Analysis of Wave Added Drag and Motion Response of Mid-high-speed Ship against Waves

In order to accurately predict the on-wave resistance and responses to hull motions of ships in actual sea conditions,the k-εmethod of the RNG model is adopted on the basis of the unsteady RANS method.The two-formula turbulence model deals with the viscous flow,the VOF method captures the free surface,the velocity boundary method makes waves,the artificial damping method is used to eliminate waves,and the nested grid technology is used to deal with the motion response of ships on waves.Combined with the 6-DOF motion formula,a three-dimensional numerical wave cell for regular waves is established.For one example,taking a KCS Container ship and fishing boat sailing at a mid-high-speed,the increase of wave resistance and motion response at different wavelengths are analyzed,and the simulation results are compared with the experimental value,the content of strip theory in potential flow theory and the panel method to prove the reliability of CFD method in predicting ship motion.

Calculation Methods of Added Resistance and Ship Motion Response Based on Potential Flow and Viscous Flow Theory

To improve the energy efficiency of ships and to predict ship motion response under actual sea conditions,the far-field theory,strip theory,and Fujii and Takahashi’s modified semi-empirical method are based and studied to calculate the wave-induced added resistance.Firstly,a new modified formula based on the Maruo method is presented to calculate the radiation added resistance for the ship with a complex surface.Meanwhile,some calculation details such as the Green function,the shape of the sections(shape below the still water level or shape below the wave level)in the strip theory,and so on are discussed.Finally,the CFD method is used to simulate the motions of the hull and the added resistance,and the results of the CFD method and those of other numerical methods are analyzed and compared with the experiment results.The modified method in the paper can predict the added resistance in waves for the complex-hull-surface ships well and quickly.

Experimental investigation of motion responses of tunnel element immerging by moored barge

In this paper, the barge effect on the motion responses of the ttmnel element immerging by the moored barge under waves is investigated experimentally. Both the motion responses of the tunnel element and the moored barge in the experiment are simultaneously acquired by the Untouched 6-D Measurement System. The results show that the sway motion responses of the tunnel element immerging by the moored barge are different from those without the barge. For the system of the tunnel element and the moored barge, the moored barge has two motion components in the sway direction. The high frequency motion of the moored barge has little effect on the high frequency motion of the tunnel element with moored barge. However, the low frequency motion of the moored barge has a significant effect on the sway motion of the tunnel element. The motion responses of the tunnel element and the barge in the heave and roll directions are mainly the high frequency motion.

URANS simulations of ship motion responses in long-crest irregular waves

In this paper, numerical prediction of ship motion responses in long-crest irregular waves by the URANS-VOF method is presented. A white noise spectrum is applied to generate the incoming waves to evaluate the motion responses. The procedure can replace a decade of simulations in regular wave with one single run to obtain a complete curve of linear motion response, considerably reducing computation time. A correction procedure is employed to adjust the wave generation signal based on the wave spectrum and achieves fairly better results in the wave tank. Three ship models with five wave conditions are introduced to validate the method. The computations in this paper are completed by using the solver naoe-FOAM-SJTU, a solver developed for ship and ocean engineering based on the open source code OpenFOAM. The computational motion responses by the irregular wave procedure are compared with the results by regular wave, experiments and strip theory. Transfer functions by irregular wave closely agree with the data obtained in the regular waves, showing negligible difference. The comparison between computational results and experiments also show good agreements. The results better predicted by CFD method than strip theories indicate that this method can compensate for the inaccuracy of the strip theories. The results confirm that the irregular wave procedure is a promising method for the accurate prediction of motion responses with less accuracy loss and higher efficiency compared with the regular wave procedure.

Motion and Dynamic Responses of A Semisubmersible in Freak Waves

The present research aims at clarifying the effects of freak wave on the motion and dynamic responses of a semisubmersible. To reveal the effects of mooring stiffness, two mooring systems were employed in the model tests and time-domain simulations. The 6-DOF motion responses and mooring tensions have been measured and the 3- DOF motions of fairleads were calculated as well. From the time series, trajectories and statistics information, the interactions between the freak wave and the semisubmersible have been demonstrated and the effects of mooring stiffness have been identified. The shortage of numerical simulations based on 3D potential flow theory is presented. Results show that the freak wave is likely to cause large horizontal motions for soft mooring system and to result in extremely large mooring tensions for tight mooring system. Therefore, the freak wave is a real threat for the marine structure, which needs to be carefully considered at design stage.

