Abstract An economical method, Sampling & Pull-Up Test (S&PUT), was proposed for investigation of the mechanical properties of the seabed for foundation design of bottom-mounted offshore wind turbine towers. After two kinds of prototype apparatus were manufactured, field experiments were carried out to investigate the feasibility of the proposed test method. The test results demonstrated that, for sounding performance, the PUTs were suitable, as the depth profiles of the wing resistances by PUTs and those of the cone resistances by CPTs were in harmony. Whereas the sampling performance was not satisfactory yet, as the sampling recovery ratios were found not greater than 80%. Introduction An economical method for investigating the mechanical properties of the surface ground on the seabed is required for foundation design of bottom-mounted offshore wind turbine towers. The authors proposed a new sampling and pull-up test, denoted as a S&PUT for short, that can perform sampling and sounding simultaneously (Tani et al., 2020a). Using a hydraulic jack and a vibro- or a percussion hammer, a test device with a sounding probe for pull-up tests (PUTs) and cone penetration tests (CPTs) is statically or dynamically and continuously driven into the ground simultaneously with samplers equipped alongside rods. The purpose of this test method is to collect continuous samples not only of soft ground but also relatively hard ground, while conducting sounding tests to evaluate a depth profile of stiffnesses and/or strengths at the same location. Although limited to soft ground, CPTs can be performed, when the probe is driven statically at a constant rate. On the other hand, PUTs can be done even in harder ground, once the probe is installed dynamically at depths. FORMATTING SAMPLING AND PULL-UP TEST (S&PUT) Fig. 1 compares the concept of S&PUTs and that of standard penetration tests (SPTs) which are most widely used for geotechnical investigations. The basic concept of these two test methods is identical in that, both sampling of disturbed soil samples and sounding for evaluation of the mechanical properties can be done at the same time in the same location. Thereby, similar results of geological columns that are the depth profiles of soil types and sounding measurements can be obtained effectively by both test methods. However, there are four-fold differences as below. The first is that, S&PUTs can be conducted much faster than SPTs. In SPTs, the works of driving the sampler while counting the number of blows, SPT-N values, for sounding, retrieval of the sampler for sampling, and drilling/boring to the next depth must be repeated every 1 meter in depth. Since installation and removal of a self-elevating platform (SEP) or a simple scaffolding to place the drilling machine are time consuming, it usually takes several days to a few weeks to do a SPT at each site. On the other hand, in S&PUTs, the works of driving/penetration and retrieval/pulling-up of the probe and the samplers are done only once. Since the operation of a pile driving barge to be used is simpler and quicker than that of a SEP, the time required to do a S&PUT at each site is estimated not longer than several hours or a day.

Abstract The COMCOT model from Cornell University has been optimized, which was validated by 2011 Japan tsunami. The simulation results agreed well with the DRAT buoys from NOAA center. Assessment were implemented by tsunami sources of Manila Trench to evaluate tsunami hazards for the GuangHai Bay of the South China Sea (SCS). The tsunami hazard rank criteria recommended by UNESCOòIOC and the State Oceanic Administration of China has been applied in this paper. Tsunami hazards classifications were divided for the GuangHai Bay by analyzing the simulation results. Preliminary assessment of tsunami hazards have been completed in the paper. INTRODUCTION In recent decades, the 2004 Indian earthquake tsunami and the 2011 Japan earthquake tsunami have caused huge loss of life, property and environmental damage to coastal areas. Considerable efforts have been devoted to study the basic theory of tsunami and improving the tsunami warning system, the coastal countries have also carried out the risk assessment of tsunami disasters for major coastal projects and key support targets. According to the study of potential tsunami seismic fault zones from USGS, the Manila Trench is regarded as the most likely source for tsunami hazards (Li and Yuan, 2016), which will undoubtedly threaten the coast of the China. Many studies mainly focused on the tsunami research (González and Geist, 2009; Burbidge and Cummins, 2009; Heidarzadeh and Kijko, 2011; Megawati and Shaw, 2009; Anawat and Imamura, 2012). The research of potential tsunami disaster in the South China Sea has been extended from the South China Sea to the coastal areas of the mainland (Yu and Ye, 2001; Yu and Wang, 2011; Wang and Yu, 2012; Ren and Wang, 2018; Zhang and Niu, 2020; Yuan and Li, 2021). The criteria of tsunami hazard grade issued by UNESCO/IOC and the China is used to grade the tsunami hazard in the GuangHai Bay of China, which results will provide technical support for the enhancement of marine services in GuangHai Bay. GuangHai Bay is the power base of GuangDong Province in China. TaiShan power plant, the largest coal–fired power plant in Asia, has been put into operation. An installed capacity of 6 million kilowatts of TaiShan Nuclear Power Plant has already been established and successfully taking into operation. Future, wind power projects will also make the TaiShan city to the largest wind power base in GuangDong. With the all–round development of society and economy in GuangHai Bay, the resources of coastline and inshore sea area decrease sharply, and the conflict of ocean utilization function exists in some areas, which is brings new problems to the sustainable development and utilization of GuangHai Bay. Lack of awareness of the conflict between limited marine resources and high–intensity exploitation, it is necessary to ascertain the potential hazard of marine disasters, to identify regional resilience and to objectively understand the level of marine disaster hazard, which provides authoritative disaster hazard information and scientific decision–making basis for national governments to effectively carry out marine disaster prevention and Emergency Management and guarantee the sustainable development of social economy.

