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BULGARIAN ACADEMY OF SCIENCES NATIONAL COMMITTEE OF THEORETICAL AND APPLIED MECHANICS Journal of Theoretical and Applied Mechanics
Print ISSN: 0861-6663 Online ISSN: 1314-8710
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JTAM, Sofia, vol. 53 Issue 3 (2023) |
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PREFACE TO THE SPECIAL ISSUE DEDICATED ON THE 80TH ANNIVERSARY OF PROF. STEFAN RADEV Sonia Tabakova Institute of Mechanics, Bulgarian Academy of Sciences
This special issue is dedicated to Prof. Stefan Radev, an eminent scientist in the field
of applied mathematics and mechanics, and a long-standing editor-in-chief of the
Journal of Theoretical and Applied Mechanics since 1999. On 25th September 2022
he celebrated his 80th birthday.
JTAM, Sofia, vol. 53 Issue 3 pp. 203-205 (2023), [Full Article]
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NOTES ON THE RESEARCH AT THE DEPARTMENT OF FLUID MECHANICS OF THE INSTITUTE OF MECHANICS OF THE BULGARIAN ACADEMY OF SCIENCES Nikolay K. Vitanov,, Krasimir Georgiev Institute of Mechanics, Bulgarian Academy of Sciences, Acad. G. Bonchev str., Bl. 4, 1113 Sofia, Bulgaria
In this article, we present several remarks on selected topics
of research in fluid mechanics at the Institute of Mechanics of the Bulgarian
Academy of Sciences. A large part of the discussed results are from the years
when Professor Stefan Radev was the Chair of the Department of Fluid Mechanics
at the Institute of Mechanics. The topics include the optimum theory
of turbulence, methodology for solving differential equations related to the motion
of waves in fluids, and the application of time series analysis to problems in
environmental fluid mechanics. Special attention is given to Professor Radev’s
participation in this research.
JTAM, Sofia, vol. 53 Issue 3 pp. 207-230 (2023), [Full Article]
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UNSTEADY POISEUILLE FLOW OF CARREAU–YASUDA FLUID IN A PIPE. SOLUTION EXISTENCE N. Kutev1, St. Radev2, S. Tabakova2 1Institute of Mathematics and Informatics, Bulgarian Academy of Sciences, Acad. G. Bontchev str., bl. 9, 1113 Sofia, Bulgaria 2Institute of Mechanics, Bulgarian Academy of Sciences, Acad. G. Bonchev str., Bl. 4, 1113 Sofia, Bulgaria
The Poiseuille flows of non-Newtonian fluids may have complicated
structures depending on the rheological characteristics of the fluid.
The Carreau-Yasuda viscosity model is often used to describe the behaviour of
many complex fluids. The Poiseuille flow of such fluids has many applications
and occurs as a fundamental problem from a practical and theoretical point of
view. At high shear rates, the flow may become unstable, then the Poiseuille
flow problem may have no solution. In this paper, we prove the condition for
the existence of its classical solution.
JTAM, Sofia, vol. 53 Issue 3 pp. 231-243 (2023), [Full Article]
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FLOW PROPERTIES IN THE PROBLEM OF SPOTS CHAIN WITH INTERVALS V.A. Gushchin, I.A. Smirnova Institute for Computer Aided Design Russian Academy of Sciences, 19/18, 2nd Brestskaya str., Moscow, Russia
Authors solves the problem of spots chain dynamics with initial
intervals of mixed liquid in stratified environment, and viscous flow using
the numerical splitting method for studying incompressible fluid flows (SMIF
method). The SMIF method is characterized by minimal scheme dissipation
and dispersion. The finite difference scheme has the second order of approximation
in terms of spatial variables. The fields of the stream function are
obtained, which are used to study the spots chain dynamics using the example
of characteristic variant with given parameters of the values of the Reynolds
and Froude numbers and initial intervals between spots.
