The EU in Rough Seas

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.

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.

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.

Performing oceanographic measurements from the sea surface to the sea bottom is technically challenging under rough or icy sea conditions. In 2011, we tested measures for protecting a buoy under such severe conditions, by incorporating anti-icing and tolerance to high winds and rough seas. Based on the results, we carried out detailed designs of a suitable buoy system. In January 2012, we succeeded in deploying the buoy in the Southern Ocean off the Adelie Coast at 60°S and 140°E. Some of the meteorological and oceanographic data being gathered by the buoy can now be monitored in real time. In this paper, we describe some details concerning the design of the sensor pole and mooring line, in addition to the data already received from the buoy.

This paper deals with a new statistical prediction method for the propeller racing of ships sailing in rough seas. The propeller racing is one of the most important sea keeping quality in relation to the safety of main engine and shafting system. The trend of the racing has been investigated mainly in order to estimate allowable maximum propeller diameter, operability of ocean-going ships etc.. In those studies, the propeller racing generally and mainly means the situation (propeller exposed) in which the relative motion amplitude between ship hull and wave surface would exceed a depth of point in rotary disk propeller. Therefore, it seems that the magnitude of the amplitude and its exceeding frequency have been examined as a principal subject of study as usual. However, the time during which the amplitude exceeds a depth of point, that is, the propeller exposes in the air over sea surface, must be also one of most important factor affecting the trend of propeller racing. Then, this paper proposes a new practical method for estimating the time lasting of exposed propeller related to propeller racing in rough confused seas on the basis of the statistics.

Triboelectric nanogenerators (TENGs) provide one of the most promising techniques for large‐scale blue energy harvesting. However, lack of reasonable designs has largely hindered TENG from harvesting energy from both rough and tranquil seas. In this paper, an oblate spheroidal TENG assembled by two novel TENG parts is elaborately designed for both situations. The TENG in the upper part is based on spring steel plates without other substrate materials, which makes it possible to output considerable power in rough seas and occupy small space. The TENG in the lower part consists of two copper‐coated polymer films and a rolling ball which can capture small wave energy from tranquil seas. The working mechanism and output performance are systematically studied. A maximum open‐circuit voltage of 281 V and a short‐circuit current of 76 µA can be achieved by one upper part, enough to charge a commercial capacitor for potential applications. More important, the proposed oblate spheroidal shell not only guarantees high sensitivity of the TENG in the lower part, but also qualifies the TENG with unique self‐stabilization and low consumables for the next generation of TENGs with new structural design toward all‐weather blue energy harvesting.

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.

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

Marine disasters pose a serious threat to economic and social development; therefore, understanding their occurrence rhythms is of great importance to disaster prevention and mitigation. As a major form of marine disaster in China, storm surges and rough seas are particularly worthy of attention. In this study, statistical data regarding storm surges and rough seas over the past 20 years were collected, and a visual approach was utilized to detect their scope, distribution, and temporal-spatial characteristics. Implementation of disaster prevention and mitigation was then discussed. The results revealed the following: (1) storm surges exhibited significant seasonality (occurring in summer and autumn), while rough sea occurrences occurred throughout the year. (2) The losses caused by storm surges showed clear regional differences. Specifically, the economic losses and death tolls in southern provinces were greater than in northern provinces, but they decreased significantly from 2000–2009 to 2010–2019. (3) The loss caused by rough seas also showed regional differences, with greater loss values in the southern provinces than northern provinces. The total loss has dropped significantly in recent years.

This paper analyzes the rough seas weather which may be encountered during the voyage and its influences on ship’s navigation safety. This paper draws lessons from related both domestic and abroad researches about ship’s navigation safety, according to the accident causes, analyzes the factors of ship’s navigation safety affected by rough seas, determines assessment index system of ship’s navigation safety in rough seas, uses Bayesian Network to realize the assessment, and eventually works out which index contributes the most to the marine accidents of ship in rough seas.

During the well-construction phase in the oil and gas industry, cementing materials are used to provide annular isolation between the casing and the wellbore. The methods and equipment used to place cementitious fluids in the annulus have evolved significantly over the last several decades. One specific area where significant changes in placement methods and equipment have occurred is in the offshore environment; specifically, cementing operations from mobile offshore drilling units (MODUs). The benefits of traditional inner-string cementing (ISC) methods have not been available to operations in rough seas from floating platforms where the ocean swells exceed the capabilities of the compensators on the rig. As such, new equipment designs are needed to enable use of the inner-string cementing method from MODUs operating in rough seas. This paper details the problems encountered when attempting inner-string cementing operations from floaters operating in the North Atlantic and newly designed equipment that enables MODU operators to benefit from the successful use of inner-string cementing methods in rough seas. Three case histories are presented that validate the successful use of the newly designed extended-length ISC equipment from a mobile platform operating in rough seas.

