Far-field Pressure Research Articles

Tensile Failure and Fracture Width of Partially Permeable Wellbores with Applications in Lost Circulation Material Design

SummaryEstimation of near-wellbore fracture widths remains central to designing the particle size distribution (PSD) and composition of lost circulation material (LCM) blends. Although elastic rock models are often used for this purpose, they fall short in capturing the substantial effect of pore fluid pressure on the fracture width. The problem is addressed in this paper by incorporating the poroelastic back stress in width estimation of axial fractures nearby an inclined wellbore. The poroelastic back stress is caused by a nonideal drilling fluid filter cake allowing for fluid pressure communication between the wellbore and pore space of the rock surrounding the wellbore. In this aspect, a proper definition of the filter-cake efficiency is made in terms of the wellbore pressure, far-field pore fluid pressure, and pore fluid pressure of the rock surrounding the wellbore. The value of this parameter is estimated from the standard drilling fluid filtration test results, as well as the formation rock permeability. The filter-cake efficiency is next used to develop the long-time, asymptotic analytical solution for the poroelastic stress of an inclined wellbore. By accounting for the obtained poroelastic back stress, an improved estimation of the wellbore tensile limit that depends on the filter-cake efficiency parameter is developed. For wellbore pressures beyond the wellbore tensile limit, the width of the near-wellbore fractures is estimated. The fracture width estimation is made through an analytical, dislocation-based fracture mechanics solution to the integral equation describing the nonlocal stress equilibrium along the fracture faces. The commonly practiced scheme for geometric design of LCM blends is enhanced by using the presented improvement in estimation of the near-wellbore fracture width. A case study is used to demonstrate the substantial effect of drilling fluid filtration properties and the resulting poroelastic back stress on the wellbore tensile limit, estimated fracture width, and consequently, composition of the recommended LCM blend.

Resolvent-based modeling of turbulent jet noise.

Resolvent analysis has demonstrated encouraging results for modeling coherent structures in jets when compared against their data-educed counterparts from high-fidelity large-eddy simulations (LES). We formulate resolvent analysis as an acoustic analogy that relates the near-field resolvent forcing to the near- and far-field pressure. We use an LES database of round, isothermal, Mach 0.9 and 1.5 jets to produce an ensemble of realizations for the acoustic field that we project onto a limited set of resolvent modes. In the near-field, we perform projections on a restricted acoustic output domain, r/D=[5,6], while the far-field projections are performed on a Kirchhoff surface comprising a 100-diameter arc centered at the nozzle. This allows the LES realizations to be expressed in the resolvent basis via a data-deduced, low-rank, cross-spectral density matrix. We find that a single resolvent mode reconstructs the most energetic regions of the acoustic field across Strouhal numbers, St=[0-1], and azimuthal wavenumbers, m=[0,2]. Finally, we present a simple function that results in a rank-1 resolvent model agreeing within 2 dB of the peak noise for both jets.

On the sound fields of oblate and prolate hemispheroids in infinite baffles for directivity control.

The hemispheroid is presented as an apodized form for controlling the beam width of a sound source by varying its height-to-radius ratio. Directivity patterns, on-axis responses, and radiation impedances are calculated for various height-radius ratios of the oblate hemispheroid using spheroidal wave functions. It turns out that, for smaller angles at least, there is a direct relationship between the internal angle of the semi-elliptic cross section and the half-cone angle within which the far-field pressure is largely contained at high frequencies. The hemispheroid is compared with both a spherical cap, which produces a much less regular response, and a high-frequency asymptotic approximation. The high-frequency asymptotic approximation is in the form of a flat circular radiator with a delay that increases radially from the center to the perimeter, as used in some electrostatic loudspeakers. With the almost complete absence of lobes, this appears to be an effective alternative means of apodization to a shaded array and is more efficient because, unlike a shaded array, constant axial velocity is maintained over the whole surface. A high-frequency approximation is also derived for a prolate hemispheroid. Since this may be formed from a planar array, a beam steering option is added.

