Journal of Theoretical and Applied Mechanics, Sofia, vol. 52 Issue 1 (2022)

Table of contents



MODELING OF CROWD FLOWS — APPLICATION ON EEKLO FOOTBRIDGE

Krumka Kasapova1, Dobromir Dinev2, Katrien Van Nimmen3, Peter Van den Broeck3
1Mott MacDonald Ltd, Bulgaria
2University of Architecture, Civil Engineering and Geodesy, Bulgaria
3KU Leuven, Belgium


The essential purpose of the footbridges is carrying over pedestrians to a certain destination, ensuring their safety and comfort. Their design is not always an easy task, considering the huge variety of load impacts induced by human motion combined with the complexity of the structure itself. The natural frequencies of the contemporary footbridges belong to a lower range, close to the one of the excitation, following from the use of lightweight materials and extravagant constructive solutions (stress ribbon footbridges, suspension footbridges, long-span footbridges).
In the present article, an extensive study of an existing footbridge is performed. The dynamic analysis of the structure is conducted by employing a load model accounting for the human-human interaction.

JTAM, Sofia, vol. 52 Issue 1 pp. 003-018 (2022), [Full Article]




ENTROPY GENERATION RATE ARISING FROM FRACTIONAL OSCILLATOR MODEL WITH NON-SINGULAR KERNEL

Norodin A. Rangaig, Alvanh Alem G. Pido
Department of Physics, Mindanao State University-Main Campus, 9700 Marawi City, Philippines


The developing potential applications of fractional calculus in science and engineering excites many researchers because it can describe different nonlinear phenomena. In this present work, we have studied another physical implication of the fractional operator on the spring-mass model. We derive the fractional equation of motion by considering a fractional action-like integral via the fractional operator and obtaining a fractionally-modified Euler-Lagrange equation with fractionalized Lagrangian function. We have shown that the dissipative effect due to the fractional operators generates an entropy proportional to the fractional-order ν.

JTAM, Sofia, vol. 52 Issue 1 pp. 019-035 (2022), [Full Article]




INFLUENCE OF THE GEOMETRICAL IMPERFECTIONS IN THE CYLINDRICAL STEEL SHELLS LOADED BY AXIAL COMPRESSION

Lyubomir A. Zdravkov
Steel, Timber and Plastic Structures Department, Faculty of Structural Engineering, University of Architecture, Civil Engineering and Geodesy, Sofia 1046, 1 Hristo Smirnensky Blvd., Bulgaria


The classical analytical expression for critical compression stresses in the cylindrical shells in meridional direction σx,Rcr has been written by Lorenz, Timoshenko and Southwell at the beginning of XX century. During the natural experiments with those shells done later, it is obtained out that the stresses which cause the loss of stability are considerably different from those calculated by the analytical expression. In 1945 Koiter suggested that the primary reason for these differences are the imperfections in the shells. M. Tekleab attempted in her PhD thesis to determine the most unfavourable geometrical imperfection in the shells, pressured by their axis. Having encountered many incorrect results and conclusions in scientific publications, the author has decided to check the obtained conclusions.

JTAM, Sofia, vol. 52 Issue 1 pp. 036-049 (2022), [Full Article]




TORSIONAL WAVES PROPAGATION IN MICROPOLAR ELASTIC HALF-SPACE

Aarti Khurana, S.K. Tomar
Department of Mathematics, Panjab University, Chandigarh – 160 014, India


The possibility of propagation of torsional surface waves in a uniform micropolar elastic solid half-space is explored. For very poor value of a micropolar constant (𝒦), there exist three torsional modes propagating with distinct speeds. Out of these three {torsional modes}, only one mode is affected by the material parameters J, μ and γ. In the absence of micropolarity, the torsional surface waves transform into classical shear wave.

JTAM, Sofia, vol. 52 Issue 1 pp. 050-063 (2022), [Full Article]




MODELLING OF ULTRASONIC TEMPORARY AND RESIDUAL EFFECTS

Ali H. Alhilfi1, Andrew Rusinko2
1Misan University, Iraq
2Obuda University, Nepszinhaz St. 8, Budapest, H-1081 Hungary


This study discusses the phenomena of ultrasonic temporary softening and ultrasonic residual hardening registered in the experiments for plastic deformation of metals in ultrasonic field. This paper is aimed to model these phenomena in terms of the synthetic theory of irrecoverable deformation. We extend the flow rule relationships by two terms constructed on the base of microstructural processes occurring in ultrasound assisted deformation. The model results show good agreement with experimental data.

JTAM, Sofia, vol. 52 Issue 1 pp. 064-074 (2022), [Full Article]




A NEW DAMAGE DETECTION INDEX BASED ON BEAM MODE SHAPE SLOPE

Dimitrina Kindova-Petrova
Department of Technical Mechanics, University of Architecture, Civil Engineering and Geodesy, 1 Hristo Smirnenski Blvd, 1046, Sofia, Bulgaria


A new damage index, called mode shape slope difference (MSSD), is proposed to predict the damage locations in beam structures. Unlike most vibration based damage detection methods, which use the undamaged state of the beam as reference, the MSSD index utilizes only the damaged state. It is derived by using two different approximation formulas for the first derivative of the damaged beam mode shape. To assess the effectiveness and the accuracy of the MSSD index method two test examples of finite element models are considered. The results obtained demonstrate that the proposed damage index correctly predicts the damage locations in beam structures with single or multiple damages.

JTAM, Sofia, vol. 52 Issue 1 pp. 075-087 (2022), [Full Article]




EARTHQAKE-INDUCED PRESSURE SURGES IN AIR VALVES ON BURIED IRRIGATION PIPELINES

S. Petkova1, Y. Tanaka2, M. Ariyoshi2, Y. Kohgo3, D. Kisliakov1
1Department of Hydraulic, Irrigation and Drainage Engineering, University of Architecture, Civil Engineering and Geodesy, 1 Hr. Smirnenski Blvd., Sofia, Bulgaria
2Institute for Rural Engineering, National Agriculture and Food Research Organization, 2-1-6 Kannondai, Tsukuba, Ibaraki 305-8609, Japan
3Graduate School of Agriculture, Tokyo University of Agriculture and Technology, 3-5-8 Saiwaicho, Fuchu, Tokyo 183-8509, Japan


The main purpose of this paper is to present some aspects of a seismic induced performance of an air valve. The considered valve is an air release type widely used in irrigation systems. Since the physical modeling is a powerful tool for dynamic behavior assessment of engineering structures, a full-scale model of a tank – pipe – air valve system was installed at NIRE`s Three-dimensional Earthquake Testing laboratory. Shaking table tests with real acceleration time histories were performed. Static tests to obtain some mechanical properties of the used air valves also were performed. Comparison of the results obtained by the different approaches is presented in attempt to achieve in-depth understanding of the complex dynamic interaction within the air valve structure and its failure mechanism.

JTAM, Sofia, vol. 52 Issue 1 pp. 088-099 (2022), [Full Article]