Ship Model Test Research Articles

Ship Maneuvering Prediction Using Grey Box Framework via Adaptive RM-SVM with Minor Rudder

Abstract A grey box framework is applied to model ship maneuvering by using a reference model (RM) and a support vector machine (SVM) (RM-SVM). First, the nonlinear characteristics of the target ship are determined using the RM and the similarity rule. Then, the linear SVM adaptively fits the errors between acceleration variables of RM and target ship. Finally, the accelerations of the target ship are predicted using RM and linear SVM. The parameters of the RM are known and conveniently acquired, thus avoiding the modeling process. The SVM has the advantages of fast training, quick simulation, and no overfitting. Testing and validation are conducted using the ship model test data. The test case reveals the practicability of the RF-SVM based modeling method, while the validation cases confirm the generalization ability of the grey box framework.

Research on Influence of Trim on a Container Ship’s Resistance performance

Faced with the double pressure of rising oil price and limitation of greenhouse gas emissions, many ship owners began to seek measures to minimize ship’s resistance under specific conditions. Trim optimization has gained more and more attention in recent years for its flexibility and effectiveness in energy saving and emission reduction. The purpose of this paper is to perform trim optimization on a container ship. First, commercial CFD code of the ANSYS FLUENT was applied to calculate the target ship’s total resistance. Then, in order to validate the effectiveness of CFD method, experimental result of ship model test was referred and it indicated that the numerical method was a reliable tool in prediction of the container ship’s hydrodynamic performance. Finally, resistance corresponding to various trim conditions and speeds of three typical drafts were investigated, and it showed that trim did have impact on resistance. Based on the attained result, optimum trim value for actual navigation was suggested.

Modelling and simulation of the ship rapids-ascending ability in Lancang River

Ship sailing resistance is an important indicator to judge the navigation capacity of a waterway. In this paper the empirical formula of Zwaan Kopf is modified according to the ship model test results in Lancang River channel, tests reveal that the navigation capacity of the channel can be represented by a critical composite flow energy indicator ΔE = 1.20. In order to validate the reliability of experimental results, this paper established a two-dimensional numerical model to simulate the water flow and ship sailing process in the channel. The relationship of flow energy indicator and the sailing velocity is studied by simulating a typical 500t ship sailing in the channel of Lancang River, and the results show that the value of critical flow energy indicator ΔE in the channel of Lancang River by simulation fits well with the tests, so the simulation method proposed in this paper is reasonable and feasible, and the critical flow energy indicator simulated by this method has important reference value in engineering.

Maneuver Control System for Collision Avoidance Based On Experimental Study

Autopilot mode in the ship navigation system is intended to assist the work of the captain in controlling the ship, but the autopilot mode still has some disadvantages such as in the case of maneuvers to avoid collisions. Many studies on design of anti-collision design. But almost all use a numerical approach. In this paper will be discussed the design of maneuver controls that will be used on the ship model to avoid the ship from the collision. Where within the control system there are several sensors, including ultrasonic sensors, gyro sensors and Qualysis cameras. From ship model testing conducted, the design of maneuver control proved able to avoid the ship from the occurrence of collisions. Minimum distance of ship and obstacle at 250 m distance is 34,17 m, at a distance of 200 m is 13,46 m while at a distance of 150 m is 13,36 m.

Estimation of Hydrodynamic Coefficients of a Nonlinear Manoeuvring Mathematical Model With Free-Running Ship Model Tests

Free-running model tests have been carried out based on a scaled chemical tanker ship model, having a guidance, control and navigation system developed and implemented in LabVIEW. In order to make the modelling more flexible and physically more realistic, a modified version of Abkowitz model was introduced. During the identification process, the model’s structure is fixed and its parameters have been obtained using system identification. A global optimization algorithm has been used to search the optimum values and minimize the loss functions. In order to reduce the effect of noise in the variables, different loss functions considering the empirical errors and generalization performance have been defined and implemented in the system identification program. The hydrodynamic coefficients have been identified based on the manoeuvring test data of free-running ship model. Validations of the system identification algorithm were also carried out and the comparisons with experiments demonstrated the effectiveness of the proposed system identification method.

