Sliding Object with Force

[CCK1]

Hello,

I want to analyze simplified project. One object is top of another and sliding with force(moving force). It is like car moving on bridge. 

I used nonlinear transient response. (I did **** with explicit dynamic but it takes to much time and I want to solution where time is 3-4 second.)

 The contact type is sliding/no separation between surfaces. 

 There is a downward force on object 1 (car) and velocity in forward direction.

 The bridge has constrain from two end.

 The problem as you can see in attached file is force is not moving with object.

I also tried separation contact and the force is actually moving but after 0.3 second, the object goes inside the bridge and falls.

Maybe I can put concrete mass in center of rigid connector but it is also not moving with object.

Any suggestion, what am I missing here?

Project file is here: https://we.tl/t-KgjYUWkVtz

[John_Holtz · Accepted solution]

Hi @CCK1 

Your model demonstrates that Sliding contact is applicable for small displacements only. The nodes in contact do not update because the displacement should be so small that updating the nodes is not necessary. Since you have large displacements, sliding contact is not appropriate.

In most models, creating contact between every combination of nodes on the the primary and secondary faces would create so much contact that the number of elements in the model would be 100 times larger. That is inefficient. That is why there is an input on the contact definition for "Maximum Activation Distance". The Maximum Activation Distance is the longest distance between nodes that will have contact elements generated. If the part moves farther than that, there is no contact (and the car falls through the bridge and people die).

The solver has no idea what will happen in the analysis, so the default value for Maximum Activation Distance is only applicable for a limited number of models. You know what is going to happen in your analysis, so I suggest that you always enter a value for the Maximum Activation Distance. (The weight will move a maximum of 442 mm before it is off the bridge. 442 is a good number for the Maximum Activation Distance. Of course, that creates a large number of contact elements that will never be used; all the contact off to the side of the car's path is wasted disk/memory space and solve time. It is a good thing you are using Inventor Nastran 2023 with its efficiency improvements to the contact!)

I see that you applied the force to the bottom face of the block; that is, the same face that is in contact. I suggest that you avoid applying loads to faces that are in contact. I would apply the force to the top of the block.

Good luck.

John

[CCK1]

First of all, thank you for your reply. You gave me a detailed explanation.

I have limited time now. However, I tried changing Maximum Activation Distance which I was completely misunderstood and it solved my problem.