Hull Shape Research Articles

Development of empirical formulations of slamming loads for displacement vessels

The paper presents an empirical method to calculate slamming load acting as bottom impact pressure on the forward region of the vessel. Firstly, hull shape coefficient as a function of the deadrise angle of the section is derived. Relative velocity is derived in terms of the extreme motions, viz. heaving and pitching due to extreme waves. Forward speed is considered in terms of threshold slamming velocity. Finally limiting condition for slamming load is derived. CFD simulations are performed to obtain the variation of the slamming load along the length of the vessel. Various hull shapes with varying block coefficients, speed and length are considered for slamming load calculations. Results are validated against the rules formulation of bottom impact pressure as given in published classification society rules. Reliable formulation for slamming loads with due consideration of geometry of the vessel, seakeeping characteristics and probability of slamming is achieved for various types of displacement vessels. Application of slamming loads on the vessel for scantling calculations of bottom plating is also discussed.

Parametric Modelling of Interacting Hydrodynamic Forces in Underwater Vehicles Operating in Close Proximity

This paper presents a parametric model of the hydrodynamic interaction forces for two underwater vehicles operating in close proximity. We first discuss the models for interacting forces in the horizontal plane of surface vessels and empirical approximations that could be applied to underwater vehicles. Then, we propose a partially-fixed model structure of the hydrodynamic interaction forces based on both potential theory and experimentally derived models available in the literature. This partially-fixed model structure is used for the identification of a full parametric model for the hydrodynamic interaction forces. The data set considered to validate the model represents a fully-submerged hull shape (an enlarged Explorer AUV hull shape) that moves holding its course at a forward speed and another hull shape (a SUBOFF hull of reduced size) that overtakes Explorer in a parallel course. We exploit the novel model structure together with the experimental data to obtain a parametric model of the interaction forces on the overtaking vessel at different transverse separation distances. We estimate the parameters using one dataset and then validate the model for other sets. The results obtained are considered accurate for the intended purpose of the model, which is the future design of a motion control system for the SUBOFF manoeuvring in close proximity to the Explorer.

CFD Analysis of Human Powered Submarine to Minimize Drag

This paper deals with finding the optimum fineness ratio, i.e. ratio of length to maximum diameter, of human-powered submarine of different shapes to reduce the drag force on the body using Computational Fluid Dynamics (CFD) analysis. These types of submarines are used in events like ISR and eISR. This paper focuses on finding the total drag force on submarine models with a constrained diameter and different fineness ratios. The analysis is done by using ANSYS Fluent. In this paper, only the fully submerged flow is considered on a hull without any appendages.The total drag on a body is caused in three different parts that are wave drag, skin friction drags and base drag.The analysis is done different shapes of submarines like Conic shape hull, Elliptical shape hull, Ogive shape hull and Parallel mid-body hull by flowing water at velocities of 3 m/s, 4m/s and 5 m/s. The fineness ratios at which the drag is minimum are found in all submarine shapes. The optimum value of fineness ratio, which gives minimum drag is obtained by the analysis is 6 for Conical shape hull, Elliptical shape hull and Ogive shape hull whereas for the submarine with Parallel mid-body hull shape the optimum fineness ratio is 7

Design and performance analysis of B-series propeller for traditional purse seine boat in the north coastal region of Central Java Indonesia

In the North Coastal Region of Central Java, the traditional fishing boat is a primary object that generates the economics activities of the social community. As an artisanal fishery, the boats generally adopt the tradition to build technique from their predecessor. Therefore the lack of practice to determine the propeller design which considered the hydrodynamic relation within the boat dimension, hull form geometry and propeller is observed. Presently, there is no a standard propeller design that particularly well designed considering the hull shape geometry for the traditional boat. The aim of the research is to identify the propeller that would be applied to the fishing boats typically found in the North Coastal Region of Central Java using B-Series marine propeller. Computational Fluid Dynamics (CFD) analysis for assessing the performance of thrust and torque of the developed propeller was performed.

