Cooling towers are used at generating stations to recirculate cooling water back to generators. The recycled water is maintained in a very clean condition, while cool water from other sources is used to exchange heat. The shape of a cooling tower is therefore arranged so that a natural updraft carries the cooling water over the recirculation elements and then drops back to a pond. This means that the shape of the tower must be a hyperbolic paraboloid or similar, and the inside of the tower is subjected to a high humidity and aggressive atmosphere. The dynamic behavior of such towers is complex but conforms to a standard type of behavior. This dynamic behavior is a function of material properties and of the geometry of the tower. STRAAM maintains a database of the normal behavior of towers and has conducted tests on many towers.