Discrete Simulation of Behavioural Hybrid Process Calculus

Hybrid systems combine continuous-time and discrete behaviours. Simulation is one of the tools to obtain insight in dynamical systems behaviour. Simulation results provide information on performance of system and are helpful in detecting potential weaknesses and errors. Moreover, the results are handy in choosing adequate control strategies and parameters. In our contribution we report a work in progress, a technique for simulation of Behavioural Hybrid Process Calculus, an extension of process algebra that is suitable for the modelling and analysis of hybrid systems

Rheophysics of dense granular materials : Discrete simulation of plane shear flows

We study the steady plane shear flow of a dense assembly of frictional, inelastic disks using discrete simulation and prescribing the pressure and the shear rate. We show that, in the limit of rigid grains, the shear state is determined by a single dimensionless number, called inertial number I, which describes the ratio of inertial to pressure forces. Small values of I correspond to the quasi-static regime of soil mechanics, while large values of I correspond to the collisional regime of the kinetic theory. Those shear states are homogeneous, and become intermittent in the quasi-static regime. When I increases in the intermediate regime, we measure an approximately linear decrease of the solid fraction from the maximum packing value, and an approximately linear increase of the effective friction coefficient from the static internal friction value. From those dilatancy and friction laws, we deduce the constitutive law for dense granular flows, with a plastic Coulomb term and a viscous Bagnold term. We also show that the relative velocity fluctuations follow a scaling law as a function of I. The mechanical characteristics of the grains (restitution, friction and elasticity) have a very small influence in this intermediate regime. Then, we explain how the friction law is related to the angular distribution of contact forces, and why the local frictional forces have a small contribution to the macroscopic friction. At the end, as an example of heterogeneous stress distribution, we describe the shear localization when gravity is added.Comment: 24 pages, 19 figure

Production optimization using discrete simulation

Mestrado APNOR e Universidade de S. PetersburgoProduction and manufacturing setups involving lean solutions and customer driven “pull” logic (e.g. kanban systems) are more and more common. Usually, these systems allow companies to increase efficiency, quality levels, work force motivation and general productivity. Although these systems are not too difficult to plan and operate, in complex situations, even small adjustments can produce some unforeseen effects. In this scenario, discrete simulation can provide the tools to model the underlying systems and test the desired changes before implementation. In this work we modelled typical pull production systems with more or less complexity using a commercial discrete simulation software (SIMIO). Once the modelling phase was completed, different adjustments in the number of Kanban cards in the system were tested and evaluated, in order to optimize the system. Also, the final simulation model was built generic enough to be used in classroom environment to familiarize students with pull production concepts.As configurações de produção e fabricação envolvendo soluções lean e a lógica pull orientada ao cliente (por exemplo, sistemas kanban) são cada vez mais comuns. Normalmente, estes sistemas permitem que as empresas aumentem a eficiência, os níveis de qualidade, a motivação da força de trabalho e a produtividade geral. Embora esses sistemas não sejam muito difíceis de planear e operar, em situações complexas, mesmo pequenos ajustes podem produzir alguns efeitos imprevistos. Nesse cenário, a simulação discreta pode fornecer as ferramentas para modelar os sistemas subjacentes e testar as alterações desejadas antes da implementação. Neste trabalho modelamos sistemas típicos de produção puxada com maior ou menor complexidade usando um software comercial para simulação discreta (SIMIO). Uma vez concluída a fase de modelação, foram testados e avaliados diferentes ajustes no número de cartões kanban no sistema, a fim de otimizar o sistema. Além disso, o modelo de simulação final foi construído de forma suficientemente genérica para ser usado em ambiente de sala de aula para familiarizar os alunos com conceitos de produção puxada (pull).Организация производства и технологическая наладка с применением концепций «бережливого» и «вытягивающего» производства, ориентированных на нужды потребителя (например, система канбан) получают все более широкое распространение. Обычно, данные системы позволяют компаниям повышать эффективность, уровень качества, мотивацию сотрудников и производительность в целом. И хотя реализация данных подходов не является слишком трудоемкой, в сложных ситуациях даже малейшие корректировки могут привести к непредвиденным последствиям. В таком случае, дискретное моделирование может предоставить инструменты для создания базовых моделей и их тестирования, до внесения изменений в реальную систему. В данной работе было смоделировано типичное, более-менее сложное вытягивающее производство с применением коммерческого программного средства дискретного имитационного моделирования (SIMIO). После создания симуляции было протестировано и оценено использование разного количества канбан карт в системе с целью ее оптимизации. Также, финальная симуляция была создана достаточно общей, чтобы ее можно было использовать во время аудиторных занятий для ознакомления студентов с концепцией вытягивающего производства