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

Suction bucket supported jackets are being considered as foundation solutions for several offshore wind farms in China. Due to the strict serviceability requirement of the wind turbine structures, long term settlement of the bucket foundations, particularly uneven settlement, is an important design consideration. This paper presents design methodologies developed for settlement calculations in soft, layered soils. Uncertainties and challenges in the settlement assessment are discussed. INTRODUCTION The offshore wind industry in China has seen a rapid development in recent years. The accumulated installed capacity had reached 4.6 GW by the end of 2018 and this will be added with over 2 GW annually in the years to come. The ground conditions in many offshore sites in China often feature normally consolidated soft clays of varying thickness near the surface, followed by more competent clays, silty clays, loose to dense sands or silty sands. In some areas, shallow bedrock combined with weak seabed sediments may lead to expensive foundation construction in rock. Over the last few years, suction bucket foundations have been applied in the offshore wind industry as an alternative foundation solution to pile foundations. Bucket supported jacket structures are most common, with several projects already completed, including Borkum Riffgrund Offshore Wind Farm 1&2 and Aberdeen Bay Offshore Wind Farm. Due to their relative quick and quiet installation process and advantage in sites with shallow rock, suction bucket supported jackets are increasingly being considered as a foundation solution for several offshore wind developments in China. However, from a geotechnical point of view, the site conditions are complex and challenging and represent a clear contrast to the conditions in the North Sea where the existing bucket supported wind turbine jackets are installed. The complex geotechnical conditions (soft and layered ground) and frequent typhoon events pose several challenges that need to be addressed. This paper focus on one of the challenges faced in the design: long term settlement assessment in soft and layered soils. The different aspects towards this assessment are discussed and a design approach is proposed. An example design calculation at a wind farm site offshore Guangdong is presented to demonstrate the process.

