73,327 research outputs found
PHYSICS-AWARE MODEL SIMPLIFICATION FOR INTERACTIVE VIRTUAL ENVIRONMENTS
Rigid body simulation is an integral part of Virtual Environments (VE) for autonomous planning, training, and design tasks. The underlying physics-based simulation of VE must be accurate and computationally fast enough for the intended application, which unfortunately are conflicting requirements. Two ways to perform fast and high fidelity physics-based simulation are: (1) model simplification, and (2) parallel computation. Model simplification can be used to allow simulation at an interactive rate while introducing an acceptable level of error. Currently, manual model simplification is the most common way of performing simulation speedup but it is time consuming. Hence, in order to reduce the development time of VEs, automated model simplification is needed. The dissertation presents an automated model simplification approach based on geometric reasoning, spatial decomposition, and temporal coherence. Geometric reasoning is used to develop an accessibility based algorithm for removing portions of geometric models that do not play any role in rigid body to rigid body interaction simulation. Removing such inaccessible portions of the interacting rigid body models has no influence on the simulation accuracy but reduces computation time significantly. Spatial decomposition is used to develop a clustering algorithm that reduces the number of fluid pressure computations resulting in significant speedup of rigid body and fluid interaction simulation. Temporal coherence algorithm reuses the computed force values from rigid body to fluid interaction based on the coherence of fluid surrounding the rigid body. The simulations are further sped up by performing computing on graphics processing unit (GPU). The dissertation also presents the issues pertaining to the development of parallel algorithms for rigid body simulations both on multi-core processors and GPU. The developed algorithms have enabled real-time, high fidelity, six degrees of freedom, and time domain simulation of unmanned sea surface vehicles (USSV) and can be used for autonomous motion planning, tele-operation, and learning from demonstration applications
Simulation of moving particles in 3D with the Lattice Boltzmann method
AbstractThe following paper presents a way to simulate the behavior of particle agglomerates in a fluid flow by coupling the Lattice Boltzmann Method to a rigid body physics engine. By extending the basic algorithm by a fluid/particle force interaction method, the hydrodynamic forces acting on the particles can be calculated. By the use of this force interaction between the fluid and the particles and by the use of the rigid body physics engine, the movement and collision behavior of particles in a flow can be simulated. Additionally, this coupled simulation system is able to simulate the internal particle forces in the connections between sintered particles, which could break due to the forces and torques of a shear flow. This permits a prediction of possible break-ups or structural displacements
Bridges wash out simulation during tsunami by a stabilized ISPH method
In 2011, the huge tsunami caused by the great east Japan earthquake devastated many infrastructures in pacific coast of north eastern Japan. Particularly, collapse of bridges caused a traffic disorder and these collapse behaviors led to delay of recovery after the disaster. In this study, the bridge wash away accident is selected as a target issue, and it is represented in order to investigate the criteria and its mechanism by a numerical simulation. For this purpose, Incompressible Smoothed Particle Hydrodynamics (ISPH) Method, which is one of the pure mesh free methods, is utilized for the rigid body motion simulation. In this study, rigid body motion is introduced for the fluid-rigid interaction behavior during bridge wash away simulation. In the numerical analysis, the upper bridge structure is washed out by receiving an impact fluid force. The validation tests in two scales showed good agreement with experimental test and the real accident on the great east Japan earthquake tsunami
Rigid body motion in viscous flows using the Finite Element Method
A new model for the numerical simulation of a rigid body moving in a viscous
fluid flow using FEM is presented. One of the most interesting features of this
approach is the small computational effort required to solve the motion of the
rigid body, comparable to a pure fluid solver. The model is based on the idea
of extending the fluid velocity inside the rigid body and solving the flow
equations with a penalization term to enforce rigid motion inside the solid. In
order to get the velocity field in the fluid domain the Navier-Stokes equations
for an incompressible viscous flow are solved using a fractional-step procedure
combined with the two-step Taylor-Galerkin for the fractional linear momentum.
