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doi: 10.1177/003754979907300602pmid: N/A
Using evolutionary algorithms, a search is per formed based on a population where each popula tion member consists of a vector of attribute values and a fitness value. A simulation of a system is run, given a particular set of the member attribute values, producing a fitness value. Fitness measures how well the system achieves its mission objectives. If the fitness has a random component, several runs are made to produce average fitness. The pro cedure is to select the best members from the popu lation based on average fitness and mutate the member attribute values to produce new popula tion members. Since population member attributes can affect process reaction times, wait logic, or decision logic, a search for the best attribute values over 50 to 100 generations can result in optimal fitness. In order to demonstrate the use of evolu tionary algorithms in system optimization, a sim ple inventory system that has a complex fitness surface is considered.
Csaszar, Peter; Tirpak, Thomas M.; Nelson, Peter C.
doi: 10.1177/003754979907300603pmid: N/A
This paper introduces the computer model established for a new family of modular type, multi-station walking beam high-speed chip mounter (also called chip shooter) machines, and the implemented high-accuracy simula tion software. The objective of the project was the de velopment of a comprehensive simulation tool that can replace the real machines in experiments regarding sys tem analysis and setup, yet provide accurate cycle time estimation. The thorough analysis of the machines led to the understanding of the characteristics of each part of the system, as well as the hierarchy of the parts and the interaction between them. This well-defined hierar chy and separability of different parts suggest the ob ject-oriented paradigm for the implementation of the simulation software. This paper highlights the major goals successfully addressed by the developed software: the identification of the system hierarchy with its rep resentation in a C++ class structure, the implementa tion providing code efficiency, and the design of I/O features that prepare the simulator to be embedded in an optimization procedure.
Lin, Shih-Tin; Lu, Jau-Huai; Hong, Ming-Chong; Hsu, Kwang-Wu
doi: 10.1177/003754979907300604pmid: N/A
A hybrid integration method is proposed in this paper for the real-time simulation of single spool turbojet engines. The nonlinear dynamic model of the J-85 turbojet engine is developed first. Three types of integration methods, including explicit integration methods, implicit integration methods, and the proposed hybrid integration method, are used to integrate the dynamic model. Simulation of the model by explicit integration methods fails to reach real time, since the stiff characteristic of the engine model requires small integration step size to maintain stability. On the other hand, al though use of an implicit integration algorithm can enlarge the step size, extra function evaluations are needed to calculate the system Jacobian for the Newton-Raphson algorithm, and the simulation still cannot reach real time. The proposed hybrid integration scheme uses an explicit method to in tegrate the non-stiff part of the system, and an implicit method to integrate the stiff part of the system. Real-time simulation can be achieved by using the proposed hybrid scheme.
doi: 10.1177/003754979907300605pmid: N/A
Due to the increasing popularity of simula tion, there are numerous simulation software tools available on the market. This paper pre sents the results of a survey on users' re quirements of discrete-event simulation software. The survey involved members of the Simulation Study Group of the Operational Research Society of Great Britain. Findings of the survey indicate which types of simula tion software are primarily being used, the most common application areas of simulation, and users' opinions about software and pos sible ways of improving simulation software.
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