Damping of Acoustic Waves in Pipelines due to End Conditions

2013 ◽  
Author(s):  
Hugh Goyder
Keyword(s):  
Acoustic Waves ◽  
Wave Amplitude ◽  
Acoustic Resonance ◽  
Resonant Mode ◽  
Structural Vibration ◽  
Acoustic Model ◽  
Simplified Models ◽  
Physical Behaviour ◽  
End Conditions ◽  
Simple Equations

Acoustic waves in pipelines are of concern because they can cause failure due to structural vibration and fatigue. The maximum wave amplitude that can be generated is limited by damping; a good understanding of damping is therefore vital. The damping considered here is due to the loss of energy from a resonant mode at a reflecting boundary. This type of damping is straightforward to analysis and consequently simple equations for damping are developed. A further aspect of damping is that it considerably modifies the description of acoustic resonance. The use of damped acoustic modes is shown to be problematic because they are complex and do not satisfy orthogonally conditions. A further and more significant observation is that damping prevents modes from being uncoupled and considered as independent. An uncoupled configuration is always found in undamped modes and is useful in forming simplified models however such uncoupling does not, in general, extend to damped modes. A condition for determining if modes can be uncoupled is derived. If a damped mode, which is not uncoupled, is used in an acoustic model it can generate energy as well as absorb energy. This non-physical behaviour greatly complicates the analysis of acoustic systems with damping.

Acoustic Resonance in an Axial Multistage Compressor Leading to Non-Synchronous Blade Vibration

2020 ◽  
Author(s):  
Anne-Lise Fiquet ◽  
Agathe Vercoutter ◽  
Nicolas Buffaz ◽  
Stéphane Aubert ◽  
Christoph Brandstetter
Keyword(s):  
Acoustic Waves ◽  
High Speed ◽  
Numerical Study ◽  
Acoustic Resonance ◽  
Structural Vibration ◽  
Wave Number ◽  
Blade Vibration ◽  
Acoustic Modes ◽  
Blade Vibrations ◽  
Circumferential Wave

Abstract Significant non-synchronous blade vibrations (NSV) have been observed in an experimental three-stage high-speed compressor at part-speed conditions. High amplitude acoustic modes, propagating around the circumference and originating in the highly loaded Stage-3 have been observed in coherence with the structural vibration mode. In order to understand the occurring phenomena, a detailed numerical study has been carried out to reproduce the mechanism. Unsteady full annulus RANS simulations of the whole setup have been performed using the solver elsA. The results revealed the development of propagating acoustic modes which are partially trapped in the annulus and are in resonance with an aerodynamic disturbance in Rotor-3. The aerodynamic disturbance is identified as an unsteady separation of the blade boundary layer in Rotor-3. The results indicate that the frequency and phase of the separation adapt to match those of the acoustic wave, and are therefore governed by acoustic propagation conditions. Furthermore, the simulations clearly show the modulation of the propagating wave with the rotor blades, leading to a change of circumferential wave numbers while passing the blade row. To analyze if the effect is self-induced by the blade vibration, a noncoherent structural mode has been imposed in the simulations. Even at high vibration amplitude the formerly observed acoustic mode did not change its circumferential wave number. This phenomenon is highly relevant to modern compressor designs, since the appearance of the axially propagating acoustic waves can excite blade vibrations if they coincide with a structural eigenmode, as observed in the presented experiments.

Acoustic-Structural Coupling in Pipework

2007 ◽  
Author(s):  
Hugh Goyder
Keyword(s):  
Acoustic Waves ◽  
Alternative Assessment ◽  
Natural Frequencies ◽  
Assessment Tool ◽  
Acoustic Resonance ◽  
Assessment Method ◽  
Structural Vibration ◽  
Simple Method ◽  
Set Up ◽  
Two Degree Of Freedom

If an acoustic resonance is set up in a pipework system then it may cause structural vibration which can lead to a catastrophic fatigue failure. An investigation is made into the coupling between acoustic waves and pipework stress with the objective of developing a simple method for determining if stresses are excessive. The analysis of the coupled acoustic and structural vibration results in a two-degree-of-freedom model with two natural frequencies and two damping ratios. This model is impractical as an assessment tool because the natural frequencies and damping ratios are either not known at all or are only known imperfectly. The model is therefore manipulated to give the stress corresponding to the most unfavourable conditions for the natural frequencies. This results in a useful assessment equation which may be used in practical circumstances. Comparisons are made with an alternative assessment method based on uncoupled behaviour.

