Systematic engineering-geological studies are carrying out, as part of the exploration of polymetallic sulphides (PMS) in the Russian Exploration Area (REA) of PMS at the Mid-Atlantic Ridge (MAR). They are aimed on a comprehensive assessment of engineering-geological conditions of potential deposits of polymetallic sulphides for their exploration and possible future exploitation. In the process of research, the main specific engineering-geological features of the ore fields within the REA that affect the design specifications of the exploration and exploitation machinery were identified. Based on these results this paper discusses the prospects for deep-water equipment design and present experimental examples of the Russian deep-water machinery for PMS study and mining. INTRODUCTION Over the past years, the Russian Federation has been exploring polymetallic sulphides at the Mid-Atlantic Ridge (Cherkashev et al., 2018), basing on the contract with the International Seabed Authority (ISA) established in 2012. Besides such obligations as: PMS exploration, legal and financial provisions, the contract includes the articles by which the contractor has to develop deep-sea exploration and mining equipment and to test them in deep-sea conditions. Contract works at the REA are carried out using the Research Vessel (R/V) Professor Logachev (Fig. 1) belonging the "Polar Marine Geosurvey Expedition" (Saint-Petersburg, Russia). Until 2019, eighteen hydrothermal ore fields were discovered in the REA, which are potential targets for PMS exploitation. In parallel with the ore fields exploration, engineering-geological studies are being conducting (Kondratenko et al., 2017, Kondratenko et al., 2018), which results will determine the requirements for the development of deepwater machinery. The development of new technical facilities relevant to the exploration and further mining operations within the REA involves the analysis of geological structures; dissection of seafloor surface (seafloor roughness); gravitational instabilities; seismic activity and the physical-mechanical properties of the bottom formations. PURPOSE OF WORK The purpose of this work is to identify specific engineering-geological conditions of the PMS deposits within the Russian Exploration Area. Based on this, this study will define the prospects of deep-water exploration and exploitation machinery design adapted for work on the hydrothermal ore fields of PMS of the Mid-Atlantic Ridge.

In the near future, the Nankai Trough earthquake is expected to occur in Japan. It may not be received by the rescue and support from the land in the event of a disaster since the Kochi Prefecture is surrounded by steep mountains. Therefore, Kochi Prefecture has placed earthquakeproof berth, but we propose that fishing ports also be used as disaster prevention bases. In this study, we investigated the liquefaction countermeasures for fishing port quay using sheet piles. As a result, ①It finds out that the construction method using sheet piles is not enough for liquefaction countermeasures. ②The method using sandbags and permeable steel sheet piles confirmed the effect of suppressing liquefaction. INTRODUCTION The Pacific coast of Tohoku Earthquake on March 11, 2011 is the largest earthquake in the observation history around Japan, caused huge damage by tsunami and liquefaction. All port of Pacific side from Hachinohe Port in Aomori Prefecture to Kashima Port in Ibaraki Prefecture were damaged. Several damages such as settlement of structure and large faulting between the quay were seen in the damaged port. But fishing ports and harbors contributed greatly to recovery after the earthquake because the port function was quickly restored. The probability of the Nankai Trough Earthquake to occur within the next 30 years is estimated to be between seventy and eighty percent. When the Nankai Trough Earthquake occurs, there is a risk of damage to a wide area from Kyushu region to Tokai region. After the earthquake, Kochi prefecture may have difficulty receiving help such as transportation of supplies from the land route as it is surrounded by steep mountains. There are 88 fishing ports in Kochi Prefecture, part of the fishing port is considered to be at the time of the earthquake will be used as disaster prevention centers as well as the Tohoku region Pacific Ocean earthquake. Currently, seismic reinforcement and maintenance of several fishing ports, which are disaster prevention bases, are forwarding.

When an explosive explodes in water, a shockwave will generate at the outset and then a pulsating bubble. The shockwave has strong discontinuity and the bubble motion is a two phase problem. The period of shockwave for a charge exploding underwater is about O(1 ms) while that of the bubble is about O(1 s). The difference between these two processes brings difficulties to the relative simulations. The Discontinuous Galerkin (DG) method is popular as well as the Boundary Element Method (BEM) which is used to solve the shockwave propagation and the bubble motion separately and highly good results are obtained. But they do not have sufficient applications in the simulation of both shockwave and bubble motion up till now. In this work, we focus on the features of shockwave propagation and bubble pulsating features under different boundary conditions. Based on the Eulerian Finite Element Method (EFEM), the Eulerian equation is discretized. In addition, the charge denotation is simulated by JWL equation. Using this method, the whole process of the shockwave emission and bubble pulsation is studied. The numerical models are validated through both theoretical and numerical methods. Then the bubble pulsations near disparate boundary conditions, such as free surface and solid wall are simulated. It is found that there are two pressure peaks in one pressure curve in these conditions, the first one comes from the shockwave and the second one is from the reflection of the shockwave at the boundary. When the bubble is near the free surface, the bubble is repelled by the free surface and a downward jet is formed, which is contrary to the case when a bubble is near the solid wall. INTRODUCTION There has been a steady growth of interest in studying the bubble dynamics for the past few years owing to its wide applications in numerous aspects, such as underwater explosion (Meng et al., 2019; Ming et al., 2016; Chen and Yao, 2016), the medical and imaging enhancement (Constantin and Ronald, 2008; Lindner, 2004; Chen and Hwang, 2013), the ship and ocean engineering field (Graaf et al., 2014; Chen et al., 2008; Thompson, 2003) and so on. When a charge explodes underwater, both a shockwave and a bubble will be generated. According to the different time scales, the whole process of underwater explosion is segmented into the shockwave stage and bubble pulsation stage, which are usually investigated respectively. In the shockwave stage, the duration of the shockwave generated by the explosion is only at the millisecond order and it exhibits strong discontinuity and nonlinearity. In the vicinity of the free surface or structure, a cavitation region may occur under the combined effect of an incident shockwave and sparse wave. The DG method has been adopted to simulate the shockwave in recent years, because it can capture the discontinuities of flow field with high resolution. Cockburn and Shu (1989; 1998; 1989) solved the conservation equations using the DG method for exploring the algorithm efficiency and calculation accuracy, and also investigated the characteristics of the shockwave propagation in different media. However, there are still many technical problems using this method to study the bubble motions.

