ABSTRACT In the field of aquaculture, gravity cages of various shapes and sizes are used. However, it may be difficult for farm designers to select the size and shape of the cage to be installed. In this study, resistance and dynamic behavior of a cage were investigated numerically in terms of currents and waves; a cage with an internal volume of 8000 m 3 was installed and divided into two, four, and eight cages. The three types of cage systems are described mathematically using a mass-spring model, and effects of the currents and waves were computed in the time domain. The numerical calculation results indicate that the resistance increased with flow rate in all cages, and internal volume reduction rate increased as well. Further, as the number of cages increased for all flow rates, total resistance increased. INTRODUCTION Recently, the importance of cage culture has piqued the interest of many researchers worldwide, and hence the transition from capture fisheries to culture fisheries. The cages used in fish culture are of various shapes and sizes. Whether a cage for aquaculture is on the coast, inland, or offshore, it is difficult for a farmer to choose a cage in terms of shape and size. Given the total volume of a cage, the number of cages to be divided must be determined appropriately. When the total production scale of the farm is determined, the total cage volume can be estimated considering the density of fish determined according to their species. The next question is how to determine the volume of one cage by dividing the total volume. This involves many cases. In this process, the biological characteristics of the species to be bred should also be considered along with the engineering and cost aspects including installation and maintenance. Studies on cages have been performed by analyzing the deformation of the shape of a cage lying in the fluid flow and analyzing the change in the internal volume and tension of the mooring line according to the waves and currents. (Huang et al., 2006, 2007; Lee et al., 2008a, 2015; Li et al., 2006, 2007, 2013). However, few cases have been reported where a cage composed of several cages is regarded as one system, and many cages are analyzed in terms of the overall system efficiency.

ABSTRACT In view of the problem that the number of meshes will be increased when the overset mesh method is used for the numerical calculation of the planing boat resistance, and additional errors will be introduced in the interpolation of the two sets of meshes, which will lead to the low calculation accuracy and efficiency, a mesh method of dynamic boundary realization -- the remesh method is introduced in this paper. First, CFD software STAR CCM+ is used to conduct numerical simulation of a model size planing boat with two mesh methods respectively. Through comparison of test results and uncertainty analysis, the numerical method is confirmed and verified. Then the remesh method is used to simulate the planing boat with different speeds. The comparison between the numerical calculation of model resistance and the experimental results shows that the method has better numerical accuracy. Lastly, that remesh method and overset mesh method are compared in the calculation precision and the calculation efficiency, and the calculation precision and calculation efficiency are both improved. INTRODUCTION Planing boat is a high-speed craft which depends on the hydrodynamic pressure generated by the hull to support most of the body mass. As its excellent resistance performance at high speed has been widely used, the research on its resistance performance has also become the focus of domestic and foreign scholars (Han et al., 2013). Azcueta et al. (2003, 2010) used commercial CFD software Comet and combined with the six-degree-of-freedom motion model to make a more in-depth study in the free motion simulation of planing boat. Caponnetto (2001, 2002) simulated the ambient flow field of the hard bilge planing boat and sought for the means to obtain the best resistance performance of the planing boat. Villa et al. (2009) studied the influence of wake plate and interceptor plate on hydrodynamic performance of planing boat with CD-Adapco software. Hongjian Cao (2008) made use of the software FLUENT to calculate and analyze the flow field characteristics of the steady flow around the planing boat during the hydrostatic direct navigation. Keqiang Chen et al. (2010) used FLUENT software to analyze the simplified model bottom pressure distribution of the planing boat, and improved the gliding surface form of planing boat. Wenju Jin et al. (2011) carried out a numerical analysis on the motion response of a two-dimensional simplified model of a planing boat in a uniform incoming flow using a hybrid mesh of structure and non-structure. Yumin Sun et al. (2012) proposed a 3D hydrodynamic numerical research method based on CFD technology for water splashing and multi-degree of freedom movement of planing boat. Wencai Dong et al. (2012) proposed a calculation method of planing boat resistance combined with RANS equation to solve the problems that the existing CFD method takes a long time to calculate the resistance of planing boat, the accuracy of the formula for estimating the resistance of planing boat is low and the scope of application is limited.

