Issue 1

JTAM, Sofia, vol. 43 Issue 1 (2013)

Full Dynamic Reactions in the Basic Shaft Bearings of Big Band Saw Machine

Boycho Marinov
Institute of Mechanics – BAS, Sofia, 1113, BULGARIA “Acad G.Bonchev” st, Block 4.

The band saws machines are a certain class woodworking machines for longitudinal or transversal cutting as well as for curvilinear wood cutting. These machines saw the wood through a band-saw blade and two feeding wheels. These wheels usually are very large and they are produced with inaccuracies. The centre of mass of the disc is displaced from the axis of rotation of the distance e (eccentricity) and the axis of the disk makes an angle with the axis of rotation. In this paper, the dynamic reactions in the bearings of the basic shaft, which drives the band saw machines, are analyzed. These reactions are caused by the external loading and the kinematics and the mass characteristics of the rotating disk. The expressions for the full dynamic reactions are obtained. These expressions allow the parameters of the machines to be chosen in such a way that the loading in the shafts and the bearings to be minimal

JTAM, Sofia, vol. 43 Issue 1 pp. 03-18 (2013), [Full Article]

Vibration Modal Solutions Developing of the Elastic Circular Membrane in Polar Coordinates Based on the Fourier-Bessel Series

Amir Javidinejad
Zodiac Aerospace 7330 Lincoln Way Garden Grove, CA USA

This paper is written to show the development of the vibration modal solutions of elastic circular membranes in polar coordinates using the Fourier-Bessel series. The ordinary differential equation approach is utilized and the Laplacian of wave equation in polar coordinates is used to develop the solution of the membrane vibrations. A Fourier-Bessel solution is developed for the vibration of the elastic circular membrane in specific separation of variables is elaborated and based on the initial and boundary conditions. A numerical example is provided to show the application of such theory.

JTAM, Sofia, vol. 43 Issue 1 pp. 19-26 (2013), [Full Article]

Software for Graphical Investigation of Planar and Spatial Closed Kinematic Chains for Robots and Manipulators

Grigor Zhelev
Institute of System Engineering and Robotics, Bulgarian Academy of Sciences Acad. G.Bonchev Str, Bl 2, 1113 Sofia, Bulgaria

The aim of this paper is to present a developed computational program for computer graphical modelling of planar and spatial robots and manipulators closed kinematic chains. In order to demonstrate the functionality of the program two types of 5-bars and two types of 8-bars closed manipulators are used for simulation of the kinematic models. The basic mathematical calculations for visual representation of kinematic models are made, as well as calculations and visualisation of the manipulators working zone frame by frame. The presented program can be used for analyzing closed kinematic chains, solving tasks from the real practice or for students training.

JTAM, Sofia, vol. 43 Issue 1 pp. 27-38 (2013), [Full Article]

Numerical Analysis of Large Telescopes in Terms of Induced Loads and Resulting Geometrical Stability

S. Upnere, N. Jekabsons, R. Joffe
Engineering Research Institute Ventspils International Radio Astronomy Center of the Ventspils University College, Inzenieru-101, LV-3600, Ventspils, Latvia

Comprehensive numerical studies, involving structural and Computational Fluid Dynamics (CFD) analysis, have been carried out at the Engineering Research Institute “Ventspils International Radio Astronomy Center” (VIRAC) of the Ventspils University College to investigate the gravitational and wind load effects on large, ground-based radio telescopes RT-32 performance. Gravitational distortions appear to be the main limiting factor for the reflector performance in everyday operation. Random loads caused by wind gusts (unavoidable at zenith) contribute to the fatigue accumulation.

JTAM, Sofia, vol. 43 Issue 1 pp. 39-46 (2013), [Full Article]

Controllable Compliance Joint for Human Oriented Robots

Mihail Tsveov, Dimitar Chakarov
Institute of Mechanics - BAS, 1113 Sofia, “Acad. G.Bonchev” Str., Block 4

In the paper, different approaches for compliance control for human oriented robots are revealed. The approaches based on the non-antagonistic and antagonistic actuation are compared. In addition, an approach is investigated in this work for the compliance and the position control in the joint by means of antagonistic actuation. It is based on the capability of the joint with torsion leaf springs to adjust its stiffness. Models of joint stiffness are presented in this paper with antagonistic and non-antagonistic influence of the spring forces on the joint motion. The stiffness and the position control possibilities are investigated and the opportunity for their decoupling as well. Some results of numerical experiments are presented in the paper too.

