Dynamic Pressure Variations Research Articles

Global Propagation of Magnetospheric Pc5 ULF Waves Driven by Foreshock Transients

AbstractPc5 (2–7 mHz) ultralow frequency (ULF) waves play a significant role in resonating with particles and transferring energy in the coupled magnetospheric and ionospheric system. Recent studies found that Pc5 ULF waves can be triggered by foreshock transients which can perturb the magnetopause through dynamic pressure variation. However, whether foreshock transient‐driven Pc5 ULF waves are geoeffective and can propagate globally is still poorly understood. In this study, we take advantage of the conjunction between in situ (by the THEMIS probes, Geotail satellite, GOES satellites, and Van Allen probes) and ground‐based (by the all‐sky imager at South Pole and ground‐based magnetometers) observations to simultaneously analyze the waves from the foreshock region to the dayside and nightside magnetosphere. Both of our two events show that the Pc5 ULF waves are generated by foreshock transients in the dayside magnetosphere. The in situ observations by THEMIS A and D and the 2‐D auroral signatures show that the compressional mode waves are likely broadband and coupled to the FLRs with different frequencies and different azimuthal phase speeds. This is the first report that foreshock transients can drive both low‐ and high‐m FLRs, with the azimuthal wave numbers varying from ~5 to ~23. Moreover, the Pc5 ULF waves propagated antisunward to midnight, this can potentially modulate magnetospheric and ionospheric dynamics globally.

Unifying Advective and Diffusive Descriptions of Bedform Pumping in the Benthic Biolayer of Streams

AbstractMany water quality and ecosystem functions performed by streams occur in the benthic biolayer, the biologically active upper (~5 cm) layer of the streambed. Solute transport through the benthic biolayer is facilitated by bedform pumping, a physical process in which dynamic and static pressure variations over the surface of stationary bedforms (e.g., ripples and dunes) drive flow across the sediment‐water interface. In this paper we derive two predictive modeling frameworks, one advective and the other diffusive, for solute transport through the benthic biolayer by bedform pumping. Both frameworks closely reproduce patterns and rates of bedform pumping previously measured in the laboratory, provided that the diffusion model's dispersion coefficient declines exponentially with depth. They are also functionally equivalent, such that parameter sets inferred from the 2D advective model can be applied to the 1D diffusive model, and vice versa. The functional equivalence and complementary strengths of these two models expand the range of questions that can be answered, for example, by adopting the 2D advective model to study the effects of geomorphic processes (such as bedform adjustments to land use change) on flow‐dependent processes and the 1D diffusive model to study problems where multiple transport mechanisms combine (such as bedform pumping and turbulent diffusion). By unifying 2D advective and 1D diffusive descriptions of bedform pumping, our analytical results provide a straightforward and computationally efficient approach for predicting, and better understanding, solute transport in the benthic biolayer of streams and coastal sediments.

Qualitative and quantitative assessment of pendelluft: a simple method based on electrical impedance tomography.

BackgroundPendelluft, defined as asynchronous alveolar ventilation, is caused by different regional time constants or dynamic pleural pressure variations. The aim of the present study was to propose a simple method to evaluate pendelluft based on electrical impedance tomography (EIT). The efficacy of this method was demonstrated in well-known pendelluft scenarios in 6 patients.MethodsTwo patients with flail chest after accidents, two patients with acute respiratory distress syndrome (ARDS) and two patients with acutely exacerbated obstructive lung disease were prospectively included. EIT measurements were performed before and after surgery (in patients with flail chest, who had video-assisted thoracoscopic surgery with ribs fixation), or at two different levels of positive end-expiratory pressure (PEEP; ARDS patients), or two different time points (obstructive lung disease). Pendelluft was assessed by regional phase shift (defined as time difference between global and regional impedance-time curves) and amplitude differences (defined as the impedance difference between sum of all regional tidal variation and the global tidal variation).ResultsIn patients with flail chest, pendelluft diminished several days after surgery (pendelluft amplitude normalized to tidal impedance variation reduced from 88% to 2% in one patient, 12% to 2% in the other). Increased PEEP reduced the amplitude of pendelluft (from 3% to 0% in one patient, 20% to 2% in the other) but not necessarily the phase shifts (average time differences were <0.1 second for both patients for both ins- and expiration) in ARDS patients. Pendelluft assessment in obstructive lung diseases reflected the change in airway resistance (from 5% to 1% in one patient after broncholytic medication administration, as airway resistance fell from 15 to 11 cmH2O/L/s; from 9% to 35% in the other patient with acute exacerbation, the corresponding airway resistance increased from 15 to 22 cmH2O/L/s).ConclusionsThe proposed EIT-based method can be used to evaluate the degree of pendelluft in dimension of phase shift and amplitude difference.

