2017 Vol. 39, No. 5
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2017, 39(5): .
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2017, 39(5): .
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2017, 39(5): 1-9.
doi: 10.3969/j.issn.0253-4193.2017.05.001
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According to the observation data in spring tide, middle tide, neap tide in flood and dry season at Modaomen Estuary from 2011 to 2012, this paper analyzes Euler residual current, Stokes residual current and Lagrange residual flow. The results show that: (1) the main direction of Euler residual current and Lagrange residual flow are southwest in winter and summer but the current in east and west branch show offshore under the strong runoff; (2) the Stokes residual current is much less than Euler residual current and much greater in summer than in winter, the direction of the Stokes residual current is in the opposite of Euler residual current; (3) there is a stable southwest alongshore current in winter in Modaomen Estuary, the driving effect of northeast monsoon in the South China Sea is the main reason, there is no consistent characteristics of alongshore current in summer, the main influencing factors is runoff and the wind, and the influence of the terrain especially the shunt effect caused by the mouth bar should not be neglected, it will influence the transport of water and sediment which under the strong runoff significantly.
According to the observation data in spring tide, middle tide, neap tide in flood and dry season at Modaomen Estuary from 2011 to 2012, this paper analyzes Euler residual current, Stokes residual current and Lagrange residual flow. The results show that: (1) the main direction of Euler residual current and Lagrange residual flow are southwest in winter and summer but the current in east and west branch show offshore under the strong runoff; (2) the Stokes residual current is much less than Euler residual current and much greater in summer than in winter, the direction of the Stokes residual current is in the opposite of Euler residual current; (3) there is a stable southwest alongshore current in winter in Modaomen Estuary, the driving effect of northeast monsoon in the South China Sea is the main reason, there is no consistent characteristics of alongshore current in summer, the main influencing factors is runoff and the wind, and the influence of the terrain especially the shunt effect caused by the mouth bar should not be neglected, it will influence the transport of water and sediment which under the strong runoff significantly.
2017, 39(5): 10-21.
doi: 10.3969/j.issn.0253-4193.2017.05.002
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In the present work a numerical highly nonlinear and dispersive Boussinesq-type model is developed based on a non-staggered finite difference technique. With the Fourier approximation method providing the incident wave boundary condition, the model is applied and verified against a set of three test cases for which analytical, numerical or experimental reference results are available: (1) propagation of linear and nonlinear periodic waves on deep and shallow depth, (2) shoaling of linear and nonlinear regular waves from deep to shallow water on a mild slope, and (3) transformation of regular waves on a mild slope and on steep slopes. Comparisons of the numerical results with the analytical, numerical and experimental ones confirm the capabilities of the model for the predictions of highly nonlinear and dispersive waves and for the computations of nonlinear wave shoaling on different slopes.
In the present work a numerical highly nonlinear and dispersive Boussinesq-type model is developed based on a non-staggered finite difference technique. With the Fourier approximation method providing the incident wave boundary condition, the model is applied and verified against a set of three test cases for which analytical, numerical or experimental reference results are available: (1) propagation of linear and nonlinear periodic waves on deep and shallow depth, (2) shoaling of linear and nonlinear regular waves from deep to shallow water on a mild slope, and (3) transformation of regular waves on a mild slope and on steep slopes. Comparisons of the numerical results with the analytical, numerical and experimental ones confirm the capabilities of the model for the predictions of highly nonlinear and dispersive waves and for the computations of nonlinear wave shoaling on different slopes.
2017, 39(5): 22-32.
doi: 10.3969/j.issn.0253-4193.2017.05.003
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An analytical model was developed to analysis the hydrodynamics and sediment transport in the South Channel of Yangtze Estuary, China. The tidal dynamics in the South Channel is controlled by semi-diurnal tide. The dominated driven factors of residual flow are river discharge and nonlinear advection terms due to tidal flow. The suspended sediment concentration over the northern channel is much higher than that over the southern channel. The essential features of the observed flow field and sediment distribution are reproduced by the model results. Closer inspection of the sediment entrapment with sediment transport function indicates that, the residual transport and tidal transport dominates, and both of them point northward (to the north deep channel). The diffusive transport points southward, since it always transports sediment from high concentration area to low concentration area.