ABSTRACT Based on the Reynolds Averaged Navier-Stokes Equations (RANSE) and volume of fluid (VOF) methods of incompressible viscous fluid, the simulation of regular waves is realized under the computational fluid dynamics (CFD) software platform by instantaneously increasing the velocity of the fluid and the wave surface at the fixed wave boundary. Taking the KRISO Container Ship (KCS) as the research object, the numerical simulation study of the ship's resistance in the top wave was carried out. Compared with the model test results, the average error value was 4.10%, and the numerical forecast of the ship's wave increasing resistance in the sea condition of 4–7 was achieved. Based on the numerical simulation method, the irregular waves in the temporary guide of the minimum installed power are simulated, and the minimum installed power is 7967.9 kW through the resistance conversion and self-navigation numerical simulation. INTRODUCTION As global environmental problems get worse, how to reduce the impact of ship operations on the environment is the key to solving the problem. The international maritime organization (IMO) has put forward quantitative requirements on greenhouse gas emissions generated by ship operation and will gradually improve them. Therefore, the ship industry focuses on the research of ship optimization methods to improve the ship's performance. One of the most effective measures to reduce greenhouse gas emissions such as CO 2 is to reduce the main engine power and ship speed, but a smaller power of the main engine may cause the ship's speed loss and cannot maintain its maneuverability. For this reason, IMO has established the minimum propulsion power (IMO, 2013; Zhang, et al., 2016) and other relevant regulations to ensure the safety of the ship under the condition of meeting the ship's energy efficiency design index (EEDI), and the calculation of wave added resistance is the key to calculate the minimum propulsive power.

ABSTRACT It is effective to utilize the closing effect at a bay mouth as protection against large storm surges. However, ships frequently pass thorough the bay mouth. Therefore, it is desirable to install a movable breakwater(Fig. 1). Currently, there are two types of movable breakwaters: Vertical Telescopic Breakwater (hereinafter, this is called "VTB") and flap gate breakwater, each of which has small gaps. Few studies have been conducted on the protection performance against storm surge due to VTB(Arikawa et al.,2007). This study investigates the effect of VTB and systematizes its effect using sectional experiment and STOC (Tomita et al., 2016). INTRODUCTION A VTB contains multiple steel pipes. To evaluate the protection performance of the VTB, it is necessary to obtain an accurate measurement of the velocity through the gap. In numerical calculations, the velocity between the gap greatly depends on the viscosity coefficient. Therefore, we study the appropriate viscosity coefficient by comparing the results of the experiment and the numerical calculation and confirm the calculation method. Moreover, we conduct a parameter study of the VTB, by using a waterway model, and the pseudo ports for evaluating the protection performance against a storm surge by using STOC-ML. This study evaluated the effects of a VTB against storm surges. SECTIONAL EXPERIMENT Method of Experiment This experiment used a sectional waterway of 10 m in length, 2.0 m in height, and 1.1 m in length (Fig. 2). Identical flow rates are set in and out, and it was used as a reflux water tank. We made the water flow from 1m 3 /min ∼ about 8m 3 /min. A vinyl chloride pipe with a diameter of 216mm was installed as a model of VTB. A wave gauge meter is placed like Fig. 2. Some of the case has Anti-rotation material. Anti-rotation material is a protuberance that prevents the steel pipe from rotating (Fig. 3). The calculation cases are shown in Table 1∼2.

ABSTRACT In this study, numerical simulations were proposed to predict the wave slamming forces on the subsea equipment bottom panels in the splash zone during installation using the explicit formulation dynamic analysis finite element (LS-DYNA). This approach adopted ALE algorithm to simulate and analyze three-dimensional panels under constant velocity lowering through the splash zone, the penalty function algorithm was applied to realize the simulation of the fluid-structure interaction (FSI) process. A novel method of numerical wave generation by dynamic boundary was applied to simulate the splash zone, the numerical wave tank based on the Keywords of LS-DYNA were developed. The focus lies on effect of wave slamming forces on the panels, the conditions of lowering velocity, mass and stiffness were discussed. INTRODUCTION As the human demand of subsea oil resources increases around the world, and the rapid development of subsea technology, so the development of subsea oil resources has moved from shallow sea to deep sea or even ultra deep sea at present. Subsea production system was used to develop subsea oil resources which can avoid the construction of expensive offshore platforms, save a lot of investments, and the subsea production system is less affected by the harsh weather, has significant reliability, so the subsea production system has become an important model of the exploitation for subsea oil resources. The installation of subsea equipment is the critical step for developing subsea production system, the facilities of subsea production system include subsea manifold, subsea tree, PLET, suction pile, pump station and so on, the bottom of these subsea structure and equipment are mainly flat structure. There are four main phases for a typical deep water installation operation, which are lift-off from the deck of a transport barge, lowering through the splash zone, deep water lowering and lifting operations, and touch down the seabed and retrieval Wang et al. (2018). An impulsive wave slamming forces occurs in the second phase, and the slamming forces from wave is concentrated on the bottom panels of subsea equipment. Not only the wave will produce strong slamming forces on structure, but also the movement and deformation of the structure will have a significant effect on the flow field during through the splash zone, therefore, there is a violent fluid-structure interaction between structure and flow field.

