FEM Solver dynamics node

Sets and configures a Finite Element solver.

The FEM Solver DOP sets objects to use the FEM solver.

If an object has this DOP as its `Solver` subdata, it will evolve itself as a cloth object.

This solver recognizes the following special subdata, if present:

It also recognizes most standard subdata:

• Geometry data with the name `Geometry`

• Constraint data

• Force data

Before each solve, the finite element solver reads the simulation state of each object from the attributes on the simulation geometry `Geometry` to get the previous state. After the solve, the new state is written to attributes the `Geometry`. In addition, the solver may maintain an `EmbeddedGeometry`. This would typically be a more higher-resolution geometry that moves and fractures along with `Geometry`. The embedded geometry can consists of polygons or tetrahedrons (or a mix of these two).

The finite element solver approximates the physics of continuous materials by splitting them up into a finite number of elements. In the case of the Solid object, the elements are determined by the tetrahedrons. In the case of the Cloth Object, the elements are determined by triangles and quadrangles. The resolution of the tetrahedrons and the orientations of the individual tetrahedrons have little influence over the overall movement; as long as the overall solid shape is the same the behavior is roughly the same (except for very coarse meshes). The finite element method (FEM) treats the elements an approximation of a continuous material. This property makes the results very predictable when you simulate the same shape using a lower-res and a higher-res mesh.

Substepping ¶

Substeps

This is the number of substeps per frame. The higher this value, the better the quality and the accuracy of your simulation will be. However, the solve time per frame may increase. When you're having trouble with a simulation’s quality or stability, the first thing to try is increasing the Substeps. One particular case where this may be needed is when you have fast moving objects that collide. When the relative velocity is large compared with the feature size, you may need to manually increase the Substeps to get better looking results.

Capabilities ¶

Enable Collisions

When this is disabled, no collisions will happen in the simulation, regardless of any other collision settings on the solver or on any of the objects that are solved. This is a convenient toggle that allows you to quickly see how an object behaves without collisions.

Enable Fracturing

When this is disabled, no fracturing or tearing will occur on any of the Solid Objects or Cloth Objects attached to this solver.

Accuracy ¶

Absolute Tolerance Implicit Solve

The absolute tolerance that is used to decide when the finite element solver has found a good enough approximate solution for the implicit integration step. This roughly indicates the amount of error allowed in the acceleration that is computed in each integration step. It is not recommended to increase this tolerance too much from its default.

Relative Tolerance Implicit Solve

The relative tolerance that is used to decide when the finite element solver has found a good enough approximate solution for implicit integration step. In contrast with the absolute tolerance, this parameter has no units. It is not recommended to increase this tolerance from its default, because this may produce results that are unstable or poor quality. In some types of simulations, it may be necessary to reduce the Relative Tolerance Implicit Solve to a lower value, say 0.0001 or even smaller. For example, the tolerance may need to be lowered in fracturing simulations with very stiff objects.

Max Collision Passes

This is the maximum number of times, within a single substep, that the solver is allowed to detect and resolve new collisions. The collision resolution step in each pass may introduce new, secondary collisions that must be resolved in later passes.

Attributes ¶

Create Quality Attributes

This creates float-valued primitive attribute `quality` on the simulation geometry. This attribute allows you to find primitives that have a bad effect on the simulation. The closer the value is to 1, the better. Bad tetrahedrons have a value close to 0 and should be removed or improved.

Create Energy Attributes

This creates float-valued vertex attributes on the simulation geometry. These attributes `potentialdensity`, `dissipationdensity`, and `kineticdensity` show the potential energy density, the density of energy dissipation, and the kinetic energy, respectively.

Create Fracture Attributes

This allows the `fracturecount` point attribute to be created. Any point that was fractured at any time in the simulation will have a `fracturecount` of 1 or higher ever after.

Float Precision

This determines the floating point precision that is used internally by the finite element solver. Float 32 bit uses less memory and is generally faster than Float 64 bit. However, the extra accuracy of 64-bit floating point numbers may be needed when you are simulating object with very high overall stiffness or when your geometry is positioned very far away from the origin.

Integrator Type

This determines the type of integration that is used. The default is `Implicit`, which is the most stable option for simulations that have fracturing stiff objects. The `Implicit Order 2` allows more lively looking simulations of higher quality for about the same solve time. This is best used when doing finite element simulation of flesh on characters.

Max Fully Implicit Passes

For highly nonlinear finite element simulations, increasing this parameter may result in better quality without having to increase the sub-steps. This may be needed for simulations in which the deformations of the tetrahedrons are relatively large.

Attributes ¶

The finite element solver will recognize and use attributes on the simulated geometry. In the DOP network, this simulation geometry is attached to the simulated object as a sim-data with name `Geometry`. When an object is created, then the geometry and all the corresponding attributes are read from the Initial Geometry. This includes the standard position and velocity point attributes `P` and `v`.

The finite element solve supports input attributes and output attributes. Some attributes, such as the simulation state, are both input and output attributes. The input attributes include multiplier attributes for material properties, fracture attributes, and attributes for controlling target positions and corresponding hard/soft constraints. The output attributes include optional attributes for tet quality, energy densities, FEM node forces, collision info attributes and fracture info attributes.

Material Property Multiplier Attributes ¶

Each of the material properties of a simulated object can be locally modified using multiplier point attributes. As a rule, each of the material properties in the Model tab of an object can be affected by a multiplier attribute. As a rule, the name of the parameter is the name of the attribute. The name of the attribute is the name that is displayed after “Parameter:” when you hover over a parameter with your mouse cursor.

You can locally change the material properties of the object using point attributes. For example, you can make some polygons resists stretching and bending more than other polygons. These attributes work as multipliers for the parameters in the Model tab: The stiffness multiplier is a convenient way to modify the local stiffness for all object types that are recognized by the finite element solver:

Name Class Type Description
`stiffness` Point Float Multiplier for all types of stiffness.
`dampingratio` Point Float Multiplier for all damping ratios.
`massdensity` Point Float Multiplier for all mass densities.

