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  • Articles  (26)
  • Articles: DFG German National Licenses  (26)
  • simulation  (26)
  • 1985-1989  (22)
  • 1970-1974  (4)
  • 1950-1954
  • 1945-1949
  • Geosciences  (17)
  • Economics  (8)
  • Energy, Environment Protection, Nuclear Power Engineering  (6)
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  • Articles  (26)
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  • Articles: DFG German National Licenses  (26)
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  • 1
    Electronic Resource
    Electronic Resource
    Stochastic analysis of estuarine hydraulics (1989)
    Springer
    Stochastic environmental research and risk assessment 3 (1989), S. 71-84 
    Details
    ISSN: 1436-3259
    Keywords: Hydraulics ; quasilinearization ; simulation ; stochastic ; estuarine system ; Monte Carlo methods ; random differential equations ; parameter uncertainty
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract A new methodology is presented for the solution of the stochastic hydraulic equations characterizing steady, one-dimensional estuarine flow. The methodology is predicated on quasi-linearization, perturbation methods, and the finite difference approximation of the stochastic differential operators. Assuming Manning's roughness coefficient is the principal source of uncertainty in the model, stochastic equations are presented for the water depths and flow rates in the estuarine system. Moment equations are developed for the mean and variance of the water depths. The moment equations are compared with the results of Monte Carlo simulation experiments. The results confirm that for any spatial location in the estuary that (1) as the uncertainty in the channel roughness increases, the uncertainty in mean depth increases, and (2) the predicted mean depth will decrease with increasing uncertainty in Manning'sn. The quasi-analytical approach requires significantly less computer time than Monte Carlo simulations and provides explicit
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01544073
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  • 2
    Electronic Resource
    Electronic Resource
    The use of renormalization for calculating effective permeability (1989)
    Springer
    Transport in porous media 4 (1989), S. 37-58 
    Details
    ISSN: 1573-1634
    Keywords: Heterogeneity ; effective permeability ; scaling ; simulation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Technology
    Notes: Abstract There is a need in the numerical simulation of reservoir performance to use average permeability values for the grid blocks. The permeability distributions to be averaged over are based on samples taken from cores and from logs using correlations between permeabilities and porosities and from other sources. It is necessary to use a suitable ‘effective’ value determined from this sample. The effective value is a single value for an equivalent homogeneous block. Conventionally, this effective value has been determined from a simple estimate such as the geometric mean or a detailed numerical solution of the single phase flow equation. If the permeability fluctuations are small then perturbation theory or effective medium theory (EMT) give reliable estimates of the effective permeability. However, for systems with a more severe permeability variation or for those with a finite fraction of nonreservoir rock all the simple estimates are invalid as well as EMT and perturbation theory. This paper describes a real-space renormalization technique which leads to better estimates than the simpler methods and is able to resolve details on a much finer scale than conventional numerical solution. Conventional simulation here refers to finite difference (or element) techniques for solving the single phase pressure equation. This requires the pressure and permeability at every grid point to be stored. Hence, these methods are limited in their resolution by the amount of data that can be stored in core. Although virtual memory techniques may be used they increase computer time. The renormalization method involves averaging over small regions of the reservoir first to form a new ‘averaged permeability’ distribution with a lower variance than the original. This pre-averaging may be repeated until a stable estimate is found. Examples are given to show that this is in excellent agreement with computationally more expensive numerical solution but significantly different from simple estimates such as the geometric mean.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00134741
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  • 3
    Electronic Resource
    Electronic Resource
    Real-time application of an oil spill movement prediction system (1989)
    Springer
    Natural hazards 2 (1989), S. 31-44 
    Details
    ISSN: 1573-0840
    Keywords: Oil spill ; pollution ; simulation ; Canada ; emergency
    Source: Springer Online Journal Archives 1860-2000
