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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Journal of Theoretical and Applied Mechanics, Sofia, vol. 55 Issue 1 (2025)
Table of contents
Pavel Venev, Dimitar Chakarov, Ivanka Veneva, Georgi Katsarov
Institute of Mechanics, Bulgarian Academy of Sciences, Sofia 1113, Bulgaria
This work investigates the pneumatic actuation of an upper limb
exoskeleton intended for physical training and rehabilitation. In order to
address specific requirements regarding transparency of movement,
simplicity, natural safety and efficiency, in this study we examine the use
of a pneumatic drive actuated with a combination of vacuum and pressurized
air sources. To evaluate transparency, we measure the force of interaction
between the patient and the exoskeleton in a passive mode. The
experimentation of the interactions between the patient and exoskeleton is
performed by harmonic movements created by the patient in a single shoulder
joint with one degree of freedom system. The results of simulations and
experiments are shown graphically. Finally, a conclusion and instructions
for future works are made.
JTAM, Sofia, vol. 55 Issue 1 pp. 003-019 (2025), [Full Article]
Vasko Kokalanov, Vlado Gicev, Natasha Stojkovikj
Faculty of Computer Science, Goce Delcev University, Krste Misirkov, 10A, 2000 Stip, North Macedonia
In this paper an analytical solution for two dimensional
Soil-Structure Interaction (2D SSI) model is presented. The model consists
of three parts: stress-free elastic, isotropic, homogeneous ground
half-space, idealized rigid semicircular foundation and rectangular
homogeneous building. The interactive system is excited by vertical incident
P-wave. The presented analytical solution satisfies the stress-free boundary
conditions at the half-space surface. The analyzed solutions for foundation
motion and the relative response of the building can be further used for
verification of numerical models developed for 2D SSI.
JTAM, Sofia, vol. 55 Issue 1 pp. 020-034 (2025), [Full Article]
Velichka Traneva1, Stoyan Tranev1, Venelin Tododorov2,3
1Prof. Asen Zlatarov University, Prof. Yakimov Blvd., Bourgas 8000, Bulgaria
2Institute of Mathematics and Informatics, Bulgarian Academy of Sciences, Acad. G. Bonchev Str., Bl. 8, Sofia 1113, Bulgaria
3Institute of Information and Communication Technologies, Bulgarian Academy of Sciences, 25A Acad. Georgi Bonchev Str., 1113 Sofia, Bulgaria
This paper introduces a novel approach to modeling humanoid robot mouth expressions using Elliptic Intuitionistic Fuzzy Sets (E-IFS). The E-IFS model employs elliptic intuitionistic fuzzy logic to capture the complexity of human emotions, enabling robots to express nuanced emotional states through mouth movements. By effectively handling uncertainties and emotional intensity variations, the model offers a flexible and adaptive alternative to traditional techniques. Results demonstrate the model's capability to generate realistic, contextually appropriate expressions, enhancing human-robot interaction. These findings highlight its potential for making robots more emotionally expressive. Future research will focus on expanding the model for multi-modal emotional expression and assessing its impact on user perception.
JTAM, Sofia, vol. 55 Issue 1 pp. 035-051 (2025), [Full Article]
M. Rashevski
Institute of Mechanics, Bulgarian Academy of Sciences
Thermal stratification due to natural convection in underground long-term hot water storage is simulated numerically over 180 days. The mathematical model is based on the unsteady two-dimensional Navier-Stokes-Fourier equations with Boussinesq approximation. Dynamic temperature boundary conditions are applied on the cavern walls. Finite difference method (FDM) is used to solve the problem in vorticity-stream function formulation. Three different cavern aspect ratios are considered. The evolution of vortices and its influence on the temperature and velocity fields is presented through graphics at the end of the studied period. The thermocline thickness and the Nusselt numbers on the cavern walls are determined. The calculations show that the highest aspect ratio leads to better thermal stratification and thermally more efficient storage design.
