numerical investigation on the stability of singular driven cavity flow by applying the singularity subtraction technique to the unsteady driven cavity problem the stability of the impulsively started flow is investigated without smoothing the corner singularity a second order spectral projection method allows localization of the critical reynolds number for the first hopf bifurcation in the interval 8017 6 8018 8

calculation and experimental validation of induced currents on coupled wires in an arbitrary shaped cavity an efficient numerical technique is presented for the calculation of induced electric currents on coupled wires and multiconductor bundles placed in an arbitrary shaped cavity and excited by an external incident plane wave the method is based upon the finite difference time domain fd td formulation the concept of equivalent radius is used to replace wire bundles with single wires in the fd td model then the radius of the equivalent wire is accounted by a modified fd td time stepping expression based on a faraday s law contour path formulation for the looping magnetic fields adjacent to the wire fd td computed fields at a virtual surface fully enclosing the equivalent wire are then obtained permitting calculation of the currents on the wires of the original bundle using a standard electric field integral equation efie substantial analytical and experimental validations are reported for both time harmonic and broad band excitations of wires in free space and in a high q metal cavity

fdtd calculation of radiation patterns impedance and gain for a monopole antenna on a conducting box the ability of the finite difference time domain fdtd method to calculate radiation patterns input impedance and gain for a monopole antenna on a conducting box is demonstrated results are given for the bare box and with the box coated with a dielectric layer radiation patterns are compared with measurements and with the method of moments for the bare box radiation patterns for the dielectric covered box and all impedance and gain results are compared with measurements only good agreement is obtained in all cases the fdtd approach includes a dielectric covering quite easily while this would be quite difficult for a method of moments approach the fdtd method requires similar computer time as the method of moments for a single frequency result but produces wide bandwidth impedance and gain results with much less computer time

coupled simulation of transient heat flow and electric currents in thin wires application to bond wires in microelectronic chip packaging abstract this work addresses the simulation of heat flow and electric currents in thin wires an important application is the use of bond wires in microelectronic chip packaging the heat distribution is modeled by an electrothermal coupled problem which poses numerical challenges due to the presence of different geometric scales the necessity of very fine grids is relaxed by solving and embedding a 1d sub problem along the wire into the surrounding 3d geometry the arising singularities are described using de rham currents it is shown that the problem is related to fluid flow in porous 3d media with 1d fractures c d angelo siam journal of numerical analysis 50 1 pp 194 215 2012 a careful formulation of the 1d 3d coupling condition is essential to obtain a stable scheme that yields a physical solution elliptic model problems are used to investigate the numerical errors and the corresponding convergence rates additionally the transient electrothermal simulation of a simplified microelectronic chip package as used in industrial applications is presented

subcell modeling of frequency dependent thin layers in the fdtd method a subcell modeling technique for frequency dependent thin layers in finite difference time domain method is introduced the proposed method is based on the application of the integral form of the maxwell ampere equation and the solution of a set of auxiliary equations to advance the field components it has the ability to handle one or several frequency dependent thin layers embedded in a frequency dependent medium without solving high order differential equations to validate our proposed method we compare the obtained results with analytical solutions and with numerical references in both time domain and frequency domain

non linear theory for elastic beams and rods and its finite element representation abstract in terms of displacement components and angular coordinates expressions are given for large curvatures of elastic beams and rods the application of these expressions to bifurcation and stability problems is discussed on the basis of the principle of virtual work this approach is compared with the finite element representation given in a previous paper 1 an error in this previous paper is corrected further it is shown that the condition of zero extension of the axis in the case of the euler column requires a division into a rather large number of finite elements to ensure an accurate result for the stability coefficient the conditions of zero extension of the axis and zero curvature about one principal axis of the cross section in the case of the lateral buckling of the end loaded cantilever have similar consequences

fdtd local grid with material traverse often a finite difference time domain fdtd calculation requires a relatively higher mesh resolution in only small subvolumes of the total mesh space by locally applying finer grids local grids to these volumes the necessary resolution can be obtained computation time and memory requirements may be far less than for an fdtd space with the smaller mesh resolution throughout in many situations it is important that these local grids function when materials traverse the main grid local grid mg lg boundary surfaces since the volumes that require local grids may not be isolated in a homogeneous medium a local grid method which allows dielectric and or conducting materials to traverse the boundaries is developed three different fdtd problems that utilize the local grid method are used as validation tests results are compared with uniform mesh fdtd solutions

