Deployment of an ice buoy at 60 °S in the Southern Ocean

Performing oceanographic measurements from the sea surface to the sea bottom is technically challenging under rough or icy sea conditions. As a measure to deal with rough seas, a new dynamic simulation program was developed and its validity was verified by comparison with the results of actual sea tests. This program can therefore be used as a design tool. To develop countermeasures against icing, we carried out basic tests in a large-scale snow and ice laboratory. Some of these countermeasures were then implemented in real sea tests and were found to be effective under icy conditions. These results indicate that deployment of moored surface buoys in regions of rough and icy sea conditions will soon be practical.

Simulation of marine operations for launch and recovery of bluff bodies such as autonomous underwater vehicles (AUV), remotely operated vehicles (ROV) or subsea templates is traditionally performed in calm to moderate sea conditions. The reason for doing so is partly due to the interaction between the complex dynamic response of an installation vessel, a moving bluff body and the wave kinematics of the rough sea condition. This is in addition to the need for accurate hydrodynamic coefficients that would enable proper simulation and modelling of the launch and recovery process. The key objective of the current methodology is to minimize risks of damage to the vessel and total loss of assets during the deployment and recovery process for marine operations in rough sea conditions. The aim of this paper is to present the results of experimental and numerical investigation on the prediction of dynamic response of a bluff body during launch and recovery from a surface vessel in rough sea condition. Experimental measurements of hydrodynamic coefficients and responses of a large scale bluff body using a scaled model were completed. Further studies using a time-domain numerical tool have been undertaken to measure the response characteristic of bluff bodies in rough seas. The study also predicted the contributions of vessel motion in rough seas to the dynamic response of the bluff bodies. The results obtained have shown that simulation of launch and recovery operations in rough seas can be carried out efficiently if their hydrodynamic coefficients through the wave active regions of the rough seas are predicted and then adequately implemented in the simulations.

Because excessive roll motions of ships in rough seas badly affect their performance, there is a continuous interest in efficient ways to mitigate these undesirable motions. There are different devices to mitigate the roll of ships with different levels of performance and operating limits. Anti-roll tanks are more effective than other roll stabilization devices when the ship is not underway or moves slowly. Here, we investigate the application of passive and active anti-roll tank systems. The tank system consists of three tanks: each one consists of two columns connected at the bottom via a horizontal pipe equipped with a pump. The tanks are arranged along the length of the ship, symmetrically located about its center of gravity. The motion of the liquid in the tank is 1-D, but it exerts loads on all degrees of freedom of the ship. The equation governing the tank-liquid motion is coupled with the equations governing the 6-DOF motion of the ship in waves; the coupled system is solved simultaneously in time. First, we derive expressions for the forces and moments exerted on the ship by the tanks. Then, we study the roll response at different sea heading angles in rough sea conditions in the absence of the tanks to identify the critical heading angles where the roll is large. We demonstrate the nonlinear behavior of roll through frequency-response curves for different beam wave amplitudes. These curves exhibit typical nonlinear phenomena (jumps and hysteresis) for high wave amplitudes. Spectral analysis shows a two-to-one frequency relationship between the roll and pitch in rough head and follower seas, which are the most critical sea headings. For passive and active tanks, we study the effect of the frequency of the tank system on its effectiveness. We consider active anti-roll tanks in which the pump power is controlled via a proportional-derivative (PD) control law using the roll angle and its rate. We compare the performances of passive and active tanks in rough sea for the critical heading angles. We found that active anti-roll tanks outperform passive ones in terms of roll reduction and size and weight, but they require power consumption. To achieve a specified roll reduction, the weight of a passive tank might be as large as five times that of an active tank. We also found that the performance of passive tanks depends strongly on their frequencies, in contrast with active tanks, which are insensitive to their frequencies.

Sea surface is rough when the weather condition at sea is rough due to strong wind, waves, swell and storms. Under the rough sea condition, the propagation of radar energy and the subsequent radar coverage is strongly influenced by various atmospheric effects, such as, strong wind, wave height, weather condition, oceanic currents and rainstorms. The identification of ship wakes in Synthetic Aperture Radar (SAR) image under the rough sea condition is viewed as a highly complex task for the real time monitoring and surveillance applications. It becomes a quite big challenge due to coherent radiation of backscattering signals and the multiplicative speckle noise found in SAR images. The objective of this work is to develop an optimized Discrete Wavelet Transform (DWT) based on Synergistic Fibroblast Optimization (SFO) algorithm for filtering speckle noise in SAR image which are captured under rough sea condition. An improved filtering technique is tested with the real time SAR images acquired from European Space Agency (ESA) sentinel scientific data hub and its efficacy is further validated by employing Discrete Radon Transform (DRT) method to detect ship wakes (linear signature) in SAR image under rough sea surface. The performance of SFO based wavelet transform is evaluated and compared with conventional DWT families, namely, daubechies, coiflet, symlet, discrete meyer, biorthogonal and reverse biorthogonal to conduct the better investigation of this study. Investigation of results illustrates the effectiveness of optimized method, in terms of, noise suppression and its implication on radon transform method to localize the identification of ship wakes in SAR imagery.

