The Antarctic runnel can be highly variable in space and time; however, this environment has provided aninteresting habitat for terrestrial algal colonization. The runnel of Reeve Hill, Casey Station (66°16.855′...The Antarctic runnel can be highly variable in space and time; however, this environment has provided aninteresting habitat for terrestrial algal colonization. The runnel of Reeve Hill, Casey Station (66°16.855′S, 110°31.045′E), Antarctica, which occurs intermittently only during the brief austral summer showed high colonization by microalgaedominated mainly by Cyanobacteria mats and diatoms. 9 freshwater microalgae species which includesOscillatoria frac-ta, Oscillatoriasp., Navicula muticopsis, Pinnularia borealis, Nitzschiasp., Prasiola crispa, Chlorococcumsp., Syene-chococcus aeruginosusandSyenechococcus maiorwere recorded during the study. The algal community in the runnel to beobserved closely resembles that in the larger running water ecosystems in the continent. However, intrusion of seawater,direct exposure to sunlight and influence of sea current in the lower part changes the species community. The lower run-nel showed total dominance consists mainly of the marine planktonic Bacillariophycea. Other species detected includes Flagilaria kerguelensis, Flagilaria linearis, Eucampia antarctica, Thalassiosira tumida,Pseudonitzschia lineola, Pseud-onitzschia turgiduloides, Achnanthes brevipesand Odontella litigiosa. Lower algal species diversity observed in this studysuggests that the number of species obtained is related to the area of environment from which the samples were derived.The local assemblages simply contain species that is favored by the environmental conditions.展开更多
Wind tunnel testing is conducted at different back pressures in a vacuum-type wind tunnel for a novel supersonic fluidic oscillator which consists of a two-dimensional Laval nozzle, a rectangular cavity and a backward...Wind tunnel testing is conducted at different back pressures in a vacuum-type wind tunnel for a novel supersonic fluidic oscillator which consists of a two-dimensional Laval nozzle, a rectangular cavity and a backward step, to obtain its characteristics and the conditions for jet oscillating. The experimental results show that periodic asymmetrical flipping of the supersonic jet appears over certain nozzle pressure ratio（NPR） range according to schlieren visualization and pressure fluctuations. The jet flipping appears only when the jet is over expanded. The normalized average amplitude of the lateral pressure difference acting on the roofs of the cavity and the step varies around 0.2 while the periodic flipping appears. The supersonic jet periodic flipping frequencies obtained from the experiments agree well with those from the modified Rossiter mode for cavity-step acoustic resonance, but further investigations are needed to discover the underlying mechanism for the jet flipping.展开更多
The effect of deficiency in tunnel crown thickness on the Yellow River Crossing Tunnel with post-tensioned concrete inner lining was investigated by the elasto-plastic finite element method. Changes in the deformation...The effect of deficiency in tunnel crown thickness on the Yellow River Crossing Tunnel with post-tensioned concrete inner lining was investigated by the elasto-plastic finite element method. Changes in the deformations and circumferential stresses of the post-tensioned concrete inner lining with the gradual decrease of the tunnel crown thickness were compared, and the potential bearing risk of insufficient tunnel crown thickness for the Yellow River Crossing Tunnel was revealed. Based on the finite element calculation results of circumferential stresses under different defective cases, the corresponding reinforcement schemes were proposed. The calculation results show that the inner lining can still maintain a satisfactory stress state when the tunnel crown thickness is equal to or greater than 0. 28 m. When the tunnel crown thickness decreases below 0.28 m, the external surface of the crown and internal surface of the crown＇s adjacent areas may be under tension. The tension stresses will incrementally increase and ultimately exceed the tensile strength of the inner lining concrete as the tunnel crown thickness further decreases gradually. Then, the Yellow River Crossing Tunnel cannot operate normally, and severe cracking, leaking or even failure may occur. When the tunnel crown thickness is equal to or greater than 0.28 m, the reinforcement suggestions are that the void spaces between the inner lining and the outer lining should be back-filled with concrete. When the tunnel crown thickness is less than 0. 28 m, the inner lining should be reinforced by steel plates after concrete back-filling.展开更多
In order to provide a technical reference and guidance for the safety and stability analysis of the submerged floating tunnel （SFT） in the future, the mechanical behaviors of SFT under the action of water current wi...In order to provide a technical reference and guidance for the safety and stability analysis of the submerged floating tunnel （SFT） in the future, the mechanical behaviors of SFT under the action of water current with different velocities were studied by experiments on an SFT tube model made of rubber. Then, a numerical simulation on the coupling interaction between SFT and water current was conducted by finite element method （FEM）. The comparison .between the results obtained from experiment and those derived from the numerical simulation shows that the experimental results approximately tally with the simulational ones. As a result, the relationships between water current velocities and the mechanical behaviors of tube, such as the annular and axial strains, internal forces （ axial force and bending moment）, and deformations of the tube structure and the forces borne by the tension cables, were concluded.展开更多
