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Social networks have been closely identified with graph theoretical models, which constitute their most familiar mode of representation. There are a number of such models which may embody symmetric, directed, or valued relationships. But the study of networks with valued linkages, using the natural formalization provided by the valued graph or digraph, has been impeded by a traditional lack of analytical machinery for dealing with valued structures. In this paper, we demonstrate the development and elaboration of formalizations for the central network concepts of reachability, joining, and connectedness through graph theoretical models of increasing complexity, culminating in their expression within a general model for valued structures. This model for valued (symmetric or directed) graphs, or vigraphs, provides a unified representation and matrix methodology for dealing with qualitative and quantitative structures, incorporates many existing methods as special cases, and suggests new applications. Some of the most interesting of these follow the recognition, consistent with the model, that the "values" assigned to network linkages may be sorts of entities other than numbers. [ABSTRACT FROM AUTHOR]

The difficulty of studying large networks is widely recognized by social network researchers. The fuzzy boundaries of networks and the high cost of data collection often nine the exhaustive exploration of a soda! network impractical. Researchers have applied a variety of alternative procedures for sampling social networks, (such as snowball sampling) and have discussed the adequacy of the statistics for estimating a variety of network population parameters. However, little empirical work has been done on these estimates of social network parameters. With the use of computer simulations, this paper examines estimates of indegree centrality in snowball samples that vary in initial sample size, number of stages, and number of choices. The effects of varying sample parameters on estimated error is discussed. [ABSTRACT FROM AUTHOR]

This paper considers the use of the Bond Energy approach of McCormick, Schweitzer, and White as an alternative to CONCOR and other methods for producing blockmodel, and to Baker's approach to three-way blockmodels. Results of analyses using artificial data and the Roethlis- berger-Dickson Bank Wiring Room data are presented, where algorithms alternative to the one of McCormick et at (including versions of simulated annealing) are considered. [ABSTRACT FROM AUTHOR]

This paper develops a mathematical framework for identifying optimal transfer times from a low-intensity, watchful waiting therapy to direct intervention. It allows for the probability that patients discharged from watchful waiting will suffer disease recurrence. Two specific functional forms for the resolution of the relevant medical condition are modeled (modified exponential and logistic). Initially structured as an expected cost minimisation problem, the analysis is extended to include the possibilities of differential benefits of the therapies and discounted cost and benefit valuations. The framework demonstrates the existence of non-synchronous transfer optima. [ABSTRACT FROM AUTHOR]

This paper summarizes the geographic information system (GIS) and modelling activities of the Munich Research Association for Agricultural Ecosystems (FAM), which is a joint project of the GSF-National Research Centre for Environment and Health, Oberschleissheim, and the Technical University of Munich. In particular, the agro-ecological information system (AIS) within the FAM will be presented. Simulation models will be provided in a GIS to forecast and assess ecological risks of different management practices. The AIS is based on two different scales: one is a farm called 'Klostergut Scheyern' (149 ha), designedas a monitoring network with a cell resolution of 50 m X 50 in, the other is the surrounding area, a landscape of 547 km2. Thepaper describes the spatial input data as well as the model structure of the two different scales. Finally, first results for calculatingthe soil water budget on the farm level, and nitrate leaching on thelandscape level will be presented. [ABSTRACT FROM AUTHOR]

A simulation model, ORWARE (ORganic WAste REsearch), for the handling of organic waste in urban areas has been constructed. The model provides a comprehensive view of the environmental effects, plant nutrient utilization and energy turnover for this large and complex system.The ORWARE model consists of several sub-models; sewage plant, incineration, landfill, compost, anaerobic digestion, truck transport, transport by sewers, residue transport and spreading of residues on arable land. The model is intended for simulating different scenarios, and the results are: emissions to air and water, energy turnover and the amount of residues returned to arable land. All results are presented, both as the gross figure for the entire system and figures for each process. Throughout the model all physical flows are described by the same variable vector, consisting of 43 substances. This extensivevector facilitates a thorough analysis of the results, but involves some difficulties in acquiring relevant data. In this paper, the model is described. Results from a hypothetical case study are presented in a companion paper. [ABSTRACT FROM AUTHOR]

