虚拟样机仿真标准化技术研究

虚拟样机标准化技术是实现大型复杂虚拟样机系统集成的根本前提,提出了虚拟样机仿真标准的制定原则,研究了虚拟样机仿真标准的主要内容,包括信息建模标准、信息交换标准、信息处理标准、信息安全标准、信息传输标准及人机界面标准等,虚拟样机标准化的研究可为虚拟样机技术的实现及进一步的应用研究提供基础。     

An algorithm for off-road routing of vehicles

An algorithm for off-road routing of vehicles for land and water under off-road conditions or in the waters of the World Ocean is described. The proposed algorithm allows us to reduce significantly the memory sizes and computing time, which is important for implementation of geoinformation systems on small platforms (handheld computers, smartphones, cell phones).     

Global-referenced navigation grids for off-road vehicles and environments

The presence of automation and information technology in agricultural environments seems no longer questionable; smart spraying, variable rate fertilizing, or automatic guidance are becoming usual management tools in modern farms. Yet, such techniques are still in their nascence and offer a lively hotbed for innovation. In particular, significant research efforts are being directed toward vehicle navigation and awareness in off-road environments. However, the majority of solutions being developed are based on occupancy grids referenced with odometry and dead-reckoning, or alternatively based on GPS waypoint following, but never based on both. Yet, navigation in off-road environments highly benefits from both approaches: perception data effectively condensed in regular grids, and global references for every cell of the grid. This research proposes a framework to build globally referenced navigation grids by combining three-dimensional stereo vision with satellite-based global positioning. The construction process entails the in-field recording of perceptual information plus the geodetic coordinates of the vehicle at every image acquisition position, in addition to other basic data as velocity, heading, or GPS quality indices. The creation of local grids occurs in real time right after the stereo images have been captured by the vehicle in the field, but the final assembly of universal grids takes place after finishing the acquisition phase. Vehicle-fixed individual grids are then superposed onto the global grid, transferring original perception data to universal cells expressed in Local Tangent Plane coordinates. Global referencing allows the discontinuous appendage of data to succeed in the completion and updating of navigation grids along the time over multiple mapping sessions. This methodology was validated in a commercial vineyard, where several universal grids of the crops were generated. Vine rows were correctly reconstructed, although some difficulties appeared around the headland turns as a consequence of unreliable heading estimations. Navigation information conveyed through globally referenced regular grids turned out to be a powerful tool for upcoming practical implementations within agricultural robotics.     

Symbolic multibody methods for real-time simulation of railway vehicles

In this work, recently developed state-of-the-art symbolic multibody methods are tested to accurately model a complex railway vehicle. The model is generated using a symbolic implementation of the principle of virtual power. Creep forces are modeled using a direct symbolic implementation of the standard linear Kalker model. No simplifications, such as base parameter reduction, partial-linearization or lookup tables for contact kinematics, are used. An Implicit–Explicit integration scheme is proposed to efficiently deal with the stiff creep dynamics. Real-time performance is achieved: the CPU time required for a very robust \(1~\text{ms}\) integration time step is 203 μs.     

Modeling software architectures with goals in virtual university environment

Recently, the coupling of goal-based and user-centered approaches has resulted in a tremendous impact on the research of software engineering. However, there is no systematic way in the extant approaches to handling the effects of requirements on the structuring of software architectures. As an attempt towards the investigation of the interactions among goals, scenarios, and software architectures, we proposed, in this paper, a goal-driven architecture trade-off analysis method to analyze and construct software architectures in an incremental manner. We also identified criteria for architecture evaluation and verification and explored the possible types of realization of software architectures for goals. The proposed approach is illustrated using the problem domain of virtual university environment.     

Modeling and controlling the mobile harbour crane system with virtual prototyping technology

Virtual simulation of the real behaviour of mobile harbour crane (MHC) without using the traditional build-and-test method is an imperative approach to the design stage that can increase the quality of the product by reducing manufacturing cost and errors. This paper introduces an engineering model that describes the mechanical behaviour of MHC, and the control design for increasing the position accuracy. Based on a concept of the MHC, a virtual mechanical model was created using SOLIDWOKS, which was then exported to the Automatic Dynamic Analysis of Mechanical System (ADAMS) environment. This model was simulated to investigate the dynamic behaviour of the MHC system. In addition, an adaptive siding mode PID controller was also developed in MATLAB/Simulink to control the crane trolley position and suppress the swing angle of the load. This co-simulation demonstrates the reliability of the mechanical and control functionalities of the developed system.     

