用数值法计算圆形沉浮式深海网箱的下潜水深

应用一系列力学关系,给出了深海沉浮式养殖网箱的运动方程组,在网箱下潜深度的研究中采用绕射理论和Morison方程进行了波浪力分析,讨论了网箱的下潜深度随波浪的波高、波长及周期的变化情况,得出下潜水深比较小时深海网箱的波力变化快,当达到某一个下潜深度以后,波力的变化趋于平缓,从而为深海网箱选用最佳工况提供了一种参考方法。     

深海网箱养殖与传统网箱养殖比较研究

深海网箱养殖技术是近20年才发展起来的一种全新的养殖方式,它充分结合了当代的计算机技术、新材料技术、防腐蚀技术、防污损技术及抗紫外线技术等高新技术。本文通过对深海网箱养殖和传统网箱养殖在箱体、框架、浮力装置和固定装置等方面进行细致的比较研究,找出深海网箱养殖的一些优势所在,希望能为以后研究者提供一些参考。     

自减流低形变网箱减流效果

本文通过在东海水产研究所,主尺度为90m×6in×3In的试验水池内进行模型试验,试验网箱是以圆柱形网箱为基础,在网箱箱体深度的1／2处设置了一个中环,将原来的圆形重力式网箱改造成新型自减流低形变网箱,网箱周长为50m、中环周长75m、深8m,研究其箱体内流速的变化。试验结果表明新型网箱的减流效果比原网箱提高5．8％一13．9％,自减流低形变离岸深水网箱的箱体内部流速比箱体外界流速平均减小25．3％,可有效降低箱体内的海水流速,减小养殖鱼类在网箱内长时间顶流游泳的强度,为养殖鱼类提供良好的生存、生长环境。     

水流作用下自升降式张力腿网箱水动力学特性试验研究

自升降式张力腿网箱因其在水流作用下能够下潜到水中,具有在恶劣海况条件下,避免海水表面的风浪冲击,降低网箱系统被破坏风险的优点,具有良好的市场前景.根据田内准则,运用水槽模型试验方法,研究了周长60 m,网高16 m张力腿网箱在水流作用下的缆绳张力、网箱下潜深度、容积损失率与流速的关系.结果显示:张力腿网箱缆绳张力随流速...     

自减流低形变网箱模型试验

通过在圆柱形网箱箱体深度的1/2处设置一个中环,将原来的圆形重力式网箱改造成新型自减流低形变网箱(改造后的新型实物网箱周长50 m、中环周长75 m、深8 m)。通过在东海水产研究所内主尺度为90m×6 m×3 m的试验水池对新型自减流低形变模型网箱进行模型试验,研究其箱体内容积和流速的变化。模型试验结果表明,新型网箱的容积保持率明显优于原型网箱,在流速1kn时容积保持率仍能达到90.4%。不同流速下,新型网箱的减流效果比原型网箱提高5.8%~13.9%,内部流速比箱体外界流速减小25.0%~31.2%。该新型网箱可有效降低箱体内的海水流速、提高箱体的容积保持率,为养殖鱼类提供更为良好的生存、生长环境。     

潜浮式船型桁架结构深海养殖网箱避浪性能研究

深海网箱作为现代海洋渔业拓展外海养殖空间的重要养殖装备，其布设环境一般较近海更为复杂恶劣，对于保障其安全性和稳定性提出了更高的要求。本研究针对一种单点系泊潜浮式船型桁架网箱开展了模型比尺为1︰40的波浪流水池试验，重点围绕该网箱在不同吃水深度受波浪作用的系泊受力、升沉、纵摇和横摇等水动力学特性进行了比较分析。试验结果显示，波高为7.5~12.5 cm时(原型3~5 m)，网箱漂浮状态即可以满足养殖需求，其系泊力及运动响应均较小，具备较高的安全性和稳定性；恶劣海况时，即本试验中波高为15.0和17.5 cm (原型6 m和7 m)，通过整体下潜的方式网箱具有良好的避浪性能，其中，系泊力减幅达70%以上，升沉、纵摇和横摇等运动分量减幅也达20%~60%；波流试验中，海流对网箱避浪性能存在一定的影响，但总体上仍然具有较好的避浪效果。研究结果可为单点系泊潜浮式深海网箱的安全运行与日常管理提供理论依据和数据参考。     

