Unusual oscillating waves at ZerolengthContactASDimplex interface

[Zhou_Jx]

Dear Stko,
I used the ZerolengthContactASDimplex to simulate a friction contact between beam-based tunnel and soil. I did a seismic analysis followed a static analysis. However, a unusual oscillating waves was appeared at the tunnel-soil interface at the begining of the seismic analysis, and which is shown below:

unusual oscillating waves.jpg (76.42 KiB) Viewed 4299 times

And I defined the contact parameters as below：

zerocontact definition.jpg (41.82 KiB) Viewed 4299 times

I have changed the penatly from 1e9-1e17, but this problem is not solved.
Additionally, I tried to uncheck the implex to conduct a implict analysis. At the conditions, the static analysis is not not convergent.
I conduct the static analysis via a transient analysis with a large step, the paramaters setting as below:

static analysis.jpg (107.83 KiB) Viewed 4299 times

Overall, I have two questions:
1. What is the reason of unusual oscillating waves?
2. How can define the algorithm and system for a convergent static analysis?
Best wishes

Jiaxing.

[Zhou_Jx]

Dear STKO,
I double-check my model again, and I find it may be caused by the zerolength between beam elements. I modeled the tunnel lining with beam element and the joint with zerolength element. So, there is a complex soil-tunnel-tunnel interaction in this model. And the model's schematic is below:

Tunnel soil.png (14 KiB) Viewed 4286 times

I have some quick questions about the setting of this model:
1. How should I define the interaction to conform a reasonable interaction between soil element and beam, especially at the joint where has two nodes with same the same coordinates?
2. Is the setting of paramaters of the ZerolengthContactASDimplex is property in my model, which I conducted a node-node link interaction to deine the element. The node of beam is defined master node, and the node of soil is defined as the slave one?
3. Can I simulate the contact with other elements?

[Zhou_Jx]

Dear Stko,
I really need your help, and the unusual oscillation is not solved, and I will show you below:

[STKO Team]

Could you share your model?
I need to check carefully everything

[Zhou_Jx]

Dear STKO，
Thanks for your reply. I cannot post my model, I have solve the problem.

[STKO Team]

I have solve the problem.

Great! what was the problem?

[Zhou_Jx]

Dear STKO,

I wanted to express my appreciation for your attention to the issue I previously brought up. It appears that the cause of the unusual oscillation was due to a mismatched master-slave order with the local direction of the zerolength element. Specifically, this occurred the zerolength element with lower tensile stiffness and much larger compressive stiffness. This mistake caused certain zerolength elements to have "zero" stiffness, leading to the growing oscillation. However, I was able to resolve this issue by correcting the error and using a TRBDF2 integrator and 3% Rayleigh damping, resulting in the disappearance of the oscillation.

I am reaching out to verify with you whether the element of zerolengthcontactasdimplex model compressive-only behavior at the normal direction, without any tension behavior.

Thank you.

Best regards,

Jiaxing

[STKO Team]

I am reaching out to verify with you whether the element of zerolengthcontactasdimplex model compressive-only behavior at the normal direction, without any tension behavior.

Yes, it's based on a simple frictional contact following a coulomb friction law.
Along the normal direction, it has not stiffness if gap is positive, or the penalty stiffness you input if gap is negative

[Zhou_Jx]

Thanks for your reply, and have a good day!

[ValentinaSB]

Thank you!