{"id":199016,"date":"2026-06-11T22:04:39","date_gmt":"2026-06-11T22:04:39","guid":{"rendered":"https:\/\/innovationspace.ansys.com\/knowledge\/?post_type=topic&p=199016"},"modified":"2026-06-15T12:57:08","modified_gmt":"2026-06-15T12:57:08","slug":"what-are-the-limitations-of-sph-adaptive-size-in-ansys-freeflow","status":"publish","type":"topic","link":"https:\/\/innovationspace.ansys.com\/knowledge\/forums\/topic\/what-are-the-limitations-of-sph-adaptive-size-in-ansys-freeflow\/","title":{"rendered":"What are the limitations of SPH Adaptive Size in Ansys FreeFlow?"},"content":{"rendered":"

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What are the limitations of SPH Adaptive Size in Ansys FreeFlow?<\/strong><\/h1>\n

SPH Adaptive Size in Ansys FreeFlow has a few important limitations that users should consider when setting up simulations and analyzing results.<\/p>\n

 <\/p>\n

1.Mass Loss Near Boundaries<\/strong><\/p>\n

When SPH Adaptive Size is used with boundary<\/strong>\u2011based refinement<\/strong>, 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.<\/p>\n

Recommendation: <\/strong>Use Region of Interest (ROI)\u2013based refinement<\/strong> instead of boundary proximity refinement. ROI refinement reduces the likelihood of refined elements intersecting boundaries and generally provides better control over refinement regions.<\/p>\n

 <\/p>\n

2.Numerical Precision and Truncation Errors<\/strong><\/p>\n

The FreeFlow solver uses single<\/strong>\u2011precision arithmetic<\/strong>. As a result, truncation errors<\/strong> may appear when SPH Adaptive Size is enabled. This issue can arise if the ratio between the finer and coarser<\/strong> elements is too big<\/strong>. This is because adaptive refinement further reduces the element size, increasing sensitivity to floating\u2011point precision.<\/p>\n

Recommendation:\u00a0<\/strong>Avoid floating point precision problems by setting up to 2 levels of refinement.<\/p>\n

 <\/p>\n

3.IISPH Solver\u2011Specific Behavior<\/strong><\/p>\n

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

To address this limitation, Ansys FreeFlow offers the Relaxed Incompressibility Constraint feature, available exclusively for the IISPH solver<\/strong>.<\/p>\n

Recommendation: <\/strong>For more stable and accurate results when using IISPH with SPH Adaptive Size, enable the Relaxed Incompressibility Constraint<\/strong>.<\/p>\n

 <\/p>\n

\u00a04.<\/strong>Post\u2011Processing and Element ID Tracking<\/strong><\/p>\n

SPH Adaptive Size dynamically creates and removes SPH elements during refinement and coarsening. As a result:<\/p>\n