a novel 3 d cpfdtd scheme for modeling grid nonconformally aligned transmitter structures in this paper a novel three dimensional 3 d subcell algorithm for modeling metallic objects which are nonconformally oriented within the finite difference time domain fdtd grid is proposed the generally applicable algorithm is based on the contour path cp technique and enables in combination with an enhanced nonconformally aligned source model a more accurate spatial representation of antenna structures than the common staircase approach to evaluate the performance of the new algorithm the simulation results are compared with the classical staircase approach for dipole antennas as well as for a generic phone significant improvements were achieved for all antenna parameters from the near and far field i e feedpoint impedance radiation pattern and field distributions

closed form solutions for analysis of cylindrically conformal microstrip antennas with arbitrary radii an efficient and accurate closed form solution based on the spectral domain method of moments mom is presented to analyze the characteristics of cylindrically conformal microstrip antennas with arbitrary radii first an algorithm that combines the recursive and the uniform asymptotic expansion method in different regions is developed to calculate the spectral domain green s functions for arbitrary dielectric coated cylinders accurately next the integrands of the spectral integrals involved in mom equation are partitioned into two parts i e the fast oscillatory slowly convergent part and the well behaved part consequently all of the integrals in mom analysis can be categorized into two types through the sommerfeld identity and its extension these integrals are cast into closed forms by using the nonlinear approximation method generalized pencil of function method in this method any time consuming numerical integration procedure is eliminated which improves the computational efficiency drastically compared with the results from published references the validity and accuracy of the method are demonstrated

numerical methods for the stokes and navier stokes equations driven by threshold slip boundary conditions abstract in this article we discuss the numerical solution of the stokes and navier stokes equations completed by nonlinear slip boundary conditions of friction type in two and three dimensions to solve the stokes system we first reduce the related variational inequality into a saddle point point problem for a well chosen augmented lagrangian to solve this saddle point problem we suggest an alternating direction method of multiplier together with finite element approximations the solution of the navier stokes system combines finite element approximations time discretization by operator splitting and augmented lagrangian method numerical experiment results for two and three dimensional flow confirm the interest of these approaches

fdtd model of electrically thick frequency dispersive coatings on metals and semiconductors based on surface impedance boundary conditions a new finite difference time domain fdtd model for conductors coated with electrically thick frequency dispersive coatings is developed the model is based on first order impedance boundary conditions as the most important original feature of the model the frequency dependence of the material parameters of the coating is very general dispersive coatings of lorentz debye or drude type with multiple pole pairs and a fixed electrical conductivity can be modeled with the proposed technique another new property of the model is the use of rational approximation in a way that enables accurate approximation of the impedance function in a wide range corresponding to several thickness resonances of the coating the conductor losses in the metal backing that are neglected in many earlier models are accounted for in the proposed model the model is formulated for planar interfaces in the general three dimensional situation for the yee algorithm and verified against analytical reference results with numerical examples in one dimensional and two dimensional problems

a parallel finite volume runge kutta algorithm for electromagnetic scattering a 3d explicit finite volume algorithm has been developed to simulate scattering from complex geometries on parallel computers using structured body conformal curvilinear grids most simulations for practical 3d geometries require a large number of grid points for adequate spatial resolution making them suitable to parallel computation the simulations have been carried out using a multi block zonal approach in the message passing paradigm on the sp 2 each zone is placed on a separate processor and inter processor communication is carried out using the message passing library interface mpl mpi integration of maxwell s equations is performed using the four stage runge kutta time integration method on a dual grid this method of integrating on a staggered grid gives enhanced dissipative and dispersive characteristics a scattered field formulation has been used and the liao boundary condition is used at the outer nonreflecting boundary the far zone transformation has also been implemented efficiently using specialized mpl functions to evaluate the far zone scattering results results show extremely good comparisons for scattering from the sphere and the ogive with the exact solution and standard fdtd type algorithms comparisons for nonaxisymmetric targets like the nasa almond with experimental data has also been found to be extremely good