JTAM, Sofia, vol. 53 Issue 3 pp. 244-252 (2023), [Full Article]
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EFFECT OF SLIP BOUNDARY CONDITIONS ON NONEQUILIBRIUM REACTING AIR FLOWS L. Shakurova1,2, I. Armenise3, E. Kustova1,2 1Saint-Petersburg State University, 7/9 Universitetskaya nab., St. Petersburg, 199034 Russia 2Federal Research Center “Computer Science and Control” of the Russian Academy of Sciences, 44-2 ul. Vavilova, Moscow, 119333, Russia 3CNR ISTP (Consiglio Nazionale delle Ricerche, Istituto per la Scienza e Tecnologia dei Plasmi), Sede Secondaria di Bari, Via Amendola 122/D, 70126, Ba
We study the effect of slip boundary conditions on the kinetics,
dynamics, and heat transfer in a strongly nonequilibrium flow with coupled vibrational
relaxation, state-specific gas-phase and surface reactions. Two types
of kinetic boundary conditions are introduced: whereas one ensures number
flux conservation, the second conserves the mass flux. Both kinetic boundary
conditions are suitable for state-to-state flow simulations and take into account
gain and loss of particles on the surface due to recombination and excitation/
deactivation of vibrational states. On the basis of the proposed kinetic
conditions, the velocity slip, temperature jump and species normal mass fluxes
on the surface are derived. The models are used for numerical simulations
of a five-component air mixture along stagnation line. The effects of kinetic
boundary condition, diffusion model, accommodation coefficients are evaluated
for different rarefaction degree. Important effect of diffusion model and
temperature jump on the fluid-dynamic variables and heat flux is shown.
JTAM, Sofia, vol. 53 Issue 3 pp. 253-269 (2023), [Full Article]
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CONTACT EQUILIBRIUM OF PLASMA SYSTEMS UNDER DIFFERENT ISOLATION CONDITIONS Maria A. Rydalevskaya, Yulia N. Voroshilova Saint Petersburg State University, 7/9, Universitetskaya nab., 199034, St. Petersburg, Russia
In this work, the influence of interactions between multi-component
plasma systems on their equilibrium compositions is studied. Equilibrium
densities of atoms, ions and free electrons in these systems are determined
by integration of distribution functions over the space of momentum and summation
over electronic energy levels. These functions correspond to the maximum
entropy for the combination of systems under different conditions of their
interaction. Special attention is given to monatomic plasma mixtures under following
situations: 1) the systems may exchange only energy; 2) the systems
may exchange energy and electrons; 3) the systems may exchange energy, electrons
and some chemical elements.
JTAM, Sofia, vol. 53 Issue 3 pp. 270-288 (2023), [Full Article]
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A STOCHASTIC NUMERICAL APPROACH CONSIDERING UNCERTAIN-INPUT PARAMETERS FOR PHOSPHORUS REMOVAL IN CONSTRUCTED WETLANDS Konstantinos Liolios International Hellenic University, Department of Environmental Engineering, Sindos, Thessaloniki, Greece
A stochastic numerical approach for the operation problem concerning
the removal of contaminants in Horizontal Subsurface Flow Constructed
Wetlands (HSF CW) is presented. Emphasis is given to uncertain-but-bounded
input-parameters, which are considered as interval parameters with known upper
and lower bounds. For the treatment of this uncertainty, the Monte Carlo
method is used. The proposed methodology consists of applying the Monte
Carlo procedure by solving the deterministic problem for each of the datasamples.
Atypical case of a HSF CW unit, concerning Total Phosphorus (TP)
removal, is used in a numerical example. The reliability of the proposed
stochastic approach is proved by comparing the numerical results with available
experimental ones.
JTAM, Sofia, vol. 53 Issue 3 pp. 289-295 (2023), [Full Article]
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A STOCHASTIC APPROACH FOR POUNDING EFFECTS ON THE SEISMIC RESPONSE UNDER UNCERTAINTY OF ADJACENT STRUCTURES STRENGTHENED BY CABLE-TIES Angelos Liolios Hellenic Open University, School of Science and Technology, Patra, Greece
The Civil Engineering structural mechanics praxis includes framed
buildings of reinforced concrete (RC). The present study deals with a stochastic
numerical treatment for the pounding problem concerning the seismic interaction
between adjacent RC framed structures strengthened by cable-ties when
the input parameters are uncertain-but-bounded. This problem concerns here
the unilateral contact between neighbouring RC structures during earthquakes
and is considered as an inequality problem of dynamic structural contact mechanics.
The Monte Carlo method is used for treating the uncertainty concerning
input parameters. The purpose here is to estimate numerically and to
control actively the influence of the cable-ties on the seismic response of the
adjacent structures. Finally, in a practical case of two seismically interacting
framed RC structures, the effectiveness of the proposed methodology is shown.
JTAM, Sofia, vol. 53 Issue 3 pp. 296-312 (2023), [Full Article]
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