This determines how strongly the Solid Object resists changes in shape. In the isotropic use case (Anisotropic Strength all 1), this physical constant is also known as shear modulus, modulus of rigidity, or Lame’s second parameter. If the units of length are set to meters, then the Shape Stiffness parameter has units of GPa.

This determines how strongly the Solid Object resists changes in volume. In the isotropic use case (Anisotropic Strength all 1), this physical constant is also known as Lame’s first parameter. If the units of length are set to meters, then the Shape Stiffness parameter has units of GPa.

This value should lie between 0 and 1. It controls the rate of energy loss as a result of the rate of deformation. A value of 0 means that there is no loss of energy due to internal damping forces. A value of 1 means that the object is critically damped, in which case the object comes to rest in the quickest possible way without oscillating. The higher the damping ratio, the less the solid oscillates and the quicker the object’s motion will come to rest. The effect of damping is independent of your geometry’s resolution.

This is the mass per cubed length unit. The mass density can be made lower or higher in parts of the object using the primitive attribute volumemassdensity, which works as a multiplier for the parameter. The higher the mass density, the less the object tends to accelerate as a result of any internal or external forces (F = m a, Newton’s second law).

This enables or disables all fracturing for this object.

The amount of relative stretch that will cause the geometry to break up into separate parts during the simulation. For example, if the threshold is set to 0.1, the geometry will break in places where there is more than 10% stretch compared to the rest geometry.

Realistic solid objects are not equally strong everywhere, there are weak parts that tend to fracture before any other parts. To create these relatively weaker parts you can create a vertex attribute called fracturethreshold. This attribute is a multiplier for the Fracture Threshold parameter, so that you can still use the Fracture Threshold to control the overall strength of the object.

The coefficient of friction of the object. A value of 0 means the object is frictionless. This governs how much the velocity that is tangential to the contact plane is affected by collisions. When two objects are in contact, the solver multiplies the friction coefficients of the involved object to get the effective friction coefficient for that contact.

These values allow you to make the internal forces of the Solid Object behave in an anisotropic way; in that case, the amount of stress will differ depending on the direction in which the object is deformed. An example of an anisotropic material is wood, which has a different strength along the grain than perpendicular to the grain. The materialuvw vertex or point attribute can be used to specify the internal directions of the Solid Object’s internal force model. For example, in the case of wood, the U direction could be aligned with the grain of the wood, while the VW coordinates are chosen perpendicular to the grain of the wood. In this case, the strength along the grain can be separately controlled using the U component of the Anisotropic Strength.

This geometry determines the initial simulated state of the object. It determines the initial position and velocity for each of the points.

This is the geometry that is used for the computation of internal forces and for collision detection. Don’t use more tetrahedrons than you need to get a good looking motion; more tetrahedrons does not always translate to more quality. The fewer tetrahedrons you use, the better the simulation speed is. If extra detail needs to be added, it is recommended that you use the Embedded Geometry.

You can use the Tetrahedralize SOP to create a suitable input mesh. It is important that you enable the quality option on the Tetrahedralize SOP. Otherwise, the interior of your Solid Object won’t have enough degrees of freedom to be flexible.

Turns on/off the use of embedded geometry.

This geometry is embedded into and deformed along with the simulated tetrahedral mesh.

This option allows you to specify and animate the rest positions that are used by the simulation inside the SOP network (without having to use a SOP solver). The option defines whether the rest positions should be imported from a SOP geometry node at each frame. When enabled, the solver will copy rest positions from the point attribute restP of the SOP geometry node onto the attribute restP on the simulation geometry at each frame. If no restP exists, then the 'P' attribute from the SOP geometry node is copied instead.

The path to the SOP node that will serve as the source of the rest positions.

This option allows you to specify and animate the target positions that are used by the simulation inside the SOP network (without having to use a SOP solver). The option defines whether the target positions should be imported from a SOP geometry node at each frame. When enabled, the solver will copy target positions from the point attribute targetP of the SOP geometry node onto the attribute targetP on the simulation geometry at each frame. If no targetP exists, then the P attribute from the SOP geometry node is copied instead.

The path to the SOP node that will serve as the source of the target positions. The positions should be stored in an attribute with the name targetP. If this attribute is not found, the P attribute is used as a fallback.

This coefficient determines how strongly the finite element solver tries to make the point positions match the target point positions. The solver creates an imaginary potential force for this purpose.

This coefficient determines how strongly the finite element solver tries to make the point velocities match the target point velocities. The solver creates an imaginary dissipation force for this purpose.

