International Scientific Journals
of Scientific Technical Union of Mechanical Engineering "Industry 4.0"

The article reviews the chemical and active compounds of the lyophilized essential oil of Thymus vulgaris L. and its preservation qualities. Thymus vulgaris is a medicinal plant belonging to the Lamiaceae family, with a long history of use for its therapeutic properties. The essential oil of T. vulgaris has been widely studied for its antimicrobial, antioxidant, and anti-inflammatory activities. The amounts and types of chemical compounds can vary depending on the genetic differences or environmental conditions of the plant materials. The primary components of the essential oil responsible for most of its biological effects include thymol, carvacrol, and p-cymene. The essential oil of T. vulgaris has been reported to exhibit a wide range of pharmacological activities, including antimicrobial, antioxidant, anti-inflammatory, antifungal, and antiviral activities. In recent years, there has been increasing interest in the use of T. vulgaris essential oil as a natural preservative in food products.

Forests tractors are inseparable part of a forest economy. Forests tractors serve for logging of logs in forests. Current forests tractors are usually equipped by hydraulic arms, which allow to expand the utility of a tractor. A tractor with a hydraulic arm is able to handle with wood logs without a need additional forest machine, which helps to reduce costs. On the other hand, it is necessary to analyse tractors abilities, which has such an additional equipment. This article is focused on assessment of stability of a forest tractor, which is equipped by such a hydraulic arm. It is a newly designed forest tractor which smaller dimensions, which is intended to be used in conditions with requirements for lower contact pressure and better manoeuvrability. As the hydraulic arm changes the centre of gravity of an entire tractor, mainly with the load, safe operation of the tractor needs to know limit conditions of stability under the maximal load and in the given slope inclination.

The dynamic stability of a cracked pipeline resting on a Winkler elastic foundation and immersed in fluid that is moving with a particular velocity is investigated. The Galerkin method is employed to approach numerically the problem. Conclusions are drawn on the influence of the rigidity of the Winkler elastic foundation on the critical flow velocity of the pipe.

This paper presents the calculation of the stress and stability of a third-cycle module of a steam boiler during the lifting process. A steam boiler is a key element of a cogeneration plant, so all calculations are performed according to prescribed standards. Before the numerical analysis of the steam boiler, the characteristics, components and function of the boiler are described, as well as the required standards. The 3D model of the boiler was created using the Abaqus/CAE 2016 program package according to the manufacturer’s technical documentation. Using the finite element method, the stresses and stability during lifting of the boiler from the horizontal and vertical positions were calculated and presented. It was found that when lifting from a horizontal position, the structural stress values of the main elements do not exceed the allowable values. On the other hand, when lifting from a vertical position, the stresses exceed the allowable values. In this case, the connection point between the lug and the profile was checked and analytically dimensioned. The obtained values of the stability analysis of the boiler module are satisfactorily defined and there is no risk of buckling in both cases of lifting. The boiler conforms with the standard and fulfils the requirements handed over to the engineer.

The dynamic stability of a cracked pipeline resting on a Winkler elastic foundation and immersed in fluid that is moving with a particular velocity is investigated. The Galerkin method is employed to approach numerically the problem. Conclusions are drawn on the influence of the rigidity of the Winkler elastic foundation on the critical flow velocity of the pipe.

The Energy method is widely applied to determine the critical loads in elastic systems. A widely used variant of the method applies the Rayleigh-Ritz approach where the approximation of the buckling mode of the column is a function that satisfies the boundary conditions. A numerical example of a two-storey column is considered. An important aspect in the problem is the solution the complex integrals that emerge during the solution process. That problem could be overcome by the use of math software. The investigated column is hinged at its both ends and has an additional lateral support in the middle. It is loaded with a compressive distributed load alongside its length.

The Picard’s successive iteration method is applied to determine the Euler critical force for a slender column. The initial approximation of the buckling mode of the column is a polynomial function that satisfies the boundary conditions. A numerical example is solved and the obtained result is compared with that obtained by the Euler formula. An assessment of the accuracy of the solution is made at each iteration step. In the paper is shown that the Picard’s iteration method could also be used for obtaining the closed form exact solution of the buckling load. The investigated column is hinged at its upper end and supported by a Q- apparatus at the other. It is loaded with a compressive force at the upper end.

The problem of convective stability in a medium containing settling heavy solid particles are discussed. A study is made of the stability of steady convective flow of a medium containing an additive between vertical plates heated to different temperatures. It is shown that the presence of settling solid particles has a significant stabilizing effect on convective stability.

The results of a solution of the problem of the stability of steady convective flow in a vertical layer with thermally insulated boundaries and a comparison with the opposite limiting case of ideally thermally conducting boundaries are presented. Study is made of the effect of thermal properties of boundaries on the convective flow stability in a closed vertical layer. The numerical solution of a spectral amplitude problem for normal disturbance is presented for thermally insulated boundaries. The critical Grashof numbers are determined. A comparison with the case of ideal conducting walls shows that there is a slight effect of thermal properties on the instability criterion.

The problem rotor’s movement in a stationary circular cylindrical chamber having finite length and filled with viscous gas is solved by the method of direct numerical integration of the set of equations describing pressure distribution in a thin layer of viscous gas and the motion of a rotating statically disbalansed cylinder. The rotor moving in the gravitational field is influenced by the impressed forces which vary periodically in time. Unsteady pressure equation is approximated by the symmetric stable finite-difference scheme of the second order accuracy. Stability criteria of a rotating rigid unstable cylinder (a rotor) motion subject to problem parameters are studied. The inner cylinder is influenced by outer forces which vary periodically in time. Trajectories of the rotor stationary motion for various velocities of rotation, disbalance values, amplitudes and frequencies of outer forces are calculated. Conditions of contact free motion of the cylinder, rotating in the chamber, are determined.

Influece of form errors of a chamber filled with a liquid on the movement and stability of a ball, rotating in the chamber, is studied. Two cases of the influence of a chamber form errors on the forces, acting on the ball, are defined. The first case describes the situation when limitations on the rotor shift are not imposed and disturbances of the chamber form are set by spherical harmonics not above the first order. Then the chamber of a disturbed form, form the point of view of the reaction forces of the liquid and their moments, does not differ from a similar spherical chamber. In the second case disturbance of a chamber form are arbitrary and the rotor shift is supposed small. Then the force, acting on the rotor, depends on its displacement only, and the momentum does not depend on shift. A chamber of any form is equivalent to an ellipsoid. A rising here diflective moment tends to direct the angular speed vector along the small semiaxis of the ellipsoid, i.e., a stable position of the rotor appears.

Paper deals with finite element buckling analysis of shear deformable beam-type structures. Displacements and rotations are allowed to be large but strains are assumed to be small. The corresponding equilibrium equations are formulated in the framework of co- rotational description, using the virtual work principle. Displacements and rotations are allowed to be large while strains are assumed to be small. Linear shape functions are used for the axial displacement, while cubic shape functions are employed for transverse displacements and angle of twist. The algorithm is validated on test examples.