Finite Element And Boundary Element Method Research Articles

Investigation of Elastic Properties of WO3 Thin Films Supported on Quartz in Surface Acoustic Wave Sensing Devices

This study aims to discuss the combined theoretical and experimental results of elastic properties of tungsten trioxide films supported on Quartz (YX)/45°/10° resonator to form surface acoustic wave (SAW) devices. The SAW systems with different thicknesses of WO3 thin films were imaged and structurally characterized by X-ray diffraction, atomic force, and transmission electron microscopy. The deposited WO3 films (100, 200, and 300 nm of thickness) crystallized in a single monoclinic phase. The acoustoelectric properties of the SAW system were obtained by combining theoretical simulations with experimental measurements. The modeling of the SAW devices has been performed by the finite element and boundary element methods (FEM/BEM). The elastic constants of the films at room temperature were assessed via electrical admittances experiments in light of theoretical calculations. The gravimetric effect of the deposited layers is observed by a shift of the resonance frequency to lower values as the thickness of the films increases. Moreover, the acoustic losses are affected by the dielectric losses of the WO3 films while the resonant frequency decreases almost linearly. SAW devices revealed strong displacement fields with low acoustic losses as a function of WO3 thicknesses. For all the deposited layers, the measured Young’s moduli and Poisson’s ratios are 8 GPa and 0.5, respectively.

A two-and-half dimensional finite element/boundary element model for predicting the vibro-acoustic behaviour of panels with poro-elastic media

Solid panels with additional poro-elastic materials are widely used in engineering, mainly for sound insulation. In many cases, the panels are constructed in such a way that they can be idealised to be infinitely long and uniform in one direction, forming a so-called two-and-a-half dimensional (2.5D) structure. Although the 2.5D finite element and boundary element methods (FEM-BEM) are particularly suitable for predicting the vibro-acoustic behaviour of such structures, up to now the presence of poro-elastic media have not been adequately considered. In this paper a 2.5D FE-BE vibro-acoustic model is presented which accounts for solids, fluids and poro-elastic media. The poro-elastic media are modelled using the 2.5D FE approach based on the mixed displacement-pressure formulation of Biot's theory. The solids are also modelled using the 2.5D FE method but based on the linear theory of elasticity. The internal fluids are modelled using the 2.5D FE method as well. For a flat panel, the external fluid on both sides of the panel can be modelled using the 2.5D BE method based on the Rayleigh integral. The coupling between the various sub-models is derived in detail. The accuracy of the model is demonstrated by applying it to simple multi-layered structures for which solutions can be produced using other well-established methods. It is demonstrated that the elasticity of the solid frame of a porous medium has a great influence on the vibro-acoustics of a structure containing the porous material. The method is then applied to investigate the sound transmission loss (STL) of a typical railway vehicle floor structure. Results show that STL can be greatly improved by proper arrangement of porous material layers between the interior wooden floor and the outer extrusion; however, the load bearing supporting beams may significantly reduce the benefit of the porous material layers.

Study on prediction methods and characteristics of ship underwater radiated noise within full frequency

One trend in ship development is low noise characteristics. As one of the major noise sources of ship underwater radiated noise is the power equipment, it is critical to predict the ship underwater radiated noise caused by power equipment during the design phase. In this study, the incentive spectrums of power plants were obtained by testing on an oil tanker ship, and the hull vibration was calculated and measured in the middle and low frequency. The results show that the calculation model satisfies the accuracy requirement. To calculate the ship underwater radiated noise in the middle and low frequency, the finite element and boundary element method (FE-BEM), finite element and infinite element method (FE-IFEM), and finite element and automatic matching layer (FE-AML) were used, respectively. It is found that the FE-BEM is the preferred method for calculating ship underwater radiated noise in modeling scale and computational efficiency. The calculation of hull vibration and underwater radiated noise in the high frequency were performed by using the statistical energy analysis (SEA). Full frequency underwater radiated noise prediction of the oil tanker was completed. In the end, the far field of ship underwater sound radiation was studied. The far field can be determined when the sound radiation directivity of the ship no longer changes with distance.

