Modular Simulation Model Research Articles

Development and validation of a modular simulation model for commercial vehicles

In this paper a modular truck semi-trailer model is developed in the multi-body toolbox SimMechanics, which is part of MATLAB/Simulink. It can be used to analyse a wide range of active control solutions (anywhere in the model), as well as the influence of passive vehicle modifications. As the model is modular, it is relatively easy (compared to conventional multi-body software packages) to modify or replace any of the components as well as the number and type of trailer axles. The model is validated using a wide range of measurement data obtained from measurements on a real air sprung tractor semi-trailer.

Integrated Modular Modeling of Water and Nutrients From Point and Nonpoint Sources in the Patuxent River Watershed1

Abstract: We present a simple modular landscape simulation model that is based on a watershed modeling framework in which different sets of processes occurring in a watershed can be simulated separately with different models. The model consists of three loosely coupled submodels: a rainfall‐runoff model (TOPMODEL) for runoff generation in a subwatershed, a nutrient model for estimation of nutrients from nonpoint sources in a subwatershed, and a stream network model for integration of point and nonpoint sources in the routing process. The model performance was evaluated using monitoring data in the watershed of the Patuxent River, a tributary to the Chesapeake Bay in Maryland, from July 1997 through August 1999. Despite its simplicity, the landscape model predictions of streamflow, and sediment and nutrient loads were as good as or better than those of the Hydrological Simulation Program‐Fortran model, one of the most widely used comprehensive watershed models. The landscape model was applied to predict discharges of water, sediment, silicate, organic carbon, nitrate, ammonium, organic nitrogen, total nitrogen, organic phosphorus, phosphate, and total phosphorus from the Patuxent watershed to its estuary. The predicted annual water discharge to the estuary was very close to the measured annual total in terms of percent errors for both years of the study period (≤2%). The model predictions for loads of nutrients were also good (20‐30%) or very good (<20%) with exceptions of sediment (40%), phosphate (36%), and organic carbon (53%) for Year 1.

Contribution to reusability and modularity of manufacturing systems simulation models: Application to distributed control simulation within DFT context

Requirements for manufacturing control evolve from traditional centralised approaches where decision making is hierarchically broadcasted to more complex distributed control architectures involving autonomous entities and processes. Moreover, manufacturing processes are facing standardisation and globalisation such as promoted by the demand flow technology (DFT) concepts. In order to evaluate these new architectures, discrete-event simulation seems the most appropriate tool. However, complexity of distributed architectures and DFT standardisation requires introducing modularity and reusability in the modelling process. This paper deals with a methodological approach, based on ASDI (analysis-specification-design-implementation), to develop a library of generic simulation components that can be, as automatically as possible, instantiated into a modular simulation model. This approach is illustrated using an industrial case study where simulation aims at evaluating the impact of operator's flexibility induced by DFT context.

Simulating Cut-to-Length Harvesting Operations in Appalachian Hardwoods

Cut-to-length (CTL) harvesting systems involving small and large harvesters and a forwarder were simulated using a modular computer simulation model. The two harvesters simulated were a modified John Deere 988 tracked excavator with a single grip sawhead and a Timbco T425 based excavator with a single grip sawhead. The forwarder used in the simulations was a Valmet 524 machine with 2.4-meter log bunks. Production rates and costs were examined for a wide range of even-age oak forest stand conditions. The simulation results suggest that when the tree’s DBH is less than 26 cm, harvesting using the Timbco T425 is about 30% more expensive than using the John Deere 988. However, if the tree is larger than 26 cm of DBH, the unit cost of the Timbco T425 was about 8% less than that of the John Deere 988. The balanced John Deere 988 CTL system was 31% more productive and 8% more expensive than the balanced Timbco T425 CTL system in the 20 to 36 cm DBH range. General regression equations were developed for estimating the productivity and cost for the range of conditions simulated. The results should be valuable to managers, planners, and loggers considering the use of CTL systems in this region.

Dynamic Modeling on the Hybrid Molten Carbonate Fuel Cell-Gas Turbine Bottoming Cycle

The intention of this paper is to present the dynamic models for the molten carbonate fuel cell (MCFC)-gas turbine hybrid cycle. This paper analyzes the performance of various components in the hybrid power plant, such as the compressor, turbine, recuperator, generator, fuel cell stack, etc. The modular simulation models of these components are presented. Based on the dynamic simulation modeling principle, one bottoming hybrid MCFC-microturbine cycle was studied to carry out the simulation. The simulation result can reflect the dynamic response of the hybrid power plant.

