共查询到20条相似文献，搜索用时 31 毫秒
1.
Mohammad Saeed SEIF Ebrahim JAHANBAKHSH Roozbeh PANAHI Mohammad Hossein KARIMI 《海洋工程》2009,(3):517-528
High speed planing hulls have complex hydrodynamic behaviors. The trim angle and drafts are very sensitive to speed and location of the center of gravity. Therefore, motion simulation for such vessels needs a strong coupling between rigid body motions and hydrodynamic analysis. In addition, free surface should be predicted with good accuracy for each time step. In this paper, velocity and pressure fields are coupled by use of the fractional step method. On the basis of integration of the two-phase viscous flow induced stresses over the hull, acting loads (forces and moments) are calculated. With the strategy of boundary-fitted body-attached mesh and calculation of 6-DoF motions in each time step, time history of ship motions including displacements, speeds and accelerations are evaluated. For the demonstration of the software capabilities, circular cylinder slamming is simulated as a simple type of water slamming. Then, a high-speed planing catamaran is investigated in the case of steady forward motion. All of the results are in good concordance with experimental data. The present method can be widely implemented in design as well as in performance prediction of high-speed vessels. 相似文献
2.
Huang Guoliang Liu Tianwei Yan Naichang
Associate Professor Shanghai Jiao Tong University Shanghai
Engineer Shanghai Jiao Tong University Shanghai .
Professor Shanghai Jiao Tong University Shanghai 《中国海洋工程》1997,(4)
In this paper,the maneuvering characteristics of a low speed submersible are investigated.First,the captive model tests are carried out to obtain the hydrodynamic forces acting on the submersibleusing a Planar Motion Mechanism(PMM).For the hydrodynamic forces within a wide range of attack an-gles,the hydrodynamic coefficients which are usually used in the conventional maneuvering motion arequite difficult to be applied.In this case,a Fourier series is adopted to represent the hydrodynamic forcesand it fits the experimental data well.Then,based on the experimental results the simulation calculationsare made to predict some of the maneuvering performance of the low speed submersible. 相似文献
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In this paper,the effects of a quay or a solid jetty on hydrodynamic coefficients and vertical wave excitation forces on a ship woth or without forward speed are discussed.A modified simple Green function technique is used to calculate the 2D coefficients while the strip theory is used to calculate the 3D coefficients. Wave excitation forces are also calculated with the strip theory. Numerical results are provided for hydrodynamic coefficients and vertical wave excitation forces on a 200000 DWT tanker ship. It is found that the quay has a considerable effect on the hydrodynamic coefficients and wave excitation forces for a ship. 相似文献
5.
扁平潜器微速操纵性研究 总被引：1，自引：0，他引：1
针对扁平潜器的特点建立了其微速操纵性运动方程,提出了忽略攻角、漂角与旋转角速度耦合影响的水动力模型,由拖曳水池模型试验确定了攻角、漂角水动力,近似估算了旋转水动力.在主辅推进器的PD控制下,数值仿真计算了水平面航向保持与改变、垂直面潜浮的微速运动控制. 相似文献
6.
建立双臂起重船从运输船上起吊大型稳桩施工平台的吊装系统模型,其中,起重船与运输船呈T型布置。首先基于势流理论,采用专业水动力分析软件AQWA开展了双船系统的频域水动力分析,分析双船起吊系统的水动力干扰特性和遮蔽效应,并对双船间隙自由液面进行黏性修正从而提高频域多体水动力分析的精度。进一步采用频域—时域方法对起吊耦合系统进行参数分析,探究起吊速度、波浪周期等对吊索张力和起重船运动的影响规律。分析多个工况下运输船的遮蔽效应对起吊系统的影响。结果表明,对间隙流体施加阻尼自由液面边界条件可以一定程度提高计算模型的精度,在某些周期的迎浪条件下运输船对起重船的遮蔽效应可以降低吊装系统的响应;起吊速度对时域动力响应的影响较小;周期为8 s的规则波引起过大的动力响应。 相似文献
7.
