How to apply acceleration on particular body?

- April 23, 2020 at 1:06 am
  
  amir007
  Subscriber
  
  Hi,
  
  I need to apply acceleration on a particular Body, but I can not select any Body in Geometry part. It incdludes all the Bodies.
- April 23, 2020 at 3:57 am
  
  peteroznewman
  Subscriber
  
  Hi,
  
  I would like to turn gravity off on this heavy laptop I am carrying but I can not do that either. It is the same problem you are having. Acceleration acts on all mass.
- July 24, 2020 at 4:32 pm
  
  ArnaudBrun
  Subscriber
  
  Hello peteroznewman,
  
  I was wondering exactly like amir007; I get what you mean with your laptop example, but let's take a structure which is partially immerged in water.
  
  This structure has 3 bodies (A, B and C). 'A' is out of water and is subjected to the gravity only; 'B' and 'C' are subjected to gravity and the Archimede effect ('buoyancy' I think in english ?). How would you consider this Archimede effect if you wish to apply an equivalent acceleration (Aeq = gravity-buoyancy) only on bodies 'B' and 'C' ?
  
  I guess you could just apply a remote force on bodies 'B' and 'C' which represent the buoyant force, but I hope my example enlights why it could be interesting to be able to apply an acceleration on selected bodies. What do you think ?
  
  Thanks for your answer. Regards,
  
  Arnaud.
- July 25, 2020 at 1:08 am
  
  peteroznewman
  Subscriber
  
  Apply the load called "Hydrostatic Pressure" which will create a pressure that is a function of depth below the free surface and a function of gravity and a function of the fluid density. This exactly computes the upward force of the Archimedes effect of buoyancy.
  
  Then you would apply standard earth gravity which creates a downward force on all the mass.
  
  If you are trying to simulate a body floating in the fluid, then you have to adjust the free surface location until the upward force from the hydrostatic pressure is exactly equal to the downward force of gravity.
- February 8, 2023 at 4:54 pm
  
  Dhaval Mysore
  Subscriber
  
  Hi Peter,
  
  I am working on a model where the top-half of an assembly is being accelerated upwards by a cylinder-piston assembly. So, I need to apply acceleration ONLY to the top-half of the assembly that's being lifted, and not the rest of the body. In classical mechanics, solving for F = ma for the top-half of the assembly free body diagram would give me the force from the piston rod to top-half of the body as: F = m(g+a), were "a" is the acceleration with which the body is being pushed upwards, and "g" being the acceleration due to gravity.
  If you need some details about the cylinder-piston assembly modeled in my ANSYS model: they are modeled simply as two beams with a body-body general joint with translational and rotational dof free about the axis of the cylinder-piston.
  Another case: if I have, say an iron block, suspended from a non-metallic rod, and the iron block experiences a body force due to some magnetic field pulling it down. I need to solve for the reaction force at the connection between the top of the non-metal rod some external object it's connected to. So, the acceleration is to be applied ONLY to the iron block and not the non-metallic rod.
  
  Thanks