For solid objects, the following multiplier point attributes can be used to modify the local behavior:

Name Class Type Description
`solidstiffness` Point Float Multiplier for both the shape stiffness and the volume stiffness of a Solid Object.
`solidshapestiffness` Point Float Multiplier for the shape stiffness of a Solid Object.
`solidvolumestiffness` Point Float Multiplier for the volume stiffness of a Solid Object.
`solidmassdensity` Point Float Multiplier for the mass density of a Solid Object.

Collision Control Attributes ¶

The FEM solver looks at collision identifiers to decide which primitive pairs are allowed to collide. The rule is that a pair of primitives may collide if they have the same collision identifier. (This mechanism may possibly be extended in a future release, allowing the user to specify exactly which collision identifier pairs may collide.) Collisions can be suppressed altogether for certain primitives by setting the special value -1. A collision id may be specified separately for the interior and the exterior side of each polygon and tetrahedron. The exterior side of a polygon is decided using the winding order convention, just like the normal direction. If `interiorcollisionid` is not specified, then the default collision id of 0 is used for triangles, but interior collisions are disabled for tets. If `exteriorcollisionid` is not specified, then the default collision id of 0 is used for both tets and triangles.

Consider, as an example, an FEM muscle simulation, we may want the muscles to collide only with the interior side of the skin polygons, so the `exteriorcollisionid` for those polygons may be set to -1 (disable).

Name Class Type Description
`exteriorcollisionid` Primitive Integer Collision identifier for the exterior side of a polygon or tet surface
`interiorcollisionid` Primitive Integer Collision identifier for the interior side of a polygon or tet surface

The following attributes can be used to locally multiply the Repulsion and Friction parameters:

Name Class Type Description
`repulsion` Primitive Float Multiplier for the Repulsion of an FEM Object
`friction` Primitive Float Multiplier for the Friction of an FEM Object

Material Space Attributes ¶

The attribute `materialP` can be thought of as the positions of the simulated object in the material space. `materialP` is the undeformed configuration relative to which the current position `P` determines the deformation of a simulated object. `materialP` must stay the same throughout the entire simulation. The finite element solver relies on assumption that the `materialP` attribute remains unchanged from frame to frame; it should never be modified externally (e.g., through a SOP solver) otherwise bad simulation results will be produced.

In the case where no Rest Shape is specified and nor `restP` attribute is provided, `materialP` can be thought of as a permanent rest position. If no animation of the rest position is required in a sim, only `materialP` should be specified (no `restP`). At any stage in the simulation, it is the mapping from `materialP` to the current `P` that determines the deformation of tets in simulated objects. The deformation in turn defines the energy stored inside the object.

To help determine the anisotropic behavior of solids, including fiber contraction, the solver can makes use of local UVW frames. These UVW frames may be specified directly using the vertex/point attributes `materialU`, `materialV`, and `materialW`. Alternatively, they may be inferred from UVW positions that may be specified by a vertex/point position attribute `materialuvw`. The FEM solver embeds the UVW directions within the material space that may be specified by the attribute `materialP`. To get the correct idea of how this works, UVW directions that are fed into the FEM solver should be visualized relative to the material position `materialP`.

For FEM muscle simulations, the easiest way to specify the muscle fiber direction is through vertex/point attribute `materialW`. It is fine if no `materialU` and `materialV` directions are specified in this case, as the solver will infer arbitrary `materialU` and `materialV` directions from `materialW` in that case.

The attribute `materialuvw` can be used to specify a UVW parametrization of the material space. The U, V and W directions that are implied by `materialuvw` matter if the anisotropic controls are used or when the fiber controls are used on a simulated object. For the FEM muscle simulation use case, the fiber controls are an important tool for controlling muscle contraction.

Similar to `materialuvw`, the `materialuv` attribute can be used to specify UV directions for cloth. This attribute is essential for triangle meshes, in particular, to define the warped and weft directions for cloth.

Name Class Type Description
`materialP` Point or Vertex Vector Material position of each point, defining the material space
`materialU` Point or Vertex Vector The U direction within the material space
`materialV` Point or Vertex Vector The V direction within the material space
`materialW` Point or Vertex Vector The W direction within the material space
`materialuvw` Point or Vertex Vector Local material uvw coordinates for each point or vertex of a tet.
`materialuv` Point or Vertex Vector Local material uvw coordinates for each point or vertex of a polygon or polysoup.

Material Property Multiplier Attributes ¶

 `fracturepart` Primitive Integer Partitions the object into unbreakable parts. Must be either -1 (no part) or a nonnegative number that indicates a part. `enablefracturing` Point/Vertex Integer Locally enable/disable fracturing for points or vertices. `fracturethreshold` Point/Vertex Float Multiplier for the object’s Fracture Threshold.

Fracturing Control Attributes ¶

When you create a simulation with fracturing, it is recommended to specify chunks of tetrahedrons that you want to stay together. Otherwise, the fracturing process may create a very large amount of separate pieces, many of which may consist of single tetrahedrons. For this purpose, you can assign a nonnegative integer to each chunk using the `fracturepart` attribute. In areas where you don’t want to specify parts, you can set `fracturepart` to -1, which means that each primitive in that region will become its own part. Real-life materials tend not to be equally strong everywhere. For realistic results, it is recommended to vary the Fracture Threshold locally using the vertex attribute `fracturethreshold`.

 `fracturepart` Primitive Integer Partitions the object into unbreakable parts. Must be either -1 (no part) or a nonnegative number that indicates a part. `enablefracturing` Point/Vertex Integer Locally enable/disable fracturing for points or vertices. `fracturethreshold` Point/Vertex Float Multiplier for the object’s Fracture Threshold.

