Issue 2
JTAM, Sofia, vol. 55 Issue 2 (2025)

FOURTH-ORDER APPROXIMATE SYNTHESIS OF SLIDER-CRANK FUNCTION GENERATORS

Iliya Andonov1, Blagoyka Paleva-Kadiyska1, Roumen Roussev2, Vitan Galabov3
1Todor Kableshkov University of Transport, Sofia, Bulgaria
2Faculty of Technics and Technology of Trakia University, Yambol, Bulgaria
3Technical University, Sofia, Bulgaria


A new computer-applicable mathematical model for the synthesis of slider-crank mechanisms has been derived, in which the Burmester curves for infinitely close relative positions are generated indirectly using the Carter-Hall circle. The characteristic of the model is that it is linear, easy to implement with any computer program for engineering calculations (eg. MathCAD, MATLAB, etc.), and would greatly ease the work of engineers in the synthesis of mechanisms. The mathematical model is composed only of equations of lines, written in Cartesian coordinates, including when determining the kinematic diagrams of slider-crank mechanisms. Introduced an additional condition for achieving a certain value of the pressure angle, of which the reactions of the forces in the kinematic pairs and the force dimensioning of the mechanism depend, which unambiguously determines the kinematic diagrams of the mechanism. Since linear equations lead to a single solution, there is no need to search for additional conditions to determine a technically adequate solution, as when using higher-degree equations. The model greatly facilitates the synthesis of slider-crank mechanisms, generating set functions near a given position. The ease of working with the model and its adequacy with graphical constructions is illustrated with an example of the synthesis of a slider-crank mechanism that generates a function with a fourth-order derivative approximation to the given function.

JTAM, Sofia, vol. 55 Issue 2 pp. 123-132 (2025), [Full Article]

ACOUSTIC WAVES MODELING FLOW IN RAREFIED GAS BETWEEN STATIONARY CYLINDERS AT OSCILLATION INHOMOGENEOUS INNER CYLINDER WALL TEMPERATURE

Dobri Y. Dankov, Mirona K. Mironova, Peter N. Gospodinov
Institute of Mechanics, Bulgarian Academy of Science

The paper aims at presenting the detailed interplay between acoustic waves, fluid flow, and self-organization phenomena in a rarefied gas environment. The study specifically focuses on the dynamics between two stationary cylinders with final length, where the inner cylinder features a non-uniform temperature distribution along its surface. The emergence of acoustic waves into this rarefied gas system is the primary interest of the current study. Moreover, the article is about to explore the role of acoustic waves in shaping fluid flow patterns. Acoustic waves are characterized by variations in pressure and density fields. The significance of these waves is particular when it comes to study rarefied gases. As the article proves, the acoustic waves can influence significantly the overall flow patterns and transport phenomena Simultaneously, the research explores self-organization phenomena, which refers to the spontaneous emergence of ordered structures or patterns in the system. The interplay between acoustic waves, rarefied gas flow, and temperature distribution along the inner cylinder contributes to the self-organization dynamics within this complex environment. Therefore, the proposed model and frequency processing can be implemented used in the modeling and design of Pirani gauge.

JTAM, Sofia, vol. 55 Issue 2 pp. 133-146 (2025), [Full Article]

IN VITRO INVESTIGATION OF LONG-TERM PROPERTIES OF HERNIA MESHES

Miglena Kirilova-Doneva1,2, Dessislava Pashkouleva1
1Faculty of Pharmacy, Medical University-Sofia, Sofia 1000, Bulgaria
2Institute of Mechanics, Bulgarian Academy of Sciences, Sofia 1113, Bulgaria

The study aims to investigate the influence of aging on the mechanical properties of non-resorbable and resorbable surgical meshes as well as heavyweight and lightweight meshes. Nine types of meshes were characterized before and after their expiration date. The maximum tensile stress, stretch at maximum stress, and elastic secant modulus of the mesh at 5% strain were calculated from derived stress- stretch curves for each specimen. The results indicate that the maximum tensile stress and elastic secant modulus of non-resorbable and lightweight meshes decrease after the expiration date. The stretch at maximum stress of non-resorbable meshes increases after the expiring date, while in other subgroups the behaviour of this parameter depends on the direction of loading.

