System Simulation Techniques Research Articles

A distributed simulation technique for multiple input multiple output systems

Abstract Distributed computing concepts have been attempted in the realm of real-time process control for a long time. This started with the systolic arrays of processors and an enormous amount of research has been done in this field. This paper proposes a methodology by which a multiple input multiple output system representing a plant and defined in terms of connected blocks of transfer functions can be decomposed into a set of parallel simulation processes in a message passing environment viz. a network of work stations. The paper also analyzes the scope of optimization of the processing time associated with each task. The methodology includes online reconfiguration of the system.

System Simulation For The Evaluation Of The Oil Barge Operation In Kaohsiung Harbor, Taiwan

The oil barge operation in Kaohsiung harbor is a typical system of resources allocation problems in a complex and dynamic environment, Such system is far more difilcult to deal with than a static and deterministic system, and often depends on experienced human experts for the oil barge assignment. This research has developed an integrated system for assessing the overall performance of such port operation. Both expert system and system simulation techniques are applied in this analysis. The role of the expert system is to translate the current heuristic of assignment into a rule-based knowledge for the human-like reasoning. To further evaluate the schedule arranged by the expert system, the system simulation model of the oil barge operation has been formulated using the software AweSirn@. This model is capable of quantifying the service quality under various assignment scenarios to support the management of the oil barge operation. With the help of such an integrated system, it is expected to facilitate the evaluation of the oil barge operation in terms of efficient resources allocation in Kaohsiung harlm.

LOCAL REDUCTION OF FOLD BIFURCATION RELEVANT TO VOLTAGE COLLAPSE IN AN ELECTRIC POWER SYSTEM

In this paper, the reduction approach based on the center manifold theory for parameter-dependent nonlinear dynamical systems is applied to simplify the analysis of the fold bifurcation relevant to voltage collapse in a simple electric power system. This technique enables us to obtain a lower-dimensional and topologically equivalent system in the neighborhood of the bifurcation value, which is a subset in the state-parameter space. Explicit formulas are presented for the computation of quadratic coefficients of the Taylor approximations to the center manifold for the fold bifurcation in parameter-dependent dynamical systems. It is demonstrated that it is the fold bifurcation but not other static bifurcations that occurs in the reduced power system, via validating the nondegenerate conditions for the fold bifurcation. The dynamics of the reduced system are visualized by two- and three-dimensional plots, which show that the reduction method is applicable and accurate to analyze local bifurcations in the power system. Furthermore, time domain simulation and modal analysis technique for linear systems are applied to distinguish the voltage stability from the rotor (angle) stability in the electric power system.

Ion beam extraction and transport for high-field electron cyclotron resonance ion sources (abstract)

The next-generation, very high magnetic-field electron cyclotron resonance (ECR) ion sources, like VENUS, SERSE, or PHOENIX, strive for substantially (a factor of 10) higher extracted heavy ion beam intensities than currently achievable. Such high-intensity ion beams present significant challenges for the design and simulation of an ECR extraction and low-energy ion beam transport system. Extraction and beam formation take place in a strong (up to 3 T) axial magnetic field, which leads to significantly different focusing properties for the different ion masses and charge states of the extracted beam. Typically, beam simulations must take into account the contributions of up to 50 different charge states and ion masses. Space charge effects must be correctly included since the extraction and mass analyzing system have to be designed for a proton-equivalent current of ∼25 mA at 30 kV extraction voltage. The article discusses state of the art two-dimensional and three-dimensional simulation techniques for such ion beam extraction and transport systems. Furthermore, the main contributions to the ion beam emittance are discussed: (1) The induced beam rotation due to the strong axial magnetic field, (2) the concentration of high charge state ions at the source center axis, and (3) the ion beam temperature. A novel large-gap analyzing magnet design is described which allows efficient correction of higher-order aberrations for high-intensity heavy ion beams. Such a magnet limits emittance blow up, and is necessary if the analyzed beam has to be further transported or accelerated, e.g., in a radio frequency quadrupole.

Fast simulation of broadband telecommunications networks carrying long-range dependent bursty traffic

A technique for the fast simulation of broadband communication systems is proposed, which is based on regenerative Importance Sampling techniques and on large-deviation results. Our algorithm is applicable to estimate the probability of rare events when modeling the offered traffic using Fractional Stable Noise (FSN) processes (including Fractional Gaussian Noise as a particular case), which have been recently proved to be able to capture both the long-range dependence and the burstiness of today's aggregate network traffic. An exact description of FSN processes is given, as well as an approximation that allows for the application of Importance Sampling techniques. The results obtained for a simple example are also included.

