Vessels with semi-closed tanks(i.e.,well docks)are widely applied in the military operation and maritime engineer-ing.The water is bound by the semi-closed floating tank and forced by both the incident waves and ship...Vessels with semi-closed tanks(i.e.,well docks)are widely applied in the military operation and maritime engineer-ing.The water is bound by the semi-closed floating tank and forced by both the incident waves and ship’s motions.The free surface oscillations inside the flooded well dock is thus distinctive and very complicated.So far,the natural modes of semi-closed floating tanks have not yet been studied.This paper investigates the characteristics of natural modes of a floating semi-closed tank by combining a mode-resolving model based on mild-slope equations and a hydrodynamic model based on computational fluid dynamics.Results show that the first three natural periods(i.e.,74,23.6,and 14 s)of the tank fall into the band of swell and infragravity waves and they could be triggered under certain circumstance.Multi-period free surface oscillations are observed inside the tank,including the longest natural period(i.e.,74 s),though the incident waves are monochromatic.A possible generation mechanism for the long-period mode is explained on the basis of liquid sloshing and harbor oscillations.Moreover,a long-period component with a period close to the natural mode of well dock is observed in the ship motions,which is generated by the interaction between the waves and ship.展开更多
Heteroatom-doped meso/micro-porous carbon materials are conventionally produced by harsh carbonization under an inert atmosphere involving specific precursors,hard/soft templates,and heteroatom-containing agents.Herei...Heteroatom-doped meso/micro-porous carbon materials are conventionally produced by harsh carbonization under an inert atmosphere involving specific precursors,hard/soft templates,and heteroatom-containing agents.Herein,we report a facile synthesis of N and O co-doped meso/micro-porous carbon(NOMC)by template-free carbonization of a small-molecule precursor in a semi-closed system.The semi-closed carbonizaiton process yields hydrophilic NOMCs with large surface area in a high yield.The porous structure as well as the elemental composition of NOMCs can be modulated by changing the holding time at a particular temperature.NOMCs as metal-free heterogeneous catalysts can selectively oxidize benzyl alcohol and its derivatives into aldehydes/ketones with>85%conversion in aqueous solution,which is much higher than that of the control sample obtained in tube furnace(21%conversion),mainly due to their high N content,high percentage of pyridinic N,and large surface area.The presence of O-containing moieties also helps to improve the hydrophilicity and dispersion ability of catalysts and thus facilitates the mass transfer process during aqueous oxidation.The NOMC catalysts also dispayed excellent activity for a wide range of substrates with a selectivity of>99%.展开更多
A preliminary study on the distribution of sediment transport and siltation within a semi-closed harbour as well as the factors affecting the siltation has been made with a suspended sediment model, in which the Liany...A preliminary study on the distribution of sediment transport and siltation within a semi-closed harbour as well as the factors affecting the siltation has been made with a suspended sediment model, in which the Lianyungang port is used as the prototype. Based on the work, this paper describes a tubid water experiment within a typical excavated harbour basin. According to the experimental results some expressions for predicting the average siltation amount for semi-closed harbour basins by means of dimensional analysis have been proposed, with tidal features, harbour geometry and properties of sediment taken into account. Through comparing the calculated results with the laboratory and field measured data, it has been shown that the expressions presented in this paper are reasonable.展开更多
In this paper, a computational case was employed to describe thecomputational procedure for inversing the tidal level open boundary conditions using an analyticmethod. The area for finding the solution is a circular a...In this paper, a computational case was employed to describe thecomputational procedure for inversing the tidal level open boundary conditions using an analyticmethod. The area for finding the solution is a circular area with a circular arc with the openingangle 60°-being the open boundary and the other circular arc being the solid wall boundary.Proceeding from the reestablished elliptic partial differential equation satisfied by the tidallevel function, the extended spectrum method was used to derive the general solution of the equationfor the sea of constant depth, and the impermeable solid wall condition (the second class boundarycondition) and the adequately specified open boundary conditions were then applied to determine theundetermined coefficients of the general solution, thus obtaining the tidal level distributionfunction. In this way, both the first and second class boundary values at the solid wall boundarywere obtained. With the above boundary values as the boundary conditions, the tidal level values atthe open boundary were then inversed by means of the general solution of tidal wave equation. Thevalidity of inversion method could be verified by comparing the inversed tidal level distributionswith the originally specified open boundary values.展开更多
