Modeling parallel and distributed systems with finite workloads

In studying or designing parallel and distributed systems one should have available a robust analytical model that includes the major parameters that determine the system performance. Jackson networks have been very successful in modeling computer systems. However, the ability of Jackson networks to predict performance with system changes remains an open question, since they do not apply to systems where there are population size constraints. Also, the product-form solution of Jackson networks assumes steady-state and exponential service centers or certain specialized queueing discipline. In this paper, we present a transient model for Jackson networks that is applicable to any population size and any finite workload (no new arrivals). Using several non-exponential distributions we show to what extent the exponential distribution can be used to approximate other distributions and transient systems with finite workloads. When the number of tasks to be executed is large enough, the model approaches the product-form solution (steady-state solution). We also, study the case where the non-exponential servers have queueing (Jackson networks cannot be applied). Finally, we show how to use the model to analyze the performance of parallel and distributed systems.     

Modeling physical systems using finite element Cell-DEVS

We propose a method to analyze complex physical systems using two-dimensional Cell-DEVS models. These problems are usually modeled with one or more Partial Differential Equations and solved using numerical methods. Our goal is to improve the definition of such problems by mapping them into the Cell-DEVS formalism, which permits easy integration with models defined with other formalisms, and its definition using advanced modeling and simulation tools. To show this, we used two methods for solving PDEs, and deduced the updating rules for their mapping to Cell-DEVS. As our simulation results show, the accuracy of the Cell-DEVS solution is the same of these previous methods, showing that we can use Cell-DEVS as a tool to obtain numerical solution for systems of PDEs. Simultaneously, this method provides us with a simpler mechanism for model definition, automated parallelism, and faster execution.     

Modeling and simulation of the open-end equity mutual fund market in Taiwan by using self-organizing map

This research applies artificial intelligence (AI) of unsupervised learning self-organizing map neural network (SOM-NN) to establish a model to select the superior funds. This research period is from year 2000 to 2010 and picks 100 domestic equity mutual funds as study object. This research used 30 days prior to the beginning of each month’s prior 30 days, 60 days, 90 days on fund’s net asset value and the Taiwan Weighted Stock Index (TAIEX) return as the fund’s relative performance evaluation indicators classified by month. Finally, based on the superior rate or the average return rate, this research select the superior funds and simulate investment transactions according to this model.The empirical results show that using the mutual fund’s net asset value and the TAIEX’s relative return as SOM-NN input variables not only finds out the superior fund but also has a good predictive ability. Applying this model to simulate investment transactions will be better than the random trading model and market. The experiments also found that the investment simulation of a three-month interval has the highest profitability. The model operation suggests that it is more suitable for short-term and medium-term investment. This research can assist investors in making the right investment decisions while facing rapid financial environment changes.     

Modeling and simulation of chaotic phenomena in electrical power systems

Modeling and simulation of nonlinear systems under chaotic behavior is presented. Nonlinear systems and their relation to chaos as a result of nonlinear interaction of different elements in the system are presented. Application of chaotic theory for power systems is discussed through simulation results. Simulation of some mathematical equations, e.g. Vander Pol's equation, Lorenz's equation, Duffing's equation and double scroll equations are presented. Theoretical aspects of dynamical systems, the existence of chaos in power system and their dependency on system parameters and initial conditions using computer simulations are discussed. From the results one can easily understand the strange attractor and transient stages to voltage collapse, angle instability or voltage collapse and angle divergence simultaneously. Important simulation results of chaos for a model three bus system are presented and discussed.     

Modeling and simulation of large-scale,linear, multiport systems

A large number of physical and engineering systems may be represented directly in terms of component energy characteristics and their power interactions. When the system elements are modeled as energetic multiports, and their interconnections by power bonds, then the bond graph language is a natural one for describing the entire system. Bond graphs may be written for dynamic systems involving various energy types, such as electrical, mechanical, fluid and thermal; all energy types may be coexistent. Useful modeling elements include multiport storages, dissipators, and junction elements and transducers, as well as sources.Bond graph models of linear multiport systems may be transformed to state-space form by a powerful algorithm based upon operational causality. From the state-space equations, dynamic responses may be obtained by the matrix exponential technique, thereby allowing the direct digital simulation of linear multiport models.The ENPORT program is a realization of the bond graph reduction algorithm. It is a principal purpose of this paper to describe the procedure upon which ENPORT is based, and to present some results. Important features of ENPORT are its choice of physically significant state variables, its use of operational causality to obtain an orderly formulation of system equations, and its ability to handle systems containing static storage subfields.     

