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1.
Failure of net cage and mooring system is of great concern to the marine aquaculture industry. To avoid the structure failure in storm waves and current during typhoon events, net cage can submerge below the water surface in practice. A submersible net cage and mooring system is analyzed by numerical simulation and physical model test. The numerical model is established based on the lumped mass method and principle of rigid body kinematics. A series of physical model tests are conducted to validate the numerical model of single net cage and grid mooring system in waves and current. Numerical results correspond well with data obtained from physical model test. The results indicate that when net cage is submerged below the water surface, the deformation of net cage in waves can be improved significantly, and the tension force on the anchor line, bridle line and grid line will decrease significantly. However, the tension force on the buoy line in the submergence condition is larger than that in the floating condition. Different relative submergence ratios are also considered in our numerical simulation, and a relative submergence ratio equal to 0.1 is suggested here. The tension reduction ratio (56%) for the four-cage system is larger than that for the single-cage (52%) and double-cage systems (44%). 相似文献
2.
An integrated dynamic model of China’s deep ocean mining system is developed and the fast simulation analysis of its longitudinal reciprocating motion operation processes is achieved. The seafloor tracked miner is built as a three-dimensional single-body model with six-degree-of-freedom. The track-terrain interaction is modeled by partitioning the track-terrain interface into a certain number of mesh elements with three mutually perpendicular forces, including the normal force, the longitudinal shear force and the lateral shear force, acting on the center point of each mesh element. The hydrodynamic force of the miner is considered and applied. By considering the operational safety and collection efficiency, two new mining paths for the miner on the seafloor are proposed, which can be simulated with the established single-body dynamic model of the miner. The pipeline subsystem is built as a three-dimensional multi-body discrete element model, which is divided into rigid elements linked by flexible connectors. The flexible connector without mass is represented by six spring-damper elements. The external hydrodynamic forces of the ocean current from the longitudinal and lateral directions are both considered and modeled based on the Morison formula and applied to the mass center of each corresponding discrete rigid element. The mining ship is simplified and represented by a general kinematic point, whose heave motion induced by the ocean waves and the longitudinal and lateral towing motions are considered and applied. By integrating the single-body dynamic model of the miner and the multi-body discrete element dynamic model of the pipeline, and defining the kinematic equations of the mining ship, the integrated dynamic model of the total deep ocean mining system is formed. The longitudinal reciprocating motion operation modes of the total mining system, which combine the active straight-line and turning motions of the miner and the ship, and the passive towed motions of the pipeline, are proposed and simulated with the developed 3D dynamic model. Some critical simulation results are obtained and analyzed, such as the motion trajectories of key subsystems, the velocities of the buoyancy modules and the interaction forces between subsystems, which in a way can provide important theoretical basis and useful technical reference for the practical deep ocean mining system analysis, operation and control. 相似文献
3.
Igor Tsukrov Oleg Eroshkin David Fredriksson M. Robinson Swift Barbaros Celikkol 《Ocean Engineering》2003,30(2):251-270
A consistent finite element is proposed to model the hydrodynamic response of net panels to environmental loading. This equivalent net element is constructed to reproduce the drag, buoyancy, inertial and elastic forces exerted on the netting by current and waves. To evaluate the accuracy of the proposed finite element modeling, numerical predictions have been compared with the experimental observations and (simplified) analytical results of other authors. This new modeling technique has been applied to evaluate the performance of a tension leg fish cage in the open ocean environment. 相似文献
4.
In the present study, the dynamic response of a coupled SPM-feeder-cage system under irregular waves and shear currents is analyzed. A numerical model is developed by using the commercial software Orca Flex. Hydrodynamics coefficients of the vessel are calculated by using a 3D diffraction/radiation panel program. First- and second-order wave forces are included in the calculations. Morison equation is used to compute the drag force on line elements representing the net. Drag coefficients are determined at every time step in the simulation considering the relative normal velocity between the structural elements and the fluid flow. The dynamic response of the coupled system is analyzed for various environments and net materials. The results of the study show the effects of solidity ratio of the net and vertical positions of the cage on the overall dynamic response of the system, confirming the viability of this type of configuration for future development of offshore aquaculture in deep waters. 相似文献
5.
A numerical study on dynamic properties of the gravity cage in combined wave-current flow 总被引：2，自引：0，他引：2
Yun-Peng Zhao Yu-Cheng Li Guo-Hai Dong Fu-Kun Gui Bin Teng 《Ocean Engineering》2007,34(17-18):2350-2363
Recent work in the area of open-ocean aquaculture-system dynamics has focused either on the response of fish cages in waves or the steady drag response from ocean currents, not on them combined. In reality, however, the forces bearing on these open-ocean structures are a nonlinear, multidirectional combination of both waves and current profiles. In this paper, a numerical model has been developed to simulate the dynamic response of the gravity cage to waves combined with currents. When current flows are combined with regular waves, gravity-cage motion response (including heave, surge, and pitch) and mooring-line forces have been calculated. To examine the validity of simulated results, a series of physical model tests have been carried out. The results of our numerical simulation are all in close agreement with the experimental data. 相似文献
6.