Numerical study on the manoeuvring of a container ship in regular waves

ABSTRACTShips operate in seaways, but ship manoeuvrability is usually studied in calm water conditions, thus ignoring the effects of wave on the ship hydrodynamic behaviour. So, the assessment of surface ship manoeuvrability in wave environment is more realistic and accurate than its estimation in calm water condition. In the present study, captive dynamic ship model tests are numerically simulated in a computational fluid dynamics environment in regular head sea waves and the hydrodynamic derivatives are derived from the estimated force/moment time series using the Fourier series expansion method. These derivatives and wave excitation forces are fitted in the manoeuvring equations of motion and are solved to simulate the ship standard manoeuvres in head sea waves. Parameters of these definitive manoeuvres in wave condition are compared with those in still-water condition.

An Application of the Tank Test with a Model Ship for Design of Ship Propulsion Plant System

Engine power reduction is now regarded as the most efficient and easy realisable measure to improve the Energy Efficiency Design Index, introduced by the IMO. However, there is a concern regarding the sufficiency of propulsion power to maintain manoeuvrability of ship in the adverse sea, and so the IMO also set the interim guideline to assess Minimum Propulsion Power (MPP). As a result of these streams, it has never been more important to evaluate the performance of the ship in actual sea conditions, even including engine characteristics deeply. Here, as a method to validate or investigate designs of ship propulsion plant system in the initial design stage, the authors have developed an intelligent motor system for the ship model test, called as a Marine Diesel Engine Simulator (MDES). The MDES consists of the cycle mean value model of engine, a speed governor and motion equation of propeller shaft. The MDES simulates the response of the engine model in real time, based on the measured propeller torque and speed, and manage the rotational speed of the motor as the calculated response. In this way, the engine matching, requirement on MPP, speed governor settings, etc., can be easily validated at the design stage without the need for full-scale tests. This paper briefly introduces the tank test methodology and then discusses the test results of propulsion plant responses in regular waves at different speed governor settings in details.

Route tracking for self-propelled ship model

To ensure the safety of the navigation, self-propelled ship model test is widely used in navigable administer engineering to visually and really reflect navigable condition, offering reasonable suggestions for the design of route. This paper proposed a video analysis based route tracking approach for self-propelled ship model that sails in large scale river models, which can realize automatic measurement for ship model motion parameters. Firstly, the captured videos of the self-propelled ship model are transferred to the computer via wireless local area network (WLAN). Then, the camera lens distortion is eliminated by rectify and aerial view is reconstructed. Third, ORB and binary BoF classifier are used to detect ship model. At last, through frame difference and Freeman chain-code, the coordinates of ship model’s markers can be obtained. Moreover, on visual interactive interface, the route of the ship model is plotted, and velocities and drift angles of ship model are also calculated. This approach was tested on the several river models, such as Jianzishan navigation junction, which is a medium-sized water conservancy project located in the middle reaches of the Minjiang River. The results from the experiments demonstrate the approach can not only realize accurate measurement of coordinates of ship model, but also can visually map out the route of the ship model that sailing in large scale river models.

대형 캐비테이션 터널 내 선박 모형의 3차원 선체 반류 계측을 위한 레이저 유속계 개발

Large Cavitation Tunnel (LCT) of KRISO enables us to conduct cavitation tests of the propeller attached to a ship model. As the ship model tests are done at rather high Reynolds number of 107~108, flow measurement system such as pitot tube cannot be employed because of structural safety problems in its system and difficulties in installing it within the test section. Thus, KRISO has developed new 3-D LDV system used in large test section of LCT. There are several difficulties in using 3-D LDV, which did not allow efficient operation of it. The first trouble was the calibration using the conventional pin hole. To make the focus with same laser-beam waists at the wanted position, the high spatial resolution CCD is utilized in the calibration procedure for 3-D LDV. The off-axis configuration provides two velocity components in the horizontal plane and on-axis configuration gives third velocity component in the vertical plane. The horizontal velocity components are also obtained in the coincidence mode, which prevents any misleading results in the off-axis configuration. The nominal wake of Aframax tanker model is measured by the developed 3-D LDV system. The measured hull wake showed good agreement with that obtained by CFD calculation.

