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。     

不同开口比人工鱼礁体水动力特性及礁体稳定性研究

为研究方型人工鱼礁体开口比的变化对其水动力特性的影响,利用Fluent软件模拟了边长为3m、开口比为0～0.6之间7种不同方型鱼礁体周围水流场,通过分析水流场变化规律得到了礁体流场效应、阻力系数随开口比的变化情况;基于Morison方程计算了礁体在波流作用下的受力及其抗滑移、抗倾覆安全系数。研究结果表明:当礁体开口比小于0.2时,背涡区范围较大,流场效应明显;随着开口比的增大,礁体产生的上升流范围及竖直向最大速度分量逐渐减小;对于方形开口礁体,阻力系数与开口比的关系式为Cd=0.875φ+1.088(R2=0.963,P<0.01);随着开口比的增大,礁体所受最大波流作用力、抗滑移及抗倾覆安全系数逐渐减小,但礁体不会发生滑移和倾覆,可为实际礁体结构的设计提供参考。     

圆筒型鱼礁体纵横布设间距下的水动力特性研究

应用计算流体力学(Computational Fluid Dynamics,CFD)软件数值计算了圆筒型人工鱼礁体在不同纵向和横向布设间距下的水动力特性,实测了圆筒型人工鱼礁体在纵向布设间距1.0L和2.0L (L为礁体长度)下的流场及受力特性,验证了物理模型实验中各个测点的流速值和阻力值,计算值与实验值吻合较好.研究...     

小型单拖网渔船V 型网板水动力性能研究

网板是拖网的重要属具之一, 广泛应用于近岸小型单拖渔船的生产作业中, 其水动力性能的优劣直接关系到拖网的生产效果和经济效益。作者以网板面积1 m²、展弦比0.55的 V 型网板为例进行小型单拖渔船的水动力性能研究。 基于田内相似准则, 相似比为2制作网板模型, 进行循环水槽模型试验, 实验冲角在10～60°范围内, 来流速度在0.2～0.7 m/s, 得出网板升阻力系数等流体动力特性曲线、临界冲角、最大升阻比。结果表明, 该型网板的最大升阻比约为1.86, 达到最大升阻比的临界冲角在15～25°附近, 该结果可为渔业生产操作中网板冲角的设置提供依据。实验结果同时显示, 该型网板的水动力效率略低于其他类型网板, 说明其板型仍有较大的改进空间。     

新型动力安装锚水动力学特性模型试验研究

相比于已有动力锚(鱼雷锚、多向受荷锚等),新型轻质动力安装锚借助助推器安装,具有质量轻、埋深大、承载效率高、在海床中下潜容易等特点。良好的水动力学特性(较小的拖曳阻力系数及稳定的下落垂直度)是确保动力安装锚准确、有效地安装到指定地点并贯入到设计深度的前提。通过4组10个工况的模型试验,研究了轻质动力安装锚的终端速度和拖曳阻力系数,及轻质动力安装锚和助推器的组合锚在水中自由下落时的方向稳定性。试验结果表明:优化后轻质动力安装锚的拖曳阻力系数为0.51~0.55,这有助于提高组合锚在水中的下落速度,从而提升组合锚的沉贯深度;增大助推器尾翼展弦比和选用轻质材料制作尾翼能减小组合锚的下落偏角,提高组合锚的方向稳定性。     

平面无结节网衣水阻力系数的试验研究

通过物理模型试验,统计分析得到了无结节网衣的水阻力系数在不同状态下随雷诺数、倾角和布置状态的变化规律,并通过网衣沉子的组合试验验证了所得经验公式的正确性和适用性,为深水网箱等渔具的水动力计算提供了依据.     

不同倒角半径下方柱绕流的数值模拟及水动力特性研究

为了研究不同倒角半径对方柱绕流特性的影响,采用有限体积法,模拟了雷诺数Re为22 500、倒角半径为0.1D(D为方柱边长的长度)、0.2D和0.3D时方柱的绕流过程。方柱近壁面采用增强壁面函数,模型采用SST k–?湍流模型。根据模拟结果给出了不同倒角半径下方柱的流场涡量图以及阻力系数Cd和升力系数Cl;利用快速傅里叶变换法得到斯托罗哈数St。结果表明,倒角半径的增加改变了方柱的分离点,使得尾流区长度增加,旋涡尺度减小;Cd和Cl的振动幅值呈现先减小后增大的趋势,倒角半径为0.1D和0.2D时方柱受力较小,不存在倒角时方柱受力较大,倒角半径为0.3D时方柱受力最大;随着倒角半径的增加,柱体截面形式越接近圆形,斯托罗哈数逐渐增大,漩涡脱落频率更快。     