透空结构与半潜式风机集成系统耦合运动响应特性分析

A novel semi-submersible platform is proposed for 5 MW wind turbines.This concept focuses on an integrated system formed by combining porous shells with a semi-submersible platform.A coupled aerodynamic–hydrodynamic–mooring analysis of the new system is performed.The motion responses of the novel platform system and the traditional platform are compared.The differences in hydrodynamic performance between the two platforms are also evaluated.The influence of the geometric parameters(porosity,diameter,and wall thickness)of porous shells on the motion response behavior of the new system is studied.Overall,the new semi-submersible platform exhibits superior stability in terms of pitch and heave degrees of freedom,demonstrating minimal effects on the motion response in the surge degree of freedom.

Numerical Simulation of Dynamic Response of A Net Cage for Flatfish in Waves

A numerical model of flatfish cage is built based on the lumped mass method and the principle of rigid body kinematics. To validate the numerical model, a series of physical model tests are conducted in the wave flume. The numerical results correspond well with the data sets from physical model test. The effect of weight of bottom frame, height of fish net and net shape on motion responses of fish cage and tension force on mooring lines is then analyzed. The results indicate that the vertical displacements of float collar and bottom frame decrease with the increase in the weight of bottom frame; the maximum tension force on mooring lines increases with the increasing weight of bottom frame. The inclination angles of float collar and bottom frame decrease with the increasing net height; the maximum tension force increases obviously with the increase of net height.

Investigation of Motion of Two Hinged Bodies Moored by Mooring Lines in Waves

In this paper, the motions are studied of a multi-body which is composed of two plates hinged together and moored by eight mooring lines in regular waves. The experimental results are compared with computational results. The linear potential theory and the perturbation method are combined to study this complicated system. The former is used to calculate the wave forces acting on the plates and the motion responses of them, while the latter is used to describe the dynamic character of the eight mooring lines coupled with the two hinged plates. Some response results of each plate are presented and comparisons between calculated results and experimental data are given. All the calculations are confined to regular beam waves.

Semi-submersible Offshore Coupled Motion in Irregular Waves

In order to predict the hydrodynamic performance of semi-submersible offshore platform accurately,based on CFD theory,continuous equation and N-S equation as the control equation,RNG type k-εmodel as turbulence model,using the finite difference method to discretize the control equation,using the Semi-Implicit Method for Pressure Linked Equation(SIMPLE)algorithm to solve the control equation,using the VOF method to capture the free surface.The numerical wave tank of irregular wave is established,and the wave force and motion response of the semi-submersible platform under irregular wave are studied.Based on the Jonswap spectrum density function,for a certain area of two irregular waves(South China sea,a-ten-year return period,a-hundred-year return period)sea condition,five wave direction Angle(0°,30°,45°,60°,90°),a total of 10 kinds of conditions of the motion response of semi-submersible platform are simulated,through analysis and comparison of simulation results,the influence law of wave angle,wave period and wave height on platform motion is obtained.Compared with the experimental values,the results of heave and pitch are close to the experimental data under the sea condition of 2,0 degree wave angles.The research results in this paper can provide reference for the design and motion response prediction of practical semi-submersible offshore platforms.

The effects of torsional ground motion on thin cylindric shell structures

The effects of torsional component of earthquake ground motion on thin cylindric shell structures were investigated qualitatively and quantitatively.The results show that the contributions of torsional component to structural response are related to the height,the radius-to-height ratio,and the stiffness of the structure.The structural response caused by torsional component can not be neglected for the containment structure of nuclear power plant and the industrial oil tank.

Analysis of structural fuzzy random seismic response

The earthquake loads specified for the aseismic structure design depend mainly on the predicted seismic intensity and the site soil classification.Earthquake excitation not only has evident randomness but also has strong fuzziness owing to the imprecision in the definition and evaluation norms of seismic intensity and site soil classification.A realistic analysis and design of structural systems subjected to such earthquake excitations must account for the uncertainty arising from both randomness and fuzziness simultaneously in a consistent and rational manner.In this paper,the models of stationary and nonstationary filtered white noise fuzzy stochastic processes of the earthquake ground motion are set up.And then the analysis methods for fuzzy random seismic response of single degree of freedom and multi degree of freedom systems are put forward by the theory of fuzzy stochastic dynamical systems(Zhang,1991;Zhang and Wang,1993).

