Finite Element Method For Solving Research Articles

A Three-Dimensional Object-Oriented Distributed Finite Element Solver Based on Mobile Agent Technology

We present an object-oriented distributed finite element method (FEM) solver for three-dimensional scattering problems, implemented on a network of workstations. The solution of the resulting sparse linear system is performed using the conjugate orthogonal conjugate gradient method. The entire implementation is based on the Java programming language, and the distributed solution is achieved via the use of mobile agent technology. Since the paper aims mainly to demonstrate the benefits of using Java and mobile agents as the technologies to develop complex FEM applications and implement them in a distributed environment, its main core is devoted to a thorough description of the distributed-object-oriented implementation, focusing on inter-agent communication and synchronization aspects. Numerical results are presented, which prove that our approach is a promising technique for the efficient solution of complex FEM modeling problems.

Dynamic hysteresis modeling based on Preisach model

A method to model dynamic hysteresis is proposed. The proposed model is based on an inverse Preisach model with the magnetic flux density and its rate as inputs, and the magnetic field as the output. Assuming that the hysteretic behavior does not depend on the history of this rate, the inverse distribution function is expressed in terms of the magnetic flux density rate. As a consequence, the classical utilization rules of the Preisach triangle can be applied, thus making the implementation of the proposed model very easy and efficient. The proposed model has been experimentally validated and compared with a classical static Preisach model. Since the inputs of the proposed model are the magnetic flux density and its rate, this model can very easily be implemented in a finite-element method solver using the magnetic vector potential as unknown.

A simulation study of IC layout effects on thermal management of die attached GaAs ICs

Power management and thermal characterization of integrated power amplifiers is crucial to the development of a number of advanced technologies including portable wireless applications. Reduction and or optimization of device operating temperatures and thermal characteristics is needed to control temperature activated failure phenomena. This paper presents the use of PATRAN, a three-dimensional (3-D) model builder and finite element method (FEM) solver as means of understanding the heat flow in integrated devices and optimizing the layout for thermal operation. The approach taken is to assume a priori knowledge of the heat generation region and decouple the semiconductor transport equations. This allows for solution of the heat equation over a sufficiently large region to be correct. After verifying the correctness of the assumption of the device temperature being relatively insensitive to the depth, thickness and shape of the heat generation region, the optimization of heat spreaders in a GaAs HBT process is presented. This optimization is performed as an example of how both the maximum temperature and temperature variation across the emitter can reduced by careful design of the emitter metallization. Finally, the use of PATRAN is presented for extracting a three resistor thermal model for two devices in close proximity.

Integration of heterogeneous CAD databases using STEP and the Internet

In a large-scale design process, designers cooperate in a complex situation where a variety of software tools run on different hardware platforms. This paper presents a data enhancement approach to integrate heterogeneous Computer-Aided Design (CAD) databases through the Internet. The data enhancement means topological changes in a geometric model and additional information in design semantics. The geometric data is enhanced using a non-manifold modeler to produce data sets valuable in downstream applications such as a Finite Element Method (FEM) solver or a detail design system. As a practical example, a shipbuilding product model database has been implemented based on the Standard for the Exchange of Product (STEP) model data methodology and shipbuilding features. The system has been implemented on a network environment that consists of a Web browser, Common Object Request Broker Architecture (CORBA) objects, a relational database management system, a data enhancement module, and various computer-aided applications.

Biological cells with gap junctions in low-frequency electric fields.

Biological effects have been observed from weak, low-frequency magnetic fields. It has been suggested that the observed effects are due to the induced currents and electric fields. The behavior of cells exposed to an electric field is investigated in this paper. The induced transmembrane potential (TMP) is examined in geometrically complex models of various cell configurations. The TMP is evaluated using the finite element method (FEM), a numerical technique that is well suited to complicated geometries. Because displacement currents can be neglected at very low frequencies, a FEM solver that considers only material conductivity is used. Therefore, our results apply only well below the relaxation frequency. Chains and clusters of gap-connected cells of various sizes are modeled. The conductivity and size of the gap junctions in the cell configurations are also varied. The results for small configurations are compared to models of ellipsoidal cells with shapes similar to those of the configurations. FEM estimates of TMP's in long, cylindrical cell chains are compared to the predictions of the leaky cable model. The FEM approach confirms that gap-junction-connected cells can be treated as a single similarly shaped cell. Gaps influence the potential in the interior of cell configurations, and these effects increase with gap size and conductivity. For configurations to which approximations such as the leaky cable model do not apply, the FEM approach can be used to estimate the TMP, if the model is adapted to fit within computational memory limits.

Design and modeling of microwave photonic devices

Different types of finite element methods (FEMs) for microwave and optical waveguides are reviewed and are utilized for modeling of a traveling-wave (TW) optical modulator, as one of the typical microwave photonic devices. Using the quasi-TEM and the full-wave vector FEM solvers for microwave waveguides and the scalar FEM solver for optical waveguides, the behaviour of a TW Z-cut Ti:LiNbO3 Mach–Zehnder optical modulator with a ridge structure is investigated.

Two‐Dimensional Model for Water, Heat, and Solute Transport in Furrow‐Irrigated Soil: I. Theory

AbstractBecause of salinity, many areas with irrigated farmland have suffered from reduced food and fiber production, especially where irrigation water or soil contains large amounts of soluble salts. In those areas, ridge‐furrow tillage is a common practice and furrow irrigation is a popular irrigation method. Effects of water content, temperature, and solute concentration on transport phenomena in soil are hard to predict without complex models. The geometry of a ridgefurrow surface contributes to complexities in heat and vapor transport, and hence, in the distribution of water, temperature, and salt in soil. To improve understanding of water, heat, and solute transport in furrow‐irrigated and salt‐affected soil, we developed a two‐dimensional mechanistic model using the Galerkin finite element method (FEM). The model was designed to consider interactive effects of water content, temperature, and solute concentration on water, heat, and solute transport. To simulate field conditions, an energy balance equation was applied to the ridge‐furrow surface to provide boundary conditions for water and heat transport. To utilize a single FEM solver, equations governing transport of water, heat, and salt in soil were generalized as a diffusive‐convective type equation. Numerical schemes for the model were tested by comparing simulated results with analytical or semianalytical solutions. Good agreements between FEM and analytically calculated soil water content, temperature, and solute concentration were obtained.

Numerical investigations on two-dimensional canard-wing aerodynamic interference

A finite element method for solving of the Euler and Navier-Stokes equations is used to study the unsteady aerodynamics of a two-dimensional canard-wing aerodynamic interference. The method used a discontinuous finite element method for spatial discretization and an explicit Runge-Kutta time integration for temporal discretization. The problems of a flow over an airfoil with/without viscosity, a flow over a pitching airfoil, and an airfoil-vortex interaction are tested to show the accuracy of the proposed numerical method. Finally, the results of two-dimensional canard-wing aerodynamic interference in steady and unsteady transonic flows are shown to demonstrate the robustness of the numerical algorithm, and qualitative and quantitative aerodynamic influence of one airfoil on the other.