Research on the Water Ridge and Slamming Characteristics of a Semisubmersible Platform under Towing Conditions

During the towing of semisubmersible platforms, waves impact and superpose in front of the platform to form a ridge shaped “water ridge”, which protrudes near the platform and produces a large slamming pressure. The water ridges occur frequently in the towing conditions of semisubmersible platforms. The wave–slamming on the braces and columns of platform is aggravated due to the water ridges, particularly in rough sea conditions. The effect of water ridges is usually ignored in slamming pressure analysis, which is used to check the structural strengths of the braces and columns. In this paper, the characteristics of the water ridge at the braces of a semisubmersible platform are studied by experimental tests and numerical simulations. In addition, the sensitivity of the water ridge to the wave height and period is studied. The numerical simulations are conducted by a Computational Fluid Dynamics (CFD) method, and their accuracy is validated based on experimental tests. The characteristics of the water ridge and slamming pressure on the braces and columns are studied in different wave conditions based on the validated numerical model. It is found that the wave extrusion is the main reason of water ridge. The wave–slamming pressure caused by the water ridge has an approximately linear increase with the wave height and is sensitive to the wave period. With the increase of the wave period, the wave–slamming pressure on the brace and column of the platform increases first and then decreases. The maximum wave–slamming pressure is found when the wave period is 10 s and the slamming pressure reduces rapidly with an increase of wave period.

DETERMINATION OF WAVE SLAMMING LOADS ON HIGH-SPEED CATAMARANS BY HYDROELASTIC SEGMENTED MODEL EXPERIMENTS

A 2.5m hydroelastic segmented catamaran model has been developed based on the 112m INCAT wave-piercer catamaran to simulate the vibration response during the measurement of dynamic slam loads in head seas. Towing tank tests were performed in regular seas to measure the dynamic slam loads acting on the centre bow and vertical bending moments acting in the demihulls of the catamaran model as a function of wave frequency and wave height to establish the operational loads acting on the full-scale 112m INCAT catamaran vessel. Peak slam forces measured on the bow of the model are found to approach the weight of the model, this being similar to the findings of full-scale vessel trials. A review of the motions of the hydroelastic segmented catamaran model found that the heave and pitch motions give a good indication of slamming severity in terms of the dimensionless heave and pitch accelerations. The dynamic wave slam forces are closely related to the relative motion between the bow and the incident wave profile.

Study on Slamming Pressure Characteristics of Platform under Freak Wave

Freak waves have great peak energy, short duration, great contingency, and strong nonlinear characteristics, and can cause severe damage to ships and marine structures. In this study, numerical simulations in conjunction with experimental tests are applied to study air gap response and wave slamming loads of a semi-submersible offshore platform under a freak wave. A three-dimensional wave tank, which is created based on the computational fluid dynamics (CFD) method, is applied to study the hydrodynamic responses of a semi-submersible platform. The numerical model of the tank and offshore platform system are checked according to the experimental results. A typical freak wave is modelled in numerical wave tanks by the linear superposition method, and its significant wave height is 13.03 m. It is found that the freak wave is closely associated with the wave slamming. The appearance of the freak wave gives rise to a negative air, gap which appears on the side of the back wave surface at the bottom of the deck box, and considerable slamming pressure is generated. Furthermore, the wave run up at the junction of the column and the buoyancy tank is also seen due to the freak wave.

Offshore Urban Extension of the Anse Du Portier In Monaco

As part of the Monaco offshore urban extension project, Bouygues TP is in charge of design & build a maritime infrastructure as the first step of the six-hectare expansion of the city into the sea. This maritime infrastructure consists of a fill enclosed by a band of trapezoid concrete caissons and will serve as base for construction of the new residential area. The paper focuses on some of the problems which had to be solved: optimization of promenade level and wave absorbing chambers in conjunction with minimal reflection and safety related to overtopping, accounting for sea level rise and correlation between extreme waves and water levels. caissons and rubble mound foundation stability related to waves and seism, including extra seismic forces due to buildings considering the high reclamation height and the immediate proximity of building foundations. the way in which caissons representing nearly 80,000 m3 of concrete can be built in a floating and continuous manner via a caisson box (or "caissonnier" in French), within a particularly short time frame presence of a small craft harbor with shops along the quays, whose location was fixed for urbanistic reasons, which requested optimizations in detail of anti-overtopping devices as much as possible integrated in the urban context, need to convert a breakwater caisson into a low crested swimming pool caisson, with plexiglas windows exposed to wave slamming from outside, but also from inside due to overtopping impacts over the swimming pool basin. Ecodesign has been closely associated with hydrodynamic and coastal engineering, based on estimation of wave pressures and induced velocities in the different possible locations (chambers, walls, structures toes …). The eco-friendly development strategy is based on the wide-scale deployment of a range of 11 solutions which will be described (potential for caissons to be colonized, nursery function development, etc…). Moreover, posidonia transplantation has been done via concrete open boxes, whose stability under storm waves has requested CFD calculations to model local velocities and optimize their shape.

Underdeck Wave Slamming Model Tests for a Drilling Semi-Submersible Unit

Negative air gap and wave slamming load on the deck box of drilling semi-submersible units in severe storm have received a great deal of attention, due to the COSL Innovator accident in 2015. Equally important is vertical slamming load on the MODU underdeck, which is less reported in the literature. The present paper attempts to derive characteristic vertical slamming pressure on the deck bottom, based on an extensive model test program for a drilling semi-submersible unit, CM-SD1000. A total of 96 3-hour wave impact tests were conducted including 4 sea states selected along the DNV steepness criterion curve in 3 wave headings. Two critical sea states were identified and each was tested with 16 random realizations in both the head and the beam waves. 8 force panels were installed on the under-deck to capture vertical wave impact events. It is found that the peak slamming pressures obtained can be fitted well with both Weibull and Gumbel probability function. The extreme vertical impact pressure predicted are of the same order of magnitude as the extreme horizontal impact pressure. The present study also shows that rise velocities of the wave surface relative to the deck bottom have a remarkable correlation with the wave slamming pressure in terms of probability distribution. The relative rise velocities can be properly derived from wave probe measurements. This offers an alternative approach to estimate the vertical impact pressure without resort to force panels. In contrast to horizontal wave slamming, the magnitude and frequency of vertical ones simply increases with significant wave height and wave steepness has much less effect. It is found that the extreme vertical impact pressure can be approximated well by a linear function of the significant wave height. The linear relationship, if validated by more tests, may help evaluate structural strength of the deck bottom before wave basin model testing.

Pressure Distributions on the Bottom of a Planing Hull During Slamming

Bottom pressures were measured on two prismatic planing hull models operating in regular waves. Testing in regular waves created repeated wave slam events, which provided information on variability of the motions, accelerations, and pressures during wave slamming events. Using a reconstructed pressure distribution based on Rosen’s method [2] and predicted pressure distributions based on empirical equations given by Morabito [3], better understanding of how the hull and water interact during wave slamming can be achieved.