针对单点系泊(SPM)网箱系泊力大于传统网箱,离岸环境承受风浪时风险更高的问题,研究设计了一种相较传统圆形网箱拥有更小系泊力的船型网箱,运用正交原理制定了三因素三水平的试验方案,对网箱浮架进行了计算机数值模拟,分析网箱在波流共同作用下的水动力特性变化。研究表明,在兼顾经济成本与网箱安全性的条件下,长24 m,宽9 m,头部角度为60°的网箱浮架具有较优良的水动力性能和相对较低的养殖成本。该网箱系统能随着潮流改变方向而在锚点周围移动,从而极大减小网箱底部的养殖残渣堆积并降低锚固安装成本,可为我国深水网箱的发展提供一定的理论参考依据。 相似文献
7.
Model experiments of a floating fish cage subjected to waves and current have been performed. The objective was to study the dynamic behaviour of the fish cage model in waves and current. The fish cage model was composed of a model net, a flexible floating collar of the circular plastic type and a weight system. It was found that there are many wave periods in which cancellation of the wave-induced forces on the model occur. These cancellation wave periods are within the range of dimensioning wave periods commonly used for testing of fish farm structures and hence are important to be aware of. Large deformations of the net under realistic wave and current conditions were observed, where contact between the net and other parts of the structure were identified. This may cause damages to the net due to abrasion. 相似文献
8.
方形网箱水平波浪力的迭加计算和实验验证 总被引：4，自引：3，他引：4
采用小直径圆柱体绕流理论和网渔具理论为基础的经验水动力计算法，分别考虑网箱框架是刚性体、网衣和绳索是柔性体的特征，结合正弦波理论对方形网箱及其构件受到的水平波浪力特性进行了分析研究，理论给出了波浪力迭加计算法，并把计算结果与小尺度的网箱水槽实验进行对比验证。结果表明，计算数值与试验数据较接近，平均误差率在15％以内。网箱水平波浪力呈周期性、不对称变化，在波浪周期小于0.72s时，主要以框架的波浪力为主，反之以网衣的为主。在波长为0.8m、周期为0.72s、水深为0.7m、波高为68.3mm情形下，计算结果显示网箱的框架尺寸和形状及其系泊、布局的选择应根据实际海况而定，网箱高度可适当增加，当设置水层下降深度相对于网箱高度比率为20％-40％，时，波浪力峰值下降相对率达68.03％-88.20％，表明可以较大程度地降低其波浪力。 相似文献
9.
波浪作用下刚性框架浮体及其锚绳运动数值模拟精度分析 总被引：2，自引：1，他引：1
由小尺度刚性杆件构成的复杂结构近年来多用于海洋平台建设和海洋监测浮标制作以及海洋增养殖人工浮鱼礁的设计。采用有限单元法和集中质量点法建立波浪作用下刚性框架浮体及其锚绳运动数值模型,探讨空间单元划分、时间离散步长、数据保存格式对刚性框架浮体和柔性锚绳运动模拟精度的影响,分别给出此三者之间的匹配关系。研究结果表明:框架浮体的单元划分可依据是否出水给定,单元的划分比建议取0.05;锚绳的单元划分与其上端连接的浮体浮力有关,当锚绳的拉力主要由上端浮体浮力产生时锚绳单元的划分影响较小,当锚绳的拉力主要由波浪力产生时锚绳单元的划分比建议取0.02;空间单元划分与时间离散步长存在匹配关系,通过减小时间步长来追求数值模拟精度时必须同时考虑保存运动物理量截断误差的影响。 相似文献
10.
本文对内孤立波作用下圆柱体的水动力特性进行了数值研究。对不同直径、不同水深比、不同浸没深度的圆柱进行了水平方向受力分析,从多个因素出发,研究了内孤立波对水下竖直圆柱的水平作用情况。通过分析水平作用力和力矩的时程曲线,得到内孤立波行进过程中对于圆柱体的横向作用力和力矩与时间的关系。通过对比不同工况下内孤立波橫向作用力幅值,得到内孤立波作用力幅值与圆柱直径、水深比以及浸没深度的关系。结果表明,内孤立波横向作用力(力矩)幅值与圆柱直径呈线性相关关系,但与水深比相关关系不明显,随着圆柱浸没深度的增加,内孤立波横向作用力幅值呈现出先增大后减小的趋势。 相似文献
11.
