The velocity dip phenomenon may occur in a part of or in the whole flow field of open channel flows due to the secondary flow effect. Based on rectangular flume experiments and the laser Doppler velocimetry, the influ...The velocity dip phenomenon may occur in a part of or in the whole flow field of open channel flows due to the secondary flow effect. Based on rectangular flume experiments and the laser Doppler velocimetry, the influence of the distance to the sidewall and the aspect ratio on the velocity dip is investigated. Through application of statistical methods to the experimental results, it is proposed that the flow field may be divided into two regions, the relatively strong sidewall region and the relatively weak sidewall region. In the former region, the distance to the sidewall greatly affects the location of maximum velocity, and, in the latter region, both the distance to the sidewall and the aspect ratio influence the location of the maximum velocity.展开更多
This work presents the hydrologic estimations of the hydraulic underground arched culvert channel (UACC) in Sabinal Basin, Chiapas, México and the hydrological problems associated with it, such as the erosion phe...This work presents the hydrologic estimations of the hydraulic underground arched culvert channel (UACC) in Sabinal Basin, Chiapas, México and the hydrological problems associated with it, such as the erosion phenomenon and abrasion cavity formation in it. On the other hand, the maximum flows that the UACC could transport were analyzed, concluding that it no longer has the hydraulic capacity to transport the flow rate associated to return periods equal to or greater than five years and that maximum permissible velocity UACC’s bottom is 3 m/s.展开更多
In the present study, an experimental investigation of the decay of the maximum velocity and its turbulent characteristics behind a ship propeller, in "bollard pull" condition (zero speed of advance), is reported....In the present study, an experimental investigation of the decay of the maximum velocity and its turbulent characteristics behind a ship propeller, in "bollard pull" condition (zero speed of advance), is reported. Velocity measurements were performed in laboratory by use of a Laser Doppler Anemometry (LDA) measurement system. Earlier researchers described that the maximum axial velocity is constant at the initial stage of a ship's propeller jet (Fuehrer and Romisch, 1977; Blaauw and van de Kaa, 1978; Berger et al, 1981; Verhey, 1983) as reported in a pure water jet (Albertson et al., 1950; Lee et al., 2002; Dai, 2005), but a number of researchers disagreed with the constant velocity assumption. The present study found that the maximum axial velocity decays in the zone of flow establishment and the zone of established flow with different rates. The investigation provides an insight into the decays of both the maximum velocity and the maximum turbulent fluctuation in axial, tangential and radial components and the decay of the maximum turbulent kinetic energy. Empirical equations are proposed to allow coastal engineers to estimate the jet characteristics from a ship's propeller.展开更多
Sound velocity profile(SVP)data is indispensable in the multi-beam data processing.The sampling density is of great importance for SVP to represent the vertical variation of sound velocity accurately and guarantee the...Sound velocity profile(SVP)data is indispensable in the multi-beam data processing.The sampling density is of great importance for SVP to represent the vertical variation of sound velocity accurately and guarantee the accuracy of sound ray tracing(SRT).However,the SVP also affects the SRT efficiency significantly,especially in deep-sea multi-beam sounding data processing.To improve SRT efficiency and ensure SRT accuracy,an adaptive SVP simplification method based on area difference is proposed in this article.Firstly,the relationship between the area difference of the raw SVP and the simplified one and SRT bias is studied,and the relationship model of them is built.Then,by considering the constraint of SRT accuracy,the SVP simplification method and the simplifying SVP procedure SVP are given.Finally,a deep water experiment is conducted to verify the proposed method.Compared to the existing method,the proposed method improves the robustness,feasibility of SVP simplification as well as the accuracy and efficiency of SRT.展开更多
Eucalyptus clones are selected according to productivity,wood quality,rooting capacity,and resistance to drought,frost and diseases.However,kinetic and morphological parameters that determine the absorption efficiency...Eucalyptus clones are selected according to productivity,wood quality,rooting capacity,and resistance to drought,frost and diseases.However,kinetic and morphological parameters that determine the absorption efficiency of nutrients such as nitrate(NO_(3)^(-)) and ammonium(NH_(4)^(+))are often not considered in breeding programs.The objective of this study was to evaluate the morphological,physiological and kinetic parameters of nitrogen uptake by clones of Eucalyptus saligna(32,864) and Eucalyptus grandis(GPC23).Morphological parameters in shoot and root systems,biomass and N concentrations in different organs,photosynthetic pigment concentrations,parameters of chlorophyll a fluorescence and photosynthetic rates were evaluated.Kinetic parameters,maximum absorption velocity(V_(max)),Michaelis-Menten constant(K_(m)),minimum concentration(C_(min)) and influx(I) were calculated for NO_(3)^(-)and NH_(4)^(+) in the two clones.E.granais clone was more efficient in the uptake of NO_(3)^(-)and NH_(4)^(+),and showed lower K_(m) and C_(min)values,allowing for the absorption of nitrogen at low concentrations due to the high affinity of the absorption sites of clone roots to NO_(3)^(-)and NH_(4)^(+).Higher root lengths,area and volume helped the E.grandis clone in absorption efficiency and consequently,resulted in higher root and shoot biomass.The E.saligna clone had higher K_(m) and Cmin for NO_(3)^(-)and NH_(4)^(+),indicating adaptation to environments with higher N availability.The results of NO_(3)^(-)and NH_(4)^(+) kinetic parameters indicate that they can be used in Eucalyptus clone selection and breeding programs as they can predict the ability of clones to absorb NO_(3)^(-)and NH_(4)^(+) at different concentrations.展开更多
基金supported by the National Natural Science Foundation of China (Grants No.50879019,50909036,and 50879020)the Research Fund for the Doctoral Program of Higher Education (Grants No.200802940001 and 200802941028)+3 种基金the Fundamental Research Funds for the Central Universities (Grants No.2010B02214,2009B08014,and 2010B14214)the Natural Science Foundation of Hohai University(Grant No. 2008426411)the Jiangsu "333" Program for High Level Talents (Grant No. 2017-B08038)the National Undergraduate Innovation Training Plan (Grant No.G20101106)
文摘The velocity dip phenomenon may occur in a part of or in the whole flow field of open channel flows due to the secondary flow effect. Based on rectangular flume experiments and the laser Doppler velocimetry, the influence of the distance to the sidewall and the aspect ratio on the velocity dip is investigated. Through application of statistical methods to the experimental results, it is proposed that the flow field may be divided into two regions, the relatively strong sidewall region and the relatively weak sidewall region. In the former region, the distance to the sidewall greatly affects the location of maximum velocity, and, in the latter region, both the distance to the sidewall and the aspect ratio influence the location of the maximum velocity.
