Tension–torsion fatigue behaviour of wire ropes in offshore moorings

An earlier paper by the author discussed the behaviour of helically spun wire ropes when subject to axial load [Ridge, I.M.L., 2008. Torsional characterization of ropes used offshore. Journal of Strain Analysis 43(2), 121–139.]. The response of the rope varied, depending upon the rope's construction and whether the end of the rope was free to rotate or was fixed. This paper presents the results of an extensive research programme which highlight the practical implications of the torsional fatigue behaviour of ropes with especial reference to their use in offshore applications. The results are also relevant to a much broader range of rope applications where long lengths of rope are employed such as deep mine hoisting and reversible aerial cableways. The torque which may be generated in the various components used offshore may have serious effects in both handling and installation, as well as in the longer term service (fatigue) performance.     

大型沉箱出运工艺的优化

沉箱预制时在沉箱底部四个角各放置一个木盒,该木盒经防腐处理,一面作为牵引孔、朝外、不封、其余五面用木板封住。木盒上面预留一个直径15㎝朝上的销钉孔,放置销钉。放置木盒时需与周边钢筋留有至少8㎝以上的钢筋混凝土保护层,浇筑混凝土时在销钉孔放置圆形预埋件。沉箱出运时以钢丝绳扣为拉鼻,通过销钉孔利用大直径圆钢作为销钉固定钢丝绳,牵引机将拖运牵引力传给沉箱,带动沉箱前移。     

A review of the acoustic-emission monitoring of wire rope

This review of existing technology on the acoustic-emission inspection of wire rope has confirmed that the most realistic application of the method is in the detection and location of wire breaks. However, the successful detection and location of wire breaks is dependent upon such factors as rope construction, diameter, length and number of wire breaks. The occurrence of large numbers of wire breaks work against the technique; although such large numbers of wire breaks are only likely to be generated in the laboratory during the fatigue testing of rope specimens. This review has shown that acoustic emission can be a useful laboratory tool, but application of the technique to ropes in service will probably be limited and specific to certain applications. In order to develop the technique for practical applications, future work needs to concentrate on the rope constructions that are most commonly used in industry, also those which are best suited to the technique, and developing wire-break signatures that could be designed into future equipment. This can be achieved through narrow-band filters, matching the resonant frequency of the transducers to the main frequency components of a wire break and pattern recognition software.     

Wave Motion Compensation Scheme and Its Model Tests for the Salvage of An Ancient Sunken Boat

1 .IntroductionIt is always hopedthat sunken merchant vessels would resume their ship performances after sal-vage ,that ancient sunkenships of archeological value would be salvagedinits entirety withlittle harmtothe cultural relics ,andthat warships with …     

A probabilistic analysis of random wave-induced liquefaction

Seabed instability caused by soil liquefaction due to build-up of excess pore pressure within the sedimentary seabed represents a serious threat to coastal structures. Models of varying sophistication exist for predicting the liquefaction process but most previous calculations are limited to regular waves while the real waves are random. In this study, a numerical study of liquefaction potential of a sand bed under narrow-band random waves is carried out employing ensemble modelling techniques. The aim of the work is to investigate the effect of random waves on excess pore pressure build-up and liquefaction processes and study the probability distribution of the maximum liquefaction depth. The computational results using a 1D liquefaction model indicate that the random wave-induced liquefaction can be much deeper than that of the corresponding regular waves with the largest individual waves in the random wave time series playing a dominant role in determining the maximum liquefaction depth. It is also found that the time for the maximum liquefaction depth to be reached can vary considerably from one random wave series to another, which suggests that in random waves notable densification may occur within the same timeframe as that for liquefaction.     

A Finite Element Based Study on Lowering Operation of Subsea Massive Structure

Subsea production system has been increasingly used in recent South China Sea offshore developments. With deepwater applications, constituent parts of subsea systems become more complicated and enlarged. Increases on the weight and geometry of each component bring challenges to installations. A recent accomplished deployment on a subsea massive jumper shows the weight and length have been up to 120 tons and 90 m, respectively with sophisticated geometry. It is considerably difficult to install heavy and large subsea structures, especially in South China Sea where severe environmental conditions are common. In addition, deepwater deployment may alter natural frequency of the hoisting system and the altered frequency may be close to possible environmental conditions. To deal with the above two issues, traditionally, engineers need to carry out series of complicated numerical analyses which are on case basis and significantly time-consuming. Existing studies focus on the optimization on analysis techniques by conducting laboratory testing and numerical simulations. However, easy-to-use guidance on massive subsea structure installation are somewhat limited. The studies presented in this paper aim to achieve a simplified guidance which can briefly screen the cases subject to axial resonance and provide visible correlations between hoisting system integrity and key installation parameters.     

