In order to study the dynamic response characteristics of the trailing suction dredger under medium-long period wave conditions, the response characteristics of the trailing suction dredger under selfpropelled and non-self-propelled conditions in 12s period are calculated by using physical model tests and numerical simulation techniques. The results show that in non-self-propelled conditions, the ship's heave increases with the increase of wave, while under the same wave action, there is little difference in heave and sink under different ship draft conditions. However, when the ship is fully loaded, the motion response characteristics are smaller than when the ship is under ballast. In the self-propelled state, with the increase of wave height and period, the heave of the ship also increases, and the heave at the bow and stern position is larger than that at the middle position of the ship. The experimental results are compared with the numerical simulation results. On this basis, the adaptive characteristics of the ship under different conditions are given by numerical simulation method. Combined with the test results, in case of the influence of long-period waves, the cross waves can be avoided from crossing the construction ship as much as possible, and the construction along the waves or against the waves should be adopted, which has certain reference significance to the actual construction. INTRODUCTION Long-period waves refer to waves that period between tides and swells. Unlike conventional waves, long-period waves have longer wavelengths, and although they have a limited wave height, they have a strong ability to penetrate. Medium and long period surges are characterized by both long wave energy and wind waves. The longperiod wave has a very high propagation speed and a relatively high energy, which can cause the ship to oscillate. In extreme cases, the hull may break. The long-period wave entering the harbor basin oscillates repeatedly, which will produce more destructive and difficult to reduce standing waves, which will bring great safety risks to the operating ships.

A single kind of wheel or track underwater walking operation robots may do not suit deep-sea complex terrain conditions. To solve these problems, a wheel/track convertor is presented in this paper, the convertor adapts to various terrains and it has both advantages of wheel and track walking system. A control algorithm is designed independently for safe changing the convertor mode. The dynamic simulation analysis demonstrates that the wheel/track convertor can transform the wheel/track mode dynamically, it can walk smoothly on two kinds of different terrains. INTRODUCTION There are a lot of complex and mixed abominable terrains in the deep sea (Liu, Hu, Zhang, Dai, and Yang, 2016). A single kind of wheel or track underwater walking operation robots may not be able to fully adapt to these complex terrains (Inoue, Takagi, and Shiosawa, 2010). Therefore, in order to fit the requirements of walking speed and crossing obstacles as far as possible, the currently underwater walking robots commonly use a fixed track walking mechanism. However, the speed of the fixed track mechanism can not be effectively improved in hard ground and a single wheel mechanism may not move quickly in soft ground. To solve these problems, a metamorphic mechanism for wheel and track conversion has been presented (Paillat, Lucidarme, and Hardouin, 2008). These deformation mechanisms can be turned into triangular tracks walking mechanisms from wheel mechanisms. Through the rapid conversion of the wheel/track, the deformation mechanisms can adapt to a variety of soft and hard grounds, which greatly improves the ability of robots to overcome obstacles (Cui, Gao, Guo, and Dong, 2016; Peng, Zhou, Hu, and Ou, 2014; Qu and Zhong, 2013). However, this kind of metamorphic mechanisms also can not be adapted to these hard or soft roads with complicated terrains. In order to solve these problems, this article is presented a wheel/track convertor, which has two modes of wheel and quadrangular track. The shape of the track mode can be adjusted in real-time according to the current road conditions.

In recent research of ice resistance simulation, the coupling effect between ice and water is usually neglected. To consider the coupling effect of ship/ice/water, based on finite element method and smoothed particle hydrodynamics method, the FEM/SPH coupling method is established. Then the ice mechanical properties and the ice resistance of a polar vessel are simulated. It is obtained that: (1) the numerical ice model is suitable for compression and bending strength calculation and has advantage on icebreaking simulation; (2) and the FEM/SPH coupling method is able to simulate the motion of broken ice in water and predict the ice resistance effectively. INTRODUCTION At present, with global warming and acceleration of sea ice melting, the opening rate of Arctic routes and the exploitation speed of polar resources are improved continually, leading to a great upsurge of polar vessel research at home and abroad. In such research area, the ice resistance is an important reference index for power analysis and hull form optimization, which has become a research hotspot. As for the ice resistance calculation, since the numerical simulation method can take into account the influence of sea ice failure model and local hull details, more and more researchers are focus on the numerical simulation to improve calculation accuracy and application scope. Ren YZ et al. (2016) verified the feasibility of crushability foam model in ice material simulation, and simulated the icebreaking process. Tan X et al. (2013) proposed a numerical model of ice with six degree of freedom to capture the ship-ice contact process. Wang YH et al. (2013) obtained the continuous icebreaking process and the motion response of a direct navigation polar ship by using idealized icebreaking hypothesis. Gürtner A et al. (2009) simulated the interaction process between ice and lighthouse and obtained the distributed loads based on the bond finite element model. Wang J et al. (2009) used commercial FEM (finite element method) software to simulate icebreaking process of an icebreaker. In these researches, the interaction between hull and ice is mainly considered. But the coupling effect between ice and water is usually neglected, leading to the disadvantage of simulating the motion of broken ice in water and calculating the ice resistance caused by the sliding of broken ice on hull surface. To solve the above problem, in this paper the FEM/SPH coupling method is proposed to consider the coupling effect of ship/ice/water in ice resistance simulation. The numerical model of ice is constructed based on FEM, and the water is considered by SPH (smoothed particle hydrodynamics) method. On these basis, by using the contact algorithm of penalty functions to calculate the contact states and forces, the FEM/SPH coupling method is established. To implement this method, the software Abaqus is secondary-developed, and the ice elements and failure elements are generated by C++ programming. After that, the ice mechanical properties including uniaxial compression strength and three-point bending strength are simulated to verify the feasibility of the numerical ice model. Finally, for a polar vessel sailing in ice area, the icebreaking process, the motion of broken ice, and the ice resistance are simulated to verify the effectiveness of the FEM/SPH coupling method.