ABSTRACT The purpose of this study is to investigate the strength development of dredged marine clay stabilized with basic oxygen furnace (BOF) steel slag from early curing to later curing times using the shear wave velocity. The vane shear test (LVS), unconfined compression test (UCS) and bender element tests were performed with various conditions including the BOF slag contents and initial water contents to obtain the strength and shear wave velocity. The results of this study demonstrate that the strength and shear wave velocity could be classified into three zones: inactive zone, active zone and moderate zone. It concluded that the strength of BOF slag-treated dredged marine clay can be usefully monitored through the relationship between the strength and shear wave velocity. INTRODUCTION A large number amount of clayey soils has annually been dredged from the maintenance of navigation channels and seaports. Even though the recycle of dredged clay has been attempted in various fields (Yilmaz and Civelekoglu 2009); (Saride et al. 2013); (Kang et al. 2017a), it is very difficult to apply due to low strength, high water content and high compressibility without the binders. Hence, in the practical terms, the dredged clay could be reused with hardening by using stabilizers, such as cement and lime as filling and reclamation materials (Saride et al. 2013); Kang et al. 2017b). Meanwhile, basic oxygen furnace (BOF) steel slag is an industrial by-product generated from the steelmaking process. Since the slag has produced in the large quantities of over 10 million tons every year including blast furnace slag, electric arc furnace slag, and basic oxygen furnace slag, its effective utilization is major issues in the steel industry (YANG 2015). Some researchers found that the BOF slag can be used as an alternative binder instead of cement and lime when a low strength such as the filling and reclamation materials in the construction field is required (Poh et al. 2006; (Weerakoon et al. 2018). In Japan, the dredged marine clay stabilized with BOF slag has been used as landfill and filling materials or submerged breakwater at the marine environment (Weerakoon et al. 2018). In spite of the use to various fields, there are few studies on the monitoring of the strength development of BOF slag-stabilized marine clay with respect to various curing times immediately after mixing. Non-destructive test is a wide group of analysis techniques, two of those are using the wave and electricity. Several researchers have been using this technique to indirectly predict the engineering properties of construction material such as concrete, soil, stabilized soil (Lee and Santamarina 2005); (Kang et al. 2017a); (Lim et al. 2017).

ABSTRACT The comprehension of the energy balance between the wind input, dissipation is still partially empirical. In this context, new field observations are still revealing important information about the sea surface dynamics. Wave breaking is the main source of wave energy dissipation on a global scale, however, the phenomena is still misunderstood. To extend the range of the breaking observation to storm conditions, an oceanographic campaign was carried on a location highly exposed to extreme sea states. The measurements acquired revealed important aspects of the sea surface under storm conditions and provided a unique dataset to explore the sea surface. INTRODUCTION Ocean wind waves take their energy from the wind. This energy can then be redistributed in the wave spectrum because of the non-linear wave-wave interactions, dissipated by wave breaking and/or propagated with wave groups. The observed sea state results from all these phenomena that occur simultaneously. As a result, the comprehension of the energy balance between the wind input, dissipation and nonlinear wave transformations is still partially empirical and not properly solved yet. In this context, new field observations are still revealing important information about the sea surface dynamics (e.g. Melville and Matusov, 2002; Campbell et al., --- Rascle et al., 2014). The breaking of surface gravity waves is the main source of wave energy dissipation. It also plays an important role in air-sea interactions and contributes to the upper ocean mixing layer (Melville 1996, Agrawal et al. 1992). However, wave breaking measurements still primarily originate from few field observations (e.g., Melville and Matusov, 2002; Mironov and Dulov, 2008; Romero et al., 2012; Thomson et al., 2012; Leckler, 2013; Sutherland and Melville, 2013, 2015; Guimaraes, 2018). Moreover, due to the difficulties of deployment and recovery of the instruments, breaking has been poorly observed during extreme conditions. Observations of breaking during extreme events are needed not only for a better understanding of the phenomenon itself, but also of the framework of the marine renewable energies for dimensioning purposes.

