Abstract: The present invention provides a riblet structure that further reduces drag, which is a sum of turbulent friction drag and pressure drag, and an object including such a riblet structure. An object such as an aircraft, plant, and pipeline includes a wavelike riblet pattern on a surface. The wavelike riblet pattern includes a large number of wavelike riblets. Each of the large number of wave riblets includes a wavelike ridge line, and a height thereof changes cyclically with respect to a fluid flow direction. With such a configuration, drag, which is a sum of turbulent friction drag and pressure drag, can be further reduced.

Abstract: The present invention provides a riblet structure that further reduces drag, which is a sum of turbulent friction drag and pressure drag, and an object including such a riblet structure. An object such as an aircraft, plant, and pipeline includes a wavelike riblet pattern on a surface. The wavelike riblet pattern includes a large number of wavelike riblets. Each of the large number of wave riblets includes a wavelike ridge line, and a height thereof changes cyclically with respect to a fluid flow direction. With such a configuration, drag, which is a sum of turbulent friction drag and pressure drag, can be further reduced.

Abstract: A tower comprises a base tower member fixed on a base in the ground, a lower tower member hingedly connected at a lower end thereof with an upper end of the base tower member through a hinge and swinging between a lying position and a standing position, a first stage connecting tower member connected at a lower end thereof with an upper end of the lower tower member, a second stage connecting tower member connected at a lower end thereof with an upper end of the first stage connecting tower member, and a third stage connecting tower member connected at a lower end thereof with an upper end of the second stage connecting tower member. Thus formed tower is raised swingingly around the hinge from the lying position to the standing position. A nacelle includes a tower penetrating hole through which the tower vertically penetrates and is formed by a plurality of nacelle sections divisible around the tower penetrating hole.