a finite difference time domain near zone to far zone transformation electromagnetic scattering an efficient time domain near zone to far zone transformation for fdtd finite difference time domain computations is presented the approach is to keep a running accumulation of the far zone time domain vector potentials due to the tangential electric and magnetic fields on a closed surface surrounding the scatterer at each time step at the end of the computation these vector potentials are converted to time domain far zone fields many far zone bistatic directions can be included efficiently during one fdtd computational run frequency domain results can be obtained via fast fourier transform wideband results for scattering from a perfectly conducting plate were obtained from a single fdtd computation transformed to the frequency domain and compared with moment method results this approach is significantly more efficient than computing many fdtd results using sinusoidally varying excitation if a wide frequency band is of interest coupled with recent advances in computing fdtd results for frequency dependent materials wideband results for far zone scattering from targets including frequency dependent materials can be obtained efficiently

an equivalent feed model for the fdtd analysis of antennas driven through a ground plane by coaxial lines for the finite difference time domain fdtd analysis of antennas excited by coaxial lines an equivalent model of the antenna feed is presented here under the quasi static approximation the coaxial aperture is simply represented as the equivalent magnetic frill current and the equivalent load circuit including the effects of the coaxial line it leads us to a simple modification of the standard fdtd update equation at the aperture without any additional cell modeling of the line the validity of the proposed model is confirmed by comparing of the fdtd results and the measured data

finite difference time domain modeling of curved surfaces em scattering the finite difference time domain fdtd method is generalized to include the accurate modeling of curved surfaces this generalization the contour path cp method accurately models the illumination of bodies with curved surfaces yet retains the ability to model corners and edges cp modeling of two dimensional electromagnetic wave scattering from objects of various shapes and compositions is presented

high re solutions for incompressible flow using the navier stokes equations and a multigrid method the vorticity stream function formulation of the two dimensional incompressible navierstokes equations is used to study the effectiveness of the coupled strongly implicit multigrid csi mg method in the determination of high re fine mesh flow solutions the driven flow in a square cavity is used as the model problem solutions are obtained for configurations with reynolds number as high as 10 000 and meshes consisting of as many as 257 x 257 points for re 1000 the 129 x 129 grid solution required 1 5 minutes of cpu time on the amdahl 470 v 6 computer because of the appearance of one or more secondary vortices in the flow field uniform mesh refinement was preferred to the use of one dimensional gridclustering coordinate transformations the past decade has witnessed a great deal of progress in the area of computational fluid dynamics developments in computer technology hardware as well as in advanced numerical algorithms have enabled attempts to be made towards analysis and numerical solution of highly complex flow problems for some of these applications the use of simple iterative techniques to solve the navier stokes equations leads to a rather slow convergence rate for the solutions the solution convergence rate can be seriously affected if the coupling among the various governing differential equations is not properly honored either in the interior of the solution domain or at its boundaries the rate of convergence is also generally strongly dependent on such problem parameters as the reynolds number the mesh size and the total number of computational points this has led several researchers to examine carefully the recently emerging multigrid mg technique as a useful means for enhancing the convergence rate of iterative numerical methods for solving discretized equations at a number of computational grid points so large as to be considered impractical previously

driven cavity flows by efficient numerical techniques abstract efficient and reliable numerical techniques of high order accuracy are presented for solving problems of steady viscous incompressible flow in the plane and are used to obtain accurate solutions for the driven cavity a solution is obtained at reynolds number 10 000 on a 180 180 grid the numerical methods combine an efficient linear system solver an adaptive newton like method for nonlinear systems and a continuation procedure for following a branch of solutions over a range of reynolds numbers

a differentially interpolated direct forcing immersed boundary method for predicting incompressible navier stokes equations in time varying complex geometries a dispersion relation preserving dual compact scheme developed in cartesian grids is applied together with the immersed boundary method to solve the flow equations in irregular and time varying domains the artificial momentum forcing term applied at certain points in cells containing fluid and solid allows an imposition of velocity condition to account for the motion of solid body we develop in this study a differential based interpolation scheme which can be easily extended to three dimensional simulation the results simulated from the proposed immersed boundary method agree well with other numerical and experimental results for the chosen benchmark problems the accuracy and fidelity of the ib flow solver developed to predict flows with irregular boundaries are therefore demonstrated