Hydrodynamic Characteristics of Three-Bucket Jacket Foundation for Offshore Wind Turbines During the Lowering Process

The three-bucket jacket foundation is a new type of foundation for offshore wind turbine that has the advantages of fast construction speed and suitability for deep water. The study of the hoisting and launching process is of great significance to ensure construction safety in actual projects. In this paper, a new launching technology is proposed that is based on the foundation of the three-bucket jacket for offshore wind turbine. A complete time domain simulation of the launching process of three-bucket jacket foundation is carried out by a theoretical analysis combined with hydrodynamic software Moses. At the same time, the effects of different initial air storage and sea conditions on the motion response of the structure and the hoisting cable tension are studied. The results show that the motion response of the structure is the highest when it is lowered to 1.5 times the bucket height. The natural period of each degree of freedom of the structure increases with the increase of the lowering depth. The structural motion response and the hoisting cable tension vary greatly in the early phases of Stages Ⅰ and Ⅲ, smaller in Stage Ⅱ, and gradually stabilize in the middle and late phases of Stage Ⅲ.

Time-domain hydrodynamic analysis of pontoon-plate floating breakwater

The hydrodynamic behaviors of a floating breakwater consisting of a rectangular pontoon and horizontal plates are studied theoretically. The fluid motion is idealized as two-dimensional linear potential flow. The motions of the floating breakwater are assumed to be two-dimensional in sway, heave, and roll. The solution to the fluid motion is derived by transforming the governing differential equation into the integral equation on the boundary in time domain with the Green＇s function method. The motion equations of the floating breakwater are established and solved with the fourth-order Runge-Kutta method to obtain the displacement and velocity of the breakwater. The mooring forces are computed with the static method. The computational results of the wave transmission coefficient, the motion responses, and the mooring forces of the pontoon-plate floating breakwater are given. It is indicated that the relative width of the pontoon is an important factor influencing the wave transmission coefficient of the floating breakwater. The transmission coefficient decreases obviously as the relative width of the pontoon increases. The horizontal plates help to reduce the wave transmission over the floating breakwater. The motion responses and the mooring forces of the pontoon-plate floating breakwater are less than those of the pontoon floating breakwater. The mooring force at the offshore side is larger than that at the onshore side.

Wave Influence on Underwater Launch and Recovery System

In this paper, the underwater vehicle, sling and the mother ship are considered as a single degree of freedom system connected by a spring. Through the analysis of this system, a physical model is established, which describes the motion of the vehicle caused by the ship motion and wave motion. Furthermore, a mathematical model based on this physical model is obtained, and a numerical solution program is made. As an example, a practical launch and recovery system fbr an underwater robot is calculated by use of the program, and the motion track of the robot is obtained.

Study on Wave Added Resistance of a Deep-V Hybrid Monohull Based on Panel Method

In this paper, a panel method based on three dimensional potential flow theory is used to study the problem of wave added resistance. The time-domain motion response of Wigely III ship in head waves is calculated by AQWA, and then the wave added resistance of ship is obtained by near-field pressure integration method. By comparing the calculated results with the experimental data in literature, it is shown that the variation trend and peak value are in good agreement, and the accuracy and efficiency meet the research requirements. Based on the above mentioned method, the wave added resistance of a deep-V hybrid monohull in head waves is studied. The motions and wave added resistances of the deep-V hybrid monohull and the deep-V original ship advancing in head waves with various forward speed and wave frequencies are calculated and analyzed. The results show that the longitudinal motion response of the deep-V hybrid monohull is effectively suppressed and the wave added resistance is obviously reduced, the new type of ship has good engineering application prospects. The present method provides an approach of satisfactory accuracy and efficiency to predict wave added resistance of ships voyaging in waves.

规则波下载人潜水器-母船布放回收耦合运动试验研究

The launching and recovery process of a human-occupied vehicle(HOV)faces more complex wave effects than other types of submersible operations.However,due to the nonlinearity between the HOV and its mother ship,difficulties occur in theoretically simulating their coupled motion and hydrodynamics.The coupled motion responses and the load under different regular wave conditions are investigated experimentally in this study.The optimized design of the experimental scheme simulated the launching and recovery process of the mother ship and HOV in regular waves.The attitude sensor performed synchronous real-time measurement of the coupled motion between the mother ship and HOV as well as obtained the load data on the coupled motion under different cable lengths.The results show that models in heading waves mainly lead to the vertical motion of the hoisting point.In beam waves,the transverse and vertical motions of the hoisting point occur in a certain frequency of waves.Under the heading and beam wave conditions,the longer the hoisting cable is,the greater the movement amplitude of the submersible is.Moreover,compared with the condition of the beam waves,the hoisting submersible has less influence on the mother ship under the condition of the heading waves.The findings provide theoretical support for the design optimization of the launching and recovery operation.

