Hull Surface Research Articles

Parametric Generation of Small Ship Hulls with CAD Software

CAD software is a daily tool in ship design offices and shipyards, and every software uses NURBS or B-splines curves and surfaces as common foundations. The CAD tools of today are not static software products and most of them now include parametric design modules, which enable users to change the shape of an object based on its key geometric feature parameters with the use of sliders or equivalent controls. Although B-spline techniques are commonly applied to the representation of the ship hull curves and surfaces, the parametric deformation of the hull surfaces based on geometric parameters is less used. This paper presents a methodology to define the parametric definition of a ship hull with the use of a standard and non-specialized CAD software that is of common use in the ship design offices and universities: Rhinoceros. The presented parametric design methodology will use specific ship hull parameters or feature parameters with a clear geometric meaning, such as displacement, waterplane area, LCB, and LCF, together with the properties of the B-spline curves and the power of Grasshopper, the parametric design tool inside Rhinoceros, to create parametric ship hulls.

Numerical Study on the Waterjet–Hull Interaction of a Free-Running Catamaran

Waterjet–hull interaction is the hot point and research focus in the research of waterjet-propelled crafts. This paper presents numerical studies on the interaction between a waterjet system and a catamaran. Numerical simulations of both bare hull and self-propulsion hull were carried out based on the URANS method. The SST k-ω model is selected for the closure of the URANS equations. The level set method together with the dynamic overset grid approach is used for the simulations. The body force model with the PI speed controller is used to simulate the rotational motion of the rotor in the simulations for the self-propulsion hull. Moreover, uncertainty analyses of the numerical method are conducted to verify the accuracy of the numerical solver. The numerical results of the bare hull and self-propulsion hull are compared in detail, such as the wave pattern, pressure distribution, hull attitude, and so on. The waterjet reduces the pressure on the hull surface near the stern and makes the height of the wave near the stern lower. This leads to a more violent change in hull attitude and the thrust deduction is positive, ranging from 0.1 to 0.2. The energy conversion is analyzed based on the ITTC recommended procedures, which shows the overall efficiency of the waterjet behind the hull is about 0.75~0.8 times the free stream efficiency.

An advanced prediction method of ship resistance with heterogeneous hull roughness

Despite the ongoing efforts for predicting the effect of hull roughness on ship resistance, the majority of the studies have been treating the hull surfaces as uniformly (i.e., homogeneously) rough. This can be a limiting factor since the real ships’ hulls are not uniform due to various reasons such as the heterogeneous accumulation of biofouling. The current study aims to propose a new prediction method for added resistance due to heterogeneous hull roughness. This newly proposed method incorporates the similarity law scaling and the Roughness Impact Factor to consider the relative impacts of hull roughness in different regions. Two separate case studies involving recent Experimental Fluid Dynamics (EFD) and Computational Fluid Dynamics (CFD) results were used to assess the newly proposed method, which showed better prediction performance compared to the conventional method.

Ship Hull Inspection Using Autonomous an Underwater Vehicle with a Stereo Camera

Regular visual inspection of the underwater surface of the ship’s hull to check its integrity and the degree of biofouling is necessary to ensure the safety and efficient operation of the ship. The article proposes a method for the automated solution of this problem using an autonomous uninhabited underwater vehicle (AUV) equipped with a stereo camera controlled by a tilt actuator. The movement of the AUV is carried out along equidistant lines along the ship’s hull with simultaneous video filming of the hull surface. The AUV trajectory is calculated using the visual navigation method (visual odometry). Estimated data on the localization of the AUV relative to the ship’s hull are used in the method of controlling the movement of the vehicle to ensure the stable movement of the vehicle at a given distance from the inspected surface. Direct calculation of AUV localization data is done using the proposed original algorithm, which is implemented in the form of a software tool "stereo rangefinder". The operation of the "stereo rangefinder" is based on the matching of features in images using the SURF detector, followed by the construction of a 3D point cloud. The technique for performing automatic inspection of the ship as a whole is described. Fixed stereo images are also used to build a 3D model of the surface being examined. The applied method of constructing a global spatial model of the surface is based on the union of 3D point clouds obtained for local views. The construction of a 3D point cloud for a particular view is based on a matching of 2D point features on images of a stereo pair (SURF detector / correlation calculation), followed by the use of the ray triangulation method to obtain the spatial coordinates of the points. The presence of a 3D model makes it possible to conduct a detailed visual analysis of the state of the ship’s hull. Simulation modeling of the functioning of the developed tools on virtual scenes was carried out. Quantitative and qualitative performance evaluations obtained as a result of testing showed the acceptability of the proposed method for automatic inspection of the underwater part of the ship’s hull.

