Computer simulation methods for launch vehicle mission and control problems

The flight control system of a launch vehicle is the result of the right tradeoff between different objectives, such as the interaction between the control, guidance and performance aspects of a mission with specified end conditions and the analysis of the mission trajectories and vehicle systems under a variety of normal and failure modes. Hence an evaluation of the design and performance of such a system is not feasible through purely analytical means even with simplified models. This, together with the necessity for step-by-step refinement of the models used for the vehicle and its environment, calls for the computer simulation approach. The various considerations involved in developing and selecting the simulation model and implementing it on a computer are discussed. To illustrate the approach, a hybrid simulation evaluation of the performance of the first stage control system of a satellite launch vehicle and that of the controlled vehicle under different operational modes is presented.     

Invited paper Perspectives and challenges for research in quality and reliability engineering

In this paper we present some of the recent advances in the quality and reliability engineering methodologies. These advances include change point detection, monitoring processes with correlated observations, monitoring and control of multivariate processes, integration of the statistical process control with engineering process control, accelerated life testing, degradation models, predictive maintenance, and software reliability engineering. Future directions of research in quality and reliability engineering and their challenges are also discussed.     

Quality and reliability information integration for design evaluation of fixture system reliability

Quality and reliability are two important factors in manufacturing‐system design. However, the analysis and optimization of manufacturing‐system reliability and product quality are normally conducted separately in practice. There is no general framework to integrate these two important factors, quantitatively analyze the interactions between them, and further study their integrated effects on the manufacturing‐system performance. In this paper, the QR‐Co‐Effect of product/part quality and manufacturing‐system component reliability is investigated in an assembly fixture system. The concept, model and analysis of QR‐Co‐Effect are addressed in this paper. Copyright © 2001 John Wiley & Sons, Ltd.     

A Monte-Carlo simulation approach for approximating multi-state two-terminal reliability

This paper describes a Monte-Carlo (MC) simulation methodology for estimating the reliability of a multi-state network. The problem under consideration involves multi-state two-terminal reliability (M2TR) computation. Previous approaches have relied on enumeration or on the computation of multi-state minimal cut vectors (MMCV) and the application of inclusion/exclusion formulae. This paper discusses issues related to the reliability calculation process based on MMCV. For large systems with even a relatively small number of component states, reliability computation can become prohibitive or inaccurate using current methods. The major focus of this paper is to present and compare a new MC simulation approach that obtains accurate approximations to the actual M2TR. The methodology uses MC to generate system state vectors. Once a vector is obtained, it is compared to the set of MMCV to determine whether the capacity of the vector satisfies the required demand. Examples are used to illustrate and validate the methodology. The estimates of the simulation approach are compared to exact and approximation procedures from solution quality and computational effort perspectives. Results obtained from the simulation approach show that for relatively large networks, the maximum absolute relative error between the simulation and the actual M2TR is less than 0.9%, yet when considering approximation formulae, this error can be as large as 18.97%. Finally, the paper discusses that the MC approach consistently yields accurate results while the accuracy of the bounding methodologies can be dependant on components that have considerable impact on the system design.     

Impact of quality variations on product reliability

The reliability of manufactured products can differ from the desired design reliability due to variations in manufacturing quality. Failure data from field provide useful information to assess if the changes in product reliability variations are significant or not and to identify the cause for the variation. In order to devise statistical methods to detect this, one needs to model the effect of quality variations in manufacturing on product reliability. This paper looks at this issue and examines the Weibull case in detail.     

导弹折叠展开机构工作可靠性的Monte Carlo模拟计算方法研究

针对导弹折叠展开机构工作可靠性计算精度较差的问题,应用力矩状态函数和功状态函数相结合的可靠性分析方法,以导弹翼面上的力矩和功作为可靠性特征变量,建立导弹折叠展开机构工作可靠性计算模型,提出了机构可靠性的Monte Carlo模拟计算方法,并对某型导弹的翼面折叠展开机构工作可靠性进行了分析计算,所得可靠度比仅仅基于力矩的计算结果提高24.34%,比仅仅基于功的计算结果提高11.74%．计算结果表明,采用所提出的方法计算得到的机构可靠度,与仅仅基于力矩或功的计算结果相比较,更接近于工程实际．     

Designing a software reliability programme

Designing reliable software is becoming an ever increasing problem because the high cost of software is largely due to reliability problems. The costs of finding and fixing the errors, better known as maintenance and testing costs, account for as much as 80 per cent of the total cost of the final software product. Software developers now have an even greater interest in preventing errors from making their way into the software and finding the errors that are present in the early stages of development. Precise software design, coding and testing play an important role. This paper presents a management plan for implementing a software reliability programme at a small software industry where no reliability programme yet exists and no reliability programme is yet established.     

