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.

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.

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.

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.

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.

Hydrodynamic Performance of Air-Filled Wave Attenuator for Wave Control:Experimental Study

Numerous types of floating breakwaters have been proposed,tested and commercialized in the past decades.The majority of these breakwaters are made of solid bodies;hence,they are relatively bulky and are not readily to be rapidly installed at the targeted sites when immediate wave protection of the coastal and offshore facilities is needed.Furthermore,the application of these hard floating structures at the recreational beaches is rather unlikely due to potential deadly marine traffic collision.To overcome these problems,a flexible air-filled wave attenuator(AFWA)has been developed in the present study.This floating breakwater is made of flexible waterproof membrane materials.The main body consists of a rectangular air-filled prism and is ballasted by sandbags located around the floating module.The objective of this study is to evaluate the wave transmission,wave reflection,energy dissipation,motion responses and mooring forces of the AFWA under the random wave actions using physical modelling.The test model located in a 20 m long wave flume was subjected to a range of wave heights and periods.The wave profiles in the vicinity of the test model were measured using wave probes for determination of wave transmission,reflection and energy loss coefficients.The motion responses in terms of heave,surge and pitch,and wave forces acting on the mooring lines were measured using a motion tracking system and load cells,respectively.The experimental results reveal that the AFWA is effective in attenuating up to 95%in the incoming wave height and has low-wave-reflection properties,which is commendable for floating breakwaters.

Liquid crystal display and organic light-emitting diode display: present status and future perspectives

Recently,‘Liquid crystal display(LCD)vs.organic light-emitting diode(OLED)display:who wins?’has become a topic of heated debate.In this review,we perform a systematic and comparative study of these two flat panel display technologies.First,we review recent advances in LCDs and OLEDs,including material development,device configuration and system integration.Next we analyze and compare their performances by six key display metrics:response time,contrast ratio,color gamut,lifetime,power efficiency,and panel flexibility.In this section,we focus on two key parameters:motion picture response time(MPRT)and ambient contrast ratio(ACR),which dramatically affect image quality in practical application scenarios.MPRT determines the image blur of a moving picture,and ACR governs the perceived image contrast under ambient lighting conditions.It is intriguing that LCD can achieve comparable or even slightly better MPRT and ACR than OLED,although its response time and contrast ratio are generally perceived to be much inferior to those of OLED.Finally,three future trends are highlighted,including high dynamic range,virtual reality/augmented reality and smart displays with versatile functions.