Herrick Technology Laboratories (United States)

When office occupants work near printers, the noise generated by printers can affect occupant comfort. To support subjective listening tests, a method to generate realistic simulations of printer noise with finely controlled variations of sound attributes was developed. Printer noise is composed of both tonal and broadband components. Both components can be intermittent, continuous but time-varying, or have constant characteristics. Tonal components are simulated by using amplitude- and frequency-modulated sinusoids. Broadband noise components are simulated by passing broadband random noise through time-varying filters whose characteristics are based on modified versions of the spectrograms of measured printer noise after removal of tonal components. The broadband noise spectrogram is split into two parts: one related to short-duration impulses, and the other to more slowly varying random noise; both can be modified independently and then recombined to form a spectrogram that is used as the target for the time-varying filter design. The complete printer noise simulation is generated by adding the tonal and broadband noise simulations. These simulations will be used in psychoacoustic tests to determine how variations in each sound attribute affect acoustic comfort.

Electrified powertrains generate less noise and vibration than internal combustion engines, making secondary sources like gear-induced noise more noticeable. One such issue, gear-growl, is increasingly concerning for passengers and manufacturers. However, its signal properties and perceptual thresholds are not well defined. This study aims to extract and select informative features from vibration and acoustic signals to analyze gear-growl phenomena better. Root-mean-square and spectral entropy effectively distinguish gear-growl in vibration signals, while acoustic signals require a broader feature set due to background noise and nonlinearity. Feature selection techniques are used to improve interpretability and reduce dimensionality. Supervised machine learning, specifically a kernel support vector machine, evaluates the selected features’ effectiveness. A multiclass model, informed by subjective listening tests, categorizes gear-growl severity levels with a test accuracy of 0.89. These classification results support the feature selection process but are not the study’s primary focus. Further listening studies are suggested to improve labeling consistency and reliability. Though this work centers on gear-growl, the feature-based framework may be applicable to other noise and vibration diagnostics.

High surface area particles, like granular activated carbon (GAC), have shown advantages in absorbing low-frequency sounds by themselves and when combined with other treatments. In this article, a novel sound absorption treatment consisting of a high surface area particle stack supported by a soft, porous layer is described. It was first experimentally observed from impedance tube measurements that the low-frequency absorption performance of GAC stacks can be significantly enhanced by inserting a melamine foam between the stack and a rigid backing. To analytically model this type of sound absorbing treatment, the interfaces between particle stacks and other materials were characterized. Further, a 1-D layered transfer-matrix approach and a 2-D axi-symmetric finite-difference approach were implemented to predict the measured absorption spectra. Because of the constraint of the stack at the impedance tube wall, the 2-D axi-symmetric model leads to more accurate absorption spectrum predictions, particularly at low frequencies. However, the difference between the two model predictions becomes negligible when applied to large-area treatments. Thus, the simpler and faster 1-D theory can be valuable for optimizing large-area sound packages. In addition, by combining both granular and porous materials, it may be possible to design sound-absorbing metamaterials that perform well at low frequencies.

It has recently been shown that adding activated carbon particles to the interior of a Helmholtz resonator can improve the resonator's absorption at low frequencies. A similar improvement has been found when a layer of activated carbon partially fills the space behind a finite, tensioned impermeable membrane. In that case, absorption peaks due to the modal response of the tensioned membrane were found to be significantly enhanced in the low frequency range. In the present work, the modeling aspects of the latter work are extended in a number of ways. First, the circular membrane is considered to be both tensioned and flexurally stiff, and further, it is micro-perforated: i.e., it has a finite flow resistance. Secondly, the particle layer behind the membrane is modeled by using a finite difference procedure that accounts for interaction of the particle layer and walls that contain it: i.e., the particle stack itself is allowed to exhibit modal behavior in the radial direction. Finally, the interaction of the membrane nearfield and the particle stack is fully accounted for. It is shown that previously observed behavior can be reproduced, and further that the modal behavior of the particle stack may also enhance the system's absorption.