Once the velocity field in the fluid domain is computed, calculation of the
rigid motion is obtained by averaging translation and angular velocities over
the solid. One of the main challenges when dealing with the fluid-solid
interaction is the proper modelling of the interface which separates the solid
moving mass from the viscous fluid. In this work the combination of the level
set technique and the two-step Taylor-Galerkin algorithm for tracking the
fluid-solid interface is proposed. The good properties exhibited by the
two-step Taylor-Galerkin, minimizing oscillations and numerical diffusion, make
this method suitable to accurately advect the solid domain avoiding distortions
at its boundaries, and thus preserving the initial size and shape of the rigid
body. The proposed model has been validated against empirical solutions,
experimental data and numerical simulations found in the literature. In all
tested cases, the numerical results have shown to be accurate, proving the
potential of the proposed model as a valuable tool for the numerical analysis
of the fluid-solid interaction.Comment: Research article; 41 pages, 40 figures, 5 tables, 91 reference
Acoustic Response of a Vibrating Elongated Cylinder in a Hydrodynamic Turbulent Flow
The present paper contains the results of the numerical analysis of the interaction between a Newtonian incompressible turbulent flow and a linear elastic slender body, together with the influence of the fluid-structure interaction (FSI) on the noise generation and propagation. The purpose is to evaluate the differences in term of acoustic pressure between the case where the solid body is rigid (infinite stiffness) and the case where it is elastic (finite stiffness). A partitioned and implicit algorithm with the arbitrary Lagrangian-Eulerian method (ALE) is used for the interaction between the fluid and solid. For the evaluation of the turbulent fluid motion, we use a large eddy simulation (LES) with the Smagorinsky subgrid scale model. The equation for the solid is solved through the Lagrangian description of the momentum equation and the second Piola-Kirchoff stress tensor. In addition, the acoustic analogy of Lighthill is used to characterize the acoustic source (the slender body) by directly using the fluid dynamic fields. In particular, we use the Ffowcs Williams and Hawkings (FW-H) equation for the evaluation of the acoustic pressure in the fluid medium. As a first numerical experiment, we analyze a square cylinder immersed in a turbulent flow characterized by two different values of stiffness: one infinite (rigid case) and one finite (elastic case). In the latter case, the body stiffness and mean flow velocity are such that they induce the lock-in phenomenon. Finally, we evaluate the differences in terms of acoustic pressure between the two different cases
OpenFOAM implementation for the study of streamwise vortex-induced vibration-based energy harvester for sensor networks
The study of streamwise vortex induced vibration has reached a level of maturity that allows it to be harnessed to generate power. However, studies have primarily concentrated on the variables that measured through point-based instruments. This severely limits our understanding of the fluid forcing mechanism that results in the vibration of the elastically supported bluff body. We proposed the usage of computational fluid dynamics: the open source C++ libraries of OpenFOAM. To implement this successfully to the streamwise vortex-induced vibration problem, which involves near-wall fluid-structure interaction, we explored the method of dynamic mesh handling in OpenFOAM for six degrees of freedom motion of a rigid body fully submerged in fluid. Finally, we argued for the usage of arbitrarily coupled mesh interface to overcome the problem of severely distorted mesh in tight gaps between two walls. We run a short simulation to test this setup and found that the case runs uninterrupted, unlike its former counterpart that relies solely on cell displacement diffusion, suggesting the potential success of a further converged solution of the setup when running on a more powerful machine
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, the learned
simulator, just like other particle-based systems, acts widely on objects of
different materials; second, the particle-based representation poses strong
inductive bias for learning: particles of the same type have the same dynamics
within. This enables the model to quickly adapt to new environments of unknown
dynamics within a few observations. We demonstrate robots achieving complex
manipulation tasks using the learned simulator, such as manipulating fluids and
deformable foam, with experiments both in simulation and in the real world. Our
study helps lay the foundation for robot learning of dynamic scenes with
particle-based representations.Comment: Accepted to ICLR 2019. Project Page: http://dpi.csail.mit.edu Video:
https://www.youtube.com/watch?v=FrPpP7aW3L
A Moving Boundary Flux Stabilization Method for Cartesian Cut-Cell Grids using Directional Operator Splitting
An explicit moving boundary method for the numerical solution of
time-dependent hyperbolic conservation laws on grids produced by the
intersection of complex geometries with a regular Cartesian grid is presented.
As it employs directional operator splitting, implementation of the scheme is
rather straightforward. Extending the method for static walls from Klein et
al., Phil. Trans. Roy. Soc., A367, no. 1907, 4559-4575 (2009), the scheme
calculates fluxes needed for a conservative update of the near-wall cut-cells
as linear combinations of standard fluxes from a one-dimensional extended
stencil. Here the standard fluxes are those obtained without regard to the
small sub-cell problem, and the linear combination weights involve detailed
information regarding the cut-cell geometry. This linear combination of
standard fluxes stabilizes the updates such that the time-step yielding
marginal stability for arbitrarily small cut-cells is of the same order as that
for regular cells. Moreover, it renders the approach compatible with a wide
range of existing numerical flux-approximation methods. The scheme is extended
here to time dependent rigid boundaries by reformulating the linear combination
weights of the stabilizing flux stencil to account for the time dependence of
cut-cell volume and interface area fractions. The two-dimensional tests
discussed include advection in a channel oriented at an oblique angle to the
Cartesian computational mesh, cylinders with circular and triangular
cross-section passing through a stationary shock wave, a piston moving through
an open-ended shock tube, and the flow around an oscillating NACA 0012 aerofoil
profile.Comment: 30 pages, 27 figures, 3 table
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