SYMMETRY WITHOUT SYMMETRY: NUMERICAL SIMULATION OF AXISYMMETRIC SYSTEMS USING CARTESIAN GRIDS

We present a new technique for the numerical simulation of axisymmetric systems. This technique avoids the coordinate singularities which often arise when cylindrical or polar-spherical coordinate finite difference grids are used, particularly in simulating tensor partial differential equations like those of 3+1 numerical relativity. For a system axisymmetric about the z axis, the basic idea is to use a three-dimensional Cartesian(x,y,z) coordinate grid which covers (say) the y=0 plane, but is only one finite-difference-molecule–width thick in the y direction. The field variables in the central y=0 grid plane can be updated using normal (x,y,z)-coordinate finite differencing, while those in the y≠ 0 grid planes can be computed from those in the central plane by using the axisymmetry assumption and interpolation. We demonstrate the effectiveness of the approach on a set of fully nonlinear test computations in 3+1 numerical general relativity, involving both black holes and collapsing gravitational waves.

LandScape Information System: A GIS approach to managing urban development

Seoul, the capital of South Korea, has been known for its original landscape, which has been molded for centuries within and around the surrounding natural topography. As a result of rapid urbanization and growth beginning in the 1960s, however, there has been significant deterioration. New and re-development in the downtown area, which have been characterized as high-rise and massive in particular, have been and are continuing to be detrimental to the landscape. In recent years, a number of attempts towards urban landscape management have emerged in the form of legislation and policies. But relevant tools to support the implementation of such attempts have unfortunately been insufficient, resulting in inefficient, unsystematic, and inaccurate urban landscape management efforts. Subsequently, this study developed the LandScape Information System (LSIS) for the purpose of managing urban landscape information and analyzing visual impacts of proposed development projects. Employing Geographic Information System (GIS) and computer graphics simulation techniques, LSIS performs such functions as, input and management of graphic and attribute data, query analysis of attributes related to urban landscape elements, and visual impact (view obstruction) analysis of development proposals. The database for LSIS was prepared in consideration to the urban information systems (UIS) database framework of Seoul in order to ensure the maximum data transferability between them. Through the application of LSIS to a sample visual impact analysis of urban redevelopment projects, it was found that valuable landscape resources could be damaged by the proposed projects. Moreover, by using LSIS, subsequent mitigation measures for such impacts could be effectively tested and developed. Therefore, it is believed that in general, LSIS can be used as the basis for decision-making in resolving urban landscape problems experienced by local governments. In addition, with the trend toward promoting more information-based societies, LSIS can be instrumental in sharing substantial amounts of data with those for UIS, developed by central and local governments. This in turn can foster maximum effectiveness and value of computer-based urban landscape management.

A new approach to critical exponents in phase-transitions of spin-systems

We investigate a method to obtain critical exponents using standard numerical simulation techniques for spin systems. We show that by analyzing the inverse of the logarithmic derivative of the susceptibility χ with respect to temperature the accuracy in determining γ can be increased significantly. The method is tested on the two- and three-dimensional Ising models but this alternative approach is thought to be most useful for spin systems on non-periodic structures like quasi-crystals and fractal lattices where the finite size scaling method is difficult to apply.

Navier-Stokes simulation with constraint forces: finite-difference method for particle-laden flows and complex geometries.

Building on an idea of Fogelson and Peskin [J. Comput. Phys. 79, 50 (1988)] we describe the implementation and verification of a simulation technique for systems of non-Brownian particles in fluids at Reynolds numbers up to about 20 on the particle scale. This direct simulation technique fills a gap between simulations in the viscous regime and high-Reynolds-number modeling. It also combines sufficient computational accuracy with numerical efficiency and allows studies of several thousand, in principle arbitrarily shaped, extended and hydrodynamically interacting particles on regular work stations. We verify the algorithm in two and three dimensions for (i) single falling particles and (ii) a fluid flowing through a bed of fixed spheres. In the context of sedimentation we compute the volume fraction dependence of the mean sedimentation velocity. The results are compared with experimental and other numerical results both in the viscous and inertial regime and we find very satisfactory agreement.

Path integral hybrid Monte Carlo for the bosonic many-body systems

In this Letter, we propose a new simulation technique for many-body systems of bosons based on the path integral formulation of quantum statistical mechanics. The indistinguishability of the bosons was handled by importance sampling in permutation space, and the path configurations for a given permutation were sampled using a hybrid Monte Carlo method. A system of 32 bosons in a harmonic well was chosen as a model problem. Calculations were performed for the system at various temperatures. The calculated thermodynamic quantities are in excellent agreement with the exact values.