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

Matched field processing (MFP) is usually performed in an ocean waveguide with a vertical line array to determine a source position. Aiming to improve depth and horizontal distance resolution of MFP, this paper introduces an optimization method that applies the Lucy-Richardson deconvolution algorithm to Bartlett MFP. Point spread function (PSF) in the deconvolution algorithm is established based on norm mode model (NM) and fast field analysis. Examples are presented to illustrate deconvolved MFP (DMFP), and DMFP yields a low sidelobe level better than Bartlett MFP. Compared with MVDP, it retains the robustness on environment mismatch. INTRODUCTION Vertical line arrays have been used for target localization in waveguide environment based on matched field processing and other methods (Sazontov and Malekhanov, 2015). MFP is performed by matching the data received by array elements with the simulated data of all possible target locations. The Bartlett MFP, similar to plane wave beamforming, is a popular and conventional method in which the received complex vector on various sensors and simulated vectors depending on location parameters are processed by linear correlation. When the simulated vector coincides with the received data of a given target, all elements of target vector are coherently summed and the Bartlett MFP gets the peak of the output in ambiguity diagram. Suppose noise is uncorrelated between the receivers and is hence incoherently summed. Consequently, the signal-to-noise ratio (SNR) at the ambiguity diagram is enhanced compared with the input SNR. The advantages of the Bartlett MFP are its robustness against signal mismatch between the assumed and the actual data (such as when there are measurement and approximation errors for waveguide parameters), and small number of samples required for a reliable estimate of the target location. The disadvantage of the Bartlett MFP is the high sidelobe level making localization of a weak signal difficult in the presence of a loud interferer. Many other methods with high resolution have been proposed based on the inverse of the signal vector covariance matrix to overcome the deficit of the Bartlett MFP. Well-known methods use the minimum-variance distortionless processor (MVDP), and eigenvector-based MUSIC algorithms (Kolev and Georgiev, 2007). These algorithms produce low sidelobe levels and narrow beamwidths, and hence allows for better interference rejection and localization of targets with a small location separation. At the same time, these algorithms are known to be sensitive to the signal mismatches. Signal mismatch can cause part of the signal to be misidentified as noise and consequently suppressed by the algorithm. To diminish the sensitivity, the MVDP algorithm is modified under additional constraints, such as the white noise gain constraint or distributed sources constraints, to produce a wider beam in the target location while keeping the sidelobe level low. The second problem with these high-resolution algorithms is that the covariance matrix of the signal is usually not known and is replaced by the sample covariance matrix. Assuming the signal is stationarity in time domain, the sampled covariance matrix requires many samples of signals to assure rapid convergence and minimum power loss in the beam output. The high-resolution algorithms usually have poor performance under certain conditions and if one were to ignore the non-stationarity and still average the sampled covariance matrix over many samples, the matched field processor's ability to reject interference is much decreased. The MUSIC algorithm has the same problem requiring a sufficient number of snapshots to obtain reliable estimates of the signal and noise eigenvectors. It also needs prior knowledge of the number of sources to separate the signal vectors from the noise vectors (Zhang and Gao, 2013).

Sediment incipient motion is the first stage of the whole process of local scour around a marine infrastructure. Most previous investigations ignored seepage flow on the mobility of bed particles except a recent study including the effects of vertical seepage flow in the prediction of sediment motion. In this paper, a new model further combing the vertical and horizontal seepage force is proposed. The modified Shields parameter by considering two-dimensional seepage is derived. Then, the effects of wave and soil parameters on sediment incipient motion are analyzed. It was found that lower water depth and saturation, higher wave height, shear modulus and permeability, will remarkably increase both modified Shields parameters and the gaps of the results considering vertical and two-dimensional seepage forces. Therefore, the horizontal seepage can not be ignored. INTRODUCTION As the first step of sediment incipient motion in the process of local scour, the critical Shields number is an important threshold condition for the sediment moving from a static condition. Numerous studies (Shields, 1936; Bagnold, 1960; Yalin, 1977) proposed various criteria. In most criteria, the Shields parameter has been commonly used to determine the threshold condition of sediment incipient motion. Initially, the Shields parameter was used for the unidirectional flows in a flat or near-flate bed. Later, several modifications to the conventional Shields diagram have been proposed for different sediments based on laboratory tests. For example, Madsen and Grant (1976) modified the Shields Criterion obtained for an oscillatory flow. They concluded that the Shields parameter is essential to consider the influence of the sediment incipient motion under the action of wave in the prediction of the local scour. Le Roux (2001) proposed a simple method to predict the threshold of particle transport under oscillatory waves, which was valid for grains of varying size and density in a laminar or turbulent flow. Whitehouse et al. (1988) and Chiew et al. (1994) modified the Shields diagram for a sloping bed with an inclination angle.

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.

