In this paper, a new type of floating marine energy generating turbine is studied. Based on the three-dimensional potential flow theory, the motion characteristics of the equipment under the combination of wind, wave and current are analyzed. Based on the finite element method, the strength analysis on the floating structure of the generator under extreme environmental load is developed and the stress concentration area of the generator is given. Finally, the procedures for safety assessment have been proposed to meet the requirement of engineering practice and could be used as a fast evaluation method for engineering. INTRODUCTION The depletion of traditional energy sources (fossil fuels) and the degradation of the environment as a result of fossil fuels consumption urge the global community to seek alternative energy sources, especially renewable sources. Tidal current as an energy source has the comparative advantages of being renewable and predictable, having low visual impact and low environmental impact, and incurring low maintenance cost. The estimated tidal energy potential worldwide reaches around 600 TWh/yr (REN21, 2019) and it is being largely underused. Also, following the International Renewable Energy Agency report (IRENA, 2018), the technically harvestable tidal energy resource from those areas close to the coast, is estimated at 1 terawatt (TW), tidal current deployments have increased to over 17MW, due largely to new projects in 2018. Marine energy generating turbines are deployed for ocean electrical industrialization in worldwide. Nowadays, the manufacture investment is growing fast and performance optimization technology is required urgently. Ma et al (2017) proposed that the hydrodynamic and strength performance of the turbine devices in harsh marine environment are very important to limit the extensive application range. In the marine environment, the marine energy generating turbines often suffer from complex environmental loads, especially wave and current loads. Design, development and optimization of tidal turbines require accurate and time efficient mathematical models. Based on the computational tools available, different models with different computational costs were developed and applied for optimization and analysis purposes. A wide variety of numerical models can be used to simulate hydrodynamic and strength performance. Hess and Smith (1960) used the Green function of aerodynamic theory to calculate the ship's wave resistant force. The finite-difference time-domain method is used to analyze dynamic response of mooring cables and the interaction between the cable and the seabed, but lift effect of the seabed on the anchor is not covered (Homas and Hearn 2008). The time-domain hydrodynamic analysis based on the N-S equation (Perez-Collazo 2015) could give the most intuitive and detailed analytical results, although the calculation process is too long and the processing of the results is much more complexly. Through the calculation of high-performance computers, the three-dimensional hydrodynamic theory has made significant progress after applying the function. For the numerical simulation of mooring systems, Wichers JEW (2010) studied the load on the mooring tanker and established a mathematical model of the mooring tanker's motion response. The results show that the lowfrequency oscillation amplitude of the mooring tanker in motion is greatly affected by the slow drift force, and the slow drift vibration force has a greater impact on the movement of the tanker mooring system. Dean (2014) used the slender rod theory to establish a numerical simulation model of the interaction between the main body of the Wave-current coupling power generation device and the mooring system. In the time domain analysis, the motion response of the platform and the anchor chain was coupled and analyzed.

A trapezoidal large floating structure discussed in this paper is one of modules of a hexagon accommodation platform which provides life accommodation, ship docking and marine supply in deep ocean. The trapezoidal large floating structure is a typical flat structure that the ratio of ship width and depth is very large so that its 3D hydroelastic response involving bending and torsion is significant. A model test for the trapezoidal large floating structure was carried out in this paper to study its load and response characteristic. Firstly, the test model of structure was designed which was made up of foam layer and plate layer, foam layer provided buoyancy and displacement while plate layer gave structural strength and deformation. Then a number of sensors measuring displacement, strain, and pressure were arranged on the model. Thirdly, a number of wave cases were determined to be generated in a tank. Lastly, the model test was performed in tank waves, a lot of time-domain research results were obtained, then frequency-domain results were analyzed. Hydroelastic mechanism of the trapezoidal large floating structure was analyzed based on these experimental results. INTRODUCTION With the rapid development of the marine economy of China, there is an urgent need for the protection support of very large floating structure (VLFS). The scale of the very large floating structure is huge and it can be stitched together by multiple modules, serving as an integrated support platform for marine development, which provides life accommodation, ship docking and marine supply in deep ocean. The trapezoidal large floating structure discussed in this paper is one of the modules of a hexagon accommodation platform, which is different from the traditional ocean floating structure, and is a typical flat structure, which is relatively rigid and the elastic deformation of the structure dominates. Therefore, the traditional hydrodynamic theory based on the hypothesis of rigid body motion is no longer applicable to very large floating structure, and the theory of hydroelasticity should be considered to evaluate structural response in waves.