scholarly journals Acoustic Modeling and Vibration Characteristics of Supersonic Inlet Buzz

Energies ◽  
2020 ◽  
Vol 13 (8) ◽  
pp. 2048
Author(s):  
Jianfeng Zhu ◽  
Wenguo Luo ◽  
Yuqing Wei ◽  
Cheng Yan ◽  
Yancheng You
Keyword(s):  
Numerical Simulations ◽  
Pressure Oscillation ◽  
Resonant Mode ◽  
Acoustic Model ◽  
Oscillation System ◽  
Nonlinear Simulation ◽  
Supersonic Inlet ◽  
Nonlinear Amplification ◽  
Oscillation Damping ◽  
The Ideal

The buzz phenomenon of a typical supersonic inlet is analyzed on the basis of numerical simulations and duct acoustic theory. Considering that the choked inlet could be treated as a duct with one end closed, a one-dimensional (1D) mathematical model based on the duct acoustic theory is proposed to describe the periodic pressure oscillation of the little buzz and the big buzz. The results of the acoustic model agree well with that of the numerical simulations and the experimental data. It could verify that the dominated oscillation patterns of the little buzz and the big buzz are closely related to the first and second resonant mode of the standing wave, respectively. The discrepancies between the numerical simulation and the ideal acoustic model might be attributed to the viscous damping in the fluid oscillation system. In order to explore the damping, a small perturbation jet is introduced to trigger the resonance of the buzz system and the nonlinear amplification effect of resonance might be helpful to estimate the damping. Through the comparison between the linear acoustic model and the nonlinear simulation, the calculated pressure oscillation damping of the little buzz and the big buzz are 0.33 and 0.16, which could be regarded as an estimation of real damping.

A Quasi-Standing-Wave Phenomenon Due to Oscillating Internal Flow

1980 ◽  
Vol 102 (1) ◽  
pp. 70-77 ◽  
Author(s):  
D. Rockwell ◽  
A. Schachenmann
Keyword(s):  
Standing Wave ◽  
Acoustic Waves ◽  
Wave Amplitude ◽  
Wave Pattern ◽  
Settling Chamber ◽  
Exhaust Pipe ◽  
Axisymmetric Cavity ◽  
Vortical Structures ◽  
Helmholtz Resonance ◽  
Standing Wave Pattern

The objective of this investigation is to characterize a quasi-standing-wave pattern having a wavelength two orders of magnitude smaller than the corresponding acoustic wavelength, and relate it to the presence of: a) a downstream travelling wave due to vortical structures generated in a free shear layer, and b) downstream and upstream propagating acoustic waves. In this experiment, the vortical structures were generated by flow past an axisymmetric cavity and their influence extended downstream through the exhaust pipe. The amplitudes of the acoustic waves were associated with Helmholtz resonance of the upstream settling chamber. A linear theory models well the measured amplitude and phase distributions of the fluctuating velocity in the core flow. As system resonance is approached, the ratio of vortex wave amplitude to acoustic wave amplitude decreases. The consequence is an increase in the magnitude and gradient of the phase change across the node, or amplitude minimum, of the resultant standing-wave pattern. In addition, the peak-to-peak amplitude of the quasi-standing-wave increases. A variety of internal (and external) flow systems, including unsteady phenomena in wind tunnels, may be subject to this flow mechanism when the frequency of coherent vortex formation in the test section lies near the Helmholtz resonance frequency of the upstream settling (or plenum) chamber.