An adaptive output feedback controller based on neural network feedback-feedforward compensator (NNFFC) which drives a surface ship at high speed to track a desired trajectory is designed. The tracking problem of the surface ship at low speed has been widely investigated. However, the coupling interactions among the forces from each degree of freedom (DOF) have not been considered in general. Furthermore, the influence of the hydrodynamic damping is also simplified into a linear form or neglected. On the contrary, coupling interactions and the nonlinear characteristics of the hydrodynamic damping can never be neglected in high speed maneuvering situation. For these reasons, the influence of the nonlinear hydrodynamic damping on the tracking precision is considered in this paper. Since the hydrodynamic coefficients of the surface ship at high speed are very difficult to be accurately estimated as a prior, it will be compensated by NNFFC as an unknown part of the tracking dynamics system. The stability analysis will be given by the Lyapunov theory. It indicates that the proposed control scheme can guarantee that all the signals in the closed-loop system are uniformly ultimately bounded (UUB), and numerical simulations can illustrate the excellent tracking performance of the surface ship at high speed under the proposed control scheme. 相似文献
8.
为研究鱼类高速游动机理,以金枪鱼月牙形尾鳍为对象,采用面元法计算分析了其非定常水动力性能。假设尾鳍在横移和摇摆的同时,以某一匀速向前运动,并假设其在弦向和展向以某一给定规律发生变形,以模仿柔性变形。探讨了前进速度、横移和摇摆的幅度、频率及其相位差对柔性尾鳍推进性能的影响,并与做相应运动的刚性尾鳍进行了对比。 相似文献
9.
Stability design of submarine pipelines is a very important procedure in submarine pipeline engineering design. The calculation of hydrodynamic forces caused by waves and currents acting on marine pipelines is an essential step in pipeline design for stability. The hydrodynamic forces-induced instabilities of submarine pipelines should be regarded as a wave/ current-pipeline-seabed interaction problem. This paper presents a review on hydrodynamic forces and stability research of submarine pipelines under waves and currents. The representative progress including the improved design method and guideline has been made for the marine pipelines engineering design through experimental investigations, numerical simulations and analytical models. Finally, further studies on this issue are suggested. 相似文献
10.
In marine cycloidal propeller (MCP), the inflow velocity vector to the propeller blade continuously changes at different blade orbit angle. Earlier marine cycloidal propellers were installed on ships that mainly performed towing operations. Recently marine cycloidal propellers are being installed on large naval vessels, which spend lot of their operating hours in cruising. Therefore, the hydrodynamic loading on the blades both during cruising maneuvers need to be investigated. The flow characteristics around the propeller blade are computed numerically by panel method. Viscous effects on the flow are then estimated by boundary layer technique. The effect of rotating disc on viscous fluid is also investigated. The corrected flow characteristics are then used for estimating the hydrodynamic loading. The operating conditions that are critical for the loading of the blade and the support structure and some aspects of the maneuvering simulation at cruising speed are investigated. 相似文献
11.
Based on linear water-wave theory, this study investigated the scattering of oblique incident water waves by two unequal surface-piercing thin vertical rigid plates with stepped bottom topography. By using the matched eigenfunction expansion method and a least square approach, the analytical solutions are sought for the established boundary value problem. The effects of the incidence angle, location of step, depth ratio of deep to shallow waters, and column width between two plates, on the reflection coefficients, the horizontal wave forces acting on the two plates, and the mean surface elevation between the two plates, are numerically examined under a variety of wave conditions. The results show that the existence of the stepped bottom between two plates considerably impacts the hydrodynamic performances of the present system. It is found that the effect of stepped bottom on the reflection coefficient of the present two-plate structure is evident only with waves of the low dimensionless frequency. Moreover, the influence of the step location on the hydrodynamic performance of the present two-plate structure is slight if the step is placed in between the two plates. 相似文献
12.