ORCHID—A computer simulation of the reliability of an NDE inspection system

CANDU pressurized heavy water reactors contain several hundred horizontally-mounted zirconium alloy pressure tubes. Following a pressure tube failure, a pressure tube inspection system called CIGARette was rapidly designed, manufactured and put in operation. Defects called hydride blisters were found to be the cause of the failure, and were detected using a combination of eddy current and ultrasonic scans. A number of improvements were made to CIGARette during the inspection period. The ORCHID computer program models the operation of the delivery system, eddy current and ultrasonic systems by imitating the on-reactor decision-making procedure. ORCHID predicts that during the early stage of development, less than one blistered tube in three would be detected, while less than one in two would be detected in the middle development stage. However, ORCHID predicts that during the late development stage, probability of detection will be over 90%, primarily due to the inclusion of axial ultrasonic scans (a procedural modification). Rotational and axial slip could severely reduce probability of detection. Comparison of CIGARette's inspection data with ORCHID's predictions indicate that the latter are compatible with the actual inspection results, though the numbers are small and data uncertain. It should be emphasized that the CIGARette system has been essentially replaced with the much more reliable CIGAR system.     

薄膜生长模型与计算机模拟

阐述了计算机模拟薄膜生长研究在纳米材料设计中的重要意义。通过最近多篇文献报道，归娄介绍了常见的薄膜生长模型、原理及方法，并详细对比了分子动力学、蒙特卡罗和量子力学3类方法、原理及应用特点。报道了国内外近几年薄膜生长模型与模拟的一些研究成果。结合不同的方法与原理，以分子动力学结合蒙特卡罗模型为重点，简要评述了这些模型及模拟特点，并提出了作者的一些见解。分析了多元化合物薄膜生长模拟的技术难点，指出了量子力学计算理论与方法同分子动力学、蒙特卡罗模型相结合的新型模型是解决这一难题的发展方向，展望了今后国内外的发展趋势。     

Mission reliability evaluation based on operational quality data for multistate manufacturing systems

Modern and intelligent manufacturing systems have a prominent multistate feature. However, previous studies of reliability analysis of multistate manufacturing systems mostly focused on the basic reliability of manufacturing systems but disregarded their operating characteristics, which has hindered the development of Prognostics and Health Management technique for intelligent manufacturing systems. Therefore, an evaluation approach of mission reliability for multistate manufacturing systems based on operational quality data is proposed in this paper. First, from the systematic viewpoint of the composition and operational principle of the manufacturing system, the relationship among production task execution state, production equipment degradation state, and produced product quality state is expounded, and the connotation of the mission reliability of multistate manufacturing systems is defined. Second, an extended state task network (ESTN) is presented to organise operational quality data by considering the quality state of work in process (WIP). Third, a fusion model of operational quality data for manufacturing systems is established with the aid of the ESTN, and an operational quality data-oriented evaluation method of mission reliability is been put forward. Finally, a case study of a manufacturing system for a cylinder head is conducted to verify the proposed approach.     

An architectural model for software reliability quantification: sources of data

Software reliability assessment models in use today treat software as a monolithic block. An aversion towards ‘atomic' models seems to exist. These models appear to add complexity to the modeling, to the data collection and seem intrinsically difficult to generalize. In 1997, we introduced an architecturally based software reliability model called FASRE. The model is based on an architecture derived from the requirements which captures both functional and nonfunctional requirements and on a generic classification of functions, attributes and failure modes. The model focuses on evaluation of failure mode probabilities and uses a Bayesian quantification framework. Failure mode probabilities of functions and attributes are propagated to the system level using fault trees. It can incorporate any type of prior information such as results of developers' testing, historical information on a specific functionality and its attributes, and, is ideally suited for reusable software. By building an architecture and deriving its potential failure modes, the model forces early appraisal and understanding of the weaknesses of the software, allows reliability analysis of the structure of the system, provides assessments at a functional level as well as at a systems' level. In order to quantify the probability of failure (or the probability of success) of a specific element of our architecture, data are needed. The term element of the architecture is used here in its broadest sense to mean a single failure mode or a higher level of abstraction such as a function. The paper surveys the potential sources of software reliability data available during software development. Next the mechanisms for incorporating these sources of relevant data to the FASRE model are identified.     