The effect of spanwise wavy blade on performance enhancement of a small vertical axis wind turbine was investigated in this study. The SST k-ω turbulence model was utilized to solve the three-dimensional numerical model of a wind turbine with different wavy blades. The results indicated that the straight blade with optimized spanwise wavy configuration could greatly improve the aerodynamic performance of wind turbine. The power coefficient was sensitive to the length and amplitude of the wavy configuration. The results demonstrated that the wavy blade could be used as an effective solution to alleviate the dynamic stall effect of wind turbine. INTRODUCTION Wind turbine is considered as an efficient device to convert sustainable wind energy into electricity to meet the growing power demands. It is supposed that the floating vertical axis wind turbine (VAWT) would show a lot of advantages as it serves on land. Compared to the traditional horizontal axis wind turbine (HAWT), however, the relative low power efficiency of the VAWT has hindered its further development. On the other hand, the modification of blade configuration is regarded as an effective way to improve the performance of wind turbine. Compared with the traditional H-type VAWT or Φ-type VAWT, some VAWT structures proposed in recent years were proven to have better aerodynamic performance. Some project progress and details about a novel V-shaped wind turbine rotor were reported by Parsons, Chatterton, Brennan, and Kolios in 2011. This wind turbine was designed specifically for the offshore wind conversion, and compared with the original one, it would reduce the greenhouse gas emissions by about 20%. Scheurich and Brown (2013) compared the aerodynamic performances of helical twisted blade, troposkein-shaped blade, and straight blade. The helical VAWT was proven to have a higher power coefficient when the blade curvature and helical twist angle were optimized. Hilewit, Matida, Fereidooni, Abo, and Nitzsche (2019) redesigned the traditional Φ-type VAWT. Both the height and frontal area of turbine blade were decreased and shifted to form a shiftedtroposkein shape VAWT. The results showed that the modified wind turbine could effectively improve the power coefficient at high tip speed ratios, and the material cost was saved by reducing the blade size and weight. Besides, the concept of V-shaped blades was recently proposed to improve the power output of VAWT by Su, Chen, Han, Zhou, Bao, and Zhao (2020). It was found that in addition to the enhancement in the power coefficient, the V-shaped blade was able to alleviate the damage caused by lateral loads to the wind turbine.

The numerical simulations using Finite Volume Coastal Ocean Model (FVCOM) forced by the eight tidal component (S2, M2, N2, K2, K1, P1, O1, Q1), river discharge, and wind speed was conducted to clarify the conditions that caused marine debris to reach the Ube Port from the river mouth of Yamakuni River on July 2012. Marine debris was modeled to be particles whose behaviors observed by Lagrangian method with an improvement that include a wind component directly driving the debris. It was found that wind plays the most important role at drifting the particles across Suo-Nada. INTRODUCTION Large amounts of marine debris (approximately 600 m 3 ) such as driftwoods were found drifted in the Ube Port, Ube City shown in Figure 1 on July 7th, 2012. This event was unprecedented in the past years. The sea port was covered by the mixed of more than 10000 m 3 marine debris such as driftwood, around 50 cm in diameter tree slumps, sofas, and tires of agricultural equipment. With a thickness of around 50 cm near the shore, the garbage made it difficult to navigate the ship and it also greatly hindered the function of Ube Port. The Ube Port Management Office carried out a cleanup on July 9 to 13, where a corpse of cow from Nakatsu City, Oita Perfecture was found which was thought to had been washed away by floods from the Yamakuni River (Ubenippo, 2012). A few days prior to the appearance of marine debris in Ube port, a heavy rainstorm with an exceptional intensity was recorded in Hita city and Yabakei town of Oita Prefecture on July 3rd, 2012 from 6 to 10 a.m. caused by a stationary front (Baiu front). It is statistically expected to occur once every 268 years (in Hita city, 52.5 mm/hours) and 5,380 years (in Yabakei town, 67.83 mm/hours). This rainstorm caused overflowed water in Kagetsu River and Yamakuni River Banks and serious flood damage in Hita and Nakatsu cities (Yamato et al., 2013).