Seasonal and spatial variability in surface pCO2 and air–water CO2 flux in the Chesapeake Bay

AbstractInteractions between riverine inputs, internal cycling, and oceanic exchange result in dynamic variations in the partial pressure of carbon dioxide (pCO2) in large estuaries. Here, we report the first bay‐wide, annual‐scale observations of surface pCO2 and air–water CO2 flux along the main stem of the Chesapeake Bay, revealing large annual variations in pCO2 (43–3408 μatm) and a spatial‐dependence of pCO2 on internal and external drivers. The low salinity upper bay was a net source of CO2 to the atmosphere (31.2 mmol m−2 d−1) supported by inputs of CO2‐rich Susquehanna River water and the respiration of allochthonous organic matter, but part of this region was also characterized by low pCO2 during spring and fall phytoplankton blooms. pCO2 decreased downstream due to CO2 ventilation supported by long water residence times, stratification, mixing with low pCO2 water masses, and carbon removal by biological uptake. The mesohaline middle bay was a net CO2 sink (−5.8 mmol m−2 d−1) and the polyhaline lower bay was nearly in equilibrium with the atmosphere (1.0 mmol m−2 d−1). Although the main stem of the bay was a weak CO2 source (3.7 ± 3.3 × 109 mol C) during the dry hydrologic (calendar) year 2016, our observations showed higher river discharge could decrease CO2 efflux. In contrast to many other estuaries worldwide that are strong sources of CO2 to the atmosphere, the Chesapeake Bay and potentially other large estuaries are very weak CO2 sources in dry years, and could even turn into a CO2 sink in wet years.

Quasi-static single bubble formation behaviour: interaction with adjacent induced flow structure

Single bubble formation behaviours which develops from submerged nozzle under the quasi-static mode in stagnant deionized water in a rectangular column are studied. Bubble formation behaviours are captured by a digital high-speed camera and information of the induced adjacent flow field is synchronously obtained via the particle image velocimetry (PIV) system. Interactions of induced bubble adjacent flow patterns with bubble formation behaviours are investigated at each stage of a three-stage bubble formation model. Results indicate that recirculation of the continuous phase near the bubble base accelerates rapid detachment of the bubble and the dynamic pressure variation in the liquid induced by bubble behaviours is the main reason why such flow pattern appears.

Concept and Operation of a Wind Turbine Driven by Dynamic Stall

Dynamic stall is exploited to produce positive torque on a large-chord/radius-ratio () vertical-axis wind turbine. An elementary kinematic analysis shows that the blades experience large variations in angle of attack that produce deep dynamic stall, combined with large relative dynamic pressure variations, that are phase shifted by approximately 90 deg. The phase shift allows dynamic lift-overshoot effects associated with the formation of a dynamic stall vortex to drive the turbine when the relative dynamic pressure is high, whereas lift stall associated with shedding of the vortex occurs when the relative dynamic pressure is low. Blades also experience variable virtual camber (or “virtual morphing”) effects and favorable chordwise pressure gradients, where the former produces a virtual leading-edge droop that reduces the leading-edge angle of attack. Open jet wind-tunnel tests of a two-bladed model turbine revealed maximum power coefficients of 16% that were almost independent of . Flow visualization confirmed that dynamic stall, with the associated dynamic stall vortex, is the mechanism that drives the turbine to maximum power. Until reliable design tools are developed, either empiricism combined with dimensional analysis or high-fidelity computational fluid dynamics are proposed for optimization and analysis.

