Distributed token circulation on mobile ad hoc networks

The design of a multi-stream plate-fin heat exchanger is a highly integrated task with multiple opposing objectives and many degrees of freedom. This work shows how it can be fully or partially automated by the combination of a detailed three-dimensional simulation model and an optimization routine. The desired task is formulated as the target of a multi-objective optimization and solved using a genetic algorithm. The workflow is presented using a cryogenic plate-fin heat exchanger with four process streams. The design is optimized towards high efficiency, low pressure drop, and low unit weight by adjusting the outer geometry, the inlet and outlet distributor configuration, and the detailed stream geometry. A detailed analysis of the Pareto-set gives a good overview of possible solutions, and the optimization routine can automatically find a feasible design with a reasonable tradeoff between the objectives. All elements of the framework are implemented in open source software. A highlight of this research is that a very comprehensive and detailed simulation model is employed in the optimization framework. Thus, the presented method can be easily adjusted to fit the needs of other engineering tasks.

Current group communication services have mostly been implemented on a homogeneous, distributed computing environment. This limits their applicability because most modern distributed computing environment are heterogeneous in nature. This paper describes the design, implementation, and performance evaluation of a CORBA group communication service. Using CORBA to implement a group communication service enables that group communication service to operate in a heterogeneous, distributed computing environment. To evaluate the effect of CORBA on the performance of a group communication service, this paper provides a detailed comparison of the performance measured from three implementations of an atomic broadcast protocol and a group membership protocol. Two of these implementations use CORBA, while the third uses UDP sockets for interprocess communication. The main conclusion is that heterogeneity can be achieved in group communication services by implementing them using CORBA, but there is a substantial performance cost. This performance cost can be reduced to a certain extent by carefully choosing a design and tuning various protocol parameters such as buffer sizes and timer values.

Many of today‟s advanced simulation tools are suitable for modeling specific systems; however, they provide rather limited support for model building and management. Setting up a detailed vehicle simulation model requires more than writing down state equations and running them on a computer. In this paper, we describe how modern software techniques can be used to support modeling and design activities, with the objective of providing better system models more quickly by assembling these system models in a “plug-and-play” architecture. Instead of developing detailed models specifically for Argonne National Laboratory‟s Autonomie modeling tool, we have chosen to place emphasis on integrating and re-using the system models, regardless of the environment in which they were initially developed. By way of example, this paper describes a vehicle model composed of a detailed engine model from GT Power, a transmission from AMESim, and with vehicle dynamics from CarSim. The paper will explain the different options available for the interface and how each of these options can be implemented. It will use a simple case study to show how the detailed expert simulation models can be used with simpler Simulink models to address different vehicle design issues. INTRODUCTION One of the basic capabilities that an enterprise-wide modeling and simulation tool needs is to provide a framework for integrating models developed in different languages/tools. Because different expert tools have distinct advantages for modeling specific phenomena, numerous tools are used across companies, such as automotive original equipment manufacturers (OEMs). When these models are available, nevertheless the attempt to integrate them into a single environment to build an accurate system model is very onerous. As a result, most vehicle models used for analysis are usually based on steady-state look-up tables. The lack of a common framework to link such expert models results in isolated pockets of model-rich design groups. The open architecture of Autonomie [1, 2], a modeling tool developed by Argonne National Laboratory (Argonne) over the past four years in collaboration with General Motors (GM), supports the rapid integration and analysis of powertrain/propulsion systems and technologies for rapid technology sorting and evaluation of fuel economy improvement under dynamic/transient testing conditions. The tool, developed in the MathWorks environment, is based on a forward-looking model architecture. Its plug-and-play architecture provides a common framework in which expert tools can be linked to build detailed vehicle models. In this paper, we will explain how Autonomie is used to act as the interface between models developed with expert tool by taking the GT-Power engine model, AMESim transmission model, and CarSim vehicle dynamics models as examples. THE NEED FOR DETAILED SYSTEM MODELS Each type of model has its own advantages and disadvantages. While Simulink models based on simple look-up tables are easy to develop and use, they lack the ability to simulate the details of the plant‟s physical interactions. As a result, simple plant models cannot support control systems development. More detailed models are also needed to evaluate the effect of new technology. Different expert tools are available to meet such needs. It is far more practical to use those tools than to build and validate an equally detailed model in Simulink. While the detailed models add accuracy, the input data needed for those models are difficult to obtain, and the models run slower. Hence, engineers must switch between the detailed and simpler models depending on the analysis and what level of accuracy in the simulation results is desired. As shown in Fig. 1, Autonomie provides a convenient way to use models of appropriate fidelity by enabling a plug-and-play function with the models and by interfacing with expert system tools.

