Study on stability of double corsair's main stand
The structure safety is numerically studied on main support of the huge pirate ship by use of finite element method (FEM). In order to the elements meshed successfully, the equivalent treatment is used for the complex structure. The static, structure instability and model analyses are carried out. The static and stability safe coefficient are 6.12 and 19, respectively, which are more than the demand in national standard. The model analysis indicates that the swing frequency is 0.08 Hz, and can be kept off the natural frequency.
Study of stability of large-scale thin-walled cylindrical shells under axial compression
The analysis of stability of large-scale thin-walled cylindrical shells in electric power engineering is a complex problem.Generally,the shells are subjected to axial compression and internal pressure.In this paper,DIN18800 is combined with GB150.The effects caused by initial imperfection,the length of adjacent stiffeners as well as large opening on stability of large-scale thin-walled cylindrical shells are studied through finite element analysis.The research shows that initial imperfection can reduce limit buckling stresses to be below one fourth of its ideal buckling stresses.In addition,the limit buckling stresses of thin-walled shells is markedly increased by ring stiffeners.Large opening can sharply weaken global stability of cylindrical shells.The results are helpful to the research on stability of thin-walled shells in both theoretical and practical significance.
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.