Overall stability performance of alternative hull forms

In this paper, two alternative corvette hull forms namely, the round bottom and deep V have been comparatively analyzed in terms of intact and damaged stability and roll performance in beam waves. The boat is planned to operate in the Navy's coastal water missions. Even though both forms are considered to comply with the design requirements, slight differences in displacement and principal dimensions are found to be inevitable due to the intrinsic characteristics of the specific forms. First part of the study concentrated on determining the conventional intact and damaged stability qualities whereas the second part was devoted to nonlinear rolling behavior of the vessels in synchronous beam waves. Nonlinear rolling amplitudes are thought to be quite important especially for resonance condition since they tend to peak in capsize conditions. Various combinations of loading conditions and damaged cases are taken into account to analyze the effects of them. Comparative results are presented graphically depicting the advantages/disadvantages of the selected forms over each other.     

An optimization approach for fairing of ship hull forms

This paper presents a numerical fairing procedure to be used at the preliminary design stage to create high-quality ship hull form geometry. The procedure is based on a variational optimization approach in which a fairness measure related to the surface curvature is the objective function to be minimized subject to a set of geometric constraints to ensure that the final form has the required geometric characteristics. The optimization variables are selected as the control points of a B-spline surface representing the initial hull form. A nonlinear direct search technique is employed to solve the problem. The methodology is applied for typical ship forms to indicate that, provided that the designer can specify appropriate design objectives and geometric constraints, the methodology can produce alternative hull forms with significantly improved fairing characteristics. The choice of the fairness objective function is shown to have a crucial effect on the quality of the hull surface. Highly nonlinear exact fairness functionals yield surfaces of high quality at the expense of high-computerized effort.     

Methodical series tests for fuller ship hull forms

In recent years many fuller ship hull forms have been designed and constructed in various shipbuilding countries, but the data available for the development of the fuller forms are inadequate from the point of view of preliminary ship design. In this paper the authors describe how they have systematically tested vessel forms of block coefficients ranging from 0.80 to 0.90. The analysis and presentation of the test results have been made in such a manner that designers can produce hull forms like those of tankers and other bulk carriers quickly and reliably.     

PIV measurements of hull wake behind a container ship model with varying loading condition

Flow characteristics of the hull wake behind a container ship model were investigated under different loading conditions (design and ballast loadings) by employing the particle image velocimetry (PIV) technique. Measurements were made at four transverse locations and two longitudinal planes for three Reynolds numbers (Re) (=U₀Lpp/ν, where U₀ is the freestream velocity, Lpp is the length between two perpendiculars of the ship model and ν is the kinematic viscosity) of 5.08×10⁵, 7.60×10⁵, and 1.01×10⁶. It was observed that symmetric, large-scale, longitudinal counter-rotating vortices (with respect to centerline) of nearly the same strength were formed in the near wake. For the ballast-loading condition, the vortices appear at propeller plane below the propeller-boss. The vortex center exhibits a significant upward shift near the propeller-boss as the Reynolds number increase, and as the flow moves downstream. Under the design-loading condition, the vortices first appear at a further downstream location than that for the ballast-loading condition above the propeller-boss. This difference in the flow structure can significantly change the inflow conditions to the propeller blades, such as the streamwise mean velocity profiles and turbulence intensity distributions at the propeller plane. In particular, under the ballast-loading condition, asymmetric inflow may weaken the propulsion and cavitation performance of the marine propeller.     

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.     

A mixed continuous and discrete nonlinear constrained algorithm for optimizing ship hull structural design

A nonlinear search algorithm for optimizing constrained design of ship structures is presented. The decision variables can be continuous or discrete and the constraints can be homogeneous or inequality nonlinear functions of those variables. The algorithm does not use gradients; therefore, it can work with non-systematized functions such as tables or another class of design routine. It was tested in the structural design of a Patrol Boat and has proved to be a powerful tool decreasing the time expended in preliminary design when it is done by the conventional spiral approach.     

An automated computational method for planing hull form definition in concept design

This paper describes the development of a computer-based method for producing chined planing boat hull forms adequate to be applied in concept design. The method is based on a principle where the designer specifies a small set of critical parameters he/she wishes obtain or keep preserved and generates a complete hull form, without the traditional skilled recourse of giving stations point by point. From this set of parameters a detailed and faired drawing with offsets is generated very quickly. The method allows, in its execution mode, the flexibility to modify, adjust and enlarge the input set of parameters. The method was created to allow both (1) automated hull form definitions when integrated to an existing computer system and (2) quick but detailed preliminary calculations of stability, lift and drag, volumes and internal space allocations, sea-keeping estimates, etc., all with very reasonable precision. As application examples some planing boat hull forms are generated. Some are typical and others less usual. The later ones are defined to show the method's limits, in order to validate it.     

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.     

