Search Results (22)

To address the difficulty of locating small-hole leaks in buried natural gas pipelines, this study conducted a comprehensive theoretical and numerical analysis of the acoustic characteristics associated with such leakage events. A coupled flow–acoustic simulation framework was developed, integrating gas compressibility via the realizable k-ε and Large Eddy Simulation (LES) turbulence models, the Peng–Robinson equation of state, a broadband noise source model, and the Ffowcs Williams–Hawkings (FW-H) acoustic analogy. The effects of pipeline operating pressure (2–10 MPa), leakage hole diameter (1–6 mm), soil type (sandy, loam, and clay), and leakage orientation on the flow field, acoustic source behavior, and sound field distribution were systematically investigated. The results indicate that the leakage hole size and soil medium exert significant influence on both flow dynamics and acoustic propagation, while the pipeline pressure mainly affects the strength of the acoustic source. The leakage direction was found to have only a minor impact on the overall results. The leakage noise is primarily composed of dipole sources arising from gas–solid interactions and quadrupole sources generated by turbulent flow, with the frequency spectrum concentrated in the low-frequency range of 0–500 Hz. This research elucidates the acoustic characteristics of pipeline leakage under various conditions and provides a theoretical foundation for optimal sensor deployment and accurate localization in buried pipeline leak detection systems. Full article

Lighthill’s theory of sound generation was developed to calculate acoustic radiation from a narrow region of turbulent flow embedded in an infinite homogeneous fluid. The theory is extended to include a simple model of non-isothermal fluid that allows finding analytical solutions. The effects of one specific temperature gradient on the wave generation and propagation are studied. It is shown that the presence of the temperature gradient in the region of wave generation leads to monopole and dipole sources of acoustic emission and that the efficiency of these two sources may be higher than Lighthill’s quadrupoles. In addition, the wave propagation far from the source is different than in Lighthill’s original work because of the presence of the acoustic cutoff frequency resulting from the temperature gradient. Full article

In acoustic deep detection technology, conventional monopole, dipole, and phased-array sound sources are far inferior to impulsive sound sources in frequency and amplitude. But impulse sound sources mostly work under high-power, high-voltage, and high-current conditions, which are difficult to be applied downhole. The purpose of this paper is to reduce the power of the impulse sound source system and at the same time to stimulate excellent impulse wave characteristics. Firstly, an experimental impulse sound source system using needle-rod electrodes was constructed, and the discharge experimental results were analysed. Secondly, a finite element model of the needle-rod electrodes of the impulse sound source was established based on the experimental conditions, and the effects of the charging voltage, electrode gap, and liquid conductivity on the power and electroacoustic parameters of the needle-rod electrodes system were investigated separately. Finally, the optimised electroacoustic parameters and curves of the needle-rod electrodes of the low-power impulse sound source were obtained. The results show that the charging voltage is the most significant parameter affecting the power of the needle-rod electrode system; a larger liquid conductivity and a suitable electrode gap are required for the optimal impulse wave parameters. The optimised low-power impulse sound source system with needle-bar electrodes with a power of 20.95 kW achieves an impulse wave intensity of 4.78 MPa, with a sound pressure level above 295 dB up to 1 kHz and above 225 dB from 1 kHz to 300 kHz. Optimised needle-rod electrodes for low-power impulse sound sources have the advantages of a wide bandwidth and high energy. This makes the downhole application of low-power impulse sound sources possible, which will play an important role in oil exploration and other drilling exploration fields. Full article

With the increasing number of complex well types in the development stage of oil and gas fields, it is becoming increasingly urgent to use remote detection logging while drilling (LWD) to explore the geological structures in a formation. In this paper, the feasibility and reliability of the dipole remote detection of logging while drilling are demonstrated theoretically. For this purpose, we use an asymptotic solution of elastic wave far-field displacement to derive the calculation formula for the radiation pattern and energy flux of an LWD dipole source. The effects of influencing factors, including the source frequency, formation property, drill collar size, and mud parameter, on the radiation pattern and energy flux are analyzed. The results show that the horizontally polarized shear wave (SH-wave) has a greater advantage in imaging the reflector compared with the cases of the compressive wave (P-wave) and vertically polarized shear wave (SV-wave), which indicates the dominance of the SH-wave in dipole remote detection while drilling. The optimal source excitation frequency of 2.5 kHz and inner and outer radii of the drill collar of 0.02 and 0.1 m, respectively, should be considered in the design of an LWD dipole shear wave reflection tool. However, the heavy drilling mud is not conducive to remote detection during logging while drilling. In addition, the reflection of the SH-wave for the LWD condition is simulated. Under the conditions of optimal source frequency, drill collar size, and mud parameters, the reflection of the SH-wave signal is still detected under the fast formation. Full article

