Removing and Redistributing Particles
While running an SPH simulation, it can happen that, due to numerical inaccuracies, individual SPH particles leave the area of interest. These particles are not held back by wall boundaries. To prevent Simcenter STAR-CCM+ from tracking outliers and thereby performing unnecessary calculations, you can remove particles when they meet certain position-based and/or velocity-based criteria. The Particle Remediation model provides the option to remove particles that exceed a specified maximum velocity or particles that reside outside specified geometry bounds.
During some simulations, the particle distribution becomes inhomogeneous, which can lead to inaccuracies in the solution such as local overpressure or particles crossing boundaries. To ensure a nearly uniform space discretization by the particles throughout the simulation, you can activate the Skillen shifting method.
To remove and redistribute particles:-
To remove particles outside the bounding box that encloses the specified
geometry:
- Select the node and activate Enable Position-Based Removal.
-
Select the node and, using the
(Custom
Editor), set Part to the
[bounded shape] part that you created in
Step 4.
You apply this type of particle removal to remove particles that escape in simulations with unbounded geometries or that leak through boundaries in bounded geometry situations. -
To remove particles that exceed a maximum velocity, select the
Particle Remediation node and activate Enable Velocity-Based Removal, then set the Velocity-Based Criterion to the maximum allowed
velocity.
You use this type of particle removal to remove particles that exhibit unphysical velocities due to local instabilities or particles that are trapped between boundaries.
-
To activate homogeneous particle distribution during the simulation, select the
Particle Remediation node and set
Shifting Option to Skillen, then
specify the following properties:
- Shifting Coefficient—defines the strength of particle redistribution for all particles.
- Shifting Limit—constrains local particle redistribution by enforcing a velocity shifting value lower than the Shifting Coefficient multiplied by the amplitude of the particle current velocity.
-
To review the number of particles that are removed per time-step by the
Particle Remediation model, right-click the Reports node
and select the following:
If you want to track removed particles over the course of the simulation, create corresponding monitors and plots.