Tidal waves in the East China Sea are simulated numerically with POM(Princeton Ocean Model) model for normal mean sea level, 30 cm higher, 60 cm higher, and 100 cm higher, respectively, and the simulated result is com...Tidal waves in the East China Sea are simulated numerically with POM(Princeton Ocean Model) model for normal mean sea level, 30 cm higher, 60 cm higher, and 100 cm higher, respectively, and the simulated result is compared with the harmonic analysis result of hourly sea level data from 19 tide gauges for more than 19 years. It is indicated that the long-term mean sea level variation affects notably tidal waves in this region. Generally, the tidal amplitude increases when the mean sea level rises, but this relationship may be inverse for some sea areas. The maximal variation of tidal amplitude takes place in the zones near the Fujian coast and the Zhejiang coast, rather than the shallowest Bohai Sea. The maximum increase of M2 amplitude can exceed about 15 cm corresponding to the 60 cm rise of the mean sea level along the Fujian coast. The other regions with large variations of tidal amplitude are those along the Jiangsu coast, the south-east coast of Shandong, and the south-east coast of Dalian. The propagation of tidal waves is also related to mean sea level variation, and the tidal phase-lag decreases generally when the mean sea level rises. Almost all the regions where the tidal phase-lag increases with rising mean sea level are close to amphidromic points, meanwhile the spatial area of such regions is very small. Because the influence of mean sea level variation upon tidal waves is spatially marked, such spatial effect should be considered in calculation of the tidal characteristic value and engineering water level. In the region where the amplitudes of the major tidal constituents increase, the probable maximum high water level becomes higher, the probable maximum low water level becomes lower, and both design water level andcheck water level increase obviously. For example, the design water level at Xiamen increases by 13.5 cm due to the variation of tidal waves when the mean sea level rises 60 cm, the total increase of design water level being 73.5 cm.展开更多
In coastal areas with complicated flow movement, deposition and scour readily occur in submarine excavation projects. In this study, a smallscale model, with a high resolution in the vertical direction, was used to si...In coastal areas with complicated flow movement, deposition and scour readily occur in submarine excavation projects. In this study, a smallscale model, with a high resolution in the vertical direction, was used to simulate the tidal current around a submarine excavation project. The finite volume method was used to solve Navier-Stokes equations and the Reynolds stress transport equation, and the entire process of the tidal current was simulated with unstructured meshes, generated in the irregular shape area, and structured meshes, generated in other water areas.The meshes near the bottom and free surface were densified with a minimum layer thickness of 0.05 m. The volume of fluid method was used to track the free surface, the volume fraction of cells on the upstream boundary was obtained from the volume fraction of adjacent cells, and that on the downstream boundary was determined by the water level process. The numerical results agree with the observed data, and some conclusions can be drawn: after the foundation trench excavation, the flow velocity decreases quite a bit through the foundation trench, with reverse flow occurring on the lee slope in the foundation trench; the swirling flow impedes inflow, leading to the occurrence of dammed water above the foundation trench; the turbulent motion is stronger during ebbing than in other tidal stages, the range with the maximum value of turbulent viscosity, occurring on the south side of the foundation trench at maximum ebbing, is greater than those in other tidal stages in a tidal cycle, and the maximum value of Reynolds shear stress occurs on the south side of the foundation trench at maximum ebbing in a tidal cycle. The numerical calculation method shows a strong performance in simulation of the hydrodynamic characteristics of tidal currents in the foundation trench, providing a basis for submarine engineering construction in coastal areas.展开更多
To study the characteristics of attenuation, hydrostatic towage and wave response of the vertical-axis floating tidal current energy power generation device (VAFTCEPGD), a prototype is designed and experiment is car...To study the characteristics of attenuation, hydrostatic towage and wave response of the vertical-axis floating tidal current energy power generation device (VAFTCEPGD), a prototype is designed and experiment is carried out in the towing tank. Free decay is conducted to obtain attenuation characteristics of the VAFTCEPGD, and characteristics of mooring forces and motion response, floating condition, especially the lateral displacement of the VAFTCEPGD are obtained from the towing in still water. Tension response of the #1 mooring line and vibration characteristics of the VAFTCEPGD in regular waves as well as in level 4 irregular wave sea state with the current velocity of 0.6 m/s. The results can be reference for theoretical study and engineering applications related to VAFTCEPGD.展开更多
The Wenzhou Shoal Reclamation Project is the core part of Wenzhou Peninsula Engineering which is a big comprehensive development project to expand the city space. The dynamics of the surrounding area was proved to suf...The Wenzhou Shoal Reclamation Project is the core part of Wenzhou Peninsula Engineering which is a big comprehensive development project to expand the city space. The dynamics of the surrounding area was proved to suffer little effect in response to the Lingni north dyke since it was built approximately along the current direction. Therefore, this paper focuses firstly on the tidal characteristics in the Wenzhou and Yueqing bays with the Lingni north dyke being built and then on the changes resulting from the implementation of the on-going Wenzhou Shoal Reclamation Project(WSRP) which will reclaim land from the whole Wenzhou Shoal. To simulate the tidal dynamics, a high-resolution coastal ocean model with unstructured triangular grids was set up for the Wenzhou and Yueqing Bays. The model resolved the complicated tidal dynamics with the simulated tidal elevation and current in good agreement with observations. In the study area, M2 is the predominant tidal component, which means the tide is semidiurnal. The new reclamation project hardly affects the Yueqing Bay and the open ocean, but there are concentrated effects on the mouth of the southern branch of the Oujiang River and the southwest of Wenzhou Shoal. This study provides an indicative reference to the local government and helps to weigh the advantages and disadvantages of the project.展开更多