The primary objective of this paper is to identify the critical components of the acoustic field for a piston-type pressure reducing valve (PRV) with a high pressure reduction ratio, as well as to predict unfavorable noise both experimentally and numerically. The numerical calculations were conducted using a hybrid approach that combines computational fluid dynamics (CFD) and computational aeroacoustics (CAA). Flow-induced pressure fluctuation from unsteady turbulent flow extracted by the throttling cone, the valve body and the baffle in the low-pressure chamber were considered as individual dipole acoustic sources during calculation of the internal acoustic field. The results indicated that the selected three dipole acoustic sources always played a vital role in the response of the acoustic field, and none of them could be ignored. In comparison, the throttling cone had the most salient contribution to acoustic field distribution, the valve body took second place, and the baffle had the least salient contribution. The radiated noise of interest was predicted using the indirect boundary element method (IBEM), incorporating all three components as dipole acoustic sources simultaneously; the numerical noise values showed strong validation against the experimental data. Furthermore, the distribution of sound pressure levels, as well as directional and planar field points, is also presented. This paper provides new insights into the role of each component in flow-induced noise, and offers technical support for noise reduction design and optimization of pressure reducing valves. Full article

The inversion of gas hydrate saturation is a critical procedure in the evaluation of hydrate reservoirs. In this paper, a theoretical model for a borehole acoustic wavefield excited by multipole sources is established for the first time. On this basis, the attenuation of the dipole flexural waves is obtained, and in combination with the results of sensitivity analysis, an approach for inverting natural gas hydrates using the attenuation characteristics of the dipole flexural wave is proposed. The results of the sensitivity analysis demonstrate that the attenuation of the dipole flexural wave is sensitive to gas hydrate saturation. Numerical results derived from synthetic logging data are provided to illustrate the viability of the inversion of gas hydrate saturation. Even when significant noise is introduced into the receiver signal arrays, the inversion method remains stable and accurately assesses gas hydrate saturation. The correctness and effectiveness of the proposed approach are substantiated through the processing of numerical simulation data. This work provides a potent processing approach for evaluating reservoir hydrate saturation utilizing acoustic well-logging information. Full article

When air flows through the mirrors, A-pillars, and other surfaces of a passenger car, airflow separation occurs to generate vorticity and generates aerodynamic noise. The dipole noise source is the main source of aerodynamic noise when the passenger car is travelling at high speed. In order to reveal the relationship between the physical quantities in the flow field and the intensity of the dipole noise source, this paper equates each dipole noise source to a sphere radiating noise to the outside. The acoustic wave fluctuation equations expressed as spherical coordinates are combined with the acoustic boundary conditions and the equations of motion of an ideal fluid medium to obtain the relationship between the intensity of the dipole noise source and the flow velocity and vorticity in the flow field. Then, through flow field simulation, we establish a method of identifying the dipole noise source and its distribution area, and analyze the generation mechanism of the dipole noise source. Through the analysis, it is concluded that the dipole noise sources are mainly concentrated in the airflow separation areas, which easily generate vortices. The size of the vorticity is the key factor affecting the intensity of the dipole noise source. When the intensity of the dipole noise source reaches its peak, the direction of the flow vorticity is perpendicular to the direction of the flow velocity and the peak of the flow velocity occurs before the peak of the dipole noise source, which indicates that the angle between the flow vorticity and the flow velocity, as well as the flow velocity, also has a certain effect on the generation of the dipole noise source. Full article

A new approach to accelerating the evaluation of monopole and dipole source integrals via the fast multipole method (FMM) in the time domain for general three-dimensional (3-D) aeroacoustic problems is presented in this paper. In this approach, the aeroacoustic field is predicted via a hybrid method that uses computational fluid dynamics (CFD) for near-field flow field calculations and the Ffowcs Williams–Hawkings (FW-H) acoustic analogy for far-field sound field predictions. The evaluation of the surface integrals of the monopole and dipole source terms appearing in the FW-H formulation is accelerated by a 3-D FMM to reduce computational cost. The proposed method is referred to as Fast FW-H in this work. The performance and efficiency of the proposed methodology are demonstrated using several examples. First, aeroacoustic predictions for the cases of a stationary acoustic monopole, moving acoustic monopole and stationary acoustic dipole in a uniform flow are studied, generally showing good agreement with the analytical solutions. Second, the sound field radiating from a flow passing a finite-length circular cylinder and the propeller of an unmanned aerial vehicle (UAV) during forward flight are studied, and the computed results obtained via the FW-H and Fast FW-H methods in the time domain with a stationary, permeable surface are compared. The overall computational efficiency of the sound field solutions obtained via the Fast FW-H method is found to be approximately two times faster than the computational efficiency of the original FW-H method, indicating that this proposed approach can be an accurate and efficient computational tool for modelling far-field aeroacoustic problems. Full article

