Estudo Geralhttps://estudogeral.sib.uc.ptThe DSpace digital repository system captures, stores, indexes, preserves, and distributes digital research material.Sun, 15 Dec 2019 20:32:27 GMT2019-12-15T20:32:27Z50131Amplification of elastic waves due to a point source in the presence of complex surface topographyhttp://hdl.handle.net/10316/4033Title: Amplification of elastic waves due to a point source in the presence of complex surface topography
Authors: Tadeu, António; Santos, Paulo; António, Julieta
Mon, 01 Jan 2001 00:00:00 GMThttp://hdl.handle.net/10316/40332001-01-01T00:00:00ZInfluence of the cross-section geometry of a cylindrical solid submerged in an acoustic medium on wave propagationhttp://hdl.handle.net/10316/4019Title: Influence of the cross-section geometry of a cylindrical solid submerged in an acoustic medium on wave propagation
Authors: Pereira, Andreia; Tadeu, António; António, Julieta
Abstract: This paper studies wave propagation in the vicinity of a cylindrical solid formation submerged in an acoustic medium generated by point blast loads placed outside the inclusion. The full 3D solution is obtained first in the frequency domain as a discrete summation of responses for 2D problems defined by a spatial Fourier transform. Each 2D solution is computed using the Boundary Element Method, which makes use of two-and-a-half-dimensional Green's functions. This model is implemented to obtain Fourier spectra responses which make it possible to identify the behavior of both the axisymmetric and non-axisymmetric guided wave modes, when the cross-section of the elastic inclusion changes from circular to smooth oval.
Tue, 01 Jan 2002 00:00:00 GMThttp://hdl.handle.net/10316/40192002-01-01T00:00:00ZThe simulation of 3D elastic scattering produced by thin rigid inclusions using the traction boundary element methodhttp://hdl.handle.net/10316/3970Title: The simulation of 3D elastic scattering produced by thin rigid inclusions using the traction boundary element method
Authors: Tadeu, António; Mendes, Paulo Amado; António, Julieta
Abstract: A mixed formulation that uses both the traction boundary element method (TBEM) and the boundary element method (BEM) is proposed to compute the three-dimensional (3D) propagation of elastic waves scattered by two-dimensional (2D) thin rigid inclusions. Although the conventional direct BEM has limitations when dealing with thin-body problems, this model overcomes that difficulty. It is formulated in the frequency domain and, taking into account the 2-1/2D configuration of the problem, can be expressed in terms of waves with varying wavenumbers in the zdirection, kz. The elastic medium is homogeneous and unbounded and it should be noted that no restrictions are imposed on the geometry and orientation of the internal crack.
Sun, 01 Jan 2006 00:00:00 GMThttp://hdl.handle.net/10316/39702006-01-01T00:00:00Z3D scattering by multiple cylindrical cavities buried in an elastic formationhttp://hdl.handle.net/10316/4035Title: 3D scattering by multiple cylindrical cavities buried in an elastic formation
Authors: António, Julieta; Tadeu, António
Abstract: This paper presents the three-dimensional scattering field obtained when multiple cylindrical circular cavities of infinite length buried in a homogeneous elastic medium, are subjected to dilatational point loads placed at some point in the medium. The solution is formulated using boundary elements for a wide range of frequencies and spatially harmonic line loads, which are then used to obtain time series by means of (fast) inverse Fourier transforms into space-time. The method and the expressions presented are implemented and validated by applying them to a cylindrical circular cavity buried in an infinite homogeneous elastic medium subjected to a dilatational point load, for which the solution is calculated in closed form. The boundary elements method is then used to evaluate the wave-field elicited by a dilatational point load source in the presence of a different number of cylindrical oval cavities. Simulation analyses using this idealized model are then applied to the study of wave propagation patterns in the vicinity of these inclusions. The amplitude of the wavefield in the frequency vs axial-wavenumber domain is presented, allowing the recognition, identification, and physical interpretation of the variation of the wavefield.