the treatment of thin wires in the fdtd method using a weighted residuals approach in this contribution the problem of accurately representing thin wires within the finite difference time domain fdtd mesh is addressed by means of a method based on the weighted residual wr interpretation of the fdtd algorithm results for wire dipoles and wire transmission lines obtained using the proposed method are presented and compared to those obtained using existing techniques it is shown that the proposed method yields results which are more accurate and are less dependent on the choice of cell size than other approaches and in addition lends itself well to being extended for more complicated structures details of the calculation of the update equations are given

finite element approximation of the nonstationary navier stokes problem i regularity of solutions and second order error estimates for spatial discretization this is the first part of a work dealing with the rigorous error analysis of finite element solutions of the nonstationary navier stokes equations second order error estimates are proven for spatial discretization using conforming or nonconforming elements the results indicate a fluid like behavior of the approximations even in the case of large data so long as the solution remains regular the analysis is based on sharp a priori estimates for the solution particularly reflecting its behavior as t to 0 and as t to infty it is shown that the regularity customarily assumed in the error analysis for corresponding parabolic problems cannot be realistically assumed in the case of the navier stokes equations as it depends on nonlocal compatibility conditions for the data the results which are presented here are independent of such compatibility conditions which cannot be verified in practice

finite difference time domain calculation of transients in antennas with nonlinear loads transient currents for an antenna with a nonlinear load are calculated using finite difference time domain fdtd methods the fdtd electric field across the nonlinear load which determines the voltage across the load is calculated by solving a nonlinear equation at each time step this allows the time step to be at the courant limit and is more efficient than reducing the time step size in all the fdtd cells to maintain stability in just the cell containing the nonlinear load the stability of this approach relative to a simpler approach of approximating the diode as a variable resistor is demonstrated as a validation of the method the transient current in a long dipole antenna with a nonlinear load excited by a pulsed plane wave is computed and compared with calculated results obtained by another method the approach given here extends the applicability of the fdtd method to problems involving radiation and scattering from antennas including nonlinear loads

time domain extrapolation to the far field based on fdtd calculations a scheme to extrapolate scattered fields calculated by the finite difference time domain fdtd method to the far zone is developed it could replace the usual extrapolation scheme for a single frequency in that it yields a spectrum with only one incident pulse the method comprises the following steps 1 using an incident pulse 2 performing an fdtd calculation and using the currently calculated data on s to extrapolate to the far field and 3 fourier transforming the far field time response to obtain the frequency domain response the approach seems to be more convenient in time domain calculations and more in agreement with the spirit of fdtd

asymptotic and numerical analysis for holland and simpson s thin wire formalism in the context of simulation of electromagnetic propagation the thin wire formalism of holland and simpson allows one to deal with scattering by perfectly conducting thin wires by coupling a standard fdtd method with a discrete 1d wave equation ruling the current inside the wires this method can be very accurate but it involves a fitting parameter that requires careful calibration we propose a consistency analysis and derive a formula for the calibration of this parameter in the case of a simplified 2d analogue of the method of holland and simpson our proof relies on the observation that this method is actually a hidden version of the singular function method well known in the context of elliptic equations in domains with a singular boundary

an improved thin wire representation for fdtd computations we have shown that finite difference time domain fdtd electromagnetic computations for a conductor system having a radius smaller than 0 15deltar or larger than 0 65 deltar deltar is the lateral side length of cells employed modeled using arbitrary radius wire representations proposed so far with a time increment determined from the upper limit of courant s stability condition result in numerical instability a primary factor causing this numerical instability is that the speed of waves propagating in the radial direction from the wire in the immediate vicinity of the wire exceeds the speed of light and therefore courant s condition is not satisfied there it is further shown that for these cases the arbitrary radius wire representation can be improved by modifying the material parameters for the axial field components closest to the wire as well as those for the radial electric and circulating magnetic field components the improved wire representation is effective in representing a wire whose radius ranges from 0 0001deltar to 0 9deltar