A Matching Algorithm Based on Voronoi Diagram for Multi-Scale Polygonal Residential Areas

Matching spatial entities (e.g., polygonal residential areas) from sources of significantly different map scales is challenging. The reason is that the same entities in two map scales have significant variations in their positions, structure shapes and numbers, and topological relationships. Traditional matching methods based on minimum boundary rectangles (MBRs) or buffers usually lead to missed matches or mismatching. Furthermore, most of the previous approaches on entity similarity calculation are designed for datasets with specified map scales, which cannot directly apply to another set of dataset with a different scale. In this paper, we present a general approach using the Voronoi diagram for spatial entity matching on multi-scale datasets. Our approach first employs an efficient algorithm to construct the Voronoi diagram from the small-scale dataset. Next, the approach traverses each Voronoi polygon to find the corresponding large-scale features as the matching candidates (for each small-scale feature). Using the Voronoi diagram for identifying matching candidates does not require a manually determined search space (in contrast to the buffer-based approach). Also, our algorithm effectively uses the Voronoi diagram to prune the number of matching candidates even when the sources for matching contain large inconsistent position deviations. Finally, our approach utilizes three similarity indexes, namely, the convex hull shape similarity, convex hull area similarity, and overlapping area ratio to confirm the final matching results. We conducted experiments on two sets of datasets of two cities in China. The scales of the tested datasets were 1:10 000 and 1:50 000 and 1:1000 and 1:10 000. We compared our Voronoi-based method to both the MBR and buffer-based methods. The experiments showed that our method outperformed both the previous methods in generality and quality. Specifically, for the datasets where the inconsistent position deviations were large (i.e., the datasets of 1:1000 and 1:10 000 scales), the average F-measure of our results were 12.46%, 20.8%, and 64.45% higher than the MBR-based, 6-m buffer-based, and 3-m buffer-based methods, respectively.

Benchmark Study of Ship Model Resistance Test

A benchmark test will insure that the equipment, procedures, and uncertainty estimates are adequate. The experiments of a well-known bulk carrier bare hull shape (the model LHI-007) has been set up and conducted at towing tank Indonesian Hydrodynamic Labotatory. The aim of the present study is to contribute data of the surface ship resistance model-scale database in calm water on one hand, and on the other – reliable Experimental Fluid Dynamics (EFD) data, as part of an internal benchmark test. Conclusions are made with regard to the available data and past uses and recommendations are provided for future uses of the available data and future data procurement.

PERANCANGAN RC (REMOTE CONTROL) BOAT PATROL 80 CM DENGAN PROPULSI WATERJET

The government is still struggling to secure all the waters of the archipelago in maintaining and overseeing the security of its territory. This is due to the many islands that need human resources (HR) and require a lot of high-tech ships. So it is necessary to design a robot Electric Remote Control Waterjet Patrol 80 (ERC_WP 80) which could serve as patrol boats and destroyers. Waterjet propulsion drive system has a motion if the vessel was excellent at relatively high speed boats and has good acceleration capabilities. Boats with jet propulsion system can operate in very shallow waters. This is due to all parts of the engine located under the hull, including propeller, shaft and shaft house. Waterjet advantages compared with the steering system / rudder is conventional waterjet propulsion system is able to turn the steering wheel with a smaller angle. Maneuverability and good seakeeping of a ship is strongly influenced by the shape of the hull. Selection of the hull shape is designed to perform parametric studies hull of the vessel Fast Patrol Boats comparator (KPC) 14 1 228 m and the vessel JS Patrol. On the back of the boat is made with a slope angle (chine angle) of about 20 degrees in order to gain the necessary lifting force without reducing the stability of the ship. While at the front end of the ship made a slope angle of about 30 degrees with the intent facilitate ship moving at high speed and reduce the impact when the waves break. Unmanned patrol boats are designed using radio control GensAce 4S 3300mAh