Arctic business is developing within the sectors of marine operations related to offshore oil and gas, mining, seafood, tourism, scientific expeditions, and world trade shipping. As offshore activities in the Arctic is a relatively new field, with only a handful relevant operations to draw experience from, and since full-scale trials are extremely expensive, there is an expressed need for more detailed and cost-efficient analysis and design review of concepts based on numerical simulations. Over the years, various numerical simulators, with different levels of technical readiness, have been developed to address issues related to Arctic Offshore Engineering. This paper focuses on the development of the Simulator for Arctic Marine Structures (SAMS), its basic theories and recent engineering applications. These include structural damage assessment for simulating the impact between a wave driven glacial ice feature with a semi-submersible structure; the decision-making support by ice load calculations on a shipwreck in the Arctic; and various Arctic vessel navigation simulations. The technical advancement in terms of multi-body dynamics, ice fracture mechanics and hydrodynamics that the simulator is built on is manifested. The presented engineering applications signify the importance, the versatility and maturity of SAMS in dealing with complex ice – structure interaction issues at different scales and at various levels of complexities. INTRODUCTION For Arctic structural design and most Arctic operation planning, ice load calculations are one of the key components. However, ice load calculation is complicated by various ice conditions and different ice failure modes. As Palmer et al. (1983) stated, ‘ it is no more likely that there should be a universal ice-force formula than that there should be a universal formula for the force on a body in a moving fluid, and in the present state of knowledge, it would be unwise to expect too much ’. Over the years, the common engineering practice, e.g., (ISO19906, 2019), in calculating ice load on a given structure takes several steps of presumptions: an assumption on the limiting mechanism and an assumption on the various possible failure modes (Løset et al., 2006, Sanderson, 1988, Palmer and Croasdale, 2013). These approaches often offer one design value and are handy for fast calculations, however, require high engineering experience in making sound judgements. As time steps into the new century, our computational power and tools are getting more advanced. In addition, our understanding towards the mechanics of ice – structure interactions are also ever growing thanks to more accumulated data and theoretical advancement. It is now at our disposal to 1) get rid of all those initially needed interaction scenario presumptions and start from the beginning with given ice condition and structure 2) to obtain time domain analysis of both the ice action and its effect on the structure; 3) in addition, these calculations can be so fast that an almost real-time domain analysis becomes possible, which opens door for simulations of Arctic marine operation. Given the background and targets, the Simulator for Arctic Marine Structures (SAMS) is developed over the past 8 years. This paper documents the theoretical background of SAMS and its recent applications.

In 2019, DNV GL was calling offshore stakeholders to join forces to align on an approach on how wind turbines structures should be designed for offshore sites in the Asian Pacific region like Taiwan, Japan, Korea as well as parts of the United States. The joint industry project (JIP) is called ACE which stand for "Alleviating Cyclone and Earthquake challenges for wind farms". The project was kicked off in November 2019 and is expected to run until August 2020. The consortium consists of 20 project partners representing some of the most relevant offshore wind farm developers, wind turbine suppliers, foundation designers and local specialists. As the results will not be fully available by the time of manuscript submission, this paper summarizes preliminary results from the early work packages. INTRODUCTION In the past, most of the offshore wind farms have been installed in European countries. Since 2018, several offshore wind farm development projects in Taiwan and Japan have started. In contrast to offshore wind projects in European waters, it became clear that impact from earthquakes and/or tropical cyclones - also called typhoons or hurricanes - is expected to be one of the major design drivers for the wind turbines and their support structures. The JIP will aim at developing an integrated approach to design wind farms against impact from earthquakes and tropical cyclones. This will be done in two separate work streams. A strong focus of the JIP will be offshore wind turbines and their support structures. However, the topics addressed within the JIP are partially important as well for other assets of an offshore wind farm like offshore substations or installation vessels during construction and also for onshore wind farms facing similar impact. The goal of the JIP in the present case is to agree on an industry approach regarding the question how wind turbine structures should be designed for tropical cyclones and earthquakes in a safe and consistent manner. It is intended to reach consensus on how to use existing knowledge.

With the increasingly prominent energy shortage problem, offshore oil and gas fields have been rapidly developed, horizontal well production technology is increasingly valued and widely used, but horizontal well production logging technology has not been well resolved. In-depth research on the multiphase flow characteristics of oil, water, oil, gas and water in the wellbore is of great significance for improving the production logging technology of horizontal wells. Since the actual horizontal wellbore is fluctuating, the flow process of multiphase fluid in the wellbore is very complicated. At present, only a few researchers have conducted limited research on the characteristics of multiphase flow in this pipeline. In order to study the characteristics of oil-gas-water three-phase flow in different dip angle fluctuating tubes, by using the VOF model in FLUENT, simulates the oil-gas-water three-phase flow in the largediameter (124mm) fluctuating tube respectively at the dip angle θ of 0°, 5°, 10°, 15°, 20° and 30° at the inlet mixture velocity of 0.5m/s at the gas content rate (Cg) of 10% and 50%, and then analyzes and compares the evolution trend of the three-phase flow pattern in the fluctuating tube, the gas hold-up of wellbore profile, the water hold-up and the pressure distribution in the wellbore. The analysis shows that at a low gas content rate, the oil-gas-water three-phase flow pattern in the fluctuating tube is transformed from stratified-stratified flow to intermittence-stratified flow, and as the dip angle becomes larger, the partial gas hold-up becomes larger, the water hold-up becomes smaller, the curve of pressure drop oscillates more strongly, and the presence of slugs causes pressure fluctuations in the wellbore; at a high gas content rate, the oil-gas-water three-phase flow pattern is basically unchanged in the fluctuating tube, and the stratified-stratified flow, the effect of the dip angle on the gas hold-up weakens, but the greater the dip angle is, the stronger the gas-liquid two-phase slippage effect and the greater the pressure drop in the wellbore will be. Through the research work of this paper, the analysis and summary of the three-phase flow, numerical simulation and other aspects of oil, gas and water, the results have certain theoretical significance and practical guidance for improving oil and gas production on the field.

