Based on theoretical analysis,the ratio of the maximal drag force of unit area D0 to the maximal buoyancy force of unit area B0 in the spray region is proposed as a new criterion for predicting the stability of smoke layer under sprinkler spray.

After analyzing the mechanism of the sand entry of perforated well,based on the theory of linear elasticity and considering the effect of temperature-change stress and drag force of the fluid flow through porous medium,a new model for forecasting the sand production of perforated well is established.

Under the hypothesis of steady uniform flow,the depth-integrated turbulence time-averaged momentum equation for the main flow direction is simplified by considering the effect of the vegetation on the flow as the drag force item as well as the secondary flows.

Flow through fissures in rock mass applies simultaneously the normal hydrostatic seepage pressure and the tangent hauling force (the dynamic seepage pressure) on fissure walls.

Flow in the fissures of rock mass applies simultaneously the normal hydrostatic seepage pressure and the tangent hauling force(dynamic seepage pressure) on fissure walls.

A new criterium based on the ratio of local spray dragging force to local smoke buoyancy was proposed to analyze the stability of smoke under sprinkler spray.

The orientation the bow of gold dredger must face to when taking up berth in flood season and the method to estimate the dragging force of gold dredger produced by the pounding of flood water are explained and introduced in this paper.