Issue 1

JTAM, Sofia, vol. 47 Issue 1 (2017)

Vibration Analysis of a Tire in Ground Contact Under Varied Conditions

Murat Karakus1, Aydin Cavus1, Mehmet Colakoglu2
1Afyon Kocatepe University, Faculty of Technology, ANS Campus, 03200 Afyonkarahisar, Turkey
2Department of Mechanical and Aeronautical Engineering, University of Pretoria, Pretoria, 0002, South Africa

The effect of three different factors, which are inflation pressure, vertical load and coefficient of friction on the natural frequencies of a tire (175/70 R13) has been studied. A three dimensional tire model is constructed, using four different material properties and parts in the tire. Mechanical properties of the composite parts are evaluated. After investigating the free vibration, contact analysis is carried out. A concrete block and the tire are modelled together, using three different coefficients of friction. Experiments are run under certain conditions to check the accuracy of the numerical model. The natural frequencies are measured to describe free vibration and vibration of the tire contacted by ground, using a damping monitoring method. It is seen, that experimental and numerical results are in good agreement. On the other hand, investigating the impact of three different factors together is quite difficult on the natural frequencies. When some of these factors are assumed to be constant and the variables are taken one by one, it is easier to assess the effects.

JTAM, Sofia, vol. 47 Issue 1 pp. 03-17 (2017), [Full Article]

Spline Parameterization of Complex Planar Domains for Isogeometric Analysis

Sangamesh Gondegaon, Hari K. Voruganti
Department of Mechanical Engineering, National Institute of Technology, Warangal, 506004 India

Isogeometric Analysis (IGA) involves unification of modelling and analysis by adopting the same basis functions (splines), for both. Hence, spline based parametric model is the starting step for IGA. Representing a complex domain, using parametric geometric model is a challenging task. Parameterization problem can be defined as, finding an optimal set of control points of a B-spline model for exact domain modelling. Also, the quality of parameterization, too has significant effect on IGA. Finding the B-spline control points for any given domain, which gives accurate results is still an open issue. In this paper, a new planar B-spline parameterization technique, based on domain mapping method is proposed. First step of the methodology is to map an input (non-convex) domain onto a unit circle (convex) with the use of harmonic functions. The unique properties of harmonic functions: global minima and mean value property, ensures the mapping is bi-jective and with no selfintersections. Next step is to map the unit circle to unit square to make it apt for B-spline modelling. Square domain is re-parameterized by using conventional centripetal method. Once the domain is properly parameterized, the required control points are computed by solving the B-spline tensor product equation. The proposed methodology is validated by applying the developed B-spline model for a static structural analysis of a plate, using isogeometric analysis Different domains are modelled to show effectiveness of the given technique. It is observed that the proposed method is versatile and computationally efficient.

JTAM, Sofia, vol. 47 Issue 1 pp. 18-35 (2017), [Full Article]

Neural Network Based Simulation of Micro Creeping Fibrous Composites SiC/Al6061 for Plastic Behaviour

Vahid Monfared
Young Researchers and Elite Club, Zanjan Branch, Islamic Azad University, Zanjan, Iran

The present work presents a new approach based on neural network prediction for simple and fast estimation of the creep plastic behaviour of the short fiber composites. Also, this approach is proposed to reduce the solution procedure. Moreover, as a significant application of the method, shuttles and spaceships, turbine blades and discs are generally subjected to the creep effects. Consequently, analysis of the creep phenomenon is required and vital in different industries. Analysis of the creep behaviour is required for failure, fracture, fatigue, and creep resistance of the optoelectronic/photonic composites, and sensors. One of the main applications of the present work is in designing the composites with optical fibers and devices. At last, a good agreement is seen among the present prediction by neural network approach, finite element method (FEM), and the experimental results.

JTAM, Sofia, vol. 47 Issue 1 pp. 36-48 (2017), [Full Article]

A Computation Fluid Dynamic Model for Gas Lift Process Simulation in a Vertical Oil Well

Arash Kadivar, Ebrahim Nemati Lay
Department of Chemical Engineering, Faculty of Engineering, University of Kashan, Kashan, Iran

Continuous gas-lift in a typical oil well was simulated using computational fluid dynamic (CFD) technique. A multi fluid model based on the momentum transfer between liquid and gas bubbles was employed to simulate two-phase flow in a vertical pipe. The accuracy of the model was investigated through comparison of numerical predictions with experimental data. The model then was used to study the dynamic behaviour of the two-phase flow around injection point in details. The predictions by the model were compared with other empirical correlations, as well. To obtain an optimum condition of gas-lift, the influence of the effective parameters including the quantity of injected gas, tubing diameter and bubble size distribution were investigated. The results revealed that increasing tubing diameter, the injected gas rate and decreasing bubble diameter improve gas-lift performance.

