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Static equilibrium between rigid/modal simulation

sylvain.grosroyat
Hello,
 
The system i simulate is a propelled vehicule that is composed of two parts : first is a rigid part, the second is a flex part.
 
Until now, i started the simulations with a sim/statics command, in modal representation => the result is the nodes of the flex part move to the equilibrium positions before the transient simulation.
Good idea (or not ?...) : i use a fixed joint, only during the sim/statics command, to link my vehicule with the ground. Without the joint, the static analysis is not successful. Note that the 2 parts are linked by bushings.
 
But now, due to controls consideration, i need to do few seconds of simulation before. As there is no interest to simulate this part of the simulation in modal mode, i tried to :
  1. realize the simulation in rigid mode during few seconds
  2. then activate modal representation of the flex part
  3. realize the sim/statics command in order to obtain equilibrium of the flex part,
  4. realize the rest of the simulation
But step 3 is never successfull, even playing with activate/deactivate commands of the fixed joint and bushings.
 
Do you have any advice please ?
 
Thanks for your help.
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  • 0
    It is always a good idea to get static equilibrium before you start the dynamic portion. But not always possible.
    Using a fixed joint might be overkill. In many cases a "stake" between the flexible part and the ground is enough. This stake can be implemented using a in-line jprim that prevents the x and y motion, but allows for all rotations and the motion along z (assuming that z is your vertical axis). This is how most vehicle model are implemented. Sometimes you would also add a perpendicular jprim to look the yaw motion.
     
    In the process you describe above, after the first few seconds of simulations, do you move the j-marker (on ground) to coincide with the i-marker (on the moving/flex part) before activating the fixed joint?
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  • 0
    It is always a good idea to get static equilibrium before you start the dynamic portion. But not always possible.
    Using a fixed joint might be overkill. In many cases a "stake" between the flexible part and the ground is enough. This stake can be implemented using a in-line jprim that prevents the x and y motion, but allows for all rotations and the motion along z (assuming that z is your vertical axis). This is how most vehicle model are implemented. Sometimes you would also add a perpendicular jprim to look the yaw motion.
     
    In the process you describe above, after the first few seconds of simulations, do you move the j-marker (on ground) to coincide with the i-marker (on the moving/flex part) before activating the fixed joint?
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