Simulation Practice and Theory最新文献

This paper presents a system of within-day dynamic railway service choice and assignment models which is used as the modelling basis for a large Decision Support System for the operational planning of rail services named System for the Analysis and Simulation of Marketing (SASM), recently developed by the Italian Railways Company. The first part of the paper describes the demand model, based on a tree-logit service/run/class choice model explicitly taking into account desired departure/arrival time, the supply model based on a diachronic (spatio–temporal) network representation of scheduled services and the assignment model which is a Stochastic Network Loading (SNL) model based on explicit (diachronic) path enumeration. The second part of the paper describes shortly the basic functionalities of the DSS and some applications of the model system to the Turin–Venice railway corridor.

A simulator based on the FDTD algorithm has been devised for full-wave electromagnetic computation inside domains having an arbitrarily complex shape, inhomogeneous materials and in the presence of general field sources. The simulator is designed in such a way that new applications can be dealt with by simple addition of pertinent models and functions. A simulation of human tissue heating by a microwave source in view of application to hyperthermia anticancer treatment planning is reported as an example.

Interconnection network is a decisive component of parallel and distributed computer systems. With the merits of simplicity and efficiency, 2-dimensional (2-D) mesh has been a popular choice of large MIMD interconnection networks. Mesh, however, has its known weaknesses in scalability and connectivity. Packed Exponential Connections (PEC) is a newly proposed network which is designed to improve the scalability and connectivity of 2-D mesh while maintaining its merits. In this study, the performance of PEC over mesh network is carefully examined through computer simulation. Characteristics of PEC networks are revealed. A novel routing scheme is proposed and used in $\text{PROTEUS}$ environment to simulate the performance of 2-D PEC network. Simulation and analytical results show that for many applications where non-local communications are required, PEC network provides superior performance to that of mesh. Based on simulation results, structural modification is also suggested to further enhance the performance of PEC network.

In this paper an analysis of the nonlinear static behaviour of cable systems is developed by assuming a full nonlinear structural model of the cables based on elastic catenary results. The work is aimed at the possible application of this kind of structure to practical engineering systems such as among others ski lifts, electrical transmission lines, and cable systems in erection procedures of long-span bridges. The structural model is then implemented in a suitable computer code program able to analyse strong nonlinearities arising from low stress levels in the cables, where the uniqueness of the solution is not assured. Therefore, an appropriate simulation technique is required to capture the static equilibrium configurations of the cable systems subjected to a given external action. After a preliminary discussion of the relevant equations governing the behaviour of the structural model, a finite element analysis is developed to account for the main inherent features related to convergence and stability of the numerical algorithm used. Then, some illustrative numerical examples are developed by suitably calibrating the input data in such a way that strong nonlinearities stand out which enable the checking of the validity of the present analysis.

This paper presents a simulation system based on the solution of forward and inverse problems of elastic wave propagation. Forward and inverse modeling have become a useful tool for interpretation in exploration geophysics and seismology. By 3D modeling, field observations can be simulated numerically, and computed results can be compared to field data. It is known that 3D seismic modeling requires the up-to-date high-performance multiprocessor computer systems which are not readily available for many geophysical firms in Russia. This situation makes us focus on the creation of efficient numerical–analytical algorithms which allow the solution of 3D forward and inverse seismic problems without supercomputers. This paper presents some algorithms and numerical experiments for different models of media. A special emphasis is given to “non-ray” waves which play an important role in seismic interpretation theory.

Under the control of a soft real-time framework for multimedia support, processes are scheduled by soft real-time scheduling algorithms and the timing overflows are handled by soft real-time handling methods. The paper conducts a simulation study to show the effects of the related schemes. Based on an abstract model for continuous media communications and applications, a simulator with versatile parameterization possibilities is constructed to simulate soft real-time effects concerning necessity of soft real-time, pros and cons for timing monitoring and enforcing, effects of soft real-time handling of timing-overflow, etc. Simulations driven by theoretical distributions are validated against trace-oriented simulations and the results are found to agree with each other well.

Hardware in the loop (HIL) simulation based on modern digital signal processors is a cost-effective technology for the design and evaluation of various sophisticated weapon and industrial systems. In this article a HIL simulation is presented through the very complex problem of modernisation of the semi-automatic command to line of sight (SACLOS) missile system. The presented examples illustrate the importance of the HIL simulation technology for the cost-effective, non-destructive prototype development of such SACLOS systems. The key role of a flexible simulation platform consisting of 4 TMS320C40 digital signal processors for efficient real-time simulation of the implemented SACLOS subsystem models is also emphasised in this paper.

Data redundancy has been widely used to increase data availability in critical applications and several methods have been proposed to organize redundant data across a disk array. Data redundancy consists of either total data replication or the spreading of the data across the disk array along with parity information which can be used to recover missing data in the event of disk failure. In this paper we present an extended comparative analysis, carried out by using discrete event simulation models, between two disk array architectures: the Redundant Arrays of Inexpensive Disks (RAID) level 1 architecture, based on data replication; and the RAID level 5 architecture, based on the use of parity information. The comparison takes both performance and cost aspects into account. We study the performance of these architectures simulating two application environments characterized by different sizes of the data accessed by I/O operations. In addition, several scheduling policies for I/O requests are considered and the impact of non-uniform access to data on performance is investigated.

The accurate verification of VLSI circuits is essential for their successful and economic production but is an extremely time consuming process for the large circuits of today. This paper describes a robust parallel circuit simulator, PARCIS, designed for a message passing multiprocessing system. It uses a demand driven technique, based on the analysis of hierarchically partitioned circuits. The computation time is reduced by decoupling the circuit equations and distributing the computational load over many processors. On each processor, the circuit blocks, compacted in hierarchical levels, are analyzed asynchronously according to their temporal activity. Currently the PARCIS system is running on a network of transputers. To demonstrate the effectiveness of the proposed simulation program, results are presented for the simulation of typical digital circuits, showing that the execution time decreases in a constant rate as the number of processors (transputers) increases.

In this paper, the authors present a modular simulation approach for the evaluation of automated material handling systems (AMHSs). The approach involves the use of high level modularity so that alternative AMHS scenarios can be evaluated using identical or nearly identical source code. The approach is implemented using the AutoMod simulation platform, and the efficacy of the strategy is demonstrated through a case study with the United States Postal Service. Results indicate that the approach is viable and that it is of value for the evaluation of AMHS scenarios in general.