Application of Signal Analysis to Cavitation

The diagnostic facilities of the cross power spectrum and the coherence function have been employed to enhance the identification of not only the inception of cavitation, but also its level. Two piezoelectric pressure transducers placed in the downstream chamber of a model spool valve undergoing various levels of cavitation allowed for the use of both functions—the phase angle of the complex cross spectrum and the dimensionless coherence function—to sense clearly the difference between noise levels associated with a noncavitating jet from those once cavitation inception is attained. The cavitation noise within the chamber exhibited quite a regular character in terms of the phase difference between instruments for limited cavitation. Varying cavitation levels clearly illustrated the effect of bubble size on the attendant frequency range for which there was an extremely high coherence or nearly perfect causality.

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An Improved Sensitivity Method for the Simultaneous Identification of Unknown Parameters and External Loads of Nonlinear Structures

Shock and Vibration ◽

10.1155/2018/1737594 ◽

2018 ◽

Vol 2018 ◽

pp. 1-12

Author(s):

Chongwen Wang ◽

Chengbin Du

Keyword(s):

Regularization Parameter ◽

Parameter Distribution ◽

Nonlinear Structures ◽

Noise Levels ◽

Unknown Parameters ◽

Key Issues ◽

The Difference ◽

Sensitivity Method ◽

Simultaneous Identification ◽

External Loads

Because structures may be subject to unknown loads and may simultaneously involve unknown parameters and because simple load identification or parameter identification algorithms cannot be applied under such conditions, it is necessary to seek algorithms that can simultaneously identify unknown parameters and external loads of structures. The sensitivity method is one of them, and this paper extends this method to nonlinear structures. In addition, the key issues associated with the sensitivity method are systematically studied, and suggestions for improvement are put forward, including the use of the difference method instead of the derivative method to calculate the sensitivity, the use of a fixed regularization parameter instead of the traditional regularization parameter calculation methods, and measures for guarantee of iterative convergence. The improved sensitivity method is applied to two types of nonlinear structures, and the effects of the regularization parameter, distribution of measured points, response types, noise levels, and the magnitude of the perturbation on the identified results are discussed.

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Cavitation Inception in Spool Valves

Journal of Fluids Engineering ◽

10.1115/1.3241768 ◽

1981 ◽

Vol 103 (4) ◽

pp. 564-575 ◽

Cited By ~ 37

Author(s):

C. Samuel Martin ◽

H. Medlarz ◽

D. C. Wiggert ◽

C. Brennen

Keyword(s):

Reynolds Number ◽

Hydraulic Systems ◽

Cavitation Inception ◽

Pressure Transducers ◽

High Frequency Response ◽

Annular Jet ◽

Directional Control ◽

Valve Opening ◽

Response Pressure ◽

Spool Valves

Cavitation has been investigated in directional control valves in order to identify damage mechanisms characteristic of components of aircraft hydraulic systems. Tests have been conducted in a representative metal spool valve and in a model three times larger. Data taken under noncavitating conditions with both valves showed that the position of the high-velocity annular jet shifts orientation, depending upon valve opening and Reynolds number. By means of high-frequency response pressure transducers strategically placed in the valve chamber cavitation could be sensed by the correlation of noise with a cavitation index. The onset of cavitation can be detected by comparing energy spectra for a fixed valve opening and a constant discharge. Another sensitive indicator of cavitation inception is the ratio of cavitating to noncavitating spectral densities. The incipient cavitation number as defined in this investigation is correlated with the Reynolds number for both valves.

