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In this paper, we consider a mathematical model which describes the equilibrium of two elastic rods attached to a nonlinear spring. We derive the variational formulation of the model which is in the form of an elliptic quasivariational inequality for the displacement field. We prove the unique weak solvability of the problem, then we state and prove some convergence results, for which we provide the corresponding mechanical interpretation. Next, we turn to the numerical approximation of the problem based on a finite element scheme. We use a relaxation method to solve the discrete problems that we implement on the computer. Using this method, we provide numerical simulations which validate our convergence results. [ABSTRACT FROM AUTHOR]

The article calls for papers for the publication's special issue on methological developments in computer simulation, along with its application in scientific, industrial and business areas.

Numerical models for vibro-acoustic analyses of complex mechanical systems are becoming more and more popular, in particular in the field of virtual product development. Therefore, reliable, comprehensive, and validated modeling methodologies remain crucial. However, system characteristics such as elasticities of the drive train components and nonlinear characteristics can lead to complex, and costly numerical models with a huge number of degrees of freedom. This may raise not only the need for novel and reasonable modeling strategies, but also exacerbates validation process, due to the wide scope in terms of operating conditions. In practice, structure-borne noise signals, for example, from accelerometers, are often used for the validation of mechanical systems. By choice of a sufficient number of measurement points, the interpretation becomes more complex. A lot of vibration response curves then need to be compared and interpreted over a wide operating range. In general, the interpretation focuses on deviations in quality and quantity. In this paper, to overcome these mentioned challenges, a validation methodology is proposed allowing a fast and transparent check of a number of captured signals. Therefore, it is shown how the original information can be reduced in a meaningful manner, making it possible to run a fast and accurate validation. The method is demonstrated on a real application with high mechanical complexity and it is shown that the chosen parameters are reliable. [ABSTRACT FROM AUTHOR]

Oil reservoir history matching is a well-known inverse problem for predicting production by optimizing enormous unknown parameters with numerical simulation. Typically it can be formulated in a Bayesian framework with geological priors. Instead of gradient-based optimization with the possibility of converging to a local minimum, evolutionary algorithms have been introduced to globally find optimal parameters. Due to the high-dimensional parameters, the optimization could become inefficient; therefore, many dimensionality reduction algorithms have been applied in history matching. However, these methods suffer from the linear assumption or the pre-image problem, which could affect the model optimization. In this paper, based on the evolutionary algorithm termed Multi-objective Evolutionary Algorithm Based on Decomposition, which is capable of simultaneously optimizing the parameters with respect to the data of several oil wells, we propose history matching with dimensionality reduction by explicitly utilizing the nonlinear dimensionality reduction model Auto-Encoder to reduce the number of unknown parameters, which can naturally handle the pre-image problem and then improve model performance in terms of precision and complexity. Experimental results based on PUNQ-S3 data verify the efficiency of the newly proposed methods. [ABSTRACT FROM AUTHOR]

This paper presents the design and implementation of adaptive control with approximate input-output linearization for underactuated open-loop unstable non-linear mechanical systems. Control of a ball and beam (BB) mechanism is selected as a benchmark problem for testing the designed control. The method of input-output linearization is reviewed and an adaptive input-output linearizing control design procedure is given. An approximate BB model is developed using Euler-Lagrange equations, and input-output linearization-based adaptive tracking control is designed for the system. The model is parameterized with respect to ball mass for adaptive tracking, and the proposed control structure is tested via computer simulations and experiments. The results present the tracking performance of designed control for various ball masses, and reveal the proposed method's capability to cover ball mass variations over non-adaptive control. The proposed control exhibits improved error performance in the presence of parametric variations in the plant. Results of the BB control case reveal successful control of underactuated non-linear mechanisms when a system parameter is unknown or time varying. [ABSTRACT FROM AUTHOR]

The simulation of modern systems may require an amount of computational resources that might not be available on a single host. Distributed simulation (DS) provides an effective way to scale up for the increased computational requirements. However, using existing DS environments remains the main obstacle to the wide adoption of DS systems, because of their inherent complexity. This complexity can be quantitatively shown by the extra effort that the development of DS systems requires compared to the development of conventional local simulation (LS) systems. In this paper we introduce SimArch, a layered architecture that eases the development of DS systems by enabling simulation developers to effortlessly obtain a DS system or derive a DS system from the equivalent LS one. A reference model is used throughout the paper to illustrate the use of SimArch in the development of DS systems and to prove how the DS development effort is lowered down with respect to the use of a conventional DS environment. [ABSTRACT FROM PUBLISHER]