The Marginal Ice Zone (MIZ) is the transition region between open waters and the sea ice, which has an important effect on ships and offshore structures. A numerical study on the hydroelastic response of ice floes under the action of regular waves in MIZ is presented in this paper. A boundary-element method based on three-dimensional linear potential flow theory is used to predict fluid field. The finite element method is used to numerically model a large ice floe within the framework of the Mindlin plate assumption. A hydroelastic model is formulated using modal superposition method to solve the fluidstructure coupling equations. The hydroelastic response of ice floes under regular waves is studied. The influences of the wavelength and the size of an ice floe on the response are studied and discussed. The results show that the wavelength has a great influence on the displacement of ice floes and the maximum stress in the ice depends on floe size. The ultimate wave height of ice fracture against the ratio of floe length to wavelength is given. The limit wave height of the ice fracture decreases sharply with the length ratio when the floe length is small, and then keeps unchanged for larger floes. INTRODUCTION Studying on interactions between sea ice and waves could help understand global warming, which attracted the attention of the scientific research in recent decades. The research methods on the interactions between ice floes and waves mainly include: experimental method, simplified analytical method and numerical simulation method. Experimentally, Wang et al. (2000) used composite material consisting of polypropylene powder, plastic particles and white cement, to simulate physical characteristics of ice sheets and studied the fracture under the action of waves in a flume, and the relationships between fracture of ice sheets and the ratio of sea floe length to wavelength were obtained. Frankenstein et al. (2001) used 6-DOF instruments to measure the motion of ice floes and inverted the changes in amplitude by the heave amplitude of ice floes. Sakai and Hanai (2002) studied the influence of the sizes and elastic modulus of the ice plate on the incident wavelength. They used a polyethylene material to simulate the ice plate and the results showed that the ice plate had no effect on the speed of wave propagation, when the length of the ice plate was very small. Mcgovern and Bai (2014) studied the relationship between wave characteristics and ice floe motion response by substituting paraffin wax for ice floes. The results showed that wavelength has a great effect on ice floe movement. Dolatshah and Bennets (2018) studied the hydroelastic interaction between regular waves and ice floes under different incident wave periods and steepnesses, and the results showed that the ice sheet would break only if the period and steepness were high enough.

In lab-scale model tests of modular floating structures, motion measurement is sensitive to mechanical influence of contact-based measurement systems. To investigate alternatives, model tests of a modular flexible floating structure interacting with regular waves was carried out in the towing tank of Delft University of Technology. Non-contact 3D digital image correlation (3D-DIC) technique was employed to evaluate the structural displacement. Stereovision based system Optotrak Certus of Northern Digital Inc., which relies on cable connection to the model, was used as a reference system to validate the DIC results. Model motions were analyzed and compared between the two systems. Comparisons show that DIC results agree well with stereovision results, indicating that the DIC system is an accurate motion measurement of floating structures in waves. INTRODUCTION Very Large Floating Structure (VLFS) is regarded as an alternative to land reclamation for ocean space utilization with various applications, such as floating bridges, floating airports, floating fuel storage facilities, and floating cities (Wang and Tay 2011). A typical feature of VLFS is a large length-to-thickness ratio because its horizontal dimensions are usually several hundred to thousand meters, while the vertical one is only a few meters. Such structure has apparent flexible body responses rather than rigid body motions under wave actions. Therefore, analyzing the hydroelastic response of wave-VLFS interaction is of great importance. The hydroelastic response of the VLFS is often studied to determine the deflection of the VLFS under the action of wave forces and also measure the influence of the floating structure on water waves. Extensive research on this problem has been carried out both theoretically and experimentally. Several methods for calculating hydroelastic response have been proposed, and those can be roughly categorized into mode superposition method (Newman 1994; Wu et al. 1995; Kashiwagi 1998a; Abul-Azm and Gesraha 2000) and direct coupling method (Hermans 2010; Kashiwagi 1998b; Namba and Ohkusu 1999; Ohkusu and Namba 2004; Taylor 2007). The mode superposition method consists of separating hydrodynamic analysis from dynamic response analysis of the structure and structural deflection is represented generally by superposition of finite eigenmodes. The direct coupling method solves the coupled equations of structure deflection and wave pressure/velocity potential directly without expanding structure motion into eigenmodes. Other numerical solutions e.g. BE-FE combination method (Utsunomiya et al. 1995; Liu and Shigeki 2002), and a method that divides continuous VLFS into rigid modules connected with elastic beam elements (Lu et al. 2019) were also developed. However, most predictions are expressed within the scope of potential theory.

To research the phenomenon of heading instability of FPSO, the model test in a scale ratio 1:80 was carried out. It was observed that heading of the model drifted significantly in regular waves. For studying the motion in transitional and stabilized zones, simulation in SESAM is established to compare motion RAO of SESAM and test. In order to find the theoretical explanation, the uncoupled nonlinear equation of yaw motion is established. Phase plane analysis are conducted to obtain the stable equilibrium points under different roll damping. INTRODUCTION Energy demand has become a primary problem in many countries. Oil resources currently satisfy 38% of energy demand worldwide. However, oil production is not enough on land. To meet the growing demand for oil, exploration and production must expand further offshore into the deep ocean. Floating Production Storage and Offloading (FPSO) vessels today have become the primary method for many offshore oil and gas production regions around the world. An FPSO is a floating system that receives oil from offshore oilfield and stores the processed oil before offloading to a shuttle tanker. Most FPSOs are kept in station by internal turret mooring system. The mooring lines are connected to turret by which the hull is able to rotate freely. In presence to the environment, a turret moored FPSO is designed to weathervane about the mooring system, thus the environment loads on the hull and mooring system are reduced to a minimum. The waves are in rough divided into three groups, wind waves, swell waves and coastal waves. Wind waves are directly created by the wind and show extreme irregularity. Swell waves can be regarded as long regular waves that propagate from other generating areas. Anecdotal evidence from offshore practice indicates that an FPSO may lose control with respect to oncoming waves, particularly when the environment is dominated by swell wave conditions. A persistent change in the mean heading angle may be defined as heading instability. Many researches have been done up to now. Bernitsas and Papoulias (1986) conducted the study on the yaw and stability of single point mooring. Yaw of turret moored vessels in regular waves was investigated by Liu et al (1999) and large yaw motion was explained by the balancing of drift forces and moments. Donoghue and Linfoot (1992) performed the model test in irregular waves and reported the effect of turret position and mooring load characteristics. Yadav et al. (2007) conducted the parametric study of large yaw motion in regular waves by doing time domain analysis. Munipalli and Thiagarajan (2007) showed the effect of wave steepness on the yaw motion and mention the relation of sway and yaw acceleration for large yaw motion case. Zangeneh and Thiagarajan (2015) researched heading instability theoretically and found the mean drift force coefficients are key factors for inducing heading instability.

