1D and 2D structured mass-spring models with preload

In this paper, the objective is to enrich the existing 1D and 2D mass-spring models with physical accuracy as well as visual realism. It is found that using nonzero preloads on the springs is a necessary condition for the models to approximate their continuum counterparts. First, the parameters of the 1D mass-spring model of a beam are derived based on pure bending and axial action. It is proved that the mass-spring model with this set of parameter has correct characteristics of resistance against lateral displacement, which is one of the most important aspects of the accuracy of the 1D mass-spring model. Then, the method is extended to the 2D mass-spring models of the continuum plate with two different mesh structures. The mass-spring model with equilateral triangle meshes is shown to be physically more accurate than that with rectangular meshes. Finally, the physical accuracy that the mass-spring models with preload can achieve is investigated under different load conditions by comparison with the finite element method (FEM) to demonstrate the efficacy of our approach.     

Real-Time Simulation of Thin Shells

This paper proposes a real-time simulation technique for thin shells undergoing large deformation. Shells are thin objects such as leaves and papers that can be abstracted as 2D structures. Development of a satisfactory physical model that runs in real-time but produces visually convincing animation of thin shells has been remaining a challenge in computer graphics. Rather than resorting to shell theory which involves the most complex formulations in continuum mechanics, we adopt the energy functions from the discrete shells proposed by Grinspun et al. [ [GHDS03] ]. For real-time integration of the governing equation, we develop a modal warping technique for shells. This new simulation framework results from making extensions to the original modal warping technique [ [CK05] ] which was developed for the simulation of 3D solids. We report experimental results, which show that the proposed method runs in real-time even for large meshes, and that it can simulate large bending and/or twisting deformations with acceptable realism.     

Coupling of two- and three-dimensional hydrodynamic numerical models for simulating wind-induced currents in deep basins

The main interest of the present study is the simulation of wind-induced currents in closed water bodies with shallow and deep regions. This paper describes a low time consumption numerical modelling technique for the simulation of free-surface flow over a geometrically complex bed. To achieve this, a technique employing coupled two- and three-dimensional flow solvers is developed for simulation of the flow. The conjunctive model consists of an upper part 2D Shallow Water Flow Solver (2D-SWFS) coupled with a 3D pseudo-compressible flow solver (3D-PCFS) for the deep regions with a proper interface boundary condition. The 2D-SWFS and 3D-PCFS solvers are coupled via an interfacial shear stress gradient and pressure effects. Time stepping is performed for the 2D solver, and an iterative procedure is employed by the 3D solver to satisfy the equilibrium constraints for the interfacial boundary. The model is able to consider 2D wetting and drying shallow regions without any underlying deep water. Both the 2D and 3D models use nodal based Galerkin finite volume method (GFVM) for solving the governing equations on the unstructured meshes. The accuracy of both models in solving the effective phenomena is examined by comparing the results of simulated test cases with readily available analytical solutions and experimental measurements. Finally, the accuracy of the conjunctive model is assessed by comparing its results for test cases with analytical solutions and experimental measurements from the literature. The new simulation method is then used to solve a wind-induced flow problem in a basin with deep water surrounded by shallow water parts.     

A virtual environment simulator for mechanical system dynamics with online interactive control

Virtual prototyping is an effective tool in the development of mechanical product. Physically accurate simulation of multi-body mechanical system enables designers to investigate, explore, and experience the performance and behavior of an evolving product and thus reduce the number of physical prototypes needed. For the sake of better support for designers to manipulate the simulation, we have developed a dynamic simulation package of mechanical system, which provides an interactive control during the simulation process. The package incorporates physical behaviors and dynamic interactions by dynamics based modeling approach in multi-body mechanical system. In the package, user’s actions (e.g., loading a model, picking and dragging objects, steering objects during simulation process, etc.) are based on an ATN task management, and a multi-modal interface is provided which supports 2D desktop devices and 3D VR devices. The main contribution of the simulator is providing supports that allow users’ interactive manipulation in the simulation loop. During the simulation process, users can modify the constraints between components, apply force/torque to interested components and change the parameters of forces/torques. The simulator automatically updates the dynamic model of the mechanical system in real time, and then continuously simulates the behavior of the model under the current condition in the loop. An example of dynamic simulation of a vehicle is implemented and the simulation result is compared to that of ADAMS to verify the correctness and accuracy of the simulator. With the real-time interaction, solution and visualization of simulation model, the package affords better support for designers to participate in the simulation interactively and effectively.     