JTAM, Sofia, vol. 47 Issue 1 pp. 49-68 (2017), [Full Article]

Thermal Instability in a Layer of Couple Stress Nanofluid Saturated Porous Medium

Ramesh Chand1, G. C. Rana2, Dhananjay Yadav3
1Department of Mathematics, Government Arya Degree College Nurpur, Himachal Pradesh, India
2Department of Mathematics, NSCM Government College Hamirpur, Himachal Pradesh, India
3School of Mechanical Engineering, Yonsei University Seoul, South Korea

Thermal instability in a horizontal layer of Couple-stress nanofluid in a porous medium is investigated. Darcy model is used for porous medium. The model used for nanofluid incorporates the effect of Brownian diffusion and thermophoresis. The flux of volume fraction of nanoparticle is taken to be zero on the isothermal boundaries. Normal mode analysis and perturbation method is employed to solve the eigenvalue problem with the Rayleigh number as eigenvalue. Oscillatory convection cannot occur for the problem. The effects of Couple-stress parameter, Lewis number, modified diffusivity ratio, concentration Rayleigh number and porosity on stationary convection are shown both analytically and graphically.

JTAM, Sofia, vol. 47 Issue 1 pp. 69-84 (2017), [Full Article]

Computation and Monitoring of the Soil Moisture Index on Bulgarian Territory

Olga Nitcheva1, Borislav Milev2
1Institute of Mechanics, Bulgarian Academy of Sciences, 4 Acad. Bonchev Str., Sofia, Bulgaria
2European Politechnical University, 23 St.St. Kiril and Methody Str., Pernik, Bulgaria

The estimation and monitoring of the soil moisture index (SMI) on the Bulgarian territory is an important task from agricultural, fire and flood safety and water resources management aspects. It is not achievable by direct measurements as in the country there are only 20 field observation points. For the purpose adequate spatially distributed mathematical models must be employed. The paper demonstrates the implementation of the task by application of the Community Land Model (CLM) and all other procedures related to the preparation of GIS maps (Geographic Information Systems) for monitoring of monthly mean soil moisture index.

JTAM, Sofia, vol. 47 Issue 1 pp. 85-93 (2017), [Full Article]

Bulgarian Journal of Theoretical and Applied Mechanics 46'Years of Science and Culture

Soufiane Haddout1, Zhiyi Chen2
1Department of Physics, Faculty of Science, Ibn Tofail University, B.P 242, 14000 Kenitra, Morocco
2University of British Columbia, 1935 Lower Mall, Vancouver, BC Canada V6T1X1, Canada

We feel highly honoured and privileged to write this: As the distinguished American poet and philosopher RalphWaldo Emerson said: “Don’t be too timid and squeamish about your actions. All life is just an experiment. The more experiments you make the better. What if they are a little coarse and you may get your coat soiled or torn? What if you do fail, and get fairly rolled in the dirt once or twice? Up again, you shall never be so afraid of a tumble.” When the authors started to write this paper, he considered what introduction to use in this section. Since 1997’s lots of papers were written by authors from around the world in Bulgarian Journal of Theoretical and Applied Mechanics are the fruits of scientific research are nourished by many roots, including the earlier work of other scientists. This fruit of science is going through by many experiences and efforts. On the other hand, the name proposed by the National Committee of Theoretical and Applied Mechanics at the Bulgarian Academy of Sciences: “Theoretical Mechanics” is wonderful, theoretical mechanics with an “applied aspect” even more wonderful. This declaration is a love story, combined the science and culture during 46’years of the journal evolution.

JTAM, Sofia, vol. 47 Issue 1 pp. 94-95 (2017), [Full Article]


13th National Congress on Theoretical and Applied Mechanics with International Participation

JTAM, Sofia, vol. 47 Issue 1 pp. 96-96 (2017), [Full Article]


IUTAM Symposium on Intelligent Multibody Systems – Dynamics, Control, Simulation

JTAM, Sofia, vol. 47 Issue 1 pp. 97-97 (2017), [Full Article]


International Conference on Engineering Vibration

JTAM, Sofia, vol. 47 Issue 1 pp. 98-99 (2017), [Full Article]