Analysis of the Dynamic System of Wave Glider with a Towed Body

Mobile observation platforms are widely used in oceanographic and marine resource exploration and other applications. Wave Glider is a mobile platform that can transform wave energy into locomotion power and overcome the bottleneck of low energy supply. Wave Glider has recently been applied to tow underwater sensors fulfilling observation tasks. In this paper, the dynamic system of Wave Glider with a towed body is studied by applying multibody mechanics, and the relevant motion conditions of the system are investigated. Dynamic models of Wave Glider with a towed body and tether are first developed individually and then integrated into a whole model. The numerical method is used to obtain the dynamic responses and assess performance of the towed body pulled by the submerged glider of Wave Glider. The effects of sea state, mass of the towed body, and length of the towed cable are investigated on the basis of simulation results. This work can be used for the design and analysis of Wave Glider-towed body systems.

A Review of Research Status and Scientific Problems of Floating Offshore Wind Turbines

With the continuous utilization of offshore wind resources,the installation depth and capacity of offshore wind turbines are increasing.In order to meet construction requirements of renewable energy,offshore wind farms are bound to develop further and deeper into the sea.As a result,a novel kind of power generation equipment,Floating Offshore Wind Turbines(FOWT),emerges as the times require.Consequently,this paper provides an objective comment on some key scientific difficulties.Firstly,The statistics and forecast of the market demand and installed capacity of offshore wind energy show a steady growth.After that,the advantages of constructing FOWT and most floating projects in various countries are summarized.And then,the reconstruction design of blades is reviewed under“Reynolds number”and“Froude number”similarity criterion,which is a prerequisite for achieving specific aerodynamic performance.So far,this paper focuses on aerodynamic researches,including aerodynamic forces and flow fields.On this basis,pitch angle control strategies are proposed to reduce aerodynamic forces on the premise of ensuring power generations.Finally,some other joint science problems to be solved are listed.Whether theoretical analysis,numerical simulations,ocean engineering basin tests,wind tunnel experiments or prototype sea measurements,FOWT is expected to break through various obstacles and finally achieve efficient and stable commercial operations.

Hydroelasticity analysis of a vessel-shaped fish cage under incident,diffraction and radiation wave fields

Vessel-shaped fish cages are promising large aquaculture structures developed in recent years,with an overall length of nearly 400 m.In this paper,a coupled hydroelasticity model of a vessel-shaped fish cage is used to calculate the motion and structural response in the time domain.First,the floating body of the cage is discretized into a multimodule system to calculate the frequency-domain hydrodynamic loads.Then,the multimodule system is connected by equivalent elastic beams to consider the hydroelastic be-havior in the time domain.The hydrodynamic loads of the multimodule system are transformed from the frequency-domain loads.Moreover,based on the velocity field transfer functions and the motion of the multimodule system,coupling wave fields considering incident,diffraction and radiation waves are built and used to calculate the loads on the net and steel frame.By iterating the motion response of the multi-module system and the hydrodynamic loads on the net and steel frame in the time domain,the balanced hydroelasticity response of the whole cage is finally obtained.The results show that the hydroelasticity effects have a significant influence on the vertical displacement and cross-sectional load effects of the vessel-shaped fish cage.

The influence of perforated plates on wave transmission and hydrodynamic performance of pontoon floating breakwater

In this study, a perforated pontoon floating breakwater（FB） consisting of an impermeable plate and a perforated plate was designed to untangle the effect of a perforated plate on wave transmission and hydrodynamic performance of floating breakwater. A series of 2-D physical model experiments were conducted to measure the wave transmission coefficient, tension acting on the mooring line, and motion response of FB under a regular wave. The experimental results of the motion responses and mooring lines indicated that the new perforated plate was evidently effective. Furthermore, the study also discussed and analyzed the influence of the perforated plate on transmission coefficients. The experimental results showed that the new perforated plate did not lead to obvious improvement in the transmission performance