Hull Parameters Research Articles

A pointwise weighting prediction variance–high-dimensional model representation model-based global optimization approach for ship hull parametric design

Ship hull optimization techniques based on computer-aided design/computational fluid dynamics can effectively enhance the efficiency and stability of ship designs, with significant application prospects. To enhance the potential of ship hull optimization, increasing design variable dimensionality is essential, but can cause a significant increase in hydrodynamic simulations. To reduce simulations required for high-dimensional ship hull optimization, a new surrogate method, pointwise weighting prediction variance–high-dimensional model representation (PWPV-HDMR), which uses pointwise weighting prediction variance (PWPV) to aggregate different a priori assumptions, is developed. Moreover, a differential evolution algorithm is used to identify promising hull design parameters, using the PWPV-HDMR model instead of costly simulation as the fitness function. The proposed approach is tested on the hydrostatic resistance optimization of KRISO Container Ship. The results show that PWPV-HDMR outperforms kriging-HDMR, with a better resistance optimization effect, illustrating the effectiveness of the PWPV-HDMR-based global optimization approach in discovering promising ship hull parameters.

АНАЛІЗ ЯКОСТІ ФУНКЦІОНУВАННЯ СИСТЕМИ НЕЧІТКОГО УПРАВЛІННЯ ЗАСПОКОЮВАЧЕМ ХИТАВИЦІ РЕАКТИВНОЇ ДІЇ

systems to stabilize its position and reduce the negative impact of various types of rocking on the crew and equipment. The corresponding devices, ship stabilizers, have many design options based on the use of different physical principles. Thus, this work considers a type of water-jet ship stabilizer, which stabilizes the ship's hull by creating mechanical moments from the reactive action of jets of a water-air mixture, which are ejected from the stabilizer in the appropriate direction. All ship stabilizers can be divided into passive ones, which do not require the supply of energy for their operation, and active ones, which usually use part of the power of the ship's power plant. It should be noted that active stabilizers make up a significant share of all their types and significantly reduce ship oscillations, although they cause significant energy costs. Accordingly, active ship stabilizers require effective control of their work, which should ensure good values of the stabilization parameters of the ship's hull at acceptable energy costs. It should be noted that the process of control the operation of a complex design stabilizer (which, in particular, is the mentioned reactive water-jet ship stabilizer) is quite complex: it includes many input and output variables of different nature, as well as dependencies between them, which are difficult to formalize during construction deterministic control system, which also cannot take into account the uncertainty of the specified values. Taking this into account, it is advisable to implement a control system for a water-jet ship stabilizer based on the principles of artificial intelligence, one of which is the theory of fuzzy sets. In this work, the implementation of a fuzzy controller for controlling a water-jet-type ship stabilizer was carried out, and its effectiveness was also studied using the Matlab Simulink model. The obtained results showed that the proposed fuzzy control system has satisfactory performance and can be recommended for implementation within the framework of the development of a ship stabilizer of the corresponding design.

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.

합성곱 신경망과 복셀화를 활용한 선박 저항 성능 예측

The prediction of ship resistance performance is typically obtained by Computational Fluid Dynamics (CFD) simulations or model tests in towing tank. However, these methods are both costly and time-consuming, so hull-form designers use statistical methods for a quick feed-back during the early design stage. It is well known that results from statistical methods are often less accurate compared to those from CFD simulations or model tests. To overcome this problem, this study suggests a new approach using a Convolution Neural Network (CNN) with voxelized hull-form data. By converting the original Computer Aided Design (CAD) data into three dimensional voxels, the CNN is able to abstract the hull-form data, focusing only on important features. For the verification, suggested method in this study was compared to a parametric method that uses hull parameters such as length overall and block coefficient as inputs. The results showed that the use of voxelized data significantly improves resistance performance prediction accuracy, compared to the parametric approach.

