Issue 4

JTAM, Sofia, vol. 29 Issue 4 (1999)

Identification of the Velocity Characteristics of a Car Crash

V. Abadjiev, P. Gospodinov
Institute of Mechanics, Bulgarian Academy of Sciences, Acad.,G.,Bonchev Str., Bl. 4, 1113 Sofia, Bulgaria


An approach to the mathematical modelling of a car crash is proposed. It is based on the design of three models: a model of the events preceding the car crash, a model describing the impact process and a model of the events that take place after the crash. The dynamic process of a real accident, i.e. oblique impact is modelled on such a basis and the numerical values of the crash kinematic characteristics are obtained.

JTAM, Sofia, vol. 29 Issue 4 pp. 01 (1999)


Dynamics Analysis of Vehicle Running Gear Independent Mechanism with Lots of Wheels

N. Lilov, N. Nikolov
``V. Levski'' Higher Military Scool, Veliko Tarnovo, Bulgaria

In this article we determinate kinematic and dynamic characteristics of vehicle running gear independent mechanism with lots of wheels. We present the vehicle as spatial variation dynamic system which is built up of corps, wheels, bars, elastical elements and damping links. The assignment of the kinematics analysis is to determine the gear ratio vector from the corps to the wheels and bars. We propose numerical method for reproducing the system position as a function of general co-ordinates. In dynamic analysis we derive the differential equations of relative movements of the system. The results of the investigation justify new moments of a vehicle movement on the curve way.

JTAM, Sofia, vol. 29 Issue 4 pp. 02 (1999)


On the Effects of a Corrugated Boundary on Convective Motion

D. N. Riahi
Department of Theoretical and Applied Mechanics, 216 Talbot Laboratory, University of Illinois, 104 S. Wright Street, Urbana, Illinois 61801 U.S.A.

Effects of a corrugated lower boundary with small corrugation amplitude d on thermal convection with small amplitude e in an infinite horizontal porous layer are investigated for the whole range in (d,e) space. New types of flow solutions are determined and it is found that, depending on particular regimes in (d,e) space, boundary corrugation can have stabilizing or destabilizing effects on the resulting flow. The stabilizing or destabilizing effects of the corrugated surface explained in this paper have not yet been reported elsewhere. In addition, the new types of flow solutions derived and reported here can lead to preferential new types of flow patterns that are stabilized by the boundary corrugation.

JTAM, Sofia, vol. 29 Issue 4 pp. 03 (1999)


Sprinkler Device Modelling by Means of Experimental - Statistical Methods

N. Philipova1, T. Popov2
1Institute of Mechanics, Bulgarian Academy of Sciences, Acad. G. Bonchev Str., Bl. 4, 1113 Sofia, Bulgaria
2Institute of Water Problems, Bulgarian Academy of Sciences, Acad. G. Bonchev Str., Bl. 2, 1113 Sofia, Bulgaria

A sprinkler device of deflector type is considered as a multifactor object, and its constructive parameters as input factors. Their alteration is ensured by the developed design. As an output quantity is examined the application rate and its radial distribution. The purpose of the model is to establish the functional dependence between the alteration of the constructive parameters of the deflector device as input factors of the multifactor object and the application rate as an output quantity.

JTAM, Sofia, vol. 29 Issue 4 pp. 04 (1999)


Dynamic Large Deflection Analysis of Elastic-Plastic Beams and Plates

E. Manoach
Institute of Mechanics, Bulgarian Academy of Sciences, Acad.,G.,Bonchev Str., Bl. 4, 1113 Sofia, Bulgaria

In this paper large deflections of elastic-plastic beams and plates are investigated by the pseudo-normal mode superposition method. The geometrical non-linear versions of the Mindlin plate theory and the Timoshenko beam theory are used in the analysis. The results obtained numerically for the responses of beams and circular plates are compared with the published experimental and numerical results, as well as with the existing analytical solutions.

JTAM, Sofia, vol. 29 Issue 4 pp. 05 (1999)


Deformation and Fracture of Materials as an Evolutionary Processes on Statistical Basis

G. Zachariev1, A. Baltov2
1Central Laboratory of Physico-Chemical Mechanics, Bulgarian Academy of Sciences, Acad. G. Bonchev Str., Bl. 1, 1113 Sofia, Bulgaria
2Institute of Mechanics, Bulgarian Academy of Sciences, Acad. G. Bonchev Str., Bl. 4, 1113 Sofia, Bulgaria

The processes of inelastic deformation and fracture in strain-rate sensitive materials are investigated from a unified standpoint. It is assumed that these processes have a probabilistic thermofluctuational nature and obey the Boltzmann statistical law. A transfer from micro- to macrolevel is made using the effective parameters of kinetic equations both for inelastic deformation and fracture. The effective parameters take into account the local nature of processes in each macrospecimen. The approach is illustrated by experimental data.

JTAM, Sofia, vol. 29 Issue 4 pp. 06 (1999)


Dynamic Viscoelastic Behaviour of Phenol Resin Near the Gel Point

T. Roshavelov1, Ya. Ivanov2
1Military University of Civil Engineering `` L. Karavelov'', Sofia
2Central Laboratory of Physico-Chemical Mechanics, Acad. G. Bonchev Str., Bl. 1, 1113 Sofia, Bulgaria

The results from the investigations of dynamic viscoelastic behaviour of phenol resin during the process of its cross-linking are presented. It is shown that during this process when the gel point is reached the exponent ``n'' is the same for the real and imaginary parts of G* moduli. The values of ``n'' are determined and it is shown that they correspond to those predicted by the Rouse model.

JTAM, Sofia, vol. 29 Issue 4 pp. 07 (1999)


Effect of External Harmonic Temperature Variations on Solid Bodies Temperatures

Al. Zlatarski1, R. Tasseva2, A. Baltov2
1Niproruda JSCo., Industrial Heat Engineering Branch, 205, Al. Stamboliyski Blvd., 1309 Sofia, Bulgaria
2Institute of Mechanics, Bulgarian Academy of Sciences, Acad. G. Bonchev Str., Bl. 4, 1113 Sofia, Bulgaria

This paper describes a numerical simulation model created for one-dimensional heat conduction process for external harmonic temperature variations. Two cases are considered: for solid bodies with large linear dimension and for bodies with small linear dimensions. After a number of numerical experiments it is determined that (i) for large bodies and quick temperature variation the harmonic fluctuations quiet down quickly in a thin layer of the body surface, and (ii) for small bodies the temperature fluctuations permeate into the entire body. A detailed analysis is done of the numerical results gathered through a number of experiments and the perspectives for future investigations are outlined.

JTAM, Sofia, vol. 29 Issue 4 pp. 08 (1999)