An ecological optimization project(semi-closed reclamation project)was implemented to control the invasion of Spartina alterniflora,and optimize the habitat of the Chongming Dongtan wetland,in the Changjiang(Yangtze)R...An ecological optimization project(semi-closed reclamation project)was implemented to control the invasion of Spartina alterniflora,and optimize the habitat of the Chongming Dongtan wetland,in the Changjiang(Yangtze)River Estuary.After project implementation,a macrobenthic ecological survey was conducted in a natural tidal flat and a semi-closed reclamation restoration area within the Chongming Dongtan wetland from 2019 to 2020.Compared with historical data before reclamation,findings showed that the groups,numbers,and species diversity of the macrobenthos increased significantly,and the ecological optimization project resulted in good ecological benefits.In addition,compared to the natural tidal flat,the number of collected macrobenthic phyla,and the macrobenthic density and biomass were significantly lower in the restoration area.Furthermore,the biodiversity index and functional redundancy of natural tidal flats were generally higher,indicating that the community composition and function of natural tidal flats were relatively more stable.Even though the species composition differed between a number of restoration areas and natural tidal flats,there was no difference in functional diversity,indicating that the effect of restoring ecological functions in restoration areas was optimal.Among them,the biodiversity and functional redundancy of Site S2 were significantly reduced,and the ecosystem function was extremely unstable.Habitat heterogeneity,vegetation community and decreasing salinity were the main factors that affected the ecological functions of macrobenthos.The ecological quality was also evaluated;the Transects N3 and N4 showed good quality.The overall ecological quality of the restoration area was generally high,but that of Site S2 was poor and that of Site S2E was merely good,which was mainly due to modifications of the ecological function of macrobenthos.It is suggested that reeds mowing and freshwater species release should be adopted in restoration areas to improve the community function and the environmental disturbance resistance of the macrobenthos.展开更多
Acoustic metasurface has attracted increasing attention due to the ability of manipulating the transmitted and reflected phase of waves to generate various acoustic functionalities with planar layer of sub-wavelength ...Acoustic metasurface has attracted increasing attention due to the ability of manipulating the transmitted and reflected phase of waves to generate various acoustic functionalities with planar layer of sub-wavelength structure.We design an acoustic metasurface with a semi-closed and nested slotted tube array,and it possesses the capacity of modulating the reflected phase with sub-wavelength thickness (about λ/23).The reflected phase shifts can be obtained from 0 to 2π by different rotation angles of internal slotted tubes.The theoretical results agree well with the numerical results by a finite element method.The results show that some excellent wavefront manipulations are demonstrated with the phase array by using acoustic metasurface such as anomalous reflection and sub-wavelength flat focusing.The design may offer a path for acoustic manipulation and promote the potential applications of acoustic metasurface in low frequency noise control,acoustic imaging and cloaking.展开更多
基金supported by the National Natural Science Foundation of China(Grant No.51979029)。
文摘Vessels with semi-closed tanks(i.e.,well docks)are widely applied in the military operation and maritime engineer-ing.The water is bound by the semi-closed floating tank and forced by both the incident waves and ship’s motions.The free surface oscillations inside the flooded well dock is thus distinctive and very complicated.So far,the natural modes of semi-closed floating tanks have not yet been studied.This paper investigates the characteristics of natural modes of a floating semi-closed tank by combining a mode-resolving model based on mild-slope equations and a hydrodynamic model based on computational fluid dynamics.Results show that the first three natural periods(i.e.,74,23.6,and 14 s)of the tank fall into the band of swell and infragravity waves and they could be triggered under certain circumstance.Multi-period free surface oscillations are observed inside the tank,including the longest natural period(i.e.,74 s),though the incident waves are monochromatic.A possible generation mechanism for the long-period mode is explained on the basis of liquid sloshing and harbor oscillations.Moreover,a long-period component with a period close to the natural mode of well dock is observed in the ship motions,which is generated by the interaction between the waves and ship.
基金supported by National Natural Science Foundation of China(Grant No.51772089 and 21872046)the Youth 1000 Talent Program of China+3 种基金the Outstanding Youth Scientist Foundation of Hunan Province(Grant No.2018JJ1009)the Natural Science Foundation of Hunan Province(Grant No.2020JJ4174)Provincial Science and Technology Innovation Platform and Talent Plan-Changsha,Zhuzhou and Xiangtan High-level Talents Accumulation Project(Grant No.2017XK2023)Research and Development Plan of Key Areas in Hunan Province(Grant No.2019GK2235)
文摘Heteroatom-doped meso/micro-porous carbon materials are conventionally produced by harsh carbonization under an inert atmosphere involving specific precursors,hard/soft templates,and heteroatom-containing agents.Herein,we report a facile synthesis of N and O co-doped meso/micro-porous carbon(NOMC)by template-free carbonization of a small-molecule precursor in a semi-closed system.The semi-closed carbonizaiton process yields hydrophilic NOMCs with large surface area in a high yield.The porous structure as well as the elemental composition of NOMCs can be modulated by changing the holding time at a particular temperature.NOMCs as metal-free heterogeneous catalysts can selectively oxidize benzyl alcohol and its derivatives into aldehydes/ketones with>85%conversion in aqueous solution,which is much higher than that of the control sample obtained in tube furnace(21%conversion),mainly due to their high N content,high percentage of pyridinic N,and large surface area.The presence of O-containing moieties also helps to improve the hydrophilicity and dispersion ability of catalysts and thus facilitates the mass transfer process during aqueous oxidation.The NOMC catalysts also dispayed excellent activity for a wide range of substrates with a selectivity of>99%.
