Research

Active Noise Control in Fluid Flows

Active Noise Control of Blade Tonals in Underwater Propulsors

This project concerns the application of active control to modify radiated noise characteristics in underwater propulsors. One noise source is the presence of fluctuating thrust and side forces that are produced due to the operation of a propulsor blade in a non-uniform wake. Each blade geometry results in a specific spectrum of noise, and therefore generates a specific "blade tonal" of the radiated noise. The goal here is to use active control to appropriately modulate a control surface (for example, a small propulsor with biomimetic blades) so that the "tonal" is modified suitably. Preliminary results have shown that a 2-D model based on potential flow and a dynamic inversion control strategy lead to a significant noise reduction (see figure). A detailed investigation of this approach that includes analysis and simulation needs to be carried out.

A benchtop experimental apparatus has been set up to validate the biomimetic alteration of the blade tonals.  The current biomimetic actuators under investigation are made from films of polypyrrole conducting polymer (CP).
The conducting polymer technology is courtesy of MIT's Bioinstrumentation Lab (director Ian Hunter). The films are formed using an electrochemical deposition on a glassy carbon beaker. Once formed, the films can be peeled off with a razor blade. In the presence of a proper electrolyte, the films contract isotropically under an
applied voltage.  To form the actuator itself, the films are laminated together to form a 3-layer actuator. The two outside layers are the conducting polymer films, while the middle layer is a special paper that serves as a spacer. When either side contracts, the actuator curls in the direction. In order to ensure that the curling takes place in a predestined direction, strategical slicing (to relieve stress in one direction) and stiffening using materials such as mylar and carbon fiber are being designed.  

The video below shows one such CP,  60  by 23 by .2 mm, rectangular in cross-section,  actuating in water.
Current results show that ~20 degrees in ~17 seconds, for an avg speed of ~1.17 degrees per second can be achieved with these CPs.

This particular actuator shown below  (made in MIT's Bioinstrumentation Lab) has a different geometry, 40 by 8 by .1 mm, and a vacuum deposited plastic coating in an attempt to seal it from the water. The sealing/coating method is still under development..

This is the next actuator deveoped, tested on 3/3/03. The "tail" is twisted slightly, and the view is top down, thus the view of the tail is slightly distorted. The actuator is oscillating at .3 Hz in water flowing at 10 cm/s. The scale at the bottom is in millimeters.

The same actuator oscillating at 1 Hz in water flowing at 10 cm/s can be seen here.
And again at 5 Hz here.

Publications:

P. Bandyopadhyay, W. P Krol, Jr., D. P. Thivierge, W. H. Nedderman, and Mehran Mojarrad, "A Biomimetic Propulsor for Active Noise Control. Experiments," NUWC-NPT Technical Report 11,351,March 2002.

W.P. Krol, Jr., A.M. Annaswamy, and P. Bandyopadhyay, "A Biomimetic Propulsor for Active Noise Control," NUWC-NPT Technical Report 11,350,, February 2002.