The simulation of the geometry of a tuna purse seine under current and drift of purse seiner 总被引：4，自引：0，他引：4
It was necessary to obtain a more practical interactive precise model of the three-dimensional (3-D) geometry during purse seine operations considering movements of fishing vessel and details of the sea condition. The changes in the shape of a purse seine from shooting to pursing during pelagic skipjack fishing was recorded in the Southwest Pacific Ocean by photographs of the scanning sonar with in situ measurements of water flow by a current meter. The modeling of 3-D geometry during purse seining was established using finite element methods, as resultant force vector from flow drag, buoyancy, sinking force, tension of pulling or pursing acting on net panels in connection with drift of fishing vessel with time elapsed from the start of shooting to the end of pursing. The simulation results were matched closely by field measurements as a heart-like shape in upper net near floatline and a water-drop shape in purse line following drift of ship towards inside net circle during pursing. This model of a purse seine can be extended to almost any kind of purse seine generating real fishing parameters and to modeling fish capture process. 相似文献
12.
《Deep Sea Research Part I: Oceanographic Research Papers》2007,54(1):1-21
Regime transitions in the meridional overturning circulation (MOC) and the rate of formation of deep and bottom waters are thought to be sensitive to changes in the freshwater flux at high latitudes. We model convective overturning in the presence of a surface freshwater input using laboratory experiments that are inverted relative to the ocean: we establish an equilibrium circulation forced by differential heating and cooling along the base of a box and perturb this flow by adding a stabilizing saltwater input at the ‘polar’ end of the box. An initially stable layer forms near the source of the salinity anomaly as a ‘polar halocline’. The subsequent circulation is governed largely by the ratio of salinity and thermal buoyancy supply. For small values of this ratio we observe periodic formation and breakdown of the halocline. Larger values of the flux ratio lead to subthermocline intrusions and stable layering laterally throughout the basin, isolating the bulk of the water column from the forcing boundary. The shutdown of deep overturning and formation of a shallow circulation occurs at a salinity buoyancy input of order 0.1 times the rate of loss of thermal buoyancy. This salinity buoyancy is then comparable to the buoyancy that forces the deep sinking plume below the thermocline in steady-state overturning. When the salinity buoyancy flux is removed, the circulation slowly returns to its original state. 相似文献
13.
14.
The computational fluid dynamics study is performed to analyze the impact of the cultured fish on the flow field through net cage and the deformation of net cage. The shear stress turbulent k-omega model is applied to simulate the flow field through the net cage, and the large deformation nonlinear structure model is adopted to conduct the structural analysis of the flexible net cage. To validate the net-fluid interaction model of the net cage in current, a series of physical model tests are conducted, which indicate that the numerical model can accurately simulate the flow field around the net cage and the deformation of the net cage. A fish model is used to simulate the effect of fish behavior on the flow pattern around the net cage and the deformation of the net cage. In addition, the flow fields around the net cage in current are investigated considering different fish group structures, fish swimming speeds, fish distributions and fish stocking densities. The results indicate that the circular movement of fish in the still water leads to a low pressure zone at the center of net cage, which causes a strong vertical flow along the center line of the net cage. The drag force on the net cage is significantly decreased with the increasing fish stocking density, but the most severe deformation of net cage occurred in the case of medium fish stocking density. 相似文献
15.
This paper presents a numerical study on the hydrodynamic behaviours of a round buoyant jet under the effect of JONSWAP random waves. A three-dimensional large eddy simulation (LES) model is developed to simulate the buoyant jet in a stagnant ambient and JONSWAP random waves. By comparison of velocity and concentration fields, it is found that the buoyant jet exhibits faster decay of centerline velocity, wider lateral spreading and larger initial dilution under the wave effect, indicating that wave dynamics improves the jet entrainment and mixing in the near field, and subsequently mitigate the jet impacts in the far field. The effect of buoyancy force on the jet behaviours in the random waves is also numerically investigated. The results show that the wave effect on the jet entrainment and mixing is considerably weakened under the existence of buoyancy force, resulting in a slower decay rate of centerline velocity and a narrower jet width for the jet with initial buoyancy. 相似文献
16.
