High-amplitude Pressure Research Articles

PS-BPC03-7: ARE OSCILLOMETRIC WAVEFORMS DIFFERENT IN PREGNANCY?

Objective: Hypertensive disorders of pregnancy are leading causes of maternal and perinatal morbidity and mortality. Automated blood pressure (BP) measurements are being used in clinical practice; however, understanding of how oscillometric waveform vary between pregnant and non-pregnant individuals remains low. Design and Methods: Pregnant individuals over 20 weeks gestational age and healthy, non-pregnant women were recruited. Healthy, non-pregnant women (HNP) were matched to healthy pregnant women (HP), and pregnant women with a hypertensive disorder of pregnancy (HDP) by age (± 10 years), arm circumference (± 6 cm), and BMI at the time of BP measurement (± 13 kg/m2). There were seven individuals in each group for a total of 21 participants. BP measurements were done per the International Organization for Standardization (ISO) protocol using a custom-built oscillometric device as the test device and 2-observer mercury auscultation as the reference measurement. Four pairs of auscultatory measurements and four oscillometric measurements were obtained for each participant. Baseline demographics, auscultatory BP and BP derived from slope-based and fixed ratio algorithms were determined. Oscillometric waveform and envelope features were compared among groups. Results: In HNP, HP, and HDP groups respectively: mean age was 31.3 ± 4.8; 32.1 ± 3.6; 32.0 ± 4.4 years; arm circumference 31.9 ± 3.3; 32.3 ± 4.9; 34.0 ± 3.3 cm; BMI 26.8 ± 3.8; 32.0 ± 7.2; 32.4 ± 3.7 kg/m2; mean auscultatory BP (systolic/diastolic) 103.3 ± 11.1/66.5 ± 7.4; 110.6 ± 4.0/56.9 ± 6.5; 132.6 ± 19.0/83.9 ± 13.3 mmHg. HDP had significantly higher auscultatory systolic (P < 0.05) and diastolic (p < 0.01) BP than the other groups. The pregnant groups (HP, HDP) had significantly higher heart rate (p < 0.01); higher pulses (p < 0.05) in the oscillometric waveform (OMV); lower average width in the pulses (p < 0.01); higher pressure amplitude at which the OMW peaks (p < 0.05) with longer time to reach this maximum pressure amplitude (p < 0.05); greater area under the curve (p < 0.01). Compared to HNP, the HDP showed significantly skewed OMW to the right (p < 0.01); greater spread in the OMW envelope (p < 0.05) and lesser random variation in the OMW envelope (p < 0.01). A typical OMV with the 3 groups superimposed is demonstrated in Figure 1. Conclusion: Significant differences in the oscillometric waveform morphology and parameters were found in pregnancy and in hypertensive disorders of pregnancy compared to healthy controls. These results suggest that pregnancy-specific algorithms may be required to optimize accuracy for oscillometric BP measurement.

Active control of coupling and its effect on near-field pressure fluctuations in supersonic rectangular twin jets

Supersonic rectangular twin jets (SRTJ) are of interest for current and future generations of tactical aircraft. However, the adverse effects of screech-loop coupling have previously been documented to significantly increase the near-field (NF) pressure fluctuations. These high-amplitude pressure fluctuations have the potential to fatigue and damage nearby aft components of the aircraft. Previous studies have documented that the NF pressure fluctuation level depends on the coupling of the jets: in-phase coupling along the twin jets’ minor axes produces stronger NF pressure fluctuations than that of out-of-phase coupling. The objective of this work is to further investigate the effects of coupling modes on NF pressure fluctuations in SRTJ and to mitigate the adverse effects of coupling using active flow control. Localized arc filament plasma actuators are employed to alter the SRTJs’ coupling mode by leveraging natural flow instabilities with minimal power input. A NF microphone array is used for simultaneous coupling and NF pressure fluctuation measurements. Schlieren imaging and spectral proper orthogonal decomposition are used to assess the effects of control on the flow field. The effect of excitation at various frequencies and actuation patterns on coupling and NF pressure fluctuations in different flow regimes are explored and discussed.

