艏艉线型优化对船舶阻力性能的影响

为提高母型船阻力性能,以船体阻力性能为优化对象,基于改造母型船法,研究船舶球鼻艏以及船尾线型的改变对船舶阻力性能的影响.采用高度集成化的Tribon系统、可视化绘图软件Auto CAD及CFD(Computational Fluid Dynamics)通用前处理软件ICEM联合建模的方法来建立船体模型.通过模拟计算结果与实验值的对比分析,验证CFD技术在船舶阻力性能预报中的合理性和有效性.通过对比3种不同球鼻艏时的船体阻力得知:从阻力性能方面考虑,对于低速丰满型船舶选用普通型球鼻艏以及中高速船舶采用上翘型球鼻艏均可以获取较好地减阻效果.同时比较不同航速下尾部线型对船体总阻力的影响表明,选优后的方形尾在相同的航速下阻力低、消耗的功率小、形状效应小、黏压阻力和摩擦阻力也相对较小.     

Some methods to obtain the added resistance of a ship advancing in waves

Added resistance in waves is an important part of ship dynamic due to its economical effect on ship exploitation. Can the ship sustain speed in a rough sea state? If not, this will produce delays and economical losses if added resistance is not taken into account in the propulsion design. There are not many simple methods to obtain the added resistance in waves of a ship, and the validity of the results is not always good enough for different ships. In this paper, some theories that can be used to predict the added resistance of a ship are studied and validated against seakeeping tests of some monohull models. Tests and results focus in head seas, which are the most severe for the added resistance. Experimental results are compared with numerical calculations and conclusions about the range of application of the presented theories are obtained.     

深远海养殖工船最小推进功率研究

针对十万吨级深远海养殖工船在波浪中的阻力和运动响应开展了船模试验与模拟计算,并对其最小推进功率进行了校核。以试验流体力学（EFD）模型试验与模型尺度计算流体力学（CFD）模拟计算的结果进行对比作为方法验证,将实尺度CFD模拟计算的结果直接用于最小推进功率的校核。结果显示,EFD模型试验结果与模型尺度CFD计算结果误差在10%左右,计算精度满足工程要求。在规定的恶劣海况下该船型波浪增阻占总阻力的比例最高可达56.3%,螺旋桨转矩可达最大转矩的63.9%。等级2简化评估法得到的最小推进功率为等级1线评估法给出的最小功率线值的58.9%。研究表明实尺度CFD模拟计算可直接用于船舶最小推进功率的校核,此深远海养殖工船使用等级2简化评估方法进行校核更容易满足规范要求,其最小推进功率应不小于6 833 kW。     

Hydrodynamic Coefficients and Wave Excitation Forces for A Ship near A Quay

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.     

VLCC油船波浪增阻预报方法的实用修正

近年来随着船舶环保和营运性能要求更高,波浪增阻预报正变得越来越重要。由于存在假设和简化,势流理论方法的短波增阻预报精度差,而经验方法在不同船型中的适用性不强。以有航速VLCC船迎浪航行为例,考虑吃水和航速影响,对理论和半经验方法的波浪增阻结果进行验证和比较分析,并总结出适用特定船型的快速精确预报方法。理论方法基于水平线段移动脉动源的三维面元法求解速度势问题,进而采用三维船体辐射能量法得到船舶辐射增阻,基于二阶波浪力定常分量公式计算得到绕射增阻;经验方法采用ISO15016-2015推荐的STAWAVE2方法。通过分析辐射和绕射增阻占比,讨论了目前方法的适用范围,进而对半经验方法的修正系数进行了研究,给出了反映相似船型和航速特征的改进公式。     

计算波浪飘移阻尼的一种切片理论方法

本文利用Ｇｅｒｒｉｔｓｍａ波浪阻力增加公式，导出一种基于切片理论的波浪漂移阻尼的计算方法。与现有理论和试验结果比较证实具有工程一致性。可以指出，这是一种简单使用，便于推广的应用的理论方法。     

Hydrodynamic interactions between two ships advancing in waves

In this paper the hydrodynamic problems between two moving ships in waves are analyzed using a three-dimensional potential-flow theory based on the source distribution technique. The potential is presented by a distribution of source over the ship hull. The corresponding Green functions and their derivatives can be easily solved numerically by using the series expansions of Telste and Noblesse's algorithm for the Cauchy principal value integral of unsteady flow. The numerical solution is evaluated by applying the present method to two pairs of models and compared with experimental data and strip theory. From the comparisons, it shows that the hydrodynamic interactions are generally important. In the resonance region, the hydrodynamic interaction calculated by the 3D method is more reasonable, which is not so significant as that by the 2D method. The technique developed here may serve as a more rigorous tool to analyze the related problems of two ships doing underway replenishment in waves.     

