Development of a general methodology for optimizing acoustic treatment using an equivalent source method

A general optimization methodology has been developed and examined for three different applications. The optimization method consists of an acoustic tool and six optimization algorithms, in which the user inputs some required parameters for the particular problem (flow field, scattering geometry, and acoustic source for the acoustic tool and initial guess and tolerance levels for the optimization algorithms) and then receives as output the optimized acoustic treatment value and desired acoustic field. The applications for this work consisted of optimizing the acoustic properties of an acoustic treatment for both realistic (commercial transport engine nacelle) and simple (rectangular duct) shaped geometries and also educing the properties of the acoustic treatment inside the rectangular duct. The acoustic results from all applications were calculated using the Fast Scattering Code (FSC). The objective function for the optimization applications was based on acoustic power, while the objective function used for the eduction application was based on an averaged L 2-norm. Prior to the optimization process, the soft surface boundary condition implemented into the FSC was validated using an analytical solution for a monopole point source above an impedance boundary plane of infinite area. The advantages and disadvantages of six well-known optimization methods were assessed during each application. The results demonstrate numerically and graphically the potential noise reduction benefits of single and segmented acoustic treatment configurations with and without flow effects. Overall, the application results show that (1) the FSC can accurately predict the effects of acoustic treatment, and (2) coupling the FSC with optimization methods provides an efficient methodology for acoustic treatment studies.