Drag Force Control Attributes ¶

The behavior of the drag force can be modified locally using the following attributes:

 `normaldrag` Primitive Float Multiplier for the object’s Normal Drag. `tangentdrag` Primitive Float Multiplier for the object’s Tangent Drag.

Reference Attributes ¶

The attribute `baseP` can be used to specify a generic base position for all the object points. This attribute’s values must not be changed during a simulation. When the user does not specify `baseP`, the solver creates this point attribute based on the point positions on the creation frame. This attribute is used as a fallback; whenever the user does not specify `materialP`, the attribute `baseP` is read instead. In the same way, `baseP` is used as a fallback for when no `restP` or `targetP` attributes are provided. Finally, `baseP` is used to bind the simulated and the embedded geometry, in the embedded workflow (e.g., a T-pose). This embedded binding looks at the `baseP` position attribute on both the simulated geometry and the embedded geometry. If no `baseP` attribute is provided by the user on the embedded geometry, the solver creates the `baseP` attribute on the embedded geometry based on the position `P` at the creation frame.

If Allow Changing Rest is enabled on the FEM Solver, then the attribute `restP` may be used to modify rest positions. The attribute `restP` can be used to specify an animated rest position for all the object points. For example, at each frame `restP` may be modified in a SOP Solver before the finite element solver. Among other things this makes it possible to create plastic deformation kinds of effects. When the rest should stay the same during an entire simulation the attribute `restP` should not be used. In that case, it is sufficient to specify only an attribute `materialP`, which would act as a permanent, unchanged rest position. If no attribute `materialP` is specified, the solver falls back to the `baseP` attribute that gets automatically created at the creation frame. table>>

Target Attributes ¶

Target attributes can be used to make a simulated object partially follow a target animation. The attribute `targetP` can be used to specify a target position for each object point. When you use the Import Target Geometry option on the simulated object, the `targetP` will be set automatically every frame. Alternatively, you can create and modify these attributes yourself, using a Multi Solver and a SOP Solver. The target positions and velocities allow the user to mix animation and simulation in a very stable way (assuming the Target Strength and Target Damping parameters have been set on the object). You can set the Target Strength and Target Damping parameters on the object to express how strongly the object should match the target position and velocity, respectively. This is a way to create soft constraints. You can use the `pintoanimation` to create hard constraints that make the simulated points follow `targetP` exactly.

Name Class Type Description
`targetP` Point or Vertex Vector Target position of each point.
`targetstrength` Point Float Multiplier for the object’s Target Strength. If this attribute is missing, a multiplier of 1 is used at all points.
`targetdamping` Point Float Multiplier for the object’s Target Damping. If this attribute is missing, a multiplier of 1 is used at all points.
`pintoanimation` Point Int When 1, the point is hard constrained to the target animation (e.g., `targetP`). When zero, the point is unconstrained.

Fiber Attributes ¶

The `fiberscale` point attribute acts as a multiplier for the rest strain in the fiber direction. The fiber direction itself can be specified using the `materialW` vertex/point attribute. Among other things, this is useful for FEM muscle simulations. If the `fiberscale` is changed from 1 to 0.5, then the muscle wants to be half as long as before in the direction of the fiber. If you animate the `fiberscale` in a SOP Solver such that it decreases from 1 to a smaller value, you will cause a muscle contraction in the sim.

The `fiberstiffness` point attribute acts as a multiplier for the stiffness along the fiber direction. The fiber direction of the material is determined by the W axis of the `materialuvw` coordinates. `fiberstiffness` works as a multiplier on top of all the other material property multipliers, including the anisotropic multipliers. If the `fiberstiffness` changed from 1 to 10, then the stiffness along the fiber direction becomes 10 stronger than before. This can be used to control how strong and how quick the effect of muscle flexing using the `fiberscale` attribute takes effect.

For `fiberscale`/`fiberstiffness` to have the desired effect, it is important that UVW directions are specified. A material-space UVWs for FEM muscles can be specified using the `materialuvw` point/vertex attribute. By providing `materialuvw` as a vertex attribute, you are able to provide a local UVW space for each individual tet, which gives you to option of providing a separate UVW frame to each tet.

Name Class Type Description
`fiberstiffness` Point Float Multiplier for stiffness along the fiber direction, the W direction implied by `materialuvw`.
`fiberscale` Point Float Multiplier for the rest strain along the fiber direction, the W direction implied by `materialuvw`.

State Attributes ¶

Below is a list of attributes that are maintained internally by the solver. Each of these attributes is written to at the end of each solve and read from at the start of the next solve. You should not modify any of these attributes yourself. When you do, the solver is likely to become unstable and you will get bad results. However, you can inspect the values in these attributes in your network for visualization or for the creation of secondary effects.

At each frame, the finite element solver computes a new physical state for each simulated object. The physical state of the object is represented by the point attributes `P` and `v`, representing the position and velocity, respectively. The solver’s integration scheme maintains additional attributes `a` for acceleration and `j` for jerk.

The point attributes `P`, `v`, `a`, and `j` store the current integration state of the object. These attributes should not be modified during the simulation because the finite element solver will become unstable and produce low-quality results.

Name Class Type Description
`P` Point Vector Do not modify! Current position of each object point.
`v` Point Vector Do not modify! Current velocity of each object point.
`accel` Point Vector Do not modify! Current acceleration of each object point.
`jerk` Point Vector Do not modify! Current jerk of each object point.