Based on the lumped-mass method and rigid-body kinematics theory, a mathematical model of a gravity cage system attacked by irregular waves is developed to simulate the hydrodynamic response of cage system, including the maximum tension of mooring lines and the motion of float collar. The normalized response amplitudes (response amplitude operators) are calculated for the cage motion response in heave and surge, and the mooring line tension response, in regular waves. In addition, a statistical approach is taken to determine the motion and tension transfer functions in irregular waves. In order to validate the numerical model of a gravity cage attacked by irregular waves, numerical predictions have been compared with the experimental observations in the time and frequency domain. The effect of wave incident angle on the float collar motion, mooring line tension and net volume reduction of the gravity cage system in irregular waves is also investigated. The results show that at high frequencies, the cage system has no significant heave motion. It tends to contour itself to longer waves. The variation amplitude of mooring line forces decreases as the wave frequency increases. With the increasing of wave incident angle, the horizontal displacement of the float collar increases. 相似文献
17.
Fish cages in the open sea are exposed to cycle loads due to irregular wave climate during their service life, and thus the fatigue reliability assessment of mooring system should be conducted to ensure the safe operation. The aim of this study is to evaluate the fatigue failure probability of mooring system for fish cage. Numerical simulation of net cage in random waves is performed and the time dependent approach is applied to conduct the fatigue reliability analysis of shackle chains based on S-N curve method. The sensitivity analysis of fatigue reliability of mooring line to the uncertainty of random variables in the fatigue limit state is conducted. In addition, the system reliability for mooring system is analyzed and the effect of the initial pretension and safety factor on system reliability is investigated. The results indicate that a case without the initial pretension on anchor lines is helpful to decrease the failure probability of mooring system and the safety factor of mooring lines in the current regulation is conservative for the system reliability against fatigue damage. 相似文献
18.
A numerical method for the dynamic simulation of towed cables is presented. The cable is loaded by fluid drag, tension, gravity and buoyancy, including the effects of weights and floats. The development of a cable can be simulated as well as the separation of a cable under excessive load and the subsequent behavior of the broken parts. The system is constructed from a set of generic elements representing such items as cable or rope strands, knots (reference points on rope sections), kinks (sliding reference points on cable sections that change length), cable ends and winches. A mathematical graph organizes these elements in a general and flexible fashion: it allows construction of complex systems and permits structural redefinition during the simulation. The nodes of the graph coincide with the various reference points of the problem, at which physical parameters are lumped and to which sets of ordinary differential equations are associated that define the motions of the points. The links of the graph describe the physical connections between the nodes. Application of new methods for solving stiff, sparse systems of coupled ordinary differential equations enables efficient simulation of snap-loads and other severe events. Results are presented that compare quantitatively with laboratory measurements. A further example shows the behavior of a breaking cable that is qualitatively reasonable. 相似文献
19.
Mixing downstream of a submerged fish cage: a numerical study 总被引：2，自引：0，他引：2
As part of the overall Hawaii Open Ocean Research Project (HOARP) a fish cage of biconical shape (OceanSpar SeaStation 3000) has been placed in the waters of the coast of Ewa, HI, to enable research on the effect of cage culture of fish in tropical waters. One of the goals of HOARP is to examine the nature of the waste product stream of the fully submerged fish cage. HOARP activities began as a research effort but now are conducted in conjunction with a commercial operator that has three cages installed. For our analysis of the impact of the farm, an estimate of the mixing downstream of an individual cage is needed to assess the potential water quality impact of the farm operation to nearby waters. Federal regulations (40 CFR 122.24) require aquaculture systems to obtain a NPDES permit if they annually produce more than 45 454 kg harvest weight (about 100 000 lbs.) of warm water fish (CWA sections 318 and 402). The current farm off Ewa meets this criterion, thus a "mixing zone" needs to be established. A CFD simulation was made to evaluate the mixing downstream of the fish cage. This mixing consists of two parts, the turbulence generated by water passing through the cage, and the vortical flow generated by the general obstruction to water flow that is caused by the cage. The small scale turbulence increases the effective diffusion, and thus increases dilution of the pollutant, within the mixing zone. Parametric studies have been made to examine the effect of current speed on the initial mixing thereby enabling an estimation of the total mixing downstream of the cage. This estimate of the effective diffusion is essential for the establishment of the boundaries of the mixing zone. 相似文献
20.
内孤立波具有较大的振幅与较强的垂向剪切,能对海洋工程设施产生极大的破坏作用。本文设计实验研究了内孤立波与直立小直径桩柱的相互作用,采用粒子图像速度测量法(PIV)测量内孤立波的流速场,并采用自行设计的测力天平测量桩柱受力,测量分析了内孤立波对小直径直立桩柱产生作用力的实验值,与Morison公式计算的理论值比较。实验结果表明,第一模态内孤立波的流速方向以及作用力在桩柱的上下部分方向相反,产生很强的速度切变和扭力,对小直径直立桩柱造成破坏。通过与Morison公式计算的理论值比较,发现实验值与理论值的大小以及分布规律基本相同。 相似文献