Ship hull surface reconstruction from scattered points cloud using an RBF neural network mapping technology

The ship hull surface reconstruction based on three-dimensional scattered points cloud is vital to Computer-Aided Design modeling of ship reverse engineering. There are several problems with traditional methods: the preprocessing of a large-scale scattered points cloud is complicated, and the result is susceptible to noise. Because of the “black box” characteristic, the surface reconstruction based on neural networks cannot apply to the practical engineering. To address these issues, combining the Radial Basis Function neural network and Non-Uniform Rational B-Spline interpolation algorithm, a new ship hull surface reconstruction method was proposed, which can satisfy the standard geometric model description in Computer-Aided Design system. Firstly, the Radial Basis Function neural network was used to pre-fit the three-dimensional scattered points cloud. Then the mathematical model of the surface was mapped. Finally, based on the bilinear interpolation algorithm, the mathematical model was transformed to a Non-Uniform Rational B-Spline surface to apply to the ship practical engineering. In addition, by comparing our method with the traditional method, the advantages of our method in surface reconstruction quality and surface repair ability were verified, which provided a new way for the application of Radial Basis Function neural network in ship reverse engineering.

Rekonstrukcija forme trupa tradicionalnog hrvatskog ribarskog broda i predviđanje efektivne snage

Recently, an increasing attention is given to preservation and popularization of Croatian traditional boat building, which plays an important role in Croatian cultural and national heritage. Reconstruction and revitalization projects of individual historical vessels are key factors within preservation process, where the lack of technical documentation is one of the main issues. In this paper, a simple and efficient procedure for taking offsets of a traditional fishing vessel guc is presented to document and preserve the traditional Croatian vessel form. A 3D model of a guc is generated using the points on the hull surface obtained by the manual measurement and a fairing process. Numerical simulations of the resistance test for a fishing vessel are carried out for a wide range of speeds, and the curve of effective power as a function of vessel speed is provided.

파수-주파수 변환을 이용한 선체 벽면 압력으로부터 선박 추진기 압축성 압력 추출

Underwater radiated noise (URN) is a compressible pressure component that propagates in the far-field from sources. Therefore, compressible pressure separation is required as a first step in developing a far-field URN monitoring technique based on hull surface pressure. In this study, a numerical method of decomposing surface total pressure induced by an underwater propeller into compressible and incompressible pressure was proposed using wavenumber-frequency transformation (WFT). First, a compressible multiphase Delayed Detached Eddy Simulation (DDES) of the hydrodynamic flow field was computed. Acoustic pressure caused by cavitation from the underwater propeller was predicted using the Ffowcs Williams–Hawkings (FW–H) integral equation and compared with the measured data to validate the numerical simulation. Finally, the compressible pressure was extracted from the total surface pressure on the stern part by using the WFT decomposition technique. In the high-frequency range, the compressible pressure appeared to be relatively high compared to the incompressible pressure in this study.

A novel method to estimate adult age from the lumbar vertebral body using 3D PMCT images in Japanese

This study evaluated the age-related changes in the vertebral body using 3D Postmortem CT (PMCT) images and proposed an alternative age estimation formula. The PMCT images of 200 deceased individuals aged 25 to 99 years (126 males, 74 females) were retrospectively reviewed and included in the study. Using the open-source software ITK-SNAP and MeshLab, a 3D surface mesh of the fourth lumbar vertebral body (L4) and its convex hull models were created from the PMCT data. Using their inbuilt tools, volumes (in mm3) of the L4 surface mesh and convex hull models were subsequently computed. We derived VD, defined as the difference in volumes between the convex hull and L4 surface mesh normalized by L4 mesh volume, and VR, defined as the ratio of L4 mesh volume to convex hull volume based on individual L4. Correlation and regression analyses were performed between VD, VR, and chronological age. A statistically significant positive correlation (P < 0.001) between chronological age and VD, (rs = 0.764, males; rs = 0.725, females), and a significant negative correlation between chronological age and VR (rs = -0.764, males; rs = -0.725, females) was obtained in both sexes. The lowest standard error of the estimate was demonstrated by the VR at 11.9 years and 12.5 years for males and females, respectively. As such, their regression models to estimate adult age were Age = 248.9–2.5VR years, males; Age = 258.1–2.5VR years, females. These regression equations may be useful for estimating age in Japanese adults in forensic settings.

