Abstract Owing to heavy criticisms of nearshore fish farming for causing environmental pollution and encroaching on sea space used for shipping, boating, recreational sea activities and marine eco-tourism, offshore fish farming has now being seriously considered. Moreover an offshore site provides more pristine water and greater space for increased fish production. However, offshore fish farming poses challenges such as a more energetic sea environment. A higher sea current can lead to large deformation of fish net and hence a net volume reduction which compromises fish welfare. With the view to identifying the effects of various important parameters on net volume reduction of a gravity-type open-net fish cage, this paper adopts a mass-spring model for the dynamic analysis of current-induced net deformations of cylindrical fish nets with discrete weights hanging at the bottom edge of the nets. In this model, the net mesh comprises knot nodes and bar nodes connected by tension-only massless springs. The spring stiffness is determined from the net bar diameters and material properties. The current-induced loads are applied to each node and calculated based on Morrison’s equation. The governing equation system for nodal motions can be established according to Newton’s second law, and solved by using the Runge-Kutta method for the real-time net deformations. The effects of net string reinforcements, weight distributions and net shapes on the net volume reduction are studied with the view to shed insights into how one may improve fish cage designs to effectively mitigate net deformation under high sea current speeds in offshore fish farming sites.

中文翻译：

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海流作用下重力式开放式网箱净体积减少的研究

摘要 由于近岸养鱼造成环境污染，侵占航运、划船、海上休闲活动和海洋生态旅游的海域，受到严厉批评，近岸养鱼已成为人们认真考虑的问题。此外，近海地点为增加鱼类产量提供了更多的原始水和更大的空间。然而，近海养鱼带来了挑战，例如更有活力的海洋环境。较高的海流会导致鱼网的大变形，从而导致网体积减少，从而损害鱼类福利。为确定各种重要参数对重力式开网网箱净体积减少的影响，本文采用质量弹簧模型对悬垂在网底边缘的离散配重的圆柱形鱼网的电流引起的网变形进行动态分析。在该模型中，网状网格包括通过仅受拉的无质量弹簧连接的节点节点和杆节点。弹簧刚度由净钢筋直径和材料特性确定。电流感应载荷施加到每个节点，并根据莫里森方程计算。节点运动的控制方程组可以根据牛顿第二定律建立，并使用 Runge-Kutta 方法求解实时净变形。网弦增强的效果，