JOURNAL OF THEORETICAL AND APPLIED MECHANICS

Volume 29 Number 4 1999
CONTENTS





V. Abadjiev, P. Gospodinov.

Institute of Mechanics, Bulgarian Academy of Sciences,
Acad.,G.,Bonchev Str., Bl. 4, 1113 Sofia, Bulgaria,
e-mail: gospodin@bgcict.acad.bg

Identification of the Velocity Characteristics of a Car Crash

Abstract. 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.

Key words: mathematical modelling, car crash, car dynamics.



 N. Lilov, N. Nikolov.

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

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

Abstract. 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.

Key words: dynamics analysis, kinematic and dynamic characteristics.



 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.,
 e-mail: d-riahi@uiuc.edu

On the Effects of a Corrugated Boundary on Convective Motion

Abstract. 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.
Key words: convective motion, convection, thermal convection, non-linear convection, thermal stability.



 N. Philipova, T. Popov.

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

Sprinkler Device Modelling by Means of Experimental - Statistical Methods

Abstract. 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.

Key words: sprinkler irrigation, deflector profile, constructive parameters influence.



E. Manoach.

Institute of Mechanics, Bulgarian Academy of Sciences,
Acad.,G.,Bonchev Str., Bl. 4, 1113 Sofia, Bulgaria
fax: + 359 2 70 74 98, e-mail: manoach@bgcict.acad.bg

Dynamic Large Deflection Analysis of Elastic-Plastic Beams and Plates

Abstract. 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.

Key words: beams, plates, large deflections, pulse and impulse loading, elastic-plastic deformation.


G. Zachariev, A. Baltov.

G. Zachariev
Central Laboratory of Physico-Chemical Mechanics, Bulgarian Academy of Sciences,
Acad. G. Bonchev Str., Bl. 1, 1113 Sofia, Bulgaria,
e-mail: mezi@bgcict.acad.bg
A. Baltov
Institute of Mechanics, Bulgarian Academy of Sciences,
Acad. G. Bonchev Str., Bl. 4, 1113 Sofia, Bulgaria

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

Abstract. 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.

Key words: kinetic theory, fracture, durability, prediction, strength, viscoelasticity, viscoplasticity, damage.



T. Roshavelov, Ya. Ivanov.

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

Dynamic Viscoelastic Behaviour of Phenol Resin Near the Gel Point

Abstract. 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.

Key words: gel point, dynamic viscoelastic behaviour, phenol resin.



Al. Zlatarski, R. Tasseva, A. Baltov.

Al. Zlatarski
Niproruda JSCo., Industrial Heat Engineering Branch,
205, Al. Stamboliyski Blvd., 1309 Sofia, Bulgaria
R. Tasseva, A. Baltov
Institute of Mechanics, Bulgarian Academy of Sciences,
Acad. G. Bonchev Str., Bl. 4, 1113 Sofia, Bulgaria

Effect of External Harmonic Temperature Variations on Solid Bodies Temperatures

Abstract. 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.

Key words: numerical simulation model, external harmonic temperature variations.


back to main page