Velocity Attenuation Research Articles

Characterization of a Volcanic Gas Reservoir Using Seismic Dispersion and Fluid Mobility Attributes

Abstract Seismic dispersion and fluid mobility attributes are used to characterize a volcanic gas reservoir in the Songliao Basin of China. A rock physics model is constructed to describe poroelastic behaviors associated with heterogeneous fluids saturation within the volcanic gas reservoirs, where velocity dispersion and attenuation of propagating waves are attributed to the wave-induced fluid flow described by the patchy saturation theory. Modeling results indicate that the frequency-dependent bulk modulus at the seismic frequency is more sensitive to gas saturation than the P-wave velocity dispersion. Accordingly, a new inversion method is developed to compute bulk-modulus-related dispersion attribute DK for improved characterization of volcanic gas reservoirs. Synthetic tests indicate that DK is more sensitive than traditional P-wave dispersion attribute DP to the variations of reservoir properties. The high value of dispersion attribute DK indicates the volcanic gas reservoirs with high porosity and gas saturation. At the same time, fluid mobility attribute FM can discriminate the volcanic gas reservoir as DK. Field data applications illustrate that DK and FM exhibit anomalies to the gas zones in the volcanic gas reservoir on the cross-well section. However, DK is more robust than FM to identify favorable zones on horizontal slices for specific target layers. Overall, rock physical modeling provides insights into the poroelastic behaviors of volcanic gas reservoirs, and inversion for seismic dispersion attribute DK improves hydrocarbon detection in the volcanic gas reservoir.

Finite element analysis and experimental investigation of ultrasonic testing of internal defects in SiCp/Al composites

Revealing the interactions of sound waves with both SiC particles and internal defects is crucial for facilitating the detectability of internal defect features in SiCp/Al by using ultrasonic testing (UT). In the present work, we demonstrate the feasibility of UT of internal flat-bottom holes with diameters ranging from 0.2 mm to 2 mm in SiCp/Al composites through the combination of finite element (FE) simulations and experiments. Specially, a 2D FE model of UT of SiCp/Al with consistent geometrical features of SiC particles with experimental one is established, the accuracy of which is validated by theoretical and experimental characterizations of P-wave velocity and ultrasonic attenuation coefficient of SiCp/Al. Subsequently, the propagation behavior of sound waves in the SiCp/Al specimen with pre-existing defects under UT, in particular the impact of defect boundary on the scattering behavior of sound waves, is revealed in detail by FE simulations and also validated by corresponding experiments. Furthermore, the UT limit of detectable size of the internal defects is revealed jointly by FE simulations and experiments, based on which a correlation map between defect size and echo signal amplitude is established. Current study provides theoretical and practical guidance for the UT of internal defects in SiCp/Al composites.

A New Anelasticity Model for Wave Propagation in Partially Saturated Rocks

Elastic wave propagation in partially saturated reservoir rocks induces fluid flow in multi-scale pore spaces, leading to wave anelasticity (velocity dispersion and attenuation). The propagation characteristics cannot be described by a single-scale flow-induced dissipation mechanism. To overcome this problem, we combine the White patchy-saturation theory and the squirt flow model to obtain a new anelasticity theory for wave propagation. We consider a tight sandstone Qingyang area, Ordos Basin, and perform ultrasonic measurements at partial saturation and different confining pressures, where the rock properties are obtained at full-gas saturation. The comparison between the experimental data and the theoretical results yields a fairly good agreement, indicating the efficacy of the new theory.

Bringing discrete-time Langevin splitting methods into agreement with thermodynamics.

In light of the recently published complete set of statistically correct Grønbech-Jensen (GJ) methods for discrete-time thermodynamics, we revise a differential operator splitting method for the Langevin equation in order to comply with the basic GJ thermodynamic sampling features, namely, the Boltzmann distribution and Einstein diffusion, in linear systems. This revision, which is based on the introduction of time scaling along with flexibility of a discrete-time velocity attenuation parameter, provides a direct link between the ABO splitting formalism and the GJ methods. This link brings about the conclusion that any GJ method has at least weak second order accuracy in the applied time step. It further helps identify a novel half-step velocity, which simultaneously produces both correct kinetic statistics and correct transport measures for any of the statistically sound GJ methods. Explicit algorithmic expressions are given for the integration of the new half-step velocity into the GJ set of methods. Numerical simulations, including quantum-based molecular dynamics (QMD) using the QMD suite Los Alamos Transferable Tight-Binding for Energetics, highlight the discussed properties of the algorithms as well as exhibit the direct application of robust, time-step-independent stochastic integrators to QMD.

