Issue 4

JTAM, Sofia, vol. 40 Issue 4 (2010)

Research on Dynamic System with Distributed and Discrete Parameters Subjected to Pulse Excitation

Y. Slavchev, G. Venkov
Technical University of Sofia, Faculty of Mechanical Engineering, 8 Kliment Ohridski, 1000 Sofia, Bulgaria

A research is performed on a system of a simply supported Euler-Bernoulli beam, modelled as a continuum with distributed parameters that serves as an elastic base carrying two oscillators connected in series. System behaviour for various cases of applied pulse load to the oscillators is studied. The loading occasions are common to hoisting cranes, bridges, trestles, etc. The problem is discretized by the finite element method. Solutions derived by the matrix exponential method and ANSYS software are proposed. System deformation due to its deadweight, beam and oscillators damping as well as the eigen-values of the system and its components are considered.

JTAM, Sofia, vol. 40 Issue 4 pp. 03-10 (2010), [Full Article]

Creation of Semifluxons in 0 - k Josephson Structures

T.L. Boyadjiev1, H.T. Melemov2
1Institute of Mechanics , Bulgarian Academy of Sciences , Acad. G. Bonchev St ,Bl. 4, 1113 Sofia, Bulgaria
2University of Plovdiv-Branch Smoljan, 32, Dicho Petrov St., Smoljan, Bulgaria

The static distributions of the magnetic flux in an infinite 0 - k Josephson junction is the object of investigation. Semifluxons in 0 - k junxons are obtained by the help with the known one-fluxons’ solutions in the homogeneous junction and the k junction. Analytic solutions of the distribution of the magnetic flux in 0 – k junction are obtained. Analytic solutions of a chain of n parallel connected homogeneous junctions and k junctions are constructed based on the obtained solutions in 0 – k and k – 0 junctions.

JTAM, Sofia, vol. 40 Issue 4 pp. 11-22 (2010), [Full Article]

Computer Modelling and Simulation of Controllable Compliance Joint

M. Tsveov, D. Chakarov
Institute of Mechanics, Bulgarian Academy of Sciences, “Acad. G.Bonchev”Str. , Bl.4, 1113 Sofia, Bulgaria

Controllable compliance of robot joint is simulated by software, using two actuators – one for position control and other for compliance control, including a leaf spring. The joint is simulated when changing spring’s dimensions. Results are shown for impact interaction and fast positioning.

JTAM, Sofia, vol. 40 Issue 4 pp. 23-30 (2010), [Full Article]

Numerical Simulation of Suspension Flow Using Direct Simulation Monte Carlo (DSMC) Method for the Particulate Phase

R. Shtinkova, E. Toshev
Institute of Mechanics, Bulgarian Academy of Sciences, Acad. G. Bonchev Str., Bl. 4,1113 Sofia, Bulgaria

We use the Direct Simulation Monte Carlo (DSMC) method to simulate 3D motion of the particulate phase in dilute gas-solid flows and investigate the influence of the Saffman lift force and the influence of the collision model for the particle-particle interactions on the flow structure. DSMC and the Smoluchowski formula for collisions in laminar shear flow are used as collision models and are compared. Vertical upward flow of gas-solid suspension in an entrance part of a tube is simulated and used as a test-case. Both the application of the Saffman force and the choice of collision model are proved to have considerable influence on the flow structure.

JTAM, Sofia, vol. 40 Issue 4 pp. 31-40 (2010), [Full Article]

New Approach to Modelling the Deformational Processes in Crystalline Solid Bodies

Anguel Baltov
Institute of Mechanics, Bulgarian Academy of Sciences, Acad. G. Bonchev St., Bl. 4, 1113 Sofia, Bulgaria

In the present paper some now-a-days approaches to modeling the deformation processes in the crystalline bulk materials are discussed:(i) multilevel models on macro and meso level; (ii) thermodynamic approach using EIT (Extended Irreversible Thermodynamic), especially for meso level; (iii) modern experimental methods; (iv) modern calculation methods.

JTAM, Sofia, vol. 40 Issue 4 pp. 41-54 (2010), [Full Article]

Modelling and Static Analysis of Two Dimensional Regions Containing Multi-Phase Inclusions by Boundary Element Method

Sonia Parvanova
University of Architecture, Civil Engineering and Geodesy, 1, Christo Smirnenski Blvd, 1046, Sofia, Bulgaria

In this paper an idea related to the effective implementation of the Boundary Element Method (BEM) is developed. This procedure is very suitable for modelling a composite medium with large number of identical inclusions, because its application results to considerable reduction of the model’s degrees of freedom. This reduction is proportional to the number of inclusion phases: larger number of phases smaller degrees of freedom compared to classical BEM modelling. A recurrent formula for excluding the inside inclusion nodal values is derived and used in the computer code. It turns out that the elaborated technique can be applied for the static micromechanical analysis of composites containing repeated geometric structures representing openings, cracks or multiphase inclusions uniformly or randomly distributed in the matrix. One numerical example is presented along with some numerical results. They are compared with the results based on the finite element method solution, performed by the well known ANSYS general purpose program.

JTAM, Sofia, vol. 40 Issue 4 pp. 55-72 (2010), [Full Article]

Segmental Parameters of Bulgarian Woman within Modified Kwon Human Body Model

Gergana Stefanova Nikolova
Institute of Mechanics, Bulgarian Academy of Sciences, Acad. G. Bonchev St., Bl. 4, 1113 Sofia, Bulgaria

We present a new geometrical biomechanical model of the Bulgarian women, which represents a modification of the one proposed by Kwon [1]. We performed our own anthropometric measurements of 50 women aged between 30–40 years in order to determine the parameters used in the Kwon’s model. The remaining set of data needed is taken from the representative anthropological investigation of Bulgarian females [2], in which data for 2855 individuals has been collected. We calculate analytically and estimate numerically the mass-inertial characteristics of the segments using the model suggested after deriving the corresponding analytical expressions needed. We present a comparison between the results obtained within this model and our previous results reported in [3], as well as with another data for Caucasian reported in literature. The present investigation provides data for a set of parameters of the Bulgarian women, for which no direct measurements are available. The model proposed is oriented to application in medicine and engineering.

JTAM, Sofia, vol. 40 Issue 4 pp. 73-80 (2010), [Full Article]

Device for Control of Active Ankle-Foot Orthosis and Monitoring System for Gait Analysis

Ivanka Veneva
Institute of Mechanics, Bulgarian Academy of Sciences, Acad. G. Bonchev St., Bl. 4, 1113 Sofia, Bulgaria

The aim of this paper is to present an intelligent device for control of an active ankle-foot orthosis, which can be used for assisting and rehabilitation in the cases of an injured ankle-foot complex together with a graphical interface for representation and analysis of the data acquired during human motion. The device proposed for control of the Ankle Foot Orthosis (AFO) consists of a microcontroller, an actuator and a sensor system. The microcontroller estimates forward speed and modulates swing phase flexion and extension during the gait in order to assure automatic adaptation of the AFO joint torque by using position control with feedback. Data acquired from the sensors is transferred to a graphical user interface for visualization, interpretation and analysis in monitoring mode.

JTAM, Sofia, vol. 40 Issue 4 pp. 81-92 (2010), [Full Article]