Journal of Theoretical and Applied Mechanics, Sofia, vol. 52 Issue 3 (2022)

Table of contents



ESTABLISHMENT OF THE NATURAL FREQUENCY OF OSCILLATIONS OF THE TWO-DIMENSIONAL CONTINUOUS MEMBER OF THE VIBRATING TABLE

Pavlo Maistruk1, Oleksii Lanets1, Volodymyr Maistruk2, Iryna Derevenko3
1Department of Robotics and Integrated Mechanical Engineering Technologies, Institute of Mechanical Engineering and Transport, Lviv Polytechnic National University, Lviv, Ukraine
2Department of Designing and Operation of Machines, Institute of Mechanical Engineering and Transport, Lviv Polytechnic National University, Lviv, Ukraine
3Department of Strength of Materials and Structural Mechanics, Institute of Civil Engineering and Building Systems, Lviv Polytechnic National Universit


In the article, using the approximate Rayleigh-Ritz method, the first natural frequency of oscillations of the continuous member (elastic plate) of the inter-resonance vibrating table with the electromagnetic drive is established. For this purpose, the kinetic and potential energies of the plate were presented in integral form, where the basic function of the plate surface deflections is given as the product of the functions of the transverse deflections along the x and y axes, taking into account the boundary conditions. The transverse deflection along the x-axis of the plate is described through Krylov-Duncan functions and along the y-axis — through circular functions. The article found the approximate value of the first natural frequency of oscillations of the continuous member. The reliability of the obtained data was confirmed experimentally.

JTAM, Sofia, vol. 52 Issue 3 pp. 199-214 (2022), [Full Article]




DETERMINATION OF ADDED MASS FOR EARTHQUAKE INDUCED HYDRODYNAMIC LOADINGS ON VERTICAL STRUCTURES

Gerald Muller1, Dimitar Kisliakov2
1Faculty of Engineering and Physical Sciences, University of Southampton, Southampton SO17 1BJ, UK
2Department of Hydraulic, Irrigation and Drainage Engineering, University of Architecture, Civil Engineering and Geodesy, 1 Hr. Smirnenski Blvd., BG-1046 Sofia, Bulgaria


Earthquakes can induce severe hydrodynamic loadings on dams and their equipment. The dynamic dam-reservoir interaction is usually modelled by the so-called added mass. There are two theoretical approaches in the literature, employing either momentum or compressibility theory. Both assume zero pressures at the top of the structure, leading to comparatively low design pressures for control structures. A new theory was developed for a simple approximation for added mass and hydrodynamic pressures. The added mass is assumed to be uniform over the dam height. The added mass becomes a linear function of acceleration and water depth. Comparison with 'classic' theories showed good agreement for accelerations up to 0.3g, and higher pressures for higher accelerations.

JTAM, Sofia, vol. 52 Issue 3 pp. 215-231 (2022), [Full Article]




SIMULATION OF ATMOSPHERIC TRANSPORT OF POLLUTANTS FROM MICRO- TO CITY-SCALE USING CFD MODEL AND UNSTRUCTURED GRIDS

Alexander Khalchenkov1,2, Ivan V. Kovalets1
1Institute of Mathematical Machines &l; Systems Problems NAS of Ukraine, prosp. Glushkova, 42, 03187, Kyiv, Ukraine
2Ukrainian Center of Environmental and Water Projects, prosp. Glushkova, 42, 03187, Kyiv, Ukraine


The OpenFoam CFD code was adapted to simulate atmospheric transport of pollutants. By performing calculations on unstructured grids and using the modifications of turbulence parameterizations to account for the influence of Earth's rotation on PBL structure, the presented model can take into account the influence of urban obstructions and complex topography on atmospheric dispersion from a city to street-scale. The normalized mean squared error of simulated results for the conditions of the known MUST experiment was comparable with the results of other models (NMSE ≈ 0.6). The value of turbulent Schmidt number in this experiment was estimated to be Sc ≈ 0.4. The example of model application for the assessment of atmospheric pollution created by the industrial site of uranium production was presented.

JTAM, Sofia, vol. 52 Issue 3 pp. 232-247 (2022), [Full Article]




ON THE MECHANICAL BEHAVIOR OF MASONRY WALLS: AN OVERVIEW OF MODELS, SIMULATIONS, EXPERIMENTS AND CODE REGULATIONS

George I. Papadopoulos, George D. Manolis
Laboratory for Experimental Mechanics, Department of Civil Engineering, Aristotle University, 54124 Thessaloniki, Greece


This paper is an overview of the mechanical behavior of masonry walls, which encompasses their response to external loads and their modes of failure as derived from experimental evidence. This material is augmented with numerical modelling techniques and brought into better perspective by examining building code regulations. Furthermore, some key experiments that were performed in the recent past are discussed and the experimental results produced are critically presented, since they are essential for calibrating numerical models and for drafting code regulations.

JTAM, Sofia, vol. 52 Issue 3 pp. 248-276 (2022), [Full Article]




DESIGN AND PERFORMANCE OF DEMONSTRATOR OF AUTONOMOUS FIXED WING UAV CATLTR

Valentin Penev
Institute of Mechanics, Autonomous Platforms, Bulgarian Academy of Sciences, Acad. G. Bonchev Str., Bl. 4, Sofia, Bulgaria


The demonstrator of fixed wing UAV is designed for visual detection, recognition, segmentation and tracking of cattle from the air. It will help veterinarian doctors with remote determination of physiology state. Some of challenges of visually tracking autonomous flying platform, that accurate trajectory control has had so far, have been in certain instances avoidable. Full simulator in SIMULINK was developed for a vehicle dynamics, sensors and its guidance algorithms. Advanced approach for determination of platform attitude is used to enhance accuracy of guidance. Novel model-based control and its algorithm for tuning are proposed and tested in the simulation and real flight. Partial flight log data is compared to that of the proposed model and it is shown that the model accurately replicates the true flight dynamics. The strapped-down seeker model passes the deflections of the target from Line-of-Sight to the autopilot. The results predict that the vehicle's performance in response to excessive roll, pitch and yaw is extremely sensitive to the quality of guidance. The joint simulation model demonstrated was highly dependent on failure of the seeker used for guidance due to oscillation at some degree of the roll, pitch and yawing of the airframe.

JTAM, Sofia, vol. 52 Issue 3 pp. 277-293 (2022), [Full Article]