Dynamic simulations of movement allow one to study neuromuscular coordination, analyze athletic performance, and estimate internal loading of the musculoskeletal system. Simulations can also be used ...to identify the sources of pathological movement and establish a scientific basis for treatment planning. We have developed a freely available, open-source software system (OpenSim) that lets users develop models of musculoskeletal structures and create dynamic simulations of a wide variety of movements. We are using this system to simulate the dynamics of individuals with pathological gait and to explore the biomechanical effects of treatments. OpenSim provides a platform on which the biomechanics community can build a library of simulations that can be exchanged, tested, analyzed, and improved through a multi-institutional collaboration. Developing software that enables a concerted effort from many investigators poses technical and sociological challenges. Meeting those challenges will accelerate the discovery of principles that govern movement control and improve treatments for individuals with movement pathologies.
We present a novel method for solid/fluid coupling that can treat infinitesimally thin solids modeled by a lower dimensional triangulated surface. Since classical solid/fluid coupling algorithms ...rasterize the solid body onto the fluid grid, an entirely new approach is required to treat thin objects that do not contain an interior region. Robust ray casting is used to augment a number of interpolation, finite difference and rendering techniques so that fluid does not leak through the triangulated surface. Moreover, we propose a technique for properly enforcing incompressibility so that fluid does not incorrectly compress (and appear to lose mass) near the triangulated surface. This allows for the robust interaction of cloth and shells with thin sheets of water. The proposed method works for both rigid body shells and for deformable manifolds such as cloth, and we present a two way coupling technique that allows the fluid's pressure to affect the solid. Examples illustrate that our method performs well, especially in the difficult case of water and cloth where it produces visually rich interactions between the particle level set method for treating the water/air interface and our newly proposed method for treating the solid/fluid interface. We have implemented the method on both uniform and adaptive octree grids.
We present a new method for the efficient simulation of large bodies of water, especially effective when three-dimensional surface effects are important. Similar to a traditional two-dimensional ...height field approach, most of the water volume is represented by tall cells which are assumed to have linear pressure profiles. In order to avoid the limitations typically associated with a height field approach, we simulate the entire top surface of the water volume with a state of the art, fully three-dimensional Navier-Stokes free surface solver. Our philosophy is to use the best available method near the interface (in the three-dimensional region) and to coarsen the mesh away from the interface for efficiency. We coarsen with tall, thin cells (as opposed to octrees or AMR), because they maintain good resolution horizontally allowing for accurate representation of bottom topography.
Nonconvex rigid bodies with stacking Guendelman, Eran; Bridson, Robert; Fedkiw, Ronald
ACM transactions on graphics,
01/07, Letnik:
22, Številka:
3
Journal Article
Recenzirano
Odprti dostop
We consider the simulation of nonconvex rigid bodies focusing on interactions such as collision, contact, friction (kinetic, static, rolling and spinning) and stacking. We advocate representing the ...geometry with both a triangulated surface and a signed distance function defined on a grid, and this dual representation is shown to have many advantages. We propose a novel approach to time integration merging it with the collision and contact processing algorithms in a fashion that obviates the need for ad hoc threshold velocities. We show that this approach matches the theoretical solution for blocks sliding and stopping on inclined planes with friction. We also present a new shock propagation algorithm that allows for efficient use of the propagation (as opposed to the simultaneous) method for treating contact. These new techniques are demonstrated on a variety of problems ranging from simple test cases to stacking problems with as many as 1000 nonconvex rigid bodies with friction as shown in Figure 1.
Melting and burning solids into liquids and gases Losasso, F.; Irving, G.; Guendelman, E. ...
IEEE transactions on visualization and computer graphics,
05/2006, Letnik:
12, Številka:
3
Journal Article
Recenzirano
We propose a novel technique for melting and burning solid materials, including the simulation of the resulting liquid and gas. The solid is simulated with traditional mesh-based techniques ...(triangles or tetrahedra) which enable robust handling of both deformable and rigid objects, collision and self-collision, rolling, friction, stacking, etc. The subsequently created liquid or gas is simulated with modern grid-based techniques, including vorticity confinement and the particle level set method. The main advantage of our method is that state-of-the-art techniques are used for both the solid and the fluid without compromising simulation quality when coupling them together or converting one into the other. For example, we avoid modeling solids as Eulerian grid-based fluids with high viscosity or viscoelasticity, which would preclude the handling of thin shells, self-collision, rolling, etc. Thus, our method allows one to achieve new effects while still using their favorite algorithms (and implementations) for simulating both solids and fluids, whereas other coupling algorithms require major algorithm and implementation overhauls and still fail to produce rich coupling effects (e.g., melting and burning solids).