Embedded Geometry Attributes ¶

These attributes are created on the Embedded Geometry of the Solid Object. The `parent` attribute is maintained by the embedding code itself, and should not be modified. The `baseP` point attribute can be provided on the Embedded Geometry by the user to control the binding between the simulated geometry and the embedded geometry. If no `baseP` is provided, it will be copied from the point positions stored in `P` at the creation frame. The alignment happens relative to the `baseP` point attribute on the simulated geometry. If the simulated geometry has a `materialP` vertex or point attribute, then this attribute takes precedence, allowing control per vertex, rather than per point, if necessary. When you want to ensure that embedded geometry ends up on the desired side of a fracture between simulated geometry, you can use the combination of vertex attributes `baseP` on the embedded geometry and `restP` on the simulated geometry. This allows you to line up the embedded geometry with the separate parts in the simulated geometry, for example using the Exploded View SOP. The `fracturepart` attribute allows you to make sure that the embedded geometry follows the right parts when it gets fractured. When both the simulated and the embedded geometry have the `fracturepart` attribute, the finite element solver will parent embedded geometry to simulated geometry that has the same fracture part.

Name Class Type Description
`parent` Primitive Float The index of a parent primitive in the simulated geometry.
`baseP` Point Float Base positions used for alignment with simulated mesh.
`fracturepart` Point or Vertex Float Optional user-specified fracture part ID.
`P` Point Float Positions that correspond to the deformed state.
`v` Point Float Velocities that correspond to the deformed state.
`N` Point or Vertex Float Normals that correspond to the deformed state.

Optional Output Attributes ¶

These are attributes that are optionally generated by the solver, when the generation is enabled on the simulated object. These attributes can be useful for visualization, for example, using the Finite Element Visualization SOP. Additionally, these attributes may be used to create secondary effects, for example, particles flying off in regions where fracturing occurs. The optional output attributes are also expected by the Finite Element Visualization SOP.

The following attribute is generated when Create Quality Attributes is turned on:

Name Class Type Description
`quality` Primitive Float A quality metric between 0 (worst) and 1 (best)

Finite element simulation tends to be sensitive to the quality of the incoming primitives. Low quality primitives may slow down, destabilize or lock a finite element simulation. Low quality primitives are best avoided by using the Tet Embed as a tool to create your tet mesh. Although various quality metrics exist for tetrahedra, the one that’s generated by the solver in this attribute is the one that best matches Houdini’s finite element solution.

The solver generates energy-density attributes for each object that has Create Energy Attributes turned on. The material property settings in the Model tab and the corresponding multiplier attributes result in potential energy, energy dissipation and kinetic energy. For each of these three contributions, local densities are computed within the solver. These densities and quantities derived from them are used to determine the motion and behavior of the objects that are solved by the finite element solver.

Name Class Type Description
`potentialdensity` Point Float The local density of deformation energy
`dissipationdensity` Point Float The local density of the rate of energy loss
`kineticdensity` Point Float The local density of the kinetic energy

The `potentialdensity` attribute is directly affected by the stiffness parameters in the Model tab. The `kineticdensity` is proportional to the mass density that is specified for the object. The `dissipationdensity` is related to the damping settings.

If Create Fracture Attributes is enabled on the simulated object, then the `fracturecount` point attribute is created. The point attribute `fracturecount` maintains for each point, the number of times that the point has been involved in a fracture. So any point with a nonzero value of `fracturecount` has been involved fracturing.

Name Class Type Description
`fracturecount` Point Integer The number of times a point was fractured during the simulation

Legacy Attributes ¶

In most situations where you want to influence a finite-element simulation, you will want to use soft constraints to achieve this, for example, target constraints, region constraints, or the target strength/damping settings on the object. These are first-class solver features that work in a stable way with the solver and should produce high quality results when used correctly. Purely for backwards compatibility, a force attribute is still supported. Because the force attribute lacks essential information that the solver needs, this attribute cannot be relied on when stability and quality are important. When setting up a new sim, alternatives such as soft targeting, region constraints and animated rest positions should be considered instead of the force attribute.

Name Class Type Description
`fexternal` Force Vector External force density
`force` Force Vector Another name for external force density

Inputs ¶

First Input

This optional input can be used to control which simulation objects are modified by this node. Any objects connected through this input and which match the Group parameter field will be modified.

If this input is not connected, this node can be used in conjunction with an Apply Data node, or can be used as an input to another data node.

All Other Inputs

If this node has more input connectors, other data nodes can be attached to act as modifiers for the data created by this node.

The specific types of subdata that are meaningful vary from node to node. Click an input connector to see a list of available data nodes that can be meaningfully attached.

Outputs ¶

First Output

The operation of this output depends on what inputs are connected to this node. If an object stream is input to this node, the output is also an object stream containing the same objects as the input (but with the data from this node attached).

If no object stream is connected to this node, the output is a data output. This data output can be connected to an Apply Data DOP, or connected directly to a data input of another data node, to attach the data from this node to an object or another piece of data.

Locals ¶

ST

The simulation time for which the node is being evaluated.

Depending on the settings of the DOP Network Offset Time and Scale Time parameters, this value may not be equal to the current Houdini time represented by the variable T.

ST is guaranteed to have a value of zero at the start of a simulation, so when testing for the first timestep of a simulation, it is best to use a test like `\$ST == 0`, rather than `\$T == 0` or `\$FF == 1`.

SF

The simulation frame (or more accurately, the simulation time step number) for which the node is being evaluated.

Depending on the settings of the DOP Network parameters, this value may not be equal to the current Houdini frame number represented by the variable F. Instead, it is equal to the simulation time (ST) divided by the simulation timestep size (TIMESTEP).

TIMESTEP

The size of a simulation timestep. This value is useful for scaling values that are expressed in units per second, but are applied on each timestep.

SFPS

The inverse of the TIMESTEP value. It is the number of timesteps per second of simulation time.

SNOBJ

The number of objects in the simulation. For nodes that create objects such as the Empty Object DOP, SNOBJ increases for each object that is evaluated.

A good way to guarantee unique object names is to use an expression like `object_\$SNOBJ`.

NOBJ

The number of objects that are evaluated by the current node during this timestep. This value is often different from SNOBJ, as many nodes do not process all the objects in a simulation.

NOBJ may return 0 if the node does not process each object sequentially (such as the Group DOP).