An analytical model was developed to analysis the hydrodynamics and sediment transport in the South Channel of Yangtze Estuary, China. The tidal dynamics in the South Channel is controlled by semi-diurnal tide. The dominated driven factors of residual flow are river discharge and nonlinear advection terms due to tidal flow. The suspended sediment concentration over the northern channel is much higher than that over the southern channel. The essential features of the observed flow field and sediment distribution are reproduced by the model results. Closer inspection of the sediment entrapment with sediment transport function indicates that, the residual transport and tidal transport dominates, and both of them point northward (to the north deep channel). The diffusive transport points southward, since it always transports sediment from high concentration area to low concentration area.
Couping of CICE5.0 with BCC_CSM2.0 model and its performance evaluation on Arctic sea ice simulation
2017, 39(5): 33-43.
doi: 10.3969/j.issn.0253-4193.2017.05.004
Abstract:
The latest Los Alamos sea ice model (CICE5.0) is coupled to the Beijing Climate Center coupled system model (BCC_CSM2.0) by replacing its original sea ice model (SIS). The performance of the new coupled model in simulating silent features of Arctic sea ice during 1985-2009 is thoroughly assessed through a comparison to both the original version and observations. The results show that the new coupled model can reasonably capture the spatial pattern, seasonal and inter-annual variation of Arctic sea ice. The CICE5.0 significantly improves the Arctic sea ice simulation, which includes a decrease (increase) of one year (multi-year) sea ice area, an increase in ice thickness, a reduction in ice motion, and a more realistic Beaufort Gyre. Further analysis indicates that, compared with the SIS, the better performance of the CICE5.0 in simulating the Arctic sea ice, especially for its thickness, results in positive ice-temperature feedbacks when coupled with the BCC_CSM2.0. As a result, the surface air temperature, sea level pressure, and the sea surface temperature are better simulated, which further improves the Arctic sea ice simulation.
The latest Los Alamos sea ice model (CICE5.0) is coupled to the Beijing Climate Center coupled system model (BCC_CSM2.0) by replacing its original sea ice model (SIS). The performance of the new coupled model in simulating silent features of Arctic sea ice during 1985-2009 is thoroughly assessed through a comparison to both the original version and observations. The results show that the new coupled model can reasonably capture the spatial pattern, seasonal and inter-annual variation of Arctic sea ice. The CICE5.0 significantly improves the Arctic sea ice simulation, which includes a decrease (increase) of one year (multi-year) sea ice area, an increase in ice thickness, a reduction in ice motion, and a more realistic Beaufort Gyre. Further analysis indicates that, compared with the SIS, the better performance of the CICE5.0 in simulating the Arctic sea ice, especially for its thickness, results in positive ice-temperature feedbacks when coupled with the BCC_CSM2.0. As a result, the surface air temperature, sea level pressure, and the sea surface temperature are better simulated, which further improves the Arctic sea ice simulation.
2017, 39(5): 44-60.
doi: 10.3969/j.issn.0253-4193.2017.05.005
Abstract:
In this study, we generate a new climatology of extra-cyclones in the Southern Ocean and the coastal area of Antarctic by applying an automated cyclone detection and tracking algorithm (developed by Hodges at the Reading University) for an improved and relatively high-resolution European Centre for Medium-Range Weather Forecasts atmospheric reanalysis during 1979-2013. The climatological characteristics of cyclones appearing in scientific investigation station of China in Antarctic are then analyzed, including track, number, density, intensity, deepening rate and explosive events. It shows that the number of cyclones in the Great Wall Station and Zhongshan Station has increased for 1979-2013, but none of them statistically significant. The number of cyclones in Taishan Station has decreased significantly for the same period. Cyclones in Great Wall Station are more frequency than others, and explosive cyclones are also more detected. In contrast, the seasonal variation of cyclone activities in both Zhongshan Station and Great Wall Station are more pronounced than that in Taishan Station. The cyclones in Zhongshan Station are less and weaker in summer. There are less cyclones appearing in Taishan Station, even if there are cyclones activities, the strength of them are too weaken to affect the station.