By taking the Yong River for example in this paper, based on the multiple measured data during 1957 to 2009, the change process of runoff, tide feature, tidal wave, tidal influx and sediment transport are analyzed. Th...By taking the Yong River for example in this paper, based on the multiple measured data during 1957 to 2009, the change process of runoff, tide feature, tidal wave, tidal influx and sediment transport are analyzed. Then a mathematical model is used to reveal the influence mechanism on hydrodynamic characteristics and sediment transport of the wading engineering groups such as a tide gate, a breakwater, reservoirs, bridges and wharves, which were built in different periods. The results showed the hydrodynamic characteristics and sediment transport of the Yong River changed obviously due to the wading engineering groups. The tide gate induced deformation of the tidal wave, obvious reduction of the tidal influx and weakness of the tidal dynamic, decrease of the sediment yield of flood and ebb tide and channel deposition. The breakwater blocked estuarine entrances, resulting in the change of the tidal current and the reduction of the tidal influx in the estuarine area. The large-scale reservoirs gradually made the decrease of the Yong River runoff. The bridge and wharf groups took up cross-section areas, the cumulative affection of which caused the increase of tidal level in the tidal river.展开更多
This study was conducted on the spatial distribution characteristics of surface tidal currents in the southwestern Taiwan Strait based on the quasi-harmonic analysis of current data obtained by two high frequency surf...This study was conducted on the spatial distribution characteristics of surface tidal currents in the southwestern Taiwan Strait based on the quasi-harmonic analysis of current data obtained by two high frequency surface wave radar(HFSWR) systems. The analysis shows that the tidal current pattern in the southwestern Taiwan Strait is primarily semi-diurnal and influenced significantly by shallow water constituents. The spatial distribution of tidal current ellipses of M2 is probably affected by the interaction between two different systems of tide wave, one from the northern mouth of Taiwan Strait and the other from the Bashi Channel. The directions of the major axes of M2 tidal current ellipses coincide roughly with the axis of the Taiwan Strait. The spatial distribution of the magnitudes of the probable maximum current velocity(PMCS) shows gradual increase of the velocity from northeast to southwest, which is in accordance with the spatial distribution of the measured maximum current velocity(MMCS). The directions of the residual currents are in accordance with the direction of the prevailing monsoon wind at the Taiwan Strait and the direction of the Taiwan warm current during summer. The bathymetry also shows a significant effect on the spatial distribution characteristics of tidal currents.展开更多
A permanent tidal station was installed at the Chinese Zhongshan Station in Feb. 2010. Harmonic constants of 170 tidal constituents were obtained from harmonic analysis of the first year' s data. The results of the e...A permanent tidal station was installed at the Chinese Zhongshan Station in Feb. 2010. Harmonic constants of 170 tidal constituents were obtained from harmonic analysis of the first year' s data. The results of the eight main constituents showed good agreement with those of two tidal models. Tidal characteristics, such as tide type, diurnal inequality, tidal range, and water levels were also analyzed.展开更多
The Liaodong Shoal is a group of linear sand ridges located in the east Bohai Sea of China.In this study,54 surface sediment samples have been collected,current measurements at 4 stations have been carried out and bat...The Liaodong Shoal is a group of linear sand ridges located in the east Bohai Sea of China.In this study,54 surface sediment samples have been collected,current measurements at 4 stations have been carried out and bathymetric data were obtained.The current directions are rightward deflected relative to the strikes of the sand ridges.Affected by the narrowing effect of the ridge,the current velocities exhibited an anti-‘C’type vertical profile.The velocities of the lower currents linearly correlate with the water depths.The near-bed current velocities over the troughs are estimated to be higher than those over the ridges,and this feature could be explained by the loss of kinetic energy together with the conversion between kinetic energy and gravitational potential energy.The sedimentary characteristics that are compatible with the tidal dynamics are developed across the ridges and troughs,including grain size compositions,grain size parameters,mineral compositions and Dhm indexes.The existence of the angles between the current directions and the strikes of the sand ridges is the key factor for the growth of the sand ridges.The asymmetric hydrodynamic features between the flood and ebb currents lead to the differences in the topographical and sedimentary characteristics on both sides of a sand ridge.Insufficient material supply led to the degradation of the sand ridges,and the reduction of the tidal current intensity has led to the development of the subordinate sand ridges in the troughs.Sand ridges are migrating.展开更多
The basic knowledge of tidal characteristics in Chesapeake Bay is a prerequisite to understand the tidal processes in Chesapeake Bay. The tidal characteristics in Chesapeake Bay were assessed in this paper using basic...The basic knowledge of tidal characteristics in Chesapeake Bay is a prerequisite to understand the tidal processes in Chesapeake Bay. The tidal characteristics in Chesapeake Bay were assessed in this paper using basic tidal hydraulic analysis. Tidal elevation, currents and salinity data of Chesapeake Bay from National Oceanic and Atmospheric Administration (NOAA) were retrieved, and analyzed to understand Chesapeake Bay tide. General knowledge of location, geometry, tides, freshwater inputs, wind, salinity, etc in Chesapeake Bay was described. Sediment distribution of Chesapeake Bay was briefly described and discussed. Amplitude and phase of the selected major constituent, form factor, phase difference between tide elevations and currents at a few tidal elevation stations within Chesapeake Bay were calculated. Tidal prism was figured out using cubature method. The analysis approach could also be used as a source of reference for basic tidal study in other tide-affected field.展开更多
