Rumiana Kotsilkova, Irena Borovanska, Peter Todorov, Evgeni Ivanov, Dzhihan Menseidov, Sudip Chakraborty and Chiranjib Bhattacharjee
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.
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.
Tsviatko V. Rangelov, Petia S. Dineva and George D. Manolis
The aim of this study is to develop an efficient numerical technique using the non-hypersingular, traction boundary integral equation method (BIEM) for solving wave propagation problems in an anisotropic, viscoelastic plane with cracks. The methodology can be extended from the macro-scale with certain modifications to the nano-scale. Furthermore, the proposed approach can be applied to any type of anisotropic material insofar as the BIEM formulation is based on the fundamental solution of the governing wave equation derived for the case of general anisotropy. The following examples are solved: (i) a straight crack in a viscoelastic orthotropic plane, and (ii) a blunt nano-crack inside a material of the same type. The mathematical modelling effort starts from linear fracture mechanics, and adds the fractional derivative concept for viscoelastic wave propagation, plus the surface elasticity model of M. E. Gurtin and A. I. Murdoch, which leads to nonclassical boundary conditions at the nano-scale. Conditions of plane strain are assumed to hold. Following verification of the numerical scheme through comparison studies, further numerical simulations serve to investigate the dependence of the stress intensity factor (SIF) and of the stress concentration factor (SCF) that develop in a cracked inhomogeneous plane on (i) the degree of anisotropy, (ii) the presence of viscoelasticity, (iii) the size effect with the associated surface elasticity phenomena, and (iv) finally the type of the dynamic disturbance propagating through the bulk material.
The hydromagnetic nanofluid flow over a stretching sheet in a porous medium with variable wall thickness in the presence of Brownian motion and thermophoresis is investigated. The heat transfer characteristics with variable conductivity are explored by using Cattaneo-Christov heat flux model. The governing non-linear ordinary differential equations are solved by using boundary value problem default solver in MATLAB bvp4c package. The impact of various important flow parameters on velocity, temperature and nanoparticle concentration as well as the friction factor coefficient and the rate of heat and mass transfer coefficients are presented and discussed through graphs and tables. It is found that the fluid velocity is accelerated with an increase in wall thickness parameter for n > 1, while the reverse trend is observed for n < 1.
Dominik Kern, Ignacio Romero, Sergio Conde Martín and Juan Carlos García-Orden
Structure-preserving integrators are in the focus of ongoing research because of their distinguished features of robustness and long time stability. In particular, their formulation for coupled problems that include dissipative mechanisms is still an active topic. Conservative formulations, such as the thermo-elastic case without heat conduction, fit well into a variational framework and have been solved with variational integrators, whereas the inclusions of viscosity and heat conduction are still under investigation. To encompass viscous forces and the classical heat transfer (Fourier’s law), an extension of Hamilton’s principle is required. In this contribution we derive variational integrators for thermo-viscoelastic systems with classical heat transfer. Their results are compared for two discrete model problems vs. energy-entropy-momentum methods.
In this paper, the governing equations of a linear, homogeneous and transversely isotropic rotating micropolar piezoelectric medium are solved for surface wave solutions. The appropriate solutions satisfying the radiation conditions are obtained in a half-space. These solutions are applied to suitable boundary conditions at the free surface of the half-space. A frequency equation for Rayleigh wave is obtained for both charge free and electrically shorted cases. Using iteration method, the non-dimensional wave speed of Rayleigh wave is computed for relevant material constants modelling the medium. The effects of rotation, piezoelectricity, frequency and material parameters are observed graphically on the propagation speed.
This paper is intended to investigate the effects of an inclined magnetic field on the mixed convection flow in a lid-driven porous enclosure filled with nanofluid. Both the left and right vertical walls of the cavity are thermally insulated while the bottom and top horizontal walls are maintained at constant but different temperatures. The governing equations are solved numerically by using finite volume method on a uniformly staggered grid system. The computational results are obtained for various combinations of Richardson number, Darcy number, Hartmann number, inclination angle of magnetic field, and solid volume fraction. It is found that the presence of magnetic field deteriorates the fluid flow, which leads to a significant reduction in the overall heat transfer rate. The inclination angle of magnetic field plays a major role in controlling the magnetic field strength and the overall heat transfer rate is enhanced with the increase of inclination angle of magnetic field. Adding the nanoparticles in the base fluid significantly increases the overall heat transfer rate in the porous medium whether the magnetic field is considered or not.
In the advanced mechanical science the well known fact is that the gravity influences on the natural frequencies and modes even for the vertical structures and pillars. But, the condition that should be fulfilled in order for the gravity to be taken into account is connected with the ration between the gravity value and the geometrical cross section inertia. The gravity is related to the earth acceleration but for moving structures there exist many other acceleration exaggerated forces and such are forces caused by the centrifugal accelerations. Large rotating structures, as wind power generators, chopper wings, large antennas and radars, unfolding space structures and many others are such examples. It is expected, that acceleration based forces influence on the structure modal and frequency properties, which is a subject of the present investigations.
In the paper, rotating beams are subject to investigations and modal and frequency analysis is carried out. Analytical dependences for the natural resonances are derived and their dependences on the angular velocity and centrifugal accelerations are derived. Several examples of large rotating beams with different orientations of the rotating shaft are presented. Numerical experiments are conducted. Time histories of the beam tip deflections, that depict the beam oscillations are presented.
The present paper is devoted to the problem of the assessment of probable crack growth at pressure vessel nozzles zone under the cyclic seismic loads. The approaches to creating distributed pipeline systems, connected to equipment are being proposed. The possibility of using in common different finite element program packages for accurate estimation of the strength of bonded pipelines and pressure vessels systems is shown and justified. The authors propose checking the danger of defects in nozzle domain, evaluate the residual life of the system, basing on the developed approach.
Saeed Ebrahimi, Nader Vahdatazad and Gholamhossein Liaghat
This paper deals with the energy absorption characterization of functionally graded foam (FGF) filled tubes under axial crushing loads by experimental method. The FGF tubes are filled axially by gradient layers of polyurethane foams with different densities. The mechanical properties of the polyurethane foams are firstly obtained from axial compressive tests. Then, the quasi-static compressive tests are carried out for empty tubes, uniform foam filled tubes and FGF filled tubes. Before to present the experimental test results, a nonlinear FEM simulation of the FGF filled tube is carried out in ABAQUS software to gain more insight into the crush deformation patterns, as well as the energy absorption capability of the FGF filled tube. A good agreement between the experimental and simulation results is observed. Finally, the results of experimental test show that an FGF filled tube has excellent energy absorption capacity compared to the ordinary uniform foam-filled tube with the same weight.