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Amasker

Some questions in Optistruct

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Hi,I am sorry to ask questions again. Now I am studying the structural optimization design of the automobile B-pillar. This time, there are about three minor problems to be solved.


1. I don't know how to set the variable thickness shell element. I saw the following method to set the variable thickness unit in a journal. Setting different thickness simulation shells for the four nodes of the shell element, but I don't know how to achieve it. Can you give me some advice?

 

2. Since  currently optimized based on the B-pillar, the B-pillar components are taken out of the vehicle as shown in the following figure. How do you impose constraints on the upper and lower ends to simulate the vehicle constraints as much as possible?  In other words, how to apply constraints to the B-pillar to simulate the constraints in a real vehicle.?

 

3. Can the size optimization in Optistruct set the coordinate value to the design variable? In addition, can velocity load be applied in optistruct?

 

Thank you in advanced.

image.png.64fe92594b8a125ad2b6ba34acd62ea2.png

  

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Hi

1) You have to edit card of that shell element and activate "Nodal_Thickness" checkbox, and input thickness values at its nodes

2) to simulate constraints in real vehicle, I think you must know stiffness matrix of real vehicle!, but if the constraints are little sensitive then you try apply fixed constraints first.

 

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On 10/8/2018 at 2:20 PM, Amasker said:

3. Can the size optimization in Optistruct set the coordinate value to the design variable? In addition, can velocity load be applied in optistruct?

 

Hi, Not sure what you mean by coordinate value here. If you are talking about thickness coordinates, you can try Gauge where you can discretize the thickness.

 

Velocity is a dynamics load, if you are using static analysis as type then try with imposed displacement..?!!

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Hi,@Prakash Pagadala

 

Regarding the third problem, for example, the shell element is used to size optimization  of the steel plate, and whether the thickness can be optimized according to the coordinate value  (such as the y-axis coordinate) in the dimension optimization, for example, the thickness of the left end element is 1, the right end  thickness is 2, how to achieve the middle part of the shell element thickness varies linearly with the Y-axis coordinate between 1 and 2. In addition, can the dynamic load be loaded in the Optistruct? I want to use Optistruct to do the size optimization of the steel plate under a speed impact. I don't know if it is feasible.

image.png.5a14f85bcbdc0715f1afdd19dfdddcdc.png

 

  

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@Amasker

 

Two ways, one is to manual divide and run the optimization,

 

Second is to you use Thickness Gradient available on DSIZE card (this is not available through GUI and one has to edit the deck and add the TG and TGX/TGY/TGZ) and OptiStruct will take care based on the gradient.  Please refer to DSIZE card for more information, 

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@Prakash Pagadala

 

Thank you very much for your reply.

I tried to change the thickness of the node(nodal thickenss) to simulate the thickness change, but as a newbie, I have been trying for a long time and I don't know how to do it. Can you provide some tutorials or examples on how to set nodal thickness? Thank you

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On 10/9/2018 at 7:50 PM, Prakash Pagadala said:

Hi, Not sure what you mean by coordinate value here. If you are talking about thickness coordinates, you can try Gauge where you can discretize the thickness.

 

Velocity is a dynamics load, if you are using static analysis as type then try with imposed displacement..?!!

@Prakash Pagadala

 

Is optistruct unable to load the dynamic load? I want to apply the velocity load. Do you mean to replace the speed load with displacement? I don't know how to do it. Can you tell us more about it? Thank you

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48 minutes ago, Amasker said:

@Prakash Pagadala

 

Is optistruct unable to load the dynamic load? I want to apply the velocity load. Do you mean to replace the speed load with displacement? I don't know how to do it. Can you tell us more about it? Thank you

You can apply dynamic loads but there are some restrictions on optimization. So, if you are using a transient load case you can apply velocity and run the analysis. 

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On 10/11/2018 at 6:53 PM, Amasker said:

@Prakash Pagadala

 

I am very grateful for your help. I have successfully set the thickness of the node. There is still a question. in size optimization by using shell element,Can I set nodal thickness  as the design variable ?