This paper presents and solves the problems of modeling and designing the necessary capacity and the adequate capacity of accepting input connections serving the calls into the system. The main aim of the research work is finding the optimum number of input server connections while minimizing the number of rejected requests according to a specific maximum number of expected calls in a specific time-interval, i.e. at peak-hour. With the results obtained we wish to model and optimize the planning and the dimensioning of the processing server as well as reduce the costs of this, since hiring an input line actually presents quite a substantial cost. Therefore it is necessary to first determine how many input connections are needed to serve a certain quota of users at a specific moment by using the methods of statistical modeling. On the basis of obtained results we can then assess whether a certain segment has too many or not enough input connections. The objective of the presented multiple-input and multiple-output (MIMO) simulator is to raise the level and the quality of service and at the same time lower the costs of hiring input connections. This paper presents the key segments composing the call and server system (ordinary, lamer and dummy caller model, statistical Gaussian curve of calls distribution, mechanisms of accepting and rejecting calls, management of input connections capacity, random call triggering, etc.). The above-mentioned segments represent the models and the sub-models of the simulator. They have been derived using the methods of statistical modeling. The optimum solution can be found manually or automatically using the method of automation of simulation runs and incrementing/decrementing the parameter of the number of input connections into the system. Searching the optimum number of input connections manually is an entirely empirical method, where the user manually changes the mentioned parameter, and is looking for a scenario in which the result of the simulator regarding the number of rejected calls is minimal. With an automatic search the simulator automatically generates the number of runs with incrementing and decrementing the mentioned parameter in each, and thus automatically finds the optimum solution. This paper also presents an automatic analysis of simulation runs and a statistical final report, which includes a conclusion on the results obtained in different scenarios. [ABSTRACT FROM PUBLISHER]

This paper illustrates the use of engine modelling in the educational setting through the development and use of software for the simulation of cycles of different internal combustion engines. Modelling and computer simulation of an internal combustion engine's operating processes offer a valuable tool for enhancing understanding of real physical phenomena and contribute significantly to optimizing and controlling the engine's operation to meet different objectives. The paper begins by describing the theoretical models of engine operation. These models are for various fluids: perfect gas, ideal gas and air/fuel mixes; and for constant volume (Otto cycle), constant pressure and mixed (diesel) cycles. The software has been developed to solve many problems and it facilitates understanding of the thermodynamic fundamentals of an internal combustion engine. Overall, this study demonstrates the power of such an engine simulation tool in an educational setting. [ABSTRACT FROM AUTHOR]

With the prevalence of net-centric environments, Service-Oriented Architectures (SOAs) have emerged as a paradigm that greatly impacts the modeling and simulation (M&S) community. This paper has two interrelated goals. The first is to give a comprehensive review of various service-oriented simulation frameworks to help researchers select the appropriate one for their specific purpose. The second goal is to combine the common features derived from the review into one unifying framework that can describe and prescribe various specific approaches. The focus of this paper is on the common functionalities of service-oriented simulations reflected in the review and unifying framework. In particular, we emphasize the way SOAs and M&S are combined, and the interoperability and composability challenges of distributed M&S services. We describe some fundamental concepts first. Then we present a comprehensive survey of several classical frameworks, including formalism-based, model-driven, interoperability protocol based, eXtensible Modeling and Simulation Framework (XMSF), Open Grid Services Architecture (OGSA) based, and ontology-driven frameworks. Based on the review, we propose a novel three-dimensional reference model that can unify the ad hoc approaches into a common framework. The model can be used as a guideline or an analytic means to find potential and possible future directions. In particular, the model inspects the crossover between the disciplines of M&S, service-orientation, and software/systems engineering. Based on the model, we present a detailed comparison of the reviewed frameworks. Finally the significance of the paper is discussed and future directions are recommended. [ABSTRACT FROM PUBLISHER]

This article concerns an investigation of the full scale evacuation of a building with a configuration similar to that of the World Trade Center (WTC) north tower using computer simulation. A range of evacuation scenarios is explored in order to better understand the evacuation of the WTC on 11 September 2001. The analysis makes use of response time data derived from a study of published WTC survivor accounts. Geometric details of the building are obtained from architects' plans while the total building population used in the scenarios is based on estimates produced by the National Institute of Standards and Technology formal investigation into the evacuation. This paper attempts to approximate the events of 11 September 2001 and pursue several 'what if' questions concerning the evacuation. In particular, the study explores the likely outcome had a single staircase survived intact from top to bottom. More generally, this paper explores issues associated with the practical limits of building size that can be expected to be efficiently evacuated using stairs alone. [ABSTRACT FROM AUTHOR]