Group communication services typically generate large multicast data streams. Delivering such massive data streams to the end system nodes at the edge of the Internet has been a challenging problem in terms of high stress on the network links and high demand on network resources and routing node capacities. Most of existing research has been dedicated on geo-distance based routing with various optimizations to alleviate the performance impact on geo-distance based routing due to unpredictable network dynamics. Most representative techniques are targeted at reducing the delivery path length or optimizing routing path by utilizing network locality. In this paper, we identify the inefficiency of geo-distance based routing protocols in many existing multicast overlay networks in terms of both resource utilization and group communication efficiency. To address this issue, we develop a utility-based routing scheme (UDR) that can provide efficient group communication services in a decentralized geographical overlay network. Our approach makes three unique contributions. First, we introduce a utility function to refine the geo-distance based routing in such a way that the routing path selection can carefully incorporate both geo-distance based metric and the network latency. Second, we enhance our utility driven routing scheme with self-adaptive capability by considering the nodes' state and network density. Thus, nodes in the multicast network can dynamically accommodate the changes of network conditions based solely on their local knowledge about the network. Third, we devise a suite of optimization techniques to minimize the maintenance cost and computational complexity of our self-adaptive and utility-drive routing scheme. We evaluate our approach through extensive experiments based on a realistic network topology model and show that the UDR method is highly scalable and it effectively enhances the multicast delivery efficiency for large scale group communication services compared to existing geo-distance based routing protocols.

Accurate prediction of fundamental properties such as melting points using direct physical simulation is challenging. Here, we investigate the melting point (Tm) of alkali halides that are often considered to be the simplest category of salts. Popular force fields that have been examined for this task leave considerable room for improvement. Recently we introduced a new force field for alkali halides (WBK) as part of the Alexandria project, featuring explicit polarisation and distributed charges. This new force field significantly improves the prediction of a large set of physicochemical properties and in this contribution we show that the same is valid for the prediction of Tm. For reference, we calculated Tm using a non-polarisable force field by Joung and Cheatham (JC), and compare our results to existing literature data on the widely used Tosi-Fumi (TF) parameters. In contrast to the predictions of the WBK model, the JC force field consistently overestimates the experimental Tm, while the accuracy of the TF model strongly depends on the investigated salt. Our results show that the inclusion of more realistic physics into a force field opens up the possibility to accurately describe many physicochemical properties over a large range of temperatures, even including phase transitions.

Track switches are essential in order to enable railway vehicles to change routes however they are also the largest single cause of failure on the railway network and remain a single point of failure. This thesis focusses on modelling and fault tolerant control of a new type of electromechanical railway track switch. Unlike conventional track switch machines, this switch needs closed loop feedback control. Firstly, a detailed simulation model of the switch is developed and validated against experimental results. Two model-based control designs are then developed and tested: a classical cascaded P/PI controller and a modern state feedback LQR controller. The two controllers are compared and it is found that, whilst there are some performance differences, both meet the requirements for use in a redundantly actuated track switch. Following this, a fault tolerant control scheme for sensor faults is developed and validated using fault detection, identification and accommodation methods applied to a detailed non-linear simulation model and then validated on the experimental test rig. The results demonstrate that using a reliable fault tolerant control configuration could increase the availability and reliability of the switch in the presence of sensor faults. Finally, a fault tolerant control approach to actuator faults on the switch with triplex redundancy is developed and validated. In order to achieve this, a dynamic model of a railway track is developed in simulation as the basis for load application to the system. Three parallel actuators with their associated controllers are used to actuate the switch showing good performance in meeting the position control requirements. Different actuator faults are applied and their control performance results are shown. A summary of the control performance is also presented highlighting the differences in performance with different permutations of actuator faults. Overall, it is shown that redundancy in actuation with a suitable control scheme provides benefits in achieving post-fault availability of a redundantly actuated electromechanical railway track switch in the presence of actuator faults.

We discuss a group protocol which supports applications with group communication service when QoS supported by networks or required by applications is changed. An autonomic group protocol is realised by cooperation of multiple autonomous agents. Each agent autonomously takes a class of each protocol function so as to support only and all QoS required. A group is composed of views for scalability. Each view is a subset of the agents where the agents autonomously take protocol classes consistent with each other. We make clear what combination of classes can be autonomously taken by agents in a view.

In distributed systems, high service availability can be achieved by letting a group of servers replicate the service state; if some servers fail, the surviving ones know the service state and can continue to provide the service. Group communication services, such as membership and atomic broadcast, have been proposed to solve the problem of maintaining server state replica consistency. Group membership achieves agreement on the history of server groups that provide the service over time, while atomic broadcast achieves agreement on the history of state updates performed in each group.