full wave analysis and wide band design of probe fed multilayered cylindrical rectangular microstrip antennas the input impedance and radiation pattern of the probe fed multilayered cylindrical rectangular microstrip antennas pmcmsa are analyzed by using a novel approach which combines the conformal finite difference time domain fdtd and gedney s unsplit version of the perfectly matched layer absorbing boundary condition method and the green s functions in cylindrically stratified media the near fields of such antennas and the current distributions on the patches are obtained by the conformal fdtd method numerically and then the modified spectral domain green s functions in arbitrary cylindrically stratified media are used to determine the radiation pattern the effect of the small radius of the probe on the performance of antennas is investigated through the thin wire algorithm in cylindrical coordinates a simple design scheme of the probe fed cylindrically stacked antennas is also proposed for increasing the impedance bandwidth

fdtd modeling of arrays and grids of lossy conductors based on impedance sheet conditions fast finite difference time domain fdtd modeling techniques for arrays of parallel wires and wire meshes are developed the analytical basis of the models lies in the use of impedance sheet conditions kontorovich conditions for dense wire arrays and grids connecting the tangential electric fields and the averaged currents in the plane of a wire array or grid the proposed methods allow us to avoid the direct discretization of the fields inside the wires greatly simplifying the modeling task the conductor losses in the wires are accounted for assuming a strong or weak skin effect the impedance sheet conditions are formulated in the time domain using the convolution integral which is evaluated recursively in fdtd numerical examples and comparisons with analytical results are provided to verify the proposed techniques

direct determination of periodic solutions of the dynamical equations of flexible mechanisms and manipulators a method based on finite elements characterized by generalized strains as functions of the nodal co ordinates is the basis for the computer program spacar for the kinematic and dynamic analysis of flexible multibody systems this program allows also the evaluation of the linearized dynamical equations which makes possible the implementation of a method for the direct determination of stationary and periodic solutions and of a continuation method for these solutions if some parameter is varied as an illustration these methods are applied to a duffing equation a double pendulum and a slider crank mechanism with an elastic connecting rod

stable loosely coupled type algorithm for fluid structure interaction in blood flow we introduce a novel loosely coupled type algorithm for fluid structure interaction between blood flow and thin vascular walls this algorithm successfully deals with the difficulties associated with the added mass effect which is known to be the cause of numerical instabilities in fluid structure interaction problems involving fluid and structure of comparable densities our algorithm is based on a time discretization via operator splitting which is applied in a novel way to separate the fluid sub problem from the structure elastodynamics sub problem in contrast with traditional loosely coupled schemes no iterations are necessary between the fluid and structure sub problems this is due to the fact that our novel splitting strategy uses the added mass effect to stabilize rather than to destabilize the numerical algorithm this stabilizing effect is obtained by employing the kinematic lateral boundary condition to establish a tight link between the velocities of the fluid and of the structure in each sub problem the stability of the scheme is discussed on a simplified benchmark problem and we use energy arguments to show that the proposed scheme is unconditionally stable due to the crucial role played by the kinematic lateral boundary condition the proposed algorithm is named the kinematically coupled scheme

a least squares finite element method for the numerical solution of the navier stokes cahn hilliard system modeling the motion of the contact line in this article we discuss the numerical solution of the navier stokes cahn hilliard system modeling the motion of the contact line separating two immiscible incompressible viscous fluids near a solid wall the method we employ combines a finite element space approximation with a time discretization by operator splitting to solve the cahn hilliard part of the problem we use a least squares conjugate gradient method we also show that the scheme has the total energy decaying in time property under certain conditions our numerical experiments indicate that the method discussed here is accurate stable and efficient

generation of fdtd subcell equations by means of reduced order modeling adapted finite difference time domain fdtd update equations exist for a number of objects that are smaller than the grid step such as wires and thin slots we provide a technique that automatically generates new fdtd update equations for small objects our presentation focusses on 2d fdtd we start from the fdtd equations in a fine grid where the time derivative is not discretised this yields a large state space model that is drastically reduced with a reduced order modeling technique the reduced state space model is then translated into new fdtd update equations that can be used in an fdtd simulation in the same way as the existing update equations for wires and thin slots this technique is applied to a number of numerical problems showing the accuracy and versatility of the proposed method

