The Effects of Capture and Time Out of Water on Sablefish (Anoplopoma fimbria) Reflexes, Mortality, and Health

It is unknown if capture coupled with time out of water on-deck affect sablefish (Anoplopoma fimbria) health and reflexes, and whether it contributes to acute or delayed mortality. In this study, 35 sablefish were caught using hook-and-line gear and given six reflex tests after capture. Thirty-two were subsequently transported to the laboratory, held for 45–52 days, and then experimentally held out of the water for either 0, 3, 6, or 11 min. After 7–10 days of holding in the laboratory after the experiment, to monitor for mortalities, reflexes were tested for a second time and necropsies and histopathology were performed. There were no histological findings and no mortalities; however, parasites and minor inflammation were observed. All occurrences were not a result of capture or experiments. Some reflexes were absent after capture (77% could right themselves, 69% responded to a tail grab, and 57% responded to sound.) The only test where the reflex did not improve to 100% in the laboratory was the sound reflex. The sound reflex was highest for control fish (63%) and there were no positive sound reflexes for fish held out of water for 11 min. The absence of reflexes may result in predation after release and present issues with feeding or communication.

Chaos and Control of Ships with Water on Deck Under Periodic Excitation with Lévy Noise

Non-linear dynamic and chaotic roll motion response of ships with water on deck induced by uncertain jumps are investigated. The huge wave with random jump can be described as Lévy noise with critical parameters [Formula: see text], [Formula: see text], [Formula: see text], and [Formula: see text]. Through sensitive study, the stability index [Formula: see text] and the scale parameter [Formula: see text] are specified as two significant parameters in chaotic motion induction. On the same [Formula: see text] condition, the motion histories, phase portraits and Poincare maps are all recorded to highlight the effect of [Formula: see text] upon uncertain jump system, and their global bifurcation characteristics with the fluctuating amplitude [Formula: see text] are analyzed. Results show that the decrement of stability index [Formula: see text] makes the curve much thicker, and leads the acceptable stable [Formula: see text] region becomes smaller. Finally, an adaptive fuzzy sliding mode control is proposed to eliminate the chaotic behavior and stabilize the system. The asymptomatic stability from the perspective of mean square convergence is analyzed and simulated results show the effectiveness of the method.

Towards an Improved Understanding of Green Water Exceedance at the Bow of an FPSO

When a permanently moored FPSO in deep draft condition finds itself in harsh weather conditions it most likely will experience freeboard exceedance at the bow and consequently green water on deck. Knowledge about how and how much water will come onto the deck, is relevant for both a turret moored and spread-moored FPSO since both are expected to experience the most severe design conditions in head to bow quartering waves. In this paper we focus on green water phenomena observed on a Suezmax FPSO in severe head seas in the model test basin. Using an on-board video in combination with deck-mounted wave probes, green water events are recorded in detail. This provides unique insights in how the water floods onto the deck. Very different flooding phenomena are observed between different events and they can strongly deviate from a dam-breaking kind of event. Through a detailed description of three typical flooding events, the present paper improves the understanding of how green water flows onto the deck. It highlights the benefit of detailed model tests and emphasizes that new and more detailed modelling is required since the dam-breaking theory has limited value for the present problem.

Numerical Study of Bilge-Keel Effect on Parametric Roll and Water on Deck for an FPSO

This research activity represents the logical continuation of the work documented in [1] and [2] on water on deck and parametric roll for an FPSO in regular waves. Here the same numerical method, based on a domain-decomposition strategy, is used to examine the platform with bilge keels, both without and with mooring-line system. It is found that bilge keels with length 40% of the ship length and with breadth the 3% of the ship breadth limit effectively the roll when instability is promoted by vertical bow motions in waves. In these conditions also the amount of the shipped water is substantially reduced. Large roll induced by the coupling with the lateral motions seems to be less well counteracted and remains close to 10° for steepness kA ≥ 0.2. This value is often set as maximum allowed amplitude for FPSOs in normal operational conditions. Also the effect on the shipped water is limited in this case. Increasing the bilge-keels breadth is confirmed to be beneficial but the combination of the mooring system with dynamic positioning appears needed for a proper control of the roll motion in the worst examined cases.

Green Water Loads Determination for FPSO Exposed to Beam Sea Conditions

Considering new offshore frontiers for oil exploration and production, specially the Santos Basin region, FPSOs will be exposed to more severe wave conditions. This scenario requires careful analysis with respect to the green water phenomenon. The complex physics involved in the water-on-deck flow implies on several uncertainties regarding green water loads analysis. Taking into account model tests, CFD simulations and analytical formulations, this paper aims to simplify the green water loads determination, proposing a methodology to estimate these loads considering the water elevation above deck measured from experiments or numerical tools. In order to accomplish this objective, CFD simulations with different solvers were run for a benchmark case, showing that it is a suitable approach for a global result in impact dam break cases. After that, a special boundary condition was calibrated to represent model test results of water propagation in a FPSO deck exposed to beam sea in terms of water elevation. Using this CFD model, the loads on exposed structures was determined and compared against the dam break analytical formulation, which was modified to take into account the gap between each structure and the deck. Finally some vane type protection structures were simulated and their efficiency in partially obstructing the water-on-deck flow was evaluated. As a global result from all these analysis, a more comprehensive strategy for green water loads determination is proposed.