Frequency Response Pressure Research Articles

Real-ear acoustical characteristics of impulse sound generated by golf drivers and the estimated risk to hearing: a cross-sectional study

ObjectivesThis study investigated real-ear acoustical characteristics in terms of the sound pressure levels (SPLs) and frequency responses in situ generated from golf club drivers at impact with a golf ball....

Experimental Investigation of Coupled Frequency and Time-Domain Transient Test–Based Techniques for Partial Blockage Detection in Pipelines

Partial blockages commonly exist in pressurized pipeline systems, and the rapid remediation of such faults is required to reduce the wastage of energy as well as to maintain the serviceability of the pipe network. Numerous transient test–based techniques (TTBT) have been developed for detecting pipe defects, with each technique providing different advantages. Two previously developed techniques—pressure signal analysis (PSA) and frequency response analysis (FRA)—are experimentally tested in this study on systems of different pipe material and characteristics. Each method is validated using the experimental data, and the results show that PSA is most accurate for locating the blockage while FRA is most accurate for determining the radial constriction and length of the blockage section. To take advantage of the different strengths of the techniques, a coupling of the two methods is proposed. Experimental application results reveal that both detection accuracy and calculation efficiency are improved when the coupled method is used instead of the original techniques applied individually. Moreover, the results indicate that current TTBTs for partial blockage detection are more reliable in elastic (metallic) pipelines compared to viscoelastic (plastic) pipes.

Modeling of the Acoustic Response of Payload Bays Within Launch Vehicle Fairings

Acoustic shielding treatments are necessary to prevent damage to the payload during launch. This paper discusses three modeling approaches used to analyze the efficacy of such treatments. Results from acoustic modeling studies based on an analytical model, a finite element model, and experimental testing are presented here. Payload bay pressure distributions and frequency response functions are developed using simple two-dimensional scale models. The two-dimensional finite element models demonstrate good agreement with analytical and experimental results and show the potential for three-dimensional full-scale finite element modeling to handle more complex acoustic load conditions.

Finite element modelling of human auditory periphery including a feed-forward amplification of the cochlea

A three-dimensional finite element model is developed for the simulation of the sound transmission through the human auditory periphery consisting of the external ear canal, middle ear and cochlea. The cochlea is modelled as a straight duct divided into two fluid-filled scalae by the basilar membrane (BM) having an orthotropic material property with dimensional variation along its length. In particular, an active feed-forward mechanism is added into the passive cochlear model to represent the activity of the outer hair cells (OHCs). An iterative procedure is proposed for calculating the nonlinear response resulting from the active cochlea in the frequency domain. Results on the middle-ear transfer function, BM steady-state frequency response and intracochlear pressure are derived. A good match of the model predictions with experimental data from the literatures demonstrates the validity of the ear model for simulating sound pressure gain of middle ear, frequency to place map, cochlear sensitivity and compressive output for large intensity input. The current model featuring an active cochlea is able to correlate directly the sound stimulus in the ear canal with the vibration of BM and provides a tool to explore the mechanisms by which sound pressure in the ear canal is converted to a stimulus for the OHCs.

Micro audio directional system for portable multimedia devices

A micro audio directional system for portable multimedia devices is investigated as a novel loudspeaker which can provide privacy listening service. It can generates audible sound with high directivity in a narrow conical beam by an ultrasonic transducer array. A piezoelectric micromachined ultrasonic transducers (pMUT) array and a PZT ceramic wafer transducers array are presented respectively. The testing results of impedance, frequency response and sound pressure level characteristics are described and compared. A prototype with PZT ceramic wafer transducers array is constructed for mobile phone usage and its acoustic characteristics are measured. The experiment results indicate the feasibility of utilising the audio directional system with low power consumption and micro size in portable multimedia devices as well as in mobile phone.