Boundary element method (BEM) with fully nonlinear boundary conditions is developed to simulate the interaction between an incident wave and a freely floating cylinder. The elastic mesh technique (EMT) is adopted to optimize the mesh on free surface in time domain. Auxiliary functions are introduced to decouple the mutual dependence between the motion of cylinder and the fluid force. The fourth-order Runge-Kutta method for time marching is used. The present method is verified through convergence study and comparison with other method. The motion responses, the hydrodynamic forces as well as the free surface elevation are studied and the resonance phenomenon is analyzed. INTRODUCTION In the field of ocean engineering, linear or weakly nonlinear potential flow method has been widely developed to study wave-body interaction problems. However in extreme sea condition or larger waves, fully nonlinear method can be used to predict more accurate results. For fully nonlinear time-domain simulation, the Mixed Eulerian-Lagrangian (MEL) method for tracking the free surface was widely used, which was proposed by Longuet-Higgins and Cokelet (1976). They tracked the material-nodes on free surface with kinematic condition in Lagrangian form and the potential was updated in Eulerian form, through which the motion of a two-dimensional floating body was calculated. Since then, MEL was referenced by many researchers to investigate the interaction between waves and bodies. There are mainly two kinds of wave-body interaction problems, of which the former can be summarized as the numerical wave tank, and one side of the tank moves to generate waves. In such cases, side wall effects on the motion responses can not be ignorable (Chen, 1994). The other kind of typical studies on wave-body interaction was proposed by Ferrant et al. (1997, 1998), in which an efficient open water model was established by separating the unknown disturbed wave from the known incident wave. The incident wave can be chosen as any theoretical wave while the disturbed wave can be obtained by solving a definite solution model. Many researchers preferred the open water method for its efficiency and easier application. Zhou et al. (2013) studied the diffraction, the forced vibration and the ringing phenomenon of a floating cylinder by fully nonlinear method in open water, and revealed the nonlinear effects of the hydrodynamic force. Bai et al. (2014) performed a fully nonlinear simulation of the motion responses of a moored cylindrical structure submerged beneath the water. Feng and Bai (2015) simulated the flow behaviors of the parallel double boxes in waves by a fully nonlinear numerical method. Harman et al. (2016) studied the effective loads of a submerged crane ship by fully nonlinear theory. Feng and Bai (2017) investigated the hydrodynamic performance of a multi-body system.

The leading-edge tubercles, which were inspired by the morphology of the Humpback whale flipper, are known to improve the post-stall performance and produce a smoother stall characteristic. In this paper, the flow characteristic of three finite-span wings with leading-edge wavelengths of 0.50c, 0.25c and 0 (i.e. baseline model) were investigated by detached eddy simulation at Reynold number Re = 4.5×10 5 with an angle of attack of 21 degree. The numerical simulation is able to predict the opposite effects of different wavelengths on the lift performance. The force coefficient at different spanwise locations were compared and it is found that the most significant difference in the lift of the three models is located near the end-wall of the finite-span wing. The flow field was analyzed in detail and the results show that the interaction between the corner separation and the streamwise vortex induced by leading-edge tubercles is the main reason for variation in hydrodynamic characteristics of the finite-span wings with different wavelengths. INTRODUCTION The Humpback whale shows high manoeuvrability while hunting. Many researchers attribute this capability to the leading-edge tubercles on its flippers (Fish et al., 1995; Miklosovic et al., 2004; Miklosovic et al., 2007). The leading-edge tubercles are able to improve the post-stall performance of airfoils and produce smoother stall characteristics (Johari et al., 2007; Pedro et al., 2008), the flow mechanism for the performance improvements is believed to be the streamwise vortex which can improve the momentum exchange in the boundary layer. Many numerical and experimental investigations have been conducted to study the influence of Reynolds number and other configurations and to gain a deeper understanding of the underlying flow mechanism (Weber et al., 2010; Skillen et al., 2014; Kim et al., 2018; Hansen et al., 2016). Many researchers reported that the full-span wings with leading-edge tubercles will reduce the maximum lift coefficient compared to the baseline wing (Miklosovic et al., 2007; Johari et al., 2007; Stein et al., 2005; Hansen et al., 2012). However, in some circumstances, the finitespan wing with leading-edge tubercles can improve the maximum lift coefficient and the stall characteristics at the same time. As a result, investigating the parameters of leading-edge tubercles which have a great influence on the overall performance of a finite-span wing and clarify the related flow mechanism is beneficial for the potential application of this technique in the design of modern pumps and propulsions.