In this paper, we propose the design of an extension of the Java distributed object model based on the group communication paradigm for building replicated fault-tolerant servers. Maintaining the correctness and integrity of replicated servers is supported by the group manager object instantiated with each replica to form a logical group and the group membership algorithms to maintain a consistent group view and a reliable multicast mechanism to communicate with other group managers. Group manager object enables the creation of groups of remote objects that cooperate towards some common goal using a join/leave group communication service. Remote object groups simulate the behavior of standard remote objects by implementing a set of remote interfaces and by enabling clients to remotely invoke the methods defined in these interfaces through the standard Java RMI mechanism. For the first time, communication among senders forming a group is based on group method invocations as well, offering a completely object-oriented framework for programmers. And then, it is completed by a state merging service, which simplifies the development of state merging mechanism needed to re-establish a consistent state after the disappearing of join/leave properties

Cycle Time-Throughput-Product mix (CT-TH-PM) surfaces give the mean cycle time as a function of throughput and product mix for manufacturing workstations. To generate the CT-TH-PM surface, detailed simulation models may be used. However, detailed models require much development time, and it may not be possible to estimate all model parameters. Instead, we propose an aggregate simulation model to generate a workstation's CT-TH-PM surface. In the aggregate model, the various workstation details are lumped into an ‘effective process time’ (EPT) distribution. The EPT distribution in the aggregate simulation model is estimated from arrival and departure data measured at the workstation in operation. We validate the proposed method using a simulation example representing a semiconductor workstation. We find that the method can accurately predict the mean cycle time in a region around the workstations’ operational product mix. We also present an industry test case; the applicability of the method is demonstrated for a workstation in the Crolles2 wafer factory.

Predicting the mean cycle time as a function of throughput and product mix is helpful in making the production planning for cluster tools. To predict the mean cycle time, detailed simulation models may be used. However, detailed models require much development time, and it may not be possible to estimate all model parameters. Instead of a detailed simulation model, we propose to use a so-called aggregate model to predict the mean cycle time as a function of throughput and product mix. The aggregate model is a lumped-parameter representation of the queueing system. We estimate the parameters of the aggregate model from arrival and departure data using the Effective Process Time (EPT) concept. The proposed method is illustrated for a simulation test case and a Crolles2 cluster tool workstation. The method accurately predicts the mean cycle time in a region around the workstations' operational product mix.

Timing-accurate simulation of circuits is an important task in design validation of modern nano-scale CMOS circuits. With shrinking technology nodes, detailed simulation models down to transistor level have to be considered. While conventional simulation at logic level lacks the ability to accurately model timing behavior for complex cells, more accurate simulation at lower abstraction levels becomes computationally expensive for larger designs. This work presents the first parallel multi-level waveform-accurate timing simulation approach on graphics processing units (GPUs). The simulation uses logic and switch level abstraction concurrently, thus allowing to combine their advantages by trading off speed and accuracy. The abstraction can be lowered in arbitrary regions of interest to locally increase the accuracy. Waveform transformations allow for transparent switching between the abstraction levels. With the utilization of GPUs and thoughtful unification of algorithms and data structures, a fast and versatile high-throughput multi-level simulation is obtained that is scalable for millions of cells while achieving runtime savings of up to 89% compared to full simulation at switch level.

Previous work regarding the vibration transmissibility control, using electrodynamic actuators, based on semi-active solutions, proved the efficiency of this strategy. The studied system is a simple, one degree of freedom system. The system integrates mechanical components for passive isolation and an electrodynamic actuator for active and semi-active control of vibrations. The most efficient solution is to design an accurate model and simulate strategies on it. Two strategies are involved: feed-forward control with an accelerometer placed on the mobile mass for acceleration detection and the second one is based on movement detection using the self-induced current due to the actuator's coil movement in a magnetic field. A detailed simulation model, using a software designed for electronic circuit simulation and experimental testing are performed in both cases. The model should be improved for considering the complex impedance of the actuator (mechanically but also electrically), this being the subject of future works.

In this paper, a novel Harmonic Axis Decoupling (HAD) method is proposed for extending the capabilities of the Generalized Averaged Modeling (GAM) technique. The conventional GAM technique is first revisited, and the problems encountered in the multiplication of two Double Fourier Series (DFS) signals in the time domain are investigated. The method of translating Fourier vectors to Discrete Fourier Images (DFI) in the frequency plane is proposed, and the ramifications of this conversion on DFS product terms in the time domain are investigated. The two-dimensional DFI convolution technique resulting from HAD is used for the dynamic modeling of power converters excited by two distinct frequencies. The novel technique efficiently incorporates a large number of harmonics present in a power converter. The proposed technique is then converted into an algorithm suitable for implementing in numerical Ordinary Differential Equation (ODE) solvers. Observations on the effects of harmonic truncation are made to validate the proposed algorithm. Finally, the efficacy of the proposed technique is assessed through a case study, wherein a single-phase inverter possesses LC filters on both the dc-link and the ac-side. The results obtained with the proposed method show an excellent congruence with a detailed simulation model.

In this paper, a detailed study and analysis has been done for investigating a technique for the location of fault in a long high voltage DC transmission line, say up-to 1000kms long. For achieving this, the paper proposes to use combination of two methods, first method is based on the travelling wave principle, and second method is wavelet transform. The wave-front i.e. the arrival time of the travelling wave is measured with the help of wavelet transform and in wavelet transform specifically continuous wavelet transform is used because of its prominent and accurate results. The presented technique can accurately predict the exact fault location, with the help of correctly measured surge arrival times obtained from continuous wavelet transform. The studies are carried out with the detailed simulation model as well as programming in MATLAB.