Simulation Flashcards
What is Rigid body simulation
A different method to simulating (opposed to particle systems)
It is a geometry
The object can rotate upon collisions instead of move off
How many DOF do particle systems have
3
(x,y,z) moving
How many DOF do rigid objects have
3 (x,y,z)
3 For rotation along each of (x,y,z)
What is torque
Rotational force of rigid bodies
What is impulse based collision
Simply skip the force term
Instead we directly modify the velocity instead of calculating acceleration for force
What does it mean for a rigid body to be “stable”
Making sure it is not vibrating
If it is sat on a surface - no constant collisions between particles
Called “rest in contact”
Essentially stopping the simulation to avoid this unnecessary vibration
What is “stacking”
When another rigid body balances on top of another - “stacked” on top
Any change of state of one of the objects will affect the rest in the stack
What is Articulated rigid body simulation
Similar to rigging step
If we have two bones and a joint with a “joint constraint” - the joint is constrained in some way
The two bones have 6DOF each and the joint has -2 rotational DOF deducted from the bones because the joint only has one rotation and -3 DOF deducted because the bones have to move as one
Essentially 6DOF(bone1) + 6DOF(bone2) -5DOF(joint) = 7DOF in the system
We can also think of the whole system as 6DOF +1 due to the rotation in the joint = 7DOF
What is deformable object simulation
Eg elastic octopus or cloth
collision detection for rigid bodies cannot be applied here
simulation technique must be different
What is the Finite Element method (FEM)
One method that can be used for deformable object simulation
We first convert the object to tetrahedrals
For each tetrahedral we know its rest shape (which it reverts to) and its deformed shape
So FEM allows us to compute the forces applied to each vertex which changes the rest shape to the deformed shape
What is mass-spring fracture simulation
springs are modelled between every two particles, but if the force is hard enough - the springs break, creating a fracture
What is fluid simulation
commonly: particle based simulation, lagrangian simulation
We can also use grid-based fluid simulation
use a gridding system to separate the bounding box (eularian fluid simulation), then analyse how much fluid is in every voxel (small box) to make sure we have not lost any fluid
What is hybrid fluid simulation
The best case situation
a hybrid of eularian and lagrangian simulation
so we have a grid as well as a particle system
each representation is used based on their purpose
this fluid simulation is not limited to liquids - smoke/ cloth/ etc
