Journal of Theoretical and Applied Mechanics
Volume 33, Number 3, 2003
Acad. G. Bonchev Str., block 4
N THE SYNTHESIS AND COMPUTER DESIGN OF SPIROID GEARS:
A REVIEW OF THE BULGARIAN APPROACH
Abstract. Some aspects of the
synthesis and computer design of Spiroid gears taking into account their specific
characteristics are treated (Spiroid and
Key words: gearing, synthesis and design pitch contact point, region of mesh, estimation criteria.
Acad. G. Bonchev Str., Bl. 4, 1113
NUMERICAL AND EXPERIMENTAL INVESTIGATION ON THE DYNAMIC RESPONSE OF VIBRATION MOUNTS SUBJECTED TO LARGE STATIC AND DYNAMIC HORIZONTAL AND VERTICAL DEFORMATIONS
Abstract. Shock protection mounts comprising viscous-elastic elements, are widely used in modern warship design to reduce the high accelerations imposed by non-contact underwater explosions. However, predictions of the behaviour of viscous-elastic materials in this severe loading regime present a significant challenge due to the large strains and strain rates imposed in the viscous-elastic elements. The objective of this paper was to investigate the dynamic response of a “benchmark” model and a “back-to-back benchmark” model, which basically is a combination of two “benchmark” models mounted in series are subjected to defined shock input loading and a correlation against the experimental test results was performed. Both ELASTIC and HYPERELASTIC options within the ABAQUS code were used in the Finite Element (FE) analysis to cover the full range of deformation magnitudes. An ELASTIC analysis suffices up to a nominal 50% strain level, above this an HYPERELASTIC analysis is needed to reproduce good correlation with experimental data. Dynamic transient responses of half-sine shock impact in vertical and lateral direction are measured and compared with the FE optimal mesh prediction.
Key words: shock and vibration protection, Finite Element (FE) analysis, viscous-elastic mounts, dynamic transient responses, half-sine shock impact.
University “Prof. Dr. Assen Zlatarov” – Bourgas,
1, Prof. Yakimov Str., 8010
Application of an Ultrafiltration Module with Screw Mixers
Abstract. An ultrafiltration process in specially designed tubular module having an insert with thread guide mixers is investigated. The experiments were carried out under stationary conditions - Re 2000 and temperature 20°C with 3% aqueous solution of dextrin with molecular weight 40 000 Da. The insert placed in the membrane is cylindrical surface with a certain number of double-start thread guides cut on it, so that they change screwing direction, and the beginning of the next thread is rotated by 90° vs. the end of the former one. The process productivity is found to increase compared to the experiments with flat cylindrical insert and a membrane without an insert.
Key words: ultrafiltration, concentration polarization gel layer.
N. Georgiev, C. Kouyumdjiev
Technical mechanics, “Angel Kanchev”
e-mail: email@example.com, firstname.lastname@example.org
Acad. G Bonchev
Str., Bl. 10, 1113
e-mail: email@example.com, firstname.lastname@example.org
Isothermal investigation of stress relaxation
IN metallic glass Co58 Ni10 Fe5 B16 Si11
Abstract. An investigation of stress relaxation in the metallic glass Co58 Ni10 Fe5 B16 Si11 is presented. Isothermal annealing of pre-stressed samples is carried out at five temperatures in the range of 573°?673° K. Using the Luborsky bending method the stress relaxation curves are plotted. They are described satisfactorily by the Kohlrausch equation. Second annealing of the samples is conducted to eliminate the anelastic deformation in the material and the related residual stress. In this way the viscous-elastic deformation is revealed. The activation energy of the relaxation and the time constant in the Kohlrausch equation are determined.
Keywords: stress relaxation, metallic glasses.
A. Baltov, M. Datcheva
Acad. G. Bontchev Str., bl.4, 1113
e-mail: email@example.com, firstname.lastname@example.org
Key words: elasto-plastic localization, conditions for localization initiation, unsaturated soil.
Central Laboratory for Seismic Mechanics and Earthquake Engineering (CLSMEE),
Bulgarian Academy of Sciences, Acad. G. Bonchev Str., Bl. 3, 113 Sofia, Bulgaria,
Abstract. An investigation of SH wave propagation trough multilayer geological media is presented. An original structural model of the geological column is developed. The layers are isotropic with constant depth and parallel to the skyline. SH rays are with arbitrary angle in regarding to the layers. The main results of the study are illustrated graphically. The comparison between the experimental and the numerical surface signals (direct problem) for the considered geological column is shown.
Key words: structural model, digital seismic signals, power spectral density.