This paper presents the results from wind load CFD calculations performed on a truss leg of a typical GustoMSC designed drilling jack-up rig. The CFD model is constructed using the STAR-CCM+ software package from Siemens. The performance of two numerical models Unsteady RANSE and Delayed DES are investigated. A number of flow angles are considered. The wind force is computed using a constant and uniform flow field at the inlet boundary of the computational domain. In order to investigate the scale effects, the calculations are performed at model-scale as well as at full-scale. The results of the CFD calculations are compared with the results that can be obtained on the basis of the recommended drag force coefficients by the SNAME which are developed largely based on wind tunnel measurements. It was found that the scale effects are present for the drag force acting on truss legs due to the Reynolds number dependency of the cylindrical components. CFD results at full-scale show that the SNAME recommendation method is on the conservative side. Based on the results of the CFD calculations at model-scale and full-scale, this paper discusses the scale effects of wind drag force acting on a truss jack-up leg. INTRODUCTION A typical drilling jack-up rig consists of a buoyant platform standing on three independent truss legs, with a large forward accommodation block, several large structures and equipment, a drilling derrick and several cranes on the deck. The truss shaped leg consists of three chords with racks connected with each other through cylindrical shaped bracings and spanbreakers. Fig. 1 shows a typical GustoMSC designed drilling jack-up with three truss legs. The design of a jack-up rig requires the prediction of the forces generated by wind on the truss legs for the transit condition. In the early design stage of a jack-up, the wind forces are usually estimated by empirical methods which are given by standards such as the SNAME (2008) and ISO (2016). The standards are based on the building block approach. The total wind force on the truss leg is estimated by summing up the forces of the chords and cylindrical members considering the projected area, orientations and flow angles. This method is efficient and fast but usually the level of detail is low and shielding effects and flow interactions by the leg components are not considered. When high accuracy is required at the design stage, wind tunnel measurements are commonly carried out. However, the wind tunnel measurements are performed at model-scale and must be carefully performed to ensure that appropriate Reynolds numbers are reached for the truss legs, since scaling effects can be significant for truss legs, due to the Reynolds number dependency on the cylindrical shape components. Predicting the drag force using Computational Fluid Dynamics (CFD) is therefore of particular interest. Because, in CFD not only the drag force can be predicted, but also valuable insight can be obtained into the flow behavior through visualization of the flow field.

Subsea production system and topside processing systems are coherent system in real field but simulators are separated into two independent program, multiphase flow simulator "OLGA" and topside process simulator "HYSYS". It requires labor to transfer the values between two simulators especially in transient cases, where step time is less than 1 second, which blocks fluent transient simulation. So integrator has been developed to automatically transferring values in two-way and controlling timesteps of both integrators. Algorithms were developed to give control between simulators, and systematic approaches were optimized for two programs using DCOM configuration and OPC DA specifications. To verify the integrator, some case studies were designed and done using pre-built simulation models. Also other modules were added to analyze the integrated simulation with in-house source code. INTRODUCTION Delivering values between the different simulators needs technical implementation and also need theoretical assurance of its consistency. To accomplish the integration of dynamic simulation in whole production field, link has been accomplished for several simulation programs like OLGA, HYSYS, PIPESIM… etc. Simulation results has been drawn with this dynamic integration, although yet not fully reliable. This paper will focus on the linkage between two specific program, one is dynamic multiphase flow simulator OLGA and the other is process simulator HYSYS. OLGA is strong in computation of multiphase flow, but not in chemical processing. On the other hand, HYSYS is strong in chemical processing but not in calculation of flow dynamics. These two programs are coupled to simulate large offshore field with subsea pipelines and topside platform more accurately. To achieve the integration, programming has been done to develop the in-house code with C# and user interface (Fig.1) with Winform. Using OPC DA library and HYSYS library (Peltoniemi et al., 2001), Automation of value delivery of selected point for each timestep were implemented satisfying mass continuity. Also, on-off control on simulators were made with this integrator with master timestep. Since the scheme of time discretization is different between two, synchronization between two simulators were loosely set and controlled. Difference by master timestep has been measured for given case study, where both simulation cases of OLGA and HYSYS can be described as chaotic system. with case study consists of different length of ramp-up cases, for fixed flowrate for single process train. Verification of integrator has been also checked within this case study.

The performance of the overset meshing tool implemented in the opensource Computational Fluid Dynamics (CFD) software OpenFOAM© is investigated in this work. The method is validated against experimental results of free decay tests of a freely-floating vertical cylinder and a Floating Offshore Wind Turbine (FOWT) available in the literature. The meshes, the numerical schemes and options, and the boundary conditions of the model are detailed. The numerical results are in good agreement with the experimental measurements, in particular for the vertical cylinder. Discussions of the discrepancies between numerical and experimental results of the FOWT case are presented. INTRODUCTION Floating Offshore Wind Turbines (FOWTs) have a great potential in deep water areas, where the metocean conditions, such as waves, wind and current, are challenging. In order to assess the hydrodynamic forces on the structures, most engineering tools use models based on linear potential theory and/or the Morison equation. Both approaches present the advantage to require a low computation time. For these models to be accurate, the following assumptions must be valid: low wave steepness (linear waves) as required by the linear diffraction problem in potential flow theory and small structure dimensions compared to the wavelength – i.e. ‘hydrodynamic transparent’ structures as required by Morison equation. These models are appropriate for predicting behavior of FOWT in ‘operational’ conditions. But extreme conditions can lead to highly nonlinear phenomena such as run-up or wave slamming. In these cases, design standards suggest simplified approaches, but their applicability is limited, especially when considering complex geometries. CFD computations may be necessary to better estimate the wave loads. It is also these conditions that drive certain aspects of the floater design. However, such methods still need to be validated before to be used in engineering for the design of a FOWT. This paper presents a method to model a freely-floating body motion using the open-source CFD code OpenFOAM©. Large displacements of the structure may also occur. To deal with these displacements, an "overset mesh" method is used based on an integrated tool in OpenFOAM©. In this method, two meshes are generated. One mesh represents the global domain and one mesh surrounds the floating body and is body-fixed (so that it moves together with the body in case of a moving body). At each time step, an interpolation is done between these two meshes to provide a single solution. This meshing technique represents an alternative to remeshing or moving mesh techniques in the cases of large body displacements. It maintains the mesh quality throughout the simulation and avoids mesh distortions.

