共查询到20条相似文献，搜索用时 15 毫秒
1.
海上石油开发油井建设中，发生了井柱弯折现象。对工程处理中可以采用的小沉箱、大沉井、定向井、人工切割开洞等方案进行了介绍和比较，最后论述了采用的方案及原因。 相似文献
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It is ideal to design the best hull shape for a floating production storage and offloading unit (FPSO) that meets all performance criteria from an engineering point of view. However, in reality, it is difficult to satisfy all the criteria at the same time. If one of the performances cannot meet the criteria, then additional equipment or systems are installed to improve that performance. In this paper, when an FPSO cannot meet the towing stability inherently, we attempt to establish a procedure for determining an auxiliary towing system. Firstly, various systems that can be applied to the FPSO are compared and reviewed to improve the towing stability of the FPSO. Among them, using three active thrusters was chosen as the auxiliary towing system. Improvement of towing stability was verified from a towing model test conducted at the Maritime Research Institute Netherlands (MARIN). However, thruster cavitation was raised as a key problem when using thrusters for a purpose for which they were not intended. A thruster cavitation model test was additionally performed to check the safety of the thrusters. Based on these results, a safe operating range under extreme condition was confirmed by observing the occurrence of thruster cavitation. The predicted maximum unit total thrust of each thruster was compared with the observed safe operating range. Finally, the effectiveness and safety of the auxiliary towing system was verified. 相似文献
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Jeremy D. Duschenes Timothy W. Barash Paul J. Mattaboni Sean C. Solomon 《Marine Geophysical Researches》1981,4(4):437-450
We describe a recent modification to the MIT Ocean Bottom Seismometer by which the geophones are housed in a separate package that is deployed on the sea floor about 1 m distance from the main unit several hours after the OBS reaches the ocean bottom. Records from deep-sea experiments and shallow-water tests show two improvements over records from geophones housed in the main instrument package. Signals recorded by the external geophones have a much better signal-to-noise ratio because tape recorder noise and instrument vibrations generated by water currents are effectively eliminated. As a result, the overall frequency response of the sensors to ground motion has a demonstrably smoother spectral shape. The second improvement is that the cross coupling of horizontal instrument motion to vertical ground motion is apparently greatly reduced because of the simpler design for the sensor package. 相似文献
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《Marine Policy》2016
With the development of the ecosystem approach to fisheries, improving fishing selectivity has increasingly been put forward as an objective for management. The aim of this paper is to clarify the limits of fishing selectivity and its use in fisheries management. Fishing selectivity would be better apprehended if restricted to the catching process only, not to the utilisation that is made of the catch once onboard, which falls under catch utilisation. Confusion would be further limited if fishing selectivity is restricted to the fishing operation scale, while exploitation pattern, i.e. the distribution of fishing mortality at the population or community level, applies to larger scales. Fishing selectively is minimizing bycatch – catching primarily the fishing trip targets. Since the ecological consequences of maximising the target catch relative to bycatch remain unknown at integrated scales, fishing selectivity cannot be used as an objective in itself. However, its small scale, high manageability and good understanding make it a convenient instrument to reach management objectives at large scales. Selectivity can serve to manage what is extracted from the ecosystem and thus what can be used, and/or to manage what is left in the ecosystem and how fishing impacts it. Different factors affect fishing selectivity, catch utilisation and exploitation patterns, some of them are manageable and thus can be used to move towards these objectives. Management tools are diverse, but need to be integrated to meet large-scale objectives. The complexity of dealing with large scales incurs a need to develop the available knowledge on exploitation patterns and catch utilisation to be able to adequately manage and monitor progress toward selectivity-related objectives. 相似文献
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James McElroy 《Marine Policy》1982,6(3):238-239
