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1.
全被动式振荡水翼是振荡水翼式潮流能装置的主要型式之一。对全被动式振荡水翼进行了数值模拟研究,构建了二维数值模型,研究了雷诺数及升沉刚度对全被动式振荡水翼水动力性能的影响。通过流场结构及水动力性能分析研究了典型参量对全被动式振荡水翼获能性能的影响机理,确定了维持其良好水动力性能的参数范围。研究发现,水翼的水动力性能对雷诺数及升沉刚度的变化较为敏感。雷诺数增大,水翼所需升沉刚度随之增加,且水翼可以在更大的参数范围下获得较优的水动力性能。另外,水翼可以在没有升沉刚度的情况下实现周期性运动,其获能甚至优于一些有升沉刚度的情况。最优工况下,平均功率系数和能量转换效率分别为1.07和27.48%。 相似文献
2.
A technique for predicting the bubble growth along a two-dimensional hydrofoil with traveling bubble cavitation is presented. The method is based on the dynamic response of ambient microbubbles to the flow field and the subsequent diffusion of dissolved air into the flow field cavities. The bubble growth model is divided into three components, including the prediction of 1) the hydrofoil surface pressure distribution, 2) the ambient microbubble response to the pressure distribution, and 3) the diffusive mass flow rate. The hydrofoil velocity and pressure field is determined by two-dimensional thin airfoil theory. The microbubble response to the pressure field is given by the Rayleigh-Plesset equation with the addition of a mass diffusion term. The diffusion of dissolved gasses into the cavitation bubbles is determined by a solution to the steady-state diffusion equation under spherically symmetric convective flow. Results are given for the bubble wake of a NACA 66-006 (a = 0.8 meanline) hydrofoil with traveling bubble cavitation. The effect of the relative velocity of the cavitation bubbles with respect to the surrounding water is investigated as well as the significance of the mass diffusion term in the Rayleigh-Plesset equation. 相似文献
3.
A finite element method is developed for the stiffened multi-layered airfoil/hydrofoil structure for the large deformation and finite strain problem. The kinematics of the airfoil/hydrofoil is set up. The Consistent Orthogonal Basis Function Space is applied for the airfoil/hydrofoil structure. Given the airfoil/hydrofoil configuration and boundary conditions, the basis function space can be uniquely determined, such that the diagonal mass matrix is obtained accurately and the basis functions are very identical with the mode shape functions of the structure. In order to satisfy the displacement compatibility condition between adjacent layers of the airfoil/hydrofoil, the traction degree-of-freedom is also induced.The post buckling analysis is presented for the wing (hydrofoil) structure of the underwater glider. The water pressure is applied on the outer surface and the critical buckling pressure is calculated. The post buckling equilibrium path is also given. The results are verified with ANSYS. The present study of the buckling analysis of the airfoil/hydrofoil under water pressure is helpful to the design of underwater glider. 相似文献
4.
Vortex generators are used extensively as a passive flow control devices to delay or remove the boundary layer separation, which affects the hydrodynamic performance of the hydrofoil. In this paper, a new approach is introduced to overcome the boundary layer separation on the NACA S1210 hydrofoil. The outcome of tube slots combination in the S1210 hydrofoil on the boundary layer separation are numerically investigated. The performance is compared with respect to the force coefficients and glide ratio. The effects of tube slot inlet positions with different diameters on S1210 hydrofoil are presented here. The results show that the smaller diameter tube slots starting near the leading edge improves the hydrodynamics performance of the hydrofoil. 相似文献
5.
A jet-controlled high-lift hydrofoil with a flap is investigated using both experimental and computational methods. Experiments were carried out in a cavitation tunnel to measure forces and moment acting on the hydrofoil, and surface pressure distribution. The measured data show the feasibility of such a device for marine applications. Computational studies have also been carried out in parallel with the measurements. The computational results are analyzed in terms of global and local quantities using available experimental data. The present computational results compare well with the well-known experimental data for circulation control flows. The results for flow around a hydrofoil with a blown flap further validate the concept behind the proposed device. The results of the study demonstrate the applicability of the technology to the design of practical control surfaces. 相似文献
6.