Simulation of Electronic Circular Dichroism with Rigid Kohn−Sham Orbitals: A Computational Experiment

Electronic circular dichroism spectra transition energies and intensities were modeled using the independent particle model within the Kohn−Sham theory. The data obtained were compared with higher level calculations and experimental data. Since the model describes main features in the experimental spectra qualitatively well, it is being proposed as a fast and efficient simulation technique for systems which cannot be dealt with by more sophisticated computations. The best results were obtained with the common B3LYP hybrid density functional.

Hybrid modelling, simulation and torque control of a marine propulsion system

A propulsion dynamics investigation of a single-screw powered ship, driven by two gas turbines in a combined gas and gas (COGAG) arrangement is presented. Distributed-lumped (hybrid) modelling techniques are applied to the propulsion drive-train consisting of two prime movers, a primary drive shaft, a reduction gearbox, a secondary drive shaft and a propeller. The study in this paper, unlike earlier studies, does not lump the drive-train components as discussed by Rubis [1] into analytically simple but unrepresentative pointwise models. By way of contrast, modelling and simulation techniques for distributed-lumped systems are presented herein, enabling the torsional vibration and stress analysis of the long drive shafts to be investigated with accuracy. As a result of this a torque control scheme can be derived for fuel flow regulation purposes, enabling superior speed and shaft torque control to be achieved. The results presented show the simulated dynamic responses associated with the propulsion unit, shaft and propeller following fuel flow changes.

GENETIC ALGORITHMS: A TOOL FOR MODELLING, SIMULATION, AND OPTIMIZATION OF COMPLEX SYSTEMS

Until very recently genetic algorithms GAs were considered to be the proprietary field of general systems theoreticians and important for esoteric or extremely complex optimization studies. This paper endeavors to show that GA are of great utility in cases where complex systems have to be designed and, therefore, rational choices have to be made. The GA approach is based loosely on the theory of natural evolution, genetic diversity, and searching for beneficial adaptations to a complicated and changing environment. GAs can be viewed as a modelling tool and as a technique for simulation of complex systems represented by communities of interacting units. The representation of units can express characteristics, capabilities, or relatively simple strategies. These units compete and are modified by external operators, so that the overall system adapts to its environment. That environment defines the criterion by which the success in adapting can be measured. Genetic algorithms have been successfully applied to many optimization problems including mathematical function optimization, very large scale integration VLSI chip layout, molecular docking, parameter fitting, scheduling, manufacturing, clustering, machine learning, etc. and are still finding increasing acceptance. Modelling and optimization of a Kanban system from the field of flexible manufacturing systems is discussed in the last section.

Crystal Structure and Packing Disorder of Poly(p-phenylenebenzobisoxazole): Structural Analysis by an Organized Combination of X-ray Imaging Plate System and Computer Simulation Technique

To clarify the crystal structure of poly(p-phenylenebenzobisoxazole) (PBO) fibers, the analysis has been made for the X-ray diffraction data collected by the imaging plate system in combination with the computer simulation technique. The characteristic features of the X-ray diffraction pattern of PBO fiber are seen in the spotlike equatorial reflections and the diffuse reflections along the layer lines. The peak positions of the diffuse layer−line reflections were found to fit well to those of the molecular transform calculated for a uniaxially oriented isolated chain, suggesting an appreciably low correlation in the relative height between the neighboring chains. Among many types of the energetically minimized crystal structural models constructed by a computer simulation technique, a model giving a good fit between the observed and calculated X-ray profiles was found, in which the chains are assumed to form the layers extending along the 110 planes with the relative heights of the adjacent chains in the sheets almost confined to either +c/4 or −c/4 (c = fiber identity period) and these sheets are stacked together in the b-axis direction with random heights along the chain axis.

Molecular Dynamics for Polymeric Fluids Using Discontinuous Potentials

Molecular dynamics simulation techniques for systems interacting with discontinuous potentials are discussed. Optimization and efficiency techniques are summarized for performing discontinuous molecular dynamics on serial computers with direct application to polymer-like fluids. Comparisons are presented for two algorithms: (1) single-event scheduling, and (2) multiple-event scheduling. The single-event scheduling algorithm is approximately 75% faster than the multiple-event scheduling algorithm for molecular fluids but yields equivalent performance for atomic fluids. For the single-event scheduling method, a combination of link lists and neighbor lists are used when searching for possible particle interactions. The combination of efficiency techniques permits multibillion time step simulations for relatively large systems on desktop workstations. Both discontinuous molecular dynamics codes for single and multiple-event scheduling algorithms are available on the Internet. The utility of the method is demonstrated for entangled chains, tethered chains, and heteronuclear chain mixtures.