Results from simulations with the ORWARE model (ORganic WAste REsearch) are presented. The model was tested on a medium-sized Swedish city. The scenarios were planned to illustrate the consequences of different waste handling systems. The modeled processes for organic solid waste were; incineration, landfilling, anaerobic digestion and composting, for the wastewater they were sewage plant and source separationof urine. Each transport and treatment facility was modeled with respect to incoming waste. Each process model generates an energy balance, liquid and/or gaseous emissions and residual products as outputs. The simulation results show that source separation of solid waste, followed by biological treatment, is beneficial with respect to the recycling of phosphorus and environmental effects. The negative results for these systems are their energy balances. Source-separating human urine seems to be the only way to get a high degree of nitrogen recycling. The results also stress the importance of including liquid waste to get an overall picture of the transports needed to get the residues to arable land. Landfilling organic waste generates the largest negative environmental effect. A model description is presented in a companion paper. [ABSTRACT FROM AUTHOR]

The chemical processes responsible for production of photochemical oxidants within the troposphere have been the subject of laboratory and field study throughout the last three decades. During the same period, models to simulate the atmospheric chemistry, transport and deposition of ozone (O3) from individual urban sources and fromregions have been developed. The models differ greatly in the complexity of chemical schemes, in the underlying meteorology and in spatial and temporal resolution. Input information from land use, spatial and temporally disaggregated emission inventories and meteorology haveall improved considerably in recent years and are not fully implemented in current models. The development of control strategies in both North America and Europe to close the gaps between current exceedances of environmental limits, guide values, critical levels or loads andfull compliance with these limits provides the focus for policy makers and the support agencies for the research. The models represent the only method of testing a range of control options in advance of implementation. This paper describes currently applied models of photochemical oxidant production and transport at global and regional scalesand their ability to simulate individual episodes as well as photochemical oxidant climatology. The success of current models in quantifying the exposure of terrestrial surfaces and the population to potentially damaging O3 concentrations (and dose) is examined. The analysis shows the degree to which the underlying processes and their application within the models limit the quality of the model products. [ABSTRACT FROM AUTHOR]

The status of computer simulation models from around the world for evaluating the possible ecological, environmental, and societal consequences of global change is presented in this paper. In addition, a brief synopsis of the state of the science of these impacts is included. Issues considered include future changes in climate and patterns ofland use for societal needs. Models discussed relate to vegetation (e.g. crop), soil, bio-geochemistry, water, and wildlife responses to conventional, forecasted changes in temperature and precipitation. Also described are models of these responses, alone and interactively, to increased CO2, other air pollutants and UV-B radiation,as the state of the science allows. Further, models of land-use change are included. Additionally, global multiple sector models of environment, natural resources, human population dynamics, economics, energy, and political relations are reviewed for integrated impact assessment. To the extent available, information on computer software and hardware requirements is presented for the various models. The paper concludes with comments about using these technologies as they relate to ecological risk assessment for policy decision analysis. Such an effort is hampered by considerable uncertainties with the output of existing models, because of the uncertainties associated with input data and the definitions of their dose-response relationships. The concluding suggestions point the direction for new developments in modeling and analyses that are needed for the 21st century. [ABSTRACT FROM AUTHOR]

Information on environmental levels and transport processes of natural and anthropogenic radioactivity, although plentiful, is widely scattered, and relatively few attempts have been made to summarize and synthesize this information. Furthermore, most experimental observations and experiments on environmental radioactivity have been designed for documentation or testing of specific hypotheses, rather than for providing key information for transport simulation models or on fundamental processes which such models seek to represent. This paper examines three basic questions, namely (1) what is the current state of the science of radioecology?; (2) how well is this science being incorporated into predictive models?; and (3) how well are the models being used to guide and improve the science? These discussions will be preceded by a brief description of the field of radioecology, and comments on its relevance to other sciences as well as to major societal problems stemming from environmental releases of radioactivity. In addition to assessing the current state of the science and its use in predictive models, specific ideas for improving both the science and its associated models will be advanced. These ideas fall under the categories of (1) environmental transport processes and model parameters,(2) estimating exposure and dose to human and ecological receptors, and (3) dose-effect relationships for plants and animals. [ABSTRACT FROM AUTHOR]

This paper traces plastics streams through the German economy. A material flow simulation model is used to analyze the production of plastics products, their use and residence times in the economy and finally to calculate the present and future amounts of waste. We find thatthere is an indirect net export of plastics products incorporated infinal products which amounts to 3/6% of domestic consumption. Residence times of plastics products range from a few months to 30 years and more, with the weighted average amounting to 14 years. In Germany, total post-consumer plastics waste will rise from 4.6 Mt in 1995 to 6.2/7.2 Mt in 2005 and could easily reach a value in the range of 12/14 Mt in 2025. At the same time, the accumulation of plastics in the economy will increase from about 72 Mt in 1995 to 180 Mt in 2025 in the business-as-usual scenario. The share of waste from long-lived products will continue to grow in the next decades. For polyolefins, PVC and polystyrene in plastics waste, we expect that the total amounts will more than double within the next 25 years. Analyses as presented in this paper can help to establish strategic waste management policies. [ABSTRACT FROM AUTHOR]

