A BEM based on the Bézier/Bernstein polynomial for acoustic waveguide modelization

42nd International Conference on Boundary Elements and other Mesh Reduction Methods, BEM/MRM 2019; ITeCons-University of CoimbraCoimbra; Portugal; 2 July 2019 through 4 July 2019; Code 155806. Publicado en WIT Transactions on Engineering Sciences, Vol 126This paper proposes a novel boundary element approach formulated on the Bézier–Bernstein basis to yield a geometry-independent field approximation. The proposed method is geometrically based on both computer aided design (CAD) and isogeometric analysis (IGA), but field variables are independently approximated from the geometry. This approach allows the appropriate approximation functions for the geometry and variable field to be chosen. We use the Bézier–Bernstein form of a polynomial as an approximation basis to represent both geometry and field variables. The solution of the element interpolation problem in the Bézier–Bernstein space defines generalised Lagrange interpolation functions that are used as element shape functions. The resulting Bernstein–Vandermonde matrix related to the Bézier–Bernstein interpolation problem is inverted using the Newton–Bernstein algorithm. The applicability of the proposed method is demonstrated by solving the Helmholtz equation over an unbounded region in a two-and-a-half dimensional (2.5D) domain.Ministerio de Economía y Competitividad BIA2016-75042-C2-1-

A 2.5D BEM-FEM using a spectral approach to study scattered waves in fluid–solid interaction problems

42nd International Conference on Boundary Elements and other Mesh Reduction Methods, BEM/MRM 2019; ITeCons-University of Coimbra, Coimbra; Portugal; 2 July 2019 through 4 July 2019. - Publicado en WIT Transactions on Engineering Sciences, Volume 126, 2019, Pages 111-123This work presents a two-and-a-half dimensional (2.5D) spectral formulation based on the finite element method (FEM) and the boundary element method (BEM) to study wave propagation in acoustic and elastic waveguides. The analysis involved superposing two dimensional (2D) problems with different longitudinal wavenumbers. A spectral finite element (SFEM) is proposed to represent waveguides in solids with arbitrary cross-section. Moreover, the BEM is extended to its spectral formulation (SBEM) to study unbounded fluid media and acoustic enclosures. Both approaches use Lagrange polynomials as element shape functions at the Legendre–Gauss–Lobatto (LGL) points. The fluid and solid subdomains are coupled by applying the appropriate boundary conditions at the limiting interface. The proposed method is verified by means of a benchmark problem regarding the scattering of waves by an elastic inclusion. The convergence and the computational effort are evaluated for different h-p strategies. Numerical results show good agreement with the reference solution. Finally, the proposed method is used to study the pressure field generated by an array of elastic fluid-filled scatterers immersed in an acoustic mediumMinisterio de Economía y Competitividad BIA2016-75042-C2-1-

A novel 2.5D spectral approach for studying thin-walled waveguides with fluid-acoustic interaction

This paper presents a novel formulation of two spectral elements to study guided waves in coupled problems involving thin-walled structures and fluid-acoustic enclosures. The aim of the proposed work is the development of a new efficient computational method to study problems where geometry and properties are invariant in one direction, commonly found in the analysis of guided waves. This assumption allows using a two-and-a-half dimensional (2.5D) spectral formulation in the wavenumber-frequency domain. The novelty of the proposed work is the formulation of spectral plate and fluid elements with an arbitrary order in 2.5D. A plate element based on a Reissner-Mindlin/Kirchhoff-Love mixed formulation is proposed to represent the thin-walled structure. This element uses approximation functions to overcome the difficulties to formulate elements with an arbitrary order from functions. The proposed element uses a substitute transverse shear strain field to avoid shear locking effects. Three benchmark problems are studied to check the convergence and the computational effort for different strategies. Accurate results are found with an appropriate combination of element size and order of the approximation functions allowing at least six nodes per wavelength. The effectiveness of the proposed elements is demonstrated studying the wave propagation in a water duct with a flexible side and an acoustic cavity coupled to a Helmholtz resonator.Ministerio de Economía y Competitividad BIA2013-43085-P y BIA2016-75042-C2-1-RCentro Informático Científico de Andalucía (CICA

