Abstract:For the failure mechanism and weakness of the existing scour protection measures for offshore wind power foundation,the standing vortex principle of disturbance flow ring is used to reduce the subsidence and destruction of the riprap layer by water flow,the riprap layer fixed with a sleeve is applied to weaken its edge destruction and a mat of biomimetic water grass,which has a function of hindering the diving flow and the lateral flow,is used to weaken the shear failure of the riprap layer.These three new types of riprap composite protection methods,i.e.'the riprap+disturbance flow ring','the riprap+sleeve'and'the riprap+mat of biomimetic water grass',are proposed respectively,and based on the arrangement of the three new measures,10 specific composite protection designs are proposed.And then,physical model tests are carried out and the protection effects of different composite protection methods are assessed.The results show that under the action of ocean currents the protection effects of the three composite protection methods are all better than that of riprap protection alone,with a protection efficiency being above 66%.When the laying range of riprap is 3 times the single pile diameter,the thickness of riprap is 2 times the median particle diameter of riprap,the inner diameter of the disturbance flow ring is set up to 2 times the single pile diameter and the distance away from the riprap layer is 0.5 times the pile diameter,the disturbance flow ring can play a better role,so that the water flow reaching the riprap layer and the surrounding sediments can be dispersed and the flow velocity can be slowed down.Such a composite protection method can be reached to 82.2%in protection efficiency and can achieve the ideal protection effect.

Abstract:Foundation scour is a common problem of offshore wind turbine pile foundation and can seriously affect the safety of wind turbine foundation structures.It is,therefore,necessary to conduct in-depth research on the protective measures for offshore wind turbine pile foundation.By using numerical simulation methods,the protective performance of scour protection ring at single pile foundation under the condition of unidirectional flow is studied.A numerical model of water flow-pile foundation-seabed interaction is established by FLOW-3D software.The influences of two parameters,the diameter and the installation height of the protection ring,on the foundation scour are analyzed,and a formula for predicting the scour depth under the case of protection ring installed is given based on the numerical simulation results of the model.It is found that for the protection rings with the same diameter the closer the protection ring is to the seabed,the higher the protection efficiency.When the installation height of the protection rings is 0.04 m,the scour depth decreases by 50%.If the installation height of the rings is 0 m the protection efficiency can achieve the highest.When the protection rings are installed too far away from the seabed,however,they will basically lose their protective function.For the protection rings which are installed closely to the seabed surface,the larger the diameter of the rings,the better the protection efficiency.When the ring diameter is 0.30 m and/or 0.35 m,the scour depth can be reduced by more than 50%.If the ring diameter exceeds a certain limit,however,the time to reach the scour equilibrium will be increased correspondingly with the increase in the diameter of the protection ring.But,the protective effect of the rings is hardly changed.

Abstract:The Yellow River Delta is a large estuarine delta with the shortest land formation time in China.Due to its special development background,unstable geological environment system and human activity influences,the land subsidence in the delta is relatively significant.This has caused many environment problems and posed a serious threat to the natural environment and socio-economic development.From the points of monitoring technology and genetic mechanism,the status of the land subsidence in the Yellow River Delta is reviewed systemtically.①The land subsidence in the delta can be affected by a variety of factors,such as natural compaction of nascent strata,gravity compaction of anthropogenic constructions,reduction of terrestrial inputs from rivers,exploitation of groundwater and brine,exploitation of oil and natural gas,relative enhancement of oceanic dynamics,and so on.To have a clear understanding a more detailed and systemetcal study is needed,especially in the aspect of quantitative separation of the contributions of the anthropogenic and natural factors to the ground subsidence.Moreover,it is needed to conduct a comprehensive quantitative analysis with other disciplines such as geology,geotechnical,mechanics,mathematics,and so on.②For the land subsidence in the delta,it is necessary to strengthen continuous monitoring of long spatiotemporal scale,historical cycle analysis and future judgment analysis,especially to pay more attention to the research on the long-and short-term incluences of sea-land interaction on land subsidence.③The surveying,monitoring,precision studying and assessing of the land subsidence in the delta,as well as the monitoring of environmental impact,are still needed to be studied deeply,particularly in the aspect of coupling relationship between the coast erosion and the land subsidence.In the future studies of the land subsidence in the delta,more attention should be paid to the exploration of theoretical models and the practice of new techniques and methods;The mechanism study should be extended to multiple models;For predicting the disasters,the ground cracking,faults and ground fissures which are closely related to the ground subsidence should be investigated.In addition,more explorations and practical applications should be made of the effects of the ground subsidence on the socio-economic and environmental impacts.A comprehensive,systematic and in-depth understanding of the land subsidence phenomenon in the Yellow River Delta can provide a theoretical basis for the effective implementation of ecological protection and resource development in the delta and has important scientific significance and socio-economic value.