A prototyping language for real-time software

PSDL is a language for describing prototypes of real-time software systems. It is most useful for requirements analysis, feasibility studies, and the design of large embedded systems. PSDL has facilities for recording and enforcing timing constraints, and for modeling the control aspects of real-time systems using nonprocedural control constraints, operator abstractions, and data abstractions. The language has been designed for use with an associated prototyping methodology. PSDL prototypes are executable if supported by a software base containing reusable software components in an underlying programming language (e.g. Ada)     

Rapid prototyping for distributed virtual environments

The authors combine rapid and exploratory prototyping techniques to capture initially unknown, interdependent requirements in the development of distributed virtual environment applications. They employ containerization to accelerate data exchange     

Vibration attenuation performance of suspension seats for off-road forestry vehicles

Four different types of vertical suspension seats were evaluated in the laboratory and in the field in order to measure their adaptability for attenuating whole-body vibration in log skidders used in the forest industry. Laboratory testing first consisted of determining the static and dynamic characteristics of the seats such as the static stiffness of the cushions and suspension systems and the hysteresis parameters and damping properties of the cushions. The vibration attenuation characteristics of the seats were then measured using a laboratory test rig simulating a driver work station. The influence of amplitude of excitation and the variations in seat height on the vibration attenuation performance of the suspension seats was evaluated for sinusoidal excitations in the frequency range of 0.2–8.0 Hz. The seats were then field tested during normal skidding operations to determine their vertical transmissibility characteristics and to compare the vibration exposure that results from operating a skidder while being equipped with a suspended seat, as opposed to having an unsuspended one. There was generally good agreement between the transmissibility characteristics measured in the laboratory and in the field. The results of vibration transmissibility and exposure are helpful in identifying one of the suspension seats as being the most appropriate for attenuating vertical whole-body vibration on skidders, while conforming at the same time to the basic dimensional characteristics and stability required for safe operation of such vehicles.     

Evaluating software architectures for real-time systems

In this paper we describe a process for evaluating the architectures of large, complex software-intensive systems. This process involves both social and technical aspects. The social aspects deal with planning and running an evaluation. The technical aspects concentrate on the representation of architectural information, standard questions, analyses, and quality attribute characterizations. We then take the generic notion of architectural evaluation, and discuss some techniques for applying this technique to the domain of real-time systems. This revised version was published online in June 2006 with corrections to the Cover Date.     

Alice: rapid prototyping for virtual reality

Virtual reality has sparked many people's imaginations, but writing VR programs remains difficult. Besides the obvious problems of managing arcane I/O devices (trackers, gloves, and so on), the programs must allow the participant to operate effectively in the immersive environment. Virtual environments present a new medium for both the participant and the programmer/author. In the University of Virginia's User Interface Group, we believe the best way to accelerate development in a new medium such as VR is to provide tools that allow people without highly technical backgrounds to create programs for it. These novice authors must be able to quickly try different nuances of an idea. They must be able to easily ask “what if” questions. To support this goal, we are developing Alice, a rapid prototyping environment that can generate VR environments. The name “Alice” honors Lewis Carroll's heroine, who explored a rapidly changing, dynamic environment     

虚拟肝脏手术中实时动态渗血效果模拟

在实际的手术中,伤口内的渗血伴随着切割过程而频繁出现。但在以往的研究中,多数集中于血液在皮肤或脏器表面的流动,而对伤口内的动态渗血过程模拟研究较少。为此,根据动态渗血模拟对真实性与实时性的要求,提出了一种结合力反馈机制的渗血模拟仿真模型。该模型结合了流体模拟中的拉格朗日粒子法,并针对肝脏切割过程中的渗血这一特定过程对传统拉格朗日方法进行了简化,实验结果表明,其能够很好地满足动态渗血模拟对真实性和实时性的需求     

A virtual prototyping system for rapid product development

This paper describes a virtual prototyping (VP) system that integrates virtual reality with rapid prototyping (RP) to create virtual or digital prototypes to facilitate product development. The proposed VP system incorporates two new simulation methodologies, namely the dexel-based and the layer-based fabrication approaches, to simulate the powder-based and the laminated sheet-based RP processes, respectively. The dexel-based approach deposits arrays of solid strips to form a layer, while the layer-based approach directly forms a complete layer by extruding the slice contours. The layer is subsequently stacked up to fabricate a virtual prototype. The simulation approaches resemble the physical fabrication processes of most RP systems, and are therefore capable of accurately representing the geometrical characteristics of prototypes. In addition to numerical quantification of the simulation results, the system also provides stereoscopic visualisation of the product design and its prototype for detailed analyses. Indeed, the original product design may be superimposed on its virtual prototype, so that areas with dimensional errors beyond design limits may be clearly highlighted to facilitate point-to-point analysis of the surface texture and the dimensional accuracy of the prototype. Hence, the key control parameters of an RP process, such as part orientation, layer thickness and hatch space, may be effectively tuned up for optimal fabrication of physical prototypes in subsequent product development. Furthermore, the virtual prototypes can be transmitted via the Internet to customers to facilitate global manufacturing. As a result, both the lead-time and the product development costs can be significantly reduced.     