I will check regarding this and update you soon.

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1 hour ago, Prakash Pagadala said:

You can apply dynamic loads but there are some restrictions on optimization. So, if you are using a transient load case you can apply velocity and run the analysis. 

 

@Prakash Pagadala 

I am trying to simulate the optimization of the B-pillar under the collision of a certain object with speed. I think this case should be regarded as a transient load. I don't know how to set the velocity. Can you give me some details, or provide some related tutorials?

Thank you

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Hi Amasker,

 

unless the collision is at slow speed (minimal kinetic compared to internal energy), this problem should be solved using an explicit time integration scheme to account for the effect of mass (inertia).

Optimization is possible via the equivalent static load method, which is basically transferring the nonlinear problem into a series of linear problems.

The problem can be solved in Optistruct transient (EXPDYN) or Radioss optimization (refer to tutorial RD-E: 5101 Thickness Optimization for B-Pillar).

 

Attached are various documents that may be helpful.

NL_Opti_Jun7.pdf

충돌_최적화_해석_2017_v01.pdf

충돌_최적화_해석_REV04.pdf

expdyn_bump_opti.hm

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23 minutes ago, Ivan said:

Hi Amasker,

 

unless the collision is at slow speed (minimal kinetic compared to internal energy), this problem should be solved using an explicit time integration scheme to account for the effect of mass (inertia).

Optimization is possible via the equivalent static load method, which is basically transferring the nonlinear problem into a series of linear problems.

The problem can be solved in Optistruct transient (EXPDYN) or Radioss optimization (refer to tutorial RD-E: 5101 Thickness Optimization for B-Pillar).

 

Attached are various documents that may be helpful.

NL_Opti_Jun7.pdf

충돌_최적화_해석_2017_v01.pdf

충돌_최적화_해석_REV04.pdf

expdyn_bump_opti.hm

To add Optimization is also available through RADIOSS which runs OptiStruct in the background for optimization.

RD-E: 5100 Optimization in RADIOSS

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As said, there are some restrictions when using Optimization with Dynamic loads. The transient analysis doesn't support optimization, but frequency does. So one has to convert to the load to either frequency domain or use ESLM optimization or use RADIOSS optimization,

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@Ivan@Prakash Pagadala

Thank you very much,

the B-pillars I am working on now include steel plates and composite materials, so the optimization of the steel plate thickness and composite materials should be optimized at the same time. However, the optimization module in RADIOSS does not seem to support composite optimization.

 

So I have an idea of equating transient loads into static concentrated loads, but how do you spread this concentrated load to a specific area? Can you give any advice?

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18 hours ago, Amasker said:

@Ivan@Prakash Pagadala

Thank you very much,

the B-pillars I am working on now include steel plates and composite materials, so the optimization of the steel plate thickness and composite materials should be optimized at the same time. However, the optimization module in RADIOSS does not seem to support composite optimization.

 

So I have an idea of equating transient loads into static concentrated loads, but how do you spread this concentrated load to a specific area? Can you give any advice?

This is a very time taking process. Instead, you can run a ESLM

ESLM for Nonlinear Response Optimization.pdf

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Thank you, @Prakash Pagadala

 

I converted the concentrated load into a pressure load. After optimization, I found that the displacement of the upper end of the B-pillar is particularly large. I want to know how to set the boundary conditions and constraints to get close to the constraint of the B-pillar in the whole vehicle.

And can you check the errors in the model ?

 

 

FS..2..(4).fem

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Hi,

 

Can you run a linear static analysis and check the results?

 

I see the displacement in Y axis is around 450mm which is very huge. Please check the loads and units.

 

BCs looks fine. I suggest you refer some papers available online on B-pillar analysis. 

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@Prakash Pagadala

 

Thanks,I also found the same problem, but the load and the unit are carefully checked. Regarding BCs, I don't know whether this constraint can really and effectively simulate the constraint of the B-pillar in the whole vehicle.Maybe BCs is wrong??I don't know.

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