Evaluation of Orifice Formulation for Leak Detection in Water Supply Systems Considering Unsteady Friction Term

Nowadays, water supply utilities in many parts of the world are concerned about water supply. Climate change, drought and population growth as well as immigration, are the most important factors for this situation. Because of limitation for availability of treated water, supplying healthy water even in areas with wet climate is difficult. In encounter with this challenge, reducing water losses in both trunk mains and distribution systems can be a temporary solution. In this research, a novel leak detection technique based on Frequency Response Method using transient flow analysis is presented in order to leak detection in water supply systems. In this method, in order to leak detection and location, steady-oscillatory flow in a pipe system, is generated by the sinusoidal maneuver of a valve in downstream of pipe and is analyzed in frequency domain with matrix transform. It is shown that leak presence in pipe, changes the shape of pressure frequency response. Pressure oscillation amplitude in even harmonies increases and in odd harmonies decreases. By this property, location of leak can be determined. Reliability of other methods depends on large amount of measured data in different parts of the system. The presented method, need to measure pressure and discharge data just in the location of valve. As an advantage of this method, leak discharge can be determined. By an example, the proposed methodology is evaluated and its advantages and disadvantages are distinguished.

Frequency responses of single and multiple partial pipeline blockages

The discrete Fourier transform (FT) of the peak pressure frequency response (PPFR) at a downstream valve generated by the transfer matrix method is used to detect a partial pipeline blockage. The location of this blockage is detected by locating the peak in the FT of the PPFR. This is also valid if multiple partial blockages are present. A methodology to detect individual blockage sizes is presented for single and double partial blockages. Yet, the present methodology is unsuccessful to predict the individual sizes if there are more than two partial blockages. However, the combined size of the partial blockages is detected by the magnitude of the zeroth frequency. In addition, special cases of partial blockage are presented to indicate the limitations of the present methodology.

Measurement of Decompression Wave Speed in Rich Gas Mixtures at High Pressures (370 bars) Using a Specialized Rupture Tube

Measurements of decompression wave speed in conventional and rich natural gas mixtures following rupture of a high-pressure pipe have been conducted. A high-pressure stainless steel rupture tube (internal diameter=38.1 mm and 42 m long) has been constructed and instrumented with 16 high frequency-response pressure transducers mounted very close to the rupture end and along the length of the tube to capture the pressure-time traces of the decompression wave. Tests were conducted for initial pressures of 33–37 MPa-a and a temperature range of 21–68°C. The experimentally determined decompression wave speeds were compared with both GASDECOM and PIPEDECOM predictions with and without nonequilibrium condensation delays at phase crossing. The interception points of the isentropes representing the decompression process with the corresponding phase envelope of each mixture were correlated with the respective plateaus observed in the decompression wave speed profiles. Additionally, speeds of sound in the undisturbed gas mixtures at the initial pressures and temperatures were compared with predictions by five equations of state, namely, BWRS, AGA-8, Peng–Robinson, Soave–Redlich–Kwong, and Groupe Européen de Recherches Gaziéres. The measured gas decompression curves were used to predict the fracture arrest toughness needed to assure fracture control in natural gas pipelines. The rupture tube test results have shown that the Charpy fracture arrest values predicted using GASEDCOM are within +7% (conservative) and −11% (nonconservative) of the rupture tube predicted values. Similarly, PIPEDECOM with no temperature delay provides fracture arrest values that are within +13% and −20% of the rupture tube predicted values, while PIPEDECOM with a 1°C temperature delay provides fracture arrest values that are within 0% and −20% of the rupture tube predicted values. Ideally, it would be better if the predicted values by the equations of state were above the rupture tube predicted values to make the predictions conservative but that was not always the case.

Development of an Active Compliance Chamber to Enhance the Performance of Hydraulic Bushings

