Abstract:ICESat-2(Ice,Cloud,and Land Elevation Satellite-2)is one of the most advanced laser altimetry satellites currently available.Using a laser wavelength of 532 nm,it can effectively acquire bathymetric data in the shallow water areas,thus greatly promoting the development of shallow water bathymetry.However,the raw data from ICESat-2 are often clouded by noisy point clouds so that great challenges can be brought to the post-processing of the data.To improve the accuracy and efficiency of data processing,a denoising algorithm based on Multilayer Perceptron(MLP)is developed to address the feature that ICESat-2 point clouds are denser in horizontal direction than in vertical direction.This algorithm takes into account comprehensively the feature values such as point density,average distance between points,and distance between the nearest neighbors(respectively 3 and 5)within a horizontal elliptical search area,thus realizing the effective identification and removal of noise points.The developed denoising model has been validated by selecting the ICESat-2 data from an reef island region in Australia as the training set and also using the data from the Jade Bangle Reef and the East Island in the Xisha Islands of China.The experimental results show that the denoising method developed in the study has an accuracy rate of over 90%,which is significantly better than the existing OPTICS denoising algorithm and the denoising results extracted by the official ATL03 algorithm.This achievement not only provides a new solution for the noise removal from ICESat-2 data,but also provides reliable data support for the research in related fields.

Abstract:The design flow velocity is an important parameter in ocean engineering.The design tide pattern,as one of the commonly used drive conditions,plays an important role in the calculation of design flow velocity.However,there is currently no universal and mature method for calculating the design tide patterns.In this study,a two-dimensional tidal flow model used in the sea area of the Dalian Changshan Archipelago is built up by numerical simulation and validated by using the current data measured in the Dalian Changhai Bridge area.By using this model,the changes of tidal flow field and the values of design flow velocity in the Changhai Bridge area are simulated under different boundary conditions of the design tide pattern,and the influences of the different drive conditions on the simulated results are studied.The results show that compared to the results worked out using the tide patterns such as'astronomical tide+increase water in different recurrence period'and'tidal range in different recurrence period',the design flow velocities worked out using'tidal range in different recurrence period+wind-driven current in corresponding recurrence period are even more close to those calculated out by using the empirical harmonic analysis methods and can provide more valuable reference for the ocean engineering.

Abstract:A two-dimensional CFD model for local scour of submarine pipelines is established based on SST k-ω model,Herschel-Bulkley clay model and VOF two-phase flow model.The inflow velocity U and soil strength τ0 are used as the variable parameters for the study of numerical simulation.By using this model,the law of the influence of different inflow velocities U and soil strength τ0 on local scour characteristics of the submarine pipelines is studied by analyzing the bed surface pressure characteristics,shape of scouring pit,duration curve of scouring depth and local flow speed distribution on both sides of the pipeline.The results show that the local scour of the submarine pipelines in the clay seabed environment is affected significantly by inflow velocity.With the increase of the inflow velocity,both the local limit equilibrium scour depth and the width of scour pit increase,and the ratio of the increase in equilibrium scour depth to the increase in flow velocity tends,as a whole,to slow down.The local scour of submarine pipelines in the clay seabed environment is affected significantly by soil strength.With the increase of the soil strength,the seepage force of the seabed is weakened,the limit equilibrium scour depth of the pipeline decreases and the mound downstream of the pipeline is closer to the pipe axis.When the soil strength is greater than or equal to 300 Pa,it is more difficult to form a gap between the bottom of the pipe and the seabed.

Abstract:The construction of ground projects in the Gwadar Port area of Pakistan is accelerating.However,the study of dynamic change of regional land subsidence in this area is relatively lacking.In this paper,the status and mechanisms of the land subsidence in the area are investigate by cellecting the land subsidence data which were obtained in about 6 years(from May 2017 to Apil 2023)in and around the Gwadar port area by using Multi Temporal Interferometric Synthetic Aperture Radar(MT-InSAR)technology as well as based on Sentinel-1 data.The results indicate that in the period from May 2017 to January 2021,there was obvious land subsidence in and around the Gwadar Port area,with the maximum rate of land subsidence reaching to 20 mm/a.Beginning from January 2021,there occurred a notable land uplift in this region and the rate of the land uplift(10 mm/a)was obviously greater than that of the local land subsidence(3 mm/a).From further analyses of artificial activities and geological conditions,it has been found that although the land subcidence in this area cannot develop sustaineously in the future,some small structural damages like cracks of buildings would be possibily caused due to the existence of the uplifting caused by plate tectonic movement in this area.As a result,it is still needed to make long-term mornitoring of the ground deformation in the study area.The results of the study have a certain reference for the security maintenance of the Gwadar Port.

