"Ref: S. Sabouri-Ghomi, M.H.K. Kharrazi, and P. Javidan, "Effect of stiffening rings on buckling stability of R.C. hyperbolic cooling towers," Thin Walled Structures, vol. 44, no. 2, pp. 152-158, 2006."
January 1, 1970
https://en.wikiquote.org/wiki/Hyperboloid_structure