Journal of Theoretical and Applied Mechanics, Sofia, vol. 51 Issue 4 (2021)

Table of contents



DELAMINATION CRACK STUDY OF A MULTILAYERED INHOMOGENEOUS BEAM EXHIBITING STRESS RELAXATION

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


The present article is concerned with a delamination crack analysis of a multi-layered inhomogeneous cantilever beam that exhibits stress relaxation. A linear viscoelastic model consisting of two springs and a dashpot is used for treating the stress relaxation. The moduli of elasticity of the springs and the coefficient of viscosity of the dashpot vary continuously along the thickness of each layer. A time-dependent solution to the strain energy release rate that accounts for the stress relaxation is derived. The J-integral approach is a in order to verify the solution to the strain energy release rate. The solution is applied to evaluate the stress relaxation induced variation of the strain energy release rate in the multi-layered cantilever beam with the time.

JTAM, Sofia, vol. 51 Issue 4 pp. 407-420 (2021), [Full Article]




OPTIMAL CONTROL OF SIMULTANEOUS TOWER CRANE SLEWING AND TROLLEY MOVEMENT

Viatcheslav Loveikin1, Yuriy Romasevych1, Lyubov Shymko2, Denis Mushtin1, Yuriy Loveikin3
1Department of Machines and Equipment Design, National University of Life and Environmental Sciences of Ukraine, Kyiv, 03041, Ukrain
2Mechanical and Technological Department, National University of Life and Environmental Sciences of Ukraine, Kyiv, 03041, Ukraine
3Mechanics and Mathematics Department, Taras Shevchenko National University of Kyiv, Kyiv, 01033, Ukraine


The article describes a mathematical model of tower crane slewing and trolley movement. Based on the model, a nonlinear problem of mechanisms' optimal control has been stated. A generalized optimization criterion was developed to cope with the constraints of the problem. In order to find an approximate solution of the problem, the metaheuristic method (ME-PSO) was applied. The obtained results are illustrated via graphical dependencies of kinematic, dynamical, and energy characteristics for the two cases of the trolley movement: toward the tower and in the opposite direction. In order to analyze the obtained results numerical indicators of the specified characteristics have been calculated. They show the reduction of energy losses, dynamical forces, and elimination of the load oscillations. This result provides an increase of the crane's efficiency exploitation. The developed in the article methodology may be applied to similar optimal control problems.

JTAM, Sofia, vol. 51 Issue 4 pp. 421-436 (2021), [Full Article]




THE PLANAR BUCKLING OF PINNED-FIXED SHALLOW ARCHES

László Péter Kiss1, Pusta Jalalova2, Ziya Mehdiyev2
1Institute of Applied Mechanics, University of Miskolc, 3515 Miskolc-Egyetemváros, Hungary
2University of Miskolc, 3515 Miskolc-Egyetemváros, Hungary


The article is devoted to the static, planar buckling problem of pinned-fixed shallow circular arches subject to a concentrated force. The nonlinear model is based on the single-layer Euler-Bernoulli theory. The related coupled differential equations of equilibrium are solved in closed-form. It is found such arches can undergo limit point buckling. The model is applicable not only to homogeneous but also for nonhomogeneous material distributions. The analytical results are compared with the results for pinned-pinned and fixed-fixed members. There are certain geometries and material distributions when the buckling load is almost the same for all these three support arrangements. Otherwise, as the included angle is increased, the difference between the critical loads also increases. The new findings are validated by means of literature and finite element results.

JTAM, Sofia, vol. 51 Issue 4 pp. 437-451 (2021), [Full Article]




DYNAMIC INDUCED FAILURE IN AIR VALVE DUE TO PRESSURE TRANSIENTS IN BURIED IRRIGATION PIPELINE

Silviya Petkova1, Yoshikazu Tanaka2, Mitsuru Ariyoshi2, Yuji Kohgo3
1Department of Hydraulic, Irrigation and Drainage Engineering, University of Architecture, Civil Engineering and Geodesy, 1 Hr. Smirnenski Blvd., Sofia, Bulgaria
2Institute for Rural Engineering, National Agriculture and Food Research Organization, 2-1-6 Kannondai, Tsukuba, Ibaraki 305-8609, Japan
3Graduate School of Agriculture, Tokyo University of Agriculture and Technology, 3-5-8 Saiwaicho, Fuchu, Tokyo 183-8509, Japan


