In this study, steel net panels with different twine diameters, mesh sized were tested in the current-wave flume. The hydrodynamic forces of the steel net panels were measured in current and regular wave, respectively. The effect of the net solidity, the Reynolds number and the Keulegan-Carpenter number on the hydrodynamic coefficients of the steel panels was discussed. Based on the crossing-element, a novel method to analyze the forces of net structure was developed and the estimation formula for net hydrodynamic coefficient was given.


As the rapid improvement of people's living standard, the demand for the aquatic product has been increased significantly. According to the report of the Food and Agriculture Organization of the United Nations in 2016, the demand for food was expected to increase 70% by 2050 and the marine production would play a key role as a source of food, nutrition, income and livelihoods around the world in the future. (referring to FAO 2016) In fact, the overfishing has led to a sharp decline in the wild fish stock, and the marine aquaculture industry is playing an important role for meeting the increasing demand of the aquatic product. The plentiful researches show that the drag force on a net cage is dependent on the physical dimensions of the net cage, the Solidity ratio, the Reynolds number and the projected area of the net. The Solidity ratio is a function of the physical dimensions of the netting, including the diameter of the twine and knots. The Reynolds number is dependent of the diameter of the twines and knots and on the inflow velocity. The projected area of the netting is a function of the physical shape of the net cage.

In last decades, comprehensive researches have focused on hydrodynamic characteristics and flow field around net panels. As a pioneer to investigate the flow passing through a screen which is similar to a net panel, Taylor (1944) proposed the relative turbulence-intensity method to analyze the wake of the screen and presented a prediction of the drag coefficient, Cd, as a function of the screen solidity. Fridman and Danilov (1967) investigated the drag force on nets in the steady current and developed an empirical formula of Cd incorporating the Reynolds number of the twine and the net solidity in current. Milne (1972) analyzed the drag force on knotted and knotless nets and proposed a formula on the drag force of net with different knot patterns. In order to ascertain the relationship between the drag force and the wake generated by the net, Løland (1993) established a ‘sum of cylinder’ model combining the linear free-wake equation with the eddy viscosity formula. Zhan et al. (2006) conducted a series of net panel experiments in the towing tank to investigate the effect of the net solidity, the incidence angle and the mesh pattern on the hydrodynamic forces of the net panel, and they proposed the formula for the total normal drag of planar and cylindrical nets. Recently, Balash et al. (2009) measured the hydrodynamic force on the net panel in the towing tank and suggested the formula for Cd, in which drag coefficients of circular cylinders and spheres were adopted to modify the original prediction.

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