ABSTRACT When towing the immersed tube element in water, the calculation of the water resistance coefficient is important. However, the variation range of the water resistance coefficient is relatively large, which makes the traditional physical model test difficult and expensive. In the present study, the water resistance coefficient of a large immersed tube element is determined by solving the Reynolds-averaged Navier-Stokes equation (RANS method). The water resistance coefficients of the tube elements are calculated at different towing speed and water depth. The comparison between numerical results and the results based on model tests proves the adopted numerical method is accurate and reliable. Therefore, the calculation method can be used to determine the water resistance coefficient of similar immersed tube elements in similar projects, and provide further guidance for the towing of the tube elements. INTRODUCTION The offshore construction of prefabricated components has adopted from gravity caisson and sea-crossing bridge to huge ocean platform, offshore floating structure and large immersed tube tunnel, etc. The difficulty and risk of construction are also increasing with the extension of human activities to the sea. As prefabricated parts develop in a larger scale and the construction area goes further away from the shore, both construction problems and technical problems become more and more complicated. One of the challenges is to determine the towing resistance of large prefabricated parts during marine towing. The distance between the prefabricated dry dock and actual tunnel construction site may vary from several hundred meters to hundreds of kilometers, and in most cases, water transportation is needed. Immersed tube elements are mostly deep-drawing bluff structures with a small freeboard, and the floating transportation speed of immersed tube element is quite short, resulting in poor maneuverability and difficult control. The stress of a box-shaped reinforced concrete immersed tube element is essentially the viscous flow of a bluff body in a restricted area. The flow around the object in infinite-field can only be calculated satisfactorily at a low Reynolds number, however, immersed tube tunnel involves not only the bluff body, but also a large Reynolds number., Moreover, it is influenced by restriction boundary and free surface. Hence, hydrodynamic model test serves as an essential approach to the research into stress and stability in the process of tube element floating transportation.

ABSTRACT This paper studied the hydrodynamic interaction of a semi-submersible type multi-modular very large floating structure (VLFS) in the frequency domain. To clarify the influence of multiple modules, the comparisons between numerical data and model tests results were performed by utilizing panel method. In consideration of the unrealistic wave elevations due to the ignore of the fluid viscosity and energy dissipation in potential flow theory, a modification called damping-lid method was adopted through introducing a damping term into the momentum equation and the free surface condition. The results demonstrated that the hydrodynamic interactions of multi-module system are important for precisely evaluating the motions of VLFS modules in a narrow gap. The connector and mooring system shows a significant impact on the RAOs of roll and yaw motions. Sensitivity analyses were carried out to figure out the dependency of the wave elevation on damping terms. INTRODUCTION The occurrence of the hydrodynamic interactions can be easily found in nowadays offshore and coastal engineering such as the Floating Liquefied Natural Gas (FLNG) and Liquefied Natural Gas Carrier (FLNC) side-by-side transfer operation, float-over operation and the modular very large floating structure (VLFS). Numerous multi-body interaction problems have been investigated for several decades. Ohkusu (1974) first investigated the hydrodynamic influence between two vessels by twodimensional (2D) strip theory. Van Oortmerssen (1979) further investigated the two-body problems based on three-dimensional (3D) linear diffraction theory. Miao et al. (2000, 2001) adopted a potential-flow model and a boundary-integral method to investigate the influence of gaps on wave forces on fixed caissons and found that the resonant-wave forces on each caisson are ten times larger than an isolated caissons. Hong et al. (2005) numerically and experimentally investigate the interaction characteristics of side-by-side moored FLNG and LNGC. Xu et al. (2014) investigated the hydrodynamics interactions of side-by-side moored three barges in float-over operation, and the reliability of their numerical algorithm was validated against model tests.