This paper analyzes the hydrodynamic performance of a planing craft with a fixed hydrofoil in regular waves. Numerical simulations are carried out based on a RANS-VOF solver to study the hydrodynamic performance of the planing craft and the influence of the fixed hydrofoil on its seakeeping. To validate the numerical method, a series of hydrodynamic experiments of a bare planing craft without the hydrofoil were carried out, from which the seakeeping performance of the planing craft was recorded, the numerical method based on overset grid was compared with the experiment and verified reliable. Eight hydrofoil design cases were then studied, whereby, their seakeeping performance in regular wave conditions were predicted through the numerical method which has been verified reliable and compared with each other. Effects of hydrofoil parameters, such as angle of attack and installation height, on the seakeeping performance were investigated. Finally, the suitable installation parameters which can optimize the performance of hydrofoil and reduce the negative influence are verified. The influence of the speed on the effect of the hydrofoil and the flow field around the planing craft are also investigated. 相似文献
7.
Peter R. Payne 《Ocean Engineering》1997,24(3):235-263
For study purposes, a simplified model of a hydrofoil craft is constructed with the assumption that it has:
- • heave only motion;
- • no surface proximity effect on the foil;
- • no foil broaching.
8.
为了降低空化造成的水动力性能损失,基于仿生学原理,参考座头鲸鳍肢剖面形状,将前缘波浪构型引入到水翼设计中,研究波状前缘水翼的非定常空化特性,并探究前缘参数改变对空化控制的效果和规律。选用NACA634-021水翼为基准模型,进行前缘参数化重构,设计出3种不同的波状水翼进行对比研究。采用大涡模拟（LES）方法对空化流场进行精细化数值模拟,针对基准水翼和不同波幅与波长参数下的波状水翼开展了空化周期、升阻力系数、压力脉动以及流向涡结构的对比分析。结果发现,波状水翼在抑制空化和降低压力脉动方面都取得了显著效果。其中,3种不同的波状水翼空化抑制率分别为15.7%、18.6%和27.9%,压力脉动幅值分别降低了55.3%、67.3%和74.6%。分析表明,波浪前缘的引入使得空化的分区效应更加凸显,空化从波谷处初生,增大波幅或减小波长都可以加强对空化的抑制效果,并可以提高升力系数以及显著降低水翼表面的压力脉动。前缘波浪构型还将诱发向下游发展的对转涡结构,不同前缘参数的波状水翼涡结构的演化是相似的,空泡发展与溃灭的整个过程对涡结构的发展也具有显著影响。 相似文献
9.
The current control system of a fully-submerged hydrofoil craft based on optimal feedback control has several problems: it has no good performance of contouring waves and it cannot reduce the effect of wave disturbance. In this paper, we apply the optimal preview servo system to the longitudinal control system of a fully-submerged hydrofoil craft in order to settle the problems of current control system. The control system based on optimal preview servo system is composed of feedback controller and feedforward controller. Also in order to design the control system, the necessary prediction range of future information, the weight function in performance index, the future reference input and wave disturbance are determined. Finally, the validity of the proposed control system in this paper is confirmed by simulation. The simulation results show that the control system has good performance of contouring waves in following seas and is effective to settle the problems of current control system of a fully-submerged hydrofoil craft. 相似文献
10.
