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-

Dynamic study of the Barqueta cable-stayed Bridge

Proceedings of a meeting held 30 January - 2 February 2006, St Louis, Missouri, USA. http://toc.proceedings.com/00102webtoc.pdf Vol. 1A theoretical and experimental research work of the Barqueta cable-stayed bridge is described in this paper. The Barqueta Bridge, across Guadalquivir river, links the city of Seville with the Scientific Park Cartuja 93. At jam hours cars may cover one half of the bridge lanes for more than one hour. Full-scale tests were carried out to measure the bridge dynamic response. The experimental program includes the dynamic study for both cases: the bridge with one half of it lanes full of cars, and empty. Modal parameters estimations were made based on the acquired data. Ten vibration modes have been identified in the frequency range of 0-6 Hz by different techniques, being two of these modes very close to each other. The traffic-structure interaction is also studied. The experimental results were compared with those obtained from a three-dimensional finite element model developed in this work. Both sets of results show very good agreement. Finally, a damage identification technique has been applied to determine the integrity of the structureMinisterio de Educación y Ciencia BIA2004-03955-C02-0

Identificación de daños en estructuras a partir de su respuesta dinámica

Trabajo reproducido y difundido en el repositorio idUS con permiso de la Asociación Española de Ingeniería Mecánica (AEIM)La presencia de daños en estructuras puede deberse a multitud de causas. Por ejemplo, debido a causas accidentales que excedieron aquellas para las cuales fueron diseñadas las estructuras o simplemente porque éstas han superado su vida útil. La presencia de un daño en un sistema mecánico implica un cambio en las propiedades dinámicas del mismo. Por tanto, la detección del dafio mediante la variación de las propiedades dinámicas tiene un gran interés, sobre todo en los casos en que los defectos están en partes de la estructura que no son accesibles. Este trabajo pretende dar una visión general de los métodos de detección y localización del daño en estructuras más usados en la actualidad, profundizando en alguno de ellos y probándolos en un banco de ensayos creado al efecto en el Laboratorio de Teoría de Estructuras de la Escuela Técnica Superior de Ingenieros de la Universidad de SevillaAppearance of damages in structures is due to several reasons. For instance, accidental causes that exceed design considerations. Damages in mechanical systems provoke changes in their dynamic properties. Therefore, damage detection by the variation of dynamic properties has a huge interest, especially in cases where damages are in non-accessible areas. This work expects to show briefly the existing methods to identify and locate damages in structures, dealing with sorne of them and testing them in a test device created in the Structures laboratory of Escuela Técnica Superior de Ingenieros (University of Seville)

Low weight additive manufacturing FBG accelerometer: design, characterization and testing

Structural Health Monitoring is considered the process of damage detection and structural characterization by any type of on-board sensors. Fibre Bragg Gratings (FBG) are increasing their popularity due to their many advantages like easy multiplexing, negligible weight and size, high sensitivity, inert to electromagnetic fields, etc. FBGs allow obtaining directly strain and temperature, and other magnitudes can also be measured by the adaptation of the Bragg condition. In particular, the acceleration is of special importance for dynamic analysis. In this work, a low weight accelerometer has been developed using a FBG. It consists in a hexagonal lattice hollow cylinder designed with a resonance frequency above 500 Hz. A Finite Element Model (FEM) was used to analyse dynamic behaviour of the sensor. Then, it was modelled in a CAD software and exported to additive manufacturing machines. Finally, a characterization test campaign was carried out obtaining a sensitivity of 19.65 pm/g. As a case study, this paper presents the experimental modal analysis of the wing of an Unmanned Aerial Vehicle. The measurements from piezoelectric, MEMS accelerometers, embedded FBGs sensors and the developed FBG accelerometer are compared.Ministerio de Economía y Competitividad BIA2013-43085-P y BIA2016-75042-C2-1-

Modal identification of a pedestrian bridge by output-only analysis

The modal parameters (natural frequencies, mode shapes and damping ratios) describe the dynamic properties of a mechanical system. The classical modal analysis, based on Frequency Response Function, require measurements of both the input force and the response. Normally, it is very difficult to measure the excitation on large structures (bridges, tall buildings, offshore platforms, etc.). However, reasonable estimates of the modal parameters can be extracted from ambient vibration or output-only response (wind, traffic, humans, etc.). The dynamic behaviour of a curved pedestrian bridge in the University of Seville (Spain) has been investigated by full-scale testing and theoretical models. Nine vibration modes have been identified in the frequency range of 0-20 Hz, by the following algorithms: Enhanced Frequency Domain Decomposition (EFDD) and Stochastic Subspace Identification (SSI). Ambient modal parameters estimation have been compared with a rigorous three-dimensional finite element model, showed very good agreement.Ministerio de Educación y Ciencia DPI2001-2377-C02-01 BIA2004- 03955-C02-0