Numerical investigation of shallow water effect on a barge ship resistance

The inland waterway cargo transport has extended over the decades, bringing up specific technical issues. From the hydrodynamics point of view, for the inland ships one of the most challenging issue is the effect of shallow water on the ship resistance. In the present study, there are developed numerical analyses for the viscous flow around a barge hull in the case of the shallow water fluid domain. The barge hull has prismatic shapes, in the cargo holds areas, with vertical sides, and geometric non-linear shapes more significant at the fore part. The hull shape CAD model is developed by Rhinoceros software. The numerical analyses are performed by CFD RANS-VOF method, with free surface and shallow-water, using the NUMECA / FineMarine software, having free sinkage and trim conditions. The shallow-water flow induces significant hydrodynamic non-linearities in compare to the deep-water flows. Several ship speeds and water depths are considered. We have focused on the identification of the ship’s induced waves system and the resulting barge resistance. The conclusions of this study are stressing out the significant influence of the shallow-water conditions on the barge resistance, making possible to draw up practical technical information’s for the barge hull design.

Shape optimisation of an AUV with ducted propeller using GA integrated with CFD

ABSTRACTThis paper adopts Genetic Algorithm (GA) -driven optimisation framework to solve the design optimisation problem of an autonomous underwater vehicle that aims to minimise the delivered power under the constraints on the geometric parameters that define the hull shape. The GA and computational fluid dynamics (CFD) solvers are seamlessly integrated into a single code so that it becomes an effective computational tool for optimisation. Adopting a hull and a ducted propeller, for which some experimental data are available for CFD validation, the optimisation is done for the shape of the hull for a single velocity, leading to significant reduction in delivered power. The hull shape is described by a 5-parameter axisymmetric form. Delivered power minimisation problem is compared with the corresponding drag minimisation problem of the chosen hull.

Variant Designing in the Preliminary Small Ship Design Process

Abstract Ship designing is a complex process, as the ship itself is a complex, technical multi-level object which operates in the air/water boundary environment and is exposed to the action of many different external and internal factors resulting from the adopted technical solutions, type of operation, and environmental conditions. A traditional ship design process consists of a series of subsequent multistage iterations, which gradually increase the design identification level. The paper presents problems related to the design of a small untypical vessel with the aid of variant methodology making use of optimisation algorithms. The computer-aided design methodology has been developed which does not need permanent reference to already built real ships and empirical-statistical relations. Possibilities were indicated for integrating together early design stages, and parallel designing of hull shape and parameters.

Multi-objective shape optimization of submarine hull using genetic algorithm integrated with computational fluid dynamics

A multi-objective optimization framework is developed for design of submarine hull shape. Internal volume of the vehicle and its hydrodynamic drag are optimized by seamlessly integrating non-dominated sorting genetic algorithm and Reynolds averaged Navier–Stokes solver in a single code. The methodology seeks a geometric shape with minimum drag and maximum volume satisfying the constraints on the geometric design parameters given by a 5-parameter formula that describes the submarine hull. The shape of the sail is not a part of the optimization process, and only its longitudinal location over the submarine hull is optimized. Two design optimization approaches are proposed, solved and compared. In the first approach, the combined hull–sail location is optimized, and in the second, the hull shape without sail is optimized first, and for this optimized hull shape, the sail location is optimized next. Our reported results show that the former approach yields significantly lower drag.

Mathematical programming basis for ship resistance reduction through the optimization of design waterline

It has been more than a decade since Calisal et al. (J Ship Res 46(3):208–213, 2002) presented their concept of wave resistance reduction by allowing an increase in the beam of a ship accompanied by smoothing the shoulders. Since then a series of computational and experimental studies have been performed to provide evidence for the design idea that an increase in the beam with waterline parabolization may give reduced wave resistance for moderate Froude numbers in most cases in contrast to the common understanding among naval architects. The procedure in the design concept mentioned has been based on a systematic search supported by computational work and validated by experimental studies. The present study attempts to rationalize the introduced design concept by establishing a mathematical programming basis which employs the thin-ship approximation for wave resistance and a quadratic programming in finding the optimal shape of the design waterline (DWL), for minimum wave resistance, for the given design constraints. In this case, the shape of the DWL and in turn the hull shape in accordance with DWL is determined by a well-defined optimization procedure, which is dictated by the mathematical programming routine. Computational tools are employed to check the hydrodynamic characteristics of the hull form determined by the optimization routine, before tank testing. An experimental work is carried out to confirm the computational results and to validate the proposed methodology. Both the computational and the experimental work point out that the present design approach is effective particularly for Froude numbers greater than 0.21 and less than 0.4 where the ship-generated wavelength along the hull is less than the body length.