ABSTRACT In this study, a 1-g large-scale shake table test was conducted to investigate the dynamic characteristics of a suction bucket foundation system. A scaled model of a suction bucket wind turbine that simulates a prototype 3.45 Megawatt (MW) offshore counterpart was manufactured and installed in a saturated dense sand stratum. A laminar soil container was employed, with a strong earthquake motion as the input excitation. Excess pore pressure and acceleration response of the soil model were measured. In addition, accelerations and displacements at different locations along the wind turbine tower were recorded. Soil acceleration and excess pore pressure records below the bucket foundation and in the free field indicated similar response characteristics. During the test, no significant increase in pore pressure was observed. The dominant frequency of the input excitation was maintained along the soil model as well as the lower part of the wind turbine tower. A lower frequency component was dominant in the acceleration response at the tower top, reflecting reduction of the natural frequency of the turbine tower induced by soil-structure interaction (SSI). Significant instantaneous tower rotations were observed during shaking. However, permanent rotation at the end of the shaking was much less. The test results allow for calibration of SSI computational tools that can be used to conduct parametric studies of full-scale response scenarios. INTRODUCTION Suction bucket foundation is a relatively new type of support system for offshore structures, currently in use over the past 30 years. The suction concept was introduced initially in the form of anchors, mainly in clays, and thereafter as foundation for offshore platforms (Houlsby et al. 2005). Typically, this foundation includes a hollow cylindrical shaped structure that is closed from the top by a flat lid and open from the bottom. Inside, it can have compartments in a honey-comb shape for instance (Figure 1). Recent research showed that suction bucket foundation has emerged as a more affordable alternative that has been used for offshore wind turbines (Houlsby and Byrne 2000; Achmus et al. 2013; Foglia and Ibsen 2014a; Wang et al. 2018).

ABSTRACT In this paper, a new prediction and evaluation method for shallow gas pressure in deep water was described. The innovation of this method lies in the establishment of the multivariate function relationship between acoustic velocity and shallow gas pressure and formation porosity, so that the risk degree of shallow gas geological disaster can be predicted more accurately in the actual prediction. INTRODUCTION Shallow gas refers to small gas reservoirs gathered within 1000m below the mudline. Shallow gas sometimes exists in the form of gasbearing sediments, high-pressure airbags under overpressure, and also directly sprays to the seabed (Gu, 2013; Fleischer,2003 and Adams, 1991). According to the International Council for the Exploration of the Sea (ICES), 22% of blowouts are caused by shallow gas, which is one of the most destructive shallow geological hazards in deepwater drilling. In the process of deep water drilling, shallow soil has the characteristics of low overburden pressure and weak cementation strength (Weber, 1997; Mayer,2002). Once high pressure shallow gas is drilled, it will cause wellbore gushing or even blowout. Moreover, blowout preventers are not installed during shallow drilling, which makes well control difficult (Savvides,2001). Therefore, it is necessary to improve the pre-drilling prediction accuracy of shallow gas. The surface layer of deep water has a two-phase medium consisting of seawater and surface solids. The propagation of longitudinal wave in surface solids is affected by many factors, including surface density, porosity, clay content and other surface solids mechanical parameters(Hou, 2013; Long, 2015 and Bu, 2007). The change of mechanical parameters may cause the obvious change of P-wave propagation velocity. Based on the geological characteristics of deep water surface soil and the characteristics of shallow gas formation (Azadpour, 2015 and Carcione, 2001), this paper designs a simulation experiment scheme for identifying the acoustic characteristics of deep water surface drilling geological hazards based on shallow seismic principle, seismic wave velocity propagation theory, similarity principle and wavelet analysis, and carries out a simulation experiment for identifying the acoustic characteristics of deep water surface drilling geological hazards. A two-parameter shallow gas prediction model with P-wave velocity, shallow gas pressure and formation porosity was established, and prediction templates with different formation porosity were made. The method has been applied in South China Sea, and the model has good adaptability after successful application in 20 wells.