The iterative method that is originally developed before both for two- and three-dimensional single cavitating hydrofoils moving with a constant speed under free surface is applied to the case of high-speed (Froude number up to 6.5) and some figures are given. The method is also extended to include the surface piercing hydrofoils (vertical struts) and the case of tandem hydrofoils into the calculations. The iterative nonlinear method based on the Green's theorem allows separating the cavitating hydrofoil problem(s) and the free surface problem. These two (or three in the case of tandem hydrofoil) problems are solved separately, with the effects of one on the other being accounted for in an iterative manner. The cavitating hydrofoil surface(s) and the free surface are modeled with constant strength dipole and constant strength source panels. The source strengths on the free surface are expressed in terms of perturbation potential by applying the linearized free surface conditions. No radiation condition is enforced for downstream and transverse boundaries. The cavitation number is expressed in terms of Froude number and the submergence depth of the hydrofoil from the free surface. An algebraic grid on the free surface has been described to get a smooth transition between the panels along the direction of uniform inflow and to have a long distance in the downstream direction depending on the wave-length (or Froude number) while keeping the number of panels fixed. First, the method is validated in the case of surface piercing hydrofoil. Then, the effects of high Froude number and the submergence depth of the hydrofoil from free surface on the results are discussed and some figures are given for interested engineers and designers. The method is later applied to the case of tandem hydrofoils and the effects of one hydrofoil on the other are discussed. 相似文献
11.
The sensitivity of the hydrofoil take-off speed to changes in foil size and angle has not been well documented. This paper first presents the verification of the UNO-HYF1 with published performance data. Following the satisfactory validation, the results are presented in hydrofoil take-off to show the change with speed when the foil area, foil angle and propeller shaft angle are changed. The calculations indicate that varying the hydrofoil area has the largest impact on hydrofoil take-off speed. 相似文献
12.
为了改善潮流能水轮机叶片表面流动分离问题,提高其升阻比,本文通过在潮流能水轮机叶片表面加装涡流发生器,来研究涡流发生器对潮流能水轮机水动力学性能的影响。本文以NACA4418翼型为研究对象,分别建立了含VGs和不含VGs的三维模型,利用CFD方法研究了VGs的高度、长度以及相邻一对VGs之间的间距等多个方面对该翼型性能的影响。结果表明:VGs可以有效地提高翼型的最大升力系数;相邻VGs间距的增加对流动分离的抑制有积极影响。此外,通过对尾迹区流线和旋涡的分析,进一步揭示了尾迹区的流场特征。 相似文献
13.
The hydrodynamic problem of a hydrofoil travelling at constant speed in water waves has been investigated through velocity potential theory. The boundary conditions on the free surface have been linearized, and the effects are accounted for through the Green function. The overall problem is decomposed into the steady forward speed problem and periodic wave radiation and diffraction problems. Each of these problems is solved using the boundary integral equation over the hydrofoil surface together with a vortex sheet behind the trailing edge. The body surface boundary condition is imposed on its mean position. As a result the steady potential will contribute a well-known mj term to the body surface boundary condition on the radiation problem. The numerical difficulty in dealing with this term is effectively resolved through a difference method. The effects of the thickness on the wave radiation and diffraction are investigated. The applicability of various reciprocity relationships in this problem is discussed. 相似文献
14.
Results of an experimental study of the effect of surface proximity on hydrofoil lift are presented. The biplane image theory, a horseshoe vortex model and momentum theory are described in relation to the effect of surface proximity on hydrofoil lift and drag. The biplane image theory and the horseshoe vortex model are shown to predict the same effect on lift, and are seen to be in good agreement with the experimental data. The Payne momentum theory is seen to differ significantly from the measured results. The data indicate a significant reduction in lift at depths less than two chords with very little effect at greater depth. 相似文献
15.
Tidal current energy is a promising renewable energy source for future electricity supply. The flapping hydrofoil is regarded as a useful tool to extract the tidal current energy in shallow water. A concept of coupled tandem flapping hydrofoils under semi-activated mode was proposed in the present study. A two-dimensional numerical model, based on the computational fluid dynamics software ANSYS-Fluent, was established to investigate the power extraction performance of the coupled tandem flapping... 相似文献
16.