A modified radiosity algorithm for integrated visual and auditory rendering

A concept on integration of 3D visual and auditory rendering is proposed in this paper. By the auditory rendering we mean the computer acoustical simulation with direct sound outputs that is based on the physical model simulation. The so-called visual rendering means the computer generation of 3D images of real world and even virtual world, but without sounds. By integration of 3D visual and auditory rendering we mean while computer generates a 3D image of physical model of real world, it generates the sound based on the physical model displayed if there is a reverberation-free sound source. Based on some kinds of similarity between the propagation nature of light and sound, a modified radiosity algorithm has been proposed for integrating implementation. The algorithm is suitable for both visual and room auditory rendering. It means for a given enclosure, once the form factors are calculated, they can be applied for calculating both the light radiosities and sound radiosities simultaneously. The features of the algorithm are indicated. The implementation techniques are given in detail. The integration of visual and auditory rendering is a big step toward real world simulation, furthermore it will extend the research direction of visualization in scientific computing (ViSC) to visualization and audiobilization in scientific computing (VAiSC). The combination of VAiSC with virtual reality technique will improve human-computer interface greatly.     

Contact and Deformation Modeling for Interactive Environments

Contact and deformation modeling for interactive environments has seen many applications, from surgical simulation and training, to virtual prototyping, to teleoperation, etc., where both visual feedback and haptic feedback are needed. High-quality feedback demands a high level of physical realism as well as a high update rate in rendering, which are often conflicting requirements. In this paper, we present a unique approach to modeling force and deformation between a rigid body and an elastic object under complex contacts, which achieves a good compromise of reasonable physical realism and real-time update rate (at least 1 kHz). We simulate contact forces based on a nonlinear physical model. We further introduce a novel approximation of material deformation suitable for interactive environments based on applying Bernoulli-Euler bending beam theory to the simulation of elastic shape deformation. Our approach is able to simulate the contact forces exerted upon the rigid body (that can be virtually held by a user via a haptic device) not only when it forms one or more than one contact with the elastic object, but also when it moves compliantly on the surface of the elastic object, taking friction into account. Our approach is also able to simulate the global and local shape deformation of the elastic object due to contact. All the simulations can be performed in a combined update rate of over 1 kHz, which we demonstrate in several examples.     

Real-time haptic incision simulation using FEM-based discontinuous free-form deformation

Computer-aided surgical simulation is a topic of increasingly extensive research. Computer graphics, geometrical modelling and finite-element analysis all play major roles in these simulations. Furthermore, real-time response, interactivity and accuracy are crucial components in any such simulation system. A major effort has been invested in recent years to find ways to improve the performance, accuracy and realism of existing systems.In this paper, we extend the work of [Sela G, Schein S, Elber G. Real-time incision simulation using discontinuous free form deformation. In: Cotin S, Metaxas DN, editors. Medical simulation: International symposium, 2004. Lecture notes in computer science, vol. 3078. Springer; 2004. p. 114-123], in which we used discontinuous free-form deformations (DFFD) to artificially simulate real-time surgical operations. The presented scheme now uses accurate data from a finite-element model (FEM), which simulates the motion response of the tissue around the scalpel, during incision. The data are then encoded once into the DFFD, representing the simulation over time. In real-time, The DFFD is applied to the vertices of the surface mesh at the actual incision location and time. The presented scheme encapsulates and takes advantage of both the speed of the DFFD application, and the accuracy of a FEM. In addition, the presented system uses a haptic force feedback device in order to improve realism and ease of use.     

