Finite Boundary Element Research Articles

A Stable FEM-BEM Hybrid Method for the Numerical Simulation of Magnetomechanical Coupled Problem With Both Inductive and Conductive Current Excitations Aiming to Application to Tokamak In-Vessel Structures

The in-vessel structures of tokamak devices sustain large electromagnetic force due to both induced eddy current and halo current. The coupling effect between the electromagnetic field and the mechanical vibration of the structures has a significant influence on the structural dynamic response. To assess the coupled mechanical behavior of in-vessel structures, a numerical method was proposed in this article based on the hybrid finite-element method and boundary-element method. The plasma current and halo current were modeled as a series of current filaments and a pair of current source–sink, respectively. To deal with the nonlinearity due to the coupling term of the magnetic flux density and the velocity, the block Gauss–Seidel iterative algorithm was adopted in the numerical method. The proposed numerical method was first validated against the experimental data of the TEAM 16 benchmark problem and then applied to the dynamic analysis of a simplified halo current problem of typical tokamak structures. The numerical method was proved both effective and numerically stable for the analysis of magnetomechanical coupled problem based on the reasonable simulation results.

Prediction of fracture toughness and crack propagation of graphene via coupling of boundary element and nonlinear beam element

A new approach of multi-scale simulation via coupling of boundary element and finite element is proposed to predict fracture toughness and crack propagation of a single layer graphene sheet. In this simulation a molecular dynamics-based nonlinear beam element is developed for the atomistic model near the crack tip, whereas a special two-dimensional boundary element is employed for the continuum model in the remaining field of the cracked specimen. The material and section properties required in the nonlinear beam element are estimated through the equivalence between the potential energy of molecular dynamics and the elastic strain energy of continuum mechanics. With the estimated properties of beam element, the material properties of boundary element are further estimated by applying loads on the specimen of graphene, which is formed by a hexagonal lattice of carbon atoms. Coupling the nonlinear beam elements by boundary elements with the local-global concept of multi-scale modeling, a vast of computational time can be saved. The accuracy of near tip stresses obtained in our simulation remedies the inaccuracy of linear elastic fracture mechanics, and can be used for the prediction of atomic bond-breaking, which leads to crack propagation. The associated critical load can then be applied in the continuum model for the cracked specimen to predict mode I and mode II fracture toughness of graphene. The obtained values are then verified by the published results measured or predicted by the other methods. By varying the size of cracks and orientation of applied loads, several interesting phenomena have been observed and discussed in this paper.

Pile induced filtering of seismic ground motion in homogeneous soil

The foundation input motion (FIM) that a structure experiences during an earthquake, is known to be different from the free field ground motion due to soil structure interaction (SSI) effects. Kinematic interaction in a single pile can also introduce a rotational component to the FIM. Conventionally, soil structure interaction is performed by applying the free field ground motion to the structure ignoring the effects of kinematic interaction. Deep foundation elements such as piles are known to suppress certain frequencies of ground motion which in turn induces kinematic bending moments in them. In this study, kinematic soil pile interaction is simulated using 3D numerical models using a coupled finite element-boundary element method. Single pile, group pile and piled raft models in a homogeneous soil profile are analysed for vertically propagating shear waves. Three earthquake time histories with varying frequency content are considered in this study. Transfer functions are then plotted together to analyse the effects of pile induced filtering of ground motion. The ratio of response spectrum at the foundation level and free field ground, for the pile group considered, is found to closely follow the behaviour of a fixed headed single pile. It is found that embedment of the pile cap, as in the case of a piled raft can result in further filtering of ground motion.

A methodology based on 2.5D FEM-BEM for the evaluation of the vibration energy flow radiated by underground railway infrastructures

In this paper, a comprehensive numerical approach for modelling track/tunnel/soil systems in the context of ground-borne railway-induced vibration problems considering a full-space model of the soil is proposed. All the approach is formulated in the wavenumber-frequency domain and it consists of a coupled finite element–boundary element model of the tunnel/soil system, a semi-analytical model of the track, a multibody model for the vehicle and a model for the vibration propagation in the soil based on semi-analytical solutions of a cylindrical cavity in a full-space. This comprehensive approach has been developed with the aim of computing the vibration energy flow radiated upwards by underground railway tunnels. An axisymmetric formulation to deal with circular underground railway tunnels is included in the approach in order to improve the computational speed of the methodology. This formulation can also be used for other types of railway tunnels if a circular boundary of the boundary element mesh is considered. Since this methodology uses finite elements to model the tunnel structure, its modelling detail is higher than the previously developed methodologies dedicated to compute the vibration energy flow radiated by underground railway infrastructures, since they are based on semi-analytical modelling of the tunnel structure. The present methodology has been specifically designed to be used in general assessment studies about ground-borne underground railway-induced vibrations where decisions on the type of track and/or the application of mitigation measures at the source, as soft rail-pads, under-ballast or under-slab mats, have to be made. Moreover, this methodology can be used for the study of the vibration radiation patterns of railway tunnels.