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract This paper deals with the prediction, in real time, of the motion of experimental oil slicks. The experiments were conducted during September 1983 offshore near Halifax on the east coast of Canada. The objectives of the experiments were (i) to determine the suitability of oil spill dispersants as countermeasures and (ii) the testing and verification of oil spill trajectory models and systems. The Atmospheric Environment Service (AES) participated in the experiments to test the capability of its oil spill motion prediction system in providing real-time trajectory forecasts. The experiment consisted of three sets of spills. Each set had a control slick and a test slick. Sixteen barrels of crude oil were used in each spill. The test slicks were used to test the effectiveness of various dispersants, the control slicks were used to verify trajectory forecasts. The spill trajectories and oil weathering information obtained from the system during the experiments demonstrated the relative ease with which the system could handle the required input and provide timely forecasts. The accuracy of these forecast trajectories was confirmed by observations, and their utility was demonstrated by their application in the operational decision-making process.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00124756
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  • 4
    Electronic Resource
    Electronic Resource
    Simulation of the time-space evolution of an extratropical cyclonic precipitation field over USA (1988)
    Springer
    Stochastic environmental research and risk assessment 2 (1988), S. 281-294 
    Details
    ISSN: 1436-3259
    Keywords: precipitation field ; stochastic time-space evolution ; simulation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract The time-space evolution of an extratropical cyclonic precipitation field over U S A is simulated in a stochastic setting as outlined in Kavvas et al. (1988). The birth of a cyclonic storm is characterized by the simultaneous birth of a cyclone center and births of subsynoptic precipitation areas (SPA) at preferred locations around the cyclone center. The precipitation cores and cells which are used as the fundamental building blocks of the SPAs are approximated by circular precipitation areas (CPA) of different sizes. The time space evolution of the precipitation field after the birth is governed by (1) the movement of the synoptic cyclone described by the cyclone center trajectory, (2) independent nonidentically distributed random velocities of the individual CPAs relative to the cyclone center, (3) the births of new CPAs in time and space relative to the cyclone center, (4) the independent evolution in time of the individual spatially uniform intensities of the existing CPAs, (5) the expansion and shrinkage of the existing CPAs in the course of movement and (6) the dissipation (death) of a random number of existing CPAs within the cyclonic system. The computer simulation, the results of which are presented in this paper, successfully reproduced the general mesoscale and synoptic scale features of the radar detected cyclonic rain fields as observed by Austin and Houze (1972), Houze et al. (1976), Hobbs (1978), Hobbs and Locatelli (1978), Houze (1981), Houze and Hobbs (1982) and others.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01544041
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  • 5
    Electronic Resource
    Electronic Resource
    Integrated production scheduling in large-scale flexible electronic parts manufacturing (1988)
    Springer
    Annals of operations research 15 (1988), S. 269-287 
    Details
    ISSN: 1572-9338
    Keywords: Production scheduling ; integer programming ; simulation ; flexible manufacturing ; hierarchical modelling
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics , Economics
    Notes: Abstract This study reports the development of a production scheduling system for the integrated management of production in large-scale, high-volume electronic assembly lines. The development of the system incorporates control and planning considerations by addressing the interaction of various subsystems. Stochastic and deterministic aspects of the problem environment are appropriately handled via relevant simulation and analytic models. By effecting a hierarchical breakdown of the problem environment, the system produces information used in practical decision making for production planning and scheduling. Procedures used encompass and address considerations for management of work-in-process, optimization of the various subsystems' performance, minimization of setup time effect, and inventory carrying costs.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02186799
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  • 6
    Electronic Resource
    Electronic Resource
    Machine utilizations achieved using balanced FMS production ratios in a simulated setting (1988)
    Springer
    Annals of operations research 15 (1988), S. 227-267 
    Details
    ISSN: 1572-9338
    Keywords: FMS ; production ratios ; mathematical programming ; levels of detail in modeling ; balanced machine workloads ; machine utilizations ; dispatching rules ; simulation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics , Economics
