Crew transfer vessels (CTVs) are the main personnel transport vehicle in offshore wind farm businesses. Accurate evaluation of the accessibility to the offshore wind turbines (OWTs) by CTVs is very important to ensure the safety of personnel and to improve work efficiency. This study developed an artificial neural network (NN) model to evaluate the accessibility based on real experimental data of CTVs. Sensitivity analysis was carried out to evaluate the effect of wave and wind parameters on the determination of the accessibility of CTVs. It is found that NN models show great potential for predicting the accessibility of CTVs. Wave condition plays a dominant role in the success of transfer by using CTVs. Using wind conditions as additional input parameters for NN models can slightly increase the classification accuracy. The classification error is believed due to the insufficiency of the objectivity of the dataset.

 This study clarified applicability of underwater drone for inspection of fishing port infrastructure performed by diver. As a result of having a fieldwork, underwater drone can discover damage such as crack of concrete or corrosion of steel material in the same way as diver, and in underwater drone, it was revealed that the detailed size measurement was possible. In addition, one piece of whole photograph which made using a method used in UAV is usable for the identification of the position of damage and grasp of the outskirts situation of damage. Furthermore, When the area of the inspection is larger than 2400 m2, cost becomes 30% lower in Underwater drone than divers.

 Underwater inspection of port structures is required to be carried out by underwater robots. However, it is difficult to control them because operators cannot know robot`s position in the muddy water. Therefore, this study examined the automation of a moving method for an underwater robot with wheels.

 This study focused on an investigation of the external shape of a structure. The robot was installed guide arms, and was attached wheels to the end of the arms. The autopilot was designed to move while maintaining a certain distance by pushing the wheels and the arms against structures with thrusters. The robot would take photographs of the structures while moving.

 To confirm performance, a simulated work test was conducted in a water tank and compared with a method using acoustic rangefinders and a doppler velocity logger. In this method, the output of the thrusters is adjusted by the results of the sensor measurements, and the robot keep the route. As a result, it was confirmed that the system with the wheels was able to move in a straight track closer to the plan than the system using rangefinders. In addition, the overcoming of steps was examined, and a method of operation when caught on a step was confirmed.

 The authors have clarified, by researching fishing ports and markets in Europe, that the implementation of ICT, such as computerization of sales operations, can improve productivity and add value, and that fishing ports and markets can function as bases for resource management. Computerization of sales operations is an urgent issue in Japan. In addition, the issues of introducing online sales, provision of information from fishing ports and markets, and one-stop services were identified.

 In this study, we devised materials and shapes of concrete blocks to address multiple factors of rocky-shore denudation and conducted verification experiments in actual sea areas. In addition, the ₂ absorption amount of seaweeds growing on the test blocks were estimated.As a result, it was confirmed that seaweeds such as kelp thrived better in the square test blocks contained with amino acids than in the conventional blocks and that seaweeds continued to thrive and diverse aquatic organisms appeared in the plate test blocks impregnated with amino acids.The ₂ absorption amount of the square test blocks was 7.995 t-₂/ha/year, 1.125 t-₂/ha/year has estimated for the board-type test block. Future work will require additional correction of data through ongoing research and verification of the effects of technologies with different characteristics, either alone or in combination.

 Coastal area of Iwate Prefecture, which is close to the Shiome where the Oyashio and the Kuroshio collide is one of the highest fishery catches in Japan, mainly catching Sea Urchin and Kombu. Kombu forms seaweed bed, takes an important role in maintaining biodiversity and preserving the marine environment, supporting the ecosystem of shallow areas. However, due to the damage caused by fishery ground subsidence caused by the Great East Japan Earthquake 2011. Isoyake phenomenon continues and the catch amount tends to decline. Futhermore the aging and reduction of fishermen triggers the decrease of catches, leading to serious problems in Iwate Prefecture's fisheries productivity. In this study, we develop a technology that enables symbiosis of Sea Urchin and Kombu, and to gather Sea Urchin to create seaweed bed in a cost-effective method prescribed by the MAFF.As a result, we gained a foundational knowledge in creating a sea area to construct a symbiotic technology of Sea Urchin and Kombu, that is also safe for older fishermen to use. Also, using AI we have confirmed a method to discriminate between the concentration of Sea Urchin and efficiently installation for enhancement substrate of Kombu.

