Issue 3

JTAM, Sofia, vol. 40 Issue 3 (2010)

Planning of Movement Laws Using Trigonometric Polynomials

V. Galabov1, R. Rousev2, N. Chivarov3
1Technical University Sofia, Department of Theory of Mechanisms and Machines,TU-Sofia, Block 4, Sofia, Bulgaria
2Technical University Gabrovo, Department of Textile Techniques and Technology,TU-Gabrovo, Block 2, Gabrovo, Bulgaria
3Central Laboratory of Mechatronics and Instrumentation, BAS, Acad.G. Bonchev St., Bl. 2, Sofia 1113, Bulgaria

Trigonometric polynomials are studied in view of their utilization in planning of movement laws of the working particles of mechanisms, machines and robots. Special attention is paid to movements in which one of the obligatory conditions is the nullification of velocities and accelerations at the beginning and at the end of the effectors displacement.

JTAM, Sofia, vol. 40 Issue 3 pp. 01 (2010)

Contaminant Removal in Horizontal Wetlands: Investigation via Numerical Simulation of Groundwater Unconfined Flow

Konstantinos Liolios1, Vassilios Tsihrintzis1, Stefan Radev2
1Democritus University of Thrace, Department of Environmental Engineering, Laboratory of Ecological Engineering and Technology, GR-67100 Xanthi, Greece
2Institute of Mechanics (IMECH), Bulgarian Academy of Sciences (BAS), Acad. G. Bonchev St ,Bl. 4, 1113 Sofia, Bulgaria

The paper presents a numerical treatment of unconfined flow and contaminant removal in porous media. Emphasis is given to the horizontal subsurface flow in the constructed wetlands and to the evaluation of their removal and remediation efficiency. First the mathematical modelling is presented, leading to a boundary-initial value problem. Next, for the numerical simulation, the Visual MODFLOW code family, based on the Finite Difference Method, is used. Finally, the numerical procedure is applied for the simulation of pilot-scale units of horizontal subsurface flow wetlands, operated in Democritus University of Thrace, Xanthi, Greece.

JTAM, Sofia, vol. 40 Issue 3 pp. 02 (2010)

A Mathematical Model of Drip Emitter Discharge Depending on the Geometric Parameters of a Labyrinth Channel

Nina Philipova1, Nikola Nikolov1, Georgi Pichurov2, Detelin Markov2
1Institute of Mechanics, Bulgarian Academy of Sciences, Acad.G.Bonchev Str., Bl.4, 1113 Sofia, Bulgaria
2Technical University of Sofia, Dept. Hydroaerodynamics and Hydraulic Mashines , 8 Kliment Ochridsky boulevard., 1000 Sofia, Bulgaria

The influence of the geometric parameters, the dentition angle, the dentition spacing, the dentition height of an emitter labyrinth channel on the emitter discharge is investigated in the present paper. Numerical simulations of water flow movement are performed by using commercial programs GAMBIT and FLUENT according to the cubic central composite design. A mathematical model of the emitter discharge is derived depending on the above mentioned geometric parameters. It is established that the most important influence on the emitter discharge has the increase of dentation spacing B followed by the increase of the height H ang angle

JTAM, Sofia, vol. 40 Issue 3 pp. 03 (2010)

Upper and Lower Numerical Solution Bounds for Shear Walls

Angelos Liolios1, Asterios Liolios1, Stefan Radev2
1Democritus-University of Thrace, Dept. of Civil Engineering, Institute of Structural Mechanics and Earthquake Engineering, GR-67100 Xanthi, Greece
2Institute of Mechanics, Bulgarian Academy of Sciences, Acad. G. Bonchev St , Bl. 4 Sofia 1113, Bulgaria

A numerical approach for obtaining two-sided solution bounds for the problem of shear walls used in civil earthquake engineering buildings is presented. The numerical approach makes use of some functional analysis concepts and of the two known dual extremum variational principles of elasto-mechanics, namely the principle of the minimum potential energy and the principle of the minimum complementary energy. Based on the above principles, two special models of the Finite Element Method are constructed for the shear walls problem. The first model is a compatible displacement one and the second a stress equilibrium one.

