In this work, the main characteristics of the Qingdao Cold Water Mass were studied by using "the comparison analysis method" based on 1980 temperature,salinity and dissolved oxygen data on the western South ...In this work, the main characteristics of the Qingdao Cold Water Mass were studied by using "the comparison analysis method" based on 1980 temperature,salinity and dissolved oxygen data on the western South Yellow Sea. The formation cause of the water mass was analyzed based on February of 1959 temperature and salinity data for this area and on some other authors’ studies. The results showed that the Qingdao Cold Water Mass has growing and vanishing processes: appears in the last ten days of March; has stable pattern in April; is biggest in its area in May; becomes small in its area in June; vanishes in July. It comes from the northern Shandong Coastal Water and is characterized by low temperature and salinity and high dissolved oxygen. The mass is formed under the joint effects of anticyclonic circulation and solar radiation.展开更多
Based mainly on TOGA-COARE data, that is, the CTD data from R/V Xiangyanghong No. 5 (Pu et al., 1993), the temperature and current data from the Woods Hole mooring and other deep current data, the layered numerical pr...Based mainly on TOGA-COARE data, that is, the CTD data from R/V Xiangyanghong No. 5 (Pu et al., 1993), the temperature and current data from the Woods Hole mooring and other deep current data, the layered numerical profiles of buoyancy frequency and mean current components are figured out. A numerical method calculating internal wave dispersion relation without background shear current, used by Fliegel and Hunkins (1975), is improved to be fit for the internal wave equation with mean currents and their second derivatives. The dispersion relations and wave functions of the long crested internal wave progressing in any direction can be calculated conveniently by using the improved method. A comparison between the calculated dispersion relation in the paper and the dispersion relation in GM spectral model of ocean internal waves (Garret and Munk, 1972) is performed. It shows that the mean currents are important to the dispersion relation of internal waves in the western equatorial Pacific Ocean and that the currents make the wave progressing co-directional with (against) the currents stretched (shrink). The influence of the mean currents on dispersion relation is much stronger than that of their second derivatives, but that on wave function is less than that of their second derivatives. The influences on wave functions result in the change of vertical wavenumber, that is, making the wave function stretch or shrink. There exists obvious turning depth but no significant critical layer absorption is found.展开更多
Based on the analysis of Levitus data, the climatic states of the warm pool in the Indian Ocean (WPIO) and in the Pacific Ocean (WPPO) are studied. It is found that WPIO has a relatively smaller area, a shallower bott...Based on the analysis of Levitus data, the climatic states of the warm pool in the Indian Ocean (WPIO) and in the Pacific Ocean (WPPO) are studied. It is found that WPIO has a relatively smaller area, a shallower bottom and a slightly lower seawater temperature than those of WPPO. The horizontal area at different depths, volumes, central positions, and bottom depths of both WPIO and WPPO show quite apparent signals of seasonal variation. The maximum amplitude of WPIO surface area’s seasonal variation is 58% larger over the annual mean value. WPIO’s maximum volume variation amplitude is 66% larger over the annual mean value. The maximum variation amplitudes of the surface area and volume of WPPO are 20. 9% and 20.6% larger over the annual mean value respectively. WPIO and WPPO show different temporal and spatial characteristics mainly due to the different wind fields and restriction of ocean basin geometry. For instance, seasonal northern displacement of WPIO is, to some extent, constrained by the basin of the Indian Ocean, while WPPO moves relatively freely in the longitudinal direction. The influence of WPIO and WPPO over the atmospheric motion must be quite different.展开更多
On the basis of an understanding of the ocean current produced under the combined forces of wind stress over the sea surface and horizontal pressure gradient force caused by the uneven distribution of seawater density...On the basis of an understanding of the ocean current produced under the combined forces of wind stress over the sea surface and horizontal pressure gradient force caused by the uneven distribution of seawater density and the elevation of sea surface , we obtained the unsteady analytic solution of the variation with time of ocean surface current velocity corresponding to the time variation of the above two forces , and the unsteady analytic solution for variation of seawater density with time by considering only the vertical turbulence . To meet different needs, the above solutions may be written in two forms for short and long time predictions . After some simplification the analytic solution was used to predict surface ocean current velocity for meteorological -navigation in the North Pacific . The monthly average current field was first obtained to get the necessary parameters for selecting the initial shipping route in the North Pacific and Bohai and Yellow Seas . The wind current field was then展开更多
A nonlinear evolution equation of 2 - D short internal waves under condition of weak stratification-cubic Schrodinger equation- is derived by using the reductive perturbation method. Because aB【0 in the Schrodinger e...A nonlinear evolution equation of 2 - D short internal waves under condition of weak stratification-cubic Schrodinger equation- is derived by using the reductive perturbation method. Because aB【0 in the Schrodinger equation, in the linear system the sideband perturbation for the harmonic wave modulation is neutrally stable. At the same time, there is also a sort of wave pack -et-KdV envelope soliton. In the nonlinear system the dark soliton is obtained under condition of weak stratification. It is shown that the vertical perturbation of the Brunt-Vaisala frequency plays a role in forming the KdV envelope soliton and dark soliton.展开更多
The composition and distribution of helium and oxygen isotopes in samples of seawater ob-tained at depths from surface to 300 m in the western Pacific Ocean (7°-26°N, 122° - 130°E) were discussed i...The composition and distribution of helium and oxygen isotopes in samples of seawater ob-tained at depths from surface to 300 m in the western Pacific Ocean (7°-26°N, 122° - 130°E) were discussed in detail. The results shaw that both δ18O and δ3He isoline extend eastward in the Pacific side of the Bashi Channel, which may suggest that the South China Sea water intrudes into the western Pacific by the Bashi Channel.展开更多
