共查询到20条相似文献，搜索用时 15 毫秒
1.
A numerical algorithm based on the boundary element method (BEM) is presented for predicting the hydrodynamic characteristics of the various planing hull forms. The boundary integral equation is derived using Green's theorem on the wetted body surface and the free surface. The ventilation function at the transom is estimated with Doctor's empirical formula. This function is defined as the transom zone free surface boundary condition. The combined boundary integral equation and modified free surface boundary condition are simultaneously solved to determine the dipole on the wetted hull surface and the source on the free surface. The method is applied to investigate three examples of planing hulls, which include flat-plates, as well as wedge-shaped and variable deadrise planing hulls. Their hydrodynamic characteristics are calculated for different speeds. Computational results are presented and compared with existing theories and experiments. On the whole, the agreement between the present method and the selected experimental and numerical data is satisfactory. 相似文献
2.
This paper discusses the numerical prediction of the induced pressure and lift of the planing surfaces in a steady motion based on the potential flow solver as well as the spray drag by use of the practical method.The numerical method for computation of the induced pressure and lift is potential-based boundary element method.Special technique is identified to present upwash geometry and to determine the spray drag.Numerical results of a planing flat plate and planing craft model 4666 are presented.It is shown that the method is robust and efficient and the results agree well with the experimental measurements with various Froude humors. 相似文献
3.
A surface panel method treating a boundary-value problem of the Dirichlet type with the free surface is presented to design a three-dimensional body corresponding to a prescribed pressure distribution. The free surface boundary condition is linearized with respect to the oncoming flow, and computed by four-point finite difference scheme. Sample designs for submerged spheroids and Wigley hull are carried out to demonstrate the stable convergence, the effectiveness and the robustness of the method. The design of a 5500TEU container carrier is performed with respect to reduction of the wave resistance. To reduce the wave resistance, calculated pressure on the hull surface is modified to have the lower fluctuation, and is applied as a Dirichlet type dynamic boundary condition on the hull surface. The designed hull form is verified to have the lower wave resistance than the initial one not only by computation but also by experiment. 相似文献
4.
高速滑行艇处于滑行状态时的阻力性能一直是滑行艇水动力性能研究的重点和难点。首先采用半经验半理论的Savitsky法对棱柱形滑行艇的航行姿态与阻力进行研究分析,计算纵倾结果与试验结果吻合良好。然后改变滑行艇的长宽比、重心纵向位置与底部斜升角参数,进一步研究三种参数变化对滑行艇航行姿态与阻力性能的影响。研究结果表明:基于半经验半理论的Savitsky方法可用于棱柱形滑行艇的阻力性能分析;在高速阶段,长宽比、重心纵向位置与底部斜升角参数对阻力影响较大。 相似文献
5.
Ship hull drag reduction using bottom air injection 总被引：1，自引：0，他引：1
Robert Latorre Dr. 《Ocean Engineering》1997,24(2):161-175
The idea of bottom air injection to reduce ship hull resistance is not new. Early patents envisioned planing hull applications. Recent planing hull tests speed realized an increase of 7–12 knots. River barges and ship fitted with an air injection system results are presented to show a 10–15% reduction in the frictional resistance. Graphs for making initial estimates for displacement hulls with bottom air injection are presented. It is clear from these results that improvements in high speed planing catamarans and full form hull resistance can be realized by using bottom air injection. 相似文献
6.
A well-known instability of the high-speed planing crafts is the porpoising instability. This instability involves periodic, coupled heave/pitch oscillations possibly experienced in a planing vessel at high speeds. The porpoising can be controlled by using external devices. Interceptors are vertical blades installed symmetrically at the aft of the craft and have been introduced as a trim control appendage. Here, based on numerical methods and Savitsky porpoising theory, the effects of hydrodynamic interceptors on the porpoising control are investigated. Using computational fluid dynamics, the pressure distribution created by interceptor and its effects on porpoising are computed and then discussed. To model the flow around the vessel model, the Reynolds Average Navier Stokes (RANS) equations are applied. The work deals with craft with and without an interceptor at different heights. A dynamic grid mode involving two degrees of freedom is used. The results show that the interceptor causes an intense pressure at the stern bottom. It also decreases the trim and resistance of the vessel and increases the lift force coefficient which directly affects the porpoising instabilities. Based on the results, the interceptor can completely control the porpoising phenomenon. 相似文献
7.
