A novel two-way method for dynamically coupling a hydrodynamic model with a discrete element model (DEM)

The effect of floating objects has so far been little considered for hazard risk assessment and structure design, despite being an important factor causing structural damage in flood-prone and coastal areas. In this work, a novel two-way method is proposed to fully couple a shock-capturing hydrodynamic model with a discrete element model (DEM) for simulation of complex debris-enriched flow hydrodynamics. After being validated against an idealized analytical test, the new coupled model is used to reproduce flume experiments of floating debris driven by dam-break waves. The numerical results agree satisfactorily with the experimental measurements, demonstrating the model’s capability and efficiency in simulating complex fluid-debris interactions induced by violent shallow flows

Coupling, Conservation, and Performance in Numerical Simulations

This thesis considers three aspects of the numerical simulations, which arecoupling, conservation, and performance. We conduct a project and addressone challenge from each of these aspects.We propose a novel penalty force to enforce contacts with accurate Coulombfriction. The force is compatible with fully-implicit time integration and theuse of optimization-based integration. In addition to processing collisionsbetween deformable objects, the force can be used to couple rigid bodies todeformable objects or the material point method. The force naturally leads tostable stacking without drift over time, even when solvers are not run toconvergence. The force leads to an asymmetrical system, and we provide apractical solution for handling these.Next we present a new technique for transferring momentum and velocity betweenparticles and MAC grids based on the Affine-Particle-In-Cell (APIC) frameworkpreviously developed for co-locatedgrids. We extend the original APIC paper and show thatthe proposed transfers preserve linear and angular momentum and also satisfyall of the original APIC properties.Early indications in the original APIC paper suggested that APIC might besuitable for simulating high Reynolds fluids due to favorable retention ofvortices, but these properties were not studied further. We use twodimensional Fourier analysis to investigate dissipation in the limit \dt=0.We investigate dissipation and vortex retention numerically to quantify theeffectiveness of APIC compared with other transfer algorithms.Finally we present an efficient solver for problems typically seen inmicrofluidic applications.Microfluidic ``lab on a chip'' devices are small devices that operate on smalllength scales on small volumes of fluid. Designs for microfluidic chips aregenerally composed of standardized and often repeated components connected bylong, thin, straight fluid channels. We propose a novel discretizationalgorithm for simulating the Stokes equations on geometry with these features,which produces sparse linear systems with many repeated matrix blocks. Thediscretization is formally third order accurate for velocity and second orderaccurate for pressure in the $L^\infty$ norm. We also propose a novel linearsystem solver based on cyclic reduction, reordered sparse Gaussian elimination,and operation caching that is designed to efficiently solve systems withrepeated matrix blocks

Combining Active and Passive Simulations for Secondary Motion

Varied, realistic motion in a complex environment can bring an animated scene to life. While much of the required motion comes from the characters, an important contribution also comes from the passive motion of other objects in the scene. We use the term secondary motion to refer to passive motions that are generated in response to environmental forces or the movements of characters and other objects. For example, the movement of clothing and hair adds visual complexity to an animated scene of a jogging figure. In this paper, we describe how secondary motion can be generated by coupling physically based simulations of passive systems to active simulations of the main characters. We discuss three coupling methods for the interface between the passive and active systems: two-way, one-way, and hybrid. These three methods allow the animator to make an appropriate tradeoff between accuracy and computational speed. We use a basketball passing through a net as an illustrative example to demonstrate each of the three coupling methods. To provide guidance as to when each method is most appropriate, we present additional examples including a gymnast on a trampoline, a man on a bungee cord, a stunt kite, a gymnast landing on a flexible mat, a diver entering the water, and several human figures wearing clothing. The information gained from analyzing these examples is summarized in a decision tree and a set of guidelines for coupling active and passive systems

Combining active and passive simulations for secondary motion

An attempt is made to explore the issues involved when passive secondary systems are coupled to another, primary, system. Methods for coupling two systems together are classified as two-way, one-way, or hybrid. Each of these methods is demonstrated using systems built by coupling simulated components