Gravitational Field

Gravity Commands

MPM simulations can include gravity or any other constant body forces. In scripted files, the command to add gravity is:

Gravity <(gravX)>,<(gravX)>,<(gravX)>

In XML files, gravity is added with the the <Gravity> element:

<Gravity>
  <BodyXForce>(gravX)</BodyXForce>
  <BodyYForce>(gravY)</BodyYForce>
  <BodyZForce>(gravZ)</BodyZForce>
</Gravity>

where (gravX), (gravY), and (gravZ) are the accelerations due to gravity in the x, y, and z directions, respectively ((gravX) and (gravY) are for R and Z directions in axisymmetric calculations). In scripted files, the units are m/sec², but in XML files, the units are mm/sec².

In scripted files, all three parameters are optional. If all are omitted, the gravitational force field is set to Earth's gravity with down being in the negative y direction (i.e., it is equivalent to the command Gravity 0,-9.8,0). If (gravX) is included, but (gravY) and/or (gravZ) are omitted, the omitted parameters will be set to zero. In XML files, any omitted forces are set to zero.

Grid Body Forces

Gravity (in general) is a constant body force. The commands in this section let you apply a more general body force that can depend on position an time (currently only available in OSParticulas and using XML comamnds. In XML files, body forces are added within the <Gravity> element:

<Gravity>
  <GridBodyXForce>(bodyX)</GridBodyXForce>
  <GridBodyYForce>(bodyY)</GridBodyYForce>
  <GridBodyZForce>(bodyZ)</GridBodyZForce>
</Gravity>

where (bodyX), (bodyY), and (bodyZ) are user-defined functions of position (x,y,z in mm) and time (t in ms) that evaluate to a body force acceleration in units of mm/².

Notes

1. If no Gravity command is used, the simulation will have no gravitational forces. Thus to have Earth's gravity you need a Gravity command, even if it has no parameters.