Issue 3
JTAM, Sofia, vol. 54 Issue 3 (2024)

EFFECT OF TEMPERATURE DEPENDENT VISCOSITY ON THERMAL INSTABILITY OF OLDROYDIAN VISCOELASTIC FLUID LAYER SATURATING POROUS MEDIUM

Joginder Singh Dhiman1, Praveen K. Sharma2, Khushboo Gupta1
1Himachal Pradesh University, Department of Mathematics & Statistics, Shimla, India, 171005
2Himachal Pradesh University, University Institute of Technology (UIT), Shimla, India, 171005


The effect of temperature-dependent viscosity on the onset of thermal convection in a viscoelastic fluid-saturating porous medium is studied for different cases of combination of rigid and dynamically free boundaries, Darcy-Brinkman-Oldroyd model is considered to investigate the rheological behaviour of the fluid. A necessary condition for the existence of overstability is derived, analytically. The values of critical Darcy-Rayleigh numbers for both stationary and oscillatory convection with linear and exponential viscosity variations (i.e. temperature-dependent viscosity) are computed numerically, using the Galerkin technique. The effects of rheological parameters, modified Darcy number, wave number and variable viscosity parameter on the stability of the system are computed numerically and depicted graphically for each case of combinations of boundary conditions. It is observed that the viscoelastic parameters; stress relaxation time and strain retardation time do not affect the onset of stationary convection, whereas the stress relaxation time has destabilizing effect and strain retardation time has stabilizing effect on the onset of oscillatory convection. It is also found that the temperature-dependent viscosity and modified Darcy number have a stabilizing effect on the onset of stationary as well as oscillatory convection for each case of boundary conditions.

JTAM, Sofia, vol. 54 Issue 3 pp. 255-277 (2024), [Full Article]

TIME-DEPENDENT DELAMINATION OF MULTILAYERED INHOMOGENEOUS BEAM LOADED IN PURE TORSION: AN ANALYTICAL SOLUTION

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

The multilayered inhomogeneous beam configuration considered in this paper exhibits delamination fracture that is time-dependent due to the viscoelastic behaviour. Besides, the two external torsion moments applied on the beam vary smoothly with time. The beam has a rectangular cross-section. The layers of the beam are continuously inhomogeneous in longitudinal direction. The two crack arms are loaded in pure torsion. A solution of the strain energy release rate for the delamination is derived by analyzing the timedependent strain energy stored in the beam structure. An alternative method based on the analysis of the beam compliances under the two torsion moments is applied in order to verify the solution of the strain energy release rate.

JTAM, Sofia, vol. 54 Issue 3 pp. 278-291 (2024), [Full Article]

TRANSVERSE CRACK AND MASS UNBALANCE INTERACTION IN A SPINNING ROTOR: A THEORETICAL STUDY

Nabam Teyi, Sandeep Singh
Department of Mechanical Engineering, North Eastern Regional Institute of Science and Technology, Nirjuli, Arunachal Pradesh, India – 791109

This paper investigates the response of a cracked rotor to varying angles between the crack front and the unbalanced force vector caused by changing centrifugal forces. A rotor with a switching crack is first mathematically represented, and then the response is generated using SIMULINK. At varied angles, the combined effect of crack and imbalance is observed. Maximum and minimum rotor deflection values are depicted on the orbit plots, and their difference with respect to the angles are noted. For various harmonics and vibration amplitudes, a full-spectrum Fast Fourier Transform (FFT) is conducted. Using FFT plots, the critical amplitude of vibrations for each variable angle is determined, and observations are given. This report finishes with some concluding remarks.

JTAM, Sofia, vol. 54 Issue 3 pp. 292-307 (2024), [Full Article]

EFFECT OF THE INFLUENCE OF THE DIFFERENT CORROSION LEVEL ON THE REPAIR EFFICIENCY OF MARINE AND OFFSHORE STRUCTURES BY BONDED COMPOSITE

B. Belarbi1, M.S. Bennouna2,3, K. Sadek2, B. Aour2, E. Abdelouahed2, B.A. Bachir Bouiadjra4, A. Talha5
1University of Tlemcen, Algeria
2LABAB Laboratory, National Polytechnic School Maurice Audin, Oran, 31000, Algeria
3Applied Science Faculty, Kasdi Merbah University, Waregla 30000, Algeria
4LMPM Laboratory, University of Sidi Bel Abbes 22000, Algeria
5Lille Mechanics Unit, University of Lille, (UML, EA 7512), University of Lille, 59655 Villeneuve d’Ascq, France