This paper deals with the modelling and analysis of a shunt active power filter by the use of a MATLAB/Simulink program. The modelling approach adopted in the paper is graphical in nature, as opposed to mathematical models embedded in code using a high-level computer language. The model is presented clearly and in a detailed manner, targetted especially at postgraduate students. The performance of the active power filter is illustrated by considering a 400kV A, six-pulse, fully controlled bridge rectifier supplied from a typical distribution system via a rectifier transformer. [ABSTRACT FROM AUTHOR]

Road safety barriers are roadside structures installed on certain sections of the road to improve highway safety by preventing a vehicle from leaving the road and colliding with roadside hazards. Road safety barriers are an effective solution for reducing the risk of injuries on modern roads. A road safety barrier must meet minimum standards of construction and materials design. Normally, they must undergo crash tests according to the European standard EN 1317 or the Manual for Assessing Safety Hardware by the American Association of State Highway and Transportation Officials. On the basis of these standards, each safety barrier must pass standardized crash tests as mandated in their approval procedures. Currently, computer simulation methods are typically used by researchers to analyze the performance of roadside safety barriers. Advancement in computer technology could facilitate the finite element method in replacing expensive experimental tests. This paper presents an approach for constructing and evaluating a finite element model for road safety barriers according to European standard EN 1317 by using the finite element code LS-DYNA. Excellent agreement between real-world test data and simulation results was achieved for behavior and impact severity values. The results obtained using the model ensure the exactness of the proposed method and prove that the numerical method is a practical approach for eliminating road safety barrier problems. Furthermore, the model was able to replace experimental tests for developing road safety barriers, thus reducing time and money. [ABSTRACT FROM AUTHOR]

A continuous-review, base-stock inventory model considering lost sales is proposed for general compound demands and random lead times. This model is a generalized form of the (S, d) policy, which has already been shown to be the best modified base-stock policy (MBSP) for Poisson demand and fixed lead times. In this paper, customers’ inter-arrival times, demand sizes, and lead times are extended in a probabilistic situation with free distributions. Then, a hybrid simulation–optimization approach is developed to handle these generalized conditions. This approach uses design of experiments, a simulation model, and regression analysis to obtain the long-run cost function of the system under this extended MBSP. The optimal settings of this policy are achieved using a mathematical optimization model. Employing a simulation model, a cost function, and mathematical models makes this approach applicable for finding the optimal settings even in the presence of realistic restrictions and uncertainties. Moreover, a simulation-based procedure is introduced to find the optimal stock level for the traditional base-stock policy. The applicability of the proposed approach is illustrated through a real-world case study. Finally, a sensitivity analysis is applied using a series of benchmark instances, and some robustness properties are shown. [ABSTRACT FROM AUTHOR]

The issue of synchronization between dynamical systems has attracted much attention, and the systems with integer-order dynamical networks have been well studied. The synchronous behavior of fractional-order dynamical systems is very interesting and importance, but has rarely been studied. In this paper, we studied the synchronization and anti-synchronization behavior between integer-order dynamical networks and fractional-order dynamical systems via a Takagi-Sugeno fuzzy model. Remarkably, there is synchronous behavior in such a system, and this is dramatically different from the behavior of integer-order dynamical networks. Moreover, we studied the impact of different coupling strengths on the dynamical process of synchronization and robustness of the designed controller to different coupling functions, different dimensions of dynamical equations and different fractional orders. Finally, we propose the theoretical analysis, which coincides well with the numerical simulations of five typical examples. [ABSTRACT FROM AUTHOR]

In this paper, a novel synchronization method of modified function projective lag synchronizations (MFPLS) between identical and nonidentical hyperchaotic complex nonlinear systems with parameter perturbations and external perturbations is proposed. In the method, the states of two hyperchaotic complex systems with parameter perturbations and external perturbations are asymptotically lag synchronized up to a desired scaling function matrix, and all the perturbations in the parameters asymptotically converge to zero. Base on the Lyapunov stability theory, the adaptive controller and updating laws of parameter perturbations are designed to achieve MFPLS between the drive and response systems. Theoretically the proof that the drive and response system will asymptotically lag synchronization and numerical simulations verify the feasibility and effectiveness of the proposed scheme. [ABSTRACT FROM AUTHOR]

