A Boundary Element Method for Simulation of Deformable Objects

In this paper,a boundary element method is first applied to real-tim animation of deformable objects and to simplify data preparation.Next,the visibleexternal surface of the object in deforming process is represented by B-spline surface,whose control points are embedded in dynamic equations of BEM.Fi-nally,the above method is applied to anatomical simulation.A pituitary model in human brain,which is reconstructed from a set of anatomical sections, is selected to be the deformable object under action of virtual tool such as scapel or probe.It produces fair graphic realism and high speed performance.The results show that BEM not only has less computational expense than FEM,but also is convenient to combine with the 3D reconstruction and surface modeling as it enables the reduction of the dimensionality of the problem by one.     

A physically-based particle model of woven cloth

Every time a tablecloth is draped over a table it will fold and pleat in unique ways. We report on a physically-based model and a simulation methodology, which when used together are able to reproduce many of the attributes of this characteristic behavior of cloth. Our model utilizes a microscopic particle representation that directly treats the mechanical constraints between the threads in woven material rather than using a macroscopic continuum approximation. The simulation technique is hybrid, employing force methods for gross movement and energy methods to enforce constraints within the material. The model is developed and demonstrated within a visualization environment that allows full interaction between the simulated material and conventional constructive-solid-geometry models.     

Combinations of collocation and finite-element methods for Poisson''s equation

In this paper, we provide a framework of combinations of collocation method (CM) with the finite-element method (FEM). The key idea is to link the Galerkin method to the least squares method which is then approximated by integration approximation, and led to the CM. The new important uniformly V⁰_h-elliptic inequality is proved. Interestingly, the integration approximation plays a role only in satisfying the uniformly V⁰_h-elliptic inequality. For the combinations of the finite-element and collocation methods (FEM-CM), the optimal convergence rates can be achieved. The advantage of the CM is to formulate easily linear algebraic equations, where the associated matrices are positive definite but nonsymmetric. We may also solve the algebraic equations of FEM and the collocation equations directly by the least squares method, thus, to greatly improve numerical stability. Numerical experiments are also carried for Poisson's problem to support the analysis. Note that the analysis in this paper is distinct from the existing literature, and it covers a large class of the CM using various admissible functions, such as the radial basis functions, the Sinc functions, etc.     

Physically based modeling and simulation with dynamic spherical volumetric simplex splines

In this paper, we present a novel computational modeling and simulation framework based on dynamic spherical volumetric simplex splines. The framework can handle the modeling and simulation of genus-zero objects with real physical properties. In this framework, we first develop an accurate and efficient algorithm to reconstruct the high-fidelity digital model of a real-world object with spherical volumetric simplex splines which can represent with accuracy geometric, material, and other properties of the object simultaneously. With the tight coupling of Lagrangian mechanics, the dynamic volumetric simplex splines representing the object can accurately simulate its physical behavior because it can unify the geometric and material properties in the simulation. The visualization can be directly computed from the object’s geometric or physical representation based on the dynamic spherical volumetric simplex splines during simulation without interpolation or resampling. We have applied the framework for biomechanic simulation of brain deformations, such as the brain shifting during surgery and brain injury under blunt impact. We have compared our simulation results with the ground truth obtained through intra-operative magnetic resonance imaging and real biomechanic experiments. The evaluations demonstrate the excellent performance of our new technique.     

Splitting cubes: a fast and robust technique for virtual cutting

This paper presents the splitting cubes, a fast and robust technique for performing interactive virtual cutting on deformable objects. The technique relies on two ideas. The first one is to embed the deformable object in a regular grid, to apply the deformation function to the grid nodes and to interpolate the deformation inside each cell from its 8 nodes. The second idea is to produce a tessellation for the boundary of the object on the base of the intersections of such boundary with the edges of the grid. Please note that the boundary can be expressed in any way; for example it can be a triangle mesh, an implicit or a parametric surface. The only requirement is that the intersection between the boundary and the grid edges can be computed. This paper shows how the interpolation of the deformation inside the cells can be used to produce discontinuities in the deformation function, and the intersections of the cut surface can be used to visually show the cuts on the object. The splitting cubes is essentially a tessellation algorithm for growing, deformable surface, and it can be applied to any method for animating deformable objects. In this paper the case of the mesh-free methods (MMs) is considered: in this context, we described a practical GPU friendly method, that we named the extended visibility criterion, to introduce discontinuities of the deformation. Electronic supplementary material  Supplementary material is available in the online version of this article at and is accessible for authorized users.     