不同布设间距下梯形台人工鱼礁体的水动力特性研究

为研究空心梯形台人工鱼礁体布设间距的变化对其水动力特性的影响,通过物模实验实测了开口比为0.1的梯形台人工鱼礁体在平行水流方向布设间距为1.0L、2.0L、3.0L(L为礁体的底边边长),前后共6个测点的流速及礁体受力。分析得到了双礁体的上升流规模、阻力系数在平行和垂直水流方向随布设间距变化的规律。采用计算流体动力学(Computational Fluid Dynamics, CFD)方法模拟了双礁体分别在垂直水流方向布设间距为0.5L、1.0L、1.5L、2.0L,平行水流方向布设间距为0.5L、1.0L、2.0L、3.0L、4.0L时的水动力场。结果表明:本研究数模与物模相同工况下,即双礁体在平行水流方向布设间距1.0L、2.0L、3.0L时,数值模拟的流速值和阻力值与相应的实验结果吻合较好,说明数值模拟方法可行,结果可靠。数值模拟结果得到双礁体的上升流规模、阻力系数均与垂直水流方向布设间距成反比。当垂直水流方向布设间距为0.5L时,流场效应最佳;双礁体的上升流规模随平行水流方向布设间距成正比,前方礁体阻力系数变化幅度较小,后方礁体阻力系数逐渐增大;当平行水流方向布设间距为4.0L...     

钱塘江古海塘水动力作用试验研究

通过古海塘原型资料调查得出古海塘现状以及存在的问题,结合历年水文资料的调研和现场水体运动形式的观测,获得荷载形式,通过波浪槽在模型比尺试验的基础上对钱塘江古海塘水动力作用进行室内模拟。试验结果验证了利用规则波模拟水动力荷载的可行性,并得出波浪对塘体的作用力受波高和波浪破碎情况的影响,波高相同时破碎点越接近海塘,破碎作用力越大;波高越大,波浪-塘体-土体相互作用越强,塘下土体中产生较大的瞬时孔隙水压力并产生孔压的累积;塘体前趾和后趾出现应力集中现象,周期1.5 s波高0.2 m时前趾压力增大后趾压力减小。     

方型人工鱼礁水动力性能试验研究

人工鱼礁水动力性能的研究对于鱼礁的设计、礁区布局具有非常重要的意义。本研究设计2种方型人工鱼礁模型,在回流水槽中测量不同水流速度下的鱼礁阻力,并计算阻力系数(Cd)与雷诺数(Re)。结果表明:无盖礁体模型正面迎流时(θ=0(°)),当Re超过7.5×104时,Cd为1.64,其自动模型区域为Re>7.5×104;45(°)方向(θ=45(°))迎流时,当Re超过6.36×104时,Cd为1.3,其自动模型区域为Re>6.36×104。有盖礁体模型正面迎流时,当Re超过6×104时,Cd为1.69,其自动模型区域为Re>6×104;45(°)方向迎流时,当Re超过8.48×104时,Cd为1.43,其自动模型区域为Re>8.5×104。1种礁体模型在不同迎流方式下所受的阻力不同,45(°)方向迎流比正面迎流时的阻力大。在相同的迎流方式下,有盖礁体所受的阻力比无盖礁体大。     

Experimental analysis of the hydrodynamic force on the net panel in wave

The hydrodynamic force on net panels in waves plays a significant role in the wave-resistant design of net cages in the open sea. To investigate the hydrodynamic force on net panels in waves, a series of experiments about different types of net panels in waves were conducted in a wave flume. The effects of the net solidity, the net material and the knot pattern were experimentally analyzed in this study. A wave force model for the net panel was proposed based on the hydrodynamics of cylinder in waves. The experimental results indicated that the horizontal force on the net panel in waves was larger than the vertical force, and the horizontal force was heavily depended on the KC number; In addition, the horizontal force on the steel net was smaller than that on the nylon net, and the knot pattern had a negligible influence on the hydrodynamic force on the net panel in waves. The model was also compared with existing experimental measurements and previous numerical results. The comparison results indicated that the wave force model could calculate the wave force on the net panel accurately.     

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.     

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…     

Treatment of Hydrodynamic Loading for Random Sea State

- In order to employ cost effective frequency domain analysis for off-shore structures treatment of hydrodynamic loading is essential. Drag and inertia dominated, resonating and antiresonating cases under random sea states are analyzed to highlight the implications and relative merits of four salient linearization techniques.     

Normalization of Hydrodynamic Coefficients in Morison Equation

-The hydrodynamic coefficients C_d and C_m are not only dependent on the size of slender cylin-der,its location in water,KC number and Re number,but also vary with environmental conditions,i.e.,in regular waves or in irregular waves,in pure waves or in wave-current coexisting field.In this paper,thenormalization of hydrodynamic coefficients for various environmental conditions is discussed.When aproper definition of KC number and proper characteristic values of irregular waves are used,a unified re-lationship between C_d,C_m and KC number for regular waves,irregular waves,pure waves and wave-cur-rent coexisting field can be obtained.     

Hydrodynamic coefficients of a harmonically oscillated tower

A tower hinged at the bottom was oscillated mechanically in a sinusoidal fashion in a plane in still water. An instrumented section in the tower measured the inline and transverse forces locally on the tower due to the hydrodynamic effects. These forces are analyzed for the added mass, drag and lift coefficients which are presented as functions of Keulegan-Carpenter and Reynolds number. The lift force frequencies are also investigated. The measured overall reactions on the tower are used to verify the values of the local coefficients. The results presented here are not only applicable to articulated towers but to other moving elements of an offshore structure, e.g. risers, tension-legs, etc.