Time domain strength and fatigue analysis of Truss Spar heave plate

This paper presents the structural and hydrodynamic design aspects of heave plates in a Truss Spar platform. From a motion point of view, the heave plates entrap a large amount of water within the hull such that the heave natural period is longer than the wave periods. The drag forces provide quadratic damping which becomes the main source of heave damping. Structurally, the heave plates provide in-plane stiffness for the truss and lateral supports to risers and caissons. The plated construction is well suited for fabrication and load-out supports. Design of the heave plates is driven by inertial loads. Because these loads are time and spatial-variant, the plates are discretized into panels and analyzed in the time domain. This paper discusses the modeling techniques and the pressure mapping procedure for strength and buckling analysis. A pressure-to-stress ratio concept is introduced for fatigue analysis. Calibrations with model tests are discussed as well.