Physically based real-time interactive assembly simulation of cable harness

In this paper, we designed and developed an interactive assembly simulation system of cable harness. First, we establish a real-time physical model of cable harness based on an extension of the mass–spring model. We use various kinds of springs to describe the different properties of the cable harness: linear springs for stretching, bending springs for bending, and torsion springs for geometrical torsion and material twisting. The constraints of connectors and clips on cable harness are both considered. We also associate the elastic coefficients of various springs with the material parameters of the cable. Moreover, we use spherical bounding volume hierarchy and triangular facets for collision detection of cable harness during the assembly simulation. By applying contact forces to both ends of the cable links that collide with the surrounding environment, we obtain the real-time contact response of cable harness. Finally, we apply the proposed model to a cable assembly task. The results show that the proposed model successfully expressed the deformation of the cable harness and the interactive manipulation is computationally efficient.     

优化灰色模型在负荷预测中的应用研究

针对传统的灰色模型在负荷增长速度较快时预测精度低的问题,提出了采用交叉遗传粒子群优化算法代替最小二乘法来优化GM(1,1)模型中参数a、b的方法;介绍了灰色预测原理及其数学模型、CGPSO算法及基于CGPSO算法的优化灰色模型,并根据实际负荷数据进行了仿真实验。结果表明,在负荷增长速度较快时,优化灰色模型的预测精度明显高于GM(1,1)模型,能够应用于电力系统的中长期负荷预测,拓展了灰色模型的适用范围。     

步态驱动的四足动物低维物理运动生成方法

目的 为了解决四足动物运动数据难以获取的问题,建立一种快速易用的四足动物运动重建和制作途径,提出了一种面向四足动物的实时低维运动生成方法。方法 首先,建立以质点、刚体和弹簧为基础的低维物理解算器,将四足动物骨架抽象为低维物理模型;其次,依据步态模式建立足迹约束,自脚向上分肢体求解全身物理质点的运动信息;最后,依据通用约束修正后的质点位置,反算全身动画骨骼节点,生成目标运动。结果 针对不同步态、不同体型、不同风格的四足动物进行多组实验,本文方法能够达到330帧/s的生成速度,且具备良好的视觉效果和通用性。结论 本文方法的输入数据易于学习和获取,计算过程实时稳定,可以快速生成符合视觉真实感的多风格运动数据。     

基于刚粘塑性有限元法的定子挤压工艺仿真

该文讨论了油泵定子传统成形方法的局限性,提出了采用温挤压工艺成形油泵定子的新工艺,为验证新工艺的可行性以及降低产品开发周期与模具成本,对油泵定子温挤成形过程的有限元仿真分析,优化了成形工艺及模具参数,通过与物理试验比较,验证了数值模拟分析的准确性。研究结果表明：①采用新工艺可以成形出机械性能好、材料利用率高的油泵定子;②采用数值模拟优化后的坯料,可以成形出锻件质量好,综合机械性能高的产品;③生产试验表明,有限元数值模拟是分析金属塑性成形问题的一种先进的、有效的方法,采用数值模拟优化后的方案对锻件进行生产试制,可以获得成形质量好的锻件,且模拟结果与生产试制结果一致。     

多介质拉氏自适应流体动力学软件LAD2D研制及其应用

拉氏方法是内爆动力学过程数值模拟的主要方法.针对高温、高压、多介质和大变形等内爆问题,采用非结构任意多边形网格底层管理、计算过程中网格邻域可变技术,以及拉氏自适应网格加密方法和层次化、模块化程序设计思想,自主研发非结构拉氏自适应网格流体动力学软件LAD2D.从物理模型、计算方法、程序设计、程序验证与确认、大变形问题数值模拟等方面系统地介绍LAD2D.LAD2D对多介质爆轰弹塑性流体大变形问题有很强的适应能力.     