To ensure the NGH extraction and long-term stability of NGH reservoir, a high-pressure and temperature-control plane strain shear apparatus with observation windows has been developed to study the timedependence behavior of methane gas hydrate-bearing sediments. Compared with the pure sand sample, the initial shear stiffness and peak strength of the hydrate sample increased significantly with the increase of the shear rate, but it was not observed that the residual strength was affected by the shear rate. The volume strain of hydrate samples gradually changes from shear compression to significant shear expansion, with increasing shear rate. INTRODUCTION Natural gas hydrate (NGH) is a possible future energy resource. To keep stability, the NGH requires relatively low temperatures and high pressure. Recently, four different production methods are the most discussed: (1) depressurization method; (2) thermal stimulation method; (3) chemical inhibitor injection method; (4) the gas exchange method. Due to the special exploitation conditions and geological environment of NGH reservoirs, it is essential to study the mechanical and deformation properties of hydrate-bearing sediments before the economical utilization of NGH. And, to predict the geomechanical response to extract natural gas from its hydrate form safely and continuously, the time-dependent behaviors of natural gas hydrate-bearing sediments is also an important research issue. The loading-rate dependence and creep property of natural gas hydratebearing sediments were considered to be of great reference value to the long-term prediction of the geological response of a reservoir. However, there are only a few related studies have been reported. Miyazaki, K et al., (2017) studied the creep life and loading-rate dependencies of the strength of the methane-hydrate-bearing Toyoura sand from three different kinds of tests: constant-strain-rate test, constant-stress-rate test and constant-stress (creep) test and all of these tests under three axialloading conditions. It was found that the time-dependence of hydratebearing sediment samples was more significant than a geomaterial. Additionally, it suggested that the loading-rate dependence of strength can estimate the creep life of hydrate-bearing sediments sample and which means loading-rate dependence of mechanical properties study is a more efficient method to investigate the time-dependent behaviors of hydrate-bearing sediments. Similar experiments have been carried out with carbon dioxide hydrate-bearing sand by Iwai, H et al., (2018). It was found that the carbon dioxide hydrate-bearing sand has a stronger strain rate dependency compared with only water-saturation sand. And that dependency becomes more significant as the hydrate saturation increases. In addition to experimental research, few constitutive models consider the time-dependent behaviors for hydrate-bearing sediments that have been proposed (Miyazaki, K et al., 2014; Yoneda, J et al., 2008 ). There is no study about time-dependent behaviors on natural gas hydratebearing sediments under the plane strain shear test. Although it was suggested that most landslide problems and other geomechanical problems are cases that can generally be seen as plane strain (Alshibli, K. A et al., 2000). Therefore, the purpose of this research is to supplement the study of the effect of strain rate on shear results under plane strain conditions.

Since natural gas hydrate(NGH) was firstly drilled in 2008 in the Muli area of Qinghai, China, a large amount of geophysical and geochemical survey work has been carried out in this area. A large amount of geophysical and geochemical information has been obtained. However, the regularity of the NGH enrichment has always been unclear, it is difficult to locate the NGH reservoir based on these information. In our work, we summarized the geophysical, geochemical and geological data obtained in the area. The favorable identification characteristics of the NGH reservoirs have been analyzed. Moreover, the prediction variable conversion rules of these favorable information has been given. We made predictions based on characteristic analysis method. The results show that the high favorable area we predicted and the drilling of the NGH matched very well. And the drilling of the non-drilling NGH is basically located in the low favorable area, so the prediction model is practical. INTRODUCTION In recent years, considerable progress has been made in NGH exploration at the Muli area of Qinghai Province, China, where altitude is above 4000 meters. More and more attempts have studied the geophysical and geochemical anomalies related to NGH in plateau permafrost regions. However, at present, each exploration method is independent of each other. Only a simple combination of multiple exploration results has been often used to conjecture the favorable area. This method is practical when the selected anomalies are very related to the NGH reservoirs. However, when the situation is more complicated, it is difficult to use a simple combination of multiple exploration results to evaluate the NGH reservoirs. The accumulation of the NGH in the plateau permafrost regions is directly controlled by conditions such as permafrost thickness, geological structure, and gas source. The situation is complicated, and it is difficult to apply the single exploration method directly to predict the favorable reservoirs. Therefore, we need to use appropriate methods to fully and reasonably make use of existing geophysical, geochemical, and geological data to make reservoir predictions and provide better guidance for subsequent exploration.

Extensive studies had been conducted aimed at the natural gas hydrate accumulation systems in the Muli frozen soil region in the Qilian Mountain, but the rule of natural gas hydrate accumulation was still unclear. Based on the audio magnetotelluric test data obtained for five consecutive years, 3D inversion was carried out aimed at the audio magnetotelluric data of the Sanlutian test area and comprehensive analysis was carried out combined with the drilling data of hydrates. The results showed that there was a good correspondence between the 3D electrical structure and the geological structure, indicating the 3D inversion results were reliable. In the 3D electrical structure model, a "chimney" channel consisting of two strata and fault structures was discovered, which corresponded well to the locations where hydrates were discovered. It was analyzed that the "chimney" channel structure played an important role on the migration and accumulation of natural gas hydrates. The results of this paper provided a basis for studying the accumulation mechanism of hydrate in the Muli region. INTRODUCTION The formation of natural gas hydrates is mainly caused by the accumulation of the deep hydrocarbon gases that migrate from deep strata to stable zone along fractures and fissures. For example, in the vast area of the Prudhoe Bay on the northern slope of Alaska, there are a series of high-angle normal faults of NW-trending. These faults act as the upward migration pathways for oil and gas, so gas sources are directly provided for the two natural gas hydrate deposits, Eileen and Tarn (Scott, 2011). Compared with the frozen soil regions in sea areas and high-latitude polar, the frozen soil regions of the Qinghai-Tibet Plateau in the mid-latitudes have thinner frozen soil layers, which are generally tens of meters to more than one hundred meters thick. The natural gas hydrate accumulation in the Muli region is obviously controlled by fault structures, most of which are scattered in sandstone reservoirs, mudstone and oil shale fractured reservoirs (Zhu, 2009).