An acoustic wave method for evaluating the effectiveness of blast to enhance fragmentation in longwall top coal caving

AbstractThe advanced deep hole blasting (ADHB) is commonly used to improve the fragmentation of thick hard top coal in longwall top coal caving (LTCC) mining. This paper presents an acoustic method to quantitatively evaluate the effectiveness of the ADHB. First, the variations of P‐wave velocity of hard coal samples under uniaxial and triaxial compression are obtained from the laboratory acoustic test. Then, an acoustic wave method based on seismic tomography is proposed to assess the effectiveness of the ADHB by introducing the P‐wave velocity attenuation model into the data processing. Finally, a field seismic tomography test is conducted to obtain the distribution of the P‐wave velocity of top coal before and after the ADHB implementation. And the P‐wave velocity attenuation is calculated to estimate the fragmentation effectiveness of ADHB. The results indicate that the P‐wave velocity attenuation model could well represent the broken degree of hard coal, suggesting that the proposed acoustic wave method could quantitatively evaluate the fragmentation effectiveness by exporting the nephogram of P‐wave velocity attenuation. The present study may provide technical support for improving the recovery ratio of thick hard top coal for LTCC mining.

Influence of overfire air rate of the two‐channel overfire air on flow and combustion characteristics in a 600‐MWe boiler

AbstractTo solve the problem of high NOx emission of 600‐MWe boilers in power plants, we established a cold gas–solid modeling testbed scaled by 1:5 for two‐channel overfire air (OFA). A phase‐Doppler anemometer was used to measure the characteristics of the outlet flow field of the two‐channel OFA under different OFA rates. We also verified the industrial feasibility of this testbed under loads of 300 and 600 MWe. The influence of the OFA rate on the divergence angle of the outlet jet was small: When the OFA rate was increased from 15% to 35%, the divergence angle only increased by 2.2°. The attenuation of the axial velocity of the outlet jet increases with increasing OFA rate. For OFA rates of 15% and 25%, the jet penetration depth was between 1.5d and 2.5d (where d is the cone diameter of the OFA model in the cold‐flow experiments). When the OFA rate was 35%, the jet penetration depth was between 2.5d and 3.5d. The jet maintained about 17% O2 concentration at 1.4 m (about 11d) in the furnace under different boiler loads, and the concentration of emitted NOx increased with decreasing load. Based on these findings, we propose the use of two‐stage OFA: The jet at the outlet of the first‐stage OFA ports should have a larger jet‐divergence angle, and the other stage should have a larger jet‐penetration depth to realize full mixing with the flue gas and to ensure high burnout and low NOx emission.

Mechanical model and numerical simulation of composite laminates subjected to low velocity impact

A mechanical model of laminated plates subjected to low velocity impact is proposed in this paper. The model studies the attenuation of impactor velocity affected by air resistance, intra-laminar damage initiation based strain, intra-laminar damage evolution based on damage parameters and delamination damage. Based on this mechanical model and ABAQUS platform, the experiment of Shi is numerically simulated. It is found that the predicted contact force, energy absorption and delamination damage of laminates are in good agreement with the experimental results, indicating that the established mechanical model can be used to predict the mechanical response and damage characteristics of composite laminates subjected to low velocity impact.

Wave Propagation for Axisymmetric Wave Motion in Buried Pipes Conveying Viscous Flowing Fluid

This work investigated the wave propagation characteristics of buried pipes conveying viscous flowing fluid under axisymmetric wave motion, where the coupling pipe–soil and pipe–fluid effects are both taken into account. The fluid was assumed to be viscous, isotropic, and irrotational. The coupled equations of wave motion were obtained based on Love’s thin shell theory. The analytical fluid-dominated (s=1) wave dispersion relations of buried fluid-conveying pipes are given. In addition, studies were carried out to scrutinize the effects of the soil, flow velocity, fluid viscosity, fluid mass density, and pipe geometry on wave propagation of buried fluid-conveying pipes. Results show that the higher fluid velocity can lead to larger phase velocity and smaller wave attenuation in buried pipes. In addition, viscous fluid leads to larger wave attenuation compared with ideal fluid.

