聚焦波作用下平面网衣结构的水动力特性研究

由于沿海区域的限制以及愈加严重的环境污染,渔业养殖正从近海走向深远海。深远海海域的海况更加恶劣,给养殖装备的设计与性能评估带来新的挑战。为解决该问题,对极端波浪与养殖装备网衣结构的相互作用开展研究。基于waves2Foam建立数值波浪水池,极端波浪模拟采用基于NewWave理论的聚焦波模型,网衣结构模拟采用多孔介质模型,并通过与Morison模型计算的网衣受力等效分析,获得多孔介质模拟网衣结构阻力系数的直接估计方法。然后将多孔介质模型嵌入waves2Foam中,开展聚焦波与网衣结构相互作用的数值模拟,同时开展水槽试验,验证数值模拟的准确性。基于数值模拟结果,系统地分析了不同网衣密实度及不同波浪参数下网衣结构的升阻力特性以及网衣结构对波浪场的扰动规律。研究表明：聚焦波波峰幅值和网衣密实度对网衣结构的升阻力影响较大,且升力峰值出现在阻力为0的时刻;网衣结构对聚焦波的时空演化特性有影响,改变了聚焦波波形。     

柔性网衣结构变形影响因素数值模拟研究

为解决柔性网衣在水流作用下容易产生较大变形,不利于网箱内鱼类生长的问题,本文利用Orcaflex软件对网衣结构变形进行了数值计算分析,并将计算结果与Kristiansen等^[10]的水槽试验和Cristian数值模拟结果进行比较,验证了数值计算的准确性,再利用“九点空间坐标法”计算了不同流速和配重情况下网箱体积剩余系数,定量分析了流速和配重对网衣变形的影响。结果表明：在低流速情况下,体积剩余系数可达0.997;在高流速情况下,体积剩余系数可达0.652;同时,在流速为0.3 m/s的情况下,增加40 g配重可以将网箱体积剩余系数从0.612提高到0.684,对网衣变形程度的影响高达10%。由此得出,流速是影响网衣变形的主要因素,流速越大,网衣变形情况越严重,在高速情况下,配重是改善网衣变形的重要因素。     

单点系泊网衣构件波浪试验研究

采用四种网箱系泊方法,设计单点系泊网衣构件水槽波浪试验。试验构件由六种网衣和框架装配而成,试验工况是规则波,周期为0．7—2．0s,波高为50—250mm。构件在水槽中作来回周期性直线运动,当试验波浪周期较小时,构件的来回运动不明显,主要以波浪运动为主,水动力峰值大体上呈周期性均匀变化;而当周期较长、波高较高时,构件在水动力的作用下产生了与波向相反的长周期漂移运动,有较大振幅的位移、速度和加速度,诱发了水动力的最大值,水动力变化呈现峰值短周期不均匀变化、最大值长周期变化和零拉力周期变化的规律。试验结果显示,与波高参数类似,随着网衣特性系数d／a的增大,网衣构件的水动力也增大,而水动力最大值长周期、零拉力周期变化规律分别是减短和增长的。在周期1．21、1．41、1．61、1．82s情况下,网衣C构件单点系泊试验水动力最大值是固定系泊计算水动力最大值平均的1．706、1．826、2．125、2．236倍,最大达3．61倍,表明单点系泊在波浪条件下构件水动力有较大的增加。     

碟形网箱水动力特性的研究

根据物模实验得到碟形网箱在不同海况条件下的受力并给出了其估算方法和公式及其相关系数的取值,同时总结了碟形网箱的运动特性。     

UCTD探头阻力系数的数值分析及试验研究

为优化海洋动力参量拖曳式剖面测量系统(Underway Conductivity-Temperature-Depth instrument,UCTD)探头下降速度与稳定性,达到设计测量深度,提高观测数据质量,本文利用外型曲线解析式和探头基本运动方程完成初步设计,通过Fluent软件建立UCTD探头的流体动力学分析模型,计算相应的阻力系数,对其进行结构优化和重量调整,以满足技术指标的要求。2017年春季航次海试数据验证了数值仿真计算与探头结构设计的科学性和合理性,研究结果为UCTD探头水下运动规律研究和探头的设计提供参考。作为走航温盐剖面测量装置,UCTD可以快速、低成本地获取海洋水文剖面资料,广泛应用于海洋环境监测、海洋科学研究以及军事领域。     

海面阻力系数的流体力学研究

利用相似理论的方法 ,把湍流问题的尼古拉兹曲线引入到风应力中 ,阐明了决定海面阻力系数的关键因素 ,并提出了阻力系数和有效波高的关系。     

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。     

海面阻力系数的流体力学研究

利用相似理论的方法 ,把解决湍流问题的尼古拉兹曲线引入到风应力的计算中。阐明了决定海面阻力系数的关键因素是海浪的平均波高及摩擦层厚度 ,并推出了它们之间的关系式。     

XCP投弃式海洋探头阻力系数数值计算及试验研究

以XCP探头为模型,采用有限体积法结合κ-ε两方程湍流模型,对XCP探头阻力系数进行了数值计算,研究了XCP探头的阻力特性。获得了不同雷诺数下阻力系数的变化趋势和水下稳定运动时的极限速度。结果表明阻力系数随着雷诺数的增加而减小,其数值计算结果与海上实测数据基本吻合,验证了该数值计算方法的正确性,可为XCP探头结构设计提供参考。     

