LS Dyna

LS Dyna

Drop test end time

    • uzairali1995
      Subscriber

      Hi to all.

      Can any one please tell me about the end time when we setup all the parameters in analysis settings what end time should we need to put to get better results for example i have considered 5ft height for drop and i want good results what end time should i need to put and how many time steps can get better results . Thanks in advance

    • Akshay Maniyar
      Ansys Employee

      Are you using drop test wizard or setting complete model by yourself?
      As when you use drop test wizard it calculates end time based on the impact velocity and geometry of the part. The end time is generally the time it would take for geometry to travel 10% of its own length in the ÔÇôY direction. About timesteps, I have described it below:
      Initial Time Step :
      ÔÇó If left on Program Controlled (recommended), the initial time step will be automatically set to ┬¢ of the smallest initial element stability time step.
      Minimum Time Step :
      ÔÇó If the time drops below this value, the simulation will stop .
      ÔÇó If left on Program Controlled (recommended), the value will be set to 1/10 of the Initial Time Step.
      Maximum Time Step :
      ÔÇó Solver will use the minimum of this value or the computed stability time step
      ÔÇó Program Controlled is recommended

      regards amaniyar
    • uzairali1995
      Subscriber
      Thanks for you response.
      I am setting up the complete model by myself. I have understood what you are saying. Lets say i am dropping the object from 5ft height or i can also setup velocity which is 5.467m/s^2. So now there is also option to setup time steps . Like initially 1 time step is there. How many time steps would give better results if we drop the object from 5ft.
    • Akshay Maniyar
      Ansys Employee

      Can you please share image of settings? Are you talking about various time steps which I explained above or number of steps option?
      regards amaniyar

    • uzairali1995
      Subscriber
      Ok i can share the image . And i am talking about number of time steps
    • Chris Quan
      Ansys Employee
      Since time step is controlled by the program and is not a constant due to material deformation, program won't be able to predict in advance how many time steps would need to finish the simulation at the specified End Time.
      Program sets the Maximum Number of Cycles to limit the maximum number of time steps to run in a single simulation. By default, it is 1E+7. This is the number you can change if you want to run the model for a specific number of time steps, for example, 100.

    • uzairali1995
      Subscriber
      What would be the end time to setup for good results like i am dropping plastic (PLA or ABS) object from 5ft. What end time should i setup to get good results . Thanks in advance
    • peteroznewman
      Subscriber
      Don't worry too much about the end time. Try 0.010 seconds.
      Explicit Dynamics solution is very easy to restart from the last cycle and continue the solution using a new larger End Time. If 0.010 s was not long enough, you can keep going. You just have to pull down the last cycle in the Restart from Cycle field to replace the 0.
      Explicit Dynamics solution is very easy to interrupt the solution to check the progress. Make sure to Interrupt and not Stop, as Stop means discard the solution! If you have waited 8 hours and it has not got to the end time, you can Interrupt and see what you have.
    • uzairali1995
      Subscriber
      So when analysis complete is there any criteria we can verify that results are acceptable?
    • peteroznewman
      Subscriber
      I would look to see that the part has finished rebounding from the ground. You can expect the peak stress to occur at the lowest point of impact with the ground.
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