In this study, we generate a new climatology of extra-cyclones in the Southern Ocean and the coastal area of Antarctic by applying an automated cyclone detection and tracking algorithm (developed by Hodges at the Reading University) for an improved and relatively high-resolution European Centre for Medium-Range Weather Forecasts atmospheric reanalysis during 1979-2013. The climatological characteristics of cyclones appearing in scientific investigation station of China in Antarctic are then analyzed, including track, number, density, intensity, deepening rate and explosive events. It shows that the number of cyclones in the Great Wall Station and Zhongshan Station has increased for 1979-2013, but none of them statistically significant. The number of cyclones in Taishan Station has decreased significantly for the same period. Cyclones in Great Wall Station are more frequency than others, and explosive cyclones are also more detected. In contrast, the seasonal variation of cyclone activities in both Zhongshan Station and Great Wall Station are more pronounced than that in Taishan Station. The cyclones in Zhongshan Station are less and weaker in summer. There are less cyclones appearing in Taishan Station, even if there are cyclones activities, the strength of them are too weaken to affect the station.
2017, 39(5): 61-67.
doi: 10.3969/j.issn.0253-4193.2017.05.006
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According to the fundamental mechanisms and recent research results of wind-generated noise, satellite-bone microwave scatterometer wind (SMSW) was applied to ocean ambient noise study in this paper. The correlation between HY-2A/ Advanced Scatterometer(ASCAT) wind and ambient noise was analyzed. The ambient noise data of subsurface buoy and SMSW in South China Sea were adopted in the experiment and the National Centers for Environmental Prediction(NCEP) wind was used in comparison. The results show that correlation between ASCAT data and ambient noise is better than HY-2A, and SMSW is better than NCEP data. The SMSW is more applicable to ambient noise study. This research expanded application field of SMSW and provided a better approached for ambient noise research.
According to the fundamental mechanisms and recent research results of wind-generated noise, satellite-bone microwave scatterometer wind (SMSW) was applied to ocean ambient noise study in this paper. The correlation between HY-2A/ Advanced Scatterometer(ASCAT) wind and ambient noise was analyzed. The ambient noise data of subsurface buoy and SMSW in South China Sea were adopted in the experiment and the National Centers for Environmental Prediction(NCEP) wind was used in comparison. The results show that correlation between ASCAT data and ambient noise is better than HY-2A, and SMSW is better than NCEP data. The SMSW is more applicable to ambient noise study. This research expanded application field of SMSW and provided a better approached for ambient noise research.
2017, 39(5): 68-77.
doi: 10.3969/j.issn.0253-4193.2017.05.007
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Beach landforms show a complicated erosion and recovery process under impacts of consecutive typhoons. In order to study the erosion and accretion response of beaches to two typhoons, representative beach profiles in the Mulan-Baohu Bay, northeastern Hainan Island, were observed and measured before and after two consecutive typhoons, Rammasun and Kalmaegi in 2014. In addition, surficial sediments in each transect backshore were collected to study their depositional environment change. The results show that the former super typhoon Rammasun led to severe beach erosion and sediment transport, which mainly revealed longshore change differences in the Mulan Bay and cross-shore change similarities in the Baohu Bay. And the latter typhoon Kalmaegi caused beach accretion and recovery, which was more obvious in Mulan Bay than in Baohu Bay. After Kalmaegi, the backshore sediments in the Mulan Bay trended to recover to the state before two typhoons and in Baohu Bay showed a greater difference before typhoons. The underwater coral reefs in Baohu Bay restrained beach erosion and accretion from typhoons. Different combinations of typhoon wind directions vs. beach orientations can also cause different beach response to consecutive typhoons. This study will contribute to a better understanding of the complicated responses of different beaches to consecutive typhoons.