Modal warping: real-time simulation of large rotational deformation and manipulation

This work proposes a real-time simulation technique for large deformations. Green's nonlinear strain tensor accurately models large deformations; however, time stepping of the resulting nonlinear system can be computationally expensive. Modal analysis based on a linear strain tensor has been shown to be suitable for real-time simulation, but is accurate only for moderately small deformations. In the present work, we identify the rotational component of an infinitesimal deformation and extend traditional linear modal analysis to track that component. We then develop a procedure to integrate the small rotations occurring at the nodal points. An interesting feature of our formulation is that it can implement both position and orientation constraints in a straightforward manner. These constraints can be used to interactively manipulate the shape of a deformable solid by dragging/twisting a set of nodes. Experiments show that the proposed technique runs in real-time, even for a complex model, and that it can simulate large bending and/or twisting deformations with acceptable realism.     

Data-driven bending fatigue life forecasting and optimization via grinding Top-Rem tool parameters for spiral bevel gears

To establish a bridge between grinding tool parameters and loaded tooth fatigue life, an innovative data-driven root flank bending fatigue life forecasting and optimization via Top-Rem tool parameters was proposed for grinding spiral bevel gears. The recent machine settings modification is extended into grinding Top-Rem tool parameters modification in case that geometric accuracy and root bending fatigue life are integrated into a collaborative optimization. The proposed Top-Rem modification includes three key steps: (I) arc-shaped blade, (II) top part, and (III) top fillet part. Then, while root bending stress is determined by using finite element method (FEM)-based simulated loaded tooth contact analysis (SLTCA), data-driven fatigue life forecasting is developed by correlating with the multiaxial fatigue damage model based assessment. Moreover, data-driven bending fatigue life optimization model is established by using Top-Rem tool parameters modification, where the important constraints in target flank determination includes: (i) root overcutting, (ii) geometric accuracy, and, (iii) fatigue life. For high accuracy and efficiency, two different strategies are proposed: (i) the different parameters modification types; and, (ii) sensitivity analysis of grinding Top-Rem tool parameters. Finally, proposed method can verify that bending fatigue life can be significantly improved by modifying the key Top-Rem tool parameters in early stage of the whole life product development for spiral bevel gears.     

Visualizing multiple error-sensitivity fields for single camera positioning

In many data acquisition tasks, the placement of a real camera can vary significantly in complexity from one scene to another. Optimal camera positioning should be governed not only by least error sensitivity, but in addition to real-world practicalities given by various physical, financial and other types of constraints. It would be a laborious and costly task to model all these constraints if one were to rely solely on fully automatic algorithms to make the decision. In this work, we present a study using 2D and 3D visualization methods to assist in single camera positioning based on error sensitivity of reconstruction and other physical and financial constraints. We develop a collection of visual mappings that depict the composition of multiple error sensitivity fields that occur for a given camera position. Each camera position is then mapped to a 3D visualization that enables visual assessment of the camera configuration. We find that the combined 2D and 3D visualization effectively aids the estimation of camera placement without the need for extensive manual configuration through trial and error. Importantly, it still provides the user with sufficient flexibility to make dynamic decisions based on physical and financial constraints that can not be encoded easily in an algorithm. We demonstrate the utility of our system on two real-world applications namely snooker analysis and camera surveillance.     

基于HPSO的自适应路由节点优化部署策略

针对无线网络中的路由节点的部署结构冗杂,经济成本高,通信质量差的问题,提出了一种基于优化混合粒子群算法(HPSO)的自适应路由节点部署策略(ADS);以最低部署成本为算法寻优目标,以无线组网节点通信,空间覆盖完整性等特点为限制条件,通过优化HPSO结合ADS,得到应用范围内的最佳的路由节点部署;首先建立无线通信网络路由节点的部署成本模型,部署通信距离关系模型,节点通信负载模型,自由空间损耗模型;依据模型确定算法寻优目标及算法限制条件;然后对HPSO进行优化,加入淘汰机制和多样性补充机制,在不降低算法效率(寻优时间)的基础上提升算法寻优准确度;对于空间相邻的路由节点,设计并采用ADS进行部署,同时优化可视域模型,缩小ADS中可行点集范围,提高下一节点的部署效率;文章方法中的HPSO与遗传算法(GA)算法和人工免疫算法(AIA)分别结合ADS进行对比试验;仿真结果表明,文章方法在保证无线通信网络通信质量的基础上,提升14％～33％算法效率,降低8％～10％的路由节点部署成本.     