    Notes: Abstract Stecke [21] has developed mathematical programming approaches for determining, from a set of part type requirements, the production ratios (part types to be produced next, and their proportions) which maximize overall machine utilizations by balancing machine workloads in a flexible manufacturing system (FMS). These mathematical programming (MP) approaches are aggregate in the sense that they do not take into account such things as contention for transportation resources, travel time for work-in-process, contention for machines, finite buffer space, and dispatching rules. In the current study, the sensitivity of machine utilizations to these aggregations is investigated through simulation modeling. For the situation examined, it is found that achieved machine utilizations are a strong function of some of the factors ignored in the MP methodology, ranging from 9.1% to 22.9% less than those theoretically attainable under the mathematical programming assumptions. The 9.1% degradation results from modeling with nonzero work-in-process travel times (i.e. 2 minutes per transfer) and using only central work-in-process buffers. Resource levels (e.g. the number of automated guided vehicles; the amount of work-in-process; the number of slack buffers) needed to limit the degradation to 9.1% correspond to FMS operating conditions which are feasible in practice.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02186798
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  • 7
    Electronic Resource
    Electronic Resource
    Saltwater transport in a heterogeneous formation: A case study (1988)
    Springer
    Transport in porous media 3 (1988), S. 217-256 
    Details
    ISSN: 1573-1634
    Keywords: Salinity ; advection ; dispersion ; aquifers ; flow model ; transport model ; simulation ; sea water ; connate water ; leakage
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Technology
    Notes: Abstract Historical information of the hydraulic and salinity aspect, detailed geological information, and information on the physical characteristics of the different layers comprising the formation, are needed for simulating the saltwater transport process in aquifers. In most simulation studies of field situations, there is an inadequacy of data and the modeller has to make justifiable assumptions to analyze a particular situation in order to provide an insight into the problem. A quasi-three-dimensional solute transport model is used to analyze the saltwater encroachment phenomena in aquifers underlying the City of Bangkok; first by calibrating the model's performance with available historical data and then by assessing the extent of future saltwater encroachment with the implementation of the regulatory pumpage to be followed in order to restrict the alarming rate of land subsidence. Model simulation indicates a substantial reduction in the rate of encroachment of the saltwater front with a reduction of pumpage after 1987.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00235330
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  • 8
    Electronic Resource
    Electronic Resource
    Dynamics of C, N, P and S in grassland soils: a model (1988)
    Springer
    Biogeochemistry 5 (1988), S. 109-131 
    Details
    ISSN: 1573-515X
    Keywords: soil organic matter ; nitrogen ; phosphorus ; sulfur ; simulation ; grasslands
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract We have developed a model to simulate the dynamics of C, N, P, and S in cultivated and uncultivated grassland soils. The model uses a monthly time step and can simulate the dynamics of soil organic matter over long time periods (100 to 10,000 years). It was used to simulate the impact of cultivation (100 years) on soil organic matter dynamics, nutrient mineralization, and plant production and to simulate soil formation during a 10,000 year run. The model was validated by comparing the simulated impact of cultivation on soil organic matter C, N, P, and S dynamics with observed data from sites in the northern Great Plains. The model correctly predicted that N and P are the primary limiting nutrients for plant production and simulated the response of the system to inorganic N, P, and S fertilizer. Simulation results indicate that controlling the C:P and C:S ratios of soil organic matter fractions as functions of the labile P and S levels respectively, allows the model to correctly simulate the observed changes in C:P and C:S ratios in the soil and to simulate the impact of varying the labile P and S levels on soil P and S net mineralization rates.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02180320
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  • 9
    Electronic Resource
    Electronic Resource
    Simulation of the movement and dispersion of oil slicks in the Arabian Gulf (1988)
    Springer
    Natural hazards 1 (1988), S. 197-219 
    Details
    ISSN: 1573-0840
    Keywords: Arabian Gulf ; oil ; oil ; simulation ; meteorology ; tides ; residual currents
    Source: Springer Online Journal Archives 1860-2000
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract The extensive oil drilling and transportation activities in the Arabian Gulf increased the possibility of oil spills and the consequent threat of oil pollution to the regional ecology. The available literature concerning the main aspects of the physical oceanographic characteristics affecting the movement and spreading of oil spill in the Gulf are reviewed. It is concluded that evaporation, wind-driven currents, and sandfall are important as weathering processes, while tidal currents cause lateral spreading of the slick. Oil spill modelling has shown some usefulness in estimating the trajectories of few major spills illustrated by reference to three models developed for the Gulf. The performance of these models, their capabilities and limitations are reviewed. Recommendations are made to gather more data on the behavior of oil spills in this particular environment.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00126615
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  • 10