Beach landforms show a complicated erosion and recovery process under impacts of consecutive typhoons. In order to study the erosion and accretion response of beaches to two typhoons, representative beach profiles in the Mulan-Baohu Bay, northeastern Hainan Island, were observed and measured before and after two consecutive typhoons, Rammasun and Kalmaegi in 2014. In addition, surficial sediments in each transect backshore were collected to study their depositional environment change. The results show that the former super typhoon Rammasun led to severe beach erosion and sediment transport, which mainly revealed longshore change differences in the Mulan Bay and cross-shore change similarities in the Baohu Bay. And the latter typhoon Kalmaegi caused beach accretion and recovery, which was more obvious in Mulan Bay than in Baohu Bay. After Kalmaegi, the backshore sediments in the Mulan Bay trended to recover to the state before two typhoons and in Baohu Bay showed a greater difference before typhoons. The underwater coral reefs in Baohu Bay restrained beach erosion and accretion from typhoons. Different combinations of typhoon wind directions vs. beach orientations can also cause different beach response to consecutive typhoons. This study will contribute to a better understanding of the complicated responses of different beaches to consecutive typhoons.
2017, 39(5): 78-88.
doi: 10.3969/j.issn.0253-4193.2017.05.008
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In this study, based on the multi-parameters measurements, including AMS14C dating, organic carbon, grain size and factor analysis of grain size data, of gravity core JB04, collected in the continental shelf of the Ross Sea during the 31st China Antarctic scientific expedition, the sedimentary strata and processes were studied and the paleocenography significance was discussed. The results shown that the age of the core sediment is 15 ka, and the core sediment can be divided into 3 types, namely as the normal ice-sea deposition, low marine hydrodynamic deposition and high marine hydrodynamic deposition, respectively. According to the distributions of sediment deposition strata, the core can be divided into 4 layers. From the bottom to the top, the first deposited layer was formed in the marine environment while the ocean was covered by ice sheet, and so the sedimentation process was mainly dominated by glacial scraping corrosion. The second deposition layer was formed under the ice shelf in low marine hydrodynamic environment and the third deposition layer was formed in front of the ice shelf in high marine hydrodynamic environment. The top deposition layer was formed in seasonal sea ice environment and was affected by iceberg. The study of marine sedimentary processes of the Ross Sea is very siginificant to complately understanding the evolution of marine environment in the Antarctica.
In this study, based on the multi-parameters measurements, including AMS14C dating, organic carbon, grain size and factor analysis of grain size data, of gravity core JB04, collected in the continental shelf of the Ross Sea during the 31st China Antarctic scientific expedition, the sedimentary strata and processes were studied and the paleocenography significance was discussed. The results shown that the age of the core sediment is 15 ka, and the core sediment can be divided into 3 types, namely as the normal ice-sea deposition, low marine hydrodynamic deposition and high marine hydrodynamic deposition, respectively. According to the distributions of sediment deposition strata, the core can be divided into 4 layers. From the bottom to the top, the first deposited layer was formed in the marine environment while the ocean was covered by ice sheet, and so the sedimentation process was mainly dominated by glacial scraping corrosion. The second deposition layer was formed under the ice shelf in low marine hydrodynamic environment and the third deposition layer was formed in front of the ice shelf in high marine hydrodynamic environment. The top deposition layer was formed in seasonal sea ice environment and was affected by iceberg. The study of marine sedimentary processes of the Ross Sea is very siginificant to complately understanding the evolution of marine environment in the Antarctica.
2017, 39(5): 89-102.
