Multicriteria discrete optimization of large scale truss systems

The paper discusses optimization problems in civil engineering structural design. The following questions are discussed: continuous or discrete optimization, single- or multicriteria optimization, one- or multi-level optimization. The paper is illustrated with examples of the multi-criteria discrete optimization of large scale truss systems. The cross-sectional areas of truss bars are taken as design variables. Minimization of mass, labour cost and displacements are chosen as optimization criteria. Optimization constraints concern stresses, displacements and stability, as well as technological and computational requirements. The results of single- and multicriteria optimization of hall structures are presented in the form of diagrams and tables.Presented at NASO ASI Optimization of Large Structural Systems, Sept. 23 – Oct. 4, 1991, Berchtesgarden, Germany     

Neural networks based subgrid scale modeling in large eddy simulations

In this paper a multilayer feed-forward neural network (NN) is used as subgrid scale (SGS) model in a large eddy simulation (LES). The NN was previously off-line trained using numerical data generated by a LES of a channel flow at Re_τ=180 with Bardina's scale similar (BFR) SGS model. Results show the ability of NNs to identify and reproduce the highly nonlinear behavior of the turbulent flows, and therefore the possibility of using NN techniques in numerical simulations of turbulent flows.     

Optimization of multigrid based elliptic solver for large scale simulations in the FLASH code

FLASH is a multiphysics multiscale adaptive mesh refinement (AMR) code originally designed for simulation of reactive flows often found in Astrophysics. With its wide user base and flexible applications configuration capability, FLASH has a dual task of maintaining scalability and portability in all its solvers. The scalability of fully explicit solvers in the code is tied very closely to that of the underlying mesh. Others such as the Poisson solver based on a multigrid method have more complex scaling behavior. Multigrid methods suffer from processor starvation and dominating communication costs at coarser grids with increase in the number of processors. In this paper, we propose a combination of uniform grid mesh with AMR mesh, and the merger of two different sets of solvers to overcome the scalability limitation of the Poisson solver in FLASH. The principal challenge in the proposed merger is the efficiency of the communication algorithm to map the mesh back and forth between uniform grid and AMR. We present two different parallel mapping algorithms and also discuss results from performance studies of the two implementations. Copyright © 2012 John Wiley & Sons, Ltd.     

Control of large scale discrete event systems: Task allocation and coordination

To control a large scale discrete event system, decentralized control and hierarchical control can be used, where several local supervisors are used to control events in local sites and a coordinator is used to coordinate the local supervisors. Two important problems that need to be solved in such a control architecture are task allocation and coordination. That is, how to allocate tasks to the supervisors, and how to coordinate those tasks. We propose and solve a task allocation problem of assigning tasks to the local supervisors and a minimal intervention problem of coordinating tasks so that the intervention by the coordinator is minimal.     

Parallel performance of large scale impact simulations on Linux cluster super computer

Three-dimensional analyses with fine solid meshes have become quite common in large deformation impact problems. As the complexity of the problem increases in size and resolution, it is necessary to utilize a parallel dynamic code on parallel systems. The purpose of this paper is to present the parallel performance of a new FEM impact code tested on self-made Linux cluster supercomputer for high speed impact problems. Almost ideal speed-up is achieved for the fixed and scaled Taylor bar model even up to 256 CPUs, although some inefficiency is still identified in parallel FE calculation resulting from the increased communication overhead. In the case of metal sphere impacting to oblique plate, the overall speed-up increases continuously even up to 128 CPUs. Investigation of elapsed time of each part reveals that most of the inefficiency comes from the load imbalance of contact. The two benchmark problems demonstrate the possibility of large scale three-dimensional dynamic simulations within a reasonable computational time.     

Multi-agent based simulations using fast multipole method: application to large scale simulations of flocking dynamical systems

This article introduces a novel approach to increase the performances of multi-agent based simulations. We focus on a particular kind of multi-agent based simulation where a collection of interacting autonomous situated entities evolve in a situated environment. Our approach combines the fast multipole method coming from computational physics with agent-based microscopic simulations. The aim is to speed up the execution of a multi-agent based simulation while controlling the precision of the associated approximation. This approach may be considered as the first step of a larger effort aiming at designing a generic kernel to support efficient large-scale multi-agent based simulations. This approach is illustrated in this paper by the simulation of large scale flocking dynamical systems.     

Pre-requisites for large scale coordination

Communication is in this paper seen as the foundation for purposeful human–human activity in dynamic environments. Coordination is a central issue in large systems such as military organisations, enterprises, or rescue organisations, and communication is needed in order to achieve coordination in such systems. This paper suggest a holistic approach to control, where control in a large system is seen as an emergent product of human interaction, focusing on human–human communication from a technical, organisational, temporal, and social perspective.