OBJ

The index of the specific object being processed by the node. This value always runs from zero to NOBJ-1 in a given timestep. It does not identify the current object within the simulation like OBJID or OBJNAME; it only identifies the object’s position in the current order of processing.

This value is useful for generating a random number for each object, or simply splitting the objects into two or more groups to be processed in different ways. This value is -1 if the node does not process objects sequentially (such as the Group DOP).

OBJID

The unique identifier for the object being processed. Every object is assigned an integer value that is unique among all objects in the simulation for all time. Even if an object is deleted, its identifier is never reused. This is very useful in situations where each object needs to be treated differently, for example, to produce a unique random number for each object.

This value is also the best way to look up information on an object using the dopfield expression function.

OBJID is -1 if the node does not process objects sequentially (such as the Group DOP).

ALLOBJIDS

This string contains a space-separated list of the unique object identifiers for every object being processed by the current node.

ALLOBJNAMES

This string contains a space-separated list of the names of every object being processed by the current node.

OBJCT

The simulation time (see variable ST) at which the current object was created.

To check if an object was created on the current timestep, the expression `\$ST == \$OBJCT` should always be used.

This value is zero if the node does not process objects sequentially (such as the Group DOP).

OBJCF

The simulation frame (see variable SF) at which the current object was created. It is equivalent to using the dopsttoframe expression on the OBJCT variable.

This value is zero if the node does not process objects sequentially (such as the Group DOP).

OBJNAME

A string value containing the name of the object being processed.

Object names are not guaranteed to be unique within a simulation. However, if you name your objects carefully so that they are unique, the object name can be a much easier way to identify an object than the unique object identifier, OBJID.

The object name can also be used to treat a number of similar objects (with the same name) as a virtual group. If there are 20 objects named “myobject”, specifying `strcmp(\$OBJNAME, "myobject") == 0` in the activation field of a DOP will cause that DOP to operate on only those 20 objects.

This value is the empty string if the node does not process objects sequentially (such as the Group DOP).

DOPNET

A string value containing the full path of the current DOP network. This value is most useful in DOP subnet digital assets where you want to know the path to the DOP network that contains the node.

Dynamics nodes

• Marks a simulation object as active or passive.

• Creates affector relationships between groups of objects.

• Blends between a set of animation clips based on the agent’s turn rate.

• Layers additional animation clips onto an agent.

• Defines a target that an agent can turn its head to look at.

• Adjusts the agent’s skeleton to look at a target.

• Adapts the legs of an agent to conform to terrain and prevent the feet from sliding.

• Project the agent/particle points onto the terrain

• Defines an orientation that aligns an axis in object space with a second axis defined by the relative locations of two positional anchors.

• Defines multiple points, specified by their number or group, on the given geometry of a simulation object.

• Defines orientations based on multiple points on the given geometry of a simulation object.

• Defines a position by looking at the position of a point on the geometry of a simulation object.

• Defines an orientation by looking at a point on the geometry of a simulation object.

• Defines a position by looking at the position of a point on the geometry of a simulation object.

• Defines an orientation by looking at a point on the geometry of a simulation object.

• Defines a position by looking at the position of a particular UV coordinate location on a primitive.

• Defines a position by specifying a position in the space of some simulation object.

• Defines an orientation by specifying a rotation in the space of some simulation object.

• Defines multiple attachment points on a polygonal surface of an object.

• Defines a position by specifying a position in world space.

• Defines an orientation by specifying a rotation in world space.

• Attaches data to simulation objects or other data.

• Creates relationships between simulation objects.

• Attaches the appropriate data for Bullet Objects to an object.

• Sets and configures a Bullet Dynamics solver.

• Applies a uniform force to objects submerged in a fluid.

• Attaches the appropriate data for Cloth Objects to an object.

• Defines the mass properties.

• Defines the physical material for a deformable surface.

• Defines the internal cloth forces.

• Creates a Cloth Object from SOP Geometry.

• Defines the plasticity properties.

• Constrains part of the boundary of a cloth object to the boundary of another cloth object.

• Defines how cloth uses target.

• Defines a way of resolving collisions involving a cloth object and DOPs objects with volumetric representations (RBD Objects, ground planes, etc.)

• Constrains an object to remain a certain distance from the constraint, and limits the object’s rotation.

• Constrains pairs of RBD objects together according to a polygon network.

• Defines a set of constraints based on geometry.

• Visualizes the constraints defined by constraint network geometry.

• Creates multiple copies of the input data.

• Sets and configures a Copy Data Solver.

• Mimics the information set by the Copy Object DOP.

• Defines a Crowd Fuzzy Logic

• Creates a crowd object with required agent attributes to be used in the crowd simulation.

• Updates agents according to their steer forces and animation clips.

• Defines a Crowd State

• Defines a transition between crowd states.

• Defines a Crowd Trigger

• Combines multiple crowd triggers to build a more complex trigger.

• Adds a data only once to an object, regardless of number of wires.

• Deletes both objects and data according to patterns.

• Applies force and torque to objects that resists their current direction of motion.

• Defines how the surrounding medium affects a soft body object.

• Controls Embedded Geometry that can be deformed along with the simulated geometry in a finite element simulation.

• Creates an Empty Data for holding custom information.

• Creates an Empty Object.

• Constrains a set of points on the surface of one FEM object to a set of points on the surface on another FEM object or a static object.

• Constrains points of a solid object or a hybrid object to points of another DOP object.

• Creates an FEM Hybrid Object from SOP Geometry.

• Constrains regions of a solid object or a hybrid object to another solid or hybrid object.

• Make a set of points on the surface of an FEM Object slide against the surface of another FEM Object or a Static Object.

• Creates a simulated FEM solid from geometry.

• Sets and configures a Finite Element solver.

• Constrains an FEM object to a target trajectory using a hard constraint or soft constraint.

• Attaches the appropriate data for Particle Fluid Objects to become a FLIP based fluid.

