Wave Propagation in Viscoelastic and Poroelastic Continua

In this book, a numerical method to treat wave propagation problems in poroelastic and viscoelastic media is developed and evaluated. The method of choice is the Boundary Element Method (BEM) since this method implicitly fulfills the Sommerfeld radiation condition. The crucial point in any time-dependent BEM formulation finding time-dependent fundamental solutions is overcome employing the Convolution Quadrature Method. This quadrature rule makes it possible to establish a boundary element time-stepping procedure based on the known Laplace domain fundamental solutions for viscoelastic and poroelastic continua. Using this method, e.g., tremors produced by earthquakes or machines can be pre-calculated and subsequent buildings prevented from such disturbances.

Klappentext

Wave propagation is an important topic in engineering sciences, especially, in the field of solid mechanics. A description of wave propagation phenomena is given by Graff effect of a sharply applied, localized disturbance in a medium soon transmits or 'spreads' to other parts of the medium. These effects are familiar to everyone, e.g., transmission of sound in air, the spreading of ripples on a pond of water, or the transmission of radio waves. From all wave types in nature, here, attention is focused only on waves in solids. Thus, solely mechanical disturbances in contrast to electro-magnetic or acoustic disturbances are considered. of waves - the compression wave similar to the In solids, there are two types pressure wave in fluids and, additionally, the shear wave. Due to continual reflec­ tions at boundaries and propagation of waves in bounded solids after some time a steady state is reached. Depending on the influence of the inertia terms, this state is governed by a static or dynamic equilibrium in frequency domain. However, if the rate of onset of the load is high compared to the time needed to reach this steady state, wave propagation phenomena have to be considered.

Inhalt

1. Introduction.- 2. Convolution quadrature method.- 2.1 Basic theory of the convolution quadrature method.- 2.2 Numerical tests.- 2.2.1 Series expansion of the test functions f1 and f2.- 2.2.2 Computing the integration weights ?n.- 2.2.3 Numerical convolution.- 3. Viscoelastically supported Euler-Bernoulli beam.- 3.1 Integral equation for a beam resting on viscoelastic foundation.- 3.1.1 Fundamental solutions.- 3.1.2 Integral equation.- 3.2 Numerical example.- 3.2.1 Fixed-simply supported beam.- 3.2.2 Fixed-free viscoelastic supported beam.- 4. Time domain boundary element formulation.- 4.1 Integral equation for elastodynamics.- 4.2 Boundary element formulation for elastodynamics.- 4.3 Validation of proposed method: Wave propagation in a rod.- 4.3.1 Influence of the spatial and time discretization.- 4.3.2 Comparison with the "classical" time domain BE formulation.- 5. Viscoelastodynamic boundary element formulation.- 5.1 Viscoelastic constitutive equation.- 5.2 Boundary integral equation.- 5.3 Boundary element formulation.- 5.4 Validation of the method and parameter study.- 5.4.1 Three-dimensional rod.- 5.4.2 Elastic foundation on viscoelastic half space.- 6. Poroelastodynamic boundary element formulation.- 6.1 Biot's theory of poroelasticity.- 6.1.1 Elastic skeleton.- 6.1.2 Viscoelastic skeleton.- 6.2 Fundamental solutions.- 6.3 Poroelastic Boundary Integral Formulation.- 6.3.1 Boundary integral equation.- 6.3.2 Boundary element formulation.- 6.4 Numerical studies.- 6.4.1 Influence of time step size and mesh size.- 6.4.2 Poroelastic half space.- 7. Wave propagation.- 7.1 Wave propagation in poroelastic one-dimensional column.- 7.1.1 Analytical solution.- 7.1.2 Poroelastic results.- 7.1.3 Poroviscoelastic results.- 7.2 Waves in half space.- 7.2.1 Rayleigh surface wave.- 7.2.2 Slow compressional wave in poroelastic half space.- 8. Conclusions - Applications.- 8.1 Summary.- 8.2 Outlook on further applications.- A. Mathematic preliminaries.- A.1 Distributions or generalized functions.- A.2 Convolution integrals.- A.3 Laplace transform.- A.4 Linear multistep method.- B. BEM details.- B.1 Fundamental solutions.- B.1.1 Visco- and elastodynamic fundamental solutions.- B.1.2 Poroelastodynamic fundamental solutions.- B.2 "Classical" time domain BE formulation.- Notation Index.- References.