Large Pressure Waves Research Articles

Evolving Outer Heliosphere: Tracking Solar Wind Transients from 1 au to the VLISM with IBEX and Voyager 1

Interstellar Boundary Explorer (IBEX) observations of energetic neutral atom (ENA) fluxes from the heliosphere have greatly enriched our understanding of the interaction of the solar wind (SW) with the local interstellar medium (LISM). However, there has been recent controversy surrounding the inability of most ENA models to produce as high an intensity of ∼0.5–6 keV ENAs as IBEX observes at 1 au, especially as a function of time. In our previous study (E. J. Zirnstein et al.), we introduced a new model that utilizes a data-driven magnetohydrodynamic simulation of the SW–LISM interaction to propagate pickup ions through the heliosheath (HS) after they are nonadiabatically heated at the heliospheric termination shock. E. J. Zirnstein et al. only simulated and analyzed IBEX observations from the direction of Voyager 2. In this study, we expand our model to include fluxes from the direction of Voyager 1, as well as in the low-latitude part (middle) of the ribbon (10° below the ecliptic plane). We show that the model results at Voyager 1 are consistent with E. J. Zirnstein et al.’s results at Voyager 2 in terms of a secondary ENA source contribution of ≲20% from both directions. Our results in the middle of the ribbon also reproduce the data, when including a time-dependent secondary ENA source. Finally, we demonstrate with our simulation that three large pressure waves likely merged in the VLISM and were observed by Voyager 1 as “pf2,” while at least one of the wave’s effects in the HS was observed by IBEX as a brief enhancement in ENA flux in early 2016.

Decomposition of the mechanical stress tensor: from the compressible Navier–Stokes equation to a turbulent potential flow model

We frame the mechanical stress tensor decomposition in a general procedure which involves the Helmholtz–Hodge decomposition. We highlight the impact of the mechanical stress tensor decomposition on the Navier–Stokes equation, with emphasis on the dissipation function. For fluids with low compressibility, we draw some insights on the Reynolds Averaged Navier–Stokes equations, and on the Reynolds stress tensor decomposition. We derive a turbulent potential flow model, and investigate the transition from viscous potential flow to turbulent potential flow. Under low Mach number approximation, we apply the turbulent potential flow model to one-dimensional propagation of large amplitude pressure waves in liquid-filled pipe.

Modeling of low Mach number unsteady turbulent pipe flows

AbstractUnder adiabatic conditions, and neglecting temperature variations due to entropy production, we present a set of Reynolds Averaged Navier–Stokes (RANS) equations for fluids of low compressibility, i.e., fluids in the liquid state. In the low Mach number limit, we specialize the RANS equations to the one-dimensional unsteady pipe flow, and we deduce the dimensionless number that plays a predominant role in the flow behavior. We reduce the system of equations to a linear damped wave equation, and use its analytical solution to investigate the propagation of large amplitude pressure waves in liquid-filled pipes (water hammer phenomenon). We test the model reliability by comparing the analytical solution of the proposed model against experimental data available in the literature.

Pressure-Volume Relationships in the Spinal Canal and Potential Neurological Complications After Epidural Fluid Injections.

High-volume fluid injections into the spinal canal may lead to severe neurological complications. But when anatomical or pathological conditions in the spinal canal are unfavorable, even small volume epidural injections can cause dangerously high epidural, subarachnoid, and intracranial pressures or pressure gradients. Data obtained from the scientific literature and direct clinical observation are used to derive a first-order approximation of epidural, subarachnoid, and intracranial pressure responses to epidural fluid injections. Maximum allowable fluid volumes for single or multiple divided fluid injections over time are calculated. In the presence of spinal pathology, 10 ml of fluids may increase epidural pressure to >100 mmHg. Injection speed >4 ml per second may also generate dangerously high intraspinal and intracranial pressures. Intermitted bolus injections provide limited protection, but intraspinal pressures may rise very fast when a critical total injected volume is reached. Potential complications of increased intracranial pressures or large pressure waves include nerve palsies, tinnitus, blindness, stroke, and death. Spinal injections or endoscopy should be performed in an awake responsive patient or with direct cerebrospinal fluid pressure monitoring. A set of guidelines for epidural fluid management is given.