이중저 형상 구조물의 음향방사효율과 수중방사소음 해석

Recently, reducing underwater radiated noise (URN) of ships has become an environmental issue to protect marine wildlife. URN of ships can be predicted by various methods considering its generating mechanism and frequency ranges. For URN prediction due to ship structural vibration in low frequency range, the fluid-structure interaction analysis technique based on finite element and boundary element methods (FE/BEM) is regarded as an useful technique. In this paper, URN due to a double bottom-shaped structure vibration has been numerically investigated based on a coupled method of FE/BEM to enhance the prediction accuracy of URN due to the vibration of real ship engine room structure. Acoustic radiation efficiency and URN transfer function in case of vertical harmonic excitation on the top plate of double bottom structure have been evaluated. Using the results, the validity of an existing empirical formula for acoustic radiation efficiency estimation and a simple URN transfer function, which are usually adopted for URN assessment in initial design stage, is discussed.

Large-Scale Magnetic Field Analysis of Laminated Core by Using the Hybrid Finite Element and Boundary Element Method Combined with the Fast Multipole Method

This paper shows a large-scale and highly accurate nonlinear magnetostatic field analysis of laminated iron core by using the hybrid finite element and boundary element (FE-BE) method. The hybrid FE-BE method is fairly effective to directly deal with the microstructure because no mesh division is required for the free space. In order to obtain the drastic reduction of the computational costs and stabilize the convergence characteristic of the Newton-Raphson method, the fast multipole method and the line search are introduced. Some numerical results that verify the effectiveness of the developed method are also presented

Large-scale analysis of eddy-current problems by the hybrid finite element-boundary element method combined with the fast multipole method

This paper shows large-scale eddy-current analysis by a hybrid finite-element and boundary-element (FE-BE) method. We introduce the fast multipole method (FMM) into the two kinds of hybrid FE-BE formulations developed by ourselves. To achieve more reduction of CPU time, we propose a novel preconditioning technique suitable for the hybrid FE-BE methods with the FMM. Furthermore, we improve the FMM calculation process in the hybrid method using magnetic field intensity. Some numerical results that demonstrate the effectiveness of these approaches are also presented

Phases of the SAW reflection and transmission coefficients for short reflectors on 128/spl deg/ LiNbO/sub 3/

We study numerically the phase of surface acoustic waves reflected by or transmitted through short reflectors comprising only 1-3 aluminium electrodes on 128 degree YX-cut lithium niobate (LiNbO3). The electrodes have a finite thickness, and they are either open-circuited or grounded. The center-to-center distance between adjacent electrodes d corresponds roughly either to half of the characteristic wavelength d proportional to lambda0/2 or to d proportional to lambda0, for the reflectors operating at the fundamental and second harmonic modes, respectively. We use software based on the finite-element and boundary-element methods (FEM/BEM) for numerical experiments with a tailored test structure having 3 interdigital transducers (IDTs), simulating experimental conditions with an incident wave and reflected and transmitted surface acoustic wave (SAW). Using artificial enhancement of time resolution in conjunction with the fast Fourier transform (FFT) and time-gating, calculation of the Y-parameters in a relatively wide frequency range allows us to determine the phase of the reflection and transmission coefficients.

Short reflectors operating at the fundamental and second harmonics on 128/spl deg/ LiNbO/sub 3/

In this work, we study numerically the operation of surface acoustic wave (SAW) reflectors comprising a small number of electrodes on the 128/spl deg/ YX-cut lithium niobate (LiNbO/sub 3/) substrate. The electrodes have a finite thickness, and they are either open circuited or grounded. The center-to-center distance between adjacent electrodes d corresponds roughly either to half of the characteristic wavelength d /spl prop/ /spl lambda//sub 0//2 or to d /spl prop/ /spl lambda//sub 0/, for the reflectors operating at the fundamental and second harmonic modes, respectively. We use software based on the finite-element and boundary-element methods (FEM/BEM) for numerical experiments with a tailored test structure having 3 interdigital transducers (IDTs), simulating experimental conditions with an incident wave and reflected and transmitted SAWs. Using the fast Fourier transform (FFT) and time-gating techniques, calculation of the Y-parameters in a wide frequency range with rather a small step allows us to determine the reflection coefficients, and to estimate the energy loss due to bulk-wave scattering. The detailed dependences of the attenuation and reflectivity on the metallization ratio and the electrode thickness are given for the classic 128/spl deg/-cut of LiNbO/sub 3/.