    Electronic Resource
    Electronic Resource
    On a stochastic description of the time-space behaviour of extratropical cyclonic precipitation fields (1987)
    Springer
    Stochastic environmental research and risk assessment 1 (1987), S. 37-52 
    Details
    ISSN: 1436-3259
    Keywords: Cyclonic precipitation ; mathematical modeling ; simulation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract A stochastic description is developed for extratropical cyclonic precipitation fields at synoptic and meso scales as they are typically observed by radars over the Earth. This description attempts to account I) for the synoptic scale behavior of a cyclonic storm (its birth, its synoptic scale motion trajectory, and its dissipation) II) for the synoptic-scale organizational structure of subsynoptic precipitation areas (rainbands, precipitation cores and raincells) within a cyclonic storm; and III) for the behavior of subsynoptic precipitation areas, in terms of their births, their spatial configuration evolutions, their motions, and their deaths (dissipation). The precipitation cores and the raincells are taken as the building blocks of the subsynoptic precipitation, areas within a cyclonic rainfield.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01543908
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  • 11
    Electronic Resource
    Electronic Resource
    Probability theory versus simulation of petroleum potential in play analysis (1987)
    Springer
    Annals of operations research 8 (1987), S. 363-381 
    Details
    ISSN: 1572-9338
    Keywords: Probability ; simulation ; petroleum ; resources ; appraisal
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics , Economics
    Notes: Abstract An analytic probabilistic methodology for resource appraisal of undiscovered oil and gas resources in play analysis is presented. This play-analysis methodology is a geostochastic system for petroleum resource appraisal in explored as well as frontier areas. An objective was to replace an existing Monte Carlo simulation method in order to increase the efficiency of the appraisal process. Underlying the two methods is a single geologic model which considers both the uncertainty of the presence of the assessed hydrocarbon and its amount if present. The results of the model are resource estimates of crude oil, nonassociated gas, dissolved gas, and gas for a geologic play in terms of probability distributions. The analytic method is based upon conditional probability theory and a closed form solution of all means and standard deviations, along with the probabilities of occurrence.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02187102
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  • 12
    Electronic Resource
    Electronic Resource
    Monte carlo estimation of the sampling distribution of nonlinear model parameter estimators (1987)
    Springer
    Annals of operations research 8 (1987), S. 243-256 
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    ISSN: 1572-9338
    Keywords: Control variates ; Monte Carlo ; nonlinear estimation ; simulation ; variance reduction
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics , Economics
    Notes: Abstract The sampling distribution of parameter estimators can be summarized by moments, fractiles or quantiles. For nonlinear models, these quantities are often approximated by power series, approximated by transformed systems, or estimated by Monte Carlo sampling. A control variate approach based on a linear approximation of the nonlinear model is introduced here to reduce the Monte Carlo sampling necessary to achieve a given accuracy. The particular linear approximation chosen has several advantages: its moments and other properties are known, it is easy to implement, and there is a correspondence to asymptotic results that permits assessment of control variate effectiveness prior to sampling via measures of nonlinearity. Empirical results for several nonlinear problems are presented.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02187095
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  • 13
    Electronic Resource
    Electronic Resource
    Response surface methodology as a means for efficient data storage and retrieval (1987)
    Springer
    Annals of operations research 8 (1987), S. 351-362 
    Details
    ISSN: 1572-9338
    Keywords: Response surface methodology ; simulation ; optimization
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics , Economics
    Notes: Abstract Managing the volume of experimental and/or simulation data required for large-scale design studies can be a significant problem. This paper describes a method for dealing with this problem, using response surface methodology. The method involves (1) determining a summary parameterization of the response of the underlying process mechanism generating the data, in order to characterize this response in terms of a manageable set of performance measures, and (2) deriving a model of the data, in order to summarize the dependence of the performance measures on selected predictor or design variables. The method is illustrated by its application to a problem in vehicle collision research.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02187101
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  • 14
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    The effect of leaching on mixing in porous media with a single heterogeneity (1987)
    Springer