Adaptive multiple model control for nonlinear constrained systems with a novel barrier Lyapunov function

AbstractThis paper investigates the problem of the multiple model control of nonlinear full state constrained systems with a novel barrier Lyapunov function. To handle the problem of unknown parameters, the identification model set containing identification models is established. The novel barrier Lyapunov functions (BLFs) are employed to guarantee that all system states do not violate their boundaries and can remove the restricted condition associated with traditional BLFs. By using the first order filter technique, the "explosion of complexity" difficulty caused by the repeated differential from the backstepping technique is removed. In addition, the estimation of unknown parameters is obtained by using the convex hull property. Based on the second level adaptation technique, the convex hull parameters are designed by using the identification error dynamics, and this algorithm has better convergence property than other algorithms. Then, a multiple model control strategy is developed, which not only guarantees that the requirement of all state constraints is realized, but also ensures that the boundedness of all signals of closed‐loop systems are not violated. The key advantage is that the proposed strategy does not require enormous identification models, that is, the number of identification model is reduced significantly. Finally, the effectiveness of the presented scheme is illustrated through the simulation results.

Bayesian based updating of hull and mooring structure parameters of semi-submersible platforms using monitoring data

The parameters of hull structures and mooring systems of offshore platforms will change during their long service lives at sea. Therefore, if assessments of platforms are based on the original design parameters, they will become less accurate over time. As sensor technology and data analysis methods have advanced, it has become possible to update hull body and mooring parameters based on field monitoring data. However, simultaneously updating the many parameters of the hull and mooring system of semi-submersible platform is complex and computationally demanding, and underwater structure monitoring is difficult, therefore this paper proposes a parameter updating method based on floating platform response monitoring data. First, the method conducts a sensitivity analysis based on the hydrodynamic theory of semi-submersible platforms and the parameters to be updated and an objective function for the semi-submersible platform is determined. Then, updating methods for hull structure parameters and mooring parameters are established using Bayesian theorem and surrogate models. Finally, the parameters of hull and mooring structure of a semi-submersible platform in the South China Sea were updated using monitoring data and the results assessed. The proposed method effectively reduced the statistical error between measured and simulated 6-DOF motion values by more than 20% compared with the model before updating. The updated platform model was used to re-evaluate the hydrodynamic responses of the platform under multi-year return period environmental loads. The evaluation showed that during the multi-year service of the platform, the displacement of the platform had decreased by 10%, which was the main reason for the changes in wave frequency responses of the platform.

Methods to Improve Accuracy of Planing Hull Resistance Prediction

_ Accurate prediction of planing hull resistance is a difficult task due to complex hydrodynamic interactions at high speeds and is often performed by three methods: model testing, empirical formulas, and computational fluid dynamics (CFD). Model testing provides the most accurate results, but is usually only used in cases of necessity due to time and cost, whereas empirical formulas and the CFD method do not always provide results with the expected accuracy and reliability. Therefore, this paper will present methods to improve and ensure the accuracy of planing hull resistance values predicted by Savitsky’s empirical formula based on using our modified computation procedure, and by the CFD method based on ensuring the quality of 3D hull mesh and defining the simulation parameters suitable for a study planing hull. This study has been applied to Vietnam’s large displacement high speed passenger vessel with design symbol K88 and obtained good results with the deviations between the resistance model test data and the corresponding values predicted by the Savitsky method using our modified computation procedure, and by the XFlow CFD software using our suitable inputs in calculation cases are within ±5% and ±3%, respectively. Introduction In planing hull design, accurate prediction of its resistance is a difficult task due to complex hydrodynamic interactions at high speeds and is often performed by three methods: model testing, empirical formulas, and computational fluid dynamics (CFD). Model testing is the most reliable approach but it is expensive and time-consuming, so it is often used in cases where it is necessary, or used to verify and validate the results predicted by others. Also, since dynamic similarity cannot be fulfilled in model tests, it is necessary to use Froude or Prohaska methods to extrapolate results from model scale to full scale, which causes certain errors. Empirical formulas or graphs are established based on the systematization of resistance data of series model tests with hull form similarities (Holtrop & Mennen 1982; Faltinsen 2006). As a result, there are many different empirical resistance formulas and graphs depending on the type of ship used in the model tests. Table 1 shows some common empirical formulas or graphs for planing hull resistance with different ranges of hull parameters that can be found in related documents, such as Kafali (1959), Nordstrom (1951), Groot (1951), Almeter (1993), etc.