Vortex-Pressure Fluctuation Interaction in the Outlet Duct of Centrifugal Pump as Turbines (PATs)

The outlet duct is the only outlet flow component of the pump as turbines (PATs). The flow state within it not only affects its operation stability but also influences the safe operation of downstream process equipment. The undesirable flow phenomenon of the vortex is the main reason for pressure pulsations and vibrations; therefore, it is important to adopt simulation and experimental methods to reveal the vortex-pressure fluctuation interaction characteristics in the outlet duct of PATs. Firstly, the spatial and temporal evolution of the vortex in the outlet duct under different operation conditions were compared based on the Q-vortex identification criterion. Subsequently, the frequency components corresponding to local high amplitude vorticity and pressure pulsations were clarified. Finally, the relationship between vortex evolution and the pressure pulsations in the outlet duct was established. The results showed that the flow rates of the turbine significantly affected the spatial and temporal evolution of the vortex rope in the outlet duct. The front chamber leakage flow and vortex shedding from the blade trailing edge also influenced the vortex distribution characteristics in the outlet duct. The dominant frequency of the pressure pulsation in the outlet duct was 6 fn under different operating conditions, and the amplitude of the pressure pulsation increased with the flow rates. The effect of vortex evolution on the local pressure pulsation characteristics decreased with increasing flow rates. The results can be used to improve and stabilize the operation and further optimization of PATs.

On the nonlinear behaviour of oscillatory flow in a high pressure amplitude standing-wave thermoacoustic heat engine

This article deals with the numerical study of the nonlinear features of oscillatory flow in a high pressure amplitude standing wave thermoacoustic heat engine. The overall performance of thermoacoustic devices can deteriorate due to nonlinearities caused by their operation at high pressure amplitudes. Acoustic mass streaming is one of these nonlinearities that can influence the performance of thermoacoustic systems by an undesirable convective heat transfer. Therefore, understanding the nonlinear phenomena within thermoacoustic devices is of fundamental and practical importance. The Navier‐Stokes and energy equations are solved on the structured meshes by resolving thermal and viscous boundary layers utilizing the open-source modelling software OpenFOAM. In particular, the paper looks in more detail at the causes of a non-uniform distribution of mean pressure along the resonator reported previously by both experimental and numerical studies. This is explained by an analogy to a “distributed fluidic pump” manifesting itself through the pumping effects of streaming patterns. Also, the non-linear regime of the mean dynamic pressure shows interesting start-up instabilities which can be influential on achievable efficiencies.

Pressure Fluctuation–Vorticity Interaction in the Volute of Centrifugal Pump as Hydraulic Turbines (PATs)

The pump as turbines (PATs) has been widely used in the petrochemical, seawater desalination, and mining industries. Volutes are critical components for flow guidance and energy conversion in the PATs. Therefore, its inner flow characteristic could significantly influence the hydraulic turbine system stability. To reveal the vortex evolution, pressure pulsation characteristics, and the interaction between the two in the volute of PATs, a single-stage cantilever hydraulic turbine is investigated by the numerical and experiment method. The effect of impeller rotation on vorticity distribution and pressure fluctuation intensity in volute is analyzed based on the numerical simulation results. By clarifying the frequency components corresponding to local high amplitude vorticity and pressure pulsations, the relationship between vortex evolution and pressure pulsations is established. The results showed that the dominant frequency of pressure pulsation in the circumferential direction of the volute is 6fn under different operating conditions, and the pressure pulsation characteristics in the inlet section of the volute were less affected by the rotor–stator interaction. Under Qb and 1.3Qb conditions, the vorticity pulsation near the walls in the circumferential direction of the volute had less effect on local pressure pulsation characteristics. The evolution of vorticity at the leading edge of the volute tongue intensified the local pressure pulsations as the flow rate increased. Under 0.7Qb conditions, the vorticity pulsation characteristics in the volute are complex and have a relatively significant influence on local pressure pulsation.

