"Zhang et al... studied the effect of the stiffening ring... to improve the dynamic properties and the wind resistance... They... concluded that for the latitude and meridian directions, the stiffness in the latitude direction contributes more... and... the location where the maximum modal displacement of the unstiffened HCT appears will not always be the most effective place for an additional stiffening ring unless the mode shapes of the unstiffened and stiffened HCTs are similar."