Effect of springing and whipping on exceedance probability of vertical bending moment of a ship

An extreme value distribution method for the vertical bending moment (VBM) is developed using a reduced order model (ROM) based on CFD-FEM coupling. A post-Panamax containership is considered to be a subject model and for which experiment was performed in our previous study. In ROM, VBM for all the components, i.e., wave-induced, whipping, and springing components, are calculated separately and superimposed. The vessel motions and wave-induced components are estimated from transfer functions derived from nonlinear strip theory and later corrected using CFD-FEM coupling. The whipping component is evaluated using von Karman's momentum theory with proper adjustment to specific hull parameters and additionally corrected using CFD-FEM coupling. A new semi-empirical springing ROM is developed based on CFD-FEM coupled analysis and experimental results. A numerous number of irregular waves are generated for a severe short-term sea state using random numbers, for which VBM time series is compared between ROM and coupled CFD-FEM analysis. The effect of springing and whipping in calculating the extreme value distribution of VBM is described for different probability levels. The effect of consecutive bow-stern slamming is also discussed. The development of this method will aid to attain real-time shipload prediction without expensive computational costs due to coupled CFD-FEM.

A machine learning approach to improve sailboat resistance prediction

In order to estimate the installed propulsion power aboard a boat, naval and ocean engineers make use of tools to assess the hull resistance through the water. It allows the designer to investigate the effect of changes on the hull parameters during the project’s first steps when there is still freedom for modifications. The available models to predict the resistance of sailboats estimate the residual resistance, while the frictional component is calculated based on ITTC-57. This approach leads to difficulties at low speeds since the calculated frictional resistance is larger than the total resistance obtained from the experiment. Therefore, its application is restricted above a minimum speed. Moreover, the available models consist of several sub-models, one for each Froude number. The present work proposes a unique model to predict the total resistance of bare-hull sailboats based on machine learning. Three systematic series were used as input. The best machine learning model could predict the total resistance efficiently even for small Froude numbers. With the presented model, the designer will have a unique tool capable of quickly predicting the total resistance of bare-hull sailboats including at low speeds. Both the input data and the predictive model are shared in complementary digital material.

Analytical surfaces for ship hulls

The choice of optimal shape of ship hull surface is one of the main problems of ship architects and designs. A choice of the form is based on empirical formulae or on intuition of designers. In the article a method of determination of explicit algebraic equations of theoretical shape of ship hull with three main cross-sections given in advance and coinciding with the design waterline, the midship section, and with the main buttock line is given. The forms of the lines in the main cross-sections are chosen from conditions taken in advance. These surfaces are called hydrodynamic. A method is illustrated for three threes of main cross-sections of the ship hulls, i.e. nine hydrodynamic surfaces were constructed. All algebraic equations were converted to parametrical form for comfort of computer modelling. With their help, all nine ship surfaces proposed for the introduction were visualized. Having changed constants containing in the surface equations, i.e. correcting the forms of three main geometric parameters of ship hull, one can select the most rational shape of hull surface for the first approach. Further, it is possible to begin planning parallel middle bodies or to combine bow and stern extremities of a ship from different fragments of algebraic surfaces but with the same midship sections. In a paper, only geometrical problems of design of theoretical hull shape are described.

Прогнозирование гидромеханических характеристик винта одновального судна

Object and purpose of research. This paper discusses hydromechanics properties of propeller and their scaling laws. The purpose of this study was to analyse existing methods of scaling model test data through their comparison with full-scale test results, identify possible sources of considerable error that might be present in them, as well as update the method of model test data scaling taking into account hydrodmechanic interaction between propeller and hull in terms of their model data extrapolation to the full scale. Materials and methods. The paper discusses general relationships between hydromechanic parameters of hull and propeller, that arise, in their turn, from the fundamental laws of mechanics. These relationships were used to analyse interconnected laws governing the full-scale extrapolation of model test data for hull resistance, propeller thrust and propeller torque. Main results. The study identified some incorrect hypotheses in current scaling methods for hydrodynamics of propeller in behind-hull conditions, that might bring about considerable error in full-scale estimates of operational advance coefficient, thrust coefficient, efficiency and RPM. Conclusion. This paper suggests alternative techniques for determination of operational advance coefficient and other hydromechanics parameters of full-scale propeller, so as to obtain the estimates that take into account physical peculiarities of scale effect and also correlate with the results of full-scale trials.

