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。     

自动返回式采水器的阻力系数计算与方法验证

摘要：应用有限元软件ANSYS,以与采水器外壳接触的周围水域为研究区域,计算其总阻力系数及最大运动速度。采用相同的数值方法计算了圆球总阻力系数,计算结果与经典实验结论吻合良好,证明了该数值方法的准确性。利用ANSYS软件计算预报采水器或其他类似的海洋仪器在流体中的阻力系数,可指导其尺寸参数设计。     

海面阻力系数与白浪覆盖率的关系

基于海上平均风速廓线和白浪覆盖率的同步测量结果,首次建立海面阻力系数C_(10)与白浪覆盖率W_c的经验关系式为C_(10)×10~3=4.13W_c~(0.255)。将此关系式与Garratt和Wu的海面阻力系数与平均风速关系式作了间接比较,符合良好。还就此关系式对海面阻力系数的变化以及此关系式在海洋遥感中的意义作了讨论。     

南海水下生产系统防沉板基础裙板贯入模拟试验与入泥阻力计算

防沉板基础裙板入泥阻力计算和长度设计是海洋工程水下生产系统基础设计的关键,基于南海番禺和荔湾地区水下防沉板基础裙板贯入模拟试验,验证了Lunne和Eide等建立的裙板入泥阻力经验计算方法对南海水下生产系统防沉板裙板设计的可靠性,确定了南海地区裙板入泥的端部阻力系数(0.320～0.360)和侧摩阻力系数(0.008～0.014 5),为南海水下生产系统防沉板基础裙板入泥阻力计算和裙板长度设计提供了依据,确保了南海地区水下生产系统的顺利安装。在工程地质调查时,既可以进行土壤钻孔取样并与已开展裙板贯入模拟试验的番禺和荔湾地区土壤组成和粒度对比,也可开展静力触探试验或裙板贯入模拟试验,得到裙板入泥的端部阻力系数和侧摩阻力系数。     

水下圆形截面缆索的流体动力性能的理论计算及试验研究

本文对锚索及水下拖索的阻力、性状及其计算问题进行了初步的探讨,得出了计算均流中圆形截面揽索的阻力、阻力系数、张力以及缆索形状的公式,并根据这些公式编制了计算机程序,同时运用此程序对水下拖索的实例进行了计算。另外,对各种不同流态、不同倾角下的圆形截面缆索、带整流扳缆索以及流线型截面缆索做了风洞试验,并将试验所得的阻力系数与本文导出的理论公式计算所得的阻力系数进行了比较,结果两者符合较好。     

湍流场多柱体绕流形态和水动力特性研究

为研究间距比对多柱体在湍流场下的互扰效应影响,利用Fluent软件模拟了雷诺数为3 900,柱间距比L/D为1.6~6.0情况下正方形排列四圆柱绕流过程。通过模拟得到了不同间距比下的升、阻力系数值以及涡量图,利用快速傅里叶变换法得到了漩涡脱落频率。结果表明,当柱间距比L/D为1.6~2时,4个圆柱后都没有漩涡脱落,随间距比增加,上游圆柱平均升力系数增大,平均阻力系数减小,下游圆柱平均升、阻力系数减小,斯特鲁哈数增大;当L/D为2~3.5时,随间距比增大,下游圆柱后开始出现漩涡脱落,平均升、阻力系数减小,斯特鲁哈数增大;当L/D为3.5~6时,随间距比增大,四个圆柱后都发生漩涡脱落,上游圆柱平均升、阻力系数减小,下游圆柱平均升力系数减小,平均阻力系数增大,斯特鲁哈数不变。L/D3.5时互扰效应逐渐增强,L/D3.5时互扰效应逐渐减弱;考虑到工程安全性和经济性,本文研究成果对于海洋工程设计具有一定的参考价值。     

人工鱼礁礁体模型阻力系数的实验研究

针对不同中心开口方式(圆孔、三角孔、方孔)的正方体人工鱼礁模型,通过风洞实验,定量探讨礁体的通透开口比、投影开口比与阻力系数之间的关系,测量模型礁体在不同角度迎流时的阻力系数。实验结果表明礁体阻力系数Cd随投影开口比γty的增加而呈下降趋势。当投影开口比γty相同且大于0.1时,阻力系数Cd随通透开口比γtt的增加而呈下降趋势。对于中心开孔方式人工鱼礁,阻力系数Cd计算公式为:Cd=-0.861γtt+0.145γty+1.268(R2=0.729,P<0.01)。回字型和正方体型人工鱼礁模型的实测值与理论公式计算值误差在8%以内,说明理论公式计算值是可靠的。在进行新礁体设计时,可以通过调整礁体开口尺寸,使礁体在满足集鱼、改善流场功效的同时,具有良好的水动力特性。     