Comparative study of realistic ship motion simulation for optimal ship routing of a bulk carrier in rough seas

The effect of two chemical dispersants (Corexit 7664 and Corexit 9524) in the emulsification of a light and heavy Arabian crude oil types was investigated in context of dispersant concentration to oil ratio, rate of mixing and time of mixing. The ability of Corexit 7664 and 9524 to emulsify light and heavy crude oil was dependant on the concentration of the dispersant, the rate of mixing and the duration of mixing. Extrapolation of the results to rough and calm sea conditions suggests that the application of 6 % Corexit 9524 to oil present in rough seas would remove 95 % of the surface oil slick. Light oil spill in calm seas can be dispersed by the application of 4 % Corexit 9524 effecting 80 % removal from the sea surface.

Wave propulsion and sea-keeping enhancement for ships in rough sea condition by flapping foils

Upwelling and scattering Deep Ocean Water (DOW) into the euphotic surface layer has been proposed by many oceanographers as a “fishing ground of artificial upwelling”. So far, however, there are no successful means to make it, because of the following difficulties; the very huge amount of DOW upwelling, the dilution of DOW’s nutrient salts in the sea, enduring the rough sea condition on offshore, the strength of very long riser pipe for upwelling, etc. The MARINO-FORUM 21, sponsored by Japanese government fisheries agency, organized the research and development project of an ocean nutrient enhancer named TAKUMI and real sea experiment using it, since the year of 2000. New technology concept, featuring the density current generator for avoiding dilution of nutrient salts, the spar type submersible floating structure for withstanding against the rough sea condition, and the design and analysis of riser pipe for not only in case of the rough sea but also in case of the upending which is world first challenge of election of steel riser pipe with gravity fall in the sub-sea, was studied and introduced for the design of TAKUMI as a proper Ocean Nutrient Enhancer. TAKUMI that upwells DOW of 100,000m3/day from 200m depth and discharges it into the euphotic layer with Diesel engine was manufactured and set-up at the center of Sagami Bay in Japan, in May 2003. More than five years continuous operation in various sea conditions, which includes very rough sea in typhoon and rapid current, caused by direction change of Kuroshio Current was carried out. Also, the behavior of the nutrient water mass and the pattern of primary production around TAKUMI was investigated using the research vessel Tansei Maru. The results from the real sea experiment lead us to believe that the TAKUMI type artificial DOW upwelling system can be feasible to increase a primary production and make a fishing ground in case of large size system of more than 1,000,000m3/day.

Increased worldwide demand for oil is accelerating offshore exploration and production and is extending its boundaries to deeper and rougher waters. New technology and equipment is required for operation in these conditions, since the utilization of conventional equipment is diminished and its use, therefore, becomes uneconomical. In June, 1969 the world's first column stabilized construction barge was christened "CHOCTAW". CHOCTAW's construction followed an extensive design and development program which included three series of tank tests. During the past year, CHOCTAW was engaged in construction and pipelaying operationsin the Bass Strait, where she compiled an impressive record of performance in rough sea conditions. This paper discusses the engineering considerations which led to the CHOCTAW design and how they were realized. Actual motion and mooring forces data obtained on board the vessel is presented and compared with tank tests predictions. Based on the available preliminary data, the paper describes a method to predict CHOCTAW's motions in various sea conditions. While conventional construction barges will no doubt continue to develop oil fields in relatively calm waters, a new generation of column stabilized construction barges will operate in rough sea areas. CHOCTAW realized actual performance in seas exceeding 16 feet, and being the first such vessel, constitutes a unique departure from the conventional design. Foreword Increased worldwide demand for oil and oil products and political uncertainties in some of the major oil producing areas. are accelerating the search for oil offshore and extending its boundaries to deeper and rougher waters. Search for oil is currently being conducted in the Norwegian North Sea. the Grand Banks of Newfoundland. New Zealand's Cook Strait. Australia's Bass Strait. the Coast of Argentina and a number of rough sea areas off the African coast. The offshore drilling industry has developed a number of exploration vessels which can operate in these areas with minimum downtime. Once oil is discovered. its production necessitates the construction of platforms and production facilities. as well as underwater storage and pipelines. A great many construction barges were built to fill this need. Until June. 1969. all construction barges had conventional box shaped hulls. a feature which limited their operations to seas not exceeding five feet. Because of the excessive motion in high seas. these barges had to be towed a way to sheltered waters whenever a storm was forecast. In June, 1969, the construction barge CHOCTAW was christened. CHOCTAW was an important turning point in the industry in that she is the first column stabilized construction barge and is capable of sustaining operations in up to sixteen foot seas and maintaining her station in unrestricted oceans.

