Uncertainty analysis of ship model vertical center of gravity and transverse moment of inertia test

The usability of test results of ship model vertical center of gravity and transverse moment of inertia is generally depends on its uncertainty. Referring to the guidelines for uncertainty analysis in examination of liquid dynamic recommended by International Towing Tank Conference （ ITTC）, the results were analyzed, bias limits and precision limits were calculated and total uncertainty was estimated. The total uncertainty of six tests on ship model vertical center of gravity is is 0. 16% of the mean value, and the total uncertainty of six tests on ship model transverse moment of inertia is 5.66% of the mean value. The test results show that the total uncertainty of both the multiple tests and the single test is from the precision limits of ship model vertical center of gravity and transverse moment of inertia tests. Thus, the improved measurement system stability can enormously decrease the total uncertainty of multiple tests and the single test.

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.

Micro-bubble Drag Reduction on a High Speed Vessel Model

Ship hull form of the underwater area strongly influences the resistance of the ship. The major factor in ship resistance is skin friction resistance. Bulbous bows, polymer paint, water repellent paint （highly water-repellent wall）, air injection, and specific roughness have been used by researchers as an attempt to obtain the resistance reduction and operation efficiency of ships. Micro-bubble injection is a promising technique for lowering frictional resistance. The injected air bubbles are supposed to somehow modify the energy inside the turbulent boundary layer and thereby lower the skin friction. The purpose of this study was to identify the effect of injected micro bubbles on a navy fast patrol boat （FPB） 57 m type model with the following main dimensions： L=2 450 ram, B=400 mm, and T=190 mm. The influence of the location of micro bubble injection and bubble velocity was also investigated. The ship model was pulled by an electric motor whose speed could be varied and adjusted. The ship model resistance was precisely measured by a load cell transducer. Comparison of ship resistance with and without micro-bubble injection was shown on a graph as a function of the drag coefficient and Froude number. It was shown that micro bubble injection behind the mid-ship is the best location to achieve the most effective drag reduction, and the drag reduction caused by the micro-bubbles can reach 6%-9%.

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.

Effect of Ship Bow Overhang on Water Shipping for Ship Advancing in Regular Head Waves

This paper presents the results of an experimental investigation dealing with the effect of bow overhang extensions on the quantity of shipping water over the foredeck in case of ships advancing in regular head waves. To perform this investigation, a series of free-running tests was conducted in regular waves using an experimental model of a multipurpose cargo ship to quantify the amount of shipping water. The tests were performed on five bow overhang variants with several combinations of wavelength and ship speed conditions. It was observed that the quantity of shipping water was affected by some parameters such as wavelength, ship speed, and bow shape in terms of an overhang extension. The results show the significant influence of an overhang extension, which is associated with the bow flare shape, on the occurrence of water shipping. These results involve the combined incoming regular waves and model speed.

NUMERICAL SIMULATION OF WAVE RESISTANCE OF TRIMARANS BY NONLINEAR WAVE MAKING THEORY WITH SINKING AND TRIM BEING TAKEN INTO ACCOUNT

Up to now, there are no satisfactory numerical methods for simulating wave resistance of trimarans, mainly due to the difficulty related with the strong nonlinear features of the piece hull wave making and their interference. This article proposes a numerical method for quick and effective calculation of wave resistance of trimarans to be used in engineering applications. Based on Wyatt＇s work, the nonlinear free surface boundary condition, the time domain concept, and the full nonlinear wave making theory, using the Rankine source Green function, the 3-D surface panel method is expanded to solve the trimaran wave making problems, with high order nonlinear factors being taken into account, such as the influence of the sinking and trim, transom, and ship wave immersed hull surface. And the software is successfully developed to implement the method, which is validated. Several trimaran models, including a practical trimaran with a sonar dome and the transom, are used as numerical calculation samples, their wave making resistance is calculated both by the present method and some other methods such as linear （Dawson） methods. Moreover, sample model resistance tests were carried out to provide data for comparison, validation and analysis. Through the validation by model experiments, it is concluded that present method can well predict the wave making resistance, sinking and trim, and the accuracy of wave making resistance calculation is significantly improved by taking the trim and sinking into account, especially at high speeds.

Study of Resistance Performance of Vessels with Notches by Experimental and Computational Fluid Dynamics Calculation Methods

Owing to the special working characteristics and operation requirements,lots of working ships have notches in different sizes and shapes in their hulls.In order to study the resistance performance of the vessel with notches,a series of model resistance tests were performed in respect to the 4 500 m 3 /h cutter suction dredger,and the tests were simulated based on the computational fluid dynamics software FLUENT.Based on analysis to the experimental data and the computational fluid dynamics(CFD) calculation results,the change of the flow field and the resistance performance caused by the notches were studied,and the reliability of the software in simulation of viscous flow around the hull was proved.It provides the basis for the future study and the design optimization of this kind of working ships.

Experimental Investigation into the Effect of Roll Amplitude on Roll Damping

An in-house large eddy simulation(LES)code has been developed in the previous study.In order to validate the code for simulation of roll motion,effect of roll amplitude on forced roll damping is experimentally investigated in a circulating water channel at Shanghai Jiao Tong University(SJTU).KRISO very large crude carrier 2(KVLCC2)is taken as a target ship,and a model with a scale of 1:128.77 is manufactured.Tests are carried out for the ship model at shallow draft with frequencies around its natural roll frequency,where natural roll frequency is attained via free roll decay.Six forced roll tests with roll amplitudes ranging from 1?to 4?are performed experimentally,and three forced roll motions are simulated with the in-house LES code for middle section of the ship model.Discrepancies between the computed roll damping coefficients and the ones from forced roll tests are quite small.By means of particle image velocimetry(PIV),velocity fields in the vicinity of the ship model,and generation and evolution of vortices near the ship bilge are measured in detail.It is shown that roll amplitude has a significant effect on the vortex behavior,and therefore on the magnitude of roll damping coefficient.Further experimental and numerical investigation into roll motions with large amplitudes is planned.