Numerical investigations on nonlinear motions of ships sailing in large-amplitude waves based on hybrid HOBEM

This paper presents a nonlinear numerical approach based on hybrid higher-order boundary element method (HOBEM) to investigate the wave-induced motion responses of ships with forward speed. The radiation and diffraction forces in time domain are determined by convolution of the impulsive response functions computed from frequency-domain hydrodynamic data of the hybrid method using a combination of Rankine source and translating-pulsating Green's function. In its numerical implementation, steady flow effects are included in the inner domain encompassing the ship, 9-node bi-quadratic curvilinear elements are employed to discretize the boundaries and analytical quadrature formulas are derived to calculate the influence coefficients related to the Green's function over the control surface so as to improve the accuracy, efficiency and stability. Meanwhile, the nonlinear incident wave force and hydrostatic restoring force are calculated over the instantaneous wetted surface of the ship hull during the motion process to capture the nonlinear properties. Based on the method, a numerical program is developed to predict and analyze the motion response of a modified Wigley hull and a non-wall-sided S175 containership advancing in waves with different amplitudes and heading angles. By comparing the present computed results with experimental data and other numerical solutions, it is found that the nonlinear calculations can produce more accurate motion responses in large-amplitude waves with strong nonlinearity. And the present nonlinear method based on hybrid HOBEM is of higher accuracy and better stability than traditional nonlinear methods based on three-dimensional pulsating source (3DP) and translating-pulsating source (3DTP), especially for S175 with large flare near the waterline.

Three-dimensional visual mapping of underwater ship hull surface using image stitching geometry

This paper presents a method for three-dimensional (3D) visual mapping of underwater ship hulls using monocular vision. Visual inspection of underwater ship hulls using unmanned underwater vehicles needs to be conducted at very close range to the target surface because of the limited visibility in underwater environments. These environmental challenges can result in ineffective photometric and geometric information in hull surface images. Therefore, the performance of conventional 3D reconstruction techniques based on monocular vision is often unsatisfactory. To address these challenges and generate a precise 3D global map of the surveyed hull surface, the proposed visual mapping method adopts a two-step approach comprising global registration in two-dimensional space and 3D reconstruction using the information of the stitching geometry drawn by the registered images. Experimental results are shown to demonstrate the feasibility of the proposed method using image datasets obtained in field experiments with two different full-scale ships in real sea environments.

A study on the matching problem of engine, propeller, and ship hull under actual service conditions

In ship design, the matching of engine, propeller, and hull is an analytical process to establish the optimal operating mode so that the engine works safely with full power and the lowest fuel consumption, and a ship reaches desired speed. In theory, the operating process of the engine, hull, and propeller is usually expressed by their characteristics, and the matching problem is solved by finding the intersection of these characteristics. The problem here is that the above characteristics are determined under design conditions, corresponding to the standard technical conditions of the engine, hull, and propeller, however, all of these will be changed under actual service conditions, leading to a change in the position of the defined design match points and thereby greatly affect the safety and performance of the ships. This paper presents a new approach to determining the actual characteristics of the engine, hull, and propeller and how to use them to solve the matching problem under service conditions. This study was verified and validated on three study ships and was also applied to solve the matching problem of the Glory Star tanker. All the obtained results are in good agreement with the published real experimental data for this ship with a power loss of 21.5% under current service conditions, including 6.5% due to changes in propeller characteristics by changing technical conditions of propeller and hull surface, 6.3% due to engine deterioration, and 8.7% due to the engine - propeller mismatch after 5 years of operation.

Computer modeling in education for the development of students’ research skills

The paper considers the need to develop some applied pedagogical issues of the general theory of modeling, as well as psychological and pedagogical problems solved by modeling in the learning process, in particular, in the formation of concepts, the interpretation of sign mathematical models and the solution of educational graphic problems, where modeling does not act as an additional method to the current verbal and logical method. The paper gives the examples of visualization in planimetry, the dynamics of proving the Pythagorean theorem by the method of equi partibility, the method of deformation of parts while preserving their areas and the method of cutting theory, as well as an example of an applied problem for three-dimensional modeling of the theoretical surface of a ship hull in a computer-aided design system KOMPAS-3D.