JTAM, Sofia, vol. 55 Issue 2 pp. 147-159 (2025), [Full Article]

TEMPERATURE DISTRIBUTION IN BI-MATERIAL SURFACE REINFORCED STRUCTURAL ELEMENTS

Ana Yanakieva, Anguel Baltov, Gergana Nikolova
Institute of Mechanics, Bulgarian Academy of Sciences, Sofia, Bulgaria

The temperature distribution in bi-material structural elements subjected to high-temperature impacts is examined. The elements are composed of a concrete core reinforced with a coating whose strength and temperature resistance are higher than those of concrete. The obtained results were compared with those of a non-reinforced concrete element. The problem statement is to find the external process temperature at which the boundary/concrete core temperature does not exceed the permissible value according to Eurocode. Results are shown for gluing and diffusion coating depositions. The temperature distribution was determined using the finite difference method.

JTAM, Sofia, vol. 55 Issue 2 pp. 160-171 (2025), [Full Article]

THE THREE-DIMENSIONAL AUGMENTED MODEL RESPONSE DURING INSTRUMENT INTERACTIONS SIMULATION

Veronika Ivanova1, Plamen Vasilev2, Ani Boneva3
1Department of Robotized and Mechatronics Intelligent System, Institute of Robotics, Bulgarian Academy of Sciences, 1113 Sofia, Bulgaria
2Department of Industrial Automation, University of Chemical Technology and Metallurgy, 1756 Sofia, Bulgaria
3Department of Communication and Computer Systems, Institute of Information and Communication Technologies, Bulgarian Academy of Sciences, 1113 Sofia,

In recent years, there has been considerable interest in simulations in surgical robotics, and in particular simulations in training surgeons. This is largely due to cost-effectiveness, the critical growing needs in surgical care and reduced training time for surgeons, improved outcomes during surgery. Simulation is a commonly required task in the design of surgical instruments also. With the help of simulation, it simulated a wide range of static and dynamic loads with linear and non-linear material properties, and optimized tool-tissue force interactions. Simulation in the surgical area is extremely challenging due to surface and anatomical soft tissues deformations and the nature of the interventions. The aim of the work is to create a suitable three-dimensional augment model to provide necessary information about the liver responses during tool-tissues interactions in the operating environment. To achieve this purpose, the following is done i) an investigation of the instrument motion is initially made to control the action under remote control ii) results from a simulating approach of liver model response during tactile instrument interactions are shown. The ultimate goal of the work is to use the accumulated results into simulators in the training of surgeons and young doctors. This work is a continuation of previous research in the field of surgical robotics, where a surgical instrument is designed, and its kinematics is considered here.

JTAM, Sofia, vol. 55 Issue 2 pp. 172-187 (2025), [Full Article]

ANALYSIS OF NATURAL FREQUENCY OF POROUS SIGMOID FUNCTIONALLY GRADED SANDWICH PLATES VIA ANOTHER QUADRILATERAL ELEMENT

Hoang Lan Ton-That
Faculty of Civil Engineering, HCMC University of Architecture, 196 Pasteur, Xuan Hoa Ward, Ho Chi Minh City, Vietnam

This paper presents a computational model for vibration behavior of porous sigmoid functionally graded sandwich (PS-FGSW) plate using another four-node quadrilateral element within the concept of considering the influence of neighboring elements on its. The plate includes three layers. The face layers are fabricated of functionally graded material, and the core is ceramic. Imperfect sigmoid functionally graded sandwich plates with porosity are studied. The numerical results are reached as well as compared with known results, and a good agreement is obtained. Frequency analysis of a complex-shaped porous sandwich plate made of functionally graded material has been performed. The effect of various parameters on the dynamic behavior of the plate, such as values of porosity index, power index, and ratio of thicknesses, has been studied.