Numerical investigation on the unsteady vortical structure and pressure pulsations of a centrifugal pump with the vaned diffuser

To investigate the internal flow structures and the emanating pressure pulsations in a centrifugal pump with a vaned diffuser, the numerical method DDES (delayed detached eddy simulation) combined with a structured computational grid were employed to simulate the unsteady flow phenomenon of the model pump at the rated working condition. The vortical structures and pressure amplitudes at the blade passing frequency were mainly investigated. Results show that a significant difference, observed for pressure pulsations at the monitoring points from the suction side to the pressure side of the diffuser blade, and a high pressure amplitude is generated at the point near the suction side. The phenomenon is caused by the vorticity sheet interacting with the diffuser blade, and high turbulence is induced at the corresponding region leading to intense pressure pulsation. Evident attenuation of pressure pulsation is generated from the leading edge to the trailing edge of the diffuser blade. Significant vorticity sheets are formed around the trailing edges of the impeller and diffuser. Vortex street is generated at the diffuser trailing edge as indicated by the alternate shedding of positive and negative vortices and the horseshoe vortex is captured within the wake flow. Intense interaction is caused by the cutting impact of the volute tongue on the large scale vortices from the diffuser. The obtained results will contribute to a better understanding of unsteady flow and pressure pulsations in the centrifugal pump with a vaned diffuser.

Experimental investigation on pressure fluctuation characteristics of a mixed-flow pump as turbine at turbine and runaway conditions

The pump as turbine (PAT) converts water energy into electricity energy, which greatly accelerates the construction of new power system. However, in the actual use of pump as turbine, its complex internal flow usually causes high-amplitude pressure pulsation, which seriously affects the operation efficiency of the PAT. The investigation on pressure-pulsation characteristics of a mixed-flow pump at turbine and runaway conditions is carried out in an open test rig, and the frequency domain characteristics of the pressure pulsation are analyzed based on FFT (Fourier Frequency Transform). The results show that, at the turbine mode, when the flow rate is greater than 0.8Q, the pressure fluctuation amplitude is almost three times that under small flow condition. Furthermore, when the flow rate is greater than 0.9Q, the shaft frequency and blade passing frequency occupy the dominant and secondary frequency positions in terms of the pressure fluctuation at the inlet of the volute, respectively. Moreover, when the flow rate is greater than 0.9Q, the pressure amplitude of the high-frequency component in the second section of the volute is very high, and the pulsation amplitude under a high flow rate condition is almost three to four times that under a low flow rate condition. The above phenomena show that the mixed-flow PAT is more suitable for operation under the flow rate conditions of 0.7Q and 0.8Q. In addition, at the runaway condition, when the head increases to 5.8 m, the pulsation amplitude at 7 times the shaft frequency increases significantly, which is almost 3.7 times that at the first two head conditions. The pressure pulsation which ranges from the double blade passing frequency to the triple blade passing frequency is significantly intensified, and the amplitude of the pressure pulsation at 7 times the shaft frequency is almost 3.7 times that at 3.75 m and 4.9 m.

Variation law of pressure pulsation during variable speed operation of pumped storage units

Variable speed operation technology has become an emerging development direction in hydropower industry. Variable-speed pumped storage plants (VSPSPs) constantly undergo various transient processes, and ensuring the amplitude of pressure pulsation within the control range is critical to the safe operation of variable-speed pumped storage units (VSPSUs). However, its extreme value is usually determined by rule of thumb in design stage, and few researches focus on the relationship between pressure pulsation and variable speed operation of VSPSUs. In this paper, characteristic curves of pressure pulsation are plotted by processing model test results with Gridfit function, taking a real VSPSP as an example. The total pressure during transient processes is predicted by simulation of a numerical model. Load rejection conditions (change initial speed) and large load regulation conditions (change speed command and power command) are simulated, and the influence of operating trajectory on pressure pulsation during variable speed operation is analyzed. The results show that with the increase of initial speed or speed command, the value of pressure pulsation increases; the trajectory passes through more high-amplitude pressure pulsation region and gradually shifts to the S-shaped region, causing the pressure oscillation. This study could provide theoretical reference for the operation of VSPSUs.

