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On 31 March 2007, strong, tsunami-like waves of 1.0–2.5 m were recorded at most tide gauges along the west coast of Korea. The following year, on May 4, unexpected, abnormal waves in the eastern Yellow Sea reached a maximum height of ∼1.3 m. Both events occurred without warning, resulting in severe loss of life and property. Subsequent analysis found that these tsunami-like waves were meteotsunamis generated by air pressure oscillations. Evidence of possible meteotsunamis has been recorded by existing observation systems. However, the lack of understanding of the phenomenon and meteotsunami-specific monitoring system has hindered community preparedness, resulting in severe damage. We utilized existing observation systems (meteorological stations, tide gauges, and radar) during 2018 to develop a real-time meteotsunami monitoring system in the eastern Yellow Sea. This system detects the intensity and propagation of air pressure oscillations to identify potential coastal hazards and prevent damage caused by meteotsunamis. Two air pressure disturbance methods for measuring intensity of air pressure oscillation (a range of pressure changes over a 60 min window vs the rate of pressure change over a 10 min window) were compared, and several test operations were performed during development of the proposed system. The progress and limitations of the current observation and monitoring system were confirmed based on recent monitoring reports of air pressure jumps during the meteotsunamis on 7 April 2019. To address the insufficient lead time of meteotsunami warnings, installation and testing of open-ocean buoys outfitted with pressure sensors commenced in 2019.

We present and analyze a robust and mass conservative virtual element method for the three-field formulation of Biot’s consolidation problem in poroelasticity. The displacement and fluid flux are respectively approximated by enriched H ( div ) virtual elements and H ( div ) virtual elements, while the pressure is discretized by piecewise polynomial functions. Optimal a priori error estimates are obtained, including the semi-discrete scheme and the fully-discrete scheme with the implicit Euler approximation in time. Moreover, our method achieves robustness with respect to the constants hidden in the error estimates, even for the Lamé coefficient tending to infinity and the arbitrarily small constrained specific storage coefficient, and therefore it is free of both volumetric (Poisson) locking and nonphysical pressure oscillations. Meanwhile, it also conserves pointwise mass conservation for Biot’s consolidation problem on the discrete level.

The low frequency pressure oscillation in an aeroacoustic wind-tunnel seriously affects the flow quality and acoustic measurement. At present, there are many measures to suppress pressure oscillation, but due to the lack of in-depth understanding of its generation mechanism, these methods are not of general significance. In this paper, based on the open-source software OpenFOAM, the SA-DDES method is used for the unsteady computations for the two-dimensional simplified wind-tunnel model. The steady and unsteady fields inside and outside the jet flow are showed. The computational results show that the nonlinear interaction between the large scale vortices rolled up by the instabilities of the shear layer and the front wall of the collector of the wind-tunnel is the main reason responsible for the low frequency oscillation in an aeroacoustic wind-tunnel. In addition, it is concluded that in the feedback loop path of the excitation-feedback effect, the pressure waves produced by the large scale vortex structures inside the shear layer impinging on the front wall of the collector are reflected by the rear wall of the plenum chamber. The end of the path that the pressure waves travel upstream is where vortex shedding happens, not the nozzle exit.

Combustion noise accounts for a large proportion of diesel engine noise. On the premise of not increasing the cost of diesel engine, the injection system parameters such as dynamic fuel supply advance angle and needle valve opening pressure are optimized, and the influence of the above parameters on the in-cylinder pressure, rate of pressure rise, in-cylinder pressure level (CPL) spectrum and high frequency pressure oscillation is analyzed. The study shows that reducing the dynamic fuel supply advance angle can effectively reduce the combustion noise, and appropriately increasing the needle valve opening pressure can also reduce the combustion noise. After the optimization of injection parameters, the combustion noise of the diesel engine with an electronically controlled VE pump-tube-nozzle injection system is significantly reduced compared with the prototype engine, and can reach the same level of combustion noise as the diesel engine with the common rail system without deterioration of fuel economy and emission performance. The experimental study can provide technical reference for diesel engines in the selection of injection system parameters and the optimization of combustion noise in the improvement stage.

The cavitation generator of fluid pressure oscillations is a promising device for productivity and efficiency improvement in the mining industry (hereinafter referred to as the generator). Due to the periodic growth, separation and collapse of cavitation cavities into generator volume, shock pressure oscillations are realized with a frequency range from 1 to 20 kHz. Oscillatory pressure peak values are up by 4 times higher than the steady-state pressure at the generator inlet. The destroyed rock takes on a fatigue character under repeated alternating effects of force impulses. Due to the development of a network of microcracks in the rock, the discontinuity of the rock mass occurs at stresses lower than the rock ultimate strength. This leads to an increase in the rate of penetration, high-quality disintegration of well productive zones and an increase in their production rate, as well as to effective loosening and degassing of outburst-prone coal seams. Purpose. To conduct a systematic analysis of the use of a cavitation generator in the mining industry and evaluate its effectiveness. To develop a simplified method for calculating the maximum values of the range of fluid pressure oscillations by the generator. Methodology. The techniques are based on the study of recent research and publications on the use of the generator as a means of impulse action, and on the processing of on its dynamic parameters experimental data. Findings. The results are given in the form of the main parameters that determine the efficiency of technological processes with hydro pulse exposure. The calculation dependences of values are presented of the cavitation parameter for which of the maximum levels of the fluid oscillation are implemented on the injection pressure and those of the maximum values of the range of fluctuations on the cavitation parameter. Originality. It has been established that the use of the generator as a means of impulse action intensifies the mining industrys technological processes and leads to a significant reduction in specific energy consumption. A new simplified method for calculating the maximum level of the oscillation range has been developed, which makes it possible to determine the rational operation modes of the generator. Practical value. At the stage of designing new equipment or upgrading existing equipment, this simplified method allows determining the effective mode of operation of the generator by engineering methods to reduce the specific energy consumption of the technological process.