空间互联系统的有限频率范围迭代学习控制

针对一类包含多个节点的空间互联系统,提出一种有限频率范围内的迭代学习控制算法.首先基于提升技术沿空间节点分布方向将重复运行的多维空间互联系统转换为一类二维等效系统,然后设计迭代学习控制律将被控系统转化为线性重复过程,并根据输出期望轨迹跟踪信号的频谱范围,利用Kalman-Yakubovich-Popov (KYP)引理将系统的频域稳定性能分析和控制律设计问题转换成以相应的线性矩阵不等式(LMI)求解问题,同时保证输出跟踪误差在时域和频域范围内的单调收敛性.最后以有源梯形电路的控制仿真验证所提算法的有效性.     

Stress analysis of perforated graphene nano-electro-mechanical (NEM) contact switches by 3D finite element simulation

Microsystem Technologies - In this article, we report the finite element method (FEM) simulation of the suspended double-clamped graphene beam-based NEM switches with standard and perforated beam...     

Computer simulation of landslides by the contact element method

In the paper, an improved contact element method was adopted to analyze the sliding process of slopes. The normal and shear strengths of materials on potential sliding surfaces of slopes were considered. The convergence of nonlinear problems on frictional contact boundaries was reached through a repeated contact calculation. A step-by-step procedure was used to simulate the process of landslides. The energy change of the slope system at each step was calculated, considering the strain energy, kinetic energy and the work of friction force, etc. In the simulation of rock slopes, it was found that there were three main states: a ‘perfectly bounded’ state, a ‘local sliding’ state and a ‘whole sliding’ state. The effects of weathering and water infiltrating into the sliding surfaces were considered, and the displacements of landslides were obtained. For a real case history, application of the code to results of an actual landslide is given. The simulation method described here may be employed to predict other kinds of landslides because it is not restricted to particular slopes, material properties of slopes or shapes of potential sliding surfaces.     

Modeling and simulation of structural components in recursive closed-loop multibody systems

Passenger cars, transit buses, railroad vehicles, off-highway trucks, earth moving equipment and construction machinery contain structural and light-fabrications (SALF) components that are prone to excessive vibration due to rough terrains and work-cycle loads’ excitations. SALF components are typically modeled as flexible components in the multibody system allowing the analysts to predict elastic deformation and hence the stress levels under different loading conditions. Including SALF component in the multibody system typically generates closed-kinematic loops. This paper presents an approach for integrating SALF modeling capabilities as a flexible body in a general-purpose multibody dynamics solver that is based on joint-coordinates formulation with the ability to handle closed-kinematic loops. The spatial algebra notation is employed in deriving the spatial multibody dynamics equations of motion. The system kinematic topology matrix is used to project the Cartesian quantities into the joint subspace, leading to a condensed set of nonlinear equations with minimum number of generalized coordinates. The proposed flexible body formulation utilizes the component mode synthesis approach to reduce the large number of finite element degrees of freedom to a small set of generalized modal coordinates. The resulting reduced flexible body model has two main characteristics: the stiffness matrix is constant while the mass matrix depends on the elastic modal coordinates. A consistent set of pre-computed inertia shape integrals are identified and used to update the modal mass matrix at each time step. The implementation of the component mode synthesis approach in a closed-loop recursive multibody formulation is presented. The kinematic equations are modified to include the effect of the flexible body modal elastic coordinates. Also, modified constraint equations that include the effect of flexibility at the joint connections and the necessary details of the Jacobian matrix are presented. Baumgarte stabilization approach is used to stabilize the constraint equations without using iterative schemes. A sample results for flexible body impeded in a closed system will be presented to demonstrate the above mentioned approach.     

