Development of an Innovative Multisensor Waveguide Probe With Improved Measurement Capabilities

2015 ◽  
Vol 137 (5) ◽  
Author(s):  
Giulio Lenzi ◽  
Andrea Fioravanti ◽  
Giovanni Ferrara ◽  
Lorenzo Ferrari
Keyword(s):  
Frequency Response ◽  
Signal Reconstruction ◽  
Attenuation Factor ◽  
Pressure Fluctuations ◽  
Complex Frequency ◽  
Operating Range ◽  
Waveguide Components ◽  
Wide Range ◽  
Temperature Capability ◽  
Monotone Trend

Currently, waveguide probes are widely used in several turbomachinery applications ranging from the analysis of flow instabilities to the investigation of thermoacoustic phenomena. There are many advantages to using a waveguide probe. For example, the same sensor can be adopted for different measurement points, thus reducing the total number of sensors or a cheaper sensor with a lower operating temperature capability can be used instead of a more expensive one in case of high temperature applications. Typically, a waveguide probe is made up of a transmitting duct which connects the measurement point with a sensor housing and a damping duct which attenuates the pressure fluctuations reflected by the duct end. If properly designed (i.e., with a very long damping duct), the theoretical response of a waveguide has a monotone trend with an attenuation factor that increases with the frequency and the length of the transmitting duct. Unfortunately, the real geometry of the waveguide components and the type of connection between them have a strong influence on the behavior of the system. Even the smallest discontinuity in the duct connections can lead to a very complex frequency response and a reduced operating range. The geometry of the sensor housing itself is another element which contributes to increasing the differences between the expected and real frequency responses of a waveguide, since its impedance is generally unknown. Previous studies developed by the authors have demonstrated that the replacement of the damping duct with a properly designed termination could be a good solution to increase the waveguide operating range and center it on the frequencies of interest. In detail, the termination could be used to balance the detrimental effects of discontinuities and sensor presence. In this paper, an innovative waveguide system leading to a further increase of the operating range is proposed and tested. The system is based on the measurement of the pressure oscillations propagating in the transmitting duct by means of three sensors placed at different distances from the pressure tap. The pressures measured by the three sensors are then combined and processed to calculate the pressure at the transmitting duct inlet. The arrangement of the sensing elements and the geometry of the termination are designed to minimize the error of this estimation. The frequency response achieved with the proposed arrangement turns out to be very flat over a wide range of frequencies. Thanks to the minor errors in the estimation of pressure modulus and phase, the probe is also suitable for the signal reconstruction both in frequency and time domain.

Development of an Innovative Multi-Sensor Waveguide Probe With Improved Measurement Capabilities

2014 ◽  
Author(s):  
Giulio Lenzi ◽  
Andrea Fioravanti ◽  
Giovanni Ferrara ◽  
Lorenzo Ferrari
Keyword(s):  
Frequency Response ◽  
Signal Reconstruction ◽  
Attenuation Factor ◽  
Pressure Fluctuations ◽  
Complex Frequency ◽  
Operating Range ◽  
Waveguide Components ◽  
Wide Range ◽  
Temperature Capability ◽  
Monotone Trend

Currently waveguide probes are widely used in several turbomachinery applications ranging from the analysis of flow instabilities to the investigation of thermoacoustic phenomena. There are many advantages to using a waveguide probe. For example, the same sensor can be adopted for different measurement points, thus reducing the total number of sensors or a cheaper sensor with a lower operating temperature capability can be used instead of a more expensive one in case of high temperature applications. Typically, a waveguide probe is made up of a transmitting duct which connects the measurement point with a sensor housing and a damping duct which attenuates the pressure fluctuations reflected by the duct end. If properly designed (i.e. with a very long damping duct), the theoretical response of a wave guide has a monotone trend with an attenuation factor that increases with the frequency and the length of the transmitting duct. Unfortunately, the real geometry of the waveguide components and the type of connection between them have a strong influence on the behavior of the system. Even the smallest discontinuity in the duct connections can lead to a very complex frequency response and a reduced operating range. The geometry of the sensor housing itself is another element which contributes to increasing the differences between the expected and real frequency responses of a waveguide since its impedance is generally unknown. Previous studies developed by the authors have demonstrated that the replacement of the damping duct with a properly designed termination could be a good solution to increase the waveguide operating range and center it on the frequencies of interest. In detail, the termination could be used to balance the detrimental effects of discontinuities and sensor presence. In this paper an innovative waveguide system leading to a further increase of the operating range is proposed and tested. The system is based on the measurement of the pressure oscillations propagating in the transmitting duct by means of three sensors placed at different distances from the pressure tap. The pressures measured by the three sensors are then combined and processed to calculate the pressure at the transmitting duct inlet. The arrangement of the sensing elements and the geometry of the termination are designed to minimize the error of this estimation. The frequency response achieved with the proposed arrangement turns out to be very flat over a wide range of frequencies. Thanks to the minor errors in the estimation of pressure modulus and phase the probe is also suitable for the signal reconstruction both in frequency and time domain.

