Transverse Shear Flow Research Articles

Transient reconnection caused by the impact and switch-off of a transverse shear flow

It is supposed that local and transient reconnection in the plasma boundary layer can be caused by the impact and switch-off of a single directional transverse shear flow. MHD (magnetohydrodynamic) simulation is used to investigate the reconnection processes in the two cases. It is found that if the inflow is homogeneous, it does not cause reconnection; if the inflow is shearing flow, no matter how great the shear of the flow is, it may cause reconnection either during impacting period or after stop impacting. It is pointed out that the sudden stop of external force may be an important triggering mechanism of energy transformation and reconnection in the plasma boundary layer region.

Pavement Analysis for Moving Aircraft Load

A finite-element analysis was conducted of flexible pavement test sections subjected to a moving aircraft tire. The test sections failed primarily as a result of shear in the base course. Excavation of the test sections at the end of the tests revealed that there was transverse shear flow of the base as a result of repetitive loading. Deflections at various depths were recorded with multidepth deflectometers. These deflections were used to calibrate the finite-element model. Subsequently, excellent agreement was obtained between measured and predicted time histories of deflections at the various depths. Also, excellent agreement was obtained between predicted and accumulated rutting. The analysis predicted that the shear stress in the base would equal the shear strength, which confirms the mode of failure observed in the test sections.

Stability of Transverse Shear Flows in Shallow Open Channels

The bed‐friction effect on the stability of transverse shear flows in shallow open channels is examined using a linear and “inviscid” theory. Numerical calculations are conducted for four groups of parallel flows with inflection‐point velocity profiles. The necessary conditions for the transverse shear flows to become unstable, so that the large‐scale transverse motion may coexist with the small‐scale bed‐generated turbulence, are determined from the calculations. The results are correlated with two dimensionless parameters: a bed‐friction number and an ambient‐velocity parameter. The bed‐friction number quantifies the stabilizing effect of the bed‐friction. The ambient‐velocity parameter characterizes the changes in depth and roughness across the open‐channel flows. In the limiting case of a weak transverse shear flow, when the change in velocity across the flow is small, the bed‐friction number becomes the only dimensionless parameter governing the stability of the transverse shear flows. The critical values of this bed‐friction number for the weak transverse shear flows with hyperbolic‐tangent and hyperbolic‐secant velocity profiles, are 0.120 and 0.145, respectively.