This paper addresses the issue of the applicability of various network measures (provided by analysis programs such as UCINET) for the analysis of a disease transmission network. A simulation was conducted to estimate HIV transmission probabilities within an empirical network of cocaine injectors. The results of the simulation were then used as a criterion to evaluate network measures of disease vulnerability and infectivity. The analysis concludes that, for the type of disease transmission network studied, relatively simple ego-network-based network measures can be adequate to the measurement of vulnerability to disease and infectivity. [ABSTRACT FROM AUTHOR]

Part I. Presents information on a study that develops the Ecological Simulation (EcoSim) model for the area around Bermuda at the Joint Global Ocean Flux Study (JGOFS) Bermuda Atlantic Time-series Study (BATS) station in the Pacific Ocean. Physical inputs of the model; Methodology of the study; Results and discussion of the study.

In the companion paper, a whole-body, mechanistic model of protein turnover in a rodent was described and evaluated with independent data sets that used the flooding dose method. On the basis of fitted fluxes, the model was able to predict specific radioactivity changes in the protein and free leucine pools and whole-body protein fractional synthesis rate (FSR). In this paper, results of model simulations of specific radioactivity changes in the flooding dose, pulse dose and continuous infusion methods were compared and the influence of recycling, channeling and multiple protein pools on model behavior were analyzed. For all methods, the percentage of channeling must be estimated to determine whether the extracellular or intracellular pool specific radioactivities better approximate the aminoacyl tRNA pool specific radioactivity. Recycling also affects the specific radioactivity of the aminoacyl-tRNA pool and therefore must be estimated. An analysis of fits of the flooding dose data indicated that 100% channeling was occurring, but the percentage of recycling could not be determined. Multiple protein pools turning over at different rates overestimated FSR by 2-3% at early time points (5 min) and underestimated FSR by 3-6% at 60 min in the flooding dose method. For the pulse dose method, FSR was underestimated by 40-50% at 5 min and underestimated by 9-10% at 60 min. An increase in time to measure FSR caused a decrease in the estimate of FSR (18% over 3 h) for the flooding dose method and an increase in the estimate of FSR (144% over 3 h) for the pulse dose method. [ABSTRACT FROM AUTHOR]

A dynamic simulation model describing long-term forest development under different grazing pressures is presented as an illustration of system analysis in forest grazing research. In this paper, a brief description of the model is presented as are some simulation results. The FORest GRAzing model (FORGRA) simulates monthly changes in the characteristics of herbaceous understory and individual trees in plots, based on underlying physiological processes. Special attention is paidto the simulation of diet composition in relation to ungulate species, food quality and food availability, and accounting for seasonal variation in these factors. The model is parameterized for 12 tree and shrub species, six species of the ground flora and four ungulate species: roe deer (Capreolus capreolus), red deer (Cervus elaphus), Highland cattle (Bos taurus) and Konik ponies (Equus caballus). The results presented in this paper concern the development of a pine forest (Pinus sylvestris L.) in the Netherlands under various grazing pressures over a period of 100 years. They show that even low densities of ungulates can have significant impacts on the regeneration and thereby on forest development. It is argued that this approach is generally applicable in forest grazing research, providing a means for quantitative interpretation of the interaction between herbivory and forest development. [ABSTRACT FROM AUTHOR]

Sustainable forest management (SFM) represents a new paradigm for forestry. Traditional forestry objectives aimed at sustainable yield management are being replaced with those of a sustainable ecosystem management. This paradigm shift in forest management requires an effective transfer of results from researchers to forest managers. To predict the potential impacts of future changes in global environment (suchas climate, land use, fire disturbance, and forest harvesting) on the sustainability of forest ecosystems, forest resource managers will require forest simulation models. There have been two basic approaches to modeling forest vegetation growth and dynamics: empirical and mechanistic forest simulation models. This paper reviews and compares three major types of forest simulation models: (1) growth and yield models (empirical approach); (2) succession models (empirical/mechanistic hybrid approach); and (3) process models (mechanistic approach), and describes three case studies as examples. The advantages and disadvantages of the different modeling approaches are discussed. The casestudies deal with predicting future forest stocks under different management options, simulating the potential effects of climate change,and effects of fire disturbance on structure and function of forest ecosystems in Canada. There is still a gap between foresters and ecologists in developing and using forest simulation models. Diversified modeling approaches integrated into a decision/support system, which will become an important tool for evaluating the sustainability of forest ecosystem in a changing environment, is emphasized. [ABSTRACT FROM AUTHOR]