Mon, 01 Jan 2001 00:00:00 GMThttp://hdl.handle.net/10316/40352001-01-01T00:00:00ZSoluções analíticas para a propagação do som em espaços bidimensionais e tridimensionaishttp://hdl.handle.net/10316/13424Title: Soluções analíticas para a propagação do som em espaços bidimensionais e tridimensionais
Authors: Tadeu, António; António, Julieta; Godinho, Luis
Abstract: Um problema de propagação de ondas de pressão pode ser resolvido com a ajuda de
expressões denominadas funções de Green. Estas funções definem a relação entre variáveis
(pressões e velocidades) em determinado ponto no espaço resultante de variações harmónicas
de pressão (forças) posicionadas algures no meio de propagação. Estas funções são
frequentemente definidas para variações de pressão tridimensionais (forças pontuais) em
espaços infinitos e variações lineares harmónicas de pressão actuando em espaços
bidimensionais. Estas escolhas devem-se à possibilidade da definição analítica deste tipo de
funções. Considerando que a propagação do som se processa na presença de barreiras
perfeitamente reflectoras poderá considerar-se a existência de fontes virtuais posicionadas de
modo a verificarem as condições fronteiras necessárias. Este artigo resume um conjunto
destas soluções para espaços tridimensionais e bidimensionais. Além destas expressões este
artigo apresenta soluções para fontes harmónicas lineares cuja amplitude varia de forma
sinusoidal na terceira dimensão. Este tipo de solução é frequentemente referido como
problema 2 1 2 D , útil no cálculo de soluções tridimensionais através do Método dos
Elementos Fronteira
Sat, 01 Jan 2000 00:00:00 GMThttp://hdl.handle.net/10316/134242000-01-01T00:00:00Z3D elastic wave propagation modelling in the presence of 2D fluid-filled thin inclusionshttp://hdl.handle.net/10316/3977Title: 3D elastic wave propagation modelling in the presence of 2D fluid-filled thin inclusions
Authors: Tadeu, António; Mendes, Paulo Amado; António, Julieta
Abstract: In this paper, the traction boundary element method (TBEM) and the boundary element method (BEM), formulated in the frequency domain, are combined so as to evaluate the 3D scattered wave field generated by 2D fluid-filled thin inclusions. This model overcomes the thin-body difficulty posed when the classical BEM is applied. The inclusion may exhibit arbitrary geometry and orientation, and may have null thickness. The singular and hypersingular integrals that appear during the model's implementation are computed analytically, which overcomes one of the drawbacks of this formulation. Different source types such as plane, cylindrical and spherical sources, may excite the medium. The results provided by the proposed model are verified against responses provided by analytical models derived for a cylindrical circular fluid-filled borehole.
Sun, 01 Jan 2006 00:00:00 GMThttp://hdl.handle.net/10316/39772006-01-01T00:00:00ZAcoustic insulation provided by circular and infinite plane wallshttp://hdl.handle.net/10316/3990Title: Acoustic insulation provided by circular and infinite plane walls
Authors: António, Julieta; Godinho, Luís; Tadeu, A.António
Thu, 01 Jan 2004 00:00:00 GMThttp://hdl.handle.net/10316/39902004-01-01T00:00:00Z2.5D scattering of waves by rigid inclusions buried under a fluid channel via BEMhttp://hdl.handle.net/10316/3981Title: 2.5D scattering of waves by rigid inclusions buried under a fluid channel via BEM
Authors: António, Julieta; Tadeu, António; Godinho, Luís
Abstract: A 2.5D Boundary Element Method (BEM) formulation, applied in the frequency domain, is developed to compute the scattering of waves by rigid inclusions buried in a semi-infinite solid under a fluid layer, when this system is excited by a spatially-sinusoidal harmonic load.
Sat, 01 Jan 2005 00:00:00 GMThttp://hdl.handle.net/10316/39812005-01-01T00:00:00ZA three-dimensional acoustics model using the method of fundamental solutionshttp://hdl.handle.net/10316/3951Title: A three-dimensional acoustics model using the method of fundamental solutions
Authors: António, Julieta; Tadeu, António; Godinho, Luís
Abstract: The method of fundamental solutions (MFS) is formulated in the frequency domain to model the sound wave propagation in three-dimensional (3D) enclosed acoustic spaces. In this model the solution is obtained by approximation, using a linear combination of fundamental solutions for the 3D Helmholtz equation. Those solutions relate to a set of virtual sources placed over a surface placed outside the domain in order to avoid singularities. The materials coating the enclosed space surfaces can be assumed to be sound absorbent. This effect is introduced in the model by imposing impedance boundary conditions, with the impedance being defined as a function of the absorption coefficient. To impose these boundary conditions, a set of collocation points (observation points) needs to be selected along the boundary.
