Multi-physics optimisation of ‘brass’ instruments—a new method to include structural and acoustical interactions

A new method of designing ‘brass’ air-column instruments to include structural and acoustical interactions in the optimisation process is introduced and used to generate initial results. It is based upon a coupling between the air-column and structure when their resonant frequencies approach each other, which accentuates the lip to wall coupling effect. The degree of wall vibration and the frequencies at which it occurs can be controlled by variation of the structure’s stiffness. The method detailed in this paper enables optimisation of the solid wall thickness variation along the bore of the instrument. The acoustic optimisation of the internal profile and subsequent structural optimisation of the wall thicknesses is carried out based on acoustic and structural resonance constraints, with secondary objectives of structural integrity and weight minimisation. The intention is to be able to optimise the sound of the instrument to include the wall vibrations effect, based upon a specified target output.