Hull form reliability-based robust design optimization combining polynomial chaos expansion and maximum entropy method

In the ship design optimization process, the neglect of the unavoidable uncertainty of parameters in the actual navigation and experimental observations, may lead to a bad result with some hidden dangers in practical applications. Considering the influence of the uncertainty, a new and effective hull form reliability-based robust design optimization (RBRDO) framework, including the hull form modification module and RBRDO module, has been developed and tested in the present work. Radial basis function method is utilized as the parametric hull surface modification technique to generate a series of smooth hull forms while combining polynomial chaos expansions (PCE) method with maximum entropy method (MEM) to conduct the uncertainty analysis for the prediction of the mean and the standard deviation of the objective and the failure probability of constraints. To verify the validity of the method, hull form design optimization of the bow of KCS model is implemented under the influence of the uncertainty. Numerical results indicate that the proposed RBRDO framework is effective compared with traditional Monte Carlo method. Meanwhile, compared with traditional DO case, RBRDO case has higher adaptability to the environmental uncertainty with the lower failure probability, which ensure the robustness and reliability of the optimal hull form.     

Design of ship's bow form by potential-based panel method

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.     

The influence of hull form on the motions of high speed vessels in head seas

Prediction of ship motions at high Froude number is carried out using a time domain strip theory in which the unsteady hydrodynamic problem is treated in terms of the motion of fixed strips of the water as hull sections pass through it. The Green function solution is described and the integration of the ship motion carried out by an averaging method to ensure stability of the solution. The method is validated by comparison with tank data for conventional slender hulls suitable for catamarans, small water area twin hull (SWATH) forms and hulls suitable for high-speed monohulls. Motion computations are then carried out for 14 designs with an operating speed of 40 kts and a displacement of 1000 tonnes. The vessels are assumed not to be fitted with motion control systems for the purposes of this comparative study. Motion sickness incidence is predicted to rise to between 42 and 72% depending upon the hull design in 3 m head seas of average period 7.5 s. MSI values reduce in smaller seas with a shorter average period to be less than 15% in all cases in 1m seas with an average period of 5.5 s.     

An inverse hull design approach in minimizing the ship wave

The Levenberg–Marquardt Method (LMM) and a panel code for solving the wave-making problem are utilized in an inverse hull design problem for minimizing the wave of ships. A typical catamaran is selected as the example ship for the present study. The hull form of the catamaran is described by the B-spline surface method so that the shape of the hull can be completely specified using only a small number of parameters (i.e. control points). The technique of parameter estimation for the inverse design problem is thus chosen. The LMM of parameter estimation, which is the combination of steepest descent and Newton’s methods, has been proven to be a powerful tool for the inverse shape design problem. For this reason it is adopted in the present study.In the present studies, the inverse hull design method can not only be applied to estimate the hull form based on the known wave data of the target ship but can also be applied to estimate the unknown hull form based on the reduced wave height. The optimal hull forms of minimizing wave for a typical catamaran in deep water at service speed and at the critical speed of shallow water are estimated, respectively. Moreover, a new hull form with the combining feature of the optimal hull forms for deep water and shallow water is performing well under both conditions. The numerical simulation indicates that the hull form designed by inverse hull design method can reduce the ship wave significantly in comparison with the original hull form.     

Propulsive performance of a tanker hull form in damaged conditions

Many disastrous oil spill accidents from damaged vessels become worse especially when the early treatment is not prompt enough. To properly handle this type of accidents and prevent further disasters, International Maritime Organization establishes and imposes various rules and regulations. Better understanding of the propulsive performance of damaged vessels is important for containing the oil spill while the vessels are being towed or self-propelled. In the present study, both experimental and computational methods were used to investigate the flow phenomena around the hull and the hydrodynamic performances of a VLCC in various damaged conditions. From the resistance and self-propulsion test results, it is found that higher power is required to propel the ship especially with the bow trim. Wake measurement data provide physical insight into the factors to be considered for the propeller operation in damaged conditions.     