ABSTRACT In this paper, flow patterns in a circular rearing tank with three different aeration rates are investigated by gas and liquid phase flow simulations. The results of the numerical calculation in this paper are approximated in agreement with the vortex center position which is measured from the visualization experiment. It was confirmed from the vorticity distribution diagram that the strength of the large vortex expands when the aeration volume increases. In addition, we reported the results of evaluating the flow field in the horizontal section near the free surface and the bottom by numerical calculation. INTRODUCTION In recent years, due to overfishing, changes in the natural environment and natural disasters, the catch of Japanese fishes and shellfishes is decreasing year by year. Also it shifted from fishing to fishery cultivation. Generally, fish after hatching from eggs is called larvae. There are cases where massive deaths occur during the periods of larvae development. This is called initial depletion. The key to whether seedling production is successful or not is how to suppress the initial developmental life cycle of a fish. Although there are many factors on the initial depletion, hence Munakata et al (2013) pointed out the influence of water flow on initial depletion, and the problem is almost untouched. Apparently, during the seedling production, the amount of air (bubbles) that generates water flow is adjusted by experience and intuition, such as sound and visual observation. If there is even a mistake in setting the ventilation, there is a possibility of causing massive death of larvae in reference Shiotani et al (2005 a) and Sakakura et al (2007). Therefore, it is necessary to clarify the relationship between flow rates as basic information. As a related study, Sakakura et al (2007) showed that there was an optimum aeration volume that maximized the survival rate of larvae by carrying out the breeding experiment and velocity measurement of them in a circular tank. However, since the measurement method is a type of speedometer that inserts a sensor in water, the sensor itself disturbs the flow and invites measurement errors. Next, Shiotani et al (2005a) carried out velocity measurement and numerical calculation of the flow field. Since the calculation treats the flow field as a single phase flow, its calculation and measurement results do not match. On the other hand, Sumida et al (2013). conducted visualization experiments and numerical calculations in a circular tank at aeration Q = 10 mL / min. Specifically, the flow field was numerically predicted using a one-pressure two-fluid model for example Takakuwa et al (2018) which is a typical numerical solution method of gas-liquid two-phase flow analysis. The calculated results agreed well with the visualization result, but the solution diverged at Q = 25 mL / min or more, so quantitative prediction could not be made. The reason for this is that the velocity difference (slip) between gas phase and liquid phase occurs as the aeration volume increases, and the solution diverges. For this reason, Sumida et al (2013) pointed out that numerical prediction of the flow in the circular aquarium for seedling production has not yet been established.

ABSTRACT Carbon Capture Storage method is expected to be counterpart for global warming but it holds also a risk of CO2 leaking in the sea. CO2 hydrate formation has the potential of solving the problem. The aim of this work is to build CO2 hydrate formation model based on previous studies. In order to determine hydrate growth rate, matching with temperature rise of experimental result, interface mobility parameter was decided. After several numerical calculations, the order of interface mobility parameter was identified. INTRODUCTION As one of the methods to suppress the global warming, Carbon Capture and Storage(CCS) attracts much attention over the world. CCS method is gathering CO2 gases from big emission source such as factory or thermal power plant and accumulating them under the seafloor. By the method, it can be expected to reduce the concentration of CO2 in the atmosphere. In the other hand, CCS method holds also the risk of CO2 defluxion in the sea. If stored CO2 leak into the sea, it may make impacts to ecological system in the sea and CO2 concentration in atmosphere. To prevent the CO2 defluxion from the seabed CO2 hydrate technology is taken into account. CO2 hydrate has cage structures that trap CO2 molecules in water molecules. Hydrate is stable under high temperature and low temperature condition. Though the areas in which CO2 is stored are unstable for hydrate structure, if accumulated CO2 gases arrived seafloor in which temperature become lowest, it makes hydrate structure. Then generated CO2 hydrates reduce the width of CO2 gases flow to the sea (Fig. 1). To estimate how much CO2 hydrate can block the CO2 gases flow, it is necessary to calculate change of permeability under the sea floor by the CO2 hydrate generation. As previous work, (Fukumoto 2013) used the Phase-Field Model (PFM), which simulates the growth of CH4 hydrate and calculated permeability change in porous media. The objective of this research is to develop a PFM for the growth of CO2 hydrate, based on the model of Fukumoto (2013) in order to evaluate how CO2 hydrate formation prevents the gas leakage.