Due to the hull characteristics of small waterplane area twinhull( SWATH) ship, seakeeping software based on traditional single and catamaran potential flow theory cannot be directly applied to SWATH ship seakeeping prediction, because the longitudinal motion of SWATH must also consider the effects of viscosity and fin lift. The experiments of SWATH ship are carried out in this paper, and different stabilized fin angles and ship speeds are studied. The CFD method is used to perform numerical simulation calculations on SWATH ship, by using STARCCM + software based on the RANS equation. This example is a multilayer encryption of the free liquid surface and the grid surrounding the hull, and is dedicated to building a computational model that can be used for numerical simulation of this ship shape. By comparing the numerical calculation results with the experiment results, the accuracy of the numerical calculations is verified. The numerical simulation results in the higher wave frequencies are highly consistent with the model experiment results. This study can provide a numerical calculation method for the research of SWATH ships. INTRODUCTION The biggest advantage of SWATH ship in terms of performance is its excellent seakeeping. It is necessary to estimate the seakeeping in the early stages of ship design. The seakeeping software based on the traditional single and double-body potential flow theory cannot be directly applied to the seakeeping prediction of SWATH ships, because the longitudinal movement of SWATH must also consider the effects of viscosity and fin lift. Due to the special type of SWATH ship, the transverse section of the submerged part is much larger than the transverse section of the pillar part, and non-linear forces will be generated when the ship is moving longitudinally. Therefore, the influence of viscosity cannot be ignored in the seakeeping prediction If we ignore the effect of viscosity and simply use slice theory to calculate, the frequency response function curve will be too large. This theoretical result is verified by comparing the previous experimental results with the calculated results. Brizzolara, Stefano (2013) used the CFD method to make in-depth research on the design direction of small waterplane area twin-hull ship in terms of its hull concept, such as transforming hull dimensions and optimizing hydrodynamic performance. Mao Xiaofei (2005), based on the slice theory, adopted a complete set of hydrodynamic calculation formulas for SWATH ship, and applied it to extend the seakeeping prediction program of conventional catamarans, and wrote a WAVMOSWATH program in order to calculate and forecast the seakeeping of the SWATH ship, this paper also uses the 390t oilfield small waterline surface transportation ship as the calculation object. The ship's shape under various sea conditions in regular waves and irregular waves is calculated. The longitudinal motion was calculated and analyzed, and the influence of setting the stabilized fin on the seakeeping was compared. The calculation shows that the setting of the stabilized fin greatly reduces the peak frequency response of the longitudinal motion. Based on the CFD uncertainty analysis procedure recommended by ITTC, Deng Lei, Peng Hongyu (2016) conducted an uncertainty analysis of the calculation results of the longitudinal motion in the SWATH ship wave based on the RANS equation, which verified the mesh convergence of the calculation model and the Convergence. Based on the determination of the longitudinal stability of SWATH, Gao Zhansheng, Cai Yan, Hou Jianjun (2014) analyzed the influence and their laws of parameters such as the installation position and fin area of the stabilized fin on the longitudinal stability of SWATH at different speeds.

