ERROR #2148

Antonio Gallo

Hi, I am new to Altair SWs. I am trying to make a lattice optimization of a model, but when I try to run the file "*_lattice.fem" which comes out of the Phase I of the lattice optimization, I always get this error message.

*** ERROR # 2148 ***
 Invalid design problem.
 All the sensitivities of response 1 (objective) are zero.

The model is made of three parts, two of which are made of aluminum and are connected to the third one, which is made of composite. For each subcase I have a force applied to a node and a maximum displacement constraint on the node itself. The analysis is inertia relief (INREL,-2) type.

The response is the mass of the aluminum parts but it seems that the size optimization of Phase II of the lattice optimization process doesn't affect the total mass of the aluminum part.  Any ideas about a possible reason for this error?

The .hm file is attached below, since the .fem file itself is too big to be uploaded.

Thanks,

Antonio.

loistf

Antonio Gallo said:

Here's the .out file, I can't see anything that may help me solve this problem. Also, taking a look at the desvars, everything seems to be ok.

Hi Antonio,

I took a look a brief look at your model. If I am not mistaken, your objective (response 1) is the mass of a certain solid property (strictly, the mass of the elements which reference a certain solid property), while your desvars are linked to beams (the lattice). If that is the case, no change of the design variables have any effect on the mass of the solid elements. In other words, the sensitivities are zero and therefore the optimizer can't do anything to "improve" the mass. 

You need to change your response / objective. (i can imagine that you might want to reference the full mass of the model, or the mass of the lattice only). 

Hope it helps. 

loistf

Hi Antonio,

Have you checked you *out file? Is there any clue there? Anything related to your desvars you can check? If the response is the mass, i suggest you chech the density.

Antonio Gallo

Here's the .out file, I can't see anything that may help me solve this problem. Also, taking a look at the desvars, everything seems to be ok.

Adriano_Koga

What is the initial mass of each aluminum part? And how is it compared the mass for the lattice structure with the whole model.

In some cases, the participation of the design region in the total mass is so small that it barely affects the total mass, thus could be insensitive.

But it is hard to tell for sure.

loistf

Antonio Gallo said:

Here's the .out file, I can't see anything that may help me solve this problem. Also, taking a look at the desvars, everything seems to be ok.

Hi Antonio,

I took a look a brief look at your model. If I am not mistaken, your objective (response 1) is the mass of a certain solid property (strictly, the mass of the elements which reference a certain solid property), while your desvars are linked to beams (the lattice). If that is the case, no change of the design variables have any effect on the mass of the solid elements. In other words, the sensitivities are zero and therefore the optimizer can't do anything to "improve" the mass. 

You need to change your response / objective. (i can imagine that you might want to reference the full mass of the model, or the mass of the lattice only). 

Hope it helps. 

Antonio Gallo

loistf said:

Hi Antonio,

I took a look a brief look at your model. If I am not mistaken, your objective (response 1) is the mass of a certain solid property (strictly, the mass of the elements which reference a certain solid property), while your desvars are linked to beams (the lattice). If that is the case, no change of the design variables have any effect on the mass of the solid elements. In other words, the sensitivities are zero and therefore the optimizer can't do anything to "improve" the mass. 

You need to change your response / objective. (i can imagine that you might want to reference the full mass of the model, or the mass of the lattice only). 

Hope it helps. 

I want to reference only the mass of the lattice structure. Tried to create another material, then assigned the solid metal parts to this one. After that I assigned as Response/Objective the material linked to the beams but it keeps giving me the same error message. Also tried assigning as Response/Objective the PBEAML properties but it does the same thing. How is it possible that the optimization does not affect the mass?