Allows the tetrahedrons of this object to break apart when impacted beyond the force set by the Fracture threshold below. The solver must also have fracturing on (which is the default for the solver).

The relative amount of stress in any direction above which dynamic fracturing will occur. This lets you control how quickly the object will break into pieces as a result of stresses inside the object.

Realistic objects don’t have the same fracture threshold everywhere. To achieve this, you can use a point attribute with the name fracturethreshold that acts as a local multiplier for the per-object fracture threshold.

It is recommended that you use the primitive attribute fracturepart to assign integer numbers to clumps of tetrahedrons that should never be broken up into smaller pieces. Creating these clumps prevents individual tetrahedrons from breaking off. The Solid Fracture SOP can be a useful tool for creating this fracturepart attribute. You can create a fracturepart on the embedded geometry as well. This way, the fractured pieces in the simulated geometry and the embedded geometry can be properly matched.

If enabled, the geometry in this object will collide with all other objects. These other objects may belong to the same solver or they may be be Static Objects, RBD Objects, or the Ground Plane. When the Collision Detection parameter on the Static Object is set to Use Volume Collisions, then the polygon vertices will be tested for collision against the signed distance field (SDF) of the Static Object. When Collision Detection is set to Use Surface Collisions, then geometry-based continuous collision detection is used. The geometry-based collisions collide points against polygons, and edges against edges.

When surface-based collisions are used, only polygons and tetrahedrons in the Static Object are considered. Other types of primitives, for example spheres, are be ignored. The geometry of the external objects (e.g. Static Object) is treated as being one-sided; only the outsides of the polygons, determined by the winding order, oppose collisions.

When volume-based collisions are enabled, only points will be colliding against the volumes, not the interiors of polygons and tetrahedrons. When colliding against small volumes, this may mean that you need to increase the number of points on your mesh to get accurate collision results.

When enabled, this object will collide with other objects that have the same solver. These collisions are handled using continuous collision detection, based on the geometry (polygons and/or tetrahedrons). For collisions between objects on the same solver, the polygons are treated as two-sided. Both sides of the polygons collide. The surface of a tetrahedral mesh only collides on one side: the outside.

If disabled, no two tetrahedrons within this object can collide with each other.

If disabled, no two tetrahedrons that belong on the same connected component may collide with each other.

This option only has an effect when fracturing is enabled on the solver. If disabled, no two tetrahedrons that belong on the same fracture part may collide with each other. Fracture parts are controlled by the integer-valued fracturepart primitive attribute.

The component of drag in the directions normal to the surface. Increasing this will make the object go along with any wind that blows against it. For realistic wind interaction, the Normal Drag should be chosen larger (about 10 times larger) than the tangent drag.

The component of drag in the direction tangent to the surface. Increasing this will make the object go along with any wind that blows tangent to the object.

The name of the external velocity fields on affectors that the object will respond to. The default is vel, which will make the object react to fluids and smoke when the Tangent Drag and the Normal Drag have been chosen sufficiently large. The Tangent Drag and Normal Drag forces are computed by comparing the object’s velocity with the external velocity.

This offset is added to any velocity that’s read from the velocity field. When there’s no velocity field, then the offset can be used to create a wind force which has constant velocity everywhere. This wind effect is more realistic and more accurate than the wind that is generated by DOP Forces.

Determines if the creation frame refers to global Houdini frames ($F) or to simulation specific frames ($SF). The latter is affected by the offset time and scale time at the DOP network level.

The frame number on which the object will be created. The object is created only when the current frame number is equal to this parameter value. This means the DOP Network must evaluate a timestep at the specified frame, or the object will not be created.

For example, if this value is set to 3.5, the Timestep parameter of the DOP Network must be changed to 1/(2*$FPS) to ensure the DOP Network has a timestep at frame 3.5.

Instead of making a single object, you can create a number of identical objects. You can set each object’s parameters individually by using the $OBJID expression.

The name for the created object. This is the name that shows up in the details view and is used to reference this particular object externally.

For the newly created objects, this parameter controls whether or not the solver for that object should solve for the object on the timestep in which it was created.

Usually this parameter will be turned on if this node is creating objects in the middle of a simulation rather than creating objects for the initial state of the simulation.

By preventing a large object from being cached, you can ensure there is enough room in the cache for the previous frames of its collision geometry.

This option should only be set when you are working with a very large sim. It is much better just to use a larger memory cache if possible.