The paper introduces an adaptive optimization framework that is used to calibrate and optimize multiple intelligent transportation strategies such as high occupancy toll (HOT), ramp metering, and variable speed limits. The framework is capable of estimating the OD (origin–destination) matrix, calibrating the model with the experimental data, and conducting system optimization in transportation. This capability is shown with simulation experiments based on the public data of I-95 Florida. The preliminary results show that the revenue increases with target speed up to a point, after which the revenue drops. Also, the throughput on the HOT increases with decreasing target speed. So, to maximize revenue and throughput together, the optimal values are observed at moderate levels of the feasible range. Also, in the presence of accidents, the total throughput is improved by decreasing the toll rate. Optimal level of vehicles on the HOT lanes is examined to minimize vehicle emissions. [ABSTRACT FROM PUBLISHER]

Weld line is aesthetically unpleasant and affects the mechanical strength of injection molded parts. Because of the ever-increasing requirements for parts performance, lots of researchers have performed various studies related to the weld lines optimization. However, research about the computer determination of weld lines in injection molding remains scarce. In this paper, a weld line computer determination method based on filling simulation with surface model is proposed, from which the positions and lengths of the weld lines can be predicted. According to the characteristics of the surface model, all weld lines are classified into two different types. Initial welding node searching and revision algorithms for the two different types of weld lines are first developed. Starting from initial welding nodes, weld lines are then extended by a pre-extension algorithm and an extension algorithm. In the weld line extension algorithm, 135° is set as a welding angle threshold for forming weld lines. Finally, the effects of cavity thickness, process parameters, and mesh densities have been investigated. Moreover, Moldflow simulation results and real parts in production have been conducted to verify the proposed determination method, which demonstrate that the proposed method is correct and effective in actual production. [ABSTRACT FROM PUBLISHER]

Multi-agent system (MAS) protection is under investigation as a potential method for distributed control in modern electrical power systems. The coordination of the MAS is based on local measurements available to each agent’s site as well as on the information exchanged between agents over the communication network. Hence, the communication network should be considered to be a main factor in determining overall system performance.Numerical simulation is a fundamental tool of the design process. Existing electric power simulation tools can satisfactorily model traditional power systems where power and communication are considered to be decoupled and MAS are not present. Similarly, the simulation tools for communication systems have been developed independently from the application, particularly power system scenarios, so they are decoupled from the actual use of the information. If the loop between communication and power is closed and the coupling is strong, as in MAS-controlled power systems, such a simulation environment may yield unrealistic results.Aiming at filling this gap, this paper proposes a co-simulation solution for power systems, communication networks, and MAS, based on the extended capability of the co-simulation platform called VPNET. VPNET consists of three parts: Virtual Test Bed for time domain simulation of power systems, OPNET for the simulation of communication networks, and the Co-simulation Coordinator for data exchange and time synchronization between the other two simulators. The Co-simulation Coordinator has been exploited for MAS integration, as the rules of each agent are defined in the modules provided by the Co-simulation Coordinator.The proposed extended co-simulation platform is tested in the analysis of the performance of the MAS-based protection schemes of a medium-voltage DC shipboard power system. Numerical simulations have been performed for communication testing and protection testing. In the communication test, the network parameters (bandwidth and transmission time) are analyzed to evaluate the performance of the communication network under various conditions; in particular, links failure. The MAS-based protection system was then tested under various operating conditions of the communication network (latency and links failure). From the simulation results it can be seen that the designed MAS protection can handle these conditions successfully. Particularly in the link failure conditions, this co-simulation platform could simulate the re-routing process of the communication network and lead to correct protection performance, which is impossible with individual simulators alone. These simulation results show the utility of VPNET in exploring the design trade-offs between protection strategies and communication in the design phase. [ABSTRACT FROM AUTHOR]

The use of two-dimensional (2D) and three-dimensional (3D) visual displays for discrete-event simulation (DES) has become very popular within the simulation community in recent years. This paper presents results from surveys of users of 3D and 2D simulation applications regarding their views of the impact, benefits and drawbacks of 3D displays. The results indicate that 3D displays can often be more effective than 2D displays in communication, verification and validation, and experimentation. This can lead to a better project outcome with an improved understanding of the real system and a better solution for the decision maker. The main drawback is the additional cost, time and complexity of building the model. Potential implications for modeling in general are the importance of being able to relate the model to the real system and of involving the decision maker in the modeling process. [ABSTRACT FROM PUBLISHER]