• Evolves an object as a FLIP fluid object.

• Applies forces on the objects as if a cone-shaped fan were acting on them.

• Fetches a piece of data from a simulation object.

• Applies forces to an object using some piece of geometry as a vector field.

• Creates a vortex filament object from SOP Geometry.

• Evolves vortex filament geometry over time.

• Imports vortex filaments from a SOP network.

• Saves and loads simulation objects to external files.

• Allows a finite-element object to generate optional output attributes.

• Attaches the appropriate data for Fluid Objects to an object.

• Applies forces to resist the current motion of soft body objects relative to a fluid.

• Attaches the appropriate data for Fluid Objects to an object.

• A solver for Sign Distance Field (SDF) liquid simulations.

• A microsolver that applies viscosity to a velocity field using an adaptive grid.

• A microsolver that advects fields and geometry by a velocity field.

• A microsolver that advects fields by a velocity field using OpenCL acceleration.

• A microsolver that advects fields by a velocity field.

• A microsolver that computes analytic property of fields.

• A microsolver that swaps geometry attributes.

• A microsolver that applies a force around an axis to a velocity field.

• A microsolver that blends the density of two fields.

• A microsolver that blurs fields.

• A microsolver that determines the collision field between the fluid field and any affector objects.

• A microsolver that builds a collision field for fluid simulations from instanced pieces.

• A microsolver that builds a mask out of positive areas of the source fields.

• A microsolver that builds a mask for each voxel to show the presence or absence of relationships between objects.

• A microsolver that calculates an adhoc buoyancy force and updates a velocity field.

• A microsolver that performs general calculations on a pair of fields.

• A microsolver that detects collisions between particles and geometry.

• A microsolver that applies a combustion model to the simulation.

• A microsolver that clips an SDF field with a convex hull.

• A microsolver that adjusts an SDF according to surface markers.

• A microsolver that computes the cross product of two vector fields.

• A DOP node that creates forces generated from a curve.

• A microsolver that scales down velocity, damping motion.

• A microsolver that diffuses a field or point attribute.

• A microsolver that dissipates a field.

• Adds fine detail to a smoke simulation by applying disturbance forces to a velocity field.

• A microsolver that runs once for each matching data.

• A microsolver that embeds one fluid inside another.

• A microsolver that enforces boundary conditions on a field.

• A microsolver that equalizes the density of two fields.

• A microsolver that equalizes the volume of two fields.

• A microsolver that emits a DOP error.

• A microsolver that evaluates the external DOPs forces for each point in a velocity field and updates the velocity field accordingly.

• A microsolver that extrapolates a field’s value along an SDF.

• A microsolver that creates a feathered mask out of a field.

• A microsolver that calculates and applies feedback forces to collision geometry.

• A data node that fetches the fields needed to embed one fluid in another.

• Runs CVEX on a set of fields.

• Runs CVEX on a set of fields.

• A microsolver that copies the values of a field into a point attribute on geometry.

• Filters spurious divergent modes that may survive pressure projection on a center-sampled velocity field.

• A microsolver that defragments geometry.

• A microsolver that creates a signed distance field out of geometry.

• A micro solver that transfers meta data on simulation objects to and from geometry attributes.

• Blends a set of SOP volumes into a set of new collision fields for the creation of a guided simulation.

• A microsolver that copies Impact data onto point attributes.

• Integrates the shallow water equations.

• A microsolver that applies forces to a particle fluid system.

• A microsolver that repeatedly solves its inputs at different rates.

• A microsolver that solves its subsolvers at a regular interval.

• A microsolver that clamps a field within certain values.

• A microsolver that keeps particles within a box.

• A microsolver that combines multiple fields or attributes together.

• A microsolver that adaptively sharpens a field.

• A microsolver that looksup field values according to a position field.

• A microsolver that rebuilds fields to match in size and resolution to a reference field.

• A microsolver that arbitrary simulation data between multiple machines.

• A microsolver that exchanges boundary data between multiple machines.

• A microsolver that exchanges boundary data between multiple machines.

• A microsolver that balances slices data between multiple machines.

• A microsolver that exchanges boundary data between multiple machines.

• Executes the provided kernel with the given parameters.

• Uses OpenCL to perform boundary enforcement for fluid fields.

• Uses OpenCL to import VDB data from source geometry into simulation fields.

• A microsolver that counts the number of particles in each voxel of a field.

• A microsolver that moves particles to lie along a certain isosurface of an SDF.

• A microsolver that separates adjacent particles by adjusting their point positions..

• A microsolver that copies a particle system’s point attribute into a field.

• A microsolver that converts a particle system into a signed distance field.

• A microsolver that removes the divergent components of a velocity field.

• A microsolver that removes the divergent components of a velocity field using an adaptive background grid to increase performance.

• A microsolver that removes the divergent components of a velocity field using a multi-grid method.

• A microsolver that removes the divergent components of a velocity field.

• A microsolver that reduces a field to a single constant field .

• A microsolver that reduces surrounding voxels to a single value.

• A microsolver that reinitializes a signed distance field while preserving the zero isocontour.

• A microsolver that repeatedly solves its input.

• A microsolver that resets fields outside of the stenciled region.

• A microsolver that changes the size of fields.

• A microsolver that resizes a fluid to match simulating fluid bounds

• A microsolver that initializes a rest field.

• A microsolver that converts an SDF field to a Fog field.

• A microsolver that computes the forces to treat the fluid simulation as sand rather than fluid.

• A microsolver that creates, deletes and reseeds particles. Tailored to be used in a fluid solver.

• A microsolver that seeds marker particles around the boundary of a surface.

• A microsolver that seeds particles uniformly inside a surface.

• Applies a Shredding Force to the velocity field specified.

• A microsolver that computes slice numbers into an index field.

• Adjusts a fluid velocity field to match collision velocities.