It has been proposed that stomatal flux of ozone would provide a more reliable basis than ozone exposure indices for the assessment of the risk of ozone damage to vegetation across Europe. However, implementation of this approach requires the development of appropriate models which need to be rigorously tested against actual data collected under field conditions. This paper describes such an assessment of the stomatal component of the model described by Emberson et al. (2000. Modelling stomatal ozone flux across Europe. Environmental Pollution 110). Model predictions are compared with field measurements of both stomatal conductance (gs) and calculated ozone flux for shoots of mature Norway spruce (Picea abies) growing in the Tyrol Mountains in Austria. The model has been developed to calculate gs as a function of leaf phenology and four environmental variables: photosynthetic flux density (PFD), temperature, vapour pressure deficit (VPD) and soil moisture deficit (SMD). The model was run using climate data measured on site, although the SMD component was omitted since the necessary data were not available. The model parameterizationfor Norway spruce had previously been collected from the scientific literature and therefore established independently from the measurement study. Overall, strong associations were found between model predictions and measured values of stomatal conductance to ozone (GO3) and calculated stomatal ozone flux (FO3). Average diurnal profiles of GO3 and FO3 showed good agreement between the field data and modelled values except during the morning period of 1990. The diurnal pattern of ozone flux was determined primarily by PFD and VPD, as there was little diurnal variation inozone concentration. In general, the model predicted instances of high ozone flux satisfactorily, indicating its potential applicability in identifying areas of high ozone risk for this species. [ABSTRACT FROM AUTHOR]

In December 1998, the Borough of Fylde, UK, reduced the frequency ofcollection of their kerbside newspaper recycling scheme from once every 2 weeks to once every 4 weeks. The scheme incurred a drop of 8% in the overall tonnage collected, though over three quarters of this was recovered elsewhere through increased activity at the borough's paper bank sites. The overall drop-out rate from paper recycling was estimated to be <2%. A computer-based behavioural model of the Fylde community was developed and it was shown that it correctly predicted the observed changes in all major recycling performance indicators. A modelling study enabled more detailed investigations into the behavioural changes that may have occurred within the community. These analysis revealed general stabilities in behaviours, with only 18% of the model community changing their recycling behaviours with the change inthe kerbside scheme. Over half of these simply picked-up on drop-offrecycling, leaving just 5% drop outs, though these were counterbalanced by 3% new recruits. Overall, the change was considered to be a success. Cost savings of 60% accrued and the target tonnages (in the sales contract for the paper) were still met. The collection frequency change produced a net environmental benefit as well. The reasons why the change may have been so successful are discussed. [ABSTRACT FROM AUTHOR]

Examines the mesoscale physical and biological processes at the Gulf Stream front by means of a four-dimensional simulation including physical and biological data assimilation. Gulf stream processes without winds; Temperature and horizontal velocity; Vertical velocity; Sinking particle export.

Springback, the elastically-driven change of shape of a part after forming, has been simulated with 2-D and 3-D finite element modeling. Simulations using solid and shell elements have been compared with draw-bend measurements presented in a companion paper. Plane-stress and plane-strain simulations revealed the dramatic role of numerical tolerances and procedures on the results. For example, up to 51 integration points through the sheet thickness were required for accuracy within 1%, compared with 5–9 typically acceptable for forming simulations. Improvements were also needed in the number of elements in contact with the tools, and in the numerical tolerance for satisfying equilibrium at each step. Significant plastic straining took place in some cases upon unloading; however the choice of elastic–plastic unloading scheme had little effect on the results. While 2-D simulations showed good agreement with experiments under some test conditions, springback discrepancies of hundreds of percent were noted for one alloy with sheet tension near the yield stress. 3-D simulations provided much better agreement, the major source of error being identified as the presence of persistent anticlastic curvature. Most of the remaining deviation in results can be attributed to inaccuracies of the material model. In particular, the presence of a Bauschinger effect changes the results markedly, and taking it into account provided good agreement. Shell elements were adequate to predict springback accurately for R/t greater than 5 or 6, while solid elements were required for higher curvatures. As R/t approaches 2, springback simulated with solid elements tends to disappear, in agreement with measurements presented in the companion paper and in the literature. [Copyright &y& Elsevier]

Forecasting of scrapped products to recycling poses severe problems to recycling and remanufacturing companies due to uncertainties in timing and quantities of returns. In this paper an extended forecasting method to provide prognoses for return values (amount and time) of scrapped products to recycling is presented. The suggested model is based on relevant influencing factors and product life cycle data and has been applied to a case study (photocopiers) for evaluation and usability. The approach employs a simulation study, the design of a fuzzy inference system for the forecasting of the return in a determined planning period and the design of a neuro-fuzzy system for the forecasting of return values with respect to time. [Copyright &y& Elsevier]