—Ocean wave propagation is slow,visible and measurable,so a wave theory can be used to approxi-mately predict the imminnent wave force on an offshore structure based on measured,real-time wave elevation nearthe struc...—Ocean wave propagation is slow,visible and measurable,so a wave theory can be used to approxi-mately predict the imminnent wave force on an offshore structure based on measured,real-time wave elevation nearthe structure.This predictability suggests the development of a more efficient algorithm,than those that have beendeveloped for structures under wind and seismic loads,for the active vibration control of offshore structures.Thepresent study delveops a mutiple-step predictive optimal control(MPOC)algorithm that accounts for multiple-step external loading in the determibation of optimal control forces.The control efficiency of the newly developedMPOC algorithm has been investigated under both regular(single-frequency)and irregular(multiple-frequency)wave loads,and compared with that of two other well-known optimal control algorithms:classical linear optimalcontrol(CLOC)and instantaneou optimal control(IOC).展开更多
The objective of the present research is to examine the effectiveness of the lateral vibration control of wave-excited re-sponse of offshore platforms with magneto-rheological (MR) damper. In this study, the offshore ...The objective of the present research is to examine the effectiveness of the lateral vibration control of wave-excited re-sponse of offshore platforms with magneto-rheological (MR) damper. In this study, the offshore platform is simplified to bewave force is determined with a white noise via a designed filter. A semi-active control method based on optimal control the-ory is proposed considering that the yield stress of the MR damper can be varied continuously within a certain range. The dy-namics of SDOF structure coupled with the MR damper is investigated. Numerical simulation demonstrates that the MRdamper with this control strategy can significantly reduce the maximum responses and the root-mean-square (RMS) values.展开更多
An obvious motivation of this paper is to examine the effectiveness of the lateral vibration control of a jacket type offshore platform with an AMD control device, in conjunction with H2 control algorithm, which is an...An obvious motivation of this paper is to examine the effectiveness of the lateral vibration control of a jacket type offshore platform with an AMD control device, in conjunction with H2 control algorithm, which is an optimal frequency domain control method based on minimization of H2 norm of the system transfer function. In this study, the offshore platform is modeled numerically by use of the finite element method, instead of a lumped mass model. This structural model is later simplified to be single-degree-of-freedom (SDOF) system by extracting the first vibration mode of the structure. The corresponding "generalized" wave force is determined based on an analytical approximation of the first mode shape function, the physical wave loading being calculated from the linearized Morison equation. This approach facilitates the filter design for the generalized force. Furthermore, the present paper also intends to make numerical comparison between H2 active control and the corresponding passive control using a展开更多
Two nematode species of the genus Dorylaimopsis (Family Comesometidae) from the Bohai Sea are described. Dorylaimopsis rabalaisi n. sp. similar to D. punctata Ditlevsen, 1918 from which it can be separated by the smal...Two nematode species of the genus Dorylaimopsis (Family Comesometidae) from the Bohai Sea are described. Dorylaimopsis rabalaisi n. sp. similar to D. punctata Ditlevsen, 1918 from which it can be separated by the small size, short and simple spicules without ventral apophyses or joint line. Dorylaimopsis turneri n. sp. differs from the closest species Dorylaimopsis angelae (Inglis, 1967) by its higher values of de Man ratio ’a’, much shorter spicules and higher ratio of gubernacular to spicules length. A key to species of the genus based on the key by Jensen (1979) is given .展开更多
Analysis and comparison of Jiaozhou Bay data collected from May 1991 to February 1994(12 seasonal investigations) provided by the Ecological Station of Jiaozhou Bay revealed the characteristic spatiotemporal variation...Analysis and comparison of Jiaozhou Bay data collected from May 1991 to February 1994(12 seasonal investigations) provided by the Ecological Station of Jiaozhou Bay revealed the characteristic spatiotemporal variation of the ambient concentration Si:DIN and Si:16P ratios and the seasonal variation of Jiaozhou Bay Si:DIN and Si:16P ratios showing that the Si:DIN ratios were < 1 throughout the year in Jiaozhou Bay; and that the Si:16P ratios were < 1 throughout Jiaozhou Bay in spring, autumn and winter. The results proved that silicate limited phytoplankton growth in spring, autumn and winter in Jiaozhou Bay. Analysis of the Si:DIN and Si:P ratios showed that the nutrient Si has been limiting the growth of phytoplankton throughout the year in some Jiaozhou Bay waters; and that the silicate deficiency changed the phytoplankton assemblage structure. Analysis of discontinuous 1962 to 1998 nutrient data showed that there was no N or P limitation of phytoplankton growth in that period. The authors consider that the annual cyclic change of silicate limits phytoplankton growth in spring, autumn and winter every year in Jiaozhou Bay; and that in many Jiaozhou Bay waters where the phytoplankton as the predominant species need a great amount of silicate, analysis of the nutrients N or P limitation of phytoplankton growth relying only on the N and P nutrients and DIN:P ratio could yield inaccurate conclusions. The results obtained by applying the rules of absolute and relative limitation fully support this view. The authors consider that the main function of nutrient silicon is to regulate and control the mechanism of the phytoplankton growth process in the ecological system in estuaries, bays and the sea. The authors consider that according to the evolution theory of Darwin, continuous environmental pressure gradually changes the phytoplankton assemblage’s structure and the physiology of diatoms. Diatoms requiring a great deal of silicon either constantly decrease or reduce their requirement for silicon. This will cause a series of huge changes in the ecosystem so that the whole ecosystem requires continuous renewal, change and balancing. Human beings have to reduce marine pollution and enhance the capacity of continental sources to transport silicon to sustain the continuity and stability in the marine ecosystem.展开更多
