The meander channel is one of the most common channel patterns in nature.The characteristics of the flow and sediment in a meander channel which have significant effect on the development of watercourse are important ...The meander channel is one of the most common channel patterns in nature.The characteristics of the flow and sediment in a meander channel which have significant effect on the development of watercourse are important subjects in river dynamics.The transition of the flow patterns in a meander channel concerns with the development mode of the channel pattern and the river regime including the generation conditions of the three-dimensional coherent vortex and secondary flow,the hierarchical scale of coherent vortex in different flow conditions,the large-scale turbulent eddy structure adapted to a meander,etc.In this paper we study the laminar flow instability of the two-dimensional channel in a meander channel.It is essentially different from that in a straight channel:The neutral curve will move forward and the critical Reynolds number will decrease.The flow is unstable in response to a wider range of the disturbance wave number,or the laminar flow instability can happen more easily.The above results could not be obtained in the traditional hydrodynamic stability theory so that our work in this paper would make up for the deficiency and blank in this aspect.展开更多
The present study has theoretically investigated the combined torsional buckling of double-walled carbon nanotubes (DWCNTs) with axial load in the multi-field coupled condition. The effects of torsion, axial load, the...The present study has theoretically investigated the combined torsional buckling of double-walled carbon nanotubes (DWCNTs) with axial load in the multi-field coupled condition. The effects of torsion, axial load, thermal-electrical change, surrounding elastic medium and the Van der Waals forces are all taken into consideration. The governing equation of buckling for CNTs subjected to thermo-electro-mechanical loadings has been established based on an elastic shell model of continuum mechanics. Reasonable simplifications are made to get the explicit expression of the critical buckling shear stress of DWCNTs, and numerical experiments are conducted for further research. It is shown that under certain electric and temperature field the critical buckling shear stress of DWCNTs only depends on the wave number of buckling modes. On the other hand, all the related impact factors have enormous influence on the critical buckling shear stress under a certain buckling mode. The critical buckling shear stress changes linearly with the axial-to-shear stress ratio, as well as the thermal and electric change. Axial compression tends to make DWCNTs unstable, while axial tension benefits the buckling stability. The critical buckling shear stress is directly proportional to the applied voltage. At room or lower temperature, the critical shear stress for infinitesimal buckling increases as the temperature change increases, while it decreases at a higher temperature. The conclusions are useful for the design of nano-structures related to the buckling stability of DWCNTs.展开更多
基金supported by the National Basic Research Program of China ("973" Program) (Grant No. 2007CB714101)the National Natural Science Foundation of China (Grant Nos. 50979066, 50809045, 51021004)
文摘The meander channel is one of the most common channel patterns in nature.The characteristics of the flow and sediment in a meander channel which have significant effect on the development of watercourse are important subjects in river dynamics.The transition of the flow patterns in a meander channel concerns with the development mode of the channel pattern and the river regime including the generation conditions of the three-dimensional coherent vortex and secondary flow,the hierarchical scale of coherent vortex in different flow conditions,the large-scale turbulent eddy structure adapted to a meander,etc.In this paper we study the laminar flow instability of the two-dimensional channel in a meander channel.It is essentially different from that in a straight channel:The neutral curve will move forward and the critical Reynolds number will decrease.The flow is unstable in response to a wider range of the disturbance wave number,or the laminar flow instability can happen more easily.The above results could not be obtained in the traditional hydrodynamic stability theory so that our work in this paper would make up for the deficiency and blank in this aspect.
基金supported by the National Natural Science Foundation of China (Grant Nos. 10902040, A020602)the Specialized Research Fund for the Doctoral Program of Higher Education(New Teachers)+2 种基金the Foundation for Distinguished Young Talents in Higher Education of Guangdong(Grant No. LYM08016)the Foundation for Outstanding Doctoral Dissertation of Guangdongthe Fundamental Research Funds for the Central Universities, South China University of Technology (Grant Nos.2009ZM0238,2009ZM0280)
文摘The present study has theoretically investigated the combined torsional buckling of double-walled carbon nanotubes (DWCNTs) with axial load in the multi-field coupled condition. The effects of torsion, axial load, thermal-electrical change, surrounding elastic medium and the Van der Waals forces are all taken into consideration. The governing equation of buckling for CNTs subjected to thermo-electro-mechanical loadings has been established based on an elastic shell model of continuum mechanics. Reasonable simplifications are made to get the explicit expression of the critical buckling shear stress of DWCNTs, and numerical experiments are conducted for further research. It is shown that under certain electric and temperature field the critical buckling shear stress of DWCNTs only depends on the wave number of buckling modes. On the other hand, all the related impact factors have enormous influence on the critical buckling shear stress under a certain buckling mode. The critical buckling shear stress changes linearly with the axial-to-shear stress ratio, as well as the thermal and electric change. Axial compression tends to make DWCNTs unstable, while axial tension benefits the buckling stability. The critical buckling shear stress is directly proportional to the applied voltage. At room or lower temperature, the critical shear stress for infinitesimal buckling increases as the temperature change increases, while it decreases at a higher temperature. The conclusions are useful for the design of nano-structures related to the buckling stability of DWCNTs.
