Multi-fidelity optimization of a high-speed foil-assisted semi-planing catamaran for low wake

The wakes of high-speed passenger-only ferries that operated through Rich Passage, on the Seattle-Bremerton ferry route, caused beach erosion and damage to habitat. A task was initiated to design a low-wake high-speed vessel using multi-fidelity CFD based design optimization by using low-fidelity potential flow solvers for initial global design optimization and by using URANS solvers for high-fidelity tuning of the optimized design. This simulation based design process involved a close collaboration between ship designers, and hydrodynamics and CFD specialists, whose collective expertise guided the evolution of the design based on both hydrodynamic and structural aspects. The initial hull shape optimization using potential flow code was carried out by blending three different initial concepts provided by the designers. Subsequently, URANS was used to evaluate the potential flow optimized hull and to further optimize the hull configuration parameters, namely, the centre-of-gravity, demihull spacing, foil location, foil angle and slenderness ratio at different displacement conditions. The URANS based configuration optimization also took into account the far field wakes’ energy spectrum with an objective of reducing the energetic, low frequency far field wakes which are associated with beach flattening on the mixed sand and gravel beaches. Calculation of the far field wake using URANS would require an unfeasibly large domain size; therefore, a Havelock code with a source distribution matching the URANS calculated near field wave elevation was used to propagate the wakes into the far field. The end result of the optimization was a design with significantly reduced far field wake, which is currently being built for experimental testing.     

Verification and validation study of URANS simulations for an axial waterjet propelled large high-speed ship

The accurate prediction of waterjet propulsion using computational fluid dynamics (CFD) is of interest for performance analyses of existing waterjet designs as well as for improvement and design optimization of new waterjet propulsion systems for high-speed marine vehicles. The present work is performed for three main purposes: (1) to investigate the capability of a URANS flow solver, CFDSHIP-IOWA, for the accurate simulation of waterjet propelled ships, including waterjet–hull interactions; (2) to carry out detailed verification and validation (V&V) analysis; and (3) to identify optimization opportunities for intake duct shape design. A concentrated effort is applied to V&V work and performance analysis of waterjet propelled simulations which form the focus of this paper. The joint high speed sealift design (JHSS), which is a design concept for very large high-speed ships operating at transit speeds of at least 36 knots using four axial flow waterjets, is selected as the initial geometry for the current work and subsequent optimization study. For self-propelled simulations, the ship accelerates until the resistance equals the prescribed thrust and added tow force, and converges to the self propulsion point (SPP). Quantitative V&V studies are performed on both barehull and waterjet appended designs, with corresponding experimental fluid dynamics (EFD) data from 1/34 scale model testing. Uncertainty assessments are performed on iterative convergence and grid size. As a result, the total resistance coefficient for the barehull case and SPP for the waterjet propelled case are validated at the average uncertainty intervals of 7.0 and 1.1%D, respectively. Predictions of CFD computations capture the general trend of resistance over the speed range of 18–42 knots, and show reasonable agreement with EFD with average errors of 1.8 and 8.0%D for the barehull and waterjet cases, respectively. Furthermore, results show that URANS is able to accurately predict the major propulsion related features such as volume flow rate, inlet wake fraction, and net jet thrust with an accuracy of ~9%D. The flow feature details inside the duct and interference of the exit jets are qualitatively well-predicted as well. It is found that there are significant losses in inlet efficiency over the speed range; hence, one objective for subsequent optimization studies could be maximizing the inlet efficiency. Overall, the V&V work indicates that the present approach is an efficient tool for predicting the performance of waterjet propelled JHSS ships and paves the way for future optimization work. The main objective of the optimization will be reduction of powering requirements by increasing the inlet efficiency through modification of intake duct shape.     