For prediction of the extreme significant wave height in the ocean areas where long term wave data are not available, the empirical method of extrapolating short term data (1 ~ 3 years) is used in design practice. In...For prediction of the extreme significant wave height in the ocean areas where long term wave data are not available, the empirical method of extrapolating short term data (1 ~ 3 years) is used in design practice. In this paper two methods are proposed to predict extreme significant wave height based on short-term daily maxima. According to the daa recorded by the Oceanographic Station of Liaodong Bay at the Bohai Sea, it is supposed that daily maximum wave heights are statistically independent. The data show that daily maximum wave heights obey log-normal distribution, and that the numbers of daily maxima vary from year to year, obeying binomial distribution. Based on these statistical characteristics, the binomial-log-normal compound extremum distribution is derived for prediction of extreme significant wave heights (50~ 100 years). For examination of its accuracy and validity, the prediction of extreme wave heights is based on 12 years′ data at this station, and based on each 3 years′ data respectively. The results show that with consideration of confidence intervals, the predicted wave heights based on 3 years′ data are very close to those based on 12 years′data. The observed data in some ocean areas in the Atlantic Ocean and the North Sea show it is not correct to assume that daily maximum wave heights are statistically independent; they are subject to Markov chain condition, obeying log-normal distribution. In this paper an analytical method is derived to predict extreme wave heights in these cases. A comparison of the computations shows that the difference between the extreme wave heights based on the assumption that daily maxima are statistically independent and that they are subject to Markov Chain condition is smaller than 10%.展开更多
Three- dimension (3-D) wind-driven currents in the Bohai Sea in both winter and summer are calculated by using a 3- D barotropic steady model, and the results are consistent with observed flow char -acteristics. Based...Three- dimension (3-D) wind-driven currents in the Bohai Sea in both winter and summer are calculated by using a 3- D barotropic steady model, and the results are consistent with observed flow char -acteristics. Based on the results, 3- D characteristics of flow, currents at different depths, compensated flow in the lower layer , long and narrow alongshore current, the area of upwelling and downwelling, main circulation in vertical profile, and the current in Bohai Strait are discussed.展开更多
An fKdV equation of two-layer flow and an averaged fKdV equation(AfKdV equation)with respect to phase are derived to determine the theoreticalamplitude and period of the precursor solitons in the present paper.In te...An fKdV equation of two-layer flow and an averaged fKdV equation(AfKdV equation)with respect to phase are derived to determine the theoreticalamplitude and period of the precursor solitons in the present paper.In terms ofthe AfKdV equation derived by the authors,a new theory on the precursor solitongeneration based on Lee et al.’s concept is presented.Concepts of asymptotic meanhydraulic fall and level are introduced in our analysis,and the theoretical amplitudeand period both depend on the asymptotic mean levels and stratified parameters.From the present theoretical results,it is obtained that when the moving velocityof the topography is at the resonant points,there exist two general relations:(1)amplitude relation (?)=2F,(2)period relation(?)=-8m1m<sub>3</sub><sup>-1</sup>6m<sub>4</sub>m<sub>3</sub><sup>-1</sup><sup>1/2</sup>.F,in which(?)and (?)are the amplitude and period of the precursor solitons at the resonantpoints respectively,m<sub>1</sub>,m<sub>3</sub> and m<sub>4</sub> are coefficients of the fKdV equation,and F isan asymptotic mean half-hydraulic fall at subcritical cutoff points.The theoreticalresults of this paper are compared with experiments and numerical calculations of two-layer flow over a semicircular topography and all these results are in good agreement.Due to the canonical character of the coefficients of fKdV equations,this theory alsoholds for any two-dimensional system,which can be reduced to fKdV equations.展开更多
This paper describes experimental and theoretical investigations of Tuned Liquid Damper (TLD) characteristics forsuppressing the wave-excited structural vibration. The structural model for the experiments is scaled ac...This paper describes experimental and theoretical investigations of Tuned Liquid Damper (TLD) characteristics forsuppressing the wave-excited structural vibration. The structural model for the experiments is scaled according to a fullsize offshore platform by matching their dynamic properties. Rectangular TLDs of different sizes with partially filled liq-uid are examined. By observing the performance and behavior of TLDs through laboratory experiments, the study inves-tigates the influence of a number of parameters, including container size, container shape, frequency ratio, and incidentwave characteristics. In an analytical study, a mathematical model that describes the nonlinear behavior of liquid inTLD and the interaction of TLD and structure is prerequisite. The validity of the model is evaluated and simulating re-sults can reasonably match the corresponding experimental results.展开更多
Using Morlet wavelet transform and harmonic analysis the multi-scale variability of subsurface temperature in the South China Sea is studied by analyzing one-year (from April 1998 to April 1999) ATLAS mooring data. By...Using Morlet wavelet transform and harmonic analysis the multi-scale variability of subsurface temperature in the South China Sea is studied by analyzing one-year (from April 1998 to April 1999) ATLAS mooring data. By wavelet transform, annual and semi-annual cycle as well as intraseasonal variations are found, with different dominance, in subsurface temperature. For annual harmonic cycle, both the downward net surface heat flux and thermocline vertical movement partially control the subsurface temperature variability. For semi-annual cycle and intraseasonal variability, the subsurface temperature variability is mainly linked to the vertical displacement of thermocline.展开更多
