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1
Das, R., and J. Kurian. "Supersonic flow over three dimensional cavities." Aeronautical Journal 117, no. 1188 (February 2013): 175–92. http://dx.doi.org/10.1017/s0001924000007934.
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AbstractThis work presents a study of acoustic oscillations generated and the wave structure associated with supersonic flow past wall mounted 3D open cavities of varying length-to-width (L/W) ratio. Experiments were conducted to investigate the acoustic signature generated by the cavities at freestream Mach number of 1·7. The effect ofL/Wratio of the cavity on the dominant modes of the acoustic signature registered on different walls of the cavities is investigated for anL/Wrange of 0·83-4. Shift in the dominant acoustic mode is observed asL/Wratio changes from 3 to 4. Statistical analysis of pressure data showed existence of acoustic waves and spreading of acoustic energy over different modes with change in cavity width. Time averaged schlieren visualisation indicated variation of shock and shear layer structure in the mainstream for the different cavities. Acoustic waves generated by the presence of the cavity and the dynamic behaviour of the shear layer were observed during instantaneous shadowgraph visualisation. Numerical simulation was done to make a prior assessment of the flow structure and the results are in good agreement with those from experiments. Ratio of mass exchange between cavity and mainflow and the cavity volume was observed to have profound effect on the magnitude of pressure oscillations generated by the cavities.
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Cong, Jiqing, Jianping Jing, and Changmin Chen. "Development of a PVDF Sensor Array for Measurement of the Dynamic Pressure Field of the Blade Tip in an Axial Flow Compressor." Sensors 19, no. 6 (March 21, 2019): 1404. http://dx.doi.org/10.3390/s19061404.
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Tip clearance flow in axial flow compressor is unavoidable and responsible for pressure losses and noise generation and influences the stability of the compressor. However, necessary flow measurement in the blade tip region is a great challenge due to the small gap width as well as the structure limitation. In this paper, a polyvinylidene fluoride (PVDF) piezoelectric-film sensor array is developed to capture the dynamic pressure field over the blade tip in an axial flow compressor. The PVDF sensor array with 40 evenly distributed sensing points is fabricated directly on a 30 μm thick aluminum-metalized polarized PVDF film through photolithography. Dynamic calibration of the sensor is accomplished using acoustic source as excitation and a microphone as a reference. The test pressure range is up to 3.5 kPa and the sampling frequency is 20 kHz. The sensor presents a high signal-to-noise ratio and good consistency with the reference microphone. Sensitivity, frequency response, linearity, hysteresis, repeatability as well as the influence of temperature are also investigated through the calibration apparatus. The calibration gives credence to the relevance and reliability of this sensor for the application in dynamic pressure field measurement. The sensor is then applied to an actual measurement in a compressor. The output of the PVDF sensor array is also compared with the results of common pressure transducers, and the features of the dynamic pressure filed are discussed. The results indicate that the PVDF sensor array is capable of the dynamic pressure field measurement over the blade tip, and superior to the conventional approaches in installation, spatial resolution, frequency response, and cost. These advantages indicate its potential broad application in pressure measurement, especially for the complex spatial surface or thin-walled structure, such as the blade surface and the thin casing wall of the compressor.
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Mosher, P., and D. W. Childs. "Theory Versus Experiment for the Effects of Pressure Ratio on the Performance of an Orifice-Compensated Hybrid Bearing." Journal of Vibration and Acoustics 120, no. 4 (October 1, 1998): 930–36. http://dx.doi.org/10.1115/1.2893922.
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This research investigates the effect of varying the concentric recess pressure ratio of hybrid (combination hydrostatic and hydrodynamic) bearings to be used in high-speed, high-pressure applications. Bearing flowrate, load capacity, torque, rotordynamic coefficients, and whirl frequency ratio are examined to determine the concentric, recess-pressure ratio which yields optimum bearing load capacity and dynamic stiffness. An analytical model, using two-dimensional bulk-flow Navier-Stokes equations and anchored by experimental test results, is used to examine bearing performance over a wide range of concentric recess pressure ratios. Typically, a concentric recess pressure ratio of 0.50 is used to obtain maximum bearing load capacity. This analysis reveals that theoretical optimum bearing performance occurs for a pressure ratio near 0.40, while experimental results indicate the optimum value to he somewhat higher than 0.45. This research demonstrates the ability to analytically investigate hybrid bearings and shows the need for more hybrid-bearing experimental data.
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Schiavi, Alessandro, Andrea Pavoni Belli, and Francesco Russo. "Estimation of Acoustical Performance of Floating Floors from Dynamic Stiffness of Resilient Layers." Building Acoustics 12, no. 2 (June 2005): 99–113. http://dx.doi.org/10.1260/1351010054037938.
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This paper describes a procedure for evaluating the reduction in impact sound pressure level of floating floors by measuring the apparent dynamic stiffness of the resilient layer, according to International Standard EN 29052-1. The impact sound pressure level experimental data, obtained according to International Standard UNI EN ISO 140-8, was compared with estimates obtained from dynamic stiffness measurements. Results confirm the effectiveness of the empirical model. Two questions are addressed. The first concerns the decrease in layer thickness over time. The second concerns the relationship between damping ratio and performance.
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Sugimoto, N. "Nonlinear theory for thermoacoustic waves in a narrow channel and pore subject to a temperature gradient." Journal of Fluid Mechanics 797 (May 26, 2016): 765–801. http://dx.doi.org/10.1017/jfm.2016.295.
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A nonlinear theory for thermoacoustic waves in a gas-filled, narrow channel and pore subject to an axial temperature gradient is developed based on the fluid dynamical equations for an ideal gas. Under the narrow-tube approximation, three small parameters are introduced as asymptotic parameters, one being the ratio of a span length to a typical thickness of the thermoviscous diffusion layer, another the ratio of the typical propagation speed of thermoacoustic waves to an adiabatic sound speed and the final parameter is the ratio of the typical magnitude of a pressure disturbance to uniform pressure in a quiescent state. No thermal interaction between the gas and the solid wall is taken into account on assuming that the wall has a large heat capacity. Using the three small parameters, the fluid dynamical equations are approximated asymptotically to be reduced to a single nonlinear diffusion wave (advection) equation for an excess pressure. All field variables are determined consistently in terms of the excess pressure so as to satisfy the boundary conditions on the wall. Supposing a time-periodic solution to the equation derived, the mean value of the excess pressure over one period is examined. It is shown that while the mean vanishes in the linear theory, it decreases monotonically due to nonlinearity. It is also shown that mean values of the shear stress and the heat flux at the wall, as well as those of the vector fields of the mass and energy fluxes representing, respectively, acoustic and thermoacoustic streaming, are expressed in terms of the mean values of the products of the spatial and/or temporal pressure gradients, which are reduced to the spatial derivatives of the mean pressure.
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Chorpening, B. T., J. D. Thornton, E. D. Huckaby, and K. J. Benson. "Combustion Oscillation Monitoring Using Flame Ionization in a Turbulent Premixed Combustor." Journal of Engineering for Gas Turbines and Power 129, no. 2 (August 30, 2006): 352–57. http://dx.doi.org/10.1115/1.2431390.
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To achieve very low NOx emission levels, lean-premixed gas turbine combustors have been commercially implemented that operate near the fuel-lean flame extinction limit. Near the lean limit, however, flashback, lean blow off, and combustion dynamics have appeared as problems during operation. To help address these operational problems, a combustion control and diagnostics sensor (CCADS) for gas turbine combustors is being developed. CCADS uses the electrical properties of the flame to detect key events and monitor critical operating parameters within the combustor. Previous development efforts have shown the capability of CCADS to monitor flashback and equivalence ratio. Recent work has focused on detecting and measuring combustion instabilities. A highly instrumented atmospheric combustor has been used to measure the pressure oscillations in the combustor, the OH emission, and the flame ion field at the premix injector outlet and along the walls of the combustor. This instrumentation allows examination of the downstream extent of the combustion field using both the OH emission and the corresponding electron and ion distribution near the walls of the combustor. In most cases, the strongest pressure oscillation dominates the frequency behavior of the OH emission and the flame ion signals. Using this highly instrumented combustor, tests were run over a matrix of equivalence ratios from 0.6 to 0.8, with an inlet reference velocity of 25m∕s(82ft∕s). The acoustics of the fuel system for the combustor were tuned using an active-passive technique with an adjustable quarter-wave resonator. Although several statistics were investigated for correlation with the dynamic pressure in the combustor, the best correlation was found with the standard deviation of the guard current. The data show a monotonic relationship between the standard deviation of the guard current (the current through the flame at the premix injector outlet) and the standard deviation of the chamber pressure. Therefore, the relationship between the standard deviation of the guard current and the standard deviation of the pressure is the most promising for monitoring the dynamic pressure of the combustor using the flame ionization signal. This addition to the capabilities of CCADS would allow for dynamic pressure monitoring on commercial gas turbines without a pressure transducer.