Optimum structure of a laval nozzle for an abrasive air jet based on nozzle pressure ratio

The effect of nozzle pressure ratio n on the flow field of an air jet was investigated to obtain the basis of nozzle design. The flow field structure and abrasive acceleration of these nozzles were numerically simulated via Fluent, which was verified by I-Scan and erosion experiment. It was concluded that n is the primary factor that affects nozzle structure design, n = 1.12 can generate a better flow field structure. The dynamic pressure of the jet was measured via I-Scan, and the range of dynamic pressure variation was low when n = 1 and n = 1.12. Improvements in the flow field structure are more advance to the abrasive acceleration. The abrasive was accelerated to the maximum velocity at n = 1.12. Thus, n = 1.12 is the most advantageous to abrasive acceleration and material erosion wear. For example, the erosion depth and volume corresponding to n = 1.12 at 15 MPa increased by 60% and 27% when compared to n = 5.

Jovian UV Aurora's Response to the Solar Wind: Hisaki EXCEED and Juno Observations

AbstractWe summarize Jupiter's ultraviolet (UV) auroral response to solar wind dynamic pressure variations during Juno's approach to Jupiter in 2016. The response time of Jupiter's aurora to external drivers has thus far been unknown owing to a sparsity of upstream in situ solar wind measurements. Combining the Juno solar wind observations with continuous UV aurora data obtained by Hisaki EXCEED (Extreme Ultraviolet Spectroscope for Exospheric Dynamics) and Juno UV spectrograph, the UV aurora brightenings in response to three major shock arrivals showed time lags of 10–15 hr. These time lags are longer than the time required for ballistic propagation of the shocks by the solar wind. In addition to that puzzle, while an enhancement in the UV auroral power was observed with an increase in dynamic pressure to ~0.03 nPa, no associated brightening was observed with a dynamic pressure elevation of &gt;0.1 nPa. These imply that internal magnetospheric aspects need to be taken into consideration to fully resolve the issue.

The Effects of Solar Wind Dynamic Pressure on the Structure of the Topside Ionosphere of Mars

AbstractWe use Mars Atmosphere and Volatile EvolutioN observations of the upstream solar wind, and Mars Express observations of ionospheric electron densities and magnetic fields, to study how the topside ionosphere (&gt;320 km) of Mars is affected by variations in solar wind dynamic pressure. We find that high solar wind dynamic pressures result in the topside ionosphere being depleted of plasma at all solar zenith angles, coincident with increased induced magnetic field strengths. The depletion of topside plasma in response to high solar wind dynamic pressures is observed in both weak and strong crustal magnetic field regions. Taken together, our results suggest that high solar wind dynamic pressures lead to ionospheric compression, increased ion escape, and reduced day‐to‐night plasma transport in the high‐altitude nightside ionosphere.

L Versus Time Structures of Dayside Magnetic Pulsations Detected by the European Quasi‐Meridional Magnetometer Array

AbstractWe studied the spatiotemporal structure of ground magnetic pulsations on the dayside by displaying magnetic field perturbations detected by the European quasi‐Meridional Magnetometer Array (EMMA) as 2‐D images in the magnetic L value versus time space, called EMMAgrams. We generated EMMAgrams from observations made on 15 August 2015, including a previously studied pulsation event associated with an interplanetary shock. In addition to signatures of field line resonance driven by a cavity mode oscillation, we found poleward propagating structures with L‐independent periods in the Pc2 band. The Pc2 structures are attributed to periodic magnetohydrodynamic pulses (upstream waves) originating from the ion foreshock and propagating in the magnetosphere along the path proposed by Tamao. Ringing of local field lines at L‐dependent periods (transient pulsations) is also clearly detected as dispersive poleward propagating structures not only immediately after the shock impact but also during time periods of less obvious external disturbances. A transient pulsation decays after a few wave periods, and cross‐spectral analysis of transient pulsations detected at two stations with a small latitudinal separation indicates elevation of the cross phase in a band delimited by the field line resonance frequencies at the stations. Successive excitation of transient pulsations by variations of the solar wind dynamic pressure appears to contribute significantly to formation of similar cross‐phase peaks that are widely used in magnetoseismic studies.

