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.

Test Study on Current Force on Mooring Ships

In respect of an offshore berthing pillar, the test study result of current force acting on mooring ships is described in this paper. Empirical and semi-empirical relationships of current force coefficient are given according to the angle between the flow direction and the ship's longitudinal axis, which are coincident with the result of theoretical analysis.

COSCO Shipping Acquisition as A Success Model for Greece-China Cooperation

On July 4th,2016,China COSCO Shipping Corporation Limited('COSCO SHIPPING'or'the Group')and the Hellenic Republic Asset Development Fund(HRADF)signed a letter in Beijing,confirming that the conditions defined in the previously signed Share Purchase Agreement(SPA)have been fulfilled.It marks a decisive achievement for COSCO SHIPPING’S

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.

Wash Waves Generated by High Speed Displacement Ships

It is difficult to compute far-field waves in a relative large area by using one wave generation model when a large calculation domain is needed because of large dimensions of the waterway and long distance of the required computing points. Variation of waterway bathymetry and nonlinearity in the far field cannot be included in a ship fixed process either. A coupled method combining a wave generation model and wave propagation model is then used in this paper to simulate the wash waves generated by the passing ship. A NURBS-based higher order panel method is adopted as the stationary wave generation model; a wave spectrum method and Boussinesq-type equation wave model are used as the wave propagation model for the constant water depth condition and variable water depth condition, respectively. The waves calculated by the NURBS-based higher order panel method in the near field are used as the input for the wave spectrum method and the Boussinesq-type equation wave model to obtain the far-field waves. With this approach it is possible to simulate the ship wash waves including the effects of water depth and waterway bathymetry. Parts of the calculated results are validated experimentally, and the agreement is demonstrated. The effects of ship wash waves on the moored ship are discussed by using a diffraction theory method. The results indicate that the prediction of the ship induced waves by coupling models is feasible.

Hybrid Energy Storage to Control and Optimize Electric Propulsion Systems

Today,ship development has concentrated on electrifying ships in commercial and military applications to improve efficiency,support highpower missile systems and reduce emissions.However,the electric propulsion of the shipboard system experiences torque fluctuation,thrust,and power due to the rotation of the propeller shaft and the motion of waves.In order tomeet these challenges,a new solution is needed.This paper explores hybrid energy management systems using the battery and ultracapacitor to control and optimize the electric propulsion system.The battery type and ultracapacitor are ZEBRA and MAXWELL,respectively.The 3-,4-and 5-blade propellers are considered to produce power and move rapidly.The loss factor has been reduced,and the sea states have been found through the Elephant Herding Optimization algorithm.The efficiency of the proposed system is greatly enhanced through torque,thrust and power.The model predictive controller control strategy is activated to reduce load torque and drive system Root Average Square(RMS)error.The implementations are conducted under the MATLAB platform.The values for torque,current,power,and error are measured and plotted.Finally,the performance of the proposed methodology is compared with other available algorithms such as BAT and Dragonfly(DF).The simulation results show that the results of the proposed method are superior to those of various techniques and algorithms such as BAT and Dragonfly.

Online interactive identification method based on ESO disturbance estimation for motion model of double propeller propulsion unmanned surface vehicle

In this paper, the online parameter identification problem of the mathematical model of an unmanned surface vehicle (USV) considering the characteristics of the actuator is studied. A data-driven mathematical model of motion is very meaningful to realize trajectory prediction and adaptive motion control of the USV. An interactive identification algorithm (ESO–MILS, extended state observer–multi-innovation least squares) based on ESO is proposed. The robustness of online identification is improved by expanding the state observer to estimate the current disturbance without making artificial assumptions. Specifically, the three-degree-of-freedom dynamic equation of the double propeller propulsion USV is constructed. A linear model for online identification is derived by parameterization. Based on the least square criterion function, it is proved that the interactive identification method with disturbance estimation can improve the identification accuracy from the perspective of mathematical expectation. The extended state observer is designed to estimate the unknown disturbance in the model. The online interactive update improves the disturbance immunity of the identification algorithm. Finally, the effectiveness of the interactive identification algorithm is verified by simulation experiment and real ship experiment.

Improved parameter identification algorithm for ship model based on nonlinear innovation decorated by sigmoid function

This paper investigates the problem of parameter identification for ship nonlinear Nomoto model with small test data,a nonlinear innovation-based identification algorithm is presented by embedding sigmoid function in the stochastic gradient algorithm.To demonstrate the validity of the algorithm,an identification test is carried out on the ship‘SWAN’with only 26 sets of test data.Furthermore,the identification effects of the least squares algorithm,original stochastic gradient algorithm and the improved stochastic gradient algorithm based on nonlinear innovation are compared.Generally,the stochastic gradient algorithm is not suitable for the condition of small test data.The simulation results indicate that the improved stochastic gradient algorithm with sigmoid function greatly increases its accuracy of parameter identification and has 14.2%up compared with the least squares algorithm.Then the effectiveness of the algorithm is verified by another identification test on the ship‘Galaxy’,the accuracy of parameter identification can reach more than 95%which can be used in ship motion simulation and controller design.The proposed algorithm has advantages of the small test data,fast speed and high accuracy of identification,which can be extended to other parameter identification systems with less sample data.

