable Oscillations of Two Circular Cylinders in Tandem Arrangement

2003 ◽  
Author(s):  
Yoshiaki Itoh ◽  
Ryutaro Himeno
Keyword(s):  
Finite Difference ◽  
Finite Difference Method ◽  
Numerical Investigation ◽  
Difference Method ◽  
Three Dimensional ◽  
Circular Cylinders ◽  
Damping Force ◽  
Negative Damping ◽  
Good Agreement ◽  
Three Dimensional Simulations

Three-dimensional simulations of incompressible and viscous flow around tandem circular cylinders at Re = 20000 in unstable oscillations can be carried out by means of finite difference method without any turbulence model. The numerical response behaviors are in good agreement with the previous experimental ones. The mechanism of negative damping force in vortex-induced oscillations and wake-galloping is investigated.

Yield and shear of rough interlocked faults: analytical solution and experimental observations

2020 ◽  
Author(s):  
Amir Sagy ◽  
Vladimir Lyakhovsky ◽  
Yossef H. Hatzor
Keyword(s):  
Surface Roughness ◽  
Analytical Solution ◽  
Normal Stress ◽  
Laboratory Experiments ◽  
Three Dimensional ◽  
Elastic Half Space ◽  
Interface Roughness ◽  
Displacement Rate ◽  
Initial Surface ◽  
Surface Geometry

<p>Natural fault surfaces are interlocked, partly cohesive, and display multiscale geometric irregularities. Here we examine the nucleation of deformation and the evolution of shear in such interlocked surfaces using a closed-form analytical solution and a series of laboratory experiments.  The analytical model considers an interlocked interface with multiscale roughness between two linear elastic half-space blocks. The interface geometry is based on three-dimensional fault surfaces imaging. It is represented by a Fourier series and the plane strain solution for the elastic stress distribution is represented as a sum of the constant background stress generated by a uniform far-field loading and perturbations associated with the interface roughness. The model predicts the critical stress necessary for failure and the location of failure nucleation sites across the surface, as function of the initial surface geometry.</p><p>A similar configuration is adopted in laboratory experiments as carbonate blocks with rough interlocked surfaces generated by tensional fracturing are sheared in a servo-controlled direct shear apparatus. Resistance to shear and surface roughness evolution are measured under variable normal stresses, slip distances and slip rates.  We find that the evolution of surface morphology with shear is closely related to the loading configuration. Initially rough, interlocked, surfaces become rougher when normal stress and displacement rate are increased. Under a fixed, relatively low normal stress and fixed displacement rate however, the surfaces become smoother with increasing displacement distance.  </p><p>The shear of the interlocked slip surfaces is associated with volumetric deformation, wear and frictional slip, all of which are typically observed across natural fault zones. We suggest that their intensities and partitioning are strongly affected by the initial surface roughness characteristics, the background stress, and the rate and magnitude of shear displacement. </p>

scholarly journals Computational Modeling of Protective Clothing

2003 ◽  
Vol os-12 (3) ◽  
pp. 1558925003os-12
Author(s):  
James J. Barry ◽  
Principal Engineer ◽  
Roger W. Hill
Keyword(s):  
Emergency Response ◽  
Protective Clothing ◽  
Three Dimensional ◽  
Convective Transport ◽  
Variable Properties ◽  
Computational Fluid Dynamics Cfd ◽  
Garment Design ◽  
Protective Garment ◽  
Good Agreement ◽  
Three Dimensional Simulations

Models based on computational fluid dynamics (CFD) have been developed to predict the performance of chemical and steam/fire protective clothing. The software computes the diffusive and convective transport of heat and gases/vapors; capillary transport of liquids; vapor and liquid sorption phenomena and phase change; and the variable properties of the various clothing layers. It can also model the effects of sweating and humidity transport to help assess the thermal stress imposed on the wearer of the clothing. Specialized geometry/grid representations of clothed humans have been created for performing two- and three-dimensional simulations. Comparisons with experimental data show good agreement in predicting the effects of fiber swell due to transients in humidity, and the models have been used to predict the sensitivity of clothing performance to material properties such as permeability under varying environmental conditions. Applications of the models include analysis of chemical protective garment design for military and emergency response personnel, comparisons of thermally protective materials for steam or fire protection, and evaluation of clothing test data.

