Simulation Of Physical Processes Research Articles

QUALITATIVE QUERYING OF PHYSICAL PROCESS SIMULATIONS

Abstract The preliminary design of a query system for the computer simulation of physical processes is presented. Most engineering simulations produce vast amounts of quantitative data. It often requires special training to interpret the data and many of them may not be directly relevant to a particular decision. Human beings usually find qualitative explanations easier to absorb than large quantities of detail. The query system described in the paper is a preliminary to the production of an interrogation system which can provide both qualitative answers and explanations. In the first part of the system, natural language queries are transformed into standard query types using a neural net. In the second part qualitative replies are formed from neural nets which are trained by data from the simulation. An object oriented hierarchy which facilitates the mappings of quantitative data into qualitative attributes is presented. The development of a more detailed and sophisticated explanation system is also disc...

AMIP: The Atmospheric Model Intercomparison Project

The Atmospheric Model Intercomparison Project (AMIP) is an international effort to determine the systematic climate errors of atmospheric models under realistic conditions, and calls for the simulation of the climate of the decade 1979-1988 using the observed monthly averaged distributions of sea surface temperature and sea ice as boundary conditions. Organized by the Working Group on Numerical Experimentation as a contribution to the World Climate Research Programme, AMIP involves the international atmospheric modeling community in a major test and intercomparison of model performance; in addition to an agreed-to set of monthly averaged output variables, each of the participating models will generate a daily history of state. These data will be stored and made available in standard format by the Program for Climate Model Diagnosis and Intercomparison at the Lawrence Livermore National Laboratory. Following completion of the computational phase of AMIP in 1993, emphasis will shift to a series of diagnostic sub-projects, now being planned, for the detailed examination of model performance and the simulation of specific physical processes and phenomena. AMIP offers an unprecedented opportunity for the comprehensive evaluation and validation of current atmospheric models, and is expected to provide valuable information for model improvement.

The effect of clay addition and gypsum application on the physical properties of a hardsetting red-brown earth, and the response of irrigated cotton

The growth of furrow-irrigated cotton on red-brown earths (Alfisols) of the lower Macquarie Valley in New South Wales (Australia) is often restricted by slow water penetration and poor seedling emergence, associated with structural instability and hardsetting of the soil surface. However, local landholders have overcome the problem to some extent by increasing clay content at the soil surface by using deep mouldboard ploughing (to 0.45 m) and subsequent gypsum applications. A study was carried out to determine how mouldboarding had changed the physical condition of a red-brown earth near Narromine, why the water relations had been improved, and why the effect of this operation does not appear to be permanent. Cotton growth was measured at two sites, one ploughed and treated with gypsum (PG) and the other without these treatments (C). Both sites were also deep ripped just before planting. Field studies were complemented with laboratory experiments in an attempt to separate the effects of texture modification and gypsum application. The hydraulic conductivities of surface soil and a surface-subsoil mix, each with and without gypsum, were measured. The time for columns of these soils 0.05 and 0.2 m in height to wet to the surface, and their degree of expansion or slumping on wetting, were also determined. Cotton growth was over 100% greater where the PG treatment had been applied. This improvement was associated with greater, and more uniform, water penetration into the furrows and ridges. Despite a reduction in organic matter content and exchangeable Ca: Mg ratio, and an increase in exchangeable sodium percentage, soil from the PG site had a lower dispersion index and strength, and higher hydraulic conductivity and electrical conductivity near the surface. It also had more clay in the surface, and a higher content of smectite. The hydraulic conductivity experiment suggested that gypsum may have a similar beneficial effect on both sites. In contrast, the rate of wetting experiment, which gave a better simulation of soil physical processes in the field, showed that even with gypsum the C treatment could not maintain a favourable structure. The need for further experimentation is discussed.

Theoretical simulation of physical processes in a discharge XeCl laser

A self-consistent model of a self-sustained discharge XeCl laser with He buffer gas is described. The validity of the model is confirmed by comparing the results with the measured time dependences of electrical variables, the lasing pulse, the densities of XeCl*, Cl-, Xe* as well as with the dependences of the laser output energy on the charging voltage and on the gas composition. For a gas pressure of 2.2 atm model optimisation of the energy density deposition and the length of the laser active medium (for a fixed stored energy of 7 J) is carried out. The quenching of XeCl* molecules by electrons is found to be the main factor limiting the enhancement of laser efficiency and output energy when the deposited energy density increases.