    Transport in porous media 2 (1987), S. 3-18 
    Details
    ISSN: 1573-1634
    Keywords: Dispersion ; heterogeneity ; leaching ; regimes ; scales ; simulation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Technology
    Notes: Abstract This paper presents an exploratory study of the effect of leaching on mixing in a porous medium containing a single heterogeneity to investigate the effect of the heterogeneity and time-dependent pore structure on dispersion. A percolation-convection simulation (PCS) model is used along with laboratory model experiments to study the mixing. The results show that mixing changes when the pores of the models are leached and that there is a change in regime influence during leaching. The simulation represents the mixing through a first leach for homogeneous media and for heterogeneous media with significant changes in permeability. If the pore structure is changing with time, prediction of mixing must include effects of heterogeneity and regime influence. Although the experimental results are representative of idealized laboratory sized systems they provide insight into the effects of leaching in heterogeneous media. Further the simulation may be useful on a field scale.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00208533
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  • 15
    Electronic Resource
    Electronic Resource
    Generating large stochastic simulations—The matrix polynomial approximation method (1987)
    Springer
    Mathematical geology 19 (1987), S. 99-107 
    Details
    ISSN: 1573-8868
    Keywords: geostatistics ; simulation ; Toeplitz matrices ; block Toeplitz matrices ; matrix polynomial approximation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Mathematics
    Notes: Abstract An algorithm for producing a nonconditional simulation by multiplying the square root of the covariance matrix by a random vector is described. First, the square root of a matrix (or a function of a matrix in general) is defined. The square root of the matrix can be approximated by a minimax matrix polynomial. The block Toeplitz structure of the covariance matrix is used to minimize storage. Finally, multiplication of the block Toeplitz matrix by the random vector can be evaluated as a convolution using the fast Fourier transform. This results in an algorithm which is not only efficient in terms of storage and computation but also easy to implement.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00898190
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  • 16
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    Regional environmental simulation of African cattle herding societies (1986)
    Springer
    Human ecology 14 (1986), S. 117-130 
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    ISSN: 1572-9915
    Keywords: regional ; East Africa ; cattle ; simulation ; food supply
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Ethnic Sciences
    Notes: Abstract Regional analyses of the interaction between human populations and natural resources must integrate landscape scale environmental problems. An approach that considers human culture, environmental processes, and resource needs offers an appropriate methodology. With this methodology, we analyze problems of food availability in African cattle-keeping societies. The analysis interrelates cattle biomass, forage availability, milk and blood production, crop yields, gathering, food subsidies, population, and variable precipitation. While an excess of cattle leads to overgrazing, cattle also serve as valuable food storage mechanisms during low rainfall periods. Food subsidies support higher population levels but do not alter drought-induced population fluctuations. Variable precipitation patterns require solutions that stabilize year-to-year food production and also address problems of overpopulation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00889213
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  • 17
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    Experimental investigation of real-time scheduling in flexible manufacturing systems (1985)
    Springer
    Annals of operations research 3 (1985), S. 355-377 
    Details
    ISSN: 1572-9338
    Keywords: Flexible manufacturing systems ; scheduling ; manufacturing systems ; simulation ; computer integrated manufacturing
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics , Economics
    Notes: Abstract This paper presents a new two-phase (TP) approximate method for real-time scheduling in a flexible manufacturing system (FMS). This method combines a reduced enumeration schedule generation algorithm with a 0–1 optimization algorithm. In order to make the combined algorithm practicable, heuristic rules are introduced for the selection of jobs to be scheduled. The relative performance of the TP method vis-a-vis conventional heuristic dispatching rules such as SPT, LPT, FCFS, MWKR, and LWKR is investigated using combined process-interaction/discrete-event simulation models. An efficient experimental procedure is designed and implemented using these models, and the statistical analysis of the results is presented. For the particular case investigated, the conclusions are very encouraging. In terms of mean flow time, the TP method performs significantly better than any other tested heuristic dispatching rules. Also, the experimental results show that using global information significantly improves the FMS performance.