Автоматизация моделирования поверхности судового корпуса

The article presents a modified algorithm for automated formation of geometric model of ship hull surface. The use of developed algorithm for construction of NURBS-surfaces allows to decrease labor input in several times in comparison with the use of manual labor when modeling surfaces in standard shipbuilding modeling systems like Sea Solution, Rhino and others. On the basis of this algorithm a software application is created, implemented in HTML5, JavaScript. The application allows to solve problems of creating and displaying three-dimensional models of ship surfaces in a standard the Internet browser. The program allows you to quickly analyze variants of the geometry of the ship hull model by adjusting the initial data, which significantly increases the productivity of the designer. It is possible to export the formed NURBS-surface for use in other design systems, including ship hull construction modeling, stability calculations, hull shell cutting and other tasks.

Fluctuation characteristics of hull surface force of a four-screw vessel in oblique flow

To study the influence of oblique flow on propeller fluctuation pressure characteristics of a four-screw vessel, the wake field and self-propulsion performance are calculated and analyzed utilizing computational fluid dynamics simulations. The characteristics of the wake field and propeller fluctuation pressure under different drift angle consisting of 0°, ±10°, and ±20° are compared and discussed in detail. The results show that negative drift angle affected the wake field of inside propeller more severely due to the generation of bilge vortex. The mean values of inside propeller fluctuation pressure are about 30% larger than those of the outside one, while the amplitudes of fluctuation pressure are reversed. The mean values of propeller fluctuation pressure experience a gradual decrease from β = −20° to 20° with an exception of inside propeller at β = −20° condition. The fluctuation amplitude of outside propeller is more affected by oblique flow due to the influence of oblique flow on flow separation point.

곡선 그물망으로부터의 초기 선형 곡면 자동 생성 방법

In the initial hull form design process, a hull form surface is essential for mesh generation and model ship for hydrodynamic analysis. In the current shipyard, when generating a hull form surface, a commercial program is used to generate the hull form surface by manual work of the worker. As it relies on manual work, there is a different in hull form surface depending on the maturity of the worker. In addition, there is a problem in that variating the hull form requires a lot of time because the hull form surface must be regenerated. Therefore, this paper proposes a method of automatically generating hull form surface from a given wireframe. A method is proposed for generating a suitable hull surface using the Skinning surface, Trimmed surface, Coons patch, and Gordon surface for each compartment. The hull form surface generated using the proposed method was verified by comparing the hull form surface used in the actual shipyard with the results of hydrodynamic analysis. As a result, the quality of the hull form surface was sufficient to generate a mesh for hydrodynamic analysis, and the actual usability in the shipyard was confirmed.

Automatic body condition scoring for dairy cows based on efficient net and convex hull features of point clouds

Body condition score (BCS) is an important indicator to evaluate the nutritional and health status of perinatal dairy cows. The insufficient accuracy of the automatic body condition score is the core bottleneck restricting the popularization and application of this technology. To further improve the accuracy of automatic scoring of cow body condition, a 3D structure feature map based on convex hull distance of point clouds was constructed and used as the input of a two-level model based on EfficientNet network, which realized the improvement of recognition accuracy within the error of 0.25 in the automatic scoring of cow body condition. First, the depth image of the cow’s back was preprocessed to obtain the point cloud from the hook bone to the needle bone region containing the main body condition information. Second, the point cloud was voxelized and convex hulled, and the distance between each peripheral voxel and the nearest convex hull surface was calculated and projected to the X-Y plane to obtain the structural feature map. Then, a two-level classification model based on the EfficientNet network was constructed, and the whale optimization algorithm (WOA) was used to optimize the network scaling coefficient in the model. Finally, 5119 depth images of 77 cows were used to train and test the model, and the dataset ratio was 1:1. The results showed that when the BCS value was in the range of 2.25 to 3.75 and the two-class classification limit was 2.75, the proportions of images with recognition errors less than 0.25 and 0.50 were 91.21% and 97.60%, respectively, and the average recognition speed was 3.446 frames/s. The recognition effect was better than that of the MobileNet-V2, XceptionNet and LeNet-5 network models. This method could realize the noncontact assessment of individual body conditions of dairy cows in large-scale farms and had the characteristics of high accuracy, strong applicability and low cost.