After the opening of the new Arctic channel, more and more ships are carrying goods through the Arctic channel. Under polar conditions, the crystallization of sea water affects the normal running of ships. This paper discusses the effects of fluid flow on sea ice crystallization from the perspective of heat-mass transfer, phase change and hydrodynamics. A microscopic mathematic model for sea ice crystallization is established based on phase-field method and lattice Boltzmann method. The two-dimensional simulation is conducted, in which the Phase field, salt-concentration field, temperature field and flow field was coupled. The sea ice crystal growth under natural convection and external forced convection is studied. The results show that the flow of seawater changes the concentration of seawater around the sea ice, and different concentrations of seawater cause different crystallization rates. The flow also changes the heat-mass transfer, which reduces the degree of subcooling. Both affect the shape and structure of sea ice crystallization. INTRODUCTION In 2009, the German shipping company crossed the Arctic along the northern coast of the Eurasian landmass for the first time, marking the opening of the Arctic Northeast Passage. The channel has a large amount of resource reserves, good navigation conditions and an important strategic position, which makes it quickly the focus of attention of all countries. When the ship is traveling in the Arctic ice zone, the water inlet pipe of the ship is extremely susceptible to freezing at low temperatures, and the continuous accumulation of sea ice gradually blocks the cooling pipe, resulting in the ship's cooling system not working properly and prone to safety accidents. Since the seawater is always in a flowing state relative to the ship's pipeline during the travel, it is necessary to study the crystallization characteristics under the seawater flowing state. At present, most of the research methods for frozen crystallization of seawater are based on the classic crystal nucleation theory from a macro perspective, using statistical methods to investigate the process of seawater crystal growth. This method can predict the growth process of ice crystals and can be verified by setting up a seawater desalination test bench, but it cannot systematically explore the heat and mass exchange during the crystallization process.

In this paper, the numerical model of level ice is developed in the framework of finite elements and the water is considered by SPH method, the numerical method is established by adopting the contact algorithm to calculate the contact forces between finite elements and water particles. Then the icebreaking process of the polar tanker is calculated and its navigation in open water simulated by CFD numerical simulation based on viscous theory. The resistance of a polar tanker under multiple load cases is predicted. INTRODUCTION The melting speed of ice in Arctic region is accelerating because of the changes in climate, which makes the marine transportation in Arctic region possible. The polar tanker will play an important role and its full route includes both ice area and open water area. And the demand of the polar tanker with self-icebreaking ability is increasing recently. For a polar tanker, the comprehensive performance in both of the ice area and the open water area should be considered in the design phase. In the resistance prediction of ice-breaking, finite element method is a commonly used numerical calculation methods. Compared with the oversimplification of the model in the empirical formula and the long period and high cost of the model test, it can take into account the effects of sea ice failure modes and more ship form parameters. The Cohesive Zone Model (CZM) has found great attention in the applied numerical fracture literature to solve problems of multiple cracking brittle and quasi-brittle solids during impacts and failure loading. Then the CZM was extended into sophisticated numerical algorithms in the framework of finite elements, termed the Cohesive Element Model (CEM), for the simulation of ice-structure interactions, (Konuk et al, 2009). Arne Gürtner et al. (2009) used the numerical method to simulate the action to a lighthouse, the simulation results indicate that the numerical method captures many of the qualitative observation as well as quantitatively derives comparable global ice loads to the lighthouse to those of the selected ice event. Wang et al. (2008) developed a collision model of crushable ice based on nonlinear dynamic finite element and analyze the ice load of a FLNG ship using commercial code DYTRAN. Yang et al. (2008) adopted the method of fluid-structure interaction and established the nonlinear finite element model of collision between ship and ocean platform by taking sea ice as medium.

