Characteristics Of Pressure Pulses Research Articles

Numerical analysis and experimental study on slurry diffusion characteristics of vortical oscillatory grouting technology considering soil interface

Based on the fluidic jet theory, this study proposes an effective vortical oscillatory grouting technology. The fluid switching mechanism and pressure pulse characteristics are investigated through numerical simulation and experiment. The slurry diffusion performance of oscillatory grouting is compared with that of steady-pressure grouting under various soil parameters and slurry parameters. The effects of soil interface on diffusion behavior are also studied. The results show that the growth and dissipation of the vortex within the tool generate periodic oscillatory fluid, which further produces pressure pulses. During oscillatory grouting, the pressure recovery process inside the fluidic oscillator reduces the pressure of the soil. With the increase in porosity and particle size, the pressure of the soil grouted by oscillatory pressure is noticeably reduced. Despite the lower pressure of the soil, oscillatory grouting demonstrates better diffusion performance, owing to the dynamic flow field and pressure fluctuation. The performance of oscillatory grouting is also influenced by the oscillatory frequency and pressure pulse amplitude. When the soil interfaces are taken into consideration, different fluid domains exhibit complex slurry diffusion patterns. It is observed that the interface that is perpendicular to the grouting direction has a greater influence on grouting behavior. The oscillatory grouting diffusion behavior is more sensitive to the soil interface. This study is expected to improve grouting efficiency and promote the development of new grouting technology.

Experimental study on pressure pulse generated by condensing subsonic/supersonic steam jet in a horizontal channel

The direct contact condensation (DCC) of submerged vapor jet in liquid, which has high heat and mass transfer efficiency, is widely applied in nuclear power generation, chemical engineering and aerospace. The pressure pulse generated by hydraulic instability during DCC may create periodical impulsive loads on the solid wall. It is important to evaluate pressure pulse characteristics using a wide range of inlet properties to avoid risky flow pattern regions where pressure pulses are strong. This paper presents an experimental study of the interface dynamics and pressure pulse of DCC using subsonic and supersonic steam jets condensing in water in a horizontal channel. The results reveal that pressure pulses in unstable region are caused by the contraction and expansion of the steam-water interface, while pressure pulses in stable region are caused by Kelvin-Helmholtz (KH) instability. Flow pattern transition is found to affect pressure pulse intensity. Pressure pulse intensity is minimal at the transition between the stable region and unstable region. The correlations of pressure pulse intensity in unstable and stable regions are given, respectively. The results of this study can inform the design, safe operation, and lifespan evaluation of equipment in various industrial applications that involve DCC.

Mechanisms of pressure pulse for condensing supersonic steam jet in a rectangular channel

Pressure pulse is a potential risk during the application of condensing supersonic vapor jet in various industrial areas, particularly in a confined space, such as a pipe system. However, the source of pressure pulse remains unknown. In this work, experimental study on the dynamics of condensing supersonic steam jet in a rectangular channel was performed. Interface dynamics were captured by high-speed photography and quantitatively studied via an image-processing technique. The pressure pulse characteristics inside the channel were investigated using dynamic pressure transducers. Results proved that pressure pulse was caused by the growth, propagation, and detachment of interface wave induced by Kelvin-Helmholtz instability for the first time. In addition, the interface wave was proved to grow exponentially by experimental and theoretical methods. The dominant frequency was negative related, whereas its amplitude was positive related to the interface penetration length, which could be explained well by the growth, propagation, and detachment of interface wave. Finally, a prediction model for the dominant frequency was proposed on the basis of the propagation characteristics of interface wave. The proposed model could predict the dominant frequency at a maximum deviation of ±30%.

Transient characteristics of fine powder flows within fluidized dense phase pneumatic conveying systems

The objective of this paper is to report the experimental findings related to the pressure fluctuations in the fluidized dense phase pneumatic conveying of fine powders in the pipeline. Investigation has also been carried out to understand the relation between pressure pulse characteristics and specific power consumption and pneumatic conveying parameters. In addition, the transition in mode of flow along the downstream of flow of fine powders has been assessed and discussed. The wavelet analysis (Daubechies db4 wavelet) of signals of air pulses revealed that the moving bed flow possesses the transient feature and pulsatile phenomenon characterized by multiple amplitudes and random frequencies. Variations of pulse structures along the length of pipeline have been observed due to occurring of frequent aeration and de-aeration of dunes during the conveying. Substantial variations in pulse structures have also been found with different types of bulk materials. Pulse velocities of air between two data points are found higher at high solid loading ratios leading to low voidage in case of dense phase flow.