Noise reduction of sinusoidal wavy cylinder in subcritical flow regime

The sinusoidal wavy cylinder of circular cross section is able to substantially reduce the fluid forces by effectively stabilizing the near wake in the subcritical flow regime. Based on the anechoic wind tunnel measurements and large eddy simulations (LESs), we investigate the capability of the sinusoidal wavy cylinder to reduce aeroacoustic noise as well as underlying flow physics. The wavy cylinder studied in this work covers a range of spanwise wavelength λz = 1.8–6.0Dm and a range of wave amplitude a = 0.15–0.25Dm, where Dm is the mean diameter of the wavy cylinder. The wind tunnel measurements are conducted at Reynolds number ReDm = 2.9–8.0 × 104, while LESs are conducted at ReDm = 3.0 × 104. It is observed that the wavy cylinder's configuration, determined by λz and a, has a profound impact on the far-field sound pressure level (SPL) of both tonal and broadband noise. Compared with the baseline smooth cylinder, the wavy cylinder with λz = 1.8Dm and a = 0.25Dm can reduce the peak value of SPL at the tonal frequency by up to 36.7 dB. The reductions in the overall SPL of the tonal and broadband noise are also tremendous, by up to 31.0 and 7.5 dB, respectively, by the wavy cylinder with the optimum wavelength. Consistent with observations on noise reduction are the significantly weakened near-wake structures and largely attenuated spanwise coherence, as well as substantially suppressed pressure fluctuations in the near wake and over the cylinder surface, based on the LES results. Dependence of the noise reduction on Reynolds number is discussed as well.

On the use of numerical Green’s functions in acoustic analogies for edge noise prediction at low Mach number

The interaction between a turbulent flow and a rigid obstacle leads to a far-field broadband acoustic radiation which can have a significant impact in many industrial applications. Depending mainly on the Mach number, different prediction methods have been developed. At low Mach number, direct noise computation methods are too expensive. Other approaches must be chosen, based on acoustic analogies which consist in separating noise generation and noise propagation mechanisms. In this study, we focus on the Lighthill’s wave equation solved using both analytical and numerical tailored Green’s functions. The latter is computed using an accelerated Boundary Element Method. Also, a statistical model for the velocity fluctuations in the turbulent flow is used to estimate the far-field radiated noise spectrum. It can be built from either a simulation of the mean flow or an estimation of the boundary layer parameters. To validate numerical predictions for the far-field acoustic pressure spectrum, a NACA 0012 airfoil is considered. Both leading edge and trailing edge predictions are validated against experimental data. Moreover, the impact of both the inflow velocity and the angle of attack on spectra and directivity diagrams is investigated.

An Analytical Solution for the Vibration and Far-Field Sound Radiation Analysis of Finite, Semisubmerged Cylindrical Shells

The vibration response and far-field sound radiation of a semisubmerged, finite cylindrical shell with low-frequency excitation are studied. The solution to this problem can be divided into two steps. The first step is to apply the wave propagation approach to determine the vibration response of the cylindrical shell. In the cylindrical coordinate system, the Flügge shell equations and Laplace equation are used to describe the cylindrical shell and surrounding fluid so that the vibration responses of the shell can be addressed analytically. The fluid free surface effect is taken into account by applying the sine series to force the velocity potential on the free surface to be zero. Furthermore, compared with the FEM (the finite element method), the present method is not only reliable but also effective. In the second step, the far-field sound radiation is solved by the Fourier transform technique and the stationary phase method in accordance with the vibration responses of the shell from the previous step. The boundary element method is applied to validate the reliability of the acoustical radiation calculation. The circumferential directivity of far-field sound pressure is discussed, and it is found that the maximum value of the sound pressure always appears directly under the structure when the driving frequencies are relatively low. Besides, in consideration of simplicity and less computation effort, the present method can be used for the rapid prediction of the vibration and far-field sound pressure of a semisubmerged cylindrical shell with low-frequency excitation.