ABSTRACT In this study, the problem of linear wave propagation over a fixed and floating poroelastic medium is studied theoretically. The floating poroelastic medium is assumed to be homogeneous, isotropic and elastic, and allows slightly heaving motion. Lan-Lee's poro-elastomer theory is extended to derive a new analytical solution for describing the problem. Using general solutions for each region and the matching boundary conditions, a set of simultaneous equations is thus developed and solved numerically. Wave reflection, transmission and energy dissipation induced by different key parameters of a poroelastic medium are studied. INTRODUCTION Humans have imitated the floating natural vegetation to build floating islands centuries ago. The ancient Peruvian population built the Islands of Uros in Lake Titicaca to escape violent attacks from more aggressive tribes of the Collas and the Inca. In order to protect the land demand for economic development of densely populated coastal cities and areas, the relevant research on wave defense and interaction between floating breakwaters, offshore floating platforms (Lee and Lee, 1993; Oliver et al., 1994; Khabakhpasheva and Korobkin, 2002; Nakamura et al., 2003; Diamantoulaki et al., 2008; Zhao et al., 2012; Ruol et al., 2013; Yeh et al., 2013; Burcharth et al., 2015; Tsai et al., 2016; Dolatshah et al., 2018; Emami and Gharabaghi, 2018; Yu et al., 2018) and VLFS (Very Large Floating Structures) (Takagi, 1996; Utsunomiya and Watanabe, 2006; Wang and Tay, 2011; Lamas-Pardo et al., 2015; Shirkol et al., 2016; Sun et al., 2018) in coastal and offshore areas have been carried out in recent decades. In addition, ecological floating islands have been widely recognized as an effective tool for habitat restoration in many European countries and the United States (Winston et al., 2013), and have been commercially used in water environments in many countries. The composition of the ecological floating island basically inherits the natural vegetation floating island with permeability and softness (deformability). Most of the research on artificial ecological floating islands focuses on issues such as ecological environment, water quality improvement, and landscape maintenance (Nakamura et al., 1996; Francis, 2009; Winston et al., 2013). Research on the reduction of wave energy to protect waterfront functions is less intensive and generally appears in case studies (Gaffney and Munoz, 2010; Zhu and Zou, 2016). Due to the flexibility of soft material, the deformation induced by water waves disturbs flow field in the vicinity of the structure when compared with impermeable reflective concrete counterparts (Lan, 2018). For the wave attenuation effect caused by the permeable structures, different structural material properties have different wave damping characteristics, such as the flow configurations of Darcy, Darcy-Forchheimer and vegetation drag resistance, etc. Therefore, in academic and practical studies, ecological floating islands need to consider both the flexibility and permeability of the floating medium composition, such as the poroelastic type.

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

ABSTRACT This paper describes dynamic processes in the sea ice observed during ice monitoring in the Kara and Laptev seas. Wave events are studied instrumentally under assumption that sea ice is an interaction indicator of the air-ice-water system. Wind waves and free swell waves from far storms in the open water are considered as background oscillations. Compression/ridging events and heterogeneity of ice drift generate periodic micro-shearings that can be registered in ice cover as mechanical horizontally polarized waves. Ice compression/fracture event can be predicted by analyses of ice micro-shearings. This shortterm method of ice compression and ridging forecast showed good results for processes in drifting and fast ice. INTRODUCTION Forecasting of extreme ice events is based on ice cover monitoring and in particular its physical and mechanical changes and large-scale dynamic reactions. Oscillation and wave processes in the ice give a lot of important information for analysis. The most typical dynamic processes in sea ice are vertical and horizontal displacements. These ice movements and failures occur continuously and determine the ice cover structure. Extensive fractures, ridges of hummocks and open-water channels can originate from significant ice compression forces. First big-scale experiments of ice cover monitoring were carried out by authors in the Kara sea during Rosneft Oil Company expedition "Kara-winter-2014". Fluctuations of ice drift velocity and ice horizontal displacements were continuously registered during the tests by special measurement complex. It is shown how sea ice drift is accompanied by ice deformations during different ice events (compression, formation of cracks). Ice drift depends not only on local wind and on sea currents but also on wind in neighboring areas. Displacement velocity in consolidated compressed ice for measurements in a distance of 100 km reached 3 cm/s (Legenkov, 1988). Estimation of ice forces in the periods of intensive compression allows to obtain external forces and investigate their distribution along the ice drift trajectory. Due to the total mass and acceleration of ice, these forces of drifting ice interaction can reach hundreds of kilonewtons (Sheikin et al., 2006).

ABSTRACT The rogue wave is a huge wave that rarely generated by wave energy focusing. The rogue wave can cause critical damage to a ship and an offshore platform due to its great wave energy and its unpredictability. However, its kinematic and dynamic effect to ships and offshore platforms have not studied well yet. In this paper, to generate the rogue wave, the bull's eye wave, which is a focusing of multi-directional waves, has simulated in numerical wave tank. In addition, the heave and pitch motions of box-shaped body in bull's eye wave condition have simulated. For bull's eye wave simulation, regular waves with different directions and different phases were created at inlet boundary of domain. The open source CFD libraries, OpenFOAM, were used to simulate bull's eye waves. INTRODUCTION The rogue wave, also called freak wave, is huge wave its wave height is higher than two times of a significant wave height. Serious studies of the rogue wave phenomenon started about 30–40 years ago and have intensified recently. The physical mechanism of the rogue wave phenomenon can explain follow, wave-current interaction, wave-wind interaction, geometrical, spatial-temporal focusing, etc. Its great wave height and unpredictability can damage to a ship and an offshore platform and also can treat safety of them. However, its kinematic and dynamic effect to ships and offshore platforms have not studied well yet. Therefore, the effects of the rogue waves are not considered to design a ship and an offshore platform. The purpose of this study is to simulate the rogue wave by directional focusing and to calculate the motion of box shaped rigid body in rogue wave. Rogue Wave The rogue waves had been considered as seamen's mythology until detection of the rogue wave called the Draupner wave or New Year's wave that occurred on the New Year's Day 1995, at the Draupner platform in the North Sea (Haver, 2004). A single giant wave was measured by a measuring instrument. The wave elevation for the time history shown in Fig. 1. About to at 240 s, the significant wave height at that moment was 11.9 m, the measured crest height is 18.5 m and the measured through height is −7.5 m. Thus, the rogue wave's wave height is 26 m and it is asymmetry about the still water level. A symmetry wave which has wave height of 26 m is 100-year wave height of that sea condition. However, an asymmetry wave which has crest height of 18.6 m is 10000-year crest height of that sea condition. This means that asymmetry rogue wave's wave height is not seems extreme, but crest height is extreme and unpredictable.

