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The Solid Object DOP creates a Solid Object inside the DOP simulation. It creates a new object and attaches the subdata required for it to be a properly conforming Solid Object. Solid Objects can be simulated using the Finite Element Solver.
Solid objects are different than rigid bodies. Solid objects are flexible, which makes it possible for them to deform, and can be used to simulate materials such as flesh, wood, and concrete. Solid objects are also able to break dynamically during a simulation, based on the deformation that happens during the simulation.
You can use a tetrahedral mesh in SOPs to create your solid object. Your solid geometry should satisfy guidelines that ensure a fast-running and good looking simulation.
See the section on solid simulation for more information.
Create a hard solid object
Create a squishy solid object
Once you convert geometry to a solid object, you can only transform, rotate, and scale it at the first frame.
This is a multiplier for all the internal stiffnesses of this object.
This controls how quickly the object stops deforming.
This is the amount of mass per volume.
This determines how strongly the object resists local changes in shape.
This determines how strongly the object resists local changes in volume.
This controls the strength of friction forces at contacts
The path to the SOP node with the initial connectivity, position and velocity.
The path to the SOP node that defines the rest shape.
The path to the SOP node with target deformation.
Strength density of the distributed soft-constraint force field that tries to match the target position.
Damping density of the distributed soft-constraint force field that tries to match the target velocity.
Turns on/off the use of embedded geometry.
This geometry is embedded into and deformed along with the simulated tetrahedral mesh.
Collide with objects
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.
Collide with other objects with same solver
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.
Collide within this object
If disabled, no two tetrahedrons within this object can collide with each other.
Collide within each component
If disabled, no two tetrahedrons that belong on the same connected component may collide with each other.
Collide within each fracture part
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.
If Non Square is chosen, the specified size is divided into the given number of divisions of voxels. However, the sides of these voxels may not be equal, possibly leading to distorted simulations.
When an axis is specified, that axis is considered authoritative for determining the number of divisions. The chosen axis' size will be divided by the uniform divisions to yield the voxel size. The divisions for the other axes will then be adjusted to the closest integer multiple that fits in the required size.
Finally, the size along non-chosen axes will be changed to represent uniform voxel sizes. If the Max Axis option is chosen, the maximum sized axis is used.
When By Size is chosen, the Division Size will be used to compute the number of voxels that fit in the given sized box.
The resolution of the key axis on the voxel grid. This allows you to control the overall resolution with one parameter and still preserve uniform voxels. The Uniform Voxels option specifies which axis should be used as the reference. It is usually safest to use the maximum axis.
This specifies the tolerance used for ray intersections when computing the SDF. This value is multiplied by the size of the geometry and is scale invariant.
Sign Sweep Threshold
After the fix signs process is complete there can still be inconsistent areas in the SDF. Large blocks can become stabilized and stick out of the SDF. A second sign sweep pass can be performed to try to eliminate these blocks.
The sign sweep threshold governs how big of a jump has to occur for a sign transition to be considered inconsistent. If the values of the sdf change by more than this threshold times the width of the cell, it is considered an invalid sign transition. The original geometry is then ray intersected to determine inside/outside and the result used to determine which sign is correct. The correct sign is then propagated forward through the model.
Max Sign Sweep Count
The sign sweeps are repeated until no signs are flipped (ie, all transitions are within the threshold) or this maximum is reached. Too low of a sign sweep threshold may prevent the process from converging. Otherwise, it tends to converge very quickly.
Allows fracturing for this object. The solver must also have fracturing enabled.
The relative amount of stress in any direction above which dynamic fracturing will occur.
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.
External Velocity Field
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.
External Velocity Offset
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.
Create Quality Attributes
This creates a primitive attribute 'quality' on the simulated geometry. The worst quality is 0, the best quality is 1. The better the quality of the primitives, the better the performance and stability of the solve will be.
Create Energy Attributes
This toggle allow the object to generate attributes that indicate the density of kinetic energy and potential energy. In addition, an attribute that indicates the density of the rate of energy loss is generated.
Create Force Attributes
This toggle allows force attributes to be generated.
Create Collision Attributes
Create Fracture Attributes
This value is the simulation time for which the node is being evaluated.
This value may not be equal to the current Houdini time represented by the variable T, depending on the settings of the DOP Network Offset Time and Time Scale parameters.
This value 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.
This value is the simulation frame (or more accurately, the simulation time step number) for which the node is being evaluated.
This value may not be equal to the current Houdini frame number represented by the variable F, depending on the settings of the DOP Network parameters. Instead, this value is equal to the simulation time (ST) divided by the simulation timestep size (TIMESTEP).
This value is the size of a simulation timestep. This value is useful to scale values that are expressed in units per second, but are applied on each timestep.
This value is the inverse of the TIMESTEP value. It is the number of timesteps per second of simulation time.
This is the number of objects in the simulation. For nodes that create objects such as the Empty Object node, this value will increase for each object that is evaluated.
A good way to guarantee unique object names is to use an expression
This value is the number of objects that will be evaluated by the current node during this timestep. This value will often be different from SNOBJ, as many nodes do not process all the objects in a simulation.
This value may return 0 if the node does not process each object sequentially (such as the Group DOP).
This value is the index of the specific object being processed by the node. This value will always run from zero to NOBJ-1 in a given timestep. This value does not identify the current object within the simulation like OBJID or OBJNAME, just 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 will be -1 if the node does not process objects sequentially (such as the Group DOP).
This is the unique object 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.
The object identifier can always be used to uniquely identify a given object. This makes this variable very useful in situations where each object needs to be treated differently. It can be used to produce a unique random number for each object, for example.
This value is also the best way to look up information on an object using the dopfield expression function. This value will be -1 if the node does not process objects sequentially (such as the Group DOP).
This string contains a space separated list of the unique object identifiers for every object being processed by the current node.
This string contains a space separated list of the names of every object being processed by the current node.
This value is the simulation time (see variable ST) at which the current object was created.
Therefore, to check if an object was created
on the current timestep, the expression
$ST == $OBJCT should
always be used. This value will be zero if the node does not process
objects sequentially (such as the Group DOP).
This value is the simulation frame (see variable SF) at which the current object was created.
This value is equivalent to using the dopsttoframe expression on the OBJCT variable. This value will be zero if the node does not process objects sequentially (such as the Group DOP).
This is a string value containing the name of the object being processed.
Object names are not guaranteed to be unique within a simulation. However, if you name your objects carefully so that they are unique, the object name can be a much easier way to identify an object than the unique object identifier, OBJID.
The object name can
also be used to treat a number of similar objects (with the same
name) as a virtual group. If there are 20 objects named "myobject",
strcmp($OBJNAME, "myobject") == 0 in the activation field
of a DOP will cause that DOP to operate only on those 20 objects. This
value will be the empty string if the node does not process objects
sequentially (such as the Group DOP).
This is 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.
Most dynamics nodes have local variables with the same names as the node’s parameters. For example, in a Position node, you could write the expression:
$tx + 0.1
…to make the object move 0.1 units along the X axis at each timestep.