 For utilizing the FSB as a large marine algal reef, the biological affinity for marine algal was verified from a settlement test in the laboratory and a block installation test in the actual sea area. The growth rate of Sargassum horneri on the FSB test piece by the laboratory experiment was almost the same as those other pieces of concrete and natural stone. In addition, a small block (30 cm square, 30 kg) was installed in the actual sea area (Uchiura bay, Chiba), and changes in the amount of marine algae settlements to the block surface were observed. The amount of marine algae settlements per unit area of the FSB surface 10 months after installing was equal to or greater than that of the concrete block, and stable marine algae settlement on the FSB was confirmed even in the actual sea area. Furthermore, the concentration of heavy metals contained in the deposited marine algae during the laboratory experiment and the actual sea area installing test was measured. As a result, the heavy metal content of marine algae settlement to the FSB was not significantly different from that of other materials such as concrete and natural stone. These values were lower than those of natural marine algae, and these results also clarify the possibility using of FSB as marine algal reef material.

 Tidal flats have many beneficial features such as water purification and habitat for organisms. In recent years, it is also expected that they will play new roles, such as creating blue carbon. Sand is required as a basic material for the creation of tidal flats and shoals. But the use of natural sand for the construction of a tidal flat may cause new environmental damage, so alternative materials must be developed. In this study, the performance of the molten slag has been studied through comparative experiments to create artificial tidal flats in a water tank using different materials. And artificial tidal flat creation in a real sea area using molten slag was conducted. The results of the study showed no significant effects on water quality, such as pH. There was no difference in the death rate of the added Manila clams(Ruditapes philippinarum). This indicates that molten slag has potential as a material for tidal flat.

 Long-term changes in longshore sand transport around Point Irago were investigated. When multiplying the area of the coastal lowland of Nishino-hama Beach northeast of Point Irago by the thickness of the sand layer of 27 m of this lowland, and divided by 6000 years after the Jomon transgression of the sea, the rate of deposition of sand became 7.4×10⁴ m³/yr. This is equal to the rate of longshore sand transport turning around the tip of Point Irago which is the only source of sand to this lowland. On the other hand, the depth of closure was estimated to be 6 m from the bathymetry around Irago Port measured in 1956, and longshore sand transport was estimated to be 6.9×10⁴ m³/yr given this depth of closure. Thus, longshore sand transport estimated in geomorphological and engineering time scales was in good agreement.

 The Philippines has many islands and complicated embayed coastlines, so the wave incident angle to the direction normal to the shoreline may be significantly large, causing beach changes due to High-angle wave instability. Along such a coast, ordinary shore protection method using groins is not applicable for the conservation of the shoreline. The southern coast of Panai Island in the Philippines has such characteristics. In this study, beach changes of this island was investigated using satellite images together with field observations. Wave field was also calculated using the energy balance equation. It was found that waves are incident at an angle larger than 45° at several locations along the coastline, causing severe beach erosion douncoast of the protruded shorelines.

 FS3M, a numerical model that can compute dynamic interaction between waves and topographic change, was applied to local scouring around piles to investigate the influence of three sediment transport parameters. Machine learning models, XGBoost and LightGBM, were trained using numerical results and the influence of the parameters was also evaluated from the machine learning. Results showed that the final scour depth increased with an increase in a coefficient of the pick-up function Cp, which had the largest contribution to the final scour depth. Furthermore, the height of the tangential flow velocity zvel from the surface of the sediment substrate used to compute the friction velocity and the vertical cell height Δz_surf near the surface of the sediment substrate had the smaller contribution than Cp. Based on the results, a method for determining the parameter values was proposed.

 Yonaha-maebama Beach on Miyako Island is a cuspate foreland formed behind Kurima Island. The beach has been stable for a long time except the tip of the cuspate foreland, and it was famous for many tourists. However, in recent years, north part of the cuspate foreland has been eroded and the facilities of the hotel behind the sandy beach were severely damaged owing to beach erosion, causing difficulty in coastal use. To investigate the real situation of the erosion of this beach, shoreline changes were investigated using satellite images together with the field observations using an UAV. Past pictures related to the beach erosion were also collected to study the cause of the beach erosion.

 Beach erosion of the coast near the Aklan River mouth on Panai Island in the Philippines was investigated. After the field observation of the coast in 2014, subsequent investigation using satellite images and field observation was carried out in 2019 together with the study on the deformation of a sand spit formed at the southeast end of a barrier island. Along the coast, beach erosion was triggered by the disruption of continuous movement of sand supplied from the Aklan River associated with the formation of a barrier island and river bed excavation in the tributary of the Aklan River. Seawall was locally constructed from upcoast, so downcoast erosion has been expanding. Large deformation of the sand spit located at the southeast end of the barrier island occurred because of the decrease in sand supply.