Numerical models of Plinian eruption columns and pyroclastic flows

Numerical simulations of physical processes governing the large‐scale dynamics of Plinian eruption columns reveal conditions contributing to column collapse and emplacement of pyroclastic flows. The simulations are based on numerical solution of the time‐dependent, two‐phase, compressible Navier‐Stokes equations for jets in a gravitational field. This modeling effort is directed toward studying the steady discharge phase of eruptions in contrast to our previous models of the initial, unsteady blast phase. Analysis of 51 eruption models covers a wide range of vent exit pressures, inertial and buoyancy driving forces, and coupling of energy and momentum between gas and pyroclasts. Consideration of three dimensionless groups (Richardson and Rouse numbers and thermogravitational parameter) facilitates this analysis and defines conditions leading to column collapse. For eruptions with similar particle size characteristics, exit pressure ratios are also very important in determining column behavior; column behavior is much more sensitive to exit pressure ratio than to the density ratio between the column and the atmosphere. Model eruption columns with exit pressures exceeding atmospheric pressure have diamond‐shaped patterns at their bases with internal dynamics that correspond closely to observations of overpressured jets in laboratory experiments. Collapsing fountains form pyroclastic flows that consist of low‐concentration fronts, relatively thick heads, vortex development along the top surfaces, and rising clouds of buoyant ash. The presence of coarse‐grained proximal deposits primarily reflects tephra size sorting within the eruption column before collapse, as opposed to that which occurs during lateral transport of the material in pyroclastic flows. The dynamics and particle behavior in the proximal zone around collapsing eruption columns is examined; the modeling indicates that flow within a few kilometers of a vent will be at its highest particle concentration relative to other parts of the flow field.

Evaluation and improvement of hyrological concepts used in PAWN

In the years 1976–1983 the PAWN-study (Police Analysis for the Water-management in The Netherlands) was carried out in order to assess data for a national water management policy as reported in the Nota Waterhuishouding 1984, submitted to the Dutch parliament in the framework of the preparation of the Water Management Act. Among the mathematical models used in PAWN, DEMGEN (DEMand GENerator) represents agriculture, by far the greatest interest in terms of water demand and economic importance. By simulating the hydrological cycle in agricultural areas the model produces data on sprinkling demand, total water demand, agricultural damage and the changes in groundwater levels due to water suppletion. Furthermore the model evaluates sprinkling costs, which enables cost/benefit analyses for water supply plans. After the PAWN exercises for various reasons the need was felt for a critical evaluation of DEMGEN, specifically with regard tro future applications. This also implied an updating of DEMGEN on basis of recent scientific developments. In the period 1982–1986 investigations were carried the following fields: • - evaluation and improvement of implemented physical concepts; • - development and implementation of new concepts; • - updating of input files and facilities with respect to physical characteristics; • - updating of the areal schematization of The Netherlands and the development of relevant standard procedures for this subdivision The paper deals with the results with respect to the follwoing physical concepts in DEMGEN: • - Unsaturated flow • - Evapotranspiration • - Drainage • - Irrigation Contributions were made by Rijkswaterstaat, the Delft Hydraulics Laboratory (DHL) and the Institute for Land and Water Management Research (ICW). Most of the studies dealt with separate concepts, whereas Rijkswaterstaat also carried out an integral sensitivity analysis and a validation of DEMGEN on basis of data from two experimental catchments in The Netherlands. In all investigations the sensitivity of certain assumptions and the estimation of reliable model parameters was the major topic, rather than the assesment of the highest possible degree of accuracy in the simulation of physical processes.

A Modified Tidal Prism Model for Water Quality in Small Coastal Embayments

A water quality model was developed for easy application to small coastal embayments. The simulation of physical transport processes is based on Ketchum's tidal prism theory, modified and expanded such that it becomes applicable to cases where the embayment is branched and/or freshwater discharge is negligibly small. A model coastal embayment was divided into segments of lengths equal to local tidal excursions. Instead of starting the segmentation from landward end with freshwater discharge and tidal prism as two non-zero parameters, the modified model subdivides the water body starting from the seaward end with the difference between tidal prism and freshwater discharge as a single parameter. The mass balance within each segment was formulated by considering the exchange of water with its neighboring segments due to the flushing of freshwater discharge, as well as the tidal prism on ebb cycle, and to the mixing of the tidal prism on flood tide. This results in an algebraic equation which may be solved for concentration in each segment by successive substitution. For a non-conservative substance, the biochemical reaction terms may be easily added to the algebraic equation without complicating the solution scheme. The model has been applied to a number of tidal creeks and coastal embayments in Virginia, USA. The application to the Lynnhaven Bay is presented.

Interpretative ability and predictive power of the simulation of physical, chemical and biological processes, considered in terms of elementary mechanical interactions

Interpretative ability and predictive power of the simulation of physical, chemical and biological processes, considered in terms of elementary mechanical interactions

Process modeling and simulation tools

An overview of modeling and simulation of physical processes which produce topographical effects in fabrication of integrated circuits is given. Resist characterization techniques, applications of optical aerial image simulation to lithography and inspection, and linking of layout with process, device, and circuit simulation are emphasized.

Parallelism in finite element modelling

AbstractParallel processes can be identified at several different levels in the computational simulation of physical processes and problems. We first briefly sketch the main steps involved in modelling physical processes and give examples where inherent parallelism is evident. We then proceed more specifically to describe both inherent and induced parallelism that occur when finite element methods are applied to the solution of boundary and evolution problems, and indicate several opportunitites for parallel processing in finite element analysis.

