Seismic waves suffer from energy attenuation and phase distortion due to viscosity when propagating through subsurface media. Inverse Q filtering, which is traditional method to compensate for viscous absorption effect, is one dimensional, thus its compensation is not accurate theoretically. To better recovery the original information of seismic waves, this paper realizes viscoacoustic reverse time migration in frequency-space domain. By employing stable compensation operator, the viscous absorption effect is compensated successfully without the problem of instability. Numerical experiments verify that our algorithm is of high accuracy and effectiveness while free from the interference of instability. Presentation Date: Tuesday, September 17, 2019 Session Start Time: 9:20 AM Presentation Start Time: 11:00 AM Location: Poster Station 11 Presentation Type: Poster
A ray-coupled mode approach to low frequency reverberation is developed for an ice covered deep ocean. Three naturally distinct propagation ray groups due to the unique upper duct of the sound channel in the Arctic area are modified by the ray theory. At the scattering patches of the irregular ice cover, the ray group is decomposed into the corresponding up and down going modes, and then the scattering kernel of reverberation is derived by coupled mode theory. A typical sound speed profile is simulated, and the calculated results show that the decay rule of the long range low frequency reverberation level in the deep ocean of the Arctic area is affected seriously by the propagation effect.
Abstract A hydrofoil blade design (HBD) is proposed to suppress the unsteady pressure pulsations in a centrifugal pump. Numerical simulation is carried out using the SST k‐ω model to obtain the unsteady flow field in the pump both with HBD and the conventional blade design (CBD). The pressure pulsations with the two types of blade profiles are compared at the nominal flow rate, whereas the jet‐wake flow patterns and vortex structures are analyzed to clarify the effect of the HBD on the flow field. The pressure pulsation amplitudes at the blade frequency ( f BPF ) are significantly reduced with the HBD, especially near the volute tongue, with a reduction of 72%. It is evident that HBD can effectively suppress the pressure pulsation. It is for these reasons that the relative velocities in the jet region at the impeller outlet are reduced, and the velocity gradients between the pressure and suction side are decreased, which contributes to improving the flow uniformity at the impeller outlet. Besides, the vorticities at the impeller outlet are reduced, and the high energy vortices shedding from the blade trailing edge are restrained. The combined effects of the uniform flow field and low vorticities contribute to the reduction of pressure amplitude with the HBD. The findings would serve as a reference for the pump designs with low noise and vibration.
In shallow water, the reverberation interference striations (RISs) are often polluted by serious random seafloor scattering, and it is the main limitation for the performance of active sonar. In this letter, a conditional generative adversarial network (CGAN) is used to recover the clear RISs from distorted ones. The experimental distorted RIS data induced by an explosive source are imported into the well-trained CGAN, and the precise interference striations are obtained. This means that the deterministic part of reverberation can be extracted exactly from the stochastic scattering field. The CGAN is robust when reverberation-to-noise ratios are higher than 2 dB.
Abstract The emitted noise and vibration induced by the unsteady flow of the centrifugal pump are always focused during its running, which is also associated with the high amplitude pressure pulsations. How to reduce pressure pulsations remains a crucial problem for the researcher considering low noise design of the centrifugal pump. In the current research, a special staggered impeller is proposed to reduce intense pressure pulsations of a centrifugal pump with n s = 69 based on alleviating rotor‐stator interaction. The numerical simulation method is conducted to illustrate the influence of staggered impeller on the pump performance and pressure pulsations, and three typical flow rates (0.8Ф N –1.2Ф N ) are simulated. Results show that the staggered impeller will lead to the pump head increasing, and at the design working condition, the increment reaches about 3% compared with the original impeller. Meanwhile, the pump efficiency is little affected by the staggered impeller, which is almost identical with the original impeller. From comparison of pressure spectra at 20 monitoring points around the impeller outlet, it is validated that the staggered impeller contributes significantly to decreasing pressure pulsations at the concerned working conditions. At the blade passing frequency, the averaged reduction of 20 points reaches 89% by using the staggered impeller at 1.0Ф N . The reduction reaches to 90%, 80% at 0.8Ф N , 1.2Ф N , respectively. Caused by the rib within the staggered impeller, the internal flow field in the blade channel will be affected. Finally, it is concluded that the proposed staggered impeller surely has a significant effect on alleviating intense pressure pulsation of the model pump and does not obviously alter the global performance of the pump, which is very promising during the low noise pump design considering its feasibility for manufacturing.
Nitrogen foam treatment is widely used to control water production in oil wells by selectively reducing water phase relative permeability in oil-water-transition zone. A novel method is proposed to analyze nitrogen gas saturation distribution under varying foam generation pressure drops, which the heat conduction coefficients and heat capacities of nitrogen gas and water are considered. A one-dimensional sand pack model was used to evaluate the impact of gravity on gas saturation distribution, tested in both horizontal and vertical orientations. The gas and water saturation varying along the flow direction of the tube can be calculated according to temperature change. The results indicate that nitrogen injection with pressure drops of 0.9 and 1.2 MPa can generate more evenly gas and water distribution as well as longer foam flow distance comparing to the higher injection pressure drops of 1.5 MPa. Average gas saturation generated in the vertical manner is found to be lower than that of horizontal one due to the higher gas flow resistance in the vertical direction. The simulation result of gas saturation distribution along the tube using Fluent software matches the experimental results well.
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