ABSTRACT The analysis of the propulsion performance considering the ship motion in waves is an important factor for the efficient operation of a ship. The interaction between the propeller and the free surface due to the ship motion in waves has a great influence on the propulsion performance. However, most of recent researches about the hydrodynamic performance of ships in waves focus on the added resistance, and the experimental or numerical data on the propulsion performance considering the ship motion in waves is very rare. In this paper, numerical investigation on the nominal wake in regular head waves is performed for a KVLCC2 model ship at a full-load condition. Phase-averaged and instantaneous wake fields during one period are compared with the experimental data measured by SPIV showing good agreement. And the effect of the ship motion on the characteristics of wake field and the propulsion performance are investigated varying the wave length. INTRODUCTION IMO(International Maritime Organization) has established the EEDI (Energy Efficiency Design Index) standard in 2013 and has been strengthening regulations on air pollutants that lower the pollutant emission standards such as SOx in ship fuel from 2020. As such regulations have been strengthened, there has been an increased interest in improving the operational efficiency of ships for fuel saving. As a result, studies on the performance of ships in waves similar to actual marine environments have been concentrated. Previous studies on resistance and propulsion performance of ships in waves have been performed mainly in terms of added resistance. However, the EEDI formula for improving the operational efficiency of a ship includes weather factors( f w ). The weather factor is determined by propeller propulsion performance as well as added resistance (Jung et al., 2017). Therefore, it is essential to analyze the flow phenomenon on the propeller plane in terms of propulsion performance for a successful prediction of the speed performance of a ship operating in waves. In case of ship operating in waves, the variation of dynamic position of the ship by vertical motion is predicted and, especially, the propeller submerged depth changes according to the behavior of the stern part. According to the change of the propeller submergence depth, the interaction between the propeller and free surface can causes some risks, such as air ventilation and surface piercing running (Paik, 2017). Therefore, it is necessary to clarify the flow phenomenon on propeller plane considering the vertical motion of the ship in order that analyze accurately the propulsion performance of the ship.

Abstract In an analysis of floating body's motion for ocean engineering, potential theory is known as a conservative method. However, This holds that viscous effects are neglected, which can deliver serious problems when predicting vessel's roll motions as well as complicated configurations such as the structures with moon pool, side-by-side moored vessels, and semi-submersible with deep draft need to be evaluated by more accurate methods other than potential theory in order to overcome inaccurate solutions which can be occurred by viscous effects. In this study, CFD simulation for a single vessel is performed as an initial study for motion analysis of side by side vessels. Introduction In this study, we performed a FVM numerical analysis with respect to a six-degree of freedom motion of a floating body by solving the non-steady state Navier-Stokes equation. For this, we employed the open source codes, OpenFOAM C++ libraries. Taking advantages of viscous damping and vortex shedding, three-dimensional numerical simulations for 6 DOF motions of a single vessel are carried out. Two wave directions, head sea and beam sea, are considered for the simulation with external linear stiffness to prevent drift away of the vessel. The results from developed analysis method were compared with linear potential theory and model test results for validation. Numerical Method Coordinate systems Euler's angle is generally used to describe the dynamic behavior of a solid body. The Euler's angle with a single rotational axis shows a "gimbal lock" where two axes are overlapped to be viewed as one single axis, and thus the rotation of two axes appears as the same rotation. In this study, to prevent gimbal lock and to avoid the effect of the order of the coordinate system rotation, quaternion was used as a technique of expressing the coordinate systems.

Abstract The numerical investigation of the passive hydrodynamic performance of the manta ray beneath the water surface is presented. The main aim is to investigate the effect of attack angle on hydrodynamic forces of the manta ray near the water's surface. Three dimensional incompressible Navier-Stokes equations are resolved with RNG k-e turbulence closure model. The undulation of the free surface is captured by the volume of fluid (VOF) method. Numerical simulations are carried out with the manta ray oriented with the longitudinal axis at attack angles of -5, -2.5, 0, +2.5 and +5 degrees with various swimming speeds ranging from 0.5m/s to 4.5m/s. The drag coefficient and the lift coefficient of the manta ray are measured and compared. Results show obvious differences between negative and positive angles of attack. Additionally, the deformation of the free surface induced by the gliding manta ray is also captured and compared.

Abstract A finite element model for the pore pressure responses under the action of combined waves and current is proposed and verified with the existing experimental data. In this numerical model, both transient and residual pore pressure responses are simulated simultaneously. The numerical results indicate that the transient pore pressure is dominant in the upper part of the seabed while the residual component prevails in the lower one. Parametric studies are conducted to investigate the effects of the current velocity, the wave steepness, and the soil permeability on the pore pressure responses. Imposing a following or opposing current upon waves has much effect on pore pressure distributions in the porous seabed.