Modeling of Autonomous Underwater Vehicles with Multi-Propellers Based on Maximum Likelihood Method

The hydrodynamic characteristics of multi-propeller autonomous underwater vehicles (AUV) is usually complicated and it is difficult to obtain an accurate mathematical model. A modeling method based on CFD calculation and maximum likelihood identification algorithm is proposed for this problem. Firstly, rough hydrodynamic parameters of AUV hull are obtained by CFD calculation. Secondly, on the basis of rough parameters, a maximum likelihood identification algorithm is proposed to adjust the parameters and improve the model precision. Besides, the method to improve the convergence of identification algorithm is analyzed by considering the characteristics of AUV model structure. Finally, the identification algorithm and identification results were validated with experimental data. It was found that this method has good convergence and adaptability. In particular, the identification results of turning force and torque parameters are highly consistent in different identification experiments, which indicates that this method can well extract the maneuvering characteristics of AUVs, thus contributing to the controller design of AUVs. The research of this paper has potential application for the modeling and control of multi-propeller AUVs.

A vector control technology of waterjet propelled crafts using synchronous and mirror-equiangular thrust control strategy

Vector control technology with single joystick for ship maneuvering is investigated on waterjet propelled crafts for excellent maneuverability and easy manipulation. In this paper, a vector control strategy of ship motion based on synchronous thrust adjustment of two waterjets with mirror-equiangular magnitude which takes the hull cross section as the benchmark was selected firstly. Then the relationship among three manipulation parameters of joystick, six operation parameters of two sets of waterjet propulsion systems, and three motion parameters of hull was established to obtain the vector correspondence between joystick operation and hull motion. On this basis, a vector controller prototype was constructed and mounted on a ship model propelled by two sets of waterjets. The vector control functions of the lateral motion, spot turn and other complex motions such as sectorial motion were realized successfully. The technology of single joystick vector control can be applied to many operation conditions of waterjet propelled crafts, such as berthing, entering and leaving port, position operations at sea, and tactical maneuver to improve the maneuverability and safety of ships. In addition, the vector control function can also be applied to the motion control module for low-speed maneuvering condition of smart ship.

Estimation of the Vessel's Sailing Resistance in the Preliminary Analyses

Abstract In this article is presented the methodology of calculation of principal parameters of hull a vessel and resistance components. The approximate method is based on the analysis of the results of model tests and surrender tests presented in the literature. Ship owners' preliminary assumptions for new ship consist of deadweight, speed-shipping line and others. This goal needs definition of principal dimensions of a vessel, which are the basis for further calculations of hull’s resistance and evaluation of necessary power of main engine to fulfil shipping requirements. The route and its environment, type of cargo, quantity to be moved, and value of the cargo and port facilities are typical features, which will be considered when evolving the size, speed, and specification of a suitable ship. Specific service requirements will be similarly considered when evolving vessels such as warships, passenger ships or fishing vessels. Selection of main dimensions of vessel is limited by related to seaways or harbours characteristic and limitations rules regarding buoyancy, stability, hull strength, manoeuvring capability, etc. The influence of the main dimensions of the ship and their coefficients of maritime and strength properties of the ship were presented. Moreover, formulas for calculation of the ship's resistance components, such as friction resistance, and wave shape, as well as the results of calculations for different types of ships, for the assumed deadweight and speed of sailing, are presented.

Fuel efficiency optimization of tanker with focus on hull parameters

Fuel efficiency optimization is of crucial importance in industries. Marine transportation industry is no exception. Multi-disciplinary optimization is a branch of engineering which uses optimization methods for solving problems in which the objective function is simultaneously affected by several different factors. As one of the tools for this type of optimization, genetic algorithm has a high quality and validity. The objective of the present study is to optimize fuel efficiency in tankers. All presented equations and conditions are valid for tankers. Fuel consumption efficiency of tankers is a function of various influential factors. Given the lack of equations for describing and modeling these factors and unavailability of valid performance database for inferring the equations as well as the lack of literature in this field, the preset study includes five optimizing factors affecting the fuel consumption efficiency of a tanker in genetic algorithm by using the genetic algorithm toolbox of MATLAB software package.

