145 research outputs found
A Simple Multi-Directional Absorbing Layer Method to Simulate Elastic Wave Propagation in Unbounded Domains
The numerical analysis of elastic wave propagation in unbounded media may be
difficult due to spurious waves reflected at the model artificial boundaries.
This point is critical for the analysis of wave propagation in heterogeneous or
layered solids. Various techniques such as Absorbing Boundary Conditions,
infinite elements or Absorbing Boundary Layers (e.g. Perfectly Matched Layers)
lead to an important reduction of such spurious reflections. In this paper, a
simple absorbing layer method is proposed: it is based on a Rayleigh/Caughey
damping formulation which is often already available in existing Finite Element
softwares. The principle of the Caughey Absorbing Layer Method is first
presented (including a rheological interpretation). The efficiency of the
method is then shown through 1D Finite Element simulations considering
homogeneous and heterogeneous damping in the absorbing layer. 2D models are
considered afterwards to assess the efficiency of the absorbing layer method
for various wave types and incidences. A comparison with the PML method is
first performed for pure P-waves and the method is shown to be reliable in a
more complex 2D case involving various wave types and incidences. It may thus
be used for various types of problems involving elastic waves (e.g. machine
vibrations, seismic waves, etc)
Modelling strong seismic ground motion: three-dimensional loading path versus wavefield polarization
Seismic waves due to strong earthquakes propagating in surficial soil layers
may both reduce soil stiffness and increase the energy dissipation into the
soil. To investigate seismic wave amplification in such cases, past studies
have been devoted to one-directional shear wave propagation in a soil column
(1D-propagation) considering one motion component only (1C-polarization). Three
independent purely 1C computations may be performed ('1D-1C' approach) and
directly superimposed in the case of weak motions (linear behaviour). This
research aims at studying local site effects by considering seismic wave
propagation in a 1-D soil profile accounting for the influence of the 3-D
loading path and non-linear hysteretic behaviour of the soil. In the proposed
'1D-3C' approach, the three components (3C-polarization) of the incident wave
are simultaneously propagated into a horizontal multilayered soil. A 3-D
non-linear constitutive relation for the soil is implemented in the framework
of the Finite Element Method in the time domain. The complex rheology of soils
is modelled by mean of a multisurface cyclic plasticity model of the
Masing-Prandtl-Ishlinskii-Iwan type. The great advantage of this choice is that
the only data needed to describe the model is the modulus reduction curve. A
parametric study is carried out to characterize the changes in the seismic
motion of the surficial layers due to both incident wavefield properties and
soil non-linearities. The numerical simulations show a seismic response
depending on several parameters such as polarization of seismic waves, material
elastic and dynamic properties, as well as on the impedance contrast between
layers and frequency content and oscillatory character of the input motion. The
3-D loading path due to the 3C-polarization leads to multi-axial stress
interaction that reduces soil strength and increases non-linear effects. The
non-linear behaviour of the soil may have beneficial or detrimental effects on
the seismic response at the free surface, depending on the energy dissipation
rate. Free surface time histories, stress-strain hysteresis loops and in-depth
profiles of octahedral stress and strain are estimated for each soil column.
The combination of three separate 1D-1C non-linear analyses is compared to the
proposed 1D-3C approach, evidencing the influence of the 3C-polarization and
the 3-D loading path on strong seismic motions
A Simple and Efficient Regularization Method for 3D BEM: Application to Frequency-Domain Elastodynamics
An efficient and easy-to-implement method is proposed to regularize integral
equations in the 3D boundary element method (BEM). The method takes advantage
of an assumed three-noded triangle discretization of the boundary surfaces. The
method is based on the derivation of analytical expressions of singular
integrals. To demonstrate the accuracy of the method, three elastodynamic
problems are numerically worked out in the frequency domain: a cavity under
harmonic pressure, diffraction of a plane wave by a spherical cavity, and
amplification of seismic waves in a semispherical alluvial basin (the second
one is also investigated in the time domain). The numerical results are
compared to semi-analytical solutions; a close agreement is found for all
problems, showing the accuracy of the proposed method
Identification of Different Seismic Waves Generated by Foundation Vibration in the Centrifuge: Travel Time, Spectral and Numerical Investigations
For the analysis of footings under dynamic loading scaled modeling in the centrifuge assumes that the soil behaves like at prototype scale. This paper demonstrates that for a container filled with dry sand, wave velocities can be described by a model based on the relation between the shear modulus and the depth dependent stress level proposed by Iwasaki and Tatsuoka. A preliminary estimation of the shear wave velocities and of the Poisson’s ratio confirms by dynamical measurements the currently use value of 0.25. A FEM modeling also helps to strengthen the validity of the model proposed, providing another insight in the propagation of waves in a soil with a velocity gradient
Interaction Site-Ville : Approches expérimentales et numériques
À l’échelle d’une ville, les structures de surface telles que les bâtiments peuvent modifier le mouvement sismique en 'champ libre' et agir comme des sources sismiques secondaires. Des observations ont en particulier été réalisées sur des données réelles. Elles montrent que cet effet peut être significatif. La conséquence directe de cette 'interaction site-ville' est la pollution du mouvement sismique en milieu urbain par un champ d’onde secondaire. Des modélisations en centrifugeuse et numériques tendent à confirmer que ce phénomène n’est pas anecdotique. En particulier, ces résultats montrent qu’entre deux bâtiments proches des interactions existent, modifiant le mouvement du sol mais aussi la réponse des structures impliquées. À l’échelle d’une ville, ce phénomène sera d’autant plus marqué lorsqu’un fort couplage existe entre la réponse du sol et la réponse du milieu urbain
Strong Ground Motion in the 2011 Tohoku Earthquake: a 1Directional - 3Component Modeling
Local wave amplification due to strong seismic motions in surficial
multilayered soil is influenced by several parameters such as the wavefield
polarization and the dynamic properties and impedance contrast between soil
layers. The present research aims at investigating seismic motion amplification
in the 2011 Tohoku earthquake through a one-directional three-component (1D-3C)
wave propagation model. A 3D nonlinear constitutive relation for dry soils
under cyclic loading is implemented in a quadratic line finite element model.
The soil rheology is modeled by mean of a multi-surface cyclic plasticity model
of the Masing-Prandtl-Ishlinskii-Iwan (MPII) type. Its major advantage is that
the rheology is characterized by few commonly measured parameters. Ground
motions are computed at the surface of soil profiles in the Tohoku area (Japan)
by propagating 3C signals recorded at rock outcrops, during the 2011 Tohoku
earthquake. Computed surface ground motions are compared to the Tohoku
earthquake records at alluvial sites and the reliability of the 1D-3C model is
corroborated. The 1D-3C approach is compared with the combination of three
separate one-directional analyses of one motion component propagated
independently (1D-1C approach). The 3D loading path due to the 3C-polarization
leads to multiaxial stress interaction that reduces soil strength and increases
nonlinear effects. Time histories and spectral amplitudes, for the Tohoku
earthquake, are numerically reproduced. The 1D-3C approach allows the
evaluation of various parameters of the 3C motion and 3D stress and strain
evolution all over the soil profile.Comment: Bulletin of the Seismological Society of America 103, 2B (2013)
1394-1410. arXiv admin note: substantial text overlap with arXiv:1308.194
MĂ©thode multipĂ´le rapide multi-niveaux en visco-Ă©lastodynamique 3D
National audienceSee http://hal.archives-ouvertes.fr/docs/00/59/28/83/ANNEX/r_4VPCS0OY.pd
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