When evaluating hyporheic exchange in a flowing stream, it is inappropriate to directly compare stream stage with subsurface hydraulic head (h) to determine direction and magnitude of the gradient between the stream a...When evaluating hyporheic exchange in a flowing stream, it is inappropriate to directly compare stream stage with subsurface hydraulic head (h) to determine direction and magnitude of the gradient between the stream and the subsurface. In the case of moving water, it is invalid to ignore velocity and to assume that stage equals the net downward pressure on the streambed.? The Bernoulli equation describes the distribution of energy within flowing fluids and implies that net pressure decreases as a function of velocity, i.e., the Venturi Effect, which sufficiently reduces the pressure on the streambed to create the appearance of a downward gradient when in fact the gradient may be upward with stream flow drawing water from the subsurface to the surface. A field study correlating the difference between subsurface head and stream stage in a low-gradient stream indicates that the effect is present and significant: shallow subsurface head increases less quickly than stage while deeper subsurface head increases more quickly. These results can substantially improve conceptual models and simulations of hyporheic flow.展开更多
Dynamic equations of motional flexible beam elements were derived considering second-order effect. Non-linear finite element method and three-node Euler-Bernoulli beam elements were used. Because accuracy is higher in...Dynamic equations of motional flexible beam elements were derived considering second-order effect. Non-linear finite element method and three-node Euler-Bernoulli beam elements were used. Because accuracy is higher in non-linear structural analysis,three-node beam elements are used to deduce shape functions and stiffness matrices in dynamic equations of flexible elements. Static condensation method was used to obtain the finial dynamic equations of three-node beam elements. According to geometrical relations of nodal displacements in concomitant and global coordinate system,dynamic equations of elements can be transformed to global coordinate system by concomitant coordinate method in order to build the global dynamic equations. Analyzed amplitude condition of flexible arm support of a port crane,the results show that second-order effect should be considered in kinetic-elastic analysis for heavy load machinery of big flexibility.展开更多
文摘When evaluating hyporheic exchange in a flowing stream, it is inappropriate to directly compare stream stage with subsurface hydraulic head (h) to determine direction and magnitude of the gradient between the stream and the subsurface. In the case of moving water, it is invalid to ignore velocity and to assume that stage equals the net downward pressure on the streambed.? The Bernoulli equation describes the distribution of energy within flowing fluids and implies that net pressure decreases as a function of velocity, i.e., the Venturi Effect, which sufficiently reduces the pressure on the streambed to create the appearance of a downward gradient when in fact the gradient may be upward with stream flow drawing water from the subsurface to the surface. A field study correlating the difference between subsurface head and stream stage in a low-gradient stream indicates that the effect is present and significant: shallow subsurface head increases less quickly than stage while deeper subsurface head increases more quickly. These results can substantially improve conceptual models and simulations of hyporheic flow.
文摘Dynamic equations of motional flexible beam elements were derived considering second-order effect. Non-linear finite element method and three-node Euler-Bernoulli beam elements were used. Because accuracy is higher in non-linear structural analysis,three-node beam elements are used to deduce shape functions and stiffness matrices in dynamic equations of flexible elements. Static condensation method was used to obtain the finial dynamic equations of three-node beam elements. According to geometrical relations of nodal displacements in concomitant and global coordinate system,dynamic equations of elements can be transformed to global coordinate system by concomitant coordinate method in order to build the global dynamic equations. Analyzed amplitude condition of flexible arm support of a port crane,the results show that second-order effect should be considered in kinetic-elastic analysis for heavy load machinery of big flexibility.
