Error during topology optimization : Non-zero stiffness matrix required

[Anonymous]

Hello everyone,

I am trying to optimize the topology of a bridge, to maximize the strength to weight ratio. I am facing issues with this. I have constrained the two edges as shown in the picture to be a fixed and I am applying a vertical load facing downwards. The pre-solver check shows no issues but after solving I get an error saying that Non-zero stiffness matrix is required. This means somewhere my constraints are wrong and my FEA analysis is failing.

When I try to optimize individual truss members with the same constraints and load, it works. This error only happens while optimizing the entire bridge. 

Any inputs are appreciated.

Thanks

[Anonymous]

Hello everyone,

I am trying to optimize the topology of a bridge, to maximize the strength to weight ratio. I am facing issues with this. I have constrained the two edges as shown in the picture to be a fixed and I am applying a vertical load facing downwards. The pre-solver check shows no issues but after solving I get an error saying that Non-zero stiffness matrix is required. This means somewhere my constraints are wrong and my FEA analysis is failing.

When I try to optimize individual truss members with the same constraints and load, it works. This error only happens while optimizing the entire bridge. 

Any inputs are appreciated.

Thanks

[shekar_sub]

Hi kchhaje,

Will it be possible to post the file? Sometimes if the problem is not setup correctly the solve fails. Without looking at the file general advice may not be helpful. Thanks

shekar

[shekar_sub]

Hi kchhaje,

Will it be possible to post the file? Sometimes if the problem is not setup correctly the solve fails. Without looking at the file general advice may not be helpful. Thanks

shekar

[Anonymous]

Sure. The link below has the file.

https://a360.co/2HqsuB9

I am new to Fusion360, so I appreciate any inputs you might have. Thank You for the response

[Anonymous]

Sure. The link below has the file.

https://a360.co/2HqsuB9

I am new to Fusion360, so I appreciate any inputs you might have. Thank You for the response

[shekar_sub]

Hi kchhaje, 

The material properties you assigned to the simulation is bad. You need to assign non-zero properties to the material.

Regards

shekar

[shekar_sub]

Hi kchhaje, 

The material properties you assigned to the simulation is bad. You need to assign non-zero properties to the material.

Regards

shekar

[shekar_sub]

In order to change the material to Aluminium or some other material you can Right Mouse Button (RMB) on the Study Materials browser node while you are in the Shape Optimization study and select the material you want in the dropdown. Please see attached image.

With Aluminium it does solve and i have attached a f3d file that solves.

Just wondering are you trying to eliminate some of the supports for the bridge? In some areas the mesh is of 2 layers of thickness which tell me its very coarse. I would increase the fineness of the mesh and then try the solve. Be careful as mesh size becomes finer the solve time increases.

I have attached a video of how to fix the material properties. You will have to get those properties from wherever you got it. 

Regards

shekar

[shekar_sub]

In order to change the material to Aluminium or some other material you can Right Mouse Button (RMB) on the Study Materials browser node while you are in the Shape Optimization study and select the material you want in the dropdown. Please see attached image.

With Aluminium it does solve and i have attached a f3d file that solves.

Just wondering are you trying to eliminate some of the supports for the bridge? In some areas the mesh is of 2 layers of thickness which tell me its very coarse. I would increase the fineness of the mesh and then try the solve. Be careful as mesh size becomes finer the solve time increases.

I have attached a video of how to fix the material properties. You will have to get those properties from wherever you got it. 

Regards

shekar

[Anonymous]

Hello, 

I am really sorry for the late reply. Thank You for the help. I tried with other materials as well and yes its working now. I think the default SolidWorks material I had assigned wasn't working. 

I have one more question Sir. So, I am actually trying to 3-D print this bridge. I want to print the organic design that comes out of topology optimization rather than "promoting" the design and then making sketches around it which is what is usually done. Is there any way to just save the design straight from topology optimization, as even though the design might seem weird, I want to try and 3-D print it? 

Thank You,

Karan

[Anonymous]

Hello, 

I am really sorry for the late reply. Thank You for the help. I tried with other materials as well and yes its working now. I think the default SolidWorks material I had assigned wasn't working. 

I have one more question Sir. So, I am actually trying to 3-D print this bridge. I want to print the organic design that comes out of topology optimization rather than "promoting" the design and then making sketches around it which is what is usually done. Is there any way to just save the design straight from topology optimization, as even though the design might seem weird, I want to try and 3-D print it? 

Thank You,

Karan

[shekar_sub]

Hi Karan

>I want to print the organic design that comes out of topology optimization rather than "promoting" the design and then making sketches around it

Unfortunately you cannot produce brep geometry directly from a shape optimization solve. You only get a mesh. If you use Generative Design you can get brep geometry from an outcome that could be directly 3D printed.

For shape optiization mesh, you can try converting the mesh to a solid body but you end up with lots of tiny faces. Once you promote the mesh, try RMB (Right Mouse button) on the mesh in the browser to convert it to a solid. I do not recommend this but it might be worth a try. Thanks

Regards

shekar

[shekar_sub]

Hi Karan

>I want to print the organic design that comes out of topology optimization rather than "promoting" the design and then making sketches around it

Unfortunately you cannot produce brep geometry directly from a shape optimization solve. You only get a mesh. If you use Generative Design you can get brep geometry from an outcome that could be directly 3D printed.

For shape optiization mesh, you can try converting the mesh to a solid body but you end up with lots of tiny faces. Once you promote the mesh, try RMB (Right Mouse button) on the mesh in the browser to convert it to a solid. I do not recommend this but it might be worth a try. Thanks

Regards

shekar

[Anonymous]

Ok sir. I will try this tonight. Thank You

[Anonymous]

Ok sir. I will try this tonight. Thank You

[shekar_sub]

Hi kchhaje,

Also the Pre-checks should detect that the material is bad. We have fixed that issue in our internal builds. It will be rolled out in the future. This way you do not need to do a solve to see the error but much earlier than that through the Pre-check command. Thanks

shekar

[shekar_sub]

Hi kchhaje,

Also the Pre-checks should detect that the material is bad. We have fixed that issue in our internal builds. It will be rolled out in the future. This way you do not need to do a solve to see the error but much earlier than that through the Pre-check command. Thanks

shekar