Current Issue : April - June Volume : 2013 Issue Number : 2 Articles : 6 Articles
The imperfection sensitive buckling loads of fibre reinforced polymeric (FRP) composite cylindrical shells under axial compression\r\ncan be optimised with respect to many material and geometric parameters. Current approaches, using mathematical algorithms\r\nto optimise the linearised classical critical loads with respect to many design variables, generally ignore the potential reductions\r\nin elastic load carrying capacities that result from the severe sensitivities of buckling loads to the effects of initial imperfections.\r\nThis paper applies a lower-bound design philosophy called the reduced stiffness method (RSM) to the optimisation design of FRP\r\nshell buckling. A physical optimisation in terms of parametric studies is carried out for simply supported, 6-ply symmetric, glassepoxy\r\ncircular cylindrical shells under uniform axial load. It is shown that under the guidance of RSM, safe lower-bound buckling\r\nloads can be enhanced greatly by choosing appropriate combinations of design parameters. It is demonstrated how this approach\r\nencourages the delineation of those components of the shell�s membrane and bending stiffness that are important and those that\r\nare unimportant within each of the prospective buckling modes. On this basis, it is argued that the RSM provides not only a safe\r\nbut also a more rational strategy for better design decision making....
Convective flows can develop naturally within the porous materials if they are subject to external heating with/without internal heat\r\nsource. In this work, the heat is assumed to be generated internally within the porous enclosure at a rate proportional to a power\r\nof the temperature difference. This relation is an approximation of the state of some exothermic chemical reaction. An inclined\r\nmagnetic field is imposed to the porous enclosure. Darcy, model is used to formulate the porous layer and finite difference method\r\nis applied to solve the governing equations. The obtained results indicate that strong internal heating can generate significant\r\nmaximum fluid temperatures above the heated wall temperature, and location of the maximum fluid temperature moves towards\r\nthe center of the top wall by strengthening the magnetic field. Local heating exponent does not have a major effect on the flow and\r\ntemperature distributions as well as the heat transfer performance within the porous medium. The large magnetic fields, regardless\r\nof direction, are effective to suppress the convective flows and reduce the rate of heat transfer....
We use molecular dynamics to simulate fluid flows between two parallel plates with constant wall temperature. Unlike the usual\r\napproach in molecular dynamics, instead of applying an external force on the molecules, the periodic boundary conditions are\r\nmodified to create a pressure difference between the inlet and the outlet sections of the computational domain. The simulation\r\nresults include velocity, pressure, density, and temperature profiles obtained by the new method. These results are compared\r\nwith approximate solutions for nonisothermal Poiseuille flows. The method is also applied to simulate a flow in a rib-roughened\r\nchannel....
Rotating machinery such as induction motors and gears driven by shafts are widely used in industry. A variety of techniques\r\nhave been employed over the past several decades for fault detection and identification in such machinery. However, there is no\r\nuniversally accepted set of practices with comprehensive diagnostic capabilities. This paper presents a new and sensitive approach,\r\nto detect faults in rotating machines; based on principal component techniques and residual matrix analysis (PCRMA) of the\r\nvibration measured signals. The residual matrix for machinery vibration is extracted using the PCA method, crest factors of this\r\nresidual matrix is determined and then machinery condition is assessed based on comparing the crest factor amplitude with the\r\nbase line (healthy) level. PCRMA method has been applied to vibration data sets collected from several kinds of rotating machinery:\r\na wind turbine, a gearbox, and an induction motor. This approach successfully differentiated the signals from healthy system and\r\nsystems containing gear tooth breakage, cracks in a turbine blade, and phase imbalance in induction motor currents. The achieved\r\nresults show that the developed method is found very promising and Crest Factors levels were found very sensitive for machinery\r\ncondition....
Compact heat exchangers (CHEs) are characterized by a high surface area per unit volume, which can result in a higher efficiency\r\nthan conventional heat exchangers. They are widely used in various applications in thermal fluid systems including automotive\r\nthermal fluid systems such as radiators for engine cooling systems. Recent development of nanotechnology brings out a new\r\nheat transfer coolant called ââ?¬Å?nanofluids,ââ?¬Â which exhibit larger thermal properties than conventional coolants due to the presence\r\nof suspended nanosized composite particles in a base fluid. In this study, a numerical investigation using different types of\r\nnanoparticles in ethylene glycol-base fluid namely copper (Cu), diamond (DM), and silicon dioxide (SiO2) on automobile flat\r\ntube plate-fin cross-flow CHE is explored. The nanoparticles volume fraction of 2% is considered for all types of nanofluids\r\nexamined in this study. The three-dimensional (3D) governing equations for both liquid flow and heat transfer are solved using\r\na standard finite volume method (FVM) for the range of Reynolds number between 4000 and 7000. The standard ?-e turbulence\r\nmodel with wall function is employed. The computational model is used to study the variations of shear stress, skin friction, and\r\nconvective heat transfer coefficient. All parameters are found to yield higher magnitudes in the developing and developed regions\r\nalong the flat tubes with the nanofluid flow than base fluid. The pressure drop is slightly larger for nanofluids but insignificant\r\nat outlet region of the tube. Hence, the usage of nanofluids in CHEs transfers more energy in a cost-effective manner than using\r\nconventional coolants....
This paper presents an experimental investigation to develop the mathematical model for various wire electric discharge machining (WEDM) characteristics of aluminium silicon carbide 10% metal matrix composite Al/SiC10% MMC. The attempt has been made to optimize the range bound process parameters for maximizing material removal rate (MRR) with minimum surface finish (Ra). Classical experimentation technique was used to perform experiments for triangular, circular and straight shape cuts on Al/SiC10% MMC as majority of industrial products are manufactured by these shapes or combinations. The machining characteristics MRR and Ra were studied using multiple linear regression models for different shape cuts. The test results proved that MRR and Ra values were significantly influenced by pulse on time, servo speed and volumetric area of Al/SiC10% MMC for different shape cuts. Linear programming (LPP) was used to compute optimized process parameters for different shape cuts and satisfy industrial wide spread application requirement by quality machining of Al/SiC10% MMC...
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