Defect identification in laminated composite structures by BEM from incomplete static data

BEM and penalty FEM models for viscous incompressible fluids

In a previous research project [SPR 2418; "Study of the performance of acoustic barriers for Indiana toll roads,"] the influence of environmental factors and of advanced sound barrier concepts was investigated. The presence of temperature gradients over pavements was found to have a strong influence on sound propagation. Refraction of sound waves emitted by tire-road interactions in the vicinity of the ground also affects sound barrier performance. Modified ray tracing model suggested that prevailing winds have an influence on barrier performance at large distances. Randomized edge configurations were found not to improve barrier performance for traffic noise. Random edges simply scatter sound energy without any net noise reduction. Although the edge can be optimized for specific frequency components and locations, it appears that optimization for broadband noise control is difficult. The study also suggested that adding sound absorptive material along the barrier edge could enhance barrier performance. The present study is the continuation of the latter effort to confirm the findings related to the sound absorptive treatment on the barrier through a more rigorous study and to apply the design concept to a realistic situation. A comparison was made between barriers that incorporated sound absorptive treatments and barriers with T-shaped tops. The results confirmed that a sound absorptive treatment near the barrier edge resulted in a performance improvement over corresponding rigid barriers. A design optimization study of the most effective shape of acoustic treatments concluded that a circular shape works best. The performance of two different acoustical materials was also compared. Use of glassfiber resulted in better performance in the high frequency region, while polyolefin foam with closed cells achieved a relatively large insertion loss at low frequencies. Efforts were made to develop a numerical predictive model. The boundary element method was used to model the infinite size surrounding fluid effectively. The disadvantage of the boundary element model is the calculation load associated with the large number of elements required for high frequency analysis. A mesh optimization procedure was successfully implemented in the boundary element model to reduce the calculation time while satisfying the tolerances for analysis accuracy at each analysis frequency. Octave band averaging was also adapted to facilitate the comparison between the numerical results and experimental data. It was found that the results from the boundary element model agree relatively well with the experimental results up to 6300 Hz at selected locations. The insertion loss distribution proved the

Recently, research on new mufflers equipped with connected curved tubes using phase cancellation techniques has been addressed in the industrial field. On the basis of the transfer matrix method and the stiffness matrix method, researchers have explored noise reduction effects within a constrained space. However, the attenuation bands are too narrow and the overall acoustical performance in dealing with broadband noise is thus insufficient. Therefore, in order to broaden the spectrum of the acoustical performance curves at various targeted tones (250, 500, and 900 Hz), a wool optimally lined within the ducts of HQ mufflers is proposed. In this paper, five kinds of HQ mufflers with rectangular sections (muffler A: a double-connected curved tube muffler; muffler B: a double-connected abrupt tube muffler; muffler C: a one-sided triple-connected curved tube muffler; muffler D: a two-sided tripleconnected curved tube muffler; muffler E: a one-sided triple-connected abrupt tube muffler) within a fixed length are assessed. In order to facilitate the assessment of optimal mufflers, a boundary element model (BEM) is adopted as the mathematical objective function. To assess the optimal mufflers, a genetic algorithm (GA) is linked with the BEM. Before the GA operation can be carried out, the accuracy of the mathematical models must be checked using the experimental data. Optimal results reveal that the maximum value of the sound transmission loss (STL) can be optimally improved at the targeted frequencies. Consequently, the optimum algorithm proposed in this study provides an efficient way to find a better silencer for industry.

In the past 20 years, the US Navy has used the physical scale modeling (PSM) technique to design effective cathodic protection (CP) systems for the ships underwater hull, nickel-aluminum-bronze props and other hull components.In more recent years, a number of computational techniques have been devised in an attempt to fulfill this purpose.Physical models have proven highly adept at ICCP design, since modeled information provides a direct relationship to the actual hull and can be scaled up directly because of confidence in the physically measured data.Boundary element (BE) models have been correspondingly devised that mimic actual hull design and even the PSM layout, but because the BE method is a computational methodology, the calculated data requires systematic validation with a physical analog to insure confidence in the control response.BE literature has discussed design issues regarding mesh layout, intrinsic geometric complexities, accuracy of material response input, the predictive engineering design capability for zonal response, and assessment of electric field response.It does not significantly discuss the accuracy of the BE model calculated work predictive design capability, without the need for "tweaking," and ultimately a rigorous validation of both the mesh and resultant system design technique.This paper presents validation requirements, for any BE model, that is inherently robust enough to be used for CP design and control, and a proposed four-point methodology that will allow for the comprehensive validation of the BE model to predict the ICCP control responses and system performance behavior.

