Various application are provided for an enclosure having a first wall and two or more second walls surrounding a cavity. The enclosure also has an inlet and outlet each in fluid communication with the cavity. The second walls each have at least a portion shaped such that a force acting on the first wall tending to deflect the element causes an amplified deflection of the second walls into the cavity. Such applications include a pump, a structure comprised of one or more enclosures, structural elements, and apparatus for storing and releasing energy.