Detection of Damage in Operating Wind Turbines by Signature Distances

Wind turbines operate in the atmospheric boundary layer and are subject to complex random loading. This precludes using a deterministic response of healthy turbines as the baseline for identifying the effect of damage on the measured response of operating turbines. In the absence of such a deterministic response, the stochastic dynamic response of the tower to a shutdown maneuver is found to be affected distinctively by damage in contrast to wind. Such a dynamic response, however, cannot be established for the blades. As an alternative, the estimate of blade damage is sought through its effect on the third or fourth modal frequency, each found to be mostly unaffected by wind. To discern the effect of damage from the wind effect on these responses, a unified method of damage detection is introduced that accommodates different responses. In this method, the dynamic responses are transformed to surfaces via continuous wavelet transforms to accentuate the effect of wind or damage on the dynamic response. Regions of significant deviations between these surfaces are then isolated in their corresponding planes to capture the change signatures. The image distances between these change signatures are shown to produce consistent estimates of damage for both the tower and the blades in presence of varying wind field profiles

An Examination of Competitive Balance within Interscholastic Football

Interscholastic football has the highest participation rates among high school students in the United States.  The popularity and nostalgic connection of football is widespread, but competitive balance is often challenged due to differing characteristics of high schools.  This study utilized the theory of distributive justice and data from high school athletic associations in all 50 states and District of Columbia to consider which variables (public/private status, school population, rural/urban location, geographical region, and policies) may impact competitive balance at the state-championship level of interscholastic football.  The results confirmed that traditionally strong private schools generally located in the Midwest and Northeast win state titles at disproportionately high rates.  No other variable was as powerful or significant as the public/private variable.  The findings of the study also challenged the effectiveness of existing policies designed to curb private school success.  These results can serve pragmatic efforts to ensure competitive balance within interscholastic football.