Issue 1

JTAM, Sofia, vol. 44 Issue 1 (2014)

A Measuring System with an Additional Channel for Eliminating the Dynamic Error

Dimitar Dichev1, Hristofor Koev1, Petr Louda2
1Department of Machine and Precision Engineering, Technical University of Gabrovo, 4, Hadji Dimitar St., 5300 Gabrovo, Bulgaria
2Department of Material Science, Technical University of Liberec, 2, Studentska St., 46117 Liberec, Czech Republic

The present article views a measuring system for determining the parameters of vessels. The system has high measurement accuracy when operating in both static and dynamic mode. It is designed on a gyro-free principle for plotting a vertical. High accuracy of measurement is achieved by using a simplified design of the mechanical module as well by minimizing the instrumental error. A new solution for improving the measurement accuracy in dynamic mode is offered. The approach presented is based on a method where the dynamic error is eliminated in real time, unlike the existing measurement methods and tools where stabilization of the vertical in the inertial space is used. The results obtained from the theoretical experiments, which have been performed on the basis of the developed mathematical model, demonstrate the effectiveness of the suggested measurement approach.

JTAM, Sofia, vol. 44 Issue 1 pp. 03-20 (2014), [Full Article]

Modelling of Acoustic Emission Source and Wave Response in Layered Materials

A. Alamin1, R. Zhang2
1Department of Mechanical Engineering, Colorado School of Mines, Golden, Colorado, USA
2Department of Civil and Environmental Engineering, Colorado School of Mines, Golden, Colorado, USA

This study proposes a model of wave propagation in layered media for the use in acoustic emission (AE) studies. This model aims to find an AE response at a free surface to the propagating waves originating at a dislocation source either in one layer medium or a layer-to-layer interface. Each of the layered media is assumed to be homogenous, linear elastic and isotropic. An integral transformation method has been applied to determine the wave response in frequency-wave number domain, which is then converted to time-space domain. In the numerical examples, we first select truncated values with the finite integral transformation, so that no wave interference happens in the responses from wave reflection at truncated boundaries. Next, we simulate wave propagation in an elastic half space, and compare results obtained with that from other kind bottom boundary. Next, we introduce a dislocation source in interface and compare a simulated AE wave response obtained with that computed in the layered medium to demonstrate the performance of the model. In each simulation, the results show good agreement with the reference solutions.

JTAM, Sofia, vol. 44 Issue 1 pp. 21-44 (2014), [Full Article]

Application of Metamodelling Techniques for Mechanized Tunnel Simulation

Kavan Khaledi1, Tom Schanz1, Shorash Miro2
1Chair of Foundation Engineering, Soil and Rock Mechanics, Ruhr Universit¨at Bochum, Germany
2Chair of Computing in Engineering, Ruhr Universit¨at Bochum, Germany

Complex engineering problems require using computationally expensive simulations which take relatively long time. In such cases, routine tasks such as design optimization, parameter identification, or sensitivity analysis become impractical since they require thousands or even millions of simulations. A common practice for engineers to solve this problem is to use metamodels in place of actual simulation models. In this paper, we investigate the performance of four metamodelling approaches, namely, Response Surface Methodology, Moving Least Squares, POD-RBF, and Neighborhood Approximation considering the effect of sample size and sampling methods. Our main goal in this work is to find a reliable and robust metamodel technique in order to construct an approximated function for mechanized tunnel simulation. For this reason, a numerical study is carried out on a 3D tunnel modeled in Plaxis3D and the accuracy and robustness of the aforementioned metamodelling techniques are discussed.

JTAM, Sofia, vol. 44 Issue 1 pp. 45-54 (2014), [Full Article]

Time–Harmonic Behaviour of Cracked Piezoelectric Solid by Boundary Integral Equation Method

Tsviatko Rangelov1, Marin Marinov2, Petia Dineva3
1Institute of Mathematics and Informatics, Bulgarian Academy of Sciences, Acad. G. Bonchev St., Bl. 8, 1113 Sofia, Bulgaria
2Computer Science Department, New Bulgarian University, 21, Montevideo St., 1618 Sofia, Bulgaria
3Institute of Mechanics, Bulgarian Academy of Sciences, Acad. G. Bonchev St., Bl. 4, 1113 Sofia, Bulgaria

Anti–plane cracked functionally graded finite piezoelectric solid under time–harmonic elecro–mechanical load is studied by a non hypersingular traction boundary integral equation method (BIEM). Exponentially varying material properties are considered. Numerical solutions are obtained by using Mathematica. The dependance of the intensity factors (IF) – mechanical stress intensity factor (SIF) and electrical field intensity factor (FIF) on the inhomogeneous material parameters, on the type and frequency of the dynamic load and on the crack position are analyzed by numerical illustrative examples.

JTAM, Sofia, vol. 44 Issue 1 pp. 55-78 (2014), [Full Article]

Linear Analysis and Simulation of Interfacial Slip Behaviour for Composite Box Girders

Pengzhen Lu1,2, Changyu Shao2, Renda Zhao3
1Faculty of Civil Engineering and Architecture, Zhejiang University of Technology, Hangzhou 310014, P. R. China
2Shanghai Municipal Engineering Design and Research Institute, Shanghai 200092, P. R. China
3School of Civil Engineering Southwest, Jiaotong University, Chengdu 610031, P. R. China

The slip at the steel-concrete interface in steel-concrete composite beams was studied analytically and numerically. A theoretical description for steel-concrete composite box beams with partial shear interaction based on the partial interaction theory was derived, and equilibrium of the rotation angle w′ was introduced to allow convenient computation of deformation of composite box beams. Numerical simulations of steel-concrete composite box beams subjected to concentrated load and/or uniformly distributed load were conducted. The analytical solutions show excellent agreement with the numerical results. For typical composite box beams used in practice, shear slip in partial composite box beams makes a significant contribution to beam deformation. Even for full composite box beams, slip effects may result in stiffness reduction. However, slip effects are ignored in many design specifications which use transformed section methods; an exception is the American Institute of Steel Construction [1] specifications, which recommend a calculation procedure in the commentary. Finally, the proposed method was extended to analyze the interface slip for shear connectors of different pitch and, to some extent, confirm the accuracy of the predictions.

JTAM, Sofia, vol. 44 Issue 1 pp. 79-96 (2014), [Full Article]

Robonaut 2: Mission, Technologies, Perspectives

Galia V. Tzvetkova
Institute of Mechanics, Bulgarian Academy of Sciences, Acad. G. Bonchev St., Bl. 4, 1113 Sofia, Bulgaria

The paper focuses on key aspects of scientific and technological solutions implemented in the joint project of NASA and General Motors, Robonaut 2, a humanoid robot designed to work in space as a real assistant to astronauts.

JTAM, Sofia, vol. 44 Issue 1 pp. 97-102 (2014), [Full Article]