CASC2D分布式水文模型异构并行算法研究

针对 CASC2D 模型精细化水文模拟时面临的计算耗时长、效率低等问题,在保持产汇流算法和流域拓扑结构的基础上,采用 CPU+GPU 的异构并行算法对 CASC2D 模型程序进行重新设计和优化,模型程序中的降雨、 产流、坡面汇流和河道汇流过程均优化为并行计算,以提高 CASC2D 模型的计算效率。将优化后的 CASC2D 模型应用于前毛庄流域的洪水流量过程模拟,计算结果与原 CASC2D 模型保持一致。在栅格分辨率为 30 m,计算步长为 3 s 时,与原 CPU 串行计算方法相比,并行加速比达到 34 倍以上,并且栅格单元数据精度越高,加速比提升越明显。异构并行算法可在不降低模拟精度的条件下显著提升 CASC2D 模型的计算效率,满足实时水文预报的应用需求。     

Efficient and Accurate Sound Propagation Using Adaptive Rectangular Decomposition

Accurate sound rendering can add significant realism to complement visual display in interactive applications, as well as facilitate acoustic predictions for many engineering applications, like accurate acoustic analysis for architectural design (Monks et al., 2000). Numerical simulation can provide this realism most naturally by modeling the underlying physics of wave propagation. However, wave simulation has traditionally posed a tough computational challenge. In this paper, we present a technique which relies on an adaptive rectangular decomposition of 3D scenes to enable efficient and accurate simulation of sound propagation in complex virtual environments. It exploits the known analytical solution of the wave equation in rectangular domains, and utilizes an efficient implementation of the discrete cosine transform on graphics processors (GPU) to achieve at least a 100-fold performance gain compared to a standard finite-difference time-domain (FDTD) implementation with comparable accuracy, while also being 10-fold more memory efficient. Consequently, we are able to perform accurate numerical acoustic simulation on large, complex scenes in the kilohertz range. To the best of our knowledge, it was not previously possible to perform such simulations on a desktop computer. Our work thus enables acoustic analysis on large scenes and auditory display for complex virtual environments on commodity hardware.     

Evaluation of stereoscopic visual fatigue in experts

Several objective or subjective measures have been employed to evaluate stereoscopic visual fatigue. Objective measures are more preferred for their capability to quantify the degree of human visual fatigue without being affected by individual variation. However, the combination of objective indicators, their sensibility in reflecting subjective fatigue and their applicability to different groups has rarely been studied. In our previous study based on non‐expert experiment, we proposed a method combining subjective assessment and objective measures to evaluate stereoscopic visual fatigue and an objective visual fatigue model (non‐expert model). In this study, we use the same procedure to conduct a contrast experiment in 2D and 3D conditions, but only with expert viewers. The results in 2D condition show that the two objective indicators are usable for visual fatigue evaluation. The difference between the results in 2D and 3D conditions shows that the stereo 3D can cause much more fatigue and the indicators can efficiently identify the extra fatigue with satisfactory accuracy. An objective visual fatigue model (expert‐only model) is developed based on the data obtained in the 3D condition and is evaluated with comparison to the non‐expert model. Both visual fatigue models show high correlation with the subjective data. The method we proposed is reasonably insusceptible to different viewer groups, and the results of repeated experiments are consistent. It is a promising approach to evaluate visual fatigue efficiently and objectively.