ABSTRACT In order to reduce the liquefaction damage to detached house during earthquakes, it is essential to predict the damage using inexpensive and simple methods. Therefore, in this study, authors proposed numerical method and some ground survey methods. From the reproduction analysis using these technologies, it was found that the damage could be sufficiently reproduced by the proposed method, and it was found that the damage was affected by the strata inclination. Based on these results, we proposed two-dimensional surface wave survey and passive linear arrays that can also be used in residential areas, and confirm their superiority and simplicity. INTRODUCTION A large settlement and tilting of detached house have been often observed due to ground liquefaction (JGS, 2011; Yamaguchi et al., 2012). Extensive damages were inflicted to lifelines and detached houses due to widespread liquefaction and lateral spreading in reclaimed or lowland areas. Liquefaction countermeasures are effective to mitigate damage of liquefaction. However to predict these damage and to determine whether countermeasures are required, we have to conduct some field investigations to understand ground condition in detail (Kazama et al., 2018). Generally, S wedish W eight S ounding tests (SWS) were conducted as ground investigation to understand the ground bearing capacity in Japan. These results are not enough to predict these damage or to determine the necessity of countermeasures. From these situations, the authors carried out ground investigations by using different survey techniques for two sites located in Japan and in New Zealand. In Kamisu city familiar for severe damage due to liquefaction during the 2011 off the Pacific coast of Tohoku Earthquake in Ibaraki Prefecture located east of Tokyo, four different ground survey techniques were employed. First, SWS and D ynamic P roving T est (DPT) were conducted. Later, the soil sampling was conducted. Finally, the survey of ground water level was carried out. On the other hand, passive linear arrays and two dimensional surface wave explorations were conducted in Christchurch, New Zealand. These methods not only can be easily conducted but also rapidly provide output results.

ABSTRACT The hydrodynamic pressures for a vertical flood gate situated in a discharge sluice are investigated. Exact analytical solutions are presented for the hydrodynamic pressures acting on the gate. This solution is first employed to investigate the hydrodynamic pressures for a horizontally vibrating rigid gate. For this case, regimes of frequencies and water depths are identified for which fluid compressibility and surface waves play a significant role in the hydrodynamic response. Subsequently, the hydrodynamic pressure is analysed for the case of a flexible gate of various boundary conditions. It is concluded that the derived regimes are applicable to flexibles gates as well. Values for the added mass coefficient are presented for various types of gate supports. INTRODUCTION A vast amount of flood defence structures contributes to the safety and water regulation in coastal areas. Flood gates form essential parts of flood defence systems as they regulate the discharge between bodies of water. It is expected that the construction of new movable barriers and the adaptation of existing ones will be necessary in the future due to land subsidence and sea level rise. During storm conditions, flood gates are often subjected to high water levels and wave loads. Impulsive wave impacts lead to vibrations of the structure, potentially amplifying internal stresses compared to the static situation. The problem of a flood gate vibrating in water is essentially a coupled one, i.e. a coupled fluid-structure interaction problem. Numerical methods do exist (Fu et al., 1987), however, these are computationally costly. For this reason, in engineering practice simplified methods are usually applied. Most common is to represent the structure as a system of finite number of degrees of freedom including the effect of the hydrodynamic pressure as an added mass, stiffness and damping to the system. Alternatively, one may apply the so-called non-dimensional added virtual mass incremental (NAVMI) factor to estimate the resonance frequencies of the gate immersed in fluid.

ABSTRACT The lateral load response of a monopile is often modelled by p - y curves. However, the traditional formulation of p - y curves is unable to describe the behavior of liquefied soil. This paper presents a numerical investigation of how to develop p - y curves for monopiles installed in liquefiable soil. A monopile is modelled in the 3D finite element software package PLAXIS 3D, where a soil model able to capture liquefied soil behavior is applied. The numerical results are used to extract relevant data to assess liquefaction in the soil. Based on this information, p - y curves are generated for the liquefied soil. INTRODUCTION Most offshore wind farms are located relatively close to the coastlines in Northern Europe, where the seismic activity is generally low. However, the interest in offshore energy has emerged in areas with high seismic activity, such as in East Asia, which requires a foundation design that is able to withstand the effects of seismic loading. The seismic load from e.g. an earthquake is cyclic by nature. This type of loading can lead to generation of excess pore pressure in the soil. In loose (contractive) soils, the generated excess pore pressure may reduce the effective stress level to zero. Hence, the soil strength and stiffness are lost. This is the liquefaction phenomena (Andersen 2009, 2015, Nielsen et al. 2013, Nielsen 2016), which can be critical for the foundation (Japan National Committee on eathquake Engineering 1964, Hsein Juang et al. 2005, Cubrinovski 2013). The most used foundation concept for offshore wind turbines is the monopile foundation concept, as illustrated in Figure 1. One of the governing design criteria for a monopile is the rotation of the foundation. To assess the rotation, the lateral displacement at seabed must be evaluated. The lateral displacement of a monopile is typically calculated using p - y curves, where the soil-structure stiffness is modelled using springs. These p - y curves have been developed to describe the monotonic load-displacement behavior. A typical p - y curve for cohesionless soil has an upward convex shape (Det Norske Veritas 2011), where the tangential stiffness of the soil decreases as the pile displaces towards the soil. Different design practices (Ashford et al. 2011) suggest to apply a multiplier ( m p ) to the p - y expression for the non-liquefied soil to assess the effect of liquefaction by simply decreasing the stiffness and ultimate resistance of the soil. Nevertheless, laboratory triaxial tests show that the stress-strain behavior of post-liquefaction monotonic loaded soil follows an upward concave shape (Rouholamin et al. 2017), where the stiffness increases as the strains increase. Standard p - y formulations will therefore not give a good representation of the post-liquefaction soil behavior. In a design where there is a risk of liquefaction, the engineer therefore requires a representation of the soil-structure interaction, which better captures the liquefaction in comparison to what is given by standard non-liquefied p - y curves.