Strip theories applied to the vertical motions of high speed crafts

The motions of a high speed craft are highly influenced by speed and dynamic forces that begin to be important for high Froude numbers. Classical ship motions theories and some seakeeping programs do not include the effect of these dynamic forces that mainly affect to the damping of vertical motions, and have to be corrected to model high speed crafts. In any other way, the use of these theories or programs would be unrealistic. In this paper, some theories that can be used to predict the seakeeping behaviour of high speed crafts, considering dynamic forces, are studied and validated against seakeeping tests of some fast monohulls models. Tests and results focus on vertical motions in head seas, which are the most severe for these fast crafts. Experimental results of vertical motions are compared with numerical calculations and conclusions about the range of application of the presented theories are obtained.     

Improvement of deep-sea dredging operations through the use of a depth meter

A battery-operated depth meter mounted inside the dredge is used to monitor the time-depth profile of a dredge haul. By comparing is profile with the water depth recorded by the ship's echosounder, the locations at which dredge samples were collected can be determined. The analysis of the time-depth profile can also be used to estimate the minimum length of the dredge wire, thus increasing the efficiency of dredging operations.     

Dynamic factor analysis considering elastic boom effects in heavy lifting operations

The dynamic factor is the ratio of the maximum dynamic load to the static load acting on the wire ropes between the boom of a floating crane and a cargo. In this paper, the dynamic factor is analyzed based on dynamic simulations of a floating crane and a cargo, considering an elastic boom. For the simulation, we designed a multibody system that consists of a floating crane barge, an elastic boom, and a cargo connected to the boom through wire ropes. The dynamic equations of motion of the system are based on flexible multibody system dynamics. Six-degree-of-freedom motions are considered for the floating crane and for the cargo, and three-dimensional deformations for the elastic boom. The hydrostatic force, the hydrodynamic force, the gravitational force, and the wire rope forces are considered as external forces. The dynamic factor is obtained by numerically solving the equation. The effects of the elastic boom on heavy cargo lifting are discussed by comparing the simulation results of an elastic boom and a rigid boom.     

模拟海底管道的阴极保护中数值计算边界条件的确定

根据相似论和因次分析,用钢丝来模拟实际海底管道.通过实验,研究了牺牲阳极及被保护钢丝的极化性能,从而得到了在阴极保护中进行数值计算的边界条件;对于从实验基础上建立的数学模型进行有限元计算,计算结果与实测结果吻合较好,证明确定的边界条件是合理的,可以将建立的数学模型用于实际海底管道的阴极保护设计.     

渤海湾魁蚶吊笼与底播增殖实验研究

本文通过进行魁蚶吊笼养殖试验,研究分析了不同入笼规格、挂养水层及放养密度对魁蚶的生长及存活率的影响,比较了魁蚶吊笼养殖与底播养殖模式的不同差异。试验表明,吊笼魁蚶的最适入笼规格为1.5 cm;越冬最适挂养水层为3.5 m以上,度夏最适水层为2.5~3 m;第一次越冬最适密度为1 000粒/层,第一次度夏最适密度为500粒/层,第二次越冬最适密度为200粒/层,第二次度夏最适密度为100粒/层;通过吊笼养殖至3~4 cm规格后进行底播养殖,能够有效提高魁蚶成活率,由此可见,吊笼—底播接力养殖,是提高魁蚶养殖效益的一种有效养殖模式。     

深远海养殖工船最小推进功率研究

针对十万吨级深远海养殖工船在波浪中的阻力和运动响应开展了船模试验与模拟计算,并对其最小推进功率进行了校核。以试验流体力学（EFD）模型试验与模型尺度计算流体力学（CFD）模拟计算的结果进行对比作为方法验证,将实尺度CFD模拟计算的结果直接用于最小推进功率的校核。结果显示,EFD模型试验结果与模型尺度CFD计算结果误差在10%左右,计算精度满足工程要求。在规定的恶劣海况下该船型波浪增阻占总阻力的比例最高可达56.3%,螺旋桨转矩可达最大转矩的63.9%。等级2简化评估法得到的最小推进功率为等级1线评估法给出的最小功率线值的58.9%。研究表明实尺度CFD模拟计算可直接用于船舶最小推进功率的校核,此深远海养殖工船使用等级2简化评估方法进行校核更容易满足规范要求,其最小推进功率应不小于6 833 kW。     