Dynamical Magnetic Resistance of HTS Maglev Vehicle in an Evacuated Tube Track

Based on the evacuated tube high-T <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> superconducting (HTS) side-suspension (SS)-maglev circular track system which reached the maximum running speed of 160km/h, we studied the dynamical magnetic resistance of the maglev vehicle moving along the magnetic track. Different magnetic field gradients are formed by stacking silicon steel sheets on the surface of permanent magnet guideway (PMG) in this work. The running resistance of the prototype vehicle under different magnetic field gradients is acquired by processing the velocity attenuation data measured via acceleration sensor during the running process. The corresponding magnetic resistance is obtained by further data processing and analysis. A peak was observed in the low speed range of the speed dependent curve of the magnetic resistance, which can be attributed to the influence of the resonance. When the running speed of the maglev vehicle exceeds a certain value, the magnitude of magnetic resistance is positively related to the running speed and magnetic field gradient. The results of this study can provide a reference for the optimization of the manufacturing cost, performance, maintenance and safety in the application of HTS maglev vehicle.

Analytical solution for distributed torsional low strain integrity test for pipe pile

AbstractLow strain integrity tests (LSITs) are the most popular non‐destructive methods for pile testing. However, traditional LSITs have encountered unprecedented challenges as the need for long pile and existing pile testing keeps multiplying. Compared to traditional longitudinal excitations, the torsional wave is less influenced by the velocity attenuation effect and can be subjected at the pile shaft for existing piles. Distributed torsional LSIT is proposed in this article with the presentation of the corresponding analytical solutions that exhibiting the velocity responses along the pile shaft. The solution is verified with previous simplified theoretical and rigorous finite element method (FEM) answers. At the end, the application of this method is exhibited through the identification of necking and concrete segregation defects on pipe piles, which shows the advantage of this method on long pile testing.

Experimental Observations of Laser-Driven Tin Ejecta Microjet Interactions.

The study of high-velocity particle-laden flow interactions is of importance for the understanding of a wide range of natural phenomena, ranging from planetary formation to cloud interactions. Experimental observations of particle dynamics are sparse given the difficulty of generating high-velocity flows of many particles. Ejecta microjets are micron-scale jets formed by strong shocks interacting with imprinted surfaces to generate particle plumes traveling at several kilometers per second. As such, the interaction of two ejecta microjets provides a novel experimental methodology to study interacting particle streams. In this Letter, we report the first time sequences of x-ray radiography images of two interacting tin ejecta microjets taken on a platform designed for the OMEGA Extended Performance (OMEGA EP) laser. We observe that the microjets pass through each other unattenuated for the case of 11.7±3.2 GPa shock pressures and jet velocities of 2.2±0.5 km/s but show strong interaction dynamics for 116.0±6.1 GPa shock pressures and jet velocities of 6.5±0.5 km/s. We find that radiation-hydrodynamic simulations of the experiments are able to capture many aspects of the collisional behavior, such as the attenuation of jet velocity in the direction of propagation, but are unable to match the full spread of the strongly interacting cloud.

Water entry simulation analysis of a truncated projectile

In order to explore the influence of the bevel angle of the projectile on the vertical velocity attenuation characteristics and cavitation of the projectile after it enters the water vertically, this paper uses numerical simulation to analyze the bevel angles of 45°, 30°, 25° and 20°. At the same time, the high-speed camera is used to study the vertical penetration of the projectile with a 45° bevel angle to verify the simulation model. The research results show that the vertical velocity decays exponentially, and the trajectory of the truncated projectile is bent after entering the water so that an asymmetric open cavitation occurs. The bevel angle will affect the degree of trajectory curvature, velocity attenuation and the shape of the cavity. The larger the bevel angle, the greater the degree of trajectory curvature; the smaller the bevel angle, the slenderer the cavity and the smaller the asymmetry.

NMR-based investigation on deterioration characterization of gypsum breccia in surrounding rock undergoing flow-by wetting-drying cycles

In underground engineering, many geological hazards caused by the cyclic actions of wetting and drying occur under flowing water conditions. Understanding the evolution of the strength and pore structure characteristics of some environmentally sensitive surrounding rocks under these conditions is critical for maintaining the long-term stability of tunnels. In this study, the deterioration characteristics of gypsum breccia in the surrounding rock of an anonymous tunnel in Shanxi under the flow-by wetting-drying cycles were investigated. After being treated by wetting-drying cycles with different flow conditions (0 and 10 l/h), the evolution characteristics of the pore structure of gypsum breccia were characterized using the nuclear magnetic resonance (NMR) technique. The relationship between the P-wave velocities and the pore characteristics of gypsum breccia was studied. The results showed that the water flow would accelerate the deterioration process of gypsum breccia in the wetting-drying process. The microstructure damage of gypsum breccia was induced by the combined action of the wetting-drying cycles and water flow. There was a significant correlation between the attenuation of P-wave velocity and the development of the pore structure of gypsum breccia. The study can provide references for the engineering design of tunnels in gypsum breccia.