doi: 10.3969/j.issn.0253-4193.2017.05.009
Abstract:
The mounded reflections of the mid-Miocene upper Meishan Formation in the Beijiao Sag of Qiongdongnan Basin have been arousing widely the attention of the geologists. Previous studies inferred that the mounded reflection originated from various genesises such as reef, combined result of gravity flow and bottom current, and contourite. Based on drilling, 2D and 3D seismic data, this paper researched on the mounds(remnant mounds) and channels in detail. In the Beijiao Uplift the remnant mounds and channels were not developed well, while in the mid part and high of the marginal slope they occurred well. The scale of them became smaller on the two blank of the highland and they are asymmetric. Mounds and channels with nearly E-W orientation are liner and sub-parallel with each others and locally conjunctive and bifurcate. The strikes of those have a small angle intersection with the strike of Beijiao Uplift. The mounds display mounded widths, heights, and length of 562-1 233 m, 29-87 m, and about 10 m, respectively. There are some seismic reflections with the truncation of the blank of the mounds and the incision of the channel. The 3D seismic attributes showed that long strip strong amplitude infilled by the interbedding of sandstone and mudstone mainly occurred in the S-W part of 3D survey, however, the interior remnant mounds with mid-lower amplitude. Integrated drilling and seismic data, the results of this research showed that mounds were composed of mudstone and calcareous mudstone, which belonged to the bathyal depositional environment. The wave impedance (5.0×106-6.5×106 kg/m3·m/s) of the mounds were lower than that of carbonate rock and igneous rock, which also belonged the scope of the wave impedance of mudstone and sandstone. According the strong amplitude of the lower Meishan Formation channel became weaker, bifurcate, progradation from W to E and the contourite depositional-erosional characteristics in the vicinity of seamount, we inferred that paleo-current of the remnant mound and channel of formation flew from W to E. And the epoch of contourite deposition and erosion could ascend to the early later Miocene(11.6 Ma BP). Integrated analysis of various mounded reflections, we inferred that in study area mid-Miocene mounded reflections originated from the remnant underlying Meishan Formation incised by bottom current in the early later-Miocene.
The mounded reflections of the mid-Miocene upper Meishan Formation in the Beijiao Sag of Qiongdongnan Basin have been arousing widely the attention of the geologists. Previous studies inferred that the mounded reflection originated from various genesises such as reef, combined result of gravity flow and bottom current, and contourite. Based on drilling, 2D and 3D seismic data, this paper researched on the mounds(remnant mounds) and channels in detail. In the Beijiao Uplift the remnant mounds and channels were not developed well, while in the mid part and high of the marginal slope they occurred well. The scale of them became smaller on the two blank of the highland and they are asymmetric. Mounds and channels with nearly E-W orientation are liner and sub-parallel with each others and locally conjunctive and bifurcate. The strikes of those have a small angle intersection with the strike of Beijiao Uplift. The mounds display mounded widths, heights, and length of 562-1 233 m, 29-87 m, and about 10 m, respectively. There are some seismic reflections with the truncation of the blank of the mounds and the incision of the channel. The 3D seismic attributes showed that long strip strong amplitude infilled by the interbedding of sandstone and mudstone mainly occurred in the S-W part of 3D survey, however, the interior remnant mounds with mid-lower amplitude. Integrated drilling and seismic data, the results of this research showed that mounds were composed of mudstone and calcareous mudstone, which belonged to the bathyal depositional environment. The wave impedance (5.0×106-6.5×106 kg/m3·m/s) of the mounds were lower than that of carbonate rock and igneous rock, which also belonged the scope of the wave impedance of mudstone and sandstone. According the strong amplitude of the lower Meishan Formation channel became weaker, bifurcate, progradation from W to E and the contourite depositional-erosional characteristics in the vicinity of seamount, we inferred that paleo-current of the remnant mound and channel of formation flew from W to E. And the epoch of contourite deposition and erosion could ascend to the early later Miocene(11.6 Ma BP). Integrated analysis of various mounded reflections, we inferred that in study area mid-Miocene mounded reflections originated from the remnant underlying Meishan Formation incised by bottom current in the early later-Miocene.