Side wall effects on ship model testing in a towing tank

Due to the existence of the side walls in a towing tank, the measured hydrodynamic forces would present some discrepancies compared to the open sea results. This phenomenon is referred to as the side wall effect. The objective of the present study is to investigate the side wall effects on ship model testing in a towing tank. The method used in the present study involves a 3D panel method based on the Rankine type Green function. Both the steady and unsteady problems were investigated numerically. The numerical results were validated against ship model test results. After the validations, a large scale computations were performed to investigate the parameters which could determine the side wall effects. Two diagrams of side wall effects (one in calm water and the other one in waves), were obtained which showed whether the side wall effect was less than the permissible error to be included in the measured values.

Analysis of the Relevant Parameters on Small Scale of Navigable Abnormal Ship Model

Abstract At present, ship model tests are based on the normal mode at home and abroad. With the development and application of abnormal hydraulic model, it is necessary to study abnormal ship model. The similarity criterion of abnormal ship model is deduced from the similarity theory of normal hydraulic model in this paper. Some factors that affect the maneuverability of the abnormal ship model are discussed by theoretical analysis of ship maneuvering. The influence of the K and T index of different variable rate on the abnormal ship model maneuvering and the dimensional effect of the abnormal ship model are obtained, which can be used as a reference for the study of the abnormal ship model.

Time-domain numerical and segmented ship model experimental analyses of hydroelastic responses of a large container ship in oblique regular waves

Real sea conditions are characterized by multidirectional sea waves. However, the prediction of hull load responses in oblique waves is a difficult problem due to numeral divergence. This paper focuses on the investigation of numerical and experimental methods of load responses of ultra-large vessels in oblique regular waves. A three dimensional nonlinear hydroelastic method is proposed. In order to numerically solve the divergence problem of time-domain motion equations in oblique waves, a proportional, integral and derivative (PID) autopilot model is applied. A tank model measurement methodology is used to conduct experiments for hydroelastic responses of a large container ship in oblique regular waves. To implement the tests, a segmented ship model and oblique wave testing system are designed and assembled. Then a series of tests corresponding to various wave headings are carried out to investigate the vibrational characteristics of the model. Finally, time-domain numerical simulations of the ship are carried out. The numerical analysis results by the presented method show good agreement with experimental results.

Measures to diminish the parameter drift in the modeling of ship manoeuvring using system identification

System identification provides an effective way to predict the ship manoeuvrability. In this paper several measures are proposed to diminish the parameter drift in the parametric identification of ship manoeuvring models. The drift of linear hydrodynamic coefficients can be accounted for from the point of view of dynamic cancellation, while the drift of nonlinear hydrodynamic coefficients is explained from the point of view of regression analysis. To diminish the parameter drift, reconstruction of the samples and modification of the mathematical model of ship manoeuvring motion are carried out. Difference method and the method of additional excitation are proposed to reconstruct the samples. Using correlation analysis, the structure of a manoeuvring model is simplified. Combined with the measures proposed, support vector machines based identification is employed to determine the hydrodynamic coefficients in a modified Abkowitz model. Experimental data from the free-running model tests of a KVLCC2 ship are analyzed and the hydrodynamic coefficients are identified. Based on the regressive model, simulation of manoeuvres is conducted. Comparison between the simulation results and the experimental results demonstrates the validity of the proposed measures.

Measurement and Analysis of Coastal Waves Along The North Sea Area of China

Abstract Taking advantage of coastal wave environment to carry out scaled ship model test is an effective testing technology for ship performance. In this paper, the method of spectral analysis is adopted to calculate the significant wave height, period, wave spectrum and some other parameters of some places along the North Sea area of China. The measured wave spectrum and the ocean spectrum are handled into non-dimensional form to evaluate their similarity. The influence of wind direction and tide on coastal waves was analyzed. And the results indicate that the coastal wave spectrum is similar to the ocean spectrum under some specific conditions.

Study on the squat of extra-large scale ship in the Three Gorges ship lock

Aiming at determining the controlling standard of extra-large ship entering or exiting the Three Gorges ship lock of China, the maximum squat of typical ships with physical model test was examined in this study. Physical model tests include hydraulic and 5000t ship model tests at the scale of 1:36.3, with the purpose of obtaining the squat of ships entering or exiting ship lock at different depths, draft and speeds. Based on the theoretical analysis and previous achievements, this study advanced the mathematical models to estimate the maximum squat of ship driving in special restricted channel. For the typical ships, it is reliable to take the ratio of water depth to draft (i.e., H/T≥1.6) as controlling standard of ship entering or exiting ship lock. The results showed that the squat obviously increased with the ship passing by moored ships in the lock. The speed of typical ship with different lanes should be slower than 0.5m/s to ensure the safety when other ship berthing in ship lock, which matched well with the observations. The proposed formula is feasible in scientific method, reasonable conclusion with accurate calculation, and therefore can be applied to the squat studies.