ABSTRACT A simple method is developed to consider the energy loss (dissipation) in the sloshing flow in a liquid tank by adding "artificial damping" in a potential flow model to better predict the sloshing effects (force/moment) on the tank near the resonance. The consistency of the mechanism of the way the "artificial damping" is introduced to the potential flow model is discussed. The rate of the energy loss (or energy absorption from the flow) is reflected by the damping coefficients. The damping coefficient will primarily be determined by comparing the numerical results to the measurement of physical tests at resonance frequency. The sensitivity of the damping coefficients to the other excitation frequency will also be examined. INTRODUCTION For a liquid cargo ship (or vessel) with large liquid tanks, the internal liquid motion in the liquid tanks can have a very significant effect on the load on the tanks and thus affecting the motions of the ship. In the design of the ship, especially at the early stage of the design, it is important to properly consider the effects of the internal liquid motion in order to achieve good vessel motion performance. A liquid tank can be fully-filled or partially-filled. The treatments of the effect of a fully-filled tank and that of a partially-filled tank are quite different. The flow in the fully-filled tank is relatively simple (no free surface presented). Conventionally, in the design practice for liquid cargo ships, the liquid in the fully-filled tank is treated as a solid matter, as part of the rigid ship structure and the effect of the liquid is included through the inertia of the corresponding "solid liquid". The main advantage of this treatment is its simplicity. However, recent studies have shown that this simple treatment may result in a significant error when the tank is located close to the rotation axes of the ship motion, (Cao & Zhang 2012, 2014, 201 7). In their studies, Cao & Zhang solve for the liquid flow in a rotating tank using a Navier-Stokes equations solver (the CFD module in COMSOL Multiphysics 201 6), a general FEM program commercially available, in a coordinate system fixed to the tank. The use of the tank fixed coordinate system makes the computational domain time-invariant and significantly simplifies the computational complexity and keeps the computational effect and time to a level of practical applications. The studies have shown that the inertial effect of the liquid dominates. The viscous effect of the fluid to the load on the tank is minimal although the viscous effect is needed in order to solve the flow problem (note: neither the ideal flow model governed by the Euler equation nor the potential flow model governed by the Laplace equation would give a meaningful solution). The studies also showed that the inertial effects of the liquid motion, in many situations, may be expressed as a fraction of the corresponding inertia of the "solid liquid". The ratio (so-called equivalent moment of inertia ratio ε ) does not depend on the tank's motion (amplitude and frequency). It only depends on the modes of the tank motion, the tank geometric shape, the distance between the rotation center/axes and the tank axes. The beauty of the equivalent moment of inertia ratio is that it, for a particular tank geometry, can be calculated before-hand and stored for the 6 motion modes and various values of the distance between the rotation center and the tank axes. The stored data can be used to account for the effect of the liquid motion (the inertia) in the tank on the ship's motion in the ship design and performance prediction in a same way as the ship with only solid matters is treated.

ABSTRACT The aim of this paper is first to present an application of Anti-Roll Tanks (ARTs) for a barge shaped ship and the subsequent roll mitigation brought by these ARTs. The roll mitigation due to ARTs is demonstrated through experimental tests and numerical calculations. These numerical calculations are based on a coupling between Computational Fluid Dynamics calculations (CFD) to predict the flow within ARTs and a linear seakeeping program for the ship's external flow. Two different coupled potential CFD approaches are presented: the first one considers forced roll motions for ARTs and the second one considers sway and forced motions. INTRODUCTION The excessive motions and accelerations induced by the large rolling of the ship may lead to operability issues. To mitigate these roll motions, devices such as bilge keels and stabilizer fins are developed. However, these devices are effective for large roll velocities (bilge keels), or forward speed (stabilizer fins), leaving room for improvements at low speeds and in case of small roll angles. Anti-Roll Tanks (ARTs) offer a solution to such problem. Only free surface ARTs are considered in this paper: U-tubes are not considered. Therefore, ARTs refer to free surface ARTs in the whole paper. The ARTs are passive devices relying on a traveling bore to provide a roll damping moment. This ART concept was first tested in the 19 th century (Watts, 1883). Later, extensive bench tests were carried out in order to provide reference datasets of ART response (van den Bosch and Vugts, 1966, Lee & Vassalos, 1996). These experiments showed that the ART response is the largest for the smallest excitation (nonlinear behavior of ART). Thus, an ART offers the most damping at low roll amplitudes. Also, it is to be noted that ART response is not affected by ship's forward speed. So, in order to predict accurately ART response, the numerical tool is to be able to take into account these non-linearities.