Studies by many scientists show that Hebei, China is an area with strong correlation between the tidal force and the occurrences of major earthquakes, the Xingtai earthquake of 1966, the Hejian earthquake of 1967 and ...Studies by many scientists show that Hebei, China is an area with strong correlation between the tidal force and the occurrences of major earthquakes, the Xingtai earthquake of 1966, the Hejian earthquake of 1967 and the Tangshan earthquake of 1976 were triggered by the tidal force, in this paper the study on the common characteristics of their occurrence times confirms these facts. The computed times of maximum horizontal of the semi diurnal solid tide tidal force show that the occurrence times of the above mentioned earthquakes were close to the times of maximum horizontal tidal force of the semi diurnal solid tide at new moon or full moon. The Longyao earthquake of M =6.8, the Ningjin earthquake of M =7.2 and the Hejian earthquake of M =6.3 occurred tens of minutes after the maximum horizontal tidal force of the semi diurnal solid tides, and the Tangshan earthquake of M =7.8 occurred 16 minutes before the maximum horizontal tidal force. The tidal forces were directed to the west. This is their temporal characteristic. It is generally accepted that the 1969 Bohai earthquake of M =7.4 and the 1975 Haicheng earthquake were not triggered by the tidal force. These events did not show such characteristics. The temporal characteristics of the earthquakes indicate that the occurrences of these events were not random, but were controlled by the tidal force from the sun and the moon, and triggered by the tidal force. These facts agree with the triggering mechanism of the tidal force, are evidences of earthquakes triggered by tidal force.展开更多
Using the single-point ground wave (GW) radar data at Shensi Station and the water level data at three stations (Shengsi, Luchaogang and Daishan), the authors obtained the flow vectors from the radial velocity of ...Using the single-point ground wave (GW) radar data at Shensi Station and the water level data at three stations (Shengsi, Luchaogang and Daishan), the authors obtained the flow vectors from the radial velocity of GW radar observation, and calculate four sub-tidal harmonic constants (O1, K1, M2 and S2). The tidal characteristics derived from the GW radar dataset agreed well with those from the tidal gauge data. The authors also analyzed the tidal energy flux and tidal energy dissipation rate. There was a good relationship between the tidal energy dissipation rate and topography. The study showed a good way to calculate tidal energy dissipation rate using GW radar data.展开更多
Based on the quasi-harmonic analysis of 11 d vector ocean currents obtained from two high frequency sur- face wave radars located at Zhujiajian Island and Shengshan Island, the spatial distribution characteristics of ...Based on the quasi-harmonic analysis of 11 d vector ocean currents obtained from two high frequency sur- face wave radars located at Zhujiajian Island and Shengshan Island, the spatial distribution characteristics of surface tidal currents in the open sea area to the east of the Zhoushan Islands of Zhejiang Province, China are studied. The following conclusions are drawn from the analysis: the tidal current pattern in the open sea area to the east of Zhoushan Islands is primarily regular semidiurnal, which is significantly affected by the shallow water constituents. The directions of the major axes of tidal current ellipses of M2 lie approx- imately in the NW-SE direction. With the increasing of distance away from the coast, the directions of the tidal current ellipses gradually shift toward the E-W direction. The tidal currents are mainly reversing cur- rents. The spatial distribution of probable maximum current velocities decreases gradually from northeast to southwest which is basically in accordance with the spatial distribution of measured maximum current velocities. The residual currents near the coast are larger than those far away from the coast. The directions of the residual currents are basically north by east, and the angle to the due north increases gradually with the increasing distance away from the coast. The topography shows a certain impact on the spatial distri- bution of shallow water constituents, the rotation of tidal currents, the probable maximum currents and the residual currents.展开更多
The growth of tidal flats off Zhejiang coasts in southwestern China has provided substantial areas for local agriculture and construction activities.To evaluate modern and future development of tidal flats in the regi...The growth of tidal flats off Zhejiang coasts in southwestern China has provided substantial areas for local agriculture and construction activities.To evaluate modern and future development of tidal flats in the region,a good understanding of sediment sources is necessary.Previous research has concluded that the Changjiang(Yangtze)River is the dominant supplier of sediments to this part of the southeast Chinese coast,despite the fact that sediment delivery from this source has been decreased markedly in the past two decades.In this study,we investigated the sources of tidal flat sediments,and the magnetic and geochemical properties of recent tidal flat sediments along the Zhejiang coast were compared with those discharged from rivers.Magnetic and geochemical properties of the tidal flat samples reveal statistically distinct sediment provenance groups.The magnetic and geochemical scatter plots show that the suspended sediment samples are naturally divided into two different groups,one including the Changjiang River and Qiantang River material,and the other including the Jiaojiang,Oujiang,and Feiyun Rivers that located in the central and southern parts of the study areas.At last,a binary source of tidal flat sediments along the Zhejiang coast was determined,with the substantial majority originating from local rivers,while a much smaller proportion emanates from the Changjiang River to the north.We conclude that the sediment contribution of the Changjiang River to tidal flat development in the region has been markedly overestimated,with important implications for management.展开更多
A study of sedimentary facies,mineral and textural characteristics of sections of conglomerates/pebbles and sandstone facies found within the Lokoja and Patti Formations in southern Bida Basin,Nigeria,is carried out t...A study of sedimentary facies,mineral and textural characteristics of sections of conglomerates/pebbles and sandstone facies found within the Lokoja and Patti Formations in southern Bida Basin,Nigeria,is carried out to evaluate the paleo-environment and reservoir quality of the sandstones of the formations through field observations and textural and mineralogical(using X-Ray Diffractogram)analyses.Nine lithofacies are identified and grouped into three main facies associations.These sedimentary facies suggest deposition in both foreshore and estuaries.The mineral analysis(XRD)shows that the quartz content in sandstone facies of the Lokoja Formation ranges between 49%and 67%,and that of the Patti Sandstone between 43%and 56%,indicating a quartz dominance.The granulometric studies reveal that the Lokoja Formation comprises coarse-to medium-grained(-0.63 to 1.30φ)sandstone with moderatepoor sorting of 0.72e1.824.On the other hand,medium to fine-grained sandstones dominate the Patti Formation,which is averagely poorly sorted(1.29-1.54φ).The sandstones are coarsely skewed to finely skewed,with the kurtosis ranging from very platykurtic to leptokurtic.Morphological results of the pebbles from both Lokoja and Patti Formations indicate that the study areas are mainly characterized by the interplay of both wave and fluvial processes,which suggests that the environment of deposition of sandstone facies is predominantly of the fluvial to the shallow marine environment with the indication of tidal influence.Integrating sedimentary facies and textural results suggests subtidal sand ridge/foreshore,estuarine mudflat,and estuarine delta environments with fluvial influences.Evidence from the textural and mineral characteristics indicate that the sandstone facies of the Lokoja and Patti Formations are fairly matured and can act as potential hydrocarbon reservoirs in the formations.The facies,XRD mineral,and textural results have revealed potential hydrocarbon reservoir areas and paleo-depositional features of the Lokoja and Patti Formations.展开更多