PBL from Real Projects and Students Initiative: a case study

The benefits of Project Based Learning (PBL) to acquire technological knowledge as well as transversal skills by students are well known. However, the implementation of PBL requires additional efforts from teachers and students, as well as additional teaching resources when compared to traditional teaching. This paper presents a case study of a singular PBL experience developed within a subject entitled Experimental Structural Analysis. This subject had PBL already implemented. However, the paper describes a new PBL experience that was suggested by some students that were part of the Formula Student (FS) team from the University of Seville. 24 students and 2 teachers took part in this new experience. The proposed PBL introduced some new challenges in the subject. The paper describes how the subject was organized in terms of theoretical and practical lessons, tutorials and assessment (including the introduction of a novel Self Assessment Factor). The paper analyzes the results from an academic point of view and describes the benefits, difficulties, advantages and opportunities arising from a PBL approach in which students play a new role as real promoters of a real project. Results from academic scores, surveys from students and teachers' perceptions are analyzed. The percentage of students who ask the teachers of the subject to supervise their final degree project is used as a new satisfaction indicator from students. The paper shows that this PBLmethodolodogy is enriching and suitable for the learning process of most the students. However, new challenges arise such as encouraging all the students to be actually involved in the cooperative work and ensuring that the main theoretical concepts are learned. The FS competition is proven to be a good opportunity for implementing PBL based on a real project. © 2017 TEMPUS Publications.Junta de Andalucía P12-TEP-254

Building dynamic response due to incident wave field considering soil-structure interaction

En este artículo se presentan dos metodologías basadas en las formulaciones de los métodos de los elementos de contorno y de los elementos finitos para estudiar el efecto de la interacción suelo-estructura en el comportamiento dinámico de edificaciones. Se ha estudiado la respuesta de un edificio de tres plantas producida por un campo de ondas incidente con los dos métodos propuestos. Los resultados obtenidos presentan un buen grado de acuerdo entre ellos. A partir de estos resultados se ha validado un modelo aproximado para estudiar este tipo de problemas y se han examinado diferentes tipolog ́ıas de edificaciones. Las conclusiones alcanzadas muestran que la respuesta global de las estructuras se debe a la deformación de los forjados, y depende de la superficie de estos, de las condiciones de apoyo y del acoplamiento con los forjados de la misma planta. Del mismo modo, se ha observado un acoplamiento del comportamiento de pilares y forjados cuando las rigideces de ambos son similaresThis paper presents two methodologies based on the boundary element method and the finite element method to study soil-structure interaction effect on building behaviour. A three-story building response induced by an incident wave field is studied using both methods. The obtained results show a good agreement. Then, a simplified model is validated from these methods and several buildings are analysed. Conclusions show that structural responses are due to floors deformation, and depend on their area, support conditions and coupling. It is also observed a coupling between floors and columns when both elements have similar stiffness.Ministerio de Economía y Competitividad BIA2010-14843Junta de Andalucía, Consejería de Economía, Innovación, Ciencia y Emple

Modeling elastic wave propagation in fluid-filled boreholes drilled in nonhomogeneous media: BEM – MLPG versus BEM-FEM coupling

The efficiency of two coupling formulations, the boundary element method (BEM)-meshless local Petrov–Galerkin (MLPG) versus the BEM-finite element method (FEM), used to simulate the elastic wave propagation in fluid-filled boreholes generated by a blast load, is compared. The longitudinal geometry is assumed to be invariant in the axial direction (2.5D formulation). The material properties in the vicinity of the borehole are assumed to be nonhomogeneous as a result of the construction process and the ageing of the material. In both models, the BEM is used to tackle the propagation within the fluid domain inside the borehole and the unbounded homogeneous domain. The MLPG and the FEM are used to simulate the confined, damaged, nonhomogeneous, surrounding borehole, thus utilizing the advantages of these methods in modeling nonhomogeneous bounded media. In both numerical techniques the coupling is accomplished directly at the nodal points located at the common interfaces. Continuity of stresses and displacements is imposed at the solid–solid interface, while continuity of normal stresses and displacements and null shear stress are prescribed at the fluid–solid interface. The performance of each coupled BEM-MLPG and BEM-FEM approach is determined using referenced results provided by an analytical solution developed for a circular multi-layered subdomain. The comparison of the coupled techniques is evaluated for different excitation frequencies, axial wavenumbers and degrees of freedom (nodal points).Ministerio de Economía y Competitividad BIA2013-43085-PCentro Informático Científico de Andalucía (CICA

3D non-linear time domain FEM-BEM approach to soil-structure interaction problems

Dynamic soil-structure interaction is concerned with the study of structures supported on flexible soils and subjected to dynamic actions. Methods combining the finite element method (FEM) and the boundary element method (BEM) are well suited to address dynamic soil-structure interaction problems. Hence, FEM-BEM models have been widely used. However, non-linear contact conditions and non-linear behaviour of the structures have not usually been considered in the analyses. This paper presents a 3D non-linear time domain FEM-BEM numerical model designed to address soil-structure interaction problems. The BEM formulation, based on element subdivision and the constant velocity approach, was improved by using interpolation matrices. The FEM approach was based on implicit Green’s functions and non-linear contact was considered at the FEM-BEM interface. Two engineering problems were studied with the proposed methodology: the propagation of waves in an elastic foundation and the dynamic response of a structure to an incident wave field.Ministerio de Economía y Competitividad BIA2010-1484