磁控过程的计算机模拟

本文基于蒙特卡罗方法,并结合SRIM软件,编制程序跟踪模拟了磁控溅射各物理过程的粒子状态.以铝靶材为例,得到了粒子在磁控溅射各物理过程的状态分布,讨论了工作参数对薄膜沉积过程的影响.模拟结果表明:溅射原子的能量主要分布在20 eV以下,当原子沉积到基片表面时,其能量主要分布在15 eV以下,但有两个分布峰值,两个分布峰值对应着快慢两种不同形式的沉积过程.原子沉积到基片 表面的位置大致服从正态分布,气压p和靶基距离d影响正态分布的方差,也即影响沉积原子在基片表 面分布的均匀性.功率与沉积速度呈良好的线性关系,在工作气压为1 Pa,靶基距离为60mm的条件下,当入射粒子的能量为250 eV时,模拟得到的功率效率最大.     

Reliability analysis in fracture mechanics using the first-order reliability method and Monte Carlo simulation

The development of a Windows‐based framework to undertake probabilistic fracture mechanics studies is reported. For a selective library of standard case problems, the reliability index of critical and sub‐critical (fatigue) problems with stochastic definition is evaluated. Both first‐order reliability method (FORM) as well as and Monte Carlo simulation method (MCS) techniques are used in critical crack growth, and only MCS is adopted for fatigue problems. Numerical predictions for the stress intensity factors (SIF) were validated with NASA/FLAGRO and reliability predictions were validated with both RELTRAN and VaP. With the advent of powerful and inexpensive personal computer, and the user‐friendliness of graphical user interface, programs such as the one developed will indeed make it possible for engineer to correctly account for the stochastic nature of most fracture problems they are confronted with.     

高可靠性软件的极值统计分析

提出了极值统计分析的方法．对于失效数据极值分布函数的拟合检验，采用了相关系数法；对于母体分布的参数估计，则分别采用了最小二乘估计（LSE）和极大似然估计（MLE）；最后通过一个实例说明了统计过程，并用模拟的方法证明了最小二乘估计较好。     

基于VRML的空间并联机器人运动仿真优化

虚拟现实技术(VRML)经常被运用于机器人仿真,针对传统的并联机器人运动学反解运算量大所引发的仿真系统效率问题,采用VRML的IndexedLineSet节点,通过负载平台的运动学参数动态更新IndexedLineSet节点,并以该节点为基础解出导杆的位姿.通过JavaScript与VRML交互编程实现了6自由度机器人的运动仿真.结果证明,优化后的系统仿真效率相比于传统的方法有很大的提升.     

Computer modelling and simulation in materials science

The paper presents a brief overview of different types of modelling and simulation along with the distinguishing features between the two. Spatial as well as temporal size scales with a special reference to multiscale modelling are explained with illustrations. The paper includes a discussion on numerical experiments and their validation based on the authors’ work on FEM simulation of crack-tip blunting during ductile fracture. Attention is drawn to the use of a 3P technique involving integrated simulation of deformation (property) at microstructural level, the process at macroscopic level and the performance at the product level.     

薄膜生长的计算机模拟

薄膜技术在现代科技领域中有着广泛的应用。人们对薄膜的生长过程通过理论和实验进行了深入的研究，其中计算机模拟是重要的方法，本文概述了对薄膜生长过程的实验观察结果及其理论分析，主要讨论了薄膜生长的计算机模拟中经常采用的方法-蒙特卡罗法和分子动力学方法、描述衬底上成膜粒子运动的一些模型以及在计算机模拟中需注意的一些问题，其中主要包括粒子间的相互作用，入射粒子的能量和粒子上的衬底上的扩散运动。     

靶材溅射及溅射原子输运的计算机模拟

用软件SRIM及蒙特卡罗法综合模拟了靶材溅射及溅射原子输运的过程。模拟结果包括溅射原子输运到衬底时的能量、入射角和入射位置。由模拟结果知,溅射原子输运主要受P×d影响(P为真空室气压,d为靶基距),P×d愈大输运到衬底的溅射原子愈少,且能量愈小;溅射原子到达衬底时,能量集中在几电子伏范围内,且在能量很低的区域有分布峰;角度分布主要集中在垂直方向,这与从靶面出射时的分布相似,但垂直方向的分布有所减小;位置分布与从靶面出射时相比,分布范围在径向扩大、趋于均匀化,但主要在靶直径范围内。