Metrics for evaluating distributed manufacturing control systems

In this paper, two classes of metrics are proposed that can be used to evaluate alternative manufacturing control architectures: those dealing with the controlled system (i.e. the manufacturing system) and those dealing with the control system. In order to illustrate the use of these metrics, the problem of scheduling a simple manufacturing cell is tackled using two test control architectures and the performance of these alternative approaches is evaluated using a modular discrete-event simulation model. The results of the paper suggest that it is worthwhile to use both manufacturing and control system performance measure to evaluate alternative control architectures, especially when considering dynamic architectures such as a Holonic Manufacturing System (HMS; i.e. architectures that adapt to changes in the manufacturing environment).

Towards self-adaptive production systems: Modular generic simulation models for continuous replanning and reconfiguration

Changing factors within markets, such as continually shortening product life cycles, increasing competition due to shorter development and order processing times, manufacturing in intercompany networks and the individualization of customer needs, create new requirements that manufacturing organizations are expected to fulfil. To be successful, manufacturing organizations and business processes have to be transformable to cope with these environmental changes. That is why the creation and implementation of self-adaptive production systems represent one vision of the near future. A first step to self-adaptive production systems is the transition from a non-recurring, static planning and operation cycle to a continuous replanning and reconfiguration of work systems, supported by new planning methods and tools. Starting with a definition of self-adaptive production systems, the requirements for planning support systems for a continuous reconfiguration and replanning are derived. The paper also presents a solution for an integrated planning tool based on object-oriented, generic simulation models. The architecture and planning procedure are described in detail. The paper finally shows the first test results of the implemented prototype.

Estimating vulnerability under global change: modular modelling of pests

Global change research and decision-making are conducted in an environment where there are many stakeholders, numerous targets and few resources. This calls for global collaboration and sharing of information on a scale that has not been attempted before. It demands a parsimonious approach to research, with the aim of enabling robust decisions to be made with the minimum of new information. Our approach to these problems has been to develop generic analytical tools, which in turn are used to foster collaboration through joint model development, testing and application. This collaboration is achieved through a workshop and networking process to establish ‘ CLIMEX’- or ‘ DYMEX’- Modelling Networks, and to extend the information to the wider community using the world wide web (WWW) (http://www.ento.csiro.au/research/pestmgmt/IPMModellingNetwork/index.htm). In this paper we outline key features of these modelling approaches and illustrate a ‘hypothesis-driven’ approach to climate-matching, using CLIMEX (http://www.ento.csiro.au/research/pestmgmt/climex/climex.htm) that contrasts with the usual, statistically based, pattern-matching of meteorological data without consideration of possible mechanisms that limit the geographical distribution. We illustrate the nature of a generic and modular simulation model built using DYMEX (http://www.ento.csiro.au/research/pestmgmt/dymex/dymexfr.htm), but emphasize the urgency for the scientific community to collect the data necessary to build reliable population models. We summarize results and conclusions from a global change workshop based on the use of both these software tools. They illustrate the advantages of the proposed approach as a means of building collaborative international research communities, which are able to avoid repetition by contributing their modules into a library of functions for sharing with other users.

An object-oriented approach to model a just-in-time production system

To produce modular and re-usable simulation models, previous studies have found out that an object oriented approach seems to be more appropriate. Various paradigms have been proposed and their results are promising. This paper illustrates how object oriented programming concept can be applied to implement a simulation model of JIT system. Another objective of this research is to implement the simulation model by visual interactive approach. The interactive interface, built in this research allows the managers to change their decisions and justify the consequence very quickly. Moreover, the program during execution can display its results in an animated manner so that users can observe and understand the process during simulation. Some illustrated operations process will be demonstrated in the paper. Computational results obtained using the JIT simulator to examine effects of different number of Kanbans or arrival time distributions are also reported. Later, this paper uses object-oriented approach to implement an animated simulation model in order to analyse the design and implementation factors of a JIT system. The results clearly show that this approach is feasible and deserves more efforts for further research.

Flow-time performance of modified scheduling heuristics in a dynamic rescheduling environment

A generic, modular simulation model was constructed using the SLAM II discrete event modeling language to investigate the flowtime performance of a job shop. The findings of earlier research using conventional scheduling heuristics were confirmed and used to validate the design of revised AWINQ and MST heuristics. These heuristics were reformulated to take into account the state of the entire job shop at each rescheduling opportunity. Simulation results indicate that the revised heuristics perform better than the conventional SPT heuristic when job load is moderate. At high loads, the SPT rule was the preferred heuristic.