Predicting the effect of biofouling on ship resistance using CFD

This paper proposes a Computational Fluid Dynamics (CFD) based unsteady RANS model which enables the prediction of the effect of marine coatings and biofouling on ship resistance and presents CFD simulations of the roughness effects on the resistance and effective power of the full-scale 3D KRISO Container Ship (KCS) hull.Initially, a roughness function model representing a typical coating and different fouling conditions was developed by using the roughness functions given in the literature. This model then was employed in the wall-function of the CFD software and the effects of a typical as applied coating and different fouling conditions on the frictional resistance of flat plates representing the KCS were predicted for a design speed of 24 knots and a slow steaming speed of 19 knots using the proposed CFD model. The roughness effects of such conditions on the resistance components and effective power of the full-scale 3D KCS model were then predicted at the same speeds. The resulting frictional resistance values of the present study were then compared with each other and with results obtained using the similarity law analysis. The increase in the effective power of the full-scale KCS hull was predicted to be 18.1% for a deteriorated coating or light slime whereas that due to heavy slime was predicted to be 38% at a ship speed of 24 knots. In addition, it was observed that the wave resistance and wave systems are significantly affected by the hull roughness and hence viscosity.     

3-D geometric modeler for rapid ship safety assessment

CAD systems are used broadly in the shipbuilding industry. CAD systems for naval architecture are a useful tool for hull form, internal arrangement and the structural design of ships. These systems require high precision and expertise for efficient use. Therefore, these systems are not appropriate in supporting emergency responses, which require rapid modeling even if it generates some errors.This paper describes a geometric modeler for rapid ship safety assessment. The modeler is developed based on the 3-D geometric modeling kernel ACIS. The definition of hull form, internal arrangement and major longitudinal structural members is a fundamental function of the modeler. The developed modeler is interfaced with other applications used for ship safety assessment such as hydrostatic calculation, ship motion analysis in wave condition, longitudinal strength analysis and so on. In addition, it can generate a new ship model by making variations in a previously defined ship model.     

船体线型曲面局部修改法研究

为建立一个简便、多功能的船体曲面修改和生成系统,提出一种船体线型曲面局部修改法,求解船体曲面修改问题。方法采用NURBS曲面技术,对曲面连接满足连续的充分条件推导,保证了局部曲面与外部曲面的光顺连接,控制顶点移动方程组的建立使得新曲面的表达简单直接,最后以某平台供应船船体曲面的修改为算例对方法进行验证,得到一个满足修改要求、光顺平滑的船体新曲面。该方法可应用于数字化造船和改进数学船型方法,也可推广应用于海洋平台等其他领域的曲面拟合、修改和生成。     

Artificial intelligence-based hull structural plate corrosion damage detection and recognition using convolutional neural network

With the support of big data and GPU acceleration training, the artificial intelligence technology with deep learning as its core is developing rapidly and has been widely used in many fields. At the same time, feature extraction operations are required by the current image-based corrosion damage detection method in the field of ships, with little effect but consuming the large amount of manpower and financial resources. Therefore, a new method for hull structural plate corrosion damage detection and recognition based on artificial intelligence using convolutional neural network is proposed. The convolutional neural network (CNN) model is trained through a large number of classified corrosion damage images to obtain a classifier model. Then the classifier model is used with overlap-scanning sliding window algorithm to recognize and position the location of corrosion damage. Finally, the damage detection pattern for hull structural plate corrosion damage as well as other types of superficial structural damage using convolutional neural network is proposed, which can accelerate the application of artificial intelligence technology into the field of naval architecture & ocean engineering.     

在AutoCAD平台上应用ActiveX技术进行船体曲面造型

论述了AutoCAD ActiveX Automation,并就应用Active技术进行二次开发AutoCAD的问题，讨论了如何引用对象和使用对象的方法和属性、使用文档对象的事件、用ADO（ActiveX Data Objects)开发基于数据库的应用程序等。通过应用ActiveX技术，在AutoCAD中构造了船体曲面。     

Bilge keel loads and hull pressures created by bilge keels fitted to a rotating cylinder

This paper presents bilge keel loads and hull pressure measurements carried out on a rotating cylinder in a free surface water basin. A flat plate bilge keel and one more complex shaped bilge keel were studied to investigate the geometry effect. The draft of the cylinder was varied to study the effect of the vicinity of the free surface on the bilge keel loads and hull pressures. The rotation axis of the cylinder was fixed to define a pure roll experiment (one degree of freedom).The cylinder was subject to forced oscillations of varying amplitude leading to a KC range of 0.3–16. Using Fourier analysis the first three harmonic coefficients representing the normal bilge keel load were derived. The first harmonic drag and inertia coefficients are in good agreement to existing experimental data obtained for wall bounded flat plates fitted in a U-shaped water tunnel as reported by Sarpkaya and O’Keefe (1996). New insight is gained by the fact that the addition of higher harmonic contributions is essential to capture the time varying bilge keel normal force.The pressure measurements next to the bilge keel are compared to measurements reported by Ikeda et al. (1979). Similar findings are obtained, showing that the pressure on the hull in front of the moving bilge keel is KC independent while the vortex system in the wake of the bilge keel leads to KC dependent hull pressure distributions. The hull pressure jump over the bilge keel correlates well to the force coefficient on the bilge keel. The complex nature of the vortex induced hull pressures is manifested. The empirically derived hull pressure distribution by Ikeda et al. (1979) for the time instant of maximum velocity is shown to correlate reasonably well to the measured data with some conservatism in the absolute value.Although a cylinder is very different from a ship-shaped section, the experiments provide essential insight into the physics associated with roll damping and into the factors that should be included in a roll damping prediction method.     

