Submarine pipeline is an important energy lifeline.However,the sandpits occurring along the route of submarine pipeline threaten seriously the in-place stability of the pipeline.In order to assess the impact of the scouring and silting of the sandpits by sea currents in the route area of the submarine pipeline from Shenzhen to Hong Kong on the in-place stability of the pipeline,the issues of the scouring and silting of the sandpits within the pipeline route area are analyzed by comparing long-term measured data and combining with numerical simulation method.The results from the established finite element model are in a good agreement with the measured data.And the law of the scouring and silting of the sandpits under the actions of waves and tidal currents and the variations in the next decade are proposed.That is,the sand mining area is dominated with a silting environment with its northern boundary extending toward northwest and being far away from the direction of the pipeline,indicating no impact on the pipeline,whereas its southern boundary extending toward southeast,which can cause the scouring of the pipeline near the Tonggu Waterway.At the eastern boundary of the sand mining area the slope of the sandpits close to the pipeline has been subjected eroding at its top,thus causing the boundary line of the sandpits expanding towards the pipeline.This study can provide a scientific and effective method for analyzing the scouring and silting of the sandpits by sea currents in the area of the Shenzhen-Hong Kong submarine pipeline route.
In order to reveal the action law of runoff and tide dynamics in the Lingdingyang Estuary,the main tide flux algorithm and the binary linear regression method are used to distinguish quantitatively the contributions of main dynamic factors to tidal flow velocities based on the fixed-point observation data over the years.The results show that the average flow velocity of the tidal cycle in the estuary has good correlation with tidal range,runoff and other dynamic factors and is always positively correlated with the tidal dynamics,but the contribution of the tidal dynamics has been weakened significantly in recent years.The runoff moved dominantly with the tidal current in the past,thus resulting in the decrease of tidal flow velocity.In recent years,however,the contribution of the runoff to the average tidal velocity becomes negative in the flood period and positive in the ebb period.Other dynamic factors mainly include vertical salt baroclinic gradient force and southwest monsoon.The contributions of these factors to the average tidal flow velocity in the main channel area are positive in the flood period and negative in the ebb period and have no significant changes.In the west beach waters,however,the contributions of these factors are opposite,showing negative in the flood period and positive in the ebb period.This is mainly related to the'tidal water capture'and the energy storage mechanism present inherently in the beach waters.Thus,the Lingdingyang Estuary has more river-channel-type water flow dynamic characteristics than before.This is mainly related to the development of the estuarine toward a narrow and deep form caused by reclaiming and water deepening in the estuary in recent years.
The lower reach of the Yellow River is famous for its frequent diversions.The Qingshuigou channel of the Yellow River has undergone a complex evolution process since its opening.The long-time-series remote sensing has the advantages of good continuity and strong timeliness and thus can realize the dynamical monitoring of river channel changes.By taking 40 Landsat remote sensing images obtained from 1976 to 2019 as the data sources and using the algorithm which is the combination of Modified Normalized Difference Water Index and maximum between-class variance method for extracting the information about the Qingshuigou channel,a monitoring research on the change law of the Qingshuigou channel since 1976 is carried out.The results show that with the deepening of the degree of human intervention,the changes of the Qingshuigou channel of the Yellow River are characterized with a natural swing dominated by human control and the frequency and amplitude of the channel avulsion and swing are less than before,expecting that the number of years of river travel could be increased.This study can provide important scientific basis for the regional governance of the Yellow River Delta.
According to the analysis of 27 microstructure pictures,we found that the cohesive soil in the central South Yellow Sea has three microstructure types:granular link-bond structure,flocculent link-bond structure,and clay matrix structure.The cohesive soil in the study area is mainly of clay matrix structure which has well developed pore and loose structure.The factors that lead to the loose microstructure feature of the cohesive soil have been analyzed for macroscopic aspects(topographic features,sediment source,hydrodynamic environment,deposition rate)and microscopic aspects(grain size distribution,mineral component,chemical composition),the analytical results revealed that flat seabed terrain,weak hydrodynamic conditions,long transportation distance cause this area has small sediment source and low deposition rate,consequently the deposition substances is mainly of silt and clay particles.The content of illite,chlorite,montmorillonite and organic matter is abundant in the cohesive soil,their hydrophilic characteristics make the cohesive soil in this area swell,thus formed the clay matrix structure with well developed pore and poor structure.The results revealed the microscopic mechanism of the macroscopic engineering properties of the cohesive soil in the muddy area of the central South Yellow Sea and deepen the understanding of the engineering properties of marine sediments.
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%.
