共查询到20条相似文献，搜索用时 125 毫秒
1.
方柱水动力系数确定方法的探讨 总被引：2，自引：0，他引：2
方柱的绕流和圆柱的绕流有着明显的不同，在确定其水动力系数时如何选用波浪理论，以何种方法分析水动力系数较为适当是首先要解决的问题。本文基于实验资料对这二个问题进行了分析论证。结果认为选用线性 波理论较为简单和适用，在正向力系数的时域分以最小二乘法为最佳，在频域分析中修正互谱法所得的正向力系数与重新定义的Kc数具有良好的相关关系。 相似文献
2.
不同排列方式和间隙比下双圆柱流致振动特性研究 总被引：1，自引：0，他引：1
采用基于ALE的流固耦合分析方法,将圆柱体振动模型简化为平面双自由度质量-弹簧-阻尼系统,进行了计算参数无关性分析。对不同θ角和间隙比T下的双圆柱流致振动进行数值模拟,并与单圆柱振动计算结果进行比较,得到了不同θ角和间隙比T下中心圆柱的升阻力系数、流场分布和运动轨迹变化情况。通过分析发现小间隙比下由于两圆柱间的相互干扰,改变了中心圆柱的尾涡结构,导致了升力和阻力系数随不同θ角而发生变化;小间隙比下由于两圆柱间的相互干扰影响,均使中心圆柱的轨迹在不同θ角下发生了较大的变化,顺流向的振动频率与单圆柱振动时相比出现了多倍频,导致其运动轨迹发生了变化。 相似文献
3.
固壁附近水平圆柱在波浪水流共存场中的流动显示及水动力特征 总被引：3，自引：0，他引：3
固壁附近的水平的圆柱体在波浪、波流作用下的受力情况与其周围的流场状态密切相关。为探讨圆柱形成的机理，应当对流场的涡结构有充分的认识，受力过程与记演化过程的同步分析万为重要。本文通过实验研究并对比数值分析的结果，对波浪、波流场中圆柱体受力与流场状态的关系做一初步讨论。 相似文献
4.
并列圆柱体在均匀流场中的涡激振动十分复杂，但又广泛存在于实际工程之中。当两柱在流体激励作用下产生振动时，由于同时存在着流固耦合作用和柱间干扰作用，而使周围流场变得更加复杂。本文对并列刚性和弹性圆柱的流场分类，Ｓｔｒｏｕｈａｌ数及流体载荷等问题进行了综述，在此基础上提出了进一步研究的建议。 相似文献
5.
波浪对海底管线作用的物理模型实验及数值模拟研究 总被引：7，自引：0，他引：7
利用物理模型实验，测量了海底管线在波浪作用下的水平力和升力，并应用Ｍｏｒｉｓｏｎ方程及流函数理论，按最小二乘原理得出ＣＤ和ＣＭ以及ＣＬ，讨论了它们与ＫＣ，Ｒｅ之间隙比ｅ／Ｄ的关系。本文带应用边界拟合坐标及二维流场的大涡模拟法，模拟了与实验相同工况下海底管线的受力及流场情况，并把物理模型实验和数值模拟的结果进行了比较。 相似文献
6.
尝试建立1种基于无单元法的涡激振动数值模拟算法,并给出适用于涡激振动分析的前处理自动布点方法.基于无单元法理论,使用动最小二乘法构造形函数,利用无单元伽辽金法,采用速度和压力分离模式,及手工布点和自动布点2种方法所得出的节点布置形式,对流场控制方程进行空间离散,模拟二维涡激振动的流场形态,并对VIV相关参数进行分析,计算不同节点布置情况下的升力系数(Cl)、曳力系数(Cd)及斯特罗哈数(St),并与物理模型实验结果进行对比.计算结果表明,无单元伽辽金法应用于立管VIV分析是可行的,且文中采用2种布点方法均能较好的模拟流场中泻涡脱落的形态,计算结果与传统方法和物理模型实验结果吻合良好.证明文中2种布点方法都能用于固定圆柱的二维VIV分析,但自动布点法能够更好地适用于复杂问题的计算及圆柱体在流场中的VIV动力响应分析. 相似文献
7.