NMOHEMS探头外形对其下沉运动的影响分析

NMOHEMS 探头是一种由无人机运载的小型投掷式探头,采用混合网格技术结合湍流模型,建立了探头下沉运动的数值计算方法,分析了导流腔、收缩段及尾翼对探头下沉运动的影响;通过6种外形探头在不同雷诺数下的阻力系数和相同质量下的极限速度对比,发现探头外形对其下沉运动数值计算的结果影响较大;其中导流腔和收缩段均具有明显的减阻作用,且收缩段的影响更大,而尾翼具有一定的增阻作用;lgRe 在2.3~3.8时,6种外形探头的阻力系数差别较大,随着雷诺数的增加,阻力系数均迅速减小;lgRe 在3.8~5.1时,6者的阻力系数比较接近,虽仍然保持减小趋势,但变化趋于缓慢.NMOHEMS 探头的体型较小,下沉速度较慢,对其下沉运动进行数值计算时,必须考虑外形对数值计算结果的影响.     

一种船载海面通量观测的校正方法

设计了一种用滤波法校正船载超声测风测量仪数据、计算海－气通量交换的方法。对１９８８，１９８９两年西太平洋海域考察期间超声测风测温仪的实测资料作了订正，订正了船体运动、特别是摇摆运动对风速的影响，用涡旋相关法计算了海面边界层的感热能量、动量通量、阻力系数和稳定度值。分析了海面上能量、阻力系数随大气状况的变化规律。计算结果表明，海面上的通量、阻力系数与水平风速和稳定度之间存在着合理的有规律的关系，证明     

不同攻角下投弃式海流剖面仪流体动力特性研究

对投弃式海流剖面仪(eXpendable Current Profiler,XCP)不同攻角下流体动力特性进行数值模拟,分析了XCP探头流场压力分布与运动趋势的关系.研究了不同攻角下XCP探头阻力系数和升力系数的变化规律.研究表明,攻角能够明显改变流场的轴对称性.0°～10°攻角下,XCP探头阻力系数和升力系数随攻角增...     

Robust design of microbubble drag reduction in a channel flow using the Taguchi method

This study attempts to obtain optimum parametric levels for robust design of the microbubble drag reduction in a turbulent channel flow. This work was carried out experimentally by measuring the frictional resistance on the upper wall of the channel to analyze the efficiency of drag reduction. Considering the mean flow speed as an indicative factor, several controllable factors that influence the effect of microbubble drag reduction were investigated in this work by using the Taguchi method. The controllable factors in this study were the amount of air injected, area of air injection, and microbubble size. For the condition of optimum parametric levels, the effect of drag reduced could reach up to 21.6%.     

SWAN模型中不同风拖曳力系数对风浪模拟的影响

本文以荷兰哈灵水道海域为实验区域,通过敏感性实验,研究了在14 m/s、31.5 m/s和50 m/s（分别代表一般大风、强热带风暴和强台风的极端条件）定常风速下SWAN模型中不同风拖曳力系数对风浪模拟的影响程度。结果表明,对于近岸浅水区域（水深小于20 m）,风拖曳力系数计算方案的选择对有效波高影响较小,而且当风速增加到一定程度后,波浪破碎成为影响波高值的主要因素;对于深水区域（水深大于30 m）,一般大风条件下风拖曳力系数计算方案的选择对有效波高影响仍然较小,随着风速的继续增大,风拖曳力系数计算方案的选择对有效波高的影响逐渐显著。对于平均周期,风拖曳力系数计算方案的选择和风速的改变对其影响均较小,而由水深变浅导致的波浪破碎对其影响较为显著。根据敏感性实验结果,本文对SWAN模型中风拖曳力系数计算方案的选择做出如下建议:计算近岸浅水区域风浪场或深水区域一般大风条件风浪场时,其风拖曳力系数可以直接采用模型默认选项;而对于深水区域更大风速条件,可首先采用模型默认选项试算,然后结合当地海域实测波浪资料进行修正。     

波浪非线性对海草消波特性的影响

海草所形成的植物消波体系能有效防止岸线的侵蚀。利用Sánchez-González等的实验数据分析了波浪非线性对海草消波特性的影响。研究结果表明,相对水深和波陡对海草床的波能衰减系数影响依赖于海草淹没度。相对波高一定时,拖曳力系数随相对水深的增大而增大。对给定的相对水深,拖曳力系数随波陡的增大而减小。波浪非线性对于规则波和非规则波海草消波特性的影响并不一致。用无量纲参数（邱卡数、雷诺数、厄塞尔数）表达拖曳力系数的效果取决于拖曳力系数与无量纲参数的关系中是否充分考虑波浪非线性对拖曳力系数的影响。     

The influence of turbulence on drag

The use of the Reynolds number as the only correlating factor for drag force measurements may be inadequate in circumstances involving highly turbulent flows. The results of previous investigations relating to the effects of turbulence scale and intensity are examined. Of special interest is the possibility of a drag minimum, even at low Reynolds number, for a free-stream turbulence intensity of about 5%. This appears to be the result of interaction between the free stream and the boundary layer. As intensity increases beyond 5%, the minimum may be succeeded by an increase in drag to values exceeding the laminar flow values. Further elucidation of the subject is required, particularly because of its importance in various problems related to geophysical flows.     