• A microsolver that calculates the forces imparted by a strain field.

• A microsolver that updates the strain field according to the current velocity field.

• A microsolver that substeps input microsolvers.

• A microsolver that snaps a surface onto a collision surface.

• A microsolver that calculates a surface tension force proportional to the curvature of the surface field.

• A microsolver that synchronizes transforms of simulation fields.

• A microsolver that applies a force towards a target object.

• Modifies the temperature of a FLIP over time.

• Applies Turbulence to the specified velocity field.

• Up-scales and/or modifies a smoke, fire, or liquid simulations.

• Scales fluid velocity based on the fluid’s current speed or a control field.

• A microsolver that reorients geometry according to motion of a velocity field.

• A microsolver that applies viscosity to a velocity field.

• A microsolver that seeds flip particles into a new volume region.

• Remaps a field according to a ramp.

• Applies a confinement force on specific bands of sampled energy.

• Applies a vortex confinement force to a velocity field.

• Applies a confinement force on specific bands of sampled energy.

• A microsolver that applies forces to a velocity field or geometry according to vorticle geometry.

• A DOP node that adds the appropriately formatted data to represent vorticles.

• A DOP node that recycles vorticles by moving them to the opposite side of the fluid box when they leave.

• A microsolver that performs a wavelet decomposition of a field.

• A microsolver that applies a wind force.

• Runs CVEX on geometry attributes.

• Runs a VEX snippet to modify attribute values.

• Applies a gravity-like force to objects.

• Creates a ground plane suitable for RBD or cloth simulations.

• Creates simulation object groups.

• Defines a constraint relationship that must always be satisfied.

• Attaches the appropriate data for Hybrid Objects to an object.

• Stores filtered information about impacts on an RBD object. The shelf tool has no effect in the viewport, it just sets up nodes in the network to record the impact data.

• Applies an impulse to an object.

• Creates an index field.

• Visualizes an index field.

• Creates DOP Objects according to instance attributes

• Marks a simulation object as intangible or tangible.

• Stores the name of the scene level object source for this DOP object.

• Apply forces on objects using a force field defined by metaballs.

• Creates a matrix field.

• Visualizes a matrix field.

• Merges multiple streams of objects or data into a single stream.

• Modifies or creates options on arbitrary data.

• Defines an object’s position, orientation, linear velocity, and angular velocity.

• Unified visualization of multiple fields.

• A DOP that transfers arbitrary simulation data between multiple machines.

• Does nothing.

• Creates position information from an object’s transform.

• Uses vortex filaments to move particles.

• A POP node that uses velocity volumes to move particles.

• A POP node that attracts particles to positions and geometry.

• The POP equivalent of the Attribute Blur SOP.

• A POP node that copies volume values into a particle attribute.

• A POP node that resets the stopped attribute on particles, waking them up.

• A POP node that applies a force around an axis.

• A POP node that reacts to collisions.

• A POP node that detects and reacts to collisions.

• A POP node marks particles to ignore implicit collisions.

• A POP node that colors particles.

• A POP node that creates forces generated from a curve.

• A POP node that creates incompressible velocity field generated from a curve.

• A POP node that applies drag to particles.

• A POP node that applies drag to the spin of particles.

• A POP node that applies a conical fan wind to particles.

• A POP node that creates a simple fireworks system.

• A POP node that floats particles on the surface of a liquid simulation.

• A POP node that applies a flocking algorithm to particles.

• Controls local density by applying forces between nearby particles.

• A POP node that applies forces to particles.

• A POP node that applies sand grain interaction to particles.

• A POP node that groups particles.

• Compute hair separation force using a VDB volume approach.

• A POP node that sets up the instancepath for particles.

• A POP node that applies forces between particles.

• A POP node that kills particles.

• A POP node that limits particles.

• A POP node that applies forces within the particle’s frame.

• A POP solver that generates particles at a point.

• A POP node makes a particle look at a point.

• A POP node that creates a mask based on whether particles are occluded by geometry.

• A POP node that applies forces according to metaballs.

• Converts a regular particle system into a dynamic object capable of interacting correctly with other objects in the DOP environment.

• A POP node that sets various common attributes on particles.

• A POP node that sets attributes based on nearby particles.

• A POP Node that generates particles from incoming particles.

• A POP node that creates a spongy boundary.

• A POP solver updates particles according to their velocities and forces.

• A POP node that generates particles from geometry.

• A POP node that sets the speed limits for particles.

• A POP node that sets the spin of particles..

• A POP node that uses the vorticity of velocity volumes to spin particles.

• A POP node that sets the sprite display for particles.

• Applies force to agents/particles to align them with neighbors.

• Applies anticipatory avoidance force to agents/particles to avoid potential future collisions with other agents/particles.

• Applies forces to agents/particles to bring them closer to their neighbors.

• Applies forces to agents/particles calulated using a VOP network.

• Applies force to agents/particles to avoid potential collisions with static objects.

• Applies force to agents/particles according to directions from a path curve.

• Applies force to agents/particles to move them toward a target position.

• Apply force to agents/particles to move them apart from each other.

• Used internally in the crowd solver to integrate steering forces.

• Constrains agent velocity to only go in a direction within a certain angle range of its current heading, to prevent agents from floating backward.

• Apply forces to agents/particles to create a random motion.

• A POP node that creates a new stream of particles.

• A POP node that applies torque to particles, causing them to spin.

• Runs CVEX on a particle system.

• A POP node that directly changes the velocity of particles.

• A POP node that applies wind to particles.

• Applies a wind shadow to particles

• Runs a VEX snippet to modify particles.

• Solves a Smoothed Particle Hydrodynamics (SPH) density constraint for fluid particles using OpenCL.

• A microsolver for particle fluid forces

• Visualizes particles.

• Creates simulation object groups based on an expression.

• Defines the base physical parameters of DOP objects.

• Applies a force to an object from a particular location in space.