Evaluation of Hydrodynamic Coefficients of Ships Oscillating in A Numerical Wave Tank

A technique for the evaluation of the hydrodynamic coefficients of ships is outlined for ship oscillating in a numerical wave tank, which is established on Computational Fluid Dynamics (CFD) theories. The numerical simulation of ship sections and bodies forced oscillating in the tank are carried out. The added mass and damping coefficients are obtained by the decomposition of the computational results, which agree well with the corresponding ones of potential theories.     

Evaluation of Hydrodynmic Coefficients of Ships Oscillating in A Numerical Wave Tank

A technique for the evaluation of the hydrodynamic coefficients of ships is outlined for ship oscillating in a numerical wave tank,which is established on Computational Fluid Dynamics (CFD) theories.The numerical simulation of ship sections and bodies forced oscillating in the tank are carried out.The added mass and damping coefficients are obtained by the decomposition of the computational results,which agree well with the corresponding ones of potential theories.     

Resistance and propulsion characteristics of various commercial ships based on CFD results

This paper uses computational tools to examine the speed performance of various types of commercial ships including resistance and propulsion characteristics. Eight commercial ships built in the last decade were selected for the study. They include four large-sized container carriers, one bulk carrier, one VLCC, and two LNG carriers. The Reynolds averaged Navier-Stokes equation has been utilized, and the computations were executed under the same conditions of the model tests to predict the speed performance, i.e., resistance and self-propulsion. The self-propulsion point was obtained from load-varying tests. The speed performance was predicted based on the model-ship performance analysis method of the revised ITTC’78 method. The limiting streamlines on the hull, wave characteristics around the model ship, and the wake characteristics on the propeller plane were also investigated. After completing the computations, a series of model tests were conducted to evaluate the accuracy of the computational predictions. The predictions clearly reveal the differences in the resistance and propulsion characteristics regarding the various types of commercial ships, and may be applicable to hull-form design.     

Simulation of Kelvin wakes in optical images of rough sea surface

Kelvin wake is one of the common wakes generated by moving ships and contains rich information about ships. In this paper, free wave elevations of Kelvin wake are calculated based on the Michell thin ship theory combined with a point source perturbation model. The probability density function of sea surface slopes is introduced to calculate the specular reflection of sunlight and skylight and the refraction of scattered light underwater. Satellite-detected Kelvin wakes are then simulated by adding surface specular reflectance and water-leaving reflectance. Simulation results agree well with satellite measurements. The specular reflection of sunlight is the decisive factor affecting the features of Kelvin wakes according to the simulation results. The main factors that influence the specular reflection of sunlight, such as the incident direction and observation direction, ship parameters, and background environment, are discussed. This study is helpful for wake detection and provides a preliminary theoretical method for the retrieval of ship information.     

Numerical Simulation on the Resistance Performance of Ice-Going Container Ship Under Brash Ice Conditions

Ice resistance prediction is a critical issue in the preliminary design of ships navigating brash ice conditions, which is closely related to the safety of a ship to navigate encounter brash ice, and has significant effects on the kinds of propellers and motor power needed. In research on this topic, model tests and full-scale tests on ships have thus far been the primary approaches. In recent years, the application of the finite element method (FEM) has also attracted interest. Some researchers have conducted numerical simulations on ship–ice interactions using the fluid–structure interaction (FSI) method. This study used this method to predict and analyze the resistance of an ice-going ship, and compared the results with those of model ship tests conducted in a towing tank with synthetic ice to discuss the feasibility of the FEM. A numerical simulation and experimental methods were used to predict the brash ice resistance of an ice-going container ship model in a condition with three concentrations of brash ice (60%, 80%, and 90%). A comparison of the results yielded satisfactory agreement between the numerical simulation and the experiments in terms of both observed phenomena and resistance values, indicating that the proposed numerical simulation has significant potential for use in related studies in the future.     

