Goods and products transported by road are subjected to vehicle vibration which, without proper protective packaging, can suffer damage. To reduce shipment costs, protection has to be optimised to limit product damage occurrence while keeping packaging weight and size to a minimum. Optimisation is realized by simulating the vibration of transport vehicles. To achieve an accurate simulation, each vehicle vibration mode has to be modelled. These include: the nonstationary random vibration induced by road roughness and speed variations, the transient vibration created by road surface aberrations and the harmonic vibration created by the vehicle engine and drive train. Identifying and indexing these mixed-modes within complex road vehicle vibration signals is essential to define the severity and occurrence of the different modes in order to develop an accurate model. This paper shows that indexing can be performed using the orthogonal wavelet transform such as Daubechies 10. Assuming that each mode is preponderant in different analysis scales, the wavelet coefficients can be used to perform the indexing. This allows more sensitive mode detection and a more precise time indexing thanks to the multi-resolution nature of the wavelet transform compared to other time-frequency analysis methods.

A signal of mechanical and acoustical vibration generated during a bearing’s quality testing contains variety of useful information about their operational conditions. At defined testing speeds, the bearings generate a periodical and a non-periodical vibroacoustic signal of different intensities, which are dependent on the quality of bearings and/or their damage type. A dynamical response of the tested bearings recorded in time characterizes also the nature of the unwanted noise of bearings. Therefore the dynamical response of the maximum acceleration recorded in time is one of the major criteria of bearing quality evaluation in terms of noisiness. The second criterion is a determination of statistically significant frequency interval for the equivalent acceleration value expressed in decibels. Consequently, from the effective acceleration value, the bearing quality can be determined in terms of its vibration severity, as well as its noise level. This objective methodology substitutes the evaluation bearing quality by means of measurement of the vibration acceleration on the given test device and simultaneously evaluation of the noise quality and its intensity auditorily. Verifying the proposed methodology 100 % conformity was achieved between the methodology currently used and the new methodology, which eliminates the subjective quality evaluation of bearings auditorily.

Recent trends in developing quieter diesel power plants in automobiles leading to unmasking the secondary sound sources. One of the major secondary sound sources of in-cabin noise is HVAC system. HVAC noise is one such sound likely to be present as long as the automobile is in use. In extreme climatic conditions, like in India, HVAC is majorly operated at higher speeds and adding to that SUV volume requires more air circulation which generates lot of flow induced noise. Under these conditions, the contribution of HVAC noise is more significant for passengers and many a times it influences subjective cognition that causes the driver’s emotional response to be unpleasant, it is more important to identify the most significant sound quality parameters that contribute to the perception of HVAC noise. Measurements were done on five different diesel SUVs with different HVAC operating conditions each having variable fan speeds with engine on and off respectively. Using the semantic differential technique subjective rating of the measured signals has been done. The psycho acoustic parameters calculated objectively for the measured interior sounds later those were compared with subjective rating by using HVAC noise function (HNF) to obtain the suitable parameters to represent HVAC noise.

The goal of this work is to propose a new strategy for the attenuation of the traffic noise, which constitutes one of the main sources of acoustic pollution in urban and suburban areas. This strategy is based on the measurement of the noise radiated by each individual vehicle using an electro-acoustic system, composed of two microphones for the acquisition of the engine and of the rolling noise. These microphones have been situated inside the engine hood and close to the right back tire respectively. The signals have been recorded for diesel and petrol engines and through typical urban and suburban courses with different persons. Using this procedure, we aim to characterise the drivers responsible of the highest noise levels producing maximum annoyance. The near-field measurements have been then extrapolated to far field positions using an analytical filter that takes into account absorbing properties of the propagation floor. For the internal signal it has been necessary to characterise the acoustic properties of the engine hood experimentally using an array of microphones surrounding the vehicle. The propagated noise is calculated considering the absorption due to the geometrical divergence, the absorption by the air, and the effect of the propagating surface. The signals extrapolated to the receiver position could be compared with the current normative to propose recommendations concerning noise control actions.

