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731.
A finite element statement of solving problems on stability of reinforced elliptic cylindrical shells taking into account
momentness and nonlinearity of their subcritical stress strain state is presented. The explicit expressions for displacements
of noncircular cylindrical shell elements as rigid bodies are determined by integrating the equations obtained by equating
the components of linear strains to zero. These expressions were used to construct the form functions for an efficient quadrilateral
finite element of natural curvature. An efficient numerical algorithm of nonlinear deformation and stability of shells was
developed. The stability of reinforced elliptic cylindrical shells under combined loading by bending moment, transverse boundary
force and internal pressure is analyzed. We also examine how the critical loads are affected by the strain nonlinearity and
ellipticity of shell deformation at the subcritical stage. 相似文献
732.
I. S. Akhmed’yanov 《Russian Aeronautics (Iz VUZ)》2010,53(2):230-234
To complete study [1], the procedure of applying the numerical quadrature method to analyzing the shells of revolution under
axisymmetrical loading is presented. 相似文献
733.
A. N. Markushin V. K. Merkushin V. M. Byshin A. V. Baklanov 《Russian Aeronautics (Iz VUZ)》2010,53(1):63-68
The test results of a conventional combustion chamber with the improved structure are presented. The concentration of toxic
substance emissions is reduced as compared with combustion chambers of the similar type. 相似文献
734.
A. Gil M.V. Alania 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2010
We study the temporal evolution of the power rigidity spectrum of the first (27 days) and the second (14 days) harmonics of the 27-day variation of the galactic cosmic ray intensity measured by neutron monitors in the period of 1965–2002. The rigidity spectrum of these variations can be approximated by a power law. We show the rigidity spectra of the first and the second harmonics of the 27-day variation of the galactic cosmic ray intensity have similar time profiles. These spectra are hard (γ ≈ 0.5 ± 0.1) and soft (γ ≈ 1.1 ± 0.2) during solar maximum and minimum activity, respectively. We ascribe this to the alternation of the sizes of the modulation regions responsible for the 27-day variation of the galactic cosmic ray intensity in different epochs of solar activity. Especially, the average radial sizes of the modulation regions of the 27-day variation and the heliolatitudinal extension of the heliolongitudinal asymmetry are smaller during solar minimum than during solar maximum. We show also, that the temporal changes of the power rigidity spectra of the first and the second harmonics of the 27-day variation of the galactic cosmic ray intensity are in a negative correlation with the changes of the rigidity spectrum of the corresponding 11-year variation. 相似文献
735.
To calculate the unsteady helicopter motion, we propose a simplifying approach consisting in the fact that the numerical solution
of equations of nonlinear nonstationary aerodynamics and flight dynamics are made successively in time intervals. As an example,
the results of calculating the helicopter motion in descent are presented. The mathematical model and algorithm can be used
for calculating the unsteady motion of different helicopters. 相似文献
736.
Monika E. Kress Alexander G.G.M. Tielens Michael Frenklach 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2010
Interstellar material is highly processed when subjected to the physical conditions that prevail in the inner regions of protoplanetary disks, the potential birthplace of habitable planets. Polycyclic aromatic hydrocarbons (PAHs) are abundant in the interstellar medium, and they have also been observed in the disks around young stars, with evidence for some modification in the latter. Using a chemical model developed for sooting flames, we have investigated the chemical evolution of PAHs in warm (1000–2000 K) and oxygen-rich (C/O < 1) conditions appropriate for the region where habitable planets may eventually form. Our study focuses on (1) delineating the conditions under which PAHs will react and (2) identifying the key reaction pathways and reaction products characterizing this chemical evolution. We find that reactions with H, OH and O are the main pathways for destroying PAHs over disk timescale at temperatures greater than about 1000 K. In the process, high abundances of C2H2 persist over long timescales due to the kinetic inhibition of reactions that eventually drive the carbon into CO, CO2 and CH4. The thermal destruction of PAHs may thus be the cause of the abundant C2H2 that has been observed in disks. We propose that protoplanetary disks have a ‘soot line’, within which PAHs are irreversibly destroyed via thermally-driven reactions. The soot line will play an important role, analogous to that of the ‘snow line’, in the bulk carbon content of meteorites and habitable planets. 相似文献
737.
A. I. Golovanov 《Russian Aeronautics (Iz VUZ)》2010,53(3):243-249
The constitutive relations and plastic flow rule are derived from the thermodynamics equations. The known procedures of determining
the plastic strain rate value are described. A calculation algorithm is presented that is based on the incremental loading,
linearization of the virtual power equation and the projection method. A numerical example is presented. 相似文献
738.
In this paper, the results of an experimental study concerning average heat transfer in an annular channel with flow swirling
by an endless screw and spherical grooves on the convex surface are presented. Also analyzed is the heat and hydraulic efficiency
of grooves application under conditions being considered. 相似文献
739.
T. Blöcker H. Holweger B. Freytag F. Herwig H.-G. Ludwig M. Steffen 《Space Science Reviews》1998,85(1-2):105-112
Based on radiation hydrodynamics modeling of stellar convection zones, a diffusion scheme has been devised describing the
downward penetration of convective motions beyond the Schwarzschild boundary (overshoot) into the radiative interior. This
scheme of exponential diffusive overshoot has already been successfully applied to AGB stars. Here we present an application
to the Sun in order to determine the time scale and depth extent of this additional mixing, i.e. diffusive overshoot at the
base of the convective envelope. We calculated the associated destruction of lithium during the evolution towards and on the
main-sequence. We found that the slow-mixing processes induced by the diffusive overshoot may lead to a substantial depletion
of lithium during the Sun's main-sequence evolution.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
740.