Numerical investigation of the seakeeping behavior of a catamaran advancing in regular head waves

A numerical study was undertaken in order to assess the capability of an unsteady RANS code to predict the seakeeping characteristics of a high-speed multi-hull vessel in high sea states. Numerical analysis includes evaluation of ship motions, effects of wave steepness on ship response, catamaran natural frequency and added resistance in waves. Computations were performed for the DELFT 372 catamaran by the URANS solver CFDSHIP-Iowa V.4. The code was validated with encouraging results for high ship speeds (0.3≤Fn≤0.75) and high wave amplitudes (0.025≤Ak≤0.1). Comparison with strip theory solutions shows that the RANS method predicts ship motions with higher accuracy and allows the detection of nonlinear effects. Current computations evidence that heave peaks occur at resonance for all Fn, and reach the absolute maximum at Fn=0.75. Maximum pitch occurs at frequencies lower than resonance, for each speed, and absolute maximum occurs at medium Fn=0.6. Maximum added resistance, R_aw, was computed at Fn=0.45, which, interestingly, is near the catamaran Fn_coincidence. Overall, we found similar results as Simonsen et al. (2008) for KCS containership, though, herein, a multi-hull geometry and higher speeds were tested. Also, our results are useful to further evaluate the exciting forces and their correlation with f_e and λ/L_pp.     

Spar平台湿拖阻力性能研究

海洋平台由拖船拖至工作地点,计算海洋平台的湿拖阻力在实际工程应用中具有重要意义。采用实验和数值模拟两种方法进行桁架式Spar平台的湿拖阻力性能研究,并将两种结果进行对比。并分析了桁架式Spar平台的垂荡板间流场的变化规律。研究结果表明,Spar平台的湿拖阻力中,摩擦阻力所占总阻力的比例小于10%;在平台拖曳运动的前几秒中,垂荡板间流体剧烈运动,速度和压力显著变化,随后就运动慢慢变缓;Spar平台在低速拖曳时会产生明显的波浪,尾部有回流。     

Hydrodynamic shape optimization by high fidelity CFD solver and Gaussian process based response surface method

A computational framework for hydrodynamic shape optimization of complex ship hull form is proposed and applied to improve the calm water performance of the KRISO Container Ship (KCS). The framework relies on three key features: a novel shape morphing method based on a combination of subdivision surfaces and free form deformations, a robust three dimensional viscous computational fluid dynamic solver based on the openFOAM open-source libraries and a Gaussian process-response surface method (GP-RSM) based on ordinary Kriging model which has been created to speed-up the evaluation of the quantity of interest (QoI) of the design process.The accuracy of the hydrodynamic solver is proven by comparing the obtained results against available experimental measurements. A preliminary sensitivity analysis on the mesh size has been carried out aiming at reducing the computational burden required by the CFD predictions. Three GP-RSMs have been trained relying on increasing number of hull designs. Each surrogate model has been cross-validated by both leave-one-out and k-fold techniques. The behaviours of these multi-dimensional surfaces have been analyzed in details by sampling the investigated design space with 10⁷ points according to a Full-Factorial algorithm, highlighting the regions of maximum deviation with respect to the resistance of the reference hull. The three optimum designs provided by the corresponding GP-RSM models have been verified by using high-fidelity CFD simulations with a refined mesh configuration. Calm water resistance, wave patterns and pressure distributions over the selected hull surfaces have been discussed in the light of the generated shape variations.     