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Wagner, Justin L., Steven J. Beresh, Katya M. Casper, Edward P. DeMauro, and Srinivasan Arunajatesan. "Resonance dynamics in compressible cavity flows using time-resolved velocity and surface pressure fields." Journal of Fluid Mechanics 830 (October 2, 2017): 494–527. http://dx.doi.org/10.1017/jfm.2017.606.
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The resonance modes in Mach 0.94 turbulent flow over a cavity having a length-to-depth ratio of five were explored using time-resolved particle image velocimetry (TR-PIV) and time-resolved pressure sensitive paint (TR-PSP). Mode switching was quantified in the velocity field simultaneous with the pressure field. As the mode number increased from one through three, the resonance activity moved from a region downstream within the recirculation region to areas further upstream in the shear layer, an observation consistent with linear stability analysis. The second and third modes contained organized structures associated with shear layer vortices. Coherent structures occurring in the velocity field during modes two and three exhibited a clear modulation in size with streamwise distance. The streamwise periodicity was attributable to the interference of downstream-propagating vortical disturbances with upstream-travelling acoustic waves. The coherent structure oscillations were approximately $180^{\circ }$ out of phase with the modal surface pressure fluctuations, analogous to a standing wave. Modal propagation (or phase) velocities, based on cross-correlations of bandpass-filtered velocity fields were found for each mode. The phase velocities also showed streamwise periodicity and were greatest at regions of maximum constructive interference where coherent structures were the largest. Overall, the phase velocities increased with modal frequency, which coincided with the modal activity residing at higher portions of the cavity where the local mean flow velocity was elevated. Together, the TR-PIV and TR-PSP provide unique details not only on the distribution of modal activity throughout the cavity, but also new understanding of the resonance mechanism as observed in the velocity field.
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Hileman, J., and M. Samimy. "Effects of Vortex Generating Tabs on Noise Sources in an Ideally Expanded Mach 1.3 Jet." International Journal of Aeroacoustics 2, no. 1 (January 2003): 35–63. http://dx.doi.org/10.1260/147547203322436935.
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The flow and acoustic fields of an ideally expanded Mach 1.3 axisymmetric jet with delta tabs were examined to explore the effects of the tabs on noise sources. This work continues research that was performed on a baseline (no-tab) jet. Noise measurements were made at an angle of 30° to the downstream jet axis to allow a direct comparison to previous work, and to relate the sound generation mechanisms to the large structures that were visualized with temporally resolved flow visualization. Additional acoustic measurements were made at 60° and 90° locations. Three cases were examined: a baseline jet, a single delta tab jet, and a dual delta tab jet. Both tab jets were operated at the same pressure ratio as the baseline jet, which was ideally expanded. Power spectra and average acoustic waveform measurements were made for a variety of azimuthal locations; apparent noise origins were estimated with a 3-D microphone array; and temporally resolved flow visualization was used to examine the dynamic flow structure of the jet's mixing-layer. The results confirm that the tabs generate strong streamwise vortices that have a significant effect on both the flow and acoustic fields of the jet. The tabs cause significant deformation in the cross-stream plane of the mixing-layer, as well as regulating the formation and roll-up of vortices due to Kelvin Helmholtz instability. With the addition of tabs, the noise field becomes azimuthally dependent and the region of noise generation moves dramatically upstream. It appears that the tabs are directly responsible for an increase in noise over a range of Strouhal numbers between 0.8 and 2.5 through generated streamwise vortices and they are indirectly responsible for the modification of the noise generating mechanisms at Strouhal numbers below 0.6 through the induced spanwise vortex roll-ups.
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Yurikov, Alexey, Roman Pevzner, Konstantin Tertyshnikov, Vassily Mikhaltsevitch, Boris Gurevich, and Maxim Lebedev. "Laboratory measurements with DAS: A fast and sensitive tool to obtain elastic properties at seismic frequencies." Leading Edge 40, no. 9 (September 2021): 655–61. http://dx.doi.org/10.1190/tle40090655.1.
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Forced-oscillation stress-strain laboratory measurements are increasingly employed to obtain elastic and viscoelastic properties of rocks at seismic frequencies. Yet these measurements are time-consuming and expensive, due in part to the use of metal or semiconductor strain gauges, which need to be glued to the sample. Such gauges are fragile, have relatively low sensitivity, and measure very local strain only so the measurements can be affected by a slight misalignment of the system assembly and local heterogeneity of the rock. The emergence of fiber-optic distributed acoustic sensing (DAS) technology provides an alternative means of measuring strain. Strain measurements with DAS involve winding an optical fiber around the sample multiple times and connecting it to a DAS recording unit. Pilot experiments performed using this setup on a range of rocks and materials show good agreement with strain gauge measurements. Advantages of DAS over strain gauges include much higher strain sensitivity (down to 10−11) and signal-to-noise ratio (and hence, shorter time required for measurements), larger dynamic range, ability to measure average (rather than local) strain in the sample, and robustness at elevated temperatures. Although the pilot experiments demonstrate the potential of DAS for rock physics measurements, further research and improvement of the proposed methodology are required to obtain independent estimates of Young's modulus and Poisson's ratio and to port the system into a pressure vessel to obtain rock properties under in-situ conditions.
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Abderrahmane, Belkallouche, Tahar Rezoug, and Laurent Dala. "Passive control of cavity acoustics via the use of surface waviness at subsonic flow." Aircraft Engineering and Aerospace Technology 91, no. 2 (February 4, 2019): 296–308. http://dx.doi.org/10.1108/aeat-01-2018-0061.
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PurposeAircraft noise is dominant for residents near airports when planes fly at low altitudes such as during departure and landing. Flaps, wings, landing gear contribute significantly to the total sound emission. This paper aims to present a passive flow control (in the sense that there is no power input) to reduce the noise radiation induced by the flow over the cavity of the landing gear during take-off and landing.Design/methodology/approachThe understanding of the noise source mechanism is normally caused by the unsteady interactions between the cavity surface and the turbulent flows as well as some studies that have shown tonal noise because of cavity resonances; this tonal noise is dependent on cavity geometry and incoming flow that lead us to use of a sinusoidal surface modification application upstream of a cavity as a passive acoustics control device in approach conditions.FindingsIt is demonstrated that the proposed surface waviness showed a potential reduction in cavity resonance and in the overall sound pressure level at the majority of the points investigated in the low Mach number. Furthermore, optimum sinusoidal amplitude and frequency were determined by the means of a two-dimensional computational fluid dynamics analysis for a cavity with a length to depth ratio of four.Research limitations/implicationsThe noise control by surface waviness has not implemented in real flight test yet, as all the tests are conducted in the credible numerical simulation.Practical implicationsThe application of passive control method on the cavity requires a global aerodynamic study of the air frame is a matter of ongoing debate between aerodynamicists and acousticians. The latter is aimed at the reduction of the noise, whereas the former fears a corruption of flow conditions. To balance aerodynamic performance and acoustics, the use of the surface waviness in cavity leading edge is the most optimal solution.Social implicationsThe proposed leading-edge modification it has important theoretical basis and reference value for engineering application it can meet the demands of engineering practice. Particularly, to contribute to the reduce the aircraft noise adopted by the “European Visions 2020”.Originality/valueThe investigate cavity noise with and without surface waviness generation and propagation by using a hybrid approach, the computation of flow based on the large-eddy simulation method, is decoupled from the computation of sound, which can be performed during a post-processing based on Curle’s acoustic analogy as implemented in OpenFOAM.
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Birdsong, C. B., and C. J. Radcliffe. "A Compensated Acoustic Actuator for Systems with Strong Dynamic Pressure Coupling." Journal of Vibration and Acoustics 121, no. 1 (January 1, 1999): 89–94. http://dx.doi.org/10.1115/1.2893953.
