Meshfree DEM Model Reference

Reference Frame Specification

The reference frame used to specify position and velocity of DEM particles in the region.

Option	Corresponding Physics Value Nodes
Lab Frame Uses the Laboratory reference frame (default). No rotation.	None
Region Reference Frame Uses the reference frame of the parent region. When the region has a rotating reference frame attached, a physically valid setup using this condition puts the boundary in the reference frame of the region. This implies that the boundary is rotating with the region at the same RPM, and has the same rotation axis and origin as the region.	None
Local Reference Frame This option allows the boundary to have its own frame (only rotating frame) attributes. For example, this can be used when both the boundary and the region are rotating at a different RPM but have the same axis and origin. A setup where the region and boundary have different values for the RPM, axis, and origin is also possible.	Boundary Reference Frame Specification Applies the chosen Reference Frame to the containing boundary.

Tangential Velocity Specification

When a Tangential Velocity Specification is used at a wall $f$, only the tangential component $v_{\tau }$ of the specified velocity ${\mathbf{\text{v}}}_{\text{spec}}^{\text{lab}}$ is used. If you specify a velocity with a component normal to the wall, the normal component of ${\mathbf{\text{v}}}_{\text{spec}}^{\text{lab}}$ is ignored, since the velocity ${\mathbf{\text{v}}}_f$ at the face is computed as:

$${\mathbf{\text{v}}}_f={\mathbf{\text{v}}}_{\text{spec}}^{\text{lab}}-({\mathbf{\text{v}}}_{\text{spec}}^{\text{lab}}\cdot \mathbf{\text{a}}-G_f)\frac{\mathbf{\text{a}}}{a^2}$$

()

where $\mathbf{\text{a}}$ is the face area vector and ${\mathbf{\text{v}}}_{\text{spec}}^{\text{lab}}$ is the velocity in the laboratory frame. The normal component contribution at the face $f$ can only come from the grid flux $G_f$ that is given by Eqn. (4868). That is, if the wall itself is moving at a velocity with a non-zero component in the wall normal direction.

Note that:

$${\mathbf{\text{v}}}_{\text{spec}}^{\text{lab}}={\mathbf{\text{v}}}_{\text{spec}}^{\text{mesh}}+{\mathbf{\text{v}}}_{\text{mesh}}^{\text{ref}}+{\mathbf{\text{v}}}_{\text{ref}}^{\text{lab}}$$

()

where:

• ${\mathbf{\text{v}}}_{\text{spec}}^{\text{lab}}$ is the specified velocity measured in the laboratory frame.
• ${\mathbf{\text{v}}}_{\text{spec}}^{\text{mesh}}$ is the specified velocity measured relative to the mesh.
• ${\mathbf{\text{v}}}_{\text{mesh}}^{\text{ref}}$ is the velocity of the mesh relative to the reference frame. This quantity is in Region > Physical Values > Motion Specification..
• ${\mathbf{\text{v}}}_{\text{ref}}^{\text{lab}}$ is the velocity of the reference frame relative to the laboratory frame.

The net tangential velocity in the laboratory frame is the vector sum of the tangential velocity with respect to the reference frame selected under the condition Reference Frame Specification and the velocity of the selected frame with respect to the laboratory frame.

Unless specified in an Axis node, axis of rotation is defined by information in the Motion Specification node under the Physics Values node.

Method	Corresponding Physics Value Nodes
Fixed Tangential velocity is zero with respect to the applicable reference frame.	None.
Vector Tangential velocity is specified by rotation rate with respect to the applicable reference frame.	Velocity Relative Velocity Sets the velocity vector in the chosen Coordinate System. When relative, the vector is defined within the reference frame applied to the boundary.
Rotation Rate Tangential velocity is specified as a vector with respect to the applicable reference frame.	Wall Rotation Wall Relative Rotation Sets the wall rotation rate around the axis of the reference frame applied to the containing boundary.
Local Rotation Rate Tangential velocity is defined by the rotation rate around the axis specified in the Axis node of the boundary and with respect to the applicable reference frame.	Local Axis Specifies a vector whose Origin and Direction define an axis of rotation. The local axes can be defined By Surface Subgrouping if the following prerequisites are fulfilled: Allow Per-Surface Values of the boundary is activated. Specify by Part Subgroup of the Local Axis node is activated. For more workflow of Applying Quantities by Subgroup, refer to Defining Subgroups. Wall Rotation Wall Relative Rotation As for Rotation Rate.

A unit length vector perpendicular (orthogonal) to the boundary.

If an axis is defined, this field function provides the distance from the axis.