The calculation of weakly non-spherical cavitation bubble impact on a solid

The effect of small spheroidal non-sphericity of a cavitation bubble touching a solid at the beginning of its collapse on its impact on the solid of a copper-nickel alloy is investigated. The impact on the solid is realized by means of a high-speed liquid jet arising at collapse on the bubble surface. The shape of the jet, its velocity and pressure are calculated by the boundary element method. The spatial and temporal characteristics of the pressure pulses on the solid surface are determined by the CIP-CUP method on dynamically adaptive grids without explicitly separating the gas-liquid interface. The solid surface layer dynamics is evaluated by the Godunov method. The results are analyzed in dimensionless variables obtained with using the water hammer pressure, the time moment and the jet-solid contact area radius at which the jet begins to spread on the solid surface. It is shown that in those dimensionless variables, the dependence of the spatial and temporal characteristics of the solid surface pressure pulses on the initial bubble shape non-sphericity is relatively small. The nonsphericity also slightly influences the main qualitative features of the dynamic processes inside the solid, whereas its effect on their quantitative characteristics can be significant.

Hydrodynamic mechanism analysis of the pump hump district for a pump-turbine

Purpose Numerically analyzed the flow characteristic and explored the hydrodynamic mechanism of the pump mode hump district formation of a Francis pump-turbine. Design/methodology/approach Numerical simulations were conducted of the entire pump-turbine flow passage under different discharge conditions by adopting the SST-CC turbulence model. The internal flow at hump district has been explained in detail combined with the model test in this paper. The unsteady flow and pressure fluctuation characteristics are analysed under five different discharge conditions in the hump and nearby region. The reason of the hump district formation is explored combined with the flow components hydraulic loss. Findings The large hydraulic loss, high relative peak-to-peak amplitudes and low dominant frequencies are on account of the disorganized internal flow condition. The formation of the hump district is concerned with the large hydraulic loss inside the draft tube, runner and guide vanes as there occurs secondary flow, backflow even vortex in the hump district. In addition, the low dominant frequencies at recording points inside the flow passage are always accompanied with the change of flow patterns and the spreading of the pressure fluctuations. Originality/value The analysis method of each flow components hydraulic loss combined with internal flow structure is adopted to explore the mechanism of pump mode hump characteristic. The flow characteristic and pressure pulse characteristics all correspond to the flow components hydraulic loss.

Effects of suspended solid particles on the propagation and attenuation of mud pressure pulses inside drill string

The attenuation of mud pressure pulses in the drilling fluid inside drill string has restricted the application of mud pulse telemetry systems in directional drilling operations. This paper aims to investigate the effects of suspended solid particles on the propagation and attenuation characteristics of pressure pulses. In this work, an analytical model estimating the wave speed and attenuation factor of pressure pulses has been proposed based on the solid–liquid two-fluid model by performing linear perturbation theory, with the interactions of the solid–liquid two phases being considered. The model calculations are compared with the results of the experiments, showing good agreement. Based on the model, the propagation behavior of pressure pulses has been analyzed to ascertain the important parameters affecting the wave speed and attenuation factor. The results indicate that the angular frequency of the pressure pulses, the volume fraction, size and density of the solid particles all exert significant influence on the pressure pulses propagation and attenuation. Lower angular frequency, solid particle size and density tend to reduce the attenuation of pressure pulses. The pressure pulses have maximum attenuation when the volume fraction falls within the range of 20%–30%. For different angular frequencies, the general effects of the volume fraction, size and density of the solid particles on the wave speed and attenuation factor are the same, although they differ in degree.

Study on effect of time parameters of laser shock peening on residual stresses using FE simulation

Laser shock peening (LSP) is the newest and most innovative surface treatment technique. LSP residual stress distribution is affected by many parameters. Of them, the parameters are main factors that determine the convergence of finite element analysis (FEA) and characteristic of pressure pulse of laser system. The parameters, related to the convergence of FE simulation, are stability limit time for the stable convergence of results, and solution time for dynamic analysis. The other parameters, related to characteristics of pressure pulse of laser system, are pressure pulse duration time and laser pulse interval time for multiple LSP. In the present work, we have conducted to confirm the influence of time parameters of LSP system on residual stress results using FEA, and we have also predicted optimized range of time parameters.