Rapid prototyping for a virtual medical campus interface

The Virtual Medical Campus Graz uses e-learning to make the human medicine curriculum digitally accessible to a target population of 4500 students and teachers. This project occurred parallel to the development of a new curriculum and thus involved all medical teachers and students. The VMC system architecture includes a multimedia repository for reusable learning objects; middleware containing the VMC logic that arranges learning objects into lectures, themes, and modules; and user interface. To ensure the interface suited the target population, we used the user-centered design method.     

虚拟人足球比赛阵法的系统建模与仿真

足球比赛阵法是进行足球比赛关键的部分,阵法应用的合适与否直接影响球队的成绩。文章首先对虚拟人足球进行了简要介绍,然后根据足球运动的特点,在机器人足球比赛仿真研究理论的基础上,对阵法仿真系统建模进行探索性研究,给出了阵法仿真系统层次结构模型,并对模型各部分做了分析,引入了亲密度矩阵（ADM）,加强了球员进攻防守协作的力度,显著提高了球队的整体进攻防守性能,最后对433阵型下的阵法进行了实验仿真,实验结果表明方法的可行性。     

虚拟环境下并联坐标测量机几何建模与运动仿真

与普通直角型坐标测量机相比，并联坐标测量机具有结构简单、测量精度高、测头位姿灵活等一系列优点。但因该坐标测量机的驱动参量与测头输出位姿之间的非线性对应关系，致使其实体样机的设计工作变得十分复杂。该文以3-RPS型三自由度并联机构坐标测量机为研究对象。在虚拟环境下对其进行了三维实体造型和运动过程仿真，从而为新型坐标测量机实体样机的开发奠定了理论基础。     

Computer-aided prototyping of production flows for a virtual enterprise

This paper presents a logistics framework to cope with the problem of planning and control of production flows processed on a set of work cells distributed among component firms of a virtual enterprise (VE). The constraints theory framework is employed to study constraint-based production flow coordination rules. The article discusses relationships linking structural parameters (e.g. buffer capacity, machine tool efficiency, and automated storage/retrieval systems) of VE components with material flow control guaranteeing efficient completion of work orders, and specified by such parameters as batch delivery periods, work-in-process (WIP) and make-span. The results are summarized in the form of a performance evaluation scheme. Examples using a software package that implements the proposed flow coordination methodology are provided.     

Modeling and simulation of longitudinal dynamics coupled with clutch engagement dynamics for ground vehicles

During the engagement of the dry clutch in automotive transmissions, clutch judder may occur. Vehicle suspension and engine mounts couple the torsional and longitudinal models, leading to oscillations of the vehicle body that are perceived by the driver as poor driving quality. This paper presents an effective formulation for the modeling and simulation of longitudinal dynamics and powertrain torsional dynamics of the vehicle based on non-smooth dynamics of multibody systems. In doing so friction forces between wheels and the road surface are modeled along with friction torque in the clutch using Coulomb’s friction law. First, bilateral constraint equations of the system are derived in Cartesian coordinates and the dynamical equations of the system are developed using the Lagrange multiplier technique. Complementary formulations are proposed to determine the state transitions from stick to slip between wheels and road surface and from the clutch. An event-driven scheme is used to represent state transition problem, which is solved as a linear complementarity problem (LCP), with Baumgarte’s stabilization method applied to reduce constraint drift. Finally, the numerical results demonstrate that the modeling technique is effective in simulating the vehicle dynamics. Using this method stick-slip transitions between driving wheel and the road surface and from the clutch, as a form of clutch judder, are demonstrated to occur periodically for certain values of the parameters of input torque from engine, and static and dynamic friction characteristics of tire/ground contact patch and clutch discs.     

面向虚拟环境的真实感漫游湖面建模算法

提出了一种面向虚拟漫游的太湖湖面建模算法。引入了Johanson投影网格法,避免了多分辨率LOD的龟裂问题,将视空间里生成的网格投影到世界空间中。为了提高渲染效率,避免对投影到世界空间中的每个湖面网格点进行噪声计算,采用了准均匀B样条曲面来构造湖水水面,将Perlin噪声施加于B样条曲面的特征控制点,间接地控制水面高度。依靠图形硬件的加速功能保证了B样条曲面的生成速度。实验表明,用该算法可以在普通PC平台上实时模拟漫游太湖的真实场景。