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Noise reduction of enhanced acoustic balconies on a high-rise building block

INTER-NOISE and NOISE-CON Congress and Conference Proceedings ◽

10.3397/in-2021-3050 ◽

2021 ◽

Vol 263 (1) ◽

pp. 5327-5334

Author(s):

SK Tang ◽

Rudolf YC Lee

Keyword(s):

Noise Reduction ◽

Natural Ventilation ◽

Traffic Noise ◽

Elevation Angle ◽

Noise Levels ◽

Indoor Space ◽

New Device ◽

Air Inlet ◽

The Difference ◽

The Impact

A new device called 'enhanced acoustic balcony' is installed in a new housing estate in Hong Kong. It is intended to help reduce the impact of traffic noise on the residents. This balcony is basically an enlarged form of a plenum window and with three openings. Apart from the outdoor air inlet, there is the balcony door and a side-hung window on the interior balcony wall for natural ventilation of the indoor space. Sound absorption of NRC 0.7 is installed on the balcony ceiling and its sidewall facing the incoming traffic noise and an inclined panel is installed outside the balcony to provide noise screening. A site measurement of its noise reduction is carried out in the present study in a newly completed housing block. A 28 m long loudspeaker array is used as the sound source. The indoor noise levels are measured according to ISO standard. The results show that the difference between indoor and outdoor noise levels in the presence of this balcony form varies over a relatively narrow range between 10 to 13 dBA for an elevation angle from 25 to 60 deg. There is a weak increase of the noise level difference with elevation angle.

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Understanding the Legendary Sound Environment in the Lobby of Hotel Okura Tokyo

Applied Sciences ◽

10.3390/app10134552 ◽

2020 ◽

Vol 10 (13) ◽

pp. 4552

Author(s):

Ryoko Nojima ◽

Natsuko Sugie ◽

Akira Taguchi ◽

Jun Kokubo

Keyword(s):

Speech Intelligibility ◽

Comprehensive Evaluation ◽

The Other ◽

Noise Levels ◽

Sound Environment ◽

Good Reputation ◽

The Difference ◽

Hotel Lobbies

The main lobby of Hotel Okura Tokyo has a good reputation for its sound environment, which affects the conversations of its users. We assumed that the lobby’s reputation was related to its speech intelligibility. In this study, first, the sound during hotel operations was measured to see if there was a difference in the sound environment between the lobby and the entrance hall. As a result, we clarified that the difference in noise levels affected by the degree of crowdedness of the room was smaller in the lobby than in the other rooms. Subsequently, the indoor noise and speech intelligibility were measured to clarify the correspondence of intelligibility with the lobby’s reputation. As a result, the indoor noise was found to be at a level suitable for hotel lobbies and the intelligibility was good. A comprehensive evaluation that included the results of other acoustical surveys revealed that the lobby of Okura is a space that is suitable for conversations, corresponding to the opinions of users.

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Numerical Investigation of Tip-Vortex Cavitation Noise of an Elliptic Wing Using Coupled Eulerian-Lagrangian Approaches

Applied Sciences ◽

10.3390/app10175897 ◽

2020 ◽

Vol 10 (17) ◽

pp. 5897 ◽

Cited By ~ 1

Author(s):

Garam Ku ◽

Cheolung Cheong ◽

Hanshin Seol

Keyword(s):

Flow Field ◽

Numerical Method ◽

Vortex Flow ◽

Acoustic Pressure ◽

Tip Vortex ◽

Experimental Result ◽

Cavitation Noise ◽

Navier Stokes Equation ◽

Tip Vortex Cavitation ◽

Cavitation Inception

In this study, a numerical methodology is developed to investigate the tip-vortex cavitation of NACA16-020 wings and their flow noise. The numerical method consists of a sequential one-way coupled application of Eulerian and Lagrangian approaches. First, the Eulerian method based on Reynolds-averaged Navier–Stokes equation is applied to predict the single-phase flow field around the wing, with particular emphasis on capturing high-resolution tip-vortex flow structures. Subsequently, the tip-vortex flow field is regenerated by applying the Scully vortex model. Secondly, the Lagrangian approach is applied to predict the tip-vortex cavitation inception and noise of the wing. The initial nuclei are distributed upstream of the wing. The subsequent time-varying size and position of each nucleus are traced by solving spherically symmetric bubble dynamics equations for the nuclei in combination with the flow field predicted from the Eulerian approach. The acoustic pressure at the observer position is computed by modelling each bubble as a point source. The numerical results of the acoustic pressure spectrum are best matched to the measured results when the nuclei number density of freshwater is used. Finally, the current numerical method is applied to the flows of various cavitation numbers. The results reveal that the cavitation inception determined by the predicted acoustic pressure spectrum well matched the experimental result.

