A systematic modelling and simulation approach for JIT performance optimisation

Robust computer aided simulation and modelling tools help to visualise, analyse and optimise complex production processes with a reasonable amount of time and investment. A review of the literature shows that simulation and modelling have not been extensively applied in just-in-time (JIT) manufacturing environments. Also there remains a lack of a comprehensive mechanism to identify the most significant JIT drivers for the purpose of system process optimisation. The prime objective of this study is to close this gap by applying computer based simulation tools and linear mathematical modelling to identify the impact of selected key JIT parameters on performance in an automotive component-manufacturing environment. Research shows that variables such as inconsistent task distribution, variation on operator performance, misconception of total quality management philosophy and lack of set-up time elimination plans disrupt ideal JIT production. In this study, ProModel simulation and modelling software is used to model and simulate different experimental scenarios in order to understand and quantify the impact of selected input key JIT variables on objective functions (i.e. process time and takt time). The outcome is a robust mathematical model that highlights the significance of JIT drivers in the manually operated mixed-model assembly lines.     

现代计算机仿真技术的研究与发展

讨论了基于模型活动的仿真概念,现代仿真方法学所涉及的系统建模方法,仿真建模方法和仿真实验,仿真建模中的常用算法和有关问题,仿真可信度概念及其研究内容,文章最后探讨了现代仿真技术的研究热点：面向对象仿真、定性仿真,智能仿真,分布交互仿真,可视化仿真,多媒体仿真,虚拟现实仿真等。     

大型火电机组实时仿真机上的发电机数学模型

该文根据３３０ＭＷ火电机组培训实时仿真的要求，建立了发电机动态数学模型，描述了发电机的全部物理过程，建模过程作了合理的简化和假设，使仿真模型适用于机组的起动、正常运行及故障等各种工况。     

410t／h Pyroflow CFB锅炉仿真系统开发

该文介绍了基于Ｗｉｎｄｏｗｓ９５环境下的４１０ｔ／ｈ Ｐｙｒｏｆｌｏｗ循环流化床锅炉的仿真系统的设计与实现方法。仿真系统包括ＣＦＢ锅炉系统动态数学模型、仿ＤＣＳ系统的运行工程师操作界面、仿真输入输出数据的设计及处理等内容。本系统可用于现场运行工程师了解和掌握ＣＦＢ锅炉的动、静态特性、分析运行方式及运行工况变化对系统的影响以及进行事故预测及事故分析等工作。     

MATLAB在化工模拟计算中的应用

通过MATLAB辅助绿色含硫气湿法直接脱硫制酸新工艺及SO2转化器的模拟计算实例,着重介绍和说明了MATLAB在化工模拟数值计算及最优化、数值过程及结果的可视化、用户图形界面设计等方面的功能与应用。化学工作者利用MATLAB语言,即使不善精通数值计算方法和其它高级编程语言,也完全可以设计出功能强大,界面优美,稳定可靠的高质量化工模拟程序,并且可实现模拟计算结果的可视化和用户图形界面的一体化。     

直流调速系统的优化与仿真

提出了一种采用计算机仿真进行直流调速系统的优化与仿真的方法：首先,根据直流调速数字控制系统的性能特点,建立了系统仿真模型,然后分析了该系统的缺点所在并进行优化,从而构成一种复合控制系统,以实现对驱动电流的控制作用,最后对优化前后的输出数据进行分析对比,结果表明,采用优化后的控制系统可使输出数据更加精确可靠。     

室温变化的数学模型及其仿真

该文介绍了一种用差分方程建立的室温变化的数学模型，并用此模型对不同条件和参数的情况的室温变化进行了模拟和仿真。其结果表明，此模型有助于热力系统的试验和设计，是十分实用的。     

A feasible timetable generator simulation modelling framework for train scheduling problem

An important problem in management of railway systems is the train scheduling/timetabling problem. This is the problem of determining a timetable for a set of trains that do not violate track capacities and satisfy some operational constraints. In this study, a feasible timetable generator framework for stochastic simulation modelling is developed. The objective is to obtain a feasible train timetable for all trains in the system. The feasible train timetable includes train arrival and departure times at all visited stations and calculated average train travel time. Although this study focuses on train scheduling/timetabling problem, the developed simulation framework can also be used for train rescheduling/dispatching problem if this framework can be fed by real time data. The developed simulation model includes stochastic events, and can easily cope with the disturbances that occur in the railway system.     