Discrete Simulation in Java: Process Scheduling

Tato práce se zabývá implementací plánování procesů pro diskrétní simulaci v Javě. Rozebírá dva přístupy: implementaci simulačních procesů pomocí vláken a implementaci simulačních procesů bez vláken. Hlavním problémem při použití vláken bylo zabezpečit jejich kooperativní přepínání. Procesy implementované bez vláken jsou rozdělené na atomické části a k přerušení může dojít pouze mezi těmito částmi. Výsledky testování poukazují na to, že implementace pomocí vláken je podstatně pomalejší a paměťově náročnější.This thesis deals with process scheduling implementation for discrete simulation in Java. Two approaches are considered: process implementation using threads and process implementation without threads. Main problem of using threads was to ensure cooperative switching. Processes implemented without threads are divided into atomic parts and suspend can be performed only between these parts. Test results show that implementation using threads is considerably slower and consumes more memory.

Closed loop models for analyzing the effects of simulator characteristics

The optimal control model of the human operator is used to develop closed loop models for analyzing the effects of (digital) simulator characteristics on predicted performance and/or workload. Two approaches are considered: the first utilizes a continuous approximation to the discrete simulation in conjunction with the standard optimal control model; the second involves a more exact discrete description of the simulator in a closed loop multirate simulation in which the optimal control model simulates the pilot. Both models predict that simulator characteristics can have significant effects on performance and workload

Basic Approaches to the Simulation of Recrystallization and Grain Growth

Simulations: Why? How? Discrete simulation methods; Examples; Conclusion

Closed loop models for analyzing engineering requirements for simulators

A closed loop analytic model, incorporating a model for the human pilot, (namely, the optimal control model) that would allow certain simulation design tradeoffs to be evaluated quantitatively was developed. This model was applied to a realistic flight control problem. The resulting model is used to analyze both overall simulation effects and the effects of individual elements. The results show that, as compared to an ideal continuous simulation, the discrete simulation can result in significant performance and/or workload penalties

A particulate basis for a lattice-gas model of amphiphilic fluids

We show that the flux-field expansion derived by Boghosian and Coveney for the Rothman-Keller immiscible fluid model can be derived in a simpler and more general way in terms of the completely symmetric tensor kernels introduced by those authors. Using this generalised flux-field expansion we show that the more complex amphiphilic model of Boghosian Coveney and Emerton can also be derived from an underlying model of particle interactions. The consequences of this derivation are discussed in the context of previous equilibrium Ising-like lattice models and other non-equilibrium mesoscale models.Comment: To appear in Phil. Trans. Roy. Soc. (Proceedings of the Xth International Conference on Discrete Simulation of Fluid Dynamics.

Cross Layer Aware Adaptive MAC based on Knowledge Based Reasoning for Cognitive Radio Computer Networks

In this paper we are proposing a new concept in MAC layer protocol design for Cognitive radio by combining information held by physical layer and MAC layer with analytical engine based on knowledge based reasoning approach. In the proposed system a cross layer information regarding signal to interference and noise ratio (SINR) and received power are analyzed with help of knowledge based reasoning system to determine minimum power to transmit and size of contention window, to minimize backoff, collision, save power and drop packets. The performance analysis of the proposed protocol indicates improvement in power saving, lowering backoff and significant decrease in number of drop packets. The simulation environment was implement using OMNET++ discrete simulation tool with Mobilty framework and MiXiM simulation library.Comment: 8 page