Methods for simulating and optimizing molded micro components and systems

Casting production of metallic and ceramic micro components is still in the research phase, and the components obtained with the current technologies are suffering of a certain lack of reproducibility. Within the scope of Collaborative Research Center 499 “Design, Production and Quality Assurance of Molded micro components made of Metallic and Ceramic Materials”, basics in a persistent process chain for micro components are acquired. The development, process preparation, mass production and material and components behavior investigation is understood under consistent chain. This work presents computer simulation based methods that contribute to optimize micro molded systems on both a component and a system basis. The introduction of such methods allows studying the behavior of components and systems with regard to their grain structure and the wide geometric tolerances required.     

Micro gas bearings fabricated by deep X-ray lithography

Micro bearing systems for Micro Electromechanical Systems (MEMS) have drawn attention for several decades as critical components for micro rotating machinery. Ideally, frictionless bearings are needed, and in practice, micro gas bearings approach the ideal. Typically, bearings function as a separate component, assembled onto sliding counterparts. However, in micro scale devices, assembly procedures are known to be very tedious and time consuming. This leads to the pursuit of single material monolithic structures. Critical issues arising from these approaches include: limitation of materials, friction, and reliability, among others. In this paper, new approaches have been pursued. Micro gas bearings were fabricated as a single component through X-ray lithography. A stainless steel gauge pin, machined to ultra precision, was used as a journal shaft. Simple and very easy assembly processes using self-aligning concepts were developed as an alternative method to conventional assembly. This article presents the design, fabrication, assembly, and testing of micro gas bearings.This project was funded from National Science Foundation (DMI-0115527) and Atoz CompuNet Ltd. The authors also acknowledge partial support from Center for Nano and Molecular Science and Technology and Welch foundation in The University of Texas at Austin.     

Optimal completed work dependent loading of components in cold standby systems

This paper considers the modelling and optimization of 1-out-of-N: G cold standby (CS) systems with non-repairable components functioning at different levels of productivity or load. The productivity heterogeneity leads to difference in component failure behaviour as well as in operational and replacement costs. Thus, the choice of load or productivity of components can greatly affect the system reliability and mission cost. To make the optimal choice of component loading, we first suggest a method for analysing the reliability and expected mission cost of 1-out-of-N: G non-repairable CS systems with heterogeneous components. The optimal dynamic load distribution problem is then formulated and solved, in which the component loading is chosen depending on the amount of work completed prior to the component activation. The optimal loading is aimed at minimizing the expected mission cost, while meeting a certain system reliability constraint. Examples are given to demonstrate the proposed methodology and the improvement in the optimal design solution through introducing the component productivity’s dependence on the completed work.     

Power-Law Distributions of Component Size in General Software Systems

This paper begins by modeling general software systems using concepts from statistical mechanics which provide a framework for linking microscopic and macroscopic features of any complex system. This analysis provides a way of linking two features of particular interest in software systems: first the microscopic distribution of defects within components and second the macroscopic distribution of component sizes in a typical system. The former has been studied extensively, but the latter much less so. This paper shows that subject to an external constraint that the total number of defects is fixed in an equilibrium system, commonly used defect models for individual components directly imply that the distribution of component sizes in such a system will obey a power-law Pareto distribution. The paper continues by analyzing a large number of mature systems of different total sizes, different implementation languages, and very different application areas, and demonstrates that the component sizes do indeed appear to obey the predicted power-law distribution. Some possible implications of this are explored.     

Research issues in testing business components

The advantages of migrating from traditional monolithic business applications to reusable object-based business components (self-contained software that carries out a certain business task) are well documented. A business system assembled from reusable components is argued to be highly reliable since these components have been tested and used in many other business applications. However, all possible uses of components are not known at design and construction stage. Additionally, integration testing is needed as components are assembled to make business application systems. Component-based software development requires that testing issues be addressed adequately. In this paper, we explore testing related issues in business components and in particular, business application systems that are made by integrating these components. An integration test strategy for business component application systems is proposed.     

