Date of Defense
Date of Graduation
Mechanical and Aerospace Engineering
As placement of washers and dryers becomes common in apartment buildings and high rises, noise generated by the dryer becomes a nuisance to the inhabitants. Whirlpool Corporation is experiencing this issue first hand with their Horizon model long vent dryers. A focus was placed on noise and vibrations caused by the dryer motor, because its vibrations are transferred throughout the structure of the dryer. The motor causing sound problems was a modified motor from the standard model, including a speed-increasing attachment in order to operate the fan at an increased speed. Through sound and vibration measurements, structural and airborne noise contributions were compared, and problematic frequencies of the system were identified. The third octave band centered at 125 Hz was a large contributor to overall sound, and was known through previous research to be created mainly by the motor. Solutions investigated included motor bracket isolation, the addition of a tuned absorber, and mass modification of the system.
Bracket isolation consisted of inserting rubber grommets between the bracket and the cabinet in order to lift the bracket slightly off the base. This served to reduce contact area between the bracket and base, which would decrease vibration transfer from the bracket to the cabinet. The grommets also changed previously hard connections (screws) to soft connections, which could absorb higher frequencies. Results were not promising, and increased the overall sound and vibration, thus leading further experimentation to be discontinued.
A tuned absorber, modeled from a cantilever beam and point mass system, was designed to vibrate at the frequency of 125 Hz. This would cancel out part of the one-third-octave band created by the motor, and therefore decrease overall sound. It was attached in two positions, in the center of the motor and near the top of the motor, vibrating in the vertical direction. Neither position showed encouraging results, and so further experimentation was not undertaken.
Mass modification was based on the idea that an addition of mass on only one side (from the speed-increasing attachment) created an imbalance in the motor, causing it to have more interaction with the bracket and transfer more of its vibrations to the system at large. To test this, additional mass was introduced onto the speed-increasing attachment to observe if overall sound and vibration became more pronounced. Initial results were mixed. The first mass addition increased noise and vibration but the second decreased both metrics. Since these results were inconclusive, a refined form of mass modification was introduced in an attempt to correct the center of gravity and rebalance the motor. A mass of 133g was added onto the opposite side of the motor to counteract the mass of the speed increasing gear set. This decreased overall noise and vibration levels and was recommended for further investigation. ii
O'Hare, Daniel, "Noise and Vibration Reduction of a Clothes Dryer" (2013). Honors Theses. 2274.
Honors Thesis-Open Access