In this study, an unresolved CFD-DEM was used to investigate a fluid flow and a behavior of sediment particles around a monopile. In order to consider the interaction between particles on the seabed and a current, an improved CFD-DEM solver was implemented within the OpenFOAM framework by proposing a void fraction method based on the kernel function. To validate computational methods, a settling velocity of a single particle, an angle of repose and an incipient motion of particles were simulated and compared with the existing experimental data. Finally, a scour around the monopole was predicted and discussed. INTRODUCTION In relatively shallow water, most offshore wind turbines are based on monopile foundations as bottom-fixed structures. Theses bottom-fixed foundations installed on an erodible seabed are exposed to scour, which may lead to structural failure. Therefore, it is essential to understand how the hydrodynamic environments affects the foundation and the interaction between flow, structure and seabed (Sumer, 2014). In particular, the scour can be defined as the phenomenon that the seabed particles around the foundation structure are transported due to the interaction of the fluid flow and the structure. The scour is a threat to the stability of the structure exposed to currents and waves. In order to alleviate the scour problem, many studies have been conducted experimentally (Dargahi, 1989, Whitehouse, 1998; Sumer and Fredsoe, 2002). In particular, most of the work has been done on scour phenomenon with monopile foundations. It led to various empirical formulas and methods to predict scouring depth and extension (Matutano et al., 2013). On the other hand, the computation can be employed as an alternative tool to study the scour process around structure (Pang et al., 2016). Recently, several computational methods have been developed to estimate the equilibrium scour depth. The scour depth and extent were estimated based on the bed shear stress exerted by the flow field in the Eulerian-based approach (Park et al., 2017). However, the single-phase model usually was not able to consider interparticle interactions in the scour around structures. To deal with this problem, many studies have adopted a two-phase model (Yeganeh-Bakhtiary et al., 2011; Hajivalie et al., 2012). These models can be divided into two types, depending on the method used. One is the so-called Euler-Euler two phase model, which treats the fluid and sediment phases as separate continuous mediums. The other calculate the particle motion individually using a discrete element method (DEM). The advantage of this method is that it can analyze a large amount of particles based on a simple collision model and analyze the exact behavior of the particles. Thus, to consider the interaction between the fluid flow and the seabed soil, a CFD and DEM coupling method is needed. Recently, studies on the sediment transport using the CFD-DEM coupling method have been carried out (Schmeeckle, 2014; Sun and Xiao, 2016), and even the scouring around a submarine pipeline was performed to investigate the flow behavior and particle motions (Yeganeh-Bakhtiary et al., 2013; Zhang et al., 2015). However, there have been only a few studies to realize the scour phenomenon around the monopile using CFD-DEM coupling method.

Internal solitary waves (ISWs) are a huge threat to submarines. In order to investigate the influence of internal solitary waves on submarine, a numerical method based on Reynolds-Averaged Navier-Stokes (RANS) equations was adopted in the paper. Besides, KdV internal solitary theory was used to modeling ISW-induced currents. Captive submarine model was simulated and analyzed. And simulation for submarine free motion with the interaction of ISWs was realized by Dynamic Fluid Body Interaction method. It indicates that flow fields become very complex when a submarine goes through solitary waves, resulting an extremely considerable loads and motion. Thus it is necessary to pay special attention to safe operation of submarine in ISWs. INTRODUCTION Internal solitary waves (ISWs) appeared frequently in South China Sea (Lien, et al., 2014). Temperature and salinity are important factors affecting the density stratification of seawater. The density difference is much smaller compared with that between water and air. It is equivalent to placing in the microgravity field. So the restoring force of ISW is smaller, only 0.1% of water wave. And because amplitude is inversely proportional to the square root of gravity, the amplitude of internal wave can be 20-30 times of water wave under the same energy condition (Li, 2015). This is the essential difference between internal waves and water waves. Internal solitary wave is a kind of non-linear large amplitude internal wave in nature, which is generally generated when strong current passing through the steep slope or ridge of seabed. There are strong amplitude dispersion and sudden strong current in internal wave. The wave length can be hundreds of meters to hundreds of kilometers, and the amplitude can be larger than one hundred meters. The maximum velocity of flow field induced by internal wave may be 2m/s or higher (Cai, et al., 2011). Therefore, the influence of internal waves on submarines should not be ignored. Nowadays, computations of viscous turbulence flow around constrained submarine has been widely adopted to study the hydrodynamic loads exerted by ISWs (Chen, You, et al., 2010). And experiments are also carried out by using constraint models (Du, et al., 2016). But influence of ISWs to free motion submarine is an important and interesting problem, while there is no condition to carry out relevant tests so far. So numerical simulation method is used to investigate the problem here. We investigate the influence of internal solitary waves, focusing on movements of SUBOFF model (Groves NC, et al., 1989) as well as hydrodynamic loads. The research work in the paper were based on own codes combining with software.

Multi-Scale Flow Structures Can Be Observed In The Process Of Droplet Impact On A Deep Pool, Such As Central Jet, Splash, Micro-Droplets. We Have Performed 3-D Direct Numerical Simulation Of This Problem. By Using Block-Based Adaptive Mesh Refinement (Bamr) Algorithm, Highresolution Can Be Achieved Near Interface To Characterize Micro Flow Phenomenon. A High-Robustness Algorithm For Large-Density-Ratio Two Phase Flow Is Used To Improve The Accuracy For Momentum And Interface Advection. Crater Depth And Central Jet Height During Impact Are Compared With Available Experimental Data. The Evolution Of Crown Splash At High Weber Number Is Analyzed Using Numerical Tools. INTRODUCTION Droplet impact onto a liquid pool has been a hot topic for decades in the research area of two phase flow. It is a common phenomenon in industrial and agricultural applications, such as oil spills (Meckenstock et al., 2014; Gopalan et al., 2010), spray cooling (Aziz and Chandra, 2000), inkjet printing (Bos et al., 2014; Chen et al., 2017) and raindrop energy harvesters (Guigon et al., 2008). The collision of interfaces and coalescence process between high speed droplet and target fluid can induce complex flow phenomenon. Large-scale flow structures, such as crown splash (Deegan et al., 2008; Zhang et al., 2010; Ma et al., 2019), daughter droplets (Castillo-Orozco et al., 2015), high speed jet (Ma et al., 2019), are usually of the same order as the initial droplet diameter. Air layer (Thoroddsen et al., 2012), micro-bubbles (Thoroddsen et al., 2012), ejecta sheet (Agbaglah et al., 2015; Zhang et al., 2012), which are micron or even nanoscale structures, require high resolution for experimental measurement and are far more difficult to be reproduced completely in numerical simulation. Droplet size, initial impact speed, physical properties of liquid and external forces can affect the evolution of these complex, unsteady flow phenomena. Previous authors performed numerous experimental studies and ultrahigh-speed video camera are widely used to study multi-scale flow phenomenon during the full or partial coalescence between droplet and liquid surface. At low impact velocity, an air layer will form between the droplet and liquid surface, Thoroddsen et al. (2012) studied the rupture of this very thin air layer and analyzed time evolution and spatial distribution of micro-bubbles caused by the punctures of air layer and the meeting of isolated holes. When the initial impact velocity is high, a deep crater will form after the impact, which is often followed by a central jet flow. Castillo-Orozco et al. (2015) investigated the effects of impact velocity, surface tension and viscosity on the central jet flow breakup and the numbers of daughter drops through systematic experiments. The larger secondary droplets come from pinching off at the tip of central jet. Ma et al. (2019) have conclude that the ratio of the secondary droplet to the initial droplet diameters is approximately within 1.2–2 and by using linear regression method, they had given the correlations between the geometric sizes of central jet, secondary droplets and Weber number. Another interesting phenomenon during impact is splash, the fast impact process will induce energy conversion from initial droplet to liquid surface of pool (Peregrine, 1981), thus a liquid sheet will splash off from the pool, which is observable at higher impact velocity. Deegan et al. (2008) has classified the splash liquid sheet into two typical types with distinct physical mechanisms: ejecta sheet and Peregrine sheet. The morphology of crown splash is shown with a phase diagram based on different We and Re and three possible mechanisms for the formation of micro-droplets have been concluded.

