Numerical simulation of the hydrodynamic behaviour of submerged plane nets in current

The aim of this paper is to investigate the shape and tension distribution of fishing nets in current. A numerical model is developed, based on lumped mass method to simplify the net. The motion equation is set up for each lumped mass. The Runge–Kutta–Verner fifth-order and sixth-order method is used to solve these simultaneous equations, and then the displacement and tension of each lumped mass are obtained. In order to verify the validity of the numerical method, model tests have been carried out. The results by the numerical simulation agree well with the experimental data.     

水流作用下渔网养殖空间变化的计算方法

渔网的动力分析是养殖网箱设计和优化的基础。通过把一系列杆相互铰接在一起,建立网的模型,模拟网在来流作用下的变形。作用在杆上的水动力可以通过Morison公式来计算,采用有限单元的离散方法,并利用网目合并的方法来减少总的自由度数目。模型的计算结果同试验成果做了对比,计算与试验在柔性网的变形方面,结果吻合良好。     

Numerical Study on the Hydrodynamic Characteristics of Biofouled Full-Scale Net Cage

The effect of biofouling on the hydrodynamic characteristics of the net cage is of particular interest as biofouled nettings can significantly reduce flow of well-oxygenated water reaching the stocked fish. For computational efficiency, the porous-media fluid model is proposed to simulate flow through the biofouled plane net and full-scale net cage. The porous coefficients of the porous-media fluid model can be determined from the quadratic-function relationship between the hydrodynamic forces on a plane net and the flow velocity using the least squares method. In this study, drag forces on and flow fields around five plane nets with different levels of biofouling are calculated by use of the proposed model. The numerical results are compared with the experimental data of Swift et al. (2006) and the effectiveness of the numerical model is presented. On that basis, flow through full-scale net cages with the same level of biofouling as the tested plane nets are modeled. The flow fields inside and around biofouled net cages are analyzed and the drag force acting on a net cage is estimated by a control volume analysis method. According to the numerical results, empirical formulas of reduction in flow velocity and load on a net cage are derived as function of drag coefficient of the corresponding biofouled netting.     

Numerical Analysis on the Effects of Submerged Depth of the Grid and Direction of Incident Wave on Gravity Cage

In this paper,the numerical model of the net cage with the grid mooring system in waves is set up by the lumped mass method and rigid kinematics theory,and then the motion equations of floating system,net system,mooring system,and floaters are solved by the Runge-Kutta fifth-order method.For the verification of the numerical model,a series of physical model tests have been carried out.According to the comparisons between the simulated and experimental results,it can be found that the simulated and experimental results agree well in each condition.Then,the effects of submerged depth of grid and direction of incident wave propagation on hydrodynamic behaviors of the net cage are analyzed.According to the simulated results,it can be found that with the increase of submerged depth of grid,the forces acting on mooring lines and bridle lines increase,while the forces on grid lines decrease;the horizontal motion amplitudes of floating collar decrease obviously,while the vertical motion amplitudes of floating collar change little.When the direction of incident wave propagation changes,forces on mooting lines and motion of net cage also change accordingly.When the propagation direction of incident wave changes from 0° to 45°,forces on the main ropes and bridle ropes increase,while the forces on the grid ropes decrease.With the increasing propagation direction of incident wave,the horizontal amplitude of the forces collar decreases,while the vertical amplitude of the floating collar has little variation.     

鲤、草鱼在400 Hz矩形波连续音驯化下对模型网的行为反应研究

定置网具是1种被动过滤性渔具,其渔获效果往往受水流、底质以及季节等因素的影响.为了改进传统的定置网具,本试验参考定置张网、多门网箱簖以及底层鱼诱捕定置网箱等定置网中拦网、八字门的设计参数,结合本次试验条件设计了由拦网、八字门组成的模型网,研究了鲤、草鱼在400 Hz矩形波连续音的刺激下对该模型网的行为反应,探讨了音响驯化技术与定置网具相结合的联合渔法中拦网、八字门的相关参数以及开发新渔具、渔法的可行性.结果表明,鲤、草鱼在声音刺激下能够通过模型网至聚集区内聚集,其平均开始进入拦网时间分别为76.9和89.4 s;平均开始进入八字门时间分别为79.3和71.2 s;平均开始聚集时间分别为120.0和96.0 s;平均聚集时间分别为125.8和87.8 s;平均聚集率为76.5%和84.2%.由此可见,结合音响驯化技术能够提高定置网具的捕捞效率.     