Design, Modeling and Virtual Validation of Mobility platform of Tracked Vehicle

Hull design of a tracked vehicle plays a critical role in the vehicle mobility, crew protection and combat performance. This work is intended to design a hull of 50 Ton tracked vehicle using conventional layout of suspension and running gear components. Driver compartment of hull is designed based upon driver height of 1.69m. Critical hull parameters such as angle of departure, location of 1st road wheel w.r.t idler wheel, location of last road wheel w.r.t sprocket and distribution of middle road wheels are calculated. Finally, designed hull is modeled in Pro/Engineer software and Recurdyn software is used to ascertain vehicle performance in various prototype tests. In the wake of scarcity of papers on this subject, this paper not only outlines the process of hull design for conventional tracked vehicles but also for unconventional ones such as autonomous tracked vehicles.

Systematic probabilistic design methodology for simultaneously optimizing the ship hull–propeller system

The proposed design methodology represents a new approach to optimize the propeller–hull system simultaneously. In this paper, two objective functions are considered, the first objective function is Lifetime Fuel Consumption (LFC) and the other one is cost function including thrust, torque, open water and skew efficiencies. The variables of the propeller geometries (Z, EAR, P/D and D) and ship hull parameters (L/B, B/T, T and CB) are considered to be optimized with cavitation, blades stress of propeller. The well-known evolutionary algorithm based on NSGA-II is employed to optimize a multi-objective problem, where the main propeller and hull dimensions are considered as design variables. The results are presented for a series 60 ship with B-series propeller. The results showed that the proposed method is an appropriate and effective approach for simultaneously propeller–hull system design and is able to minimize both of the objective functions significantly.

A sensitivity analysis of a hull’s local characteristic parameters on ship resistance performance

Simulation-based design hull form optimization has become one of the most effective ways to develop energy-saving ships. However, the traditional method is time consuming and inefficient, so it is difficult to apply it to practical engineering. One of the reasons for this difficulty is that there are numerous parameters for expressing the hull form, making it difficult to find the optimal solution within a short amount of time. Therefore, this paper presents a sensitivity analysis method based on radial basis function and partial least squares regression neural network with uniform design for sampling, to study the sensitivity of local hull parameters of a class of container ships on wave-making resistance performance, and to reduce the number of dimensions in the design space. According to the results of sensitivity analysis, the parameters that are of negligible influence on the objective function can be removed from the optimization model. Comparison of results of the original model and the simplified model shows that the presented sensitivity analysis method can effectively reduce the dimension of the design space so that the time consumed to achieve the optimum is decreased.

Comparative modeling of hull form resistance for three ocean going vessels using methodical series

This paper presents a comparative estimation of the hull form resistance for Cargo ship, Ocean-going Tug and Container ship. The research study evaluates the influences of various ship hull parameters in relations to the vessel speeds and level of turbulence (Reynolds number). The modeling was done using MATLAB software and the model test technique based on the ITTC, ATTC, Granville and Hughes friction line application. The result shows that the hull form resistances follow the same trend in the ITTC, ATTC and Granville models, while the Hughes model gave a different trend with other techniques. It further revealed that as the speed increases by 10knots, the frictional resistance coefficients decrease by 11.86% for the ITTC & Granville models, and 12.03% for the Hughes model. For Ocean-going Tug and Container Ship, the frictional resistance coefficient decrease by 12.31% for the ITTC & Granville models, and 12.14% for the Hughes model. The Reynolds number increase by 62.52% for every 10knots increase in the speed of the Cargo ship and 62.23% for every 10knots increase in the speed of the Ocean going tug and Containership. At various experimental speeds, the results showed that for every 1 knots increase in the speed of the Containership, the effective power developed increases by 9.45%. This provides a technical and analytical guide on hull form resistance trend for engineers and ship operators.

A Hydrodynamic Methodology And CFD Analysis For Performance Prediction Of Stepped Planing Hulls

Abstract Nowadays all efforts in planing hull research are focused on resistance reduction for achieving the highest speed in fast planing crafts. Furthermore, many fruitful research projects have been carried out on marine coatings, planing equipment, and optimization of propeller and hull form, which revolutionized industry of high - speed crafts and made them an efficient survival vehicle in coastal areas and rivers. In this paper the hydrodynamic performance of planing hulls are investigated by means of a modified Savitsky model for both non-stepped and stepped bodies. Meanwhile, in order to meet this goal reasonably, effective geometrical parameters of planing hull are investigated and then operational hydrodynamic characteristics of the craft are predicted by using a computational program. Finally, the calculation results are verified by means of a CFD-analysis model.