JTAM, Sofia, vol. 55 Issue 1 pp. 052-062 (2025), [Full Article]
Ivan K. Yanakiev
Institute of Mechanics, Bulgarian Academy of Sciences
Musical systems for organizing tonal space are the
foundation of music. Since Pythagoras, the topic has been a fruitful field
for experiments for composers and music theorists. This is possible due to
the correlation between human auditory perception specifics and how two or
more frequencies relate to one another. The current approach towards
modeling musical systems is focused on digitalizing the process for
establishing the notes' frequencies and applying additive synthesis for
designing timbre for the tone sets. Moreover, a possible application of the
digital modeling process of the timbre for devising musical systems with a
higher degree of intrinsic consonance in relation to the tonal system's
specificities.
JTAM, Sofia, vol. 55 Issue 1 pp. 063-074 (2025), [Full Article]
Orlin Antonov1, Emil Yankov2, Margaritka Filipova1, Ivanka Zheleva1
1Department of Heat, Hydraulics and Environmental Engineering, Angel Kanchev Univesity of Ruse, Bulgaria
2Department of Material Science and Technology, Angel Kanchev Univesity of Ruse, Bulgaria
This paper presents the mechanical experimental measurements conducted on five different tiles made from composite materials containing rubber particles sourced from end-of-life tires (EoLT). Each specimen features varying quantities of rubber particles, quartz sand, and resin. The study focuses on collecting and organizing experimental data, which are then compiled into tables for comparative analysis. The summarized results of these measurements are also presented graphically and thoroughly discussed. The mechanical characteristics of these composite materials, including hardness, strength, and other mechanical attributes, are comprehensively analyzed to assess their viability for various applications. The findings provide valuable insights into the potential of these composites in addressing EoLT waste management challenges.
JTAM, Sofia, vol. 55 Issue 1 pp. 075-090 (2025), [Full Article]
Omar Belhadj1, Hamidou Benzenine1,2, Salim Newaz Kazi3, Rachid Saim1
1Laboratory of Energetic and Applied Thermal ETAP, Department of Mechanical Engineering, Faculty of Technology, B.P 230, University of Tlemcen, 13000, Algeria
2Department of Mechanical Engineering, Faculty of Science and Technology, University Belhadj Bouchaib, BP 284 RP, Ain Témouchent, 46000, Algeria
3Department of Mechanical Engineering, Faculty of Engineering, University Malaya, 50603 Kuala Lumpur, Malaysia
A numerical analysis of a two-dimensional turbulent air flow in a
solar chimney, with a Venturi device at the outlet, was conducted. The
Venturi device creates a pressure drop, significantly enhancing the air
evacuation at the outlet. Simulations were performed using Ansys Fluent,
employing the finite volume method to determine and analyze the dynamic and
thermal fields under the influence of wind velocity.
The validation of the numerical model with the experimental results shows
good agreement. The results demonstrate a linear and direct proportionality
between the increase in wind speed and the ventilation flow rate at the
outlet, keeping other factors constant. The system also showed the presence
of ventilation even in the absence of wind.
JTAM, Sofia, vol. 55 Issue 1 pp. 091-104 (2025), [Full Article]
Ihor Rudko1, Borys Bakay1, Abdullah Emin Akay2, Viatcheslav Loveikin3, Yuriy Romasevych3
1Ukrainian National Forestry University, Department of Forest Engineering, Lviv, Ukraine
2Bursa Technical University, Department of Forest Engineering, Bursa, Turkey
3National University of Life and Environmental Sciences of Ukraine, Department of Machines and Equipment Design, Kyiv, Ukraine
Based on classical principles of suspension system
calculations, theoretical approaches are proposed for determining the
geometric and force parameters of their supporting elements. The calculation
of suspension systems with one or multiple spans is proposed to be performed
by constructing and solving systems of transcendental equations. For finding
solutions to such systems of equations, the graphical-analytical method and
the method of successive approximations are used. The paper presents a
schematic representation of the diagrams of vertical load, tensions, and sag
of the supporting element of the suspension system, the results of numerical
modeling (on specific examples), indicates the areas of possible use of the
obtained results, and the prospects for further scientific research on the
issues under consideration.
JTAM, Sofia, vol. 55 Issue 1 pp. 105-119 (2025), [Full Article]