The demand for high-speed craft (mainly catamarans) used as passenger vessel has increased significantly in the recent years. Looking towards the future and trying to respond to the increasing requirement, high-speed crafts international market is passing through deep changes. Different types of high-speed crafts are being used for passenger transport. However, catamarans and monohulls have been the main choice not only for passenger vessel but also as ferryboat.Generally speaking, the efficient hydrodynamic hull shapes, engine improvements, and lighter hull structures using aluminum and composite materials make possible the increase in cruising speed.The high demand for catamarans are due to its proven performance in calm waters, large deck area compared to monohull crafts and higher speed efficiency using less power. Although the advantages aforementioned, the performance of catamaran vessels in wave conditions still needs to be improved.The high-speed crafts (HSC) market is demanding different HSC designs and a wide range of dimensions focusing on lower resistance and power for higher speed. Therefore, the hull resistance optimization is a key element for a high-speed hull success.In addition to that, trade-off high-speed catamaran (HSCat) design has been improved to achieve main characteristics and hull geometry. This paper presents a contribution to HSCat preliminary design phase. The HSCat preliminary design problem is raised and one solution is attained by multiple criteria optimization technique.The mathematical model was developed considering: hull arrangement (area and volume), lightweight material application (aluminum hull), hull resistance evaluation (using a slender body theory), as well as wave interference effect between hulls, calculated with 3D theory application. Goal programming optimization system was applied to solve the HSCat preliminary design.Finally this paper includes an illustrative example showing the mathematical model and the optimization solution. An HSCat passenger inland transport in Amazon area preliminary design was used as case study. The problem is presented, the main constrains analyzed and the optimum solution shown. Trade off graphs was also included to highlight the mathematical model convergence process. 相似文献
8.
Computation of wave-making resistance of a catamaran in deep water using a potential-based panel method 总被引：1，自引：0，他引：1
This paper presents a potential-based boundary element method for solving a nonlinear free-surface flow problem for a Wigley catamaran moving with a uniform speed in deep water. Since the interior flow of each monohull of the catamaran is different from the exterior flow, both monohulls must be considered as lifting bodies. The pressure Kutta condition is imposed at the trailing-edge of the lifting body by determining the dipole distribution, which generates required circulation on the lifting part. The effects of wave interference and hull separation on the hydrodynamic characteristics of the catamaran hull are analyzed and the validity of the computer scheme is examined by comparing the wave resistance with the numerical results of others. The present method could be a useful design tool for screening the suitable combinations of hull parameters and hull spacing at the preliminary design stage of catamaran hull. 相似文献
9.
The hydrodynamic problem of 3D planing surface is studied by a finite element approach. The planing surface is represented by a number of pressure patches whose strengths are constant at each element. The unknown pressure strength is obtained by using the free surface elevation condition under the planing surface and Kutta condition at the transom stern. Previous studies indicate that, when the constant pressure distribution method is used, the number of buttocks should be less than five or six, otherwise the calculated pressure distribution will start to oscillate and even become divergent. In the present study, after careful examination of the influence coefficients, it is found that the accuracy of the influence coefficients matrix is very important to the convergence of the solution, especially when the number of elements is relatively high. The oscillation of the pressure distribution can be avoided by constant element method if the influence coefficients are sufficiently accurate. The predicted results of the present paper with more number of buttocks are in good agreement with other researchers'. It is concluded that the irregularity of the pressure distribution found in previous studies is most likely caused by the low accuracy in their calculation of the influence coefficients, not by the method itself. 相似文献
10.
A full time-domain analysis program is developed for the coupled dynamic analysis of offshore structures. For the hydrodynamic loads, a time domain second order method is developed. In this approach, Taylor series expansions are applied to the body surface and free-surface boundary conditions, and the Stokes perturbation procedure is then used to establish the corresponding boundary value problems with time-independent boundaries. A higher-order boundary element method (HOBEM) is developed to calculate the velocity potential of the resulting flow field at each time step. The free-surface boundary condition is satisfied to the second order by fourth order Adams–Bashforth–Moultn method. An artificial damping layer is adopted on the free surface to avoid the wave reflection. The mooring-line/tendon/riser dynamics are based on the rod theory and the finite element method (FEM), with the governing equations described in a global coordinate system. In the coupled dynamic analysis, the motion equation for the hull and dynamic equations for mooring-lines/tendons/risers are solved simultaneously using the Newmark method. The coupled analysis program is applied for a truss Spar motion response simulation. Numerical results including motions and tensions at the top of mooring-lines/risers are presented, and some significant conclusions are derived. 相似文献
11.