Bottom Smoothing to Prevent Numerical Instability

Numerical simulation of sediment transport and the changes in plan form of the shoreline near coastal structures may produce results where the bottom slope exceeds the maximum slope which would be expected to occur on the real (prototype) shoreline. This may cause instability in the numerical solution and prevent an accurate simulation of the transport processes. A numerical subroutine has been developed to redistribute the sediment at pints where the numerically produced bottom slope exceeds the maximum expected slope. This subroutine has no dependence on time. The smoothing is accomplished numerically after the completion of one or more iterations of time-dependent, numerical simulation of physical processes, e.g., sediment transport associated with wave action or currents. It should be noted that the smoothing subroutine will smooth any input data to reach a maximum slope between points, even random numbers. This subroutine should not be used as a substitute for good simulation of the physical processes, but may be used to smooth errors resulting from the inexact nature of numerical modeling.

A model of scientific data bank and its applications to geological data

This paper presents a new model for a scientific data bank applicable to geological data. It is composed of four concentric rings, described from outside to inside as: 1. (1) an optional conversational module for graphic display, 2. (2) a data structure (indicated as DS), 3. (3) an interface data structure/storage structure, and 4. (4) a storage structure which is a file system. The users do not need to know the nature of 3 and 4. In this paper, I emphasize the DS and the principles to build it correctly; it must never be created to answer to a particular problem; it only depends on the analysis of the nature of geological phenomena and of the relations among them. The DS is composed of four abstract data types and consists of an arborescence with links. The programming language of the entire system is SIMULA 67, which is ideal for data structuring and for geological progressing. The result is a powerful DS which may resolve almost all problems. Two applications in geology are presented. The first example concerns geological, mining, and topographical cartography. The graphic elements are considered as belonging to oriented multigraphs, according to a method based on graph theory and used originally to digitize maps. Among the problems which may be resolved are selective two- and three-dimensional drawings with isolines and boundaries, estimates of dips, surfaces and volumes, correlations, etc. This system establishes a base for geological simulation and modeling. The second example, discussed briefly relates to the collections of paleontology of Université P. et M. Curie. This project is in progress and shows potential for a wide application in the natural sciences. As part of the overall objective, the concept of the data bank developed is intended to allow for scientific and industrial applications, in which display and simulation of natural and physical processes may be necessary. At present, many aspects of this research are experimental.

The Local Surface Energy Balance and Subsurface Temperature Regime in Antarctica

Abstract The physical processes occurring within a perennial snow cover and at its surface are discussed with particular emphasis on monthly variations in Antarctic snow. Results of a one-year simulation of physical processes In snow are compared with 1958 data at Mirny and Pionerskaya, Antarctica. The simulation demonstrates the following: first, solar radiation is effective to a depth of 50 cm or so, but longwave radiation cools the surface alone, causing the “greenhouse” effect first observed in snow at least four decades ago. Highest summertime temperature and initial snowmelt thus occur not at the surface but roughly 10 cm below It. Second, the percolation of meltwater with eventual refreezing during the subsequent winter is the most efficient mechanism for modifying the temperature profile at depths of several meters of more. Third, concerning the surface energy budget, at temperatures below −20C, atmospheric sensible heat flux approximately compensates net radiation throughout the year. When the te...

A Three-Dimensional Stochastic Gamma-Ray Transport Method for Shielding Calculations

This paper examines a new probabilistic formulation and development of a model for the investigation of three-dimensional gamma-ray transport problems. This model assumes that gamma-ray motion may be sampled at predetermined points. A medium is considered to be filled with a cubic lattice whose unit distance between lattice points may be some fraction of the mean-free-path. The random walk of gamma rays from one point to another is constructed using the lattice framework as reference points.Using this model, a new type of stochastic gamma-ray transport code, PUGT I (Purdue University Gamma Ray Transport I), has been developed based on direct simulation of physical transport process. In another version of the code (PUGT II), capture of gamma rays is taken into account analytically by associating a weight factor to the gamma rays.The codes are used to calculate the transmission and reflection characteristics of gamma rays for different thicknesses of slabs of aluminum and iron. The contribution of annihilation radiation to reflection and transmission is investigated. The results of our calculations are in good agreement with other similar calculations and with experimental results.Gamma-ray streaming through two-legged rectangular concrete ducts was investigated. Results of these studies are in very good agreement with experimental results and demonstrate the ability of the codes and the power of the lattice model to calculate quickly and efficiently the transmission of gamma rays in three-dimensional complex shielding geometries. The method is several times faster than ordinary Monte Carlo.

On the simulation of physical processes occurring in clouds

on the simulation of physical processes occurring in clouds

A method of mathematical simulation of physical processes without limiting the range of parameter changes-application to problems of automatic control of nuclear reactors

A method of mathematical simulation of physical processes without limiting the range of parameter changes-application to problems of automatic control of nuclear reactors