A Novel Micromechanical Resonator Using Two-Dimensional Phononic Crystal Slab

2011 ◽  
Vol 254 ◽  
pp. 195-198
Author(s):  
Nan Wang ◽  
Fu Li Hsiao ◽  
Moorthi Palaniapan ◽  
Ming Lin Julius Tsai ◽  
Jeffrey B.W. Soon ◽  
...  
Keyword(s):  
Acoustic Waves ◽  
Phononic Crystal ◽  
Acoustic Resonance ◽  
Two Dimensional ◽  
Free Standing ◽  
Sensing Applications ◽  
Aln Film ◽  
Digital Transducers ◽  
Square Array ◽  
Quality Factor Q

Two-dimensional (2-D) Silicon phononic crystal (PnC) slab of a square array of cylindrical air holes in a 10μm thick free-standing silicon plate with line defects is characterized as a cavity-mode PnC resonator. Piezoelectric aluminum nitride (AlN) film is deployed as the inter-digital transducers (IDT) to transmit and detect acoustic waves, thus making the whole microfabrication process CMOS-compatible. Both the band structure of the PnC and the transmission spectrum of the proposed PnC resonator are analyzed and optimized using finite element method (FEM). The measured quality factor (Q factor) of the microfabricated PnC resonator is over 1,000 at its resonant frequency of 152.46MHz. The proposed PnC resonator shows promising acoustic resonance characteristics for RF communications and sensing applications.

Optimal design of shear vertical wave electromagnetic acoustic transducers in resonant mode

2020 ◽  
Vol 64 (1-4) ◽  
pp. 639-647
Author(s):  
Zhichao Cai ◽  
Zhenyong Zhao ◽  
Lan Chen ◽  
Guiyun Tian
Keyword(s):  
Permanent Magnets ◽  
Signal To Noise Ratio ◽  
Acoustic Resonance ◽  
Element Model ◽  
Response Characteristic ◽  
Resonant Mode ◽  
Thickness Measurement ◽  
Frequency Interval ◽  
Resonant Amplitude ◽  
The Common

In this paper, a new electromagnetic acoustic resonance (EMAR) transducer is proposed for precise thickness measurement in specimen. The new EMAR is composed of a mirror symmetric coil (MSC) and a pair of Nd-Fe-B permanent magnets with the different polarity for enhancing the generation and detection of resonant signals. Firstly, a finite element model was established to simulate the distributions of Lorentz force produced by new EMAR and the resonant process of shear waves. Furthermore, the relationship between the frequency response characteristic of the new EMAR and the common EMAR were explored. Finally, to verify the performance of the EMAR, several experiments were performed. Compared with the common EMAR transducer, the resonant amplitude of the new EMAR transducer was increased by 121.74% and the signal-to-noise ratio was increased by 28.35%, and the resonance frequency interval of the new EMAR was twice that of the common mode in the frequency domain simulation experiment, this advantage effectively reduced the error rate of measurement. The results show that the new EMAR transducer with mirror coil structure has higher accuracy in thickness detection of specimens.

scholarly journals Flow in the exit of open pipes during acoustic resonance

1980 ◽  
Vol 99 (2) ◽  
pp. 293-319 ◽  
Author(s):  
J. H. M. Disselhorst ◽  
L. Van Wijngaarden
Keyword(s):  
Boundary Layer ◽  
Mathematical Model ◽  
Boundary Condition ◽  
Acoustic Wave ◽  
Acoustic Waves ◽  
Acoustic Radiation ◽  
Acoustic Resonance ◽  
The Other ◽  
Open Tube ◽  
Theoretical Predictions

The flow near the mouth of an open tube is examined, experimentally and theoretically, under conditions in which resonant acoustic waves are excited in the tube at the other end. If the edge of the tube is round, separation does not occur at high Strouhal numbers, which enables us to verify theoretical predictions for dissipation in the boundary layer and for acoustic radiation. Observation with the aid of schlieren pictures shows that in the case of a sharp edge vortices are formed during inflow. The vortices are shed from the pipe during outflow. Based on these observations a mathematical model is developed for the generation and shedding of vorticity. The main result of the analysis is a boundary condition for the pressure in the wave, to be applied near the mouth. The pressure amplitudes in the acoustic wave measured under resonance are compared with theoretical predictions made with the aid of the boundary condition obtained in the paper.