燃油热水锅炉水循环动态数学模型及仿真

该文介绍“锅炉仿真培训系统”中采暖燃油热水锅炉水循环动态数学模型及仿真策略,提出了补水泵、循环泵和压力节点的基本方程,给出了模型参数估算方法和模型求解策略,举例说明了热水锅炉采暖外网持水量估算方法,最后介绍了该模型的特点和实际应用情况。     

基于Excel的设备投资仿真分析

电子表格Excel具有强大的计算功能,它提供了一种描述问题、建立模型、处理数据与求解的有效工具。通过汽车维修设备投资中的一个实例,说明它在计算机仿真决策中的应用。     

CHEOPS: A tool-integration platform for chemical process modelling and simulation

A large number of modelling tools exist for the construction and solution of mathematical models of chemical processes. Each (chemical) process modelling tool provides its own model representation and model definition functions as well as its own solution algorithms, which are used for performing computer-aided studies for the process under consideration. However, in order to support reusability of existing models and to allow for the combined use of different modelling tools for the study of complex processes, model integration is needed. This paper presents a concept for an integration platform that allows for the integration of modelling tools, combining their models to build up a process model and performing computer-aided studies based on this integrated process model. In order to illustrate the concept without getting into complicated algorithmic issues, we focus on steady-state simulation using models comprising only algebraic equations. The concept is realized in the component-based integration platform CHEOPS, which focuses on integrating and solving existing models rather than providing its own modelling capabilities.     

Characterization of server performance bottlenecks in distributed interactive simulation environments

Servers running distributed simulation applications need to process a large number of small packets at the network level. This becomes a burden on the server CPUs and exhibits itself as high CPU utilization. In this paper, first, we confirm this phenomenon, then, we utilize performance analyzer tools from major processor vendors to characterize the major sources of CPU usage. In addition, the experiments run on real hardware reveal server bottlenecks within the context of new architectural features such as hyper-threading, hyper-transport and multi-core processors.     

人体生理系统计算机仿真

人体生理系统是一个复杂的非线性动态系统，本文根据人体生理系统的数学模型Ｈｕｍａｎ，介绍了基于这种数学模型的仿真方法，并在微机上实现了计算机仿真系统ＨＰＳＳ，在文章的最后给出了若干仿真实验的结果。     

城市协调发展动力学模型

该文根据系统动力学原理,以城市的人口、就业、住宅为三个互相作用,互为因果的子系统,建立起城市协调发展的数学模型,并用MATLAB的Sireulink构建相应的计算机仿真模型。用南宁市的实际数据对模型中的变量进行长达一百年的仿真：人口数量、就业岗位、住宅供给量、住宅需求量、劳动力、建成区面积、人口密度、土地占用率。这些具体的数据结果勾勒出了一个城市未来一百年的发展状况,对政府机构的经济及政治决策提供了科学的、明确的依据。     

The design and calibration of a simulation model of a star computer network

A simulation model of the CERN (European Organization for Nuclear Research) SPS star computer network is described. The model concentrates on simulating the message handling computer, through which all messages in the network pass. The paper describes the main features of the model, the transfer time parameters in the model and how performance measurements were used to assist in the calibration of the model.     

