Numerical benchmarking of fluid-rigid body interactions

A remeshed vortex method for mixed rigid/soft body fluid--structure interaction

We outline a 2D algorithm for solving incompressible flow--structure interaction problems for mixed rigid/soft body representations, within a consistent framework based on the remeshed vortex method. We adopt the one--continuum formulation to represent both solid and fluid phases on an Eulerian grid, separated by a diffuse interface. Rigid solids are treated using Brinkman penalization while an inverse map technique is used to obtain elastic stresses in the hyper-elastic solid phase. We test our solver against a number of benchmark problems, which demonstrate physical accuracy and first to sec…

Benchmarking between fluid and global models for low-pressure oxygen DC glow discharges

This work focuses on the benchmarking between a zero-dimensional (0D) global model (LoKI) and a one-dimensional (1D) radial fluid model for the positive column of oxygen DC glow discharges in a tube of 1 cm inner radius at pressures between 0.5 Torr and 10 Torr. The data used in the two models are the same, so that the difference between the models is reduced to dimensionality. A good agreement is found between the two models on the main discharge parameters, with relative differences below 5%. The agreement on species average number densities, charged and neutral, is slightly worse, with rela…

Finite Element Simulation of the Motion of a Rigid Body in a Fluid with Free Surface

In this work a finite element simulation of the motion of a rigid body in a fluid, with free surface, is described. A completely general referential description (of which both Lagrangian and Eulerian descriptions are special cases) of an incompressible, Newtonian fluid is used. Such a description enables a distorting finite element mesh to be used for the deforming fluid domain. A new scheme for the linearised approximation of the convective term is proposed and the improved, second order accuracy of this scheme is proved. A second theorem, which provides a guideline for the artificial adjustm…

粘弹性流动中浸入边界法的基准测试

Benchmarking the Immersed Boundary Method for Viscoelastic Flows

本文通过二维算例和流变实验，对浸入边界法在Oldroyd-B和Rolie-Poly粘弹性流动中的精度与收敛性进行基准测试，并与有限元、有限体积法比较，给出正则化delta函数和拉格朗日网格间距的推荐选择。

流体-结构相互作用中格子玻尔兹曼方法（LBM）的约束惩罚法

Constraint Penalization Method in the Lattice Boltzmann Method (LBM) for Fluid-Structure Interaction

本文在LBM框架内提出约束惩罚法，通过直接对流体速度场施加惩罚项来强制刚体运动，无需显式拉格朗日乘子，实现了流固隐式耦合，能高效准确模拟流体-结构相互作用及颗粒沉降。

A unified diffuse interface method for the interaction of rigid bodies with elastoplastic solids and multi-phase mixtures

This work outlines a new multi-physics-compatible immersed rigid body method for Eulerian finite-volume simulations. To achieve this, rigid bodies are represented as a diffuse scalar field and an interface seeding method is employed to mediate the interface boundary conditions. The method is based on an existing multi-material diffuse interface method that is capable of handling an arbitrary mixture of fluids and elastoplastic solids. The underlying method is general and can be extended to a range of different applications including high-strain rate deformation in elastoplastic solids and reac…

Capillary interactions between soft capsules protruding through thin fluid films

When a suspension dries, the suspending fluid evaporates, leaving behind a dry film composed of the suspended particles. During the final stages of drying, the height of the fluid film on the substrate drops below the particle size, inducing local interface deformations that lead to strong capillary interactions among the particles. Although capillary interactions between rigid particles are well studied, much is still to be understood about the behaviour of soft particles and the role of their softness during the final stages of film drying. Here, we use our recently-introduced numerical meth…

Efficient classical density-functional theories of rigid-molecular fluids and a simplified free energy functional for liquid water

Classical density-functional theory provides an efficient alternative to molecular dynamics simulations for understanding the equilibrium properties of inhomogeneous fluids. However, application of density-functional theory to multi-site molecular fluids has so far been limited by complications due to the implicit molecular geometry constraints on the site densities, whose resolution typically requires expensive Monte Carlo methods. Here, we present a general scheme of circumventing this so-called inversion problem: compressed representations of the orientation density. This approach allows us…

Learning Particle Dynamics for Manipulating Rigid Bodies, Deformable Objects, and Fluids

Real-life control tasks involve matters of various substances---rigid or soft bodies, liquid, gas---each with distinct physical behaviors. This poses challenges to traditional rigid-body physics engines. Particle-based simulators have been developed to model the dynamics of these complex scenes; however, relying on approximation techniques, their simulation often deviates from real-world physics, especially in the long term. In this paper, we propose to learn a particle-based simulator for complex control tasks. Combining learning with particle-based systems brings in two major benefits: first…