JTAM, Sofia, vol. 55 Issue 2 pp. 188-201 (2025), [Full Article]

NUMERICAL STUDY ON COOLING PERFORMANCE OF HORIZONTAL EARTH HEAT EXCHANGER IN HOT SEMI-ARID CLIMAT

Safia Safi1, Ihab Anis Zergua2
1Applied Energetics and Pollution Laboratory, Department of Mechanical Engineering, Universit&\eacute; de Constantine, Algeria
2University Seddik Benyahia, Jijel, Algeria

In this paper we numerically study the performance of an earth-to-air heat exchanger (EAHE) using the finite volume method. The impact of some parameters , like air temperature, humidity, soil temperature, diameter and length of the pipe, and the air flow at the inlet of the EAHE, on the performance of the EAHE, under the climatic conditions of Constantine city in eastern Algeria, have been examined. The main findings of the study indicate that there is a direct correlation between the length of the pipe and the outlet air temperature from the EAHE. The air relative humidity increased faster under high inlet temperatures. Increasing the diameter of the pipe led to an increase in the outlet air temperature of the EAHE. The humidity ratio under a small diameter pipe declined at a faster rate compared to a large diameter pipe. The outlet air temperature of EAHE increases with the tube's surface temperature. The main conclusions of this work are useful for designing and optimizing the geothermal system (EAHE).

JTAM, Sofia, vol. 55 Issue 2 pp. 202-217 (2025), [Full Article]

INFLUENCE OF POINT MASS RELATIVE MOTION ON DELAMINATION IN MULTILAYERED BEAMS

V. Rizov
Department of Technical Mechanics, University of Architecture, Civil Engineering and Geodesy, 1 Chr. Smirnensky blvd. 1046-Sofia, Bulgaria

This paper deals with analysis of delamination in moving multilayered beams in the case when a point mass performs non-uniform relative motion along a straight line on the beam upper surface. The beam itself undergoes rotation in horizontal plane. The study is focussed mainly on the influence of the relative motion of the point mass on the strain energy release rate (SERR) in the beam. One of the peculiarities of the problem under consideration is that some of the inertia forces are directed perpendicular to the plane of the beam structure which loads the beam in double bending and torsion. The analysis yields results clarifying the effect of the parameters of the motion law and layers inhomogeneity on the SERR.

JTAM, Sofia, vol. 55 Issue 2 pp. 218-233 (2025), [Full Article]

UNIQUENESS THEOREMS IN THE QUASI-STATIC PROBLEMS OF THE COUPLED LINEAR THEORY OF ELASTIC NANOMATERIALS WITH TRIPLE POROSITY

Mariam Mikelashvili
Ilia State University, K. Cholokashvili Ave., 3/5, 0179 Tbilisi, Georgia

The paper focuses on the coupled linear quasi-static theory of elasticity for nanomaterials with triple porosity, incorporating concepts of Darcy's law and volume fractions of three levels of pores (macro-, meso-, and micropores). It formulates the general governing equations in terms of the displacement vector field, pores volume fractions and fluid pressures in the pore networks in three levels of pores. Then, the 3D internal and external basic boundary value problems (BVPs) of steady vibrations of this model are formulated. Green's first identity is obtained and finally, the uniqueness theorems for classical solutions of the above mentioned BVPs are proved.

JTAM, Sofia, vol. 55 Issue 2 pp. 234-249 (2025), [Full Article]

A NUMERICAL ANALYSIS OF A NEWLY DESIGNED ALL-TERRAIN ELECTRIC SCOOTER FRAME UNDER VARIOUS LOAD CONDITIONS

Tsvetan Iliev
St. Ap. and Gospeller Matthew Institute of Robotics, Bulgarian Academy of Science, Bulgaria

This study employs finite element analysis (FEA) to evaluate a novel all-terrain electric scooter frame, the Vinghen Ti1, under four loading conditions aligned with bicycle frame standards. Motivated by safety concerns in dynamic, varied terrains, the analysis adapts ISO 4210-6:2023 guidelines to simulate steady motion with potholes, a vertical drop, horizontal loading on the head tube, and rear wheel braking. A 3D FEA model with 63,734 tetrahedral elements and 124,544 nodes predicted stress distributions, revealing critical concentrations around welded joints, especially at the head tube and L-beams, with peak von Mises stresses up to 460 MPa. The study suggests design enhancements and underscores the importance of robust computational and experimental methods for advancing personal mobility safety and ensuring long-term durability.

JTAM, Sofia, vol. 55 Issue 2 pp. 250-260 (2025), [Full Article]