Based on constructal theory,the constructs of three "volume-point" heat conduction models with three-dimensional cylindrical element and rectangular and triangular elements on microscale and nanoscale are op...Based on constructal theory,the constructs of three "volume-point" heat conduction models with three-dimensional cylindrical element and rectangular and triangular elements on microscale and nanoscale are optimized by taking minimum entransy dissipation rate as optimization objective.The optimal constructs of the three "volume-point" heat conduction models with minimum dimensionless equivalent thermal resistance are obtained.The results show that the optimal constructs of the three-dimensional cylindrical assembly based on the minimizations of dimensionless equivalent thermal resistance and dimensionless maximum thermal resistance are different,which is obviously different from the comparison between those of the corresponding two-dimensional rectangular assembly based on the minimizations of these two objectives.The optimal constructs based on rectangular and triangular elements on microscale and nanoscale when the size effect takes effect are obviously different from those when the size effect does not take effect.Because the thermal current density in the high conductivity channel of the rectangular and triangular second order assemblies are not linear with the length,the optimal constructs of these assemblies based on the minimization of entransy dissipation rate are different from those based on the minimization of maximum temperature difference.The dimensionless equivalent thermal resistance defined based on entransy dissipation rate reflects the average heat transfer performance of the construct.The studies on "volume-point" heat conduction constructal problems at three-dimensional conditions and microscale and nanoscale by taking minimum entransy dissipation rate as optimization objective extend the application range of the entransy dissipation extremum principle.展开更多
When the spider orb web stops a prey, the web dissipates impact energy by three routes： internal dissipation within the radial silk, internal dissipation within the spiral silk and aerodynamic dissipation. This paper...When the spider orb web stops a prey, the web dissipates impact energy by three routes： internal dissipation within the radial silk, internal dissipation within the spiral silk and aerodynamic dissipation. This paper investigates the energy dissipation mechanism of spider orb webs from the mechanics point of view. Firstly, the dynamic response and energy dissipation of a single spider silk under transverse impact are studied analytically and numerically. The congruence of dynamic response curve validates the accuracy of finite element analysis. Then the whole web is modeled using the finite element method and the respective contribution of each route to total energy dissipation during the simulated prey impact is obtained, which agrees with published experimental results. Finally, the influence of initial impact kinetic energy on the fraction distribution of three routes is demonstrated based on the finite element model. The mechanical mechanism of energy dissipation of spider orb webs is discussed and the reason for the differences among the existing opinions is speculated.展开更多
基金supported by the National Natural Science Foundation of China (Grant No. 51176203)the Natural Science Foundation of Naval University of Engineering (Grant No. HGDYDJJ10011)the Natural Science Foundation for Youngsters of Naval University of Engineering (Grant No. HGDQNJJ10017)
文摘Based on constructal theory,the constructs of three "volume-point" heat conduction models with three-dimensional cylindrical element and rectangular and triangular elements on microscale and nanoscale are optimized by taking minimum entransy dissipation rate as optimization objective.The optimal constructs of the three "volume-point" heat conduction models with minimum dimensionless equivalent thermal resistance are obtained.The results show that the optimal constructs of the three-dimensional cylindrical assembly based on the minimizations of dimensionless equivalent thermal resistance and dimensionless maximum thermal resistance are different,which is obviously different from the comparison between those of the corresponding two-dimensional rectangular assembly based on the minimizations of these two objectives.The optimal constructs based on rectangular and triangular elements on microscale and nanoscale when the size effect takes effect are obviously different from those when the size effect does not take effect.Because the thermal current density in the high conductivity channel of the rectangular and triangular second order assemblies are not linear with the length,the optimal constructs of these assemblies based on the minimization of entransy dissipation rate are different from those based on the minimization of maximum temperature difference.The dimensionless equivalent thermal resistance defined based on entransy dissipation rate reflects the average heat transfer performance of the construct.The studies on "volume-point" heat conduction constructal problems at three-dimensional conditions and microscale and nanoscale by taking minimum entransy dissipation rate as optimization objective extend the application range of the entransy dissipation extremum principle.
基金The work described in this paper is financially supported by the National Natural Science Foundation of China （No. 11032001）.
文摘When the spider orb web stops a prey, the web dissipates impact energy by three routes： internal dissipation within the radial silk, internal dissipation within the spiral silk and aerodynamic dissipation. This paper investigates the energy dissipation mechanism of spider orb webs from the mechanics point of view. Firstly, the dynamic response and energy dissipation of a single spider silk under transverse impact are studied analytically and numerically. The congruence of dynamic response curve validates the accuracy of finite element analysis. Then the whole web is modeled using the finite element method and the respective contribution of each route to total energy dissipation during the simulated prey impact is obtained, which agrees with published experimental results. Finally, the influence of initial impact kinetic energy on the fraction distribution of three routes is demonstrated based on the finite element model. The mechanical mechanism of energy dissipation of spider orb webs is discussed and the reason for the differences among the existing opinions is speculated.