The response of plate subjected to underwater explosion loading is of major concern in a variety of marine, ship and offshore platform applications. This paper first conducts the theoretical analysis of the shock loading acting on the plate exposed to underwater explosion. Thereafter, an effective numerical method is adopted to compute the central plastic deformation of the rectangular plates shocked by primary shock wave without regard to the modeling of surrounding water. Therefore numerical computation efficiency is highly improved. Due to the disregard of the gas bubble pulsation energy, numerical central deflections of the rectangular plates are less than the experimental results. Thus, an energy-modified method is advanced to modify the numerical results according to the energy distribution during underwater explosion. The comparison of two types of modified numerical predictions with experimental results piece-wise shows good agreement. [ABSTRACT FROM PUBLISHER]

The heavily loaded flows usually occupy more bandwidth than that of the lightly loaded flows under congested traffic conditions. Without effective bandwidth management mechanisms, malicious users may violate congestion control principles in order to get maximum bandwidth. Therefore, how to provide fair bandwidth sharing with low implementation complexity is a critical issue for high-speed networks. An active queue management mechanism, stateless fair admission control (SFAC), is proposed in this paper, which can provide good fairness on bandwidth allocation. Furthermore, the SFAC does not have to maintain per-flow state in each router. The main idea of the SFAC is that two admission thresholds can optimally change according to traffic variations. By comparing the admission thresholds with the hit number of each arrival packet, the SFAC is able to guarantee fair buffer occupancy for each flow. The SFAC employs a single first in, first out buffer, so that it can provide fair bandwidth sharing. In a word, the SFAC is completely stateless, so it possesses the great advantage of being easy to implement. Computer simulations concluded that the SFAC is capable of providing good fair bandwidth sharing under a range of traffic conditions. [ABSTRACT FROM PUBLISHER]

Modeling languages play a cornerstone role in model-driven software development for representing models and metamodels. Modeling languages are usually defined in terms of their abstract and concrete syntax. This allows the rapid development of languages and some associated tools (e.g. editors), but does not allow the representation of their behavioral semantics, something especially important in certain industrial environments in which simulation and verification are critical issues. In this paper we explore the use of Maude as a formal notation for describing models, metamodels, and their dynamic behavior, making models amenable to formal analysis, reasoning, and simulation. [ABSTRACT FROM AUTHOR]

Language engineering is a key factor in Multi-Paradigm Modeling (MPM). Since MPM strongly builds on metamodeling, the applied language engineering methods must also be generic enough to support various metamodels. Besides the generic methods to build the abstract and concrete syntax of a visual language, only a few solutions are available to describe the dynamic behavior ('animation') of the models. The aim of this paper is to contribute (i) an event-based conceptual architecture to support animation, (ii) a set of visual languages to describe the animation of the models and their execution. These concepts were used to implement the animation support in our tool called Visual Modeling and Transformation System (VMTS). The VMTS animation framework introduces novel languages to describe certain aspects of animation, while integrating the benefits of the existing approaches. Our solution clearly separates the domain knowledge and the animation description both on a conceptual and implementation level. Thus, the VMTS offers a concise and systematic solution to provide a highly customizable animation framework for metamodeled languages with strong integration support to external systems such as simulation engines. The efficiency of the approach is illustrated with a rather complex animation case study implementing a model transformation debugger. [ABSTRACT FROM AUTHOR]

Recent years have witnessed a tremendous growth of research in the field of wireless systems and networking protocols. Consequently, simulation has appeared as the most convenient approach for the performance evaluation of such systems and several wireless network simulators have been proposed in recent years. However, the complexity of the wireless physical layer (PHY) induces a clear tradeoff between the accuracy and the scalability of simulators. Thereby, the accuracy of the simulation results varies drastically from one simulator to another. In this paper, we focus on this tradeoff and we investigate the impact of the physical layer modeling accuracy on both the computational cost and the confidence in simulations. We first provide a detailed discussion on physical layer issues, including the radio range, link and interference modeling, and we investigate how they have been handled in existing popular simulators. We then introduce a flexible and modular new wireless network simulator, called WSNet. Using this simulator, we analyze the influence of the PHY modeling on the performance and the accuracy of simulations. The results show that the PHY modeling, and in particular interference modeling, can have a significant impact on the behavior of the evaluated protocols at the expense of an increased computational overhead. Moreover, we show that the use of realistic propagation models can improve the simulation accuracy without inducing a severe degradation of scalability. [ABSTRACT FROM AUTHOR]