COTCO2: a cotton growth simulation model for global change

In conjunction with the Free-Air-CO2-Enrichment (FACE) project, a new, physiologically based, mechanistic, modular simulation model of cotton (Gossypium hirsutum L.) physiology, growth, development, yield and water use has been constructed. It is named COTCO2 for cotton response to atmospheric CO2 concentration. The model is capable of predicting cotton crop responses to elevated atmospheric CO2 concentrations and potential concomitant changing climate variables. The major plant processes known to be influenced by CO2 are simulated explicitly, i.e. photosynthesis, photorespiration, and stomatal conductance, and its role in leaf energy balance. The model explicitly simulates the impact of atmospheric CO2 concentration on C3 photosynthesis and photorespiration at the level of carboxylation and oxygenation. Growth is simulated for individual organs, i.e. leaf blade, stem segment, taproot and lateral roots, and fruit which includes squares and bolls. Potential growth is calculated and the carbohydrate and nitrogen required to meet this potential are calculated. Actual growth is based on substrate availability, the potential growth, and water stress. Our intent here is to describe the overall structure of the model, its present status, and future development plans. Further development, documentation, calibration, and validation of the model is in progress. The long range goal of the project is to provide quantitative estimates of global cotton production in a future higher-CO2 world.

Feasibility of modular simulation models for FMSs

This paper presents the work done in the feasibility study of modular simulation models for flexible manufacturing systems (FMS). The objective is to assess the feasibility of developing a package of simulation logic modules, together with a supervisory program to select and link them to form a model of a system from its engineering description, to develop an initial proposal for such a system up to demonstration capacity, and to evaluate it in consultation with others. The simulation software, SIMAN/CINEMA with animation, has been used for case studies. Results show that it is a promising tool for research work.

A modular BLSS simulation model

The coordination of material flows in Earth's biosphere is largely made possible by the buffering effect of huge material reservoirs. Without similarly-sized buffers, a bioregenerative life support system (BLSS) for extraterrestrial use will be faced with coordination problems more acute than those in any ecosystem found on earth. A related problem in BLSS design is providing an interface between the various life-support processors, one that will allow for their coordination while still allowing for system expansion. Here we present a modular model of a BLSS that interfaces system processors only with the material storage reservoirs, allowing those reservoirs to act as the principal buffers in the system and thus minimizing difficulties with processor coordination. The modular nature of the model allows independent development of the detailed submodels that exist within the model framework. Using this model, BLSS dynamics were investigated under normal conditions and under various failure modes. Partial and complete failures of various components, such as the waste processor or the plants themselves, drive transient responses in the model system, allowing us to examine the effectiveness of the system reservoirs as buffers. The results from simulations of this sort will help to determine control strategies and BLSS design requirements. An evolved version of this model could be used as an interactive control aid in a future BLSS.

THEORY OF DISCRETE EVENT SPECIFIED MODELS: MODULARITY, HIERARCHY, EXPERIMENTAL FRAMES

Representation mechanisms for discrete event simulation models are intended to facilitate the important conceptualization and communication components of model building science. Moreover, effective design of future computer-based decision support systems will rely upon well founded principles of model management. Modular and hierarchical concepts facilitate model building. This article extends the theory of discrete event system specification to provide a rigorous basis for modular and hierarchical simulation model construction. Practical applications of the theory are discussed and include programming constructs for modular and hierarchical simulation, inter-translation between modular and non-modular model description, and implementation of modular separation between model and experimental frame components of simulation programs.

A pasture production model for use in a whole farm simulator

Modular simulation models of crop and animal enterprises can be used in concert to simulate a particular whole farm operation and thus provide management information for individual farmers and farm advisers. This paper reports the development of a pasture module for such a whole farm simulator designed to study irrigation management in New Zealand. The model (CANPAS) describes the production of perennial ryegrass/white clover pastures under either dryland or irrigated conditions. Seasonal growth studies and the principles of ecological physiology form the theoretical base of CANPAS. Whenever possible, parts of other models were also used. With time steps of one day, CANPAS predicts the net above-ground yield of live and dead herbage, herbage digestibility, leaf area index and soil water supply. Harvested yields are also predicted for simulated grazing or cutting managements, assuming part of the above-ground yield of live and dead herbage is left as stubble. Field measurements of harvested pasture yields from the Canterbury Plains of New Zealand were used to validate the model. Validation procedure included the use of a simple set of statistical tests. The final version (CANPAS III) gave an overall r 2 of 0·83, but poorer performance was found under some test managements. Discussion covers the general aspects of this kind of modelling as well as the specific details of the pasture module.

A COMPUTER SIMULATION MODEL OF LIBRARY OPERATIONS

Aslib is interested in developing modular simulation models of aspects of library systems in order to investigate the use of such models as aids to systems design and operation. The conceptual model of library procedures, developed during the OSTI‐supportcd project on the use of bibliographic records in libraries, offered a suitable basis for a pilot study. The pilot study was aimed at investigating the practicality of developing and using simulation models of library operations, and gaining experience in the application of simulation techniques to problems in the library and information field. The simulation language used was GPSS, in accordance with the 1968 edition of the IBM GPSS/360 User's Manual, H20–0326–2.