Shape Optimization of Aerostat Envelopes
C. Vijay Ram,
M.Tech,
06,
56 pp.
Department of
Aerospace Engineering
Indian Institute of Technology Bombay,
Powai, Mumbai 400 076.
Supervisor(s):
R. K. Pant
Aerostat envelope shapes are normally determined
solely from aerodynamic considerations, viz. low drag and lift
coefficients and their volume is a direct indication of their payload
carrying capacity. This study investigates a multidisciplinary approach
for shape optimization of aerostat envelopes. The problem is formulated
in terms of optimization of a single objective function namely payload,
which is to be maximized while incorporating structural, and flight
mechanical considerations, for an aerostat envelope of a given volume.
The envelope geometry is parameterized in terms of six shape generation
variables, and a response surface fit for envelope drag coefficient is
obtained, which obviates the need for carrying out a detailed CFD
evaluation in each iteration of the optimization cycle. Estimation of
tether profile as a function of ambient wind conditions, operating
altitude and aerodynamic coefficients of the aerostat is carried out,
to determine the actual length of tether required, which results in a
more accurate estimation of its weight. A procedure for sizing of the
fins to provide adequate level of static stability is presented. A
multi-fabric construction of the envelope is implemented enabling usage
of lighter fabrics in areas with low structural loading, thus resulting
in further weight saving. Optimum shapes of the envelope for maximizing
the payload capacity for single and multi-fabric constructions have
been obtained by coupling a shape generation algorithm to a standard GA
optimization code.