scholarly journals Magnetic levitational bioassembly of 3D tissue construct in space

2020 ◽  
Vol 6 (29) ◽  
pp. eaba4174 ◽  
Author(s):  
Vladislav A. Parfenov ◽  
Yusef D. Khesuani ◽  
Stanislav V. Petrov ◽  
Pavel A. Karalkin ◽  
Elizaveta V. Koudan ◽  
...  
Keyword(s):  
Tissue Engineering ◽  
Three Dimensional ◽  
Label Free ◽  
Tissue Constructs ◽  
Advanced Stages ◽  
Feasible Alternative ◽  
New Perspective ◽  
First Time ◽  
Conceptual Advance ◽  
Good Agreement

Magnetic levitational bioassembly of three-dimensional (3D) tissue constructs represents a rapidly emerging scaffold- and label-free approach and alternative conceptual advance in tissue engineering. The magnetic bioassembler has been designed, developed, and certified for life space research. To the best of our knowledge, 3D tissue constructs have been biofabricated for the first time in space under microgravity from tissue spheroids consisting of human chondrocytes. Bioassembly and sequential tissue spheroid fusion presented a good agreement with developed predictive mathematical models and computer simulations. Tissue constructs demonstrated good viability and advanced stages of tissue spheroid fusion process. Thus, our data strongly suggest that scaffold-free formative biofabrication using magnetic fields is a feasible alternative to traditional scaffold-based approaches, hinting a new perspective avenue of research that could significantly advance tissue engineering. Magnetic levitational bioassembly in space can also advance space life science and space regenerative medicine.

scholarly journals Mix experiments using a two-dimensional convergent shock-tube

2003 ◽  
Vol 21 (3) ◽  
pp. 403-409 ◽  
Author(s):  
D.A. HOLDER ◽  
A.V. SMITH ◽  
C.J. BARTON ◽  
D.L. YOUNGS
Keyword(s):  
Shock Tube ◽  
Turbulent Mixing ◽  
Three Dimensional ◽  
Gas Mixture ◽  
Mixing Process ◽  
Dense Gas ◽  
Atomic Weapons ◽  
Air Void ◽  
Good Agreement ◽  
Three Dimensional Simulations

This article reports the first Richtmyer–Meshkov instability experiments using an improved version of the Atomic Weapons Establishment convergent shock tube. These investigate the shock-induced turbulent mixing across the interfaces of an air/dense gas/air region. Multipoint ignition of a detonatable gas mixture produces a cylindrically convergent shock that travels into a test cell containing the dense gas region. The mixing process is imaged with shadowgraphy. Sample results are presented from an unperturbed experiment and one with a notch perturbation imposed on one of the dense gas interfaces. The unperturbed experiment shows the mixing across the dense gas boundaries and the motion of the bulk dense gas region. Imposition of the notch perturbation produces a mushroom-shaped air void penetrating the dense gas region. Three-dimensional simulations performed using the AWE TURMOIL3D code are presented and compared with the sample experimental results. A very good agreement is demonstrated. Conducting these first turbulent mixing experiments has highlighted a number of areas for future development of the convergent shock-tube facility; these are also presented.

scholarly journals Damping of quasi-two-dimensional internal wave attractors by rigid-wall friction

2018 ◽  
Vol 841 ◽  
pp. 614-635 ◽  
Author(s):  
F. Beckebanze ◽  
C. Brouzet ◽  
I. N. Sibgatullin ◽  
L. R. M. Maas
Keyword(s):  
Viscous Dissipation ◽  
Gravity Waves ◽  
Three Dimensional ◽  
Rigid Wall ◽  
Internal Gravity Waves ◽  
Shear Layers ◽  
Wall Friction ◽  
Extended Model ◽  
Two Dimensional ◽  
Lateral Walls