This paper builds a simulation model in which technological advance is stochastic, and largely endogenous. Technology consists of two main components, research and development (R&D) and residual technical advance. R&D comprises a government-funded component, which is treated as exogenous, and a component funded by private industry, which is determined within the model. Industry-funded R&D is modeled as analogous to a stock of capital: investments depend on the rental price, or user cost of research, and the accelerator. The R&D elasticity in the production function is time-varying and increasing: R&D becomes more efficient over time. The increase in the R&D elasticity is determined in the model by computer quality. There is a relationship between residual technical advance during the 1990s and the increased share of computers and software in final demand, although this does not hold for all earlier periods. The production function also includes disaggregated capital stocks: equipment and software, housing, nonresidential structures, and government capital. The econometric model is used to conduct simulation experiments. The basic simulation illustrates how changes in computer quality affect both the R&D elasticity and residual technology. The remaining simulations examine policy issues: the R&D tax credit, and government funding for basic research. [Copyright &y& Elsevier]

In this paper, an implicit simulation code which can simulate a general three-dimensional sheet-metal forming is presented. An 8-node degenerated shell element is employed to approximate the continuous updated Lagrangian formulation of the global mechanical problem. Emphasis is put on expressing the contact conditions and taking into account the geometrical non-linearity. The characteristics of the authors’ contact algorithm is that the contact conditions just act as the boundary conditions of the FEM equations and need not be introduced into the stiffness matrix. Finally, two numerical examples demonstrating the effectiveness of the present approach are given. [Copyright &y& Elsevier]

A considerable amount of research has been carried out in order to improve the quality and feasibility of stents in recent years. However, published works on simulation of stent expansion using computer software are relatively rare. In this paper, a nonlinear finite-element method was employed to analyse the expansion of a stent using internal pressure. The pressure was applied as a surface load on the inner surface, expanding the stent radially past its elastic limit to a maximum diameter. The total reduction in length as the stent expands radially was also calculated. The analyses were performed using finite-element packages LS-DYNA for solution of the problem and ANSYS (version 5.5) as a pre- and post-processor. Two different load application speeds were investigated in the simulations and the results were compared. This paper concentrates on the effect of the speed of pressure applied on a stent during the expansion process. The issues discussed in this study include the extent of expansion, foreshortening of the stent and the stress levels at different increments of pressure due to the different speeds of application of the pressure. [Copyright &y& Elsevier]

Bulge forming is a manufacturing process that is becoming increasingly important as a technology that can be used to produce seamless, lightweight and near-net-shape industrial components. The process is being increasingly applied in the automotive and aerospace industries where the demand for increased structural strength and decreased vehicle weight make it a very attractive manufacturing method. This paper discusses the application of bulge forming to the manufacture of near-net-shape components and discusses machine and tool design, and illustrates how finite-element simulation is playing a growing role in the design of bulge-forming processes. [Copyright &y& Elsevier]

The inverse eigensensitivity method and the response function method of analytical model updating have become relatively more popular among other methods and have been successfully applied to the practice of analytical model improvement. This paper gives a detailed comparison of these two approaches of model updating on the basis of computer simulated experimental data with the objective of studying the convergence of the two methods and the accuracy with which they predict the corrections required in a finite element model. The effect of the amount of experimental data used in the process of model improvement on the quality of an updated model is also studied. The test cases of complete, incomplete and noisy experimental data are considered. The updated models are compared on the basis of some error indices constructed to quantify error in the predicted natural frequencies, mode shapes and response functions. [Copyright &y& Elsevier]

The process of rotational symmetric tube bulging with inside pressure and axial compression enables the standard tubes to be formed into different rotational symmetric hollow parts in such a way that their central part is expanded into a desired shape while the ends remain unchanged. The superposition of axial compression contributes to a more favorable forming stress state, which is reflected in larger forming limits and smaller wall thinning in the widened area. The problems characterizing the process are a limited range of compression stability and difficulties met when establishing and optimizing the technological parameters of the process whose course cannot be defined in an analytical way. Based on a physical model of the forming process a numerical model was built. Using ABAQUS code the model was simulated over the entire stress/forming region. The comparison of the computer simulated forming process with the experimentally obtained results showed that the model was highly accurate. Finally, the paper studies the influences of particular parameters on the stability of the process, showing on a practical example how it is possible to achieve tube bulging without wall thinning. [Copyright &y& Elsevier]

