February 2, 2023 at 3:18 pmYuqian TUSubscriber
Is there a keyword or a way to constrain nodes (either in a shell/solid element or rigid node set) at X and Y directions that nodes are only allowed to move forward. When the nodes want to move backward, the displacement is set to 0.
I was thinking about local coordinate system with rigidwall, but didn’t seem to work.
Thanks a lot!
February 7, 2023 at 4:17 pmJim DayAnsys Employee
A couple of possibilities:
- Attach a stiff *ELEMENT_SEATBELT and an accompanying *ELEMENT_SEATBELT_RETRACTOR such that the seatbelt resists backsliding and is reeled in as the part moves forward.
- To resist backsliding, a feedback control system of sorts could be employed to apply a resisting force.
For example, here’s an example in which a force is applied to part #1 in accordance with the control law shown below so that it translates to a specified target point.
Force = -gain1 * (displacement – target) – gain2 * velocity
The feedback control system is governed by the following keywords which are used to:
- define the gains and other pertinent parameters
- define the feedback control law
- apply the load
R gain1 0.060000
R gain2 0.010000
R target 2.000000
$# lcid sidr sfa sfo offa offo dattyp
100 0 0.000 0.000 0.000 0.000 0
-gain1*(dx(28)-target) – gain2*vx(28)
$# pid dof lcid sf cid m1 m2 m3
2 1 100 0.000 0 0 0 0
In *DEFINE_CURVE_FUNCTION dx(28) is used to monitor the x-displacement of node #28 while vx(28) returns the node’s velocity. These responses are updated continuously with the current values as the simulation progresses. The function itself could be a control law that involves any type of model response, such as, nodal forces, accelerations, stresses, etc.
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