During the 1970s, several factors conspired together to turn the attention of many of the world's major fishing nations towards some of the untapped resources of the oceans. Since that time, the Antarctic krill fishery has been developing quickly — but hardly dramatically. Nonetheless, it has been in an exponential growth phase which, if maintained, would push krill to the top of the species table in the next few years. 相似文献
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棉兰老岛以东反气旋涡的Argo观测研究 总被引：1，自引：0，他引：1
报道了2003年1月至10月期间,由布放于西北太平洋中的Argo剖面浮标捕获的位于棉兰老岛以东海域的反气旋涡。该涡中心位于8.7°N、127.6°E附近,距大陆坡不远,沿等深线走向呈椭圆形分布。其长轴(NW-SE)约200km,短轴(NE-SW)长约120km。Argo浮标的漂移轨迹及其在表层及1 500db层的漂移速度场表明,该反气旋涡位于温跃层以下,中层海洋特征。在1 500db层上,涡的外围平均切向速度为11.9—14.0cm.s-1,旋转周期约为40d。温、盐度断面分布表明,该反气旋涡内的温盐结构非常复杂,可能与源自南、北半球的中层水团在涡旋内交汇并发生变性有关。 相似文献
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G. I. Gorchakov E. G. Semoutnikova B. A. Anoshin A. V. Karpov A. B. Kolesnikova 《Izvestiya Atmospheric and Oceanic Physics》2009,45(3):314-323
Statistical characteristics of variations in surface-layer concentrations of methane, non-methane and aromatic hydrocarbons, carbon dioxide, and formaldehyde are compared with the characteristics of variations in the concentration of carbon monoxide in the air basin of Moscow. Differences in the annual cycle of concentrations of methane, carbon dioxide, non-methane hydrocarbons, and carbon monoxide are determined. It is found that the maximum concentration of carbon monoxide at most sites with an elevated surface-air pollution level and over the city as a whole tends to occur in the summer season. The seasonal variability of the diurnal mean cycle of methane, carbon dioxide, and non-methane and aromatic hydrocarbons is analyzed. 相似文献
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为了验证波谱仪反演二维海浪谱的功能,根据海浪波谱仪的信号形成机制,总结了机载波谱仪反演海浪的流程。利用机载波谱仪回波数据,通过自相关和互相关两种功率谱估计方法,反演了二维海浪谱。最后通过与浮标测量的二维海浪谱进行对比,验证了该机载波谱仪探测二维海浪谱的有效性。结果表明,无论采用自相关函数还是互相关函数进行功率谱估计,得到的主波波长和有效波高与实际二维海浪谱基本一致。互相关函数法得到的交叉谱能去除180°模糊现象,其在计算有效波高时相对于自相关函数会稍微偏小。在计算斜率方差时可以采用5°~12°入射角范围的后向散射系数进行公式拟合,因此定标与否并不影响最后的二维海浪谱结果,未来星载波谱仪只有靠多波束联合才能实现。 相似文献
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Pan-Mook Lee Bong-Huan Jun Kihun Kim Jihong Lee Aoki T. Hyakudome T. 《Oceanic Engineering, IEEE Journal of》2007,32(2):327-345
This paper presents an integrated navigation system for underwater vehicles to improve the performance of a conventional inertial acoustic navigation system by introducing range measurement. The integrated navigation system is based on a strapdown inertial navigation system (SDINS) accompanying range sensor, Doppler velocity log (DVL), magnetic compass, and depth sensor. Two measurement models of the range sensor are derived and augmented to the inertial acoustic navigation system, respectively. A multirate extended Kalman filter (EKF) is adopted to propagate the error covariance with the inertial sensors, where the filter updates the measurement errors and the error covariance and corrects the system states when the external measurements are available. This paper demonstrates the improvement on the robustness and convergence of the integrated navigation system with range aiding (RA). This paper used experimental data obtained from a rotating arm test with a fish model to simulate the navigational performance. Strong points of the navigation system are the elimination of initial position errors and the robustness on the dropout of acoustic signals. The convergence speed and conditions of the initial error removal are examined with Monte Carlo simulation. In addition, numerical simulations are conducted with the six-degrees-of-freedom (6-DOF) equations of motion of an autonomous underwater vehicle (AUV) in a boustrophedon survey mode to illustrate the effectiveness of the integrated navigation system. 相似文献
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P. Choukroune J. Francheteau B. Auvray J. M. Auzende J. P. Brun B. Sichler F. Arthaud J. C. Lepine 《Marine Geophysical Researches》1988,9(2):147-163
The results of 26 dives with the diving saucer Cyana in the Gulf of Tadjoura and Ghoubbet al Kharab (Republic of Djibouti) are presented. One can demonstrate that the sites of recent volcanism, tectonics and hydrothermal activity within the axial part of the Gulf of Tadjoura coincide with topographic highs trending at a high angle (azimuth 135°) with respect to the average trend of the axial trough of the Gulf (azimuth 080°). The highs owe their relief to both volcanism and normal faulting along a trend of 130–140°. Recent faulting on the bounding walls of the axial trough is also found along a trend of 130–140° where the faults interfere with another set of apparently older faults trending 070° parallel to the axial trough. Spacing between the active zones of the Gulf is regular and about 30 km. No evidence for transform faulting has been found, in contradiction to all previous kinematic models of the Gulf of Tadjoura. There is evidence that the presently active phase of opening associated with 130–140° faults is less than 0.7 my old and that there was an older phase associated with 070°–080° faults creating the main trough of the Gulf. The basaltic lavas created during the two phases have evolved from transitional to tholeiitic. 相似文献