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    URL: http://dx.doi.org/10.1007/BF02023749
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  • 18
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    An overview of evaluative models for flexible manufacturing systems (1985)
    Springer
    Annals of operations research 3 (1985), S. 13-21 
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    ISSN: 1572-9338
    Keywords: Flexible manufacturing systems ; queueing models ; simulation ; performance evaluation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics , Economics
    Notes: Abstract Flexible manufacturing systems (FMSs) are a class of automated systems which can be used to improve productivity in discrete parts manufacturing. Due to the complexity of these systems, it is useful to have models that can aid in the design and operation of FMSs. We specifically differentiate here betweengenerative (or prescriptive) models, whichfind candidate decisions, andevaluative (or descriptive) models, whichevaluate a given set of decisions. We briefly cover, in a practical context, the pros and cons of these two classes of models. Then we focus on the latter class of models. Evaluative models for FMSs fall into five main classes, based on the technique used, namely: static allocation, queueing network theory, simulation, perturbation analysis, and Petri nets. Each of these approaches is briefly described, advantages and disadvantages mentioned, and references given to more detailed papers.
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    URL: http://dx.doi.org/10.1007/BF02023766
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  • 19
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    A technique for on-line sensitivity analysis of flexible manufacturing systems (1985)
    Springer
    Annals of operations research 3 (1985), S. 379-391 
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    ISSN: 1572-9338
    Keywords: Flexible manufacturing systems ; discrete event systems ; real-time systems ; monitoring ; simulation ; performance evaluation ; perturbation analysis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics , Economics
    Notes: Abstract The recent perturbation analysis approach to discrete event systems is applied to flexible manufacturing systems (FMS). While analytic (queueing) models are useful in preliminary design of such systems, they are not accurate enough at the detailed design/operation stage. Thus, experimentation on detailed simulations or on the actual system has been the way to optimize system performance. Perturbation analysis allows us to derive the sensitivity of system performance, with respect to several design/operating parameters, by observing a single experiment (and without having to actually alter the parameters — often a costly operation). Thus, observation of one experiment can give accurate directions for the improvement of several parameter values. Here we give a simulation example illustrating how perturbation analysis could be used on-line on an FMS to improve its performance, including reducing its operating cost. Experimental results are also presented validating the estimates obtained from this technique.
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    URL: http://dx.doi.org/10.1007/BF02023776
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  • 20
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    Spectral-type simulation of spatially correlated fracture set properties (1985)
    Springer
    Mathematical geology 17 (1985), S. 41-52 
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    ISSN: 1573-8868
    Keywords: fracture set ; simulation ; spectral density ; Fourier transform
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Mathematics
    Notes: Abstract Fracture set properties such as orientation, spacing, trace length, and waviness tend to be spatially correlated. These properties can be efficiently simulated by spectral analysis procedures that take advantage of the computational speed of the fast Fourier transform. The covariance function of each property to be simulated is obtained from the variogram function estimated from mapped fracture set data and is typically referenced to the mean vector of the set. Simulation procedures for normally and exponentially distributed data involve generating uncorrelated Fourier coefficients that are assigned proper variance according to the spectral density, which is the Fourier transform of the covariance function. These coefficients are then reverse Fourier transformed to produce simulated set properties that have the desired variance and variogram function.
