[Gmsh] FW: Two bodies in contact

nankali h-nankali at ncc.neda.net.ir
Mon Jul 30 13:32:10 CEST 2007




From: nankali [mailto:h-nankali at ncc.neda.net.ir] 
Sent: Monday, July 30, 2007 3:25 PM
To: 'Riad.Hassani at univ-savoie.fr'
Subject: FW: [Gmsh] Two bodies in contact





From: nankali [mailto:h-nankali at ncc.neda.net.ir] 
Sent: Monday, July 30, 2007 3:13 PM
To: 'riad hassani'
Subject: RE: [Gmsh] Two bodies in contact



Hi again 



Thanks for your description to me ,I want to use the numerical modeling  for
the lithosphere deformation , and I need some guidelines  for this task

Would you please help me ?


What is the role of  gravity , it must be apply before the model run , I
mean that first compress the model  and then run  the model with boundary


What is the solution analysis (transient or static) ? how can we determine
the time step size and load step ?


Is for the lithosphere the element size important in horizontal and vertical


If we want to do thermal analysis , and our model is consist of 3
blocks(volumes) ,so what about the heat  generation rate , it must be
applied on the area of volume or it must be apply on the each volume
separately ? do you have an example with figures?


How do we find the Transition from elastic to viscoelastic in the model


Tell me how can I apply the Euler pole to the model?


 how can I consider the effect of topography with free air gravity anomaly?
And also for the sediment? 


Best Regard










From: riad hassani [mailto:Riad.Hassani at univ-savoie.fr] 
Sent: Monday, July 30, 2007 1:36 PM
To: nankali
Subject: Re: [Gmsh] Two bodies in contact



you can view a Winkler condition like the action done by a spring, i.e. a
force proportional to the normal displacement in the foundation. In
geodynamics applications where a lithosphere overlies a fluid asthenosphere,
this force is simply du to the pressure force exerted by the asthenosphere
on the lithosphere. Thus, you have to considere a normal stress boundary
condition on the base of the lithosphere : 

sigma_nn = Pa 

where Pa is the pressure in the asthenosphere. This pressure is Pa(z') =
rho*g*z'  (in the simple case of an incompressible fluid) where z' is the
distance to the  hydrostatic level  zh (the depth where Pa = 0) : z' = zh -

Knowing the initial configuration (assumed in an isostatic equilibrium), you
can compute zh by the hydrostatic law : Pa(zh-zb) = pmax 

with zb the depth of the lithosphere bottom where the pressure (in the
lithosphere) is pmax. You find zh = zb + (pmax/rho*g).


In a finite elements context, you have to compute at each time step the
boundary integral over the base of the lithosphere:  integral(n*Pa*N_i)
where N_i is the shape function of the node i, n is the unit normal vector.
To implement this, there are two ways depending on your time discretization

- explicit manner: you compute Pa(z') using the node positions at the
preceding time step. The resulting integral is added to the nodal force of
node i

- implicit method: z' is an unknown since it depends on the current
position.  Writting z' in term of displacements, the corresponding integral
is added to the stiffness matrix.


best wishes,

R. Hassani


Le 30 juil. 07 à 06:42, nankali a écrit :





From: nankali [mailto:h-nankali at ncc.neda.net.ir] 
Sent: Monday, July 30, 2007 9:11 AM
To: 'gmsh at geuz.org'
Subject: [Gmsh] Two bodies in contact



 Dear Dr Hassani


I saw many article from you about the numerical modeling , I want to know
how to apply the wrinkler force in the base of the lithosphere?






Riad Hassani

Laboratoire de Géophysique Interne et de Tectonophysique

Campus scientifique

Université de Savoie

73376 Le Bourget du Lac, Cedex, France


Tel : (33) 4 79 75 87 96

Fax : (33) 4 79 75 94 06





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