A robust a posteriori error estimate for the Fortin-Soulie finite-element method

The subject of a posteriori error estimation is widely studied, and a variety of such error estimates have been used for elasticity problems in recent years. Of particular interest is the work carried out in ^{1. and 2.}. In this paper, we derive a new a posteriori error estimator for the quadratic nonconforming Fortin-Soulie element for the error in an energy-like norm. Then, we illustrate the new error bound by presenting some numerical examples, and show an example of a sequence of adaptively refined meshes.     

An improved entropic lattice Boltzmann model for parallel computation

In this paper, we suggest two kinds of approximation methods based on Taylor series expansion which can solve the non-linear equation in entropic lattice Boltzmann model without using any iteration methods such as Newton–Raphson method. The advantage of our methods is to be able to avoid the load imbalance in parallel computation which occurs due to the differences of iteration number on each calculation grid. In this study, ELBM simulations using our methods were compared with those using Newton–Raphson method for the channel flow past a square cylinder in Re = 1000 and the validity of the results and computational effort were investigated. As a result, it was found that the solutions obtained by our methods are qualitatively and quantitatively reasonable and CPU time is shorter than those obtained by Newton–Raphson method.     

Assembly simulation of multi-branch cables

Cable assembly simulation is a key issue in the computer-aided design (CAD) of products with complex electrical components. In this study, an assembly simulation method is developed to simulate the assembly process of multi-branch cables. First, based on the Cosserat theory of elastic rods, a novel scheme is introduced to model the joints of multi-branch cables. The potential energy of joints is calculated by taking the topology and anatomical features into consideration. Various physical properties are considered. Various constraints, including connectors, collars, and handles are analyzed, based on which the initial conditions of assembly simulation are determined. The configuration of the cable is then calculated by minimizing its potential energy. To increase computational efficiency, GPU acceleration is introduced, which makes the simulation run at interactive rates even for a cable with resolution up to 1000 discrete points. Finally, the proposed algorithm is integrated into the commercial assembly simulation system, DELMIA. Several simulations were performed with our system. It was demonstrated that the proposed method is able to handle cables with complex topologies. In addition, the proposed method is about four times as efficient as a previous method, and it is able to generate realistic configurations of multi-branch cables at interactive rates. Thus, the proposed method is helpful in the assembly process planning of cables.     

Collision avoidance in cloth animation

For cloth modeling and animation, we use a physically based model to simulate the dynamic formation of folds, pleats, and wrinkles and the final static appearance of cloth draped over a rigid object. To simulate the behavior of the cloth and its final static appearance on the model, we propose a new collision and self-collision avoidance method to prevent penetration between the cloth and rigid objects and between parts of the cloth. At each time step, we enforce constraints over those grid points about to penetrate other objects. Our method is easier and more robust than conventional methods at representing interaction between the cloth and various objects.     

An improved immersed finite element particle-in-cell method for plasma simulation

The particle-in-cell (PIC) method has been widely used for plasma simulation, because of its noise-reduction capability and moderate computational cost. The immersed finite element (IFE) method is efficient for solving interface problems on Cartesian meshes, which is desirable for the PIC method. The combination of these two methods provides an effective tool for plasma simulation with complex interface/boundary. This paper introduces an improved IFE–PIC method that enhances the performance in both IFE and PIC aspects. For the electric field solver, we adopt the newly developed partially penalized IFE method with enhanced accuracy. For PIC implementation, we introduce a new interpolation technique to ensure the conservation of the charge. Numerical examples are provided to demonstrate the features of the improved IFE–PIC method.     

Visualization and pre-processing of independent finite-element meshes for car crash simulations

Published online: 15 March 2002     

软件问题生命周期模型研究

软件问题管理是软件测试的核心活动,也是软件测试管理的灵魂.探讨了软件问题管理的重要性,介绍了两种软件问题生命周期建模的基本模型,提出了一种包含子状态控制的状态可定制的改进的生命周期模型,最后基于提出的生命周期模型给出与其相应的建模方法.     