• Creates position information from a point on some SOP geometry.

• Associates a position and orientation to an object.

• Sets and configures a Pyro solver. This solver can be used to create both fire and smoke.

• Performs a sparse pyro simulation on the given object. This solver can be used to create both fire and smoke.

• Constrains an RBD object to a certain orientation.

• Constrains an RBD object to have a certain orientation, but with a set amount of springiness.

• Automatically freezes RBD Objects that have come to rest

• Constrain a RBD Car Rig along a path.

• Attaches the appropriate data for RBD Objects to an object.

• Creates a number of RBD Objects from SOP Geometry. These individual RBD Objects are created from the geometry name attributes.

• Guide Bullet Packed Primitives.

• Constrains an object to two constraints, creating a rotation similar to a hinge or a trapeze bar.

• Creates an RBD Object from SOP Geometry.

• Creates a single DOP object from SOP Geometry that represents a number of RBD Objects.

• Constrains an RBD object a certain distance from the constraint.

• Creates a simulation object at each point of some source geometry, similarly to how the Copy surface node copies geometry onto points.

• Sets and configures a Rigid Body Dynamics solver.

• Constrains an object to remain a certain distance from the constraint, with a set amount of springiness.

• Alters the state information for an RBD Object.

• Serves as the end-point of the simulation network. Has controls for writing out sim files.

• Saves the state of a DOP network simulation into files.

• Saves the state of a DOP network simulation into files.

• Applies forces to an object according to the difference between two reference frames.

• Sets and configures a Rigid Body Dynamics solver.

• Attaches the appropriate data for Ripple Objects to an object.

• Creates an object from existing geometry that will be deformed with the ripple solver.

• Animates wave propagation across Ripple Objects.

• Creates a signed distance field representation of a piece of geometry that can be used for collision detection.

• A microsolver that performs general calculations on a pair consisting of a DOP field and a SOP volume/VDB.

• Creates a scalar field from a SOP Volume.

• Creates a vector field from a SOP Volume Primitive.

• Creates a scalar field.

• Visualizes a scalar field.

• Defines the internal seam angle.

• Defines the mass density of a Cloth Object.

• Divides a particle system uniformly into multiple slices along a line.

• Specifies a cutting plane to divide a particle system into two slices for distributed simulations.

• Constrains an object to rotate and translate on a single axis, and limits the rotation and translation on that axis.

• Attaches the appropriate data for Smoke Objects to an object.

• Creates an Smoke Object from SOP Geometry.

• Creates an empty smoke object for a pyro simulation.

• Sets and configures a Smoke solver. This is a slightly lower-level solver that is the basis for the Pyro solver.

• Performs a sparse smoke simulation on the given object. This is a slightly lower-level solver that is the basis for the sparse pyro solver.

• Constrains a set of points on a soft body object to a certain position using a hard constraint or soft constraint.

• Constrains a point on a soft body object to a certain position.

• Constrains a point on a soft body to a certain position, with a set amount of springiness.

• Defines how a soft body object responds to collisions.

• Defines how a Soft Body Object responds to collisions.

• Defines how a Soft Body Object responds to collisions.

• Defines how a Soft Body Object responds to collisions.

• Allows the user to import the rest state from a SOP node.

• Sets and configures a Soft Body solver.

• Defines the strengths of the soft constraint on a soft body object.

• Controls the anisotropic behavior of a Solid Object.

• Attaches the appropriate data for Solid Objects to an object.

• Defines the mass density of a Solid Object.

• Defines how a Solid Object reacts to strain and change of volume.

• This builds a tree of spheres producing bounding information for an edge cloud.

• This builds a tree of spheres producing bounding information for a point cloud.

• Splits an incoming object stream into as many as four output streams.

• Creates a Static Object from SOP Geometry.

• Allows you to inspect the behavior of a static object in the viewport.

• Control the thickness of the object that collides with cloth.

• Passes one of the input object or data streams to the output.

• Creates a Terrain Object from SOP Geometry.

• Defines a way of resolving collisions between two rigid bodies.

• Applies a uniform force and torque to objects.

• Applies forces on the objects according to a VOP network.

• Creates a vector field.

• Visualizes a vector field.

• Modifies common Vellum constraint properties during a Vellum solve.

• Microsolver to create Vellum constraints during a simulation.

• Creates a DOP Object for use with the Vellum Solver.

• Blends the current rest values of constraints with a rest state calculated from the current simulation or external geometry.

• Sets and configures a Vellum solver.

• A Vellum node that creates Vellum patches.

• Applies an impulse to an object.

• A microsolver to create soft references to visualizers on itself.

• Uses instance points to source packed source sets into DOP fields.

• Imports SOP source geometry into smoke, pyro, and FLIP simulations.

• Defines a way of resolving collisions involving two rigid bodies with volume.

• Attaches the appropriate data to make an object fractureable by the Voronoi Fracture Solver

• Defines the parameters for dynamic fracturing using the Voronoi Fracture Solver

• Dynamically fractures objects based on data from the Voronoi Fracture Configure Object DOP

• Applies a vortex-like force on objects, causing them to orbit about an axis along a circular path.

• Creates a Whitewater Object that holds data for a whitewater simulation.

• Sets and configures a Whitewater Solver.

• Applies forces to resist the current motion of objects relative to a turbulent wind.

• Constrains a wire point’s orientation to a certain direction.

• Constrains a wire point’s orientation to a certain direction, with a set amount of springiness.

• Attaches the appropriate data for Wire Objects to an object.

• Defines the elasticity of a wire object.

• Constraints a wire point to a certain position and direction.

• Creates a Wire Object from SOP Geometry.

• Defines the physical parameters of a wire object.

• Defines the plasticity of a wire object.

• Sets and configures a Wire solver.

• Defines a way of resolving collisions involving a wire object and DOPs objects with volumetric representations.

• Defines a way of resolving collisions between two wires.