Abstract:The local scouring of marine piles under the action of wave currents seriously threatens their structural stability and safety.In order to improve the service life of marine piles and reduce the maintenance cost,a new type of radial plate device is designed based on the principle of butyl dam shore protection for the protection of scouring of marine piles and Flow-3D numerical simulation is used to investigate the effect and mechanism of radial plate device of two different configurations,namely,curved and straight,under the action of wave currents on the protection of local scouring of pile foundations.The results show that the new radial plate device is effective in protecting the pile foundation from localized scour under the combined effect of wave current.The results show that the new radiation plate device can effectively protect the pile foundation from local scour,and compared with the unprotected condition,the radiation plate device does not produce obvious scour in the radial range of the pile perimeter,and siltation occurs in some areas,and the protection effect of the curved radiation plate is better than that of the linear shape.Radiation plate device has a good effect of water blocking,picking flow and deceleration of silt,water impact radiation plate after the reduction of flow velocity,flow direction change,the formation of water stagnation area within the radial range of the pile perimeter,stagnation area within the flow velocity is much smaller than the flow velocity outside the stagnation area,resulting in the sediment carried by the water in the pile perimeter as well as the radiation plate around the deposition of the scouring protection effect.

Abstract:Islands are an important part of natural resources.Currently,most of the islands in China are distributed in the form of island groups,archipelagos and island chains.Due to the unregulated and disordered quarrying and developing in the middle and late 20th century,most of the inhabited bedrock islands in the coastal areas of China are generally suffering from slope instability.This is not only threatening the safty of life and property of the island residents,but also destroying the ecological environment of the islands.It is,therefore,of great significance to monitor the slopes of the islands.Ensuring the stability and real-time transmission of slope monitoring data is the key to support the normal operation of the island slope monitoring system.However,there are currently still many gaps in research on the monitoring the multi-island and multi-slope in archipelagos.In this study,a monitoring network is designed by taking 25 damaged slopes in the Changdao Archipelago as the example.For the communication among multiple slopes within a single island,the communication among the islands and the communication between the monitoring center in archipelago and the remote data center on land,the characteristics and applicability of several common wireless communication technologies(e.g.Wi-Fi,ZigBee,4G/5G,LoRa and NB-IoT)are compared.A comprehensive evaluation is conducted from the aspects of transmission distance,rate,time-delay,networking mode,battery life,stability and cost.The results show that the combination of LoRa with 4G can effectively meet the data transmission among the slopes within a single island.For the communications among the islands and between the monitoring center in archipelago and the remote data center on land,4G technology is recommended to achieve efficient data exchange.Through the actual analysis of several damaged slopes in the Changdao Archipelago,the feasibility and effectiveness of the selected communication technology solutions are verified.The results of the study can provide references for the monitoring of slopes in other archipelagos.

Abstract:Beach maintenance is the core content of the sandy coast remediation and restoration project and is also a landmark project type for building beautiful bays and beautiful China.For the demand of the supervision technology of beach maintenance project in the sandy coastal areas,the main contents,technical processes and technical points of the supervision work for sandy coastal beach maintenance project are discussed on the basis of analysing the structural compositions of the sandy coastal beach maintenance project.By taking the beach maintenance project in Dolphin Bay of Guishan Island,Zhuhai as an example,the supervisions of the sandy coastal beach maintenance project include the supervision of the beach replenishment project and that of the embankment project.The key technical indices for the supervision of the beach replenishment project include the volume,particle size and environmental quality of sand replenishment,the elevation and width of beach shoulder,and the slope of tidal beach,and those for the embankment project include the length,width,position and orientation and wave resistance strength of dam and the elevation of dam top.The on-site supervision of the technical indices mentioned above can not only provide a guarantee for the quality and quantity guaranteed construction of the beach maintenance project in Dolphin Bay,but also offer a technological reference for the supervision of beach maintenance projects in the sandy coasts of China.