A simple and practical method for separating low-frequency internal waves from low-frequency barotropic waves was employed to analyze the observation data. Analysis of some data gathered in the northestern China Seas ...A simple and practical method for separating low-frequency internal waves from low-frequency barotropic waves was employed to analyze the observation data. Analysis of some data gathered in the northestern China Seas revealed strong semidiurnal internal tides and near-inertial internal waves at the stations in the East China Sea and near-inertial waves but no semidiurnal internal tides at the station in the centre of the Yellow Sea. The geographic properties of low-frequency internal waves in the region are discussed primarily on the basis of the mechanism of internal tide generation on the continental shelfbreak,and the mechanisms of local generation and global generation.展开更多
Sediment-water fluxes of N and P species in the Bohai Sea were investigated in Septem-ber-October 1998 and April-May 1999. The benthic fluxes of nutrient species were determined by incubating sediment core samples wit...Sediment-water fluxes of N and P species in the Bohai Sea were investigated in Septem-ber-October 1998 and April-May 1999. The benthic fluxes of nutrient species were determined by incubating sediment core samples with bottom seawater bubbled with air or nitrogen. -2NO,+4NH, dissolved organic nitrogen (DON) and phosphorus (DOP), total dissolved nitrogen (TDN) and phosphorus (TDP), and -34PO showed a net exchange flux from seawater to sediment, while -3NO, dissolved inorganic nitrogen (DIN) and -23SiO were released from sediment to seawater in the Bohai Sea. Sediment-water nutrient exchange increases DIN and reduces the phosphorus load in the Bohai Sea. The release of silicate from sediment to overlying seawater reduces potential silicate limitation of primary production resulted from decrease of riverine discharge. The exchange flux of nutrients showed no obvious seasonal variation. The present study showed that the concentrations and composition of nutrients in the water column were affected by suspended sediment, and that not all the exchangeable phosphate in sediment could be released via sediment resuspension.展开更多
-- The South China Sea warm water (SCSWW) is identified as the warm water body with temperature no less than 28C. There are three stages in the seasonal variation of the SCSWW. The SCSWW expands rapidly and deepens qu...-- The South China Sea warm water (SCSWW) is identified as the warm water body with temperature no less than 28C. There are three stages in the seasonal variation of the SCSWW. The SCSWW expands rapidly and deepens quickly in the developing stage. The warm water thickness decreases near the coast of Vietnam and increases near Palawan Island in the steady stage. The SCSWW flinches southward while its thickness off Palawan Island remains no less than 50 m in the flinching stage. The maximum thickness of the SCSWW is always located near the southeastern SCS. The seasonal variation of the SCSWW has a close relationship with seasonal variation of the thermocline. According to the analysis of the numerical experiment results from the Princeton Ocean Model (POM),the mechanism of the seasonal variation of the SCSWW can be interpreted as: ( 1 ) in the developing stage, the rapidly expanding and thickening feature of the SCSWW is mainly due to buoyancy flux effect (67% contribution). The weak wind and anticyclonic wind stress curl (22% contribution) present an environment which facilitates the accumulation of warm water; (2) in the steady stage, the decrease feature near the Vietnam coast and increase eature in southeast of the SCSWW thickness are mainly caused by wind stress (70% contribution); (3) in the flinching stage, the thickness reduction of the SCSWW is mainly due to upwelling and enhanced turbulent mixing caused by wind stress accounts for 60% ).展开更多
The interannual variability of the At lantic tropical cyclone (TC) frequency is well known. Separately,recent studies have also suggested that a much longer, multidecadal (40-60 year) trend might be emerging from the ...The interannual variability of the At lantic tropical cyclone (TC) frequency is well known. Separately,recent studies have also suggested that a much longer, multidecadal (40-60 year) trend might be emerging from the recent increase in Atlantic TC activity. However, the overall structure of the intrinsic frequencies (or temporal modes) of Atlantic TC activity is not yet known. The focus of this study is to systematically analyze the intrinsic frequencies of Atlantic TC activity using hurricane and tropical storm landfall data collected along the southeast coast (SEC) of the United States. Based on an Empirical Mode Decomposition (EMD) analysis of the frequency of landfall TCs along the SEC from 1887-1999, we have found that Atlantic TC activity has four primary, temporal modes. The interannual and multidecadal modes reported in the published literature are two such modes. After identifying all primary modes, the relative importance of each mode and its physical cause can be analyzed. For example, the most energetic mode is the interannual mode (2-7 year period). This mode is known to be associated with the 2-7 year El Nino / La Ni na cycle. The average number of annual landfalling TCs along the SEC decreased by 24% during El Nino years, but did not show significant increase during weak and moderate La Nina years. However, intense La Nina years were generally associated with more than average landfalling TCs along the SEC. The effects of El Nino and La Nina also became more significant when only hurricanes were considered. The significance of the effects of El Nino and La Nina on landfalling TCs and hurricanes in different US southeast coastal states showed significant differences.展开更多
文摘In this work, the main characteristics of the Qingdao Cold Water Mass were studied by using "the comparison analysis method" based on 1980 temperature,salinity and dissolved oxygen data on the western South Yellow Sea. The formation cause of the water mass was analyzed based on February of 1959 temperature and salinity data for this area and on some other authors’ studies. The results showed that the Qingdao Cold Water Mass has growing and vanishing processes: appears in the last ten days of March; has stable pattern in April; is biggest in its area in May; becomes small in its area in June; vanishes in July. It comes from the northern Shandong Coastal Water and is characterized by low temperature and salinity and high dissolved oxygen. The mass is formed under the joint effects of anticyclonic circulation and solar radiation.