An inverse design approach for minimising wake at propeller plane using CFD

Knowledge of wake characteristics in the stern region is important for ensuring good propeller design and performance. This work examines the utility of CFD in the analysis of flow in the case of full aft beam vessels having characteristic cut stern shape to facilitate propeller aperture. The underwater stern shape may be more complex due to the occurrence of stern appendages such as bossings, strut supports and local shape variations. To this extent, CFD offers an effective tool for both qualitative as well as quantitative assessment of the local geometry. Wake estimate is required for choice of the most favorable propeller geometry. In the present method, the analysis quantifies the effects of small changes in stern rake angles and offers an inverse design approach towards finalising the stern shape. The method consists of solving the standard k-ε turbulent model of RANS equations in cell centered finite volume multi zone grid in the flow domain. This approach has been used in estimating the velocity at the propeller plane. The results have been compared with experimentally obtained values of nominal wake. The approach suggests that CFD can provide a cost effective and quick assessment of flow. It is also an attractive means of pre-empting heterogeneous flow related problems such as vibration and noise due to unfavorable wake in the stern region.     

Robust design of microbubble drag reduction in a channel flow using the Taguchi method

This study attempts to obtain optimum parametric levels for robust design of the microbubble drag reduction in a turbulent channel flow. This work was carried out experimentally by measuring the frictional resistance on the upper wall of the channel to analyze the efficiency of drag reduction. Considering the mean flow speed as an indicative factor, several controllable factors that influence the effect of microbubble drag reduction were investigated in this work by using the Taguchi method. The controllable factors in this study were the amount of air injected, area of air injection, and microbubble size. For the condition of optimum parametric levels, the effect of drag reduced could reach up to 21.6%.     

采用射线追踪法的天然气水合物海底地震观测系统设计

射线追踪法是以建立的地下地质模型为基础,研究不同的激发点发出的射线经地下地质界面反射后可以被接收到的信息,从而了解不同的观测系统对于特定地质条件地震资料采集的效果,对于海上地震采集相关参数的确定十分关键.在天然气水合物地震勘探中,丰富的多波勘探信息对于查清水合物内部速度结构、提高地层的分辨率具有重要意义.本文在分析国外天然气水合物海底地震仪(OBS,ocean bottom seismometer)勘探的应用成果基础上,采用射线追踪法理论计算和海上实验,实现了针对天然气水合物的海底地震观测系统设计,试验获得了转换横波记录,取得了良好的应用效果.     

发展基于集合样本估计的SST张驰逼近方法用于气候模式的次表层海温场订正

An ensemble-based assimilation method is proposed for correcting the subsurface temperature field when nudging the sea surface temperature(SST) observations into the Max Planck Institute(MPI) climate model,ECHAM5/MPI-OM. This method can project SST directly to subsurface according to model ensemble-based correlations between SST and subsurface temperature. Results from a 50 year(1960–2009) assimilation experiment show the method can improve the subsurface temperature field up to 300 m compared to the qualitycontrolled subsurface ocean temperature objective analyses(EN4), through reducing the biases of the thermal states, improving the thermocline structure, and reducing the root mean square(RMS) errors. Moreover, as most of the improvements concentrate over the upper 100 m, the ocean heat content in the upper 100 m(OHT100 m)is further adopted as a property to validate the performance of the ensemble-based correction method. The results show that RMS errors of the global OHT100 m convergent to one value after several times iteration,indicating this method can represent the relationship between SST and subsurface temperature fields well, and then improve the accuracy of the simulation in the subsurface temperature of the climate model.     

两层流体中多个圆柱浮体波浪力的解析方法

采用解析方法研究了线性入射波作用下两层流体中多个圆柱形淹没浮体的渡浪力特性.首先基于多极子展开方法,建立了散射势函数的解析表达式,并进一步得到浮体散射渡浪力的计算公式,然后利用边界元方法验证了本文的解析解,最后分析了不同参数的变化对双圆柱形浮体结构波浪力的特有影响.