The possibility of using resistivity to measure the foot protection diameter of a bored pile was investigated. Both laboratory experiments and on-site experiments were conducted using a four-pole electrode arrangement. In the laboratory experiments, we investigated the relationship between the resistivity and the exploration depth for determining the boundary position of dissimilar soil strata. With the results, we developed a measuring method that uses in situ resistivity. The on-site tests confirmed that the resistivity was extremely effective for measuring the hole diameter, including the foot protection. INTRODUCTION In the approximate half-century since the bored pile construction technique was developed in the early 1960s, a variety of construction techniques have emerged that have brought a steady trend of increasingly higher load-bearing capacities. However, in contrast to the technological innovations that have accompanied these increasing bearing capacities, quality management often adheres to conventional methods, and quality innovation has clearly lagged behind current boring capabilities. The reason for this is thought to be because previously there were no doubts about the soundness of the solid mass formed at the tip of the bored pile for foot protection, and nobody had any doubts that uniform solid masses for foot protection were being constructed according to design specifications. Similarly, strength management only extended as far as checking the raw liquid strength of the cement milk as mixed at the mixing plant (Copita, 2011). However, in recent years, it has no longer been possible to ignore the fact that dirt gets mixed into the foot protection liquid, and research has started examining methods for predicting the strength when this is taken into account (Tuchiya and Kuwabara, 2013). This is because there has been a growing awareness of the importance of quality management of foot protection as bearing capacities of bored piles have increased with the development of drilling blades with expansion mechanisms that have enabled the construction of larger foot protection bulbs. Against this background, methods for checking the shape of the foot protection bulb by using borehole sonar (Nakamura et al., 2006) and methods for checking the strength of a soil-cement mixture sampled from the foot protection immediately after construction have been developed (Technical Committee on Quality Control of the Hardened Foot Protection Part of High Bearing Capacity Piles, 2014). Furthermore, the importance of process management for soil stabilization, such as by mixing for uniformity, is being revised anew by treating the foot protection liquid as soil cement (BCJ and BL, 2018).

Cracks may be created in clays after gas hydrate dissociates. More cracks can be created in clays with a high degree of gas saturation after dissociation and the degree of gas saturation is linked to peak undrained shear strength of the clays through experimental tests. A damage model is proposed in this study to characterize strength reduction of clays after cracks are developed. NGI ADP model and damage model are implemented to Plaxis software. A variable distribution of gas hydrate was revealed in Shenhu area, in northern continental slope of the South China Sea. Geotechnical models for two critical slopes are proposed based on seismic profiles. Submarine slope stability is evaluated for these slopes in this area if gas hydrate is dissociated. The finite element analysis showed that safety factor is reduced by 6% to 13% after gas hydrate dissociation. INTRODUCTION Gas hydrate dissociation is often considered as a triggering factor for submarine slope failures occurring in relatively deep waters where the bulk of the gas hydrate is found in fine-grained sediments. Physical and mechanical properties of sediments with gas hydrate have been intensively studied in recent years (Soga, et al., 2006, Yun, 2007, Sultan and Garziglia, 2011, Zhang et al., 2017). It was concluded that strength of soil is increasing with increasing of hydrate saturation and confining pressure. However, there are relatively few studies that focus on the effect of gas hydrate dissociation on the geotechnical behavior of clays, and very few on how gas hydrate dissociation affects the undrained shear strength of clays with cracks caused by dissociation. Sample cracking due to gas hydrate dissociation was observed on the continental slope Keathley area, Gulf of Mexico (Fugro, 2006). Jin et al., (2015) studied crack extension induced by dissociation of fracturehosted methane gas hydrate. Lee et al., (2010) reported volume change associated with formation and dissociation of hydrate in sediment using miscible TetraHydroFuran (THF) as a hydrate, and the result indicated that large axial strains were caused due to dissociation by heating. Yang et al. (2010 and 2015) illustrated the effects of hydrate dissociation in clays from laboratory tests. The tests were combined with visualization including very-high-resolution CT scanning using R11 as the hydrate forming fluid in both laponite and Onsøy clay. The results showed that gas hydrate melting in clay leads to formation of gas bubbles; with increasing volume bubble shape changes to disk shape and fractures develop; continued release of gas leads to connection of fractures from different locations and formation of gas migration pathways. The study developed a mechanistic understanding on how cracks developed in clays due to hydrate dissociation.

