Current blockage in steady flow: Interaction of uniform and sheared flow with a porous body having uniform and non-uniform resistance

This paper presents analysis of steady flow passing through a porous body in 3D, representing a steady current passing through a space-frame offshore structure such as an offshore jacket or a compliant tower. A porous body is used as a proxy for a space-frame structure to model the effect of current blockage, which may be interpreted as a global flow and force reduction relative to the standard Morison drag formulation due to the presence of the structure as a distributed obstacle. Both uniform and sheared approach flows are simulated with CFD in OpenFOAM for a porous body with uniformly distributed resistance. The behaviour of the blockage due to both types of flow are compared and contrasted using flow visualisation to illustrate the interaction of the flow with the body and the evolution of the resultant wake downstream of the body. The numerical results are compared with the actuator disc model for uniform flow due to [8] and the actuator disc model for sheared flow due to [1]. A porous body with non-uniform vertically distributed resistance is also considered, and the difference in the flow interaction relative to body with uniform resistance is analysed and discussed. The analysis provides the framework for applications for wind loading on offshore structures such as a space-frame during load-out and transportation on a barge, as well as numerical comparisons for an extension of the [1] model to an actuator disc with non-uniform resistance.