Hello everyone,
I have written implicit user subroutine element (VUEL) for an 4-node shell before, in which the stiffness matrix (k) and RHS (f = - k*u) defined can give better results for various models in quasi-static implicit analysis.
I'm currently trying to write an explicit subroutine for an 4-node shell explicit user subroutine element (VUEL). I've defined the Uniform mass matrix, the stabilization time increment is defined according to the characteristic length method, the internal energy is the integral of displacement multiple force, the stiffness matrix (k) and RHS (f = - k*u) are the same as in UEL.
To validate it, I've defined a single element with an ENCASTRE constraint on two nodes and a velocity boundary condition imposed on the other two nodes. However, the total energy of the first step of the analysis step overflows the data.
In addition, in the bullet hitting target model, once the bullet (C3D8R) touches the flat plate (VUEL), the kinetic and total energies suddenly increase or even data overflow, and some nodes in the impact area on the flat plate also experience excessive rotational displacement or floating point overflow.
Is there a problem with my definitions in the above section, or are there less variables defined (e.g. acceleration, damping, etc.)
If any of you can solve the problem, I'd appreciate it.
Thanks!
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