基金National Natural Science Foundation of China,Project under contract No.49676275,No.49976002 and Research Fund for the Docto
文摘Based mainly on TOGA-COARE data, that is, the CTD data from R/V Xiangyanghong No. 5 (Pu et al., 1993), the temperature and current data from the Woods Hole mooring and other deep current data, the layered numerical profiles of buoyancy frequency and mean current components are figured out. A numerical method calculating internal wave dispersion relation without background shear current, used by Fliegel and Hunkins (1975), is improved to be fit for the internal wave equation with mean currents and their second derivatives. The dispersion relations and wave functions of the long crested internal wave progressing in any direction can be calculated conveniently by using the improved method. A comparison between the calculated dispersion relation in the paper and the dispersion relation in GM spectral model of ocean internal waves (Garret and Munk, 1972) is performed. It shows that the mean currents are important to the dispersion relation of internal waves in the western equatorial Pacific Ocean and that the currents make the wave progressing co-directional with (against) the currents stretched (shrink). The influence of the mean currents on dispersion relation is much stronger than that of their second derivatives, but that on wave function is less than that of their second derivatives. The influences on wave functions result in the change of vertical wavenumber, that is, making the wave function stretch or shrink. There exists obvious turning depth but no significant critical layer absorption is found.
基金This work was supported by NSFC under Grant No.49876011 and 40136010by the Chinese Ministry of Science and Technology under Grant No.2001CCB00500.
文摘Based on the analysis of Levitus data, the climatic states of the warm pool in the Indian Ocean (WPIO) and in the Pacific Ocean (WPPO) are studied. It is found that WPIO has a relatively smaller area, a shallower bottom and a slightly lower seawater temperature than those of WPPO. The horizontal area at different depths, volumes, central positions, and bottom depths of both WPIO and WPPO show quite apparent signals of seasonal variation. The maximum amplitude of WPIO surface area’s seasonal variation is 58% larger over the annual mean value. WPIO’s maximum volume variation amplitude is 66% larger over the annual mean value. The maximum variation amplitudes of the surface area and volume of WPPO are 20. 9% and 20.6% larger over the annual mean value respectively. WPIO and WPPO show different temporal and spatial characteristics mainly due to the different wind fields and restriction of ocean basin geometry. For instance, seasonal northern displacement of WPIO is, to some extent, constrained by the basin of the Indian Ocean, while WPPO moves relatively freely in the longitudinal direction. The influence of WPIO and WPPO over the atmospheric motion must be quite different.
文摘On the basis of an understanding of the ocean current produced under the combined forces of wind stress over the sea surface and horizontal pressure gradient force caused by the uneven distribution of seawater density and the elevation of sea surface , we obtained the unsteady analytic solution of the variation with time of ocean surface current velocity corresponding to the time variation of the above two forces , and the unsteady analytic solution for variation of seawater density with time by considering only the vertical turbulence . To meet different needs, the above solutions may be written in two forms for short and long time predictions . After some simplification the analytic solution was used to predict surface ocean current velocity for meteorological -navigation in the North Pacific . The monthly average current field was first obtained to get the necessary parameters for selecting the initial shipping route in the North Pacific and Bohai and Yellow Seas . The wind current field was then
基金This project is supported by the National Natural Science Foundation of China
文摘A nonlinear evolution equation of 2 - D short internal waves under condition of weak stratification-cubic Schrodinger equation- is derived by using the reductive perturbation method. Because aB【0 in the Schrodinger equation, in the linear system the sideband perturbation for the harmonic wave modulation is neutrally stable. At the same time, there is also a sort of wave pack -et-KdV envelope soliton. In the nonlinear system the dark soliton is obtained under condition of weak stratification. It is shown that the vertical perturbation of the Brunt-Vaisala frequency plays a role in forming the KdV envelope soliton and dark soliton.