Numerical simulations are presented on a feedback active control strategy for flow-induced off-track vibration of the head gimbals assembly (HGA) supporting the slider in hard disk drives, through suppressing pressure fluctuations around the HGA. A virtual sensing method is employed to enable the feedback signal changeable from pressure fluctuations at the physical sensor position to those at single “virtual sensor” positions closely around the HGA or a spatial average of pressure fluctuations along an HGA surface. Based on a linear control methodology, performance of the proposed active control strategy with different feedback signals has been investigated in two-dimensional simulations, where a physical pressure sensor and a pressure actuator are assumed on the inner-surface of the HDD cover to detect the pressure fluctuations and to actuate active pressure oscillations into HDD space respectively. The results show effective control on the HGA off-track vibration when the feedback signal is configured to minimize pressure fluctuations at specific positions closely around the HGA, such as the wake region. It is also shown that satisfying control effect can be achieved on the HGA off-track vibration in the global spectrum when the feedback signal is configured to minimize the spatial average of pressure fluctuations along the upper surface of the HGA.

This paper presents beamforming techniques for source localization on aicraft in flight with a focus on the development at DLR in Germany. Fly-over tests with phased arrays are the only way to localize and analyze the different aerodynamic and engine sources of aircraft in flight. Many of these sources cannot be simulated numerically or in wind-tunnel tests because they they are either unknown or they cannot be resolved properly in model scale. The localization of sound sources on aircraft in flight is performed using large microphone arrays. For the data analysis, the source signals at emission time are reconstructed from the Doppler-shifted microphone data using the measured flight trajectory. Standard beamforming techniques in the frequency domain cannot be applied due transitory nature of the signals, so the data is usually analyzed using a classical beamforming algorithm in the time domain. The spatial resolution and the dynamic range of the source maps can be improved by calculating a deconvolution of the sound source maps with the point spread function of the microphone array. This compensates the imaging properties of the microphone array by eliminating side lobes and aliases. While classical beamfoming yields results that are more qualitative by nature, the deconvolution results can be used to integrate the acoustic power over the different source regions in order to obtain the powers of each source. ranking of the sources. These results can be used to rank the sources, for acoustic trouble shooting, and to assess the potential of noise abatement methods.

Blast noise from military installations often has a negative impact on the quality of life of residents living in nearby communities. This, in turn, negatively impacts the military’s testing & training capabilities due to restrictions, curfews, or range closures enacted to address noise complaints. In order to more directly manage noise around military installations, accurate noise monitoring around bases has become a necessity. Although most noise monitors are simple sound level meters, more recent ones are capable of discerning blasts from ambient noise with some success. Investigators at the University of Pittsburgh (Pitt) developed a more advanced noise classifier that can discern between wind, aircraft, and blast noise, while simultaneously lowering the measurement threshold. Here, more recent work between Pitt and the US Army Engineer Research and Development Center will be presented from the development of a more advanced classifier that identifies additional classes of noise such as machine gun fire, vehicles, and electronic noise. Additional signal metrics were explored given the increased complexity of the classifier. By broadening the types of noise the system can accurately classify and increasing the number of metrics, a new system was developed with increased blast noise accuracy, decreased number of missed events, and significantly fewer false positives.

Measuring infrasonic sound sets high requirements on the instruments used. Typically the measurement chain consists of a microphone and a preamplifier. As the input resistance of the preamplifier forms a high pass filter with the capacitance of the microphone in the picofarad range, measuring ultra low frequencies becomes a challenge. The electric preamplifier presented in this paper together with a prepolarized condenser microphone form a measurement system. The developed preamplifier connects the microphone signal directly to the input of an operational amplifier with ultra high input impedance. The bias current for the preamplifier further complicates the signal amplification. A configuration of two diode-connected FETs provide the input bias current. The resulting input impedance of nearly 1 T Ω yields a total lower limiting −3 dB cutoff frequency of 8 mHz and a dynamic range of 95 dB. Being able to measure down to ultra low frequencies in the infrasonic frequency range will aid actors in the debate on wind turbine noise. Sonic booms from supersonic flights include frequencies down to 10 mHz and the preamplifier proposed in this paper will aid scientists trying to modify the N-shaped shock wave at high level which prohibits flights in land zones.

