Numerical study of nonlinear freak wave impact underneath a fixed horizontal deck in 2-D space

Experimental investigation of wave-in-deck impact events on a TLP model

This article describes a series of model tests conducted to examine extreme wave events associated with tropical cyclonic conditions and their impacts on an offshore deck structure. Extreme waves of a representative cyclonic sea state were examined in a towing tank within long-crested irregular wave trains. Experimental results presented include global forces and localised slamming pressures acting on a rigidly mounted box-shaped deck, which represents a simplified topside structure of a tension leg platform. The effect of static set-down on the still-water air gap was investigated by applying an equivalent reduction for the deck clearance. It was found that a small reduction of 20 mm (2.5 m full scale) in the original deck clearance can lead to a doubling of the magnitude of the horizontal force and the vertical upward-directed force components, as well as significantly increased slamming pressures in many locations on the deck underside.

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Measurements of global and local effects of wave impact on a fixed platform deck

This paper describes a series of model tests of a rigidly mounted tension leg platform (TLP) subjected to extreme wave events corresponding to long-crested irregular wave trains of a 10,000-year cyclonic sea state. The experimental setup was instrumented to simultaneously measure wave surface elevations in the vicinity of the model, global wave impact forces and local pressure distribution on the underside of the model's topside deck. Model accelerations were also monitored for each wave impact event so that the inertial force due to structural dynamic response could be identified. The deck–column intersection areas were found to experience large wave-in-deck slamming pressures, in particular around the aft columns. A reduction of the deck clearance was found to increase the magnitude of the global horizontal forces; however, the global vertical forces and local wave-in-deck slamming pressures did not follow this trend.

/pdf/experimental-investigation-of-extreme-wave-impacts-on-a-15oj8pgt2h.pdf

Experimental investigation of extreme wave impacts on a rigid TLP model in cyclonic conditions

A Constrained Interpolation Profile method following Hu and Kashiwagi (2004) is developed for wave impact applications. Two-dimensional, unsteady, viscous and incompressible flow is assumed. The numerical model is a finite difference high-order up-wind scheme for solving the Navier.Stokes equations. A domainembedding, staggered Cartesian grid is used for the spatial discretization. The water and air phases are modeled as one fluid. The material properties vary across the domain, and the free surface is modeled as a layer rather than a sharp interface. Different surface capturing schemes based on density functions are tested.Benchmark tests focusing on marine applications are used to develop the code and demonstrate the capabilities and limitations of the method. A numerical wave tank is developed and validated using both higher order wave theory and experimental results from physical wave tanks. Progressive, regular waves are simulated. Wave impact simulations are performed for a simplfied, fixed deck structure. Horizontal and vertical global forces are computed. Different combinations of wave height, wave period and airgap are used in the simulations. The impact process is studied. Parameter studies for wave crest variation and airgap changes are performed. Results are compared with existing experimental results. The global loading process for multiple impacts on the deck box is discussed using both numerical and experimental results.

Rolf Baarholm

Papers

Experimental and Theoretical Study of Three-Dimensional Effects on Vertical Wave-in-Deck Forces