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This study improves the performance of a previously developed acoustic actuator in the presence of an acoustic duct system with strong pressure coupling. The speaker dynamics and the acoustic duct dynamics are first modeled separately. The two systems are then coupled, and the resulting system is modeled. A velocity sensor is developed and used in feedback compensation. The resulting speaker system has minimal magnitude and phase variation over a 20–200 Hz bandwidth. These conclusions are verified through experimental results.
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WU, JIFEI, ZHAOLIN FAN, and YANG TAO. "INVESTIGATION ON AEROACOUSTIC CHARACTERISTICS IN CAVITY FLOW." Modern Physics Letters B 24, no. 13 (May 30, 2010): 1417–20. http://dx.doi.org/10.1142/s0217984910023761.
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An experiment was conducted in a high speed wind tunnel to study the effects of dynamic pressure waves in a cavity from subsonic speeds to supersonic speeds. The effects on dynamic pressure of various parameters such as the Mach number, cavity length to depth ratio and the number of generic store were demonstrated. Detailed static-pressure and fluctuating pressure were measured on the cavity floor to determine the variation of the steady and unsteady pressures. Results show that cavity flow aero-acoustic characteristics are closely related to the Mach number and the cavity length to depth ratio. It is also found that installing store/stores in cavity can effectively improve the aero-acoustic environment in the cavity.
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Geng, Biao, Xudong Zheng, Qian Xue, Geng Liu, and Haibo Dong. "A Numerical Study of the Sound and Force Production of Flexible Insect Wings." Fluids 3, no. 4 (October 31, 2018): 87. http://dx.doi.org/10.3390/fluids3040087.
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We numerically solved the acoustic and flow field around cicada wing models with parametrically varied flexibility using the hydrodynamic/acoustic splitting method. We observed a gradual change of sound directivity with flexibility. We found that flexible wings generally produce lower sound due to reduced aerodynamic forces, which were further found to scale with the dynamic pressure force defined as the integration of dynamic pressure over the wing area. Unlike conventional scaling where the incoming flow velocity is used as the reference to calculate the force coefficients, here only the normal component of the relative velocity of the wing to the flow was used to calculate the dynamic pressure, putting kinematic factors into the dynamic pressure force and leaving the more fundamental physics to the force coefficients. A high correlation was found between the aerodynamic forces and the dynamic pressure. The scaling is also supported by previously reported data of revolving wing experiments.
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Anavaradham, T. K. G., B. U. Chandra, V. Babu, S. R. Chakravarthy, and S. Panneerselvam. "Experimental and numerical investigation of confined unsteady supersonic flow over cavities." Aeronautical Journal 108, no. 1081 (March 2004): 135–44. http://dx.doi.org/10.1017/s0001924000151589.
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Abstract Experimental investigations were carried out to study the acoustic radiation from a rectangular wall mounted cavity in a confined supersonic flow. The free-stream Mach number was maintained at 1·5 and the cavity length-to-depth ratio was varied from 0·43 to 5·0. Acoustic measurements made on the top wall show jumps in the dominant frequency as the cavity behaviour changes from shallow-to-square-to-deep cavity. Numerical simulations of this unsteady two-dimensional flow using the commercially available software FLUENT have also been carried out. Unsteady pressure data at the same location in the flow field as the pressure transducers in the experiments was collected. FFT analysis of the unsteady pressure data was performed to obtain the dominant acoustic frequencies. The values for these dominant frequencies predicted by the numerical calculations agree well with experimental data. The numerical study also predicts the frequency jump observed in experiments.
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Shahin, Alireza, Robert Tatham, Paul Stoffa, and Kyle Spikes. "Optimal dynamic rock-fluid physics template validated by petroelastic reservoir modeling." GEOPHYSICS 76, no. 6 (November 2011): O45—O58. http://dx.doi.org/10.1190/geo2010-0275.1.
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Separation of fluid pore pressure and saturation using inverted time-lapse seismic attributes is a mandatory task for field development. Multiple pairs of inversion-derived attributes can be used in a crossplot domain. We performed a sensitivity analysis to determine an optimal crossplot, and the validity of the separation is tested with a comprehensive petroelastic reservoir model. We simulated a poorly consolidated shaly sandstone reservoir based on a prograding near-shore depositional environment. A model of effective porosity is first simulated by Gaussian geostatistics. Well-known theoretical and experimental petrophysical correlations were then efficiently combined to consistently simulate reservoir properties. Next, the reservoir model was subjected to numerical simulation of multiphase fluid flow to predict the spatial distributions of fluid saturation and pressure. A geologically consistent rock physics model was then used to simulate the inverted seismic attributes. Finally, we conducted a sensitivity analysis of seismic attributes and their crossplots as a tool to discriminate the effect of pressure and saturation. The sensitivity analysis demonstrates that crossplotting of acoustic impedance versus shear impedance should be the most stable way to separate saturation and pressure changes compared to other crossplots (e.g., velocity ratio versus acoustic impedance). We also demonstrated that the saturation and pressure patterns were detected in most of the time-lapse scenarios; however, the saturation pattern is more likely detectable because the percentage in pressure change is often lower than that of the saturation change. Imperfections in saturation and pressure patterns exist in various forms, and they can be explained by the interaction of saturation and pressure, the diffusive nature of pressure, and rapid change in pressure due to production operations.
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Prasad, Manika. "Acoustic measurements in unconsolidated sands at low effective pressure and overpressure detection." GEOPHYSICS 67, no. 2 (March 2002): 405–12. http://dx.doi.org/10.1190/1.1468600.
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Shallow water flows and over‐pressured zones are a major hazard in deepwater drilling projects. Their detection prior to drilling would save millions of dollars in lost drilling costs. I have investigated the sensitivity of seismic methods for this purpose. Using P‐wave information alone can be ambiguous, because a drop in P‐wave velocity (Vp) can be caused both by overpressure and by presence of gas. The ratio of P‐wave velocity to S‐wave velocity (Vp/Vs), which increases with overpressure and decreases with gas saturation, can help differentiate between the two cases. Since P‐wave velocity in a suspension is slightly below that of the suspending fluid and Vs=0, Vp/Vs and Poisson's ratio must increase exponentially as a load‐bearing sediment approaches a state of suspension. On the other hand, presence of gas will also decrease Vp but Vs will remain unaffected and Vp/Vs will decrease. Analyses of ultrasonic P‐ and S‐wave velocities in sands show that the Vp/Vs ratio, especially at low effective pressures, decreases rapidly with pressure. At very low pressures, Vp/Vs values can be as large as 100 and higher. Above pressures greater than 2 MPa, it plateaus and does not change much with pressure. There is significant change in signal amplitudes and frequency of shear waves below 1 MPa. The current ultrasonic data shows that Vp/Vs values can be invaluable indicators of low differential pressures.
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Disimile, Peter J., Norman Toy, and Eric Savory. "Effect of Planform Aspect Ratio on Flow Oscillations in Rectangular Cavities." Journal of Fluids Engineering 122, no. 1 (October 4, 1999): 32–38. http://dx.doi.org/10.1115/1.483223.
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An experimental investigation was undertaken to examine the effect of cavity lateral width on the flow oscillations that occur in an open cavity placed within a turbulent subsonic boundary layer. A rectangular cavity with a length to depth ratio L/D=1 and planform aspect ratio L/W=0.115 was placed within a thick turbulent boundary layer with a corresponding Reθ=10.5×103. Pressure time histories were acquired at six separate cavity widths (or L/W values) using microphone-type pressure transducers. The spectral character of these signals was analyzed and the pressure levels and dominant frequencies determined. This study indicates that large changes in the pressure level occur as L/W varies from 0.115 to 0.682. A state of fluid dynamic resonance was observed at L/W=0.137 and fluid–acoustic resonance at L/W=0.682, the smallest cavity width. Relative sound pressure level calculations indicate that the energy within the cavity compared with that of the boundary layer, was observed to increase by approximately 40 percent at L/W=0.137. [S0098-2202(00)00601-5]
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XIAO, ZHENGHUA, BO HAN, HONGJIAN LIAO, and AKENJIANG TUOHUTI. "EXPERIMENT STUDY ON DYNAMIC STRENGTH OF LOESS UNDER REPEATED LOAD." International Journal of Modern Physics B 22, no. 31n32 (December 30, 2008): 5825–30. http://dx.doi.org/10.1142/s0217979208051236.