2017, 39(5): 103-114.
doi: 10.3969/j.issn.0253-4193.2017.05.010
Abstract:
In this paper, through the analysis of geotechnical test, sediment of the sea around Nanpu-Caofeidian is mainly composed of mud, silty sand, clay, silty soil, which account for 85% of the total number of analyzed samples. Muddy clay, silty clay, fine sand and medium sand are relatively less. According to the most prominent factor which influence the geotechnical conditions of Nanpu-Caofeidian area: submarine landform unit, potential geological hazards, combined with submarine soil type and its physical and mechanical properties, the research area can divide into four engineering geological zone, they are subaqueous slope mixed engineering geological zone(Ⅰ), erosion plain and depression sandy soil engineering geological zone(Ⅱ), erosion depression mixed engineering geological zone(Ⅲ), shelf accumulation plain fine grained soil engineering geological zone (Ⅳ) respectively. Through comprehensive analysis of the factors which influence the geotechnical conditions of sea floor by marine environment factors, seismic activity, disaster geology and soil stability, the seabed stability of the four engineering geological zones are unstable area(Ⅰ), relatively stable area (Ⅱ), relatively unstable area(Ⅲ), stable area (Ⅳ). The research results have important guiding significance for the construction and disaster prevention and reduction of the sea floor in this area.
In this paper, through the analysis of geotechnical test, sediment of the sea around Nanpu-Caofeidian is mainly composed of mud, silty sand, clay, silty soil, which account for 85% of the total number of analyzed samples. Muddy clay, silty clay, fine sand and medium sand are relatively less. According to the most prominent factor which influence the geotechnical conditions of Nanpu-Caofeidian area: submarine landform unit, potential geological hazards, combined with submarine soil type and its physical and mechanical properties, the research area can divide into four engineering geological zone, they are subaqueous slope mixed engineering geological zone(Ⅰ), erosion plain and depression sandy soil engineering geological zone(Ⅱ), erosion depression mixed engineering geological zone(Ⅲ), shelf accumulation plain fine grained soil engineering geological zone (Ⅳ) respectively. Through comprehensive analysis of the factors which influence the geotechnical conditions of sea floor by marine environment factors, seismic activity, disaster geology and soil stability, the seabed stability of the four engineering geological zones are unstable area(Ⅰ), relatively stable area (Ⅱ), relatively unstable area(Ⅲ), stable area (Ⅳ). The research results have important guiding significance for the construction and disaster prevention and reduction of the sea floor in this area.
2017, 39(5): 115-122.
doi: 10.3969/j.issn.0253-4193.2017.05.011
Abstract:
Wave-induced seabed instability is an important problem considered by ocean engineers. On basis of analyzing the present calculation methods for wave-induced seabed sliding instability, a new method, referred to the overall stress state method, is established to calculate the seabed sliding stability under wave loading. The new method has been compared with others, and the wave-induced sliding failure characteristics of sandy seabed and the soft clay one has been analyzed. The results have shown that the overall stress state method is applicable to compute the seabed sliding instability. For sandy seabed, saturation has great influence on its sliding instability, and the sliding depth will reach the maximum when the seabed thickness is 0.2 times of the wave length. For homogeneous soft clay seabed with slope angle no larger than 2°under wave loading, location of the most dangerous sliding surface is only related with the wave length, that is, the sliding depth is 0.21 times of the wave length and the half chord length of sliding arc is 0.33 times of the wave length. The wave pressure has influences only on factor of safety of the most dangerous sliding surface of the soft clay seabed, not on the sliding depth.
Wave-induced seabed instability is an important problem considered by ocean engineers. On basis of analyzing the present calculation methods for wave-induced seabed sliding instability, a new method, referred to the overall stress state method, is established to calculate the seabed sliding stability under wave loading. The new method has been compared with others, and the wave-induced sliding failure characteristics of sandy seabed and the soft clay one has been analyzed. The results have shown that the overall stress state method is applicable to compute the seabed sliding instability. For sandy seabed, saturation has great influence on its sliding instability, and the sliding depth will reach the maximum when the seabed thickness is 0.2 times of the wave length. For homogeneous soft clay seabed with slope angle no larger than 2°under wave loading, location of the most dangerous sliding surface is only related with the wave length, that is, the sliding depth is 0.21 times of the wave length and the half chord length of sliding arc is 0.33 times of the wave length. The wave pressure has influences only on factor of safety of the most dangerous sliding surface of the soft clay seabed, not on the sliding depth.