The paper presents a comparison between experimental data and numerical results of the hydrodynamic coefficients and also of the wave induced motions and loads on a fast monohull model. The model with 4.52 m length was constructed in Fibre Reinforced Plastic (FRP), and made up of 4 segments connected by a backbone in order to measure sectional loads. The objective of the investigation was to assess the capability of a nonlinear time domain strip method to represent the nonlinear and also the forward speed effects on a displacement high speed vessel advancing in large amplitude waves. With this objective in mind the experimental program included forced oscillation tests in heaving and pitching, for a range of periods, three different amplitudes and several speeds of advance. In head regular waves comprehensive ranges of wave periods, wave steepness and speeds, were tested in order to measure heave, pitch and loads in three cross sections.
The numerical method assumes that the radiation and diffraction hydrodynamic forces are linear and the nonlinear contributions arise from the hydrostatics and Froude–Krilov forces and the effects of green water on deck. The assumption of linearity of the radiation forces is validated by comparing calculated hydrodynamic coefficients with experimental data for three different amplitudes of the forced oscillations. Both global coefficients and sectional coefficients are compared. The motions and loads in waves are compared in terms of first and higher harmonic amplitudes and also in terms of sagging and hogging peaks. 相似文献
13.
In this paper, motion response of a moored floating structure interacting with a large amplitude and steep incident wave field is studied using a coupled time domain solution scheme. Solution of the hydrodynamic boundary value problem is achieved using a three-dimensional numerical wave tank (3D NWT) approach based upon a form of Mixed-Eulerian–Lagrangian (MEL) scheme. In the developed method, nonlinearity arising due to incident wave as well as nonlinear hydrostatics is completely captured while the hydrodynamic interactions of radiation and diffraction are determined at every time step based on certain simplifying approximations. Mooring lines are modelled as linear as well as nonlinear springs. The horizontal tension for each individual mooring line is obtained from the nonlinear load-excursion plot of the lines computed using catenary theory, from which the linear and nonlinear line stiffness are determined. Motions of three realistic floating structures with different mooring systems are analyzed considering various combinations of linear and approximate nonlinear hydrodynamic load computations and linear/nonlinear mooring line stiffness. Results are discussed to bring out the influence and need for consideration of nonlinearities in the hydrodynamics and hydrostatics as well as the nonlinear modelling of the line stiffness. 相似文献
14.
A deep-sea Manned Submarine Vehicle (MSV) is usually required to move at a low forward speed and a low rotational speed when it executes investigation tasks. In this condition, the motion is in large drift angles, and the maneuverability hydrodynamic forces cannot be expressed properly in the conventional mathematical model of submersible motion. In this paper, firstly, a general equation of MSV with six-freedom motion is presented, and the numerical simulation of descent/ascent motion and helix motion is c... 相似文献
15.
The hydrodynamic problem of a two-dimensional asymmetrical wedge entering calm water obliquely at constant speed is analyzed based on the velocity potential theory. The gravity effect on the flow is ignored based on the assumption that the ratio of the entry speed to the acceleration due to gravity is much larger than the time scale of interest. The problem of this similarity flow is solved by a boundary element method together with an analytical solution for the jet based on the shallow water approximation. Various results are provided for the wave elevation, pressure distribution and force at different deadrise angles and at different oblique entry. The effects of asymmetry and horizontal speed on these results are investigated. 相似文献
16.
Hydrodynamic Interactions of Three Barges in Close Proximity in A Floatover Installation 总被引：1，自引：1，他引：0
The hydrodynamics of side-by-side barges are much more complex than those of a single barge in waves because of wave shielding, viscous effects and water resonance in the gap. In the present study, hydrodynamic coefficients in the frequency domain were calculated for both the system of multiple bodies and the isolated body using both low-order and higher-order boundary-element methods with different element numbers. In these calculations, the damping-lid method was used to modify the free-surface boundary conditions in the gap and to make the hydrodynamic results more reasonable. Then far-field, mid-field and near-field methods were used to calculate wave-drift forces for both the multi-body system and the isolated body. The results show that the higher-order method has faster convergence speed than the low-order method for the multi-body case. Comparison of different methods of computing drift force showed that mid-field and far-field methods have better convergence than the near-field method. In addition, corresponding model tests were performed in the Deepwater Offshore Basin at Shanghai Jiao Tong University. Comparison between numerical and experimental results showed good agreement. 相似文献
17.
