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Optimization failure, minimize mass

Altair Forum User

Dear hyperworks users,

Currently I am using optistruct for my graduation project. The subject is about the optimization of a special type bridge.

The goal is to generate/optimize the design for a minimum mass. I performed several runs with a volumefraction constraint to maximize the stiffness, which worked fine.

Now I would like to perform a weight optimization but I am not able to generate any result.

I applied a displacement constraint at several locations and defined the allowable bounds.

The objective is set to minimize the volumefrac. But I also tried: volume, mass and massfraction.

I also tried to use stress constraints allthough I know it is not recommended. But so far i only obtain errors or incorrect results.

So my question is: Can someone help my solving this problem or is there any tutorial available which describes a similar problem?

Your response is welcome.

Regards,
Michael

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Altair Forum User

Hi @michaelv

Now I would like to perform a weight optimization but I am not able to generate any result.

Can you please let us know what the errors, results are like with some pictures?

Altair Forum User

Dear Prakash,

Thanks for your response. The problem was solved by doing an analysis. The value of the youngst modulus was too low which causes large deflections of the model. This was due to the use of incorrect units. By changing the material parameters the optimizer was able to solve the problem. Another question that I have is that I would like to add gravity and operational accelerations to my model. But I am not sure which load type to use and if the GRAV card is automatically is included in the load cases. Where can I find these types of information? I am looking forward to your response

Regards, Michael

Altair Forum User

Hi @michaelv

Please create a load collector with GRAV as card image.

You can find more information OptiStruct Reference guide>> Bulk data section

Altair Forum User

Dear Prakash,

Thanks for your help! I have read all the information available. The problem is that I would like to include the gravity acceleration in my model, but I would also like to include the operational accelerations for the different loads cases. I have no clue how to achieve this. Now the gravity is included in my model. Now my question is: How can I include the operational accelerations in my model? How should I apply the accelerations in my model en how can I include them into my loadsteps?

Thanks and regards,

Michael

Altair Forum User

Hi @michaelv

Please ACCEL if you want to apply acceleration to all nodes in your model.

If the Acceleration is for specific grids, please use ACCEL1/ACCEL2

Altair Forum User

Thanks, I have already tried that but I received the following error.

** Error # 1125 ** in the input data:

Accel requires at least one continuation card

What am I doing wrong? Because I could not track the error.

Regards,

Michael

Altair Forum User

@michaelv

Are you applying ACCEL or ACCEL1?

Altair Forum User

Thanks for your quick reply.

The accelerations may apply to my complete model. Therefore I applied Accel and included it into my force load collector.

Regards,

Michael

Altair Forum User

OK, can you card edit the ACCELs and provide LOCi and VARi as for ACCEL at least 2 entries are required.

Here I am attaching a model with ACCEL as the load.

Unable to find an attachment - read this blog

Altair Forum User

Dear Prakash,

Sorry I do not completely understand your question. I defined an acceleration, with load type accel with my force load collector set as current. I specified three constant components for the X, Y and Z-direction. The acceleration is applied to the global system. The card image is set to none in the load collector, which is the same as in the model that you have provided. I am not able to use the card edit function for this load collector. I understand from the reference guide, that a minimum of two pairs of (LOCi and VALi) should be specified.

Regards

Michael

Altair Forum User

Please watch the attached video

Unable to find an attachment - read this blog

Altair Forum User

Dear Prakash,

Thanks for your supporting video. I have tried to specify the LOCi and VALi values but I find it difficult to specify these values.

It is not clear to me how I should set up the accelerations in my model. Could you explain that for me? Or are there any tutorials available regarding this subject?

My goal is to include different accelerations for the different load cases. But it is not clear how to achieve this. I am looking forward to your reply.

Regards,
Michael

Altair Forum User

My goal is to include different accelerations for the different load cases. But it is not clear how to achieve this. I am looking forward to your reply.

Hi @michaelv

Since you want to include different accelerations for different loadcases, you can create multiple GRAV loads with different values and use the same for respective loadsteps. I think this makes your life easier.

Altair Forum User

Dear Prakash,

Thanks! I will try that and will let you know the results.

Should I then use the card image GRAV in the force load collector and then include this load collector into the loadstep?

Regards,

Michael

Altair Forum User

Should I then use the card image GRAV in the force load collector and then include this load collector into the loadstep?

Yes, so if you have four loadsteps, create four load collectors with GRAV as card image and use them in loadsteps.

Altair Forum User

Thanks for your support, Now it is clear to me.

Regards, Michael

Altair Forum User

Hi all,

I have gone through the topic, and i see similarities to mine.

I would like to apply a very simple acceleration to the whole model, therefore using only ACCEL loads.

But during the application of the loadsteps I feel I am making a mistake and it gives me the following error when I try to hit the optistruct analysis button.

*** ERROR # 1125 *** in the input data:
ACCEL requires at least one continuation card.

Could any of you tell me what error i may be doing?

Thanks a lot for the replies.

Rahul Rajan_21763

In accel card you need to specify at least two entries for the LOCi and VALi values.

LOCi - Location of the scale factor to the applied acceleration load along direction DIR in the coordinate system CID. (Real)
VAL - Load scale factor at the location LOCi. (Real)

The acceleration load applied to all grid points in the model is given by: EQ. 1.

a=VAL*N

Where, a is the acceleration load and N is a vector with components N1, N2, and N3.

So if you have a uniform acceleration in your model, by card editing the loads ACCEL, you can enter your two pairs of LOCi and VALi values.

So I don’t know what your accel card looks like in your model but if you go by using these values then this should fix your error:

LOC1 = 0, VAL1 = 1

LOC2 = 1, VAL2 = 1

Please let me know how you get on with this. Hope this helps!

Altair Forum User

Thansk a lot for the reply. Is there an example of how to apply that on Hypermesh Environment?

Rahul Rajan_21763

PFA.

Unable to find an attachment - read this blog