ABSTRACT Acoustic Doppler velocimeter (ADV) measurements of the velocity field under breaking waves in the laboratory are presented. By comparing the changes of water particle velocities, it can be seen that the momentum flux from breaking waves into the water column is more remarkable in horizontal direction than that in vertical direction. The local period-averaged depth-integrated kinetic energy, potential energy and total energy under different wave steepness were computed. The results show that the potential energy loss is more significant than that of the kinetic energy in the breaking interval, which means the equipartition assumption cannot work in the breaking interval. Furthermore, the approximate linear relationship between the energy loss and the initial wave steepness has been revealed. INTRODUCTION As one of the significant hydrodynamic processes in the ocean, breaking wave affects the development of wind-wave, the generation of surface current and the distribution of near surface turbulence. An improved understanding of the mechanism of the wind wave breaking is essential for ocean development. In theory, the field measurement with high accuracy is the most appropriate method to achieve this goal. Unfortunately, wave breaking in natural water is random and discontinuous in time and space. This method suffers serious difficulties. Therefore, the laboratory experiment of deep water wave breaking is practicable and meaningful in grasping the mechanism of breaking, revealing the dissipation of energy and quantify the momentum flux. Traditionally, as a simplified method, one may estimate the energy loss due to wave breaking with surface elevation measurements and control volume analysis (Rapp and Melville 1990, Meza and Zhang 2000, Banner and Peirson 2007, Tian and Perlin 2010). However, this method has a significant shortcoming. Based on the linear wave theory, these experiments suggest that the wave energy is divided by the kinetic energy and the potential energy equally. In fact, wave breaking is a strong nonlinear process, the linear theory not hold in this case. The most reliable method is to measure both the surface elevation fluctuation and the wave-induced water particle velocity simultaneously. It can help us to understand the kinematic and dynamic characteristics of the breaking wave, to quantify the wave energy loss without any hypothesis. This method also has the advantage in calculating the momentum flux from breaking waves into the water column, and in calculating the turbulent kinetic energy induced by breaking.

ABSTRACT The exploitation of oil and gas fields which located in Bo Hai Bay has lasted more than half a century. The continued development of the oil and gas cause a lot of buried well head which bring hidden danger to the offshore operation. Oil and gas field operators usually discard the well by strict technical procedures. The top level of well head should be 4m below the seabed base on the requirements of State Oceanic Administration (SOA). It is necessary to check the wellhead for safe when the well is filled with concrete. In general, the wellhead is buried under the seabed deeply, so it has any effect on offshore operation. However when the time goes by the depth decreased due to washing on the seabed. Therefore it is still important to verify the position exactly in order to avoid the wellhead. Side-scan sonar, magnetometer and other marine geophysical devices can be used to detect the exposed wellhead location on practical experience. Marine magnetometer is the only effective choice for buried wellhead. This paper introduced a field magnetic test method and discussed the analyzes methods. INTRODUCTION The well is cut and sealed by operators when oil production is shut down. Wellhead is buried below a certain depth of the seabed sediment. Buried wellhead usually brings more uncertain risk to offshore operation. For example, Buried wellhead may lead to many risks such as jack-up platform penetration failure, Bottom-Supported platform tilt, mooring force reducing etc. Therefore, it is necessary to determine the location and depth of the buried wellhead by high-precision detection and analysis, which will provide the basis for the subsequent engineering practice. At present, obstacles surveys are limited to above seabed. Marine survey equipment include multi-beam bathymetric system, side scan sonar, sub-bottom profiler, marine magnetometer and so on. It is difficult to detect the buried wellhead by side scan sonar and multibeam bathymetric system. To detect metal objects buried under the seabed, magnetometer and sub-bottom profiler are often used. Magnetic survey based on magnetic field strength principle and subbottom profiler based on acoustic principle. Magnetic survey and subbottom profiler survey are effective technique to search for buried pipeline. Few reports are available on buried wellhead detection.

