Model Ship Test Research Articles

MMG 3DOF model identification with uncertainty of observation and hydrodynamic maneuvering coefficients using MCMC method

The trajectory prediction using ship maneuverability mathematical models is one of the essential technologies implemented in autonomous surface ship. Several ship maneuverability mathematical models and each one with a particular hydrodynamic coefficient approximation using towing tank tests are existed. However, it is presented difficult to directly inverse estimate the hydrodynamic maneuvering coefficients of a ship maneuverability mathematical model from operational data consisting of ship trajectory and maneuvering operation records. This paper proposed a method for estimating the hydrodynamic maneuvering coefficients of the MMG 3DOF model using three types of time-series ship motions (surge, sway, and yaw velocity) as observed data. In the assumption of this paper, there is uncertainty in observations and the hydrodynamic maneuvering coefficients of the MMG 3DOF model. The proposed method outputs samples of the simultaneous posterior probability distribution of the hydrodynamic maneuvering coefficients by the MCMC method using the observed data and stochastic model. A robust trajectory with a wide range can be presented by conducting ship maneuvering simulations using these samples. To verify the feasibility of the proposed method, this paper conducted observation system simulation experiments (OSSE) using the KVLCC2 L7 model and applied the proposed method to several free-running model ship tests. Results showed that on the assumption that MMG 3DOF model can explain the ship's state and trajectory in real world, the proposed method can estimate the ship hydrodynamic maneuvering coefficients of the MMG 3DOF model corresponding to the observed ship trajectory and control data including the error of observed data.

Drag reduction performance and mechanism of flexible conical microstructure film inspired by pufferfish epidermis

Flexible bionic drag reduction surfaces have attracted increasing attention in recent years owing to its potential to address the daunting energy crisis. Inspired by the skin of pufferfish, a flexible conical microstructure film with effective drag reduction is designed. The film has the advantages of cost-effective and tensile-bending resistance to meet commercial applications. The low price of raw materials and rapid solidification at room temperature are the core of cost reduction, and the manufactured film can withstand a maximum tensile force of 70 N and a strain of 484%. The practical application effect of the film has been confirmed by model ship tests, and it still has stable drag reduction ability after multiple stretching and bending. The water tunnel experiment results show that the drag-reducing efficiency of the flexible conical microstructure film is 10.65%–12.04% compared to the rigid plane, in which the conical topography suppresses turbulence burst, whereas the flexible surface has the effect of absorbing turbulent energy to buffer the near-wall fluid. The coupling effect enhances drag-reducing efficiency. Therefore, the flexible conical microstructure film in this work provides a practical and commercialized fluid drag reduction approach for ships, underwater vehicles, and pipeline transportation.

빔형성 방법을 이용한 함정 추진기 소음 위치 추정에 대한 실험적 연구

In this study, an experimental investigation was conducted to estimate the location of propeller cavitation using a beamforming method with a hydrophone array. The sensors were mounted on the hull surface above the port side propeller and arranged in a single-armed spiral. To validate the performance of the sensor array, a test was performed using a reference source ITC-1032. The results showed that the location of the sound source was well predicted. A scaled model-ship test was conducted for various test conditions in the large cavitation tunnel of KRISO. Propeller cavitation was observed using a video camera with stroboscopes, and the propeller noise were measured by on-board sensors. From the observations and estimations, we concluded that the dominant cavitation was well estimated.

자유항주모형시험을 이용한 KCS 선형의 축척비별 조종성능에 관한 연구

There have been many experimental studies on the manoeuvrability of KRISO Container Ship (KCS). However, the scale ratio of the model ship and the test procedure for each institute are slightly different, so direct comparison for the data is technically difficult to perform. This paper presents the manoeuvrability of the ship with different scale ratios: 1/65.8, 1/42.0, and 1/31.6 in model scale. KRISO conducted Free Running Model Tests (FRMT): 35°turning circle tests and 20/20(10/10) zigzag manoeuvring tests. The test results indicated that advance and tactical diameter in turning circle tests were similar, and overshoot angles in two zigzag manoeuvring tests increased as the model ship size increased. In addition, a basic concept for the FRMT method with an auxiliary X-thrust device was proposed so that the scale effect could be considered in model ship tests.

Estimation of pack ice concentration using histogram peak analysis and image subdivision

Numerous studies on icebreaking vessels have been reported recently owing to a potential increase in the number of passable Arctic routes. Model ship tests of pack ice models in ice basins have been actively conducted to investigate the performance of different icebreakers. The estimation of the pack ice concentration is critical as pack ice directly affects the performance of such experiment. In this paper, an algorithm that automatically determines the concentration of pack ice is proposed. This study aimed to measure the area of pack ice, based on digital images captured in an ice basin, using an image processing technique. A local binarization technique, coupled with image subdivision based on a quadtree structure, was developed. Independent thresholds were calculated for the subdivided images and rapid image separation was achieved. To demonstrate the accuracy of the proposed method, the concentration results obtained with the developed algorithm were compared with the manually measured data, with both results and data showing good agreement. The main advantage of the developed algorithm is that it facilitates the near-real-time estimation of the pack ice concentration from captured digital images.

