SIMULATION: Transactions of The Society for Modeling and Simulation International

Mukherjee, Amalendu; Rastogi, Vikas; Dasgupta, Anirvan

doi: 10.1177/0037549706068285pmid: N/A

The purpose of this article is to obtain conservation laws (invariants of motion) for different energy domains through the extended Noether theorem and bond graphs. Bond graphs are profitably used in representing the physics of a system as well as obtaining its umbra-Lagrangian. The article extends Lagrangian-Hamiltonian mechanics to deal with asymmetries in the system, which incorporates dissipative and nonpotential fields in a compact Lagrangian form, such that one may obtain invariants of motion through extension of Noether’s theorem. A detailed methodology is outlined in this article for obtaining the invariants of motion for a general class of asymmetric systems with a gauge-transformed umbra-Lagrangian. Symmetrization of an asymmetric system is introduced through the concept of gauge functions, for which the classical Noether theorem is extended over vector fields in the extended manifold comprising real and umbra displacements and velocities, as well as real time. A generalization of the variational principle or least action principle is also presented, which leads to the proposed form of the umbra-Lagrange equation through recursive minimization of functionals. Several illustrative examples are given to elucidate this concept in different physical contexts.

Jianliang, Guo; Rongdi, Han

doi: 10.1177/0037549706067647pmid: N/A

Slender bar is widely applied in practice, but its turning operation is much more difficult than that of ordinary workpiece.The major problem lies in the fact that the high transversal deflection of workpiece results in high diameter error in turning slender shaft. In order to investigate the development of diameter error, the turning operation is simulated by using the Rayleigh beam theory. Through this theory, the dynamic response of a rotating workpiece under the cutting force is determined. Then, the diameter error of slender bar is determined based on the geometric correlation between the workpiece deflection and the diameter error. In this simulation, the cutting force is obtained using an empirical model, which is extensively used. Finally, a series of experimental tests are carried out to validate the simulation of diameter error. The experimental results demonstrate that the simulated values are considerably accurate. In addition, in order to eliminate the diameter error through error compensation method, the nominal depth of cut corresponding to a certain actual depth is determined by using the proposed model. The originality of this work is that the rotational motion of workpiece is taken into account in determining the diameter error of slender bar.

Rao, Dhananjai M.; Wilsey, Philip A.

doi: 10.1177/0037549706067271pmid: N/A

The steady growth in the multifaceted use of broadband asynchronous transfer mode (ATM) networks for time-critical applications has significantly increased the demands on the quality of service (QoS) provided by the networks. Satisfying these demands requires the networks to be carefully engineered based on inferences drawn from detailed analysis of various scenarios. Analysis of networks is often performed through computer-based simulations. Simulation-based analysis of the networks, including nonquiescent or rare conditions, must be conducted using high-fidelity, high-resolution models that reflect the size and complexity of the network to ensure that crucial scalability issues do not dominate. However, such simulations are time-consuming because significant time is spent in driving the models to the desired scenarios. In an endeavor to address the issues associated with the aforementioned bottleneck, this article proposes a novel, multiresolution modeling-based methodology called dynamic component substitution (DCS). DCS is used to dynamically (i.e., during simulation) change the resolution of the model, which enables more optimal trade-offs between different parameters such as observability, fidelity, and simulation overheads, thereby reducing the total time for simulation.The article presents the issues involved in applying DCS in parallel simulations of ATM networks. An empirical evaluation of the proposed approach is also presented.The experiments indicate that DCS can significantly accelerate the simulation of ATM networks without affecting the overall accuracy of the simulation results.

Cortés, Pablo; Muñuzuri, Jesús; Onieva, Luis

doi: 10.1177/0037549706066986pmid: N/A

Nowadays, most of the main companies in the vertical transport industry are researching tools capable of providing support for the design process of elevator systems. Numerous decisions have to be taken to obtain an accurate, comfortable, and high-quality service. Effectively, the optimization algorithm is a key factor in the design process, but so are the number of cars being installed, their technical characteristics, the kinematics of the elevator group, and some other design parameters, which cause the selection task of the elevator system to be a complex one. In this context, the design of decision support tools is becoming a real necessity that most important companies are including as part of their strategic plans. In this article, the authors present a user-friendly planning and simulating tool for dynamic vertical traffic. The tool is conceptualized for giving support in the planning and design stage of the elevator system, in order to collaborate in the selection of the type of elevator (number, type of dynamic, capacity, etc.) and the optimization algorithm.