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    URL: http://dx.doi.org/10.1007/BF01030366
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  • 21
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    Two-dimensional simulation by turning bands (1985)
    Springer
    Mathematical geology 17 (1985), S. 81-90 
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    ISSN: 1573-8868
    Keywords: simulation ; turning bands ; covariance ; semivariogram ; geostatistics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Mathematics
    Notes: Abstract Journel (1974) developed the turning-bands method which allows a three-dimensional data set with specified covariance to be obtained by the simulation of several one-dimensional realizations which have an intermediate covariance. The relationship between the threedimensional and one-dimensional covariance is straightforward and allows the one-dimensional covariance to be obtained immediately. In theory a dense uniform distribution of lines in three-dimensional space is required along which the one-dimensional realizations are generated; in practice most workers have been content to use the fifteen axes of the regular icosahedron. Many mining problems may be treated in two dimensions, and in this paper a turning-bands approach is developed to generate two-dimensional data sets with a specified covariance. By working in two dimensions, the area on which the data is simulated may be divided as finely as desired by the lines on which the one-dimensional realizations are first generated. The relationship between the two-dimensional and one-dimensional covariance is derived as a nontrivial integral equation. This is solved analytically for the onedimensional covariance. The method is applied to the generation of a two-dimensional data set with spherical covariance.
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    URL: http://dx.doi.org/10.1007/BF01030369
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  • 22
    Electronic Resource
    Electronic Resource
    The Bi-Gaussian approach: A simple method for recovery estimation (1985)
    Springer
    Mathematical geology 17 (1985), S. 625-644 
    Details
    ISSN: 1573-8868
    Keywords: recoveries ; multi-Gaussian ; bi-Gaussian ; simulation ; disjunctive kriging
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Mathematics
    Notes: Abstract A new and simple method is proposed to obtain estimates of recovery functions: the Bi-Gaussian approach. Existing methods estimate recovery functions with conditional distributions where the conditioning set is all the data available. Here instead the simple kriging estimate of the Gaussian transform is proposed to be used. Results in the point recovery case are identical to the multi-Gaussian approach of Verly (1983, 1984), whereas in the non-point-support situation, an approximation is derived which saves computer time as compared to employing the strict multi-Gaussian hypothesis. Two examples compare favorably with the well-established disjunctive kriging method (discrete Gaussian model).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01030857
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    Electronic Resource
    Electronic Resource
    Analytical comparison of two methods of assay weighting using vein assays from Butte, Montana (1974)
    Springer
    Mathematical geology 6 (1974), S. 219-233 
    Details
    ISSN: 1573-8868
    Keywords: sampling ; simulation ; statistics ; assay weighting ; economic geology ; geochemistry ; mining ; ore-reserve calculations
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Mathematics
    Notes: Abstract Weighting of vein assays is desirable where assays represent variable vein widths and variable distances along the vein. The method of weighting used is important in ore-reserve calculations and other investigations. Two possible methods are considered here. The first method, commonly applied in mining, assumes in effect linear variation of assay-width products between assay points. The second method, developed in this paper, assumes linear variation of assays and widths separately. The weighted average assay in an interval dby the second method (aw1, 2)is given by the expression $$a_{w1,2} = V/[(w_1 + w_2 )/2]$$ where $$\begin{gathered} v = (1/3)(\Delta a)(\Delta w)d + (1/2)(\Delta a)w_1 d + (1/2)(\Delta w)a_1 d + a_1 w_1 d \hfill \\ \Delta a = a_2 - a_1 {\text{,}}\Delta w = w_2 - w_1 \hfill \\ \end{gathered} $$ a1, w1 are assay and width at point 1, a2, w2 are assay and width at point 2,and dis the distance between points 1and 2.Statistical testing of the two methods, using 8,913 pairs of copper assay-width data from the Belmont mine area at Butte, suggests the following: within major veins or within veins which show near-linear width variations, the second method may be used with the expectation that the average grade calculated will more closely represent the actual average grade than if the first method were used.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02082888