Alternator noise reduction based on claw-pole optimization

The high-frequency aerodynamic noise of claw-pole alternator presents a harsh sound in human subjective perception, which has an important impact on the car passengers’ comfort. Therefore, experimental and optimization studies have been conducted to investigate the high-frequency aerodynamic noise during the high-speed operation of claw-pole alternator. In this study, a claw-pole alternator was first tested under no-load conditions. The experimental results revealed that the 6th, 9th, 12th, 18th, 30th and 36th orders are the main noise orders. Meanwhile, the dipole was the main noise source at a speed range of 8000–14,000 rpm. Subsequently, a hybrid simulation method was applied to solve the acoustics field problem. The simulation and experimental results of the acoustics field characteristics satisfactorily agreed for all main orders of the aerodynamic noise at both speeds of 8000 and 12,000 rpm. The minimum error for the 9th order was 0.35dBA at 8000 rpm, whereas the minimum error of the 8th order reached 0.51 dBA at a speed of 12,000 rpm. Thus, the proposed simulation model could be considered a reliable approach. Additionally, the pressure amplitude distribution on the rotor surface for different orders was analyzed. The higher-pressure amplitudes at higher orders, such as the 30th and 36th orders, are mainly distributed at the claw-pole near the stator and root of the claw-pole, indicating that higher acoustics levels corresponding to the higher orders are mainly associated with the claw-pole. Finally, the claw-pole notching was parametrically modeled, and the eigenvalues of the radial, the notch inclination angle and the axial stretch length were optimized by using Latin hypercube sampling method. After notching, the air mass flow through the front and rear blades exhibited small changes, which slightly affected the cooling performance of the alternator. The claw-pole notching yielded the highest optimization, when the eigenvalues of radial, notch inclination angle and axial stretch length were 46.82 mm, 63.3° and 14.65 mm respectively.

Multi-objective optimization of guide vane closure scheme in clean pumped-storage power plant with emphasis on pressure fluctuations

In this study, multi-objective optimization was conducted for the guide vane closure scheme during the load-rejection process of a pump turbine, considering pressure fluctuation, maximum rotational speed, maximum pressure at the volute, and minimum pressure at the draft tube inlet to decrease the low-frequency high-amplitude pressure fluctuations at conditions near no-load. Two quantitative indicators, minimum discharge (Qmin) and the ratio of rotational speed to hydraulic head (NDH) of the pump turbine, were proposed to represent the backflow-induced pressure fluctuations. Two objective functions were defined to optimize the guide vane closure scheme and two optimized guide vane closure schemes, OPS-Q (based on Qmin) and OPS-NDH (based on NDH), were developed. The enhancements resulting from these vane closure schemes were verified using a one-dimensional–three-dimensional coupling flow simulation method. NDH was revealed to comprehensively represent backflow-induced pressure fluctuations, whereas Qmin partially represented the backflow. Consequently, OPS-NDH suppressed the pressure fluctuations by appropriately increasing the maximum pressure at the volute and the maximum vacuum at the draft tube inlet within the allowance ranges of the pumped-storage power plant. OPS-Q suppressed the pressure fluctuations; however, the minimum pressure at the draft tube inlet could not be controlled to satisfy the design requirements of the pumped-storage power plant. The findings of this study can be used as a theoretical reference for suppressing the pressure fluctuations in a clean pumped-storage power plant under near-no-load conditions.

Developing high intensity ultrasonic cleaning (HIUC) for post-processing additively manufactured metal components

The high energy phenomenon of cavitation bubble collapses has enabled numerous applications, including cleaning. In ultrasonic cleaning, cavitation intensity is typically lower than in other applications, such as sonochemistry and material processing. However, there has been an emerging application in intense cleaning of metal additively manufactured (AM) components. The presence of partially melted powders on AM surfaces is undesirable, contributing to high surface roughness and posing contamination risks during usage. We designed a high-intensity cavitation cleaning process that has significantly higher inertial cavitation intensity – i.e., erosion potential – than a conventional ultrasonic cleaning tank. Through acoustic signal characterisation, we showed that placing transducer sets on four sides of the tank could effectively focus and generate high-amplitude pressure waves directed towards the central region. Strong subharmonic signals indicate intensely inertial cavitation throughout the tank. Cavitation intensities were measured at various locations to understand the wave transmission characteristics and distribution patterns. Our results show that the cavitation intensity distribution is highly dependent on the height position. Finally, we demonstrated that the high intensity ultrasonic cleaning (HIUC) process could remove partially melted powders from an AM surface – which was not possible through conventional ultrasonic cleaning. HIUC could lead to higher cleaning efficiency and enhanced AM specimen cleanliness.