Abstract:With the development of computer and other electronic technologies,Autonomous Underwater Vehicle(AUV)have shown great potential in the field of marine scientific research and other underwater engineering,assisting engineering personnel in completing various underwater tasks.In most ocean exploration scenarios,AUVs need to autonomously plan routes and navigate according to the specified routes.Traditional path planning methods using intelligent optimization algorithms such as cuckoo search algorithm have issues such as unreachable search targets,slow convergence speed,and poor obstacle avoidance capabilities.Although the A*algorithm based on grid maps solves these problems,it fails to meet the smoothness requirements of AUV routes.Therefore,this study integrates the A* algorithm with Bézier curves to improve path planning,focusing on maintaining AUV underwater posture.The improved algorithm is validated through simulation experiments using a simulation environment built with Python on the Windows 11 operating system.The results show that the AUV path planning based on the A*algorithm and Bézier curves can not only make the path shortest,but also further smooth the entire path while ensuring safe navigation,which is beneficial for maintaining the stable attitude of the AUV during operation.

Abstract:Large ocean buoys are needed to have the abilities of working independently,monitoring continuously and transmitting data in real time and a stable and convenient power supply system is the key to ensuring the normal operation of the buoy.The hybrid power supply system composed of solar energy and storage battery and widely used in the present is not only affected greatly by the alternation of day and night,the length of sunshine and the high salt and humidity sea environment,but also needs a high maintenance costs.As a kind of clean energy source and meanwhile having the character of uninterrupted energy acquisition,the wave energy can provide continuous power supply to the buoys.Thus,a large ocean buoy power supply system based on the principle of oscillating water column is designed,and the aerodynamic performance of the device is studied under different structural forms through numerical simulation.The calculation results show that the device has an optimal ratio of power to capture width when the ratio of wave length to gas chamber diameter Ld=5.5,the ration of orifice area to plate area e=1.25%and the ratio of wave length to gas chamber spacing Lk=7.By the structural optimization of the basic dimensions of the device,the ratio of power to capture width can be increased from 0.178 m-1 to 0.260 m-1,being enhanced by about 46.1%.

Abstract:The Liaodong Bay is one of the three big bays in the Bohai Sea.It can be affected frequently by large area of sea ice disasters in every winter season.To study the correlation and mutual influences between the sea ice and the air temperature,sea surface temperature and salinity,the remote sensing data of Sentinel-1 A/B obtained in winters from 2015 to 2023 are used,the SAR image textural features are extracted by contrasting Landsat-8 satellite imagery and utilizing gray scale co-occurrence matrix,the precisions of classification methods such as neural network,support vector machine and maximum likelihood classification are compared and the information about sea ice in the Liaodong Bay from 2015 to 2023 is summarized.The results show that for the Sentinel-1 A/B data,the maximum likelihood classification method has the highest precision,being up to 82.75%.The sea ice in the Liaodong Bay begin to form usually at the end of December or the beginning of January and follows a freezing order of north to south and near-shore to far-shore.The sea ice melting order is,however,from west to east and far-shore to near-shore.In the Liaodong Bay the Pearson correlation coefficient is-0.502(P<0.01)between the air temperature and the sea ice and-0.553(P<0.01)between the sea surface temperature and the sea ice,indicating that the sea ice in the Liaodong Bay has a significant negative correlation both to the air temperature and to the sea surface temperature.This suggests that both the air temperature and the sea surface temperature have an impact on the formation,development and melting process of the sea ice,of which the sea surface temperature may exert an even greater influence.As to the salinity,its influence on the sea ice exhibits a certain lag.