JTAM, Sofia, vol. 40 Issue 3 pp. 04 (2010)

Motion of the Particles Due to a Viscoelastic Surface Wave of an Assigned Wavelength

Ts. Ivanov1, R. Savova2
1Faculty of Mathematics and Informatics, Sofia University St.Kl.Ohridski, 5, J.Bourchier Blvd, 1164 Sofia, Bulgaria
2Institute of Mechanics, Bulgarian Academy of Sciences, Acad. G. Bonchev St., Bl. 4, 1113 Sofia, Bulgaria

The motion of the material particles due to viscoelastic properties of the half-space is considered when the propagating surface wave has an assigned wavelength. The detailed examination shows that in the elastic case as well as in the viscoelastic case at different values of the viscous part of the Lame moduli the sense of the particle path along the ellipse is retrograde on the surface of the half-space and changes into direct inly once at depth about one seventh – one fourth of the wavelength. In contrast to the elastic case the ellipse axes in the viscoelastic case are not parallel and orthogonal to the surface of the half-space, respectively. Their orientation depends on the magnitude of the viscous part of the Lame moduli and tends to a constant at great depth. The numerical computations in the paper refer to some typical values of the Lame moduli and to some real materials (granite and shale).

JTAM, Sofia, vol. 40 Issue 3 pp. 05 (2010)

Seismic Structural Mechanics: Vulnerability Functions for Bridges of Egnatia Motorway in Northern Greece

Asterios Liolios1, Angelos Liolios1, Panagiotis Panetsos2
1Democritus University of Thrace, Department of Civil Engineering, Institute of Structural Mechanics and Earthquake Engineering, Xanthi, Greece
2Egnatia Odos S.A., Bridge Departement, Thermi-Thessaloniki, Greece

Fragility curves in Earthquake Civil Engineering represent a critically important step in seismic damage estimation process. In the present article, a simplified analytical methodology for the evaluation of vulnerability functions for bridges is presented. This methodology combines the nonlinear static pushover procedure and the capacity spectrum method, and is applied for establishing fragility curves for concrete bridges with seismic stoppers in mountains section of Egnatia Motorway, Northern Greece.

JTAM, Sofia, vol. 40 Issue 3 pp. 06 (2010)

Wear Behavior of a Peak Aged Cu-Co-Be Alloy

Yahya Altunpak
Mechanical Program, Abant Ä°zzet Baysal University, Gerede Campus, Bolu, Turkey

JTAM, Sofia, vol. 40 Issue 3 pp. 07 (2010)

Arch Dam Shape Optimisation Procedure Accounting for Dam Seismic Response

Stoyan Grigorov1, Stephan Tasev1, Anton Tzenkov2, Michele Fanelli3, Russell Gunn4
1IWP, Bulgarian Academy of Sciences, Acad. G. Bonchev Street, Bl.1, 1113 Sofia, Bulgaria
2EPFL, Swiss Federal Inst. of Technology, GC A3505, Station 18, CH-1015 Lausanne
3Former Director of the Centre for Hydraulic & Structural Research of ENEL, Italy
4STUCKY Ltd, Renens, Switzerland

The present study extends the procedure proposed by the authors in [1] and [2] for optimisation of the geometrical shape of arch dams subjected to static loads by taking into account the system’s dynamic characteristics and response to earthquake excitations. The dam shape geometrical parameters whose values are varied in order to satisfy a set of optimisation criteria are referred to as optimisation factors. A reasonable optimisation can be achieved by considering fifteen optimisation factors. The optimisation criteria include both a condition for a minimal volume of the dam body concrete and a condition for maximum dam safety. By means of a rational utilisation of the proposed procedure and a judicious selection of the factors, a significant reduction of the computing effort can be achieved which requires a definition of the optimal shape. The stress state caused by strong ground motions of Design Earthquake Level is defined by means of the spectral method and is superimposed to the usual load combination of self-weight and hydrostatic pressure for Maximum Impoundment Water Level. The optimal shape of the dam with minimum concrete volume is then defined by comparing the shapes for which the safety criteria are mat under usual and unusual load combination. The stress and strain fields, as well as the dynamic characteristics of the dam are defined by means of the Finite Element Method. Based on the proposed procedure, a computer program has been developed and used for shape optimisation analysis of existing and planned arch dams.