With the new improvements in the fuel economy engines and to enhance the passenger’s comfort, the topic of active vibration cancellation has received a lot of attention recently by both the automotive industry and researchers. Engine mounts and bushings are the devices used to suppress the transverse and tensional vibrations of engines, respectively. Engine mounts and bushings are primarily designed for the first order vibration of engine. Higher order vibrations, however, are neglected due to their lower amplitudes. Although lots of research has been focused on the improvement of the design and performance of engine mounts, engine bushings has not been addressed well in the literature. This paper focuses on the modeling and design of an active bushing, which addresses the higher order vibrations in engines. Such a bushing has a significant advantage in the ride quality of the newly commercialized variable displacement engine (VDE), where the amplitude of vibration induced by switching is higher than normal engines. For VDEs the higher amplitude of vibration makes the higher orders sensible. Isolation of these vibrations is beyond the capabilities of the passive hydraulic bushings. In this paper the design of a novel active chamber is proposed, which is ultimately utilized to control the fluid pressure inside the bushing. It is evident that the fluid pressure significantly contributes to the dynamic performance of the hydraulic bushing. The active chamber described in this paper utilizes a magnetic actuator, excited by electrical current signal, which is fed to a solenoid coil. The pulses produced by the magnetic actuator are used to adjust the pressure at any specific frequency. This feature enables the active chamber not only to alter the frequency response characteristic of the hydraulic bushing, but also to generate complex pressure frequency responses. A mathematical linear model for the magnetic actuator, and the active bushing assembly, is provided and then verified experimentally. The experimental results confirm that the active hydraulic bushing can well address the sophisticated vibration isolation requirements particular to the VDE systems.

旋回流を用いた非接触搬送系に関する研究（第２報，スクイズ効果を考慮した動的モデリング）

Vortex levitation can achieve non-contact handling by blowing air into a vortex cup through a tangential nozzle to generate a swirling air flow. In this paper, its dynamical characteristics are investigated by means of pressure frequency response to note that inside the cup pressure response relative to movement of a work piece is very rapid. Furthermore, an obvious pressure hysteresis is observed while the work piece repeats sinusoidal movement under the cup, which results from squeeze film effect of thin air layer entrapped between the work piece and the skirt of the cup. According to those experimental observations, we proposed a spring-damper model by modelling the lifting force caused by swirling air flow and the resistive force related to squeeze film air damping separately. Finally, the validity of the proposed model is confirmed through an experiment of loading process.

Detection of Partial Blockage in Single Pipelines

A methodology is presented for the detection of partial blockages in single pipelines by the frequency response method. A steady-oscillatory flow produced by the periodic opening and closing of a valve located at the downstream end is analyzed in the frequency domain by using the transfer matrix method, and a peak pressure frequency response at the valve is developed. The comparison between the peak pressure frequency responses obtained by using the frequency response method and the method of characteristics is satisfactory. If there is a single partial blockage in a piping system, its location may be detected by the pattern and the number of peaks in the peak pressure frequency response. The size of the partial blockage may be determined from the mean peak pressure fluctuation. For two partial blockages, the effective size of the blockages can be determined from the peak pressure frequency response. Knowing the pre- and postdevelopmental frequency responses of a system with an additional partial blockage, the location and size of this additional partial blockage can be detected.

Principles of pressure transducers, resonance, damping and frequency response

The most commonly used pressure transducer in clinical practice is the piezoresistive strain gauge. The transducer is usually placed some distance from the patient and the pressure signal conveyed by a fluid-filled manometer. Deformation of a silicon wafer diaphragm produces an alteration in electrical resistance, which is measured by a Wheatstone bridge. To maximize accuracy, any transducer must be correctly set up and zero balanced before clinical use. Resonance occurs when the frequency of the driving oscillations matches the natural frequency of the measuring system, and results in significant measurement error. The natural frequency may be raised by incorporating a stiff diaphragm, and reducing the mass of fluid in the manometer pathway. Optimal damping of an invasive pressure measuring system allows accurate pressure measurement at frequencies up to two-thirds of the natural frequency. Accurate representation of the arterial pressure waveform is achieved by summation of the first eight harmonics of the pressure signal using Fourier analysis. Eight times the fundamental frequency of the heart rate represents the minimum required bandwidth for a measuring system. The frequency response, or flat range of a system is the highest frequency that can be measured before significant overshoot error (over 10%) occurs. An optimally damped manometric transducer system with a resonant frequency of 36 Hz or more will accurately reproduce the shape of the arterial waveform up to a heart rate of 180 beats/min.