文摘The composition and distribution of helium and oxygen isotopes in samples of seawater ob-tained at depths from surface to 300 m in the western Pacific Ocean (7°-26°N, 122° - 130°E) were discussed in detail. The results shaw that both δ18O and δ3He isoline extend eastward in the Pacific side of the Bashi Channel, which may suggest that the South China Sea water intrudes into the western Pacific by the Bashi Channel.
基金National Science Foundation of U.S.A.under grant CMS-9503533
文摘—Ocean wave propagation is slow,visible and measurable,so a wave theory can be used to approxi-mately predict the imminnent wave force on an offshore structure based on measured,real-time wave elevation nearthe structure.This predictability suggests the development of a more efficient algorithm,than those that have beendeveloped for structures under wind and seismic loads,for the active vibration control of offshore structures.Thepresent study delveops a mutiple-step predictive optimal control(MPOC)algorithm that accounts for multiple-step external loading in the determibation of optimal control forces.The control efficiency of the newly developedMPOC algorithm has been investigated under both regular(single-frequency)and irregular(multiple-frequency)wave loads,and compared with that of two other well-known optimal control algorithms:classical linear optimalcontrol(CLOC)and instantaneou optimal control(IOC).
基金This work was financially supported by the National Natural Science Foundation of China.(Grant No.50179014)
文摘The objective of the present research is to examine the effectiveness of the lateral vibration control of wave-excited re-sponse of offshore platforms with magneto-rheological (MR) damper. In this study, the offshore platform is simplified to bewave force is determined with a white noise via a designed filter. A semi-active control method based on optimal control the-ory is proposed considering that the yield stress of the MR damper can be varied continuously within a certain range. The dy-namics of SDOF structure coupled with the MR damper is investigated. Numerical simulation demonstrates that the MRdamper with this control strategy can significantly reduce the maximum responses and the root-mean-square (RMS) values.
基金This work was partly supported by the Japan Society for the Promotion of Science (JSPS) for RONPAKU program by Foundation for University Key Teacher by the Ministry of Education of China
文摘An obvious motivation of this paper is to examine the effectiveness of the lateral vibration control of a jacket type offshore platform with an AMD control device, in conjunction with H2 control algorithm, which is an optimal frequency domain control method based on minimization of H2 norm of the system transfer function. In this study, the offshore platform is modeled numerically by use of the finite element method, instead of a lumped mass model. This structural model is later simplified to be single-degree-of-freedom (SDOF) system by extracting the first vibration mode of the structure. The corresponding "generalized" wave force is determined based on an analytical approximation of the first mode shape function, the physical wave loading being calculated from the linearized Morison equation. This approach facilitates the filter design for the generalized force. Furthermore, the present paper also intends to make numerical comparison between H2 active control and the corresponding passive control using a
基金This project was supported by the National Science Foundation, No: 3860804
文摘Two nematode species of the genus Dorylaimopsis (Family Comesometidae) from the Bohai Sea are described. Dorylaimopsis rabalaisi n. sp. similar to D. punctata Ditlevsen, 1918 from which it can be separated by the small size, short and simple spicules without ventral apophyses or joint line. Dorylaimopsis turneri n. sp. differs from the closest species Dorylaimopsis angelae (Inglis, 1967) by its higher values of de Man ratio ’a’, much shorter spicules and higher ratio of gubernacular to spicules length. A key to species of the genus based on the key by Jensen (1979) is given .
基金funded by the NSFC(No.40036010)subsidized by Special Funds from the National Key BaBic Research Program of P.R.China(G19990437)+2 种基金the Postdoctoral Foundation of Ocean University of Qingdaothe Director’s Foundation of the Beihai Monitoring Center of the State Oceanic Administrationthe Foundation of Shanghai Fisheries University
文摘Analysis and comparison of Jiaozhou Bay data collected from May 1991 to February 1994(12 seasonal investigations) provided by the Ecological Station of Jiaozhou Bay revealed the characteristic spatiotemporal variation of the ambient concentration Si:DIN and Si:16P ratios and the seasonal variation of Jiaozhou Bay Si:DIN and Si:16P ratios showing that the Si:DIN ratios were < 1 throughout the year in Jiaozhou Bay; and that the Si:16P ratios were < 1 throughout Jiaozhou Bay in spring, autumn and winter. The results proved that silicate limited phytoplankton growth in spring, autumn and winter in Jiaozhou Bay. Analysis of the Si:DIN and Si:P ratios showed that the nutrient Si has been limiting the growth of phytoplankton throughout the year in some Jiaozhou Bay waters; and that the silicate deficiency changed the phytoplankton assemblage structure. Analysis of discontinuous 1962 to 1998 nutrient data showed that there was no N or P limitation of phytoplankton growth in that period. The authors consider that the annual cyclic change of silicate limits phytoplankton growth in spring, autumn and winter every year in Jiaozhou Bay; and that in many Jiaozhou Bay waters where the phytoplankton as the predominant species need a great amount of silicate, analysis of the nutrients N or P limitation of phytoplankton growth relying only on the N and P nutrients and DIN:P ratio could yield inaccurate conclusions. The results obtained by applying the rules of absolute and relative limitation fully support this view. The authors consider that the main function of nutrient silicon is to regulate and control the mechanism of the phytoplankton growth process in the ecological system in estuaries, bays and the sea. The authors consider that according to the evolution theory of Darwin, continuous environmental pressure gradually changes the phytoplankton assemblage’s structure and the physiology of diatoms. Diatoms requiring a great deal of silicon either constantly decrease or reduce their requirement for silicon. This will cause a series of huge changes in the ecosystem so that the whole ecosystem requires continuous renewal, change and balancing. Human beings have to reduce marine pollution and enhance the capacity of continental sources to transport silicon to sustain the continuity and stability in the marine ecosystem.
