Approximation formulae for natural frequencies of simply supported skew plates

By using the reduction method proposed previously by the author and the exact relation between natural frequencies of an isotropic simply supported skew plate and a skew membrane with the same boundary shape, a few approximation formulae for estimating the natural frequency of simply supported isotropic and orthotropic skew plates are derived from the natural frequency of skew membranes without solving the partial differential equation governing the free vibration of the orthotropic skew plate.