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Contact mechanics tolerance #957
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Very good idea as I have very little intuition for its impact (it being absolute for instance) and thus having always some doubts. I will try to do this in the following two days. |
I believe this is also related to issue #926 about possibly re-defining the friction bound. |
I agree that it's related. But I don't think it's covered by that issue, is it? |
While I do mention the possibility of changing the tolerance in that issue, the main focus of that issue is still the definition of the friction bound. But resolving one of these issues could influence the other one, since the tolerance is related to the definition of the friction bound. |
While looking at the code for the first time I am raising some stupid questions. I will make use of this platform to collect them. I do not necessarily expect them to be relevant for the actual topic. My first question is. Should one be afraid of a switch in sign of the derivative of the tangential_fracture_deformation_equation when b < tol and b>tol? In the former it is 1, while in the latter it is Maybe this comment is completely off, I wanted to state it nevertheless. |
Are you talking about the derivative w.r.t. t_t? Should we discuss in person? |
After discussion with @IvarStefansson:
@keileg @mariusnevland what do you think, especially regarding point 2? If this is meaningful for you, one suggestion would be, that @mariusnevland who has identified cases in which the choice of the tolerance of interest plays an important role, runs his test cases and compare the current setup. @IvarStefansson would implement the possibility to choose the tolerance from outside prior to testing. |
I think point 2 sounds reasonable. Since we check whether a cell is open or closed based on the value of t_n, it would make sense to have the tolerance somehow related to some "characteristic value" of t_n. Also, as I mention in issue #926, changing the definition of the friction bound from Regarding the derivative with respect to t_t, I can mention that for the regularized complementary functions that I use in the Uzawa algorithm I'm working on, this derivative becomes 1 for both open and closed cells. |
To elaborate a bit on the second paragraph above: If |
It all makes sense to me. |
We need to decide what to do with the tolerance in the tangential contact mechanics equation. This at least involves revisiting Hüeber/Wohlmuth and ensuring our value does not violate their recommendations.
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