In this paper, experimental work conducted on a 52 span Venlo-type glasshouse (Hoxey and Moran, Full scale wind pressure and load experiments—Multispan 167×111 m glasshouse (Venlo), Divisional note 1594, AFRC Institute of Engineering Research, Wrest Park, Silsoe, Bedford, January, 1991) is used to validate the prediction of pressure distributions on the external side of the glasshouse roof made using the commercial CFD package Fluent 5.3.18. In addition, the validation of predictions of the pressure on a 7 span Venlo-type glasshouse is demonstrated and a comparison with numerical data by Mistriotis et al. (Neth. J. Agric. Sci. 45 (1997) 81) was made. The results of the presented CFD predictions are shown to be in good agreement with the experimental data and give confidence for future glasshouse simulations. [Copyright &y& Elsevier]

In this paper, after introducing a classification of dynamic network loading (DNL) procedures (based on time, space, and demand discretization), many new methodologies recently presented are discussed. Some analytical properties of the point packet approach, recently studied by Chabini and Kachani [1], using generalized Dirac functions, are discussed, and results are extrapolated to the proposed procedure (called MICE [2]).The connection between the dynamic network loading procedure MICE and the analytical formulation presented in [3] is explained. The same demand discretization is suggested in the solution of all analytical traffic flow models. [Copyright &y& Elsevier]

This paper highlights the roles of property models in simulation and synthesis/design of products and processes. Property models play a service role in simulation and a service cum advice role in synthesis/design. The service role is played by property models when, for the selected property model, the corresponding model parameters are available. The advice role is played by property models in terms of definition of design targets and evaluation of design feasibility. In both cases, model selection and derivative information influences accuracy and efficiency of simulation/design results. The paper also highlights the need for alternative simulation-based synthesis/design approaches where aspects of modelling, simulation, synthesis and design are solved simultaneously. Two simultaneous approaches—one employing a generalised modular framework to define the combined problem as an optimisation problem, and the other employing reduction techniques and lumped variables for graphical (visual) design, are presented. Illustrative examples highlighting the various roles and synthesis/design approaches are also presented. [ABSTRACT FROM AUTHOR]

In this paper, we propose a new clustering method for the first phase of a two-phase method of the vehicle routing problems (VRPs) and the traveling salesman problems (TSPs). In the first phase, the customers are grouped as several delivery areas for vehicle by using maximum neuron model. In the second phase, the TSPs for each areas are solved by using elastic net model proposed by Andrew et al. Conventional maximum neuron model proposed by Takefuji et al. is not suitable for these continuous problems. But by including a self-organization rule to this model, the solution quality is improved. Our simulation results show that maximum neuron model can achieve to obtain better solutions than other methods for some kinds of problems in VRPs and TSPs. [Copyright &y& Elsevier]

Nowadays, many apartments in residential buildings in Hong Kong are equipped with air-conditioners to provide comfort cooling for the living, dining and bedrooms. Air-conditioners serving the living and dining rooms would be operated mostly in the evenings and sometimes during daytime as well, but those serving the bedrooms could remain operating overnight. Other rooms, such as bathrooms and kitchens, will not normally be air-conditioned. The paper describes a study into the influence of the building envelope construction on the space cooling loads in residential buildings. The yearly cooling loads of apartments were predicted by using HTB2, a detailed building heat transfer simulation program. The study includes modifications to the base-line characteristics of walls and doors of two typical apartments. The modified walls have an additional 50 mm thick thermal insulation and/or a thickness of up to 400 mm of concrete. Modified doors have an additional 38 mm thick thermal insulation. The simulation predictions indicate that the highest reduction in the yearly cooling load could be obtained when the modified walls and doors were used at suitable locations. In addition, the study results show that the yearly cooling load would increase when the thermal insulation was applied to external walls without increasing the thickness of the concrete layer, and when the concrete layer was thickened but without addition of insulation. [Copyright &y& Elsevier]

This paper describes a new simulation tool for the prediction of aerosol formation and behaviour in gas–liquid contact devices such as absorbers, scrubbers, quench coolers, and condensers as well as multistage gas cleaning processes, respectively.Aerosol formation can impact severely the separation efficiency of gas cleaning processes. Aerosol or fog formation can arise by spontaneous condensation or desublimation in supersaturated gas phases.The rigorous description of the mass and energy transfer between the gas phase, the liquid phase, and the growing aerosol droplets leads to a system of partial differential and algebraic equations. For the solution of these systems, we have developed the plant simulation tool AerCoDe. This programme bases upon the linearly-implicit Euler discretization, which in combination with extrapolation permits an adaptive step size and order control.Typical simulation results of a multistage industrial flue gas scrubbing process are presented. It is shown, that experimental data can be confirmed if the number concentration of condensation nuclei as an input parameter is roughly known. [Copyright &y& Elsevier]

