Since 2015,the newly discovered slit-type Danxia landform on the Chinese Loess Plateau has become a hot topic in the field of geomorphology worldwide.However,the relationships among its formation,evolutionary mechanis...Since 2015,the newly discovered slit-type Danxia landform on the Chinese Loess Plateau has become a hot topic in the field of geomorphology worldwide.However,the relationships among its formation,evolutionary mechanism,and mechanical characteristics of its strata and rocks are not clear.In this paper,the Ganquan canyon group is used as the research object.Basic physical and mechanical indices of sandstone in the Ganquan canyon group were measured through field investigation and indoor experiments,and the deterioration trends for the mechanical parameters of sandstone in this area under the action of infiltration,acid dry-wet cycles,and freeze-thaw cycles were revealed.Lastly,the formation and evolutionary mechanism of the slit-type Danxia landform were discussed.The results showed that:(1)The sandstone in the canyon group had a low cementation degree and weak cohesive force,which was easily weakened under the action of water,resulting in a decrease in compressive strength and elastic modulus.(2)Acidic dry-wet cycles caused the mineral composition of the sandstone to be dissolved,and the micropores continued to grow and develop until new cracks were produced.Macroscopically,the compressive strength and elastic modulus of sandstone were greatly reduced,and this damage was cumulative and staged.The greater the acidity,the greater the damage.(3)As the number of freeze-thaw cycles increased,the uniaxial compressive strength and elastic modulus of the sandstone decreased continuously.During the freeze-thaw cycle process,the growth and development of cracks were primarily in fracture mode and usually developed along parallel bedding positions.(4)The interaction of tectonic activity and lithology with different weathering processes was a key factor in the formation and evolution of the slit-type Danxia landform.In conclusion,the intricate process of weathering influenced by historical climatic fluctuations has been pivotal in shaping the topography of Danxia landform.展开更多
Slit-Type Energy Dissipater （STED） has been a kind of important devices for energy dissipation. The flow through the STED is longitudinally extended and the velocity is decreased by means of the cross-section increa...Slit-Type Energy Dissipater （STED） has been a kind of important devices for energy dissipation. The flow through the STED is longitudinally extended and the velocity is decreased by means of the cross-section increase of the flow, which is closely related to geometric and hydraulic parameters of the STED. Therefore, it is necessary to investigate and control the hydraulic condi- tions through the STED, including the nappe section form, the conversion condition, and the effect of energy dissipation with the geometric and hydraulic parameters. In the present work, ＂I-type＂ and ＂T-type＂ nappe forms were experimentally classified, the con- version conditions of the nappe forms were empirically provided, and the effects of geometric parameters of the STED on energy dissipation were roughly analyzed. It is concluded that the contraction angle of the STED is a key factor influencing the hydraulic characteristics of the STED.展开更多
In this paper, the behavior of the flow choking, including the critical and developing states, was experimentally investiga- ted by means of five slit-type outlets, characterized by the outlet width, the contraction a...In this paper, the behavior of the flow choking, including the critical and developing states, was experimentally investiga- ted by means of five slit-type outlets, characterized by the outlet width, the contraction angle and the opening of the working gate. The results showed that the approach flow Froude number of the critical choking decreases if the outlet width increases, or the con- traction angle decreases, or the opening increases. There is the hysteresis when the flow choking develops, i.e., the Froude numbers of the appearance and disappearance of the flow choking at the increasing discharge regime are all larger than those at the decreasing discharge regime. For various widths of the outlets, the differences between the critical Froude numbers at small opening are much larger than thoset at large opening. The change range from appearance to disappearance of the flow choking at small opening is smaller than that at large opening.展开更多
The flow choking may occur for weir flow slit-type flip buckets trader common operation conditions. An estimation method is developed through introducing a comprehensive coefficient to determine the approach flow Frou...The flow choking may occur for weir flow slit-type flip buckets trader common operation conditions. An estimation method is developed through introducing a comprehensive coefficient to determine the approach flow Froude number for the flow choking to occur in those flip buckets. The error of the present method relative to the experimental data is less than 5%. The results show that, the Froude number for the flow choking to occur is related to the contraction ratio and the contraction angle of the flip buckets. When the flow choking occurs, the upper jet trajectory decreases and the lower one is almost not affected, and the dynamic pressures on the bottom and the sidewalls increase due to the flow profile rising on the flip buckets.展开更多
