Tetrahedrons are controlled by segment and volume constraints, which allow the application of volume preservation on a local basis. Global volume preservation is achieved by guaranteeing local volume preservation for all the individual tetrahedrons.
Carbon Tissue is an extension of tetrahedral simulation where users can specify parts of the tetrahedral mesh to additionally receive surface and dihedral (i.e. bend) constraints.
This is an important add-on for all types of flesh and skin simulation.
Carbon Tissue has been extensively used in movies for flesh, skin, viscous materials like saliva, and muscles.
Facial and Muscle Simulation using FACS
As part of the Digihuman project in 2019, we have developed Carbon Tissue as an extension to our existing tetrahedral simulation.
In addition, we have added a reference interpolation process, which allows to provide FACS as input to your Tissue simulation.
This means that you can run a facial animation through Carbon physics to achieve more believable results due to the non-linear and secondary motion.
Also, you can rig muscle behavior to bone animations, i.e. angle / position of bones to get a full physics rig of a character.
Check out the videos below... all using the same technology!
NON-UNIFORM BEHAVIOR
Just like Carbon Cloth, Carbon Tetrahedrons accepts paint maps for nodal customization of simulation behavior. Below is shown a mattress which is painted to identify soft and stiff regions.
Painted tetrahedral mattress with non-uniform behavior.
Geometry Caging For Deformable Bodies
Body deformations rely on volume preservation. This deformable head is 100 percent volume preserving and realistically responds to the rods. For visualization purposes, the low resolution simulation tetra geometry can be captured with a high resolution render geometry.
Low resolution simulation geometry and high resolution render geometry.
Result after the caging process.
Below is a stress test for the Carbon Tissue, which it passes with flying colors.
Skin Layers
The following examples cover the main deformation cases, such as twisting, bending and poking.
These setups take advantage of Carbon's Soft Binding, which is a Binding constraint that has a non-zero radius to allow movement.
By binding a layer of Tetras to the surface of an animated Collider and filtering collision between those two objects,
the Tetras will follow the animation up to a point where the Tetra constraints win over the soft Binding constraints.
This handles situations where the tetrahedrons would otherwise be pushed inside each other and eventually corrupt or blow up.
Additionally, as you can see in twisting and poking, skin shearing/sliding is achieved as in real life.
The hippo skin in Jumanji was simulated with Carbon Tets.
Ropes And Cables
There are multiple ways to simulate ropes: Using a very stiff Carbon Cloth, creating a long chain of Carbon Rigid Bodies which are connected by Carbon Joints, or using Carbon Tetrahedrons. It is not necessary to use a high resolution simulation geometry to capture characteristic behavior.
Low resolution simulation geometry and high resolution render geometry.
Result after the caging process.
And, similarly, here is a steel cable:
Plants
Plants are very suitable for tetrahedral simulations if the intention is to show some deformations.
Very stiff plants are best modeled with low resolution tetra geometry and then simulated with a large numbers of iterations and subdivisions.
The low resolution plant simulation geometry can then be captured by high resolution render geometry.
Low resolution simulation geometry and high resolution render geometry.
Result after the caging process.
Shoes
The soles of modern sports shoes display a wide range of behavior. Some are very stiff, others deform while preserving their volume, and few show similar properties to sponges, i.e. non-volume preserving deformations due to air chambers within the material.
Shoe using a sole made from Carbon Tetra. Simulation geometry.
This shoe example is set up to lose a maximum of 10 percent volume during even the strongest deformations.
Another very interesting fact about this example is that it combines all major features in the Carbon portfolio. The shoe sole is made from tetrahedrons i.e. simulated using Carbon Tetra. All three straps (front, middle and back) are simulated as Carbon Cloth and the buckles are Carbon Rigid Bodies. The components are held together with Carbon Seaming and the floor and foot which deform the shoe are Carbon Colliders.
Rendered shoe simulation.