An isogeometric FE-BE method and experimental investigation for the hydroelastic analysis of a horizontal circular cylindrical shell partially filled with fluid

Abstract In this study, the dynamic characteristics (i.e. natural frequencies and associated mode shapes) of a partially filled horizontal cylindrical shell are investigated experimentally and by an isogeometric finite element-boundary element method. The proposed numerical procedure is divided into two parts. In the first part, the dynamic characteristics of the cylindrical shell under in-vacuo conditions are obtained by the isogeometric finite element method (IGAFEM) based on a linear Kirchhoff-Love shell formulation. In the second part, the fluid-structure interaction effects are calculated in terms of generalized added mass coefficients by using the isogeometric boundary element method (IGABEM), assuming that the structure vibrates in its in-vacuo principle mode shapes. By adopting the linear hydroelasticity theory, it is assumed that the fluid flow is ideal, i.e., an incompressible flow and inviscid fluid. In order to show the versatility of the numerical method, the results are compared with those obtained by the conducted experiments. Relevant numerical challenges in the hydroelastic vibration analysis are highlighted and it is shown that the numerical predictions and experimental results are in good agreement.

Scattering by cracks in a conducting surface

PurposeThe purpose of this study is the formulation of an efficient method to compute and analyse the scattering characteristics of cracks or grooves in a conducting object, where the size of the crack is significantly larger than the wavelength of an incident plane wave.Design/methodology/approachA hybrid finite element-boundary element procedure is formulated for the computation of the scattering properties of the object, where the fast multipole method is used in the boundary integral formulation. The basic fast multipole procedure is enhanced by utilising a fast Fourier transform-based convolution algorithm for the computation of the interactions between groups of source and field elements.FindingsThe algorithm accelerates the evaluation of the group interactions and enables the reduction of the memory requirements without introducing an additional approximation into the procedure.Originality/valueThe fast multipole method with convolution algorithm shows to be more efficient for the computation of scattering problems with a large number of unknowns than the conventional procedure.

Analysis of water coolant pressure fluctuation induced by piston slap

Liner cavitation is caused by water pressure fluctuation in water coolant passage. When the negative pressure falls below the saturated vapor pressure, the impulsive pressure following the implosion of cavitation bubbles causes cavitation erosion on wet cylinder liner surface. Prediction of coolant pressure fluctuation is crucial to relieve liner cavitation erosion. Vibration of internal combustion engine especially liner vibration is thought of as the primary cause of liner cavitation. Piston slap is deemed as the major factor of engine vibration. The present work establishes a coupled system between entire engine structure and water coolant passage acoustic field considering their vibration characteristics by finite element method and boundary element method. Mechanism of piston slap is proposed and the resulting slap forces are applied on cylinder to predict water coolant pressure fluctuation. The influence of sound speed variation of acoustic field on pressure fluctuation is discussed. The contributions of natural modes of engine and water acoustic field to largest negative pressure are analyzed.

Noise Prediction of Traction Gear of High-Speed EMU Base on Acoustic-Structural Coupled Method

The dynamic characteristics of traction gear transmission system have great influence on the safety, comfort and reliability of EMU. Base on acoustic-structural coupled theory, the noise radiation characteristics of gear transmission system in high-speed train CRH380A are studied by finite element-boundary element method. The acoustic radiation analysis model is built by using acoustic BEM. The radiated noise is predicted by Helmholtz boundary integral equation. The research results can provide a theoretical basis for the optimization design of the low noise gear in EMU.

Convection heat transfer in a porous medium saturated with an Oldroyd B fluid - A Review

In this review paper, the important milestones in model studies such as Darcy and Brinkman on heat transfer through porous medium were summarized. Mathematical expressions pertaining to models were studied to understand the response of theaOldroyd B fluid flowing through aaporous medium with a finite element boundary conditions. Research papers on Linear stretched sheet and circular tube flow models gave the clear picture of the extent of work carried out by the heat transfer researchers. Handful of verticals are identified as research gaps which still remains unexplored. Hence Provides an opportunity to carryout in-depth analysis for complete understanding of heat transfer thorough a Oldroyd B fluid filled porous media.

Analysis of spherical shell structure based on SBFEM

Purpose The purpose of this paper is to present an accurate and efficient element for analysis of spherical shell structures. Design/methodology/approach A scaled boundary finite element method is proposed, which offers more advantages than the finite element method and boundary element method. Only the boundary of the computational domain needs to be discretized, but no fundamental solution is required. Findings The method applies to thin as well as thick spherical shells, irrespective of the shell geometry, boundary conditions and applied loading. The numerical solution converges to highly accurate result with raising the order of high-order elements. Originality/value The modeling strictly follows three-dimensional theory of elasticity. Formulation of the surface finite elements using three translational degree of freedoms per node is required, which results in considerably simplifying the computation. In the thickness directions, it is solved analytically, no problem of high aspect ratio arises and transverse shear locking can be successfully avoided.

