Issue 2

JTAM, Sofia, vol. 45 Issue 2 (2015)

Two Dimensional Functionally Graded Material Finite Thick Hollow Cylinder Axisymmetric Vibration Mode Shapes Analysis Based on Exact Elasticity Theory

Masoud Asgari
Faculty of Mechanical Engineering, K. N. Toosi University of Technology, Pardis Street, Molla-Sadra Avenue, Vanak Square, Tehran, Iran

A thick hollow cylinder with finite length made of twodimensional functionally graded material (2D-FGM) is considered and its natural modes are determined, based on great importance of mode shapes information in order to understand vibration behaviour of structures. Three dimensional theory of elasticity implemented for problem formulation, since mode shapes of a thick cylinder are three dimensional even with axisymmetric conditions. The axisymmetric conditions are assumed for the 2D-FGM cylinder. The material properties of the cylinder are varied in the radial and axial directions, with power law functions. Effects of volume fraction distribution on the different types of symmetric mode shapes configuration and vibration behaviour of a simply supported cylinder are analyzed. Three dimensional equations of motion areused and the eigen value problem is developed, based on direct variation method.

JTAM, Sofia, vol. 45 Issue 2 pp. 003-20 (2015), [Full Article]

The Generalized Two Dimensional Thermal-Electro-Elastic Solution for the Cracked-Half-Elliptical-Hole Problem in a Half Plane

Y. J. Wang1,2, C. F. Gao2, H. P. Song2, S. C. Xing2
1College of Engineering, Nanjing Agricultural University, Nanjing 210031, China
2State key Laboratory of Mechanics and Control of Mechanical Structures, Nanjing University of Aeronautics & Astronautics, Nanjing 210016, China

The half elliptical hole with an edge crack in a thermopiezo electric material is studied by using the complex variable method. First, the mapping function which maps the outside of the elliptical hole and the crack in the right half plane into the outside of a circular hole in a full plane is given by the method of conformal mapping. Then, the complex potential functions and the field intensity factors (FIF) are presented according to the boundary conditions, respectively. Some useful results can be found by numerical analysis: 1) The influence of the heat flux on FIF depends on the model of the crack; 2) The shape and the size of the hole possess a significant effect on the field distribution at the crack tip.

JTAM, Sofia, vol. 45 Issue 2 pp. 021-44 (2015), [Full Article]

Adaptive Control and Synchronization of Sprott J System with Estimation of Fully Unknown Parameters

Mitul Islam1, Nurul Islam2, Svetoslav Nikolov3,4
1203, B.T. Road, Indian Statistical Institute, Kolkata 700108, India
2Ramakrishna Mission College (Autonomous), Narendrapur, Kolkata 700103, India
3Institute of Mechanics, Bulgarian Academy of Sciences, Acad. G. Bonchev St., Bl. 4, 1113 Sofia, Bulgari
4University of Transport, 158, G. Milev St., 1574 Sofia, Bulgaria

This communication develops an adaptive scheme for control and synchronization of Sprott J system with fully unknown parameters. The scheme provides an elegant strategy of designing estimators for identification of the unknown parameters of the underlying dynamical system. Adaptive control and update laws are proposed to globally stabilize the chaotic Sprott J system. A pair of identical Sprott J systems with unknown parameters are globally synchronized with the help of adaptive control and parameter update laws. The results are established using LaSalle invariance principle, which lays down weaker restrictions on the derivatives of the Lyapunov function, and producing more general results. All the results obtained in the paper are global in nature. Numerical simulations are performed to illustrate the validity and effectiveness of the proposed adaptive control and synchronization scheme in the context of the Sprott J system. The parameter identification capability of the scheme is also explored.

JTAM, Sofia, vol. 45 Issue 2 pp. 045-58 (2015), [Full Article]

Wave Propagation Due to an Embedded Seismic Source in a Graded Half-Plane with Relief Peculiarities. Part II: Parametric Study

I.-K. Fontara1, F. Wuttke1, S. Parvanova2, P. Dineva3
1Institute of Applied Geo-science, Christian-Albrechts-University of Kiel, Germany
2University of Architecture, Civil Engineering and Geodesy, Faculty of Structural Engineering, Structural Mechanics, 1, Hr. Smirnenski Blvd, 1046 Sofia, Bulgaria
3Institute of Mechanics, Bulgarian Academy of Sciences, Acad. G. Bonchev St., Bl. 4, 1113 Sofia, Bulgaria

The mechanical model and the accompanied computational technique, based on the boundary integral equation method (BIEM) and Green’s function for continuously inhomogeneous half-plane were described in the first part of this work. 2D elastodynamic problem for quadratically inhomogeneous and heterogeneous geological area was defined in the first part of our work. The aim of the current second part is to demonstrate the accuracy and the convergence of the proposed computational tool. Furthermore, subsequent extensive parametric study will illustrate, that the seismic wave field is a complex result of mutual play of different key factors as free-surface relief, wave characteristics, as frequency and wavelength, seismic source properties, type and characteristics of the material gradient, existence of different type of heterogeneities and their interactions.

JTAM, Sofia, vol. 45 Issue 2 pp. 059-74 (2015), [Full Article]

Temperature Non-Homogeneieties in a Catalytic Reactor with a Periodic Change in the Direction of the Reaction Mixture Feed

Ivanka Zheleva
Ruse University, 8 Studentska str., 7017 Ruse, Bulgaria

Temperature non-homogeneities in a catalytic reactor with periodic change in the direction of the reaction mixture feed is investigated in the present work. The temperature of the reaction mixture is described using a numerical algorithm for simulation of the work of the catalytic reactor, graphically shown and commented. The influence of the higher catalyst layer porosity in the wall area upon the temperature distribution in the reactor is studied. The existence of two different regimes is shown – a high temperature one in the middle part of the layer and a low temperature one in the high porosity area of the layer in contact with the reactor wall. This leads to not very effective usage of the catalyst in these parts of the catalyst layer in the reactor. This simulation can be used for better understanding and controlling of the examined catalytic process.

JTAM, Sofia, vol. 45 Issue 2 pp. 075-90 (2015), [Full Article]

Stress Analysis of Lap Joints with Embedded Cover Plate

Bahattin İşcan
Department of Mechanics, Vocational School of Higher Education, Batman University, Batman 72060, Turkey

In this study, the effects of the bonding joints that are partly embedded in the adherent on the tensile behaviour of reinforcing plate adhesive joint have been investigated by 2D finite element method. In the study, the SBT 9244 material was used as the adhesive, and the adherent was the AA2024-T3 material. Three different models were built for the height of the embedded part in the adherent (a) and five models for the length of the embedded part (b), while three models were built for the total overlap length (c). Results showed that with the increase of the height of the embedded part and total overlap length, the strength of the joint was considerably increased. The increase of the length of the embedded part was initially led to an increase in the strength of the joints but after 0.25 value of the b/c the strength was reduced.

JTAM, Sofia, vol. 45 Issue 2 pp. 091-100 (2015), [Full Article]

In Memoriam Dr. Vijay Kumar Verma

Joginder Singh Dhiman
Department of Mathematics Himachal Pradesh University Summerhill, Shimla (H.P.)-171005

JTAM, Sofia, vol. 45 Issue 2 pp. 101-102 (2015), [Full Article]