Vol.2, No 8, 1998 pp. 801 - 805
UDC: 531
CONTEMPORARY PROBLEMS OF MECHANICS
VIEWED THROUGH THE 5TH GREEK NATIONAL CONGRESS
ON MECHANICS
Petar V. Vukoslavčević
Department of Mechanical Engineering, University of Montenegro, Yugoslavia
Abstract. A view of contemporary problems on Mechanics through the
paper presented on the 5th Greek National Congress on Mechanics is given.
The analysis is primarily based on the invited papers because they should
present "the state of art" in a given area. A short report on the Congress
organization is also given.
1. INTRODUCTION
The 5th Greek National Congress on Mechanics was held at the University
of Ioannina in Greece from the 27 to 30 of August 1998. Congress was organized
by the Hellenic Society for Theoretical and Applied Mechanics (HSTAM),
a member of IUTAM, founded 1978. Congress general chairman was Christos
V. Massalas, rector of the University of Ioannina, and the organizing committee
was formed by the representatives from the best known Greek universities
(university of Patras, Athens, Ioannina, Thessaloniki, ...) and Academy
of Athens, whose main subject of interest was Mechanics. The scientific
sponsor of the Congress was HSTAM and besides the universities of Ioannina,
Patras, Athens and Chaina, Congress was sponsored by the General Secretariat
of Research and Technology, Ministry of Culture, Technical Chambre of Greece
and several companies, like System Informatics, Epsilon Software and so
on.
Although organized as a national congress and attended mainly by Greek
scientists, a large number of contributions from all of the world were
presented: USA, Yugoslavia, France, England, Canada, Ukraine, Bulgaria,
Sweden, Russia, Germany, Kuwait, Poland, Ireland, Netherlands and Israel.
The most of foreign presentation came from USA, having a common characteristics
of joint research programs between USA and Greek universities. The similar
situation was with the paper from Germany and England while the contributions
from Yugoslavia were mainly done by Yugoslav authors only. The social part
of Congress was conducted in an excelant way.
2. CONTEMPORARY PROBLEMS ON MECHANICS
As it is usually for this type of congresses a broad range of topics was
covered. The program contained following sections: Special Topics on Mechanics,
Non-Smooth Mechanics, Scattering Theory and Elasticity, Non-Linear Problems,
Beams, Plates and Shells, Numerical Method in Solids, Composite Materials
and Structures, Mixtures, Fluid Mechanics, Numerical Methods in Fluids,
Micromechanics, Structural Analysis and Design, Biomechanics, Stability
of Systems, Fracture Mechanics, Numerical Methods for Evaluation PDEs,
Thermal Effects, Vibrations and Waves and Boundary Element Method.
To give a good analysis of presented papers and point out the best
contributions, it would be necessary to have an expert for each topic.
One other approach could be to give a presentation of invited papers because
they should be the "State of Art" in a given area. Almost all sections
had an invited paper, so all topics were practically covered.
The Congress started with Plenary section, Special Topics on Mechanics,
with three presentations and then at the beginning of almost all of the
sections an invited lecture was presented as follows:
M. Hayes, University College Dublin, Ireland, gave a presentation on
wave propagation in homogeneous anisotropic elastic materials. For
homogeneous plane waves it is shown that the group velocity is normal to
the slowness surface. The argument presented is valid whether or
not there are internal constraints such as incompressibility. The
Fedorov & Fedorov decomposition of the acoustical tensor valid for
RTHC (orthorhombic, tetragonal, hexagonal, cubic) crystals is introduced
and used to show how bounds may be obtained on the squared wave speeds.
Inhomogeneous plane waves are also considered.
F. P. J. Rinwott, University of Toronto, Toronto, Canada, proposed
a physical principle to describe the behavior of dissipative gyroscopic
systems, based upon the tendency of the angular momenta with respect to
the common mass centre of the individual gyros forming the system to strive
for collinearity.