Single- and multiobjective design optimization of a fast multihull ship: numerical and experimental results

Numerical optimization of the initial design of a fast catamaran (high-speed sealift research model B, HSSL-B) has been carried out through a simulation-based design (SBD) framework, based on an advanced free-surface unsteady Reynolds-averaged Navier–Stokes (URANS) solver and a potential flow solver, and global optimization (GO) algorithms. The potential flow computational fluid dynamics (CFD) SBD was used to guide the more expensive URANS CFD SBD. The fluid-dynamic analysis of the flow past the catamaran proved that the use of the URANS solver was fundamental in dealing with the multihull interference problem. In the case investigated, the separation distance was small and the viscous flow quite distorted by the proximity of the hulls, so that only viscous solvers could correctly capture the flow details. Sinkage and trim effects, due to the high speed range and again to the small separation distance investigated, are also relevant. The initial HSSL-B geometry and three optimization problems, including single- and multiobjective optimization problems, proposed by designers from Bath Iron Works, were successfully optimized/solved, and finally an experimental campaign was carried out to validate the optimal design. A new verification and validation methodology for assessing uncertainties and errors in simulation-based optimization was used based on the trends, i.e., the differences between the numerically predicted improvement of the objective function and the actual improvement measured in a dedicated experimental campaign, including consideration of numerical and experimental uncertainties. Finally, the success of the optimization processes was confirmed by the experimental measurements, and trends for total resistance, sinkage, and trim between the original and optimal designs were numerically and experimentally verified and validated.     

Uncertainty quantification of Delft catamaran resistance,sinkage and trim for variable Froude number and geometry using metamodels,quadrature and Karhunen–Loève expansion

A framework for assessing convergence and validation of non-intrusive uncertainty quantification (UQ) methods is studied and applied to a complex industrial problem in ship design, namely the high-speed Delft Catamaran advancing in calm water, with variable Froude number and geometry. Relationship between UQ studies and deterministic verification and validation is discussed. Computations are performed using high- (URANS) and low- (potential flow) fidelity simulations. Froude number has expected value and standard deviation equal to 0.5 and 0.05, respectively, on a truncated normal distribution. Geometric uncertainty is related to the research space of a simulation-based design optimization, and assessed through the Karhunen–Loève expansion (KLE). Monte Carlo method with Latin hypercube sampling (MC-LHS) is used to compute expected value, standard deviation, distribution and uncertainty intervals for resistance, sinkage and trim. MC-LHS with CFD is used as a benchmark for validating less costly UQ methods, including MC-LHS with metamodels and standard quadrature formulas. Gaussian quadrature is found the most efficient method; however, MC-LHS with metamodels is preferred since provides with confidence intervals and distributions in a straightforward way and at reasonably small computational cost. UQ results are compared to earlier deterministic single- and multi-objective optimization; reduced-dimensional KLE studies for geometric variability indicate that stochastic optimization would not be of great benefit for the present problem.     

穿浪双体船兴波阻力数值计算

利用基于面元法的船舶兴波阻力和兴波波形的势流计算方法,将CFD与CAD技术联系在一起,数值计算高速穿浪双体船的兴波阻力与兴波波形。兴波阻力的计算与实船的剩余阻力曲线趋势符合,对实船船型参数的选择和优化有一定的指导意义。     

双体甲板运输船波浪载荷

以某双体甲板运输船为例,使用DNV船级社的SESAM软件对其波浪载荷进行直接计算分析,并对比分析了采用“规范方法”与“直接计算方法”得到的波浪载荷值。结果表明,该双体甲板运输船属于低速排水型船,其波浪载荷的计算方法与高速双体船差别较大,“规范方法”主要适用于高速双体船及尺度较小的低速双体船。对于船长为60m及以上的低速双体船,采用“直接计算方法”更能准确地计算出其波浪载荷。     

方尾边界条件在高速多体船兴波阻力计算中的应用

将一种由典型的方尾流动物理模型(水流沿方尾下缘切向脱体)导出的数值方尾边界条件应用于高速多体船兴波问题计算。兴波波形与兴波阻力的数值计算采用基于非均匀有理B样条的广义高阶面元法,所得到的高速双体船算例与高速三体船算例的计算结果合理。     

基于CFD的三体船侧体布局优化

三体船构型复杂,侧体布局对其阻力性能有很大的影响。基于计算流体动力学(Computational Fluid Dynamics, CFD)理论,利用SHIPMDO-WUT软件平台构建一种侧体布局自动优化方法。以某高速三体船为例,进行侧体布局的优化,结果表明:在4个不同弗劳德数下,优化船较母型船的兴波阻力均有所下降,总阻力也相应减小。得出在4个不同弗劳德数下总阻力最小的侧体布局方案,表明该方法的可行性与有效性。研究内容可为三体船减阻优化设计提供参考依据。     

高速排水型船舶艉浪数值计算

采用近、远域结合的方法,对高速排水型船舶在深水状态下的NPL单体船、双体船以及三体船的艉浪进行数值计算,计算与试验比较表明该方法是可行性的,初步探讨了深水条件下单体船艉浪的衰减规律。     