This study proposes a centrifugal pump that features a single-suction pipe with a double-suction impeller to enhance dynamic characteristics. Performance tests were conducted at 10000 r/min to investigate the effects of single- or double-suction impellers on pressure oscillation and radial force. Results indicate good agreement between numerical and experimental data. Transient-state numerical simulations were performed for centrifugal pumps equipped with both single- and double-suction impellers. The results demonstrate that pumps with double-suction impellers reduces pressure oscillation and significantly alleviates radial force, with a 24 % reduction in peak-to-peak value compared with pumps with single-suction impellers. Internal flow analysis reveals that a double-suction impeller promotes a relatively uniform flow at the impeller exit and mitigates the interaction effects between the impeller and the volute casing. Therefore, a centrifugal pump with a double-suction impeller is promising for special applications that demand stable and safe fluid transportation.

Storm geysers have received significant attention lately due to its more frequent occurrences and the induced severe local flooding and infrastructure damages. Previous studies suggested that the air pocket pressure oscillated during geyser events especially in rapid filling process, but only the peak values were studied and the oscillation period was not discussed in detail. In this paper, a theoretical model was developed focusing on the period of the pressure oscillation induced by the expansion/compression of the air pocket below a water column in a vertical riser with film flow. It was found that the oscillation period was a function of the initial air pocket volume, initial air pocket pressure head, the riser diameter, and the initial water column length. The oscillation period increased with the air pocket pressure head and the air pocket volume, but decreased with the riser diameter and the polytropic coefficient. The oscillation period increased then decreased with an increasing water column length. Further, when considering the film flow along the riser, the oscillation period decreased slightly from the analytical solution. It was also found that the inflow rate change did not significantly influence the oscillation period.

It is difficult to decompose the in-cylinder pressure of combustion of the direct injection (DI) diesel engine, a transient process associated with complicated oscillation components, because of its steep property. An adaptive cyclic average method based on time varying filter based empirical mode decomposition (TVF-EMD) is proposed to decompose the in-cylinder pressure signal, and the cyclic number is determined adaptively with protruding ratio of high-frequency oscillation. The proposed method is used to compare with the ensemble empirical mode decomposition and original TVF-EMD. The results indicate that the proposed method can overcome the drawbacks of these methods and extract high-frequency oscillations accurately and effectively. Three evaluation indexes, center frequency, normalized energy, and average center frequency are defined to analyze the frequency and energy characteristics of high-frequency oscillation quantitatively. The influence of speed, load, rail pressure, main injection timing, pilot injection interval, and pilot injection quantity are investigated systematically. The energy of high-frequency oscillation reaches the peak at medium-high speed, and increase with engine load and rail pressure. However, the relationship of high-frequency oscillation with fuel injection parameters are non-monotonic.

Due to pressure gain characteristics, the rotating detonation combustor (RDC) can be integrated into gas turbines by further improving the system's performance. The matching of unsteady flows in the RDC and turbine is a key challenge. Here, interactions in an RDC and planar turbine cascade are investigated using the unsteady Reynolds time‐averaged Navier‐Stokes method. The effects of the blade profiles on interactions between the oblique shock wave (OSW) and turbine cascade are analyzed, and the suppression effect of the turbine cascade on high‐frequency pressure oscillations is evaluated. The results show that the OSW interacts with the leading edge, pressure side, suction side, and trailing edge of the turbine stator and rotor blades, which generates complex wave systems in the cascade passage. The opposite propagation direction causes the OSW to be aligned or misaligned with the stator blade. The position of the OSW that operates on the turbine cascade changes, and two different wave system structures appear. The various pitches of the turbine cascade at different blade heights cause differing intensities and propagation directions in the reflected wave as generated by the action of the OSW and turbine cascade and the variable flow fields at different blade heights. The turbine cascade can significantly suppress the high‐frequency pressure oscillations, while the pressure amplitude attenuation rate can reach over 80% when the OSW propagates through the turbine cascade. These findings expound on the interaction mechanism between the rotating detonation wave complex and the turbine stator and rotor blades. A numerical model of a rotating detonation combustor with a turbine cascade is established. Effects of blade profiles on the interactions between the shock wave system and turbine cascade are analyzed. Distinct wave system structures are formed by varying the blade profile and rotating detonation propagation direction. The turbine cascade could significantly suppress the high‐frequency detonation pressure oscillations.

Pressure oscillations are one of the important challenges of segmented solid rocket motors with high slenderness ratio. The reason for these oscillations can be searched in vortex shedding due to grain burning areas, holes and slots. In this paper, the pattern of four segments grain of space shuttle boosters and structure of Ariane5 sub-scaled motors have been used for evaluation of aeroacoustic pressure oscillations. First, the related parameters to scale down using Buckingham’s Pi-theorem were determined and then a sub-scaled 1:31 motor was designed and manufactured. Going on, Strouhal number in various grain forms and vortex shedding prediction criteria was discussed. Next, for a relative understanding of motor internal flow and vortex shedding formation, steady state computational fluid dynamic calculation was done in seven regression steps and finally, for validation of analysis and simulation, two static tests performed. Results show that various definitions for Strouhal number are useful only for primarily glance on vortex shedding and pressure oscillations and so CFD solution and the test program is inevitable for a correct understanding of the ballistic operational condition of the motor. In addition, despite aggress of pressure test data and grain-burning regression of sub-scaled motor to full-scale motor, the internal flow phenomenon may be different due to small-scale time and dimension with the full-scale motor.