The purpose of this review paper is to show the possibilities of carbonate reservoir characterization using well logging and laboratory measurements. Attention was focused on standard and new methods of well logging acquisition and interpretation including laboratory experiments to show a part of the history of carbonate rock investigations as hydrocarbon or water reservoirs. Brief information on the geology, mineralogy and petrography of carbonate rocks was delivered. Reservoir properties, i.e., porosity (including fracturing), permeability, and saturation, were defined to emphasize the specific features of carbonates, such as fractures, and vugs. Examples of methodologies were selected from the commonly used laboratory techniques (thin sections examination, mercury and helium porosimetry, X-ray diffraction—XRD) combined with the standard well logs (bulk density—RHOB, neutron porosity—NPHI, sonic slowness—DT, and deep resistivity—Rd) to show the methods that have been used since the very beginning of the scientific and engineering studies of carbonates. Novelty in well logging, i.e., resistivity and acoustic imaging, nuclear magnetic resonance–NMR, dipole shear sonic imaging–DSI, and a spectral neutron-gamma log-geochemical device–GLT combined with modern laboratory investigations (NMR laboratory experiments, scanning electron microscopy SEM), showed how continuous information on mineral composition, porosity and saturation could be obtained and juxtaposed with very detailed laboratory data. Computed X-ray tomography (CT) enabling the 2D and 3D analyses of pores and fractures was presented as a quantitative methodology, effective in pore space characterization, revealing rock filtration abilities. Deep learning and artificial intelligence were used for joining various types of data. It was shown that thanks to new computational technologies original data from very small samples (micro scale), extensively describing the flow ability of the reservoir, could be extended to mezzo scale (core samples) and macro scale (well log images). Selected examples from the published papers illustrated the review. References cited in the text, together with the issues included in them, were the rich source of the practical knowledge processed These were checked by the authors and could be used in other projects. Full article

An axial flow pump is a kind of high-specific revolution vane pump that has the characteristics of large flow, low head, and high efficiency. Due to its unique properties, it is widely used in large water diversion projects, such as the South-to-North Water Diversion Project. However, during the operation of the pump, some fish enter the axial flow pump together with the water flow through the screen before the entrance of the pump station. Consequently, some fish are inevitably damaged or even die in the process of traversing through the pump. Meanwhile, the decay of dead fish directly affects the quality of water, hence, posing serious ecological pollution and destabilizing the ecological balance. Therefore, understanding the dynamics of axial flow pumps in relation to fish species in water bodies for biodiversity and ecosystem services remain vital for nature conservation. In this paper, the impact of damage of the model pump on fish is exhaustively investigated according to the theory of blade impact model, impact probability, impact mortality, and mortality distribution under different working conditions. Through the simulation of the flow state inside the impeller, the areas that are lower than the pressure threshold, higher than the shear strain rate threshold, and higher than the pressure gradient threshold in the impeller at different flow rates are analyzed. Based on the unsteady results, the volume fluctuation characteristics of the three damage mechanisms in the impeller are analyzed. Furthermore, Powell vortex acoustic equation is used to locate the high noise source region of the axial flow pump. After extensive comparison of the dipole sound source intensity, it is revealed that the dipole noise source in the impeller and guide vane is dominant. In conclusion, this study provides a holistic perspective for evaluating fish damage caused by the flow in the impeller of the axial flow pump. Furthermore, it will proffer significant references to the construction of ecological water conservancy projects. Full article

Flapping-foil thrusters are systems that operate at a substantially lower frequency compared with marine propellers and are characterized by a much smaller power concentration. These biomimetic devices are able to operate very efficiently, offering desirable levels of thrust required for the propulsion of small vessels or autonomous underwater vehicles (AUVs), and can be used for the standalone propulsion of small vessels or for augmenting ship propulsion in waves, alleviating the generation of noise and its adverse effects on sea life, particularly on marine mammals. In this work, we consider the generation of noise by flapping foils arranged in the neighborhood of the above vessels including the scattering effects by the hull, which, in addition to free-surface and seabed effects, significantly contribute to the modification of the characteristics of the acoustic field. A Boundary Element Method (BEM) is developed to treat the 3D scattering problem in the frequency domain forced by monopole and dipole source terms associated with the Ffowcs Williams and Hawkings (FW-H) equation. Numerical results are presented in selected cases illustrating that the hull geometry and acoustic properties, as well as the sea surface and seabed effects, are important for the determination of the directionality of the generated noise and significantly affect the propagation in the underwater ocean environment. Full article

