Time-dependent constrainment

Dear community,

I’d like to use a time-dependent constrainment, but I fail to implement that.

Imagine a solid which is allowed to move freely (unconstrained) along the Y-axis, while X and Z are constrained at 0 from the beginning. After half-time of the simulation, I’d like to fix the Y-axis at its current state within the simulation, so it is not allowed to move anymore.

How would you implement such a time-dependent constrainement?

Hey there, and thanks for using the forum!

The way you describe it, there is currently no way to apply such a boundary condition.

Could you please elaborate on why you need such model, what is the application and the expected outcome? There might be a different approach to solve your case.

Thank you for your reply!

I will invite you to the simulation, so you can better understand the following issue:

As you can see, “solid13” moves towards and merges with the “mouth” part as a result of negative pressure applied on “solid13”. In future simulations, “solid13” will be replaced by individual geometries, all being slighlty different, which requires the simulation to be flexible for this approach-phase. In other words, this phase can’t be statically modelled. After half of the time, when the approach is finished, another part of the simulation, resulting in a compression of “solid13” performed by the “mouth” begins. As you can see, “solid13” starts to evade of the mechanical compression forces along the Y-Axis, which should not be allowed, as “solid13” will not be moving anymore in the real-world scenario after the first approach-phase.

I was thinking about ramping up a supporting force for “solid13” parallel to the mechanical forces of the mouth compression, but its exact strength is also unknown to me in advance, because the mechanical force is generated through a displacement condition (top-plate and bottom-plate)

Can I provide anymore information to you?

Hi, and sorry for the late reply.

This is a little bit of an uncommon case. I think your setup looks ok, is the behavior as expected?

Keeping the negative pressure constant at the end of the curve is the more reasonable approach to me, also the most physical as you will not over-constrain the deformation of the breast part. I think you can do this with a simpler approach than your current formula, that is with a table. Just add the key point times and pressure values.

No problem, and thank you for getting back to me.

Yes it is, but actually simscale does a very good job in this special case. Thank you fort that.

You asked me, whether the result is as expected. Actually, it is, but I think it could be even more precise. Once the maximum pressure is reached, I need the breast base to withstand any positive Y-axis movements, as this is not realistic behavior. You can observe that from time-stamp 0.5 on, there are some movements back in the Y-axis. Still, I do not know how to model that, as the initial (desired) Y-axis movement is not known in advance.

Changing the formula to a table version wouldn’t solve that problem, right?

Yes, the table change would be only for convenience.

I don’t think that what you want is possible, at least with our current feature set.