《Table 2Parameters of the floating collar, net cage, and sinker tube used in the model tests.Both mo

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《波浪和海流对浮式海洋牧场的作用（英文）》

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Many investigations have been performed to investigate the mooring loads of marine fish farms in regular waves and currents（Huang et al.2008；Xu et al.2013a，b）and in irregular waves（Dong et al.2010；Xu et al.2011）.Common to previous works is that the hydrodynamic part of the problem is often oversimplified；for instance，the floater was assumed to be rigid，and the hydrodynamic forces of the floater were predicted by 2D hydrodynamic strip theory.The viscous force on the net cage was predicted by Morison’s equation，neglecting the shadowing effect of the net and the wake due to current inside the net cage.Also，the fish farm including the mooring system is simplified compared with a realistic setup.Shen et al.（2018）presented comparison of numerical calculations with model test results of mooring loads of a marine fish farm in waves and currents.The physical model is representative for a single cage commonly used in Norway.It included two concentric floating tubes，an elastic sinker tube，a cylindrical net cage with a conical bottom，mooring system comprising bridle lines，mooring frame lines，mooring buoys，coupling plates，chains connecting the coupling plates to the buoys，and the anchor lines attaching the system to the bottom of the basin（see Table 2 and Fig.2）.A model test scale of 1:16was adopted，and Froude scaling with geometric similarity except for the net twines was assumed.The reason for Froude scaling in current is the bottom weight system and not gravity waves.We can understand why Froude number matters by considering in calm water a partly submerged vertical net panel that is hinged above the free surface and has a bottom weight.The equilibrium angle of the panel in current depends on the bottom weight，i.e.p，ffiffiaffifficfficeleration of gravity.In that way，the Froude number U=gLwhere U is the current velocity and L is a characteristic length becomes a parameter.For the net twines，geometric similarity cannot be applied，as the net twine diameter and net E-module are too small to be realized in model scale if using geometric similarity.So，nylon net twines were used in the model tests with correct solidity ratio of the net cage.According to the screen model proposed by Kristiansen and Faltinsen（2012），the solidity ratio and the Reynolds number of the twines are two important parameters to estimate the drag force on the cage.Correct solidity ratio was used in the model test while the Reynolds number of the twine in model scale（Rn=100–300）is smaller than that in a full-scale cage（Rn=500–1000）.Here，the cross section of the net twine is assumed to be circular，which is a reasonable first approximation.In terms of the drag coefficient of the twine，it is larger in model scale（CD=1.25–1.35）than that in full scale（CD=1.0–1.1）.To represent a more realistic full-scale value，we should use a twine diameter as large as possible in the model tests to keep the twine Reynolds number as high as possible.Two linear springs were inserted in the front two anchor lines where the forces were measured，as shown in the upper part of Fig.2.The sinker tube was attached directly to the net in the present study，without vertical chains between the floating collar and the sinker tube to avoid chafing between the chain and the net cage.