With the release of PLAXIS 2D/3D CONNECT Edition V21, a new User Defined Soil Model is introduced: the Fluid model.

This constitutive model has been specifically created to simulate the effects of free water on water-retaining structures and quay walls or any other situation involving fluid-structure interaction. Like any other material model in PLAXIS, the fluid is simply modeled as a solid continuum, with the capability to support an indefinite level of hydrostatic pressure and, more importantly, to exhibit negligible shear stresses. The only specific parameter to be defined is the bulk modulus of the fluid (e.g. K = 2.2GPa in case of water) whereas the shear modulus is internally calculated to avoid numerical issues due to the incompressibility constraint, that is Poisson’s ratio approaching 0.5. This model comes in handy when hydrodynamics pressure build-ups need to be taken into serious consideration in the design, specifically when more simplified and straightforward procedures based on the added mass concept, also available in PLAXIS, prove to be not suitable or sufficiently accurate for the purpose.

Dynamic displacement response of a dam comparing the Fluid model against the Added mass feature

With the release of PLAXIS 2D/3D CONNECT Edition V21 (January 2021), this PLAXIS User Defined Soil Model is delivered with the PLAXIS installation. When using the PLAXIS Advanced or PLAXIS Ultimate version and enabling the Geotechnical SELECT Entitlement [GSE] when starting the PLAXIS application, this model becomes available in the Parameters tab when selecting "User-defined" for the Material model.