Abstract:The Nanjian coast of Zhuanghe City is one of the typical cape-type muddy coasts in China and has experienced a complex evolution process under the influence of human activities in the watershed and along the coast for nearly a century.Therefore,it is of great significance to study the evolution features of this coast for understanding the evolution of such kind of coast topography.Based on a total of 85 years(from 1938 to 2023)of bathymetric data and remote sensing images,the changes in the scour and silting of tidal flat and underwater topography are analyzed by means of 3S technology.The results show that:①The area of the Nanjian tidal flat has been decreasing since 1938,being reduced by 85.74％by 2023 and with a total decrease being 49.68 km2.And the main factor leading to the shrinkage of the tidal flat is reclamation.②The underwater topography has been being in a siltation state on the whole,with an average siltation thickness being 0.57 m.The evolution law of the scour and silting of the underwater topography is complicated on the scale of decades,tending to show an alternation of scour and silting at different stages and having a poor stability.The isobath lines vary significantly,with the 0 m isobath line retreating 0.47 km toward the mainland on the whole,while the 2,5 and 8 m isobath lines advancing 0.66,0.99 and 0.16 km toward the sea,respectively.

Abstract:The conflict in the use of sea area between the offshore wind power and the offshore oil-gas exploitation projects in the Bohai Sea is focused.The causes,characteristics and existing coordination mechanisms of their conflict in the use of sea area are analyzed and the feasible routes for their compatible development are discussed.The research indicates that although the modes of the sea area use are different between the offshore wind power and the offshore oil-gas exploitation projects,the characteristics of their use of sea area are similar.And the spatial overlap of the sea area used is the main reason for the conflict,which is particularly prominent in the Bohai Sea region and specifically shows as the overlapping of offshore wind farm sites with oil and gas safety operation zones and the crossing of cables and pipelines.Thus,in order to reduce effectively the conflict in the use of sea area between the offshore wind power and the offshore oil-gas exploitation projects and realize finally the model of compatible development,coordinations should be made by the ways such as adjusting air turbine layout,adopting high-capacity air turbines,signing strategic cooperation agreements,and so on.This study can provide ideas and references for further promoting the development of offshore energy.

Abstract:With the rapid development of global offshore wind power industry,the impact of offshore wind farm(OWF)on marine ecosystem has received a widespread attention.By selecting the Bozhong offshore wind farm and its adjacent waters as the research object,the changes in water quality and sediment quality indices,as well as in community structures and diversity indices of planktons,benthonic organisms and necton in the waters of wind farm site before the construction of wind farm and after its official operation are compared and analyzed by using the data obtained during the ecological environment surveys carried out in the wind farm site watwes and its adjacient sea areas before the wind farm construction(April 2019)and after its official operation(May 2024).And the influences of offshore wind farms on marine ecological environment are evaluated comprehensively.The results show that the water quality in the Bozhong offshore wind farm and its adjacent waters has a trend of improvement after the official operation of the wind farm.Compared with the situation before the construction of the wind farm,the propotions of dissolved inorganic nitrogen(DIN),plumbum(Pb)and mercury(Hg)concentrations exceeding Class Ⅰ water quality standards have decreased by 45.7％,22.5％and 6.8％respectively and the surface sediment concentrations all meet the sediment quality standards of Class Ⅰ.The average content of copper,however,increases by 9.4％in water and 52.2％in sediment after the wind farm operation.This should be observed as a key indicator for long-term monitoring.Aafter the official operation of the wind farm,moreover,the abundance of phytoplankton and the biomass of zooplankton and benthos decrease by 16.9％,64.5％and 20.0％respectively,while the species number,diversity index and richness index of the plankton community increase significantly,indicating that the community stability of phytoplankton enhances,the community stability of zooplankton improves,the community stability of benthos deteriorates and the dominance of polychaeta which has smaller individual size and higher tolerance to environmental change becomes more obvious.Meanwhile,the artificial fish reef effect generated by the foundation structure of the offshore wind farm leads to an addition of fish with tactile characteristics among the dominant fish species.The fish catch volume has increased by 6.6％(in the mass)and 30.3％(in the length)after the operation of the wind farm.This study can provide a theoretical basis for the construction of intelligent supervision system of offshore wind farm ecosystems and offer technical support for the supervision of the whole life cycle and the entire chain ecological environment for offshore wind farms.

