Issue 4

JTAM, Sofia, vol. 18 Issue 4 (1987)

Kinematics and Kinetostatics of Spatial Mechanisms. Part 1. Kinematics of Spatial Mechanisms

E. Zahariev1, P. Genova2
1Inst. Mach. Biomech., Bulg. Acad. Sci., Bl. 8, Sofia
2High. Inst. Mech. Electr. Eng., Sofa

A generalized algorithm and a programme system are developed to model the kinematics of open and closed spatial mechanisms. The model itself is based on coordinate transformations and matrix equations. The closed kinematic chain analysis is reduced to a simultaneous analysis of loop chains, that form the polycontour mechanism. Generalized matrices of relative link disposition are used for the purpose. The numerical results are directed at force analysis, which is the next destination.

JTAM, Sofia, vol. 18 Issue 4 pp. 011-018 (1987), [Full Article]

Noise Generation in Vibrations of Mechanical Systems with Concentrated and Distributed Masses

S. Butchvarov, A. Djondjorov, K. Arnaoudov, L. Kountchev, K. Valtchev
High. Inst. Mech. Electr. Eng., Sofia

The paper studies dynamic processes in a mechanical system, which consists of a deformable beam and a non-deformable disk. The end of the beam represents a joint while the disk itself has been attached to the other end of the beam. The beam is subjected to linear elasticity and linear damping forces, which are applied at corresponding points. The mechanical system is a simple model of the front car suspension. It is used to examine high frequency vibrations that cause noise generation. The equations of motion and the average external resistance power are derived. The results are compared to the case, when the beam elasticity has not been taken into consideration.

JTAM, Sofia, vol. 18 Issue 4 pp. 019-024 (1987)

On the Decoupled Drive System Design of Industrial Robots

P. Kiriazov, P. Marinov
Inst. Mech. Biomech., Bulg. Acad. Sci., Bl. 8, Sofia

Industrial robots are strongly nonlinear and coupled dynamic systems. The dynamics becomes more complicated under load-velocity rise. A natural approach to dynamic complexity is a more independent link drive, which requires a modified design of the robot links and the joint actuators. The solution of the decoupled drive system design problem is based on the inertial matrix diagonal domination. A subsequent condition concerns the independent dynamic controllability of the joint motions. The existence of this condition is discussed. The purpose is to improve the dynamic performance, and the concepts are in accordance with it. Reliability of the robot control systems is ensured as well.

JTAM, Sofia, vol. 18 Issue 4 pp. 025-029 (1987), [Full Article]

Electric Interaction in Osteons

G. Brankov
Inst. Mech. Biomech., Bulg. Acad. Sci., Bl. 8, Sofia

The bone tissue electric properties are of great interest. They are caused by the outer form change, which is due to tissue dependence on the stressed-strained state and the electric effect appearance. The osteons are considered to be basic structure elements of the living bone. They are considered to be consisted of alternating collagen and hydroxylapatite concentric layers. Experimental investigations show that only the collagen layers (cylinders) are with piezoelectric properties. The electric charge average density is established by means of a molecular model. The electrostatic equations and the equations of elasticity are applied to determine the electric field. The Gauss law and the Poisson equation are used. Experimental investigations of Pollack, Korostoff, and others are used too.

JTAM, Sofia, vol. 18 Issue 4 pp. 030-037 (1987)

Similarity Analysis of a Dynamic Problem of Coupled Thermoelasticity

E. Varbanova
High. Inst. Mech. Electr. Eng., Sofia

One-dimensional dynamic problem of coupled thermoelasticity is studied. The coefficient of thermal conductivity is assumed to be strain dependent. Two classes of similarity solutions are obtained.

JTAM, Sofia, vol. 18 Issue 4 pp. 038-044 (1987), [Full Article]

Examination of Strain Wave Propagation in Thin Plates

M. Lozev

The paper presents experimental results of investigating the strain wave propagation peculiarities in thin plates. The peculiarities themselves are generated by an acoustic emission stimulator. The investigations have been carried out by means of standard installations, which enable bi-localization and spectral analysis realization of the acoustic emission signal. What is presented in connection with two steel types are some dependences of the basic acoustic emission parameters on the distance between the stimulator and the receiving sensor. The results are used to develop technologies in sheet material fractureless control.