A novel design framework for generation and parametric modification of yacht hull surfaces

This paper proposes a new design framework for the parametric design and shape modification of a yacht hull. In this framework, the hull is divided into three regions (entrance, middle and run) and each region is represented separately. In this way, a designer has better design flexibility so that higher design variations of the hull can be achieved. Each region consists of keel line(s), deck line, chine line(s) and station lines that are represented using Bezier curves and these lines are called feature curves. A 3D surface model of a yacht hull is obtained by generating Coons patches using feature curves. Shape operators are also introduced and implemented for the modification of the given hull shape while considering some quality criteria such as hull fairness. Experiments in this study show that a variety of hull shapes can be generated using the proposed design framework with the application of the shape operators.

Numerical investigation on the hydrodynamic performance of fast SWATHs with optimum canted struts arrangements

Small Waterplane Area Twin Hulls (SWATHs) are known to have superior seakeeping performance but higher resistance compared to equivalent catamarans or mono-hulls. A way to improve their resistance characteristics is to use unconventional hull forms parametrically defined and optimized by CFD methods. This study builds on previous SWATH optimization studies proposing a comprehensive, systematic investigation on the effect of different shapes and canting angles of the struts. For the first time we demonstrate the importance of considering the shape of the strut that is fully parametrized in our study. The effect of the design speed on the best shape is addressed through a multi-objective optimization targeting the minimum total resistance at two very different speeds, namely the cruise and slow transfer speeds. Optimum hull shapes are discussed in terms of maximum resistance reduction, together with the predicted free waves patterns.

An Optimization Method of Stern Hull Form to Minimize Brake Horse Power (2nd Report)

This is the second report of hull form optimization to minimize Brake Horse Power (BHP). In the previous report, two hull form optimization techniques, Sequential Quadratic Programming (SQP) and Surrogated-Based Optimization (SBO), for minimizing BHP were proposed, and it was shown that the optimization methods are effective for obtaining high performance hull forms. Recently most of ships are equipped Energy Saving Device (ESD) to improve their performance. Some ESDs have energy saving effect of over 5%. However their effect is strongly dependent of a shape of a main hull. Similarly dimensions of a propeller are dependent of a shape of a main hull. Therefore hull form optimization considering ESD effect and propeller design is necessary for total BHP reduction.

耐圧殻変形による像歪みの低減を可能とする全球カメラ用球形ハウジングの開発

This paper discusses the relationship between pressure hull and camera lens. In preceding study, monitoring by the full spherical camera is considered usefully because there is not blind spot. Therefore, the authors focused on the following two points in order to use the full spherical camera in underwater, and developed the pressure hull. One is the compatibility between the shape of pressure hull and the camera lens, and the other is the distortion of the image by deformation of the pressure hull.As a result, we judged that the combination of spherical pressure hull and full spherical camera is the most compatible. And, we succeeded in photographing without distortion with a spherical pressure resistant hull.

Energy Efficiency Design Index (EEDI) for Inland Vessels in Bangladesh

This paper attempts to evaluate EEDI for inland vessels in Bangladesh. To assess the present situation of inland class vessels in terms of CO2 emission, 526 cargo ships, 247 passenger ships, 70 oil tankers and 36 ferries have been taken in this study. The formulated baseline equations based on the study of different types of Inland vessels have been compared with the IMO evaluated baseline equations for International Shipping. The effect of EEDI with respect to vessels draft, type of fuel, block coefficient, specific fuel consumption (SFC) and power has also been investigated. Finally, some viable recommendations have been proposed to reduce the detrimental effects of C02 emission by optimizing hull shape of some existing vessels.