Hierarchical simulation model with animation

There are many issues in computer simulation such as verifying model code, validating models, understanding the dynamics of systems and training the personnel. The developers of simulation tool have been interested in the animation, since it can help solve theproblems related to the above listed issues. Trying to display all the graphic objects representing the dynamics of the models being simulated, however, causes the distractionof focus, which results in solving the above listed problems difficult. The redundant graphic objects also increase the computer computation overhead. This paper presents a hierarchical animation environment in which the users can have better focus on the dynamics of system components by selectively choosing the hierarchical level and components within a level of the hierarchically structured model. When the model is large and complex in particular, the selection of observation level is needed. The design of the hierarchical animation is based on the DEVS (Discrete EVent system Specification) formalism, which is theoretically well grounded means of expressing modular and hierarchical models.     

Flexible coordinator design for modeling resource sharing in multi-agent systems

One approach to modeling multi-agent systems (MASs) is to employ a method that defines components which describe the local behavior of individual agents, as well as a special component, called a coordinator. The coordinator component coordinates the resource sharing behavior among the agents. The agent models define a set of local plans, and the combination of local plans and a coordinator defines a system’s global plan. Although earlier work has provided the base functionality needed to synthesize inter-agent resource sharing behavior for a global, conflict-free MAS environment, the lack of coordination flexibility limits the modeling capability at both the local plan level and the global plan level. In this paper, we describe a flexible design method that supports a range of coordinator components. The method defines four levels of coordination and an associated four-step coordinator generation process, which allows for the design of coordinators with increasing capabilities for handling complexity associated with resource coordination. Colored Petri net based simulation is used to analyze various properties that derive from different coordinators and synthesis of a reduced coordinator component is discussed for cases that involve homogeneous agents.     

业务流程驱动的森林仿真构件组装技术及应用研究

针对森林仿真系统的需求或应用目标不断发生变化的问题,提出了一种业务流程驱动的森林仿真构件组装方法。该方法设计和实现了森林仿真领域的构件模型和仿真构件接口,并通过业务流程驱动的构件组装框架实现了森林仿真系统的业务流程、模型算法等的软件复用,解决了现有森林仿真系统存在的快速构建或重构困难的问题。通过在虚拟森林仿真系统开发中的应用表明,基于构件组装的方法与代码级重用、重新开发方式相比,可以大幅减少开发工作量,降低系统的开发难度,实现森林仿真系统的快速搭建或重构。     

Sensor-guided micro assembly of active micro systems by using a hot melt based joining technology

This article presents (the most) recent results of the subprojects B4 and B8 of the Collaborative Research Center 516—Design and Manufacturing of Active Micro Systems—which are concerned with the assembly of active micro systems. While subproject B4 investigates sensor guided assembly processes, subproject B8 develops suitable assembly techniques on the basis of non-viscous adhesive systems (hot melts). Process development focuses on the suitability for automation, process times and the applicability of batch processes. The article discusses certain hot melt application techniques that are suitable for batch production, a sensor-guided assembly system as well as different approaches for heat conduction in an automated assembly process for hot melt coated micro components.     

Critical issues in the development of component-based discrete simulation

The development of computer simulation methods has proceeded in parallel with those in other areas of computing. Thus, interest in component-based approaches is evident both in general software engineering and in computer simulation, with advocates arguing that component-based approaches are far superior to more conventional ways of developing software and applications. Potential benefits are reduced cost and development time arising from reuse of components, as well as easier model adaptation due to the features of extensibility and evolvability. If these are to be realised, then organisations must develop ways to ensure that costs and benefits are shared and should ensure that suitable libraries and component distribution frameworks are available. In a simulation context it is also crucial to ensure that the issue of model credibility and validity is addressed even if the components are thought valid.     