The rogue wave is one sort of raging and unforeseen surface wave with enormous energy and exceptional wave height, which might have a devastating impact on the floating structure. In this paper, a new theory of rogue wave based on second-order wave theory is integrated with the wave library of waves2Foam. A series of numerical simulations of wavestructure interaction of a moored floating breakwater under the rogue wave has proceeded. Duration curves of dynamic response, wave loads, and images of flow fields are obtained through numerical simulations. The effect of focused point, wavelength, motion under the different layout of mooring systems are gained. The results reveal that the motion of floating breakwater under the rogue wave exhibits different characteristics compared with those under the regular and irregular waves. INTRODUCTION With the booming development of international trade, the large-scale vessel, such as ultra-large container ships, has become increasingly prevailing in freight transport. Therefore, the requirement for the depth of ports is also much higher compared with the past. After the full development of natural harbour, the construction of ports has started to concentrate on open sea areas directly exposed to severe environment. As a critical component of the offshore structure in port, the breakwater is capable of mitigating the energy of waves and alleviate the accumulation of sediment. Due to its burdensome foundation, the traditional breakwater is not suitable for deepwater ports. Hence, people start to seek new forms of the breakwater. The floating breakwater is a dominant structural form in deep water owing to its handiness and low cost. When operating in deep water, the floating breakwaters may suffer from severe environmental conditions such as rogue waves. Usually, the rogue wave always has a relatively large amplitude and consist of enormous energy, which may provoke a devastating impact on floating structures. Hence, the investigation of hydrodynamic loads on floating breakwater is of considerable significance to improve its design. Unfortunately, the interaction between rogue waves and the floating breakwaters is such a sophisticated phenomenon which is difficult to be illuminated by an analytical method, while the experimental investigation is costly. In this case, numerical simulation is a reasonable choice for probing into this problem.

In the process of long-distance ocean transportation, the wave and the tank sloshing have a great influence on the ship motion. The sloshing of the liquid in the tank will produce a large moment to the hull, which may cause the ship to overturn; and the strong impact force of the sloshing on the bulkhead may also cause damage to the hull structure. In this paper, sloshing coupled ship motions are solved numerically in a time domain approach, such as numerical method based on Reynolds-averaged Navier–Stokes (RANS) equation. Through comparison with the experimental data of S175 ship model loaded with tank at zero speed, present numerical methods are validated. Under the head sea conditions with forward speed, the movement effects of ship with or without tank are compared and analyzed. Furthermore, the influence of tank sloshing under different working conditions and the wave contour around ship are systematically studied. INTRODUCTION With the development technology of liquefied natural gas (LNG) ships and liquefied petroleum gas (LPG) ships, the impact of tank sloshing on ship movements has received increasing attention. During the navigation of such liquid-laden ships in the ocean, multi-degree-of-freedom motions will occur under the action of wind and waves, and the liquid contained in ship tanks will also cause sloshing due to the corresponding movement of the hull. With such sloshing phenomenon, when the frequency of the external incoming wave and the natural frequency of the tank are relatively close, the fluid attack effect caused by its severe resonance phenomenon acts on the bulkhead, which not only has a great possibility of causing serious damage to the bulkhead structure but also increase the amplitude of the motion of the hull. Serious conditions may cause the ship to capsize, which will have a more serious impact on the ship's navigation environment and safety factors.

The pressure distribution of ship hull can be influenced by a interceptor, which is installed at the stern of ship, to induce a moment for reduing the pitch motion of the ship. However, the phase and amplitude of the moment provided by the interceptor is difficult to determine. This paper aims to design an automatically controlled interceptor to reduce the pitch motion of the ship in wave. Control strategy based on energy reduction is proposed, it uses the pitch angular velocity as feedback to control the interceptor, It increases the damping of pitch motion, thereby reducing the pitch motion of the ship. The model tests in regular head waves are carried out in towing tank, Experimental results indicate that it is effective to use the pitch angular velocity as feedback to control. The amplitude of pitch in waves can be reduced by 20%. INTRODUCTION The pitch motion of the ship in the wave will reduce the comfort and safety of the ship. Improving the seakeeping characteristics through optimization of hull form parameters meant that one had to compromise on the calm water resistance performance. For the vertical motions reduction of in head waves, control systems such as trim flaps, T-foils and interceptor were adopted. One of the simplest and effective way to control the pitch motion is to use a controllable interceptors. The interceptor at the stern can change the pressure distribution at the bottom of the ship, forming a moment and changing the longitudinal attitude of the ship. If the interceptor is properly controlled, it can reduce the pitch motion of the ship. However, the phase and amplitude of the moment provided by the interceptor is difficult to determine. The interceptor produced by Humphree is used in high-speed planing craft, It can adjust the attitude of the planing boat. Model experiments conducted by Wang(1984) demonstrated the reduction in heave and pitch motions of a planing vessel equipped with active transom flaps. The deflection angle of the flaps was controlled proportional to the pitch velocity of the vessel. This control scheme proved to be very effective in reducing the motions of the model sailing in regular head waves. Steen(2007) summarised the experimental results suggesting various approaches to empirical formulas for the coefficients of added lift and drag due to interceptors. Rijkens (2011) conducted the vertical motion modeling based on the model test data, the deflection of the control devices based on a pitch velocity feedback. Karimi (2015) designed a vertical motion controller of planning boats using an optimal control technique. It proved that a feedback of pitch angle and pitch velocity to the interceptors are effective for vertical motion damping of planing boat in calm water and head waves. Choi (2018) designed a differential control algorithm to control attitude of the ship by controllable stern interceptor in calm water. As mentioned above, Most studies mainly explore the control law of the interceptor through experiments, the summarized control strategy is effective but not optimal. This study analyzes the principle of the interceptor, and proposes a control law based on energy reduction to control the interceptor.