This paper describes the numerical simulation of the far field problems with loads having non-vanishing time average encountered in some dynamic problems, such as the foundation for a transmission line tower when the cables on one side snap and pile driving analysis, by using the modified generalized Smith boundary. This is obtained by the simplification of the boundary conditions of the generalized Smith boundary, by performing the reinitiating and update process of the constant velocities and constant stress conditions for each time step through only one layer of finite elements. The theory is simplified, hence allowing a substantial gain in memory space and also machine time. Furthermore, the spurious reflections are cancelled for each time step calculation. This transmitting boundary is implemented with a mixed time marching algorithm, i.e. implicit/explicit for the interior domain and explicit for the boundary nodes, and its performance is verified for loads having non-vanishing time average. Obtained results are compared to the viscous boundary and the algorithm of extrapolation solutions, and are found satisfactory as the curves for two-dimensional problems oscillate continuously around the static value, leading thus to a reliable simulation of this kind of loading. [Copyright &y& Elsevier]

In this paper, the authors propose to apply the full vehicle model of multibody dynamics to a driving simulator with a 6 degrees of freedom motion system. The characteristics of the driving simulator become very similar to the actual automobiles. It becomes possible to predict the performance of vehicle dynamics and the riding comfort by feeling test without prototyping an automobile. To realize the real-time calculation that is necessary for a driving simulator, the authors proposed an approximated real-time analysis method. By this method, real-time vehicle analysis of 2 ms step time of numerical integration is achieved with a 91 degrees of freedom vehicle model. [Copyright &y& Elsevier]

This paper presents a dynamic flotation simulator intended for designing and testing automatic control strategies, for evaluating the transient behaviour of the flotation process, and for training purposes. The simulator is based on a non-linear dynamic model that is derived from phenomenological and empirical relationships. It incorporates a new way of representing the loading of the bubbles with the various mineral species considered. The simulator was designed for a particular flotation circuit and was fitted with plant data in order to reproduce the plant behaviour both qualitatively and quantitatively. Both identification and validation data sets were used. Model dynamics had to be tested using ARMAX type models identified with plant data, due to the highly stochastic characteristics of the process. Plant and simulator responses were compared in steady-state and in transient conditions using these models. Results indicate the simulator is adequate for the stated purposes. [Copyright &y& Elsevier]

Failure mode and effects analysis (FMEA) is typically performed by a team of engineers working together. In general, they will only consider single point failures in a system. Consideration of all possible combinations of failures is impractical for all but the simplest example systems. Even if the task of producing the FMEA report for the full multiple failure scenario were automated, it would still be impractical for the engineers to read, understand and act on all of the results.This paper shows how approximate failure rates for components can be used to select the most likely combinations of failures for automated investigation using simulation. The important information can be automatically identified from the resulting report, making it practical for engineers to study and act on the results. The strategy described in the paper has been applied to a range of electrical subsystems, and the results have confirmed that the strategy described here works well for realistically complex systems. [ABSTRACT FROM AUTHOR]

A hybrid computer model, SOFIS, has been developed for the simulation of an enclosed virtual sound field in an arbitrary shaped enclosure. It can be used to calculate the impulse response and acoustical parameters of different positions in a virtual enclosure. This paper describes the way in which SOFIS models the sound source, the receiver and the sound propagation throughout the enclosed space with curved surfaces or barriers. A phase tracing method and the calculation of acoustic indexes are also discussed in this paper. [Copyright &y& Elsevier]

This paper discusses a formalism in which plant, processes and products are represented as structural, behavioral, and operational interrelated objects. A metamodel approach based on this paradigm is exploited to develop a simulation model representation that supports model exchange with varying level of detail and coarseness. This work evaluates Modelica as an interchange modeling language to represent equation-models in this context. [Copyright &y& Elsevier]

The process modules developed and integrated in the simulation model SPASS (Soil-Plant-Atmosphere Systems Simulation) and the simulation results using these modules parameterized for winter wheat are presented in this paper. These modules have been developed based largely on the existing model theories and can be used generally to simulate the dynamic processes in different soil-plant-atmosphere systems. They are exchangeable and are programmed in the form of C functions and stored in a Dynamic Link Library (DLL). The simulation results for three winter wheat varieties in the Netherlands, North and South Germany show that the parameterised model can simulate biomass growth, water uptake, and nitrogen uptake of wheat crop reasonably well if no extreme conditions or damage (by pest and disease) occur. The soil water contents and the contents of mineral nitrogen were also predicted with acceptable accuracy. Further, the importance of component level modelling is demonstrated using the modular SPASS framework. [ABSTRACT FROM AUTHOR]