不同下潜深度状态下重力式与碟形网箱的锚绳受力特性比较

本文针对常见的重力式、碟形和拟碟形网箱在不同下潜深度状态下的锚绳受力特性进行了试验研究.结果表明:重力式网箱的配重形式及下潜形式对网箱的受力具有重要影响.在纯流条件下,重力式网箱采用沉降圈及单管灌水的下潜方式实现下潜时,锚绳受力不但没有衰减,反而呈现较大幅度的增加;在波浪条件下也较其它网箱更为不利.因此从受力的角度来看,实际应用中不宜采用这一配重形式及下潜方式.总体上,碟形网箱及拟碟形网箱在相同条件下的锚绳受力大于重力式网箱,拟碟形则大于碟形网箱的锚绳受力.在综合比较网箱价格和性能的前提下,作者认为选用重力式网箱将更符合实际.     

浮式防波堤与网箱组合结构的动力特性

兼具网箱养殖功能的浮式防波堤结构,为深水浮式防波堤和深海网箱养殖提出了一条新的研究思路,不仅解决了海洋工程与海水养殖争地的矛盾,基于防波堤开展养殖的模式更较大降低海水养殖的成本。通过对浮式防波堤兼做网箱的结构进行物理模型试验,得到该结构在不规则波作用下,不同吃水深度、网箱深度以及周期对其水动力特性的影响,结果表明,在短周期波浪作用下,网箱深度为0.1～0.15 m时结构的水动力特性最好。该结构具有良好的工程应用前景。     

海上风机与养殖网箱融合系统中网箱系泊绳张力与导管架基础结构安全性研究

海洋牧场与海上风电融合发展是现代渔业和清洁能源产业融合发展的典型代表,能够构建“海上粮仓+清洁能源”的新产业模式。本文基于福建漳浦六鳌海上风电场风机导管架构建养殖网箱与海上风机融合系统,运用Aqua-FE?有限元工具探究极端波流条件下不同网箱布设深度、波流入射角、生物附着程度对网箱系泊绳张力的影响;采用海洋工程专用设计软件SACS,计算分析风机导管架结构在波流及网箱系泊绳张力作用下的应力分布,评估养殖网箱系泊绳张力对风机导管架基础结构安全性的影响。结果表明,网箱布设深度的增加能够减少网箱系泊绳最大张力,显著改善网箱风机整体结构受力状态;波流入射角的改变对于网箱风机整体结构安全性影响不大;网衣生物附着程度的增加会显著增加网箱系泊绳最大张力,从而造成风机导管架基础杆件大量失效。综上所述,养殖网箱可布设于适当水深以减少受力,同时应及时清理附着生物,适当增加网箱系泊点附近的导管架杆件和导管架底部桩土点杆件的壁厚,以确保养殖网箱与海上风机融合系统结构安全。该结果可为深入研究网箱与风机融合系统的受力,评估该系统的安全性,优化设计养殖网箱与风机融合系统提供数据支撑。     

波浪作用下可升降式筏式养殖设施水动力特性数值模拟研究

在极端海况下,可升降式筏式养殖设施能够通过下潜来躲避风浪,降低波浪力作用,减免损失。为研究波浪作用下可升降式筏式养殖设施的水动力特性,采用集中质量法建立了筏式养殖设施漂浮及下潜时的数学模型,采用龙格库塔法对其进行求解,并将数值模拟结果与物理模型试验结果进行比较,二者吻合程度较好且变化趋势相同,表明数值模拟的方法能够较好地模拟可升降式筏式养殖设施的水动力特性。在此基础上,用数值模拟法进一步研究波高和周期变化对浮筏运动特性的影响,以及下潜对浮筏运动和锚绳力的影响。模拟结果显示,不同波高和周期变化对浮筏运动特性产生不同程度的影响,同时浮筏下潜后的运动幅度和锚绳力幅值明显减小。     

