Error 789

Altair Forum User

Dear community,

 

I have a problem with the composite size optimization if I set a value for TMANUF for the plies.

 

After the free-sizing, I use the sized model to perform a sizing optimization setting a specific manufacturable thickness for the plies involved (TMANUF).

The solver is able to run the iteration zero, but it stops giving me the following error when iteration 1 starts.

  *** ERROR # 789 ***  Invalid design properties w.r.t. the design variables were found.     number of invalid property items = 6

This happens only if I set a value for TMANUF and also if I delete all the settings for maximum and minimum laminate thickness.
 

Unfortunately, I cannot share the model I am working on.

 

Any suggestion on the matter?

 

 

Thanks in advance,

Alessandro

 

Altair Forum User

Hi,

 

I would like to add that sometimes the solver seems to be able to go beyond the first iterations if I set the TMANUF value only for a limited number of plies (not all of them) and, then, it stops later (e.g., iteration 8), writing the same error 789.

 

Thanks again,

Alessandro

Altair Forum User

Hi @Alessandro

 

Looks like the sum of TMANUF of all plies is violating the laminate thickness (maximum constrain) and this is the reason when you delete max and minimum laminate thickness the solver progresses. 

 

Make sure that the sum of TMANUF is between the minimum and maximum laminate thickness constrains. 

Altair Forum User

Hi Prakash,

 

Thank you for your reply.

 

I was probably not clear in explaining. Unfortunately, I have the same problem even if I delete the minimum and maximum laminate thickness constrains.

 

Can you see other possible sources of the error?

 

Thanks again,

Alessandro

Altair Forum User

Hi @Alessandro

 

Can you share the .out file,please?

Altair Forum User

Hi Prakash,

 

I have found that the problem is not the sum of all the TMANUF but the fact that, having zero as lower bound in the DESVARs, the solver is allowed to go to zero thickness for the laminates during the optimization. When this happens for some elements, the solver stops and gives the error 789.

Of course, I cannot solve setting a non-zero lower bound for all the DESVARs. In that case the resultant structure will not be optimised at all, forcing the solver to have at least one TMANUF thickness for every ply.

Instead, I solved setting TMANUF as lower bound only for the DESVARs related with ply shapes covering the entire laminates, assuring that the laminates cannot go to zero in any elements.

 

Finally, the only thing I do not understand is why the behaviour described above happens even if a minimum laminate thickness is defined for the laminates in the DCOMPs. This is probably due (I don't know if you can confirm) to the fact that the solver does not try to satisfy all the constraints together but priorities based on violation percentage. It could be nice (for future developments) having the possibility of manually defining a set of constraints that needs to be satisfied, with maximum priority, at each iteration. Also the possibility of defining low priorities for others could be useful.

 

I would consider this issue solved.

Thanks for the support.

 

 

Regards,

Alessandro

Altair Forum User

Hi Alessandro,

 

This is strange. During sizing,  TMANUF is considered over DESVARs upper and lower bounds. I am going to check this issue. 

Altair Forum User

I would like to add something else that helped me to bypass the problem keeping zero as lower bound in the DESVARs.

 

I set a constraint on the composite failure and this stops the solver to go for zero-thickness laminates to avoid failure.

 

I hope this is helpful for other users.

 

Regards,

Alessandro