 The purpose of this study is to develop a three-dimensional numerical model that can accurately predict local scour phenomena around a cylinder under a wave-current coexistence field in order to contribute to scour countermeasures at the foundation of offshore wind power generation facilities. Verification of the wave-generation performance of the developed numerical model indicates that the model can reproduce water level variations well in wave alone and in wave-current coexistence conditions. In addition, the calculated results show that extremely complicated three-dimensional flow around a cylinder occurs in a wave-current coexistence field under the targeted experimental condition. Finally, a comparison of the scour phenomena shows that, except for the area directly behind the cylinder, the numerical model can qualitatively reproduce the local scour phenomena in a wave-current coexistence field.

 Shoreline changes associated with the extension of offshore breakwaters during half century since 1964 were investigated, taking the coasts of a 12.5 km stretch between Hitachi Port and Isozaki fishing port facing the Pacific Ocean as the examples. On the Naka coast in the northern part of the study area, shoreline changes were triggered by the wave-diffraction effect of the offshore breakwater of Hitachi and Hitachinaka Ports. The coastline of the eroded area has been completely covered with a seawall and concrete blocks until present. At Ajigaura Beach in the south part of the study area, clockwise shoreline rotation took place owing to the extension of the offshore breakwater of Hitachinaka Port. Future measures to preserve sandy beach was proposed on the basis of field data.

 Deformation of sand mound formed by beach nourishment associated with a sand back pass was investigated at Ajigaura Beach. The erosion process of the sand mound and the deposition of the material owing to waves were investigated. UAV images were taken on 16 July 2021 immediately after the nourishment and 15 October 2021, and three-dimensional beach topographies were measured together with the field observations on the conditions of the beach. Nourishment sand was quickly transported again in a short period while losing the effect, and entire nourishment sand was transported away from the nourishment site after three months, implying the inefficiency of the present method. After the improvement, by which nourishment sand is stably maintained at the nourished beaches, beach nourishment should be carried out.

 In the windy season (from the mid-December to the early March) when wind-blown sand generates, beach topography surveys by the Terrestrial Laser Scanner (TLS survey) and the Unmanned Aerial Vehicle (UAV survey) were carried out 4 years at the Hiyoriyamahama beach on the west coast of Niigata. Accurate TLS survey makes it possible to calculate reliable sand volume.

 From the sand budget analysis of the beach topography, it became possible to confirm the fact of the generation of wind-blown sand from the swash zone and to estimate its volume. The amount of sand blown off from the swash zone during a winter season ranged from approximately 1.6 to 2.5 m³/m. In a particular area where is named the Second District by the beach management office, the volume of blown sand estimated from the accumulated sand volume around the fences installed at the land side edge of the beach was 4.6 m³/m in 2016 and 7.5 m³/m in 2017, respectively. The ratios of the volume generated from the swash zone and the volume estimated at the land side edge were 2.27 / 4.6 =0.49 in 2016，and 3.66/7.5=0.49 in 2017, respectively. It results that approximately 50% of blown sand is generated from the run-up zone. The width of the swash zone was about 20m to 40m. The maximum run-up height read from the topographical data was roughly in match up with the value estimated by the revised imaginary slope method.

 The field survey and numerical simulations of morphological changes associated with the typhoon Lupit (2021) were carried out near the detached breakwaters at Aoyama beach, Niigata coast. The topography and bathymetry data were obtained by UAV photogrammetry, RTK-GNSS and GPS sonar when we carried out field survey. Numerical simulations of morphological changes were performed by XBeach. As a result of numerical simulations, erosion in the land area and deposition in sea area near shoreline were calculated, which is consistent with the field survey. In addition, Brier skill score (BSS) was employed to quantitatively evaluate the simulated morphological changes. BSS was higher in the case where the observation of water level was used than that in the case where the astronomical tide levels were employed. Finally, salient was formed behind the breakwaters in the numerical simulation under the influence of diffracted waves and nearshore currents associated with the typhoon.

 On the Suruga coast, Typhoon Hagibis caused three-dimensional topographic changes near the embankment. The slope of the beach profile in the offshore direction became steeper and became more gradual as wave height increased. The slope of the beach profile after high waves was equal to the previous empirical equation. The slope of the coastal profile in the longshore direction was uniformly changed by high waves, but became steeper only on the north side in the later stage of the typhoon, resulting in a three-dimensional topographic change. The three-dimensional topographic changes was caused by the outflow of coastal vegetation, which caused a difference in elevation, and the development of a dominant longshore current.