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The Damage Capacity of Cavitating Flow From Pulse Height Analysis

Journal of Fluids Engineering ◽

10.1115/1.3243675 ◽

1989 ◽

Vol 111 (4) ◽

pp. 502-509 ◽

Cited By ~ 2

Author(s):

S. A. Fry

Keyword(s):

Circular Cylinder ◽

Pulse Height ◽

Pulse Amplitude ◽

Flow Conditions ◽

Noise Levels ◽

Linear Calibration ◽

Cavitation Noise ◽

Pulse Height Analyser ◽

Pulse Height Analysis ◽

Digital Pulse

Digital pulse amplitude acquisition systems are reviewed and an analogue pulse height analyser (PHA) is described. Cavitation experiments are reported in which pressure pulses in the liquid (water) are picked up by a flush mounted pressure transducer and measured using the PHA. Tests were carried out on two cavitation sources: a 60 deg symmetric wedge and a circular cylinder. Despite generating similar r.m.s. noise levels the wedge is 21 times as damaging as the circular cylinder at peak noise flow conditions (at V = 16 m/s). By imposing thresholds on the spectra parameters it had been possible to find a linear calibration beween noise and erosion applicable to both cavitation sources over a range of flow velocities. A good correlation between cavitation noise and erosion was found by simply measuring the number of pulses above a suitable threshold.

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Seismic and Rainfall Induced Displacements of an Existing Landslide: Findings from the Continuous Monitoring

Geosciences ◽

10.3390/geosciences10030090 ◽

2020 ◽

Vol 10 (3) ◽

pp. 90 ◽

Cited By ~ 1

Author(s):

Paolo Ruggeri ◽

Viviene M. E. Fruzzetti ◽

Antonio Ferretti ◽

Giuseppe Scarpelli

Keyword(s):

Continuous Monitoring ◽

Average Rate ◽

Central Italy ◽

Back Analysis ◽

Pressure Transducers ◽

Long Time ◽

The Difference ◽

One Year ◽

National Road

“La Sorbella” is a deep-seated existing landslide in a Miocene clayey formation located in central Italy. Given the interaction with a national road, this landslide has been monitored for a long time with inclinometers and hydraulic piezometers. Recently, the monitoring system was implemented by adding pressure transducers in the Casagrande cells and by equipping the old inclinometers with in-place probes, to allow a remote reading of the instruments and data recording. This system allowed to identify that the very small average rate of movement observed over one year (1.0–1.5 cm/year) is the sum of small single sliding processes, strictly linked to the sequence of rainfall events. Moreover, data recorded by in-place inclinometer probes detected the response of the landslide to the seismic sequence of 2016 occurring in central Italy. Such in situ measurements during earthquakes, indeed rarely available in the scientific literature, allowed an assessment of the critical acceleration of the sliding mass by means of a back-analysis. The possibility to distinguish the difference between seismic and rainfall induced displacements of the slope underlines the potential of continuous monitoring in the diagnosis of landslide mechanisms.

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OPTICAL SIGNAL ANALYSIS AND PROCESSING OF OPTICAL IMAGING WITH STRAY LIGHT BEAMS

International Journal of Modern Physics C ◽

10.1142/s0129183110015750 ◽

2010 ◽

Vol 21 (09) ◽

pp. 1183-1195

Author(s):

YING LIU ◽

YUANPING ZHOU ◽

WEIGUO WANG ◽

WENMING TANG

Keyword(s):

Optical Imaging ◽

Signal Analysis ◽

Optical Signal ◽

Optical Image ◽

Stray Light ◽

Analysis Method ◽

Image Edge ◽

The Mean ◽

The Difference ◽

Light Beams

For the optical signal analysis and processing of optical imaging with stray light beams, a new analysis method for smoothing the optical image edge and maintaining the spectrum signal well is presented in this paper. By calculating the mean gray value of the light pixel in the filter window of adaptive algorithm, we can analyze and compare the difference between the mean gray value and the current gray value with the light pixel of stray light beams, and can determine the smoothness of the optical image edge. This method can increase greatly the ability of optical image analysis and processing, and effectively reduce the false edge and the edge loss for the optical imaging with stray light beams, so that the optical image with high quality can be obtained.