Combustion Instabilities in Industrial Gas Turbines—Measurements on Operating Plant and Thermoacoustic Modeling

2000 ◽  
Vol 122 (3) ◽  
pp. 420-428 ◽  
Author(s):  
David E. Hobson ◽  
John E. Fackrell ◽  
Gary Hewitt
Keyword(s):  
Time Delay ◽  
Gas Turbines ◽  
Acoustic Resonance ◽  
Resonant Mode ◽  
Combustion Stability ◽  
Combustion Instabilities ◽  
Strong Function ◽  
Fuel Supply ◽  
Industrial Gas Turbines ◽  
Stability Limits

Measurements of vibration and combustion chamber dynamic pressures have been taken on a number of 150 MW industrial gas turbines operating on pre-mixed natural gas, both during long periods of base-load operation and during short duration load-swings. The data has been analyzed in terms of the frequency and bandwidth of the principle peak in the vibration and pressure spectra as a function of load and other operating parameters. It is observed that bandwidth, which is a measure of the damping of the resonant mode of the combustion chamber’s acoustic resonance, decreases towards zero as the machines approach their combustion stability limits. A theoretical model of the thermoacoustic behavior of the combustion system has been developed to see to what extent the observed behavior on the operational machines can be explained in terms of an acoustic model of the ductwork and a flame characterized simply by a time-delay. This time delay is obtained from the frequency response function of the flame in response to unsteady perturbations in inlet velocity and is calculated using computational fluid dynamics. The model has also been used to illustrate the importance of fuel supply system design in controlling combustion stability. It is shown that stability can be a strong function of the acoustic impedance of the fuel supply and that this can lead to enhanced or reduced stability depending on the flame characteristics. [S0742-4795(00)01403-4]

Combustion Instabilities in Industrial Gas Turbines — Measurements on Operating Plant and Thermoacoustic Modelling

1999 ◽  
Author(s):  
David E. Hobson ◽  
John E. Fackrell ◽  
G. Hewitt
Keyword(s):  
Time Delay ◽  
Gas Turbines ◽  
Acoustic Resonance ◽  
Resonant Mode ◽  
Combustion Stability ◽  
Strong Function ◽  
Fuel Supply ◽  
Industrial Gas Turbines ◽  
Observed Behaviour ◽  
Stability Limits

Measurements of vibration and combustion chamber dynamic pressures have been taken on a number of 150MW industrial gas turbines operating on pre-mixed natural gas, both during long periods of base-load operation and during short duration load-swings. The data has been analysed in terms of the frequency and bandwidth of the principle peak in the vibration and pressure spectra as a function of load and other operating parameters. It is observed that bandwidth, which is a measure of the damping of the resonant mode of the combustion chamber’s acoustic resonance, decreases towards zero as the machines approach their combustion stability limits. A theoretical model of the thermoacoustic behaviour of the combustion system has been developed to see to what extent the observed behaviour on the operational machines can be explained in terms of an acoustic model of the ductwork and a flame characterised simply by a time-delay. This time delay is obtained from the frequency response function of the flame in response to unsteady perturbations in inlet velocity and is calculated using computational fluid dynamics. The model has also been used to illustrate the importance of fuel supply system design in controlling combustion stability. It is shown that stability can be a strong function of the acoustic impedance of the fuel supply and that this can lead to enhanced or reduced stability depending on the flame characteristics.

Nuclear acoustic resonance in europium vanadate

1995 ◽  
Vol 450 (1940) ◽  
pp. 719-722
Keyword(s):  
Acoustic Waves ◽  
Magnetic Moments ◽  
Preceding Paper ◽  
Electric Quadrupole ◽  
Acoustic Resonance ◽  
Magnetic Interactions ◽  
Nuclear Spins ◽  
Europium Ion ◽  
Nuclear Magnetic Moments ◽  
Hyperfine Splittings

The trivalent europium ion has a ground manifold 4f 6 , 7 F, in which the lowest state is J = 0, some 360 cm -1 below the first excited state J = 1. The two stable isotopes of mass 151, 153 each have nuclear spins I = 5/2. Experiments to determine the hyperfine structure are discussed in the preceding paper I; a further alternative is the use of acoustic waves. These have no direct interactions with the nuclear magnetic moments, but absorption arises through modulation of the electronic contributions to the hyperfine splittings. Nuclear electric quadrupole interactions are larger than magnetic interactions, and modulation of the electric field gradient of the lattice is expected to give a stronger effect.

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