摘要:

AbstractAccurate estimation of extreme flood events having a specified probability of occurrence is a key element in the planning and operation of water resources systems. Guidelines that specify a particular approach (statistical distribution and fitting technique) for flood-flow frequency determination have been introduced by a number of counlries seeking uniformity in the management of their water resources among government and private agencies. We present an expert system thet gives a general framework for choosing among distributions and among the most commonly used fitting techniques (methods for parameter estimation) for these distributions. The expert system will make it easier to see some of the advantages and disadvantages of each method. In particular, the system would be used (a) to help the user decide about the criteria of independence, homogeneity, stationarity, and outliers in the sample; (b) to help the user decide about the results of the fitting operations by providing a large number of fitting methods and statistical distributions as options; and (c) to provide graphical options.

ISSN:0228-6203    

DOI:10.1080/02286203.1993.11760168

出版商:Taylor&Francis    

年代:1993

数据来源: Taylor

摘要:

AbstractKnowledge of the manner in which machines break down is a vital component in any simulation model. It is this information that is used to interrupt the cycling of the model and to simulate the interaction of machine downtime. Usually, of all the parameters such as toolchangc and manning, the downtime has the greatest effect on the model throughput. It is essential, therefore, that the method simulation models used to simulate breakdown behavior are made as accurate as possible. This paper describes the results of a four-month study on 10 transfer line machines. The machines perform the first few machining operations on an engine cylinder block line. Information relating to the breakdown behavior was collected and tested for goodness of fit with standard statistical distributions. As a further comparison two simulation models of the 10 machines were built. Breakdowns on the first model were simulated by sampling standard distributions, and on the second model they were simulated using actual historical data. This comparison verified that the use of simulated breakdowns produed results as accurate as those found using historical data.

ISSN:0228-6203    

DOI:10.1080/02286203.1993.11760169

出版商:Taylor&Francis    

年代:1993

数据来源: Taylor

摘要:

AbstractThis paper is a broad overview of techniques in modelling of geometries and simulation of high-speed flow fields by explicit algorithms as applied to advanced aerospace vehicles, performed at the NASA Langley Research Center by the author. Software developed by the author for generating surface geometries and field grids for blended wing-body geometries is described. An explicit finite- volume algorithm for the solution of highly supersonic flow fields for aerospace vehicles is presented, together with results obtained from its applications. The use of these algorithms as analysis tools in related interdisciplinary areas, such as aerodynamic optimization and sensitivity analysis, is described.

ISSN:0228-6203    

DOI:10.1080/02286203.1993.11760170

出版商:Taylor&Francis    

年代:1993

数据来源: Taylor

摘要:

AbstractThis paper describes a group problem solving method called 1TM (Iterated Task Migration) for dynamic task allocation problems. ITM initially assigns unoptimal task allocations to agents. Then the agents try to change their task allocations, toward the globally optimal allocation, by iteration of task migrations. The cooperation by the agents results in adaptability and parallelism, which contribute to solving the dynamic task allocation problems. ITM works in two ways, in a synchronized way (called ITM-S) and in an asynchronized way (called ITM-A). To evaluate ITM-S and ITM-A, we have applied them to the trouble recovery problem in the area of transportation. The experimental results show that ITM-S improves adaptability while ITM-A improves run time.

ISSN:0228-6203    

DOI:10.1080/02286203.1993.11760171

出版商:Taylor&Francis    

年代:1993

数据来源: Taylor

摘要:

AbstractOvervoltages of atmospheric origin which propagate along elpctrica! lines are attenuated and distorted by the corona effect and the skin effect. The attenuation is significant. We propose a mathematical line model taking into account skin effect in the conductors and the ground, and taking into account the corona effect. Simulation results are compared with Gary’s tests performed on a real 220 kV three phase line. It can be seen that the incident lightning wave and the induced wave are highly influenced by skin effect and corona effect. The proposed model is very close to the values recorded during the test.

ISSN:0228-6203    

DOI:10.1080/02286203.1993.11760172

出版商:Taylor&Francis    

年代:1993

数据来源: Taylor

摘要:

AbstractHydrological model testing for spatial and temporal robustness is an important part of the simulation procedure but which faces particular difficulties when a model is intended to simulate surface run-off and other hydrological variables under hypothetical environmental conditions different from the historical ones. These difficulties are dealt with in this paper by constructing a water balance model intended to be used under hypothetical changes of climatic parameters and employing a variation of the differential split sample test. The model is applied to four Greek drainage basins of varying similarity in terms of their specific morphoclimatic characteristics. Results show that the predictive efficiency of the model is not affected by variations in the key climatic parameters, average air temperature and average precipitation, and that the model can be adapted to different basins with coherent adjustments of its calibration parameters.

ISSN:0228-6203    

DOI:10.1080/02286203.1993.11760173

出版商:Taylor&Francis    

年代:1993

数据来源: Taylor

摘要:

AbstractPerformance evaluation of several routing algorithms is made by discrete event simulation of a computer network consisting of 10 nodes. Both nonadaptive and adaptive routing algorithms are discussed and then the fixed (nonadaptive routing technique), the shortest-rpieue (isolated routing technique), and the shortest-path (distributed routing technique) routing algorithms are selected and described for simulation. We used average packet delay and network throughput as measures of network performance. We give results for each of the following goals:a) To evaluate and compare the network performance for the routing algorithms under light, moderate and heavy load conditions, during a transient period subject to changes in the mean arrival rate of messages and network link failures.b) To develop innovative design tools.c) To discuss and shed light on the characteristics of an ideal routing technique (correctness, computational simplicity, adaptiveness to changing traffic and topologies, stability, fairness and optimality).

ISSN:0228-6203    

DOI:10.1080/02286203.1993.11760174

出版商:Taylor&Francis    

年代:1993

数据来源: Taylor

摘要:

AbstractAdaptive algorithms are required in order to resolve the problems involved in improving the convergent property and reducing the number of multiplications per sample time. This paper presents an adaptive algorithm that can solve these problems: an algorithm in which a parameter called overlap-length that is based on orthogonal projection onto multidimensional space. This parameter can be set in compliance with the priorities of the above mentioned problems and can realize various execution forms, including conventional algorithms. With this parameter, this algorithm can reduce the number of multiplications per sample time, though it may cause a small drop in convergent property in comparison to conventional orthogonal projection algorithms.

ISSN:0228-6203    

DOI:10.1080/02286203.1993.11760175

出版商:Taylor&Francis    

年代:1993

数据来源: Taylor

摘要:

AbstractThe recent increase in international competition has spurred the application of on-board process diagnostics to consumer products for improved system performance and reduced maintenance costs. Failure detection and isolation strategies monitor a system's operation for degradations, and if detected, classify the failure source. In this paper, a real-time refrigerator model and two state estimators are designed to predict the system behavior for a model- based failure detection processor. The nonlinear fourth-order refrigerator compressor and condenser model provides an effective description of the system operation for diagnosis, while also minimizing problem complexity and computational time. Several recent nonlinear observer design strategies arc reviewed, and then applied to this model to reconstruct the system states. The evaluation of overall observer performance will provide insight into the application of these estimation strategies to nonlinear thermofluid systems. A number of design issues encountered while deriving the dynamic system model and applying the observer formulations will be discussed.

ISSN:0228-6203    

DOI:10.1080/02286203.1993.11760176

出版商:Taylor&Francis    

年代:1993

数据来源: Taylor