三疣梭子蟹人工育苗试验初报

三疣梭子蟹 (Portunus tritubeyculatus)简称梭子蟹,是著名的大型海产食用蟹类。其肉味鲜美,营养丰富,国内外素享盛名。这种蟹子遍布我国沿海,尤以黄渤海产量最大。日本、朝鲜等国均有出产。近年来,由于捕捞强度的不断增加,世界梭子蟹资源日     

Parallel Force/Position Crane Control in Marine Operations

A parallel force/position controller is proposed for the control of loads through the wave zone in marine operations. The controller structure has similarities to the parallel force/position control scheme used in robotics. The parallel force/position controller is tested for crane control in simulations and model experiments and the results are presented in this paper. To evaluate the performance of the proposed controller, we study three different control strategies for control of loads through the wave zone: active heave compensation, wave synchronization, and parallel force/position control. The parallel force/position controller gave improved results, in particular, a significant improvement of the minimum value of the wire tension, which is important to avoid snatch loads that may break the wire. The three strategies are tested and compared in simulations and experiments     

On the nonlinear hydrodynamic forces for a ship advancing in waves

In this paper, using a second-order steady-state approach and a three-dimensional (3D) pulsating source distribution method derives the nonlinear hydrodynamic forces on a ship advancing in waves. The nonlinear hydrodynamic forces considered here consist of the mean lateral drifting force and the added resistance, which can be expressed as products of the ship-motion responses, the radiation potential, diffraction potential and the incident-wave potential. All related velocity potentials applied in the calculations are in 3D form. The Series 60 and Marine ship hulls are used for numerical calculations and the results are compared with existing experimental data and two-dimensional (2D) solutions. The comparisons show that the results obtained in the paper generally agree with experimental data well. It is also found that the nonlinear hydrodynamic forces obtained based on the present 3D source distribution methods are indeed improved in some calculations compared with the 2D method, especially for the mean lateral drifting force.     

Investigation of the influence of cyclonic disturbances on the dynamic processes and the evolution of impurities in the Sea of Azov in the presence of stationary currents

A three-dimensional nonlinear mathematical model is used to study the dynamic processes under the action of cyclonic disturbances in the field of stationary wind in the Sea of Azov and the specific features of transformation of the impurities. The results of numerical calculations enable us to conclude that the maximum velocities of currents generated by a cyclone depend on the direction of its motion. It is shown that the cyclones moving westward generate currents with higher maximum velocities than the cyclones of other directions. It is also demonstrated that the motion of atmospheric disturbances leads to a significant enlargement of the area of propagation of pollutants as compared with the case of action solely of stationary currents. The influence of the velocities of stationary currents on the maximum current velocities caused by the passage of a cyclone is also analyzed.     

Long term prediction of non-linear vertical bending moments on a fast monohull

An assessment is made of the maximum wave induced bending moment expected to occur during the operational lifetime of a fast monohull, based on long term distribution calculations of the non-linear vertical bending moment at mid-ship. The ship is assumed to operate in the Northern North Sea, with an operational life of 25 years. A succession of short-term stationary ship responses represented by Rayleigh distributions of peaks results in the long-term distribution of the structural loads. Non-linear pseudo transfer functions are used in the procedure to calculate the variances of the short-term responses. The amplitudes of these transfer functions are calculated by a non-linear time domain seakeeping program. The results are compared with rules minimum required values and also with results from simpler calculation procedures such as adopting design sea states.     

环境流体动力学数学模型在太平水道潮流场计算中的应用

采用环境流体动力学数学模型对太平水道潮流场进行了计算，计算中用水平方向上的曲线正交坐标与垂直方向上的Sigma坐标相结合以及三维数学模型二维化的方法。计算结果与实测结果比较表明：模型较好地重演太平水道潮流场，可以用于工程实际中的沿岸及受潮汐影响的水道潮流场问题的计算。     

单元管件灌浆卡箍的吊装及安装设计研究

针对用于单元管件的非自应力灌浆卡箍和膨胀式自应力灌浆卡箍,讨论了灌浆卡箍水下安装的几个吊装和安装设计问题。首先介绍灌浆卡箍水下安装的总体设计及其安装步骤;然后进行了下水吊装时保持卡箍进浆口在下、出浆口在上的姿态分析和设计,计算出了合适的吊装悬挂距离;对帮助卡箍两瓣自动包拢受损管件的一个辅助闭合机构进行了力学分析和液压系统设计;介绍了卡箍对中及端部密封装置的工作原理;最后介绍了卡箍安装的海上试验情况,列出了各工序安装时间。为灌浆卡箍水下安装技术走向实际工程应用提供了设计和试验经验。