a hybrid moment method finite difference time domain approach to electromagnetic coupling and aperture penetration into complex geometries an approach is presented for the direct modeling of electromagnetic penetration problems which involves a hybrid technique combining the frequency domain method of moments mm and the finite difference time domain fd td method the hybriding is based upon a novel use of a field equivalence theorem due to schelkunoff which permits a field penetration problem to be analyzed in steps by treating the relatively simple external region and the relatively complex internal region separately the method involves first determination of an equivalent short circuit current excitation in the aperture regions of the structure using mm for a given external illumination this equivalent current excitation over the aperture is next used to excite the complex loaded interior region and the penetrating fields and induced currents are computed by the fd td method a significant advantage of this frequency domain time domain hybriding is that no green s function need be calculated for the interior region this hybrid approach takes advantage of the ability of mm to solve exterior problems using patch models and also takes advantage of the ability of fd td to model in great detail localized space regions containing metal structures dielectrics permeable media anisotropic or nonlinear media as well as wires

an efficient surface impedance boundary condition for thin wires of finite conductivity to include dispersive loss into a sub cell thin wire model a new implementation of a surface impedance boundary condition sibc is proposed the surface impedance function is approximated in the frequency domain by a series of first order rational functions allowing straightforward transform into time domain the contribution of the wire radius is included in the surface impedance function extending the model to very thin or poorly conducting metal wires further the sibc includes the direct current dc resistance the approximation for the sibc is chosen such that the dependence on the wire radius and conductivity can be removed prior to the computation of the approximation coefficients consequently the wire radius and conductivity can be varied without re computing the coefficients the proposed model is compared with an existing sibc wire model based on the high frequency approximation and prony s method nec 2 generated reference data and analytical results the results indicate enhanced accuracy at a reduced computational cost as compared with an existing model

new oblique thin wire formalism in the fdtd method with multiwire junctions a new oblique thin wire formalism based on holland s approach is proposed in the fdtd method the principal achievement of this new formalism is to enable us to model a junction correctly between several oblique wires to this end an important criterion is proposed the continuity of the current traces in the grid must be maintained at each node of the yee cell that contains a part of one or several wires this condition prevents undamped parasite oscillations on the wire current responses in addition our approach offers versatility in its usage first the extremities of the wire can be placed freely in a yee cell second it operates in lossy medium and finally the sensitivity of the wire is minimized when inclined or shifted with regards to this last point the in cell inductance of a wire segment is formulated to take account of the segment position and its obliquity in the yee cell

a fictitious domain method for conformal modeling of the perfect electric conductors in the fdtd method we present a fictitious domain method to avoid the staircase approximation in the study of perfect electric conductors pec in the finite difference time domain fdtd method the idea is to extend the electromagnetic field inside the pec and to introduce a new unknown the surface electric current density to ensure the vanishing of the tangential components of the electric field on the boundary of the pec this requires the use of two independent meshes a regular three dimensional 3 d cubic lattice for the electromagnetic field and a triangular surface patching for the surface electric current density the intersection of these two meshes gives a simple coupling law between the electric field and the surface electric current density an interesting property of this method is that it provides the surface electric current density at each time step furthermore this method looks like fdtd with a special model for the pec numerical results for several objects are presented

an rwg basis function based near to far field transformation for 2 d triangular grid finite difference time domain method a near to far field transformation ntft based on the rao wilton glisson rwg basis function is proposed for a 2 d triangular grid fdtd method the surface equivalence theorem is applied and the equivalent current density j sub z in the tm sub z case or m sub z in the te sub z case on the radiation contour is interpolated by using rwg basis functions the interpolation is valid for the ntft in either the time or frequency domain formulations for the interpolation scheme and the ntft are presented for the tm sub z case the scattering by an infinite dielectric circular cylinder due to an electric line source is simulated by using the triangular grid fdtd as well as the proposed ntft numerical results in both the time domain and frequency domain are demonstrated and verified by comparison with analytical solutions