The present work investigates the response of an air valve in terms of dynamic pressure due to kinematic support excitation. For the purpose of the analysis a full-scale model was installed in a laboratory setting, employing a shaking table to induce the dynamic input excitation in the form of a sine wave. The considered valve is an air release type, as a representative of those widely used in Japanese irrigation systems. Experiments were performed regarding the initial static pressure and the shaking parameters. The dynamic pressure and the movement of the valve's float was measured to establish the relation between the peak pressure and the mechanical response of the valve. After the analysis of the measured data some results and discussions are presented.

JTAM, Sofia, vol. 51 Issue 4 pp. 452-467 (2021), [Full Article]




NUMERICAL MODELING OF THE VENOUS VALVE FUNCTIONING

Elena Goranova1, Nikola Nikolov2
1University Medical Center Alexandrovska, Sofia, Bulgaria
2Institute of Mechanics, Bulgarian Academy of Sciences, Acad. G. Bontchev street Bl. 4, 1113 Sofia, Bulgaria


The present work investigates the response of an air valve in terms of dynamic pressure due to kinematic support excitation. For the purpose of the analysis a full-scale model was installed in a laboratory setting, employing a shaking table to induce the dynamic input excitation in the form of a sine wave. The considered valve is an air release type, as a representative of those widely used in Japanese irrigation systems. Experiments were performed regarding the initial static pressure and the shaking parameters. The dynamic pressure and the movement of the valve's float was measured to establish the relation between the peak pressure and the mechanical response of the valve. After the analysis of the measured data some results and discussions are presented.A 3-D numerical model of the function of saphenous venous valve with a constant elastic modulus Ekl = 500 kPa is developed depending on vein elastic modulus in series of Ev = 100 kPa and 30 kPa, diameter 4 mm, thickness 0.66~mm and length 600 mm, and constant blood flow pressure at inlet 4.5 kPa and pulsatile one at outlet from 0 to 6 kPa according to the law of cosines. The mechanical behavior of the system "blood flow-vein-valve" is modeled using the Fluid-Structure Interaction application of computer program Ansys, in a case of initially damaged vein valve, unclosed with two-sided aperture of 0.1 mm. The established distributions of the blood flow pressure and velocity in the deformed vein volume in a set with the established displacements and Mises stress in the valve and vein wall obtained during the cyclic valve opening/closing lead to stable working regimes in a vein with elastic modulus 100 kPa and to unstable ones in a vein with elastic modulus 30 kPa. Closing/proximal and opening/distal differences in the blood pressure are definite for the normal valve function. It is established with Ev = 100 kPa that under cosine-pulsatile inlet pressure from 3.6 to 4.8 kPa, an out-side pressure on the vein wall in the range of 4.25–4.5 kPa influences essentially the vein extensions and leaflet displacements and leads to decreasing aperture and/or to impact in the leaflets.

JTAM, Sofia, vol. 51 Issue 4 pp. 468-487 (2021), [Full Article]




ANALYTICAL AND NUMERICAL DETERMINATION OF THE FULL DYNAMIC REACTIONS IN THE BEARING SUPPORTS OF BIG BAND SAW MACHINES

Boycho Marinov
Institute of Mechanics, Bulgarian Academy of Sciences, Acad. G. Bonchev St., Bl. 4, 1113 Sofia, Bulgaria


In this paper, the influence of dynamic loads that cause dynamic reactions in the upper shaft supports of big band saw machines is investigated. These loads are created by the dynamic forces and moments that occur in operating mode, as well as by the kinematic and mass characteristics of the rotating disk. Expressions for calculation of the dynamic reactions caused by the external load are obtained, as well as expressions for calculation of the dynamic reactions due to the change of the kinematic and mass characteristics of the leading wheel. With the help of these expressions, final expressions to calculate the full dynamic reactions in the bearing supports are obtained. Using the obtained analytical expressions, planar and spatial diagrams are constructed, which show the change of the full dynamic reactions when changing different parameters.

JTAM, Sofia, vol. 51 Issue 4 pp. 488-501 (2021), [Full Article]