Flexible floating structures received increasing attention in recent years as support structures for floating offshore solar installations and other forms of oceans space utilization. An early example for such structures was the Mega-Float structure proposed as floating airport runway for Tokyo Bay. More recent examples can be found in the large inland floating solar parks where interconnected pontoons form a flexible floating structure. The common denominator of these structures is their small height compared to their length and width resulting in low bending stiffness in the vertical direction. Structural length being much longer than the wavelength and low bending stiffness result in large vertical deflections of the floating structures and strong hydroelastic interaction with the waves. Similar behavior can be observed for sloshing mitigation measures with flexible membranes. In this study, we investigated the wave structure interaction of a floating flexible sheet with a length to height ratio of 1000 in regular long-crested head waves in the small towing tank of Delft University of Technology. Wave-length was varied between 1/20 and 1/5 of structure length with wave steepness in the range of 0.02 to 0.05. Digital Image Correlation (DIC) was used to measure the surface elevation of the entire structure and wave elevation was measured in three different locations to provide reference data. The results show that the floating sheet mainly followed the local wave elevation and a reduction of motion amplitude was observed over the length of the structure. Further, the results reveal 3D effects of different elevation amplitude across the width of the sheet, which suggests strong interaction with the waves. INTRODUCTION Over the past decennia, investigation of hydroelastic response of floating structures was mainly motivated by research on sea ice and Very Large Floating Structures (VLFS), see the reviews of Karmakar et al. (Karmakar, Bhattacharjee, & Sahoo, 2011) as well as Squire (Squire, 2007; Squire, 2011), Chen et al. (Chen, Wu, Cui, & Jensen, 2006), and Lamas-Pardo et al. (Lamas-Pardo, Iglesias, & Carral, 2015). As Squire (Squire, 2008) points out there are modelling parallels between VLFS and sea ice investigations. On the other hand, Lamas-Pardo et al. (Lamas-Pardo et al., 2015) observe that none of the designed VLFS have ever been built, with the sole exception of the Mega-Float floating runway (Suzuki, 2005). However, these projects did spark the scientific interest and progress in the field of hydroelasticity.

ABSTRACT This study investigates the effect of wave obliquity on overtopping for rubble mound breakwaters with a CoreLoc armour layer. In particular, the study is based on experimental investigations on fishing harbours in the Sultanate of Oman, comprising 2D and 3D tests. In both cases, overtopping under perpendicular and oblique cyclonic waves was measured. The physical model tests were carried out in the wave flume and in the wave basin of Padova University. The scales of the experiments have been defined according to the dimension of the available artificial model units (CoreLoc). The overtopping discharge was evaluated in 2D and 3D tests collecting water passing over the structure crest, neglecting the percolation through the upper layer. For the wave basin tests, the overtopping discharge was evaluated in up to 4 different positions. As expected, overtopping discharge is smaller under oblique waves. However, the measurements are very dis-homogenous along the crest. Visually, it looks like the incident oblique wave is scattered by the initial portion of the breakwater and propagates along the structure, merging with the same wave. Crests and troughs are combined in specific points, determined by wave obliquity and wavelength. Possible scattering points are the roundhead, breakwater bents and other discontinuities. The aim of this paper is to verify if the experimental reduction of overtopping due to wave obliquity can be interpreted by a diffraction pattern. INTRODUCTION Overtopping can cause severe damage to people and structures, therefore it is an essential factor in the design of a harbour. The prediction of the average overtopping rate for a particular structure geometry, water level, and wave conditions is usually based on empirical formulae (EuroTop, 2018; Formentin et al., 2018), fitted to full-scale measurements or model test results. Prototype scale measurements are provided e.g. by Troch et al. (2004), who described the wave overtopping at the Zeebrugge (BE) rubble mound breakwater during the period 1999–2003. Similarly, Briganti et al. (2005) presented field measurements at the Rome yacht harbour rubble mound breakwater in Ostia (Italy), carried out during the winter season 2003–2004. Among the several experimental investigations carried out at small scale, there are several noteworthy extensive studies, such as Bruce et al. (2009), that focused on the influence of various types of armour units, and Franco et al (2009), that focused on scale effects.