Assessment of Slat Extensions and a Cove Filler for Slat Noise Reduction

The slat of a high-lift wing can be a significant noise source during approach and landing. This paper describes an experimental study of the effects of two passive devices (namely, slat extensions and a cove filler) on the aerodynamics and acoustic radiation from a 30P30N model. Test conditions include three effective free-air angles of attack of 5.5, 7.5, and 13 deg, as well as three Reynolds numbers of 1.2, 1.5, and . Steady surface pressure measurements are used to assess the aerodynamics near the midspan section. Unsteady surface pressure and far-field acoustic array measurements are performed to evaluate the near- and far-field pressure fluctuations, respectively. Delay-and-sum beamforming is applied to localize the noise sources and to provide integrated spectra. The slat cusp extensions barely affect the mean distribution, whereas the longest extension achieves up to a 5.4 dB reduction in the overall sound pressure level. The slat-cove filler yields an even higher noise reduction that is lower than the baseline by up to 14 dB. Even though the aerodynamic assessment of the cove filler is incomplete due to the covered pressure ports, the mean distribution over the remaining surface of the model indicates a rather small change compared with the baseline measurements.

Wake-aerofoil interaction noise control with trailing-edge serrations

The present study experimentally investigates the effective reduction of wake-aerofoil interaction noise in a tandem aerofoil configuration using trailing-edge sawtooth serrations. The far-field noise results clearly show that at the ‘head-on’ wake impingement, the use of sawtooth serrations on the trailing-edge of the front aerofoil can lead to substantial reduction of the wake-aerofoil interaction noise of approximately 10 dB without any noticeable increase at other frequencies and changes to directivity pattern. Subsequently, detailed near-field measurements were carried out to investigate further the flow dynamics associated with the reduction of the interaction noise. The flow field and unsteady loading results suggest that the wake-aerofoil interaction primarily takes place within the first 30% of the chord close to the leading-edge area, while towards the trailing-edge, the flow is influenced more heavily by the boundary layer development. The velocity and wall pressure fluctuation spectra show significant decrease of the energy frequency content of the flow structures over the wake-aerofoil interaction frequency range after the wake impingement, due to the modification of the wake turbulence by trailing-edge serrations. This leads to notable reduction in the unsteady aerodynamic loading, particularly in the lift direction. Further coupled pressure–velocity analyses reveal that the sawtooth serrations modify the energy frequency content associated with the dominant turbulence eddies by spreading it over a wider frequency range. Near-field to far-field pressure coherence also reveals the loss of coherence, and thus abatement of the radiated far-field noise. The experimental results are relevant to practical applications in rotor–stator and outlet guide vanes.

Experimental Research on Noise Load Characteristics of Supersonic Jets in Rectangular Nozzles with Different Mach Numbers

Aiming at the jet noise problem of the rectangular supersonic nozzle, rectangular nozzle test models with Mach numbers of 1.35 and 1.65 were designed and processed. Using the jet noise test platform in a full anechoic chamber, the nozzle supersonic jet noise characteristic test was carried out. The test results show that the surface noise load of the model gradually increases along the nozzle axis; the unsteady flow field structure at the nozzle exit position has complex evolution, with strong turbulent pulsation and high noise load; the directivity trend of the far-field noise total pressure level of the two nozzles is basically the same, and the directivity is obvious in the upstream and 90° direction of the nozzles; from the far-field sound pressure spectrum, it can be seen that the far-field noise is composed of broadband noise and discrete frequency noise. The amplitude of the second order frequency varies significantly from 70° to 90° of upstream, and the fourth harmonic frequency of the whistling mode is captured in the direction of 90°.

The influence of nonlinearities on jet noise modeling based on parabolized stability equation

With the aid of a large eddy simulation (LES) model of a turbulent jet, we study the modeling of jet noise based on wavepackets by considering a certain degree of nonlinearity. Linear parabolized stability equations (PSEs) are utilized to solve the spatial evolution of wavepackets with the base flow obtained from the LES. The spectral proper orthogonal decomposition (SPOD) is performed to extract the most energetic coherent structures. Since the mean flow includes partial nonlinearity, improved agreement of hydrodynamic pressure fields between SPOD-filtered results and linear-PSE solutions is obtained in the near field. Deviations only occur when the coherent structures decay. Although linear-PSE solutions represent the near-field hydrodynamics reasonably, the far-field noise propagated from this linear model shows a large deviation from the LES results. Then, a small external harmonic forcing is added to the right-hand side of the PSE to mimic the effects of nonlinearity due to incoherent fluctuations on the late evolution of near-field wavepackets, and an adjoint approach is further utilized to search for optimal forcing distribution. Optimized forcing is mainly located near the critical layer; enhances the energy of wavepackets; and raises the sound radiation efficiency, but to a limited extent. Meanwhile, the coherence-matched PSE wavepacket is proposed to incorporate the coherence decay of wavepackets calculated based on LES. An improved agreement in far-field sound pressure levels for low-frequency components is achieved. In short, these findings all prove the vital role of nonlinearity in jet noise modeling, and the current modeling approaches have made some progress. However, a more physics-based and generalized nonlinear model is still required.