基金This project was supported by the 9-th National Five-Year Key Program of China 96-922-03-03
文摘For prediction of the extreme significant wave height in the ocean areas where long term wave data are not available, the empirical method of extrapolating short term data (1 ~ 3 years) is used in design practice. In this paper two methods are proposed to predict extreme significant wave height based on short-term daily maxima. According to the daa recorded by the Oceanographic Station of Liaodong Bay at the Bohai Sea, it is supposed that daily maximum wave heights are statistically independent. The data show that daily maximum wave heights obey log-normal distribution, and that the numbers of daily maxima vary from year to year, obeying binomial distribution. Based on these statistical characteristics, the binomial-log-normal compound extremum distribution is derived for prediction of extreme significant wave heights (50~ 100 years). For examination of its accuracy and validity, the prediction of extreme wave heights is based on 12 years′ data at this station, and based on each 3 years′ data respectively. The results show that with consideration of confidence intervals, the predicted wave heights based on 3 years′ data are very close to those based on 12 years′data. The observed data in some ocean areas in the Atlantic Ocean and the North Sea show it is not correct to assume that daily maximum wave heights are statistically independent; they are subject to Markov chain condition, obeying log-normal distribution. In this paper an analytical method is derived to predict extreme wave heights in these cases. A comparison of the computations shows that the difference between the extreme wave heights based on the assumption that daily maxima are statistically independent and that they are subject to Markov Chain condition is smaller than 10%.
基金Project supported by the National Natural science Foundation of China
文摘Three- dimension (3-D) wind-driven currents in the Bohai Sea in both winter and summer are calculated by using a 3- D barotropic steady model, and the results are consistent with observed flow char -acteristics. Based on the results, 3- D characteristics of flow, currents at different depths, compensated flow in the lower layer , long and narrow alongshore current, the area of upwelling and downwelling, main circulation in vertical profile, and the current in Bohai Strait are discussed.
基金The project supported by the foundation of The State Education Commission"The dynamics of upper ocean"the open grants of Physical Oceanography Laboratory
文摘An fKdV equation of two-layer flow and an averaged fKdV equation(AfKdV equation)with respect to phase are derived to determine the theoreticalamplitude and period of the precursor solitons in the present paper.In terms ofthe AfKdV equation derived by the authors,a new theory on the precursor solitongeneration based on Lee et al.’s concept is presented.Concepts of asymptotic meanhydraulic fall and level are introduced in our analysis,and the theoretical amplitudeand period both depend on the asymptotic mean levels and stratified parameters.From the present theoretical results,it is obtained that when the moving velocityof the topography is at the resonant points,there exist two general relations:(1)amplitude relation (?)=2F,(2)period relation(?)=-8m1m<sub>3</sub><sup>-1</sup>6m<sub>4</sub>m<sub>3</sub><sup>-1</sup><sup>1/2</sup>.F,in which(?)and (?)are the amplitude and period of the precursor solitons at the resonantpoints respectively,m<sub>1</sub>,m<sub>3</sub> and m<sub>4</sub> are coefficients of the fKdV equation,and F isan asymptotic mean half-hydraulic fall at subcritical cutoff points.The theoreticalresults of this paper are compared with experiments and numerical calculations of two-layer flow over a semicircular topography and all these results are in good agreement.Due to the canonical character of the coefficients of fKdV equations,this theory alsoholds for any two-dimensional system,which can be reduced to fKdV equations.
基金This research was financially supported partially by the National Science Foundation of Japan under grant No.10555173 This work was partially supported by the Scholarship from Japan Ministry of Education,Science and Culture.
文摘This paper describes experimental and theoretical investigations of Tuned Liquid Damper (TLD) characteristics forsuppressing the wave-excited structural vibration. The structural model for the experiments is scaled according to a fullsize offshore platform by matching their dynamic properties. Rectangular TLDs of different sizes with partially filled liq-uid are examined. By observing the performance and behavior of TLDs through laboratory experiments, the study inves-tigates the influence of a number of parameters, including container size, container shape, frequency ratio, and incidentwave characteristics. In an analytical study, a mathematical model that describes the nonlinear behavior of liquid inTLD and the interaction of TLD and structure is prerequisite. The validity of the model is evaluated and simulating re-sults can reasonably match the corresponding experimental results.
基金This work was supported by both the Research Fund for the Doctoral Program of Higher Education under contract No. 1999042308 the Ministry of Science Technology of China under contract No. 2001 DIA 50041.