Energy dissipation and scour control are all the key issues for the design of hydraulic structures.On the basis of the high energy dissipation for the multiple slit-type energy dissipaters(M-STED)developed by the auth...Energy dissipation and scour control are all the key issues for the design of hydraulic structures.On the basis of the high energy dissipation for the multiple slit-type energy dissipaters(M-STED)developed by the authors,in this work,the characteristics of the scour hole for the M-STED were experimentally investigated through three sets of those physical models with five cases and a scour hole form index was proposed.The results show that,the M-STED results in not only the high energy dissipation but also the mild upstream slope of the scour hole thanks to the scour hole form index of larger than 0.5,which is in favor of the safety of the release works.展开更多
The radial vibration characteristic of an annular ultrasonic concentrator with multi- slits is studied. Based on the electro-mechanical analogy and by introducing an area ratio coef- ficient, the radial vibrational eq...The radial vibration characteristic of an annular ultrasonic concentrator with multi- slits is studied. Based on the electro-mechanical analogy and by introducing an area ratio coef- ficient, the radial vibrational equivalent circuit and the frequency equation of the concentrator are derived. The radial displacement amplitude magnification factor of it is obtained. By nu- merical calculating, the relationship between the radial displacement amplitude magnification factor, the resonance frequency of the concentrator at the first and second resonance and its radius ratio are investigated. Also, the relationship between the radial displacement amplitude magnification factor, the resonance frequency of the concentrator and the length, the angle and the number of the silts are analyzed. It is illustrated that a maximum of displacement ampli- tude magnification factor of the concentrator appears with the increase of the radius ratio, and the amplitude magnification factor increase as the length, the angle and the number of the silts increase, while the radial resonance frequency of the concentrator decreases as the length, the angle and the number of the silts increase. The theoretical resonance frequencies are in good agreement with that of the FEM simulations and measurement.展开更多
The slit-type energy dissipater（STED）is widely used in hydraulic projects of high water head,large discharge,and narrow river valley,thanks to its simple structure and high efficiency.However,the water wing caused b...The slit-type energy dissipater（STED）is widely used in hydraulic projects of high water head,large discharge,and narrow river valley,thanks to its simple structure and high efficiency.However,the water wing caused by the shock waves in the contraction section of the STED may bring about harmful effects.A coefficient is introduced for the application of Ippen？s theory in the STED.The expression of the coefficient is experimentally obtained.Simplified formulas to calculate the shock wave angle and the water wing scope are theoretically derived,with relative errors within 5%.展开更多
基金This research was funded by the National Natural Science Foundation of China(42077282).
文摘Since 2015,the newly discovered slit-type Danxia landform on the Chinese Loess Plateau has become a hot topic in the field of geomorphology worldwide.However,the relationships among its formation,evolutionary mechanism,and mechanical characteristics of its strata and rocks are not clear.In this paper,the Ganquan canyon group is used as the research object.Basic physical and mechanical indices of sandstone in the Ganquan canyon group were measured through field investigation and indoor experiments,and the deterioration trends for the mechanical parameters of sandstone in this area under the action of infiltration,acid dry-wet cycles,and freeze-thaw cycles were revealed.Lastly,the formation and evolutionary mechanism of the slit-type Danxia landform were discussed.The results showed that:(1)The sandstone in the canyon group had a low cementation degree and weak cohesive force,which was easily weakened under the action of water,resulting in a decrease in compressive strength and elastic modulus.(2)Acidic dry-wet cycles caused the mineral composition of the sandstone to be dissolved,and the micropores continued to grow and develop until new cracks were produced.Macroscopically,the compressive strength and elastic modulus of sandstone were greatly reduced,and this damage was cumulative and staged.The greater the acidity,the greater the damage.(3)As the number of freeze-thaw cycles increased,the uniaxial compressive strength and elastic modulus of the sandstone decreased continuously.During the freeze-thaw cycle process,the growth and development of cracks were primarily in fracture mode and usually developed along parallel bedding positions.(4)The interaction of tectonic activity and lithology with different weathering processes was a key factor in the formation and evolution of the slit-type Danxia landform.In conclusion,the intricate process of weathering influenced by historical climatic fluctuations has been pivotal in shaping the topography of Danxia landform.