Wall-modeled large-eddy simulation of a trailing-edge serration–finlet configuration

This paper proposes a novel trailing-edge treatment to reduce airfoil self-noise: a serration–finlet configuration. According to the current literature, while serrations are good at reducing low-frequency noise, finlets are able to significantly reduce noise at high frequencies. Therefore, it is possible that their combination can reduce noise at all frequencies. Wall-modeled large-eddy simulations are performed to compare a serration–finlet configuration to a clean airfoil, an airfoil with serrations only, and an airfoil with finlets only. It is shown that the serration–finlet configuration reduces the far-field overall sound pressure level by 20.2 dB and has an improved aerodynamic performance. The detailed flow physics of noise reduction with the serration–finlet configuration is also investigated. It is found that the serration–finlet configuration remarkably reduces far-field noise by improving the hydrodynamic field at source locations. In particular, near-wall velocity and turbulence kinetic energy are reduced. Large coherent eddies are also broken into smaller turbulent structures. The interactions between serrations and finlets are proven to be beneficial from both aerodynamic and aeroacoustic perspectives. Overall, the current research provides a low-noise solution for wind turbines and the future’s ultra-quiet aircraft.

Finite Element Simulation and Shape Optimization of Acoustic Horn

Horn refers to the tube with continuous change of cross-sectional area, which can improve the matching of diaphragm and air load, so as to improve the electro acoustic conversion efficiency. For long-distance strong sound equipment, the purpose of using horn is to pursue higher sound pressure level, and control directivity and smoothness of sound pressure level response. In order to obtain higher sound pressure level and sharper directivity, parametric curve expressions of conical, exponential, hyperbolic and parabolic horn were derived. By using COMSOL multiphysics software, two-dimensional axisymmetric finite element simulation models of conical, exponential, hyperbolic and parabolic horn were established. Combined with if + end if programming function of the software, the effects of different cross-section shapes of horn on far-field sound pressure level and directivity were analyzed. The simulation results show that the parabolic horn can achieve a higher sound pressure level, and the sound pressure level is more than 3dB higher than the other three in the frequency band above 2000Hz. In the aspect of directivity, the beam width of parabolic horn is the smallest and more stable, and the overall directivity is the strongest. By using the shape optimization function of the software and constructing 8-order Bernstein polynomials, based on the parabolic horn, the shape of the horn was optimized for the most sensitive frequency range of 2000-4000hz, and the sound pressure level of the optimized horn was significantly improved in a large frequency range. This paper can provide technical reference for the design and development of horn loudspeaker.

A sharp interface immersed boundary method for flow-induced noise prediction using acoustic perturbation equations

In this paper, a hybrid computational aero/hydro-acoustic approach is proposed to deal with acoustic scattering and flow-induced noise problems based on the sharp interface immersed boundary method (IBM). For the flow field, the incompressible Navier–Stokes equations are solved by an in-house direct numerical simulation solver. The acoustic field is predicted by solving acoustic perturbation equations (APEs). Both flow and acoustic solid boundaries with complexity and mobility are dealt with by the sharp interface IBM. Benchmark acoustic problems with varied scatterers in two and three dimensions are presented to validate the accuracy of the acoustic codes and boundary treatments. Then, the feasibility and accuracy of the present hybrid approach are validated by considering the problem of flow past a circular cylinder at a Reynolds number of 200. Subsequently, the present method is used to predict the noise generated by flow around a four-cylinder array in two-dimensions with two arrangements (i.e., square array and diamond array), and the flow and acoustic physics are investigated in detail. The results show that the square array retains a monopole-like sound-radiation shape, while the directivity pattern of the diamond array produces a dipole-like shape. In both the square and diamond arrays, the propagation of acoustic waves is affected by the Doppler effect, and the latter array results in a larger alternation of the propagation angle compared with the single cylinder due to the influence of the geometric configuration. The intensity of the radiated acoustic pressure is much greater for the diamond array compared to the square one in most circumferential directions, and the acoustic intensity of both arrays is greater than that of the single cylinder. The spectrums of the far-field acoustic pressure indicate that the two arrays and the single cylinder have similar peak frequencies and profiles, with vortex shedding playing the predominant role in noise generation in all three configurations.