《Ocean Engineering》2004,31(3-4):253-267
Artificial air cavity ship concept has received some interest due to its potential on viscous resistance reduction for high speed craft. Although a small number of ships were designed and built by using this concept, further research on resistance components is required to improve the understanding of artificial air cavity forms. A method based on tank testing with wave pattern measurements to identify resistance components was adopted in the current work. Resistance tests were conducted with two forms; first of which was conventional prismatic planing hull form with a deadrise angle of 10°, and second one was an alternative form with an artificially cavity which was tested both without any air injection, and with two different air injection rates.Total resistance, running trim, sinkage, supply airflow to artificial cavity, air pressure in the cavity and wave pattern generated by the hulls were measured. Frictional resistance was calculated from wetted surface area and compared with resistance component obtained by subtracting wave pattern resistance from the total resistance. Wave pattern spectrums with air cavity configurations were compared across the speed range. 相似文献
12.
Running attitudes of semi-displacement vessels are significantly changed at high speed and thus have an effect on resistance performance and stability of the vessel. There have been many theoretical approaches about the prediction of running attitudes of high-speed vessels in calm water. Most of them proposed theoretical formulations for the prismatic hard-chine planing hull. In this paper, running attitudes of a semi-displacement round bilge vessel are theoretically predicted and verified by high-speed model tests. Previous calculation methods for hard-chine planing vessels are extended to be applied to semi-displacement round bilge vessels. Force and moment components acting on the vessel are estimated in the present iteration program. Hydrodynamic forces are calculated by ‘added mass planing theory’, and near-transom correction function is modified to be suitable to a semi-displacement vessel. Next, ‘plate pressure distribution method’ is proposed as a new hydrodynamic force calculation method. Theoretical pressure model of the 2-dimensional flat plate is distributed on the instantaneous waterplane corresponding to the attitude of the vessel, and hydrodynamic force and moment are estimated by integration of those pressures. Calculations by two methods show good agreements with experimental results. 相似文献
13.
Peter R. Payne 《Ocean Engineering》1982,9(4):373-384
Earlier papers (Payne, 1981 a,b,c) have developed what might be called a virtual mass theory which in principle permits the forces on any planing hull form to be calculated. In the present paper, this methodology is extended to calculate the thickness and momentum of the jet or spray sheet thrown off by the planing surface. For a two-dimensional flat planing plate—the only case where comparison is possible—the theory gives essentially the same result as that of Pierson and Leshnover (1948). For a three-dimensional flat plate and prismatic hulls, the results seem physically reasonable.For the small trim angles associated with efficient planing, on a weightless inviscid fluid the total pressure drag of any hull can be reduced to close to zero by deflecting the jet rearwards and parallel to the undisturbed surface, the residual resistance being due to the cross-flow force which varies as (trim angle)2. 相似文献
14.
Peter R. Payne 《Ocean Engineering》1984,11(2):129-184
This paper gives an overview of the development of the supercritical planing hull concept during the last two decades. Our starting point was the body of theoretical and tank testing work on supercritical displacement ships which was completed by Lewis and others by 1960. In 1964 we launched a manned model small waterplane twin hull (SWATH) craft having a very low pitch stiffness, and thus very little pitching motion at wave encounter frequencies above resonance. A second craft was launched the following year, after which we changed the emphasis of our program to the higher speeds associated with planning craft. Planning catamarans occupied us between 1967 and 1971, when the first Sea Knife monohull supercritical planning hull was launched. The most recent Sea Knife is 34 ft L.O.A., displaces 16,000 lb with full fuel and crew, has been timed at 80 mph in sea state 3, and (from model tests) can do the same in sea state 4 with a comfortable ride. We conclude that supercritical planing hulls are very suitable for high speed ferries, patrol craft and crewboats, and that the technology is now mature. 相似文献
15.
Research on Design Method of the Full Form Ship with Minimum Thrust Deduction Factor 总被引：1，自引：1，他引：0
In the preliminary design stage of the full form ships, in order to obtain a hull form with low resistance and maximum propulsion efficiency, an optimization design program for a full form ship with the minimum thrust deduction factor has been developed, which combined the potential flow theory and boundary layer theory with the optimization technique. In the optimization process, the Sequential Unconstrained Minimization Technique(SUMT) interior point method of Nonlinear Programming(NLP) was proposed with the minimum thrust deduction factor as the objective function. An appropriate displacement is a basic constraint condition, and the boundary layer separation is an additional one. The parameters of the hull form modification function are used as design variables. At last, the numerical optimization example for lines of after-body of 50000 DWT product oil tanker was provided, which indicated that the propulsion efficiency was improved distinctly by this optimal design method. 相似文献
16.