This research examined the influence “quiet” (e.g., hybrid and electric) vehicles may have on the ability of blind pedestrians to perform common orientation and mobility tasks under low vehicle speed conditions. The research involved blind participants detecting forward approaching vehicles and approaching backing vehicles, deciding whether a vehicle coming from behind or from the front but across an intersection would continue to go straight or turn across the intended path of travel of a pedestrian seeking to cross a street (i.e., a pathway discrimination task), and taking parallel and perpendicular alignment from passing traffic. Participants included some with normal hearing and some with impaired hearing. Testing was conducted on a public roadway and a parking lot in Kalamazoo, Michigan under ambient sound conditions consistent with a typical urban travel environment. Conditions involved evaluating internal combustion engine (ICE) Chevrolet Malibu and a set of hybrid Chevrolet Volts capable of operating in a “quiet” mode (referred to as Electric Mode or EM) or operating in EM but augmented with one of five different artificially-generated sounds emanating out of a front-bumper mounted speaker. All of the artificial sounds generally performed better against the baseline the Chevrolet Volt EM than the Chevrolet Malibu. This suggests that, to some extent, putting any one of these artificial sounds on a hybrid or electric vehicle may improve pedestrian performance on the measures examined relative to not adding any sound at all. One sound (sound 5) did not outperform against the Chevrolet Malibu in any measure and had the fewest instances of outperforming the Chevrolet Volt EM. Of the remaining 4 sounds, two sounds outperformed both the Chevrolet Malibu and the Chevrolet Volt EM on several measures. Against the Chevrolet Malibu, sound 2 was slightly better in detection distance and crossing margin while sound 4 was better in the path discrimination tasks. The two sounds were equivalent on the alignment tasks. The pathway discrimination task reflects one of the more potentially threatening situations in which a blind pedestrian might encounter a quiet vehicle (e.g., turning to cross the pedestrian’s path). Sound 4 performed much better than sound 2 on this measure, making it the most effective of all the artificial sounds examined. While these two sounds were equitable in the right-straight task, sound 4 showed almost half as many missed vehicle surges (i.e., forward movement from a stop) and 1/4 the rate of missed paths and incorrect judgments. Vehicle sound condition did not impact participants’ alignment. Normal hearing participants performed significantly better than hearing impaired participants on this task, but not as well as would be expected based on previous data [1]. These results support the potential for artificially-generated sounds to improve the ability of blind pedestrians to detect approaching vehicles relative to what is being achieved with ICE vehicles. Regression analysis of the detection data supports previous results that sound energy in the 500 to 1000 Hz range is important for detection. However, the analysis indicates it is not that energy in this region that makes the signal more noticeable, but that energy in this region in the ambient environment hinders detection. Previous findings in low ambient conditions showing a predictive value for the amplitude modulation of an artificial sound were not supported in these data.

The utilization of guided waves generated and sensed by an array of phased sensors allows steering the wave-front in a specific direction (beamforming technique). In this work a linear array of sensors is used to generate an ultrasonic wavefront steered in a specific direction. Numerical simulations are carried out with the LS-DYNA, an explicit Finite Element (FE) code, on a CFRP plate. The damage to be identified is a delamination produced by an impact (BVID). The array of sensors consists of a number of disk-shaped piezo patches. From the echo reflected and returning back to the array, it’s possible to evaluate the time of flight of the signal (TOF) from which the distance of the damage from the sensors array can be determined, and the angular position of the crack by evaluating the time shift of the signal received by each sensor in the array. The experimental tests are carried out in a 0.5m × 0.5m ×2.2 mm CFRP plate with the same sensor array and delamination used in the simulation. A number of receivers located along the panel edges have been also used to detect the damage direction in pitch-catch mode.

Accurate measurement of the composition of oil-water emulsions within the process environment is a challenging problem in the oil industry. Ultrasonic techniques are promising because they are non-invasive and can penetrate optically opaque mixtures. This paper presents a method of determining the volume fractions of two immiscible fluids in a homogenized two-phase flow by measuring the speed of sound through the composite fluid along with the instantaneous temperature. A linear chirp signal is transmitted through the fluid and de-chirp method is applied to calculate the sound speed in the medium. Two separate algorithms are developed by representing the composite density as (i) a linear combination of the two densities, and (ii) a non-linear fractional formulation. Both methods lead to a quadratic equation with temperature dependent coefficients, the root of which yields the volume fraction. The densities and sound speeds are calibrated at various temperatures for each fluid component, and the fitted polynomial is used in the final algorithm. We present results when the new algorithm is applied to mixtures of crude oil and process water from two different oil fields, and a comparison of our results with a Coriolis meter; the difference between mean values is less than 1%.