Numerical predictions of pressure pulses in a Francis pump turbine with misaligned guide vanes

Previous experimental and numerical analyses of the pressure pulse characteristics in a Francis turbine are extended here by using the unsteady Reynolds-averaged Navier-Stokes equations with the shear stress transport (SST) turbulence model to model the unsteady flow within the entire flow passage of a large Francis pump turbine with misaligned guide vanes at the rated rotational speed. The S-curve characteristics are analyzed by a combined use of the model test and the steady state simulation with the aligned guide vane firstly. Four misaligned guide vanes with two different openings are chosen to analyze the influence of pressure pulses in the turbine. The characteristics of the dominant unsteady flow frequencies in different parts of the pump turbine for various misaligned guide vane openings are investigated in detail. The predicted hydraulic performance and the pressure fluctuations show that the misaligned guide vanes reduce the relative pressure fluctuation amplitudes in the stationary part of the flow passage, but not the runner blades. The misaligned guide vanes have changed the low frequencies in the entire flow passage with the change of the pulse amplitudes mainly due to changes in the rotor-stator interaction and the low frequency vortex rope flow behavior.

Experimental and numerical analysis of blade channel vortices in a Francis turbine runner

PurposeThe purpose of this paper is to investigate, experimentally and numerically, the pressure pulse characteristics and unsteady flow behavior in a Francis turbine runner for moderate flow heads. The pressure pulses in the runner blade passage were predicted numerically for both moderate and high heads. The calculations were used to partition the turbine operating regions and to clarify the various for the unsteady flow behavior, especially the blade channel vortex in the runner.Design/methodology/approachExperimental and numerical analyses of pressure pulse characteristics at moderate flow heads in a Francis turbine runner were then extended to high heads through numerical modeling with 3D unsteady numerical simulations performed for a number of operating conditions. The unsteady Reynolds‐averaged Navier‐Stokes equations with the k‐ω‐based shear stress transport turbulence model were used to model the unsteady flow within the entire flow passage of a Francis turbine.FindingsThe dominate frequency of the predicted pressure pulses at runner inlet agree with the experimental results in the head cover at moderate flow heads. The influence of the blade passing frequency causes the simulated peak‐to‐peak amplitudes in the runner inlet to be larger than in the head cover. The measured and predicted pressure pulses at different positions along the runner are comparable. At the most unstable operating condition of 0.5a0 guide vane opening, the pressure pulses in the runner blade passage are due to the blade channel vortex and the rotor‐stator interference. The predictions show that the frequency of the blade channel vortex is relatively low and it changes with the operating conditions.Originality/valueThe paper describes a study which experimentally and numerically investigated the pressure pulses characteristics in a Francis turbine runner at moderate flow heads. The pulse characteristics and unsteady flow behavior due to the blade channel vortex in the runner at high heads were investigated numerically, with the turbine operating regions then partitioned to identify safe operating regions.

Using pressure pulse seismology to examine basal criticality and the influence of sticky spots on glacial flow

Here we report results of water pressure pulse studies conducted at Storglaciären (Sweden) and West Washmawapta Glacier (British Columbia, Canada). Comparison of pressure pulse records with meteorological conditions at Storglaciären indicates that several periods of increased basal slip activity observed during a 10 day interval of summer 2008 were due to precipitation loading of the glacier surface, rather than to infiltration of surface water to the glacier bed; this indicates that the glacier bed was close to the failure strength for much of this interval. Pressure pulse magnitudes for the two glaciers were well‐fit by power law distributions similar to those earlier observed at Trapridge Glacier (and similar in form to the Gutenberg‐Richter relationship commonly used in seismology), suggesting that the mechanical processes that give rise to these distributions are robust features of soft‐bedded glaciers. In contrast, interevent time distributions for both glaciers diverge from those observed at Trapridge Glacier for short recurrence intervals, suggesting that the factors that govern the rate at which these processes occur differ between glaciers. An examination of pressure pulse characteristics at West Washmawapta Glacier indicates that the establishment of a basal drainage system in summer 2008 resulted in increased stability and reduced sensitivity to meltwater input, suggesting that common assumptions about the relationship between meltwater production and ice flow are oversimplified. These results demonstrate that water pressure pulse observations can provide valuable insight into the dynamics of soft‐bedded glaciers.