2017, 39(5): 123-137.
doi: 10.3969/j.issn.0253-4193.2017.05.012
Abstract:
This study carried out extensive experiments to investigate the wave loads on the twin-plate breakwater under freak waves. The characteristics of wave forces were checked under various relative plate width, relative wave height as well as freak waves parameters. The results show that the maximum wave pressure occurred on the offshore side of the twin-plate, and decreased along the wave propagating direction. The wave pressures on the four surfaces of the twin-plate showed significant difference in both magnitude and phase, and the phase difference ranged in 0.1Tp~0.4Tp. In addition, the measured maximum wave pressure and total vertical force on the twin-plate were compared to those under irregular waves. There is no significant difference in the distribution of the wave pressure envelop for irregular and freak waves. However, the magnitude under freak waves is significant larger than that under irregular waves. Basically, the ratio of the maximum total uplift forces for under freak waves to irregular waves ranges in 1.06-2.45; the ratio of the maximum downward vertical force ranges in 1.22 to 2.07. The increment of the maximum wave pressure is subjected to the freak waves parameter α1.With α1 from 2.04 to 3.1, the maximum pressures under freak waves can be 20% to 80% larger than those under irregular waves. The ratio of the maximum wave suction force between the irregular and freak waves is decreased with α4. With α4=0.62-0.75, the ratio of the maximum wave suction force changes from 1.61 to 0.87. It should be noted that, the critical value of α4 turns out to be 0.72, below which the maximum wave suction forces under freak waves are larger than those under irregular waves, and above which is the other way round.
This study carried out extensive experiments to investigate the wave loads on the twin-plate breakwater under freak waves. The characteristics of wave forces were checked under various relative plate width, relative wave height as well as freak waves parameters. The results show that the maximum wave pressure occurred on the offshore side of the twin-plate, and decreased along the wave propagating direction. The wave pressures on the four surfaces of the twin-plate showed significant difference in both magnitude and phase, and the phase difference ranged in 0.1Tp~0.4Tp. In addition, the measured maximum wave pressure and total vertical force on the twin-plate were compared to those under irregular waves. There is no significant difference in the distribution of the wave pressure envelop for irregular and freak waves. However, the magnitude under freak waves is significant larger than that under irregular waves. Basically, the ratio of the maximum total uplift forces for under freak waves to irregular waves ranges in 1.06-2.45; the ratio of the maximum downward vertical force ranges in 1.22 to 2.07. The increment of the maximum wave pressure is subjected to the freak waves parameter α1.With α1 from 2.04 to 3.1, the maximum pressures under freak waves can be 20% to 80% larger than those under irregular waves. The ratio of the maximum wave suction force between the irregular and freak waves is decreased with α4. With α4=0.62-0.75, the ratio of the maximum wave suction force changes from 1.61 to 0.87. It should be noted that, the critical value of α4 turns out to be 0.72, below which the maximum wave suction forces under freak waves are larger than those under irregular waves, and above which is the other way round.
2017, 39(5): 138-148.
doi: 10.3969/j.issn.0253-4193.2017.05.013
Abstract:
Monitoring coastline changes is the basis of understanding the change of coastal erosion and deposition. Considering the gentle slope of muddy tidal flat and the influence of tide, this paper improves the ‘Water-Line’ method by valuing discrete points of waterlines based on multiple tide monitoring stations and calculating average slope of tidal flat. The results were tested by measured slope of tidal flat. The study chose Biandan River Estuary to Chuandong Harbor coast, frequent change of erosion and deposition and high retention rate of the natural shoreline, to monitoring remote sensing coastline changes. Results showed that, slope of study area is between 0.001 to 0.002 and the intertidal zone is becoming wider from north to south. Biandan River Estuary to Sheyang River Estuary coast is in the eroding environment. A mass of artificial shoreline mainly composed of pond cofferdams are continuously eroded backwards to the sea; Sheyang River Estuary to Simaoyou River Estuary coast is mainly in the change under natural state. The average eroding rate of this area is less than 10 m/a, which is little; Simaoyou River Estuary to Chuandong Harbor coast is in the depositional environment. And the artificial shoreline in this area continuously advances to the sea because of reclamations. According to the results, this paper argues that Xinyang Harbor to Doulong Harbor coast should be the transition zone of study area from northern erosion to southern deposition.