Development of a small-scale piezoelectric-driven thermoacoustic cooler

With the continuous increase of system power and shrinkage of size, heat removal from central processing units in electronic devices becomes more challenging. In this study, a small-scale piezoelectric-driven thermoacoustic cooler (TAC) is proposed as a novel method for electronic cooling. A prototype of the TAC that is merely 7.5 cm long, 2.3 cm in diameter, and uses ambient air as working fluid, has been built and tested. Theoretical models based on linear acoustics and thermoacoustics are established to predict the acoustical and thermal characteristics of the TAC. Results show that the piezoelectric-driven TAC achieves high pressure amplitudes at 1743 Hz (i.e., the acoustic resonance frequency of the acoustic cavity) and 2717 Hz (i.e., the mechanical resonance frequency of the piezoelectric actuator). A maximum temperature difference of 4.4 ℃ is obtained when the TAC operates at 2717 Hz with an electric power input of around 0.4 W. Approaches to further improve the cooling performance of the TAC are suggested. This work demonstrates the great potential of TACs, extending the application of thermoacoustic technology in thermal management of miniature electronics.

Snapping shrimp have helmets that protect their brains by dampening shock waves

Shock waves are supersonic high-amplitude pressure waves that cause barotrauma when they transfer kinetic energy to the tissues of animals.1-4 Snapping shrimp (Alpheidae) produce shock waves and are exposed to them frequently, so we asked if these animals have evolved mechanisms of physical protection against them. Snapping shrimp generate shock waves by closing their snapping claws rapidly enough toform cavitation bubbles that release energy as an audible "snap" and a shock wave when they collapse.5-8 We tested if snapping shrimp are protected from shock waves by a helmet-like extension of their exoskeleton termed the orbital hood. Using behavioral trials, we found shock wave exposure slowed shelter-seeking and caused a loss of motor control in Alpheus heterochaelis from which we had removed orbital hoods but did not significantly affect behavior in shrimp with unaltered orbital hoods. Shock waves thus have the potential to harm snapping shrimp but may not do so under natural conditions because of protection provided to shrimp by their orbital hoods. Using pressure recordings, we discovered the orbital hoods of A.heterochaelis dampen shock waves. Sealing the anterior openings of orbital hoods diminished how much they altered the magnitudes of shock waves, which suggests these helmet-like structures dampen shock waves by trapping and expelling water so that kinetic energy is redirected and released away from the heads of shrimp. Our results indicate orbital hoods mitigate blast-induced neurotrauma in snapping shrimp by dampening shock waves, making them the first biological armor system known to have such a function. VIDEO ABSTRACT.

Acoustic-Fluid-Structure Interaction (AFSI) in the Car Underbody

<div class="section abstract"><div class="htmlview paragraph">The turbulent flow around vehicles causes high amplitude pressure fluctuations at the underbody, consisting of both hydromechanic and acoustic contributions. This induces vibrations in the underbody structures, which in turn may lead to sound transmission into the passenger compartment, especially at low frequencies. To study these phenomena we present a run time fully coupled acoustic-fluid-structure interaction framework expanding a validated hybrid CFD-CAA solver. The excited and vibrating underbody is resembled by an aluminium plate in the underbody of the SAE body which allows for sound transmission into the interior.</div><div class="htmlview paragraph">Different excitation situations are generated by placing obstacles at the underbody upstream of the aluminium plate. For this setup we carry out a fully coupled simulation of flow, acoustics and vibration of the plate. The simulation results are compared and validated with experimental results of surface microphones, acceleration measurements and sound spectra of the interior. The analysis of the results focuses on the ratio of hydromechanic and acoustic excitation in frequency space and on possible back coupling effects of the structural vibration on the results. In the outlook, one example of an application of this method in the vehicle development is given.</div></div>

Anti-phase oscillations of an elliptical cavitation vortex in Francis turbine draft tube