Currently, most researches use signals, such as the coil current or voltage of solenoid, to identify parameters; typically, parameter identification method based on variation rate of coil current is applied for positi...Currently, most researches use signals, such as the coil current or voltage of solenoid, to identify parameters; typically, parameter identification method based on variation rate of coil current is applied for position estimation. The problem exists in these researches that the detected signals are prone to interference and difficult to obtain. This paper proposes a new method for detecting the core position by using flux characteristic quantity, which adds a new group of secondary winding to the coil of the ordinary switching electromagnet. On the basis of electromagnetic coupling theory analysis and simulation research of the magnetic field regarding the primary and secondary winding coils, and in accordance with the fact that under PWM control mode varying core position and operating current of windings produce different characteristic of flux increment of the secondary winding. The flux increment of the electromagnet winding can be obtained by conducting time domain integration for the induced voltage signal of the extracted secondary winding, and the core position from the two-dimensional fitting curve of the operating winding current and flux-linkage characteristic quantity of solenoid are calculated. The detecting and testing system of solenoid core position is developed based on the theoretical research. The testing results show that the flux characteristic quantity of switching electromagnet magnetic circuit is able to effectively show the core position and thus to accomplish the non-displacement transducer detection of the said core position of the switching electromagnet. This paper proposes a new method for detecting the core position by using flux characteristic quantity, which provides a new theory and method for switch solenoid to control the proportional valve.展开更多
[Objective] The research aimed to study three-dimensional structure and echo characteristic quantity of a supercell storm in central Gansu on May 30,2005.[Method] By monitoring data of Lanzhou CINRAD/CC Doppler radar,...[Objective] The research aimed to study three-dimensional structure and echo characteristic quantity of a supercell storm in central Gansu on May 30,2005.[Method] By monitoring data of Lanzhou CINRAD/CC Doppler radar,the three-dimensional structure characteristics of a rare supercell storm which happened in central Gansu on May 30,2005 were analyzed.We tried to reveal three-dimensional structure and echo characteristic index of supercell storm in the northeast of Qinghai-Tibet Plateau,and find reason of rare heavy hail appearance.[Result] The large-scale strong storm was formed by the common effect of Mongolia cold vortex,low-level jet and ground cold front.When the development of main echo was mature,on reflectivity factor map,it presented obvious inverted 'V' shaped structure in left front of low-level storm,typical hooked and 'person'-type echo characteristics in the right rear.The bounded weak echo zone(vault) in low level corresponded with strong echo overhanging body in high level.It surpassed 60 dBz in the strong reflectivity factor zone.It presented one weak meso-cyclone on corresponding radial velocity map.The jumped increase characteristic of VIL could be as one of indices for judging that hail started to grow.Almost all storms(VILD ≥4.0 g/m3) had more obvious indication significance than VIL for judging heavy hail(diameter ≥20 mm).[Conclusion] The research provided reference for nowcasting of strong convection weather and artificial hail suppression.展开更多
Based on a ship survey during January 1998, the characteristics of the flow, the thermohaline properties and the volume transport of the Arabian Sea are discussed. A strong westward flow exists between 10.5?N and 11?N...Based on a ship survey during January 1998, the characteristics of the flow, the thermohaline properties and the volume transport of the Arabian Sea are discussed. A strong westward flow exists between 10.5?N and 11?N, part of which turns to the south as the Somali current near the coast at about 10?N and the rest turns north. At the passage between the African continent and the So- cotra Island, the northern branch separates into two flows: the left one enters the passage and the right one flows eastward along the southern slope of the island. Off the island the flow separates once more, most of it meandering northeast and a small fraction flow- ing southeast. Volume transport calculation suggests that the tidal transport is one or two orders of magnitude smaller than the total transport in this region and it becomes more important near the coast. The average velocity of the flow in the upper layer (0-150 m) is about 20 cm s-1, with a maximum of 53 cm s-1 appearing east of the Socotra Island, and the subsurface layer (200-800 m) has an aver- age velocity of 8.6 cm s-1; the velocity becomes smaller at greater depths. The depth of the seasonal thermocline is about 100 m, above which there is a layer with well mixed temperature and dissolved oxygen. High-salinity and oxygen-rich water appears near the surface of the northern Arabian Sea; a salinity maximum and oxygen minimum at 100 m depth along 8?N testifies the subduction of surface water from the northern Arabian Sea. Waters from the Red Sea and the Persian Gulf also influence the salinity of the area.展开更多
Using fluid dynamics software Fluent, the spray characteristics of an effervescent atomizer in a downstream flow field was simulated and analyzed, the results show that on the cross sections of the atomizer downstream...Using fluid dynamics software Fluent, the spray characteristics of an effervescent atomizer in a downstream flow field was simulated and analyzed, the results show that on the cross sections of the atomizer downstream flow field, the distribution of the atomized droplet size is small and mainly concentrated about Sauter mean diameter ( SMD), and the distribution of the axial velocity is large, but mainly concentrated about the gas peak velocity in the closer nozzle axis area; the gas peak velocity of the atomized droplet increases, while the droplet SMD decreases with increase of the nozzle caliber and the air pressure; with the increase of the flow rate of cuttingfluid, the atomized droplet SMD increases, while the gas peak velocity rises first and then decreases, but the decrease trend is very small after the air pressure is more than 0. 4 MPa. The simulation results have significance in guiding for designing and applying the effervescent atomizer.展开更多