文摘Using Morlet wavelet transform and harmonic analysis the multi-scale variability of subsurface temperature in the South China Sea is studied by analyzing one-year (from April 1998 to April 1999) ATLAS mooring data. By wavelet transform, annual and semi-annual cycle as well as intraseasonal variations are found, with different dominance, in subsurface temperature. For annual harmonic cycle, both the downward net surface heat flux and thermocline vertical movement partially control the subsurface temperature variability. For semi-annual cycle and intraseasonal variability, the subsurface temperature variability is mainly linked to the vertical displacement of thermocline.
基金Project supported by the National Natural Science Foundation of China
文摘A simple and practical method for separating low-frequency internal waves from low-frequency barotropic waves was employed to analyze the observation data. Analysis of some data gathered in the northestern China Seas revealed strong semidiurnal internal tides and near-inertial internal waves at the stations in the East China Sea and near-inertial waves but no semidiurnal internal tides at the station in the centre of the Yellow Sea. The geographic properties of low-frequency internal waves in the region are discussed primarily on the basis of the mechanism of internal tide generation on the continental shelfbreak,and the mechanisms of local generation and global generation.
基金This study was funded by NSFC (Nos. 40036010 and 40206017) and the Special Funds from National Key Basic Research Program of P. R. China (No. 2001CB409703).
文摘Sediment-water fluxes of N and P species in the Bohai Sea were investigated in Septem-ber-October 1998 and April-May 1999. The benthic fluxes of nutrient species were determined by incubating sediment core samples with bottom seawater bubbled with air or nitrogen. -2NO,+4NH, dissolved organic nitrogen (DON) and phosphorus (DOP), total dissolved nitrogen (TDN) and phosphorus (TDP), and -34PO showed a net exchange flux from seawater to sediment, while -3NO, dissolved inorganic nitrogen (DIN) and -23SiO were released from sediment to seawater in the Bohai Sea. Sediment-water nutrient exchange increases DIN and reduces the phosphorus load in the Bohai Sea. The release of silicate from sediment to overlying seawater reduces potential silicate limitation of primary production resulted from decrease of riverine discharge. The exchange flux of nutrients showed no obvious seasonal variation. The present study showed that the concentrations and composition of nutrients in the water column were affected by suspended sediment, and that not all the exchangeable phosphate in sediment could be released via sediment resuspension.
基金This study was supported by the Special Program of the Ministry of Science Technology of China under contract No. 2001IDIA50041.
文摘-- The South China Sea warm water (SCSWW) is identified as the warm water body with temperature no less than 28C. There are three stages in the seasonal variation of the SCSWW. The SCSWW expands rapidly and deepens quickly in the developing stage. The warm water thickness decreases near the coast of Vietnam and increases near Palawan Island in the steady stage. The SCSWW flinches southward while its thickness off Palawan Island remains no less than 50 m in the flinching stage. The maximum thickness of the SCSWW is always located near the southeastern SCS. The seasonal variation of the SCSWW has a close relationship with seasonal variation of the thermocline. According to the analysis of the numerical experiment results from the Princeton Ocean Model (POM),the mechanism of the seasonal variation of the SCSWW can be interpreted as: ( 1 ) in the developing stage, the rapidly expanding and thickening feature of the SCSWW is mainly due to buoyancy flux effect (67% contribution). The weak wind and anticyclonic wind stress curl (22% contribution) present an environment which facilitates the accumulation of warm water; (2) in the steady stage, the decrease feature near the Vietnam coast and increase eature in southeast of the SCSWW thickness are mainly caused by wind stress (70% contribution); (3) in the flinching stage, the thickness reduction of the SCSWW is mainly due to upwelling and enhanced turbulent mixing caused by wind stress accounts for 60% ).
基金Acknowledgments. The National Oceanic and Atmospheric Administration is acknowledged for support of this work under Grant NA060C0 with Waterstone Group Inc. and NCSU. This study is benefited from scientific collabo-rations between the Coastal Fluid Dynam
文摘The interannual variability of the At lantic tropical cyclone (TC) frequency is well known. Separately,recent studies have also suggested that a much longer, multidecadal (40-60 year) trend might be emerging from the recent increase in Atlantic TC activity. However, the overall structure of the intrinsic frequencies (or temporal modes) of Atlantic TC activity is not yet known. The focus of this study is to systematically analyze the intrinsic frequencies of Atlantic TC activity using hurricane and tropical storm landfall data collected along the southeast coast (SEC) of the United States. Based on an Empirical Mode Decomposition (EMD) analysis of the frequency of landfall TCs along the SEC from 1887-1999, we have found that Atlantic TC activity has four primary, temporal modes. The interannual and multidecadal modes reported in the published literature are two such modes. After identifying all primary modes, the relative importance of each mode and its physical cause can be analyzed. For example, the most energetic mode is the interannual mode (2-7 year period). This mode is known to be associated with the 2-7 year El Nino / La Ni na cycle. The average number of annual landfalling TCs along the SEC decreased by 24% during El Nino years, but did not show significant increase during weak and moderate La Nina years. However, intense La Nina years were generally associated with more than average landfalling TCs along the SEC. The effects of El Nino and La Nina also became more significant when only hurricanes were considered. The significance of the effects of El Nino and La Nina on landfalling TCs and hurricanes in different US southeast coastal states showed significant differences.