Short Reflectors Operating at the Fundamental and Second Harmonics on 128 degrees LiNbO3

In this work, we study numerically the operation of surface acoustic wave (SAW) reflectors comprising a small number of electrodes on the 128 degree YX-cut lithium niobate (LiNbO3) substrate. The electrodes have a finite thickness, and they are either open circuited or grounded. The center-to-center distance between adjacent electrodes d corresponds roughly either to half of the characteristic wavelength d proportional to lambda0/2 or to d proportional to lambda0, for the reflectors operating at the fundamental and second harmonic modes, respectively. We use software based on the finite-element and boundary-element methods (FEM/BEM) for numerical experiments with a tailored test structure having 3 interdigital transducers (IDTs), simulating experimental conditions with an incident wave and reflected and transmitted SAWs. Using the fast Fourier transform (FFT) and time-gating techniques, calculation of the Y-parameters in a wide frequency range with rather a small step allows us to determine the reflection coefficients, and to estimate the energy loss due to bulk-wave scattering. The detailed dependences of the attenuation and reflectivity on the metallization ratio and the electrode thickness are given for the classic 128 degree-cut of LiNbO3.

Single Crystal Growing Problem in the FZ Method under Microgravity : Three-dimensional Numerical Simulation with the Hybrid FEM-BEM applying LSM on the Free Surface

This paper presents the hybrid finite element and boundary element method (FEM-BEM) with a level set method (LSM) for the analysis of a free surface deformed in the alternating current magnetic field. Three-dimensional numerical simulations In the floating zone (FZ) method under microgravity are carried out to investigate the deformation process of a silicon liquid bridge with two types of coil positions, the upper case and the middle case. The results clearly show the deformation processes. The liquid parts which are the same position as each coil yield to pressure caused by strong Lorentz force and both ends swell out. This phenomenon conforms well to behavior of melt in the real growing process qualitatively.

Dynamic characteristics of synchronous motors applying a plural sub-magnets scheme to the rotor

This paper treats the optimization of rotor construction in the permanent magnet synchronous motor (PMSM). While the field system of PMSM has generally one magnet per pole, we replace the magnet with plural sub-magnets. The dimensions of each sub-magnet are determined by the concept of pulse width modulation (PWM). By adopting the proposed rotor construction, we can not only reduce the spare harmonics of the air-gap field but also provide space for damper winding around the direct-axis. From the investigation by hybrid FE-BE (coupled finite element and boundary element) method combined with both electric circuit and motion equation, we verify that the proposed construction is effective for practical use in view of both the harmonics reduction and the damping effects.

Rigorous analysis of coupling between laser and passive waveguide in multilayer slab waveguide

An approach that combines the finite-element and boundary-element methods (FEM/BEM) is extended to the analysis of arbitrarily shaped discontinuities in a multilayer slab waveguide. Here all the eigenmodes, namely, guided modes, substrate radiation modes, and substrate-cover radiation modes, are taken into account and are constructed by an extended matrix method. Computed results are given for the rigorous analysis of the coupling between a five-or six-layer laser and a four-layer passive waveguide in a monolithically integrated circuit. Some of the results are for multimode incidence. Since the coupling is one of the most important discontinuity problems in practice, this result confirms the usefulness of the approach.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Multi-scattering and boundary effects in soil-structure interaction

This paper presents two applications of a coupled finite element and boundary element method (FEBEM) to two-dimensional, transient problems of scattering of elastic SH waves. One application concerns multi-scattering: examples are shown for scattering from two semi-cylindrical inclusions embedded in a half-plane and separated by a small distance. Responses of one inclusion in the time and frequency domains are compared with those associated with a single inclusion. The other application concerns the effect of the size of the finite element mesh and boundary on accuracy. Response of the flat foundation with rectangular shape and seated on a half-plane is analyzed. It is shown that while simple silent boundaries are quite effective for large models, Rayleigh damping cannot model radiation damping effectively.