测深拼接的组网平差判定方法

从网平差角度研究两相邻图幅的重叠测线间拼接问题，提出3种组网平差模型和图幅间系统误差的判定方法，并通过实例计算比较了组网平差判定法和常用的重叠线直接比对法，计算结果表明，组网平差判定法克服了常用的直接比对法对重叠测线依赖，能有效准确地判定图幅间的系统差异，为测深网拼接提供了更为实用的方法。     

网衣对波浪传播影响的三维数值模拟

为研究网衣对波浪传播的影响,采用多孔介质模型模拟网衣,建立了模拟网衣与波浪相互作用的三维数值波浪水槽模型。基于该数值模型研究了波浪经过网衣作用后波高衰减的变化规律,并与物理模型试验结果进行比较。通过对比数值模拟和物理模型试验的结果,证明了该三维数值模型模拟网衣对波浪传播影响的可行性。     

Numerical simulation of the influences of sinker weight on the deformation and load of net of gravity sea cage in uniform flow

1IntroductionThe fish farming and aquaculture industry areexpanding and the demand for suitable locations forfish farms is increasing.In the future,more of thefish farms will be located offshore,as the number ofsuitable nearshore locations is limited.Futu…     

绷紧式系泊缆冲击张力特性研究

采用集中质量法研究了绷紧式系泊系统中系缆由于松弛-张紧过程产生的冲击张力。建立系泊缆绳离散的集中质量模型,对其独立单元进行受力分析并建立了单元的运动方程。给定缆绳上端点简谐激励,通过Ansys中的Aqwa模块,分析了缆绳的运动响应;针对缆绳运动响应过程中的三种状态进行了模拟计算,探讨了冲击张力产生的条件;研究了缆绳初始预张力、上端点激励幅值和频率、拖曳力系数、弹性模量以及单位长度质量对动态张力的影响。研究结果表明:这些影响因素不仅会影响缆绳动态张力的大小,也会对缆绳中的冲击张力产生一定的影响。     

Numerical Study on the Hydrodynamic Characteristics of Biofouled Full-Scale Net Cage

The effect of biofouling on the hydrodynamic characteristics of the net cage is of particular interest as biofouled nettings can significantly reduce flow of well-oxygenated water reaching the stocked fish. For computational efficiency, the porous-media fluid model is proposed to simulate flow through the biofouled plane net and full-scale net cage. The porous coefficients of the porous-media fluid model can be determined from the quadratic-function relationship between the hydrodynamic forces on a plane net and the flow velocity using the least squares method. In this study, drag forces on and flow fields around five plane nets with different levels of biofouling are calculated by use of the proposed model. The numerical results are compared with the experimental data of Swift et al.(2006) and the effectiveness of the numerical model is presented. On that basis, flow through full-scale net cages with the same level of biofouling as the tested plane nets are modeled. The flow fields inside and around biofouled net cages are analyzed and the drag force acting on a net cage is estimated by a control volume analysis method. According to the numerical results, empirical formulas of reduction in flow velocity and load on a net cage are derived as function of drag coefficient of the corresponding biofouled netting.     

Numerical analysis of hydrodynamic behaviors of two net cages with grid mooring system under wave action

Based on rigid kinematics theory and lumped mass method,a mathematical model of the two net cages of grid mooring system under waves is developed.In order to verify the numerical model,a series of physical model tests have been carried out.According to the comparisons between the simulated and the experimental results,it can be found that the simulated and the experimental results agree well in each wave condition.Then,the forces on the mooring lines and the floating collar movement are calculated under different wave conditions.Numerical results show that under the same condition,the forces on the bridle ropes are the largest,followed by forces on the main ropes and the grid ropes.The horizontal and the vertical float collar motion amplitudes increase with the increase of wave height,while the relationship of the horizontal motion amplitude and the wave period is indistinct.The vertical motion amplitude of the two cages is almost the same,while on the respect of horizontal motion amplitude,cage B(behind cage A,as shown in Fig.4) moves much farther than cage A under the same wave condition.The inclination angle of the floating system both in clockwise along y axis and the counter one enlarges a little with the increase of wave height.     

渔网水动力试验研究及分析

根据流体力学实验结果 ,研究了雷诺数 ,网的密实度 ,网型以及流向等对网的阻力影响 ,同时讨论了侧向力问题 ,对同样网面积的平面网及圆型网的阻力进行了比较 ,结果圆型网阻力较小。     

水下拖曳系统运动姿态仿真研究

采用凝集参数法建立了水下拖曳系统的三维离散模型,该模型由一系列的质量点和不计重量的弹簧组成.采用数学模型编程对NCEL浮球实验和四个典型拖曳系统进行了仿真计算.计算结果表明此数学模型具有一定的理论意义和工程实用价值.     