 The 3D topographic measurement system was constructed to measure a gravel beach during a hydraulic model experiment. It was possible to create a DSM and an ortho-mosaic of the gravel beach using the SfM/MVS technology applied to multiple images taken simultaneously. Furthermore, the influence of wave-dissipating blocks placed on the gravel beach on the topographic change was investigated using the constructed measurement method. The results indicate that the placement of wave-dissipating blocks on the beach increases the time required for the topography to reach equilibrium, and that the gravel may be deposited more landward. The usefulness of the 3D topography measurement system was confirmed for measuring the 3D topographic changes that occur in hydraulic model experiments.

 In this study, the performance of a two-layer filter as a countermeasure against internal erosion of backfilling sands at the back sides of seawall and quay walls was systematically studied through a series of sand filtration tests and prototype-scale experiments for the purpose of enhancing the countermeasure by considering the grain shape of the backfilling sand and various external forces at the waterfront. As a result, in cases where angular sand with a low degree of roundness is used as the backfilling sand, it was verified that the filter maintained a sufficient deterrent effect under various external forces when the uniformity coefficient of the filter (D_F60/D_F10) was higher than 2.5, and the median particle diameter ratio (D_F50/D_S50) was less than or equal to 25.

 In nearshore morphodynamic modeling, the simulation of offshore-directed mean current or so-called undertow is necessary for sediment transport as a significant driver. XBeach model is wildly used in predicting storm impacts on natural coasts, yet in regard to morphodynamic predictions, the undertow simulations have been rarely discussed. Recent improvements in the XBeach undertow prediction have been made by modifying the wave roller model. However, despite the improvements for high-wave conditions, the XBeach still performs poorly in predicting undertow under low-wave conditions, where the water depth is a dominant factor controlling undertow current instead of wave mass flux. To improve the XBeach undertow prediction, this paper proposes a modification based on the water depth effect. XBeach performance was tested by comparing two-dimensional simulations with the field observations during low-wave period conditions at Hasaki coast, Japan.

 Calibration of model coefficients yielded good results for waves, though low accuracy for the simulated undertow. Here, the individual contributions of Stokes drift and Lagrangian velocity (wave forcing term) were respectively modified by including a water depth coefficient. This adjustment caused the undertow’s water depth to be considered from under the wave trough level. The temporal undertow comparisons show a small improvement in the whole period and the accuracy correlates with tidal elevation. When the comparisons of undertow spatial distribution were considered at the different water levels, the undertow results were significantly improved especially at low tide, with an increase in accuracy from bad to fair.

 Chirihama Beach, where drivers are allowed to drive their cars over the sand beach, is an important site for tourism. However, since the 1980s, the area has been actively eroded and the shoreline is reported to have receded by approximately 50 meters. This report reviews the characteristics of the littoral drift of the Chirihama Beach based on a field survey of the shoreline and the numerical calculation of the beach profiles. The results showed that the wave direction of incident waves from the north-north-west and north-west predominated over the course of the year. Seasonal variation in the significant wave height was clear and large wave heights emerged during the winter period. On the Chirihama Beach, the multiple bar was formed, and the littoral drift in the south direction occurred.

 There are many sand ripples of small size topography on tidal flats. It is essential to grasp the processes of sand ripple deformation and migration because these processes have much influence on sand movement and topographic change in coastal areas. In this study, continuous sand ripples photography in the water was conducted, and the investigation of characteristics of sand ripple’s migration was attempted by comparing with sea conditions and sand ripple shape. The results showed that the sand ripple migration was generated in a limited duration when the water depth was very shallow, and the sand ripple shape became asymmetry and sharp during the migration. It was indicated that strong instantaneous currents greatly affected sand ripple migration. Moreover, it was also inferred that the estimation of sand ripple migration might be possible using the information on wave conditions, water depth and sand diameter in the field.

 Narrow multi-beam surveying (hereinafter abbreviated as NMB) is being put to practical use as a technology that can visualize underwater parts, and is being put to practical use in ICT dredging work completion inspection and ICT foundation work quantity calculation. However, the completed inspection of the rubble mound has not been realized. This is largely due to the complicated shape of the rubble mound, the high accuracy required for management standards, and the point cloud characteristics of NMB. Therefore, in this study, we examined the construction of a finished product inspection method based on the NMB point cloud characteristics of the rubble mound.

 As a result, it became clear that the unevenness of the rubble mound was dominant in the influence on the acquisition point cloud of the NMB survey for the rubble mound. We constructed a method to calculate the evaluation value from the point cloud, which enables the evaluation of slope height, extension, and width. This made it possible to evaluate the entire rubble mound.

