New Method For Simulation Research Articles

Simulation of microscopic elastic-plastic contacts by using discrete dislocations

A new method for simulation of microscopic elastic-plastic contacts, such as those be­tween surface microasperities, is developed. Asperity plastic deformation is described in terms of nucleation and motion of discrete crystal dislocations, which allows the model to be made scale-sensitive. The new method allows elastic-plastic microcon­tacts to be investigated on the scales too small to apply conventional continuum mechanics methods, but still too large for atomistic simulations. Using the devel­oped method, several microcontact simulations are performed. The junction growth effect for asperity microcontacts is studied and found to be very strong in certain cases. Subsurface stress distributions at an asperity microcontact are analysed. High-magnitude tensile stress spikes, apparently caused by groups of dislocations piling up against one another, are found below the contact area. Interaction between a pair of microasperities is simulated and an estimation of the plasticity contribution to friction is obtained. The new approach appears promising, although the present model is simplistic.

New Methods for Simulation of Fractional Brownian Motion

We present new algorithms for simulation of fractional Brownian motion (fBm) which comprises a set of important random functions widely used in geophysical and physical modeling, fractal image (landscape) simulating, and signal processing. The new algorithms, which are both accurate and efficient, allow us to generate not only a one-dimensional fBm process, but also two- and three-dimensional fBm fields.

Clamped state solution of artificial neural network for real-time economic dispatch

This paper presents a novel method for the real-time economic dispatch using clamped state variable formulation of the Kennedy, Chua and Lin (1988) artificial neural network (ANN). An efficient economic power dispatch algorithm must use real-time load conditions and the loss penalty-factor for representation of transmission losses in power system. The approach described in this paper assumes that an interface program will calculate the penalty factors for the current power flow state, as calculated by a state estimation program. The proposed method employs an ANN to enhance the speed and capability of algorithms which may use heuristics for online use. The ability of processing feedbacks in a collective parallel analog mode enables a neural network to simulate the dynamics that represent the optimization of an objective function subjected to its constraints for a given optimization model. Different techniques may be used to simulate the neural dynamic system. In this study, the authors propose a new method of simulation called the clamped state variable (CSV) technique. The new approach is very simple and it takes smaller computer time for the algorithm to converge than the complete circuit simulation. The results obtained by the CSV method are very close to that of numerical methods and are reported in this paper. >

Modification of the method of simulation of truncated random variables

A new method for simulation of truncated random variables is described. Several similar methods are considered. It is shown that a substantial reduction in computation time is achieved by utilizing the proposed method.

A new iterative method for the global simulation of power electronic multi-converter systems

Power electronic converters generate harmonic currents that can disturb the network. To study the perturbations on the power line, it is necessary to perform a functional analysis via a global simulation. However, when the plant contains several static power converters feeding direct-current loads, global simulation becomes difficult, even impossible, because of the limitations of the software or the microcomputer used. There are no simulation tools that allow the quantitative evaluation of harmonic voltages and currents generated by a multistatic converter system. To fulfil this goal, the authors propose a new iterative analysis method for such systems and a new model for electronic power converters in terms of nonlinear current sources. This methodology has been included in a modified version of the ATOSECS software, renamed ATOSECM. The methodology is illustrated with an example of the use of ATOSECM on a personal computer for the study of two single-phase power converters connected to the same power line. A comparative analysis between global simulation (ATOSECS) and the new method of simulation (ATOSECM) is also presented for the case of two three-phase full-wave thyristor converters, with different firing angles and loads.

Random fields in the limit analysis of elastic-plastic shell structures

The purpose of this work is to analyse the problem: what is the effect of the assumed types and intensities of random initial geometrical imperfections on the equilibrium paths and the limit loads? To this end a new method of simulation of nonhomogeneous two-dimensional random fields on regular nets has been developed. The method is based on two concepts: an envelope of the random field and local covariance matrices classified according to the symmetry groups. The numerical examples deal with post-buckling responses of FEM models of shallow shells with different types of imperfections (whitenoise, Wiener and degenerated fields) using a Monte Carlo approach.

Experimental study of condensation of vapors in the presence of noncondensable gas on a short horizontal tube.

Measurements of the rates of condensation of a steam, methanol and benzene vapor in the presence of air on a short horizontal tube for wide ranges of inlet air concentrations and vapor flow rates were carried out. The observed vapor phase heat and diffusion fluxes were compared with results of the authors’ previous numerical solution to heat and mass transfer on a cylinder with diffusive surface mass suction and injection under laminar forced flow conditions.By considering the results of our previous numerical solution and the present experiments, a new method for simulation of condensation of vapors in the presence of noncondensable gas on a short horizontal tube was proposed and compared with the experimental data. The effect of noncondensable gas on the rate of condensation was also discussed.