The present study focuses on the implementation of PISO algorithm to simulate cavitating flows. For simulation of unsteady behaviors of cavitation which have practical applications, the development of unsteady PISO algorithm based on the non-conservative approach is investigated. The effects of mixture compressibility are considered to improve accuracy of simulations. For multi-phase simulation, single-fluid Navier–Stokes equations, along with the volume fraction transport equation, are employed. The bubble dynamics model is utilized to simulate phase change. To prove capabilities of the developed PISO algorithm to simulate cavitating flows, unsteady simulation of cavitation around NACA0015 hydrofoil, a two dimensional flat plat, and a three dimensional circular disk are performed. The frequency of flow, pressure distributions, cavitating vortex shedding, and cavity characteristics are analyzed to discern results accuracy. To investigate accuracy of results, comparisons with available published experimental data are made and good agreement is achieved. 相似文献
17.
Several species of Gastrotricha were found among samples of nematodes extracted from a sandy ocean beach, South Broulee beach, in southeastern Australia. One of these Gastrotricha turned out to be a species new to science which is described as Halichaetonotus australis sp. nov. in this study. Although the spines of the hydrofoil scales resemble those of the cosmopolitan H. aculifer, a distinctive feature of the new species is the presence of three prominent posterior dorsal spines. These are exaggerations of the keels found on the dorsal overlapping scales that cover the dorsal surfaces of the head, neck, and trunk. The spines are almost as long as the rami of the terminal furca. H. australis sp. nov. also resembles H. marivagus, but differs in lacking both a cephalion and hypostomion. Freeze drying is introduced as a preparation method for scanning electron microscopy of Gastrotricha. 相似文献
18.
This paper describes an effort to develop a predictive tool for the design of a new promising marine transport — the WIG craft. The presented mathematical model of the WIG craft is capable of modeling the aerodynamics of a WIG system including the ground effect, the hydrodynamics of a stepped planing hull with a hydrofoil and also the simulation of motion for the craft. Based on extensive experience using the model, it is shown that the most important and necessary features of WIG aero- and hydrodynamics are taken into account. The results of simulations have been validated through comparison with other theoretical approaches and also with model experiments. The mathematical model is applied to investigate the dynamics of the small manually piloted WIG craft: “Hydrowing VT01”. The numerical study resulted in recommendations allowing the pilot to overcome the pitch-up tendency and also to perform the take-off manoeuvre smoothly. The stability of the WIG with a hydrofoil and also the dynamic properties of anti-collision manoeuvres have been studied and are presented. 相似文献
19.
Numerical simulation for hydrodynamic characteristics of a bionic flapping hydrofoil 总被引：2，自引：1，他引：1
In order to study the propulsion mechanism of the bionic flapping hydrofoil (BFH), a 2-DoF (heave and pitch) motion model is formulated. The hydrodynamic performance of BFH with a series of kinematical parameters is explored via numerical simulation based on FLUENT. The calculated result is compared with the experimental value of MIT and that by the panel method. Moreover, the effect of inlet velocity, the angle of attack, the heave amplitude, the pitch amplitude , the phase difference, the heave biased angle, the pitch biased angle and the oscillating frequency are investigated. The study is useful for guiding the design of bionic underwater vehicle based on flapping propulsion. It is indicated that the optimal parameters combination is v=0.5m/s, θ0=40°.θ0=30°,Ψ=90°,Фbias=0°,θbias=0°and f=0.5Hz . 相似文献
20.
Au et al.'s arguments against the hypothesis that humpback whale songs function as long-range sonar are based on questionable assumptions rather than on empirical data. Like other echolocating mammals (e.g., bats), singing humpback whales: 1) localize targets in the absence of visual information; 2) possess a highly innervated peripheral auditory system; and 3) modulate the temporal and spectral features of their sounds based on environmental conditions. The sonar equation is inadequate for determining whether humpback whale songs generate detectable echoes from other whales because it does not account for temporal variables that can strongly affect the detectability of echoes. In particular, the sonar equation ignores the fact that much of the noise encountered by singing humpback whales is spectrally and temporally predictable, and that audition in mammals is a dynamic and plastic process. Experiments are needed to test the hypothesis that singing humpback whales listen for and respond to echoes generated by their songs 相似文献