A computergraphics algorithm for simulating the propagation of light and its interaction with matter on a massively parallel computer is presented. This algorithm, called the tagged shooting method, is designed for a...
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A computergraphics algorithm for simulating the propagation of light and its interaction with matter on a massively parallel computer is presented. This algorithm, called the tagged shooting method, is designed for a virtual machine containing a great number of simple communicating processors arrayed into a cubical three-dimensional lattice. Only nearest neighbor communication among processors is assumed, and there is no reliance on global shared memory. The algorithm is similar in spirit to the classical progressive refinement radiosity method designed for more conventional computers but is not an adaptation of that technique to massive parallelism. Instead, the new algorithm uses a discretization of the wave equation as a local rule for shuttling radiant energy values between processors that correspond to regions of space. A number of example images that were created with an implementation of the algorithm on a Connection Machine are depicted and critiqued.< >
A formulation for the contact forces between curved surfaces in resting (non-colliding) contact is presented. In contrast to previous formulations, constraints on the allowable tangential movement between contacting s...
ISBN:
(纸本)9780897913447
A formulation for the contact forces between curved surfaces in resting (non-colliding) contact is presented. In contrast to previous formulations, constraints on the allowable tangential movement between contacting surfaces are not required. Surfaces are restricted to be twice-differentiable surfaces without boundary. Only finitely many contact points between surfaces are allowed; however, the surfaces need not be convex. The formulation yields the contact forces between curved surfaces and polyhedra as well. Algorithms for performing collision detection during simulation on bodies composed of both polyhedra and strictly convex curved surfaces are also presented. The collision detection algorithms exploit the geometric coherence between successive time steps of the simulation to achieve efficient running times.
The numerical sensitivity of a constant-feedback-gains controller to random structural imperfections is examined using the results of a series of finite element analyses. The basic finite element model, which uses lin...
A procedure for numerical approximation to two-dimensional, hydraulically-driven fracture propagation in a poroelastic material is described. The method uses a partitioned solution procedurè to solve a finite ele...
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A procedure for numerical approximation to two-dimensional, hydraulically-driven fracture propagation in a poroelastic material is described. The method uses a partitioned solution procedurè to solve a finite element approximation to problems described by the theory of poroelasticity, in conjunction with a finite difference approximation for modelling fluid flow along the fracture. An equilibrium fracture model based on a generalized, Dugdale–Barenblatt concept is used to determine the fracture dimensions. An important feature is that the fracture length is a natural product of the solution algorithm. Two example problems verify the accuracy of the numerical procedure and a third example illustrates a fully-coupled simulation of fracture propagation. Photographs taken from a high-performance engineering workstation provide insight into the nature of the coupling among the physical phenomena.
We present a real-time robot motion planner that is fast and complete to a resolution. The technique is guaranteed to find a path if one exists at the resolution, and all paths returned are safe. The planner can handl...
ISBN:
(纸本)9780897913447
We present a real-time robot motion planner that is fast and complete to a resolution. The technique is guaranteed to find a path if one exists at the resolution, and all paths returned are safe. The planner can handle any polyhedral geometry of robot and obstacles, including disjoint and highly concave unions of *** planner uses standard graphics hardware to rasterize configuration space obstacles into a series of bitmap slices, and then uses dynamic programming to create a navigation function (a discrete vector-valued function) and to calculate paths in this rasterized space. The motion paths which the planner produces are minimal with respect to an L1 (Manhattan) distance metric that includes rotation as well as *** examples are shown illustrating the competence of the planner at generating planar rotational and translational plans for complex two and three dimensional robots. Dynamic motion sequences, including complicated and non-obvious backtracking solutions, can be executed in real time.
We describe the main algorithms used in an interactive lighting simulation program based on a twopass extension of the radiosity method. The system allows interactive walk-through as other systems based on radiosity c...
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A method for analytically calculating the forces between systems of rigid bodies in resting (non-colliding) contact is presented. The systems of bodies may either be in motion or static equilibrium and adjacent bodies...
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ISBN:
(纸本)0897913124
A method for analytically calculating the forces between systems of rigid bodies in resting (non-colliding) contact is presented. The systems of bodies may either be in motion or static equilibrium and adjacent bodies may touch at multiple points. The analytic formulation of the forces between bodies in non-colliding contact can be modified to deal with colliding bodies. Accordingly, an improved method for analytically calculating the forces between systems of rigid bodies in colliding contact is also presented. Both methods can be applied to systems with arbitrary holonomic geometric constraints, such as linked figures. The analytical formulations used treat both holonomic and non-holonomic constraints in a consistent manner.
computer simulations can be used to generate the spatial and temporal data describing the acoustical behavior of performance halls, but typically the analytical results are difficult to assimilate and compare. By usin...
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ISBN:
(纸本)0897913124
computer simulations can be used to generate the spatial and temporal data describing the acoustical behavior of performance halls, but typically the analytical results are difficult to assimilate and compare. By using computergraphics to display the multi-dimensional data, substantially greater amounts of information than that conveyed by standard techniques can be communicated to the designer. This allows designs of different acoustical spaces to be tested, evaluated, and compared. An example comparing the acoustical behavior of three different concert halls demonstrates these techniques and allows for the simultaneous assimilation of much of the information necessary to evaluate the acoustical nature of a space. The use of three-dimensional images, color, animation and abstract representation allows for the comprehension of the complex results of a scientific simulation. Specifically, the simultaneous display of particular icons familiar to the discipline enabled the simultaneous presentation of up to twelve parameters. From a more general point of view, the procedures demonstrate how computergraphics can be utilized for the portrayal of multi-dimensional time dependent data. The visualization techniques are potentially useful for the display of three-dimensional vector fields in many scientific and design applications.
The Q9 membrane finite element is unable to experience arbitrary change of uniaxial curvature without the occurence of artificial membrane stains. The error which accumulates due to this inability can be significant w...
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The Q9 membrane finite element is unable to experience arbitrary change of uniaxial curvature without the occurence of artificial membrane stains. The error which accumulates due to this inability can be significant when a large change of curvature is experienced by this element. This paper investigates the effect of element shape distortion on the accumulation of error in the Q9 membrane element, and presents two methods for evaluating shape distortion effects in problems with large changes of curvature: a series of ‘patch tests’, and single element tests.
A reformulated radiosity algorithm is presented that produces initial images in time linear to the number of patches. The enormous memory costs of the radiosity algorithm are also eliminated by computing form-factors ...
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