在构件化嵌入式操作系统中应用抢占阈值调度

现有基于构件的嵌入式实时软件开发过程着重于从结构的角度分解系统成若干构件,以及重用构件。实践证明,该开发过程还应从运行角度将构件映射成任务,并选择适当的实时调度算法。为此,根据目前的工程实践提出一种实时构件模型,包含将构件映射成任务的方式。描述了当前构件化嵌入式操作系统可以使用的4种调度算法,并比较这些算法的性能特点。提出抢占阈值(preemptionthreshold)调度模型更适合构件化嵌入式实时系统,仿真实验的结果证明了该结论。比较结果和结论对构件化嵌入式实时系统的设计和开发有一定的参考价值。     

Performance of Scheduling Strategies for Client–Server Systems

Two approaches to the improvement of the performance of client–server systems, multithreading and scheduling of servers, are investigated. Both of these approaches are observed to have a significant impact on system performance. The use of multithreading improves throughput characteristics of systems, whereas the deployment of appropriate scheduling strategies at servers can produce a significant improvement in mean client response times. Based on a simulation model a number of basic questions that are important in the context of scheduling on nonmultithreaded, as well as multithreaded, systems are analyzed. Two important factors, monopolization of servers by large requests and software bottlenecks, are observed to be important in the context of scheduling on client–server systems. Both server scheduling, as well as multithreading, can be used to control these effects and lead to a higher system performance. Scheduling policies based on request characteristics are observed to perform well. A new request characteristic that is useful in the scheduling of client–server systems in the presence of software bottlenecks is proposed. Selection of both the server process, as well as the thread within the server, is required when multiple server, are co-located on the same CPU. A comparison between two scheduling approaches, single level and two level is presented in the paper. The results of this research are useful primarily in the design of operating systems for client–server systems and are also of interest to system designers and users.     

Professional negligence and financial‐legal expert systems: Architectures to enable the reasonableness defence

The legal implications of professionals relying on expert systems have been extensively studied by analysts who have considered the ‘macro’ issues such as whether products liability can be invited for loss resulting from errors in expert systems, and apportionment of liability. These macro‐analyses do not distinguish programming errors from what we call ‘errors of reasoning’. The latter errors may be considered to be advertent on the part of developers and/or user‐professionals; may potentially be directly compared with the reasoning ascribable to a reasonably competent professional; and cannot be removed merely by better quality assurance in the sense prevalent in software engineering. In this paper we consider the mechanisms by which a court may examine errors of reasoning in expert systems used to assist professionals working in certain areas of financial services ('the financial‐legal domain'). Our analysis of the ‘micro’ issues of liability shows that the advertent nature of errors of reasoning makes it difficult to argue that using the best possible quality assurance methods during development is sufficient to make the reliance on an expert system reasonable. However, certain valuable defences that are available to professionals acting unaided can be made out even when expert systems are employed as part of the reasoning process, though these defences will be disabled if certain conceptual structures of the knowledge of professionals are not distinctively maintained in the knowledge base. As such, opacity of a knowledge base assists, rather than hinders, a plaintiff in establishing professional negligence. The results of an analysis of the micro‐issues of liability have been applied by us in the design of a system for financial/tax planning. A case‐based reasoning approach is employed, deductive rules being employed strictly in a subsidiary role. Consequently, the primary justification for a decision is a ‘case’ ‐ an instance of problem‐solving by a professional ‐ that is likely to be accepted by the court as being representative of the actions of reasonably competent professionals.     

Building a Digital Wind Farm

The purpose of this paper is to provide a high level, holistic overview of the work being undertaken in the wind energy industry. It summarises the main techniques used to simulate both aerodynamic and structural issues associated with wind turbines and farms. The motivation behind this paper is to provide new researchers with an outlook of the modelling and simulation landscape, whilst highlighting the trends and direction research is taking. Each section summarises an individual area of simulation and modelling, covering the important historical research findings and a comprehensive analysis of recent work. This segregated approach emphasises the key components of wind energy. Topics range in geometric scales and detail, ranging from atmospheric boundary layer modelling, to fatigue and fracture in the turbine blades. More recent studies have begun to combine a range of scales and physics to better approximate real systems and provide higher fidelity and accurate analyses to manufacturers and companies. This paper shows a clear trend towards coupling both scales and physics into singular models utilising high performance computing system.     

