Journal of Theoretical and Applied Mechanics, Sofia, vol. 55 Issue 1 (2025)

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.

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.

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.

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.

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.

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.

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.

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.