Optimal Design of Large Circular Vibrating Screen Based on MultipleFrequencies Constraints and Analytical Sensitivity Methods
Multiple frequencies constraints and analytical sensitivity methods were used in structural optimization design of the side plate of 4YK1860 vibrating screen to lower the damage of side plate caused by high dynamic stress. The mass of side plate of the vibrating screen was taken as object function, mode frequencies were regarded as state parameters, size of plate were used as constraint parameters and an optimization criterion which is applicable to solve this kind of problem was given. Meanwhile, sensitivity characteristics of variable parameters were considered during the process of optimization. The results show that the optimization program with embedded analytical sensitivity calculation methods is of a higher solving precision and with a more stable calculating process. After structure optimization, the thickness of side plate to withstand large impact is increased, the thickness of stiffener and peripheral angle are decreased, the mass of side plate is reduced by 7.75% and a better optimization effect is achieved. The analysis of the optimal vibrating screen presents that the mass of vibrating screen decreases by 3.5%, elastic deformation frequency which is close to the working frequency increases by 8.8% and the dynamic stress decreases by 48%. The natural frequencies of vibrating screen are improved and modal frequency is far from the working frequency of the exciting motor, stress concentration of vibrating screen is weakened and thus the structural stiffness and reliability of vibrating screen is enhanced.
Optimal design of large vibrating screen based on multiple frequencies constraints and analytical sensitivity methods
Multiple frequencies constraints and analytical sensitivity methods were used in structural optimization design of stiffeners on the side plate of vibrating screen to lower the damage of side plate causing by high dynamic stress when the large vibrating screen works.The mass of side plate of vibrating screen was taken as object function,multiple frequencies were regarded as state parameters and an optimization criterion which is applicable to solve this kind of problem was given.Meanwhile,sensitivity characteristics of variable parameters were considered during the process of optimization.The results show that the optimization program with embedded analytical sensitivity calculation methods is of a higher solving precision and a more stable calculating process.After structure optimization,the mass of side plate is reduced by 8.27% and two elastic deformation frequencies are increased by 1.37% and 2.97%,respectively,and a better optimization effect is achieved.The analysis of the optimal vibrating screen presents that the mass of vibrating screen decreases by 2.35% and three elastic deformation frequencies which are close to the working frequency increase by 14.17%,12.29% and 23.01%,respectively.The natural frequencies of vibrating screen are improved and modal frequency is far from working frequency of the exciting motor and thus the structural stiffness and reliability of vibrating screen is enhanced.
Control of the homopause level
Abstract This paper reviews the hypothesis that internal gravity wave breaking in the factor responsible for upper atmosphere turbulence generation and control of the number density at the homopause level. Available data from Mars and Earth support the hypothesis, originally introduced by Lindzen, that breaking thermal tides are responsible for the necessary turbulence. The lowest-order, equatorially trapped, westward-propagating diurnal tidal mode is the primary cause on the Earth, and lower-order westward-propagating semidiurnal modes are the primary cause on Mars. The frequencies and vertical wavenumbers of the responsible modes determine the eddy diffusion coefficients; energy density is only indirectly involved by determining which modes can break. A general scale relationship between tidal heating and velocity amplitude can be used to assess the breaking potential of tidal modes, and is used here as the basis for arguing that the number density at the Martian homopause is likely to have been stable over much of geologic time. Difficulties with this approach arise in the cases of Venus and Titan because of their peculiar zonal winds. For Jupiter and Saturn, internal gravity waves generated by nontidal mechanisms probably control the homopause.