Characteristics of pressure pulses propagating through water-filled cracks

A series of experiments was conducted at Queen's University Belfast with a specially designed experimental apparatus in order to investigate the characteristics of, and the effect of crack geometry on, impact-induced pressure pulses propagating through water-filled cracks. The pressure pulses propagated with speeds of ranging from 50 to 300 m/s, whereby the speed increased with increasing crack width. It was found that changes in crack geometry such as right angle corners do not affect the propagation of the pressure pulse. The slow speed of propagation was attributed to the aeration of the water, which changes the water into a two-phase medium with dramatically increased compressibility. The pressure pulses also attenuated; the slowest most quickly with higher frequencies being damped out preferentially, whereby the rate of attenuation appeared to be mainly a function of time. A previously proposed theoretical model, which was based on the assumption of a two-phase medium, was improved and shown to model the experimental results satisfactorily. The experimental and numerical results suggested that, within the very short time scale of the pulse propagation, the water inside of a crack constitutes an elastic medium with viscoelastic damping.

Dynamic Loading of Casing String during Explosion within a Well

The experimental data on explosions in the casing strings of water-producing wells are analysed. The features are revealed for the change in amplitude-frequency characteristics of pressure pulse in liquid with an increase in distance from the explosion center.

Measurement of the Displacement of a Shear Mode Piezoelectric Transducer Using Laser Doppler Vibrometer

The ink jet print heads produced by Spectra utilize piezoelectric material's shear mode movement to deflect one pressure chamber wall, generating a pressure differential for the ejection of a drop of ink from the orifice connected with the pressure chamber. The responses of a piezoelectric transducer to the applied voltages determine the characteristics of pressure pulses that drive the jets. Direct measurement of the dynamic responses of piezoelectric transducer can provide valuable information not only for a better understanding of the shear mode movement, but also for the optimization of a print head design. It also provides reliable information to verify numerical models that can be applied quickly to various aspects of future printhead development work. However, owing to high operating frequency and tiny shear mode movement of the piezoelectric transducer the measurement is often challenging.This paper investigates the capability of laser Doppler vibrometer in measuring the displacement of Spectra's shear mode piezoelectric transducer. Measurements have been conducted on a fully functional 128 jets, 600 dpi commercial compact print head (CCP128/600). Displacements smaller than 0.02 μm at high jetting frequency have been successfully measured. It has been demonstrated that laser Doppler vibrometer can be effectively used to evaluate printhead dynamics, identify potential problems, verify numerical models and optimize the printhead designs.

Detection of small pressure pulses in an ion pumped ultrahigh vacuum system

Pressure stability in the ultrahigh vacuum (UHV) system of a gravitational wave detector is a crucial point for its sensitivity limit. We carried out an investigation in order to detect pressure fluctuations in an UHV system pumped with an ion pump. The expected characteristics of pressure pulses caused by desorption were simulated with Monte Carlo methods. Test equipment was developed with a sensitivity limit for relative pressure changes of 10−3 at a base pressure of 10−6 Pa in the range up to 1 kHz, and of 10−4 below 40 Hz. Pressure fluctuations in the 10−4 range of working pressure were found in the frequency range <40 Hz and larger pressure pulses in the percent range with a frequency of about 1 in 4 h.

Near-Surface Measurements of Deep Explosions I. Pressure Pulses from Small Charges

The characteristics of pressure pulses recorded near the surface directly above small explosions at great depths are summarized. Charge weights ranged from 0.04 to 10 lb and burst depths varied from 3000 to 22 000 ft. Significant pressure and time parameters of the initial shock wave, the subsequent negative-pressure phase, and the first bubble pulse are shown in graphs and Tables. The vertical measurements of shock-wave peak pressure can be represented by the same power function that Arons previously determined from horizontal measurements of shallow explosions. These data extend the range of measurement for this parameter over an additional logarithmic cycle of the similitude curve to a distance R (ft) of 4×104 W12, where W is charge weight in pounds. The first period of the bubble oscillation also continues to show the same weight and depth dependence previously reported for depths ⩽500 ft down to depths of 22 000 ft.