This work investigates the behavior of CURVIC® [1] couplings through twoand three-dimensional boundary and finite element models. The CURVICs are used to couple multiple rotors in an aircraft engine compressor, and are subjected to rotational loading. The models generated include a geometrically complex three-dimensional linear elastic body with curved surfaces, and are analyzed with the BEASY® [2] boundary element and ANSYS® [3] finite element software packages. The following comparisons are made between BEASY and ANSYS: Three-dimensional modelling capabilities, the effort required to generate the models, the accuracy of results and the ability to adequately post-process the results into meaningful data.

Parameter identification for two-dimensional orthotropic material bodies by the boundary element method

Comparison of spherical and realistically shaped boundary element head models for transcranial magnetic stimulation navigation

Tunnels buried deep within the earth constitute an important class geomechanics problems. Two numerical techniques used for the analysis of geomechanics problems, the finite element method and the boundary element method, have complementary characteristics for applications to problems of this type. The usefulness of combining these two methods for use as a geomechanics analysis tool has been recognized for some time, and a number of coupling techniques have been proposed. However, not all of them lend themselves to efficient computational implementations for large-scale problems. This report examines a coupling technique that can form the basis for an efficient analysis tool for large scale geomechanics problems through the use of an iterative equation solver.

<p>Liquid motion in partially filled tanks may cause large structural loads if the period of tank motion is close to the natural period of fluid inside the tank. This phenomenon is called sloshing. Sloshing means any motion of a free liquid surface inside a container. The effect of severe sloshing motion on global seagoing vessels is an important factor in safety design of such containers. In order to examine the sloshing effects, a shake table experiments were conducted for different water fill depth of aspect ratio 0.163, 0.325 and 0.488. The parametric studies were carried out to show the liquid sloshing effects in terms of slosh frequencies, maximum free surface elevation and hydrodynamic forces acting on the tank wall. Sloshing oscillation for the excitation frequency f<sub>1</sub>, f<sub>2</sub>, f<sub>3</sub>, f<sub>4 </sub>and f<sub>5</sub> are observed and analysed. The excitation frequencies is varied between 0.4566 Hz to 1.9757 Hz and constant amplitudes of 7.5mm was adopted. The movement of fluid in a rectangular tank has been studied using experimental approach and different baffle configurations were adopted for analysing the sloshing oscillation, natural frequencies and variation in wave deflection. The adopted porosities in the present study is 15% – 25 %. Porous screen is placed inside the tank at L/2 location and study is extended for single porous screen for better wave energy absorption. Capacitance wave probes have been placed at tank ends to record the free surface water elevation. Load cells are used to measure the sloshing force inside the tank. Linear variable displacement transducers is used to measure the displacement of shake table. In the present study single porous screen under the action of wave were analysed to understand the wave control performance due to porosity parameters. A boundary element model is developed to calculate problems of wave interaction with a porous screen structure. The numerical results from the present boundary element methods (BEM) are compared with series of experiments conducted in a rectangular tank with various baffle porosities and submerged depths.</p><p> </p>