A ship motion simulation system

In this article, efficient computational models for ship motions are presented. These models are used to simulate ship movements in real time. Compared with traditional approaches, our method possesses the ability to cope with different ship shapes, engines, and sea conditions without the loss of efficiency. Based on our models, we create a ship motion simulation system for both entertainment and educational applications. Our system assists users to learn the motions of a ship encountering waves, currents, and winds. Users can adjust engine powers, rudders, and other ship facilities via a graphical user interface to create their own ship models. They can also change the environment by altering wave frequencies, wave amplitudes, wave directions, currents, and winds. Therefore, numerous combinations of ships and the environment are generated and the learning becomes more amusing. In our system, a ship is treated as a rigid body floating on the sea surface. Its motions compose of 6 degrees of freedom: pitch, heave, roll, surge, sway, and yaw. These motions are divided into two categories. The first three movements are induced by sea waves, and the last three ones are caused by propellers, rudders, currents, and winds. Based on Newton’s laws and other basic physics motion models, we deduce algorithms to compute the magnitudes of the motions. Our methods can be carried out in real time and possess high fidelity. According to ship theory, the net effects of external forces on the ship hull depend on the ship shape. Therefore, the behaviors of the ship are influenced by its shape. To enhance our physics models, we classify ships into three basic types. They are flat ships, thin ships, and slender ships. Each type of ship is associated with some predefined parameters to specify their characteristics. Users can tune ship behaviors by varying the parameters even though they have only a little knowledge of ship theory.     

Development of a simulation model to predict LiDAR interception in forested environments

Airborne scanning LiDAR systems are used to predict a range of forest attributes. However, the accuracy with which this can be achieved is highly dependent on the sensor configuration and the structural characteristics of the forest examined. As a result, there is a need to understand laser light interactions with forest canopies so that LiDAR sensor configurations can be optimised to assess particular forest types. Such optimisation will not only ensure the targeted forest attributes can be accurately and consistently quantified, but may also minimise the cost of data acquisition and indicate when a survey configuration will not deliver information needs.In this paper, we detail the development and application of a model to simulate laser interactions within forested environments. The developed model, known as the LiDAR Interception and Tree Environment (LITE) model, utilises a range of structural configurations to simulate trees with variable heights, crown dimensions and foliage clumping. We developed and validated the LITE model using field data obtained from three forested sites covering a range of structural classes. Model simulations were then compared to coincident airborne LiDAR data collected over the same sites. Results indicate that the LITE model can be used to produce comparable estimates of maximum height of trees within plots (differences < 2.42 m), mean heights of first return data (differences < 2.27 m), and canopy height percentiles (r² = 0.94, p < 0.001) when compared to airborne LiDAR data. In addition, the distribution of airborne LiDAR hits through the canopy profile was closely matched by model predictions across the range of sites. Importantly, this demonstrates that the structural differences between forest stands can be characterised by LITE. Models that are capable of interpreting the response of small-footprint LiDAR waveforms can facilitate algorithm development, the generation of corrections for actual LiDAR data, and the optimisation of sensor configurations for differing forest types, benefiting a range of experimental and commercial LiDAR applications. As a result, we also performed a scenario analysis to demonstrate how differences in forest structure, terrain, and sensor configuration can influence the interception of LiDAR beams.     

Definition, modelling and simulation of a grid computing scheduling system for high throughput computing

In this paper, we study and compare grid and global computing systems and outline the benefits of having a hybrid system called DIRAC. To evaluate the DIRAC scheduling for high throughput computing, a new model is presented and a simulator was developed for many clusters of heterogeneous nodes belonging to a local network. These clusters are assumed to be connected to each other through a global network and each cluster is managed via a local scheduler which is shared by many users. We validate our simulator by comparing the experimental and analytical results of a M/M/4 queuing system. Next, we do the comparison with a real batch system and we obtain an average error of 10.5% for the response time and 12% for the makespan. We conclude that the simulator is realistic and well describes the behaviour of a large-scale system. Thus we can study the scheduling of our system called DIRAC in a high throughput context. We justify our decentralized, adaptive and opportunistic approach in comparison to a centralized approach in such a context.     

基于蔡氏电路的混沌仿真研究

混沌是非线性系统中的常见现象。该文对产生混沌现象的最简单三阶自治电路——蔡氏电路进行了研究,建立了数学模型,分析了产生混沌的原因,并根据建立的数学模型对其进行了仿真研究,仿真结果表明在一定的条件下该电路能够出现混沌双涡卷吸引子和稳定周期轨道。