为了深入研究亚临界雷诺数下光滑和沟槽圆柱绕流阻力及流场特性。采用SSTk-w模型对雷诺数Re分别为2×104,6×104,1×105和1.4×105的光滑圆柱和V型沟槽圆柱绕流进行三维流场数值模拟,首先以光滑圆柱绕流为算例与相关实验研究结果进行了对比,验证了SSTk-w方法的准确性,然后在不同雷诺数条件下,开展了V型沟槽圆柱绕流数值模拟研究;与光滑圆柱相比,V型沟槽圆柱具有较好的减阻效果,最大减阻率达28.4%;在相同雷诺数下,沟槽圆柱表面边界层分离点与光滑圆柱表面分离点相比更靠后。V型沟槽织构可有效改变尾流区旋涡脱落频率和尾流区湍流的发展,为隔水管减阻和提高隔水管柱系统的稳定性提供参考。 相似文献
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本文对圆形桩柱列在静水中振动时的流场进行了分析,把文献[1]中的方法应用到无限圆柱列振动时的流场分析中去,并从理论上证明了这类解存在的条件。将所得结果应用到计算无限圆柱列的附加质量中去,所得结果与文献[4]中的实验结果进行了比较,两者吻合良好,因此文中所给曲线可供设计应用。 相似文献
10.
黑鲪生态生长效率周年变化的研究 总被引：3，自引：0，他引：3
于1983年12月-1984年5月和1990年6月-1991年1月以中国科学院海样研究所生物培育楼养殖黑为材料，进行黑周年的摄食-生长实验，以探讨其生态生长效率变化规律。结果表明，作为冷温性鱼，黑在4．0－27．3℃水温条件下都有摄食；平均日摄含量为2．4－10．0g，相对体重的百分比为1．1%-4.4%．单见，这二者的周年变化趋势基本一致；平均体重日增长量以4，6，7月和10－12月份较高。生态生长效率波动于6．5%-34．7%范围内，年平均为16．7％。 相似文献
11.
The lift forces on horizontal cylinder near bottom is experimentally investigatde at Reynolds(Re)in the range lf 2500~10000and Keulegan~CARPENTER NUMBERS(kc) inthe intervalof5~20,and gap ratio (e/D) is from (a0)are analyzde by using the Fourier analyses method.It is found that found that both Cl& a0 are the functions lf the Kc number. 相似文献
12.
Li Yucheng Zhang Ningchuan
Professor Dalian University of Technology Dalian . Lecturere Delian University of Technology Dalian 《中国海洋工程》1994,(1)
- A composite pipeline is defined as a main big pipe composed of one or several small pipes. The flow behaviour around a submarine composite pipeline is more complicated than that around a single submarine pipeline. A series model test of composite pipelines in a wave-current coexisting field was conducted by the authors. Both in-line and lift forces were measured, and the resultant forces were also analyzed. The results of lift forces and resultant forces are reported in this paper. It is found that the lift force coefficients for composite pipelines are well related to the KC number. The lift force coefficients for an irregular wave-current coexisting field are smaller than those for a regular wave-current coexisting field. The frequency of lift force is usually twice the wave frequency or higher. The authors test indicates that the resultant forces are about 10 to 20 percent larger than in-line forces (horizontal forces). The effect of water depth is analyzed. Finally, the relationship between lift f 相似文献
13.
Based on model tests, the lift and resultant forces on small square cylinders caused by waves (regular and irregular) and currents are analyzed in this paper. The lift and resultant force coefficients CL and Cf related to KC number and the effect of direction of wave propagation are also given, which may be useful for practical engineering application. 相似文献
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The Wake II model for the determination of the hydrodynamic forces on marine pipelines is extended to include currents and waves. There are two main differences between the Wake II and the traditional model. First, in the Wake II model the velocity is modified to include the pipe's encounter with the wake flow when the velocity reverses. Second, the model uses time dependent drag and lift coefficients. The flow field is assumed to be the linear superposition of regular waves and uniform current and is treated as wave only but in two different phases. The model requires eight empirical parameters that are obtained from comparisons with field data for various Keulegan–Carpenter numbers and current to wave ratios. The effective velocity and the force predictions are compared with field data from Exxon Production Research Company and with the conventional model. The model gives satisfactory results and predicts lift forces that in shape, magnitude and phase relative to the velocity are in very close agreement with measured forces. For the horizontal forces the results are very accurate. A substantial improvement is obtained over the predictions with the conventional model. This work is applicable to the design of submarine pipelines laying on the sea bottom in water depths where waves or waves and currents contribute to the hydrodynamic forces. 相似文献
16.