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Nonlinear path-following control of an AUV 总被引：3，自引：0，他引：3
A new type of control law is developed to steer an autonomous underwater vehicle (AUV) along a desired path. The methodology adopted for path-following deals explicitly with vehicle dynamics. Furthermore, it overcomes stringent initial condition constraints that are present in a number of path-following control strategies described in the literature. Controller design builds on Lyapunov theory and backstepping techniques. The resulting nonlinear feedback control law yields convergence of the path-following error trajectory to zero. Simulation results illustrate the performance of the control system proposed. 相似文献
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Even where mean gradients of temperature T and salinity S are both stabilizing, it is possible for the larger molecular diffusivity of T to result in differential diffusion, the preferential transfer of T relative to S. The present note reviews existing evidence of differential diffusion as provided by laboratory experiments, numerical simulations, and oceanic observations. Given potentially serious implications for proper interpretation of estimates of diapycnal density diffusivity from both ocean microscale measurements and ocean tracer release experiments, as well as the sensitivity of predictive global ocean models to this diffusive parameter, it is essential that this process be better understood in the oceanographic context. 相似文献
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Natural beaches tend to be concave-up rather than planar and are reasonable to be modeled by an equilibrium beach profile. A governing equation for longshore current on an equilibrium beach is derived and its analytical solution is given in this paper. Through comparisons of the present solution and field data of longshore current for a step-type beach, the present solution is found to have fairly agreeable prediction to longshore current inside the surf zone. The effects of the shape of a concave-up beach and turbulent mixing stress on longshore current inside the surf zone are discussed in the present paper. 相似文献
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AQUA is an underwater hexapod robot that uses its paddles to propel itself and control its orientation. To aid in the vehicle development, a simulation was needed to predict the motion of the robot based on its paddle oscillations. The most difficult aspect of this simulation was the characterization of the forces generated by the paddles oscillating in the water. In this work, a model predicting the forces produced by an oscillating rigid paddle was developed and validated experimentally. Tests were performed on an experimental setup, which was designed and built to measure the forces and torques produced by a paddle oscillating in a water tank. Also, the forces produced by a flexible fin were determined experimentally and were compared to those generated by the rigid paddle. Finally, a simulation of the AQUA robot was developed, based on the validated rigid paddle model. 相似文献
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Observations in 1929 of the tidal variation of surface gradients in the Tees estuary were combined with measurements of the velocity and density structure in 1975 to compute the internal and boundary shear stresses. Drag coefficients were generally higher on ebb than on flood tides and this inequality is explained using established boundary layer theory. The results suggest that the wide variation in drag coefficients in estuaries may depend, in addition to roughness changes, on the bed slope and the available kinetic energy of the mean flow. 相似文献
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Robust diving control of an AUV 总被引：1，自引：0，他引：1
Lionel Lapierre 《Ocean Engineering》2009,36(1):92-104
Mobile systems traveling through a complex environment present major difficulties in determining accurate dynamic models. Autonomous underwater vehicle motion in ocean conditions requires investigation of new control solutions that guarantee robustness against external parameter uncertainty. A diving-control design, based on Lyapunov theory and back-stepping techniques, is proposed and verified. Using adaptive and switching schemes, the control system is able to meet the required robustness. The results of the control system are theoretically proven and simulations are developed to demonstrate the performance of the solutions proposed. 相似文献