In an attempt to investigate blood unit ordering policies, researchers have created a discrete-event model of the UK National Blood Service (NBS) supply chain in the Southampton area of the UK. The model has been created using Simul8, a commercial off-the-shelf (COTS) discrete-event simulation package (CSP). However, as more hospitals were added to the model, it was discovered that the length of time needed to perform a single simulation severely increased. It has been claimed that distributed simulation, a technique that uses the resources of many computers to execute a simulation model, can reduce simulation runtime. Further, an emerging standardized approach exists that supports distributed simulation with CSPs. These CSP Interoperability (CSPI) standards are compatible with the IEEE 1516 standard, the High Level Architecture (HLA), the de facto interoperability standard for distributed simulation. To investigate if distributed simulation can reduce the execution time of NBS supply chain simulation, this paper presents experiences of creating a distributed version of the CSP Simul8 according to the CSPI/HLA standards. It shows that the distributed version of the simulation does indeed run faster when the model reaches a certain size. Further, we argue that understanding the relationship of model features is key to performance. This is illustrated by experimentation with two different protocols implementations (using Time Advance Request (TAR) and Next Event Request (NER)). Our contribution is therefore the demonstration that distributed simulation is a useful technique in the timely execution of supply chains of this type and that careful analysis of model features can further increase performance. [ABSTRACT FROM AUTHOR]

This paper presents a novel analytical approach to calculate the saturation throughput of the Distributed Queuing Medium Access Control protocol for Ad Hoc Networks (DQMAN) in single-hop scenarios. DQMAN integrates a near-optimum MAC protocol into a passive clustering algorithm based on Carrier Sensing Multiple Access (CSMA). Therefore, based on models of both CSMA and centralized MAC protocols, a new model is presented to accurately calculate the saturation throughput of DQMAN in single-hop networks. In addition, the model presented can be extended to any MAC protocol based on the spontaneous clustering concept of DQMAN. The accuracy of the overall model has been assessed through link-level computer simulations. A performance evaluation of the protocol under different configurations is also presented together with a performance comparison with the IEEE 802.11 standard. [ABSTRACT FROM AUTHOR]

The very simple model known as Stupid Model was proposed in 2005. Stupid Model could be implemented within a couple of hours, and was later extended to demonstrate the use of common ABM platform functionality. Implementations of the model in several agent-based modeling platforms were provided, and platforms were compared for ease of implementation and performance. In this paper, Stupid Model is implemented in the EcoLab simulation platform (a C++ based modeling platform), demonstrating that it is a feasible platform for these sorts of models. The performance of the implementation is compared with the Repast, Mason and Swarm versions. [ABSTRACT FROM AUTHOR]

HLA/RTI is one of the dominant middleware for large-scale distributed simulation. However, traditional RTI design and resulting implementations have been facing several difficulties, especially in satisfying the requirements for real-time distributed simulations. Many improved or novel RTI designs have been proposed in recent years, which aim to improve the real-time capabilities of RTI systems. Such designs are in general non-formalized, and the realizations of the designs are highly time-consuming and error-prone practices. In this paper, we propose a formal real-time RTI (RT-RTI) design approach using Discrete Event System Specification (DEVS). We discuss the feasibility of using DEVS and, as an additional step, we consider the case study of two recently proposed RT-RTI designs through a formalized DEVS model system. Our focus is how a DEVS component-based formalized design approach can predict some of the key design factors before the design is realized, or can further validate and consolidate realized RT-RTI designs. [ABSTRACT FROM AUTHOR]

A commonly used task scheduling algorithm for parallel and distributed systems is gang scheduling. In this paper, we study gang scheduling performance in the presence of critical sporadic jobs. A simulation model is used to address performance issues associated with gang scheduling on distributed processors for various workloads. Simulated results indicate that the relative performance of the gang scheduling policies depends on the arrival rates of gangs and critical sporadic jobs and also on the variability in the critical sporadic jobs inter-arrival times. [ABSTRACT FROM AUTHOR]