ABSTRACT The double M-craft is a new type of high performance ship which combines the gliding characteristics of conventional planing craft and the use of air to generate lift similar to hovercraft to reduce drag. However, most of the researches on double M-craft are based on model experiment method, and the theoretical research is limited to resistance and sailing mode prediction. Fewer researchers have analyzed the motion of double M-craft in waves, because it is difficult to simulate waves in CFD, and the craft has higher speed and more complex motion. Because of the complex change of the craft's navigation state and the influence of water-gas two-phase flow, it is not suitable to use the potential flow method to simulate. Based on the viscous theory and overlapping grid technology, the VOF method is used to capture the water-gas two-phase flow field. The 6-DOF motion of a rigid body is simulated by DFBI. The pitch and heave motions of a double M-craft under head waves are numerically simulated. Reliability of background grid case is proved by wave decay and waveform verification. Then, the independency of grid is discussed through uncertainty analysis, and the appropriate overset grid case is selected. Different speeds (Fr ▽ =1.2, 2.4, and 3.6) under head wave are selected as calculation conditions to obtain the motion responses of double M-craft in waves. The accuracy of numerical simulation is proved by comparing with experimental values. Compared with the motion response of the conventional planing craft with same displacement, the results show that the double M-craft has better seakeeping performance. INTRODUCTION The M-hull is a kind of M-yacht originated from the Venice River. It combines the advantages of conventional planing boat and hovercraft, and achieves wave elimination and drag reduction only by its unique shape advantages. There are good prospects for both civilian and military use. The "Stiletto" is a successful case of transformation on the basis of the M-type yacht.

ABSTRACT A fiber optic spectrometry system with a miniature nearinfrared (range of 640∼1050 nm) spectrometer was designed to test and evaluate the performance of the mini-spectrometer in extremely cold conditions. The relationship between the output of the spectrometer and temperature was examined over the range of −50°C to 30°C, and the linear working range was derived by modeling the output of the spectrometer. The signal output was calculated and modeled to create a calibration method to correct the temperature-induced biases. Results indicated that the spectrometer used in this system can work stably in cold polar environment, and the designed calibration method can at least correct the 894 counts of signal output, which is good enough for the system. INTRODUCTION In the last few decades, the environment of the Arctic is undergoing tremendous changes, especially in terms of sea ice. The sea ice in Arctic is not only greatly reduced in coverage, but the multiyear ice is also rapidly melting (Comiso JC et al., 2007; Comiso JC, 2012), which causes significant influence to Arctic ecological environment, marine ecosystem and global climate changes (Serreze MC et al., 2007; Serreze MC et al., 2012). These changes are determined by many factors, like ocean current movement, geological movement in Arctic, however, it denotes that solar radiation is one of the most important reasons (Perovich DK et al., 2007; Perovich DK et al., 2011). Based on the solar radiation spectrum, it can be find that almost half of the energy is concentrated in the nearinfrared (Iqbal M, 2012). Therefore, it's necessary to measure the intensity of the near-infrared solar radiation in sea ice and find out how it affects the climate in Arctic. However, due to many factors, research in this area is still limited, the most important reason is the low-temperature environment of the Arctic led to many instruments and equipment can not to be deployed and used in the field.

ABSTRACT There are structural and economic limitations to expend the installation range of the current mooring lines for the stationkeeping of the floating structures. To take advantage of the resource of the far-deep sea, we carried out several experiments with the passive flapping foils as an alternative to overcome those limitations. Initial studies have shown that although the passive flapping foils have sufficient effect for the stationkeeping of a floater in the various wave conditions, it was ineffective during the extreme conditions. In this paper, we introduced an experimental study of a floater with multiple flapping foils and suggest the initial design of an autonomous controller as a solution to overcome the shortfall. INTRODUCTION The floating Offshore structures usually keep their position using mooring lines. However, the application of mooring lines in the far-off seas and deep-sea waters is clear in both structural and economic limitations. Therefore, a new stationkeeping system should be developed as an alternative to the mooring lines that can be installed regardless of the water depth. Also, there should be a control system to keep the position of the floating structure for all the wave conditions. Therefore, we are studying the application of flapping foils as a new method for the stationkeeping of a floater. Previously, it has been revealed by researchers that passive flapping foils can generate thrust force against the propagation of waves (Young et al., 2013), and that the floating structures can be promoted without additional power. Many theoretical and experimental studies are being conducted to utilize flapping foil such as ship propulsion or energy harvesting (Zhu, Q., 2012). The experimental results show that the flapping foils can be used for the stationkeeping of a floater, which could be a potential solution for the limitations of the water depth and the complex mooring installations. The final goal of this study is to develop a new concept floater that can overcome the 6 degrees of freedom and the stationkeeping system of floater by using only flapping foils.

