Static friction, differential algebraic systems and numerical stability

AbstractWe show how Differential Algebraic Systems (Ordinary Differential Equations with algebraic constraints) in mechanics are affected by stability issues and we implement Lubich’s projection method to reduce the error to practically zero. Then, we explain how the “numerically exact” implementation for static friction by Differential Algebraic Systems can be stabilized. We conclude by comparing the corresponding steps in the “Contact mechanics” introduced by Moreau

Simulating the Influence of Particle Geometry and Arrangement on the Collapse of a Submerged Granular Step

Insights into the behaviour of fluid-saturated granular media, by using a simulation that combines the Discrete Element Method for the granular particles and the Finite Element Method for the fluid

Avalanching of variously shaped DEM particles

Grains in most technically relevant granular materials are non-convex, while in discreteelement-simulations, convex particle shapes dominate. While differences in the physical behavior can be expected, the actual observables where these effects manifest are far from clear. In this research, we investigate how in a rotating two-dimensional drum, the physical behavior for rounded, irregular convex as well as non-convex shapes differs

Simulation of incompressible viscous flow using finite element method

This study focused on simulating incompressible viscous flow using the finite element method. This study used velocity and pressure as unknowns known as primitive variable formulations. Simulation of incompressible fluid flow poses numerical challenges due to the presence of nonlinear convective terms in Navier-Stokes equations and the incompressible nature of the fluid. If the connection between velocities and pressure is not discretized correctly, the stable and convergent velocities might be gained, but the obtained pressure will be oscillatory. To avoid these difficulties, continuous quadratic and additional cubic bubble functions will be used for the velocity field and linear functions for the pressure field. This kind of discretization satisfies the Ladyzhenskaya-Babuška-Brezzi (LBB) stability condition. Two cases of different Reynolds numbers were used to test the formulation's effectiveness. In the case of Reynolds number 0.12, no vortices were formed, suggesting that the flow is primarily governed by fluid friction, and fluid inertia has minimal effect. In the case of Reynolds number 120, the vortex formation, which is known as Von Kármán vortex street, appeared. These results concluded that the formulation using the finite element method is correct

Combining tomographic imaging and DEM simulations to investigate the structure of experimental sphere packings

We combine advanced image reconstruction techniques from computed X-ray micro tomography (XCT) with state-of-the-art discrete element method simulations (DEM) to study granular materials. This "virtual-laboratory" platform allows us to access quantities, such as frictional forces, which would be otherwise experimentally immeasurable.Comment: 20 pages, 17 figure

Rheology of moist food powders as affected by moisture content

Dynamic testing to determine rheological characteristics of moist food powders (semolina, coarse wheat flour, potato starch) was carried out using a powder rheometer of a new construction. The unique feature of the rheometer is that scale of shearing was confined to the thickness of shearing band of powder bed only. It was found that flow pattern of moistened samples was noticeably and diversely affected by both moisture content (varying in the range of 0–15% w/w) and shear rate. The observed changes showed statistical significance p < 0.01 in all trials carried out. What is noteworthy about the conducted research is that at some shear rate values, the shear stress of the bed reached the maximum for specific moisture content levels, irrespective of particle size of the bed. Such behavior may provide an indication of complex interference of different powder shearing mechanisms in the presence of moisture. For beds consisted of larger particles, shear stress values decreased considerably with increasing moisture content. To explain this, modeling of the shearing process with Discrete Element Method (DEM) was performed. The results obtained supported the idea that friction coefficients of particulate material were significantly reduced at higher moisture content of the powder bed in the whole range of shear rates applied

Quantum Monte Carlo Evidence for d-wave Pairing in the 2D Hubbard Model at a van Hove Singularity

We implement a Quantum Monte Carlo calculation for a repulsive Hubbard model with nearest and next-nearest neighbor hopping interactions on clusters up to 12x12. A parameter region where the Fermi level lies close to the van Hove singularity at the Saddle Points in the bulk band structure is investigated. A pairing tendency in the $d_{x^2-y^2}$ symmetry channel, but no other channel, is found. Estimates of the effective pairing interaction show that it is close to the value required for a 40 K superconductor. Finite-size scaling compares with the attractive Hubbard model.Comment: 11 pages, REVTex, 4 figures, postscrip

Mechanics and Computational Modeling of Pharmaceutical Tabletting Process

Reference Module in Materials Science and Materials EngineeringPharmaceutical Manufacturing Technology Centre (PMTC) in Irelan

Influence of the geometry on the agglomeration of a polydisperse binary system of spherical particles

Within the context of the European Horizon 2020 project ACDC, we intend to develop a probabilistic chemical compiler, to aid the construction of three-dimensional agglomerations of artificial hierarchical cellular constructs. These programmable discrete units offer a wide variety of technical innovations, like a portable biochemical laboratory that e.g. produces macromolecular medicine on demand. For this purpose, we have to investigate the agglomeration process of droplets and vesicles under proposed constraints, like confinement. This paper focuses on the influence of the geometry of the initialization and of the container on the agglomeration