Week 5 - Simulation Flashcards
How many degrees of freedom does a rigid body simulation have? (position and rotation)
6 degrees of freedom (1 for position on each axis, 1 for rotation on each axis)
How many degrees of freedom does a particle have? (position and rotation)
3 degrees of freedom (1 for position on each axis)
What is torque?
A purely rotational force
What is different about impulse-based collision do with the force-term? What type of simulation is it commonly used for? What else can it be applied to from Week 4?
Skips it, Instead an impulse is defined which directly effects the velocity, instead of force affecting the acceleration
It is commonly used by rigid body simulations
It can also be applied to mass-spring models
What is rest in contact? Why is rest in contact important for rigid body simulations? What stops it?
The collision calculation is slightly inaccurate, so if we constantly re-calculate the position of the rigidbody when it is resting, it will vibrate. When the body is stable we stop simulating it all-together, to prevent inaccuracies from adding up.
We start calculating collisiosn again when. force arrives to push it out of its stable position.
How many degrees of freedom does an articulated rigid body simulation with three RBs connected by two joints have?
8 DOF, one for each joint, and 6 for position and rotation of the whole system
What is FEM used for?
FEM (Finite element method) is used in deformable object simulation
How does FEM (finite element method) work?
Tetrahedralization of the mesh, because tetrahedrons are the simplest 3D object for volume, same as triangles in 2D.
For each tetrahedron we know its rest position, and how it is deformed.
We can compute the forces to go back to the rest shape, so on a high level we can compute the forces applied to every vertex to get back to the overall objects rest shape
What is tetrahedralization? What technique uses it?
Converting a triangle mesh into tetrahedrons.
FEM (Finite element method) for deformable object simulation
What method can be used for fracture simulation?
Mass spring, the springs break if the stiffness is too high and the amount of force passes a threshold, this then propagates through the connected springs which break as well.
What are the fluid simulation methods are there?
Particle-based fluid simulation
Grid-based fluid simulation
Lagrangian fluid simulation (don’t need to know this one in detail, but do need to know of the name)
Hybrid method (the best one, grid-based + lagrangian)
How does particle based fluid simulation work?
It simulates lots of particles which are interact with each other in a simulation phase, then we wrap the particles in a mesh for the rendering phase
How does grid based fluid simulation work?
We take a bounding box of the fluid and discretise it into voxels, the we analyse the attribute of the object for every voxel
Need to be careful that we don’t lose any fluid, the same amount leaving the box as going into other boxes
Common technique to solve it is called Eulerian fluid simulation
What else can fluid simulations be used for?
smoke, fire, cloth, etc…