Interceptors are vertical blades installed symmetrically aft of the craft. This article aims to investigate the main geometrical (height and span length) parameters in interceptors. Different Models with and without interceptors at different heights and spans have been analyzed based on the finite volume method and SIMPLE algorithm using dynamic mesh. In order to validate CFD results, the grid convergence index (GCI method) has been used to estimate the uncertainties caused by grid-spacing and time-step. Although it has been proved that the interceptors are very useful in trim control and resistance reduction, choosing wrong size interceptors could not only destroy their effectiveness, but also endanger the planing boat due to the creation of a strong moment leading to negative trim. The results of this study show that among all effective variables, the boundary layer thickness (h) at the stern (where the interceptor is installed), is far more important than, some other particular parameter, on interceptor performance and should be taken into account in estimating the interceptor height (d) and span (s). Generally, the interceptor height should not be higher than 60 percent of boundary layer thickness at transom. For optimum efficiency, when the interceptor height equals 60 percent of the boundary layer, the interceptor span length should be seven times as much as the interceptor height. At the end, based on Reynolds number the paper presents three figures, setting the basis for optimal interceptor sizes for its use in planing boats. 相似文献
17.
A numerical investigation of the bottom pressure and wave elevation generated by a planing hull in finite-depth water is presented. While the existing literature addresses the free-surface deformation and pressure field at the seafloor independently, this work proposes a direct comparison between the two hydrodynamic quantities. The dependence of the pressure disturbances at the ocean floor from the waves generated at the free-surface by a planing hull is studied for several values of both the depth and hull Froude numbers. The methodology employed is Smoothed Particle Hydrodynamics (SPH), a numerical technique based on the discretization of the continuum fields of hydrodynamics through mesh-less particles. The SPH code herein chosen is initially validated against experimental data for transom-stern flow. Subsequently, numerical simulations are presented for a planing hull in high-speed regimes. The results show a direct correlation between surface wave dynamics and hydrodynamic pressure disturbances at the seafloor as the value of the Froude number is varied. This is assessed by studying the inverse dependence of the low-pressure wake angle with the Froude number and by comparison of SPH results with similar works in the cited literature. 相似文献
18.
A boundary element method is developed for calculating the flare ship hull slammingproblem.The nonlinear free surface elevation and the linear element assumption are employed.The meth-od has been verified by comparisons with results for the water entry of wedges with various deadriseangles.Numerical results show that the pressure distribution varies greatly with the ship hull with differentcurvilinear equations,and the slamming features are also different.From the numerical simulation,the au-thors found that the structural damage of the flare hull might be caused by the increasing hydrodynamicpressure over an extensive area on the flare when the upper part of the flare comes into contact with water. 相似文献
19.
A time-domain method is applied to simulate nonlinear wave diffraction around a surface piercing 3-D arbitrary body. The method involves the application of Taylor series expansions and the use of perturbation procedure to establish the corresponding boundary value problems with respect to a time-independent fluid domain. A boundary element method based on B-spline expansion is used to calculate the wave field at each time step, and the free surface boundary condition is satisfied to the second order of wave steepness by a numerical integration in time. An artificial damping layer is adopted on the free surface for the removal of wave reflection from the outer boundary. As an illustration, the method is used to compute the second-order wave forces and run-up on a surface-piercing circular cylinder. The present method is found to be accurate, computationally efficient, and numerically stable. 相似文献
20.
This work addresses the experimental and numerical study of a stepped planing hull and the related fluid dynamics phenomena typically occurring in the stepped hull in the unwetted aft body area behind the step. In the last few years, the interest in high-speed planing crafts, with low weight-to-power ratios, has been increasing significantly, and, in such context, naval architects have been orienting toward the stepped hull solution. Stepped planing hulls ensure good dynamic stability and seakeeping qualities at high speeds. This is mainly due to the reduction of the wetted area, which is caused by the flow separation occurring at the step. This paper presents the experimental results of towing tank tests in calm water on a single-step hull model, which is the first model of a new systematic series. The same flow conditions are analyzed via Reynolds Averaged Navier-Stokes (RANS) and Large Eddy Simulations (LES), with different moving mesh techniques (overset/chimera and morphing grid), performed at different model speeds. The numerical results are in accordance with experimental data, and overset/chimera grid is found to be the best approach between the analyzed ones. The flow patterns obtained numerically through LES on a refined grid appear similar to the ones observed in towing tank investigations through photographic acquisitions. These flow patterns are dominated by a rather complex 3D arrangement of vortices originating from air spillage at both sides of the step. The understanding of these phenomena is important for the effectiveness of stepped hull designs. 相似文献