JTAM, Sofia, vol. 18 Issue 4 pp. 045-048 (1987)

Numerical Experiments on the Process of Drop Formation in a Liquid Jets

S. Radev, V. Rakidzi
Inst. Mech. Biomech., Bulg. Acad. Sci., Bl. 8, Sofia

The present paper gives some numerical results in solving the break-up process problem of an infinite periodic axisymmetric jet that flows from a viscous incompressible fluid. Drop-formation is presented too. Different values of the surface-tension, the initial perturbation and the viscosity have been accounted for. The equations, the boundary value conditions and the problem algorithm are formulated.

JTAM, Sofia, vol. 18 Issue 4 pp. 049-052 (1987), [Full Article]

Closed Domain Convection Due to Particle Action

O. Melyhov1, I. Nikolova2
1Inst. Mech. Probl., Acad. Sci. USSR
2Inst. Mech. Biomech., Bulg. Acad. Sci., Bl. 8, Sofia

What is examined numerically is a closed domain gas convection due to the action of a particle distributed generator, which has been placed in the upper domain boundary. A two-speed model of the medium is used by a discrete description of the dispersed phase. An effect of particle focusing has been observed. Physical parameter influence on this effect is analyzed.

JTAM, Sofia, vol. 18 Issue 4 pp. 053-058 (1987)

Asymptotic Interpolation in Heat and Mass Transfer Convection Problems for Drops, Bubbles, and Flowing Solid Particles

A. Polyanin1, N. Kovatcheva2
1Inst. Mech. Probl., Acad. Sci. USSR
2Inst. Mech. Biomech., Bulg. Acad. Sci., Bl. 8, Sofia

A new simple method is proposed to construct approximation formulae. Some well-known asymptotics of the corresponding asymptotic interpolation problem are used. The method allows for a direct application of the asymptotic investigation results to engineering. New formulae are derived to calculate the heat and mass transfer intensity of solid particles, drops and bubbles with various flows. The results are compared with several particular cases, which can be verified by the existing exact and approximate formulae. Good accuracy and large possibilities of the assymptotic interpolation method are shown.

JTAM, Sofia, vol. 18 Issue 4 pp. 059-065 (1987)

On the System of Equations Solving Ferro-Concrete Sloping Shells with a Double Curvature and a Rectangular Base When the Material Creep Is Accounted for

Ch. Bin, I. Marchokov
High. Inst. Arch. Civ. Eng., Sofia

The investigation of ferro-concrete sloping shells with a double curvature and a rectangular base requires construction of the corresponding system of resolution equations. The paper proposes a system of integro-differential equations with a structure, that is. simpler than the structures already known. A simpler solution is obtained as a result. The system of resolution equations is applied to experimental investigations in the Institute of Architecture and Civil Engineering, Sofia.

JTAM, Sofia, vol. 18 Issue 4 pp. 066-070 (1987)

The Constitutive Equations of Thin Flexible Plate Behaviour under Impulsive Dynamic Loading and the Investigation of their Nonlinear Member Influence

O. Mintchev
Inst. Mech. Biomech., Bulg. Acad. Sci., Bl. 8, Sofia

The paper considers inelastically deformable thin flexible plates, which have been subjected to dynamic loading. The plates receive suspensions, that exceed the repeated order of the plate thickness. Criteria are derived to add nonlinear members to the equations, which describe total deformations and curvatures of rectangular and circular plates, respectively. The results have been compared. The change of a rectangular plate thickness under the indicated loading is considered specially.

JTAM, Sofia, vol. 18 Issue 4 pp. 071-079 (1987)

High Temperature Creep and Continuous Material Strength of Light Drill Pipes under Torsion

V. Gorbatenko
Polytechn. Inst., Kuibyshev, USSR

The continuous strength limit of light drill pipe materials depends on the loading type. It has been determined experimentally by means of pipe shape models. It is necessary to correct the computed light pipe efficiency by accounting for the anisotropy of the material mechanical properties. The efficiency itself has been computed near the continuous strength limit and under temperature rise.

JTAM, Sofia, vol. 18 Issue 4 pp. 080-084 (1987)