Presented is a real-time simulator of a permanent magnet synchronous motor (PMSM) drive implemented on an FPGA card. Real-time simulation of PMSM drives enables thorough testing of control strategies and software protection routines and therefore allows rapid deployment of vehicular or industrial applications. The proposed PMSM model is a phase domain model with sinusoidal flux induction. A 3-phase IGBT inverter drives the PMSM machine. Both models are implemented on an FPGA chip, without any VHDL coding, with the RT-LAB real-time simulation platform of Opal-RT Technologies using a Simulink blockset called Xilinx System Generator (XSG). The paper explains various aspects of the design of the motor drive models in fixed-point representation in XSG, as well as simulation validation against a standard PMSM drive model built in Simulink. The PMSM drive, along with a open-loop test source for the pulse width modulation, is coded for an FPGA card. The model has user-selectable dead time, modulation index, source angle offset, and frequency. The PMSM drive is completed with various encoder models (quadrature, Hall effects and resolver). The overall model compilation and simulation is entirely automated by RT-LAB. The drive can also run in a closed loop with a controller executing on a CPU of a real-time simulator. The phase-domain PMSM drive model runs with an equivalent 10 nanosecond time step (100 MHz FPGA card) and has a latency of 300 nanoseconds (PMSM machine and inverter). The motor drive is directly connected to digital inputs and analog outputs with 1 microsecond settling time on the FPGA card and has a resulting total hardware-in-the-loop latency of 1.3 microseconds. [ABSTRACT FROM AUTHOR]

Time Warp parallel simulations need efficient schemes to cancel erroneous event messages in order to achieve acceptable performance levels. Lazy cancellation depends on delaying the cancellation of incorrect computations until rolled-back events are re-processed. An antimessage is then sent for cancellation only if an output message re-produced after rollback is found to be unequal to its counterpart produced before rollback. One drawback of this approach is that antimessages are sent too late to catch the wave of incorrect computations, which results in more rollbacks. In this paper, we suggest an enhanced lazy cancellation technique that aims to throttle incorrect computations. It asks logical processes (LPs) that have received any output messages, generated from the first execution of a rolled-back input event in some neighboring LP, to mark those messages as temporarily blocked. Those messages remain in a blocked state until it is later decided whether or not they must be cancelled. The receiving LP becomes blocked only after a blocked input message becomes the next message to process. After re-executing the rolled-back input event, the sending LP sends each of its receiving LPs either an `Unblock' message or an antimessage for each previously marked output message, depending on the result of the equality test of that output message's versions before and after rollback. Experimental results for a synthetic benchmark show that our technique can yield better performance than both lazy and aggressive cancellation. [ABSTRACT FROM AUTHOR]

The cross-entropy and minimum cross-entropy methods are well-known Monte Carlo simulation techniques for rare-event probability estimation and optimization. In this paper, we investigate how these methods can be eXtended to provide a general non-parametric cross-entropy framework based on -divergence distance measures. We show how the χ 2distance, in particular, yields a viable alternative to the Kullback—Leibler distance. The theory is illustrated with various eXamples from density estimation, rare-event simulation and continuous multi-eXtremal optimization. [ABSTRACT FROM AUTHOR]

Tandem Jackson networks and more sophisticated variants have found widespread application in various domains. One such variant is the tandem queue with server slow-down, in which the server of the upstream queue reduces its service speed as soon as the downstream queue eXceeds some prespecified threshold, to provide the downstream queue some sort of `protection'. This paper focuses on the overflow probabilities in the downstream queue. Owing to the Markov structure these can be solved numerically, but the resulting system of linear equations is usually large. An attractive alternative could be to resort to simulation, but this approach is cumbersome due to the rarity of the event under consideration. A powerful remedy is to use importance sampling, i.e. simulation under an alternative measure, where unbiasedness of the estimator is retrieved by weighing the observations by appropriate likelihood ratios. To find a good alternative measure, we first identify the most likely path to overflow. For the standard tandem queue (i.e. no slow-down) this path was known, but we develop an appealing novel heuristic which can also be applied to the model with slow-down. The knowledge of the most likely path is then used to devise importance sampling algorithms, both for the standard tandem system and for the system with slow-down. Our eXperiments indicate that the corresponding new measure is sometimes asymptotically optimal, and sometimes not. We systematically analyze the cases that may occur. [ABSTRACT FROM AUTHOR]