Numerical Investigation of Flow Field Behaviour and Pressure Fluctuations within an Axial Flow Pump under Transient Flow Pattern Based on CFD Analysis Method

In this present work, CFD numerical method is applied to analyses the flow field in an axial flow pump qualitative and quantitative analyses. Qualitative analysis for these parameters comprise static pressure variations, dynamic pressure variations, velocity magnitude, turbulent kinetic energy, shear stress. Quantitative analysis including the pressure fluctuations in frequency domain analysis under different operation conditions. Also, sliding mesh method and turbulence model type k-epsilon are used. Various monitoring points are stalled in order to analyses pressure fluctuation mechanism in the impeller blade. The numerical results revealed that the flow field for pressure and velocity are increase start from the suction side of the pump to discharge side. Also, the results found that the high pressure occurs at the discharge side along the axial direction of the impeller. The maximum value of pressure fluctuations is occurred at tip blade region due to high interaction flow at this particular area. Moreover, the pressure decreases as flow rate in the pump increases. Additionally, the results shown that the pressure fluctuations have four peaks and four valleys the similar impeller blades number. Furthermore, there are different positive and negative pressure regions, the negative pressure area occurs due to lower pressure zone at inlet impeller area and hence which can lead to cause occurrence of cavitation in this specific area. The current numerical demonstration results can help the researches for further axial flow pump design.

Long‐Term Variations in Solar Wind Parameters, Magnetopause Location, and Geomagnetic Activity Over the Last Five Solar Cycles

AbstractWe use both solar wind observations and empirical magnetopause models to reconstruct time series of the magnetopause standoff distance for nearly five solar cycles. Since the average annual interplanetary magnetic field (IMF) Bz is about zero, and the annual IMF cone angle varies between 54.0° and 61.2°, the magnetopause standoff distance on this timescale depends mostly on the solar wind dynamic pressure. The annual IMF magnitude well correlates with the sunspot number (SSN) with a zero time lag, while the annual solar wind dynamic pressure (Pdyn) correlates reasonably well with the SSN but with 3‐year time lag. At the same time, we find an anticorrelation between Pdyn and SSN in cycles 20–21 and a correlation in cycles 22–24 with 2‐year time lag. Both the annual solar wind density and velocity well correlate with the dynamic pressure, but the correlation coefficient is higher for density than for velocity. The 11‐year solar cycles in the dynamic pressure variations are superimposed by an increasing trend before 1991 and a decreasing trend between 1991 and 2009. The average annual solar wind dynamic pressure decreases by a factor of 3 from 1991 to 2009. Correspondingly, the predicted standoff distance in Lin et al.'s (2010, https://doi.org/10.1029/2009JA014235) magnetopause model increases from 9.7 RE in 1991 to 11.6 RE in 2009. The annual SSN, IMF magnitude, and magnetospheric geomagnetic activity indices display the same trends as the dynamic pressure. We calculate extreme solar wind parameters and magnetopause standoff distance in each year using daily values and find that both extremely small and large standoff distances during a solar cycle preferably occur at solar maximum rather than at solar minimum.

Velocity Rotation Events in the Outer Magnetosphere Near the Magnetopause

AbstractWe report velocity rotation events with amplitudes more than a few tens of kilometers per second observed by the Magnetospheric Multiscale mission. The events are detected in the outer magnetosphere near the magnetopause at approximately noon magnetic local time. When we examine one event, velocity and magnetic field variations are correlated. Accelerated electrons &gt;100 eV are present. The azimuthal propagation direction is opposite to that of the background convection, implying that the structure and the background have different sources. The magnetic field variation can be approximately fitted to that of the line current. It is inferred that bundles of magnetic field lines with the same helicity propagate with the Alfvén velocity along the background magnetic field. One possible source is a flux transfer event. In addition, the variation in the solar wind dynamic pressure may also affect the velocity rotation. We have found 18 events during the first 2 years of Magnetospheric Multiscale operations. The derived properties are generally similar to those from the event study. For some events, we have identified a flux transfer event as a possible source. Again, the dynamic pressure variation may be the cause as well. The events reported resemble in some respects crewcuts and midday auroral brightening sequence, as measured by ground‐based optical instruments.

Small‐Scale Aurora Associated With Magnetospheric Flow Vortices After a Solar Wind Dynamic Pressure Decrease

AbstractSudden changes of the solar wind dynamic pressure have significant impacts on the dynamics of the magnetosphere‐ionosphere system. On 18 February 2011, a sudden decrease in solar wind dynamic pressure was observed by the Wind satellite, which drove the entire magnetosphere‐ionosphere system as recorded in many ground‐based and space‐based measurements. In the magnetosphere, Time History of Events and Macroscale Interactions during Substorms (THEMIS) spacecraft observed a counterclockwise plasma flow vortex propagating tailward. Near the magnetic footprints of the THEMIS spacecraft, the ground magnetometers observed magnetic field variations that corresponded to a counterclockwise vortex in the equivalent ionospheric currents, which in turn indicated the presence of upward field‐aligned currents. The all‐sky imager at RANK station near the THEMIS footprints also observed a simultaneous enhancement of the auroral brightness. Therefore, this comprehensive case study demonstrates a causal chain that links the solar wind dynamic pressure variations to magnetospheric, ionospheric, and auroral activities.

