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In this paper, a closed-form solution to determine location of yield in rotating thick-walled cylindrical shells made of functionally graded materials (FGMs) using both Tresca's and von Mises yield criteria is presented. The cylindrical shell is subjected to uniform internal and external pressure. The material properties are assumed to vary according to power law functions and the Poisson's ratio is assumed to be constant. Moreover, the plane strain condition is used to drive expressions for distributions of stresses and radial displacement. In the present work, rotation, internal and external pressure and variation of material properties are considered simultaneously. To the best of authors' knowledge, in previous researches in which onset of yield is investigated, variation of material density is ignored, while density is not constant in FGM rotating thick cylindrical shells. Our results show that the density variation has a significant effect on the stress distributions. Our research has also tried to explain the effect of different Poisson's ratio on the value of the critical material parameter.

The spectral element method, a direct numerical technique, is used to study the behavior of flow past two cylinders in tandem array. A control cylinder is employed in front of the main cylinder to study the drag reduction performance and flow patterns. Three major flow patterns are found, including single cylinder vortex shedding, two cylinders vortex shedding and suppression. The flow patterns are affected by the distance between two cylinders, Reynolds number and the diameter ratios of cylinders. In a bistable regime, when there is a critical distance between cylinders, drag is reduced dramatically.

In this paper, transient response of a simply supported finite length hollow cylinder made of functionally graded piezoelectric material (FGPM) subjected to coupled hygrothermal loading was investigated. The coupled equations of heat conduction and moisture diffusion as well as motion equations and the electrostatic equation of FGPM were solved employing the Fourier series expansion method through the longitudinal direction, the differential quadrature method (DQM) along the radius and Newmark method for time domain. Finally, the distribution of temperature, humidity, electric potential, stresses and displacements was achieved. The effect of coupled and uncoupled hygrothermal loading, grading index and hygrothermal loading was illustrated in the numerical examples. The results show that using the coupled model is vital for analysis of transient response of the cylinder subjected to hygrothermal loading.