An optimal termination testing procedure for discrete event simulations

In this paper we consider discrete-event simulations which yield results until a termination condition is satisfied. The simulation can proceed beyond this time, but no useful information is generated. The time at which the termination condition will be satisfied is not known initially, and is taken to be randomly distributed with some prescribed density. It is necessary, therefore, to periodically check the termination condition, and this consumes CPU time. The question that we address is how to distribute checking time to minimize expected CPU expenditure. We do this by taking a limit in which the cost of checking is small, and then minimizing the limiting expected CPU expenditure. In general, uniformly distributed checking times are not optimal. The layouts of checking times which are generated by our minimization procedure can significantly outperform constant checking intervals.     

An optimum time scale for discrete Laguerre network

Any discrete-time stable transfer function can be expressed by a discrete-time Laguerre series with a chosen time scale. An optimum time scale such that an index is minimized is derived. This index ensures that the coefficients of higher-order Laguerre functions go toward zero quickly. The solution derived requires the knowledge of the impulse response of the discrete plant. Cases of first-order plants, second-order underdamped plants, and plants with multiunit delay are also discussed     

A consistent discrete elements technique for curved members

A general solution method of a system of coupled differential equations governing the elastic behavior of curved members is presented. The finite element displacement method is formulated based on a variational principle. The stiffness, stability and mass matrices of the discrete finite element are consistent and are obtained within the bounds of linearized displacement theories. Examination of a convergence test indicated an extremely fast converging upper bound solutions, as expected, due to the utilization of the variational procedure. Critical loads and natural frequencies were obtained using computer programs developed. A measure of warping contribution to torsional behavior is assessed and the effects of antisymmetry of the cross sections are examined. An excellent correlation has been observed in comparative studies.     

Predicting the behavior of large scale P2P systems by parallel discrete event simulation

P2P systems are becoming the dominator of Internet.Such systems are typically composed of thousands to millions of physical computers,which make it difficult to predict their behaviors without a large scale distributed system simulator.This paper is an attempt to predict the behavior of large scale P2P systems by building a novel parallel simulator:AegeanSim,which provides parallel discrete event simulation of such systems on high performance server clusters.We abstract the execution of P2P applications wit...     

一种大型软件测试方法

总结了一种结合功能测试和性能测试的测试方法,其中功能测试方法由功能测试流程和功能测试用例设计方法组成.性能测试方法由性能测试流程、测试工具选择、性能测试指标设计和性能调优方法组成.实践证明,该方法能够达到对大型软件进行功能和性能把关的目的.     

Approximations for large scale closed queueing networks

Evaluation of closed queueing networks with product form solutions is very time-consuming if the population sizes or the network size is large. This paper provides an analysis of an approximation technique, based upon mean value analysis which requires considerably less computation time, and yet achieves a high degree of accuracy. The approximates are unique in some feasible regions. Error analysis and illustrative examples are provided.     

Video traffic analytics for large scale surveillance

The video traffic analysis is the most important issue for large scale surveillance. In the large scale surveillance system, huge amount of live digital video data is submitted to the storage servers through the number of externally connected scalable components. The system also contains huge amount of popular and unpopular old videos in the archived storage servers. The video data is delivered to the viewers, partly or completely on demand through a compact system. In real time, huge amount of video data is imported to the viewer’s node for various analysis purposes. The viewers use a number of interactive operations during the real time tracking suspect. The compact video on demand system is used in peer to peer mesh type hybrid architecture. The chunk of video objects move fast through the real time generated compact topological space. Video traffic analytics is required to transfer compressed multimedia data efficiently. In this work, we present a dynamically developed topological space, using mixed strategy by game approach to move the video traffic faster. The simulation results are well addressed in real life scenario.     

Stochastic Petri net representation of discrete event simulations

In the context of discrete event simulation, the marking of a stochastic Petri net (SPN) corresponds to the state of the underlying stochastic process of the simulation and the firing of a transition corresponds to the occurrence of an event. A study is made of the modeling power of SPNs with timed and immediate transitions, showing that such Petri nets provide a general framework for simulation. The principle result is that for any (finite or) countable state GSMP (generalized semi-Markov process) there exists an SPN having a marking process that mimics the GSMP in the sense that the two processes (and their underlying general state-space Markov chains) have the same finite dimensional distributions     

Engineered hydrophobicity of discrete microfluidic elements for double emulsion generation

Microfluidic device fabrication has classically utilized methods that have limited devices to specific applications. More recently, discrete microfluidic elements have reimagined the design process of microfluidic device fabrication to that of building blocks that can be constructed in various forms to produce devices of many applications. Here, surface modification of discrete microfluidic elements via initiated chemical vapor deposition is demonstrated. Coated modular elements can quickly assemble to form complex 2-D or 3-D structures with step-like surface energy gradients for applications requiring discrete control of channel surface wettability. This platform is applied toward the generation of double emulsions to show the ease of design and manufacturing over existing methods developed to manage two-phase flows.