引入拖曳系数参数化的海冰自由漂流模拟研究

Many interesting characteristics of sea ice drift depend on the atmospheric drag coefficient(C_a) and oceanic drag coefficient(C_w).Parameterizations of drag coefficients rather than constant values provide us a way to look insight into the dependence of these characteristics on sea ice conditions.In the present study,the parameterized ice drag coefficients are included into a free-drift sea ice dynamic model,and the wind factor α and the deflection angle θ between sea ice drift and wind velocity as well as the ratio of C_a to C_w are studied to investigate their dependence on the impact factors such as local drag coefficients,floe and ridge geometry.The results reveal that in an idealized steady ocean,C_a/C_w increases obviously with the increasing ice concentration for small ice floes in the marginal ice zone,while it remains at a steady level(0.2-0.25) for large floes in the central ice zone.The wind factor α increases rapidly at first and approaches a steady level of 0.018 when A is greater than 20%.And the deflection angle θ drops rapidly from an initial value of approximate 80° and decreases slowly as A is greater than20%without a steady level like α.The values of these parameters agree well with the previously reported observations in Arctic.The ridging intensity is an important parameter to determine the dominant contribution of the ratio of skin friction drag coefficient(C_s' /C_s) and the ratio of ridge form drag coefficient(C_r'/C_r) to the value of C_a/C_w,α,and θ,because of the dominance of ridge form drag for large ridging intensity and skin friction for small ridging intensity among the total drag forces.Parameterization of sea ice drag coefficients has the potential to be embedded into ice dynamic models to better account for the variability of sea ice in the transient Arctic Ocean.     

A rapid assessment method for calculating the drag coefficient in wave attenuation by vegetation

Vegetation in wetlands is a large-scale nature-based resource that can provide multiple benefits to human beings and the environment,such as wave attenuation in coastal zones.Traditionally,there are two main calibration approaches to calculate the attenuation of wave driven by vegetation.The first method is a straightforward one based on the exponential attenuation of wave height in the direction of wave transmission,which,however,overlooks the crucial drag coefficient (C_D).The other method is in accordance with more complicate equations for predicting the damping factor,which is regarded as a function of C_D.In this study,a new relation,combining these above two conventional approaches,is proposed to predict the C_D in an operative approach.Results show that values yielded by the new assessment method perform a strong linear relationship with a collection of historical observations,with a promising R~2 value of 0.90.Besides,the linear regression derives a new predictive equation for the bulk drag coefficient.Additionally,a calibrated value of 4 for the empirical plant drag coefficient(C_P) is revealed.Overall,this new equation,with the superiority of the convenient exponential regression,is expected to be a rapid assessment method for calculating wave attenuation by vegetation and predicting the drag coefficient.     

The accuracy of surface elevations in forward global barotropic and baroclinic tide models

This paper examines the accuracy of surface elevations in a forward global numerical model of 10 tidal constituents. Both one-layer and two-layer simulations are performed. As far as the authors are aware, the two-layer simulations and the simulations in a companion paper (Deep-Sea Research II, 51 (2004) 3043) represent the first published global numerical solutions for baroclinic tides. Self-consistent forward solutions for the global tide are achieved with a convergent iteration procedure for the self-attraction and loading term. Energies are too large, and elevation accuracies are poor, unless substantial abyssal drag is present. Reasonably accurate tidal elevations can be obtained with a spatially uniform bulk drag c_d or horizontal viscosity K_H, but only if these are inordinately large. More plausible schemes concentrate drag over rough topography. The topographic drag scheme used here is based on an exact analytical solution for arbitrary small-amplitude terrain, and supplemented by dimensional analysis to account for drag due to flow-splitting and low-level turbulence as well as that due to breaking of radiating waves. The scheme is augmented by a multiplicative factor tuned to minimize elevation discrepancies with respect to the TOPEX/POSEIDON (T/P)-constrained GOT99.2 model. The multiplicative factor may account for undersampled small spatial scales in bathymetric datasets. An optimally tuned multi-constituent one-layer simulation has an RMS elevation discrepancy of 9.54 cm with respect to GOT99.2, in waters deeper than 1000 m and over latitudes covered by T/P (66N to 66S). The surface elevation discrepancy decreases to 8.90 cm (92 percent of the height variance captured) in the optimally tuned two-layer solution. The improvement in accuracy is not due to the direct surface elevation signature of internal tides, which is of small amplitude, but to a shift in the barotropic tide induced by baroclinicity. Elevations are also more accurate in the two-layer model when pelagic tide gauges are used as the benchmark, and when the T/P-constrained TPXO6.2 model is used as a benchmark in deep waters south of 66S. For Antarctic diurnal tides, the improvement in forward model elevation accuracy with baroclinicity is substantial. The optimal multiplicative factor in the two-layer case is nearly the same as in the one-layer case, against initial expectations that the explicit resolution of low-mode conversion would allow less parameterized drag. In the optimally tuned two-layer M₂ solution, local values of the ratio of temporally averaged squared upper layer speed to squared lower layer speed often exceed 10.     

