[Geoqus] On Geostatic Step

[Kasper Fischer]

Hi,

I assume you have allready tried to do a *geosatic calculation and this
still results in the 10 cm displacement. I would suggest that you try
also to constrain all nodes to have zero displacement in the *geostatic
step and then relax all constrains but the one you have to leave in your
model in a subsequent step. If that still doesn't help try to calculate
the stress by abaqus itself an import them in your calculations as
initial conditions. This approach was suggested by S. Ellis and you may
have to take a look at her poster, which is available at
http://www.geophysik.ruhr-uni-bochum.de/geoqus2007

Best regards

Kasper

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| Dr. Kasper D. Fischer             <kasper.fischer at ruhr-uni-bochum.de> |
| Ruhr-Universität Bochum                                               |
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bsaad at po-box.mcgill.ca schrieb:

>Does any one have some remarks on how can I establish equilibrium and 
>get zero displacement out of Geostatic Step. I have avery simple plain 
>strain (2D) model and I applied the following initial stress that 
>balances the gravity load of g=-10 m/s^2 operating in z direction 
>throughout a zone that extends vertically from z=0 to z=100 m
>
>I am estimating the intial vertical stress as follows. I have  the zone 
>density of 2066 kg/m^3 and therefore bulk unit weight is (2066 * g=-10) 
>=-20060 N/m^3
>the stress at depth of 100 is 100*-20060= -2006000 N/M^2
>
>Therefore Initial Geostatic Stress is
>
>*initial conditions, type=STRESS, geostatic
>Ground, -2006000, 0, 0, 100, 0.38, 0
>Where 0.38 is the coefficient of earth pressure calculated from 
>K0=v/1-v  (v is poission ratio).However I am getting ridicules 
>displacement : in the order of 0.10 m
>
>Background
>In fact (in plain strain) the exact geostatic stresses in the body is 
>done through Calculating stress and displacement fields resulted from 
>gravity (assuming elastic media) is done through elasticity relations 
>Inserting initial stresses based on
>\sigma_v = \gamma*h, \sigma_h = K*\sigma_v, where h and K are distance 
>of the calculated point from the surface and Coef earth pressure, 
>respectively,  is just a very approximate way for the existing stress 
>field and hence displacement field. One should play with these 
>approximate field until it becomes very close to the above exact stress 
>field (calculated based on FE elasticity). This game may regretfully 
>last hours and hours.
>
>
>
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