 The Ministry of Land, Infrastructure, Transport and Tourism (MLIT) promotes “i-Construction” which drastically improves productivity in all construction processes. As a part of “i-Construction”, multibeam echo sounding is used to measure bathymetry for dredging works. Although multibeam echo sounding can measure many point data at one time, it takes considerable time and labor to remove the noise from multibeam echo sounding data.

 This research applies the deep learning method to the noise removal for multibeam echo sounding. The training data uses the multibeam echo sounding data observed at the actual dredging works. The accuracy and work efficiency of the developed denoising model using the deep learning method are examined by other data collected at the actual dredging works. The results show that the proposed model can remove the noise with a certain degree of accuracy and that the working time can be reduced.

 Steel slag-dredged soil mixture is a material used for landfill and shallow field construction. As a result of calculating the CO₂ emissions during the construction of the steel slag-dredged soil mixture, the CO₂ emissions during backhoe mixing were reduced by about 40% by using the Calcia bucket.

 In addition, CO₂ emissions during construction were reduced by 30% or more compared to backhoe mixing by using a drop mixing vessel and putting it into water through a tremie pipe.

 Since the wave-dissipating block has a long shape in the extension direction and it is difficult to work directly above the block in terms of safety management, the "Surveying Manual Using ICT Equipment (Block Installation Work)" will also be updated based on the latest research. It is expected that UAV surveying will be used. However, there are few cases in which the evaluation and utilization methods of the acquired data of the wave-dissipating block have been examined, and sufficient knowledge is lacking in utilization. Therefore, in this study, we clarified the point cloud characteristics of the wave-dissipating block using a model and locally acquired data, and examined the evaluation method for utilization.

 As a result, it was confirmed that the applicability to the appearance confirmation method using the point cloud data, the point cloud characteristics of the wave-dissipating block in the installation direction, and the validity of adopting the highest value in the area evaluation based on the point cloud characteristics were confirmed. The area evaluation is an effective means for grasping the shape and current status of a long wave-dissipating block in the extension direction, and is expected to be applied to efficient management in the future.

 In recent years, the efficiency of rubble trimming work and the manpower shortage of divers have become problems, and the dead-weight rubble trimming method has been adopted as one of the countermeasures. However, the flow generated by falling dead-weight causes relatively small rubble to be scattered, which reduces the efficiency of the work. Since it is important to evaluate the velocity generated by falling dead-weight, this study examines the applicability of DualSPHysics to the flow generated on the rubble mound when dead-weight is dropped. The time series of the free-fall of the dead-weight was reproduced well. Reproducibility of the flow generated by falling dead-weight was good for particle size dp = 3 mm. It was also found that almost no flow occurred just below the center of the dead-weight, and that the maximum velocity occurred near the sides of the bottom plate of the deadweight. Furthermore, the maximum velocity generated at hc = 50 mm was reduced by approximately 50% compared to a drop height of hc = 300 mm.

 Ordinally, for corrosion protection in marine steel structures, cathodic protection methods is applied to M.L.W.L. or less, and coating protection methods is applied to L.W.L. -1.0m or more. Therefore, we considered to expand the effective range of cathodic protection in under-seawater to the coating protection area by applied high-conductivity mortar mixed with carbon as a covering material. it can reduce the resistance to 1/100 compared to ordinary concrete and confirmed that it can be protected with suppling 1mA/m² or more in underwater environment and 100 mA/m² or more in dry environment as corrosion protection current. Sufficient corrosion protection performance was confirmed at a range of L.W.L. +235 cm or less from result of 3.5 years-exposure test in marine environment.

 This paper evaluated the soil resistance during installation by a vibratory hammer. Steel pipe piles with a diameter of 1800 mm were constructed at Niigata airport signal bridge construction. During installation, dynamic measurements with axial strain and acceleration of the vibratory hammer body were performed. As the calculation method of the soil resistance for vibratory hammer installation, the singlemass model analysis method and the CASE method (Rausche et al., 1985) based on the one-dimensional wave theory were adopted. We attempted to separate the soil resistance into the shaft and the toe from the shape of the soil resistance – displacement curve. The calculated soil resistance curve trends were in good agreement with the N values in the ground survey results.

 In harbor facilities such as caisson type seawalls and quays, the geotextile sheet laid between the backfill stone and the sand is often damaged by the time the landfill is completed, which is a factor in sand leakage into backfill stones. The main causes of damage are as follows. 1) When it flutters or swings due to waves or wind, it comes into contact with the backfill stone and wears. 2) Abnormal tension is generated by being drawn in by the sinking of the geotextile sheet after it floats due to waves or tides. 3) Abnormal tension is generated because the geotextile sheet is pulled in by throwing in landfill sand.

