Modelica - A Language for Physical System Modeling, Visualization and Interaction

Modelica is an object-oriented language for modeling of large, complex and heterogeneous physical systems. It is suited for multi-domain modeling, for example for modeling of mechatronics including cars, aircrafts and industrial robots which typically consist of mechanical, electrical and hydraulic subsystems as well as control systems. General equations are used for modeling of the physical phenomena, No particular variable needs to be solved for manually. A Modelica tool will have enough information to do that automatically. The language has been designed to allow tools to generate efficient code automatically. The modeling effort is thus reduced considerably since model components can be reused and tedious and error-prone manual manipulations are not needed. The principles of object-oriented modeling and the details of the Modelica language as well as several examples are presented

SIMULATION TOOLS AND SERVICES FOR MOBILE USERS: HISTORY, STATE-OF-THE-ART AND FUTURE

One of main ideas of this paper is a hypothesis that the simulation play an essentially more significant role in a human history and culture than it is usually assumed. On some examples it can be demonstrated that modern computational simulation has ancient prototypes and some artefacts can be interpreted as special simulation tools and environments. As typical examples of ancient simulation tools the “life/world tree” on mammoth bone and megalithical “models of the world” are presented. These artefacts were interpreted earlier as calendars, observatories or “ancient computers”. The proposed hypothesis considers the following interpretation as most exact and appropriate: “special computational simulation tools and environments with real-time functions (calendar) and real-world interface (observatory)”

Modelling of a stochastic continuous system

The key objective is to develop a method which can be utilized to model a stochastic continuous system. A system from the "real world" is used as the basis for the simulation modelling technique that is presented. The conceptualization phase indicates that the model has to incorporate stochastic and deterministic elements. A method is developed that utilizes the discrete simulation ability of a stochastic package (ARENA), in conjunction with a deterministic package (FORTRAN), to model the continuous system. (Software packages tend to specialize in either stochastic, or deterministic modelling.) The length of the iteration time interval and adequate sample size are investigated. The method is authenticated by the verification and validation ofthe defined model. Two scenarios are modelled and the results are discussed . Conclusions are presented and strengths and weaknesses of this method are considered and discussed .Presented at the 11th European Simulation Multiconference (ESM'97) in Istanbul. Turkey (1-4 June 1997) and included in the conference proceedings.http://sajie.journals.ac.z

Exploring the use of local consistency measures as thresholds for dead reckoning update packet generation

Human-to-human interaction across distributed applications requires that sufficient consistency be maintained among participants in the face of network characteristics such as latency and limited bandwidth. Techniques and approaches for reducing bandwidth usage can minimize network delays by reducing the network traffic and therefore better exploiting available bandwidth. However, these approaches induce inconsistencies within the level of human perception. Dead reckoning is a well-known technique for reducing the number of update packets transmitted between participating nodes. It employs a distance threshold for deciding when to generate update packets. This paper questions the use of such a distance threshold in the context of absolute consistency and it highlights a major drawback with such a technique. An alternative threshold criterion based on time and distance is examined and it is compared to the distance only threshold. A drawback with this proposed technique is also identified and a hybrid threshold criterion is then proposed. However, the trade-off between spatial and temporal inconsistency remains

Business process re-engineering (BPR): The REBUS approach

Many organisations undertake business process re-engineering (BPR) projects in order to improve efficiency and reduce costs. Although this approach can result in significant improvements and benefits, there are high risks associated with radical changes of business processes and the failure rate of BPR projects is reported to be as high as 70%. The Centre for Re-engineering Business Processes (REBUS) was established at Brunel University to provide a multidisciplinary environment for research into BPR and its success factors. This paper describes the REBUS approach to research concerning the success of BPR projects and presents examples of some of the projects carried out

Multi-rate relaying for performance improvement in IEEE 802.11 WLANs

It is well known that the presence of nodes using a low data transmit rate has a disproportionate impact on the performance of an IEEE 802.11 WLAN. ORP is an opportunistic relay protocol that allows nodes to increase their effective transmit rate by replacing a low data rate transmission with a two-hop sequence of shorter range, higher data rate transmissions, using an intermediate node as a relay. ORP differs from existing protocols in discovering relays experimentally, by optimistically making frames available for relaying. Relays identify themselves as suitable relays by forwarding these frames. This approach has several advantages compared with previously proposed relay protocols: Most importantly, ORP does not rely on observations of received signal strength to infer the availability of relay nodes and transmit rates. We present analytic and simulation results showing that ORP improves the throughput by up to 40% in a saturated IEEE 802.11b network