Optimistic replication provides high data availability in the presence of network outages. Although widely deployed, this relaXed consistency model introduces concurrent updates, whose behavior is poorly understood due to the vast state space. This paper introduces the notion of permuted states to eliminate system states that are redundant and unreachable, which can constitute the majority of states (4069 out of 4096 for four replicas). With the aid of permuted states, we are for the first time able to construct analytical models beyond the two-replica case. By eXamining the analysis for 2 to 4 replicas, we can demystify the process of forming identical conflicts—the most common conflict type at high replication factors. Additionally, we have automated and optimized the generation of permuted states, which allows us to eXplore higher replication factors (up to 10 replicas) using hybrid techniques. It also allows us to validate our results with eXisting simulations based on actual replication mechanisms, which previously were analytically validated with only one pair of replicas. Finally, we have discovered that update locality and bimodal access patterns are the primary factors contributing to the formation of identical conflicts. [ABSTRACT FROM AUTHOR]

Computer simulation has become an efficient and cost-effective tool for the liquid composite molding (LCM) processes, including the RTM, VARTM, and resin infusion, compared to trial-and-error. The purpose of simulation is to accurately reflect the real situation. Since the simulation is predominantly based on the control volume finite element method (CVFEM), the boundary conditions such as gate and vent definition need to be properly defined. In this paper, the errors of the CVFEM based mold filling simulation were analyzed. The error sources were identified as the mesh near gates and vents, and gate definition. By conducting 3-D and 2-D simulation case studies, the influence of the gate definition on the simulation result was studied. Because many composite parts are shells and can be regarded as surfaces. 2-D simulation is favorable because of the better efficiency and simpler pre-processing. For this purpose, a method for mold filling simulation incorporating the gate size effect the effective gate method (EGM) - was developed. This method was validated through case studies. It shows that the EGM provides an effective and efficient approach to the CVFEM mold filling simulation incorporating the effect of injection gate size. [ABSTRACT FROM AUTHOR]

FleXible yet efficient eXecution of heterogeneous simulations benefits from concepts and methods that can support distributed simulation eXecution and independent model development. To enable formal model specification with submodels implemented in multiple programming languages, we propose a novel approach called the Shared Abstract Model (SAM) approach, which supports simulation interoperability for the class of Parallel Discrete Event System Specification (DEVS) compliant simulation models. Using this approach, models written in multiple programming languages can be eXecuted together using alternative implementations of the Parallel DEVS abstract simulator. In this paper, we describe the SAM concept, detail its specification and eXemplify its implementation with two disparate DEVS-simulation engines. We demonstrate the simplicity of integrating simulation of component models written in the programming languages Java, C++ and Visual Basic. We describe a set of illustrative eXamples that are developed in an integrated DEVSJAVA and Adevs environment. Further, we stage simulation eXperiments to investigate the eXecution performance of the proposed approach and compare it with alternatives. We conclude that application domains, in which independently-developed heterogeneous component models consistent with the Parallel DEVS formalism, benefit from a rigorous foundation and are also interoperable across different simulation engines. [ABSTRACT FROM AUTHOR]

In this paper we describe a new solution for stable haptic interaction with deformable object simulations featuring low servo rates and computational delays. The solution presented is a combination of the local model and the virtual coupling concepts proposed in the past. By varying the local model impedance depending on the local stiffness of the deformable object, the interaction between local model and simulation can always be made stable independently of low servo rates or computational delays. Moreover by using more complex local impedances that feature an integral term, we are able to control the steady-state error between the device and the surface of the deformable object This allows us to maximize the Z-width of the simulation, while obtaining overall stable behavior without using any added damping. The local model is always computed using the current deformable object surface, thus allowing for multi- point contact interaction, i.e., allowing multiple users to feel each other's influence on the object The proposed solution is presented and analyzed in a multirate setting. Experimental results employing a Phantom haptic interface are presented. [ABSTRACT FROM AUTHOR]

Proportional and integral (PI) control parameters are determined by approximating a dynamic matrix control (DMC). Since accuracy of the approximation depends on DMC parameters in a complicated manner, a combination of direct and indirect optimization methods are employed in this paper. Quadratic programming (QP) is used to determine PI parameters, and a simple grid method is used to find optimal DMC parameters. A tuning formula for the PI controller based on a curve-fitting technique, is suggested. Computer simulations are performed to compare performance of the new PI design method with those achievable using some existing PI controllers. [ABSTRACT FROM AUTHOR]