 Therefore in this study, we conducted elemental tests and load confirmation and demonstration experiments of the "geotextile sheet pull-in reduction method", which is a measure against pull-in using auxiliary materials, and clarified the pull-in suppression effect.

 The rate of landward component of windblown sand was estimated on the basis of the profile changes along transects No. 102, 88, 86 and 84 measured between 2015 and 2020 in the vicinity of the Kikugawa River facing the Enshu-nada Sea. Field observation was carried out on 20 April 2021, and the beach material was sampled. The rate of landward sand transport was estimated to be 2.7 m³/m/yr (No. 102), 3.4 m³/m/yr (No. 88), 3.9 m³/m/yr (No. 86) and 8.1 m³/m/yr (No. 84) with an average of 4.5 m³/m/yr. This rate had the same order of magnitude with the value of 3 m³/m/yr estimated from the long-term topographic changes in the previous study. It was concluded that the value estimated from the long-term beach changes corresponds well with that estimated from the survey results.

 The dynamic relationship between grain size and beach face slope, obtained by applying the law of constrictions to sediment transport in the upwelling area, was used to compare the characteristics of coral reef beaches.

 In the relationship between grain size and shape, a negative correlation was observed in coral reef beaches, where Rc increased with decreasing grain size, and the opposite positive correlation was observed in sandy beaches. The analysis of sediment grain size and beach face slope showed that when the beach type was changed to reflective or deviatoric, there were differences in grain size and foreshore gradient between coral reef and sandy beaches, and these differences were attributed to the grain size distribution of the beaches.

 Beach erosion of the Seisho coast was investigated on the basis of shoreline analysis using aerial photographs. The hotspots of erosion of the coast were located on the Kozu and Maekawa coasts east of the Morito River mouth, and the area between Ninomiya IC of the Seisho Bypass and the Kuzu River mouth. The cause of the erosion on the Kozu and Maekawa coasts was due to the offshore discharge of sand via a submarine canyon offshore of the Morito River. In the latter case, sand has been transported away by eastward longshore sand transport. The entire volume of eroded sand was estimated to be 2.86×10⁶ m³ between 1973 and 2020. Assuming that the entire volume of sand was transported into the submarine canyon, the rate of discharge was estimated to be 6.1×10⁴ m³/yr.

 The direction of the prevailing waves incident to a pocket beach of the Ogimi coast in Okinawa was ivestigated using satellite images. The direction of incident waves has changed counterclockwise from N33°W to N57°W by an angle of 24° since 2009, resulting in the rotation of the shoreline. Detached breakwaters have been constructed along the shoreline of the convex shape and the shoreline orientation changes by 56° at the middle of the detached breakwaters. So, eastward longshore sand transport took place at No. 3 detached breakwater, located at the location where the orientation changes, in response to the change in the direction of prevailing waves, causing large beach changes around the detached breakwaters.

 Among implantable offshore wind turbine foundations, monopiles, which are the least expensive to fabricate as a structure, are widely used in Europe and other countries. Although there are many cases where monopiles have been used in Japan, there are also cases where monopiles are not suitable depending on local conditions. Therefore, we focused on the suction bucket foundation, which is expected to reduce costs depending on conditions, and conducted hydraulic model experiments on its scouring characteristics. The results showed that suction buckets reduce the maximum scour depth by about 13% compared to monopiles. The scouring characteristics of the piles in this study, where the pile diameters were in the middle range, were different from those of small- and large-diameter piles. The maximum scouring depth of the suction bucket was found to occur just below the bucket, and it was expected that scouring could be suppressed by installing scour protection around the edge of the bucket.

 The main cause of drowning accidents on beaches is rip currents. There are various locations that rip currents occur, but particularly they occur regularly around structures, such as jetties. Therefore, it is effective in preventing drowning accidents that clarification of which conditions rip currents occur. In this study, the occurrence of rip currents around the jetty was investigated by applying image analysis to images taken by a fixed-point camera along the Wakasa-Wada coast of Fukui Prefecture, and by comparing them with observation data of wave and tide. As a result, rip currents were detected in 340 cases (81 %) out of 420 cases. It was considered that rip currents occur regularly regardless of wave and tidal conditions, in the area near the jetties on the subject beach. Therefore, for preventing drowning accidents, it was considered that it was important to thoroughly avoid use near the jetties.