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A series of dynamic triaxial tests are performed on normal anisotropic consolidation and over anisotropic consolidation specimens of loess. Based on the test results, the variable regularity of dynamic shear stress, axial strain and pore water pressure of loess under dynamic loading are measured and analyzed. The influences of the dynamic shear strength and pore water pressure at different over consolidation ratio are analyzed. The relationship between dynamic shear strength and over consolidation ratio of loess is obtained. The evaluating standard of dynamic shear strength of loess is discussed. Meanwhile, how to determine the effective dynamic shear strength index of normal anisotropic consolidated loess is also discussed in this paper. Several obtained conclusions can be referenced for studying the dynamic shear strength of loess foundation.
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Andriollo, Débora Bonesso, Gabriele Rodrigues Bastilha, Letícia Fernandez Frigo, and Carla Aparecida Cielo. "Vocal characteristics of athletes from an american football team." Research, Society and Development 9, no. 4 (March 12, 2020): e11942813. http://dx.doi.org/10.33448/rsd-v9i4.2813.
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The objective of this study was to verify the vocal measurements of athletes from an american football team from a municipality in the countryside of the state. With participation of eight men, aged between 18 and 39 years old (average of 24.25 years old). The collection of maximum phonation time of the vowels /a/, /i/, /u/, /s/, /z/, /e/ and number counting in normal pitch and loudness and the maximum phonation time of the [ė] was performed. Modal Sound Pressure Level and dynamic range were obtained by emission of /a:/. Acoustic evaluation of glottal and spectrographic sources. Maximum phonation times were below normality; the s/z ratio within the normality; the ratio ė/e below normality; the difference between vowels and number counting, the modal sound pressure level and the dynamic range were above normality. The acoustic vocal analysis showed impairment of the glottic source while the spectrographs were considered normal. In these American football athletes, pneumo-phono-articulatory incoordination with hyperfunctional characteristics and acoustic signal with presence of instability, aperiodicity and vocal emission failures were found, probably due to the incorrect vocal uses practiced in the sport.
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Peracchio, A. A., and W. M. Proscia. "Nonlinear Heat-Release/Acoustic Model for Thermoacoustic Instability in Lean Premixed Combustors." Journal of Engineering for Gas Turbines and Power 121, no. 3 (July 1, 1999): 415–21. http://dx.doi.org/10.1115/1.2818489.
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Lean premixed combustors, such as those used in industrial gas turbines to achieve low emissions, are often susceptible to the thermoacoustic combustion instabilities, which manifest themselves as pressure and heat release oscillations in the combustor. These oscillations can result in increased noise and decreased durability due to vibration and flame motion. A physically based nonlinear parametric model has been developed that captures this instability. It describes the coupling of combustor acoustics with the rate of heat release. The model represents this coupling by accounting for the effect of acoustic pressure fluctuations on the varying fuel/air ratio being delivered to the flame, causing a fluctuating heat release due to both fuel air ratio variations and flame front oscillations. If the phasing of the fluctuating heat release and pressure are proper, an instability results that grows into a limit cycle. The nonlinear nature of the model predicts the onset of the instability and additionally captures the resulting limit cycle. Tests of a lean premixed nozzle run at engine scale and engine operating conditions in the UTRC single nozzle rig, conducted under DARPA contract, exhibited instabilities. Parameters from the model were adjusted so that analytical results were consistent with relevant experimental data from this test. The parametric model captures the limit cycle behavior over a range of mean fuel air ratios, showing the instability amplitude (pressure and heat release) to increase and limit cycle frequency to decrease as mean fuel air ratio is reduced.
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He, Chengjun, Jianqiang Li, Zhaolin Fan, Yaohua Li, Jingmin Liang, Lei Miao, and Rongzhao Gao. "Wall pressure unsteadiness in an over-expanded single expansion ramp nozzle." International Journal of Modern Physics B 34, no. 14n16 (May 30, 2020): 2040102. http://dx.doi.org/10.1142/s0217979220401025.
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To evaluate the unsteady nature of wall pressure in an over-expanded single expansion ramp nozzle, under fixed nozzle pressure ratio (NPR) of 5.92, 6.55 and 7.19, an experimental investigation has been conducted based on focusing Schlieren techniques and dynamic pressure measurement. For all cases, the results show fully formed restricted shock separation (RSS) on the upper wall, which experiences flow reattachment on the wall downstream of separation resulting in the formation of a separation bubble. The separation mode is also RSS on the lower wall at [Formula: see text]. However, the lower wall pressure is randomly larger or lower than ambient pressure near the nozzle exit at [Formula: see text], the separated shear-layer can intermittently impinge on the lower wall, and the separation mode is partially restricted shock separation (pRSS). At [Formula: see text], the separation flow does not reattach downstream of the lower wall. That is, it occurs free shock separation (FSS).
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Ziyi, Guo, Hu Yongquan, Zhang Yong, Xiong Tingsong, Mao Chun, Lin Hai, Wan Youyu, and Liu Shiduo. "Study on the Acoustic Characteristics of Rocks and Fracability in Wunan Oilfield." E3S Web of Conferences 53 (2018): 03068. http://dx.doi.org/10.1051/e3sconf/20185303068.
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The acoustic characteristics under P&S wave velocity of 56 samples from Low Youshashan Formation in Wunan Oilfield were tested by SCMS-E high temperature and high pressure core multi parameter test instrument, the measured velocity ratio of P wave and S wave is 1.32-1.67 and the conversion between the P and S wave velocity of rock sample was established. The corresponding dynamic elastic modulus and Poisson's ratio were obtained on the base of the elastic wave propagation theory formula. So, according to the transformation relationship between static and dynamic mechanical parameters, rock brittleness index is calculated and average value is only equal to 38. Therefore, it is difficult to form a fully developed network model during the hydraulic fracturing. These achievements provide a guiding significance for fracturing development at Low Youshashan Formation in Wunan Oilfield.
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Dong, Jun, Kyung K. Choi, and Nam H. Kim. "Design Optimization for Structural-Acoustic Problems Using FEA-BEA With Adjoint Variable Method." Journal of Mechanical Design 126, no. 3 (October 1, 2003): 527–33. http://dx.doi.org/10.1115/1.1701879.
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A noise-vibration-harshness (NVH) design optimization of a complex vehicle structure is presented using finite element and boundary element analyses. The steady-state dynamic behavior of the vehicle is calculated from the frequency response finite element analysis, while the sound pressure level within the acoustic cavity is calculated from the boundary element analysis. A reverse solution process is employed for the design sensitivity calculation using the adjoint variable method. The adjoint load is obtained from the acoustic boundary element re-analysis, while the adjoint solution is calculated from the structural dynamic re-analysis. The evaluation of pressure sensitivity only involves a numerical integration process over the structural part where the design variable is defined. A design optimization problem is formulated and solved, where the structural weight is reduced while the noise level in the passenger compartment is lowered.
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Underwood, John H., David B. Moak, Michael J. Audino, and Anthony P. Parker. "Yield Pressure Measurements and Analysis for Autofrettaged Cannons." Journal of Pressure Vessel Technology 125, no. 1 (January 31, 2003): 7–10. http://dx.doi.org/10.1115/1.1526857.
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Yield pressure corresponding to a small permanent OD strain was measured in quasi-static laboratory tests of autofrettaged ASTM A723 steel cannon pressure vessels. Yield pressure was found to be a consistent ratio of the yield strength measured from specimens located in close proximity to the area of observed yielding. Yield pressure measurements for dynamic cannon firing with typically a 5-ms pressure pulse duration gave 14% higher yield pressures, attributed to strain rate effects on plastic deformation. Calculated Von Mises yield pressure for the laboratory test conditions, including the Bauschinger-modified ID residual stress and open-end vessel conditions, agreed with measured yield pressure within 3–5%. Calculated yield pressure was found to be insensitive to the value of axial residual stress, since axial stress is the intermediate value in the Von Mises yield criterion. A description of yield pressure normalized by yield strength was given for autofrettaged A723 open-end pressure vessels over a range of wall ratio and degree of autofrettage, including effects of Bauschinger-modified residual stress. This description of yield pressure is proposed as a design procedure for cannons and other pressure vessels.