文摘The Antarctic runnel can be highly variable in space and time; however, this environment has provided aninteresting habitat for terrestrial algal colonization. The runnel of Reeve Hill, Casey Station (66°16.855′S, 110°31.045′E), Antarctica, which occurs intermittently only during the brief austral summer showed high colonization by microalgaedominated mainly by Cyanobacteria mats and diatoms. 9 freshwater microalgae species which includesOscillatoria frac-ta, Oscillatoriasp., Navicula muticopsis, Pinnularia borealis, Nitzschiasp., Prasiola crispa, Chlorococcumsp., Syene-chococcus aeruginosusandSyenechococcus maiorwere recorded during the study. The algal community in the runnel to beobserved closely resembles that in the larger running water ecosystems in the continent. However, intrusion of seawater,direct exposure to sunlight and influence of sea current in the lower part changes the species community. The lower run-nel showed total dominance consists mainly of the marine planktonic Bacillariophycea. Other species detected includes Flagilaria kerguelensis, Flagilaria linearis, Eucampia antarctica, Thalassiosira tumida,Pseudonitzschia lineola, Pseud-onitzschia turgiduloides, Achnanthes brevipesand Odontella litigiosa. Lower algal species diversity observed in this studysuggests that the number of species obtained is related to the area of environment from which the samples were derived.The local assemblages simply contain species that is favored by the environmental conditions.
基金supported by a grant from the Natural Science Foundation of Jiangsu Province (No. BK20150781)
文摘Wind tunnel testing is conducted at different back pressures in a vacuum-type wind tunnel for a novel supersonic fluidic oscillator which consists of a two-dimensional Laval nozzle, a rectangular cavity and a backward step, to obtain its characteristics and the conditions for jet oscillating. The experimental results show that periodic asymmetrical flipping of the supersonic jet appears over certain nozzle pressure ratio（NPR） range according to schlieren visualization and pressure fluctuations. The jet flipping appears only when the jet is over expanded. The normalized average amplitude of the lateral pressure difference acting on the roofs of the cavity and the step varies around 0.2 while the periodic flipping appears. The supersonic jet periodic flipping frequencies obtained from the experiments agree well with those from the modified Rossiter mode for cavity-step acoustic resonance, but further investigations are needed to discover the underlying mechanism for the jet flipping.
基金The Natural Science Foundation of Hubei Province(No.2017CFB667)the National Natural Science Foundation of China(No.51079107)
文摘The effect of deficiency in tunnel crown thickness on the Yellow River Crossing Tunnel with post-tensioned concrete inner lining was investigated by the elasto-plastic finite element method. Changes in the deformations and circumferential stresses of the post-tensioned concrete inner lining with the gradual decrease of the tunnel crown thickness were compared, and the potential bearing risk of insufficient tunnel crown thickness for the Yellow River Crossing Tunnel was revealed. Based on the finite element calculation results of circumferential stresses under different defective cases, the corresponding reinforcement schemes were proposed. The calculation results show that the inner lining can still maintain a satisfactory stress state when the tunnel crown thickness is equal to or greater than 0. 28 m. When the tunnel crown thickness decreases below 0.28 m, the external surface of the crown and internal surface of the crown＇s adjacent areas may be under tension. The tension stresses will incrementally increase and ultimately exceed the tensile strength of the inner lining concrete as the tunnel crown thickness further decreases gradually. Then, the Yellow River Crossing Tunnel cannot operate normally, and severe cracking, leaking or even failure may occur. When the tunnel crown thickness is equal to or greater than 0.28 m, the reinforcement suggestions are that the void spaces between the inner lining and the outer lining should be back-filled with concrete. When the tunnel crown thickness is less than 0. 28 m, the inner lining should be reinforced by steel plates after concrete back-filling.
基金The National Natural Science Founda-tion of China (No.10572121)Huo Yingdong Foundationof the China State Ministry of Education (No.94024)
文摘In order to provide a technical reference and guidance for the safety and stability analysis of the submerged floating tunnel （SFT） in the future, the mechanical behaviors of SFT under the action of water current with different velocities were studied by experiments on an SFT tube model made of rubber. Then, a numerical simulation on the coupling interaction between SFT and water current was conducted by finite element method （FEM）. The comparison .between the results obtained from experiment and those derived from the numerical simulation shows that the experimental results approximately tally with the simulational ones. As a result, the relationships between water current velocities and the mechanical behaviors of tube, such as the annular and axial strains, internal forces （ axial force and bending moment）, and deformations of the tube structure and the forces borne by the tension cables, were concluded.