文摘This work presents the hydrologic estimations of the hydraulic underground arched culvert channel (UACC) in Sabinal Basin, Chiapas, México and the hydrological problems associated with it, such as the erosion phenomenon and abrasion cavity formation in it. On the other hand, the maximum flows that the UACC could transport were analyzed, concluding that it no longer has the hydraulic capacity to transport the flow rate associated to return periods equal to or greater than five years and that maximum permissible velocity UACC’s bottom is 3 m/s.
基金supported by SPUR Studentship from Queen's University Belfastsupported by the National Natural Science Foundation of China (Grant No. 51006019)Petro China Innovation Foundation from China National Petroleum Corporation (Grant No. 2010D-5006-0208)
文摘In the present study, an experimental investigation of the decay of the maximum velocity and its turbulent characteristics behind a ship propeller, in "bollard pull" condition (zero speed of advance), is reported. Velocity measurements were performed in laboratory by use of a Laser Doppler Anemometry (LDA) measurement system. Earlier researchers described that the maximum axial velocity is constant at the initial stage of a ship's propeller jet (Fuehrer and Romisch, 1977; Blaauw and van de Kaa, 1978; Berger et al, 1981; Verhey, 1983) as reported in a pure water jet (Albertson et al., 1950; Lee et al., 2002; Dai, 2005), but a number of researchers disagreed with the constant velocity assumption. The present study found that the maximum axial velocity decays in the zone of flow establishment and the zone of established flow with different rates. The investigation provides an insight into the decays of both the maximum velocity and the maximum turbulent fluctuation in axial, tangential and radial components and the decay of the maximum turbulent kinetic energy. Empirical equations are proposed to allow coastal engineers to estimate the jet characteristics from a ship's propeller.
文摘Sound velocity profile(SVP)data is indispensable in the multi-beam data processing.The sampling density is of great importance for SVP to represent the vertical variation of sound velocity accurately and guarantee the accuracy of sound ray tracing(SRT).However,the SVP also affects the SRT efficiency significantly,especially in deep-sea multi-beam sounding data processing.To improve SRT efficiency and ensure SRT accuracy,an adaptive SVP simplification method based on area difference is proposed in this article.Firstly,the relationship between the area difference of the raw SVP and the simplified one and SRT bias is studied,and the relationship model of them is built.Then,by considering the constraint of SRT accuracy,the SVP simplification method and the simplifying SVP procedure SVP are given.Finally,a deep water experiment is conducted to verify the proposed method.Compared to the existing method,the proposed method improves the robustness,feasibility of SVP simplification as well as the accuracy and efficiency of SRT.
基金funded partly by the Conselho Nacional de Desenvolvimento Científico and Tecnológico(CNPq)。
文摘Eucalyptus clones are selected according to productivity,wood quality,rooting capacity,and resistance to drought,frost and diseases.However,kinetic and morphological parameters that determine the absorption efficiency of nutrients such as nitrate(NO_(3)^(-)) and ammonium(NH_(4)^(+))are often not considered in breeding programs.The objective of this study was to evaluate the morphological,physiological and kinetic parameters of nitrogen uptake by clones of Eucalyptus saligna(32,864) and Eucalyptus grandis(GPC23).Morphological parameters in shoot and root systems,biomass and N concentrations in different organs,photosynthetic pigment concentrations,parameters of chlorophyll a fluorescence and photosynthetic rates were evaluated.Kinetic parameters,maximum absorption velocity(V_(max)),Michaelis-Menten constant(K_(m)),minimum concentration(C_(min)) and influx(I) were calculated for NO_(3)^(-)and NH_(4)^(+) in the two clones.E.granais clone was more efficient in the uptake of NO_(3)^(-)and NH_(4)^(+),and showed lower K_(m) and C_(min)values,allowing for the absorption of nitrogen at low concentrations due to the high affinity of the absorption sites of clone roots to NO_(3)^(-)and NH_(4)^(+).Higher root lengths,area and volume helped the E.grandis clone in absorption efficiency and consequently,resulted in higher root and shoot biomass.The E.saligna clone had higher K_(m) and Cmin for NO_(3)^(-)and NH_(4)^(+),indicating adaptation to environments with higher N availability.The results of NO_(3)^(-)and NH_(4)^(+) kinetic parameters indicate that they can be used in Eucalyptus clone selection and breeding programs as they can predict the ability of clones to absorb NO_(3)^(-)and NH_(4)^(+) at different concentrations.