The quality evaluation of the grout in rock bolts based on the stress wave propagation

Nondestructive testing of rock bolt is essential for evaluating the grouted quality in rockmass. The stress wave propagation in the fully grouted rock bolts and defectively anchored bolt was investigated, where the mortar between the rock and bolt is subjected to different curing ages and stress wave induced by a dynamic excitation hammer impacting the bolt. First of all, it is found that both velocity and amplitude decrease with the increment of curing age of the anchor agent, based on the experiment of stress wave propagation in the fully grouted rock bolts. Velocity and amplitude attenuation decrease drastically within the first 14 curing ages and maintain steadily thereafter. The energy proportion manifests no change in the same waveform with the increment of curing ages, but the proportion taken by high-frequency harmonic wave increases. The crossing point of energy proportion curves moves towards low-frequency area, whereas the decrease of total energy tends to be stable. Secondly, the experiment of stress wave propagation in anchored bolt with different size of defects is also investigated. The variation of velocity and amplitude of stress wave in the defectively anchored bolt is similar to that of stress wave propagation in the fully grouted rock bolts. The crossing point of energy proportion curves moves towards low-frequency area, which is similar to the fully grouted rock bolts. But the velocity and amplitude attenuations in defectively anchored bolt are less than those in fully grouted rock bolts. The larger the defect size is, the smaller the amplitude attenuation is. Finally, the experiment of stress wave propagation in anchored bolt with different location of defects is also conducted. The magnitude of amplitude attenuation increases with the increase of distance. But the crossing point of energy proportion curves remains unchanged. The anchoring quality of bolts can be evaluated by the anchoring effect of anchoring agent, which can be estimated by the attenuation amplitude of stress wave velocity and amplitude, based on the experiment of stress wave propagation in defectively anchored bolt.

Controlling Vibration Speed in Tunnel Excavation Using Fine Blasting Method under Complex Environmental Conditions

It is very important to reduce the impact of blasting vibration on the surrounding structures during the tunnel drilling-blasting excavation. Taking the diversion tunnel of the urban water supply project in Zhumadian, Henan Province, China, as an example, the segmentation linear function between the drilling rig and borehole depth was established by fining blasting design. The test of the blasting number and particle vibration velocity was designed. The propagation and attenuation characteristics of blast vibration velocity in the surrounding rocks of the tunnel were analyzed by using theoretical calculation and field monitoring methods. Results show that the fine blasting design can realize the superposition of negative phase of shock waveform to reduce the vibration speed. With the increase of the blasting number, the attenuation of the particle vibration velocity shows a negative exponential function, and the dimensionless vibration velocity loss increases in a power function. The greater the loss, the greater the energy loss during the shock wave propagation process, which is more conducive to ensuring the stability of the protected buildings. The research results can provide the reference for similar engineering practices.

Effects of porosity, orientation and connectivity of microcracks on dispersion and attenuation of fluid-saturated rocks using an upscaling numerical modelling of the squirt flow mechanism

Squirt flow is a wave-induced fluid flow mechanism to account for the velocity dispersion and attenuation of fluid-saturated porous media. Theoretical models of squirt flow cannot deal with complex microcrack-pore networks and thus cannot give accurate dispersion and attenuation curves with respect to frequency. We adopt a numerical oscillatory compressibility test method, based on the quasi-static poroelastic equation of Biot, to model the squirt flow and calculate corresponding P-wave modulus dispersion and attenuation. We also designed nine porous medium models containing different crack-pore configurations and investigated the effects of microcrack porosity, orientation and connectivity on the elastic responses. Modelling results show that not only microcrack porosity but also their orientation has control on the magnitude of the P-wave modulus dispersion and attenuation. Preferentially aligned microcracks may cause frequency-dependent anisotropy in the P-wave modulus and attenuation. Microcrack connectivity has a negligible influence on the dispersion and attenuation magnitude but a large influence on the characteristic frequency of the squirt flow, which is not predicted by theoretical models based on simple representative element volume of crack-pore structure. Therefore, detailed geometry of crack-pore network, of which microcrack porosity, orientation, aspect ratio and connectivity are vital factors, dictates the unique variations in the elastic modulus and associated attenuation with frequency caused by the squirt flow. Pore structure obtained by CT scanning representative of that of the whole rock is needed to obtain more accurate poroelastic responses of the rock with the numerical oscillatory compressibility test method. In this regard, we provide a powerful tool for evaluating dispersion and attenuation of fluid-saturated rock media with complex crack-pore structure, which have potential applications in seismic exploration of hydrocarbon in the subsurface.

