Fluid particles go across a solid boundary with modified dynamic boundary conditions
I grew interested in testing the modified dynamic boundary conditions for rapid fluid-structure interactions (problems of water entry and wave slamming).
I have simply replayed the 3D dam-break test case of [pkg]/examples/mdbc/04_Dambreak/CaseDamBreak3D_Def.xml. Data, code and tools are taken as is from DualSPHysics5 v5.10.164 (21-11-2020). In the path above [pkg] is the root of the package downloaded from the website.
This is the dam-break benchmark endorsed by SPHERIC (https://spheric-sph.org/tests/test-2) and is different from the dam break of the 'main' suite of examples. In this benchmark, the central point for attention is a low object in the middle, a mock container, where pressure sensors were mounted. There, the fluid flow looks fine. However, unexpectedly for me, the solid boundary does not quite hold back the fluid elsewhere.
I have attached three snapshots. They show a side view of the 3D domain sliced along the plane of symmetry. The view is clean of perspective effects (purely 2D).
An animation of the first three of six simulated seconds is available from this unlisted Youtube link
Fluid particles do enter in great numbers into the solid boundary, and keep on roaming in there. This anomaly is not caught by the 'particle out' total, arguably because these particles neither leave the greater simulation domain nor suffer from otherwise abnormal state values.
While the evidence is contrary to a basic expectation of physical solidity, I am fine that this anomaly shows up. Its extent can be appreciated visually at least. This raises concerns, however, on the accuracy of the fluid-structure interactions where these spurious effects might occur, discounting any why they do.
It would be important, rather, to know whether this escape of fluid particles across a solid boundary is consequential for sound results, and how much. I might have missed thousands of resources where this limitation is already acknowledged.
Is the current implementation of the modified boundary conditions in DualSPHysics5 still subject to research? Are there any caveats and provisos with a quantitative backing?
From a user's perspective, are there ways to mitigate these effects? Or is falling back on the conventional dynamic boundary conditions still the practitioner's failsafe option?
Thanks for looking into this.