This paper focuses on how notions of inference can be fostered in middle school through the use of carefully designed tasks, open-ended software simulation tools, and social activity that focuses on making data-based arguments. We analyzed interactions between two sixth-grade students who used software tools to formulate and evaluate inferences during a 12-day instructional program that utilized Probability Explorer software as a primary investigation tool. A variety of the software tools enabled students to understand the interplay between empirical and theoretical probability, recognize the importance of using larger samples to make inferences, and justify their claims with data-based evidence. [Copyright &y& Elsevier]

The increasing complexity of data converter architectures makes it necessary to use behavioral models to simulate electrical performances and to determine the relevant data converter features. For this purpose, special input stimuli and specific output data processing are required. In view of that, it is necessary to offer a specific data-converter simulation environment that permit the designer to validate the data converter specification and to extract the basic blocks key features before starting the transistor level design. Pointed toward this objective, this paper analyses the most utilized architectures and identifies the basic (active and passive) building blocks used. Behavioral models of such basic blocks are discussed. The proposed behavioral models are then used in a pipeline and a Σ–Δ converter. Specific routines for the determination of data converter parameters are presented. Simulations show how specific features of basic blocks affect the overall performances. Thus, guidelines on how to design the circuit in order to meet specifications are given. [Copyright &y& Elsevier]

All sheet-forming processes suffer from a limitation that tooling in the form of molds/dies is a precursor for realizing any simple or complex shape. In order to overcome this limitation, discrete surface tooling has been proposed in the past. This consists of a large number of closely spaced surface tool elements arranged in a matrix form whose heights can be adjusted to approximate the contour of desired surface shapes. Such a tooling has been successfully demonstrated experimentally. In this paper, a variation of discrete surface tooling, called as flexible surface tooling, has been proposed. The proposed tooling consists of discrete surface tool elements draped with flexible sheet of rubber-like material to provide a continuous surface required for tooling applications. Computational simulation of the proposed tooling is carried out for feasibility studies. Computational simulation involves the deformation analysis of rubber-like membranes in multiple contact by FEM. The results of the analysis indicate that the flexible surface tooling is an option for sheet-forming processes in general and for processes like composite layup in particular. [Copyright &y& Elsevier]

The paper describes the development of a virtual vehicle system using virtual prototyping computer tools. The virtual vehicle is used for the prediction of the structural dynamics. Since the modelling process for complete rail vehicle systems becomes increasingly more complex, time and cost can be saved by the use of a database concept and an automated assembling process for the vehicle of interest.Supported by a modular design concept, vehicle components for a metro train have been modelled and stored as substructures in a specific vehicle component database. Using this database, train configurations up to a three-car train can be assembled very quickly to perform structural dynamics analyses and to predict the ride comfort.Experimental results have been compared with simulation results of the rail vehicle to improve the modelling technique and the accuracy of the developed virtual vehicle system.The mathematical modelling of the rail vehicle system featuring elastic components, the structure of the database as well as numerical and experimental results are presented in this paper. [Copyright &y& Elsevier]

In this paper, we study the effect of particle number in the N-body simulation of the formation of giant molecular clouds. The result shows that in the case of formation by aggregation of “unit” clouds, if we take the mean density of the unit clouds to be a constant (or their effective radius to be proportional to the cubic roots of their mass), then the disruption rate of the GMCs will be independent of the initial number of unit clouds. [Copyright &y& Elsevier]

This paper describes the development of a riding simulator for two-wheeled vehicles, which use to analyze the human factor of riders. We have already produced longitudinal motion of the simulator system. Therefore, in this study, we constructed a model for lateral motion of simulator system using transfer function from the equations of motion and scale factor from the results of experiments. And finally, we confirmed the total simulator system using riders’ heart rate when they control the riding simulator. [Copyright &y& Elsevier]

This paper deals with the operation of a hybrid wind/hydro power system aiming at producing low cost electricity. A specific application on the island of Ikaria in Greece is analysed and typical results are presented and compared to the results produced from a simulation program. The simulation program, which is based on the stochastic behaviour of the weather conditions, uses as input data the monthly wind-speed distribution and, to a smaller extent, which is determined from the use of an appropriate weighting factor, the rate of rain water which is stored in the hydro reservoir. Useful conclusions were drawn regarding the feasibility of these applications in Greek islands and the expected electric energy saving. [Copyright &y& Elsevier]