What are the limitations of SPH Adaptive Size in Ansys FreeFlow?

[FAQ]

What are the limitations of SPH Adaptive Size in Ansys FreeFlow?

SPH Adaptive Size in Ansys FreeFlow has a few important limitations that users should consider when setting up simulations and analyzing results.

 

1.Mass Loss Near Boundaries

When SPH Adaptive Size is used with boundary‑based refinement, mass loss may occur near walls. During refinement close to a geometry boundary, some refined SPH elements can be placed partially inside or overlapping the wall. To maintain numerical stability, these elements are excluded from the simulation, which may result in a local loss of mass.

Recommendation: Use Region of Interest (ROI)–based refinement instead of boundary proximity refinement. ROI refinement reduces the likelihood of refined elements intersecting boundaries and generally provides better control over refinement regions.

 

2.Numerical Precision and Truncation Errors

The FreeFlow solver uses single‑precision arithmetic. As a result, truncation errors may appear when SPH Adaptive Size is enabled. This issue can arise if the ratio between the finer and coarser elements is too big. . This is because adaptive refinement further reduces the element size, increasing sensitivity to floating‑point precision.

Recommendation: Avoid floating point precision problems by setting up to 2 levels of refinement.

 

3.IISPH Solver‑Specific Behavior

When SPH Adaptive Size is combined with the IISPH solver, users may observe pressure fluctuations that can affect simulation results. This behavior is less pronounced when using WCSPH.

To address this limitation, Ansys FreeFlow offers the Relaxed Incompressibility Constraint feature, available exclusively for the IISPH solver.

Recommendation: For more stable and accurate results when using IISPH with SPH Adaptive Size, enable the Relaxed Incompressibility Constraint.

 

 4.Post‑Processing and Element ID Tracking

SPH Adaptive Size dynamically creates and removes SPH elements during refinement and coarsening. As a result:

• Original SPH elements are deleted when refinement occurs
• New refined elements receive new Element IDs
• Element ID numbering is reorganized at each refinement iteration

Because of this behavior, Element IDs are not consistent over time, making element tracking unreliable.

Recommendation: Do not rely on Element ID tracking for adaptive simulations. However, if an original Element ID disappears from the simulation, this indicates that the element was refined.

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Ansys FreeFlow™ smoothed-particle hydrodynamics (SPH) simulation software