Vibrations induced by HST passage on ballast and non-ballast tracks

Soil Dynamics and Earthquake Engineering, Sept. 2010 - Special Issue in honour of Prof. Anestis Veletsos. PostprintThe use of ballastless slab track is significantly increasing in HST line technology. This development is due to some structural and operational advantages over ballasted track. In addition, floating slab tracks can be used to control ground-borne vibrations generated by surface and underground rail transportation systems. In this paper, a general and fully three dimensional multi-body-finite element-boundary element model is used to study vibrations due to train passage on ballast and non-ballast tracks. The vehicle is modelled as a multi-body system, the track, in both cases, using finite elements and the soil is represented using boundary elements. The three components of the load are considered; the quasi-static excitation (force generated by moving axle loads), the parametric excitation due to discrete supports of the rails and the excitation due to wheel and rail roughness and track unevenness. Track receptances are computed for both track systems and vibrations induced by high-speed train passage at the track and the free-field are evaluated for different train speeds. Soil behaviour changes significantly with the track system. Finally, a floating slab track is studied to show how this type of solution leads to a significant vibration reduction for surface tracks.Ministerio de Educación y Ciencia BIA2007-67612-C02-02CEDEX PT-2006-024-19CCP

Enseñanza de Teoría de Estructuras mediante el diseño, cálculo, construcción y ensayo de modelos

CNIM 2010 : Ciudad Real, 3-5 noviembre 2010. Anales de ingeniería mecánica, 2010, 18: 1-7Este trabajo presenta los resultados de una experiencia de innovación docente dentro de la docencia en el ámbito de las estructuras en la titulación de Ingeniería Industrial en la Universidad de Sevilla. La metodología docente aplicada pretende motivar al alumno al aprendizaje promoviendo el diseño, cálculo, construcción y ensayo de estructuras. De esta forma, el alumnado se forma no sólo como calculista, sino también desarrolla habilidades que le permiten comprender el funcionamiento de las estructuras. El proyecto abarca asignaturas impartidas en tercer y quinto curso de la titulación. En tercer curso, los estudiantes inician su formación estructural con la asignatura Teoría de Estructuras en la cual se les transmiten los fundamentos básicos mediante el diseño, fabricación y ensayo de estructuras de madera de balsa. Los alumnos disponen de programas informáticos para optimizar el diseño de sus modelos previamente a su construcción y posterior ensayo en el laboratorio. Tras esta primera aproximación a la Teoría de Estructuras, el alumno se forma en conceptos mas avanzados, como el comportamiento dinámico de las estructuras y las inestabilidades, en tipos estructurales particulares como son los casos de las placas y las estructuras laminares, y en materiales estructurales como el acero y el hormigón. Antes de finalizar sus estudios, el alumno se vuelve a encontrar con una metodología docente basada en el aprendizaje a través de proyectos en la asignatura Análisis Experimental de Estructuras. En este caso los proyectos que resuelve el alumno recorren parte de la casuística que se encontrará profesionalmente una vez egresado. Este trabajo presenta las ventajas de esta metodología desde el punto de vista de la enseñanza en ingeniería

Fully three-dimensional analysis of high-speed traintracksoil-structure dynamic interaction

In this paper, a general and fully three dimensional multi-body-finite element-boundary element model, formulated in the time domain to predict vibrations due to train passage at the vehicle, the track and the free field, is presented. The vehicle is modelled as a multi-body system and, therefore, the quasi-static and the dynamic excitation mechanisms due to train passage can be considered. The track is modelled using finite elements. The soil is considered as a homogeneous half-space by the boundary element method. This methodology could be used to take into account local soil discontinuities, underground constructions such as underpasses, and coupling with nearby structures that break the uniformity of the geometry along the track line. The nonlinear behaviour of the structures could be also considered. In the present paper, in order to test the model, vibrations induced by high-speed train passage are evaluated for a ballasted track. The quasi-static and dynamic load components are studied and the influence of the suspended mass on the vertical loads is analyzed. The numerical model is validated by comparison with experimental records from two HST lines. Finally, the dynamic behaviour of a transition zone between a ballast track and a slab track is analyzed and the obtained results from the proposed model are compared with those obtained from a model with invariant geometry with respect to the track direction.Ministerio de Educación y Ciencia BIA2007-67612-C02-02CEDEX PT-2006-024-19CCP