George,

Can you post your model? Its hard to answer that question in the abstract. I believe the problem is when you add the "similar set of components" to the other side, you MUST set their stateselect (in the Advanced tab) to "never". Your state is fully determined by the first set of components. You can't add redundant components unless you tell WSM to never select them as states.

I attached a model of a bar that falls under gravity and has an elastogap on each end-- I set the damping to zero so it will bounce around forever. Is this what you want? Notice all of the elements on the right (the upper end of the bar) have the stateselect to never.

Attachments:

hi Neil, thank you for your help. I have attached my model, which, looking at yours, seems a bit too simplistic . It had been a series of trial and errors on my model.

I have tried to run your model and got the error at the bottom of this reply. I have tried adjusting the "states" for components on the RHS to "blank" and then again to "avoid" When I do this, the program compiles and runs, but ends up with a 'divide by zero' error. Do you know what might be happening here?

Finally, none of this is really intuitive to a newbie. Do you have a good reference you can recommend for mechanics/dynamics problems in WSM?

Thank you again for your help George

Building "RodExample" as experiment "RodExample 3" started at 08:01:42 Error: Error: Deselecting states, too many variables have StateSelect.never (or StateSelect.default or StateSelect.avoid and does not appear differentiated) (in set: universal2.w_b). Build finished at 08:01:44 (took 00:01). Error: No executable generated C:/Users/gethiel/AppData/Local/Temp/WolframSystemModeler-4.3.1/sme.4.3.1150047650215724.exe Error: No settings file generated C:/Users/gethiel/AppData/Local/Temp/WolframSystemModeler-4.3.1/sme.4.3.1150047650215724_init.sim

Attachments:

George,

Your model had multiple issues.

1. First, the elastogap pointed the wrong direction -- in one direction it provides resistance/stiffness in the other direction is does nothing.

2. You should enter numbers as "0.1" and not ".1" -- the leading zero in WSM is more compatible with Modelica

3. When you try to add the prismatic joint to the other end of the mass you overconstrain the system. Remember -- prismatic allows for no side motion and the only way for your rod to fall under gravity is for it to also rotate.

Start with my model -- It works because I allow sided-to-side planar motion and the prismatic joint (with elastogap) to model the contact with the ground (in the correct direction!) and then the universal joint allows the bar to rotate as needed to make everything "fit".

As for good references I must defer to the WSM people in Sweden. I wish I had a good one as well. -- What do you guys recommend? ( @Patrik Ekenberg , @Otto Tronarp , @Malte Lenz )

George,

I wish I could say that "I figured the preferences setting from first principles and that I can't believe how stupid you were not to know that", however, actually I had the same problem you had with an over constrained loop. I got the information from the guys in Sweden!

That was a hard one to figure out. I also had to spend time trying out models as you are doing and figure it out. Contact me at Neils at my domain in the profile if you want to talk about some strategies on modeling.

Regards