A New Approach to Describing Three-Dimensional Orientation Distribution Functions in Textured Materials–Part I: Formation of Pole Density Distribution on Model Pole Figures

New method for simulation of orientation distribution functions of textured materials has been proposed. The approach is based on the concept to describe any texture class by a superposition of anisotropic partial fibre components. The texture maximum spread is described in a “local” coordinate system connected with the texture component axis. A set of Eulerian angles γ1,γ2,γ3 are introduced with this aim. To specify crystallite orientations with respect to the sample coordinate system two additional sets of Eulerian angles are introduced besides γ1,γ2,γ3. One of them, (Ψ0,θ0,ϕ0), defines the direction of the texture axis of a component with respect to the directions of the cub. The other set, (Ψ1,θ1,ϕ1), is determined by the orientation of the texture component and its texture axis in the sample coordinate system. Analytical expressions approximating real spreads of crystallites in three-dimensional orientation space have been found and their corresponding model pole figures have been derived. The proposed approach to the texture spread description permits to simulate a broad spectrum of real textures from single crystals to isotropic polycrystals with a high enough degree of correspondence.

A new method for simulation of atmospheric effect on the emergent radiation over non-uniform terrain

For a precise atmospheric correction over the non-uniform terrain in satellite imageries, a numerical method for evaluating the upwelling radiation at the top of the atmosphere bounded by the non-uniform surface is developed as an extended doubling-adding method. The present method enable us to treat quantitatively the case of hazy atmosphere and (or) large albedo of the surface.

New Simulation of Polymers on Surfaces

AbstractA new method of simulation based on the output of the analytical equilibrium calculation of the Cluster Variational Method (CVM) is used to obtain information about the properties of the polymers adsorbed on a surface. We find a strong preferential adsorption of longer chains, in agreement with experimental observations. This tendency is more pronounced in neutral polymers than in polyelectrolytes. Other geometrical properties like trains, tails, and loops of adsorbed polymers are also calculated.

New Simulation of Polymers on Surfaces

AbstractA new method of simulation based on the output of the analytical equilibrium calculation of the Cluster Variational Method (CVM) is used to obtain information about the properties of the polymers adsorbed on a surface. We find a strong preferential adsorption of longer chains, in agreement with experimental observations. This tendency is more pronounced in neutral polymers than in polyelectrolytes. Other geometrical properties like trains, tails, and loops of adsorbed polymers are also calculated.

Simulation of ethylene epoxidation in a multitubular transport reactor

It has been demonstrated that increased yields of ethylene oxide are obtained with a fixed-bed reactor operating with multiple injection of oxygen and cyclic adsorption-desorption of the desired reaction product. In certain conditions, this reactor simulates the operation of a larger two-tube transport reactor; the latter reactor may, in turn, be used to simulate large-scale commercial multitubular transport reactors. The small fixed-bed reactors may also be used for optimization of the process. The reaction of ethylene epoxidation on a silver catalyst is a good illustration of the advantages of a multitubular transport reactor and of this new method of simulation and optimization.

The use of an image processing system in radiotherapy simulation.

Image quality produced in radiotherapy simulation is often so poor in certain anatomical sites (e.g. the pelvis) that it can adversely affect clinical judgement with regard to treatment set-up. In treatment planning both the field arrangement and the availability of accurate anatomical information are important, and should ideally be provided at the time of simulation by methods based on the principle of computerised tomography. In this work an image processing system has been used as a link between the video output from the simulator and the treatment planning computer in order to implement a CT facility on the simulator, as well as allowing real-time image enhancement to be investigated as a method of improving picture quality. This approach also enables a new method of simulation to be considered which reduces patient dose and prolongs the useful working life of the X-ray tube.

A new method for simulation of real chains: scanning future steps

A new method for simulating real polymer chains is developed and applied to self-avoiding walks (SAWs) of length 49-599 on a three-choice square lattice. Very good results for the entropy are obtained which deviate from the series expansion estimates by 0.1-2%. The author also discusses how to extend the method to models of polymer chains with both excluded volume and finite interactions (attractive or repulsive). The author's method is expected to be more efficient than other simulation methods for treating self-interacting SAWs and chains which are subject to various lattice constraints.