基金Project supported by the National Natural Science Foundation of China(Grant No.51179056)
文摘Slit-Type Energy Dissipater （STED） has been a kind of important devices for energy dissipation. The flow through the STED is longitudinally extended and the velocity is decreased by means of the cross-section increase of the flow, which is closely related to geometric and hydraulic parameters of the STED. Therefore, it is necessary to investigate and control the hydraulic condi- tions through the STED, including the nappe section form, the conversion condition, and the effect of energy dissipation with the geometric and hydraulic parameters. In the present work, ＂I-type＂ and ＂T-type＂ nappe forms were experimentally classified, the con- version conditions of the nappe forms were empirically provided, and the effects of geometric parameters of the STED on energy dissipation were roughly analyzed. It is concluded that the contraction angle of the STED is a key factor influencing the hydraulic characteristics of the STED.
基金supported by the National Natural Science Foundation of China(Grant No.51179056,51279013)
文摘In this paper, the behavior of the flow choking, including the critical and developing states, was experimentally investiga- ted by means of five slit-type outlets, characterized by the outlet width, the contraction angle and the opening of the working gate. The results showed that the approach flow Froude number of the critical choking decreases if the outlet width increases, or the con- traction angle decreases, or the opening increases. There is the hysteresis when the flow choking develops, i.e., the Froude numbers of the appearance and disappearance of the flow choking at the increasing discharge regime are all larger than those at the decreasing discharge regime. For various widths of the outlets, the differences between the critical Froude numbers at small opening are much larger than thoset at large opening. The change range from appearance to disappearance of the flow choking at small opening is smaller than that at large opening.
基金Project supported by the National Natural Science Foundation of China(Grant No.51179056)the PAPD(Grant No.3014-SYS1401)the Fundamental Research Funds for the Central Universities of China(Grant No.2014B03114)
文摘The flow choking may occur for weir flow slit-type flip buckets trader common operation conditions. An estimation method is developed through introducing a comprehensive coefficient to determine the approach flow Froude number for the flow choking to occur in those flip buckets. The error of the present method relative to the experimental data is less than 5%. The results show that, the Froude number for the flow choking to occur is related to the contraction ratio and the contraction angle of the flip buckets. When the flow choking occurs, the upper jet trajectory decreases and the lower one is almost not affected, and the dynamic pressures on the bottom and the sidewalls increase due to the flow profile rising on the flip buckets.
基金Project supported by the National Natural Science Foundation of China(Grant No.51879129).
文摘Energy dissipation and scour control are all the key issues for the design of hydraulic structures.On the basis of the high energy dissipation for the multiple slit-type energy dissipaters(M-STED)developed by the authors,in this work,the characteristics of the scour hole for the M-STED were experimentally investigated through three sets of those physical models with five cases and a scour hole form index was proposed.The results show that,the M-STED results in not only the high energy dissipation but also the mild upstream slope of the scour hole thanks to the scour hole form index of larger than 0.5,which is in favor of the safety of the release works.
基金supported by the Natural Science Foundation of China Under Grant(11274279,11074222)the College Scholar Professional Development Program of Zhejiang Province Under Grant(FX2013017)
文摘The radial vibration characteristic of an annular ultrasonic concentrator with multi- slits is studied. Based on the electro-mechanical analogy and by introducing an area ratio coef- ficient, the radial vibrational equivalent circuit and the frequency equation of the concentrator are derived. The radial displacement amplitude magnification factor of it is obtained. By nu- merical calculating, the relationship between the radial displacement amplitude magnification factor, the resonance frequency of the concentrator at the first and second resonance and its radius ratio are investigated. Also, the relationship between the radial displacement amplitude magnification factor, the resonance frequency of the concentrator and the length, the angle and the number of the silts are analyzed. It is illustrated that a maximum of displacement ampli- tude magnification factor of the concentrator appears with the increase of the radius ratio, and the amplitude magnification factor increase as the length, the angle and the number of the silts increase, while the radial resonance frequency of the concentrator decreases as the length, the angle and the number of the silts increase. The theoretical resonance frequencies are in good agreement with that of the FEM simulations and measurement.
基金supported by the National Nature Science Foundation of China(Grant Nos.51279013,51379020 and 51509015)the National Key R&D Program of China(Grant No.2016YFC0401900)
文摘The slit-type energy dissipater（STED）is widely used in hydraulic projects of high water head,large discharge,and narrow river valley,thanks to its simple structure and high efficiency.However,the water wing caused by the shock waves in the contraction section of the STED may bring about harmful effects.A coefficient is introduced for the application of Ippen？s theory in the STED.The expression of the coefficient is experimentally obtained.Simplified formulas to calculate the shock wave angle and the water wing scope are theoretically derived,with relative errors within 5%.