Ducted propeller is a kind of special propeller widely used in unmanned underwater vehicles, its flow characteristics and hydrodynamic noise are very important for marine environmental protection and equipment concealment. The hybrid techniques based on the acoustic analogy theory are adopted in the present study to calculate the unsteady flow field and sound field characteristics of a ducted propeller. The full scale flow filed and hydro-acoustic sources of the propulsion system are simulated by Detached-Eddy computational fluid dynamics (CFD) method. Hydrodynamic noise are calculated by FWH equation based on the CFD results. The frequency domain and directivity of sound pressure level at different sound field monitoring points are analyzed at four navigational speeds. The results show that the navigational speed that is in the inflow condition of the ducted propeller play important roles in the flow structure and underwater radiated noise. Under the fixed impeller rotational speed, the propulsion efficiency of ducted propeller increases first and then decreases with the raise of navigational speed. The maximum errors of thrust and power between simulation and experiment values are 0.5% and 0.1% respectively, which means that the adopted DES numerical simulation method has high credibility in calculating the acoustic source. At impeller rotational speed of 2000 r/min, the best state of flow field distribution is at the navigational speed of 1.54 m/s, which is corresponding to the highest propulsion efficiency condition. The propeller noise presents dipole characteristic in all working conditions, and at the obvious blade passing frequency, multiple characteristics are presented; most of the noise contribution is also concentrated below four times of the blade passing frequency. The total sound pressure level of the hydrodynamic noise is the smallest at the optimal efficiency condition (the navigational speed is 1.54 m/s). At high navigational speed, the low frequency characteristics below blade passing frequency increase and the amplitude becomes larger. This indicates that the component of turbulent noise becomes more important with the increase of navigational speed. The research focuses on analyzing the relationship between the energy loss of the ducted propeller wake field and the noise level, and it is found that the vortex at the tail makes a certain contribution to the noise. The research conclusions could provide some reference for the acoustic performance evaluation and noise reduction optimization of ducted propeller design as well as the improvement of UUV stealth performance. Full article

Precise stochastic approaches to quantitatively calculate the source uncertainties offers the opportunity to eliminate the influence of anisotropy on moment tensor inversion. The effects of ignoring anisotropy were tested by using homogeneous Green’s functions. Results indicate the influence of anisotropy and noise on fault plane rotation is very small for a pure shear source whether it is restricted to double couple solution or full moment tensor solution. Green’s functions with different prior rough anisotropy information were tested, indicating that the complex source is more sensitive to velocity models than the pure shear source and the fault plane rotation caused by full moment tensor solution is larger than the pure double couple solution. Collaborative P-wave velocity inversion with active measurements and passive acoustic emission data using the fast-marching method were conducted, and new Green’s functions established based on the tomography results. The resolved fault plane solution rotated only 3.5° when using the new Green’s functions, but the presence of spurious isotropic and compensated linear vector dipole components was not completely eliminated. It is concluded that the cooperative inversion is capable of greatly improving the accuracy of the fault plane solutions and reducing the spurious components in the full moment tensor solution. Full article

To obtain qualified logging while drilling (LWD) data, a new acoustic LWD tool was designed. Its overall design is introduced here, including the physical construction, electronic structure, and operation flowchart. Thereafter, core technologies adopted in this tool are presented, such as dominant exciting wave bands of dipole source, a sine wave pulse excitation circuit, broadband impedance matching, and an intellectualized active reception transducer. Lastly, we tested this tool in the azimuthal anisotropy module well, calibration well, and normal well, working in the model of the cable, sliding eye, and logging while drilling. Experiments showed that the core technologies achieved ideal results and that the LWD tool obtained qualified data. Full article

This paper is devoted to an analytical approach to the magnetoacoustic tomography with magnetic induction (MAT-MI) problem for three-layer low-conductivity objects. For each layer, we determined closed-form analytical expressions for the eddy current density and Lorentz force vectors based on the separation of variables method. Next, the analytical formulas were validated with numerical solutions obtained with the help of the finite element method (FEM). Based on the acoustic dipole radiation theory, the influence of the transducer reception pattern on MAT-MI was investigated. To obtain acoustic wave patterns, as a system transfer function we proposed the Morlet wavelet. Finally, image reconstruction examples for objects of more complex shapes are presented, and the influence of the MAT-MI scanning resolution and the presence of the noise on the image reconstruction quality was studied in detail. Full article