In this work, we study the effects of the width of the sound source in several acoustical virtual room models with different topologies, sizes and uses, calibrated with commercial software. To achieve this aim, a square distribution of sound sources with variable side length has been considered. We have auralized four channels of speech signal and musical signal in three different locations in each room. By using signal processing techniques, a comparison of multisource auralizations with the ones obtained from a single source in the middle of the stage is made. Also, the variations between the usual room parameters obtained from these simulations are analyzed, in order to show the effect of the hall in the objective evaluation according to the source width. Paper NCAD2012-72001 is available online only.

FIR filter for a adaptive filter algorithm, is mostly used for an active noise control system. However, FIR filter needs to have more large size of the filter length than it of IIR filter. Therefore, the control system using FIR adaptive filter has slow calculation time. In the active noise control system of the short duct, the reference signal can be affected by the output signal, so IIR filter for ARMA system can be more suitable for the active noise control of the short duct than FIR filter for MA system. In this paper, the recursive LMS filter, which is adaptive IIR filter, is applicated for the active noise control inside the short duct. For faster convergence and more accurate control, a variable step size algorithm is introduced for this recursive LMS filter (R-VSSLMS filter). Using this algorithm and considering the secondary path, the filtered-u R-VSSLMS is conducted successfully on the real experiment in the short duct. The performance of the active control using the filtered-u R-VSSLMS filter, is compared with the performance of the active control using a filtered-x LMS filter.

The consumer today places greater demands upon the vehicle acoustical engineer than in the past. Product quality has always been associated with a quiet ride. Automotive engineers recognize that the predominant sources of vehicle interior noise are wind, tire-road or rolling noise, and the powertrain. This paper suggests a test protocol for measuring wind and rolling noise using a chassis rolls dynamometer and road tests. Automotive engineers are frequently confronted by customer complaints concerning wind noise. Usually, engineers resort to using wind tunnels to address these concerns and to conduct diagnostic studies to remedy wind noise problems. Unfortunately, wind tunnels are expensive to rent and difficult to schedule. As an alternative, the engineer can learn a great deal about the wind noise of a vehicle by using a chassis rolls dynamometer along with road tests [1,2]. If the chassis rolls surface texture closely matches that of the road surface, the tire-road or rolling noise signal in both situations can be assumed to be equivalent. The powertrain noise source can be minimized by shifting the vehicle into neutral and coasting. Wind noise is a source for the road measurements, but not for the chassis rolls. Hence, the wind noise can be calculated by measuring the cab interior noise for both operating conditions, and subtracting the rolling noise measured on the chassis rolls. The two vehicles tested in this study included a pickup truck and a sport utility vehicle. The acoustical data revealed significantly different rolling and wind noise characteristics. The pickup truck had significantly louder rolling noise, and the wind noise was dominated by low frequency sound. The sport utility vehicle was much quieter overall and was significantly quieter for rolling noise than the pickup. The wind noise of the sport utility vehicle also was dominated by high frequency components. Both vehicles showed that rolling and wind noise trends increase linearly with speed. However, the slope of wind noise data for the sport utility vehicle was much steeper than the pickup, which suggested that it was more sensitive to wind noise as speed increased. Exterior noise data from both vehicles showed that the tire-road signal from the road differed significantly from that of the chassis rolls dynamometer. Rolling & wind noises will become even more critical as the motor vehicle industry adopts hybrid electric and, in the future electric fuel cell vehicles, because powertrain noise sources in the vehicle will likely be reduced. The procedure suggested here provides an inexpensive simple approach to assessing rolling and wind noise in the vehicle.