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Tian, Zhang Fu, Chang Chao Gong, Xiao Peng Kong, and Hai Yang Sun. "The Experiment and Simulation Study of the Powered Resonance Tube Driven by Annular Jet." Applied Mechanics and Materials 602-605 (August 2014): 3013–16. http://dx.doi.org/10.4028/www.scientific.net/amm.602-605.3013.
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In order to generate low frequency acoustic wave and minish the ratio of the length to diameter, it is appropriate to instead the circular jet by annular jet as the high pressure gas power. So the larger diameter of jet and resonator are got in the condition of the same pressure and flux. Flow simulations and experiments have been performed in order to better understand the behavior of the powered resonance tube (PRT) driven by annular. Simulation and experiment results show the PRT can be excited by a annular jet, and produce low frequency high-amplitude dynamic pressures and acoustic emission. The compression wave and expansion wave transmit into and out of the resonance tube alternately in a cycle and a cycle can be decomposed to two distinct stages of filling and evacuation. In experiment PRT can work in the low frequency at very low pressure, and PRT can generate intense sound wave at frequency from 50~3200Hz.
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Mahmood, Waqas, and Qing Zhao. "First principles calculations on structural, elastic, acoustic and optical properties of fluorite phase TiO2 under pressure." International Journal of Modern Physics C 25, no. 07 (May 21, 2014): 1450020. http://dx.doi.org/10.1142/s012918311450020x.
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The electronic, elastic, acoustic and optical properties of fluorite phase TiO 2 are calculated by using the first principles method. Different exchange-correlation functionals are used with the ultrasoft plane wave pseudopotential method under pressure from 0 GPa to 90 GPa. The calculated values of the lattice constant, cell volume, bandgap, bulk modulus and the pressure derivative of bulk modulus are in agreement with the prior published results. The calculated elastic parameters show that the fluorite structure is mechanically stable, the ratio of bulk to shear modulus [Formula: see text] indicates that it is brittle, and pressure derivative of the bulk modulus shows that it is not a super hard material, but a hard material. The longitudinal and transverse acoustic velocities in the direction [100], [110] and [111] are computed by using prior determined data. Besides, the optical properties are also studied under the aforementioned range of pressure, and the results show more photolytic activity over the other phases.
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Hwang, D., Y. Song, and K. Ahn. "Combustion instability characteristics in a dump combustor using different hydrocarbon fuels." Aeronautical Journal 123, no. 1263 (April 30, 2019): 586–99. http://dx.doi.org/10.1017/aer.2019.19.
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ABSTRACTThe combustion instability characteristics in a model dump combustor with an exhaust nozzle were experimentally investigated. The first objective was to understand the effects of operating conditions and geometric conditions on combustion instability. The second objective was to examine more generalised parameters that affect the onset of combustion instability. Three different premixed gases consisting of air and hydrocarbon fuels (C2H4, C2H6, C3H8) were burnt in the dump combustor at various inlet velocity, equivalence ratio and combustion chamber length. Dynamic pressure transducer and photomultiplier tube with a bandpass filter were used to measure pressure fluctuation and CH* chemiluminescence data. Peak frequencies and their maximum power spectral densities of pressure fluctuations at same equivalence ratios showed different trends for each fuel. However, the dynamic combustion characteristics of pressure fluctuations displayed consistent results under similar characteristics chemistry times regardless of the used hydrocarbon fuels. The results showed that characteristic chemistry time and characteristic convection time influenced combustion instabilities. It was found that the convective-acoustic combustion instability could be prevented by increasing the characteristic chemistry time and characteristic convection time.
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Gascón-Pérez, Manuel. "Thermo-Acoustic Effects on the Natural Frequencies of Vibration of an Elastic Rectangular Panel." International Journal of Applied Mechanics 13, no. 02 (March 2021): 2150019. http://dx.doi.org/10.1142/s1758825121500198.
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In this paper, the thermo-acoustic behavior of a rectangular panel fully immersed in a compressible fluid at rest is investigated. A boundary element method (BEM) has been employed taking into account the Kirchhoff–Helmholtz (K-H) integral equation for the acoustic pressure and with the fluid-plate interface boundary condition the acoustic pressure jump over the panel is calculated. The thermal effects are considered regarding in the form of a uniform increment of temperature of the panel and are analyzed in order to prevent the buckling phenomena. The deformation modes of the panel correspond to the vacuum case. Applying a collocation method for the panel equation, the natural frequencies are obtained. The effects of several geometric parameters regarding different thermal loads on these frequencies are evaluated. Furthermore, the influence of the wave number for different temperatures of the panel on the acoustic damping ratio is evaluated, as well as the acoustic radiation efficiency for the different modes. The verification of the method is proven with other works.
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Lee, Jong Do, Jae Hyeon Shin, Young Min Park, Yong Sik Kwak, and Gil Cho Ahn. "A 2nd Order Delta-Sigma ADC for Pressure Sensor Interface." Applied Mechanics and Materials 475-476 (December 2013): 554–59. http://dx.doi.org/10.4028/www.scientific.net/amm.475-476.554.
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A second order delta-sigma analog-to-digital converter (ADC) including a bandgap reference, a bias circuit for sensor, and a digital filter for the interface of piezoresistive pressure sensor is presented. The proposed sensor interface circuit is designed to target a pressure range from 0 to 100 psi. The prototype sensor interface circuit is implemented in a 0.35 μm CMOS process. The single-loop, 1-bit, second-order delta-sigma ADC operates at OSR of 256 achieves 80.5 dB dynamic range (DR), 79.6 dB peak signal-to-noise ratio (SNR), and 74.4 dB peak signal-to-noise and distortion ratio (SNDR) over a signal bandwidth of 7.8 kHz with 3.3V supply while consuming 0.33mW including on-chip reference and bias current for sensor. (in Performance Summary: 0.95mW)
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Meyer, Patrick, Sebastian Lück, Tobias Spuhler, Christoph Bode, Christian Hühne, Jens Friedrichs, and Michael Sinapius. "Transient Dynamic System Behavior of Pressure Actuated Cellular Structures in a Morphing Wing." Aerospace 8, no. 3 (March 20, 2021): 89. http://dx.doi.org/10.3390/aerospace8030089.
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High aspect ratio aircraft have a significantly reduced induced drag, but have only limited installation space for control surfaces near the wingtip. This paper describes a multidisciplinary design methodology for a morphing aileron that is based on pressure-actuated cellular structures (PACS). The focus of this work is on the transient dynamic system behavior of the multi-functional aileron. Decisive design aspects are the actuation speed, the resistance against external loads, and constraints preparing for a future wind tunnel test. The structural stiffness under varying aerodynamic loads is examined while using a reduced-order truss model and a high-fidelity finite element analysis. The simulations of the internal flow investigate the transient pressurization process that limits the dynamic actuator response. The authors present a reduced-order model based on the Pseudo Bond Graph methodology enabling time-efficient flow simulation and compare the results to computational fluid dynamic simulations. The findings of this work demonstrate high structural resistance against external forces and the feasibility of high actuation speeds over the entire operating envelope. Future research will incorporate the fluid–structure interaction and the assessment of load alleviation capability.
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Spadoni, A., and M. Ruzzene. "Structural and Acoustic Behavior of Chiral Truss-Core Beams." Journal of Vibration and Acoustics 128, no. 5 (March 23, 2006): 616–26. http://dx.doi.org/10.1115/1.2202161.
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This paper analyzes the structural and acoustic behavior of sandwich beams with a chiral truss-core. This particular core configuration is considered to exploit some of the unique properties of the chiral geometry and to explore their potential benefits in terms of sound-transmission reduction and vibration isolation. The chiral core is composed of circular elements or nodes, joined by ligaments or ribs. The arrangement of nodes and ribs is such that chiral assemblies exhibit in-plane negative Poisson’s ratio behavior as well as unique deformation patterns. The vibroacoustic performance of the considered beams is evaluated through a numerical model, formulated by employing dynamic shape functions derived directly from the distributed parameter model of beam elements. This formulation allows an accurate evaluation of the dynamic response of the considered structures at high frequencies with a limited number of elements. Furthermore, such a numerical model can be coupled with a Fourier-transform-based analysis of the sound radiated by the structure in a surrounding fluid medium. The structural-acoustic behavior of the proposed beams is investigated in terms of kinetic energy of the constraining layers and sound pressure levels corresponding to an incident pressure wave. A sensitivity study investigates the influence of core configuration and geometry on the beam performance. Moreover, the performance of the chiral core is compared to that of cores with “square” and hexagonal topologies. The results demonstrate the design flexibility offered by the proposed core design, whose configuration is defined by a number of independent parameters that can be modified and optimized to enhance the structural-acoustic performance of the beam.
