Acoustic design of enclosures to minimize noise

Acoustic design of enclosures to minimize noise
20
Jan

Bangalore-based B.M.S. College of Engineering (BMSCE) is an autonomous engineering college affiliated with the Visvesvaraya Technological University. It has the distinction of being India’s first private engineering college and is known as a quality educational institution.

As part of their curriculum, final year engineering students of the College are expected to undertake a project that solves a specific real-life/industry challenge. One group of final year chemical engineering students from the College decided to use this opportunity to address the issue of equipment noise in the chemical engineering department laboratories on campus. The chemical engineering laboratories have several noisy machines and equipment. The noise levels force certain restrictions in terms of the time of day during which the machines can be used for experiments, so as to minimize disturbance to other students. The group decided to focus on solving the acoustics problem associated with the enclosures that housed these noisy machines, as part of their final year project.

Initially, the students planned to physically create acoustic boards using different materials, test them through experimentation, and then follow this up with simulation. However, there were several challenges to this approach. First, there were issues such as non-availability of certain components such as impedance tubes, due to the pandemic-induced lockdown. Second, the organizations that possessed the physical testing capability for these materials had certain confidentiality clauses and restrictions around data sharing. Given these circumstances, the team decided to go ahead with a simulation-only set-up to solve the problem at hand. Simulating for different eco-friendly materials and enclosure dimensions.

Using Actran Student Edition, the team conducted simulations with three different materials, and two different enclosure dimensions, to identify the best material as well as the optimum enclosure size to minimize noise. They considered three materials made out of natural waste materials – corn cobs, corn stovers, and banana stalks. The students studied the sound pressure level at a distance of one meter, along with sound pressure and enclosure deformation contours for the different iterations. The team found that the larger enclosure had a better performance up to 65 Hz, and beyond this frequency, the smaller enclosure was better. Changing material properties too had an effect, especially for the frequency range of 40 Hz – 75 Hz for the smaller enclosure and 30 Hz – 65 Hz for the larger enclosure. The results showed that banana stalks had better sound absorption potential followed by corn cobs and corn stovers at frequencies in the range 40 Hz – 70 Hz. Ease of use and in-built material properties.

 

The various in-built features allowed the students to set values for parameters such as thickness of the board/equipment, the inner and outer air volume, and porous materials properties. Using Actran, the students could achieve desired results, plot graphs with in-built plotters, and iterate with material properties through various options to get detailed insight into the enclosure performance. Given the ease of use and quick results, the students were able to get the desired results in a timely manner. Despite the lockdown, the students could get the results using just their laptops, without the need for any high-end physical infrastructure. The students were also able to publish the results of their study through a paper in the Global Journal of Material Science and Engineering, also winning a prize for Best Presentation.

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