An approximate method for determining the maximum amplitude of higher-order duct modes

Previous investigations have used Hankel transforms to establish the amplit udes of the wave fields resulting from arbitrary angle impingement on a cir cular orifice in a baffle. Investigations have also been undertaken on the effects of model coupling between the higher modes in the orifice. In parti cular, these studies concentrated on establishing the contributions at the cut-on wave number for a particular mode. This work is extended to introduc e a method of simply approximating the complex amplitude of the forward and backward waves in the duct at the cut-on wave number, based only on the mo dal wave number. The interest focuses on the cut-on wave number because the forcing functions for the various fields will be at a maximum at cut-on. T his technique is established by observing the relationships between the pea k values of the driving functions and the modal wave number. If simple appr oximations are established for the in-duct field, it is also possible to ap proximate the maximum amplitude of the scattered field. (C) 2001 Acoustical Society of America.