Numerical Simulation of Hydrodynamic Behaviors of Gravity Cage in Waves

This paper aims at investigation of the dynamic properties of gravity cage exposed to waves by use of a numerical model. The numerical model is developed, based on lumped mass method to set up the equations of motion of the whole cage; meanwhile the solutions of equations are solved by the Runge-Kutta-Verner fifth-order and sixth-order method. Physical model tests have been carried out to examine the validity of the numerical model. The results by the numerical simulation agree well with the experimental data.     

Analysis of hydrodynamic behavior of a submersible net cage and mooring system in waves and current

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%).     

Numerical Simulation of Dynamic Response of A Net Cage for Flatfish in Waves简

A numerical model of flatfish cage is built based on the lumped mass method and the principle of rigid body kinematics. To validate the numerical model, a series of physical model tests are conducted in the wave flume. The numerical results correspond well with the data sets from physical model test. The effect of weight of bottom frame, height of fish net and net shape on motion responses of fish cage and tension force on mooring lines is then analyzed. The results indicate that the vertical displacements of float collar and bottom frame decrease with the increase in the weight of bottom frame; the maximum tension force on mooring lines increases with the increasing weight of bottom frame. The inclination angles of float collar and bottom frame decrease with the increasing net height; the maximum tension force increases obviously with the increase of net height.     

A Finite Element Solution of Wave Forces on Submerged Horizontal Circular Cylinders

In this paper, a numerical model is established for estimating the wave forces on a submerged horizontal circular cylinder. For predicting the wave motion, a set of two-dimensional Navier-Stokes equations is solved numerically with a finite element method. In order to track the moving non-linear wave surface boundary, the Navier-Stokes equations are discretized in a moving mesh system. After each computational time step, the mesh is modified according to the changed wave surface boundary. In order to stabilize the numerical procedure, a three-step finite element method is applied in the time integration. The water sloshing in a tank and wave propagation over a submerged bar are simulated for the first time to validate the present model. The computational results agree well with the analytical solution and the experimental data.Finally, the model is applied to the simulation of interaction between waves and a submerged horizontal circular cylinder.The effects of the KC number and the cylinder depth on the wave forces are studied.     

基于桁架模型和多孔介质模型的柔性网衣和周围流场单向耦合方法研究

柔性网衣作为渔业养殖的重要组成部分,其水动力的计算分析对网箱的安全使用至关重要。基于桁架模型和多孔介质模型对柔性网衣和流场单向耦合计算的数值模拟方法进行了研究。通过code_aster软件基于桁架模型计算出网衣变形后节点坐标和网衣受力,然后将节点坐标导入OpenFOAM识别出网衣变形后的多孔介质区域,并基于多孔介质模型模拟水流作用下网衣周围的流场和计算网衣的受力。为了验证模型的正确性,将不同工况对圆形网衣的数值模拟结果与物理试验数据进行比较,包括code_aster中计算的网衣变形形状、OpenFOAM模拟的网衣周围流场以及在code_aster和OpenFOAM中计算的网衣受力。计算结果表明,圆形网衣在单纯来流下变形明显,与试验结果保持一致,证明了网衣变形和水动力单向耦合方法的准确性。     

海上风电高桩承台基础关键部位受力特性研究

海上高桩承台基础结构承台部分的设计主要依靠高桩码头和桥梁等其他高桩承台结构的经验，基于在建工程，为解决设计时容易设计出过厚承台和多余配筋的问题，本文采用有限元对包括土体在内的整个风机基础进行精细化数值模拟计算，计算结果与规范算法进行对比，得到承台设计时规范算法的安全余量，同时提出配筋优化方向。结果表明：基于弹性材料模型计算结果，有限元计算结果小于规范算法计算结果，基桩最大压力相差22.43%，最大上拔力相差2.08%，弯矩差别最大为57.89%，最小为18.85%；基于弹塑性材料模型计算结果，钢筋最大应力出现在钢管桩桩头，承台顶层钢筋受力较小，设计时可加强钢管桩桩头配筋，减少承台顶层钢筋数量。     

An integrated dynamic model of ocean mining system and fast simulation of its longitudinal reciprocating motion

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.