带横隔板圆柱绕流特性数值模拟   总被引：1，自引：0，他引：1       下载免费PDF全文

水庆象  王大国  王伟 《水科学进展》2016,27(4):586-593

为揭示尾迹区添加横隔板对圆柱绕流流场特性影响,把多步格式引入到特征线算子分裂有限元法中,建立了基于多步格式的特征线算子分裂有限元法:在每个时间步内将Navier-Stokes方程分裂成对流项和扩散项,对流项时间离散采用多步格式,在每一子时间步内沿特征线展开并显式求解。方腔流数值模拟结果表明该算法既可降低对整体时间步长的要求又可提高计算精度。对比有无横隔板圆柱绕流流场和圆柱表面压力变化表明,横隔板可以有效地抑制绕流尾迹区涡旋脱落,提高圆柱背流面压力,减少圆柱上下表面的压力差。  相似文献   

Variation of Flow Field Around Twin Cylinders with and Without the Outer Perforated Cylinder ? Numerical Study     

Chandrasekaran SRINIVASAN  N. MADHAVI 《海洋工程》2016,(5):763-771

Presence of the outer perforated cylinder reduces the direct wave impact on the inner cylinder, which has been testified by many researchers. However, the force reduction mechanism, which is complicated due to the wave-porous structure interaction, needs to be addressed in detail. The present study explains the mechanism with the aid of the computational fluid dynamics (CFD) tool STAR CCM+. This package is chosen for its capabilities to simulate viscous and turbulence effects caused by passage of waves. For the present study, flow fields around the twin cylinders with different orientations are examined with and without the outer perforated cover. Mechanism contributing to the reduction of force on the existing structure is explained in physical terms, and force reduction is quantified. The present study has direct application in the retrofitting application of offshore members.  相似文献   

多圆环柱域上解析函数边值问题再论     

王莉萍 《中国海洋大学学报(自然科学版)》2001,31(2):293-296

讨论多圆环柱域上多个复变量的解析函数的一般形式的 Riemann- Hilbert边值问题。通过函数的解析变换 ,导出了解析函数一般形式的 Riemann- Hilbert边值问题的可解性 ,并给出了解的积分表达式。  相似文献   

In-line force on a cylinder translating in oscillatory flow   总被引：2，自引：0，他引：2  

T. Sarpkaya  M. Storm 《Applied Ocean Research》1985,7(4):188-196

Experiments were conducted with smooth and sand-roughened cylinders moving with constant velocity in a sinusoidally oscillating flow to determine the drag and inertia coefficients and to examine the effect of wake biasing on the modified Morison equation. The various flow parameters such as the relative cylinder velocity. Reynolds number, and the Keulegan-Carpenter number were varied systematically and the in-line force measured simultaneously. The principal results, equally valid for both smooth and rough cylinders, are as follows: the drag coefficient decreases with increasing relative current for a given Reynolds number and Keulegan-Carpenter number; the effect of wake biasing on the drag and inertia coefficients is most pronounced in the drag-inertia dominated regime; and the two-term Morison equation with force coefficients obtained under no-current conditions is not applicable to the prediction of wave and current induced loads on circular cylinders.  相似文献   

Analysis of single and tandem cylinder data using an orthogonal Volterra model approach     

I.A. Sibetheros  J.M. Niedzwecki   《Ocean Engineering》2005,32(2):881-156

The development of a definitive predictive model that accurately accounts for the nonlinear hydrodynamics and structural response behavior observed in arrays of closely spaced risers on deep water structures will require a more detailed understanding of this fluid–structure interaction. Through the analysis and interpretation of data from model basin tests on single and paired tandem cylinder configurations this study is directed at uncovering the nature of some aspects of this nonlinear response behavior using an orthogonal third-order Volterra technique that can delineate between linear, quadratic and cubic nonlinear frequency dependent behavior. As part of the analysis procedure the data was organized in input–output pairs that would provide logical groupings of the measured quantities. The data pairs presented in this study include wave excitation and inline cylinder displacement, wave excitation and transverse cylinder displacement, wave excitation and inline reaction force, and, upstream cylinder and downstream cylinder response. This information is presented in terms of spectral and coherence plots. The single cylinder data is presented as a means to contrast the behavior of the tandem cylinders. Both configurations were analyzed at two different pretensions adding another dimension to this investigation. It is shown that although a primary variable such as displacement may be more easily measured, pretension and force measurements provide an important key to our understanding of this difficult problem.  相似文献   

