Abstract:

Radiation of noise from exhaust stacks is a significant source of community disturbance. In this paper an exhaust stack with an adaptive length is proposed. The effective length of the stack is changed by altering the level of water in a sump at the base of the stack, this level is controlled as a function of the radiated noise from the top of the stack. The system is modelled as a pipe with an adaptive side branch. A gradient descent algorithm is used to minimise the radiated sound. The response to a step change in frequency and a chirp signal is shown. A simple heuristic controller is compared to the performance obtained with the gradient descent algorithm and is shown to be acceptable and computationally simpler.