Cavitation upon low-speed solid\u2013liquid impact

When a solid object impacts on the surface of a liquid, extremely high pressure develops at the site of contact. Von Karman’s study of this classical physics problem showed that the pressure on the bottom surface of the impacting body approaches infinity for flat impacts. Yet, in contrast to the high pressures found from experience and in previous studies, we show that a flat-bottomed cylinder impacting a pool of liquid can decrease the local pressure sufficiently to cavitate the liquid. Cavitation occurs because the liquid is slightly compressible and impact creates large pressure waves that reflect from the free surface to form negative pressure regions. We find that an impact velocity as low as ~3 m/s suffices to cavitate the liquid and propose a new cavitation number to predict cavitation onset in low-speed solid-liquid impact-scenarios. These findings imply that localized cavitation could occur in impacts such as boat slamming, cliff jumping, and ocean landing of spacecraft.

A combined water hammer protective method for optimizing the volume of the air vessel in water supply systems

Abstract An air vessel, as an effective and reliable water hammer protective device, is widely used in long-distance water supply systems. However, the volume of the air vessel must be extra-large to guarantee security of the system, especially in a system with a high head and large flow. In this paper, to reduce the volume of the air vessel, a novel protective method combining an air vessel and over pressure relief valve was proposed and verified using a numerical simulation based on a practical project. In addition, the protection performance under the combined protective method was compared with the traditional method. The results show that the combined protective method can significantly reduce the volume of air vessel and exhibit a better protection performance. Furthermore, after analysis and optimization of the rule of opening and closing over the pressure relief valve, the valve should be opened in a short time to produce fast discharge so as to eliminate the large pressure rise rapidly. The duration of opening the over pressure relief valve has little effect on the maximum pressure. The closing time of the over pressure valve should be slow, as much as possible, to avoid producing large pressure wave.

Developments in multiple-valve water-hammer control

This paper investigates multiple-valve closures in a simple reservoir-valve-pipeline-valve system. Multiple closing (or opening) of valves may induce large positive or low negative pressure waves due to wave interference (superposition of the waves). The effect of multiple-valve closure can be either beneficial or detrimental, with the outcome being entirely dependent on the position of the valves and the sequence and delay of the closures. Valves are incorporated as boundary conditions in the method of characteristics model. The staggered (diamond) grid with consideration of unsteady skin friction is applied. Experimental investigations of multiple-valve induced water-hammer have been performed in the University of Montenegro laboratory pipeline apparatus. The apparatus consists of an upstream end high-pressurized tank, horizontal steel pipeline (length 55.37 m, inner diameter 18 mm), four valve units positioned along the pipeline including the end points, and a downstream end tank. The transient event is initiated first by rapid closure of the downstream-end valve followed by the delayed closure of the upstream-end valve. Calculated and measured results are compared and discussed in the light of the effects of pressure wave interference.

Experimental and numerical study of two underwater explosion bubbles: Coalescence, fragmentation and shock wave emission

This work presents experimental and numerical investigations on the nonlinear interaction, coalescence, collapse and rebound of two pulsating bubbles, which are generated by underwater explosions (2.5 g PETN for each). The transient physical phenomena are captured by a high-speed camera and the near-field pressure signals measured by pressure sensors. The boundary integral simulations gain further insight into the high-speed liquid jet formation, jet impact, splash, fragmentation, and the associated flow field characteristics. Particularly, the numerical simulation reproduces the multiple splits of the coalesced bubble, which partly reveals the mechanism of the bubble cloud formation. These sub-bubbles collapse with different velocities and reach their minimum volumes at different times, leading to the emission of multiple bubble pulse pressures (shock waves) at the final collapse phase. Interestingly, we find that the last pressure peak is the largest one for non-axisymmetric configurations, which is attributed to the asymmetric collapse of the coalesced bubble about the centerline of the two bubbles at inception. More specifically, the lower bubble segments collapse earlier and generate large pressure waves, which further drives the remaining part of the bubble to collapse more violently. We also make quantitative comparisons of the pressure impulse between different configurations.

