I have two models variations:
- a mass model in which I generate the my load from a block and apply gravitational acceleration
- force model in which I apply a force of the same magnitude as the mass from the mass model
I have applied mesh control to specific regions on a support pin and measured strain in those regions. The support pin and mesh control on the pin is identical in both model varients. I get a 10% difference in the measurements between the two models even though the contact force on the support pin is identical between the two model varients when measured after the simulation is complete. The mass model is quite larger, so is it possible that the additional mesh elements outside of my mesh controlled regions are causing that big of a deviation?
Thanks,
Ian
Can you post some pictures of the model so that we can get a better idea of what we're dealing with?
One key point here is that you're measuring and comparing the strain, which is determined by differentiating the displacement field, so very small changes in the displacement solution can cause a large change in the strain solution.
Now, between the two models, does one have this block while the other doesn't? If so, how is the block interfaced to the model? These specifics can have a large impact on the results depending on the characteristics of the model. For example, imagine you have a very thin plate (support on its edges) that you're resting a block on (where the block is about 50% the size of the plate). If you were to compare the results between a model where you represented the block with a force vector and one where you modeled the block (both models have gravity), then you'd see different results; the magnitude of the difference depends on how you modeled the block in. Think of a force load as water weight; it has absolutely zero stiffness to it and gets uniformly distributed over the surface it's applied to. The block does not do this. If you bond the block to the plate, then you're adding a significant amount of stiffness to the model (the bonded interface between the block and the plate increases the local stiffness). If you apply a contact interface, then you'll end up biasing the weight of the block around it's edges due to how the plate deforms.
Finally, in your force model, did you keep the gravity load active? Key in mind that a gravity load is for the entire model, and that if you excluded it from your force model then you're essentially excluding the weight of your other components from the model. How much of an impact this has depends on the specifics of the model.