Abstract:With gradual development of offshore substations towards lightweight,the design of topside structure of the substation is becoming more refined and compact,which puts higher requirements on the safety analysis of the structure.To ensure the safe and stable operation of the lightweight offshore substation in complex marine environments,a safety design assessment of the offshore substation is carried out according to the Fire and Explosion Analysis(FEA)method.An offshore substation located in the Bohai Sea is taken as the target object.Firstly,the hazard sources to the target offshore substation are identified.Then,simulation calculations are carried out for the working conditions with higher hazard levels through three-dimensional CFD software.Finally,the damage to the offshore substation caused by fire and explosion is evaluated.The results indicate that there are some hazard sources to the target offshore substation,among which the hazard sources with higher risk level are the main transformer system and the diesel engine system.It is revealed by calculations that under the case of major leakage the maximum heat flux density(160 kW/m2)and the explosion over pressure value(28 kPa)of the diesel generator system can occur,of which the maximum heat flux density is lower than the fire damage threshold and the maximum explosion over pressure value has a lower probability of occurrence.Therefore,under the current passive design of fire and explosion protection,the fire and explosion will not cause severe damage to the main structure.This study can provide references for the structural design and security maintenance of lightweight offshore substations.

Abstract:As the service life of the existing offshore oil platforms has been close to the end of their operational period,the dismantling,recycling and reusing of the marine platforms become a new technical challenge in the field of offshore engineering.Compared with the float-crane removal,the float-over dismantling has the advantages of no need of large lifting vessels and short cycle of operation so that it has been attached importance to and applied in the offshore platform dismantling projects.In this paper,the float-over dismantling process of the jacket platform on a catamaran is investigated.And based on this,the dismantling process is simulated and analyzed by establishing a dynamical model for the catamaran-topside system as well as by using multi-body dynamics software.The results show that the lifting arms show a good coordination during the dismantling process and have played a compensatory role to the motion of the topsides.Additionally,the results have also revealed the potential risk points in the dismantling operation process.Through the analysis of the float-over dismantling operation process,references can be provided for evaluating the performance of the dismantling operation and ensuring its safety.

Abstract:Extreme climate changes have led to the proposals of higher demands on the ability of coastal protection facilities to withstand extreme waves.And the construction of an ecological coast by combining the traditional concrete-based seawalls with the coastal vegetations is a trend of coastal protection and restoration in the future.In this paper,the run-up motion of the waves on an ecological dike is studied,and the maximum run-up height of regular waves on a compound slope dike under the intervention of flexible structures is discussed based on physical flume tests.For the experiment,the materials(TPU95 and nylon)with two types of different elastic modulus are used and the salt marsh vegetations are simulated by 3D printing.The influences of the stiffness,height,density and location of the vegetations on the maximum rin-up height of the regular waves when the vegetations located in the platform area of the dike are discussed emphatically.The results indicate that the increase of the flexible vegetation zone in the platform of the compound slope dike can further reduce the maximum run-up height of the regular waves.The vegetation density is positively correlated to the attenuation rate of the wave run-up height.The maximum attenuation rate of the wave run-ip height is about 0.35 and the wave dissipation effect of the flexible TPU95 vegetation is better than that of the nylon.Moreover,the influence of the flexible vegetation height on the maximum run-up height of waves is related both to the vegetation density and to the wave period.

Abstract:Technology readiness level and reliability of marine energy need to be validated through at-sea experiments.Marine energy test site(METS)would be a professional public testing platform for at-sea experiments.In this paper,the development of marine energy technologies is introduced.We can know that tidal current energy and wave energy technologies are at the stage of pre-commercialization,which need to be tested and validated at sea.Internationally representative METSs in UK,US,Japan and so on.are introduced.Their progress and achievements are analyzed.Then construction progress of METSs of China is summarized,and their functions as well.Through analyzing progress of METSs in China and other countries,we can get some inspiration,which is about support from policies and funds,body for construction and operation,streamlined procedure for permit,and etc..It can be concluded that we should give more support to METSs of China,which are constructed and operated normatively and internationally.It will help to break down the barriers at the stage of pre-commercialization of tidal current energy and wave energy devices.Technology development and transfer in marine energy will accordingly be promoted.