以床面瞬时剪应力作为泥沙起动及输运的水动力机制,建立了结构物周围复杂流场下床面局部冲刷的数学模型。并应用大涡模拟方法对后台阶下游三维湍流流动进行数值模拟,得到台阶下游床面瞬时剪应力的分布规律。为了确定床面瞬时剪应力与泥沙上扬通量的关系,先应用数学模型对不同模型参数下,冲刷开始后5分钟时台阶下游床面形状进行试算。通过试算与实验结果的比较,确定床面瞬时剪应力与泥沙上扬通量关系中需要的模型参数。进一步对冲刷开始后30分钟内台阶下游床面演化规律进行模拟,模拟结果与实验结果相符合。 相似文献
18.
The Direct Matrix Method Interaction Theory (IT) proposed by Kagemoto and Yue [1] speeds up the computation of hydrodynamic coefficients for large arrays of bodies when compared to direct calculations using standard Boundary Element Method (BEM) solvers. One of the most computationally expensive parts of the matrix method is the calculation of two hydrodynamic operators, known as Diffraction Transfer Matrix (DTM) and Radiation Characteristics (RC), which describe the way an isolated geometry scatters and radiates waves, respectively. A third operator, called Force Transfer Matrix (FTM), was introduced by McNatt et al. [2] to facilitate the calculation of the forces exerted on the bodies. In this paper, a novel set of relations between the FTM and RC components is obtained using the Kochin functions specific to the cylindrical basis solutions. They extend the classical Haskind's relations, valid with incident plane waves, to the cylindrical components of the scattered and radiated fields. Moreover, an alternative demonstration of the identities is given, which does not rely on the far-field asymptotic representation of the potential. Additional expressions are provided that relate the hydrodynamic coefficients and the RC for isolated bodies as well as for arrays, and numerical checking of the derived mathematical expressions is presented. These new relations can be used to speed up calculation of the hydrodynamic operators required for the use of the IT and to test its accuracy. 相似文献
19.
水平轴海流能发电机叶片设计与性能分析 总被引：2，自引：1，他引：1
全球海洋蕴藏着丰富的海流能,合理利用海流能可以有效缓解能源危机。以额定工况下获能系数达到最大值为目标,利用叶素-动量理论设计了150 kW水平轴海流能发电机的叶片。使用叶素-动量理论结合普朗特修正和葛劳渥修正的方法,预测了海流机在不同尖速比以及不同桨距角下的水动力性能,分析了攻角和载荷沿着叶片径向的分布规律。使用CFD方法计算了海流机在不同尖速比下的水动力性能,并与理论方法的计算结果进行了比较。理论方法和CFD方法的结果均表明,所设计的海流机最大获能系数位于设计尖速比处,证明基于叶素-动量理论的水平轴海流机叶片设计方法是有效的。 相似文献
20.
This study examines the hydrodynamic performance of a highly simplified eel-like structure consisting of three articulated segments with the two aft segments oscillating. A physical model was built and tested to determine the forces developed with the model stationary, to find the self-propulsion speed, and to explore the effect on hydrodynamic performance of different swimming patterns. It was found that hydrodynamic performance increases with increasing oscillation frequency; the highest forces when stationary, and the highest self-propulsion speeds were produced by swimming patterns in which the amplitude in the aft segment is larger than that in the forward segment, and in which the motion of the aft segment lags the forward segment.A simple semi-empirical model based on Morison’s equation was implemented to predict the hydrodynamic forces. This was shown to predict mean thrust well in cases in which the aft segment oscillates in phase with the forward segment, but less reliably when the phase difference between the segments increases. Force time histories are generally not well-predicted using this approach. Nonetheless, self-propulsion speeds are predicted within 30% in all cases examined. 相似文献