ABSTRACT: Results of measuring the relative brine content ( Ql) in the liquid phase of frozen sea water (SW) at temperatures between -2oC and -43oC with variable rate and direction of temperature change and with the use of various pulsed and steady-state NMR methods are presented and compared with analogous known literature data. Hysteresis loops corresponding to the crystallization range of SW salts, mainly NaCl, which partially precipitates as the crystalline hydrate NaCl.2H2O at temperatures below -23oC, are detected on the temperature dependence of Ql in brine. The main causes of hysteresis are indicated. Brine salinity in pores ( S) is calculated from the results of determining Ql and agrees well with current literature data in a wide temperatures range. Empirical equations for determination mass of brine are given. INTRODUCTION Knowledge about brine content in sea ice pores and its brine composition under various conditions of sea water freezing are important for understanding the formation of the physicochemical properties of sea ice. The volumes of sea ice brine and ice porosity determine heat exchange processes between sea water and atmosphere via the ice surface, particularly at the polar caps. These processes to a considerable extent determine our planet" s climate. There have been many studies (e.g., Ringer, 1906; Gitterman, 1937; Nelson and Thompson, 1954; Thompson and Nelson, 1956; Assur, 1958; Blinov, 1965; Richardson and Keller, 1966; Nazintsev and Nazintseva, 1972; Doronin and Kheisin, 1975; Tzurikov, 1976; Richardson, 1976; Cox and Weeks, 1983; Franks, 1985; Bogorodskiy and Gavrilo, 1988; Cho et al., 2002; Maus, 2007), as well as many other publications. Brine properties near eutectic points have been insufficiently studied, even for binary systems (salt and water), to say nothing of such a complex natural object as sea water. The mechanical strength of sea ice depends on brine salinity and ice porosity (Assur, 1958).

ABSTRACT: New results of numerical hydrodynamic analysis of the novel offshore cross-flow vertical axis wind turbine with large floating rotor (WEMU design) are presented. The research goals are to investigate a spatial movement of rotary pontoon in incoming regular and irregular waves as well as their influence upon the water ring. Waves are launched by two components of flow velocity and free surface elevation at inlet boundary. Irregular wave is presented according to Pierson - Moskowitz spectrum by sum of first order waves with random phases. Wave loads acting on the pontoon are predicted and hydrodynamic power loss due to waves is calculated. INTRODUCTION Offshore wind power engineering is among leaders in the renewable energy sector already for years. And potentially, after solving essential technological and economical problems, its leadership can become absolute. Offshore wind power plants have obvious advantages against located onshore. First, their ecological restrictions are softer; blade speed can be higher, and therefore, an increased efficiency is reachable offshore. Moreover, visual impact of distant offshore wind farms is diminished and territory cost is practically excluded. At the same time, modern offshore turbines inherited their design (propeller installed on tall tower) from onshore and differ only by support structures. So, wellknown drawbacks of propellers could not be excluded. We must indicate here the limited unit power capacity, infrasound emission, and harmful effects on birds and animals. Wind energy cost is still higher than that from conventional power plants. Technological problems quickly grow in large-scale turbines so some research (e.g., Klinger F. et al, 2002) has revealed that an efficient 10MW turbine could not be developed in the one-propeller concept. In this case, wind energy cost will remain relatively high. A technological breakthrough in offshore wind power engineering is still absolutely necessary.

ABSTRACT: Overtopping Wave Energy Convertor (OWEC) is an offshore wave energy convertor for collecting the overtopping waves and converting the water pressure head into electric power through the hydro turbines installed in the vertical duct which is fixed in the sea bed. The numerical wave tank based on the commercial computational fluid dynamics code Fluent is established for the corresponding analysis. The Reynolds Averaged Navier-Stokes and two-phase VOF model are utilized to generate the 2D numerical linear propagating waves, which has been validated by the overtopping experiment results. Several incident wave conditions and shape parameters of the overtopping device are calculated. The straight line type and parabolic type of the sloping arm are compared in the optimal designing investigation of the overtopping characteristics and discharge for OWEC device. The numerical results demonstrate that the parabolic sloping arm is available for wave running up and the overtopping discharge increasing. INTRODUCTION Among various ocean renewable resources, wave energy is most abundantly available and applicable in most coastal and offshore areas. Due to the advantages of simple converting techniques and producing cost over other types of ocean energy, the wave energy conversion system is feasible to be established for the commercial power production. Plenty of wave energy absorption devices and plants have been invented, and several of them have been utilized in the electricity generation. Recently, the oscillating water column type has been widely employed in the application for the wave energy conversion. The disadvantage of this type is the low wave energy converting efficiency. Overtopping Wave Energy Convertor (OWEC) has the sloping walls and reservoirs to lift water waves to the levels above the average surrounding ocean. The released reservoir water is used to drive hydro turbines or other converting devices.