Acoustic Noise Computation of Electrical Motors Using the Boundary Element Method

This paper presents a numerical method and computational results for acoustic noise of electromagnetic origin generated by an induction motor. The computation of noise incorporates three levels of numerical calculation steps, combining both the finite element method and boundary element method. The role of magnetic forces in the production of acoustic noise is established in the paper by showing the magneto-mechanical and vibro-acoustic pathway of energy. The conversion of electrical energy into acoustic energy in an electrical motor through electromagnetic, mechanical, or acoustic platforms is illustrated through numerical computations of magnetic forces, mechanical deformation, and acoustic noise. The magnetic forces were computed through 2D electromagnetic finite element simulation, and the deformation of the stator due to these forces was calculated using 3D structural finite element simulation. Finally, boundary element-based computation was employed to calculate the sound pressure and sound power level in decibels. The use of the boundary element method instead of the finite element method in acoustic computation reduces the computational cost because, unlike finite element analysis, the boundary element approach does not require heavy meshing to model the air surrounding the motor.

FEM and BEM Implementations of a High Order Surface Impedance Boundary Condition for Three-Dimensional Eddy Current Problems

We implement a three-dimensional formulation for eddy current problems based on the reduced magnetic scalar potential enforcing a high order surface impedance boundary condition (SIBC) which takes into account the curvatures of the conductor surface. Based on perturbation theory, the formulation reduces to three Laplace boundary value problems with Neumann boundary conditions and hence can be easily implemented in any existing Finite Element Method (FEM) or Boundary Element Method (BEM) code for the Laplace equation. The appropriate choice of the small parameter in the perturbation approach correctly represents the order of accuracy of the SIBC. The validation is carried out by comparison with full FEM solutions of a canonical test problem and of a more realistic example of a non-destructive testing probe. The validity of the extension of a high order SIBC to lower frequencies is verified and the fields can be obtained at any frequency in the range of interest once the formulation is solved only once.

A New Finite-Element Approach to Contact Problems

The use of boundary and volume finite elements in contact problems permits determination of the influence function for bodies of any specific form, with elimination of the indeterminacy at the point of load application; and direct construction of the system of equations for determining the contact regions and the corresponding contact-stress distribution, without the need for complex transformations and without loss of physical significance. As an illustration, the proposed method is used to solve a contact problem.

Proportional Boundary Finite-element Method Applied to Two-dimensional Elastostatic Problem

Proportional Boundary Finite-element Method Applied to Two-dimensional Elastostatic Problem

Numerical Study on Dynamic Noise and Radiated Noise of Oil Sump

This paper studies EQ4H engine oil pan. Finite element method and boundary element method are utilized to calculate and predict the vibration and noise radiation of the oil pan. Based on the analysis results, the oil pan is optimized and redesigned. By comparing the vibration and noise performance of the oil pan before and after optimization, the effectiveness of the optimized design is verified.

Performance of vertically loaded pile group embedded in layered transversely isotropic saturated viscoelastic soils

The flexibility matrices of layered transversely isotropic saturated viscoelastic soils are obtained by the extended precise integration method. The time-dependent solution to vertically loaded single pile in the soils is achieved through the coupling of finite element method (FEM) and boundary element method (BEM). The interactions among piles, as well as the compatibility condition of rigid cap on pile group, are considered to get the solution to the vertically loaded pile group in the soils. Several numerical examples are then presented to study the influences of soil and pile group properties, including viscoelasticity, transverse isotropy and stratification of soil, as well as length-diameter ratio and pile spacing. Finally, parametric analyses are performed to give the changing trend of displacement at the cap and the axial force of pile tops over time.

Investigation of Ring Touch Mode Capacitive Pressure Sensor With an Electrothermomechanical Coupling Contact Model

Ring touch mode capacitive pressure sensor, characterized by ring stopper and stepped circular diaphragm, is developed to eliminate or greatly alleviate some disadvantages existing in conventional or small-area touch mode capacitive pressure sensor. An electrothermomechanical coupling model is developed to calculate the deformation, stress and so on of the diaphragm, and it is universally available for different touch modes and non-touch mode. The model is with rapid calculation speed and it is verified by a combination of the finite element method (FEM) and boundary element method (BEM). Benefiting from the high calculation speed of the model, optimization designs of the sensor are carried out. By adjusting the height dimensions or radial dimensions, high sensitivity and strength can be achieved by such a sensor in different pressure ranges of interest without changing its planar package size and masks, or achieved in a very wide pressure range by an array composed of such sensors with a same set of process parameters of each sensor. On the other hand, optimal ratios of height dimensions or radial dimensions are acquired, which can suppress significantly the temperature’s influence on sensor operation, and furthermore, the optimal ratios are advisable for different pressure ranges and different material parameters of the sensor.

