A Concept of Radial Pseudo-Force for Damage Detection in Wind Turbine Towers

Damage in a plane structure can cause perturbation to the equation of out-of-plane motion, which can be equivalently regarded as the transverse pseudo-force (TPF) applied to the plane structure. Thereby, the detection of damage in the plane structure can be achieved by identifying the TPF. Nevertheless, it is difficult to formulate the pseudo-force in a cylinder structure such as a wind turbine tower because its radial, longitudinal, and circumferential motions are coupled. The aforementioned limitation leads to a noticeable barrier to extending the TPF to a cylinder structure. To overcome this barrier, a new concept of radial pseudo-force (RPF) is formulated to represent the damage-caused perturbation to the radial equilibrium of a cylinder structure, whose motions are dominated by radial components. The RPF is applied on the lateral surface of the cylinder and is an ideal indicator for the detection of damage in the cylinder structure because it appears in the damage region only and almost vanishes in intact locations. The concept of the RPF is experimentally validated on a wind turbine tower model, on the internal surface of which a pit was manufactured. The results reveal that the RPF-based approach is capable of detecting internal damage in cylinder structures such as wind turbine towers by graphically characterizing the occurrence, location, and size of the damage.