Identificación Dinámica de Elementos de Hormigón Armado Fisurados Reforzados Externamente con Fibras de Carbono

XVI Congreso Nacional de Ingeniería Mecánica, celebrado en León en 2004Las estructuras de hormigón armado pueden sufrir daños a lo largo de su vida causados, por ejemplo, por cargas subestimadas o imprevistas o condiciones medioambientales. Una técnica usada para reparar estructuras de hormigón armado consiste en la adhesión de láminas de fibras de carbono (CFRP) en la zona traccionada de éstas. En cualquier caso, una inspección regular de las estructuras hace posible una rápida detección del daño que minimiza los costes de reparación. Basándose en la pérdida de rigidez debida a la fisuración del hormigón, en este trabajo, se usan los cambios en las frecuencias naturales y los modos de vibración de seis vigas de hormigón armado ensayadas a flexión en cuatro puntos para determinar el daño en estructuras de hormigón reforzadas y sin reforzar.Underestimated or accidental loads or environmental conditions may cause damage to reinforced concrete structures. A method used to repair and strengthen concrete structures consists on bond composite laminates to the surfaces of RC beams. Anyway, regular inspection of the structures makes possible an early detection of the damage, thereby minimising costs. The damage structures results in a stiffness reduction in the cracked sections. In this work, the changes in modal parameters are used for detecting damage in six RC beams strengthened with extemally bonded CFRP plates.Ministerio de Ciencia y Tecnología DPI200l-2377-C02-0

High-speed train-induced ground motion and interaction with structures

A general numerical model for the analysis of soil motion due to high-speed train passage and effects on nearby surface and underground structures is presented in this paper. Soil, ballast and structures are represented using a three-dimensional time domain boundary element approach. Material damping has been included in the time domain formulation. Equilibrium and compatibility between soil and underground or surface structures is established in a rigorous manner in order to take into account soil–structure interaction. In contrast to other existing approaches, effects on a particular structure and the influence of non-uniform soil conditions along the track can be evaluated. Numerical results are obtained for different situations and some of them are compared with existing experimental records. The experimental values are to a large extent reproduced by the present numerical approach. Ballast influence and effects of high-speed train passage on a concrete underpass structure are analysedMinisterio de Educación y Ciencia BIA2004-03955-C02-01Ministerio de Fomento Proyecto ‘‘Evaluación de efectos dinámicos del ferrocarril’

Dynamic analysis of a cable-stayed deck steel arch bridge

A theoretical and experimental research work in relation to Barqueta cable-stayed bridge is described in this paper. Barqueta Bridge, across Guadalquivir river, links the city of Seville with the Scientific Park Cartuja 93. At jam hours cars may cover one half of the bridge lanes for more than one hour. Full-scale tests were carried out to measure the bridge dynamic response. The experimental program included the dynamic study for two different live load conditions: the bridge with one half of it lanes full of cars, and the bridge empty of cars. Modal parameters estimations were made based on the acquired data. Ten vibration modes were identified in the fre-quency range of 0-6 Hz by different techniques, being two of these modes very close to each other. The traffic-structure interaction is also studied. Experimental results were compared with those obtained from a three-dimensional finite element model developed in this work. Both sets of results show very good agreement. Finally, a damage identification technique has been applied to determine the integrity of the structure. Results obtained from a test developed in July 2005 have been correlated to experimental results obtained in October 2006 using the damage index methodMinisterio de Educación y Ciencia BIA2004-03955-C02-01Ministerio de Foment

A 3D Numerical Mode for HST Induced Vibrations

A general numerical model for the analysis of soil motion due to high-speed train passage and effects on nearby surface and underground structures is presented in this paper. In contrast to other existing approaches, effects on a particular structure and the influence of non-uniform soil conditions along the track can be evaluated. Numerical results are obtained for different situations and some of them are compared with existing experimental records. The experimental values are to a large extent reproduced by the present numerical approach

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-