The glossary below includes the definition of the main terms and concepts used in the description of the Rocky Solver SDK in the remainder of this manual.

Adhesive contact

A contact in which the interaction force is adhesive. There is no need of physical contact for an adhesive force to exist between two entities (two particles or a particle and a boundary triangle). In Rocky, an adhesive contact will exist if an adhesive model is active and the gap between the two entities is smaller than the adhesive distance.

Adhesive distance

A value defined per material interaction, that specifies the limiting distance (gap) for an adhesion contact to exist between two entities associated to that material interaction.

Boundary

A boundary or geometry is each one of the individual surfaces, formed by boundary triangles, that interacts with the particles during a simulation. A custom module can define custom geometry properties whose values can be specified in runtime through the Rocky UI for each boundary in a project.

Boundary triangle

Each one of the triangles that make up a geometry or boundary.

CUDA

Acronym for Compute Unified Device Architecture, which is a parallel computing platform that allows developers to use a CUDA-enabled GPU for general purpose processing. It is the platform used by Rocky to process simulations in GPU.

CUDA

Computational representation of any pair particle/particle or particle/boundary-triangle that has a force interaction at a given time in a simulation. Rocky is constantly updating the list of active contacts, according to the instantaneous positions of the particles in a simulation.

Contact model pipeline

The sequence of calculations made by a contact model, where the output of one calculation is passed as an input to the next one. It can be customized through the implementation of a custom contact model on an external module.

Device

In CUDA-related operations, it refers to the GPU and its memory.

Discrete breakage

Breakage modeling applicable only to flexible particles (fibers, shells, and solid) in which the bonding action of a joint is disabled when the breakage criterion is satisfied.

Element

Each one of the pieces that make up a flexible particle. In Rocky, elements are sphero-cylinders in a flexible fiber, sphero-triangles in a flexible shell, and tetrahedra in a solid flexible particle.

Frictional contact

A contact in which the two entities are physically touching each other. That is, there is an actual overlap between the entities and, therefore, a contact force acting on both of them.

Home entity

In contexts where a pair of entities is involved, one of these entities is always labeled as home. In contacts, it is always a particle, independent of the contact type. In joints, it is always an individual element making up the particle. There is no special rule for labeling an entity as home when the two entities have the same type.

Hook

Location within the Rocky solver at which the Rocky Solver SDK allows modules to insert custom C++ code in order to implement new functionalities or modify some specific behavior

Host

In CUDA-related operations, it refers to the CPU and its memory.

Instantaneous breakage

Breakage modeling applicable only to non-flexible polyhedral particles in which all the resulting fragments are generated at the same time when the breakage criterion is satisfied.

Joint

A joint is the entity that links two elements in a multi-element flexible particle. A joint applies forces and moments over the joined elements as a reaction to translational and angular deformations, respectively. A joint model specifies how those forces and moments are related to those deformations

Known scalar

A type of scalar variable that is defined within the Rocky solver, but can be accessed from a custom module, if necessary.

Material

An abstraction of the material that makes up particles or boundaries in Rocky. A material has associated values of physical properties that are common to all particles in a particle group or to a whole boundary.

Material interaction

Any of the combinations of two materials defined in a project. A material interaction is a computational abstraction that associates common properties to all contacts in which each one of the two contacting entities is made of one of the two materials considered in the material interaction. A custom module can define custom material interaction properties whose values can be specified in runtime through the Rocky UI for each material interaction in a project.

Module

A component which is external to the Rocky core solver and that implements a specific feature or overrides a built-in model. The main purpose of the Rocky SDK is to enable users to implement custom modules.

Multi-element particle

A flexible particle formed by more than one element. Rocky supports three types of multi-element particles: fibers, shells and solid particles.

Near entity

In contexts where a pair of entities is involved, one of these entities is always labeled as near. In contacts, it is always the entity (particle or triangle) in contact with the home particle. In joints, it is always the individual element that is linked to the home element by a joint.

Particle group

A collection of particles with the same shape, material, and other defining characteristics, such as size distribution, flexibility, breakage capabilities, etc.

Point cloud

A set of points without a connectivity structure, located inside the solution domain. The spatial distribution of one or more physical quantities can be defined by assigning values to each point belonging to a point cloud. Those values can be retrieved during the execution of a simulation though special SDK methods, in order to be used in custom models.

SPH element

Each one of the material particles that make up a fluid phase described numerically using the SPH method. By construction, the mass of a SPH element is invariable throughout the simulation. There are two main types of SPH elements considered in Rocky: free elements and linked or coupled elements. The former are regular SPH elements within the fluid phase, while the latter are auxiliary SPH elements placed inside solid particles in order to model the physical interaction between those particles and the fluid.

SPH interaction

A computational representation of a pair formed by two SPH elements or by a SPH element and a boundary triangle that have physical interaction at a given instant of time. Within the code, an interaction of the former type is usually referred to as a SPH element interaction, while an interaction of the latter type is called a SPH triangle interaction. Thoughout the simulation, Rocky periodically updates the lists of SPH interactions, based on the instantaneous positions of SPH elements and boundary triangles.

SPH kernel

A bell-shaped function of compact support used to approximate the fluid dynamics equations in SPH. In the discretization process, the physical quantities associated to a SPH element are smoothed over a spherical region around the element by applying the SPH kernel function. The value of the kernel function decreases monotonically to zero over that region, whose radius is commonly called the kernel radius. Only SPH elements located at a distance smaller than the kernel radius of other SPH elements are considered to have a force interaction between them

Scalar

A special type of variable associated to a specific type of entity in Rocky (particles, boundary triangles, joints, or contacts) that is designed to store values that persist throughout a simulation.

Smoothed Particle Hydrodynamics (SPH)

A numerical method for solving the equations of fluid dynamics. This method is closely related to the Discrete Element Method (DEM) used in Rocky for simulating the motion of solid particles, since the fluid is represented by discrete elements of constant mass whose motion is determined by integration of Newton’s second law.

Transfer scalar

A type of scalar variable whose values are reset automatically at the beginning of each new time iteration. Currently defined only for particles, it is typically used to sum values coming from different contacts associated to a particle at a given time