Unrealistic displacement

[Mohamedsayed]

Hello there,

I have a problem in my model, it gives my un-realistic answer for the displacement.

the model is a three dimensional model, the first step is geostatic step. in the second step, I make an excavation (delete elements), the displacement from the model result after making the excavation is very small (un-logic at all).

I expect the roof to touch the floor or at least, i should see big displacement. the modulus of elasticity is not big, it is within the range that we normally used in rock mechanics.

In the geostatic step, the density of the rock is in Slug/ft3. and the gravitational accelaration is in ft/sec2.


I guess, i doing a mistake, but i checked the model several times, but i could not see that mistakes.

please check it for me, the model is simple it will not much time from you.

Thank you in advance

 

[IceBreakerSours]

Based on a quick look, everything seems to be alright. By increasing the deformation scale factor, the displacement and stress fields seem reasonable.

Check your units again. Are the modulus and initial stress in consistent units? Both are supposed to be in lbf/sq.ft. Make sure the magnitude of the applied pressure also is in the correct unit.

Are you new to this forum? If so, please read these FAQ:

http://www.eng-tips.com/faqs.cfm?fid=376

http://www.eng-tips.com/faqs.cfm?fid=1083

 

[Mohamedsayed]

Hello Icebreaker,

Thanks for helping me.

I checked the units, The unit system is ok: for stress lbf/sq.ft, and ft for length, and slug for the mass.

So, no problem with the units. In reality if we excavate a big area like that in the model, the roof might touch the floor in the excavated region or at least the displacement should be big.
I do not know where is the mistake.

Try to think with me
Thank you

 

[IceBreakerSours]

I am not familiar with the problem that you are trying to solve and the application area, so you will have to do some thinking on your own; it is your project, after all. Now, if I had to bet, I'd say there's a problem in the modulus or the applied pressure (units or magnitude). Another suspect would be the area of the deleted region.

Are you new to this forum? If so, please read these FAQ:

http://www.eng-tips.com/faqs.cfm?fid=376

http://www.eng-tips.com/faqs.cfm?fid=1083

 

[Mohamedsayed]

Ok, let me ask you question about the units

if the force is in Lbf, and the mass is in Lbm, and length is ft. what should be the value of gravitational acceleration is it 32.174 ft/sq. s or 1 ft/sq.s.

Thank you in advance

 

[IceBreakerSours]

You should figure this problem out on your own.

Are you new to this forum? If so, please read these FAQ:

http://www.eng-tips.com/faqs.cfm?fid=376

http://www.eng-tips.com/faqs.cfm?fid=1083

 

[Mohamedsayed]

you know in Abaqus, a consistent unit of system is Lbf/ft/slug.
and the graviational acceleration is 32.174 ft/sq.s.

1 slug=32.174 lbm
i want you to read this file, it is about the unit system. it will not take much time from you.

please read it.

Thanks again.

 

[Mohamedsayed]

Hello icebreaker,

I changed the system of units from EE to SI system to make sure that the problem is not in the system of units, and i still have the same problem. The system of unit used now in the model is Kg/m/S., so the stress is in Pa, density is in kg/cu.m.

I Just apply load on the top of model and remove some elements, the displacement is un-realistic at all.

I uploaded the new input file, please check it for me.

Thank you.