Additional parameters for physical material¶
When user uses AGXDynamics Plugin the following physical material (properties) can be used.
Sample¶
User can find the sample of AGXDynamicsPlugin material from below. The motion will be changed as per value of parameters.
- choreonoid/samples/AGXDynamics/agxMaterialSample.cnoid
How to set the material¶
Friction coefficient and restitution coefficient of links in AGXSimulator can be set by below procedure.
- Describe Material and ContactMaterial in material file.
- Set Material defined in material file in body file.
How to describe in material file¶
choreonoid/share/default/materials.yaml
, and automatically loaded.materials:
-
name: Ground
roughness: 0.5
viscosity: 0.0
-
name: agxMat5
density: 1.0
contactMaterials:
-
materials: [ Ground, agxMat5 ]
youngsModulus: 1.0e5
restitution: 0.1
spookDamping: 0.08
friction: 0.416667
surfaceViscosity: 1.0e-8
adhesionForce: 100
adhesivOverlap: 0.2
frictionModel: [ cone, direct ]
contactReductionMode: reduceGeometry
contactReductionBinResolution: 3
Explanation of material parameters¶
Bulk material¶
parameter | default value | unit | data type | explanation |
---|---|---|---|---|
density | 1000 | kg/m3 | double | density that is used for calculating of mass of link, inertia tensor, and center of mass. |
youngsModulus | 4.0e8 | Pa | double | Young’s modulus that represents the hardness of link(rigid body). Smaller value may cause penetration between links. |
viscosity | 0.5 | - | double | viscous restitution.The pair of viscous restitution becomes restitution coefficient. |
spookDamping | 0.075 | s | double | spook damping. Relax the penetration of links(rigid bodies). |
poissonRatio | 0.3 | - | double | Poisson’s ratio (deprecated since AGX 2.27.0.0) |
Surface material¶
parameter | default value | unit | data type | explanation |
---|---|---|---|---|
roughness | 0.5 | - | double | Roughness, Corresponds to friction coefficient. |
surfaceViscosity | 5e-09 | - | double | Surface viscosity. The pair of each surface viscosity becomes the surfaceViscosity of ContactMaterial. It defines how “wet” a surface is. |
adhesionForce | 0.0 | N | double | adhesion force that determines attactive force acting between two colliding rigid bodies in the normal direction. Acting like adhesive agent. |
adhesivOverlap | 0.0 | m | double | an absolute distance that defines the contact overlap where the adhesive force is active. It becomes active when penetration of link is larger than adhesiveOverlap |
Note
If ContactMaterial is set, it is prioritized. Surface material of Material is not used.
Wire Material¶
Parameter | Default value | unit | data type | explanation |
---|---|---|---|---|
wireYoungsModulusStretch | 6e10 | Pa | double | young’s modulus for strech |
wireSpookDampingStretch | 0.075 | s | double | spook damping for stretch |
wireYoungsModulusBend | 6e10 | Pa | double | young’s modulus for bending. |
wireSpookDampingBend | 0.075 | s | double | spook damping for bending |
Explanation of ContactMaterial parameters¶
parameter | default value | unit | data type | explanation |
---|---|---|---|---|
youngsModulus | 2.0e8 | Pa | double | young’s modulus |
restitution | 0.0 | - | double | restitution coefficient. 0:completely inelastic collision、1:completely elastic collision |
spookDamping | 0.075 | s | double | spook damping |
friction | 0.5 | - | double | friction coefficient |
secondaryFriction | -1.0 | - | double | secondary friction coeefient. It is activated when friction model is orientedBox and secondaryFriction>=0. |
surfaceViscosity | 1.0e-8 | - | double | surface viscosity coeeficient. Complaiance for friction constraint. |
secondarySurfaceViscosity | -1.0 | - | double | secondary surface viscosity coefficient. It is activated when friction model is orientedBox and secondaryFriction>=0. |
adhesionForce | 0.0 | N | double | adhesion force |
adhesivOverlap | 0.0 | m | double | adhesive overlap |
frictionModel | [ default, default ] | - | string
string
|
friction model : default(cone), cone, box, scaledBox, orientedBox
solver : default(split), split, direct, iterative, iterativeAndDirect
|
contactReductionMode | default | - | string | the way of contact reduction: default(reduceGeometry), reduceGeometry, reduceALL, reduceNone |
contactReductionBinResolution | 0 | - | uint8_t | bin resolution(number of bins per dimension) of contact reduction. In case of zero, the parameters of AGXSimulator item are used. |
primaryDirection | [ 0, 0, 0 ] | Unit vector | Vec3 | primary direction of the vector when orientedBox friction model is used. |
referenceBodyName | - | - | string | reference body name when orientedBox friction model is used. |
referenceLinkName | - | - | string | reference link name when orientedBox friction model is used. |
Note
AGX Dynamics does not distinguish between dynamic friction coefficient and static friction coefficient. Actually, the difference in value is around 10-20%, and most situations do not have to worry about it.
