This study aims to achieve effective analysis and fast modeling in free vibRATIOn and flutter analyses of low ASPECT RATIO composite wings in subsonic flow for the preliminary design stage instead of using the computationally expensive finite element method. It uses an equivalent plate method for structural modeling. Also, it uses the doublet point and the U-g methods for calculation of unsteady aerodynamic loads and carrying out flutter analysis, respectively. We investigate the effects of different parameters on the flutter behavior. The present results confirm that the structural tailoring can make a harmonious balance to the wing sweep angle effect upon the flutter behavior of composite wings, and a considerable improvement upon flutter performance is achieved by using composite materials.

A computational modelling of microchannel heat sinks with high ASPECT RATIO has been performed to compare the geometrical features in the plane parallel to the heating surface and to determine the optimum configuRATIOn for the best heat transfer characteristics. A periodic thermal development of flow can cause significant heat transfer enhancement. A consensus on a particular geometrical configuRATIOn that provides the best heat transfer characteristics has not been reached in the literature, although many novel ideas have been proposed recently. Firstly the validity and applicability of microchannel sink modelling is presented followed by an optimization of parameters of interrupted microchannel heat sink. Consequences of the multichannel effect due to the introduction of transverse microchamber are also presented. It has been shown that the average Nusselt number of the microchannel heat sink increases by the introduction of a transverse microchamber with the additional advantage of a lower pressure drop. There exists an optimum width for the transverse microchamber for which the interrupted microchannel heat sink shows optimum characteristics.

Wing geometry, kinematics and flexibility are the fundamental components which contribute towards the aerodynamics performance of micro aerial vehicles. This research focuses on determining the role of isotropic flexibility in the aerodynamic performance of high ASPECT RATIO (AR = 6. 0) wings with different shapes in hovering flight. Three shapes are chosen, defined by the radius of the first moment of wing area 𝑟 ̅ 1, which are 0. 43, 0. 53 and 0. 63, where low (resp. high) value of 𝑟 ̅ 1 corresponds to less (resp. more) spanwise area distribution towards the wingtip. The leading edges of flexible wings are modelled as rigid and the wings, therefore, predominantly deform in the chordwise direction. Flexible wings are categorized as flexible FX2 and more flexible MFX2 for brevity. The governing equations of fluid flow are solved using a sharp interface immersed boundary method, coupled with an in-house finite element structure solver for simulations of flexible wings. The results indicate that the rigid wings produce one lift peak per stroke during the mid-stroke and its magnitude increases with an increase in 𝑟 ̅ 1 due to strong leading-edge vortex. For flexible wings, the numbers of lift peaks per stroke and their timings during a flapping cycle depend on the deformation that affects the pitch angle and pitch rotation rate of the wings. The lift coefficient for a given shape decreases as flexibility increases because the pitch angle decreases during the mid-stroke. This decrease in lift coefficient with flexibility is pronounced for 𝑟 ̅ 1= 0. 63 wing (up to 66 % less lift as compared to rigid equivalent) due to pitch down rotation at the commencement of the stroke, resulting in vortical structures on the bottom surface of the wing. For more flexible wings at high AR considered in this study, a wing with low 𝑟 ̅ 1 (= 0. 43) may be suitable for the wing design of micro-aerial vehicle, as in general, it has better aerodynamic performance (24. 5 % more power economy and similar lift coefficient) than high 𝑟 ̅ 1 (= 0. 63) wing.

The shape deformation of three bubbles with equilateral triangle arrangement continuously rising in shear-thinning non-Newtonian fluids was numerically investigated using the three-dimensional volume of fluid method (3D-VOF). The shape deformation of three continuously rising bubbles was compared with that of a single bubble under consistent opeRATIOns to analyze the effect of interaction between bubbles. The influences of bubble diameter, initial bubble distance, bubble formation frequency, and liquid rheological property on the ASPECT RATIO of the bubble were investigated. The results indicate that the ASPECT RATIO of the bubble for multi-bubble systems with greater bubble diameter, initial bubble distance, and more intense shear-thinning effect of the liquid decreases and the shape of the bubble deforms flatter. However, as the bubble formation frequency increases, the deformation of the bubble weakens, and the bubble ASPECT RATIO increases. In comparison with the single bubble rising freely, the ASPECT RATIO of the bubble for the multi-bubble systems is larger. Moreover, a modified model of the ASPECT RATIO of the bubble was proposed by considering the interaction between bubbles for the multi-bubble system.

In the present work, an analytical study is proposed to investigate the flutter behavior of low-ASPECT-RATIO wings in subsonic flow. An equivalent plate model is used for structural modelling of a semi-monocoque main wing, consisting of ribs, skins, and spars. Legendre polynomials are used in the Rayleigh-Ritz method as trial functions, and the first-order shear deformation theory is utilized to formulate the structural deformation. Boundary conditions are enforced by applying proper artificial springs. A doublet point method is used to calculate the unsteady aerodynamic loads. Chordwise pressure coefficient distribution at the tip and root of a rectangular wing oscillating in pitching motion is calculated. Flutter analysis is performed using the k method. Instead of using the computationally expensive finite element method, the proposed approach is intended to achieve purposes of quick modelling and effective analysis in free vibRATIOn and flutter analyses of low-ASPECTRATIO wings for preliminary design applications. The effects of ASPECT RATIO on the flutter behavior of wings in subsonic flow are investigated. The obtained results are validated with the results available in the literature.