文摘Tidal waves in the East China Sea are simulated numerically with POM(Princeton Ocean Model) model for normal mean sea level, 30 cm higher, 60 cm higher, and 100 cm higher, respectively, and the simulated result is compared with the harmonic analysis result of hourly sea level data from 19 tide gauges for more than 19 years. It is indicated that the long-term mean sea level variation affects notably tidal waves in this region. Generally, the tidal amplitude increases when the mean sea level rises, but this relationship may be inverse for some sea areas. The maximal variation of tidal amplitude takes place in the zones near the Fujian coast and the Zhejiang coast, rather than the shallowest Bohai Sea. The maximum increase of M2 amplitude can exceed about 15 cm corresponding to the 60 cm rise of the mean sea level along the Fujian coast. The other regions with large variations of tidal amplitude are those along the Jiangsu coast, the south-east coast of Shandong, and the south-east coast of Dalian. The propagation of tidal waves is also related to mean sea level variation, and the tidal phase-lag decreases generally when the mean sea level rises. Almost all the regions where the tidal phase-lag increases with rising mean sea level are close to amphidromic points, meanwhile the spatial area of such regions is very small. Because the influence of mean sea level variation upon tidal waves is spatially marked, such spatial effect should be considered in calculation of the tidal characteristic value and engineering water level. In the region where the amplitudes of the major tidal constituents increase, the probable maximum high water level becomes higher, the probable maximum low water level becomes lower, and both design water level andcheck water level increase obviously. For example, the design water level at Xiamen increases by 13.5 cm due to the variation of tidal waves when the mean sea level rises 60 cm, the total increase of design water level being 73.5 cm.
基金supported by the National Natural Science Foundation of China(Grant No.41406005)
文摘In coastal areas with complicated flow movement, deposition and scour readily occur in submarine excavation projects. In this study, a smallscale model, with a high resolution in the vertical direction, was used to simulate the tidal current around a submarine excavation project. The finite volume method was used to solve Navier-Stokes equations and the Reynolds stress transport equation, and the entire process of the tidal current was simulated with unstructured meshes, generated in the irregular shape area, and structured meshes, generated in other water areas.The meshes near the bottom and free surface were densified with a minimum layer thickness of 0.05 m. The volume of fluid method was used to track the free surface, the volume fraction of cells on the upstream boundary was obtained from the volume fraction of adjacent cells, and that on the downstream boundary was determined by the water level process. The numerical results agree with the observed data, and some conclusions can be drawn: after the foundation trench excavation, the flow velocity decreases quite a bit through the foundation trench, with reverse flow occurring on the lee slope in the foundation trench; the swirling flow impedes inflow, leading to the occurrence of dammed water above the foundation trench; the turbulent motion is stronger during ebbing than in other tidal stages, the range with the maximum value of turbulent viscosity, occurring on the south side of the foundation trench at maximum ebbing, is greater than those in other tidal stages in a tidal cycle, and the maximum value of Reynolds shear stress occurs on the south side of the foundation trench at maximum ebbing in a tidal cycle. The numerical calculation method shows a strong performance in simulation of the hydrodynamic characteristics of tidal currents in the foundation trench, providing a basis for submarine engineering construction in coastal areas.
基金supported by the National Natural Science Foundation of China(Grant Nos.51309068,51309069,51579055 and 11572094)the Special Funded of Innovational Talents of Science and Technology in Harbin(Grant No.RC2014QN001008)+1 种基金the China Postdoctoral Science Foundation(Grant Nos.2014M561334 and 2015T80330)the Heilongjiang Postdoctoral Science Foundation(Grant No.LBH-Z14060)
文摘To study the characteristics of attenuation, hydrostatic towage and wave response of the vertical-axis floating tidal current energy power generation device (VAFTCEPGD), a prototype is designed and experiment is carried out in the towing tank. Free decay is conducted to obtain attenuation characteristics of the VAFTCEPGD, and characteristics of mooring forces and motion response, floating condition, especially the lateral displacement of the VAFTCEPGD are obtained from the towing in still water. Tension response of the #1 mooring line and vibration characteristics of the VAFTCEPGD in regular waves as well as in level 4 irregular wave sea state with the current velocity of 0.6 m/s. The results can be reference for theoretical study and engineering applications related to VAFTCEPGD.
基金supported by the National Basic Research Program of China(Grant no.2010CB428704)the National Nature Science Foundation of China(Grand nos.4127608341430963)
文摘The Wenzhou Shoal Reclamation Project is the core part of Wenzhou Peninsula Engineering which is a big comprehensive development project to expand the city space. The dynamics of the surrounding area was proved to suffer little effect in response to the Lingni north dyke since it was built approximately along the current direction. Therefore, this paper focuses firstly on the tidal characteristics in the Wenzhou and Yueqing bays with the Lingni north dyke being built and then on the changes resulting from the implementation of the on-going Wenzhou Shoal Reclamation Project(WSRP) which will reclaim land from the whole Wenzhou Shoal. To simulate the tidal dynamics, a high-resolution coastal ocean model with unstructured triangular grids was set up for the Wenzhou and Yueqing Bays. The model resolved the complicated tidal dynamics with the simulated tidal elevation and current in good agreement with observations. In the study area, M2 is the predominant tidal component, which means the tide is semidiurnal. The new reclamation project hardly affects the Yueqing Bay and the open ocean, but there are concentrated effects on the mouth of the southern branch of the Oujiang River and the southwest of Wenzhou Shoal. This study provides an indicative reference to the local government and helps to weigh the advantages and disadvantages of the project.