Impulse-Based Control of Joints and Muscles Weinstein, R.; Guendelman, E.; Fedkiw, R.
IEEE transactions on visualization and computer graphics,
2008-Jan.-Feb., 2008 Jan-Feb, 2008-01-00, 20080101, Letnik:
14, Številka:
1
Journal Article
Recenzirano
We propose a novel approach to proportional derivative (PD) control exploiting the fact that these equations can be solved analytically for a single degree of freedom. The analytic solution indicates ...what the PD controller would accomplish in isolation without interference from neighboring joints, gravity and external forces, outboard limbs, etc. Our approach to time integration includes an inverse dynamics formulation that automatically incorporates global feedback so that the per joint predictions are achieved. This effectively decouples stiffness from control so that we obtain the desired target regardless of the stiffness of the joint, which merely determines when we get there. We start with simple examples to illustrate our method and then move on to more complex examples including PD control of line segment muscle actuators.
We present a new method for the efficient simulation of large bodies of water, especially effective when three-dimensional surface effects are important. Similar to a traditional two-dimensional ...height field approach, most of the water volume is represented by tall cells which are assumed to have linear pressure profiles. In order to avoid the limitations typically associated with a height field approach, we simulate the entire top surface of the water volume with a state of the art, fully three-dimensional Navier-Stokes free surface solver. Our philosophy is to use the best available method near the interface (in the three-dimensional region) and to coarsen the mesh away from the interface for efficiency. We coarsen with tall, thin cells (as opposed to octrees or AMR), because they maintain good resolution horizontally allowing for accurate representation of bottom topography.
We consider the simulation of nonconvex rigid bodies focusing on interactions such as collision, contact, friction (kinetic, static, rolling and spinning) and stacking. We advocate representing the ...geometry with both a triangulated surface and a signed distance function defined on a grid, and this dual representation is shown to have many advantages. We propose a novel approach to time integration merging it with the collision and contact processing algorithms in a fashion that obviates the need for ad hoc threshold velocities. We show that this approach matches the theoretical solution for blocks sliding and stopping on inclined planes with friction. We also present a new shock propagation algorithm that allows for efficient use of the propagation (as opposed to the simultaneous) method for treating contact. These new techniques are demonstrated on a variety of problems ranging from simple test cases to stacking problems with as many as 1000 nonconvex rigid bodies with friction as shown in Figure 1.
This dissertation presents algorithms for the simulation of solids and fluids, and for two-way coupling between the two. Physically-based simulation has a wide range of applications, and the focus in ...this dissertation is on creating visually plausible animation for computer graphics and visual effects. Novel techniques for rigid body simulation are described first. These include a new approach to time integration, merging it with the collision and contact processing algorithms in a fashion that obviates the need for ad hoc threshold velocities. In addition, a novel shock propagation algorithm allows for efficient use of the propagation (as opposed to the simultaneous) method for treating contact. Examples are given involving many nonconvex rigid bodies undergoing collision, contact, friction, and stacking. A brief overview of existing techniques for simulation of thin deforming shells (such as cloth) is also given. Our fluid simulator is described next. Techniques for both smoke and water simulation are presented, with the latter making use of the particle level set method to represent the water-air interface. A node-based approach is described which allows both uniform and octree grid discretizations to be handled in a consistent and efficient manner. Next, a novel method for coupling infinitesimally thin solids to the fluid is presented. The proposed method works for both rigid and deformable shells. Leaks across the solid are prevented by using robust ray casting and visibility. Incompressibility is properly enforced at the solid-fluid interface so that fluid does not incorrectly compress (and appear to lose mass). Furthermore, computation of a smoother pressure for coupling alleviates some of the stiffness associated with coupling to an incompressible fluid. Finally, coupling to volumetric solids is described. The coupling strategy is similar to that used for thin shells, except ghost values, rather than one-sided stencils, are used to enforce boundary conditions at the solid-fluid interface. In addition, a more accurate approach to computing the coupling pressure is suggested. For both thin shells and volumetric solids, our coupling framework treats the solids simulation as a black box, allowing any alternative simulators to replace the ones used here.
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