B. Tabarrok, University of Victoria, Canada, reviewed on the conservation
properties in certain functionals in classical dynamics as well as the
functional of higher order and several independent variables. These inherent
properties are then generalized and used in finite element analysis to
check the quality of computed solutions and to improve the mesh for more
accurate solutions.
Z. Naniewicz, Warsaw University, Poland, discussed on the regularity
of the nonlinear term in hemivariational inequalities considered on vector-valued
Sobolev spaces. This term expresses the virtual work of the nonmonotone
multivalued stress-strain or reaction-displacement law, which gives rise
to the hemivariational inequality under consideration.
G. Simitses, University of Cincinnati, U.S.A., gave a presentation
about the problem of instability of imperfect, laminated, moderately thick,
circular cylindrical shells under the action of individual and combined
application of uniform axial compression and external lateral pressure.
The analysis is based on nonlinear kinematics relations, where the effect
of transverse shear deformation is taken into account The buckling is assumed
to be elastic and the geometry to have initial geometric imperfections.
A solution methodology has been developed and employed in generating results.
The imperfection sensitivity is investigated. The results obtained
indicate that geometric imperfections have small effect on the limit point
load for moderately thick cylindrical shells. In addition, limited
parametric studies have been made in order to assess the effect of length
to radius ration, radius to thickness ration and stacking sequence on the
critical loads.
D. Weichert, Institute of General Mechanics RWTH Aachen, Germany, presented
numerical and experimental results on the geometrically and physically
non linear dynamic response of metal plates to impulsive pressure loading.
He also discussed the efficiency of alternative material models to represent
correctly the measured vibrations of the investigated plates.
S. Radev, Bulgarian Academy of Sciences, Bulgaria, in a joint research
with the scientist from the University of Provence – France, gave a presentation
on the disintegration of an infinite axisymmetric viscous liquid column
surrounded by a gaseous or viscous liquid medium, simulated numerically
by using a streamfunction-vorticity formulation of the Navier-Stockes equations.
Along one wavelength the evolution of the disturbances is followed from
a given initial perturbation to the jet break-up. It is shown that
initial cosinusoidal disturbance retains a similar form at the first stages
of its evolution in time. Due to the appearance of multiple harmonics
the surface profile is transformed to a cosinusoidal form, which contains
a satellite drop attached to the main one. It is shown that the size
of the satellite is strongly connected to the wavelength and that the amplification
rate of the temporally growing disturbances is time dependent except for
the initial time interval.
M. Fremond, Laboratoire des Materiaux et des Structures du Genie civil,
France, showed on three examples that in three-dimensional solid mechanics
the macroscopic power of the interior forces seems to have a very fixed
even intangible expression what can be modified or adapt to the problem
under consideration. The first example is devoted to microscopic movements
which modify the macroscopic properties of materials. The second
example deals with new materials of civil engineering made of a large number
of long fibres buried in a solid. The last example is devoted to
the old and complex problem on collisions of rigid bodies. The basic
idea which is developed is that the system made of a point moving with
respect to a rigid body is deformable since the distance of the point to
the body changes.
Ch. C. Chamis, NASA Lewis Research Center, Cleveland, USA, described
a computational simulation methodology for probabilistic design/analysis
of engine blades. The methodology is demonstrated by applying it
to rotating engine structural components subjected to cyclic mechanical
and thermal loads. A unified multi-factor interaction model developed
at NASA Lewis Research Center is used to account for the degradation of
material properties caused by cyclic loads. Computational simulation
of acoustic fatigue in composite blades is also described. Results
show that fatigue of metal blades is ten times the number of cycles to
initiate damage. Additionally, degradation of vibration frequencies and
modes proved guidelines for configuring in-service health monitoring systems.
K. Hedrih, University of Niš, Yugoslavia, introduced the "support"
vectors of the body mass linear moment as well as of the body mass inertia
moment for the pole 0 and axis oriented by unit vector . Some
knowledge about change (rate) in time and time derivatives of the body
mass linear moment vectors and body mass inertia moment vectors for the
pole and axis for the different properties of the body dynamics are pointed
out. By using mass moment vectors and their derivatives, the linear momentum
and angular momentum of the rotor which rotates around one or two rotation
axes are expressed simpler then the other ways.