ABSTRACT The Fiber Optical Micro- Cable (FOMC) provides much facility for the operation of the deepsea Autonomous Remotely Vehicle (ARV). It avoids the expensive umbilical cable and the heavy winch which are necessary for the conventional Remotely Operated Vehicle (ROV). Due to the small diameter and low weight of FOMC, the deepsea ARV can get a large range of motion and much high maneuverability. However, the fiber optical micro-cable deployed in the deepsea ARV system is very long (>5000m), and is fragile to be broken by the current and the ARV motion. In that case, the underwater vehicle will miss communication with the supporting system on the mother ship, and lose in the ocean. To avoid this kind of disaster, the safety of the underwater fiber optical micro-cable should be analyzed before the underwater operation. The motion of the fiber optical micro-cable is simulated by a numerical calculation method. The shapes and tensions of the micro-cable are shown. A lot of practical conclusions are drawn. The dangerous cases for the ultra-long fiber optical micro-cable are highlighted to be avoided in the operations. INTRODUCTION The FOMC has been widely used in a real-time control of underwater vehicle system. FOMC is a combination of an optical fiber for communicating and surrounding materials for providing tensile strength. Due to its small diameter, rapid signal transmission and good signal stability, FOMC is increasingly applied to the communication between supporting ship and underwater vehicles. Compared with traditional heavy cable, the advantages of using FOMC as a connection are as follows: reducing the requirements for the winch and the supporting ship in surface; enlarging the range of underwater vehicle motion and improving the maneuverability due to its low water resistance; increasing the speed of signal transmission; lowering the cost of underwater vehicle system. Aoki et al. (1999) verified that the "UROV7K" system developed by JAMSTEC enables high-speed communication with supporting vessels with light cable of diameter less than 1 mm, with the operators onboard operating the submersible vehicle through video. Similarly, Webster and Bowen (2003) demonstrated the feasibility of deploying a FOMC of 0.8 mm diameter in a real-time remote control solution of a hybrid remotely operated vehicle (HROV), which is a new type of underwater vehicle, and can be used both as a conventional ROV by connecting cable and as an untethered Autonomous Underwater Vehicle (AUV). By conducting a series of field tests, Young et al. (2006) validated the feasibility and utility of using a buffered fiber as a connection in the ROV mode.

ABSTRACT Practical experience reveals that the physical and mechanical properties of the ice cover can strongly depend on various external factors with using traditional methods of increasing ice resistance. In this connection, the task of increasing the bearing capacity of ice by using alternative methods, for example, the introduction of reinforcing elements into the ice is becoming very relevant. The aim of the work was experimental and numerical study of stress-strain state of ice samples reinforced by surface reinforcing frame. The results of experiments on loading the samples were compared to the numerical results of calculations of ANSYS. INTRODUCTION In winter period in the case of absence of bridge structures or when the arrangement of ferry crossings is impossible the ice crossings arrange when the ice cover of required thickness is formed on the water barriers. If the thickness of the ice cover is not sufficient for the safe operation of the crossing, traditional methods of increasing of ice bearing capacity can be used, such as ice freezing from below, ice frosting from above, or ice strengthening with a wooden cover (Common house needs 218.010–1998). Practical experience reveals that the physical and mechanical properties of the ice cover, strengthened by these methods can strongly depend on various external factors (ambient temperature and presence of snow and wind when freezing). Ice, produced by the accelerated sprinkling method is often a firn mass capable of adhering to the wheels of vehicles and breaking away from the natural ice. This method is effective only for the ice cover of a certain thicknesses, and it increases the probability of formation of deep cracks in the ice. In this connection, the task of increasing the bearing capacity of ice by using alternative methods, for example, the introduction of reinforcing elements into the ice is becoming very relevant. Yakimenko (2015) describes experimental studies on the "surface reinforcement" of ice crossings by geosynthetic materials. Surface reinforcement by freezing the steel meshes was proposed by Nikitin (2015). A number of solutions are known in which steel elements are frozen to increase the bearing capacity in the ice cover (Kostenko, 2005; Kozin, 2003; Kozin, 2011; Kozin, 2012). The method of surface reinforcement by introducing the welded steel frames into the relatively thin ice cover of 0.3–0.4 m thick can actually be sufficiently promising.