Automatic waterline detection and 3D reconstruction in model ship tests using stereo vision

The changes of the waterlines alongside ship hulls in model ship tests provide important information to estimate the resistance performance of the full-scale ships and to improve its hull form design. This Letter presents a systematic procedure for detecting a waterline and reconstructing its three-dimensional (3D) geometry using a stereo vision system. The proposed method utilises the information from non-distinctive geometric features and shapes characterised in the waterline around a model ship without using any specified colours or artificial landmarks. For reconstructing the 3D geometry of the detected waterline, a vertical stereo system and a direct disparity estimation method are employed along with the consideration of uncertainties in the stereo correspondence matching. Experimental results are shown to demonstrate the feasibility of the proposed method using an image dataset obtained in a model ship test in a towing tank environment.

Numerical Simulation on the Resistance Performance of Ice-Going Container Ship Under Brash Ice Conditions

Ice resistance prediction is a critical issue in the preliminary design of ships navigating brash ice conditions, which is closely related to the safety of a ship to navigate encounter brash ice, and has significant effects on the kinds of propellers and motor power needed. In research on this topic, model tests and full-scale tests on ships have thus far been the primary approaches. In recent years, the application of the finite element method (FEM) has also attracted interest. Some researchers have conducted numerical simulations on ship–ice interactions using the fluid–structure interaction (FSI) method. This study used this method to predict and analyze the resistance of an ice-going ship, and compared the results with those of model ship tests conducted in a towing tank with synthetic ice to discuss the feasibility of the FEM. A numerical simulation and experimental methods were used to predict the brash ice resistance of an ice-going container ship model in a condition with three concentrations of brash ice (60%, 80%, and 90%). A comparison of the results yielded satisfactory agreement between the numerical simulation and the experiments in terms of both observed phenomena and resistance values, indicating that the proposed numerical simulation has significant potential for use in related studies in the future.

Model Ship Control and Estimation of Full-scale Propeller Torque in Wind and Waves

This paper presents free-running model ship test data estimating full-scale propeller torque fluctuating in wind and waves. The model ship control using the auxiliary thruster ensures the similarity of model ship motion to full scale that leads the similar propeller situation The wind load simulator controls six duct fans on the model ship for simulating the wind loads. The estimation algorithm converts the measured model propeller torque to full scale assuming no scale effect on the wave component in the effective inflow velocity to propeller. The analysis reveals the differences of the fluctuating propeller torque between model and full-scale ships.

쿼드트리 분할영상의 국부이진화를 통한 팩아이스 집적도 측정 알고리즘

Recently, many research works on the icebreaking vessels have been published as the possibility of passing Arctic routes has been increasing. The model ship test on the pack ice model in the ice basin is actively carried out as a way to investigate the performance of icebreaking vessels. In this test, the concentration of pack ice is important since it directly affects the performance. However, it is difficult to measure the concentration because not only the pack ice has uneven shape but also it keeps floating around in the basin. In this paper, an algorithm to identify the concentration of pack ice is introduced. From a digital image of pack ice obtained in the ice basin, the goal is to measure the area of pack ice using an image processing technique. Instead of the general global binarization that yields numerical errors in this problem, a local binarization technique, coupled with image subdivision based on the quadtree structure, is developed. The concentration results obtained by the developed algorithm are compared with the manually measured data to prove its accuracy.

Estimation of full-scale propeller torque and thrust using free-running model ship in waves

The authors propose a method to estimate full-scale propeller torque and thrust consisting of low-frequency and high-frequency components in waves by free-running model ship test. The duct fan auxiliary thruster (DFAT) (Tsukada et al., 2013, 2014) and the rudder-effectiveness and speed correction (RSC) (Ueno and Tsukada, 2015; Suzuki et al., 2014, 2015) ensure similar model ship motion to full-scale in wind and waves, where RSC controls the model ship propeller rate of revolution and the auxiliary thrust depending on instantaneous model ship speed. Analyzing wave component in the effective inflow velocity to propeller, the method estimates full-scale fluctuating propeller torque and thrust in waves. Trial application of the method exemplifies the property of full-scale fluctuating propeller torque and thrust comparing with those of a model ship.This method also makes it possible to incorporate into free-running model ship tests any engine model simulating interaction between propeller torque and engine torque.