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Most Comfortable Listening Levels, Background Noise Levels, and Acceptable Noise Levels for Children and Adults with Normal Hearing

Journal of the American Academy of Audiology ◽

10.3766/jaaa.22.5.5 ◽

2011 ◽

Vol 22 (05) ◽

pp. 286-293 ◽

Cited By ~ 10

Author(s):

Robert Moore ◽

Susan Gordon-Hickey ◽

Alisha Jones

Keyword(s):

Young Adults ◽

Noise Level ◽

Background Noise ◽

Developmental Change ◽

Pediatric Population ◽

Strong Predictor ◽

Normal Hearing ◽

Noise Levels ◽

Cross Sectional ◽

The Difference

Background: For adults the acceptable noise level (ANL) has been shown to be a strong predictor of hearing aid success. ANL is calculated as the difference between most comfortable listening level (MCL) and background noise level (BNL). No studies have made direct comparisons of these measures between adults and children. Purpose: To evaluate and compare MCLs, BNLs, and ANLs in children and young adults. Research Design: A cross-sectional design was used in this study. Two groups (children and adults) were tested for each dependent variable. MCLs and BNLs were measured for each participant, and ANLs were computed from these two measurements. Study Sample: The participants were 34 children (8–10 yr) and 34 young adults (19–29 yr) with normal hearing. Results: Significant main effects were found for MCLs and BNLs. There was no main effect for ANLs. MCLs and BNLs were significantly lower for the children than for the adults. Conclusions: These results suggest that while ANLs are unchanged from childhood to adulthood, there appears to be a developmental change in MCLs and BNLs. These findings have implications for the use of ANLs in the pediatric population.

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Is there a problem with methods skills in cognitive neuroscience? Evidence from an online survey

10.1101/329458 ◽

2018 ◽

Cited By ~ 3

Author(s):

Olaf Hauk

Keyword(s):

Data Analysis ◽

Linear Algebra ◽

Cognitive Neuroscience ◽

Signal Analysis ◽

Online Survey ◽

Complex Data ◽

Multiple Choice Questions ◽

Neuroimaging Data ◽

The Difference ◽

Training Programmes

AbstractCognitive neuroscience increasingly relies on complex data analysis methods. Researchers in this field come from highly diverse scientific backgrounds, such as psychology, engineering and medicine. This poses challenges with respect to acquisition of appropriate scientific computing and data analysis skills, as well as communication among researchers with different knowledge and skills sets. Are researchers in cognitive neuroscience adequately equipped to address these challenges? Here, we present evidence from an online survey of methods skills. Respondents (n=305) mainly comprised students and post-doctoral researchers working in the cognitive neurosciences. Multiple choice questions addressed a variety of basic and fundamental aspects of neuroimaging data analysis, such as signal analysis, linear algebra, and statistics. We analysed performance with respect to the following factors: undergraduate degree (grouped into Psychology, Methods, Biology), current researcher status (undergraduate student, PhD student, post-doctoral researcher), gender, and self-rated expertise levels. Overall accuracy was 72%. Not surprisingly, the Methods group performed best (87%), followed by Biology (73%) and Psychology (66%). Accuracy increased from undergraduate (59%) to PhD (74%) level, but not from PhD to post-doctoral (74%) level. The difference in performance for the Methods versus non-methods (Psychology/Biology) groups was particularly striking for questions related to signal analysis and linear algebra, two areas especially relevant to neuroimaging research. Self-rated methods expertise was not strongly predictive of performance. The majority of respondents (93%) indicated they would like to receive at least some additional training on the topics covered in this survey. In conclusion, methods skills among junior researchers in cognitive neuroscience can be improved, researchers are aware of this, and there is strong demand for more skills-oriented training opportunities. We hope that this survey will provide an empirical basis for the development of bespoke skills-oriented training programmes in cognitive neuroscience institutions.

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