Analytical representation of hydrophone complex frequency response

2021 ◽  
pp. 16-20
Author(s):  
Alexander E. Isaev
Keyword(s):  
Frequency Response ◽  
Complex Variable ◽  
Active Element ◽  
Analytical Representation ◽  
Complex Frequency ◽  
Minimum Phase ◽  
Experimental Frequency ◽  
Resonance Properties ◽  
Fractional Rational Function ◽  
Sound Diffraction

The problem of analytical representation of hydrophone complex frequency response based on a model consisting of an advance line and a minimum-phase part, which describing the effect of sound diffraction and resonance properties of an active element, is considered. Algorithms are proposed for approximating the hydrophone complex frequency response by a fractional-rational function of the complex variable according to the data of the hydrophone amplitude-frequency and/or phasefrequency responses. Examples of the application of these algorithms for processing experimental frequency characteristics of hydrophones are given.

Experimental Study for Extraction of Normal Modes

1995 ◽  
Author(s):  
S. Y. Chen ◽  
M. S. Ju ◽  
Y. G. Tsuei
Keyword(s):  
Frequency Response ◽  
Normal Mode ◽  
Normal Modes ◽  
Measurement Data ◽  
Mode Shapes ◽  
Complex Frequency ◽  
Response Functions ◽  
Frequency Response Functions ◽  
Incomplete System ◽  
Coupled Structures

Abstract A frequency-domain technique to extract the normal mode from the measurement data for highly coupled structures is developed. The relation between the complex frequency response functions and the normal frequency response functions is derived. An algorithm is developed to calculate the normal modes from the complex frequency response functions. In this algorithm, only the magnitude and phase data at the undamped natural frequencies are utilized to extract the normal mode shapes. In addition, the developed technique is independent of the damping types. It is only dependent on the model of analysis. Two experimental examples are employed to illustrate the applicability of the technique. The effects due to different measurement locations are addressed. The results indicate that this technique can successfully extract the normal modes from the noisy frequency response functions of a highly coupled incomplete system.

Fitting Frequency-Lowering Signal Processing Applying the American Academy of Audiology Pediatric Amplification Guideline: Updates and Protocols

2016 ◽  
Vol 27 (03) ◽  
pp. 219-236 ◽  
Author(s):  
Susan Scollie ◽  
Danielle Glista ◽  
Julie Seto ◽  
Andrea Dunn ◽  
Brittany Schuett ◽  
...  
Keyword(s):  
Signal Processing ◽  
Frequency Response ◽  
Hearing Aids ◽  
Hearing Aid ◽  
Fine Tuning ◽  
Sensation Level ◽  
Response Level ◽  
Strong Basis ◽  
Wide Range ◽  
Signal Processors