Thickness Measure and Characteristic Length for Effective Young's Modulus of Model Ice Plate in the Ice Basin

Abstract The model ice is created at KRISO (Korea Research Institute for Ships and Ocean Engineering) ice basin where model ship is tested to obtain the necessary data in order to design the ice breaking vessels and ocean structures operating in the northern pole sea area. Through the model ship test, ice breaking, clearing, ice-ship and ice-propeller interaction behavior can be obtained. Since mechanical properties of ice plate are required for the model test, some tests are performed to obtain the properties in this paper. First, ultrasonic devide is used to measure the thickness of the model ice plate and the results show the possibility of using ultrasonic method, yet more sophisticated device or special sensors are required to measure the ice thickness completely. And the defection of ice plate is measured using LVDT to compute the characteristic length of ice plate on the fluid, which is used to get the effective Young's modulus of model ice. Keywords :ice basin(tank), model ice effective elastic modulus, plate characteristic length. LVDT(Linear Variable Differential Transformer), ultrasonic

Time Resolved PIV Investigation on the Skin Friction Reduction Mechanism of Outer-Layer Vertical Blades Array

The drag reducing efficiency of the outer-layer vertical blades, which were first devised by Hutchins (2003), have been demonstrated by the recent towing tank measurements. From the drag measurement of flat plate with various vertical blades arrays by Park et al. (2011), a maximum 9.6% of reduction of total drag was achieved. The scale of blade geometry is found to be weakly correlated with outer variable of boundary layer. The drag reduction of 2.8% has been also confirmed by the model ship test by An et al. (2014). With a view to enabling the identification of drag reduction mechanism of the outer-layer vertical blades, detailed flow field measurements have been performed using 2D time resolved PIV in this study. It is found that the skin friction reduction effect is varied according to the spanwise position, with 2.73% and 7.95% drag reduction in the blade plane and the blade-in-between plane, respectively. The influence of vertical blades array upon the characteristics of the turbulent coherent structures was analyzed by POD method. It is observed that the vortical structures are cut and deformed by blades array and the skin frictional reduction is closely associated with the subsequent evolution of turbulent structures.

빙해수조 모형빙에 관한 네트워크형 데이터베이스 구축

In the KIOST MOERI model ice basin, a lot of experiments to find the material properties of model ice and model ship tests are being performed. And therefore many data information was produced, yet it was saved as excel data format. In order to manage and use the data more effectively and systematically, a proper database management is required. To make realistic engineering DBMS(database management system), understanding of test process, the usage of data, design of data schema and computer language and system management are required. In this paper, basic design process and usage of DBMS based on network and multiple user concept is introduced.

自由航走模型試験のための補助推力装置の開発

The free-running model ship test is one of effective measures to estimate ship performance and response in various situations. However, since Reynolds numbers are quite different between model and full-scale ships, phenomena of model ship especially those concerning propeller load are not necessarily similar to those of full-scale. The authors developed an auxiliary thruster to assist a free-running model ships’ propeller. The auxiliary thruster consists of a duct fan, a signal amplifier, a load cell, and a PC. The PC can control the longitudinal force of the duct fan arbitrarily using feed-back data of the force measured by the load cell and instantaneous model ship speed. A prototype confirms through verification test basic capabilities and adequacy of the authors' design of the auxiliary thruster.

A Study on Shape and Height of Shipwaves

Shipwaves am have harmful effects on ships working on the sea, in a harbour or navigational channel and caused beach erosion, seawall destruction. This study aims to investigate describe the characteristics of the wave pattern generated by an individual model ship tested at different velocities and hull forms for a given water depth and to investigate the variations at a given distance from the sailing line under the same conditions. As a result, the angles a's by model ship tests are smaller than those by real ship ones. Wave heights decreases with an increasing the mid-ship cross sectional area . The maximum wave height and period increase rapidly in the subcritical speed, and beyond the critical speed the height and period decrease with increasing depth Froude number. And the period keeps constant with the distance from the sailing line.

肥大船型を対象とした操縦流体力微係数の推定に関する研究

Since International Maritime Organization (IMO) has adopted The Standards of Ship Manoeuvrability as IMO Resolution MSC.137(76), the ship manoeuvrability is evaluated under this standard. Therefore, ship designers have to know the accurate ship manoeuvring characteristics at the initial design stage. One of the estimation methods for ship manoeuvring characteristics is a computational simulation. Some papers have proposed approximate formulas for hydrodynamic derivatives based on the model ship tests, so we can simulate the ship manoeuvring motion with the hydrodynamic derivatives.However recent full ships aren't included in the range of ship types on the papers. We need to adjust the formulas for hydrodynamic derivatives, so as to simulate the manoeuvring motion of recent full ships.In this paper, we propose the method to revise the approximate formulas for hydrodynamic derivatives of full ships. We confirm the effectiveness of the practical prediction method using proposed formulas. It will be expected that this method is very useful to estimate the manoeuvring characteristics of recent full ships at the initial design stage.