Hollow rectangular camber otter board was mainly adopted in low-speed trawl systems in Antarctic krill fisheries. In this study, hydrodynamic analyses were performed on a hollow rectangular camber otter board with a projected area of 13.02 square meters, an aspect ratio (AR) of 1.66 and a relative camber of 10%. First, A flume tank experiment was used to validate the accuracy of numerical simulation. Then, the effects of aspect-ratio, relative camber on hydrodynamic characteristics of the hollow rectangular otter board were investigated by Computational Fluid Dynamics (CFD) simulations. According to the numerical results, (1) lift coefficient ( C L ) and lift-drag ratio ( K ) first increased and then decreased with the increasing angle of attack (AOA); (2) the maximum C L and K were obtained with when AOA=25° and 5°, respectively; (3) C L slowly increased and drag coefficient ( C D ) slowly decreased with increasing AR. (4) C L quickly increased and C D slowly increased with increasing relative camber; (5) K increased with increasing AR; (6) K increased first and then decreased with the increasing relative camber. At last, low C D , high C L and high K were selected as the targets for optimization, aiming to improve the working efficiency of otter board. The optimization indicated that when the AR was 2.06 and the relative camber was 10%, the otter board has the optimal working efficiency. This research has provided the scientific reference for the pre-design and optimization of the hollow high AR otter board. INTRODUCTION Otter board, known as a vital component in the single-boat trawling industries, is used to keep the trawl net horizontally opening while working. (Mukundan, 1970; Niedzwied, et al. 1998). Based on the previous research, resistance of the otter board accounts up to 30% of the total resistance of trawl system (Sterling, 2000). Besides, compared with trawl door used in bottom trawling industry, the otter board adopted in Antarctic krill trawling has the unique features of high-aspect-ratio and its hollow structures result in low density, leading to different hydrodynamic performances compared with other kinds of otter board. Therefore, it is necessary to carry out the study of the hydrodynamic performance of the otter board.

A dynamic model was proposed with the features of high precision and fast response. The dynamical equations of the flexible cable were established by using Newton's second law. Lumped mass method was used to discretize equilibrium equation and continuity equation. The motion excitation was input at the head or tail end of the cable. The model equations were iteratively solved by fourth order Runge-Kutta method. Four cases of simulation of a towed system were presented to prove feasibility and effectiveness of the model, including equilibrium state in different currents, sailing with constant propeller rotary speed, turning motion and the spiral descending motion of the submersible. INTRODUCTION A towed system is an efficient device for underwater measurement, oceanic detection and submarine mapping, which usually consists of a mother ship, a cable and a submersible. Since reliable and rapid motion prediction can ensure good operation and prolong service life, it is necessary to accurately establish a reasonable dynamic model of a towed system. Usually, discrete model is the most important part in the modeling process. Finite difference method, finite element method and lumped mass method are the common discrete methods. Therein, lumped mass method is the most acceptable one because of its simple theory and concise form. Walton and Polachek (1960) firstly proposed lumped mass method in solving the nonlinear partial differential equations governing 2D transient motion of a cable. Delmer and Stephens (1983) utilized lumped mass method to analysis the breaking process subsequent behavior of a cable under excessive load. The computed results show a fine consistency with the experimental ones. Huang (1994) considered the linear elasticity of the cable materials and promoted lumped mass method in discretizing a 3D dynamic model. The new model enabled larger time step and faster iteration time. Driscoll and Lueck (2000) used lumped mass method analyze the motion and load characteristics of a deep-sea ROV system, which consist of a ship, a cage, a remotely operated vehicle (ROV) and towed cables. Results prove that the model is effective and rapid for the prediction of snap loads. Liu (2012) and Wang (2012) further studied the dynamic model of towed systems on the basis of the previous work. In their research, bending and torsional moments were added to the elastic cable segment divided by lump mass method. Besides, the cable in Wang's (2012) investigation was covered streamlined sleeves to reduce the drag force, which lead to a steady axial rotation of the cable. Thus, a 4D dynamic model was successfully developed.