A stochastic importance sampling methodology for the efficient simulation of adaptive systems in frequency nonselective Rayleigh fading channels

We present an IS stochastic technique for the efficient simulation of adaptive systems which employ diversity in the presence of frequency nonselective slow Rayleigh fading and additive, white, Gaussian noise. The computational efficiency is achieved using techniques based on importance sampling (IS). We utilize a stochastic gradient descent (SGD) algorithm to determine the near-optimal IS parameters that characterize the dominant fading process. After accounting for the overhead of the optimization algorithm, average speed-up factors of up to six orders of magnitude [over conventional Monte Carlo (MC)] were attained for error probabilities as low as 10/sup -11/ for a fourth-order diversity model.

Design of serial production systems using discrete event simulation and nonconvex programming techniques

Efficient techniques for discrete event simulation and sensitivity analysis of production systems are used to accelerate the solution of nonconvex optimization problems which are quite often encountered in practice. The design algorithm is of the branch and bound type and solves a sequence of convex problems resulting from successive partitions of the feasible set. Examples are given, and computational considerations are discussed.

A general-oriented simulation technique for power electronic systems using quadratic branch voltage extrapolation

A new general oriented time-domain simulation technique for power electronic systems is developed. The algorithm is based on stepwise quadratic extrapolations on the branch voltages across each reactive element, together with progressive validation of the switches' operation. The power of this new technique lies in its simplicity in solving purely resistive networks for each topological configuration, generality in requiring no a priori understanding of the switching relationships and sequence of operations, inclusion of the effects of the parasitic elements, effectiveness of using computer memory and ease of implementation on a desktop computer. Several examples illustrating the generality and computational efficiency of this new approach are presented and verified with experimental measurements and other available literature.

Dependence of trajectory accuracy on the spatial and temporal densities of wind data

An investigation has been carried out to evaluate the dependence of trajectory accuracy on the density of wind data. The present study has applied an observing system simulation technique to 3 meteorological episodes over eastern Asia. A mesoscale numerical model with a horizontal grid size of 20 km has been employed to generate the reference atmospheric fields. Particles are initially located at 3 isobaric levels (925, 850 and 700 hPa). The results indicate that the 3-dimensional trajectories are sensitive to both the temporal and spatial densities of wind data. The trajectories show relatively strong sensitivity to the temporal density change between 6- and 12-h intervals in general, and also to the spatial density change between 160- and 320-km intervals in one of the cases. The effectiveness of enhancing either the temporal or spatial resolution of wind data for the improvement of trajectory accuracy is found to vary with the meteorological situation. When the intervals of 12 h and 320 km are assumed to be the resolution of wind observations, enhancing the spatial resolution to 160-km interval improves the accuracy more than enhancing the temporal resolution to 6-h intervals in a case with an excursion of the Siberian High. However the opposite is true in the other 2 cases in which either a synoptic scale cyclone or a low pressure system with significant diabatic heating is important, although the difference in the accuracy improvements is small in 1 of the 2 cases. It is also found that the estimated accuracy of a trajectory model and its sensitivity to wind data density may vary significantly with the resolution of the reference wind data sets: the use of reference wind data with low resolution can result in a significant underestimation of transport error and may exaggerate the effectiveness of enhancing the temporal resolution for the improvement of trajectory accuracy. The accuracy of an isobaric model is generally comparable to that of a 3-dimensional model, when data sets with 12-h, 320-km resolution are used. Under a strongly baroclinic condition, however, the isobaric model can give a very large trajectory error.

Simulation of communication systems

When both a complex system and a complex channel model are encountered, the result is typically a design or analysis problem that cannot be solved using traditional (pencil and paper) mathematical analysis. Computer-aided techniques, which usually involve some level of numerical simulation, can be a very valuable tool in these situations. The purpose of this article is to provide a tutorial review of some of the basic techniques of communication system simulation. The authors consider the basic techniques used to represent signals, generate signals, and model linear systems, nonlinear systems, and time-varying systems within a simulation. They consider the important problem of using a simulation to estimate the performance of a communication system.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>