DYNAMIC ANALYSIS OF A GRADIENT ELASTIC POLYMERIC FIBER

A dynamic analysis of an elastic gradient-dependent polymeric fiber subjected to a periodic excitation is considered.A nonlinear gradient elasticity constitutive equation with strain-dependent gradient coefficients is first derived and the dispersive wave propagation properties for its linearized counterpart are briefly discussed.For the linearized problem a variational formulation is also developed to obtain related boundary conditions of both classical(standard)and non-classical(gradient)type.Analytical solutions in the form of Fourier series for the fiber’s displacement and strain fields are provided.The solutions depend on a dimensionless scale parameter(the diameter to length radio d = D/L)and,therefore,size effects are captured.     

FREE TRANSVERSE VIBRATIONS OF A DOUBLE-WALLED CARBON NANOTUBE：GRADIENT AND INTERNAL INERTIA EFFECTS

This is a modest contribution on higher-order continuum theory for predicting size effects in small-scale objects. It relates to a preceding article of the journal by the same authors（AMSS, 2013, 26： 9-20） which considered the longitudinal dynamical analysis of a gradient elastic fiber but, in addition to an internal length, an internal time parameter is also introduced to model delay/acceleration effects associated with the underlying microstructure. In particular, the free transverse vibration of a double-walled carbon nanotube（DWNT） is studied by employing gradient elasticity with internal inertia. The inner and outer carbon nanotubes are modeled as two individual elastic beams interacting with each other through van der Waals（vdW） forces. General explicit expressions are derived for the natural frequencies and the associated inner-to-outer tube amplitude ratios for the case of simply supported DWNTs. The effects of internal length（or scale）and internal time（or inertia） on the vibration behavior are evaluated. The results indicate that the internal length and time parameters of the adopted strain gradient-internal inertia generalized elasticity model have little influence on the lower order coaxial and noncoaxial vibration modes,but a significant one on the higher order modes.     

Efficient Oxidation of Cyclohexane over Bulk Nickel Oxide under Mild Conditions

Nickel oxide powder was prepared by simple calcination of nickel nitrate hexahydrate at 500 °C for 5 h and used as a catalyst for the oxidation of cyclohexane to produce the cyclohexanone and cyclohexanol—KA oil. Molecular oxygen (O₂), hydrogen peroxide (H₂O₂), t-butyl hydrogen peroxide (TBHP) and meta-chloroperoxybenzoic acid (m-CPBA) were evaluated as oxidizing agents under different conditions. m-CPBA exhibited higher catalytic activity compared to other oxidants. Using 1.5 equivalent of m-CPBA as an oxygen donor agent for 24 h at 70 °C, in acetonitrile as a solvent, NiO powder showed exceptional catalytic activity for the oxidation of cyclohexane to produce KA oil. Compared to different catalytic systems reported in the literature, for the first time, about 85% of cyclohexane was converted to products, with 99% KA oil selectivity, including around 87% and 13% selectivity toward cyclohexanone and cyclohexanol, respectively. The reusability of NiO catalyst was also investigated. During four successive cycles, the conversion of cyclohexane and the selectivity toward cyclohexanone were decreased progressively to 63% and 60%, respectively, while the selectivity toward cyclohexanol was increased gradually to 40%.     

Effect of unbalanced rotor whirl on blade vibrations

In this paper, vibration of a bladed unbalanced flexible rotor is studied. The blade that is attached to the disk is considered as a fixed-free Euler-Bernoulli beam. Position of the blade with respect to the eccentric mass is taken into consideration. Coupled equations of the motion of unbalanced rotor and the blades are obtained through Lagrange equations. The dynamic equations have time variant periodic coefficients. Transient vibration analysis showed that rotor acceleration excites the blade vibration with its own natural frequency. While the rotor passes through its own natural frequency (critical speed) the blade vibration is again excited but this time with the rotor natural frequency. Modal behavior of the blades are different for subcritical, supercritical and for critical speed of the rotor. In the subcritical run of the rotor, blades located from 0° to 180° with respect to the eccentric mass are deflected in the negative direction while the rest are deflected in the positive direction. For supercritical run of the rotor, modal behavior of the blades is just the opposite. For critical speed of the rotor, blades located 90° to 270° from the eccentric mass are deflected in the positive direction while the rest of the blades are deflected in the negative direction. Blades have also different deflections. When the deflections of the blades are plotted with respect to their position angle, distribution of the blade deflections has a sinusoidal shape.     

The effects of using corrugated booster reflectors to improve the performance of a novel solar collector to apply in cooling PV cells-Navigating performance using ANN

Journal of Thermal Analysis and Calorimetry - In this study, turbulent flow and heat transfer of water in a solar collector equipped with corrugated booster reflectors to apply in cooling...     

An analytical solution of the dynamics of a symmetrically operated parallel flow heat exchanger

An investigation of an analytical solution of the dynamics of a symmetrically operated parallel flow heat exchanger in the form of transfer matrix was performed. Perturbation method was used to linearize the usual non-linear model of such systems. A non-interactive controller to decouple the outputs and a controller to offset any expected disturbances in the boundary temperature was considered. A discrete model was established and found to predict the heat exchanger dynamics adequately. The results are acceptable and encouraging and the model has been found to be sufficient enough to achieve the objective of countering uncontrolled disturbance without requiring precise knowledge of process dynamics. The validity of the proposed control design is examined by comparing it with other models in the literature.