In this paper, the dynamic behavior of a precessing cavitation vortex featuring an elliptical cross section in Francis turbine draft tube is investigated. This phenomenon may occur for values of discharge coefficient within 70%–85% of the discharge coefficient at the best efficiency point, for which Francis turbines can experience the onset of the so-called upper-part load (UPL) instability. The latter is characterized by the propagation of high-amplitude synchronous pressure fluctuations through the complete hydraulic circuit. High-speed visualizations of the cavitation vortex are performed on a Francis turbine model by means of two cameras synchronized with pressure sensors arranged along the draft tube for different Thoma numbers at a given discharge coefficient. A simplified analytical model of the cavitation vortex is proposed. It enables the interpretation of the video post-processing results in the frequency domain and the estimation of both the vortex cross section dimensions and their oscillations with time. It is first demonstrated that both the vortex cross section ellipticity (given by the ratio between its semi-major and semi-minor axes) and the amplitude of its oscillations are directly correlated with the amplitude of UPL pressure fluctuations during intermittent UPL instability. Furthermore, the evolution along the draft tube of the dimensions of the elliptical vortex cross section and their oscillations during fully developed UPL instability is highlighted. The ellipticity of the vortex cross section increases as the vortex center position gets closer to the draft tube wall away from the turbine outlet. In addition, the vortex cross section dimensions oscillate with opposite phase from either side of a pressure node located along the draft tube. This results in low oscillations of the total void fraction in the draft tube, compared with results obtained locally. This effect should be considered in the one-dimensional modeling of the cavitation flow during UPL instability for further stability analysis. The new insights on UPL instability presented in this paper may potentially lead to a better theoretical understanding and modeling of this phenomenon in Francis turbines draft tube.

Evidence for universal rupture behavior during coal and gas outbursts

Every catastrophic coal and gas outburst begins as a tiny coal failure at almost a point, followed by violent ejection of enormous amounts of gas and pulverized coal. Whether the initial rupture of a large outburst produces observable signatures different from those of smaller events is a fundamental question associated with the potential for outburst prediction. Although outburst processes have been investigated both experimentally and theoretically, the underlying mechanism responsible for outburst rupture behavior is still poorly understood. Here, we performed a series of physical simulations and recorded the infrasound during each outburst. We found that a sharply high-amplitude (∼300 Pa) pressure wavelet followed by long (∼1 s) low-pressure acoustic waves is a common feature of outburst-generated infrasounds. These pulse-like waveform signatures have been observed during explosive volcanic eruptions, suggesting that outburst dynamics can be characterized as gas-driven eruptions. Furthermore, we used waveform cross-correlation analysis and a simple method to demonstrate that all outbursts in the investigated size range (relative intensity of outburst < 38.5%) share a universal initial rupture behavior and discuss ensuing implications for physical rupture processes. The results of this study provide evidence of the identical onset of large and small events. Energy analysis also further showed that the final size of an outburst lies in the energy contribution of gas desorption and thus can be independent of its initial conditions. If our results hold true for natural outbursts, a size dependency of the rupture onset is unlikely, and consequently, estimating the destructiveness of a future outburst event would be difficult.

Intraluminal Pressure, Multi‐Dimensional Field Imaging and Fluid Volume Recordings as a Useful Tool to Determine Peristaltic Propulsion

IntroductionPeristalsis is a collective process of intestinal muscle contractions for the passage of food through the gastrointestinal tract. Although, peristalsis has been extensively studied using spatiotemporal mapping and pressure transducers both in vivo and in vitro, the quantitative analysis of peristaltic propulsion is not fully understood. Lack of a definitive tool therefore, limited drug discovery in the field of constipation including IBSC. In this study, we used directional lighting, advanced field‐imaging techniques together with intraluminal pressure recordings to determine intestinal diameter, frequency of longitudinal muscle activity and pressure changes as well as velocity of anterograde and retrograde contractions and volume output measurements to help determine the net peristaltic activity.MethodsThe basal activity of intestinal peristalsis in terms of intraluminal pressure (ILP) changes, real‐time changes in longitudinal muscle activity and intestinal lumen diameter were measured in approximately 5 cm long segments from jejunum of mouse small intestine (male, NIH Swiss) in physiological Ringer solution. Intraluminal pressure was recorded using pressure transducers connected to the oral and aboral end of each segment mounted in Perfusion Bath for Tubular Organs, (Harvard apparatus, USA). Longitudinal muscle activity was studied using CVX400 series vision system, and LumiTrax™multi‐spectrum light (Keyence, USA) using multiple tracking points in each intestinal segment. The number, strength, and amplitude of oscillations in terms of intraluminal pressure changes and longitudinal muscle activity was analyzed using custom written programs. Luminal volume output was measured using a photo‐electric drop counter unit.ResultsThe number, amplitude, duration, and frequency of high and low amplitude changes in ILP and longitudinal muscle activity was determined using a lab‐written program. The frequency of longitudinal muscle activity correlated well with the frequency of low and high amplitude pressure changes. Frequency of both these oscillations were found to be 0.7 Hz. A reduction in the ILP was found to induce high amplitude contractions which subsided as the ILP increased. Changes in intestinal diameter with time correlated to ILP changes. A reduction in luminal diameter caused an increase in ILP and when not fully compensated caused increased fluid output. The mean velocity of the contractions over time in the regions tracked was determined to be 2.5 – 2.7mm/sec with peak anterograde contraction velocity of ‐4.06 mm/sec and retrograde contractions of 12 mm/sec. This mean velocity in presence of physiological Ringer solution was thought to determine the direction of contractions along the length of the GI tract under normal conditions.InferenceFrequency of longitudinal muscle activity and ILP oscillation showed similar frequency suggesting common pacemaker activity. The velocity of the contraction and volume output over time will help determine the overall peristaltic movement and could be used as a helpful index to gauge constipation.