Hydrodynamic shape optimization of thin floating plates

In this work, the problem of optimizing the shape of a thin floating plate (sometimes called a dock) to maximize radiation damping is investigated. The plate is modeled with zero draft and floats on the surface of an irrotational, incompressible ocean of infinite extent. For simplicity, only rigid heave motions are considered. The flow problem is analyzed using the Chen and Mei variational principle wherein the potential field inside a hemisphere surrounding the plate is represented using a spherical harmonic expansion and matched on the hemisphere to an outer field described by distributing sources on the hemisphere. The plate shape is parameterized using a Fourier series which is suitable for use with the variational principle. Gradients of the damping coefficient with respect to the shape parameters are developed by solving an adjoint flow problem whose potential is shown to be a scalar multiple of the original flow potential. Optimal plate shapes are determined using the well-known optimization code NPSOL which makes use of the damping coefficient calculation and gradients.     

Optimum design of multiple intersecting spheres deep-submerged pressure hull

The multiple intersecting spheres (MIS) pressure hull is a logical derivative of the single unstiffened sphere, which is frequently used for deep operating, small submersibles because of its attractive low buoyancy factor. This paper investigates the optimum design of an MIS deep-submerged pressure hull subjected to hydrostatic pressure, using a powerful optimization procedure combined the extended interior penalty function method (EIPF) with the Davidon–Fletcher–Powell (DFP) method. In this study, the thickness of the shell, the width of the rib-ring, the inner radius of the rib-ring and the angle of intersection of the spherical shell are selected as design variables, and structural failure and human requirements are considered to minimize the buoyancy factor. Additionally, a sensitivity analysis is performed to study the influence of the design variables on the optimal structural strength design. The results reveal that the shell thickness is most important to lobar buckling strength, and that rib-ring width, rib-ring inner radius and spherical shell intersection angle are most important to rib-ring hoop strength. Optimization results may provide a valuable reference for designers.     

A numerical modeling of hydrodynamic characteristics of various planing hull forms

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.     

Hull hydrodynamic optimization of autonomous underwater vehicles operating at snorkeling depth

Traditionally autonomous underwater vehicles (AUVs) have been built with a torpedo-like shape. This common shaping is hydrodynamically suboptimal for those AUVs required to operate at snorkeling condition near the free surface. In this case, the wave resistance associated to the wavy deformation of the sea surface induced by the motion of the platform is an important component of the drag. This work has investigated the optimum hull shape of an underwater vehicle moving near the free surface. Specifically a first-order Rankine panel method has been implemented to compute the wave resistance on a body of revolution moving close to the free surface. A simulated annealing algorithm was then employed to search those set of parameters defining the hull shape that minimize the wave resistance. The optimization was constrained to keep constant the total volume of the vehicle. The total drag of scaled models of the torpedo-like and resulting optimum shapes was measured in the naval tank of the University of Trieste. Measurements showed a smaller resistance of the optimized shape in the range of the considered Froude numbers.     

A critical CAE analysis of the bottom shape of a multi stepped air cavity planing hull

One of the most important aspects, in the ACS and multi stepped hull design, is the choice of the geometrical shape of the cavity and the steps. In this article a complete experimental and numerical campaign on a multi stepped ACS has been carried out, varying the velocity and the air flow rate under the hull. The experimental tests have been conducted in an ITTC Towing Tank allowing to validate the numerical simulations obtained by means of a CFD U-RANSe (Unesteady Reynolds Averaged Navier-Stokes equations) code. The CFD setup is described in detail. From this campaign a critical analysis of the Froude number influence on the air cushion shape has been argued. The authors identified four different behaviours, from low to very high Froude numbers. The use of CFD has allowed to observe quantities of difficult evaluation by means of traditional experimental test, as e.g. the frictional component of the resistance, the airflow path lines and the volume of fraction in transversal and longitudinal sections. The results have been discussed.     

船体曲面几何表达及水动力性能计算的NURBS方法

采用非均匀有理B样条(NURBS)对船体曲面形状进行几何表达,所生成的网格直接用于后续的有关船体水动力性能计算工作中。对Wigley船型的线性兴波阻力和斜航操纵运动的船体,结合近似的Kutta条件作了相应的数值计算,从与试验结果的比较来看,该方法具有较好的工程精度,对船舶及海洋工程领域中的计算机辅助设计(CAD)与计算流体动力学(CFD)之间的相互集成,具有推动与促进作用。