Impact of parameterized lee wave drag on the energy budget of an eddying global ocean model

The impact of parameterized topographic internal lee wave drag on the input and output terms in the total mechanical energy budget of a hybrid coordinate high-resolution global ocean general circulation model forced by winds and air-sea buoyancy fluxes is examined here. Wave drag, which parameterizes the generation of internal lee waves arising from geostrophic flow impinging upon rough topography, is included in the prognostic model, ensuring that abyssal currents and stratification in the model are affected by the wave drag.An inline mechanical (kinetic plus gravitational potential) energy budget including four dissipative terms (parameterized topographic internal lee wave drag, quadratic bottom boundary layer drag, vertical eddy viscosity, and horizontal eddy viscosity) demonstrates that wave drag dissipates less energy in the model than a diagnostic (offline) estimate would suggest, due to reductions in both the abyssal currents and stratification. The equator experiences the largest reduction in energy dissipation associated with wave drag in inline versus offline estimates. Quadratic bottom drag is the energy sink most affected globally by the presence of wave drag in the model; other energy sinks are substantially affected locally, but not in their global integrals. It is suggested that wave drag cannot be mimicked by artificially increasing the quadratic bottom drag because the energy dissipation rates associated with bottom drag are not spatially correlated with those associated with wave drag where the latter are small. Additionally, in contrast to bottom drag, wave drag is a non-local energy sink.All four aforementioned dissipative terms contribute substantially to the total energy dissipation rate of about one terawatt. The partial time derivative of potential energy (non-zero since the isopycnal depths have a long adjustment time), the surface advective fluxes of potential energy, the rate of change of potential energy due to diffusive mass fluxes, and the conversion between internal energy and potential energy also play a non-negligible role in the total mechanical energy budget. Reasons for the <10% total mechanical energy budget imbalance are discussed.     

Influence of Kinematic Analysis Parameters of Drag Anchor Trajectory Prediction Using Yield Envelope Method

Drag anchor is widely applied in offshore engineering for offshore mooring systems. The prediction of the invisible trajectory during its drag-in installation is challenging for anchor design in determining the anchor final position for ensuring sufficient holding capacity. The yield envelope method based on deep anchor failure for kinematic analysis was proposed as a promising trajectory prediction method for drag anchor. However, there is a lack of analysis on the effects of the parameters applied in the kinematic analysis. The current work studies the effects of the yield envelope parameters, anchor line bearing capacity factor and the anchor/soil interface friction. It is found that the accuracy of the yield envelope parameters has large impact on the prediction results based on deep yield envelopes.Analyses of cases with smooth fluke predict deeper embedment depth than that from analyses of cases with rough fluke. The decrease of the capacity factor results in the increase of the anchor embedment depth, the anchor line load,the anchor chain angle and the stable value of the normalized horizontal load component for the same drag length,while the stable value of the normalized vertical load component decreases when the capacity factor decreases. This illustrates the importance in applying reasonable parameters and improving the method for more reliable prediction of the anchor trajectory.     

拖曳锚在海床中运动特性的大变形有限元分析

拖曳锚由于其承载性能和深水中便于安装被广泛应用于海洋工程系泊系统中,如:适用于悬链式系泊系统的传统拖曳锚和适用于绷紧式系泊系统的法向承力锚。拖曳锚安装过程中涉及诸多运动特性:锚板运动方向、系缆点处拖曳力和拖曳角及运动轨迹。基于大变形有限元分析技术耦合的欧拉-拉格朗日法,并引入缆绳方程,建立起锚-缆绳-海床土耦合作用的有限元分析模型;模拟了拖曳锚在均质和线性强度黏土中的嵌入安装过程,研究了锚板运动方向、系缆点处拖曳力和拖曳角及运动轨迹等运动特性;通过与已有的有限元分析方法及理论方法进行对比,验证了该分析模型的有效性;与已有的有限元分析方法相比,提出的分析模型有效地提高了计算效率。