Full scale CFD seakeeping simulations for case study ship redesigned from V-shaped bulbous bow to X-bow hull form

Increasing propulsion efficiency, safety, comfort and operability are of the great importance, especially for small ships operating on windy sites like the North Sea and the Baltic Sea. Seakeeping performance of ships and offshore structures can be analysed by different methods and the one that is becoming increasingly important is CFD RANS. The recent development of simulation techniques together with rising HPC accessibility enables performance of advanced seakeeping simulations for ships in a full scale. The paper presents CFD seakeeping analysis for a case study vessel in two variants: V-shaped bulbous bow hull form (as built) and innovative hull form (X-bow type). The study presents the influence of redesigning the ship on selected seakeeping aspects. The advanced CFD model, with the application of overset mesh technique, was described in detail. Selected numerical results were validated on the basis of experimental testing in a towing tank and showed good agreement. The approach demonstrated here of performing the CFD seakeeping simulations for the analysis of ship performance in a full scale and close to real loading conditions has direct application to the design process as well as in determination of optimal operational parameters of any ship.     

Numerical study on scale effect of form factor

The scale effect of form factor is investigated via a numerical approach in this paper, where the turbulent ship flow is computed by solving the steady and incompressible Reynolds-averaged Navier-Stokes and continuity equations. A wall function approach is employed to bridge the near-wall and outer turbulent flow region. The numerical scheme based on a finite-volume formulation is applied to discretize the coupled governing equation. For the sake of numerical stability, accuracy and economy, an identical grid is employed to compute ship flow at different Reynolds number, where the grid is optimized for the medium Reynolds number of the investigated range. Four surface ships and two sub-bodies with notably different geometrical characteristics are chosen as the investigated cases, where double-model flow without appendages is computed. The calculated total resistance coefficient shows a decreasing tendency against Reynolds number among all studied hulls. Similar to the calculated total resistance coefficient, the calculated friction resistance coefficient decreases with the Reynolds number and varies relatively little for a given Reynolds number among different hulls. The viscous pressure resistance coefficient is less insensitive to the Reynolds number but apparently depends on hull form. Compared with the form factor calculation based on empirical friction lines, the flat-plate friction prediction based on CFD approach clearly gives smaller Re-dependent form factor, which should more realistically reflect the scale effect of form factor. The form factor exhibits a near linear and increasing dependence on Reynolds number. The numerical results show that the dependence of r_P on Reynolds number mainly governs the scale effect of form factor.     

Optimization Design of Minimum Total Resistance Hull Form Based on CFD Method

In order to reduce the resistance and improve the hydrodynamic performance of a ship, two hull form design methods are proposed based on the potential flow theory and viscous flow theory. The flow fields are meshed using body-fitted mesh and structured grids. The parameters of the hull modification function are the design variables. A three-dimensional modeling method is used to alter the geometry. The Non-Linear Programming (NLP) method is utilized to optimize a David Taylor Model Basin (DTMB) model 5415 ship under the constraints, including the displacement constraint. The optimization results show an effective reduction of the resistance. The two hull form design methods developed in this study can provide technical support and theoretical basis for designing green ships.     

尺度自适应分层多阈值热红外遥感舰船检测

针对热红外遥感图像由于低对比度、条带噪声、低空间分辨率等特点而导致的检测效果不佳问题,提出了一种近岸舰船目标尺度自适应选择分层多阈值检测方法。采用舰船模板图像尺度归一化高斯拉普拉斯函数取极大值准则进行尺度自适应选择,利用所选的高斯多尺度空间差分多阈值筛选进行近岸舰船检测,并根据不同类型舰船模板图像尺度和分块数选择对热红外图像舰船目标检测的影响进行验证实验。实验结果表明:所提方法能根据模板尺度特征滤除相似区域,通过设置合理尺度和阈值参数能实现有效检测,且具有一定的抗噪能力。     

Application of potential flow methods to fast displacement ships at transcritical speeds in shallow water

Computer codes implementing three different numerical methods for the prediction of ship squat at transcritical speeds in shallow open-water are tested. SlenderFlow is a potential flow code specifically for ships in very shallow water, based on partially dispersive slender body theory. Flotilla is a potential flow code based on fully dispersive thin-ship theory. Rapid is a general nonlinear free-surface panel code. Code predictions of transcritical sinkage, trim and resistance in laterally unrestricted water were compared to the experimental results of Graff (1964) for two Taylor series hulls in a finite-width towing tank. Once tank width effects were accounted for, each of the three codes was found to give good predictions within the valid range of the underlying theory. A simple method for estimating transcritical wave resistance from trim is presented.