Predictors of people's responses to noise inside cars are used by car companies to identify and address potential noise problems. Because significant advances have been made in the reduction of engine, powertrain, and tire/road noise, it is now important to pursue reductions in wind or aerodynamic noise. While models of loudness are commonly used to predict people's responses to stationary wind noise, some wind noises are less acceptable than is predicted by the loudness metric. Additional sound characteristics may account for this. Two listening studies were designed to examine the usefulness of including sound quality metrics in addition to loudness and sharpness in models used to predict acceptability for non-stationary wind-noise sounds, particularly noise with the kind of variations that are expected from wind gusts. Test sounds were based on recordings made in cars in a wind tunnel. A simulation method was implemented to generate sounds with controlled gusting features by modifying stationary noise recordings. A gusting metric was designed to predict subjects' acceptability responses based on the strength, modulation rate, and duration of the gusts.

Single-screw machines are currently employed as both compressors and expanders in vapor compression systems and organic Rankine cycles (ORCs), respectively. The working principle of single-screw machines is based on the simultaneous meshing of two starwheels with one central grooved rotor. The performance of the machine is heavily affected by the wear of the tooth meshing profile after several hours of running. In order to improve the wear resistance of the conventional straight-line profile, multi-column tooth flank designs have been introduced and investigated by several researchers. Cylindrical multi-column envelope profiles are able to distribute the local contact over a larger surface area reducing the wear of the tooth flank profile. Nevertheless, the manufacturability of such profiles is directly linked to the accuracy and limitations of CNC machines.In this work, an attempt is made to overcome the aforementioned limitations. To push the boundaries of possible tooth and rotor profile designs, 3D printing is utilized as manufacturing technique. Such approach allows the investigation of more complex designs that improves the sealing lines during the meshing process.A detailed geometry model based on polygon intersections is utilized to calculate the sealing lines, groove volume curves, and surface areas of the different designs. As a result of this study, a novel rotor design has been manufactured.

During the mid-1970s, following the first oil embargo, heat pumps became of great interest to northern U. S. electric power companies, particularly for those experiencing large peak demands during the heating season, as shortages of natural gas and oil led to increased usage of direct electric heating. Air-source heat pumps (ASHP), given their wider market presence relative to other heat pump types, almost universal applicability, and inherent efficiency and capacity issues at cold outdoor temperatures were of primary interest as an electrical heating system alternative at that time. ASHPs based on the simple vapor compression cycle suffer both heating capacity (output) and efficiency (coefficient of performance or COP) degradation as the outdoor ambient temperature drops.

Wave propagation and vibration‐based structural health monitoring methodologies are presented to detect, locate and quantify dent/crack, thermal debond, and corrosion damage in a solid aluminum friction stir weld plate and a sandwich honeycomb thermal protection panel. A wave propagation based method can identify small defects because propagating waves typically consist of small wavelengths while a vibration‐based scheme is better equipped to quantify damage over wide areas of large structures. Near‐real time online diagnostics is achieved by using localized sensing (wave propagation) and distributed sensing (vibration‐based) in an active measurement array. Sensor/actuator arrays have been developed to implement these techniques and portable health management systems have been developed based on the combination of damage detection algorithms, active sensing, and graphical user interfaces. Propagating waves are shown to have a heightened sensitivity to damage located at the anti‐nodes of a friction stir wed plate forced by low frequency environmental vibrations. Measurement of the input forcing in the vibration‐based method is shown to enable damage quantification.

<div class="htmlview paragraph">Sunroof buffeting of a simplified car model was investigated experimentally and numerically in order to assess the potential of numerical methods to design sunroofs that are quiet and functional. The numerical results have been obtained using the commercially available software PowerFLOW. The simulation kernel of this software is based on the numerical scheme known as the Lattice Boltzmann Method (LBM), combined with an RNG turbulence model. This scheme accurately captures time-dependent aerodynamic behavior of high Reynolds number flows over complex geometries, together with the acoustic response of resonant systems.</div> <div class="htmlview paragraph">In this work, a simplified car model with a sunroof was used for validation. A simulation methodology to determine the acoustic response of the passenger cabin was investigated and verified experimentally. The sunroof buffeting phenomenon was simulated over a range of flow conditions, and the results were found to be in good agreement with experimental data. Small discrepancies in the buffeting onset and offset velocities were observed, attributed to small geometric and flow differences between physical and simulated domains.</div>