ABSTRACT In ice milling condition, the ice-class propeller will suffer extreme ice loads, which pose a threat to the safe operation of propeller. By using ANSYS/LS-DYNA, this paper introduces a numerical method to predict ice contact dynamic loads and propeller strength. In the simulation of a certain operational condition, the characteristics of ice failure processes, dynamic loads, blade stress, and the deformation of the propeller are analyzed. The effects of depth of cut on the numerical results are studied. The results show that the stress of the propeller is great in ice milling condition and mainly concentrates in the leading edges of propeller tip. INTRODUCTION With the development of Arctic sea Route and exploitation of polar resource, the number of ice-going ship continues to increase. The propeller, as vital components for ice-going ship, has a significant effect on the vessel's safety navigation. When ice-going ships navigate in ice covered waters, the submerged piece or pieces of ice may approach and contact the propeller. In this process, the propeller blades will suffer extreme loads. Ice load and hydrodynamic load are two main loads to the propeller during the interaction among ice, propeller and water, which will cause the deformation and damage of propeller blades. Evaluation of propeller strength plays a crucial role to the design and safe operation of ice-class propellers. The study of propeller strength in this condition shows its importance to the design of ice class propeller. The characteristics of propeller dynamic forces have been reported. However, certain mechanisms are not fully understood and are still under discussion. In most cases, the researches (i.e. Searle et al., 1999; Moores, 2002; Wang et al., 2005) of propeller-ice contact problem are based on experimental measurements. Due to the technical difficulties, experimental measurements can only be done in certain condition, and detailed description of the load distribution is not available. For the complexity of propeller-ice interaction, numerical simulations have historically been based on some empirical interaction models(i.e. Kotras et al.,1985; Veitch, 1995; Jones et al., 1997; Soininen, 1998) without much consideration of detailed ice mechanics, so their applications are limited to specific conditions. Numerical simulation is nonetheless an effective method. With the development of computer technology and numerical techniques, Finite Element Method (FEM) has been used to model the propeller-ice interaction by scholars. Lee (2007) discussed some concerns on general practice on ice propeller strength assessment according to IACS URI3 Rule by using FEM. Based on FEM, Vroegrijk et al. (2014) proposed a new material model to describing the orthotropic rate-dependent properties of sea ice, focusing on propeller-ice interaction.

ABSTRACT The propeller is one of main vibration sources and cabin noise of a ship. This study utilized numerical simulation of CFD to analyze the characteristics of pressure fluctuation induced by propeller of a new generation of river-to-sea ship beyond rules. The pressure fluctuation in the area of D × D above propeller and the effects of ship speed and propeller rotational speed are calculated and analyzed. The results show that maximum pressure fluctuation in the direction of length is in front of propeller approximately 0.1D and the magnitude is determined by amplitude of blade frequency. Centered on propeller, the amplitude in front of propeller is greater than that behind propeller and the amplitude on the outside of propeller is greater than that inside. It's also found that propeller rotational speed has a great influence on pressure fluctuation, and the effect of ship speed is small. This study provides a numerical computation method for pressure fluctuation induced by propeller of new generation of river-to-sea ship beyond rules, and has a great significance for the design of reducing vibration and noise. INTRODUCTION The vibration will not only affect the comfort, but also endanger the health of persons on board. At the same time, it will cause fatigue damage of local structures. It has an impact on safety of navigation and also will reduce the stealth performance of warships. The propeller is one of main vibration sources and cabin noise of ships. And, the pressure fluctuation induced by propeller also has an important effect on vibro-acoustic characteristics of ships. With the development of health consciousness and shipbuilding technology, people have higher requirements on acoustic and vibration comfort of ships under the precondition of safety and rapidity. Our country focuses on developing the Yangtze River economy and promoting the construction of a resource-saving and environment- friendly society, considering the current development situation of economy and environment. Therefore, the new generation of river-to- sea ship beyond rules plays an important role in the Yangtze River economy. The shape of this ship is wide and flat due to the need of function, and this ship is in the form of twin-propeller. On the one hand, the main engine is increasing continuously in order to improve the efficiency of transportation. And the propeller rotational speed is also increasing because of the limitation of stern form and draft. If the pressure fluctuation induced by propeller is not considered in the design stage, the acoustic and vibration comfort of this ship will be damaged seriously. At the same time, the calculation method of propeller pressure fluctuation for this specific ship is not yet available in all criteria. On the other hand, the large scale of river-to-sea ship is the developing direction of the Yangtze River transportation, and this river-to-sea ship is also moving in the high-speed and lightweight direction. So, it will avoid excessive vibration and cabin noise, and provide accurate excitation for cabin noise prediction, if we can predict the pressure fluctuation induced by propeller accurately at the design stage. Therefore, it is necessary to study the calculating method and research the characteristics of propeller pressure fluctuation. This has a great significance for the design of reducing vibration and noise of propeller. At the same time, it is very important to improve the acoustic and vibration comfort of the new generation of river-to-sea ship beyond rules.