高速双体船的阻力计算

本文根据16条对称片作圆舭型高速双体船的阻力试验资料，运用多元线性回归分析方法，研究高速双体船剩余阻力系数C_r随傅汝德数Fn的变化规律，提出了剩余阻力系数曲线（C_r～Fn曲线）的表达方法。用本文提出的方法计算圆船型高速双体船的剩余阻力系数，在95％的概率下，误差小于5％，较目前使用的其它方法计算简便、精确度高、适用的速度范围广，可供高速双体船设计时估算阻力使用。     

EFD and CFD for KCS heaving and pitching in regular head waves

The KCS container ship was investigated in calm water and regular head seas by means of EFD and CFD. The experimental study was conducted in FORCE Technology’s towing tank in Denmark, and the CFD study was conducted using the URANS codes CFDSHIP-IOWA and Star-CCM+ plus the potential theory code AEGIR. Three speeds were covered and the wave conditions were chosen in order to study the ship’s response in waves under resonance and maximum exciting conditions. In the experiment, the heave and pitch motions and the resistance were measured together with wave elevation of the incoming wave. The model test was designed and conducted in order to enable UA assessment of the measured data. The results show that the ship responds strongly when the resonance and maximum exciting conditions are met. With respect to experimental uncertainty, the level for calm water is comparable to PMM uncertainties for maneuvering testing while the level is higher in waves. Concerning the CFD results, the computation shows a very complex and time-varying flow pattern. For the integral quantities, a comparison between EFD and CFD shows that the computed motions and resistance in calm water is in fair agreement with the measurement. In waves, the motions are still in fair agreement with measured data, but larger differences are observed for the resistance. The mean resistance is reasonable, but the first order amplitude of the resistance time history is underpredicted by CFD. Finally, it seems that the URANS codes are in closer agreement with the measurements compared to the potential theory.     

采用遗传算法进行球鼻艏优化的流体动力计算(英文)

Computational fluid dynamics(CFD) plays a major role in predicting the flow behavior of a ship.With the development of fast computers and robust CFD software,CFD has become an important tool for designers and engineers in the ship industry.In this paper,the hull form of a ship was optimized for total resistance using CFD as a calculation tool and a genetic algorithm as an optimization tool.CFD based optimization consists of major steps involving automatic generation of geometry based on design parameters,automatic generation of mesh,automatic analysis of fluid flow to calculate the required objective/cost function,and finally an optimization tool to evaluate the cost for optimization.In this paper,integration of a genetic algorithm program,written in MATLAB,was carried out with the geometry and meshing software GAMBIT and CFD analysis software FLUENT.Different geometries of additive bulbous bow were incorporated in the original hull based on design parameters.These design variables were optimized to achieve a minimum cost function of "total resistance".Integration of a genetic algorithm with CFD tools proves to be effective for hull form optimization.     

半滑行船扰流板阻力试验研究

半滑行船的航行姿态对船体阻力影响较大。为研究扰流板对半滑行船的降阻作用,首先在3种典型载况下,确定了船模未加扰流板的阻力、纵倾及升沉;然后在这3种载况下,于船模艉部添加扰流板,与静水未添加扰流板时船模的阻力和航态作比较,且不同航速时扰流板的设置不同。实验结果表明:合理的扰流板高度可以减小半滑行船的纵倾角和阻力;扰流板的降阻效果与船模的压载有关,其中满载情况下的降阻效果最为明显,最大可达6%。     

基于CFD技术对2800TEU船的线型优化

基于CFD技术对线型优化是目前业界比较流行的做法。本文依托于实船2800TEU船项目,探索基于NAPA和CFD软件的一体化优化(传统经验模式)和基于CAESES和CFD软件的一体化优化(先进数值评估模式)的有机结合,以船模阻力系数为目标函数,对线型优化。结果显示,航速达到优化目标要求。     

可调长度高速三体船的概念及水动力研究

文章提出了一种新型高速三体船,阐述了它的优点及其应用前景。以DTMB5415为基础,构造了高速三体船型,并设计了8种布置情况,然后利用CFD对高速三体船的八种布置情况和单体船匀速航行时候的水动力性能进行了计算,并分析了不同布置情况下的兴波干扰情况和阻力性能,得出高速三体船的最佳布置方案,单位排水量的阻力下降约32%。     