A unified theory model is developed for a three-dimensional anisotropic acoustic cloak based on the sound speed matching and boundary impedance matching. A crucial parameter δ , which denotes the material properties, is involved in this multilayered acoustic cloak model. Based on the effective medium approximation theory, each layer in the multilayered acoustic cloak could be constructed using the homogeneous isotropic materials. The different values of the parameter δ are discussed to investigate the invisible effects of the multilayered acoustic cloak. By analyzing the invisible effect of the acoustic cloak, it is found that the incident sound wave can pass through the acoustic cloak smoothly with the less backscattering TS using an appropriate δ value. More importantly, it is seen that the essential requirement for the infinite mass density in Cummer's acoustic cloak can be circumvented in the present multilayered acoustic cloak model. This paper can offer a practical guidance to design and construct the acoustic cloak using the multilayered structures which are composed by the existing materials in natural world. INTRODUCTION Recently, there is an increasing interest in the possibility of the electromagnetic (EM) cloaks, which could hide the objects from the electromagnetic illumination. By using the coordinate transformation, a cylinder electromagnetic cloak composed by metamaterials was formulated for the electromagnetic field (Schurig, Mock, 2006). Both the theory model and the related experiment results showed that this cylinder electromagnetic cloak could indeed be obtained. Meanwhile, the three-dimensional spherical cloaks are also proposed based on the invariance of the Maxwell's equations (Pendry, Schurig, 2006). Following the related concepts and methodologies for electromagnetic cloaks, many researchers have also devoted their time and efforts to the acoustic cloak study. An ideal cylinder acoustic cloak was proposed by comparing the electromagnetic field and the acoustic field (Cummer, Schurig, 2007). Later, an ideal three-dimensional acoustic cloak shell was developed through acoustic scattering theory, indicating that the acoustic cloak requires an anisotropic mass density (Cummer, Popa, 2008). Therefore, the acoustic cloak should be composed of anisotropic materials, but the anisotropic materials are difficult to realize due to the limited natural resources. Thus, one possible approach for this issue is to use the multilayered shell structure with isotropic materials to replace the anisotropic materials. Based on the effective medium approximation theory, the parameters of the multilayered acoustic cloak structure were investigated and the low reflection and wave-frontbending phenomenon could be found from the obtained acoustic pressure fields (Cheng, Liu, 2009). The invisible effects for the near-field and the far-field scattering patterns are described distinctly, indicating that the plane wave could be deflected smoothly around the object shielded by the acoustic cloak and the scattering could be reduced in almost all directions. Besides, the acoustic cloak with multilayered structures has great potentials in practical engineering applications.

The world's demand for energy is growing everyday and special attention is being given to sustainable energy sources like wind energy. This leads to the need for implementation of offshore wind turbines. In German sea regions, the water depths are predominately between about 20.0 m and maximum 50.0 m. Here, the cyclic loading by wind and waves leads to cyclic loads acting on the foundation. At the time being, in most cases monopile foundations are applied. However, for certain subsoil conditions also a gravity base foundation might be suitable and economic. Offshore support structures are exposed to millions of load cycles during their service time. Under such high cycle numbers, accumulated permanent deformation may affect the serviceability of offshore support structures. In particular, the accumulated rotation of the foundation structure is crucial regarding serviceability proofs of offshore wind turbines. The objective of this paper is to investigate the applicability of the ‘stiffness degradation method’ (SDM) to predict the behaviour of gravity base foundation under cyclic loading. The SDM uses the results of cyclic triaxial tests to account for the cyclic soil behaviour in a numerical simulation with the finite element method. This approach was initially developed to describe the behavior of monopile foundation systems. The method and its adaptations for gravity base foundations are briefly described. The measurements at a full-scale prototype of the gravity base foundation conducted a few years ago are utilized as a benchmark problem. Based on the comparison of the SDM results to the measurements, hints and recommendations regarding the application of SDM to gravity base foundations are given. INTRODUCTION In the North Sea and the Baltic Sea in Europe a large number of offshore wind farms are being planned and several farms have already been installed in the recent years. In the beginning, in most cases wind farms were erected in moderate water depths (less than 20.0 m) and monopile foundations have been built as support structures for the wind tower and the turbine.

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.