Design and simulation of broadband multiphase pentamode metamaterials

Pentamode metamaterial (PM) has great potential in controlling underwater waves due to its broadband and solid-state merits. The reported underwater PM devices were all designed with single metallic materials, which largely limited the realizable properties range of PM. Pentamode metamaterials for simulating water with dual phase and triple phase were proposed and investigated in this article. It was revealed that the acoustic scattering of the proposed PM in water is very weak within the simulation frequency range except at some resonance frequencies. The mean total scattering cross section of the proposed pentamode metamaterials is about two orders smaller than that of the titanium alloy block, while the far-field sound pressure of pentamode microstructures was only about 1/3 of that of titanium alloy block. It also illustrates that the second and third phase of the unit cell could not only broaden the realizable properties range of PM but also suppress the bending and rotational vibration modes, demonstrating the efficacy and broadband characteristic of the multiphase pentamode metamaterial.

A Long-Range and Self-Powered Intelligent Food Monitoring System Based on Far-Field Energy Harvesting and Pressure Measurement

Introduction In recent decades, food safety is becoming a top concern in the world because it is directly related to human health. According to World Health Organization statistics, about 550 million people are poisoned each year because of unsafe food consumption. One of the leading causes of foodborne illnesses is the consumption of rotten and expired foods. Therefore, the development of a food monitoring system is essential. Indeed, many studies have focused on developing battery-free food monitoring systems based on radio frequency energy harvesting (RFEH) technology due to its benefits such as durability, low cost, and safety for stored food [1]-[2]. The major disadvantage of these studies is that they estimated food quality using gas sensors, which require large energy consumption (typically over 10mW). Moreover, the gas sensors need a long time to heat up to obtain accurate sensor data. These drawbacks reduce the feasibility of implementing these systems in practice.This paper aims to develop a self-powered battery-free food monitoring system based on far-field RFEH technique and pressure measurement, which can overcome the problems with the conventional methods. Methods and Experiments The overview architecture of our proposed system is depicted in Fig.1. The self-powering capability of the sensor tag is provided by converting the radio wave transmitted from an RF generator into electrical signals. The antenna is the first component and plays a vital role in an energy harvesting system. To improve the received power and enhance the distance of power transfer, we have developed a printed Yagi-Uda Three element (driver, director, and reflector) because of its simplicity in design, high gain, compact size, and low cost [3]. The operating frequency of the antenna is chosen at the unlicensed Industrial Scientific Medical (ISM) band of 915MHz. Besides, in this study, we focus on monitoring the gradual increase of the air pressure inside the food container due to gas emission during food degradation. The air pressure sensor has ultra-low energy consumption and high precision, suitable for the limited energy condition of far-field RFEH system. Finally, we conduct a set of experiments with different sorts of food, such as pork, fish, and chicken, to demonstrate the feasibility of the proposed method. Results and Conclusions As a result, the designed Yagi antenna has a high gain of 6.54dBi in the direction of the maximum radiation, better than the isotropic antenna in some conventional systems that usually achieve about 1.7 dBi [1]. The reflection coefficient of the Yagi-Uda antenna achieved -26.8dB and voltage standing wave ratio (VSWR) better than 1.3 in approximately 60 band (890-950 MHz). At a distance of 6 meters, the harvested RF power reach -10.9dBm , and the rectifying voltage was obtained at 380mV , which is high enough for the tag to launch its functions. The sensor unit is designed with ultra-low power components and consumes only 300μW on average. The air pressure, temperature, and humidity data obtained from the sensor tag are used to evaluate and estimate the food quality, demonstrating the proposed method's effectiveness.

