Dynamic analysis

[gfraulini]

Hi all,
in the dynamic analysis we have (Creo 2):
- time analysis
- shock analysis
- frequencies analysis
- random analysis

I need always a modal analysis before; but I have the problem that I can't use contact surfaces. So I can analyze only parts or "solid assemblies".
Or not?

In shock analysis you apply the load only at the constraints and you can insert the data as dependent by time.
In random, frequencies and time analysis you can insert the load from the base OR from the "typical load".

But even in non-linear static analysis you have the possibility to impose the dependency by the time.

1. What is the real difference?

Can I have more details about dynamic analysis? (PTC pdf)

I need studying the contact pressures between a shaft and a cam keyed on it and moved by a key.

The axial movement is prevented by a collar closed by a screw.

I have more forces on the system that vary on a cycle of 0.428 ms (in primarily the force of the cam)

I need a non-linear analysis (there are contact regions) and to vary the forces in the time.

2. How can I do?

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[sdensberger]

I need always a modal analysis before; but I have the problem that I can't use contact surfaces.

Correct; Simulate can only doing linear dynamics (and a linear modal analysis), so all non-linear effects (contact, plasticity, large-deformations, etc.) will be ignored.

In shock analysis you apply the load only at the constraints and you can insert the data as dependent by time.

A shock analysis is based of the Response Spectrum Method, and is typically used to simulate seismic events. The curve that you define is the Response Spectrum Curve, which is a function of displacement/velocity/acceleration vs. the frequency response of the structure itself. The RSM is suited for base excitation.

But even in non-linear static analysis you have the possibility to impose the dependency by the time.

Be careful with this. The "time steps" in a non-linear analysis are pseudo time steps, not real time steps. Simulate does not support non-linear dynamics. Non-linear dynamics is typically done with an explicit code (Simulate is only implicit) and requires significantly more attention from the user (it's harder to obtain numerical stability with an explicit integration scheme). If you really need to do explicit dynamics, then I suggest looking at a more robust code like LS-DYNA (but be ready for a very steep learning curve).

Now, for the problem you want to simulate, this is technically something you can do in Simulate. I personally don't have any experience with this, but I believe others do. You can simulate the contact forces and rigid body dynamics of your system in Mechanism and then take those time-dependent loads and do a dynamic-time analysis (after doing a modal analysis of course) in Simulate. Make sure that your Simulate results remain linear (such as elastic material response).

[gfraulini]

Thanks Shaun,
my objective is to understand how is the distribution of contact pressure between the shaft and the "red" cam. So the problem is, by itself, a non linear problem.
You have told me that Simulate can't do non-linear time based analysis (dynamic), so I can't insert the load that varies in time.
I think I'll do some dynamic analysis with static loads, that correspond to the dynamic load at a certain time.

Do you have some material to better learn this type of analysis?