Wave–current interaction with a vertical square cylinder     

Pengzhi Lin  C. W. Li   《Ocean Engineering》2003,30(7):855-876

A three-dimensional numerical model is developed in this study to investigate the problem of wave–current–body interaction. The model solves the spatially averaged Navier–Stokes equations. Turbulence effects are modeled by a subgrid-scale (SGS) model using the concept of large eddy simulation (LES). The model is employed to study the wave–current interaction with a square cylinder that is mounted on the bottom and vertically pierces the free surface. The force analysis demonstrates that the presence of waves can reduce both the strength and frequency of vortex shedding induced by a uniform current due to the nonlinear wave–current interaction. The free surface elevation, strain rates of the mean flow, and eddy viscosity are found to closely correlate with the mechanism of vortex shedding. It is also shown that when the vortex shedding is neglected in the calculation such as by the potential flow approach, one may significantly underestimate the magnitude of in-line force. The energy spectral analysis reveals that there exist initiating, growing, and decaying regions for shedding vortices around the cylinder. In the vortex initiating region, both coherent and turbulent structures are nearly two-dimensional that become three-dimensional in the vortex growing region. The kinetic energy of both coherent and turbulent motions is dissipated in the vortex decaying region, within which the mean flow gradually returns back to two-dimensional.  相似文献   

Coupled BEM-FEM Analysis of the Large-Diameter Cylinder Structure System   总被引：2，自引：0，他引：2  

Zhou Xireng  Duan Xudong  Sang Xuezhu Zhang Rui  Dai Jialu Professor  Tianjin University  Tianjin Engineer  Xiamen Port Office  Fujian Lecturer  Tianjin University  Tianjin Senior Engineer  Tianjin Port Office  Tianjin 《中国海洋工程》1992,(2)

A method of coupled BEM-FEM analysis for the elastic spatial structure system is presented. It can be applied to the calculation of the stress and deformation of the large-diamater cylinder structure system and it is suitable for symmetric or non-symmetric structures under the distributed or concentrated load. Numerical examples show that the proposed method and computer program BEFEM are quite efficient in the analysis of the large-diameter cylinder structure problems in ocean engineering.  相似文献   

A Study of Lift Force and Instantaneous Velocity Field Around an Oscillating Circular Cylinder     

C.A.Greated 《中国海洋工程》1997,(4)

-Force measurements of oscillatory flow acting on a single circular cylinder have been carriedout.The experiments were done by oscillating a circular cylinder in still water.Instantaneous forces and ve-locity fields around the cylinder were measured by Particle Image Velocimetry(PIV).The Keulegan-Car-penter number(KC)varied in the range from 5 to 20 and the viscous parameter β=Re/KC was set at500(Re is Reynolds number).It was found that the strength and frequency of the lift force increased withKC number,the main frequency of the lift force being three times the frequency of the oscillatory flow atKC=20.The movement and strength of the vortices around the cylinder are discussed for differentKC numbers.  相似文献   

Experimental study of forces on a cylinder in oscillatory flow with a cross current     

P.K. Stansby  N. El-Khairy  G.N. Bullock 《Applied Ocean Research》1983,5(4):195-203

Forces on a circular cylinder have been measured with nominally two-dimensional current and oscillatory flow at right angles. Previous results for purely oscillatory flow defined by a Keulegan-Carpenter number, Kc, have been extended for reduced velocities, Vr, in the range 3–10. For Kc<7 modification of the Karman street by oscillation is complex and locking-on has a dominant influence. For Kc > 7 simply adding forces due to the current and oscillation as though in isolation generally gives conservative results. The ‘current’ drag shows considerable variation and can even be negative. The Morison fit to the in-line force is generally less satisfactory when there is a current and can be wholly inadequate.  相似文献   

紧密角管藻雄配子的超微结构     

王团老  林均民  胡韧  杨听林  谢宏 《台湾海峡》2001,20(1):61-65,T003,T004

紧密角管藻精子发生是由精母细胞减数分裂产生双鞭毛体，然后双鞭毛体分裂形成单裂毛的精子。精子鞭毛器的结构包括鞭毛轴丝和集体，鞭毛轴丝含有9对二联体组成的周位微管，但无中央微管，属于“9＋0”微管构型，基体靠近细胞核，由9对二联体周位微管和中央结构组成“车轮”状结构，在过渡区存在基板，精原细胞、双鞭毛体和精子的细胞器组成及结构与营养细胞相似，在生殖细胞中未发现高尔基体，却存在电子致密体。  相似文献