A compliant contact model with nonlinear damping for simulation ofrobotic systems

Contact modeling is an important aspect of simulation of many robotic tasks. In the paper, a compliant contact model with nonlinear damping is investigated, and many previously unknown characteristics of the model are developed. Compliance is used to eliminate many of the problems associated with using rigid body models with Coulomb friction, while the use of nonlinear damping eliminates the discontinuous impact forces and most sticky tensile forces which arise in Kelvin-Voigt linear models. Two of the most important characteristics of the model are the dependence of the coefficient of restitution on velocity and damping in a physically meaningful manner, and its computational simplicity. A full mathematical development for an impact response is given, along with the effects of the system and model parameters on energy loss. A quasistatic analysis gives results which are consistent with energy loss characteristics of a more complex distributed foundation model under sustained contact conditions. A foot contact example for a walking machine is given which demonstrates the applicability of the model for impact on foot placement, sustained contact during the support phase, and the breaking of the contact upon liftoff of the foot     

Modeling and simulation of the nonsmooth planar rigid multibody systems with frictional translational joints

The main purpose of this paper is to present a modeling and simulation method for the rigid multibody system with frictional translational joints. The small clearance between a slider and guide is considered. The geometric constraints of the translational joints are treated as bilateral constraints and the impacts between sliders and guides are neglected when the clearance sizes of the translational joints are very small. The contact situations of the normal forces acting on the sliders are described by inequalities and complementarity conditions, while the frictional contacts are characterized by a set-valued force law of the type of Coulomb’s law for dry friction. The dynamic equations of the multibody systems with normal and tangential contact forces are written on the acceleration-force level using the Lagrange multiplier technique. The problem of the transitions of the contact situation of the normal forces acting on sliders and the transitions of the stick-slip of the sliders in the system is formulated as a horizontal linear complementarity problem (HLCP), which is solved by event-driven method. Baumgarte’s stabilization method is used to decrease the constraint drift. Finally, two typical mechanisms are considered as demonstrative application examples. The numerical results obtained show some dynamical behaviors of the systems with frictional translational joints and constraint stabilization effect.     

数字实现混沌系统的建模、仿真与实验

为提高混沌信号源的稳定性和精确性,提出了数字实现混沌系统的方法.在综合新提出的三维混沌系统和四维超混沌系统的基础上,通过将它们的微分方程转化为积分方程,采用离散化累积运算方法,建立了基于数字实现的离散模型.在Matlab/Simulink下数值仿真观察到了系统参数变化时动力学行为的演变过程,并基于ATmega128L微控制器芯片实现了相应的混沌和超混沌系统.仿真和实验结果表明了混沌和超混沌现象的存在性以及数字实现的可行性.     

Modeling and simulation of closed loop multibody systems with bodies-joints composite modules

Modular approaches are effective in improving the modeling efficiency in multibody system dynamics. A modular method, called bodies-joints composite simulation (BJCS) is presented in this paper. Two types of bodies-joints composite modules, i.e., f modules and 0 modules, are defined according to topology design rules of closed loop mechanisms. By this module partitioning, the differential-algebraic equations of motion of the system can be separated into purely algebraic and differential equations by structure decomposition. The stability criterion for the simulation is derived and a closed-form formulation to solve the algebraic loop problem is proposed. Simulation results of the forward dynamics of a 5R mechanism and a 6-UPS platform are presented to show the feasibility of the method. The CPU times of these two case studies are provided and compared with the generalized coordinate partitioning of Wehage and Haug and the modular simulation method of Kübler and Schiehlen, which indicate that the closed-form algebraic loop solver is more efficient than the numerical ones.     

Modeling rule-based systems by stochastic programmed production systems

A new tool, the stochastic programmed production system (SPPS), is proposed for representing rules and control mechanisms in rule-based systems. This approach is based on the stochastic programmed grammars, and its peculiarity is both its well-formalized semantics and its ability to represent most reasoning and control methods used in expert systems today. Since the proposed method is not limited by the particular heuristic organization of the rule-based system it is modeling, the SPPS is more general than existing knowledge-domain-independent expert-system development languages and may help bring a better understanding of the theory of expert systems.     

Determining the directional contact range of two convex polyhedra

The directional contact range of two convex polyhedra is the range of positions that one of the polyhedra may locate in along a given straight line so that the two polyhedra are in collision. Using the contact range, one can quickly classify the positions along a line for a polyhedron as “safe” for free of collision with another polyhedron, or “unsafe” otherwise. This kind of contact detection between two objects is important in CAD, computer graphics and robotics applications. In this paper we propose a robust and efficient computation scheme to determine the directional contact range of two polyhedra. We consider the problem in its dual equivalence by studying the Minkowski difference of the two polyhedra under a duality transformation. The algorithm requires the construction of only a subset of the faces of the Minkowski difference, and resolves the directional range efficiently. It also computes the contact configurations when the boundaries of the polyhedra are in contact.