objectivity tests for navier stokes simulations the revealing of non physical solutions produced by laplace formulations abstract laplace formulations are weak formulations of the navier stokes equations commonly used in computational fluid dynamics in these schemes the viscous terms are given as a function of the laplace diffusion operator only despite their popularity recently it has been proven that they violate a fundamental principle of continuum mechanics the principle of objectivity it is remarkable that such flaw has not being noticed before neither detected in numerical experiments in this work a series of objectivity tests have been designed with the purpose of revealing such problem in real numerical experiments through the tests it is shown how for slip boundaries or free surfaces laplace formulations generate non physical solutions which widely depart from the real fluid dynamics these tests can be easily reproduced not requiring complex simulation tools furthermore they can be used as benchmarks to check consistency of developed or commercial software the article is closed with a discussion of the mathematical aspects involved including the issues of boundary conditions and objectivity

cartesian shift thin wire formalism in the fdtd method with multiwire junctions the holland and simpson thin wire formalism is a versatile technique to deal with wires in the fdtd method this paper develops an approach to correctly perform a junction between several wires at any yee s cell location the application context is the wires parallel to cartesian axes with any translation in the yee s cell the sensitivity of the thin wire current to cartesian shift is also minimized in our enhanced formalism the method is presented in a general framework with non uniform fdtd spatial steps beside the wire segment length can be different of the fdtd spatial steps and also the wire position does not need to coincide with any edge or node of the yee s cell

wall driven incompressible viscous flow in a two dimensional semi circular cavity the main goal of this article is to investigate the capability of an operator splitting finite elements based methodology at handling accurately incompressible viscous flow at large reynolds number re in regions with corners and curved boundaries to achieve this goal the authors have selected a wall driven flow in a semi circular cavity on the basis of the numerical experiments reported in this article it seems that the method under investigation has no difficulty at capturing the formation of primary secondary and tertiary vortices as re increases it has also the capability of identifying a hopf bifurcation phenomenon taking place around re 6600

fdtd calculation of wide band antenna gain and efficiency absolute gain and radiation efficiency are calculated using the finite difference time domain fdtd method the method described utilizes pulsed excitation so that wideband results are available from a single fdtd computation the approach is demonstrated for a simple wire antenna geometry and is validated by comparison with results obtained using the method of moments

green s functions for probe fed arbitrary shaped cylindrical microstrip antennas the efficiency of a method of moments procedure for microstrip antennas is strongly dependent on the convergence of the inverse fourier transformation ift from the spectral to the spatial domain this is especially true when considering cylindrical microstrip antennas cmas in the cylindrical case the calculation of the two dimensional green s functions stays inherently time consuming in the planar case green s function can be reduced to a one dimensional function the problem however becomes a real bottle neck when probe feeding of a cma is considered as the traditional ift used to calculate the excitation in the spatial domain results in a huge ift time in this paper this problem is explicitly treated the asymptotical behavior of the probe related spectral green s functions gfs is rigorously derived subtracted and the corresponding reaction integrals are inverse fourier transformed without the occurrence of any cylindrical functions this results in a much improved calculation efficiency for this type of feeding evident for both thin and thick substrates numerical results for cmas with complex shaped patches are presented applicable to both smaller and larger bandwidths several structures are fabricated and measurements are in good agreement with simulations

linearization of dynamic equations of flexible mechanisms a finite element approach a finite element based method is presented for evaluation of linearized dynamic equations of flexible mechanisms about a nominal trajectory the coefficient matrices of the linearized equations of motion are evaluated as explicit analytical expressions involving mixed sets of generalized co ordinates of the mechanism with rigid links and deformation mode co ordinates that characterize deformation of flexible link elements this task is accomplished by employing the general framework of the geometric transfer function formalism the proposed method is general in nature and can be applied to spatial mechanisms and manipulators having revolute and prismatic joints the method also permits investigation of the dynamics of flexible rotors and spinning shafts application of the theory is illustrated through a detailed model development of a four bar mechanism and the analysis of bending vibrations of two single link mechanisms in which the link is considered as a rotating flexible arm or as an unsymmetrical rotating shaft respectively the algorithm for the calculation of the matrix coefficients is directly emenable to numerical computation and has been incorporated into the linearization module of the computer program spacar

finite element approximation of the nonstationary navier stokes problem part ii stability of solutions and error estimates uniform in time in this paper assumptions about the stability of a solution are introduced in the numerical analysis of the nonstationary navier stokes problem for the purpose of extending local a priori error estimates and local a posteriori error estimates globally in time