An aerodynamic model for tandem flapping wings is proposed. The model attempts to represent insects such as the dragonfly. Two advances are presented: the aerodynamic model with tandem wings flapping simultaneously, and the wing stroke optimization. The aerodynamic model accounts for the inflow effects of the front wing (fore-wing) on the rear wing (hind-wing). The stroke is optimized at two flight conditions (acceleration and level flight) by using a heuristic optimization procedure (particle swarming). The vector of the design variables consists of 28 independent parameters (14 per wing), each with a constrained range derived from the maximum available power, the flight muscle ratio and kinematics of real insects. The cost function is the propulsive efficiency coupled with constraints for flight stability. Prediction of the level flight efficiency is in agreement with the flight muscle efficiency. The maximum acceleration is found to be dependent on the size of the flight muscle. Finally, a study of the wing shape is presented for both level and accelerating flight conditions. = normalized chord c = mean chord length= rate of the wing rotation dr = wing section dt = time step D = drag f = frequency (motion frequency)

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In the present study, non-equilibrium molecular dynamics (MD) simulations have been performed to reveal the effect of solid-liquid interfacial wettability on the evaporation characteristics of thin liquid argon film placed over the flat solid surface. The atomistic model considered herein comprises of a three-phase simulation domain having a solid wall over which liquid argon and argon vapour co-exist. Initially, the system is thermally equilibrated at 90 K for a while after which rapid increase in the solid wall temperature induces a phase change process, i.e. evaporation. Both hydrophilic and hydrophobic wetting conditions of the solid surface have been considered at an evaporation temperature of 130 K for three different surface materials such as platinum, silver, and aluminium. The simulation results show that both the surface wettability and surface material have a significant role in phase transition phenomena of thin liquid film, particularly the surface wettability for the present system configuration. The thermal transport phenomena between the wall and liquid thin film have been studied thoroughly and discussed in terms of wall heat flux, evaporative mass flux, upper bound of maximum possible heat flux etc. The results obtained in the present MD simulation study are compared with the macroscopic predictions based on classical thermodynamics. Interestingly, a very good agreement has been found indicating that macroscopic thermodynamics approach can predict the characteristic of phase change phenomena of nanoscale thin liquid film.

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