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    Electronic Resource
    Electronic Resource
    Application of autocorrelation criteria to the analysis of mapped geologic data from the coal measures of central England (1971)
    Springer
    Mathematical geology 3 (1971), S. 281-295 
    Details
    ISSN: 1573-8868
    Keywords: analysis of variance ; autocorrelation ; simulation ; trend analysis ; sedimentology ; stratigraphy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Mathematics
    Notes: Abstract It is proposed that the variance in mapped geologic data should be formally considered to be composed of three components which arise on different geographic scales. The three components (regional, local, and residual) should be defined solely in terms of the parameters of the sample data set. A two-step analysis is required to separate three components. Applying autocorrelation criteria, trend-surface analysis has been used, in the first step, to remove the residual component and, in the second step, to separate regional and local components from the resulting noise-free data. This procedure has made it possible to quantify local components in stratigraphic thickness data from the East Midlands coalfield (central England) which can be identified in terms of the known geology.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02045796
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    Electronic Resource
    Electronic Resource
    The dynamics of shale compaction and evolution of pore-fluid pressures (1971)
    Springer
    Mathematical geology 3 (1971), S. 239-263 
    Details
    ISSN: 1573-8868
    Keywords: simulation ; hydrology ; petroleum ; sedimentology ; high fluid pressures ; compaction ; primary migration
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Mathematics
    Notes: Abstract A mathematical model of sedimentation and compaction of fine-grained rocks such as shale has been constructed. Water is considered to flow upward or downward out of a compacting rock according to Darcy's law until the pore-water pressure within the rock is normal for the depth in question. The porosity decreases during compaction until a minimum porosity, determined by the difference between total vertical stress (overburden pressure) and pore-water pressure, is obtained. The model takes into account the dependence of permeability on porosity for a given rock type, and the dependence of water viscosity on salinity, temperature, and pressure. The derived equations have been computer programmed to obtain the time dependence of porosity, pressure, water velocity, permeability, and other factors within a compacting shale during (a) shale sedimentation, (b) a time lapse following shale deposition, (c) the deposition of normally pressured sediments over the shale, and (d) a second time lapse following deposition of the normally pressured unit. Solutions to these problems are given for the situation when the unit underlying the shale is normally pressured, and for the situation when the underlying unit is impermeable. The calculations show that a portion of a thick shale adjacent to a normally pressured unit may have a considerably reduced porosity and permeability, and act as a seal for the remainder of the shale. High fluid pressures may persist for many millions of years in thick shales with low permeability. The computations can be extended to cover more complicated cases of interbedded shales, sands, and other lithologies.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02045794
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    Electronic Resource
    Electronic Resource
    Use of random-genetic models in the study of sedimentary processes (1971)
    Springer
    Mathematical geology 3 (1971), S. 265-279 
    Details
    ISSN: 1573-8868
    Keywords: simulation ; mathematical models ; sedimentology ; stratigraphy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Mathematics
    Notes: Abstract To study sedimentary phenomena, we introduce random-genetic models in which genetic hypotheses and structural random elements occur for the main part. Starting from geologic hypotheses we choose principal factors which may be random functions or random variables. These factors are: depth, nature of the facies, sedimentation rate, and subsidence. Equations of evolution link the factors. Depth is a Markov process, but generally the resultant sequence does not make a Markov chain or Markov process. Three examples of such models are given with the results of simulations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02045795
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