P. D. Spanos, Rice University, Houston, USA, reviewed on recent developments
in ARMA based simulation of random fields in conjunction with Monte Carlo
studies of probabilistic mechanics problems. The presentation complemented
some of the previous review articles and compared various simulation algorithms,
assesses their relative computational efficiency and versatility. Univariate,
uni-dimensional, Gaussian, and homogeneous fields for tutorial effectiveness
are considered. Nevertheless, appropriate reference are included
addressing the simulation of more general fields.
G. Zloković, Serbian Academy of Sciences and Arts, Yugoslavia, presented
his novel concept of group supermatrices based on utilization of symmetry
properties of a configuration in mechanics, with the object to derive mathematical
description in the most reduced form and to construct the algorithms which
bring the amount of numerical calculation to a minimum. The new method,
called the group supermatrix procedure, provides maximum utilization of
symmetry properties of the configuration, which is realized by a straightforward
and uniform process. In comparison with conventional formulation,
the group supermatrix procedure provides substantially shorter derivation
and much simpler mathematical description, as well as drastically reduced
amount of computation and need for memory space of the computer. The procedure
is also extended for systems without symmetry properties, which is accomplished
by symmetrization of the structure, i.e. by adding fictitious structural
parts or removing existing ones, which is formulated by additional conditions
at the borders of these parts.
3. CONCLUSION
The congress covered a broad range of topics giving a good insight in actual
problems in Mechanics, not only in Greece but at the many research centers
and universities all over the world. Both, the scientific and social programs
were very well organized and it was a real pleasure to take part in such
an event.
APPENDIX
Lectures and authors from Yugoslavia:
P. V. Vukoslavčević and D. V. Petrović: The probability density distribution
of the vorticity vector field in the mear wall region of turbulent bondary
layer;
D. Ivanović: Magnetic induction influence on velocity field and separation
point of MHD unsteady plane incopressible boundary layer on aerofoil;
R. M. Bulatović and M. Kazić: Some results on the stability of conservative
gyroscopic systems;
M. Kazić: Potential energy of the nonconservative systems. Energy integral;
N. Kažić: On the steady-state of storage device with phase change material.
Sponsors of Yugoslav authors:
Montenegro Academy of Sciences and Aluminijumski kombinat Podgorica
and Yugoslav Federal Ministry for Development, Science and Environmental
Protection.
Sessions:
Special Topics in Mechanics,
Non-smooth Problems,
Non-Linear Problems,
Scattering theory and Elasticity,
Beams, Plates and Shels,
Numerical Methods in Solids,
Composite Materials and Structures, Mixtures,
Fluid Mechanics,
Micromechanics,
Structural Topics on Mechanics,
Structural Analysis and Design;
Biomechanics,
Vibrations and waves,
Fractures Mechanics,
Thermal Effects,
Stability of Systems
Boundary Element Method
Numerical Methods for Evolution PDE.
Publications:
- 5th National Congress on Mechanics - Congress Programm, University
of Ioannina, 1998, pp. 31;
- 5th National Congress on Mechanics - Abstracts, University of Ioannina,
1998, pp. 132;
- 5th National Congress on Mechanics - Proceedings Vol. 1 and Vol.
2, edited by Academician P. S. Theocaris,
Professors D. I. Fotiadis and C. V. Massalas, University
of Ioannina, 1998, pp. 1149.
SAVREMENI PROBLEMI MEHANIKE
KROZ PRIKAZ PETOG GRČKOG NACIONALNOG KONGRESA
MEHANIKE
Savremeni problemi mehanike su istaknuti kroz prikaz predavanja i naučnih
saopštenja učesnika Petg grčkog nacionalnog kongresa mehanike. Analiza
se primarno bazira na radovima po pozivu jer oni predstavljaju "poslednju
reč" u datoj oblasti. Kratak prikaz organizacije kongresa je takođe dat.
