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giannibruno

Surfaces interaction

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Hello everyone,

 

I have a problem with this simple landing gear. The shaft (orange) is fixed to the fuselage. The torsion springs (green) are inserted  in the shaft end engage the two arms (yellow) that are connected to the wheel. At the same time the arms are bonded to the shaft.

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I need to create an interaction between the follow surfaces:

1 Spring tail/shaft (slip)

2 Spring tail/arm (slip)

3 Arm/shaft (slip)

4 Inner part of the spiral's spring/shaft (avoid compenetration)

I tried to create this interactions but i failed. I had an "accetable" result only for 1 and 2  without slide but with freeze interaction.

 

Can you help me with this problem?

Thanks.

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Hi @Premanand Suryavanshi

I tried again creating the contacts like in you video. When i run Optistruct there are strange results with stresses.

It seems as if the contact blocks the two surfaces together.

Can you see this video and explain me why i have these results?

 

Thank you so much for you help.

 

 

Landing Gear Optistruct.zip

 

 

 

 

 

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Hi @Premanand Suryavanshi. Sorry for my late reply.

 

I tried all the permutation of Master and Slave for each group (also considering the load flow) but there is no way for acceptable results. 

For all the groups there aren't  big differences if i switch master and slave. But the problem is for both contacts arm-shaft.

When i set the arm as Master and the shaft as Slave (should be the right load flow) i have the same results of the video (strange stress distribution)

If i swicth Master and Slave everything explodes. 

 

There is a way to solve this problem?

Thank you

 

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Hi @Premanand Suryavanshi

Well ... I think that this stresses are more realistic than the previous ones.

However the springs should be stressed but seems that aren't stressed .

There are also areas with strange stress concentration on the shaft( but this is a minor problem).

 

Is really better than the mine but I don't think that this is the true stress distribution due the problem on the springs.

 

What was the problem with my model?

 

Thank you so much.

 

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Hi

I have your same results now in my model but there is still the problem of stresses and load flow.

The problem is that the spring doesn't work properly. Seems that the two arms and the shaft are welded together.

The load flow has to go through the springs and not completely through the arms.

 

Thank you

 

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Hi giannibruno,

 

It is because the spring is not making proper contact with any of the components. When you examine the model closely, you'll find distinct gap between the spring surface and other components. I think you need increase the diameter of the spring and try again.

 

 

Thank you

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Hi @Premanand Suryavanshi

I will try to increase the diameter of the shaft because i can't change the spring.

Is it anyway necessary to add a contact surface between the inner part of the spring and the shaft with the new diameter?

 

I will try in this way but i have some doubt about the spring. Because this is a torsion spring that need to works following the same winding direction of the helix. When i load the spring in this way the inner diameter decreases a bit. So the spring can't work properly if i remove the gap between the spring and the shaft,.

Maybe it could be better if the shaft's diameter is smaller than the spring's one and the spring can slides on the shaft's surface in only one point.

 

Anyway now i will try to  removing the gap between the spring and the shaft and see if the results are better.

 

Thank you

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Hi @Premanand Suryavanshi

 

In this days i tried some solutions but all with the same results.

 

I can't apply your solution (Increase the diameter of the springs) 

 

I tryed to increase the diameter of the shaft but there is a problem because the shaft's axis isn't the same of the spring. But I will try to change the axis of the shaft part that is inside the spring and increase its diameter in order to create a contact surface between the shaft and the inner part of the spring. I will update you about this.

 

I tryed also other configurations but without good results.

 

I will try changing the CAD (with one point of contact between the shaft and the inner part of the spring) and remesh. In this way what kind of contact will I have to add between shaft and the inner part of the spring?

 

Thank you.

 

 

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7 hours ago, giannibruno said:

I tryed to increase the diameter of the shaft but there is a problem because the shaft's axis isn't the same of the spring. But I will try to change the axis of the shaft part that is inside the spring and increase its diameter in order to create a contact surface between the shaft and the inner part of the spring. I will update you about this.

I think you need to decrease the inner dia of the shaft (middle part) in order to make contact with the spring. 

 

Thank you

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Hi @Premanand Suryavanshi

 

I tried to reduce the two diameters but i have the same results.

Is it possible that the landing gear still has some DOF that i didn't block? 

I tought that there isn't a constraint in the x direction for the springs and the two arms. I tried to add this contsraints but still the same results.

 

Do you have other advice for my problem?

 

Thank you

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Hi giannibruno,

 

I think we need to add some constraint to the spring. Because, when you animate the motion, you can see that spring is not doing actual work (Resisting work), it is simply behaving as a part of Arm and moving along with it. I'm trying to constraint the spring in different ways and checking the results. I'll share my findings once i'm done. Until then, please can you also try it.

 

Thank you

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