Second Conference of Computational Methods in Offshore Technology and First Conference of Oil and Gas Technology (COTech & OGTech 2019)

November 27 – 29, 2019, University of Stavanger, NorwayPrefaceThis conference is organized as a joint event of the COTech (Computational Methods in Offshore Technology) and OGTech (Oil and Gas Technology) conferences. The COTech conference started as part of the research and dissemination activities of the Program Area for research “COTech - Computational methods in Offshore Technology” at Faculty of Science and Technology, University of Stavanger (UiS). This Program Area for Research was founded in 2015 with seven professor, four associate professors, two adjunct professors and five research (PhD) students from the Department of Mechanical and Structural Engineering and Materials Science (IMBM), whose expertise and competence lies primarily within use of computational methods such as finite element methods, boundary and volume element methods, computational fluid dynamics and the like in marine and subsea technology, marine operations, design and analysis of mechanical systems, integrity and reliability of offshore structures and mechanical systems, renewable energy and wind engineering. In the offshore-related engineering area in particular, numerical computation approach is nowadays not only serving as a means to cultivate and realize innovative ideas, but also it is becoming the primary choice to solve complex engineering problems for the harsh and unfriendly environment in the Arctic.The OGTech conference is organized as part of a collaborative project called UTFORSK between a team of researchers from University of Stavanger and Gubkin Russian University of Oil and Gas. The overall aim of the project is to make the team stronger and more sustainable. Among others, the project focuses on building a bridge of collaboration in research and education between the two countries, Norway and Russia, that share the Arctic region and to strengthen the research aspects of the Offshore Technology field in Arctic environment. By facilitating mobility of researchers and staff in both directions, the project aims to provide a common and successful learning environment for young researchers (Masters and PhDs) to make sure that students have skills and knowledge required in order to face the challenges that the Offshore industry meets in the North - such as environmental aspects and Offshore Technology within subsea/marine structures in cold climate.List of Conference Organizing Committee, Topic Area Coordinators, Invited Keynote Speakers, Technical Committee Members and Reviewers are available in the pdf

Micromechanics Analysis of Elastic Properties of Flexible Matrix TWF Composites

Using carbon fibers triaxial woven fabric (TWF) as a reinforcing material and compounding with a suitable flexible matrix material to form a composite shell film structure. It is a new type of high precision deployable antenna implementation. In this paper, the elastic properties of TWF composites using silicone rubber are studied. Using the micromechanics method, the three-dimensional unit cell characterizing the structural properties of the braided composite material is carried out. Homogenization finite element analysis will ultimately yield the elastic modulus of the entire composite. Firstly, considering the fiber bundle interlacing, the unit cell is finely geometrically modelled. Next, the unit cell is analyzed by finite element and periodic boundary conditions are applied. The method of homogenization is used to obtain the volume average stress and strain through six independent loading analysis, and the stiffness matrix is obtained, and the engineering constant is finally obtained. Finally, the effect of fiber volume fraction on elastic properties is analyzed. At present, there are few researches on flexible matrix TWF composites at home and abroad. The research on the elastic properties of the material has laid a solid foundation for further research on the performance of the material in the future.

Wave propagation and scattering in reinforced concrete beams

Steel reinforcement bars (rebars) are vital to the strength of reinforced concrete (RC) structures, but can become damaged due to corrosion. Such damage is generally invisible and non-destructive testing methods are needed to assess their integrity. Guided wave methods are popular because they are capable of detecting damage using sensors placed remotely from the damage site, which is often unknown. This paper predicts free wave propagation in RC beams from which the concept of a guided wave based damage detection method emerges. The wave solutions are obtained using the wave finite element framework where a short section of a beam's cross section is modeled in conventional finite element (FE) and periodic boundary conditions are subsequently applied. Reinforcement elements are used in the FE model of the cross section as a neat and efficient means of coupling the concrete to the rebars and imposing prestress. The results show that prestress, important for static behavior, has a negligible effect on wave dispersion. A RC beam with a damaged section is modeled by coupling three waveguides, the center waveguide being identical to the outer ones except for a thickness loss in one rebar. Only small differences in cut-on frequencies are observed between the damaged and undamaged sections. However, these small differences give rise to strong reflection of some waves at frequencies close to cut-on. Below cut-on, most incident power is transmitted but experiences wave mode conversion, whereas above cut-on most power is transmitted to the same wave type. These observations form the basis for ongoing work to develop a damage detection technique premised on wave reflection near cut-on.