Leak detection by monitoring pressure to preserve integrity of agricultural pipe

Leakage of agricultural pipes has been increasingly frequent problems due to corrosion, loosening of joints, and cracks, which result in the subsidence of peripheral roads and dwelling land in the worst case. Generally, leakage has been detected by listening for noisy leak signals or measuring water loss during 24 h in a section closed by a valve. But these methods have weak points: They are costly, inaccurate, and time-consuming. This study investigated a new method of leakage detection that is accurate and easily accomplished by monitoring pressure for the purpose of preventing the destruction of pipes. During a transient event, where a large pressure wave is generated suddenly by sharp valve closure, the pressure wave damps out and the reduction wave is reflected when passing through a leakage point. Applying the propagation characteristics to leak detection, two methods were proposed: In the first method, a location and leakage volume was estimated by reading the signal of reflected wave from the leakage point and the validity of the method was confirmed by experiment in case that the ratio of leakage volume to flow rate in the pipe was more than approximately 5%. In the second method, which focuses on damping of pressure due to leakage, the leakage location could be estimated with an accuracy of < 5% of the total pipe length by fitting the calculated “damping rate” to the measured “damping rate” using method of characteristics in the cases where the leakage could not be detected by the first method.

RELAP5 analysis of hydrodynamic loads in response to PORV actuation

A fluid transient analysis was performed for the Power Operated Relief Valve (PORV) discharge piping to evaluate hydrodynamic loads caused by a sudden opening of the PORV within 0.05 s. The system fluid was immediately accelerated and a large axial load was observed. This result is expected with the criterion for the disturbance time. In this analysis, the disturbance time is the PORV opening time, which is faster than the pressure wave propagation time of 0.171 s. If the disturbance time is at least 10 times larger than the calculated pressure wave propagation time, the pressure wave propagation is insignificant. Given the complexity and highly transient nature of this phenomenon, a detailed calculation of the fluid transient was performed using the RELAP5/MOD3.3 (Patch 03) computer code. The capability of RELAP5 was previously validated for the analysis of large and rapid pressure waves propagating with the speed of sound along the reactor piping systems. The model was finely nodalized to allow the detailed computation of hydrodynamic loads with a maximum time step which is well below the acoustic courant limit. Consequently, it is important to ensure whether the hydrodynamic load will challenge the allowable stresses for the piping and its supports.

Numerical simulation of the Reynolds number effect on the aerodynamic pressure in tunnels

With an increase in train speed, the aerodynamic effects caused by the train could escalate, especially for a train running in a tunnel. A number of large transient pressure waves are generated owing to the confined spaces within the tunnel, resulting in possible damage to the vehicle structure and the facilities in the tunnel. Therefore, it is necessary to study the aerodynamic performance of a train running in a tunnel. A scaled moving model test system was constructed to facilitate the simulation of the aerodynamic effects caused by a train running in a tunnel. In this study, the influence of grid density, calculation time step, and turbulence model on the pressure caused by the train entering the tunnel was analyzed, which is helpful for choosing suitable values of the aforementioned parameters to simulate the aerodynamic performance of the train in the tunnel. The impacts of Reynolds number effect on the distribution of the surface pressure and peak of pressure wave along the train, and the pressure waveform were also studied through numerical simulation on three scaled model trains (full scale, 1/8, 1/20, and 1/32 scaled). The findings aid in understanding the relationship between the Reynolds and pressure amplitude, and the results of the scaled test can be applied to a full-scale train.

Cascading pulse tubes on a large diaphragm pressure wave generator to increase liquefaction potential

Fabrum Solutions, in collaboration with Absolut System and Callaghan Innovation, produce a range of large pulse tube cryocoolers based on metal diaphragm pressure wave generator technology (DPWG). The largest cryocooler consists of three in-line pulse tubes working in parallel on a 1000 cm3 swept volume DPWG. It has demonstrated 1280 W of refrigeration at 77 K, from 24 kW of input power and was subsequently incorporated into a liquefaction plant to produce liquid nitrogen for an industrial customer. The pulse tubes on the large cryocooler each produced 426 W of refrigeration at 77 K. However, pulse tubes can produce more refrigeration with higher efficiency at higher temperatures. This paper presents the results from experiments to increase overall liquefaction throughput by operating one or more pulse tubes at a higher temperature to pre-cool the incoming gas. The experiments showed that the effective cooling increased to 1500 W resulting in an increase in liquefaction rate from 13 to 16 l/hour.