Fluid Challenge During Anesthesia: A Systematic Review and Meta-analysis.

Assessing the volemic status of patients undergoing surgery is part of the routine management for the anesthesiologist. This assessment is commonly performed by means of dynamic indexes based on the cardiopulmonary interaction during mechanical ventilation (if available) or by administering a fluid challenge (FC). The FC is used during surgery to optimize predefined hemodynamic targets, the so-called Goal-Directed Therapy (GDT), or to correct hemodynamic instability (non-GDT). In this systematic review, we considered the FC components in studies adopting either GDT or non-GDT, to assess whether differences exist between the 2 approaches. In addition, we performed a meta-analysis to ascertain the effectiveness of dynamic indexes pulse pressure variation (PPV) and stroke volume (SV) variation (SVV), in predicting fluid responsiveness. Thirty-five non-GDT and 33 GDT studies met inclusion criteria, including 5017 patients. In the vast majority of non-GDT and GDT studies, the FC consisted in the administration of colloids (85.7% and 90.9%, respectively). In 29 non-GDT studies, the colloid infused was the 6% hydroxyethyl starch (6% HES; 96.6% of this subgroup). In 20 GDT studies, the colloid infused was the 6% HES (66.7% of this subgroup), while in 5 studies was a gelatin (16.7% of this subgroup), in 3 studies an unspecified colloid (10.0% of this subgroup), and in 1 study albumin (3.3%) or, in another study, both HES 6% and gelatin (3.3%). In non-GDT studies, the median volume infused was 500 mL; the time of infusion and hemodynamic target to assess fluid responsiveness lacked standardization. In GDT studies, FC usually consisted in the administration of 250 mL of colloids (48.8%) in 10 minutes (45.4%) targeting an SV increase >10% (57.5%). Only in 60.6% of GDT studies, a safety limit was adopted. PPV pooled area under the curve (95% confidence interval [CI]) was 0.86 (0.80-0.92). The mean (standard deviation) PPV threshold predicting fluid responsiveness was 10.5% (3.2) (range, 8%-15%), while the pooled (95% CI) sensitivity and specificity were 0.80 (0.74-0.85) and 0.83 (0.73-0.91), respectively. SVV pooled area under the curve (95% CI) was 0.87 (0.81-0.93). The mean (standard deviation) SVV threshold predicting fluid responsiveness was 11.3% (3.1) (range, 7.5%-15.5%), while the pooled (95% CI) sensitivity and specificity were 0.82 (0.75-0.89) and 0.77 (0.71-0.82), respectively. The key components of FC including type of fluid (colloids, often 6% HES), volume (500 and 250 mL in non-GDT studies and GDT studies, respectively), and time of infusion (10 minutes) are quite standardized in operating room. However, pooled sensitivity and specificity of both PPV and SVV are limited.

Temporal-spatial variation of dynamic water pressure at interface crack of double-block ballastless track under high-speed vehicle dynamic loads

By combining the vehicle-track coupled dynamics method and the fluid-structure coupled method, an analysis model for predicting dynamic water pressure (DWP) at the interface crack of double-block ballastless track is developed in this work. The influence of the interface cracking and interface water states on the DWP, the temporal-spatial distribution characteristics due to vehicle dynamic loads, and the parameters influence law with considering the temporal-spatial variation of the DWP are analyzed in details. Results show that the DWP reaches the maximum positive and negative pressures when a high-speed vehicle passes the calculation section; the distribution of the DWP along the lateral direction is complicated, the variations of the DWP at different crack depths are different, so that it is difficult to represent the DWP characteristics by using the DWP at a single point, and the method of partition loading can be adopted; By simplifying the dynamic water pressure to the point at the interface crack tip, the obtained principal vector and principal moment can not only describe the overall mechanical behavior of the spatial distributed DWP, but also their variation with the time reflect the time-varying characteristics of the DWP; the principal vector and principal moment gradually increase with the increases the interface crack depth and the vehicle running speed, as well as the decrease of the interface crack height; the upward action of the DWP on the track slab will exceed the downward action of the bearing pressure at rail supporting point on the track slab, which would accelerate the interface damage the ballastless track.