基金financially supported by the National Science Foundation for Distinguished Young Scholars of China(Grant No.51125034)the National Natural Science Foundation of China(Grant Nos.51279046 and 50909037)the Fundamental Research Funds for the Central Universities(Grant No.2010B01114)
文摘By taking the Yong River for example in this paper, based on the multiple measured data during 1957 to 2009, the change process of runoff, tide feature, tidal wave, tidal influx and sediment transport are analyzed. Then a mathematical model is used to reveal the influence mechanism on hydrodynamic characteristics and sediment transport of the wading engineering groups such as a tide gate, a breakwater, reservoirs, bridges and wharves, which were built in different periods. The results showed the hydrodynamic characteristics and sediment transport of the Yong River changed obviously due to the wading engineering groups. The tide gate induced deformation of the tidal wave, obvious reduction of the tidal influx and weakness of the tidal dynamic, decrease of the sediment yield of flood and ebb tide and channel deposition. The breakwater blocked estuarine entrances, resulting in the change of the tidal current and the reduction of the tidal influx in the estuarine area. The large-scale reservoirs gradually made the decrease of the Yong River runoff. The bridge and wharf groups took up cross-section areas, the cumulative affection of which caused the increase of tidal level in the tidal river.
基金supported by the National High Technology Research and Development Program (‘863’ Program) of China under contract No. 2012AA091701the Fundamental Research Fund for the Central University of China under the contract No. 2012212020211
文摘This study was conducted on the spatial distribution characteristics of surface tidal currents in the southwestern Taiwan Strait based on the quasi-harmonic analysis of current data obtained by two high frequency surface wave radar(HFSWR) systems. The analysis shows that the tidal current pattern in the southwestern Taiwan Strait is primarily semi-diurnal and influenced significantly by shallow water constituents. The spatial distribution of tidal current ellipses of M2 is probably affected by the interaction between two different systems of tide wave, one from the northern mouth of Taiwan Strait and the other from the Bashi Channel. The directions of the major axes of M2 tidal current ellipses coincide roughly with the axis of the Taiwan Strait. The spatial distribution of the magnitudes of the probable maximum current velocity(PMCS) shows gradual increase of the velocity from northeast to southwest, which is in accordance with the spatial distribution of the measured maximum current velocity(MMCS). The directions of the residual currents are in accordance with the direction of the prevailing monsoon wind at the Taiwan Strait and the direction of the Taiwan warm current during summer. The bathymetry also shows a significant effect on the spatial distribution characteristics of tidal currents.
基金Supported by National Major Scientific Research Projects(2012CB957701)Natural Natural Science Foundation(41176172,41176173,41076126,41106163)Polar Environment Comprehensive Expedition the Resources Potential Evaluation Project(CHINARE2012-01-03,CHINARE2012-02-02,CHINARE2012-03-03)
文摘A permanent tidal station was installed at the Chinese Zhongshan Station in Feb. 2010. Harmonic constants of 170 tidal constituents were obtained from harmonic analysis of the first year' s data. The results of the eight main constituents showed good agreement with those of two tidal models. Tidal characteristics, such as tide type, diurnal inequality, tidal range, and water levels were also analyzed.
基金supported by the National Natural Science Foundation of China (Nos. 41106039 and 41776059)
文摘The Liaodong Shoal is a group of linear sand ridges located in the east Bohai Sea of China.In this study,54 surface sediment samples have been collected,current measurements at 4 stations have been carried out and bathymetric data were obtained.The current directions are rightward deflected relative to the strikes of the sand ridges.Affected by the narrowing effect of the ridge,the current velocities exhibited an anti-‘C’type vertical profile.The velocities of the lower currents linearly correlate with the water depths.The near-bed current velocities over the troughs are estimated to be higher than those over the ridges,and this feature could be explained by the loss of kinetic energy together with the conversion between kinetic energy and gravitational potential energy.The sedimentary characteristics that are compatible with the tidal dynamics are developed across the ridges and troughs,including grain size compositions,grain size parameters,mineral compositions and Dhm indexes.The existence of the angles between the current directions and the strikes of the sand ridges is the key factor for the growth of the sand ridges.The asymmetric hydrodynamic features between the flood and ebb currents lead to the differences in the topographical and sedimentary characteristics on both sides of a sand ridge.Insufficient material supply led to the degradation of the sand ridges,and the reduction of the tidal current intensity has led to the development of the subordinate sand ridges in the troughs.Sand ridges are migrating.
文摘The basic knowledge of tidal characteristics in Chesapeake Bay is a prerequisite to understand the tidal processes in Chesapeake Bay. The tidal characteristics in Chesapeake Bay were assessed in this paper using basic tidal hydraulic analysis. Tidal elevation, currents and salinity data of Chesapeake Bay from National Oceanic and Atmospheric Administration (NOAA) were retrieved, and analyzed to understand Chesapeake Bay tide. General knowledge of location, geometry, tides, freshwater inputs, wind, salinity, etc in Chesapeake Bay was described. Sediment distribution of Chesapeake Bay was briefly described and discussed. Amplitude and phase of the selected major constituent, form factor, phase difference between tide elevations and currents at a few tidal elevation stations within Chesapeake Bay were calculated. Tidal prism was figured out using cubature method. The analysis approach could also be used as a source of reference for basic tidal study in other tide-affected field.