ABSTRACT The compaction condition, effect of relative density, was the dominant factor affecting the erosion property than ground depth, effect of pre-consolidation pressure. It was shown that the behavior of critical shear stress with the relative density and pre-consolidation pressure is similar to that of the soil resistivity. On the basis of this result, the equation for estimating the critical shear stress of coarse-grained soils could be proposed using the relationship between the critical shear stress and soil resistivity. INTRODUCTION An erosion of coarse-grained soils happens very quickly with respect to a water flowing, and the erosion rate also occurs rapidly over time (Briaud et al. 1999 and 2001). An erosion arisen from a ground-water runoff and from a leakage of water of aging water pipeline around compacted coarse-grained soils used as filling material in a construction site can causes the artificial sinkhole in an urban area, (Greyvenstein and Zyl, 2007). This can become a serious social issue for stability of infrastructure. Hence, the new method of measurement for erodibility of coarse-grained soils used as construction filling materials over a wide area should be required as alternative previous methods. A number of apparatuses for measuring hydraulic resistance properties for erodible rock, sandy soil, and clayey soil have been invented by several researchers: flume-style device, rotating cylinder device, drill hole device, and submerged jet erosion device. Even though these apparatuses can be used for determining the shear stress and erosion rate of sample, where is taken from the site, the evaluation of erodibility in a wide area require a number of samples at various site because taken samples have only site-specific properties, and thus a great deal of time and cost is necessary. Electrical resistivity test to measure the soil resistivity have been used to assess the physical and mechanical properties in a geotechnical engineering field (Archie, 1942; Jackson et al. 1978; Klein and Sill 1982; Lee et al. 2007). According to literature, the characteristics of electrical resistivity showed fairly good relationships with various geotechnical properties, such as porosity and density of soil, unconfined compressive strength, and secant modulus.

ABSTRACT Usually, the lifetimes of geogrid are assessed as the long-term creep behavior which causes shape deformation and collapse of the slopes and embankments. During an earthquake, the structure is subjected to additional loads, which may influence the creep characteristics of the reinforcement. The SIM (stepped isothermal method) test provides an opportunity to study the effect of simulated seismic events or the influence of other additional loads, occurring at different intervals of the life of the structure, on the long-term strength of geosynthetic reinforcement. In this paper, two simulated seismic event related to SIM tests were performed, one with a simulated seismic event at 23°C step, the other tests carried out after 79°C step. Creep strain decreased after seismic event cause of recovery force, then strain increased again. After same conditions of seismic event in different times were applied, strain finally overlapped. INTRODUCTION For assessing the long-term tensile deformation of geogrid, 10% creep strain has been used as critical value but, there is no basic theory or empirical data to 10% creep strain (Cho, Lee, Cazzuffi, Jeon 2006; Farrag, Shirazi, 1997;Farrag 1998). In real 10% is relatively big one that of allowable long-term strain in reinforced earth wall. Another criteria for creep related properties of geogrid, is creep rupture strength (Allen, 2005; Koo, Kim 2005). Creep rupture in geogrid shows brittle tendency because of rapid loading rate in test procedure. Besides each improper aspect, creep factors for long-term allowable strength from each criterion are different each other. Also these 2 characteristics never are able to explaining the long-term deformation of geogrid. So it is required that the replacement method to explain the long-term deformation (Jones, Clarke 2007). The isochronous creep curve was used to define the relation between creep strain and allowable strength. In the isochronous curve at given time, we can read the allowable strength at allowable creep strain. The allowable strain gets from specification by directors or manufacturers. The allowable creep strain can be various according to its facing batter, facing type and critical aspect. Otherwise, the required service lifetime of geogrid used for reinforcement of soil structure varies according to the sensitivity of the environmental conditions (Den Hoedt, 1986; Hsieh, Wu, Lin, Hsieh, 2000). This service lifetime implies that the functional engineering properties of the geogrid should remain within acceptable limits during the required service life. Usually, the lifetime of geogrid are assessed as the long-term creep behavior which causes shape deformation and collapse of the soil structure (Tatsuoka, Kongkitkul, 2007). In this study, the creep behavior of geogrid was evaluated by the stepped isothermal method (SIM). For the engineering design perspective, the creep reduction factor was determined from the creep rupture and limited strain. As an accelerated creep test, the SIM test provides an opportunity to study the effect of simulated seismic events or the influence of other additional loads, occurring at different intervals of the life of the soil structure, on the long-term strength of geogrid. Two simulated seismic event related to the SIM tests were performed, one with a simulated seismic event at 23°C step, the other tests carried out after 79°C step. The reason for varying the time of application of the simulated seismic load was to study the effect of the timing of real-life earthquakes. The second was to quantitatively calculate creep reduction factor considering seismic event and to reflect this in the design property.