基于FUNWAVE-TVD模型的离岸养殖围网内外波浪场数值模拟研究

本研究利用完全非线性Boussinesq数值模型FUNWAVE-TVD耦合多孔介质模型,建立了模拟围网波浪场的数值模型。将计算结果和实验数据进行对比分析,验证了该模型计算规则波在穿过网箱后传播过程的准确性。进一步研究了波高和周期等因素对围网内外波浪场特性的影响,探讨了围网波浪场特性与这些水动力因素的内在联系。结果显示,离岸养殖围网的存在使波浪场背浪侧出现衰减,波高衰减率受波浪周期影响较大,最大波高衰减达到93.3%。同时,较低频规则波的波高衰减区域呈辐射状趋势扩散,并随着波浪进一步传播,最大波高衰减位置开始向两侧扩散,围网背浪侧的波高衰减程度减小,波高有恢复趋势,而高频波浪的波高衰减区域则较为集中。本研究可为实际海域桩网围护的位置和构造提供分析依据。     

Evaluation of the structural strength and failure for floating collar of a single-point mooring fish cage based on finite element method

Deep-water fish cage floating collar also referred to as float, bears a load in the form of waves, fishing nets, and moorings, in which the longitudinal wave force is the main type of loading. The long-term continuous effects caused by wave force could cause reduction in strength, or vibration failure in the floating collar. In this study, the peak responses of a single-point mooring (SPM) cage floating collar, due to either static or vibration loadings, were calculated by the finite element method (FEM) based on an elastic model. In this model, the float exhibited macro-plastic deformation when the stress of 26.1 MPa, generated under 100 kN load, was greater than the yield limit (25 MPa). With the increase in order modes from 1 to 18 (1.2–7.9 Hz), the stress increased. Moreover, the harmonic stress corresponding to 8 and 0.1 Hz was clearly higher than that for 0 Hz under 100 kN loads, due to structural resonance. The range of stress values due to the random vibration was 16.0–63.7 MPa, when the angular velocities (k) were in the range of 0.01–16 rad s^―1. Moreover, the transient response (34.4 MPa) was maximum when the angular velocity was 10 rad s^―1 (range 1–100 rad s^―1). The reliability rate of the entire body was 53.1% and 97.0% after 10⁸ loading cycles for 100 kN and 10 kN loads, respectively. Furthermore, the fatigue modes of the key components were determined from the outer triangular tops and inner hexagonal intersections. In short, static analysis, vibration analysis, and fatigue analysis of FEM could be used as reliable ways to evaluate structural strength and failure for floating system. Finally, the floating parts could be strengthened with partially double pipes or optimized by increasing the stiffness, and appropriate damping could be widely used.     

海水网箱网衣防污技术的研究进展

海水网箱养殖中,网衣污损附着物会影响网箱设施安全及其养殖鱼类的健康生长,因此,网衣防污是网箱养殖业备受关注的问题。本文在简述海水网箱网衣分类与特点的基础上,重点介绍了人工清除法、防污涂料法、机械清除法、金属合金网衣防污法、箱体转动防污法、生物防污法、网衣本征防污法等网衣防污技术最新研究进展;结合本课题组在网衣防污方面的研究成果,分析上述防污技术的特点,为网衣防污技术的深入研究以及水产养殖业的绿色发展提供参考。我国海水网箱养殖业大有可为,但网衣防污工作仍任重道远。     

Examination of net volume reduction of gravity-type open-net fish cages under sea currents

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.     

