Multidisciplinary approach for solar area optimization of high altitude airships

This paper describes a methodology for determining the optimal envelope shape that minimizes the solar array area of a high altitude airship to be deployed at a specified geographical location. It identifies the critical day of the year and the optimal altitude of deployment on that day, and determines the smallest area of solar array that is just sufficient to meet all the operating requirements. This ensures that the airship can be deployed round the clock throughout the year at that specific geographical location, without any power shortfall. The methodology involves eleven design variables whose values are affected by parameters stemming from four disciplines, viz., Environment, Geometry, Aerodynamics, and Energy. Candidate envelope profiles are generated using a standard shape generation algorithm, and their volumetric drag coefficient is estimated using a surrogate based aerodynamic model. Envelope shapes corresponding to minimum solar area obtained by coupling the methodology to an optimizer based on Genetic Algorithms. To study the effect of the season of deployment, optimal envelope shapes were obtained for deployment on three specific days of the year (viz., Winter solstice, Summer solstice and Equinox) for an assumed altitude of deployment. It was seen that area of solar arrays needed for the airship were 4-9% lower than that for the baseline airship envelope. However, when the altitude of deployment and day of operation were allowed to vary, the optimal envelope shapes obtained had 35% lower solar area.