Background: Although guidelines for fitting hearing aids for children are well developed and have strong basis in evidence, specific protocols for fitting and verifying technologies can supplement such guidelines. One such technology is frequency-lowering signal processing. Children require access to a broad bandwidth of speech to detect and use all phonemes including female /s/. When access through conventional amplification is not possible, the use of frequency-lowering signal processing may be considered as a means to overcome limitations. Fitting and verification protocols are needed to better define candidacy determination and options for assessing and fine tuning frequency-lowering signal processing for individuals. Purpose: This work aims to (1) describe a set of calibrated phonemes that can be used to characterize the variation in different brands of frequency-lowering processors in hearing aids and the verification with these signals and (2) determine whether verification with these signal are predictive of perceptual changes associated with changes in the strength of frequency-lowering signal processing. Finally, we aimed to develop a fitting protocol for use in pediatric clinical practice. Study Sample: Study 1 used a sample of six hearing aids spanning four types of frequency lowering algorithms for an electroacoustic evaluation. Study 2 included 21 adults who had hearing loss (mean age 66 yr). Data Collection and Analysis: Simulated fricatives were designed to mimic the level and frequency shape of female fricatives extracted from two sources of speech. These signals were used to verify the frequency-lowering effects of four distinct types of frequency-lowering signal processors available in commercial hearing aids, and verification measures were compared to extracted fricatives made in a reference system. In a second study, the simulated fricatives were used within a probe microphone measurement system to verify a wide range of frequency compression settings in a commercial hearing aid, and 27 adult listeners were tested at each setting. The relation between the hearing aid verification measures and the listener’s ability to detect and discriminate between fricatives was examined. Results: Verification measures made with the simulated fricatives agreed to within 4 dB, on average, and tended to mimic the frequency response shape of fricatives presented in a running speech context. Some processors showed a greater aided response level for fricatives in running speech than fricatives presented in isolation. Results with listeners indicated that verified settings that provided a positive sensation level of /s/ and that maximized the frequency difference between /s/ and /∫/ tended to have the best performance. Conclusions: Frequency-lowering signal processors have measureable effects on the high-frequency fricative content of speech, particularly female /s/. It is possible to measure these effects either with a simple strategy that presents an isolated simulated fricative and measures the aided frequency response or with a more complex system that extracts fricatives from running speech. For some processors, a more accurate result may be achieved with a running speech system. In listeners, the aided frequency location and sensation level of fricatives may be helpful in predicting whether a specific hearing aid fitting, with or without frequency-lowering, will support access to the fricatives of speech.

Mechanical Contact Frequency Response Measurements

2000 ◽  
Vol 122 (4) ◽  
pp. 828-833 ◽  
Author(s):  
S. S. Kupchenko ◽  
D. P. Hess
Keyword(s):  
Frequency Response ◽  
Phase Lag ◽  
Lithium Grease ◽  
Mineral Oils ◽  
Vibration Data ◽  
Response Data ◽  
Lubricated Contacts ◽  
Wide Range ◽  
Contact Frequency ◽  
Dry Conditions

This paper presents friction frequency response measurements taken from a planar steel contact subjected to controlled random broadband normal vibration. Data are included from both dry and various lubricated contact conditions under different vibration input levels and different sliding velocities. Frequency response data for dry contacts are found to have nearly steady magnitude and negligible phase lag over a relatively wide range of frequencies. This suggests a coefficient of friction, independent of frequency but dependent on levels of normal acceleration and sliding velocity, may adequately define the dry contact frequency response. The frequency response data for lubricated contacts are mixed. For example, with MoS2 grease the frequency response may adequately be defined by a constant, as with dry conditions. However, frequency response data for contacts with pure mineral oils, mineral oils with additives, and lithium grease are found to be dependent on frequency. [S0742-4787(11)00101-9]

Nonlinear Dynamics of a Dielectric Elastomer Membrane Under Compressive Loading

2020 ◽  
Author(s):  
Robert L. Lowe ◽  
Christopher G. Cooley
Keyword(s):  
Nonlinear Dynamics ◽  
Dynamic Response ◽  
Frequency Response ◽  
Compressive Loading ◽  
Excitation Frequency ◽  
Harmonic Excitation ◽  
Dielectric Elastomer ◽  
Large Strains ◽  
Membrane Stretch ◽  
Wide Range

Abstract This paper investigates the nonlinear dynamics of square dielectric elastomer membranes under time-dependent, through-thickness compressive loading. The dielectric elastomer is modeled as an isotropic ideal dielectric, with mechanical stiffening at large strains captured using the Gent hyperelastic constitutive model. The equation of motion for the in-plane membrane stretch is derived using Hamilton’s principle. The static response of the membrane is first investigated, with equilibrium stretches calculated numerically for a wide range of compressive pre-loads and applied voltages. Snap-through instabilities are observed, with the critical snap-through voltage decreasing with increasing compressive pre-load. The dynamic response of the membrane is then investigated under forced harmonic excitation. Frequency response plots characterizing the steady-state vibration reveal primary, subharmonic, and superharmonic resonances. Near these resonances, two stable vibration states are possible, corresponding to upper and lower branches in the frequency response. Significant and practically meaningful differences in the dynamic response are observed when the system vibrates at a fixed frequency about the upper and lower branches, a feature not discussed in previous research.