Simulation of some spatial hard core models, and the complete packing problem

A commonly used model for spatial point patterns exhibiting inhibition between points is the hard core model, in which the points of the pattern may be regarded as being the centres of non-overlapping discs of fixed diameter. It is often necessary in spatial statistics to be able to simulate many realisations of various models for point patterns. In this paper, the computer simulation of two stochastic hard core models is considered. The first of these, the Kelly-Ripley model, is simulated using a spatial birth and death process, while, for the second, the “SSI” model, a birth process is used. In each case, a new method of simulation, which is considerably faster than the existing method at high densities of discs, is described. Both algorithms use the Dirichlet tessellation of the points. The properties of the algorithm for simulating the SSI process make it possible to investigate random sequential packing of discs in a rectangular container. An estimate of the limiting packing density at complete packing of the rectangle is obtained; this should be an improvement on previous estimates.

A new method for simulation of EPR spectra with particular application to nitroxide spin labels

The simulation program presented in this work makes use of the spectral density function for the electron spin precession movement in a laboratory magnetic field H 0 for the computation of the EPR spectrum. The method suggested is capable of treating molecular motion and/or spin exchange in a satisfactory way. The rotational correlation time, τ c , and the spin-exchange frequency are given in real physical time units. Nitroxide spin label EPR absorption spectra for τ c in the range of 5.0 × 10 −8 to 1.0 × 10 −9 sec are presented. Moreover, spectra for spin-exchange frequencies in the range of 5.0 × 10 7 to 1.0 × 10 9 sec −1 are given for two different values of τ c . In the generation of molecular rotational motion a Monte Carlo procedure is used.

New Method of Monte Carlo Simulations and Phenomenological Theory of Phase Transition in the Two-Dimensional XY-Model

Simulations of the two-dimensional XYmodel showing the appearance of vortices have been reported in previous papers. 1) •2) It seems, however, necessary for studying the feature of phase transition to find out a more rapid method of simulation. The purposes of this short note are (i) to describe such a new method of simulation together with explicit results, and (ii) to represent briefly an idea to explain a new phase transition with vortices and without long-range order. 3) In contrast to the ordinary method!) our method has the following two new points: (1) The 2 d-classical XY-model is described approximately except at very low temperatures by the discrete vector model which can assume u discrete angles e j = 2rrj/n with j=1, 2, ···, n, and (2) each step of simulation is determined by generating a uniform random number p in the range O:c;:ps;1 and by making each local spin jump to a state e j> if p comes into the region pj as shown in Fig. 1, in which the probability pj rs given by Pj= exp ([3Ej) /~k exp ([3Ek) with a local energy Ej in the state e j· This procedure assures the detailed balance and equilibrium state. Clearly this gives a very rapid simulation for our problem. In fact, our preliminary calculations have already shown the system-size dependence of vortexsize and 'time' -dependence of disclina tion formation, as shown in Figs. 2 and 3. It is seen from these results together with P, P,

Mechanics of the Compression Wood Response

A new method for simulation of cross-sectional growth provided detailed information on the location of normal wood and compression wood increments in two tilted white pine (Pinus strobus L.) leaders. These data were combined with data on stiffness, slope, and curvature changes over a 16-week period to make the mechanical analysis. The location of compression wood changed from the under side to a flank side and then to the upper side of the leader as the geotropic stimulus decreased, owing to compression wood action. Its location shifted back to a flank side when the direction of movement of the leader reversed. A model for this action, based on elongation strains, was developed and predicted the observed curvature changes with elongation strains of 0.3 to 0.5%, or a maximal compressive stress of 60 to 300 kilograms per square centimeter. After tilting, new wood formation was distributed so as to maintain consistent strain levels along the leaders in bending under gravitational loads. The computed effective elastic moduli were about the same for the two leaders throughout the season.

Subharmonic Oscillations in Power Systems-Theory and Practice

This work makes a comprehensive single phase study of the most commonly observed subharmonic oscillation, that is the one- third order subharmonic. The theoretical methods employed may be extended to other subharmonic frequencies and also to combinations of subharmonics. A theory is developed to enable the calculation of the existence region for all practical cases concerned with static magnetic circuits. Further, in a detailed comparison of the theoretical results of all commonly used static magnetic circuits with the results obtained in experimental studies using a specially designed Transient Network Analyser, TNA, differences of less than 5% in every case were recorded. This TNA includes a new method of simulation of the power transformer and its associated nonlinearities, and an outline of the method of representation is given.

Briefs - "New Method for Simulation of Multicomponent Distillation"

Briefs - "New Method for Simulation of Multicomponent Distillation"