Hydraulic characteristics of countercurrent jets on adverse-sloped beds

Abstract The counter-current jet (CCJ) acts like a reverse surface jet layer covering the free jump surface and has potential applications in the energy dissipation of hydraulic engineering. The present study investigated the hydraulic characteristics of CCJs on adverse-sloped beds. The results showed that, compared to the horizontal bed, the slope didn't increase the energy dissipation rate of CCJ but reduced the return flow length and upstream depth. The velocity distribution along the depth was divided into the boundary layer region, mixing region, and reverse surface jet region. The velocity distribution in the boundary layer region and the mixing region was similar to the classical wall jet. The jet Froude number and the bed slope had no significant effect on the turbulence intensity distribution and turbulence kinetic energy (TKE) distribution of CCJ. The distribution of TKE was similar to that of a submerged jump. The maximum absolute turbulence intensity appeared at exactly half of the maximum velocity. The maximum TKE appeared at the mixing region. Besides, empirical formulas for estimating length scales and maximum velocity attenuation are proposed. The results could provide a reference for the potential application of CCJ in energy dissipation in hydraulic engineering.

Investigation of the nonlinear phenomena of a Langevin ultrasonic transducer caused by high applied voltage

In the field of power ultrasound, Langevin ultrasonic transducers (LUTs) usually operate at a large displacements output power by applying high voltages. However, empirically, a LUT exhibits nonlinearities such as amplitude jumping and peak hysteresis for high voltages in actual operations. The nonlinearities would reduce the efficiency and output accuracy of an LUT. In this research, the burst-mode method was used to measure the longitudinal vibration velocity of the LUT, which gradually decreased with time after the excitation voltage was turned off. The equivalent mechanical losses and equivalent spring constants were determined using the velocity attenuation rate and resonant frequency and they were found to be the linear functions of velocity, helping to develop a novel nonlinear model. This model contained two quadratic nonlinear terms based on the linear model. Furthermore, the developed nonlinear model was analyzed using the Lagrangian method as well as the multiscale method, which confirmed that the model was effective in describing the nonlinear behavior. It was also found that the frequency-amplitude curve bent when the nonlinear term was taken into account, which resembled the nonlinear phenomenon tested experimentally. From a physical point of view, this bending was meaningful because it led to the formation of multi-valued response regions with jumping phenomena. Additionally, according to the obtained results, the maximum value of the system response was independent of the degree of nonlinearity of the system.

Jet noise reduction of spherical tuyeres with serrated trailing edges

The geometry of a jet nozzle has a direct effect on the noise of spherical tuyeres. The addition of a serrated structure to the trailing edge of a spherical tuyere is proposed to reduce the jet noise. A full-scale test bed is built to verify the jet velocity distribution of the spherical tuyere, and the tuyere jet noise prediction is verified through analogy experiments. The large eddy simulation (LES) model and Ffowcs Williams–Hawkings (FW–H) equation are used to predict the jet flow field and jet noise, respectively. The results show that the serrated trailing edge reduces the velocity attenuation and turbulent kinetic energy (TKE) on the downstream axis of the jet, and the radiated noise is significantly reduced at 10–60 Hz. However, when the serration width is excessively large, the serration increases the radiated sound pressure level (SPL) of the tuyere. In addition, optimal serration parameters can be used to reduce the effect of tuyere radiation noise on the standing and sitting postures of residents. The maximum radiated overall SPL can be reduced by 3.78 dB at the sitting height. The simulation data and analysis results can provide reference for the low-noise optimization design of spherical tuyeres.

A Study of Vibration Velocity Attenuation Induced by Pneumatic Rock Breaking with Carbon Dioxide Ice Powder for Safety Assessment

A Study of Vibration Velocity Attenuation Induced by Pneumatic Rock Breaking with Carbon Dioxide Ice Powder for Safety Assessment