 In this study, we investigated a method for detecting the occurrence of unsteady rip currents using image averaging from images taken by a web camera installed on the Wakasa-wada coast. As a result of comparison between the judgment of the occurrence of rip currents by this method and that of three experienced lifesavers, the accuracy rate was 99.4% in the analysis using the test data, and 56.9% in the validation data. It was found the accuracy decreased under the following conditions: early morning (7 to 8 a.m.), evening (16 pm or after), cloudy and rainy. On the other hand, for wave heights of 0.5 m or greater in the validation data, the accuracy was 75 %. Therefore, it was found that this method has a certain level of accuracy in detecting the occurrence of rip currents at wave heights of 0.5 m or greater.

 Miyazaki Sun Marina, which was constructed on the north side of Miyazaki Port, has been suffering from a sedimentation problem at the entrance to the marina channel since it was opened. No drastic solutions to this problem have been shown yet, and a dredging work has been done repeatedly around the entrance to the channel in order to keep safety navigation. This study investigated this sedimentation problem with using 3-dimensional numerical model, Delft-3D. The numerical simulation reproduced the sedimentation phenomenon around the entrance to the channel, and the sediment transport was discussed by referencing flow fields. This study also discussed the relationship between this sedimentation problem and the beach restoration program that has been implemented on the north of the marina. Furthermore, this study proposed a solution to mitigate the sedimentation problem at Miyazaki Sun Marina.

 Sediment Microbial Fuel Cells (SMFC) is a device that converts the reduced enrgy of sediment into electric power. SS-SMFC, which is a mixure of steel slag (SS) and sediment, has high power generation capacity. On the other hand, SS-SMFC has not been put into practical use because the current processing capacity of the cathode is the rate-determing factor and the internal resistance is lager than that of general cells. The purpose of this study is to construct a practical power generation spscification for SS-SMFC. We investigated an energization method to reduce the cathode overvoltage, then succeeded in developing an air cathode with an improved cathode oxygen supply rate, and experimentally determined the external resistance and cathode-anode ratio that maximize the power density, and SS-SMFC.

 In recent years, the offshore wind turbines industry has become more active in response to the movement toward carbon neutrality by 2050, and technological development of large-scale offshore wind turbines with improved power generation efficiency and greater economic efficiency has progressed. However, their response characteristics and the relationship between the scale of power generation and wind turbine response remain largely unknown. In this study, coupled load analyses in wind and waves were performed on fixed-bottom offshore wind turbines with different power generation scales to investigate the differences in the response characteristics of each turbine. As a result, it was found that wind response characteristics are similar between wind turbines of different power generation scales, that wind turbines become structurally more stable against external forces as they become larger, and that the response amplification characteristics due to waves differ between wind turbines of different power generation scales depending on wind response characteristics even under the same wave conditions.

 The effectiveness of flume-type anti-oscillation tanks against the motion of a floating caisson under regular, unidirectional irregular, and multi-directional irregular waves was investigated using hydraulic experiments. From experimental results, it was found that the non-dimensional total amplitude of the pitch was reduced with an increase in the mass of free water filled in the anti-oscillation tanks. Moreover, the non-dimensional total amplitude of the roll was reduced by loading free water and could be increased by loading additional free water. This suggested that there can be an effective mass of free water in each anti-oscillation tank in the surge and sway directions.

 A numerical analysis method using the boundary element method (BEM) was developed for motion of a floating caisson with flume-type anti oscillation tanks. Fluid forces were calculated in the fluid calculation region around the floating caisson and in the fluid calculation region inside the anti oscillation tank, respectively, and the momentum was calculated by the equation of motion coupled with the fluid force calculations. Free-motion experiments were conducted on a floating caisson with Flume-type anti oscillation tanks. The natural period of the roll increased and that of the pitch decreased with different lengths of anti oscillation tank in the roll and pitch. The numerical analysis reproduced the change in the natural period of the free-motion. Comparison with previous experiments confirms that the amount of the Pitch and Heave under regular wave and the damping effect of the anti oscillation tank are reproduced.

 Hydraulic model experiments were conducted to understand the characteristics of the motion of a spar-type floating tow under the action of transverse waves and during turning in the construction of a floating spar-type offshore wind turbine. In the case of towing under the action of transverse waves, the amount of roll motion tended to increase with longer period waves and higher towing speeds. In the turning towing experiment, we confirmed that the spar rolled outward significantly due to centrifugal force when the turning radius was small in relation to the towing speed, and evaluated the towing speed and turning radius during construction. In addition, we focused on the difference depending on whether an auxiliary towing tug is used or not, and confirmed that in the case without an auxiliary tug, the wave drift force becomes large when the wave period is small, and therefore, the tug cannot turn the head. Therefore, the necessity of an auxiliary tug for turning towing construction was confirmed.

