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711.
712.
The sway, heave and roll added masses of three uniform cylinders with semi-circular, rectangular and triangular cross-sectional shapes in shallow and narrow water are numerically analysed. The method is based on simulation of the potential flow induced by the cylinder's mode of motion. The effects of shallow and narrow water on added mass are analysed and presented. It is concluded that the shallow and narrow water effects on added mass depend on the different cross-section shapes of the cylinders. In particular, the water depth effect on sway added mass is stronger than that on heave added mass while the narrow water effect on sway is weaker than that on heave. The shallow water effect on added mass tends to weaken the narrow water effect. Lastly the effect of shallow and narrow water on added mass on a rectangular cylinder is the strongest while that on a triangular cylinder is the weakest. 相似文献
713.
714.
715.
The regular wave interaction with a twin concentric porous circular cylinder system consisting of an inner impermeable cylinder and an outer perforated cylinder was studied through physical model and numerical model studies. The experiments were carried out on the twin concentric cylinder model in a wave flume to study the wave runup and rundown at the leading and trailing edges of the perforated cylinder. It was found that the maximum wave runup on the perforated cylinder is almost same as the incident wave height. The experimental results were used to develop the predictive formulae for the wave runup and rundown on the perforated cylinder, which can be easily used for design applications. The wave runup profiles around the perforated cylinder for different values of ka and porosities were studied numerically using Green's Identity Method. The results of the numerical study are presented and compared with the experimental measurements. 相似文献
716.
R. Pocklington 《Marine Chemistry》1977,5(4-6)
The concepts which have guided our thinking about chemical processes and interactions of organic matter in seawater are identified and their utility assessed. Some recommendations for the future are made. 相似文献
717.
R. S. Bortkovski 《Izvestiya Atmospheric and Oceanic Physics》2006,42(2):228-235
Current estimations of gas exchange between the ocean and the atmosphere are based on the concepts about diffusive gas transfer across the interface and about a stationary character of the processes; however, under a strong wind, these concepts are invalid. Transfer equations for gas constitutents of the air are incorporated into a numerical model of a nonstationary upper layer of the ocean. These equations contain the source function—gas transfer by bubbles, which becomes noticeable even at a wind speed of 8–10 m/s. The fluxes of oxygen and CO2 are calculated at a specified wind speed, dependences of these fluxes on the wind speed are constructed, and estimates for the average annual fluxes are obtained for several areas of the Gulf Stream and Kuroshio. A substantial change in the difference of the air-water gas contents under a strong wind, caused by the turbulent exchange growth and appreciably affecting the gas exchange, is noted. The influence of the carbonate system of seawater on the CO2 transfer during a storm is estimated. The results obtained are compared to the estimates based on the traditional approach. 相似文献
718.
719.
A simple and effective method of heating divers in extreme cold water has been developed. The local heating concept utilizes a uniformly distributed granular mixture of magnesium and iron particles packed in small sachets. Upon activation by sea water, the two metal mixture behaves as a multitude of short-circuited electrolytic cells, producing thermal energy rather than electrical energy. The 45 mm-square sachets may be placed where heating is required on the diver's body, thus giving rise to the term “local heating”, obviously, the heating system requires no pumping device, or distribution network. Heating rate and duration of output of the sachets are controlled by particle size, and mixture ratio of the constituent Mg and Fe particles.This paper described the development, testing and performance of the heating sachets. Results of live tests in different dive situations are also presented and discussed. 相似文献
720.
This paper proposes a nonlinear robust adaptive control strategy to force a six degrees of freedom underactuated underwater vehicle with only four actuators to follow a predefined path at a desired speed despite of the presence of environmental disturbances and vehicle’s unknown physical parameters. The proposed controller is designed using Lyapunov’s direct method, the popular backstepping and parameter projection techniques. The closed loop path following errors can be made arbitrarily small. Interestingly, it is shown that our developed control strategy is easily extendible to situations of practical importance such as parking and point-to-point navigation. Numerical simulations are provided to illustrate the effectiveness of the proposed methodology. 相似文献