Elastic Turbulence: An Experimental View on Inertialess Random Flow

2021 ◽  
Vol 53 (1) ◽  
pp. 27-58
Author(s):  
Victor Steinberg
Keyword(s):  
Spectral Properties ◽  
Pressure Fluctuations ◽  
Random Motion ◽  
Back Reaction ◽  
Formal Similarity ◽  
Chaotic Flow ◽  
Physical Mechanisms ◽  
Tiny Amount ◽  
Wide Range ◽  
Random Flow

A viscous solvent laminar flow may be strongly modified by the addition of a tiny amount of long polymer molecules, resulting in a chaotic flow called elastic turbulence (ET). ET is attributed to polymer stretching, which generates elastic stress and its back reaction on the flow. Its properties are analogous to those observed in hydrodynamic turbulence, although the formal similarity does not imply a similarity in physical mechanisms underlining these two types of random motion. Here we review the statistical and spectral properties and the spatial structure of the velocity field, the statistical and spectral properties of pressure fluctuations, and scaling of the friction factor of ET in wall-bounded and unbounded flow geometries, as observed in experiments and numerical simulations and described by theory for a wide range of control parameters and polymer concentrations.

Experimental Validation of a Wide-Range Centrifugal Compressor Stage for Supercritical CO2 Power Cycles

2019 ◽  
Vol 141 (6) ◽  
Author(s):  
Timothy C. Allison ◽  
Natalie R. Smith ◽  
Robert Pelton ◽  
Jason C. Wilkes ◽  
Sewoong Jung
Keyword(s):  
Centrifugal Compressor ◽  
Operating Conditions ◽  
Successful Implementation ◽  
Compressor Stage ◽  
Test Results ◽  
Power Cycles ◽  
Casing Treatment ◽  
Centrifugal Compressor Stage ◽  
Operating Range ◽  
Wide Range

Successful implementation of sCO2 power cycles requires high compressor efficiency at both the design-point and over a wide operating range in order to maximize cycle power output and maintain stable operation over a wide range of transient and part-load operating conditions. This requirement is particularly true for air-cooled cycles where compressor inlet density is a strong function of inlet temperature that is subject to daily and seasonal variations as well as transient events. In order to meet these requirements, a novel centrifugal compressor stage design was developed that incorporates multiple novel range extension features, including a passive recirculating casing treatment and semi-open impeller design. This design, presented and analyzed for CO2 operation in a previous paper, was fabricated via direct metal laser sintering and tested in an open-loop test rig in order to validate simulation results and the effectiveness of the casing treatment configuration. Predicted performance curves in air and CO2 conditions are compared, resulting in a reduced diffuser width requirement for the air test in order to match design velocities and demonstrate the casing treatment. Test results show that the casing treatment performance generally matched computational fluid dynamics (CFD) predictions, demonstrating an operating range of 69% and efficiency above air predictions across the entire map. The casing treatment configuration demonstrated improvements over the solid wall configuration in stage performance and flow characteristics at low flows, resulting in an effective 14% increase in operating range with a 0.5-point efficiency penalty. The test results are also compared to a traditional fully shrouded impeller with the same flow coefficient and similar head coefficient, showing a 42% range improvement over traditional designs.

Unsteady Flow Structure on a Centrifugal Pump: Experimental and Numerical Approaches

2002 ◽  
Author(s):  
Jose´ Gonza´lez ◽  
Carlos Santolaria ◽  
Eduardo Blanco ◽  
Joaqui´n Ferna´ndez
Keyword(s):  
Numerical Model ◽  
Centrifugal Pump ◽  
Pressure Field ◽  
Pressure Fluctuations ◽  
Side Wall ◽  
Relative Effect ◽  
Pressure Transducers ◽  
Unsteady Pressure ◽  
Blade Passing Frequency ◽  
Wide Range

Both experimental and numerical studies of the unsteady pressure field inside a centrifugal pump have been carried out. The unsteady patterns found for the pressure fluctuations are compared and a further and more detailed flow study from the numerical model developed will be presented in this paper. Measurements were carried out with pressure transducers installed on the volute shroud. At the same time, the unsteady pressure field inside the volute of a centrifugal pump has been numerically modelled using a finite volume commercial code and the dynamic variables obtained have been compared with the experimental data available. In particular, the amplitude of the fluctuating pressure field in the shroud side wall of the volute at the blade passing frequency is successfully captured by the model for a wide range of operating flow rates. Once the developed numerical model has shown its capability in describing the unsteady patterns experimentally measured, an explanation for such patterns is searched. Moreover, the possibilities of the numerical model can be extended to other sections (besides the shroud wall of the volute), which can provide plausible explanations for the dynamic interaction effects between the flow at the impeller exit and the volute tongue at different axial positions. The results of the numerical simulation are focused in the blade passing frequency in order to study the relative effect of the two main phenomena occurring at that frequency for a given position: the blade passing in front of the tongue and the wakes of the blades.

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