If the ContactMaterial is not defined¶
- youngsModulus = (m1.youngsModulus * m2.youngsModulus)/(m1.youngsModulus + m2.youngsModulus)
- restitution = sqrt((1-m1.viscosity) * (1-m2.viscosity))
- spookDamping = max(m1.spookDamping, m2.spookDamping)
- friction = sqrt(m1.roughness * m2.roughness)
- surfaceViscosity = m1.surfaceViscosity + m2.surfaceViscosity
- adhesionForce = m1.adhesionForce + m2.adhesionForce
How to describe the material in the body file¶
massType: mass # Use values of center of mass, mass, inertia which described in the body file
massType: density # Calculate values of center of mass, mass, inertia automatically
material: Default # Default material
material: Ground # Ground material defined in choreonoid_dev/share/default/materials.yaml or user defined material file
material: useLinkInfo # Use parameters of material described in the body file
Below are examples of how to describe.
Note
Currently, you could not get or check the result values of center of mass, mass, inertia from the Choreonoid Links and GUI when using massType: density
Conventional description¶
- Conventional description of Choreonoid
- Use centerOfMass, mass inertia which are described in the body file
- Parameters of material are set default values except density
- ContactMaterial will be default vs xxxxxx
links:
-
name: box1
centerOfMass: [ 0, 0, 0 ]
mass: 1.0
inertia: [
0.02, 0, 0,
0, 0.02, 0,
0, 0, 0.02 ]
Using material file (Recommended)¶
- Use material file to set material including density
links:
-
name: box1
massType: density # Use density to calculate center of mass, mass, inertia automatically
material: steel # Use material steel defined in the material file
density: 1.0 # If density is written here, use this value. It override density of steel material.
Using conventional description and material file (Recommended)¶
- massType: mass <- use center of mass, mass, inertia described in body file
- Other material parameters use the value of the material file
links:
-
name: box1
massType: mass # Use center of mass, mass, inertia described in body file
centerOfMass: [ 0, 0, 0 ]
mass: 1.0
inertia: [
0.02, 0, 0,
0, 0.02, 0,
0, 0, 0.02 ]
material: steel # Use steel material described in the material file
Describe all material paramters directly (Not recommended)¶
- When set material: useLinkInfo, you can describe material parameters in body file
- The values of ContactMaterial are calculated according to If the ContactMaterial is not defined
links:
-
name: box1
massType: density
material: useLinkInfo
density: 1.0
youngsModulus:
poissonRatio:
viscosity:
spookDamping:
roughness:
surfaceViscosity:
adhesionForce:
adhesivOverlap:
Describe everything (Not recommended)¶
- Every paramters are described in the body file
- You will be confused which parameters are used in the simulation
- So this is absolutely not recommended
links:
-
name: box1
massType: density # Use center of mass, mass, inertia described in body file
centerOfMass: [ 0, 0, 0 ]
mass: 1.0
inertia: [
0.02, 0, 0,
0, 0.02, 0,
0, 0, 0.02 ]
material: steel # Use material defined in the material file
density: 1.0 # Use this density for automatic calculate
youngsModulus: # Below are not used
poissonRatio:
viscosity:
spookDamping:
roughness:
surfaceViscosity:
adhesionForce:
adhesivOverlap: