Issue 1
JTAM, Sofia, vol. 28 Issue 1 (1998)

Global Vector Field Reconstruction for Non-Autonomous Systems

L. Le Sceller, C. Letellier, G. Gouesbet
University of Rouen, France


The problem of reconstructing a model of a non-autonomous system starting from a scalar time series is addressed. We consider the case when the driving force, also called the input, is unknown but assumed to be governed by a low-dimensional deterministic dynamics. It is then shown that an autonomous model whose dimension is higher than the non-autonomous system may be globally reconstructed.

JTAM, Sofia, vol. 28 Issue 1 pp. 01 (1998)

Modelling of Interfacial Separation of MMC Composites

M. Sejnoha, J. Sejnoha, P. Procházka
Czech Technical University, Czech

An efficient micromechanics-based approach is used to evaluate local stress and strain fields in two phase composite medium with debonded or imperfectly bonded interfaces. An finite element analysis of the unit cell model of a fibrous ply is used to obtain changes in local stress and strain fields caused by normal and tangential separation at the fiber-matrix interfaces. The evolution of decohesion process confined to a narrow region between the fiber and matrix is analyzed with the help of a simple cohesive zone model. In the present work, the onset of interfacial damage is governed by critical normal and shear tractions that are prescribed as interface fracture criterion. In addition, the constant shear resistance is assumed to account for presence of asperities at sliding parts of the interface. An interface element, derived to carry out the numerical analysis, is incorporated into representative unit cell and the local fields are found with the ABAQUS finite element code. Examples are presented for metal matrix SCS6/Timetal-21S system. The effect of time dependent behaviour of titanium based alloys is also considered.

JTAM, Sofia, vol. 28 Issue 1 pp. 02 (1998)
Convective Instabilities Obtained by a Local Heating of a Liquid

C. Rozé, S. Meunier-Guttin-Cluzel, G. Gouesbet
University of Rouen, France

Thermal lens oscillations and hot wire experiments are similar experiments in which a liquid is heated locally near and below its free surface by a focused laser beam in the first case or a hot wire in the second case. Last results concerning these two experiments are presented: Thermal lens oscillations have been conducted during the 23rd ESA parabolic flight campaign, showing that the instability stops during microgravity phase proving its convective character. On the other hand, infra-red imaging of the free surface in the hot wire experiment allows to visualize the spatio-temporal structure of the travelling waves.

JTAM, Sofia, vol. 28 Issue 1 pp. 03 (1998)
Electrohydrodynamic and Thermal Stimulation of Capillary Instability of a Conducting Jet

P. Atten, B. Barbet
Joseph Fourier University, Grenoble, France

Two different stimulation techniques are investigated. They consist in imposing an initial perturbation on a circular jet in order to obtain a very regular production of droplets. In the first technique, a periodic electrostatic pressure is applied on the jet surface. Results on multi- electrode EHD stimulation are given for synchronized and desynchronized regimes. With the two mode EHD stimulation the deformation shape can be modified and, in particular, a break-up of the jet without creation of satellite droplets can be obtained. The second stimulation technique is a thermal one where the light of a laser diode is focused on the jet surface. Imposing a one mode or two mode periodic modulation of the light intensity leads to results fully similar to those obtained with the EHD stimulation. It is shown that Marangoni convection associated with the gradients of surface tension is the dominant mechanism for inducing the perturbation.

JTAM, Sofia, vol. 28 Issue 1 pp. 04 (1998)
Kinetic Description of the Transfer Processes in Porous Media

N. Pavlyukevich1, St. Stefanov2, St. Radev2, V. Leitsina 1
1A. V. Luikov Heat and Mass Transfer Institute, Nat. Acad. Sci. Belarus, Minsk
2Institute of Mechanics, Bulg. Acad. Sci., Sofia

Different approaches of kinetic description of the transfer processes in porous media are considered. The Monte Carlo simulation results are presented for one- and two-layer porous medium.

JTAM, Sofia, vol. 28 Issue 1 pp. 05 (1998)
The Use of Speckle Photography in Composite Material Rheology

Ya. Ivanov1, V. Kavardjikov2, R. Kotsilkova2, D. Pashkouleva2, V. Stoyanov 2
1Central Laboratory of Physico-Chemical Mechanics, Bulg. Acad. Sci., Sofia
2Institute of Mechanics, Bulg. Acad. Sci., Sofia

The change in particles orientation in different zones of flow is established. An estimation of the wall sleep and the presence of conjugated flow on the behaviour of the anisometric particles in the stream is made. A special attention is paid to the evaluation of the effect of observed phenomena on the chaneges of flow velocity profile. Some results, obtained by using speckle photography in hemorheological studies: the solidification process of the filled liquid polymer composite and the change of its rheological properties, are demonstrated also.

JTAM, Sofia, vol. 28 Issue 1 pp. 06 (1998)
Theory for Type Deformational Sensitive Material

A. Baltov
Institute of Mechanics, Bulg. Acad. Sci., Sofia

A new theory for type deformational sensitive materials is proposed. Many materials possess such properties. We prefer to describe the mechanical processes with strain type control which insure in many cases the uniqueness of the stress-strain relation. The theory is based on: (1) the concept of strain space and strain subspaces with uniform type; (2) the introduction of the quadratic surfaces with constant stress level.

JTAM, Sofia, vol. 28 Issue 1 pp. 07 (1998)
Structural Simulation of Supercompressible Materials

S. Shilko, S. Stelmakh, D. Chernous, Yu. Pleskatchevskii
Metal-Polymer Research Institute, Nat. Acad. Sci., Gomel, Belarus

The work is devoted to study of supercompressibility effect, i.e. anomaly of elasticity, when Poisson's ratio becomes negative. The numerical results provide the conclusion that structural modelling of granular media, honeycomb structures and foams demonstrates the phenomena mentioned above. The new localization method for structural unity creation and control with predictable elastic and non-elastic properties has been developed.

JTAM, Sofia, vol. 28 Issue 1 pp. 08 (1998)
Prof. Dr. Dr. h. c. Franz Ziegler - 60 years!



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JTAM, Sofia, vol. 28 Issue 1 pp. 09 (1998)