ABSTRACT The fate of the energy, momentum, and volume (or mass) of the leading-elevation N-type tsunami considering geophysical scale is studied. From the epicenter to the land the physical properties of the positive wave of tsunami are calculated using a second order depth integrated model. Not only the incident wave characteristics but also the scale and shape of bathymetry are very important for the propagation of tsunami physics. INTRODUCTION Tsunami is caused by undersea earthquake and usually propagates across the entire ocean. Tsunami is not detected well over deep and intermediate ocean area due to its very long length and small crest amplitude. As tsunami enters shallow coastal region, its wavelength reduces and the amplitude increases, which is believed to lead low altitude inland around coast to catastrophic inundation damage. For decades, various aspects of tsunami propagation have been studied experimentally, numerically and theoretically. Because the inundation is directly related with water surface elevation, interests have been focused on water surface elevation of tsunami. For example, Synolakis (1987) presented an analytical model for non-breaking solitary wave runup on plane beach. Briggs et al. (1995) presented intensively measured data of solitary wave runup heights around a circular island in laboratory scale. Matsuyama et al. (2007) carried out relatively undistorted experiment on the shoaling and fission of tsunami. Considering the complexity in real fluid motion and bathymetry, numerous numerical models based on shallow water equation (Titov and Synolakis, 1995; Li and Raichlen, 2002) and Boussinesq equation (Goring, 1987; Fuhrman and Madsen, 2008; Lynett, 2007; Kim and Lynett, 2012; Kalisch and Senthilkumar, 2013) have been developed and applied. Based on many analytical, experimental and numerical studies, it was proposed that the runup height and amplification of nonbreaking wave generally increased as the bottom slope was milder (Synolakis, 1987; Suh et al., 1997; Li and Raichlen, 2002). In field experience, however, tsunami damage has not been frequently reported where a continental shelf with very gentle slope existed, for example, the sea of north Australia, east China and west Korea. On the contrary, east coast of Japan, India and Sri lanka where the under sea bathymetries are relatively steep have experienced severe tsunami attacks. Recently, Madsen et al. (2008) and Kim and Son (submitted) studied on the contradictory results: They examined the importance of geophysical scale for the tsunami wave study and proposed that unrealistic wave could be developed under improper scale and geometry considerations. For the damping by friction Horsburgh et al. (2008) found that the frictional dissipation was not primarily responsible for tsunami attenuation using a numerical model on tsunami crossing ocean and continental shelf. This implies the damping could be resulted by the geometry of geophysical scale, not by frictional effect.

ABSTRACT This paper is part of a research project titled Modelling wash -assessing fuel consumption and erosivity, which is financed by Trafikverket, Swedish Transport Administration. The project aims at developing a computational model to calculate the shoreline erosion caused by ships travelling in inland waterways. This paper covers a field study into possible linear methods which could be implemented to find the wave inputs required to predict shoreline erosion. Thin-ship theory was decided upon and implemented to calculate wave resistance and elevation. Results show the thin-ship model to be accurate for all tested ships between Froude numbers of 0.35-0.7. However, the model does under predict the wave resistance at Froude numbers below 0.35 for vessels with a transom stern. INTRODUCTION There is currently a strong need for research into the shoreline erosion caused by inland waterway ships. Independent studies have been carried out by various organisations, which are discussed by working group PIANC, (Andreas, Linke and Zimmermann 2000; Kofoed-Hansen & Parnell, 2001; Parnell, Mcdonald and Burke, 2007). (Stumbo, Fox, Dvorak and Elliot, 1999; Glamore, 2008 and Macfarlane & Phil, 2012) have also made attempts to model the impact of ship waves on inland waterways, with results from Macfarlane & Phil (2012) proving to be promising within reasonable limits. A conclusion drawn across this research is that there is a need for more quantitative studies, with the key limitations being outlined by Gourlay (2011). The erosion process is affected by the waterway bank form, material properties, water level and salinity. These parameters are what make it difficult to quantitatively estimate the effect of vessel traffic on erosion. Continued waterway erosion can result in concerns for the quality of drinking water, loss of property and loss of aquatic habitat. The purpose of this research project is to develop a computational model to calculate the risk of erosion caused by both ships in their initial design phase and existing ships operating in inland waterways. The model should be able to rank a variety of ships with respect to the risk of erosion that they could cause. When addressing this problem as a naval architect, the first step is to model the vessel's wave inputs required to calculate the erosion potential. According to (Gourlay, 2011 and Reynolds, 2003) the key wave inputs are the wave length, wave elevation and wave energy. The differences in nature between boat waves and wind waves make it difficult to derive an exact equation for sediment movement, however, both authors agree that in order to understand shoreline erosion from ships it is first important to calculate the total transmitted wave energy from the ship. It is this task of finding the wave energy and other required inputs that will be addressed in this paper. It is estimated that there are well over 1000 papers published on the study of ship waves. The research dates to the 19 th century with scientists such as Green, Airy and Stokes discovering foundational concepts for surface waves and potential. Some of these concepts, along with work from Froude, Lord Kelvin and Lamb were then applied directly to the prediction of a ships wave prediction by Michell, (1898). Michell's thin-ship theory was recognized in 1923 by Havelock and Wigley, with both researchers investigating the theories applicability and advancing on the concepts. Additional linear potential methods were proposed over the 20 th century, with the most well-known examples being Neuman-Kelvin theory, low speed theory, slender ship theory and linear panel methods from (Hess & Smith, 1962; Gadd, 1976; and Dawson, 1977).