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Dehner, Rick, Ahmet Selamet, Emel Selamet, and Keith Miazgowicz. "A computational study on compressor inlet restriction to suppress surge instabilities in turbochargers." Noise Control Engineering Journal 69, no. 3 (May 1, 2021): 262–74. http://dx.doi.org/10.3397/1/376925.
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Operation of centrifugal compression systems below their stability limit causes surge to occur, resulting in large amplitude pressure fluctuations near the natural frequency of the system. Deep surge in the compression system of turbocharged internal combustion engines degrades performance and drastically increases noise. The current computational work demonstrates elimination of surge instabilities by incorporating sufficient restriction at the inlet of a turbocharger compressor. Both one-dimensional (1D) gas dynamics and three-dimensional (3D) computational fluid dynamics (CFD) models were developed to study the impact of a flow restriction on the amplitude of pressure and mass flow rate fluctuations and, therefore, system stability. The analyses were performed at a fixed operating point with a (time-averaged) mass flow rate below the deep surge boundary. As the inlet restriction was partially closed with the 1D model, the compression system remained in deep surge over a majority of the area ratio (of restriction to adjacent duct) range, and the amplitude of mass flow rate fluctuations gradually reduced with decreasing area of restriction. With sufficient inlet restriction, pressure and flow rate fluctuations were eliminated and the system was stabilized. In order to gain further insight into the importance ofmulti-dimensional physics, a simulation with the 3D model was carried out. Qualitatively, the 1D and 3D modeling results at equal pressure drop across the restriction were found to be similar. These unsteady predictions highlight the role of mass balance in the intermediate volume (between the restriction and compressor) toward reducing the amplitude of mass flow rate fluctuations.
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Sarkar, Soumalya, Satyanarayanan R. Chakravarthy, Vikram Ramanan, and Asok Ray. "Dynamic data-driven prediction of instability in a swirl-stabilized combustor." International Journal of Spray and Combustion Dynamics 8, no. 4 (July 8, 2016): 235–53. http://dx.doi.org/10.1177/1756827716642091.
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Combustion instability poses a negative impact on the performance and structural durability of both land-based and aircraft gas turbine engines, and early detection of combustion instabilities is of paramount importance not only for performance monitoring and fault diagnosis, but also for initiating efficient decision and control of such engines. Combustion instability is, in general, characterized by self-sustained growth of large-amplitude pressure tones that are caused by a positive feedback arising from complex coupling of localized hydrodynamic perturbations, heat energy release, and acoustics of the combustor. This paper proposes a fast dynamic data-driven method for detecting early onsets of thermo-acoustic instabilities, where the underlying algorithms are built upon the concepts of symbolic time series analysis (STSA) via generalization of D-Markov machine construction. The proposed method captures the spatiotemporal co-dependence among time series from heterogeneous sensors (e.g. pressure and chemiluminescence) to generate an information-theoretic precursor, which is uniformly applicable across multiple operating regimes of the combustion process. The proposed method is experimentally validated on the time-series data, generated from a laboratory-scale swirl-stabilized combustor, while inducing thermo-acoustic instabilities for various protocols (e.g. increasing Reynolds number ( Re) at a constant fuel flow rate and reducing equivalence ratio at a constant air flow rate) at varying air-fuel premixing levels. The underlying algorithms are developed based on D-Markov entropy rates, and the resulting instability precursor measure is rigorously compared with the state-of-the-art techniques in terms of its performance of instability prediction, computational complexity, and robustness to sensor noise.
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Dowd, Cody, and Joseph Meadows. "The effects of ring-shaped porous inert media on equivalence ratio oscillations in a self-excited thermoacoustic instability." International Journal of Spray and Combustion Dynamics 13, no. 1-2 (May 27, 2021): 3–19. http://dx.doi.org/10.1177/1756827721991776.
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Gas turbine operation increasingly relies on lean premixed (LPM) combustion to reduce harmful emissions, which is susceptible to thermoacoustic instabilities. Most combustion systems are technically premixed and exhibit a degree of equivalence ratio inhomogeneity. Thermoacoustic pressure oscillations can couple with the heat release oscillations through the generation of equivalence ratio fluctuations at fuel injection sites, which are then convected to the flame front. Previous experimental studies have shown that porous inert media (PIM) can passively mitigate these instabilities by adding acoustic damping and by reducing the thermoacoustic feedback mechanism. To understand the role of PIM on these equivalence ratio oscillations, spatially resolved, phased averaged equivalence ratio fluctuations are measured using the ratio of OH*/CH* chemiluminescence. Spatial imaging of OH* or CH* radicals produce integrated line of sight intensity values and an Abel transformation is used to obtain spatially resolved values. Phase averaged images are synced with dynamic pressure measurements, and an axisymmetric atmospheric burner is used to study the effects of ring-shaped PIM on the spatially resolved equivalence ratio field with self-excited thermoacoustic instabilities. The results show that PIM significantly reduces these fluctuations, and the effects on the stability of the system are discussed.
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Hasheminejad, Seyyed M., and Naemeh Safari. "Dynamic Viscoelastic Effects on Sound Wave Diffraction by Spherical and Cylindrical Shells Submerged in and Filled with Viscous Compressible Fluids." Shock and Vibration 10, no. 5-6 (2003): 339–63. http://dx.doi.org/10.1155/2003/434612.
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An analysis for sound scattering by fluid-filled spherical and cylindrical viscoelastic shells immersed in viscous fluids is outlined. The dynamic viscoelastic properties of the scatterer and the viscosity of the surrounding and core fluids are rigorously taken into account in the solution of the acoustic scattering problem. The novel features of Havriliak-Negami model for viscoelastic material dynamic behaviour description along with the appropriate wave-harmonic field expansions and the pertinent boundary conditions are employed to develop a closed-form solution in form of infinite series. Subsequently, the associated acoustic field quantities such as the scattered far-field pressure directivity pattern, form function amplitude, transmitted intensity ratio, and acoustic force magnitude are evaluated for given sets of medium physical properties. Numerical results clearly indicate that in addition to the traditional fluid viscosity-related mechanisms, the dynamic viscoelastic properties of the shell material as well as its thickness can be of major significance in sound scattering. Limiting cases are examined and fair agreements with well-known solutions are established.
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Nakano, Masami, Eisuke Outa, and Kiyohiro Tajima. "Noise and Vibration Related to the Patterns of Supersonic Annular Flow in a Pressure Reducing Gas Valve." Journal of Fluids Engineering 110, no. 1 (March 1, 1988): 55–61. http://dx.doi.org/10.1115/1.3243511.
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Cause of intense aerodynamic noise and vibration from a contoured type valve is revealed in close relation to the supersonic flow patterns. Simple conical plugs are used in the experiments, and the valve pressure ratio is up to twenty. Four typical patterns of the flow are observed by schlieren photography. In one of these patterns, the jet flow along the plug separates from the wall to form an annular jet impinging on the inner wall of the valve chest. Such flow oscillates significantly in resonance with the acoustic modes of the chest cavity. The radiated noise and the dynamic force acting on the valve stem reach intense levels, dominated by some discrete components of the corresponding frequencies. The mechanisms to generate or to suppress the flow oscillation, leading to the intense noise and vibration, are discussed.
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Liou, Chuen-Huei, Hsiang Hsi Lin, F. B. Oswald, and D. P. Townsend. "Effect of Contact Ratio on Spur Gear Dynamic Load With No Tooth Profile Modifications." Journal of Mechanical Design 118, no. 3 (September 1, 1996): 439–43. http://dx.doi.org/10.1115/1.2826905.