JTAM, Sofia, vol. 43 Issue 1 pp. 47-60 (2013), [Full Article]

Diagnosis of Type, Location and Size of Cracks by Using Generalized Differential Quadrature and Rayleigh Quotient Methods

Majid Akbarzadeh Khorshidi1, Delara Soltani2
1School of Mechanical Engineering, College of Engineering, University of Tehran, Iran
2School of Mechanical Engineering, Mazandaran Institute of Technology, Iran

In this paper, an appropriate and accurate algorithm is proposed to diagnosis of lateral or vertical cracks on beam, based on beam natural frequencies. Clamped-free boundary conditions are assumed for the beam. The crack in beam is modelled by without mass torsion spring. Then, the relationship between the beam natural frequencies, location and stiffness of the crack is presented by using the Rayleigh quotient and the governing equation is solved by using generalized differential quadrature method (GDQM). If there is only one crack in the beam, then three natural frequencies are used as inputs to the algorithm and mode shapes corresponding to each the natural frequencies are calculated. Finally, type, location and severity of cracks in beam, are diagnosed.

JTAM, Sofia, vol. 43 Issue 1 pp. 61-70 (2013), [Full Article]

Computer Simulation of the Heat Transfer Process and the Prediction of Microstructure during Crystallization of Metal Alloys

Georgi Georgiev, Sasho Popov, Valentin Manolov, Rositsa Dimitrova, Pavel Kuzmanov
Institute of Metal Science, Equipment and Technologies “Acad. A.Balevski” with Hydroaerodynamics Centre 67, Shipchenski Prohod Blvd, 1574 Sofia, Bulgaria

Processes of crystallization during casting formation from aluminum alloys, steel and cast iron have been studied using 3-D computer simulation. Temperature fields of castings have been obtained and the microstructure distribution of these castings has been predicted. A comparison between numerical results and experimental measurement has been made. It is proved that the proposed approach is suitable for study and analysis of casting technologies.

JTAM, Sofia, vol. 43 Issue 1 pp. 71-78 (2013), [Full Article]

Two-Temperature Green and Naghdi Model on Thermoelastc Interaction in an Infinite Fibre-Reinforced Anisotropic Plate Containing a Circular Hole

Ibrahim A. Abbas1,2
1Department of Mathematics, Faculty of Science and Arts - Khulais, King Abdulaziz University, Jeddah, Saudi Arabia
2Department of mathematics, Faculty of Science, Sohag University, Sohag, Egypt

The present work is aimed at the study of thermoelastic interactions in an infinite fibre-reinforced anisotropic plate containing a circular hole in the context of a theory of generalized thermoelasticity in which the theory of heat conduction in deformable bodies depends on two different temperatures - conductive temperature and dynamic temperature. The two-temperature generalized thermoelastic model and one-temperature generalized thermoelastic model are formulated on the basis of Green and Naghdi theory of type II (2TGNII). The circular hole surface is assumed to be stress free and is subjected to a thermal shock. The problem is solved numerically using a finite element method. The effects of the presence and absence of reinforcement on the conductive temperature, the dynamical temperature, the stresses and the displacement distributions are studied. A comparison is made with the results predicted by the two theories. Results carried out in this paper can be used to design various fibre-reinforced anisotropic elements under thermal load to meet special engineering requirements.

JTAM, Sofia, vol. 43 Issue 1 pp. 79-94 (2013), [Full Article]

Prof. Zapryan Zapryanov (Scientist and Teacher in Fluid Mechanics)

Stefan Radev, Sonia Tabakova
Institute of Mechanics, the Bulgarian Academy of Sciences, Acad. G. Bonchev St., Bl. 4, 1113 Sofia, Bulgaria

JTAM, Sofia, vol. 43 Issue 1 pp. 95-102 (2013), [Full Article]