Wavepacket modelling of broadband shock-associated noise in supersonic jets

Abstract

Changes in reaction surface during the methane hydrate dissociation and its implications for hydrate production

The reaction surface area of hydrate (RSAH) inherently controls the reaction rate of hydrate dissociation in the pore spaces, which further affects the gas production behaviour of the hydrate-bearing sediments. The objective of this work is to measure and describe the RSAH evolution during MH dissociation and analyse its implications for gas production. The CT images obtained from different dissociation stages showed the RSAH decreased slowly in the early stage of dissociation and rapidly in the later stage. By considering the pore structure features of sediment, a fractal method was proposed to predict the relationship between RSAH and hydrate saturation, which showed better agreement with the CT experimental results than that of Yousif's model. Further hydrate production numerical simulations embedded with different RSAH predictions indicated that the hydrate production process was significantly influenced by the variations in RSAH. The simulated gas production rate based on the fractal model was lower than that of Yousif's model, the far-field pressure drop in the fractal model was slower, and the advance of the dissociation front and the transfer of the pressure field in Yousif's model was faster than that of the fractal model.

A general model for trailing edge serrations simulation on wind turbine airfoils

Trailing edge serrations (TESs) are capable of noticeably suppressing the turbulent trailing edge noise induced by rotating wind turbine blades and become an integral part of a blade. However, the challenges involved in the dimensional design of serration height 2h, wavelength λ and flap angle φ are yet to be dealt with in a satisfactory manner. To address the problem, a general model for simulating the effects of serrations on the hydrodynamic and aeroacoustic performance is proposed due to its ease of use and relatively low requirements for user input. The solid serrations are replicated by momentum sources calculated by its aerodynamic forces. Then, a case relevant to wind turbine airfoil is examined, a hybrid improved delay detached eddy simulation (IDDES) method coupled with FW-H integration is deployed to obtain the flow features and far-field sound pressure level. It is found that the modeling method could reproduce the flow field and noise as serrated airfoil.

Data assimilation for modeling cavitation bubble dynamics

The original or modified Rayleigh Plesset equation (RPE) is often used to analyze cavitation bubble dynamics. The prediction accuracy of these equations is governed by the initial values of the physical parameters. However, even for higher fidelity models, deviations from experimental measurements are observed due to the models' underlying assumptions. Here, we present a novel state-observer data assimilation technique designed to fuse time-resolved cavitation bubble diameter measurements with a governing model to yield enhanced spatiotemporal prediction of the cavitation bubble dynamics. This technique places an observer variable in the original or modified RPE and uses a proportional–integral–derivative (PID) control law on the difference between the predicted and measured cavitation bubble diameter. The data-assimilated modeling most accurately estimates the bubble diameter and far-field pressure as the deviation of bubble diameter and far-field pressure predictions from measurements decrease by up to 90% and 60%, respectively. Although the assimilated model is not a substitude for high fidelity models, this technique overcomes the inherent model assumptions, and make the model’s outputs more robust with respect to the physical parameters' initial values.

Hybrid Equivalent Circuit/Finite Element/Boundary Element Modeling for Effective Analysis of an Acoustic Transducer Array with Flexible Surrounding Structures

Transducer arrays are commonly analyzed by the finite element method (FEM) with high accuracy, but it is costly, particularly when having flexible surrounding structures. In this study, we developed an equivalent circuit (EC)-based model of an array of transducers with flexible surrounding structures for effective analysis. The impedance matrix was first constructed by coupling the electrical, mechanical impedance, and the acoustic radiation impedance obtained by the EC method and finite element-boundary element (FE-BE) coupling method. The transfer matrix of far-field pressure to the transducer response was then constructed by the FE-BE coupling method, and finally the sound pressure of the external acoustic field was obtained. To verify the accuracy, the results of the proposed method were compared with those of the conventional FEM. To evaluate the efficiency of the proposed method, the reduction in the degrees of freedom (DOFs) of the proposed method from the conventional FEM analysis was investigated. The simulation results of the proposed method are highly accurate and efficient. The proposed method is expected to be useful for conceptual design.