Abstract Nowadays, comfort is becoming the principal goal for designers. But what does onboard comfort really mean? It is possible to define it as a sense of physical or psychological ease, often characterized as a lack of hardship, and it is therefore a subjective sensation. In fact, the perception of a comfort condition is due to a complex mechanism in which the different senses are involved and interact with each other. When trying to improve the comfort onboard, it should be considered that the interaction between the surrounding environment and the people on board is realized through the perception of stimuli related to hearing (noise), smell, breathing and transpiration (air quality and temperature), the sight (aspect of the environment), physical contact (vibration) and the sensation of movement of the body in space (ship motions). Until now, the most important Classification Societies impose severe rules and regulations only for the evaluation of noise and vibration maximum levels for different zones of the ship. Many other aspects that influence the comfort on board are currently under study. The incentive to provide the market with more comfortable products gave rise to high awareness for the analysis of sound transmission and absorption of the main materials used in shipbuilding. There are two driving parameters to describe the behavior of sound absorber materials: Transmission Loss (TL) and Insertion Loss (IL). In case of metals, with particular reference to steel, it is well known that the internal damping is very low. In contrast, there are so-called viscoelastic materials, which show high dissipation of mechanical energy. In this paper, a measurement campaign in real scale, carried out to investigate the dynamic behavior of different materials used to absorb vibration and sound propagating through steel decks, is described. During the tests, a comparison of velocity level measured under the naked metal plate obtained from experimental data and from finite element analyses has been carried out. Furthermore, the TL and IL values of the four different floor configurations obtained from experimental data are compared to understand which type of floor shows the best damping behavior. Introduction

Abstract This paper presents a numerical and experimental investigation of the water entry of a rigid flat plate. The experimental work was carried out in the Ocean Basin at Plymouth University's COAST laboratory. An in-house CFD code AMAZON-CW, which is based on a compressible multiphase flow model, was used to simulate the slamming problem. The impact loads on the structure recorded in experiments agree well with the numerical computations. A difference from the impact of sharp, wedge-type bodies, is that the slamming loads exerted on flat plates have pulsations due to the compressibility of fluids.

Abstract In recent years, great attention has been paid to the trimaran because of its great navigation performance. Its principal dimensions, hull lines, side hulls location and the allocation of volume displacement between the main hull and side hull have a significant impact on the trimaran performance. In this paper, the author has studied on the optimization design of trimaran side hull location based on the theory of viscosity with the minimum total resistance as the optimization objective, and obtained a scheme of the optimal resistance performance. Results indicate that the optimization method of trimaran side hulls location adopted in this paper is feasible, and this research can provide reference for trimaran hull form design.

ABSTRACT This study examined the flow fields in a rearing tank by numerical calculation. In this calculation, we modified the numerical calculation by Shiotani et al. (2005) by assuming that flow fields are two-phase flows, and changing the boundary conditions. We numerically calculated the flow fields in a cylindrical tank having different aspect ratios (AR, the ratio of water depth H to tank radius r i ). Flows were modeled with AR = 0.5, 1.0, and 2.0 and an aeration rate Q of 10 ml per minute. The model results were verified by comparison with flow visualization results.

ABSTRACT The spudcan foundation has been widely used in offshore engineering for jack-up rigs. However, "punch through" failure often occurs during marine operation in areas where a stronger soil layer overlays a softer soil layer. Punch-through analysis of jack-up rigs is required before conducting marine operation. The traditional analytical method as indicated in some regulations such as "SY/T6707-2008 Specification for marine well site survey" is the projected area method, which is based on theories by Hanna and Meyerhof. In this paper, a non-linear numerical calculation by the finite element software ABAQUS is performed to simulate the penetration of spudcan. The displacements caused by loading on the stronger soil layer are calculated, and a more accurate result is obtained by applying The projected area method. INTRODUCTION In consideration of mobility, jack-up rigs have been a popular choice in areas of shallow to medium water depth in offshore oil/gas exploration at present. Most jack-up units have three or four individual legs with a conical footing as its spudcan (LIU Jun, HU Yuxia, KONG Xianjing, 2005). However, "punch through" failure often occurs in jack-up rigs with the spudcan foundation where a stronger soil layer overlays a softer soil layer. After initial set down of the legs on the sea bed and loading on the legs, the spudcans will penetrate the soils until equilibrium is reached between the capacity of the soil and the forcing load. If a soft layer exists below a stronger layer such as granular soils, the profile of capacity with depth may reduce over a range of depth. The failure usually occurs in this case, with a sudden penetration within a short time —"punch through" failure (Health & Safety Executive, 2004).