The reflection of internal gravity waves at sloping boundaries leads to focusing or defocusing. In closed domains, focusing typically dominates and projects the wave energy onto ‘wave attractors’. For small-amplitude internal waves, the projection of energy onto higher wavenumbers by geometric focusing can be balanced by viscous dissipation at high wavenumbers. Contrary to what was previously suggested, viscous dissipation in interior shear layers may not be sufficient to explain the experiments on wave attractors in the classical quasi-two-dimensional trapezoidal laboratory set-ups. Applying standard boundary layer theory, we provide an elaborate description of the viscous dissipation in the interior shear layer, as well as at the rigid boundaries. Our analysis shows that even if the thin lateral Stokes boundary layers consist of no more than 1 % of the wall-to-wall distance, dissipation by lateral walls dominates at intermediate wave numbers. Our extended model for the spectrum of three-dimensional wave attractors in equilibrium closes the gap between observations and theory by Hazewinkel et al. (J. Fluid Mech., vol. 598, 2008, pp. 373–382).

scholarly journals Stratification effects on shoaling internal solitary waves

2021 ◽  
Vol 933 ◽  
Author(s):  
Samuel G. Hartharn-Evans ◽  
Magda Carr ◽  
Marek Stastna ◽  
Peter A. Davies
Keyword(s):  
Density Gradient ◽  
Solitary Waves ◽  
Lower Layer ◽  
Three Dimensional ◽  
Internal Solitary Waves ◽  
Wave Steepness ◽  
Topographic Slope ◽  
Upper Boundary ◽  
Good Agreement ◽  
Three Dimensional Simulations

This combined numerical/laboratory study investigates the effect of stratification form on the shoaling characteristics of internal solitary waves propagating over a smooth, linear topographic slope. Three stratification types are investigated, namely (i) thin tanh (homogeneous upper and lower layers separated by a thin pycnocline), (ii) surface stratification (linearly stratified layer overlaying a homogeneous lower layer) and (iii) broad tanh (continuous density gradient throughout the water column). It is found that the form of stratification affects the breaking type associated with the shoaling wave. In the thin tanh stratification, good agreement is seen with past studies. Waves over the shallowest slopes undergo fission. Over steeper slopes, the breaking type changes from surging, through collapsing to plunging with increasing wave steepness $A_w/L_w$ for a given topographic slope, where $A_w$ and $L_w$ are incident wave amplitude and wavelength, respectively. In the surface stratification regime, the breaking classification differs from the thin tanh stratification. Plunging dynamics is inhibited by the density gradient throughout the upper layer, instead collapsing-type breakers form for the equivalent location in parameter space in the thin tanh stratification. In the broad tanh profile regime, plunging dynamics is likewise inhibited and the near-bottom density gradient prevents the collapsing dynamics. Instead, all waves either fission or form surging breakers. As wave steepness in the broad tanh stratification increases, the bolus formed by surging exhibits evidence of Kelvin–Helmholtz instabilities on its upper boundary. In both two- and three-dimensional simulations, billow size grows with increasing wave steepness, dynamics not previously observed in the literature.

The Effect of Roughness Features on Mos Surface Electric Field and Fowler-Nordheim Tunneling Behavior

1997 ◽  
Vol 473 ◽  
Author(s):  
Heng-Chih Lin ◽  
Edwin C. Kan ◽  
Toshiaki Yamanaka ◽  
Simon J. Fang ◽  
Kwame N. Eason ◽  
...  
Keyword(s):  
Electric Field ◽  
Three Dimensional ◽  
Tunneling Current ◽  
Gate Oxide ◽  
Oxide Thickness ◽  
Interface Roughness ◽  
Normal Electric Field ◽  
Surface Electric Field ◽  
Tunneling Behavior ◽  
Nordheim Tunneling

ABSTRACTFor future CMOS GSI technology, Si/SiO2 interface micro-roughness becomes a non-negligible problem. Interface roughness causes fluctuations of the surface normal electric field, which, in turn, change the gate oxide Fowler-Nordheim tunneling behavior. In this research, we used a simple two-spheres model and a three-dimensional Laplace solver to simulate the electric field and the tunneling current in the oxide region. Our results show that both quantities are strong functions of roughness spatial wavelength, associated amplitude, and oxide thickness. We found that RMS roughness itself cannot fully characterize surface roughness and that roughness has a larger effect for thicker oxide in terms of surface electric field and tunneling behavior.

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