Journal of Theoretical and Applied Mechanics, Sofia, vol. 49 Issue 4 (2019)

Table of contents



A LINEAR ANALYTICAL STUDY OF CORIOLIS FORCE ON SORET-DRIVEN FERROTHERMOHALINE CONVECTION IN A DARCY ANISOTROPIC POROUS MEDIUM WITH MFD VISCOSITY

R. Sekar, D. Murugan
Department of Mathematics, Pondicherry Engineering College, Pillaichavady, Puducherry — 605 014, India


The double diffusive effect of magnetic field dependent (MFD) viscosity on Soret driven thermoconvective instability in a ferrofluid, saturating a densely packed rotating anisotropic porous medium has been investigated theoretically. The horizontal fluid layer is assumed to be heated from below and salted from above and the Darcy model is used. The effect of salinity has been combined in the magnetization and density of the ferrofluid. An exact solution is obtained for the case of two free boundaries. The critical thermomagnetic Rayleigh number for onset of instability is also determined numerically for sufficient large values of buoyancy magnetization parameter M1 and results are depicted graphically. The onset of Soret driven ferrothermohaline convection is analyzed both by stationary as well as oscillatory modes using a linear stability analysis and a normal mode technique. In all the cases, it is found that the rotation and MFD viscosity tend to stabilize the system whereas destabilization of the system occurs due to the non-buoyancy magnetization parameter M3. Further, the ratio of mass transport to heat transport decides the stabilizing factor.

JTAM, Sofia, vol. 49 Issue 4 pp. 299-326 (2019), [Full Article]




MODELING OF THE ELASTICALLY-MOUNTED CYLINDER BEHAVIOR IN THE CROSS-FLOW

Sabine Upnere1,2
1Riga Technical University, Viskalu Street 36, Riga, Latvia
2Ventspils University of Applied Sciences, Inzenieru Street 101, Ventspils, Latvia


This study investigates the Proper Orthogonal Decomposition (POD) combined with Radial Basis Functions (RBF) and Response Surface Method (RSM) based metamodels to appreciate the influence of the system parameters on elastically-mounted test cylinder (TC) behavior excited by water cross-flow. The TC mass, stiffness and damping coefficients and excitation forces are chosen as the design parameters. System responses at selected training points are obtained by full, two-dimensional model simulations using Computational Fluid Dynamics. Obtained results show that POD-RBF metamodel has good accuracy to predict the system parameters, which is not time-dependent, whereas the RSM metamodel can reconstruct the time-dependent TC movement trajectory with high precision.

JTAM, Sofia, vol. 49 Issue 4 pp. 327-342 (2019), [Full Article]




NUMERICAL STRESS STATE EVALUATION OF POWDER NANOFILLED METAL-POLYMER COMPOSITE MATERIALS AT ELECTROCONTACT SINTERING

Vadim Kovtun1, Mitko Mihovski2, Vladimir Pasovets1, Victor Biryuk1, Yordan Mirchev2
1State Educational Establishment, University of Civil Protection of the Ministry for Emergency Situations of the Republic of Belarus, Mashinostroiteley 25, 220118 Minsk, Belarus
2Institute of Mechanics, Bulgarian Academy of Sciences, Acad. G. Bonchev Str., Block 4, 1113 Sofia, Bulgaria


The technique, design schemes and adaptive finite element models for an assessment of the stress states are developed. Processes of contact interaction of components of powder systems of "microdispersed metal--plated polymer--carbon nanostructures" have been researched with application of approaches of computer modeling. The regularities of formation of fields of internal stresses in the zone of contact interaction components at electrocontact sintering on the multicomponent system are investigated.

JTAM, Sofia, vol. 49 Issue 4 pp. 343-359 (2019), [Full Article]




NEW THEORY TO PREDICT THE ELASTIC MODULUS OF CARBON NANOTUBE BASED-COMPOSITES

Naser Kordani1, Ali Sadough Vanini2, Rezvan Adibipour2
1Department of Mehanical Engineering, University of Mazandaran, Iran
2Department of Mehanical Engineering, Amirkabir University of Technology, Tehran, Iran


The relatively weak mechanical properties of polymer have prevented its application in the components which demand high mechanical strength and stability. There are numerous theories with special assumption on the mechanics of nanocomposite to predict the elastic modulus. However, some of these theories can be efficient to consider the influences of CNTs on elastic properties of nanocomposite reinforced CNTs. Current research focuses on creation a new model base on new assumption with just having single fiber to predict the elastic modulus of nanocomposite reinforced CNTs. To verify the predictions of the new model we used experimental data and some well-known theories. Errors at most of the models were more than 10%, while by using this new model, errors has been decreased.

JTAM, Sofia, vol. 49 Issue 4 pp. 360-368 (2019), [Full Article]




THE SYMMETRIES AND CONSERVED QUANTITIES OF MECHANICAL MULTI-BODY SYSTEM DYNAMICS

Zheng Mingliang
School of Mechanical and Electrical Engineering of Wuxi Taihu University, Wuxi 214064, China


The paper provides a powerful new tool for quantitative and qualitative analysis of complex mechanical multibody system. The symmetry theory in modern mechanics is introduced into the study of mechanical multibody dynamics. Firstly, the Euler-Lagrange equations of constrained mechanical multibody system dynamics are derived by analytical mechanical method; Secondly, the theory of group analysis is introduced, according to the invariance principle, we get the conditional equations of Noether and Lie symmetry and the corresponding form of conserved quantity about mechanical multibody system, which provides an effective way to analytic integral calculate the dynamic equations. Finally, the dynamic of a bionic robot mechanism is taken as an example for practical application. The result shows that we can get deeper mechanics rules and motion phenomena of mechanical multibody system dynamics with the help of symmetries and conserved quantities, which lay a theoretical foundation for more precise dynamic optimization design and advanced control.

JTAM, Sofia, vol. 49 Issue 4 pp. 369-380 (2019), [Full Article]




IMPACT OF THE LOADING FREQUENCY AND AMPLITUDE ON SELF-HEATING OF ELASTOMERS UNDER LARGE CYCLING DEFORMATIONS

Kliment Hajov, Verjinia Alexandrova
Department of Applied Mechanics, University of Chemical Technology and Metallurgy, 8 Kliment Ohridski Blvd., 1756 Sofia, Bulgaria


The aim of this work is to study the influence of the loading frequency and loading amplitude on the self-heating of elastomers at large deformation cycles.

JTAM, Sofia, vol. 49 Issue 4 pp. 381-392 (2019), [Full Article]