The linear channel is one of the key components of a linear-type marine magnetohydrodynamic (MHD) thruster. The cross-section of a linear channel directly affects the energy conversion process and performance of an MHD thruster. In this paper, the flow loss, distribution of the internal electromagnetic and flow field, and performance characteristics of a linear-type MHD thruster with three cross-sections are investigated using the finite volume method and 3D numerical simulations. The results show that under the same conditions, the performance of an MHD thruster with a rectangle cross-section is better when Re is less than 250,000, and that with a drum-shaped cross-section is better when Re is more than 250,000. INTRODUCTION Marine MHD propulsion uses an electromagnetic force (Lorentz force) acting on seawater to generate a thrust. So few mechanical moving parts are required with MHD propulsion. As a result, this type of propulsion may be very quiet and simple. And MHD propulsion receives more attention recently (Ali, Pruiu and Ail, 2016; Hojati, Marashi and Kanzi, 2017; Mortaza, Mohammad and Diako, 2018; Mortaza, Mohammad, 2019). According to the configuration of the magnet and channel shape, marine MHD thrusters are classified into two main types, the linear-type MHD thruster with a linear channel and saddle-shaped magnet, and the helical-type MHD thruster with a helical channel and solenoid magnet. As shown in Fig. 1, the linear channel of a linear-type MHD thruster is composed of insulating walls and two flat/arc electrodes. It is very simple and easy to manufacture. And it has a small flow resistance. Therefore, the linear-type MHD thruster has been studied theoretically and experimentally since marine MHD propulsion was put forward. Doss(1990) and Thibault(1991) investigated the inner electrical field and electrolysis effect of linear-type MHD thrusters. The first superconducting MHD propulsion test ship "YAMATO-1" in the world used linear channels. Many experiments and calculations on performance of linear channels had been done, which got many good and significant results (Tasaki, Sugawara and Mori, 1991; Roy, 1993; Sasakawa, Takezawa and Sugawara, 1993). Gilbertt, Lint (1990) and Kom, Brunet (1995) used multiple linear channels arranged around a circle to reduce the leakage magnetic field. Tan, Yun and Ling (1997) established a mathematical model of a linear-type MHD propulsion system with a rectangular cross-section. Chai (2000) established a two-dimensional mathematical model of a linear-type MHD thruster using the finite element and finite difference method. He investigated the electromagnetic and flow field and influence of Hartmann effect in a linear channel with a rectangular cross-section. Zhao and Kong (2007) proposed a global calculation method for a linear-type MHD propulsion system based on the conservation of momentum and energy, and studied the influence of the geometry and size of a linear channel with a rectangular cross-section on the flow loss and propulsion efficiency. Hojati and et al. (2017) set up a simplified analysis model of a linear-type MHD thruster with a rectangular cross-section. Considering the influence of the seawater electrolysis and end loss, Mortaza, Mohammad and Diako (2018) studied the influence of the magnetic flux density and seawater conductivity on the performance of a linear-type MHD thruster with three-dimensional numerical simulations.

A 3D Numerical Wave Tank (NWT) has been implemented in the inhouse Large Eddy Simulation (LES) code to study wave-structure interaction problems in deep, intermediate and shallow water-depths. For the purpose of this study, a three dimensional solitary wave interacting with a submerged finite plate is considered. The direction of the wave relative to the plate orientation is examined by considering a rotating plate of several angles of attack ( θ ). The NWT is capable of generating solitary, linear and non-linear periodic waves using Dirichlet boundary conditions based on relevant wave theories. Experimental data obtained from a previous study of a solitary wave-fixed plate interaction are used to evaluate the accuracy of the refined code, by comparing wave elevations, forces and moments. Then, a finite plate of various angles of attack is considered and plots of the free-surface evolution and contours of the flow vorticity reveal the variations and similarities between different cases and confirm that complex local flow hydrodynamics exist in such more realistic problems. INTRODUCTION Due to climate change and global worming, shorelines and coastal protection suffer from the impact of extreme events such as storms and extreme wave conditions. Breakwaters, wave energy converters and other near-coast structures are usually designed to operate in calm water conditions, however, under extreme conditions, they may experience high impact pressures and forces critical for the stability and durability of the design. Understanding the impact of extreme waves like tsunami waves on coastal structures will result to safer and more efficient designs. Different theories have been adopted to develop numerical models to estimate the hydrodynamic properties in coastal engineering problems. Based on potential theory, Liu et al. (2009) consider regular waves propagating over a thin flat plate and good agreement with relevant experimental data achieved. Similarly, based on velocity potential Dong et al. (2018) examined the forces acting by monochromatic waves on a thin flat plate located over an uneven floor bed. Different bottom geometries were also tested to study their effect on wave reflections. Alternatively, Hayatdavoodi and Ertekin (2015a,b) based their numerical model in level 1 Green-Naghdi (GN) equations to study the interaction of solitary and regular waves with a submerged thin plate. Similar models such as Boussinesq-type models (Nwogu, 1993; Wei and Kirby, 1995) are widely used in coastal engineering problems. However, relevant experimental studies (Poupardin et al., 2012; Lo and Liu, 2014) revealed a dominant rotational flow near the edges of the submerged plate that alter the near-field hydrodynamics. Not all models are capable of accurately simulating the above. In a comprehensive review Hayatdavoodi and Ertekin (2016) presents the key studies relevant to waves interacting with bridge decks and flat plates.