Unsteady Stolid Propellant Pressure Combustion Responses Using a Piston Burner

A small-scale solid-propellant laboratory burner has been designed to operate under piston-driven oscillating conditions from 40-400 Hz and 300-900 kPa mean pressure, with 10% amplitudes. The device was used to investigate the burning-rate response of a wide-distribution, bimodal AP (2:200 μm)-HTPB (IPDI) composite propellant (MURI TKC#5b). Results show that mean pressure and exit temperature decrease with increasing frequency because of increased heat transfer associated with oscillatory gas motion. Propellant burning rate is calculated numerically from pressure, volume, and frequency data using mass and energy balances. The dynamic burning rate response appears to be nearly linear at low frequencies (<150 Hz) and increasingly nonlinear at higher frequencies because of an increasing combustion response magnitude with frequency and nearly constant relative pressure amplitude. In the range of frequencies determined to be most linear (40-150 Hz), the magnitude of the pressure-coupled frequency response ranges from 2 to 7 ′ 1, with burning rate lagging pressure by 50-75 deg. The results demonstrate the potential for the piston burner to measure pressure frequency response at low frequencies and also to measure nonlinear dynamic burn rates over a range of frequencies at high spectral resolution within a single test. The results also demonstrate that nonlinear response can appear as spectral structure in the apparent linear response when the data are interpreted linearly.

Evaluation of sound field systems in elementary school classrooms

Our primary purpose in this study was to determine the relevant ergonomic issues associated with daily use of sound field systems in elementary school classrooms, in order to develop a purchasing guideline and technical specification. The secondary purpose was to evaluate these systems to identify if one or more acoustical parameters could be used to determine the quality and effectiveness of a system. Six sound field systems, with varying numbers and types of speakers, were chosen as a cross-section of available systems on the market. Six representative classrooms, currently in use, were selected based on a range of reverberation times and background noise levels. All systems were installed for two weeks in each classroom. Student speech intelligibility (SI) tests using phonetically balanced word lists were conducted, as well as teacher interviews. The acoustical parameters measured were clarity ratios C50 and C80, speech transmission indices STI and R(rapid)STI, sound pressure level (SPL) uniformity and frequency response. An improvement in SI was found for all systems. Only SPL uniformity and frequency response were found to be useful distinguishing performance parameters between systems. Ergonomic design aspects of sound field systems had a significant influence on the acceptance and usage in the classroom.

Vibration of Pressure Loaded Nonlinear Rectangular Plates with Cross Stiffener

The resonant frequency response of large static pressure loaded, nonlinear rectangular plates with a cross stiffener have been investigated theoretically. The nonlinear Berger equation was solved by applying the finite-difference method. Replacing the partial differential equation governing the small amplitude vibration of static pressure loaded plates and the boundary conditions by the finite-difference equations approximately, the simultaneous, homogeneous, and algebraic equations are obtained. Under the condition that the determinant of coefficient matrix must be equal to zero, the resonant frequencies are determined. The numerical procedure is simpler than the procedures based on the von Kármán theory, and reasonable results are obtained.

An experimental investigation of water level effects on the dynamic behaviour of a large arch dam

AbstractThe need for full‐scale dynamic tests, which are recognized as the most reliable method to evaluate a structure's vibration properties, is increasing as new analysis techniques are developed that take into account the complex interaction phenomenons that occur in dam–reservoir–foundation systems. They are extremely useful to obtain reliable data for the calibration of newly developed numerical methods.The Earthquake Engineering and Structural Dynamics Research Center (CRGP) at the University of Sherbrooke has been developing and applying dynamic testing methods for large structures in the past 10 years. This paper presents the experimental evaluation of the effects of the varying water level on the dynamic response of the 180 m Emosson arch dam in Switzerland. Repeated forced‐vibration tests were carried out on the dam during four different periods of the reservoir's filling cycle during a one‐year span. Acceleration and hydrodynamic pressure frequency responses were obtained at several locations while the dam was subjected to horizontal harmonic loading. The variation of the resonant frequencies as a function of the reservoir level is investigated. A summary of the ongoing numerical correlation phase with a three‐dimensional finite element model for the dam–reservoir–foundation system is also presented. Copyright © 2001 John Wiley &amp; Sons, Ltd.

