Issue 3
JTAM, Sofia, vol. 48 Issue 3 (2018)

FLEXURAL MOTION UNDER MOVING MASSES OF PRESTRESSED SIMPLY SUPPORTED PLATE RESTING ON BI-PARAMETRIC FOUNDATION

T.D. Awodola
Department of Mathematical Sciences, Federal University of Technology, Akure, Nigeria


In this investigation, the flexural vibration of a prestressed and simply supported rectangular plate carrying moving concentrated masses and resting on bi-parametric (Pasternak) elastic foundation is considered. In order to solve the governing fourth order partial differential equation, a technique based on separation of variables is used to reduce the equation with variable and singular coefficients to a sequence of coupled second order ordinary differential equations. The modified method of Struble and the integral transformations are then employed for the solutions of the reduced equations. The numerical results in plotted curves show that as the value of the axial force in x-direction (Nx) increases, the response amplitudes of the plates decrease, the same effect is produced as the axial force in y-direction (Ny) increases for both cases of moving force and moving mass problems of the prestressed and simply supported rectangular plate resting on Pasternak elastic foundation. The deflection of the plate also decreases in each case as the values of the Shear modulus G0 and the rotatory inertia correction factor R0 increase. Also, the transverse deflections of the prestressed rectangular plates under the actions of moving masses are higher than those when only the force effects of the moving loads are considered, the analysis of resonance shows that resonance is attained earlier in moving mass problem than in moving force problem and the critical speed for the moving mass problem is reached prior to that of the moving force problem which implies that it is risky to rely on a design based on the moving force solution. Furthermore, the response amplitudes of the moving mass problem increase with increasing mass ratio and approach those of the moving force as the mass ratio approaches zero for the prestressed and simply supported rectangular plates resting on uniform Pasternak elastic foundation.

JTAM, Sofia, vol. 48 Issue 3 pp. 03-22 (2018), [Full Article]

MULTISCALE MONITORING OF DEFORMATION FIELDS BY DIGITAL IMAGE CORRELATION METHOD

G. Stoilov, V. Kavardzhikov, D. Pashkouleva
Institute of Mechanics, Bulgarian Academy of Sciences, Acad. G. Bonchev Str., Bl. 4, 1113 Sofia, Bulgaria

The review of progress in numerical synthesis and study of strain sensors patterns, which can be used for realization of digital image correlation (DIC) and its applications in engineering practice, is presented. Problems related to monitoring a large area of an objects surface while subsequently increasing the image scale and concentrating observation only to the area where the largest deformation has taken place are considered. An algorithm for numerical synthesizing of specialized strain sensor patterns is proposed. Results from a physical experiment are also reported.

JTAM, Sofia, vol. 48 Issue 3 pp. 23-40 (2018), [Full Article]

PERFORMANCE OF A MICRO/NANO WEDGE-PLATFORM THRUST SLIDER BEARING BASED ON THE LIMITING SHEAR STRENGTH MODEL

Linyue Guan, Mingjun Pang, Xuedong Jiang, Yongbin Zhang
College of Mechanical Engineering, Changzhou University, Changzhou, Jiangsu Province, China

This paper presents an analysis for a micro/nano wedge-platform thrust slider bearing by using the flow factor approach model. The contact-fluid interfacial shear strength was taken into account for describing the interfacial slippage. The carried load and friction coefficient of the bearing were calculated when different contact-fluid interactions were used. It was found that the interaction strength between the contact and the fluid has a significant contribution to the load-carrying capacity of the bearing, a weak contact-fluid interaction in the bearing inlet zone and its resulting interfacial slippage on the stationary contact surface is beneficial for both the load-carrying capacity and the friction coefficient of the bearing, while a strong contact-fluid interaction in the bearing outlet zone is contrarily harmful. The relative slip amount is linearly distributed in the bearing inlet zone, when the interfacial slippage occurs on the stationary surface in this subzone because of the low interfacial shear strength.