Design evaluation of a fish cage mooring system with different bridle line connections using model experiments and simulations

Because fish cage systems are strongly influenced by various marine environmental conditions such as currents and waves, structural safety design is of crucial importance during their installation. It is particularly important to design a technical solution for a mooring system. In this study, we designed four types of fish cage systems with different bridle connection arrangements (two single-rope and two multiple-rope connection methods) to evaluate the structural safety of fish cage systems based on the bridle connection arrangement and to propose an efficient design direction. The level of the structural safety of the fish cage system in terms of the resistance force, shape, and inside volume reduction ratio was found to vary according to the position of the frame lines connected to the bridle lines, the number of bridle lines, and the angle between the frame line and the direction of currents and waves. Improved structural safety was observed when the bridle lines were connected to the midpoints of the frame lines compared to those connected to the vertices, and the multiple-rope connection method was found to provide higher structural safety than the single-rope connection method. Increased fish cage system structural safety was also confirmed when the frame line orientation was 90° to the direction of currents and waves compared to that at 45°. From these findings, it can be concluded that the structural safety of a fish cage system can be improved by using multiple bridle lines to disperse the tension of the mooring lines connected to the frame lines and by installing the fish cage with the frame lines aligned at an angle that minimizes the projected area exposed to currents and waves. Moreover, the simulation technique presented in this study is expected to contribute to the efficient evaluation of the structural safety of various fish cage mooring systems designed using multiple-rope connection methods, accounting for the number and position of bridle lines connected on a frame line.     

Field measurements of cage deformation using acoustic sensors

As aquaculture continues to supply an increasing share of the worldwide seafood demand, it will become critical for farmers to maximize their efficiency. Presently, the majority of marine finfish are produced in gravity type net pens which can deform when they are subjected to currents. The water velocity loading affects the overall net shape which results in net cage volume loss and consequently, increases fish stress and decreases growth rates.In this study, an acoustic method is utilized to monitor the deformation of a small-scale fish cage deployed in currents. Twelve acoustic sources and four hydrophones were deployed on and around a small scale net pen for 60 days to monitor the net cage movement and volume. Local current velocities were recorded using two current meters, one inside and one outside the net pen. Three volume approximation techniques were examined, using the positions of the acoustic sources to predict net chamber volume as it responded to the currents. A numerical model of the system was then configured, set with loads under similar water velocities and results between field measurements and the model were compared.The use of acoustic sources and hydrophones to monitor cage deformation was shown to accurately monitor net deformation. Field measurements compared well to numerical model predictions, with errors ranging from −3.8% to 32%, depending upon the number of acoustic sources employed in the volume calculations. At low water velocities, six acoustic sources were found to accurate predict the net pen volume. In higher currents, a minimum of nine acoustic sources was recommended.     

水流作用下重力式网箱浮架结构的动力响应研究

近年来深水网箱养殖设施得到了广泛的应用,浮架作为网箱结构的重要组成部分,其安全性对网箱的设计至关重要。基于有限单元法采用SHELL单元建立了浮架结构的荷载-变形数值模型,对水流作用下浮架的应力和变形进行了数值模拟,并开展物理模型试验对该数值模型进行验证。结果表明,该数值模型可以准确模拟浮架的变形,采用该数值模型,分析了不同流速条件下浮架的变形和应力,数值模拟结果显示:随着流速的增加,浮架的变形和应力逐渐增加。相同流速条件下,注水下潜后,浮架的应力和变形能够显著减小;因此,在强流条件下,可以采用浮架注水的方式,使浮架处于下潜状态,以改善浮架结构的变形和应力分布。     

方形结构网箱单箱体型锚泊系统的优化研究

以方形结构网箱的单箱体型锚泊系统为研究对象,通过力学分析和程序计算得出锚绳张力以及不同来流角度下的阻力系数之和(SRC)两项安全性能指标。结果表明,在理论的最危险受力情况下,单锚绳系统中锚绳张力的最大值为网箱阻力R,在双锚绳系统中则小于R。当双锚绳系统的锚绳安装角度β设置在最佳值22.5°时,SRC获得最小值34.65,该值相比β=1°时的SRC(39.59)下降了约12.5%,相比单锚绳系统的SRC(41.36)则降低了16.2%。