Abstract:The first phase of the marine reclamation land project for the equipment manufacturing base in the Caofeidian Industrial Zone,called shortly as Manufacture Phase I Project,began to construct in 2009 and the construction of sea reclamation was completed in 2010.In the construction.sand extracting at the sea and blow-filling way were applied for the land formation.The elevation of the blow-filled area was+4.5m(i.e.the lowest theoretical tidal level in Caofeidian).Due to the holistic nature of ocean form,the complex pattern of motion and the continuity of dynamic process,the role of ocean engineering can alter the ocean hydrodynamic state under the natural conditions and affect directly or indirectly the environmental elements such as topography,geomorphology,erosion and deposition state,material transport,seawater quality,sediment quality,habitat of benthic organisms,and so on.Therefore,the analysis and assessment of marine hydrodynamic environmental impact are crucial.Based on the MIKE21 model and by using 2-D tidal current basic equation and referring to the hydrological data measured in the study area over the years,the impact on the hydrodynamic enivronment in the sand extraction area(where a warehousing and logistics project will be located)before and after the reclamation construction in the Manufacture Phase I Project is simulated.Through the verification of the calculation results of the tidal current field and the calculations of the changes of the tidal current field in the sand extraction area,it is obtained that after the constructions of the sand extraction and blow filling at the sea in the Manufacture Phase I Project,the tidal flow velocity in the sand extraction area decreases,with the maximum reduction being about 0.16 m/s,while on the east and west sides of the sand extraction area there is an increase in tidal flow velocity,with the maximum increase being about 0.14 m/s.The areas where the change in flow velocity exceeds 0.005 m/s can be controlled within a 2.5 km range of the sand extraction area,which will have no significant impact on the overall hydrodynamic conditions in the area.

Abstract:To address the easy instability of 41 rock and soil slopes in the Changdao Islands,the potential slope instability mechanisms and their influencing factors are analyzed on the basis of data collection and field geological investigations.Based on the methods for the saturated-unsaturated seepage simulation of finite element and for the finite element strength reduction,the stability of the target slopes is analyzed and simulated under the conditions of non-rainfall and potential extreme rainfall,and the dynamic destabilization processes induced by potential rock collapse and soil slope sliding are quantitatively simulated by using respectively the nonlinear finite element contact algorithm and the coupled Eulerian-Lagrangian approach.The analysis results show that the rocky slopes have a better overall stability,but the potential risk of collapse caused by loose rock mass on the slope surface is relatively higher.Although the scale of the soil slopes is relatively smaller,some high and steep slopes have a certain possibility of instability under the conditions of extreme rainfall and adverse crack.Finally,the treatment urgency of the two easy instable slopes mentioned above is comprehensively ranked by using fuzzy comprehensive evaluation method,which can provide certain reference for the future detailed evaluation and treatment of the slopes in the Changdao Islands.

Abstract:With the development of large ships,mooring safety of the large ships represented by LNG transport ship has gradually attracted wide attention.In order to study the mooring state of the LNG ships under different working conditions,a mooring simulation model for the LNG ship terminal in Qingdao is established by using hydrodynamic software AQWA on the basis of ship motion model.The six degrees of freedom hull amplitude response operator of the LNG ships under frequency domain analysis is studied and the influences of the traditional rope mooring and the pre-tension cable mooring on the response of ship mooring dynamics under different sea conditions are compared during time domain analysis.The results show that applying a certain pre-tension to the cable can effectively restrain the ship's motion response in direction of rolling,pitching,yawing,etc.and improve the stability of the mooring.In a certain range,a 50 t pre-tension has better inhibiting effect on ship motion than a 30t pre-tension and the effect becomes more obvious with the increase of environmental load.These results can provide technical reference for guiding ship docking,dock mooring design and mooring safety control.

