“…The applications of the Kirchhoff method have been discussed in the literature [12][13][14]. Contrary to the Kirchhoff method, the analytical solution of the FW-H method involves the nonlinear effects on and outside the integral surface [7,15,16]. Theoretical and numerical differences have been evaluated to predict the noise from, for example, helicopter rotors [6,7,15,16] and jets [17].…”