Global Distribution of ULF Waves During Magnetic Storms: Comparison of Arase, Ground Observations, and BATSRUS + CRCM Simulation

AbstractsDuring 26–29 March 2017 magnetic storm, the Arase satellite observed typical ultra low frequency (ULF) waves and acceleration of relativistic electrons. We simulate the global distribution of these ULF waves using CRCM with BATSRUS global magnetospheric magnetohydrodynamic model. The simulation can qualitatively reproduce the ULF waves observed by Arase at frequencies of 2–3 mHz. However, the simulated ULF wave power is 1–2 orders of magnitude smaller than the observation. The simulated ULF wave activity has a good correlation with the solar‐wind dynamic pressure variation, while the wave activity on the ground is enhanced even during the recovery phase, possibly due to the Kelvin‐Helmholtz instability and/or substorms. We also study the 3–6 April 2017 magnetic storm, in which low ULF wave activity and weak acceleration of relativistic electrons are seen. We suggest that the existence of ULF waves plays an important role in accelerating electrons up to relativistic energies.

Trajectory Design of a Rocket–Scramjet–Rocket Multistage Launch System

The integration of a reusable scramjet vehicle as the second stage of a multistage space launch system has the potential to reduce the cost of small-payload orbital launches. This paper determines the maximum payload to orbit trajectory of a multistage rocket–scramjet–rocket system. This trajectory is calculated by formulating the problem as an optimal control problem, and then solving it using the pseudospectral method. Using this method, it is determined that the optimal trajectory for the scramjet stage involves an initial decrease in dynamic pressure, followed by constant-dynamic-pressure flight, and finally a pullup maneuver. This optimal trajectory results in an 8.35% improvement in payload mass to orbit when compared to a constant-dynamic-pressure trajectory with minimum pullup. Furthermore, the optimal pullup maneuver decreases the maximum dynamic pressure experienced by the final rocket stage by 20.3%. The sensitivity of the trajectory is tested by varying the maximum allowable dynamic pressure and the drag produced by the vehicle. A maximum dynamic pressure variation of is shown to produce only and variations in the payload mass. A drag increase of 10% is shown to produce a similar optimal trajectory shape, indicating robustness with variation of the vehicle aerodynamics.

A pneumatic sensor for grinding wheel condition monitoring

This paper presents the proof-of-concept of a pneumatic sensor for monitoring the performance of grinding wheels. The system concurrently considers the static and dynamic components of the back pressure signal, which refer to the position and topography of the functional wheel surface, respectively. Auxiliary experiments and numerical simulations are presented to demonstrate that the dynamic back pressure variations do indeed correspond to wheel topographic features. The performance of the sensor is evaluated with respect to wheel dressing, progressive wheel wear and grinding burn. The monitoring capability of the sensor is confirmed to be not compromised by the application of a flood coolant.

Microseismic Emissions During Pneumatic Fracturing: A Numerical Model to Explain the Experiments

AbstractModeling of fluid injection processes into a deformable porous medium is a challenging area of physics that has a wide range of applications like the food, construction, and petroleum industries. In this research, we investigate pneumatic fracturing of a porous medium experimentally and numerically in a Hele‐Shaw cell. In the experiments, we inject air into the porous medium (initially random loose packed) to create compaction, channeling, and fracturing while monitoring the cell with accelerometers and a high‐speed camera. Furthermore, we develop a numerical model in two steps: (1) a poroelastoplasticity‐based model to explain dynamic fluid pressure variations and (2) a solid stress model based on Janssen's theory. The contributions of the different pressure sources air in channels and solid stress in the experiments, and the simulations are compared with respect to amplitude and frequency. Afterward, the variations of the normal stress exerting on the plates are convolved with a Lamb Wave green function to generate acoustic emissions numerically. The physics behind the evolution of the experimentally recorded power spectrum of the out‐of‐plane plate vibrations are explained using numerical models. The frequency bands (in the simulated power spectra) are influenced by the size of the opened channels and the Hele‐Shaw cell and are in the same range with the experimentally measured peaks of the acoustic emissions.