Dynamics of chugging phenomenon induced by subsonic and supersonic steam–air jet condensation in water flow

Chugging, a typical unstable flow pattern caused by steam-water direct contact condensation, should be paid more attention in engineering applications due to its accompanying low-frequency and high amplitude pressure pulse. In this paper, it was experimentally found that both subsonic and supersonic steam–air jet condensation could trigger chugging in a confined channel. As for such conditions, the chugging-caused pressure pulses all had two dominant frequencies with different amplitudes, and the one with larger amplitude was mainly distributed in the low-frequency zone of 15–45 Hz and 30–50 Hz. The brilliant image of steam-water phase interface captured by a high-speed camera showed that the mechanism of chugging was the sharp and low-frequency stretching and shrinking of the phase interface because of the periodic aggregation and dissipation of air layer. The subsonic steam–air jet condensation could trigger chugging only with a small amount of air, which therefore should be prevented as far as possible in engineering. However, for supersonic steam–air jet condensation, chugging could be triggered as soon as the air mass fraction reached a critical value because the incoming flow had severely damage effect on the air layer. By considering the steam mass flux, condensation driven potential, water Reynolds number and air mass fraction, the correlations of dominant frequency of chugging for subsonic and supersonic steam–air jet condensation were given, with deviations in the range of ± 20% and 15%, respectively.

Reduction of inertial end correction of perforated plates due to secondary high amplitude stimuli.

The decrease in reactance of perforated plates at high sound pressure amplitudes is of interest for the design of Helmholtz resonator liners. It is associated with the loss of end correction due to flow separation at the orifices. In practical applications, complex acoustic signals impinge on perforations. The loss of end correction due to multiple stimuli of unrelated frequency and phase has not been considered yet. This study assesses and presents an empirical approximation for the reduction of end correction of perforated plates at primary frequencies when flow separation is induced by an additional secondary unrelated high amplitude stimulus.

Features of the impact of high-amplitude short pulses of hydrodynamic pressure on perforation channels

The features of the impact of high-amplitude short pressure pulses on perforation channels in the bottomhole zone of the well are analyzed. It is shown that in the channels formed in the rock with the use of cumulative perforation and having a conical shape, there is an increase in pressure pulses when a certain condition is fulfilled, which limits the duration of this pulse. It has been established that in the negative phase of the pressure pulse, destruction of the cured rock layers adjacent to the walls of the perforation channel can occur, which improves the filtration-capacitive properties of the bottomhole zone of the well. It is shown that when using explosive charges of low mass, pressure pulses are formed with parameters similar to those of pulses generated by electric discharges in the wellbore. To apply the technology of explosive action with low-mass charges on the bottomhole zone, the standard equipment used for cumulative perforation of wells can be used. A method for screening pressure pulses is proposed, which increases the effectiveness of their impact on the bottomhole zone of the well and simultaneously reduces the excessive load on the casing pipes above the productive formation. Keywords: bottomhole zone of a well; perforation channels; electric discharge impact; low-mass charges; reflecting screen.