Object-oriented simulations in mechatronics

The artificial word 'mechatronics' represents the symbiosis of 'classical' mechanical systems and 'modern' electmnics that has opened up a wide range of new possibilities. A typical application is an anti-lock braking system (ABS), a very complex combination of sensors, microprocessor-based controllers, electromagnetic actuators and mechanical as well as hydraulic components. Increasing complexity and their mostly non-linear behaviour are the major challenges in designing, implementing and testing these systems. A very promising design methodology is based on the idea of integrating real hardware via interfaces into a system simulation ('hardware-in-the-loop'). Development may start with a completely simulated model. With hardware being designed and becoming available, it is step by step incorporated into the system. This methodology significantly reduces development time since there is early feedback on the design approaches and the final solution is proved under real operating conditions. Obviously the real-time simulation of fast mechatronical systems requires tremendous computing power. Supposing one finds a way to express the simulation problem in a parallel form, a multi-transputer system could provide the necessary computing power for a relatively low price. One solution is a modelling approach that decomposes the systems hierarchically into components with a strong relationship to the physical world. Each component is described by a set of equations operating on the component's own local state. The communication of physical interface data is modelled by sending messages via connections between the components. This approach may be attributed as 'object-oriented' since computer science defines objects as independent elements maintaining their own internal state and communicating via message-passing mechanisms. Taking a close look at a transputer, it reveals a very 'object'-like architecture: local memory to maintain its own local state and links designed to pass messages between transputers. Therefore transputers are the ideal vehicle for fast real-time simulation by following the principle of object-orientation, from system modelling all the way down to simulation.     

分布式系统可靠性研究的问题和挑战

分布式系统中软件可靠性是应用软件的发布者和用户关心的重要问题。针对大规模分布式应用,包括电子政务、电子商务、多媒体服务和端到端的自动化解决方案,已经产生了各种各样的模型来评价或预测其可靠性,但是这些系统的可靠性问题依然存在。相反,为了确保分布式系统的可靠性,要求在预测或评价整个系统可靠性之前,检查与企业分布式应用相关的每一个单个构件或因素的可靠性,且实现透明的错误检测和错误恢复机制为用户提供无缝交互。因此,文章从检查单个构件可靠性的角度,提出了在分布式系统上运行的应用软件可靠性的问题和挑战。     

Importance analysis by logical differential calculus

The physical objects or processes include many interconnected components representing a complex systems. Their reliability analysis usually considers two states interpreted as failure and operability. They are described in terms of the binary mathematical model. Importance analysis of the system elements is a traditional component of the reliability analysis. It enables one to estimate the impact of individual components on the system’s operability or failure. The present paper proposed a new approach to analysis and estimation of the system importance on the basis of the logical differential calculus.     

Structural dynamics and ride comfort of a rail vehicle system

The paper describes the development of a virtual vehicle system using virtual prototyping computer tools. The virtual vehicle is used for the prediction of the structural dynamics. Since the modelling process for complete rail vehicle systems becomes increasingly more complex, time and cost can be saved by the use of a database concept and an automated assembling process for the vehicle of interest.Supported by a modular design concept, vehicle components for a metro train have been modelled and stored as substructures in a specific vehicle component database. Using this database, train configurations up to a three-car train can be assembled very quickly to perform structural dynamics analyses and to predict the ride comfort.Experimental results have been compared with simulation results of the rail vehicle to improve the modelling technique and the accuracy of the developed virtual vehicle system.The mathematical modelling of the rail vehicle system featuring elastic components, the structure of the database as well as numerical and experimental results are presented in this paper.     

基于适应性构件模型的软件产品线设计和实现(英文)

在当前面向特征的软件产品线开发方法中,需求级的可变性分析、可变点表示以及面向应用的定制已经得到了较好的支持。但是,从需求级的定制和裁剪( 特征模型) 到实现级( 体系结构和构件) 的映射仍然存在许多困难。针对这一问题,文章提出了一种基于适应性构件模型的软件产品线开发方法。这种适应性构件模型引入基于特征的领域模型作为构件端口( 包括内部端口和外部端口) 的语义基础。另一方面, 适应性构件模型所具有的微体系结构使得面向特定应用的构件行为定制成为可能。为了实现构件级面向特征的定制, 构件内部负责内部和外部协作的控制中心与构件的计算逻辑被分离开来执行经定制后的构件行为协议和端口语义。构件协作和计算功能的分离使针对构件行为的面向应用的定制更加便利。这样,产品线应用开发中需求级的特征定制就可以映射为体系结构和构件级的结构和行为调整。