EXPERIMENTAL STUDY AND NUMERICAL CALCULATION OF HYDRODYNAMIC FORCES AND MOMENTS ACTING ON A HIGH-SPEED TRANSOMSTERN SHIP RUNNING OBLIQUE TO THE COURSE

On the basis of oblique towing tests and flow visualizations of ship models, the flow pattern around a high-speed transom-stern ship, its motion attitudes (sinkage and trim) and the characteristics of hydrodynamic forces are analysed. It is concluded that the variation of ship motion attitudes, caused by ship speed, has a great influence over the coefficients of hydrodynamic forces and moments acting on the oblique running ship. Ship attitudes related to different speed and drift angles are calculated by Hess-Smith method. By distributing complex singularities over the surface of a double model and by considering separated vortex sheets in the wake at the lee side of the model, pressures and velocities of the fluid around the model may be calculated directly by solving a three-dimensional body with lift problem. The transom stern stream-lines are extended to form a virtual length. In this way, the hydrodynamic lateral forces, yaw moments and pressure distribution are calculated. The results show good agreement with those measured from model tests.

The flow characteristics around bridge piers under the impact of a ship

The complicated flow structure around the pier threatens the safe navigation of ships.This paper studies the mechanism of the flow with a ship around the pier,passing or not passing and with consideration of the interval between the ship and the pier.The flow field model and the moving ship model are constructed by the six degrees of freedom(6DOF)solver combined with the virtual unit immersed boundary method and the level set method,both of which are based on the three-dimensional Navier-Stokes equations.The simulation results show that the ship significantly influences the flow around the pier,increasing the flow velocity by 50%to 140%.Away from the bridge pier,the cross-flow velocity decreases.The cross-flow velocity near the side of the pier also increases but in the opposite direction.The ship is affected by the negative yaw moment because of the reverse cross-flow between the pier and the ship.The size of the ship has an important impact on the extent of the affected flow areas but the velocity distribution is roughly in the same shape.The results show double impacts of ship and pier should be considered when determining the safe area of navigation.

Basic models of farfield ship waves in shallow water

Basic models of the farfield waves created by a monohull ship or a catamaran that travels at a constant speed in calm water of uniform finite depth are considered.A classical basic model is the 1-point ship model introduced by Kelvin in 1887 for deep water and extended to uniform finite water depth by Havelock in 1908.Another basic model is the 2-point ship model,which considers the two dominant waves created by the bow and the stern of a monohull ship or by the twin bows of a catamaran,and therefore accounts for main wave interference effects.These 2-point ship models contain information that cannot be found in the classical patterns for the 1-point ship model commonly used since Kelvin.In particular,whereas Havelock’s classical wave patterns for the 1-point model only depend on the Froude number based on the water depth,the farfield waves for the 2-point models of a monohull ship or a catamaran also depend on the Froude number associated with the length of the monohull ship or the spacing between the twin hulls of the catamaran.Moreover,the‘apparent wake angles’associated with the highest waves that result from constructive wave interferences can greatly differ from the cusp or asymptote angles of Havelock’s wave patterns.

Fractal Brownian motion model of ship radiated noise

On the basis of the fractal geometry, a nactional Brownian Motion (FBM) model for the noise radiated by ship was established, under which its fractal dimension has been obtained and the Fractal Characteristic Vector (FCV) was constructed in the fractional Brownian random field (FBRF). By using of them, a new technique of the characteristic analysis for target recognition in the underwater acoustics was presented. A comparative experiment for classification shows us that the FCV can be used as essential quantity by which some defects existing in the methods to do the characteristic extraction elsewhere can be remedied.

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.

ON THE RELATION BETWEEN CAVITATION INCEPTION AND FLOW PATTERN ON PROPELLER BLADES

Experimental results of model propeller are obvious different from that of prototype for the stage of cavitation inception, which is called scale effect. The differences in flow pattern between model and full-scale condition can be eliminated using tripping devices at leading edge of model propeller. In this paper, oil flow visualization on the model propeller with and without tripping devices at the leading edge was revealed. The cavitation inception was observed at different Reynolds numbers to examine the dependence of cavitation inception with flow pattern. Detection of cavitation erosion was made and compared the location erosions of model propeller and prototype to investigate cavitation phenomena on the model propeller. The calculations of pressure distribution and the behaviour of boundary layer on the propeller blade were done by theoretical method. For better understanding of cavitation inception, further study is necessary.

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.