 Elastic mooring lines can keep stable bearing force even if the position of the attachment point on the floating body side move up and down and it is possible to suppress the motion of the floating structure. But it has never been applied to very large floating structures (VLFS) over 500 m. In addition, there is no description of mooring design by elastic mooring line in technical standards and guidelines of mooring design.

 Therefore, in this study, the motion response of VLFS according to the restoring force characteristics of elastic mooring lines was clarified, and a chart showing the mooring specifications within the applicable range of elastic mooring lines was created. Then, the living performance of VLFS was evaluated using the acceleration obtained from the motion response analysis in irregular waves. And a series of procedures up to the determination of mooring specifications were shown in consideration of the safety of the elastic mooring lines and the constant operation.

 In the construction of a monopile foundation for offshore wind power generation facilities, it is important to know how much the operation rate can be secured against the motion of the suspended load in order to calculate the process and costs, assuming that a large crane ship is used to set the monopile in the open sea. Therefore, analysis of the ship oscillations among waves was conducted with the suspended monopile to study the behavior of the suspended load. The analysis results showed that the suspended load moves significantly around the natural period of the hull and the load, and that the motion sometimes behaves like a double pendulum that the upper and lower ends of the suspended load move in opposite phases. It was also confirmed that the swing of the suspended load affects the sway of the ship via the boom motion. Furthermore, in the case where the monopile is half submerged in water, it was confirmed that the motion of the monopile is reduced compared to the case where that is in air, and it rotates with part of monopile as the fulcrum near the water surface.

 Subsea Hydrogen Production and Storage Facility (SHPS) has been proposed by us that uses ocean renewable energy to produce compressed hydrogen. SHPS consists of subsea production facilities that produce and store compressed hydrogen, a small floating body that sends electricity and alkaline water from the sea to the seabed, and risers that connect the floats to the subsea facilities. And SHPS aims to produce compressed hydrogen of about 40MPa, so its submarine production facilities are expected to be installed in the sea area at a depth of 4000m. As a riser system used in ocean development, there are Flexible Riser and Steel Catenary Riser (SCR) among other things. However, flexible riser is expensive, and SCR has problems with fatigue at touchdown zone (TDZ). Therefore, Steel Lazy Wave Riser (SLWR) with buoyant materials attached to SCR was developed. Due to the effect of buoyant materials, SLWR reduces breakage due to the riser's own weight and fatigue in TDZ, and realizes miniaturization of the floating part of SHPS. And SLWR is cheaper than other riser systems. However, SLWR is mainly analyzed for FPSO, and the response characteristics of small floating body with SLWR are not fully understood. In addition, since the small floating body is permanently installed in the installation sea area, it is not possible to evacuate even in stormy weather, so it is necessary to confirm the safety in the ultimate limit state. Therefore, in this study, the characteristics of SLWR were first grasped, and a parametric study on dynamic behavior in a regular wave including a mooring device for a small floating body with four SLWRs was conducted, and efforts were made to understand the response characteristics.

 Measures for achieving carbon-neutral ports have been progressing in Japan and decarbonization of international shipping has been discussing at IMO. Whereas, numerous of container ships have been waiting offshore of various world ports, the increase of CO₂ emission by this waiting was concerned.

 This study estimated additional CO₂ emission by offshore waiting ships at all container terminals in Tokyo Bay and the effect of countermeasures. As a result, it was revealed that the emission of offshore waiting corresponds to 15% of that of berthing ships and the three fourths of the emission possibly be decreased by the adjustment of entering time into Tokyo Bay and slow steaming in the bay.

 In recent years, beach users have been required to practice a "new lifestyle" in order to prevent the spread of novel coronavirus infection. In this study, we developed a method for beach management that reduces the risk of infection. The developed system, based on a proprietary AI camera, is capable of monitoring and distributing real-time information on the crowded beach to beachgoers, including bathers, while maintaining low power consumption and privacy. The developed system was installed at the Yamanoshita Funaehama beach in Higashi-ku, Niigata City, and the accuracy of the AI in detecting beach users was verified. The results showed that the system could automatically distribute congestion information in real time with sufficient accuracy, even using a pre-trained model. Furthermore, we proposed a direction (Coastal Management DX) to solve not only the congestion situation but also future coastal management issues by utilizing AI.