ABSTRACT Offshore tsunami records recorded by deep ocean bottom pressure gauges are very helpful in developing a real-time tsunami forecast system and substantially improving theoretical understanding. In these studies and systems, a simplified proportional relationship in which the ocean bottom pressure changes are linearly proportional to tsunami wave height is usually used under the long-wave approximation. However, the ocean bottom pressure changes should be attenuated by the product of the wavenumber of the tsunami and the water depth at the location of observation. In order to evaluate this effect of this attenuation, we investigated a short-wavelength tsunami in real-time tsunami forecasting. INTRODUCTION Widely distributed offshore tsunami observation networks, such as the Deep-ocean Assessment and Reporting of Tsunamis (DART; Bernard and Meinig, 2011; Table 1; Fig. 1), have tremendously improved the theoretical understanding of tsunami propagation, such as confirming the existence of dispersive waves (e.g., Saito et al., 2010; Saito et al., 2011; Miyoshi et al., 2015; Baba et al., 2017). DART stations, which has 51 stations in the world ocean as of March 22, 2019 (Fig. 1), are located at sites in regions generating historical destructive tsunamis to perform real-time tsunami forecast. Each station is located at the range of water depth from approximately 2,000 m to 6,000 m (Table 1). In addition, recent dense offshore observation networks will possibly help us to develop a real-time tsunami forecast system for reducing damage (Tsushima et al., 2009; Baba et al., --- Yamamoto et al., 2016a; Takahashi et al., 2017). These observation networks consist of a number of ocean bottom pressure gauges connected by a satellite network or optic fiber cables to transfer the data in real time. For example, the Dense Oceanfloor Network system for Earthquakes and Tsunamis (DONET; Kaneda et al., 2015; Kawaguchi et al., 2015; Fig. 2) has been constructed by the Japan Agency for Marine-Earth Science and Technology (JAMSTEC) and started observations in August, 2011. DONET is consisted of 51 stations in Kumano-nada and off Kii Channel, to monitor earthquakes and tsunamis in the Nankai Trouph region southwest Japan. These stations are located at the depth of approximately from 1,000 m to 4,500 m. The data is transmitted to research institutes and universities in real-time, and improves precision and warning times of earthquake early warning and tsunami warnings and/or advisories by Japan Meteorological Agency (JMA). DONET is currently operated by the National Research Institute for Earth Science and Disaster Resilience (NIED).

ABSTRACT The tidal power station system is the study object in mooring state, and model tests are carried out to study the motion characteristics of the carrier and mooring chains in uniform wave with different wave parameters while equipped with the hydraulic turbine and equipped without the hydraulic turbine. Motion characteristics of the carrier in the free state is checked in tests. When test data match calculating data, tests will be conducted to research on motion response of the carrier in mooring state and dynamic characteristics of mooring line. The motion pattern of the tidal power plant carrier in wave and flow is obtained through comparative analysis of test results. INTRODUCTION Recently, some practical problems are widely concerned by governments around the world such as greenhouse effect, environmental pollution, depletion of energy resources etc.. Finding and taking advantage of ‘new energy resources’ and ‘clean energy’ has become one important topic of people from all circles, various universities and scientific research institutions all over the world (S.H. Salter, 2001; L. Zhang and S. Salter, 2004). Ocean energy, which is a kind of renewable energy sources, not only reserves abundant but also is inexhaustible, and could satisfy the growing energy demand of mankind. Tidal current energy generation is one of the key technologies of developing and making use of marine energy. It is significant to study the structural style and hydrodynamic performances of its generating device. Although devices of acquiring tidal current energy are various, they must be placed below the water surface. As a consequence, there should be a kind of construction, which has the capacity of bearing the weight of those devices, make them gain the tidal current energy regularly and stably. Catamaran, a kind of special ship type, is superior to single hull ship on many aspects such as the deck area, stability, the ability to resist floating etc.. During the last several years, catamarans have been developed rapidly by the virtue of its specific advantages, and been adopted by more and more working ships. The requirement of the floating power station for stability is strict, and its carrier normally applies the catamaran hull form and the hydraulic turbine set is supported by the pound-sign-shaped structure in the center (Y.Z. Li, Q. Yin and Y. Liu, 2004; F.M. Jing, B. He, H.Q. Wang and L. Zhang, 2013). Moreover, the loads of the carrier structure are very complicated, because it even needs to bear the periodic dynamic load generated by the rotating of hydraulic turbine except for environmental loads like wind, wave, flow and others (P.L. Fraenkel, 2006; N.E. Turner, A. Areas and S. Owen, 2007). Although many research on hydrodynamic calculation of floating structure has been carried out in domestic and overseas, due to the complexity of the loads of floating power station carrier, it is difficult to calculate the coupling hydrodynamic characteristics directly by using the existing standard or mature theories. So it is of great significance to conduct experimental study on the hydrodynamic response of the floating tidal power station.

ABSTRACT Water surface and bottom boundary layer measurements and analyses are presented. These form a protocol to characterize wind driven surface gravity waves in shallow water near shorelines or in shallow open coastal waters and fluid mud movement in a bottom moving lutocline. Synthetic images predict wave patches and their energy (watts m −2 ). Space-time video imagery collected at ∼10 to 120 frames per second, hyperspectral imagery, wave gauges and line targets are presented. The scientific methods have applications related to management of coastal lagoons, estuaries, near coastal waters. Applications in coastal engineering such as wind farms, protection of structures (canals, seawalls, docks) and vegetated shorelines can benefit from improved understanding of wind driven gravity waves. Associated fluid mud movement in the bottom boundary layer is demonstrated. INTRODUCTION The measurement and statistical analysis of water surface gravity waves are important in ship design and operations, design of marine structures such as breakwaters, ports, harbors, seawalls, canals, and jetties. Waves also impact shorelines, oil and gas rigs and wind turbines located in coastal waters (Goda, 2000; Saha, et al, 2017). In coastal areas such as lagoons and estuaries, surface gravity waves and sea state conditions are responsible for shore erosion, resuspension and liquefaction of bottom sediments and the transport of muck and fluid mud in the bottom boundary layer (Bauer, Lorang and Sherman, 2002). Measurements of water wave and sea state conditions utilize wave buoys, pressure transducers, wave staff gauges, capacitance and resistance probes, optical imaging, high frequency radar, and even visual observations. Water wave variability, high wind and wave conditions present challenges to observation equipment and observation platforms (Shand and Bailey, 1995; Shand, Bailey, Shand, 2012). Disadvantages of in-situ methods include difficulty in the placement of instruments, maintenance costs due to biological fouling, corrosion, as well as to high risk to personal safety and equipment during field deployments. These risks and issues are offset by the value of characterizing wind driven water waves for use in engineering of ocean and coastal structures as well as in helping to understand the movement of cohesive and non-cohesive sediment regimes. Water surface gravity wave energy impacts the movement of fluid mud and lutoclines, especially in canals and waterways. The purpose of this paper is to present combined measurement techniques and an analysis protocol that utilizes optical and acoustic methods and inexpensive instrumentation compared to alternative approaches to measre surface and bottom boundary layers.