JTAM, Sofia, vol. 40 Issue 3 pp. 08 (2010)

Window Security Film Investigation by Optical Techniques

A. Shulev1, I. Roussev1, W. V. Paepegem2, J. Degriek2, S. De Pauw2, V. Sainov3, E. Stoykova3
1Institute of Mechanics , Bulgarian Academy of Sciences, Akad. G. Bonchev St., Bl. 4, 1113 Sofia , Bulgaria
2Ghent University, Dept. of Mechanical Construction and Production, Sint-Pietersnieuwstraat 41, 9000 Gent, Belgium
3Central Laboratory of Optical Storage and Processing of Information (CLOSPI-BAS),Bl. 101, Akad. G. Bonchev St., 1113 Sofia , Bulgaria

Knowing exact behaviour of the existing window security films when subjected to mechanical stresses is important for their further improvement and development. Security films are laminated to the glass windows by means of special adhesives and when breaking, the film keeps all glass fragments together. In this paper we present an experimental study of standard glass samples retrofitted with security film. To reveal their properties two different tests were made. First, round specimens were impacted with dropping weights. The dynamic out-of-plane deformations were measured by a fringe projection (moiré) technique. To extract the phase from the obtained fringe patterns, numerical algorithms based on Windowed Fourier Transform were used. Next, to learn more about unsticking resistance of the composite, the security film behaviour was studied via stretching parallel samples across a linear crack in the glass pad. To measure the 2D in-plane deformations a digital speckle-photography was applied. The local displacement fields were calculated by digital image correlation technique with sub-pixel resolution routine.

JTAM, Sofia, vol. 40 Issue 3 pp. 09 (2010)

Segmental Parameters of Bulgarian Man within Modified Know Human Body Model

Gergana Stefanova Nikolova
Institute of Mechanics, Bulgarian Academy of Sciences, Acad. G. Bonchev St., Bl. 4, 1113 Sofia, Bulgaria

We present a new modified geometrical model of the Bulgarian man. The model, which represents a modification of the one suggested in [1], is based on our own anthropometric measurements of 50 men aged between 30 - 40 years that complement the data taken from the representative anthropological investigation of Bulgarian males [2], in which data for 2435 individuals have been collected. Using the model, we calculate the mass-inertial parameters for all the segments of the human body deriving the corresponding analytical expressions needed. Wherever possible, we present a comparison between the results obtained within this model with our previous results reported in [3], as well as with other data for Caucasian reported in literature. We observe an overall good agreement among all of them. The investigation presented provides data for a set of parameters of the Bulgarian men for which no direct measurements are available. The model proposed is oriented to application in medicine (orthopaedics and traumatology) and engineering. It can predict parameters for the inertial parameters of a given male individual provided the corresponding easily measurable geometrical data for this individual are known.

JTAM, Sofia, vol. 40 Issue 3 pp. 10 (2010)

Multifractal Analysis of Narrow Band Filtered EEG Signals

P. Dojnow
Institute of Inorganic and General Chemistry, Bulgarian Academy of Sciences, Acad. G. Bonchev St., Bl.11, 1113 Sofia, Bulgaria

The ElectroEncephaloGrams (EEG) are multifractal time series with power-law decaying frequency spectrum from 0 Hz to over 100 Hz. In clinical practice the narrow-band filtered brain waves δ, θ, α, β, γ are used but their multifractal analysis is meaningless because as broad frequency spectrum and the phase changes which are diminished in the case of separation of the EEG signal into the brain waves.

JTAM, Sofia, vol. 40 Issue 3 pp. 11 (2010)