Reverse Analysis of Scan Strategies for Controlled 3D Laser Forming of Sheet Metal

Laser forming is an advanced manufacturing technique for the shaping and adjustment of metallic and non-metallic components by controlled laser induced thermal stress. Important advantages of laser forming include the absence of external mechanical tooling, flexibility and potential for automatic control. A large number of relevant two-dimensional laser forming studies have been completed to date. However, for the production of complex 3D shapes, such as ship hull components, airplane fuselages and automotive bodies, two-dimensional laser forming is limited. Therefore, in order to advance process for realistic applications, the investigation of the 3D scanning strategies becomes essential. This includes both in plane shortening and out-of-plane bending. In order to determining the scanning patterns and process parameters for forming any arbitrary 3D shape, numerical simulation is a strong tool to analyse the required stress and strain distribution and related processing parameters. In the presented investigation, the object is to develop optimal irradiation patterns and parameters to form a S275 steel square thin plate to a given generic ship hull shape through finite element simulation and experiment verification. A novel approach was used for the development of scan strategies for controlled 3D laser forming of sheet metal components based on a reverse analysis. A patched modular virtual press tool was employed in a commercial FE package COMSOL Multiphysics to extract the required strain-displacement map to achieve a given shape from a starting condition. The laser processing conditions have then been extracted from the magnitude of strain and displacement of each patch. A closed loop control iterative approach has then been used to ensure part accuracy during experimental verification.

Comparison of Tree Species Classifications at the Individual Tree Level by Combining ALS Data and RGB Images Using Different Algorithms

Individual tree delineation using remotely sensed data plays a very important role in precision forestry because it can provide detailed forest information on a large scale, which is required by forest managers. This study aimed to evaluate the utility of airborne laser scanning (ALS) data for individual tree detection and species classification in Japanese coniferous forests with a high canopy density. Tree crowns in the study area were first delineated by the individual tree detection approach using a canopy height model (CHM) derived from the ALS data. Then, the detected tree crowns were classified into four classes—Pinus densiflora, Chamaecyparis obtusa, Larix kaempferi, and broadleaved trees—using a tree crown-based classification approach with different combinations of 23 features derived from the ALS data and true-color (red-green-blue—RGB) orthoimages. To determine the best combination of features for species classification, several loops were performed using a forward iteration method. Additionally, several classification algorithms were compared in the present study. The results of this study indicate that the combination of the RGB images with laser intensity, convex hull area, convex hull point volume, shape index, crown area, and crown height features produced the highest classification accuracy of 90.8% with the use of the quadratic support vector machines (QSVM) classifier. Compared to only using the spectral characteristics of the orthophotos, the overall accuracy was improved by 14.1%, 9.4%, and 8.8% with the best combination of features when using the QSVM, neural network (NN), and random forest (RF) approaches, respectively. In terms of different classification algorithms, the findings of our study recommend the QSVM approach rather than NNs and RFs to classify the tree species in the study area. However, these classification approaches should be further tested in other forests using different data. This study demonstrates that the synergy of the ALS data and RGB images could be a promising approach to improve species classifications.

Numerical study on stern flow fields of ship hulls with different transom configurations

One of the reasons making the optimal design for a stern shape of a ship hull still difficult even nowadays is the complexity of flow field behind a transom stern. Study on effects of transom configurations on flow fields as well as on the ship resistances is therefore necessary and useful for the transom shape optimization. In this paper, the simulated results of flow fields behind transom stern of a container ship hull with various transom configurations using a CFD method are presented. Transom stern of an original container ship hull is modified in both breadth and height to get new models with various stern shapes. A flow solver which solves the Reynolds Averaged Navier-Stokes (RANS) equations for incompressible flows is employed in the computations of flow fields around ship hulls. The computational results are compared with each other to investigate correlations of the transom shapes with flow fields behind the ship stern and ship resistances. It is considered that the achieved results provide useful information for the practical optimization design of a stern shape of a ship hull.