## 1 April 2018

### Spindel

Spindel is a circular hyperboloid of one sheet also known as a hyperboloid of revolution because it is obtained from revolving a hyperbola around its semi-minor axis.

$x^2+y^2-z^2=1$

The hyperboloid of one sheet is used in construction. For example, it is used in cooling towers of nuclear power stations. As the hyperboloid of one sheet is a doubly ruled surface, i.e., for each of its points there are two distinct straight lines that lie on the surface, it can be constructed by straight steel beams, allowing a minimization of cross winds, keeping the structural integrity with a minimum use of construction materials. Another example are some buildings that use this surface as an architectural element.

Cooling towers of the Chooz Nuclear Power Station (France)

Corporation Street, Manchester (UK)

Cathedral of Brasília (Brazil)