An improved EZ-GCD algorithm for multivariate polynomials

The EZ-GCD algorithm often has the bad-zero problem, which has a remarkable influence on polynomials with higher-degree terms. In this paper, by applying special ideals, the EZ-GCD algorithm for sparse polynomials is improved. This improved algorithm greatly reduces computational complexity because of the sparseness of polynomials. The author expects that the use of these ideals will be useful as a resolution for obtaining a GCD of sparse multivariate polynomials with higher-degree terms.     

Reactive 2D/3D garment pattern design modification

This paper presents a new 3D garment simulation result update algorithm for the 2D garment pattern design modification. The proposed algorithm enables the 3D garment fitting simulation result directly to react to the modification in the 2D patterns. The algorithm performs a topological invariant deformation of the 2D pattern mesh after the boundary of the 2D pattern undergoes a topological consistent modification. The length of each of the edges in the mesh defined as the equilibrium state parameter is updated and then directly used in the 3D garment fitting simulation to update the original simulation result. The advantage of the proposed algorithm is that the mesh topology of the 2D garment pattern is preserved and thus simplifies the numerical scheme by maintaining the consistency of the matrix equation. With this approach, the 3D garment fitting simulation does not need to repeat the entire simulation for every modification and can react to the 2D pattern modification efficiently and speedily.     

An improved control-variate scheme for particle-in-cell simulations with collisions

Particle-in-cell methods combined with a δf approach constitute an established and powerful method for simulating collisionless kinetic equations in e.g. plasma physics. Including collisions in such simulations requires a modified approach leading to a two-weight scheme, which has the drawback of giving a statistical error that increases with time. As in the collisionless case, this scheme can be interpreted as an application of an ordinary control variate. Using an enhanced control variate approach, an improved scheme is constructed. This approach has been applied to a model problem with the result of a much better behaviour of the error, which, instead of growing indefinitely, becomes bounded by the error of a full-f scheme. In addition, the application of the enhanced control variate is illustrated for a collisionless simulation of ITG turbulence. Here it can be used both as a diagnostic tool and as a means to eliminate the spurious violation of particle number conservation inherent to δf simulations due to statistical noise.     

An improved model for vehicle routing problem with time constraint based on genetic algorithm

A vehicle routing problem (VRP) with time constraint is one of the important problems in distribution and transportation. Thus the generic VRP and its practical extensions are discussed in great detail in the literatures. In the VRP, the service of a customer must start and finish within a given time interval. The objective of this problem is to minimize the cost of servicing the set of customers without being tardy or exceeding the capacity or travel time of the vehicles. In this research we concentrated on developing a GA–TSP model by improving the genetic algorithm (GA) operators and the initial population. For the computational purpose, we developed a GUI (graphic user interface)-type computer program according to the proposed method. The computational results show that the proposed method is very effective on a set of standard test problems and it can be potentially useful in solving the VRPs.     

An interactive computer‐based simulation system for endovascular aneurysm repair surgeries

This paper presents an interactive simulation system for surgical procedures of endovascular aneurysm repair. It extracts anatomical structure of clinic interest from patient‐specific X‐ray computed tomography or magnetic resonance imaging data by image segmentation techniques, and then reconstructs surface triangular meshes of these anatomical structures from the volumetric data. The core of the system is an interactive computer‐based simulation module. It consists of a physical modeling unit, a collision detection unit, a visualization unit, and a control unit. The integration of these units together makes it possible for users to interact with the system in real time, performing virtual catheterization, angiography, and stent graft deployment under a user‐specified rendering mode. The prototype system can be used as a cost‐efficient tool for surgical planning with patient‐specific anatomical geometry and for practice of surgical procedures before actual operation. Copyright © 2016 John Wiley & Sons, Ltd.     

An improved hybrid firefly algorithm for capacitated vehicle routing problem

Firefly algorithm (FA) is a new meta-heuristic which is successfully applied to solve several optimization problems. However, it suffers from a drawback of easily getting stuck at local optima. This paper proposes a new hybrid FA, called CVRP-FA, to solve capacitated vehicle routing problem. In CVRP-FA, FA is integrated with two types of local search and genetic operators to enhance the solution’s quality and accelerate the convergence. The experiments are conducted over 82 benchmark instances. The results demonstrate that CVRP-FA has fast convergence rate and high computational accuracy. It significantly outperforms the other state-of-the-art FA variants in majority of the tested instances.