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This paper presents a computer simulation showing how the gear contact ratio affects the dynamic load on a spur gear transmission. The contact ratio can be affected by the tooth addendum, the pressure angle, the tooth size (diametral pitch), and the center distance. The analysis presented in this paper was performed by using the NASA gear dynamics code DANST. In the analysis, the contact ratio was varied over the range 1.20 to 2.40 by changing the length of the tooth addendum. In order to simplify the analysis, other parameters related to contact ratio were held constant. The contact ratio was found to have a significant influence on gear dynamics. Over a wide range of operating speeds, a contact ratio close to 2.0 minimized dynamic load. For low-contact-ratio gears (contact ratio less than two), increasing the contact ratio reduced gear dynamic load. For high-contact-ratio gears (contact ratio equal to or greater than 2.0), the selection of contact ratio should take into consideration the intended operating speeds. In general, high-contact-ratio gears minimized dynamic load better than low-contact-ratio gears.
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Fenini, Luca, and Stefano Malavasi. "Prediction of flow-control devices' noise with modified acoustic perturbation equations." Journal of Hydroinformatics 22, no. 3 (March 23, 2020): 619–27. http://dx.doi.org/10.2166/hydro.2020.156.
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Abstract Fluid-dynamic noise emissions produced by flow-control devices inside ducts are a concerning issue for valve manufacturers and pipeline management. This work proposes a modified formulation of Acoustic Perturbation Equations (APE) that is applicable to industrial frameworks where the interest is addressed to noise prediction according to international standards. This formulation is derived from a literature APE system removing two terms allowing for a computational time reduction of about 20%. The physical contribution of the removed terms is discussed according to the literature. The modified APE are applied to the prediction of the noise emitted by an orifice. The reliability of the new APE system is evaluated by comparing the Sound Pressure Level (SPL) and the acoustic pressure with the ones returned by LES and literature APE. The new formulation agrees with the other methods far from the orifice: moving over nine diameters downstream of the trailing edge, the SPL is in accordance with the other models. Since international standards characterize control devices with the noise measured 1 m downstream of them, the modified APE formulation provides reliable and faster noise prediction for those devices with outlet diameter, d, such that 9d < 1 m.
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Fan, S. C., S. M. Li, and G. Y. Yu. "Dynamic Fluid-Structure Interaction Analysis Using Boundary Finite Element Method–Finite Element Method." Journal of Applied Mechanics 72, no. 4 (August 20, 2004): 591–98. http://dx.doi.org/10.1115/1.1940664.
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In this paper, the boundary finite element method (BFEM) is applied to dynamic fluid-structure interaction problems. The BFEM is employed to model the infinite fluid medium, while the structure is modeled by the finite element method (FEM). The relationship between the fluid pressure and the fluid velocity corresponding to the scattered wave is derived from the acoustic modeling. The BFEM is suitable for both finite and infinite domains, and it has advantages over other numerical methods. The resulting system of equations is symmetric and has no singularity problems. Two numerical examples are presented to validate the accuracy and efficiency of BFEM-FEM coupling for fluid-structure interaction problems.
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Peters, John M. "The Impact of Effective Buoyancy and Dynamic Pressure Forcing on Vertical Velocities within Two-Dimensional Updrafts." Journal of the Atmospheric Sciences 73, no. 11 (October 27, 2016): 4531–51. http://dx.doi.org/10.1175/jas-d-16-0016.1.
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Abstract This research develops simple diagnostic expressions for vertical acceleration dw/dt and vertical velocity w within updrafts that account for effective buoyancy and the dynamic pressure gradient force. Effective buoyancy is the statically forced component of the vertical gradient in the nonhydrostatic pressure field. The diagnostic expressions derived herein show that the effective buoyancy of an updraft is dependent on the magnitude of the temperature perturbation within an updraft relative to the air along the updraft’s immediate periphery (rather than relative to an arbitrary base state as in ), the updraft’s height-to-width aspect ratio, and the updraft’s slant relative to the vertical. The diagnostic expressions are significantly improved over parcel theory (where pressure forces are ignored) in their portrayal of the vertical profile of w through updrafts from a cloud model simulation and accurately diagnosed the maximum vertical velocity wmax within updrafts. The largest improvements to the diagnostic expressions over parcel theory resulted from their dependence on rather than . Whereas the actual wmax within simulated updrafts was located approximately two-thirds to three-fourths of the distance between the updraft base and the updraft top, wmax within profiles diagnosed by expressions was portrayed at the updraft top when the dynamic pressure force was ignored. A rudimentary theoretical representation of the dynamic pressure force in the diagnostic expressions improved their portrayal of the simulated w profile. These results augment the conceptual understanding of convective updrafts and provide avenues for improving the representation of vertical mass flux in cumulus parameterizations.
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Jiang, Yuan-Wu, Dan-Ping Xu, Zhi-Xiong Jiang, Jun-Hyung Kim, and Sang-Moon Hwang. "Analysis and Development of Hybrid Earphone Combining Balanced-Armature and Dynamic Receivers." Applied Sciences 9, no. 23 (November 22, 2019): 5047. http://dx.doi.org/10.3390/app9235047.
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With the rapid progress in the development of multimedia devices, earphones have become increasingly important as audio output tools. Hybrid earphones combining balanced-armature (BA) and dynamic receivers can produce better performance over a wider range when compared to the earphones with BA receiver alone (BA earphones) or dynamic receiver alone (dynamic earphones). BA and dynamic earphones are multi-physics products that exhibit coupling between the electromagnetic, mechanical, and acoustic domains. In this study, an analysis tool is developed to design a hybrid earphone based on the conventional BA and dynamic earphones. Using the developed analysis tool, an acoustic tube is optimized to match the earphone target curve and obtain improved sound quality. A prototype is manufactured and tested, and the experimental results verify the feasibility and effectiveness of the developed analysis tool. The root-mean-square value of the sound pressure level (SPL) deviation of the hybrid earphone with the optimized acoustic tube is 4.60, whereas those for the dynamic and BA earphones are 8.94 and 6.04, respectively. Thus, it is verified that the frequency response is improved using the hybrid earphone developed herein.
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Ma, C. C., and L. B. Freund. "The Extent of the Stress Intensity Factor Field During Crack Growth Under Dynamic Loading Conditions." Journal of Applied Mechanics 53, no. 2 (June 1, 1986): 303–10. http://dx.doi.org/10.1115/1.3171756.
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The phenomenon considered is fracture initiation and crack growth in a plate due to dynamic pressure loading on the faces of a pre-existing crack. The problem is formulated within the framework of two-dimensional elastodynamics, and the system is viewed as a semi-infinite crack in an otherwise unbounded body. At a certain instant of time, a spatially uniform pressure begins to act on the crack faces. The pressure magnitude increases linearly in time for a certain period (the rise time T), and it is constant thereafter. The crack begins to extend at constant speed at some time after the pressure begins to act (the delay time τ). The pressure acts only over the original crack faces, and both τ > T and τ < T are considered. The ratio of the normal stress on the fracture plane to the value due to the singular term in the stress field alone is computed for some point at a small fixed distance ahead of the crack tip, with a view toward establishing the conditions under which the stress intensity factor controlled singular term accurately describes the near tip stress distribution in this highly transient process. Measured and calculated histories compare very well for relatively low crack face pressures, but there is significant disagreement beyond crack growth initiation for higher pressures. Possible reasons for the discrepancies are discussed.
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Parati, G., A. Frattola, M. Di Rienzo, P. Castiglioni, A. Pedotti, and G. Mancia. "Effects of aging on 24-h dynamic baroreceptor control of heart rate in ambulant subjects." American Journal of Physiology-Heart and Circulatory Physiology 268, no. 4 (April 1, 1995): H1606—H1612. http://dx.doi.org/10.1152/ajpheart.1995.268.4.h1606.
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The effects of aging on the dynamic modulation of baroreflex sensitivity over 24 h was assessed in eight elderly (mean age +/- SD, 63.9 +/- 3.2 yr) and in eight young (23.9 +/- 6.1 yr) mild or moderate essential hypertensive patients, who were subject to a 24-h intra-arterial (Oxford technique) blood pressure recording in ambulatory conditions. The sensitivity of baroreflex control of the heart rate was dynamically assessed by quantifying 1) the slope of the regression line between pulse interval (the reciprocal of heart rate) and systolic blood pressure changes over spontaneously occurring hypertension-bradycardia or hypotension-tachycardia sequences (time domain analysis) and 2) the ratio between spectral-powers of pulse interval and systolic blood pressure around 0.1 Hz (alpha-coefficient: frequency domain analysis). The 24-h average sequence slope was lower in old than in young individuals (4.4 +/- 0.5 vs. 9.9 +/- 1.3 and 4.8 +/- 0.7 vs. 8.4 +/- 1.4 ms/mmHg for hypertension-bradycardia and hypotension-tachycardia sequences, respectively; P < 0.05 for both). Similar results were obtained by using the alpha-coefficient approach. The marked nighttime increase in baroreflex sensitivity observed in young individuals was much less evident in the elderly. Thus 24-h baroreflex sensitivity is markedly impaired by aging. The impairment becomes manifest also as an inability to increase baroreflex sensitivity at night.