It has recently been recognized that structural failures of large ocean-going vessels are essentially related to the dynamic stresses induced by bottom and bow-flare slamming in rough seas. Bottom slamming may cause an excessive vertical bending moment in a hull girder which may lead buckling of the upper deck, while bow-flare slamming may cause an excessive torsional moment in the fore-body of high speed ships in oblique waves. Local dents and cracking failures due to slamming are also observed in the fore body of large ships, they might be accelerated by severe corrosion.In high speed ocean-going ships, cracking failures are sometimes observed in middle and aft parts of the hull girders after passing through a rough sea. Since this type of failure is not necessarily exceptional to newly build ships, it may be caused by low cylce fatigue due to repeated whipping stresses induced by bow-flare slams. In the present paper, fatigue strength is investigated for structural members with high stress concentration factors in the neighbourhood of the front end of the superstructure of a container ship, where the applied stress is composed of a wave induced bending stress including non-linear effects, whipping components of stresses, and possibly coupled vibratory stresses of the superstructure.Having calculated the dynamic stress components among regular waves in head seas, the fatigue strength of highly stressed portions are examined by using appropriate S-N curves, in which effects of ship speeds and wave heights are taken into considerations. When a high speed vessel passes through very rough seas, the fatigue strength may be reduced due to the significant elevation of the repeated stress range caused by the whipping components of stresses superposed on the wave induced bending stress.

Slamming responses and the effects of axial force on deck stress are discussed regarding a large bulk carrier. Axial force may not be neglected in full-formed ship like bulk carriers particularly in rough seas, because of the high wave height and her large pitching and/or heaving motions. In rough seas, moreover, slamming may occur, so the deck stress is raised due to both the whipping vibrations and the axial force.In order to clarify the characteristics of slamming responses of a large bulk carrier in rough seas, model tests and numerical calculations are carried out : A series of tank tests for slamming is conducted in regular high waves with the use of an elastic model ship, and the deck strains are measured using strain gauges. On the other hand, numerical calculations are performed by virtue of a computer program for nonlinear ship responses in waves called TSLAM, to which a routine for calculation of axial force is newly added in the present paper.Comparing the results of experiments with the calculations and performing the numerical calculations for an actual bulk carrier, following conclusions are obtained : The effects of axial force on deck stress cannot be neglected for large bulk carriers in rough seas and are significant in the fore-body. Pressure force due to pitching motion is dominant in the axial force.

VARIOUS workers have tried measuring the roughness of the sea by observing wave heights at a particular position as well as by compiling wave profiles along large distances by air observations. Glitter photographs of the sea surface have also been statistically analysed for finding the relation between development of wavelets and wind velocity. It has been recognized that description of sea roughness is very difficult by any of the above means. On the other hand, it is well known that radar clutter increases in amplitude with sea roughness, and estimation of sea roughness should be possible by observations of radar clutter. Recently, one aspect of analysis of sea roughness became imperative in view of the hypothesis that microseisms may be caused by means of interaction of wind and sea roughness. According to such ideas, the periods observed in microseisms should correspond to any autocorrelativ periods in sea roughness.

For modern ship design — as confirmed by many examples of ship design and operation — the current intact stability code (IMO (2002)) does not provide a reliable basis for the assessment of ship safety in rough seas. In ship design the application of the IS-Code is not supporting design decisions towards increased safety in rough seas (Cramer and Kru¨ger (2001)), and ship operators find their cargo and/or vessels endangered by large roll angles and accelerations (France et al. (2001)). Thus, there is a great need for procedures to analyze ship safety in rough seas. This paper presents innovative deterministic seakeeping test procedures which are used to identify the physical mechanism endangering intact ships by evaluating cause-reaction relations of wave/structure interaction. Rogue wave sequences are embedded in severe seas for computer controlled capsizing tests of different vessels at the Hamburg Ship Model Basin. The model test results are used as a basis for the development of non-linear numerical methods to simulate ship motions in extreme seas with the target to design safer ships with reduced capsizing risk. Polar plots following from the non-linear simulations allow the evaluation of ship safety in severe seas with reference to course, speed and trim.