The research objective of this award is to develop an active noise control method that senses and controls a structure in a manner that minimizes acoustic radiation. There are numerous applications where it is desirable to reduce noise radiated from vibrating structures into an enclosed acoustic field, such as a vehicle cabin. The research builds on a newly developed measure of vibration that is referred to as composite velocity. The use of standard vibration measurements for active control systems does not result in a minimization of acoustic radiation, since the structural vibration and the radiated power are not directly correlated. However, composite velocity is directly correlated with acoustic radiation. Furthermore, the composite velocity is quite uniform across the structure, making the method less sensitive to sensor location. These properties will be exploited in complex structures, and the method will be developed for structures including ribbed plates and cylindrical shells, which are typical for important applications such as vehicles and aircraft fuselages.
If successful, the results of this research will provide a compact, efficient solution for reducing noise exposure in numerous applications, such as vehicle cabins (automobiles, locomotive engines, and heavy equipment cabins) as well as aircraft cabins. The advantage of this active control approach is that there is little sensitivity to sensor location (meaning the sensor can largely be placed wherever convenient), the system is compact, and the method achieves global reduction of the enclosed sound field. This will result in improved communication, increased comfort, reduced noise fatigue, and improved safety for vehicle occupants. Graduate and undergraduate science and engineering students will benefit through involvement in the research and classroom instruction based on the research. Results will be disseminated to the scientific community, allowing others to explore and further develop the method, as well as providing opportunities for commercial development.
This research has resulted in the development and validation of an active noise control (ANC) method that can lead to significant societal benefits with applications ranging from improved room acoustics for classrooms, office spaces, and concert halls to reduced noise in vehicle cabins, aircraft, and spacecraft. Benefits include reduced occupant fatigue and annoyance, improved teaching and learning environments, and improved safety, communication, and sound quality. ANC is a technology that focuses on attenuating unwanted sound by introducing an additional noise source capable of generating sound that will add with the original unwated sound in a manner that provides attenuation of the resulting sound field. This project has focused specifically on active structural acoustic control. With this technique, a vibrating source (such as a plate or shell) is controlled by a secondary source in a manner that alters the radiation of sound from the vibrating source and yields global attenuation of the sound field. Previous attempts to actively control the noise in these types of environments have shown some promise. However, these methods typically require an impractically large number of sensors distributed throughout the enclosure or on the structure. The method developed in this research overcomes the inefficiencies of current methods by providing control throughout the entire sound field using a single localized error sensor on the structure. Results on simple structures have shown that this method, known as the Weighted Sum of Spatial Gradients (WSSG) method, obtains better control than previous methods reported, and does it with a sensor at a single location on the structure. The experimental results of the sound power attenuation achieved from radiating simply supported and clamped plates are shown respectively in Figs. 1 and 2. The regular dashed line indicates the sound power in an uncontrolled condition. The other two lines which are significantly below the dashed line show the reduced level of sound power due to the active control using WSSG control with two different sets of weighting parameters implemented. This research has provided the development of an ANC method that allows practical whole-field noise reduction in sound fields. It is expected that this cost-effective, feasible approach will be utilized in applications such as vehicles, aircraft, office spaces, and other enclosures. Several graduate and undergraduate students, including a female PhD student, developed improved research skills and broad backgrounds in acoustics and dynamics. Teamwork with faculty, graduate, and undergraduate students was emphasized. The Brigham Young University (BYU) Acoustics Research Group (ARG) has weekly seminars with typically over 30 students and faculty attending. Results from this research were disseminated at these seminars and on the ARG website. Faculty involved with the research have worked with high school principals, and K-12 teachers to improve the local school district science and engineering curriculum. Results from this research can be used to excite students about careers in these fields. Recently, three K-12 students working with our group won outstanding science fair awards. One was invited to meet the President at the White House. The team has been engaged in outreach activities, and will continue to do so. Results from the proposed research have been developed into an ANC demonstration that has been introduced into our "Sounds to Astound" outreach event (see Fig. 3), and will continue to be refined and upgraded over time. This outreach demo show attracts hundreds oe people annually, where they are exposed to many exciting concepts in acoustics, including this research, annually. Results will also be used by our students that annually provide tours for hundreds of visitors from the community. Involvement of students from underrepresented groups will continue to be a focus of the PIs. Current enrollments in our graduate level courses have had 2-3 times more females than are in the general program student body. Our success has been obtained by announcing research opportunities in classes, physical and electronic advertising, and coordinating with campus organizations that support underrepresented students such as Society of Women Engineers, Women in Physics, and on-campus groups for students with disabilities.