南海区虾拖网方目与菱目混合网囊渔获性能初步研究

虾拖网是南海区常见的作业方式,由于其网囊网目选择性差,虾拖网作业常产生大量的副渔获物。为了优化虾拖网网囊结构,提高其选择性,2015年8月在南海北部渔场用方形网目与菱形网目混合网囊进行试验。结果表明:虾拖网的渔获种类有34种;渔获种类中,康氏小公鱼(Anchoviella commersoni)、黑尾吻鳗(Rhynchoconger ectenurus)、中线天竺鲷(Apogon kiensis)和杂食豆齿鳗(Pisoodonophis boro)的尾数逃逸率均超过80%;周氏新对虾(Metapenaeus joyneri)和刀额新对虾(Metapenaeus affinis的尾数逃逸率最低,仅为6.18%和2.07%;周氏新对虾和刀额新对虾的50%选择体长(L50)分别为50.79 mm和53.858 mm;脊突猛虾姑(Harpiosquilla raphidea)的L50为62.51 mm;丽叶鲹(Caranx kalla)、中华青鳞鱼(Harengula nymphaea)、中线天竺鲷(Apogon kiensis)、赤鼻棱鳀(Thrissa kammalensis)和黄斑蓝子鱼(Siganus oramin)的L50分别为53.77、78.87、47.17、60.92和60.55 mm;混合网囊对鱼类副渔获的释放率较高,但对幼虾的释放率较低。建议今后放大网囊菱目段的网目尺寸进行相应的试验,提高混合网囊对目标种类的L50值,使其在释放鱼类副渔获物的同时释放幼虾,达到渔业资源的合理利用。     

高风速下海面阻力系数的研究

利用由于海面摩擦造成的台风角动量的损失，推算出高风速下的海面阻力系数．高风速条件下的阻力系数迅速增大，与风速的平方成正比．此结论对于研究高风速下的海浪、风暴潮有着实际意义．     

A Model for the Calculation of Velocity Reduction Behind A Plane Fishing Net

1 .IntroductionOpen oceanaquacultureis becominga newfisheriesindustryasthe human demandfor seafoodin-creases .Consideringthe requirement of environmental protection,thelackof suitable shelteredsitesisforcingfishfarmers to move to more exposed offshore loc…     

Dependence of sea surface drag coefficient on wind-wave parameters

The relationships between sea surface roughness z 0 and wind-wave parameters are analyzed,and spurious self-correlations are found in all of the parameterization schemes.Sea surface drag coefficient C D is fitted by four wind-wave parameters that are wave age,wave steepness,windsea Reynolds number R B and R H ,and the analyzed data are divided into laboratory,field and combined data sets respectively.Comparison and analysis of dependence of C D on wind-wave parameters show that R B can fit the C D most appropriately.Wave age and wave steepness are not suitable to fit C D with a narrow range data set.When the value of wave age has a board range,R H is not suitable to fit C D either.Three relationships between C D and R B are integrated into the bulk algorithm COARE to calculate the observational friction velocity,and the results show that the relationship between C D and R B which is fitted with field data set can describe the momentum transfer in the open ocean,under low-moderate wind speed condition,most appropriately.     

Effect of the drag coefficient on a typhoon wave model

The effect of the drag coefficient on a typhoon wave model is investigated.Drag coefficients for Pingtan Island are derived from the progress of nine typhoons using COARE 3.0 software.The wind parameters are obtained using the Weather Research and Forecasting model.The simulation of wind agrees well with observations.Typhoon wave fields are then simulated using the third-generation wave model SWAN.The wave model includes exponential and linear growths of the wind input,which determine the wave-growth mode.A triple triangular mesh is adopted with spatial resolution as fine as 100 m nearshore.The SWAN model performs better when using the new drag coefficient rather than the original coefficient.     

Wind speed scaling and the drag coefficient

[1]Banner M L, Chen W, Walsh E J, et al.     

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.     

On the parameterization of drag coefficient over sea surface

Six parameterization schemes of roughness or drag coefficient are evaluated on the basis of the data from six experiments. They present great consistency with measurement when friction velocity u*<0.5 m/s (approximately corresponding to 10 m wind speed U10 <12 m/s) and large deviation from measurement when u*≥0.5 m/s (approximately U10≥12 m/s). In order to improve the deviation, a new parameterization of drag coefficient is derived on the basis of the similarity theory, Charnock relationship and Toba 3/2 power law. Wave steepness and wind-sea Reynolds number are considered in the new parameterization. Then it is tested on the basis of the measurements and shows significant improvement when u*≥0.5 m/s. Its standard errors are much smaller than the ones of the other six parameterizations. However, the new parameterization still needs more tests especially for high winds.     

Comparison of Drags on Fish Cages of Different Shapes

1 .Introduction Commercial fishfarming in net cages is becoming widespread around the world as an importantsource of food.In PRChina ,mostfishfarmingtakes placeincalmcoastal areas .Fishcages work wellat these sites becausethe environmental forces are usua…