文摘A preliminary study on the distribution of sediment transport and siltation within a semi-closed harbour as well as the factors affecting the siltation has been made with a suspended sediment model, in which the Lianyungang port is used as the prototype. Based on the work, this paper describes a tubid water experiment within a typical excavated harbour basin. According to the experimental results some expressions for predicting the average siltation amount for semi-closed harbour basins by means of dimensional analysis have been proposed, with tidal features, harbour geometry and properties of sediment taken into account. Through comparing the calculated results with the laboratory and field measured data, it has been shown that the expressions presented in this paper are reasonable.
文摘In this paper, a computational case was employed to describe thecomputational procedure for inversing the tidal level open boundary conditions using an analyticmethod. The area for finding the solution is a circular area with a circular arc with the openingangle 60°-being the open boundary and the other circular arc being the solid wall boundary.Proceeding from the reestablished elliptic partial differential equation satisfied by the tidallevel function, the extended spectrum method was used to derive the general solution of the equationfor the sea of constant depth, and the impermeable solid wall condition (the second class boundarycondition) and the adequately specified open boundary conditions were then applied to determine theundetermined coefficients of the general solution, thus obtaining the tidal level distributionfunction. In this way, both the first and second class boundary values at the solid wall boundarywere obtained. With the above boundary values as the boundary conditions, the tidal level values atthe open boundary were then inversed by means of the general solution of tidal wave equation. Thevalidity of inversion method could be verified by comparing the inversed tidal level distributionswith the originally specified open boundary values.
基金The Shanghai Chongming Dongtan Bird National Nature Reserve Resource Monitoring Project under contract No.CMDT-JC202101the Shanghai Municipal Science and Technology Commission under contract No.19ZR1436900。
文摘An ecological optimization project(semi-closed reclamation project)was implemented to control the invasion of Spartina alterniflora,and optimize the habitat of the Chongming Dongtan wetland,in the Changjiang(Yangtze)River Estuary.After project implementation,a macrobenthic ecological survey was conducted in a natural tidal flat and a semi-closed reclamation restoration area within the Chongming Dongtan wetland from 2019 to 2020.Compared with historical data before reclamation,findings showed that the groups,numbers,and species diversity of the macrobenthos increased significantly,and the ecological optimization project resulted in good ecological benefits.In addition,compared to the natural tidal flat,the number of collected macrobenthic phyla,and the macrobenthic density and biomass were significantly lower in the restoration area.Furthermore,the biodiversity index and functional redundancy of natural tidal flats were generally higher,indicating that the community composition and function of natural tidal flats were relatively more stable.Even though the species composition differed between a number of restoration areas and natural tidal flats,there was no difference in functional diversity,indicating that the effect of restoring ecological functions in restoration areas was optimal.Among them,the biodiversity and functional redundancy of Site S2 were significantly reduced,and the ecosystem function was extremely unstable.Habitat heterogeneity,vegetation community and decreasing salinity were the main factors that affected the ecological functions of macrobenthos.The ecological quality was also evaluated;the Transects N3 and N4 showed good quality.The overall ecological quality of the restoration area was generally high,but that of Site S2 was poor and that of Site S2E was merely good,which was mainly due to modifications of the ecological function of macrobenthos.It is suggested that reeds mowing and freshwater species release should be adopted in restoration areas to improve the community function and the environmental disturbance resistance of the macrobenthos.
基金supported by the National Natural Science Foundation of China (No.51575431)the China Postdoctoral Science Foundation Funded Project (Nos. 2014M550485, 2015T81019)+1 种基金the Fundamental Research Funds for the Central Universities (No.xjj2015098)the Shaanxi Province Postdoctoral Science Foundation Funded Project
文摘Acoustic metasurface has attracted increasing attention due to the ability of manipulating the transmitted and reflected phase of waves to generate various acoustic functionalities with planar layer of sub-wavelength structure.We design an acoustic metasurface with a semi-closed and nested slotted tube array,and it possesses the capacity of modulating the reflected phase with sub-wavelength thickness (about λ/23).The reflected phase shifts can be obtained from 0 to 2π by different rotation angles of internal slotted tubes.The theoretical results agree well with the numerical results by a finite element method.The results show that some excellent wavefront manipulations are demonstrated with the phase array by using acoustic metasurface such as anomalous reflection and sub-wavelength flat focusing.The design may offer a path for acoustic manipulation and promote the potential applications of acoustic metasurface in low frequency noise control,acoustic imaging and cloaking.