Monitoring coastline changes is the basis of understanding the change of coastal erosion and deposition. Considering the gentle slope of muddy tidal flat and the influence of tide, this paper improves the ‘Water-Line’ method by valuing discrete points of waterlines based on multiple tide monitoring stations and calculating average slope of tidal flat. The results were tested by measured slope of tidal flat. The study chose Biandan River Estuary to Chuandong Harbor coast, frequent change of erosion and deposition and high retention rate of the natural shoreline, to monitoring remote sensing coastline changes. Results showed that, slope of study area is between 0.001 to 0.002 and the intertidal zone is becoming wider from north to south. Biandan River Estuary to Sheyang River Estuary coast is in the eroding environment. A mass of artificial shoreline mainly composed of pond cofferdams are continuously eroded backwards to the sea; Sheyang River Estuary to Simaoyou River Estuary coast is mainly in the change under natural state. The average eroding rate of this area is less than 10 m/a, which is little; Simaoyou River Estuary to Chuandong Harbor coast is in the depositional environment. And the artificial shoreline in this area continuously advances to the sea because of reclamations. According to the results, this paper argues that Xinyang Harbor to Doulong Harbor coast should be the transition zone of study area from northern erosion to southern deposition.
2017, 39(5): 149-160.
doi: 10.3969/j.issn.0253-4193.2017.05.014
Abstract:
Intertidal zone is one of the most important coastal wetland types, which contains immeasurable value in biodiversity protection and global environmental changes. Remote-sensing technology has become an important tool for coastal wetland monitoring. However, there are still challenges to map intertidal zones due to the discrepancy between imagery acquisition time and the local time of the highest and lowest tide. Here, we improve the method of restoring ranges of intertidal zones by combining remote-sensing images and tide model with the aid of GIS. In this way, we using multi-temperal Landsat TM images in 1995, 2000, 2005 and 2010, and Landsat OLI images in 2015, Yancheng intertidal zones are successfully mapped. Results show that the area of Yancheng intertidal zones is about 809.27 km2, decreased by 47% compared with 1995. And the area of intertidal zones, in fact, has been decreasing continually since 1995. The maximum area loss, about 205.67 km2, happened during 1995 to 2000. What's more, intertidal zones are mainly distributed in the south part of Yancheng coastal region, which accounts for 66% of the whole area. And the main loss happened here also, which accounts for 84% of the total area loss.Changes of intertidal zone range can be attributed to both natural and human factors: sea level rising moving the tidal flats toward to land, while intense coastal development moving high-tide lines toward to sea, finally result in "squeezing effects" of the intertidal zones, which ultimately lead to the loss of the study area.
Intertidal zone is one of the most important coastal wetland types, which contains immeasurable value in biodiversity protection and global environmental changes. Remote-sensing technology has become an important tool for coastal wetland monitoring. However, there are still challenges to map intertidal zones due to the discrepancy between imagery acquisition time and the local time of the highest and lowest tide. Here, we improve the method of restoring ranges of intertidal zones by combining remote-sensing images and tide model with the aid of GIS. In this way, we using multi-temperal Landsat TM images in 1995, 2000, 2005 and 2010, and Landsat OLI images in 2015, Yancheng intertidal zones are successfully mapped. Results show that the area of Yancheng intertidal zones is about 809.27 km2, decreased by 47% compared with 1995. And the area of intertidal zones, in fact, has been decreasing continually since 1995. The maximum area loss, about 205.67 km2, happened during 1995 to 2000. What's more, intertidal zones are mainly distributed in the south part of Yancheng coastal region, which accounts for 66% of the whole area. And the main loss happened here also, which accounts for 84% of the total area loss.Changes of intertidal zone range can be attributed to both natural and human factors: sea level rising moving the tidal flats toward to land, while intense coastal development moving high-tide lines toward to sea, finally result in "squeezing effects" of the intertidal zones, which ultimately lead to the loss of the study area.
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