Parameter Identification of Ship Maneuvering Model Based on Support Vector Machines and Particle Swarm Optimization

Combined with the free-running model tests of KVLCC ship, the system identification (SI) based on support vector machines (SVM) is proposed for the prediction of ship maneuvering motion. The hydrodynamic derivatives in an Abkowitz model are determined by the Lagrangian factors and the support vectors in the SVM regression model. To obtain the optimized structural factors in SVM, particle swarm optimization (PSO) is incorporated into SVM. To diminish the drift of hydrodynamic derivatives after regression, a difference method is adopted to reconstruct the training samples before identification. The validity of the difference method is verified by correlation analysis. Based on the Abkowitz mathematical model, the simulation of ship maneuvering motion is conducted. Comparison between the predicted results and the test results demonstrates the validity of the proposed methods in this paper.

Simulation Analysis on Navigation Indexes of Wanzhou Yangtze River Highway Bridge after the Anti-Collision Device Construction by Ship Model Test

After the anti-collision facility construction of Wanzhou Yangtze River Highway Bridge, the conditions of navigation in bridge area are complex. In order to study the navigation conditions of the reach and layout optimization measures, ensuring the safety of the ship navigation test has been carried out on the ship model navigation in the bridge area. According to the requirements of the maximum safety limit of the ship model test, the paper puts forward the best route, the control method and the difficulty of navigation through the analysis of the test results, and finally gives the recommendations and suggestions.

Prediction of wave resistance by a Reynolds-averaged Navier–Stokes equation–based computational fluid dynamics approach

The prediction of wave resistance in naval architecture is an important aspect especially at high Froude numbers where a great percentage of total resistance of ships and submerged bodies is caused by waves. In addition, during hull form optimization, wave resistance characteristics of a ship must closely be observed. There are potential, viscous and experimental methods to determine the wave resistance of a ship. Reynolds-averaged Navier–Stokes equation–based methods usually follow the experimental method that determines the form factor first. However, it is proven in recent studies that the form factor changes with the Reynolds number. As the Reynolds number increases, this change in the form factor is being neglected. In this study, a Reynolds-averaged Navier–Stokes equation–based prediction of wave resistance is presented that overcomes this flaw. The methodology is validated with the benchmark problems of submerged and surface-piercing bodies to determine the effectiveness of the proposed method. The method is also validated by experiments carried out at the Ata Nutku Ship Model Testing Laboratory of Istanbul Technical University for a totally submerged ellipsoid and the benchmark KRISO Containership. Results reveal the robustness of the present methodology.

Experimental Study of Forces Exerted on Ships Due to the Vertical Walls of Navigation Channels

Ship maneuvering in restricted waters of harbor basins and navigation channels had been the main concern in recent years due to sudden increase of ship’s size. When the ship enters a navigation channel the lateral boundary of the channel exerts a transverse force and turning moment on the ship hull. These forces are so important in the analysis of safety of ship navigation in the channels. Ship model test in the towing tank is a reliable method to evaluate these forces. Therefore systematic model tests are held for modeling of the forces exerted on the tanker ship and dhow model traveling alongside a vertical wall. A database of the interaction forces is developed and the specific hydrodynamic effects related to the phenomena are discussed. The results can be used for simulation of ship maneuvering and assessment of safety limits for navigation of ships alongside the quay walls and breakwaters.

Research on Navigable Ship Model Test in Curved Waterway

The flow of bend reach is complicated, which is difficulty for intersection of ship,and is accident prone. According to the lower reaches of the Hanjiang River MaKou reach of ship model test results, the relationship between channel width and flow are summarized when ship navigation sail in bend reach, which indicated that at approximately the same speed, navigation width of sailing through the bend upward are much smaller than down. As velocity or flow angle increases, the ship track width is broader, and channel width is also broader. the ship control and peer safety management points are forwarded in the lower reaches of Hanjiang river bend, which can provide reference for similar engineering designand research of waterway.