Abstract:Extreme sea conditions pose a significant threat to the safety of offshore structures.Generally,the extreme sea conditions under the case of future climate change and within a certain time range are predicted by extreme value theory in order to evaluate the response of the offshore structures to the extreme sea winds,currents and waves.However,the values of extreme recurrence period obtained through the extreme value analysis may vary due to the differences in extreme value samples,probability distribution functions and parameter estimation methods,and the differences in extreme values may further affect the safety and economy of the structures.For this reason,the hydrological simulation time series data spanning 43 years from 1979 to 2021 are collected from a proposed wind turbine site located in the Wenzhou Offshore Area of Zhejiang Province and used to study the sensitivity of once-in-50-year wave height to different extreme value samples,probability distribution functions and parameter estimation methods.The results indicate that under the cases of good fitting performance,both the sampling method and the probability distribution function have a significant impact on the once-in-50-year wave height,while the parameter estimation method shows a relatively smaller impact.To ensure the safety margin of the structures,it is recommended that the sensitivity analysis of the extreme wave height should be prioritized.In this case,the Pearson Ⅲ distribution and the annual sampling method show a high stability and a low sensitivity in the extreme value estimation.The results of this study can provide a reliable reference for determining the extreme recurrence period reasonably.

Abstract:With the increasing of power plants along the coast,the warm water discharge from the thermal power plants causes the increase of water temperature in the surrounding sea area.This problem becomes increasingly obvious and has been one of the most important issues of coastal environmental protection.In this paper,the three-demensional diffusion characteristics and dynamic change process of the warm water discharge are deeply analyzed by using the hydrological data observed in the sea area surrounding the Hongshan Thermal Power Plant in winter of 2023 as well as combined with the hydrodynamic characteristics of different tidal states during the observation period.The results show that the warm water discharge from a bottom-discharge power plant rises rapidly to the surface under the action of thermal buoyancy,resulting in the highest temperature increase in the surface water.Affected by the tidal dynamic factors,horizontally,the maximum surface temperature rise occurs at the time of ebb slack tide and the maximum diffusion area of the warm water discharge(by taking 1℃temperature rise as the standard)occurs at the time of flood peak tide;vertically,because the tidal dynamic force of the spring tide is stronger than that of the neap tide,the thermocline becomes deeper during the spring tide.The results of correlation analysis show that both the degree of the temperature rise and the area of the warn water diffusion in the study area are positively correlated to the amount of heat carried by the warm water discharge.This study intuitively reflects the three-dimensional diffusion characteristics and dynamic mechanisms of the warm water discharge from a bottom-discharge thermal power plant in winter.The results of the study lay a foundation for understanding the influence of warm water discharge on the surrounding aquatic ecosystem and also provide references for parameter optimization of warm water drainage numerical simulation.

Abstract:The Lingdingyang area of the Pearl River Estuary is affected by superposition of multiple dynamic forces including tides,river runoffs and typhoons,resulting in a complex sediment transport process.However,study of the impact of seabed sediment erodibility(characterized by critical erosion stress)on sediment transport remains insufficient.For this reason,the sediment transport process under the influence of spring tide,neap tide and Typhoon Hato is simulated and the effect of seabed erodibility on sediment movement in the Lingdingyang area is investigated by integrating the sediment consolidation model proposed by Sanford into the ECOMSED 3D water-sediment model and setting up a reference case(the actual critical erosion stress)and two experimental cases with enhanced erodibility(with the critical erosion stress being 1/2 and 1/8 of the reference value,respectively).The results show that the seabed erodibility has a significant impact on the spatial distribution of suspended sediment.The decrease of critical erosion stress can increase the concentration of suspended sediment in high turbidity zones and tend to expand toward downstream the distribution range of suspended sediment,which is more obvious in strong dynamic scenarios such as typhoons.The response of seabed scour and silting to erodibility varies:changing from silting to scour in the northern area during low tides,increasing erosion intensity during high tides and changing to strong erosion across the entire area in typhoon periods.The sediment exchange between the estuary and the open sea is affected by critical erosion stress.When the critical erosion stress decreases to 1/8 of the reference value,the proportion of sediment transported to the open sea increases significantly and when to 1/2 of the reference value the sediment output changes gently.This study clarifies the mechanism of influence of seabed erodibility on sediment transport in the Lingdingyang area and can provide a basis for optimizing the seabed sediment parameters of the Lingdingyang water-sediment model and also has reference value for the study on similar estuaries with cohesive sediments.