Aspects of the general Vlasov theory are examined separately as applied to a thin-walled channel section cantilever beam under free-end end loading. In particular, the flexural bending and shear that arise under trans...Aspects of the general Vlasov theory are examined separately as applied to a thin-walled channel section cantilever beam under free-end end loading. In particular, the flexural bending and shear that arise under transverse shear and axial torsional loading are each considered theoretically. These analyses involve the location of the shear centre at which transverse shear forces when applied do not produce torsion. This centre, when taken to be coincident with the centre of twist implies an equivalent reciprocal behaviour. That is, an axial torsion applied concentric with the shear centre will twist but not bend the beam. The respective bending and shear stress conversions are derived for each action applied to three aluminium alloy extruded channel sections mounted as cantilevers with a horizontal principal axis of symmetry. Bending and shear are considered more generally for other thin-walled sections when the transverse loading axes at the shear centre are not parallel to the section = s centroidal axes of principal second moments of area. The fixing at one end of the cantilever modifies the St Venant free angular twist and the free warping displacement. It is shown from the Wagner-Kappus torsion theory how the end constrained warping generates an axial stress distribution that varies with the length and across the cross-section for an axial torsion applied to the shear centre. It should be mentioned here for wider applications and validation of the Vlasov theory that attendant papers are to consider in detail bending and torsional loadings applied to other axes through each of the centroid and the web centre. Therein, both bending and twisting arise from transverse shear and axial torsion applied to each position being displaced from the shear centre. Here, the influence of the axis position upon the net axial and shear stress distributions is to be established. That is, the net axial stress from axial torsional loading is identified with the sum of axial stress due to bending and axial stress arising from constrained warping displacements at the fixing. The net shear stress distribution overlays the distributions from axial torsion and that from flexural shear under transverse loading. Both arise when transverse forces are displaced from the shear centre.展开更多
Turbulence structure in a helically coiled open channel flow is numerically simulated using three different turbulence models--the Launder and Ying model, the Naot and Rodi model, and the nonlinear k-ε Model (SY mode...Turbulence structure in a helically coiled open channel flow is numerically simulated using three different turbulence models--the Launder and Ying model, the Naot and Rodi model, and the nonlinear k-ε Model (SY model). Simulation results were compared with observation of (i) turbulent flows in alternating point-bar type channel bends with rectangular sections, and (ii) straight open channel flows with compound cross-sections. Based on calculations of the impact of various channel curvatures on turbulence characteristics, accuracy of the three turbulence models was analyzed with observed data as a qualitative reference. It has been found out that the Launder and Ying model and the nonlinear k-ε Model are able to predict the same general trend as measured data, and the simulation of the effect of the centrifugal force on the formation of secondary currents produces a correct pattern.展开更多
文摘Aspects of the general Vlasov theory are examined separately as applied to a thin-walled channel section cantilever beam under free-end end loading. In particular, the flexural bending and shear that arise under transverse shear and axial torsional loading are each considered theoretically. These analyses involve the location of the shear centre at which transverse shear forces when applied do not produce torsion. This centre, when taken to be coincident with the centre of twist implies an equivalent reciprocal behaviour. That is, an axial torsion applied concentric with the shear centre will twist but not bend the beam. The respective bending and shear stress conversions are derived for each action applied to three aluminium alloy extruded channel sections mounted as cantilevers with a horizontal principal axis of symmetry. Bending and shear are considered more generally for other thin-walled sections when the transverse loading axes at the shear centre are not parallel to the section = s centroidal axes of principal second moments of area. The fixing at one end of the cantilever modifies the St Venant free angular twist and the free warping displacement. It is shown from the Wagner-Kappus torsion theory how the end constrained warping generates an axial stress distribution that varies with the length and across the cross-section for an axial torsion applied to the shear centre. It should be mentioned here for wider applications and validation of the Vlasov theory that attendant papers are to consider in detail bending and torsional loadings applied to other axes through each of the centroid and the web centre. Therein, both bending and twisting arise from transverse shear and axial torsion applied to each position being displaced from the shear centre. Here, the influence of the axis position upon the net axial and shear stress distributions is to be established. That is, the net axial stress from axial torsional loading is identified with the sum of axial stress due to bending and axial stress arising from constrained warping displacements at the fixing. The net shear stress distribution overlays the distributions from axial torsion and that from flexural shear under transverse loading. Both arise when transverse forces are displaced from the shear centre.
基金This work was supported by the National Natural Science Foundation of China (Grant Nos. 50179015, 59879009, 50221903)
文摘Turbulence structure in a helically coiled open channel flow is numerically simulated using three different turbulence models--the Launder and Ying model, the Naot and Rodi model, and the nonlinear k-ε Model (SY model). Simulation results were compared with observation of (i) turbulent flows in alternating point-bar type channel bends with rectangular sections, and (ii) straight open channel flows with compound cross-sections. Based on calculations of the impact of various channel curvatures on turbulence characteristics, accuracy of the three turbulence models was analyzed with observed data as a qualitative reference. It has been found out that the Launder and Ying model and the nonlinear k-ε Model are able to predict the same general trend as measured data, and the simulation of the effect of the centrifugal force on the formation of secondary currents produces a correct pattern.