In this research paper, we examined the effectiveness of repairing corroded marine structures using bonded composites through finite element analysis (FEM) to evaluate the J Integral. Our focus is to provide an overview of the behavior of a cracked and corroded plate repaired with a boron patch and bonded with (Araldite 2015). To obtain optimized results, we studied the effects of eight corrosion levels under different loading and temperature conditions. The selected temperatures were T = 80°C and room temperature T = 25°C. The structure is under different mechanical loading of amplitude F = 220, 240, 260, 280, 300, 320, 340, 360 MPa.The analysis shows that increasing loading and corrosion levels result an increase in J Integral. The detachment of patches was evaluated under high loading (F = 360 MPa) for corrosion level a = 4.0 mm/year.

JTAM, Sofia, vol. 54 Issue 3 pp. 308-322 (2024), [Full Article]

GENERATING NON-MONOPHONIC MUSIC WITH VARIATIONAL AUTOENCODER: A CASE STUDY

Ivan K. Yanakiev
Institue of Mechanics, Bulgarian Academy of Sciences, 1113 Sofia, Bulgaria

The paper proposes an approach for generating musical pieces based on the Variational Auto Encoder (VAE) and realized in the MATLAB framework. In the work the architecture of the used VAE is described and also its training with dataset from the MAESTRO MIDI Dataset. The aim of the work is to study to what extent the used VAE is suitable for learning and representing musical structure. The resulting pieces show some features of musical structure on a mid-term temporal scale. It is concluded that the model successfully represents traits of general musical structure on the broader timescale as well as some short-scale musical figures. However, it fails to account for time-related musical structure of the long-term musical architectonics.

JTAM, Sofia, vol. 54 Issue 3 pp. 323-338 (2024), [Full Article]

NUMERICAL STUDY OF 2D STEADY FLUID FLOW IN LID-DRIVEN RECTANGULAR DOMAIN WITH TEMPERATURE EFFECT USING HYBRID FINITE VOLUME METHOD

V. Ambethkar, Jyoti
Department of Mathematics, Faculty of Mathematical Sciences, University of Delhi, Delhi-110007, India

This paper investigates the numerical simulation for the two dimensional (2D) steady fluid flow by using hybrid finite volume method in the lid-driven rectangular domain. The top wall is moving with a constant speed in the positive horizontal direction and other walls are in rest. Different constant temperature are applied to the top and bottom wall and left and right walls are thermally insulated. The dimensionless governing equations are discritized using the hybrid scheme of finite volume method. The SIMPLE algorithm is used to compute the numerical solution of the flow variables such as u-velocity, v-velocity, pressure (p) and temperature (θ). u-velocity is maximum on the top wall and it is decreasing as we go down till the geometric center. v-velocity is maximum near the top left corner and minimum near the top right corner of the domain. Pressure contour graph shows the maximum pressure near the top right corner and minimum near top left corner. Temperature contour graph shows the maximum temperature on the bottom wall and it will decrease as we goes towards the top wall.

JTAM, Sofia, vol. 54 Issue 3 pp. 339-355 (2024), [Full Article]

ANALYTICAL STUDY OF PARALLEL PLATE FLOW OF A NEWTONIAN FLUID WITH SPATIAL VARIATIONS IN VISCOSITY

Mehmet Pakdemirli
Mechanical Engineering Department, Manisa Celal Bayar University, 45140, Muradiye, Yunusemre, Manisa, Turkey

One dimensional Newtonian fluid flow between fixed parallel plates is considered. The viscosity is not constant but changes with the spatial variable of height. Two different classes of problems are treated: 1) Continuous changes in the viscosity, 2) Discontinuous changes in the viscosity. In the first class, general integral form solutions are given first and then, for the four different viscosity functions, the velocities and the discharges are calculated. For the second class of discontinuous changes, two problems are solved: 1) Two different immiscible fluids one laying on top of the other, 2) An intermediate high viscosity fluid lubricated by a low viscosity thin layer fluid at the boundaries. Velocity profiles and discharges are calculated for both cases. It is found that spatial viscosity variations have substantial effects on the velocity profiles and discharges and cannot be ignored for a precise treatment.

JTAM, Sofia, vol. 54 Issue 3 pp. 356-365 (2024), [Full Article]