Modeling seismic wave propagation and amplification in 1D/2D/3D linear and nonlinear unbounded media

To analyze seismic wave propagation in geological structures, it is possible to consider various numerical approaches: the finite difference method, the spectral element method, the boundary element method, the finite element method, the finite volume method, etc. All these methods have various advantages and drawbacks. The amplification of seismic waves in surface soil layers is mainly due to the velocity contrast between these layers and, possibly, to topographic effects around crests and hills. The influence of the geometry of alluvial basins on the amplification process is also know to be large. Nevertheless, strong heterogeneities and complex geometries are not easy to take into account with all numerical methods. 2D/3D models are needed in many situations and the efficiency/accuracy of the numerical methods in such cases is in question. Furthermore, the radiation conditions at infinity are not easy to handle with finite differences or finite/spectral elements whereas it is explicitely accounted in the Boundary Element Method. Various absorbing layer methods (e.g. F-PML, M-PML) were recently proposed to attenuate the spurious wave reflections especially in some difficult cases such as shallow numerical models or grazing incidences. Finally, strong earthquakes involve nonlinear effects in surficial soil layers. To model strong ground motion, it is thus necessary to consider the nonlinear dynamic behaviour of soils and simultaneously investigate seismic wave propagation in complex 2D/3D geological structures! Recent advances in numerical formulations and constitutive models in such complex situations are presented and discussed in this paper. A crucial issue is the availability of the field/laboratory data to feed and validate such models.Comment: of International Journal Geomechanics (2010) 1-1

Viscoroute 2.0: a tool for the simulation of moving load effects on asphalt pavement

As shown by strains measured on full scale experimental aircraft structures, traffic of slow-moving multiple loads leads to asymmetric transverse strains that can be higher than longitudinal strains at the bottom of asphalt pavement layers. To analyze this effect, a model and a software called ViscoRoute have been developed. In these tools, the structure is represented by a multilayered half-space, the thermo-viscoelastic behaviour of asphalt layers is accounted by the Huet-Sayegh rheological law and loads are assumed to move at constant speed. First, the paper presents a comparison of results obtained with ViscoRoute to results stemming from the specialized literature. For thick asphalt pavement and several configurations of moving loads, other ViscoRoute simulations confirm that it is necessary to incorporate viscoelastic effects in the modelling to well predict the pavement behaviour and to anticipate possible damages in the structure.Comment: 27 pages

Modelling of multiple impacts for the prediction of distortions and residual stresses induced by ultrasonic shot peening (USP)

During a manufacturing process, the ultrasonic shot peening (USP) technique can be used as the final surface treatment. The aim of this operation is to introduce surface compressive residual stresses in order to prevent crack propagation advancement. Although the numerical simulation method is able to predict the level of residual stresses in a peened part, the 3D modelling of the real USP process, in which many successive and shifted impacts take place, is very delicate to perform and costly in terms of computing time and memory space required. In this paper, a two step method based at first on the calculation of the averaged plastic strain tensor in a half-space by using a semi-analytical method and in a second time on the transfer of this plastic strain field to a finite element model is proposed in order to simulate the effects of the USP process in thin structures. The accuracy and advantages of the semi-analytical method are validated by a benchmark with several finite element codes. Experiments, similar to the Almen test, are performed on thin plates of Inconel 600. Numerical results in terms of distortions and residual stresses are compared with the experimental data

The variational theory of complex rays for the calculation of medium-frequency vibrations

A new approach called the ``variational theory of complex rays’’ (VTCR) is developed for calculating the vibrations of weakly damped elastic structures in the medium-frequency range. Here, the emphasis is put on the most fundamental aspects. The effective quantities (elastic energy, vibration intensity, etc.) are evaluated after solving a small system of equations which does not derive from a finite element discretization of the structure. Numerical examples related to plates show the appeal and the possibilities of the VTCR

Super-Radiant Dynamics, Doorways, and Resonances in Nuclei and Other Open Mesoscopic Systems

The phenomenon of super-radiance (Dicke effect, coherent spontaneous radiation by a gas of atoms coupled through the common radiation field) is well known in quantum optics. The review discusses similar physics that emerges in open and marginally stable quantum many-body systems. In the presence of open decay channels, the intrinsic states are coupled through the continuum. At sufficiently strong continuum coupling, the spectrum of resonances undergoes the restructuring with segregation of very broad super-radiant states and trapping of remaining long-lived compound states. The appropriate formalism describing this phenomenon is based on the Feshbach projection method and effective non-Hermitian Hamiltonian. A broader generalization is related to the idea of doorway states connecting quantum states of different structure. The method is explained in detail and the examples of applications are given to nuclear, atomic and particle physics. The interrelation of the collective dynamics through continuum and possible intrinsic many-body chaos is studied, including universal mesoscopic conductance fluctuations. The theory serves as a natural framework for general description of a quantum signal transmission through an open mesoscopic system.Comment: 85 pages, 10 figure

Vibroacoustic response of structures and perturbation Reynolds stress near structure-turbulence interface

The interaction between a turbulent flow and certain types of structures which respond to its excitation is investigated. One-dimensional models were used to develop the basic ideas applied to a second model resembling the fuselage construction of an aircraft. In the two-dimensional case a simple membrane, with a small random variation in the membrane tension, was used. A decaying turbulence was constructed by superposing infinitely many components, each of which is convected as a frozen pattern at a different velocity. Structure-turbulence interaction results are presented in terms of the spectral densities of the structural response and the perturbation Reynolds stress in the fluid at the vicinity of the interface

Numerical modelling of behaviour of reinforced concrete columns in fire and comparison with Eurocode 2

The paper describes a two-step finite element formulation for the thermo-mechanical non-linear analysis of the behaviour of the reinforced concrete columns in fire. In the first step, the distributions of the temperature over the cross-section during fire are determined. In the next step, the mechanical analysis is made in which these distributions are used as the temperature loads. The analysis employs our new strain-based planar geometrically exact and materially non-linear beam finite elements to model the column. The results are compared with the measurements of the full-scale test on columns in fire and with the results of the European building code EC 2. The resistance times of the present method and the test were close. It is also noted that the building code EC 2 might be non-conservative in the estimation of the resistance time. (c) 2005 Elsevier Ltd. All rights reserved

Phantoms in medicine: the case of ophthalmology

Physical and in-silico phantoms have revealed extremely useful in the development of new surgical techniques and medical devices and for training purposes. The fabrication of eye phantoms requires knowledge of anatomy and physical principles beyond the eye physiology and medical instruments used in the clinical scenario. After a proper definition of phantoms and the discussion about their classification, the present work reviews the various phantoms developed in ophthalmology, illustrating the rationale of their design