This paper addresses the construction, measurement, and analysis of a double-panel active partition (DPAP) and its accompanying analog feedback controllers. The DPAP was constructed by attaching an aluminum cone loudspeaker at each end of a short segment of a circular duct. Two analog feedback controllers were designed and built using the measured frequency response function of each panel. Two independent (decoupled) feedback controllers were then used to minimize the vibration amplitude of each panel in the presence of an acoustic disturbance. A normal-incidence transmission loss measurement system was used to assess the performance of the DPAP and of a single panel passive partition. Error signal attenuations show that it is both feasible and effective to simultaneously control both panels with decoupled feedback controllers, and that simultaneously controlling both panels of the DPAP has a distinct advantage over controlling a single panel. The reduction in vibration amplitude across the surface of the transmitting panel was confirmed with scanning laser vibrometer measurements. Transmission loss results were obtained for two passive and three active configurations. The average normal incidence transmission loss over the active measurement bandwidth (50–1,000 Hz) for the active double-panel was 60 dB. This is an average of 39 dB more transmission loss than a passive single panel partition.

In this paper we develop a data based model, design a high performance robust controller, and apply the controller in real-time to reduce narrowband acoustic noise from a cooling fan. A custom, portable enclosure houses the cooling fan. One end of the enclosure is fitted with four speakers and four microphones, inside of a short duct, connected to a data acquisition system and a personal computer. Passive materials mounted at the other end of the enclosure reduce backside noise. The frequency of the narrrowband noise is assumed unknown and therefore a control design that can be updated in realtime is needed. The control design that is presented uses a nominal model and a nominal controller. The nominal controller is enhanced by using closed loop signals and taking into account the modeling error. The end result is a data-based method for updating a nominal controller to improve performance.

This paper deals with the effects of atmospheric absorption on the propagation of high-speed jet noise. The common practice for determining the far-field jet noise spectra at a distance far from the jet exit (>100D, where D is the nozzle exit diameter) involves extrapolating data that is typically obtained between 35D and 100D from the nozzle exit. The data is extrapolated along a radial line from the nozzle exit by accounting for the effects of spherical spreading and atmospheric absorption. A previous paper discussed far-field measurements that were obtained for a twin engine aircraft at three locations along a radial line in the peak noise radiation direction. The authors were unable to extrapolate the spectra from the nearest location to either of the further locations and the observed differences were attributed to nonlinear effects in the jet noise signal. It is the purpose of this paper to show that the common extrapolation practice is valid for high speed jets, except in the peak radiation direction and its surrounding angles. Mach wave radiation is present at these locations and the common practice will yield unsatisfactory results, similar to those observed in the previous paper. The data used in this paper is taken from experiments carried out at 1/5th-scale and full scale and the experimental conditions of these high-speed jets are quite similar to those of the previous paper.

An acoustic localization method is applied in a reverberant environment to locate the sources of discrete sounds having unknown timing and waveform. In particular, the localization method is applied to study low event rate cavitation in a vortical flow in a water-tunnel test-section with characteristic cross section dimension of 0.3 m. The primary frequency and bandwidth of the acoustic pulses from the small isolated cavitation bubbles are 10 kHz and 200 kHz respectively, and the measured pulse duration is ∼15–20 micro-seconds. The localization method involves using an array of receiving hydrophones to record the cavitation sound pulses. These hydrophone recordings, which include direct-path signal, reflected path signal, and noise, are time windowed and cross-correlated to obtain direct-path arrival-time differences. These arrival time differences are used in conjunction with a simple ray-based acoustic model to estimate the source location in three dimensions via a robust Monte-Carlo routine. The ratio of the primary-frequency wavelength to the water-tunnel cross-section dimension is ∼1/2. Consequently the time-windowing is tight; only 1 to 1.5 center-frequency cycles at the beginning of a signal pulse are readily useful for localization purposes. The remainder of the signal is contaminated by reflections and is not used in the present effort. To check and validate the results of the acoustic method, two-camera high-speed video data was taken synchronously with the acoustic data for 53 cavitation events. The acoustic localization scheme provided an unambiguous location estimate for all 53 cavitation bubbles. The average distance between the optical and acoustic measurement of the bubble location was 18.4 mm, or ∼1/8 of the wavelength of the primary signal frequency.