Anchors are indispensable and important structures in ocean engineering. The majority of previous studies on anchors were mostly based on Finite Element Analysis, but the large deformation of soil was not well handled. This study applied smoothed particle hydrodynamics (SPH) to simulate the anchor which buried in the soil. In this calculation, soil is modeled as elastic-perfectly plastic material, and the Drucker-Prager yield criterion is applied to describe the stress states of soil. Simulation test of anchor moved in the soil is calculated as a challenging example to verify the broad applicability of the SPH method. This study verified the feasibility of SPH in the numerical study of anchor and the results were encouraging. INTRODUCTION Anchor is one of the most widely used safety equipment in many fields such as Marine engineering and civil engineering. By burying the anchor in the soil, the anchoring strength is obtained, thus providing safety guarantee for Marine engineering and civil engineering. When external drawing force is too large, the anchor will be dragged in the soil and the large deformation of soil will occur. Once the soil deformation is too large, the anchoring effect of anchor will fail, and then a great threat to the safety of the engineering practice will emerge. Selecting the anchor with enough holding force is the necessary premise to ensure the safety of the project, and accurately measuring the movement and force of the anchor in the soil is the necessary premise to select the appropriate anchor. In the past, the research on anchor mostly used the finite element method (FEM), but the finite element method which based on grid can not effectively deal with large deformation. The mesh of FEM may distort severely and must be remeshed periodically when dealing with the large deformation and post-failure movement. SPH is mesh free Lagrangian particle method, which particles carry all the states: velocity, position, acceleration, etc. It can well deal with the large deformation of soil. SPH was originally proposed for astrophysical applications (Lucy, 1977 or Gingold and Monaghan, 1977).Since then, It has developed rapidly and successfully applied in many fields such as dynamic response of material strength (Libersky and Petschek, 1990; Libersky, Petschek, Carney, Hipp and Allahdadi 1993;Benz and Asphaug, 1995), free surface fluid flows (Monaghan, 1994), low-Reynolds number viscous fluid flows (Takeda and Miyama, 1994; Morris, Fox and Zhu, 1997), incompressible fluid flows (Cummins and Rudman, 1999; Shao and Lo, 2003), heat transfer problems (Clear and Monaghan, 1999), multi-phase flows (Monaghan and Kocharyan, 1995; Monaghan, 1997; Morris, 2000), geophysical flows (Gutfraind and Savage, 1998; Cleary and Prakash, 2004), turbulence flows (Monaghan, 2002), seepage failure flow (Maeda and Sakai, 2004) and elasto–plastic soil (Bui, Fukagawa, Sako and Ohno, 2008).

ABSTRACT The recurrent interactions between ocean waves and sea ice are a widespread feature of the polar regions, and their impact on sea-ice dynamics and morphology has been increasingly recognized as evidenced by the surge of research activity during the last two decades. The rapid decline of summer ice extent that has occurred in the Arctic Ocean over recent years has contributed to the renewed interest in this subject. Continuum models have recently gained popularity to describe wave propagation in various types of ice cover and across a wide range of length scales. In this paper, we propose a continuum wave-ice model where the floating sea ice is described as a homogeneous poroelastic material and the underlying ocean is viewed as a slightly compressible fluid. The exact dispersion relation for linear traveling wave solutions of this coupled system is established and compared to predictions from existing theories. INTRODUCTION Wave-ice interaction is a two-way process. Ice scatters ocean waves and redistributes wave energy, in turn gravity waves stress and potentially fracture ice. In this paper, we focus on the phenomenon of ice-induced wave attenuation (Wadhams et al, 1988). A common place where waveice interactions play an important role is the marginal ice zone (MIZ), which is the outer edge of the ice cover, closest to the open ocean. It typically consists of ice floes, brash ice and open water. Several linear models have been proposed to study wave-ice interactions and can generally be classified into two categories: solitary-floe models and continuum models (Squire, 2007; Kohout and Meylan, 2008). Of special interest here is the latter category. The mass-loading (ML) model is probably the most basic continuum formulation. It treats ice floes as a simple mass load on the ocean surface. The thin elastic plate model (hereafter referred to as FS) incorporates the elastic response of the ice layer into the formulation, with the ice layer being described as a Kirchhoff-Love plate (Fox and Squire, 1994). Alternatively, Keller (1998) proposed a two-layer formulation where a viscous fluid layer lies on top of an ideal fluid region. In this context, viscosity stems from the fact that the ice cover is viewed as a suspension of solid particles in water. Building upon Keller's work, Wang and Shen (2010, now referred to as WS) included elasticity in the upper layer and described the ice layer as a homogeneous incompressible viscoelastic medium according to Voigt's model. Their viscoelastic fluid model synthesizes the thin elastic plate and viscous layer models as limiting cases under suitable conditions. Recently, Mosig et al (2015) extended the FS model by introducing a complex Voigt shear modulus to account for viscous dissipation. This extended model is referred to as EFS in the following sections.