ABSTRACT: A simplified 3D dynamic model of tracked vehicle crawling on cohesive soft soil is investigated. The vehicle is assumed as rigid body with 6-dof. Cohesive soft soil is modeled through relations: pressure to sinkage, shear displacement to shear stress, and shear to dynamic sinkage. Equations of motion of vehicle are derived with respect to the body-fixed coordinates. In order to investigate 3D transient dynamics of tracked vehicle, Newmark's method is employed by means of incremental-iterative algorithm. 3D dynamic simulations are conducted for a tracked vehicle model and steering performance is investigated. INTRODUCTION Tracked vehicles find their marine applications, for instances, to underwater trenches, cable or/and pipe burying systems, dredges and support of researches, and military purposes (e.g. Ivanov and Karev 1990). Herrmann (1978) proposed a lightweight tracked vehicle together with Archimedean screw for a deep ocean running gear module. Muro (1983, 1988) studied on the trafficability of tracked vehicle on very soft bottom. Hong and Choi (2001) experimentally investigated grouser shape effects on trafficability of extremely soft seabed. In order to investigate the performance of tracked vehicles, a number of studies have been carried out since Bekker's pioneering study (1956). For soft ground, the interactions between track, road wheels and soil become so complex that the basic theory on pressure-sinkage and sheartraction force is restricted in its application. Wong et al. (1984) developed an analytical method for predicting the normal pressure distribution under a moving tracked vehicle, taking into account the response of the terrain to repetitive shear loading. Kitano and Kuma (1977) developed an analytical method for investigation of the steerability of tracked vehicles in time domain. They used the ground pressures at the road wheels to calculate the traction force of tracks in form of Coulomb friction, and assumed the motion of vehicle is planar.

ABSTRACT: A formulation for calculating the steady hydrodynamic loading on a slender ship moving at a constant forward speed and small attack angle in finite water depth is developed. The study is motivated by the need to predict the manoeuvrability of ship with large draft in relatively shallow water. The slender body assumption is used to reduce the problem into a series of two-dimensional boundary value problems that are solved using the boundary element method. The fully non-linear free water surface conditions are imposed on the instantaneous water level. The numerical calculations are performed for the Wigley hull model ship. Effects of the attack angle and finite depth are assessed in the subcritical region. INTRODUCTION Predictions of ship manoeuvrability have drawn recent attention after the introduction of the IMO interim standards on ship manoeuvrability in 1993. The ship manoeuvrability prediction requires amongst other things, knowledge of the ship resistance and propulsion characteristics. Part of the resistance arises from the hydrodynamic forces acting on the ship body moving at a constant speed in calm seas. The hydrodynamic force computation is further complicated in that the problem is non-linear due to the non-linear boundary conditions at the unknown free water surface. The computation of ship hydrodynamics had received very significant attention in the past. Maruo and Song (1990) had developed a boundary element solution for a slender ship based on Green's functions in three-dimensions and using the Kelvin sources which satisfied the linearized free surface conditions exactly. Results were presented for the cases of a Wigley hull, a sailing yacht hull and a Series 60 C B = 0.60 hull, with good agreement with existing experimental data. They found that the non-linearity had an insignificant effect on the water surface elevation alongside the ship hull but significantly affected wave resistance.

ABSTRACT: The dynamic characteristics involved in the loading process in the ocean environment are complicated and difficult for exact evaluation of the response of offshore structures From the engineering point of view, it is Important to obtain reasonably reliable results by means of simplified descriptions of the complex problems. This paper investigates the effects of those simplified descriptions on the dynamic response evaluations of offshore structures Parametric studies based on the perturbation method are presented to assess the influence of uncertainties associated with various assumptions and approximations. These uncertainties are represented by the inertha coefficient, the drag coefficient, the mean wave height and the shear wave velocity of the soil it is found that among -all the parameters considered in the present study, variations in the mean wave height provide the most significant contributions to the dynamic response it is suggested that in order to perform reliable design of offshore structures, it is important to clarify the uncertain parameter effects on the response evaluation. INTRODUCTION The environmental loads such as waves, winds and earthquakes acting on any offshore structure are dynamic and highly random in nature. On the other hand, the uncertainties in the properties of the material and in the characteristics of the foundation soil may also give use to some statistical variation in the eigen values and eigenvectors of the structure (Boyce, 1968) and consequently the dynamic response may be affected (Kareem and Sun, 1986). The analysis and design of offshore structures is an extremely complicated process and requires several assumptions and approximations. Empirical models such as the Monson equation for the wave force or the expressions for the wave energy such as the Bretschneider" s spectrum involve several coefficients which have to be determined by experiments or field observations and have to be extrapolated to a particular problem.