文摘Studies by many scientists show that Hebei, China is an area with strong correlation between the tidal force and the occurrences of major earthquakes, the Xingtai earthquake of 1966, the Hejian earthquake of 1967 and the Tangshan earthquake of 1976 were triggered by the tidal force, in this paper the study on the common characteristics of their occurrence times confirms these facts. The computed times of maximum horizontal of the semi diurnal solid tide tidal force show that the occurrence times of the above mentioned earthquakes were close to the times of maximum horizontal tidal force of the semi diurnal solid tide at new moon or full moon. The Longyao earthquake of M =6.8, the Ningjin earthquake of M =7.2 and the Hejian earthquake of M =6.3 occurred tens of minutes after the maximum horizontal tidal force of the semi diurnal solid tides, and the Tangshan earthquake of M =7.8 occurred 16 minutes before the maximum horizontal tidal force. The tidal forces were directed to the west. This is their temporal characteristic. It is generally accepted that the 1969 Bohai earthquake of M =7.4 and the 1975 Haicheng earthquake were not triggered by the tidal force. These events did not show such characteristics. The temporal characteristics of the earthquakes indicate that the occurrences of these events were not random, but were controlled by the tidal force from the sun and the moon, and triggered by the tidal force. These facts agree with the triggering mechanism of the tidal force, are evidences of earthquakes triggered by tidal force.
基金supported by projects (No. 40976012 and No. 40906030)
文摘Using the single-point ground wave (GW) radar data at Shensi Station and the water level data at three stations (Shengsi, Luchaogang and Daishan), the authors obtained the flow vectors from the radial velocity of GW radar observation, and calculate four sub-tidal harmonic constants (O1, K1, M2 and S2). The tidal characteristics derived from the GW radar dataset agreed well with those from the tidal gauge data. The authors also analyzed the tidal energy flux and tidal energy dissipation rate. There was a good relationship between the tidal energy dissipation rate and topography. The study showed a good way to calculate tidal energy dissipation rate using GW radar data.
基金The National High Technology Research and Development Program of China(863 Program)under contract No.2012AA091701the Fundamental Research Fund for the Central Universities of China under contract No.2012212020211
文摘Based on the quasi-harmonic analysis of 11 d vector ocean currents obtained from two high frequency sur- face wave radars located at Zhujiajian Island and Shengshan Island, the spatial distribution characteristics of surface tidal currents in the open sea area to the east of the Zhoushan Islands of Zhejiang Province, China are studied. The following conclusions are drawn from the analysis: the tidal current pattern in the open sea area to the east of Zhoushan Islands is primarily regular semidiurnal, which is significantly affected by the shallow water constituents. The directions of the major axes of tidal current ellipses of M2 lie approx- imately in the NW-SE direction. With the increasing of distance away from the coast, the directions of the tidal current ellipses gradually shift toward the E-W direction. The tidal currents are mainly reversing cur- rents. The spatial distribution of probable maximum current velocities decreases gradually from northeast to southwest which is basically in accordance with the spatial distribution of measured maximum current velocities. The residual currents near the coast are larger than those far away from the coast. The directions of the residual currents are basically north by east, and the angle to the due north increases gradually with the increasing distance away from the coast. The topography shows a certain impact on the spatial distri- bution of shallow water constituents, the rotation of tidal currents, the probable maximum currents and the residual currents.
基金Supported by the Natural Science Foundation of Zhejiang Province,China(No.LY20D040001)the National Undergraduate Innovation and Entrepreneurship Training Program of China。
文摘The growth of tidal flats off Zhejiang coasts in southwestern China has provided substantial areas for local agriculture and construction activities.To evaluate modern and future development of tidal flats in the region,a good understanding of sediment sources is necessary.Previous research has concluded that the Changjiang(Yangtze)River is the dominant supplier of sediments to this part of the southeast Chinese coast,despite the fact that sediment delivery from this source has been decreased markedly in the past two decades.In this study,we investigated the sources of tidal flat sediments,and the magnetic and geochemical properties of recent tidal flat sediments along the Zhejiang coast were compared with those discharged from rivers.Magnetic and geochemical properties of the tidal flat samples reveal statistically distinct sediment provenance groups.The magnetic and geochemical scatter plots show that the suspended sediment samples are naturally divided into two different groups,one including the Changjiang River and Qiantang River material,and the other including the Jiaojiang,Oujiang,and Feiyun Rivers that located in the central and southern parts of the study areas.At last,a binary source of tidal flat sediments along the Zhejiang coast was determined,with the substantial majority originating from local rivers,while a much smaller proportion emanates from the Changjiang River to the north.We conclude that the sediment contribution of the Changjiang River to tidal flat development in the region has been markedly overestimated,with important implications for management.
文摘A study of sedimentary facies,mineral and textural characteristics of sections of conglomerates/pebbles and sandstone facies found within the Lokoja and Patti Formations in southern Bida Basin,Nigeria,is carried out to evaluate the paleo-environment and reservoir quality of the sandstones of the formations through field observations and textural and mineralogical(using X-Ray Diffractogram)analyses.Nine lithofacies are identified and grouped into three main facies associations.These sedimentary facies suggest deposition in both foreshore and estuaries.The mineral analysis(XRD)shows that the quartz content in sandstone facies of the Lokoja Formation ranges between 49%and 67%,and that of the Patti Sandstone between 43%and 56%,indicating a quartz dominance.The granulometric studies reveal that the Lokoja Formation comprises coarse-to medium-grained(-0.63 to 1.30φ)sandstone with moderatepoor sorting of 0.72e1.824.On the other hand,medium to fine-grained sandstones dominate the Patti Formation,which is averagely poorly sorted(1.29-1.54φ).The sandstones are coarsely skewed to finely skewed,with the kurtosis ranging from very platykurtic to leptokurtic.Morphological results of the pebbles from both Lokoja and Patti Formations indicate that the study areas are mainly characterized by the interplay of both wave and fluvial processes,which suggests that the environment of deposition of sandstone facies is predominantly of the fluvial to the shallow marine environment with the indication of tidal influence.Integrating sedimentary facies and textural results suggests subtidal sand ridge/foreshore,estuarine mudflat,and estuarine delta environments with fluvial influences.Evidence from the textural and mineral characteristics indicate that the sandstone facies of the Lokoja and Patti Formations are fairly matured and can act as potential hydrocarbon reservoirs in the formations.The facies,XRD mineral,and textural results have revealed potential hydrocarbon reservoir areas and paleo-depositional features of the Lokoja and Patti Formations.