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Sun, Y. "Modeling the dynamic interaction between left ventricle and intra-aortic balloon pump." American Journal of Physiology-Heart and Circulatory Physiology 261, no. 4 (October 1, 1991): H1300—H1311. http://dx.doi.org/10.1152/ajpheart.1991.261.4.h1300.
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An analog model is developed to characterize how alterations of some intra-aortic balloon pump (IABP) parameters affect the coupling between left ventricle (LV) and aorta. The time-varying elastance concept is applied to modeling both active components (LV and IABP) in the assisted circulation. Pressure and flow waveforms in the system are determined by numerically integrating five simultaneous state equations that represent the system dynamics. Validity of the model is supported by good agreement between model predictions and published data on LV pressure-volume (P-V) loops, end-systolic P-V relations, and hemodynamic consequences of adjusting IABP timing and speed. The model also predicts that increasing balloon volume increases the diastolic aortic pressure augmentation but has a negative effect of increasing LV load. Increasing balloon diameter over length ratio and holding a constant volume increases the diastolic augmentation and decreases the LV demand. Positioning the balloon closer to the heart improves systolic unloading but affects neither diastolic augmentation nor cardiac output. These results suggest that occlusivity is a major determinant of IABP effectiveness and plays a more important role than balloon volume and position.
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Becze, Sigismund, and Gheorghe Ioan Vuscan. "Comparison study regarding bearing performance on 3 types of air bearingsusing Dyrobes software." MATEC Web of Conferences 299 (2019): 04001. http://dx.doi.org/10.1051/matecconf/201929904001.
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The gas bearings have low load capacity and high stiffness requirements beside the high precision which all are a concern in their development. The 2 large categories of gas bearings have each of them a drawback: the static gas bearing have the performances depending by the system which maintain the pressure, while the dynamic one's performances are increasing with speed. The article creates a comparison between 3 different type of dynamic gas bearing, using air as lubricant. While all 3 types of bearing having similar performances at max speed in term of eccentricity ratio vs. rpm, minimum film thickness and equilibrium locus, the cross-coupled damping and stiffness shown a rotor destabilization tendency. The 3 lobe rotor presented the highest pressure profiles at every speed. The pressure profiles present same shapes after 80000 rpm. The results shown potentially a multilobe rotor can over perform the plain bearing also in low speed.
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Sha, Yun Dong, Fei Xu, and Zhi Jun Gao. "Nonlinear Response of Carbon-Carbon Composite Panels Subjected to Thermal-Acoustic Loadings." Applied Mechanics and Materials 117-119 (October 2011): 876–81. http://dx.doi.org/10.4028/www.scientific.net/amm.117-119.876.
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Carbon-Carbon composite materials are widely used as the surface thermal protection systems (TPS) of advanced high-speed air-craft and spacecraft. The thin-walled structures with this kind of materials would exhibit large displacement response under high-level acoustic loads and possibly display buckling at elevated temperatures. Reliable experimental data are difficult to acquire because of the high costs and difficulties with instrumentation at high acoustic intensity and elevated temperatures. Thus, in the design process greater emphasis will likely be placed on improved mathematical and computational prediction methods. Among these researches, the simulation methods for nonlinear response of thin-walled composite panels under thermo-acoustic loadings are being developed emphatically .This paper presents a nonlinear finite element model for analyzing nonlinear random dynamic behaviors of Carbon-Carbon composite panels under the combined effects of thermal and random acoustic loads. The acoustic excitation is assumed to be a band-limited Gaussian random noise and uniformly distributed over the structural surface and the thermal load is assumed to be a steady-state with different predefined temperature distribution. Three types of motion: 1) linear random vibration about one of the two buckled positions, 2) snap-through motion between the two buckled positions, and 3) nonlinear random vibration over the two thermally buckled positions can be predicted. And the dynamic response behaviors of the structures are discussed. Based on this, the influences of sound pressure level (SPL) and elevated temperatures on the dynamic responses are analyzed emphatically.
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Gascón-Pérez, Manuel. "Interactions of an Oscillating Rectangular Membrane with a Compressible Fluid." International Journal of Applied Mechanics 10, no. 02 (March 2018): 1850016. http://dx.doi.org/10.1142/s1758825118500163.
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Interaction of an oscillating membrane with a fluid is important because the wide variety of technological applications. A boundary element method has been employed for the analysis of a vibrating rectangular membrane in contact with a compressible fluid at rest. The deformation modes of the membrane correspond to the vacuum case. For the calculation of the pressure jump over the membrane, the Helmholtz’s integral equation for the fluid pressure is employed taking into account the fluid-membrane interface boundary condition. Considering the membrane equation and applying a collocation method, the natural frequencies of the interacting system are obtained. The influence of various parameters such as aspect ratio, fluid density and membrane dimension on these frequencies is evaluated. Furthermore, the influence of the wave number on the fluid mass coefficient and the acoustic damping ratio are evaluated. The validity of the method is deduced when comparing the results obtained by other authors and theories.
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Wang, Wen Lin, Xiao Feng Xia, and Gao Xin Xu. "A Dynamic Fluid Property Model for the Engineering Design of Hydraulic Dampers." Key Engineering Materials 450 (November 2010): 35–38. http://dx.doi.org/10.4028/www.scientific.net/kem.450.35.
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To improve accuracy in the engineering design of hydraulic dampers, a dynamic mathematic model for its working fluid density, viscosity, modulus and stiffness is established. The dynamic flow loss due to volumetric change and pressure leakage is also formulated, wherein the dynamic back pressure in the air chamber is coupled. Simulation results show that most of the fluid properties change obviously when the damper is subjected to external excitations, they are not constant values. The viscosity would drop 74.68% and the flow loss would soar 298.68% with the increase of fluid temperature; the modulus and the stiffness would also drop over 20% when the entrapped air ratio increases, but the density is relatively robust to both variations. The established mathematic model gives a dynamic representation of the fluid property under real service conditions, it has already been applied to the engineering design of several hydraulic damper products in industry, and the effectiveness is validated by pertinent product experiments.
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Banishev, A. F., and A. A. Banishev. "Mechanoluminescence of a composite based on polymethylmethacrylate and fine-disperse powder of phosphor excited by short acoustic pulses and dynamic action of the stylus." International Journal of Modern Physics B 33, no. 30 (December 10, 2019): 1950366. http://dx.doi.org/10.1142/s0217979219503661.
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A composite mechanoluminescent layer has been produced on the surface of polymethylmethacrylate by liquid-phase embedding of [Formula: see text] phosphor microparticles into the polymethylmethacrylate surface layer. The photoluminescence and mechanoluminescence of the obtained layer have been investigated. The mechanoluminescence was excited by the short acoustic pulses and by the dynamic pressure of the stylus sliding over the mechanoluminescent layer surface. A possible mechanism of mechanoluminescence excitation is under discussion. The produced composite layer is shown to exhibit high efficiency of “mechano-optical” transformation.
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Popescu, Mihaela, Stein Tore Johansen, and Wei Shyy. "Flow-Induced Acoustics in Corrugated Pipes." Communications in Computational Physics 10, no. 1 (July 2011): 120–39. http://dx.doi.org/10.4208/cicp.301209.230710a.
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AbstractWhen gas flows through corrugated pipes, pressure waves interacting with vortex shedding can produce distinct tonal noise and structural vibration. Based on established observations, a model is proposed which couples an acoustic pipe and self-excited oscillations with vortex shedding over the corrugation cavities. In the model, the acoustic response of the corrugated pipe is simulated by connecting the lossless medium moving with a constant velocity with a source based on a discrete distribution of van der Pol oscillators arranged along the pipe. Our time accurate solutions exhibit dynamic behavior consistent with that experimentally observed, including the lock-in frequency of vortex shedding, standing waves and the onset fluid velocity capable of generating the lock-in.