Echocardiographic Assessment of Diastolic Function

The stepwise approach in evaluation of left ventricular (LV) diastolic function is essential in any patients with dyspnea on exertion or heart failure. Many of them have normal to near-normal ejection fractions (EFs). These subsets of patients are labeled as diastolic heart failure or heart failure with preserved EF. It is important to differentiate diastolic dysfunction from dyspnea of pulmonary origin for further management and future prognosis. LV filling pressures is usually synonymous with pulmonary capillary wedge pressure (PCWP), mean left atrial pressure (LAP), mean LV diastolic pressure, and LV end-diastolic pressure (LVEDP). PCWP on the other hand is also an indirect estimate of LV diastolic pressures. LVEDP is often elevated in early diastolic dysfunction because of a large atrial pressure wave, while mean PCWP and LAP remain normal. While mean PCWP and LAP increased during tachycardia and where there is increased LV afterload which is the basis for the diastolic stress test. It is essential that certain Doppler variables correlate well with an increase in LVEDP only and not reflecting the increase in either LAP or LVEDP. Therefore, early evaluation of LV filling pressures and LVEDP are more important than mean LA pressure which is elevated later. Echocardiography is the best evaluation tool to evaluate LV diastolic function. The purpose of this article is to provide the simplest stepwise approach of different diastolic parameters which are used as routine protocol with minimal use of the newer modalities at various clinical settings.

Ventricular arrhythmias and sudden cardiac death

### Key points There are 50–100 unexpected, sudden cardiac deaths (SCDs) per 100 000 population per year in Europe and USA, categorized by symptom onset to cardiac arrest time of <1 h.1 Despite the decline in coronary artery disease mortality and advancements in resuscitation services, survival from these events remains low. Unfortunately, they often occur outside the hospital environment and are associated with a survival rate of <10%. The majority occur in adults over 35 yr of age and at least half of these events can be attributed to ventricular arrhythmias, although the true incidence is unknown due to inevitable degeneration to asystole if unwitnessed. These arrhythmias may be the presenting complaint in the emergency department and may feature throughout the perioperative period, including at preoperative assessment, during surgery and in the recovery phase, for example in intensive care. They may also be the direct target of therapy in the case of electrophysiological catheter ablation and implantable cardioverter defibrillators (ICDs). They are more frequent and carry greater risks in patients with structural heart disease, but younger patients with ion-channel abnormalities can also be susceptible.2 This review classifies the causes and significance of ventricular arrhythmias based on the presence or absence of structural heart disease and provides a simple system to aid confident distinction from supraventricular arrhythmias. …

Exploitation of Acoustic Effects in Film Cooling

There have been numerous studies of the behavior of shaped film cooling holes for turbine applications. It is known that the introduction of coolant is an unsteady process, and a handful of studies have described and characterized the unsteadiness. To the best of our knowledge, there are no studies in which unsteady acoustic effects have been actively exploited such that they have led to novel designs with improved cooling performance. This paper discusses the fundamental mechanism of pressure wave propagation through cooling holes and describes systems in which holes which have been acoustically shaped have led to a direct improvement in film cooling hole performance. The mechanism relies on sequential pressure wave reflection within an acoustically shaped hole and is therefore applicable in regions where the external surface is subject to large pressure wave fluctuations at high frequency. The principle is developed analytically, and then demonstrated with a number of computational fluid dynamics (CFD) simulations. We demonstrate that a desired temporal mass flow rate profile can be achieved by appropriate acoustic shaping of the cooling hole. The purpose of this paper is to describe the fundamental design considerations relevant to acoustic shaping. The discussion is developed with reference to a film cooling system for the over-tip region of an unshrouded rotor. The performance benefit of the system in terms of modulation of unsteady mass flux and ingestion characteristics is quantified. It is believed that this is the first time this significant effect has been exploited in film cooling design.

Experimental Quantification of Intrusion Due to Transients in Distribution Systems

Abstract In water distribution systems, rapid changes in flow can create short duration large magnitude pressure waves, known as transients. Previous research has linked extreme low-pressure transients with contaminant intrusion, which presents a risk to public health. Representative physical experiments have been undertaken at the University of Sheffield using a novel large-scale system. This has allowed for the quantification of the volume of intrusion drawn into the pipe for a range of initial system conditions. Analysis of the results demonstrates that the volume of intrusion is connected to the duration and magnitude of the negative pressure transient.

대심도 지하정거장에서 수직구 위치에 따른 수치적 연구

When a high-speed train passes an underground station, large pressure waves are generated due to the piston effect. These pressure waves can cause the problems of vibration and noise as well as the ear discomfort of passengers at the underground station. This work numerically analyzed the pressure wave generation and propagation in an high-speed railway underground station, and the optimal location for vent shafts was studied to improve the passenger comfort by reducing the magnitude of the pressure wave and its rate of change. The evolution of pressure field in the underground station was calculated using a CFD(Computational Fluid Dynamics) software(Fluent), where the axis-symmetric two-dimensional model verified by Wu was used. And this study is applied to modelling of the underground station and the tunnel from Daegok station A-line of GTX(Great Train Express). From the result, we can have a conclusion that the role of vent shafts respectively were different according to the position in and out the underground station. Also Vent shaft in the underground station widely reduced pressure magnitude. And vent shaft out underground station reduced initial pressure peak value. Double vent shafts installed at tunnel toward station entrance and inside of the tunnel are the most efficient to reduce pressure. and pressure reduction increases according to the number of vent shaft.