基金supported by National Natural Science Foundation of China(Grant No.51175362)
文摘Currently, most researches use signals, such as the coil current or voltage of solenoid, to identify parameters; typically, parameter identification method based on variation rate of coil current is applied for position estimation. The problem exists in these researches that the detected signals are prone to interference and difficult to obtain. This paper proposes a new method for detecting the core position by using flux characteristic quantity, which adds a new group of secondary winding to the coil of the ordinary switching electromagnet. On the basis of electromagnetic coupling theory analysis and simulation research of the magnetic field regarding the primary and secondary winding coils, and in accordance with the fact that under PWM control mode varying core position and operating current of windings produce different characteristic of flux increment of the secondary winding. The flux increment of the electromagnet winding can be obtained by conducting time domain integration for the induced voltage signal of the extracted secondary winding, and the core position from the two-dimensional fitting curve of the operating winding current and flux-linkage characteristic quantity of solenoid are calculated. The detecting and testing system of solenoid core position is developed based on the theoretical research. The testing results show that the flux characteristic quantity of switching electromagnet magnetic circuit is able to effectively show the core position and thus to accomplish the non-displacement transducer detection of the said core position of the switching electromagnet. This paper proposes a new method for detecting the core position by using flux characteristic quantity, which provides a new theory and method for switch solenoid to control the proportional valve.
基金Supported by Science Research Special Item of Public Welfare Industry (Meteorology) (GYHY200906024)New Meteorological Technology Spreading Item of China Meteorological Administration(CMATG2009MS38)
文摘[Objective] The research aimed to study three-dimensional structure and echo characteristic quantity of a supercell storm in central Gansu on May 30,2005.[Method] By monitoring data of Lanzhou CINRAD/CC Doppler radar,the three-dimensional structure characteristics of a rare supercell storm which happened in central Gansu on May 30,2005 were analyzed.We tried to reveal three-dimensional structure and echo characteristic index of supercell storm in the northeast of Qinghai-Tibet Plateau,and find reason of rare heavy hail appearance.[Result] The large-scale strong storm was formed by the common effect of Mongolia cold vortex,low-level jet and ground cold front.When the development of main echo was mature,on reflectivity factor map,it presented obvious inverted 'V' shaped structure in left front of low-level storm,typical hooked and 'person'-type echo characteristics in the right rear.The bounded weak echo zone(vault) in low level corresponded with strong echo overhanging body in high level.It surpassed 60 dBz in the strong reflectivity factor zone.It presented one weak meso-cyclone on corresponding radial velocity map.The jumped increase characteristic of VIL could be as one of indices for judging that hail started to grow.Almost all storms(VILD ≥4.0 g/m3) had more obvious indication significance than VIL for judging heavy hail(diameter ≥20 mm).[Conclusion] The research provided reference for nowcasting of strong convection weather and artificial hail suppression.
基金supported by NSFC project of Nos.40376005,40506006,40676015,NCET-04-0646 and SRFDP project of No.20060423014The NCEP reanalysis wind data are provided by the NOA A/OAR/ESRL PSD,Boulder,Colorado,USA,from their Web site(http://www.cdc.noaa.gov/).The gnidded monthly mean anomaly of sea level height data of TOPEX/Poscidon are provided by The Center for Space Research/The Univer sity ofTexas at Austin
文摘Based on a ship survey during January 1998, the characteristics of the flow, the thermohaline properties and the volume transport of the Arabian Sea are discussed. A strong westward flow exists between 10.5?N and 11?N, part of which turns to the south as the Somali current near the coast at about 10?N and the rest turns north. At the passage between the African continent and the So- cotra Island, the northern branch separates into two flows: the left one enters the passage and the right one flows eastward along the southern slope of the island. Off the island the flow separates once more, most of it meandering northeast and a small fraction flow- ing southeast. Volume transport calculation suggests that the tidal transport is one or two orders of magnitude smaller than the total transport in this region and it becomes more important near the coast. The average velocity of the flow in the upper layer (0-150 m) is about 20 cm s-1, with a maximum of 53 cm s-1 appearing east of the Socotra Island, and the subsurface layer (200-800 m) has an aver- age velocity of 8.6 cm s-1; the velocity becomes smaller at greater depths. The depth of the seasonal thermocline is about 100 m, above which there is a layer with well mixed temperature and dissolved oxygen. High-salinity and oxygen-rich water appears near the surface of the northern Arabian Sea; a salinity maximum and oxygen minimum at 100 m depth along 8?N testifies the subduction of surface water from the northern Arabian Sea. Waters from the Red Sea and the Persian Gulf also influence the salinity of the area.
文摘Using fluid dynamics software Fluent, the spray characteristics of an effervescent atomizer in a downstream flow field was simulated and analyzed, the results show that on the cross sections of the atomizer downstream flow field, the distribution of the atomized droplet size is small and mainly concentrated about Sauter mean diameter ( SMD), and the distribution of the axial velocity is large, but mainly concentrated about the gas peak velocity in the closer nozzle axis area; the gas peak velocity of the atomized droplet increases, while the droplet SMD decreases with increase of the nozzle caliber and the air pressure; with the increase of the flow rate of cuttingfluid, the atomized droplet SMD increases, while the gas peak velocity rises first and then decreases, but the decrease trend is very small after the air pressure is more than 0. 4 MPa. The simulation results have significance in guiding for designing and applying the effervescent atomizer.