ABSTRACT This paper investigates the sloshing effect in an enclosed water surface due to the hydrodynamic interaction and hydroelastic response of large floating multi-bodies under regular waves by using the coupled finite-element boundary-element (FE-BE) method. The wave elevations surrounding the floating bodies under headsea and oblique sea condition are studied. The effect of the structure rigidity and geometry as well as the enclosed water surface areas are investigated. It is found that the sloshing motion of the enclosed water bodies is affected by the wavelength, structural stiffness and spacing between the floating bodies. In addition, the hydroelastic response of these multi-bodies as well as the relative motion between the adjacent floating bodies are presented and discussed. INTRODUCTION The presence of large floating multi-bodies is often sighted in real engineering application where the hydrodynamic interaction of the adjacent bodies have to be taken into consideration for accurate prediction of the wave loading and response. Examples of multiple floating bodies with enclosed water surface are closed-cage fish farm surrounded by floating boardwalk (Halwart et al. , 2007, Beveridge, 1984) and multiple oil storage tanks protected by floating breakwater (Tay et al. , 2007, Tay et al. , 2009, Wan et al. , 2018). The enclosed water surfaces by these large floating bodies are subjected to sloshing effect due to the hydrodynamic interaction and has to be taken into consideration in the design stage to ensure the structural integrity of the floating structures and safety of the personnel on board. In addition, the relative motion between the wave elevation and structural motion should not be neglected as green water on deck might cause instability to the floating structures. This paper considers the case of a very large floating structure surrounded by floating breakwaters that attenuate the wave forces impacting on the structure. Due to the enclosed water domain formed between the breakwaters and floating structures, sloshing behavior is expected and will be investigated. It is hypothesized that the wave elevation at the enclosed water surface and the wave diffraction surrounding the floating bodies are affected by the breakwater width and rigidity as well as the gap formed between the floating breakwater and floating structures.

ABSTRACT Inhomogeneous media can change the nonlinear properties of waves propagating on them. In the ocean, this phenomenon can be observed when waves travel on a surface current. In the case of negative horizontal velocity gradients (i.e. an accelerating opposing current or a decelerating following current), waves shorten and heighten, enhancing wave steepness. As a result, a nonlinear mechanism known as modulational instability develops, leading to the formation of large-amplitude waves (the so-called rogue waves), even if they would otherwise be unexpected. Laboratory experiments and numerical simulations with a current-modified version of the Euler equations are presented to assess the role of an opposing current in changing the statistical properties of unidirectional random wave fields. Results demonstrate in a consistent and robust manner that an opposing current induces a sharp and rapid transition from weakly to strongly non-Gaussian properties with a consequent increase of the probability of occurrence of rogue waves. Agreement with numerical simulations confirms that this transformation can be attributed to quasi-resonant nonlinear interactions triggered by the background current. INTRODUCTION Extreme waves larger than two times the significant wave height (also known as rogue waves) represent a serious threat for marine structures and operations (e.g. Clauss, 2002). Therefore, an accurate description of the statistical properties of the surface elevation and wave height can contribute to improving the design process and warning criteria for marine operations (Toffoli et al., 2005). There are many mechanisms that cause large amplitude waves to occur (see Kharif and Pelinovsky, 2002; Onorato et al., 2013, for a complete review). Among them, nonlinear energy focusing due to the modulational instability of uniform wave trains to side band perturbations remains the most accredited (e.g. Janssen, 2004; Onorato et al., 2006; Toffoli et al., 2008; Onorato et al., 2009; Waseda et al., 2009; Babanin et al., 2011, Toffoli et al. 2013, among others). It has been verified theoretically and experimentally, however, that such mechanisms occur if waves are sufficiently steep and narrow banded both in the frequency and directional domain. Under these circumstances, rogue waves may occur within a fairly short scale of tens of wavelengths leading to substantial deviations from Gaussian and second-order-based statistics (e.g. Mori and Yasuda, 2002; Socquet-Juglard et al., 2005; Onorato et al., 2006; Onorato et al., 2009; Janssen, 2004; Toffoli et al. 2008; Waseda et al., 2009,; Toffoli et al., 2010; Toffoli et al. 2017 among others).