A mesh insensitive finite element method to compute statical stability curve of floating bodies with arbitrary configurations based on a force‐oriented approach

AbstractFor any floating body, statical stability curves play a critical role in its stability analysis. In this article, a force‐oriented approach, in conjunction with finite element procedure, is proposed in order to compute those curves of floating bodies with complicated hull forms. The hull surface is meshed by triangular elements. The buoyant force and restoring moments are directly computed through the load redistribution of the hydrostatic pressure over the facet of each triangular element. Computations of a statical stability curve require a series of floating conditions that lead to the change of waterline with respect to the hull surface. In order to do all computations by using a unique finite element mesh, techniques regarding nodal coordinate update and non‐matching element treatment are developed. The procedure has been established and the algorithm has been developed. Results from three examples with simple but representative geometries are compared to those by hand calculations to verify the accuracy of the approach. Then, two standard reference hull forms, a very large crude carrier (KRISO KVLCC2) and a trimaran (NPL Round Bilge 4a), have been investigated to demonstrate the validation of the approach. Results of all examples show that the proposed approach is insensitive to the mesh pattern.

Predicting the Effect of Hull Roughness on Ship Resistance Using a Fully Turbulent Flow Channel

The consequences of poor hull surface conditions on fuel consumption and emissions are well-known. However, their rationales are yet to be thoroughly understood. The present study investigates the hydrodynamics of fouling control coatings and mimicked biofouling. Novel experimental roughness function data were developed from the “young” fully turbulent flow channel facility of the University of Strathclyde. Different surfaces, including a novel hard foul-release coating, were tested. Finally, the performance of a benchmark full-scale containership was predicted using Granville’s similarity law scaling calculations. Interestingly, the numerical predictions showed that the novel hard foul-release coating tested had better hydrodynamic performance than the smooth case. A maximum 3.79% decrease in the effective power requirements was observed. Eventually, the results confirmed the practicality of flow channel experiments in combination with numerical-based methods to investigate hull roughness effects on ship resistance and powering. The present study can also serve as a valuable guide for future experimental campaigns using the fully turbulent flow channel facility of the University of Strathclyde.

In Vitro Evaluation of Seagrass Extracts as a Prevention of Microfouling Formation

Microfouling is the attachment and colonization of bacteria and microalgae on the surface of objects immersed in the sea. So far, the control of biofouling on the surface of marine hulls has been using paints containing Tributylin Organotin (TBT) which have adverse effects on non-target organisms and are not friendly to the environment. The development of environmentally friendly antifouling paint is a solution to overcome the growth of biofouling. This study aimed to evaluate in vitro extract of Thalassia hemprichii as an anti-microfouling agent. Extraction of bioactive from Thalassia hemprichii was carried out by maceration. The filtrate is divided into five kinds of concentration, namely 0%, 25%. 50%, 75%, and 100% were then added to paint A as an anti-microfouling agent. The observed variables were microfouling biomass and the density of bacteria and microalgae attached to the steel plate. The results showed that with increasing concentration applied to the plate caused a decrease in the number of bacteria. The average decrease in each bacterial concentration was 84 x 10^6 CFU/mL, 65 x 10^6 CFU/mL, 41.5 x 10^6 CFU/mL, 28.7 x 10^6 CFU/mL, and 15.8 x 10^6 CFU/mL, respectively. Microalgae attached to the steel plate also experienced a reduction with the average values sequentially being 37 x 10^4 cells/mL, 14 x 10^4 cells/mL, 8 x 10^4 cells/mL, 5 x 10^4 cells/mL, and 2 x 10^4 cells/mL. Likewise, the microfouling biomass on steel plate also decreased in amount with the average values being 99.27 mg, 93.4 mg, 66.43 mg, 59.13 mg and 30.2 mg, respectively. Thus, Thalassia hemprichii extract has the potential to prevent the formation of microfouling.

Design and analysis of a wheel-leg compound variable curvature ship hull cleaning robot

Underwater robotic cleaning devices are promising in ship hull maintenance for biofouling removal, but there are still some challenges for commercial application. Due to the complex surface of the ship hull, larger adsorptive force is needed for climbing robots to solve the problem of poor fitting between rigid structure and ship hull, which calls for more driving power. To mitigate the gap, this paper proposed a flexible wheel-leg composite moving mechanism for ship hull cleaning robots. The designed adjustable wheel leg, which is composed of three leg frames on the rotating shaft, eliminates the magnetic wheel's position constraints and expands the movement space. The relation equations of flip angle, pitching angle, turning angle, and hull curvature radius are generated and analyzed based on the robot's posture and steering motion. The mechanical properties of anti-slippage and anti-shedding under different motion states were studied so that the robot's critical point and limit adsorption force could be determined and verified. Simulation results show that the robot has good motion stability.