The inline and lift forces on bipiles in parallel array induced by both irregular waves and currents were investigated experimentally in this paper. The characteristics in both time and frequency domains of inline, lift and resultant forces as well were analyzed. The grouping effect coefficients of inline and resultant forces on two piles related to KC number and relative spacing parameters are given. A comparison of the magnitude and direction of resultant forces on two piles in parallel array with the corresponding values for single cylinder is also made. 相似文献
17.
The planing trimaran possesses distinctive hybrid hydrodynamic and aerodynamic performance due to the presence of tunnel. The research described in this paper was carried out based on the observation of wave characteristics of a planing trimaran model in towing tests, in which the resistance drops as soon as the wave surface separates from tunnel roof. In order to gain a deeper insight into the relationship between wave flow and forces in tunnel region, a comprehensive series of viscous CFD simulations considering free-surface and 2-DOF motion of the hull (heave and pitch) have been performed for the tested model at the volume based Froude numbers ranging from 3.16 to 5.87. The calculated results were validated by comparison with experimental data and showed good agreement. Numerical results of wave contours, longitudinal wave cuts and lifting force distributions at the calculated speeds were presented for the analysis of ventilation process in tunnel region and the corresponding variation of tunnel forces. It is found that, for the speeds higher than Froude number of 4.52, the aerodynamic forces provide major tunnel lift and mainly act on the straight section of the tunnel. And, therefore, numerical simulations of two modified models have also been performed for the analysis of influence of straight section length on the hydrodynamic and aerodynamic performance of planing trimaran. 相似文献
18.
Animals display a variety of control surfaces that can be used for propulsion and maneuvering devises. For nonpiscine vertebrates, these control surfaces are primarily evolutionary modifications of the paired appendages (i.e., legs). The diversity of control surfaces can be classified with regard to the forces used for stability and maneuverability. For animals, the pertinent forces are pressure drag, acceleration reaction, and lift. These forces can be generated actively by motion of the control surfaces or passively from flows produced by movements of the body or external flow fields. Drag-based control surfaces are associated with paddling and rowing movements, where the limbs are oriented either in the vertical parasagittal plane or horizontal plane, respectively. The paddle is unstreamlined and has a triangular design with a broad distal end, thereby affecting a large mass of water. Appendages, which are used to generate lift-based forces, are relatively stiff hydrofoils. To maximize lift, the hydrofoil should have a crescent wing-like design with high aspect ratio. This shape provides the hydrofoil with a high lift-to-drag ratio and high propulsive efficiency. The tail flukes of cetaceans are streamlined control surfaces with a wing-like design. The flukes of cetaceans function in the hydrodynamic generation of forces for thrust, stability, and maneuverability. The three-dimensional geometry of flukes is associated with the production of lift and drag. Previous studies of fluke geometry have been limited in the number of species examined and the resolution of measurements. 相似文献
19.
A scale model of a flexible circular net with different weights attached to the bottom was tested in a flume tank. Global forces and net deformation were measured for different steady current velocities. Three different sizes of bottom weights were used in the tests. The results from these tests are presented and discussed with the emphasis on the dependency between the forces and the geometry. Comparison is also made to empirical based formulas for calculation of drag and lift forces on net structures. Findings show that i) the forces on, and deformation of a flexible net structure are mutually highly dependent on each other; ii) estimates of global forces on a flexible net structure calculated using simple drag formulas derived from stiff net panel experiments give large errors when compared to experimental measurements; iii) numerical models taking into account the dependency between force and deformation should be used to obtain accurate estimates of forces on flexible net structures; and iv) the forces on a flexible net structure are dependent on Reynolds number, and their dependency are similar to that of a regular cylinder. 相似文献
20.
C.H.K. Williamson 《Applied Ocean Research》1985,7(3):124-127
The present brief paper is intended to show that the fluid forces on a small cylinder can be considerably magnified when it is in the flow field of a larger cylinder. Two cylinders of unequal diameter are oscillated in a tank of fluid, and the lift and in-line forces on the smaller cylinder are measured when the pair of cylinders is placed at various orientations and spacings. 相似文献