Characterization of air-coupled ultrasound transducers in the frequency range 40 kHz–2 MHz using light diffraction tomography

The aim of this work was to show the applicability of light diffraction tomography on airborne ultrasound in the frequency range 40 kHz–2 MHz. Seven different air-coupled transducers were measured to show the method's performance regarding linearity, absolute pressure measurements, phase measurements, frequency response, S/N ratio and spatial resolution. A calibrated microphone and the pulse–echo method were used to evaluate the results. The absolute measurements agreed within the calibrated microphone's uncertainty range. Pulse waveforms and corresponding FFT diagrams show the method's higher bandwidth compared with the microphone. Further, the method offers non-perturbing measurements with high spatial resolution, which was especially advantageous for measurements close to the transducer surfaces. The S/N ratio was higher than or in the same range as that of the two comparison methods.

Simulation of Vortex Shedding in a Turbine Stage

Vortex shedding in a turbomachine blade row is affected by the passing of blades in the adjacent downstream blade row, but these effects have not been examined in the literature. A series of flow simulations has been performed to study vortex shedding in a turbine stage, and to quantify the blade interaction effects on the unsteady pressure response. The numerical issues of spatial order of accuracy and the use of Newton subiterations were investigated first. Second-order spatial accuracy was shown to be inadequate to model the shedding frequency response and time-averaged base pressure accurately. For the small time step employed for temporal accuracy, Newton iterations were shown to be unnecessary. The effects of the adjacent blade row were examined by comparing the shedding frequency response for the stage simulations to the response for isolated cascades. The vane shedding was shown to occur exactly on a series of harmonics of the blade passing frequency for the stage case, compared to a single predominant frequency for the isolated cascade. Losses were also examined in the wake region. It was shown that close to the trailing edge, losses were mainly due to wake mixing. Farther downstream of the trailing edge, losses were predominantly due to the trailing edge shock wave.

An apparatus for adsorption dynamics studies using infrared measurement of the adsorbent temperature

An apparatus has been built for kinetics measurement in adsorption processes. It consists of a variable volume chamber where the adsorbent sample is placed. During the adsorption process the pressure and the sample temperature are measured. The temperature is measured by infrared detection achieving fast, sensitive, and nonintrusive measurements. Two methods are used for adsorption kinetics measurement: the volume step and the thermal frequency response. In the volume step method the volume is suddenly reduced and the adsorption process occurs at constant volume. Due to the sorption heat released during adsorption, the adsorbed mass is closely related to the sample temperature. This method permits one to determine the relevant thermodynamic parameters of the system and the kinetics up to 20 ms. The different mass transfer modes may then be separated. The thermal frequency response (TFR) method consists of achieving a periodic volume of the chamber. The amplitude and phase lag of the temperature, taking the pressure function as a reference, may be used to measure with great accuracy very fast kinetics (up to 1 ms). Moreover, it permits the easy discrimination of surface barrier from Fickian diffusion. Finally it allows one to measure microporous and macroporous mass transfer in the same experiment. It is shown that substantial improvements are obtained with the TFR method compared with the pressure frequency response method which was, until now, the best macroscopic method. Moreover, the TFR method has produced results in good accordance with the microscopic pulsed field gradient-nuclear magnetic resonance method. Volume step and TFR methods are limited to low pressure (less than ∼4 kPa) in consequence of nonisothermal gas compression. Experimental results are given to illustrate the possibilities of both methods.

Estimation of Damping Coefficient of Acoustic Vibration.

Acoustic resonant vibration occurs in a cavity with a tube bundle when flow velocity reaches some value. The vibration mode is usually transverse to the flow direction and its prevention is easy. However, recently, parallel mode vibration sometimes occurs. The mechanism of vibration was discussed in our previous paper and it seems that the vibration is a kind of self-excited vibration induced by unsteady fluid dynamic force. The damping factor of a system plays a very important role in the vibration; thus the method for estimating the damping factor of acoustic vibration was discussed. The boundary element method is usually used for calculating acoustic vibration; however, it is not able to estimate the damping coefficient. The frequency response of pressure can be calculated by the boundary element method and was used for calculating the damping coefficient. In this paper we describe a method of estimation of damping coefficient and results of calculations based on the method.