An operating propeller is the main source of vibration on the ship hull, especially on the stern. In this article, an improved numerical scheme is presented to predict the pressure fluctuations on the ship hull due to the unsteady sheet cavitation of a propeller. The calculated results are compared with the published results and experimental data carried out in the hydrodynamics and cavitation tunnel of Hamburgische Schiffbau-Versuchsanstalt to verify the improvement. The present method is based on a two-cycle iterating scheme which satisfies the boundary integral equation in time domain. The hull pressure fluctuations calculated by the first-cycle iterations are treated as the initial values for the second-cycle iterations. The solid angles of the elements will deviate from the standard value, .5, as the dramatic variation in geometry appears, and accumulate numerical errors in the calculating process. During the second-cycle iterations, a filter based on the solid angles on hull elements is proposed to minimize the iterating error. A container ship is treated as the computing sample in this study, and evidence is offered regarding the 16% improvement achieved by the present method. 1. Introduction A propeller operating in a nonuniform wake field in the ocean is one of the prime sources of vibration and noise affecting the ship. The prediction of hull pressure fluctuations caused by propellers is an important consideration for many vessels and worthy of being researched. Hull pressure fluctuation caused by the marine propeller has been widely investigated since the 1980s. Huse and Guoqiang (1982) developed a semi-empirical prediction method, in which the cavitation volume on the propeller blade surface can be estimated using experimental data. Breslin et al. (1982) proposed a model based on the potential flow theory, which simulates the ship hull by means of a simple panel method and the propeller by means of a lifting surface vortex lattice method. Kinns and Bloor (2004) used an acoustic boundary element (BE) model to simplify the problem of hull vibration excitation due to propeller sources and dipoles. The convergence of results for a cruise liner model was demonstrated with different element distributions. Kehr and Kao (2004) derived the incident blade rate pressure induced by unsteady sheet cavitation (monopole) and unsteady forces (dipole) of an operating propeller, for calculating the hull pressure fluctuations. Brouwer (2005) applied a stationary set of rings of monopole and dipole sources in the frequency domain to solve the propeller-induced noise and vibrations. Lee et al. (2006) integrated computational fluid dynamics (CFD) and the finite difference method for the computation of propeller-induced hull vibration. It was recommended that the phase difference of the propeller-induced pressure should be considered for preventing overprediction. Kao and Kehr (2006) developed a time domain iteration method to calculate the hull pressure fluctuations induced by the operating propeller. The phase difference is included in the iterating scheme, and the computation is robustly convergent. Seol and Moon (2009) derived the governing equation of pressure fluctuation induced by sheet cavitation according to the Ffowcs Williams approach. In the study by van Wijngaarden (2011), a potential flow boundary element method (BEM) with measured hull pressure data as input was applied to solve the hull pressure fluctuations, and the model experiments were also carried out. It was concluded that the computed hull pressure fluctuations due to non-cavitating propellers is reasonably accurate compared with the experimental data. Kehr and Kao (2011) calculated the pressure fluctuations on ship hull due to propeller sheet cavitation by using the method presented in Kao and Kehr (2006). The numerical result is higher than the experimental data provided by the hydrodynamics and cavitation tunnel (HYKAT) of HSVA (Wiemer 1999) by approximately 27%. The pressure fluctuations on ship stern induced by cavitating propellers were solved by Kanemaru and Ando (2011) with a surface panel method. The maximum amplitude appears in the first blade frequency and overestimates the experimental data by about 30%. Kim et al. (2012) predicted the hull pressure fluctuations induced by marine propeller sheet cavitation, and the Doppler effect was considered at the same time. Wei and Wang (2013) employed CFD to simulate the propulsion of a submarine. The finite element method and BEM were then combined to solve the submarine's structure and acoustic responses under the propeller excitations. The matched-field inversion technique applied in Lee et al. (2014) uses the fluctuating hull pressure field measured by receivers and the acoustic field calculated by BEM to define the sheet cavitation noise, source strengths, source positions, and number of sources. The equivalent source model for the propeller can result in more accurately extrapolated hull pressure distribution. In Wei et al. (2016), the unsteady forces of a submarine propeller were predicted by CFD, and the hull pressure fluctuations due to the non-cavitation propeller were calculated by the method proposed in Kao and Kehr (2006).

The driving force and mode mixity for cracks near interfaces was examined via experimental measurements of the crack tip displacement field with moire interferometry, verified using boundary element modeling, and further explored with finite element modeling. The stress intensity factor was obtained by a collocation method in which the Westergaard crack tip expansions are used for displacements [1]. The method of fundamental solutions was employed so that displacements across the material interface could be used [2]. Boundary element simulations provide verification of the method and allow a comparison with experiment. Systematic finite element simulations enable a study of how residual stresses may affect crack trajectories and driving forces.

Computer simulation has been widely used to predict the corrosion related electric and electromagnetic signatures of naval vessels. The modelling strategy has varied from simple dipole type models to detailed boundary element models of the vessel and its environment. For the dipole models users have had to choose the location and strength of the dipoles based upon experience, using range data or data from similar vessels. Whereas the boundary element model enables the user to define the actual geometry of the vessel, the electrochemical properties of the materials and the properties of the environment as data to the model and obtain predictions of the electric and magnetic signatures. This paper describes the simulation tools developed as part of the BEASY software to predict electric and magnetic signatures. Comparison is made between results of the boundary element detailed models and the dipole type models.

The interface boundary between two domains with different conductivity is to be determined from the impedance measured at the domain surface. This is an inverse problem. Two approaches, influence coefficient approach and boundary integral approach, using a boundary element model are presented. To examine the validity of the approaches, numerical experiments are carried out for a two‐dimensional field, and the suitability and limitation of the methods for application to impedance plethysmography are discussed.

A nonlinear elastic boundary element method (NBEM) approach is developed as an innovative deforming mesh generator for computational aeroelastic simulation. The computational fluid dynamics (CFD) mesh is assumed to be embedded in an infinite nonlinear elastic medium of a hardening material, leading to the formulation of a pseudononlinear elastostatic problem. Whereas the CFD surface mesh is treated as a boundary element model and the CFD flowfield grid as domain sample points, the NBEM approach solves Navier's equations using a particular solution scheme that removes the requirement of the domain integral in the conventional NBEM formulation. The NBEM approach has a unified feature that is applicable to all mesh systems, including unstructured, multiblock structured, and overset grids. An optimization strategy is employed to determine the optimum hardening material properties by minimizing the mesh distortion in the viscous region where grid orthogonality must be preserved. Three test cases are performed to demonstrate the robustness and effectiveness of the NBEM approach for deforming mesh generation.

A new variational boundary element model for potential problems