The S. P. Timoshenko Institute of Mechanics at the beginning of the third millennium

A brief historical review of the main scientific activities at the S. P. Timoshenko Institute of Mechanics, National Academy of Sciences of Ukraine, is outlined. Current trends are examined, in the Institute as a whole and in particular departments. As a resource, reviews of the Institute's activity published between 1955 and 1999 in this journal and elsewhere are listed in a bibliography. S. P. Timoshenko Institute of Mechanics, National Academy of Sciences of Ukraine, Kiev. Translated from Prikladnaya Mekhanika, Vol. 36, No. 1, pp. 6–24, January, 2000.     

III. Awards of the Presidium of the National Academny of Sciences of Ukraine to Scientists of the S. P. Timoshenko Institute of Mechanics

International Applied Mechanics -     

异面腔激光陀螺中的S-P各向异性效应

─本文理论分析了异面腔激光陀螺中由Ｓ一Ｐ相位和Ｑ的各向异性所引起的左、右旋椭圆偏振模式的非对称性。这种非对称性对激光陀螺性能的影响是至关重要的。     

A Numerical Solution of the Inverse Problem in Classical Celestial Mechanics,with Application to Mercury's Motion

It is attempted to obtain the masses of the celestial bodies, the initial conditions of their motion, and the constant of gravitation, by a global parameter optimization. First, a numerical solution of the N-bodies problem for mass points is described and its high accuracy verified. The osculating elements are also accurately computed. This solution is implemented in the Gauss iterative algorithm for solving nonlinear least-squares problems. This algorithm is summarized, and its efficiency for the inverse problem in celestial mechanics is checked on a 3-bodies problem. Then it is used to assess the accuracy to which a Newtonian calculation may reproduce the DE403 ephemeris that involves general-relativistic corrections. The parameter optimization allows one to reduce the norm and angular differences between the Newtonian calculation and DE403 by a factor 10 (Mercury, Pluto) to 100 (Venus). The maximum angular difference of the heliocentric positions of Mercury is ca. 220 per century before the optimization, and ca. 20 after it. The latter is still far above the observational accuracy. On the other hand, Mercury's longitude of the perihelion is not affected by the optimization: it keeps the linear advance of 43 per century.     

A critical re-appraisal of the jet-thrust technique for normal stresses,with particular reference to axial velocity and stress rearrangement at the exit plane

It is shown that the thrust, T, exerted by a jet on the tube from which it flows, and the corresponding die-swell ratio, D, are closely related and dependent on the axial velocity and stress profiles at the exit plane. Velocity-profile data, calculated by Tanner using a finite element method, have been used to demonstrate that for a Newtonian liquid the reduction in measured thrust from the expected value arises from a re-arranged, non-parabolic axial velocity profile and the related re-arranged non-zero axial stress profile at the exit plane. The axial stress re-arrangement is the major effect.Using the correction-curve thus derived to determine the normal stresses, ν₁ + $\text{1}\text{2}$ν₂ aqueous and non-aqueous polymer solutions gives values that are higher than the “correct” results by a significant, substantial amount. The difference is not due to neglect of the second normal stress difference, ν₂, nor to the neglect of the wall pressure at the exit plane, which is shown experimentally to be very small. It is suggested that the difference, which is a function only of the shear stress (or rate of shear) at the wall, may arise from a difference in the stress profile associated with the velocity re-arrangement at the exit between Newtonian liquids and elasticoviscous liquids for which the extensional viscosity may be high.