JTAM, Sofia, vol. 48 Issue 3 pp. 41-58 (2018), [Full Article]

WAVE MECHANICS AND HYDRODYNAMIC WAVE FORCES IN DRINKING WATER UNDER THE LAKE PIPELINE IN BURDUR LAKE — TURKEY

F. Ebru Yildiz
Technical Expert at Bank of Provinces (İller Bank), Department of Project, Design of Waste Water Treatment Plants and Outfalls Group Yeni Ziraat Mah., Ankara, Turkey

Burdur Lake is one of the largest lakes of Turkey consisting of about 23 700 ha. Unfortunately, Burdur Lake area and the lake depth decrease each year. Additionally, the salinity increased twice in 30 years because of the aridity. Burdur Municipality Drinking Water Pipeline had been constructed under Burdur Lake in 2002. Groundwater drained from deep wells was flowed to Burdur city under Burdur Lake. Burdur drinking water pipe line under Burdur Lake was broken to pieces during the storms in 2008, 2010 and 2013. In this study, the stability analyses of Burdur Drinking Water Underlake Pipeline system were made for 2002-2008, 2008-2010 and 2010-2013 time periods by using the techniques of wave mechanics. Stability analysis was also made for the pipeline in the ditch with the gabions as a projection. Horizontal and vertical wave forces, weights of the cement bags and marble filled gabions were used at the calculations of wave mechanics. Soil mechanics parameters of the Burdur Lake and water hammer effect of the drinking water in the pipe line were also investigated in the content of this study. Burdur Lake's depth decreases every year because of the aridity, so the horizontal and vertical wave forces over the pipeline increase due to the decrease of the depth. Burdur Municipality could not use this pipeline system, so pipeline system must be placed in a ditch and suitable gabions that must be used in order to obtain the stability.

JTAM, Sofia, vol. 48 Issue 3 pp. 59-73 (2018), [Full Article]

A MODEL OF A MOTION OF SUBSTANCE IN A CHANNEL OF A NETWORK

Nikolay K. Vitanov, Roumen Borisov
Institute of Mechanics, Bulgarian Academy of Sciences, Akad. G. Bonchev Str., Bl. 4, 1113 Sofia, Bulgaria

We study the problem of the motion of substance in a channel of a network for the case of channel having two arms. Stationary regime of the flow of the substance is considered. Analytical relationships for the distribution of the substance in the nodes of the arms of the channel are obtained. The obtained results are discussed from the point of view of technological applications of the model (e.g., motion of substances such as water in complex technological facilities).

JTAM, Sofia, vol. 48 Issue 3 pp. 74-84 (2018), [Full Article]

TENSILE AND SURFACE MECHANICAL PROPERTIES OF POLYETHERSULPHONE (PES) AND POLYVINYLIDENE FLUORIDE (PVDF) MEMBRANES

Rumiana Kotsilkova1, Irena Borovanska1, Peter Todorov1, Evgeni Ivanov1, Dzhihan Menseidov1, Sudip Chakraborty2, Chiranjib Bhattacharjee2
1Institute of Mechanics, Bulgarian Academy of Sciences, Akad. G. Bonchev Str., Bl. 4, 1113 Sofia, Bulgaria
2Dept. of Chemical Engineering, Jadavpur University, Kolkata-700032 India

Mechanical properties of polymer membranes (strength, hardness and elasticity) are very important parameters for the application performance, e.g. water purification. We study the tensile and surface mechanical properties of hollow fiber and flat sheets mat membranes based on PES and PVDF polymers. Tensile test, nanoindentation and atom force microscopy are used for characterization at macro and nanoscale. Mechanical properties are correlated with pore structure of membranes. The reinforced PVDF HF hollow fiber membranes show 30-fold higher stiffness and 3-fold higher hardness compared to non-reinforced PES HF. Surface mechanical properties of flat sheet membranes are strongly improved by decreasing the pore size. The smoothest surface with 100–200 nm roughness has the best surface mechanical performance obtained by nanoindentation.

JTAM, Sofia, vol. 48 Issue 3 pp. 85-99 (2018), [Full Article]