Tue, 01 Jan 2008 00:00:00 GMThttp://hdl.handle.net/10316/39512008-01-01T00:00:00ZThe use of monopole and dipole sources in crosswell surveyinghttp://hdl.handle.net/10316/3983Title: The use of monopole and dipole sources in crosswell surveying
Authors: António, Julieta; Tadeu, António
Abstract: This paper implements a boundary element method (BEM) solution, formulated in the frequency domain, to simulate the crosswell S wave surveying technique. In this technique, one fluid-filled borehole hosts the source, and the other the receivers. The system is excited by a monopole or a dipole source placed near the first wall of the borehole wall, while the pressure field is recorded in the second borehole. The three-dimensional solution is computed as a summation of 2.5D solutions for different axial wave numbers.This model is used to assess the influence of the distance between boreholes and the material properties of the medium on the pressure field generated in the second borehole. Slow and fast formations are both simulated. It was found that the responses recorded the contribution of the non-dispersive body waves (the dilatational (P) and shear (S) waves) as well as the effect of dispersive waves associated with different wave modes. The final time solutions are thus intricate, exhibiting wave patterns that may make it difficult to interpret the arrival times of the refracted P and S waves.
Thu, 01 Jan 2004 00:00:00 GMThttp://hdl.handle.net/10316/39832004-01-01T00:00:00ZGreen's functions for 2.5D elastodynamic problems in a free solid layer formationhttp://hdl.handle.net/10316/4021Title: Green's functions for 2.5D elastodynamic problems in a free solid layer formation
Authors: Tadeu, António; António, Julieta
Abstract: This work presents analytical Green's functions for the steady state response of a homogeneous three-dimensional free solid layer formation (slab) subjected to a spatially sinusoidal harmonic line load, polarized along the horizontal, vertical and z directions. The equations presented here are not only themselves very interesting but are also useful for formulating three-dimensional elastodynamic problems in a slab-type formation, using integral transform methods and/or boundary elements. The final expressions are validated by comparing them with the results obtained by using the Boundary Element Method solution, for which both free surfaces of the slab are discretized with boundary elements.
Tue, 01 Jan 2002 00:00:00 GMThttp://hdl.handle.net/10316/40212002-01-01T00:00:00ZSound propagation around rigid barriers laterally confined by tall buildingshttp://hdl.handle.net/10316/4016Title: Sound propagation around rigid barriers laterally confined by tall buildings
Authors: Godinho, Luís; António, Julieta; Tadeu, António
Abstract: This paper focuses on the propagation of sound waves in the presence of acoustic barriers placed close to very tall buildings. The boundary element method (BEM) is used to model the acoustic barrier, while the presence of the tall buildings is taken into account by using the image source method. Different geometries are analyzed, representing the cases of a single building, two buildings forming a corner and three buildings defining a laterally confined space. The acoustic barrier is assumed to be non-absorbing, and all the buildings and the ground are modeled as infinite rigid plane surfaces. Calculations are performed in the frequency domain and time signals are then obtained by means of Inverse Fourier Transforms. The sound pressure loss provided by the acoustic barrier is computed, illustrating the importance of the lateral confinements.
Tue, 01 Jan 2002 00:00:00 GMThttp://hdl.handle.net/10316/40162002-01-01T00:00:00Z3D seismic response of a limited valley via BEM using 2.5D analytical Green's functions for an infinite free-rigid layerhttp://hdl.handle.net/10316/4488Title: 3D seismic response of a limited valley via BEM using 2.5D analytical Green's functions for an infinite free-rigid layer
Authors: António, Julieta; Tadeu, António
Abstract: This paper presents analytical solutions for computing the 3D displacements in a flat solid elastic stratum bounded by a rigid base, when it is subjected to spatially sinusoidal harmonic line loads. These functions are also used as Greens functions in a boundary element method code that simulates the seismic wave propagation in a confined or semi-confined 2D valley, avoiding the discretization of the free and rigid horizontal boundaries.
Tue, 01 Jan 2002 00:00:00 GMThttp://hdl.handle.net/10316/44882002-01-01T00:00:00Z