Considering the nonlinearity, parameters perturbation and random waves disturbance to the ship fin stabilizer system during ship sailing on the rough sea, a robust controller based on sliding mode control which incorporates fuzzy tuning technique is proposed in this paper. The sliding mode control is used to force the ship roll to zero. The fuzzy tuning is adopted to eliminate the chattering of control input. The system stability is analyzed by using the Lyapunov theory. Simulation results show that the method is effective to decrease ship roll motion in rough sea conditions, and when the speed and initial metacentric height of ship change, high anti-rolling efficiency is still maintained, which prove that the control strategy presented in this paper has strong robustness.

Environmental motion can affect shipboard sleep of crewmembers. Slamming and similar harsh motion may interfere with sleep, whereas mild motion and sopite syndrome may enhance sleep. If sleep needs vary by sea condition, this factor should be considered when assessing human performance at sea. The goal of this study was to assess sleep duration in different sea conditions. Crewmembers (N = 52) from a U.S. Navy vessel participated in the study while performing their normal daily schedule of duties. Sleep was assessed with wrist-worn actigraphy. Motion sickness and sopite syndrome were assessed using standardized questionnaires. In rough sea conditions, crewmembers experienced increased severity of motion sickness and sopite syndrome compared to their ratings during calmer sea conditions. Crewmembers slept significantly longer during sea state 5-6 compared to sleep on days with sea state 4 (25% increase) and sea state 3-4 (30% increase). Specifically, daily sleep increased from 6.97 ± 1.24 h in sea state 3-4, to 7.23 ± 1.65 h in sea state 4, to 9.04 ± 2.90 h in sea state 5-6. Although the duration of sleep in rough seas increased significantly compared to calmer sea conditions, causal factors are inconclusive. Accumulated sleep debt, motion-induced fatigue, and sopite syndrome all may have contributed, but results suggest that motion sickness and sopite syndrome were the predominant stressors. If sleep needs increase in severe motion environments, this factor should be taken into account when developing daily activity schedules or when modeling manning requirements on modern ships.

Efficient removal of the ghosts is key to achieving broadband seismic data. Accurate deghosting on the receiver-side can only be performed when both pressure and vertical particle velocity information is available. We use acoustic reciprocity to derive a relationship that defines the total pressure wavefield as a function of the up-going pressure wavefield and the ghost function. Utilizing this relationship, and assuming the shape of the sea surface is known, we propose a pre-stack deghosting method based on integral inversion for a pressure-only dataset. Deghosting by spectral division with a flat sea surface or a statistical ghost function is shown to be special cases of this new inversion based method. The behavior of the pressure ghost function under rough sea condition is analysed in comparison to the flat and the statistical pressure ghost functions. The error of deghosting rough sea pressure-only data with a flat sea surface or a statistical ghost function is quantified using both synthetic and real seismic data.

Understanding of the uncertainty of ocean surface wind forecast is of great importance for optimal ship routing, especially in rough sea condition. Data was collected from a bulk carrier during 2010–2016 covering both the Southern and Northern Hemispheres with high seasonal variability. Using the meteorological model, the Weather Research and Forecasting Model (WRF), numerical weather simulations were conducted for eight rough sea cases using the grid point value (GPV) datasets NCEP-FNL and ERA-Interim. Model results were validated by on-board observations. Results showed that optimum ship routing should use the high-resolution WRF model with NCEP-FNL initial and boundary conditions, when compared with the ERA-Interim, to generate ocean surface winds for a more accurate simulation performance in heavy weather.

Comparative assessment of NCEP and ECMWF global datasets and numerical approaches on rough sea ship navigation based on numerical simulation and shipboard measurements

H023 QUANTIFICATION OF SWELL NOISE ON SEISMIC LINES GATHERED IN ROUGH AND CALM SEAS Abstract 1 Seismic surveys collected in rough sea conditions are subject to significant swell noise which reduces the data quality to a greater or lesser extent. This noise occurs in bursts throughout the data and is accentuated in the lower depths by amplitude gain functions during processing. Numerical modelling of ocean swell was carried out in order that a much clearer understanding of the way in which the water movement due to waves acts on seismic equipment. The numerical modelling analyses were not only conducted on