Lenz experiment example: oscillations in total energy

- September 23, 2024 at 8:34 am
  
  quemener
  Subscriber
  
  In LS-DYNA I have ran the Lenz experiment example. Looking at the total energy versus time, I get numerical oscillations when the permanent magnet enters the copper tube. I do not know how to get rid of these oscillations. They remain even when decreasing the time step (common to both mechanical and EM solvers).
  Does anyone has hints on how to solve this?
- October 1, 2024 at 5:33 pm
  
  Reno Genest
  Ansys Employee
  
  Hello Gilles,
  The magnet (part #2) in this model only has kinetic energy and so the total energy is equal to the kinetic energy. The kinetic energy oscillates because the velocity of the magnet in the z direction also oscillates when it enters the copper tube:
  I don't think this is numerical noise. In explicit dynamics, you will usually get vibration if you don't add damping to the model.
  You expect smooth braking for this experiment? Do you have experimental data for the velocity of the magnet vs time?
  Try adding damping and see if you can get smoother braking.
  You will find more information about damping in LS-DYNA here:
  https://ftp.lstc.com/anonymous/outgoing/support/FAQ/damping
  
  Let me know how it goes.
  
  Reno.