The combined effect of aortic stiffness and pressure wave reflections on mortality in the very old with cardiovascular disease: the PROTEGER Study

Aortic stiffness (pulse wave velocity, PWV) and pressure wave reflections (augmentation index, AI) are two interrelated markers of mortality. Their potential synergistic effect on mortality has never been studied. We sought to investigate the association as well as the combined effect of PWV and AI on mortality in a cohort (PROTEGER Study) of very old (>70 years, mean age ( ± s.d.): 85.4 ± 7.4 years). Aortic PWV and pressure wave AI were assessed by pulse wave analysis; carotid structure and cardiac function were analyzed by ultrasound. The analysis was performed in 259 patients who had all the data available. Neither PWV nor AI was, in separate, predictors of mortality (log-rank test: P=0.278 and P=0.433, respectively, Kaplan-Meier analysis). No linear association was found between PWV and AI (P=0.278). To investigate the possible synergistic effect of PWV and AI on mortality, the population was analyzed according to the tertiles of PWV and AI. Subjects with combined high PWV (third tertile) and moderate-to-high AI (second and third tertiles) had lower survival compared with the rest of the population (Kaplan-Meier survival curve, log-rank test: P=0.030). Cox regression analysis showed that this effect was independent from age, gender, blood pressure, cardiac/carotid parameters and other confounders, except creatinine and insulin resistance. The present study provides further insight on the pathophysiological association between large artery stiffness and pressure wave reflections, suggesting that when both are elevated they may increase the mortality in the elderly.

Short-time pressure response during the start-up of a constant-rate production of a high pressure gas well

The start-up flow of a constant-rate production of a high pressure gas well is studied, with emphasis on the effect of gas acceleration. Gas acceleration is important in the near wellbore region for a high pressure gas in a high permeability formation. It is shown that when gas acceleration is important, the system of governing equations for the porous media flow becomes hyperbolic. In response to an impulsively imposed mass flow-rate, a steep pressure front is created at the wellbore and it propagates into the formation. This steep pressure front is trailed by large amplitude pressure waves. As they travel away from the wellbore, the pressure front becomes less steep and the amplitude of the trailing waves decreases due to viscous damping. It is found that the pressure drawdown experiences a rapid increase followed by an oscillatory behavior in short times before approaching the classical logarithmic rise regime. The pressure gradient at the wellbore wall can grow to a large magnitude in the early times, which can cause a tensile failure of the rock materials near the wellbore.

Central Blood Pressure Under Angiotensin and Calcium Channel Blockade

Hemodynamic studies have shown that, in healthy subjects, there is a gradual widening of the height of the pressure waveform as it travels from the central (aortic) elastic arteries to the peripheral muscular arteries (brachial artery)1 (Figure). This disparity, which tends to disappear in the presence of vascular disease/aging, does not require any additional energy input within the arterial system, because the mean arterial pressure (MAP) and even the diastolic blood pressure (BP) remain almost unchanged between the 2 arterial sites. This finding is mainly attributed to the gradual increase (ie, amplification) of systolic BP (SBP) or pulse pressure (PP) along the arterial tree and is conventionally quantified as the ratio of the SBP or PP between the 2 sites (eg, SBP arm:SBP aorta)1 (Figure). Figure. Schematic personal representation of the forward and reflected pressure waves in the aorta and the influence of their timing on local PP. The definition of SBP amplification is indicated. In the present issue of Hypertension , Matsui et al2 have shown the superiority of calcium channel blockers (CCBs) over diuretics using the following protocol: the angiotensin receptor blocker olmesartan was combined with the CCB azelnidipine and compared with the same olmesartan associated with the diuretic hydrochlorothiazide. Central SBP was reduced to a greater degree with the CCB than with the hydrochlorothiazide. This resulted in an increase of SBP and PP amplification with the CCB, despite the lack of a significant difference in the brachial SBP reduction between the 2 …