Computational fluid dynamics-based multiobjective optimization of a surface combatant using a global optimization method

The main objective of this article is to describe the development of two advanced multiobjective optimization methods based on derivative-free techniques and complex computational fluid dynamics (CFD) analysis. Alternatives for the geometry and mesh manipulation techniques are also described. Emphasis is on advanced strategies for the use of computer resource-intensive CFD solvers in the optimization process: indeed, two up-to-date free surface-fitting Reynolds-averaged Navier-Stokes equation solvers are used as analysis tools for the evaluation of the objective function and functional constraints. The two optimization methods are realized and demonstrated on a real design problem: the optimization of the entire hull form of a surface combatant, the David Taylor Model Basin—Model 5415. Realistic functional and geometrical constraints for preventing unfeasible results and to get a final meaningful design are enforced and discussed. Finally, a recently proposed verification and validation methodology is applied to assess uncertainties and errors in simulation-based optimization, based on the differences between the numerically predicted improvement of the objective function and the actual improvement measured in a dedicated experimental campaign. The optimized model demonstrates improved characteristics beyond the numerical and experimental uncertainty, confirming the validity of the simulation-based design frameworks.     

On Wavemaking Characteristics of Catamarans and Trimarans

A method for calculating wavemaking resistance of a multihull vessel and corresponding computer program have been developed. The wavemaking characteristics of catamarans and trimarans were analysed based on theoretical calculations. The ranges of Froude numbers at which beneficial and adverse interferences occur, have been indicated and the interference mechanism been preliminarily shown as well.     

基于遗传算法的带有调纵倾尾板及拦截器的滑行艇水动力性能评估及优化（英文）

Nowadays, several stern devices are attracting a great deal of attention. The control surface is an effective apparatus for improving the hydrodynamic performance of planing hulls and is considered an important element in the design of planing hulls. Control surfaces produce forces and a pitching moment due to the pressure distribution that they cause, which can be used to change the running state of high-speed marine boats. This work elaborates a new study to evaluate the hydrodynamic performance of a planing boat with a trim tab and an interceptor, and optimizes them by using an optimization algorithm. The trim tab and the interceptor have been used to optimize the running trim and motion control of semi-planing and planing boats at various speeds and sea conditions for many years. In this paper, the usage of trim tab is mathematically verified and experimental equations are utilized to optimize the performance of a planing boat at a specificd trim angle by using an optimization algorithm. The genetic algorithm(GA) is one of the most useful optimizing methods and is used in this study. The planing boat equations were programmed according to Savitsky's equations and then analyzed in the framework of the GA-based optimization for performance improvement of theplaning hull. The optimal design of trim tab and interceptor for planing boat can be considered a multiobjective problem. The input data of GA include different parameters, such as speed, longitudinal center of gravity, and deadrise angle. We can extract the best range of forecasting the planing boat longitudinal center of gravity, the angle of the trim, and the least drag force at the best trim angle of the boat.     

22万立方米LNG船双尾鳍线型设计研究

结合22万立方米N096薄膜型LNG船舱型特点,利用CFD（计算流体动力学）软件分析结合模型试验的方法,就带有型值控制点的双尾鳍线型做了设计研究,从尾鳍形状及与首尾线型匹配等入手,对阻力、推进性能、尾部伴流场等方面进行了分析。     

Slam events of high-speed catamarans in irregular waves

Slam events experienced by high-speed catamarans in irregular waves were characterised through experiments using a hydroelastic segmented model. The model was designed to represent the dynamic behaviour of the full-scale Incat 112 m vessel and to allow the measurement of the slam load on the centrebow and wet deck. It was tested in irregular head seas at two speeds relating to Froude numbers of 0.32 and 0.60. Nearly 300 slams were identified in the test data and analysed with respect to kinematic parameters. Slams were found to have a large range of magnitudes, with the largest equivalent to 1785 tonnes full scale (approximately 70% of vessel displacement); however, the majority of events were of relatively low severity. Differences in slam characteristics were found for the two model speeds tested; slams at the slower speed generally occurred further forward on the hull, prior to the wave crest and with a bow down pitch angle. Immersion of the centrebow to the two-dimensional filling height of the cross-section between the centrebow and demihulls is shown to be a better indicator of slam occurrence than immersion to the top of the archway.