High Pressure Zone Research Articles

Использование численного моделирования при анализе аэроупругого взаимодействия подвижного состава с тоннельными сооружениями

Purpose of the work: study of the formation of a complex air structure under conditions of rolling stock movement along extended underground structures using numerical modeling methods. Methods: an analysis of the influence of aerodynamic factors on rolling stock, passengers and railway infrastructure was carried out based on the finite element and volume method. The reasons for the occurrence of a compacted air zone, which appears in front of the head car of the train and exerts significant resistance to the movement of the train using the “Frozen Rotor” method, have been investigated. The indicators of energy efficiency and safety of the process of freight and passenger transportation are analyzed, taking into account the processes of aerodynamic interaction of moving rolling stock and artificial tunnel-type structures. Results: using numerical modeling and the use of the “Frozen Rotor” method, it was possible to obtain a qualitative picture of the distribution of transverse vortex air flows resulting from the occurrence of viscous friction. Regularities were discovered in the changes in the dynamics of pressure and speed of air masses on the surface of the head fairing when a train enters a tunnel. The fact of the negative impact of zones of high and low pressure, as well as their sharp drop, on the locomotive crew and passengers has been established. Practical significance: the possibility of conducting research in the field of aerodynamics of railway transport using modern numerical modeling methods is shown. This topic is very relevant in the field of designing high-speed rolling stock.

Flow and spray characteristics of a gas–liquid pintle injector under backpressure environment

Both the flow and spray characteristics of a gas–liquid pintle injector element under the backpressure environment were investigated experimentally and numerically. The cold atomization tests were conducted with the backpressure range from 0.50 to 1.54 MPa. Both the interaction process between gas film and liquid jets and the detail distribution of the spray were obtained by the verified volume of fluid to discrete phase model. Results showed that there is a local high-pressure zone at the root of the liquid jets resulted by the collision of gas film and liquid jet. A semi-empirical model for predicting the discharge coefficient of the orifices is proposed considering the effect of local high-pressure zones based on the experiments. It was found that the discharge coefficient is mainly affected by the local momentum ratio (LMR) and ambient pressure. The discharge coefficient increases with the increase in LMR and ambient pressure. Before the primary breakup occurs, the liquid jets deform from rectangle jets to bow-shaped liquid films under the effect of the gas film. Then, both the gas and liquid mix in the range included by the gas passed by the windward surface and side of liquid jets. The droplet size is larger at the edges of the spray and the Sauter mean diameter (SMD) is beyond 100 μm. On the contrary, it is relatively small and uniform at the spray central, and the corresponding SMD is about 50 μm.

Temporal dynamics of urban gas pipeline risks

Urban gas pipelines pose significant risks to public safety and infrastructure integrity, necessitating thorough risk assessment methodologies to mitigate potential hazards. This study investigates the dynamics of population distribution, demographic characteristics, and building structures to assess the risk associated with gas pipelines. Using geospatial analysis techniques, we analyze population distribution patterns during both day and night periods. Additionally, we conduct an in-depth vulnerability assessment considering multiple criteria maps, highlighting areas of heightened vulnerability in proximity to gas pipelines and older buildings. This study incorporated the concept of individual risk and the intrinsic parameters of gas pipelines to develop a hazard map. Hazard analysis identifies areas with elevated risks, particularly around main pipeline intersections and high-pressure zones. Integrating hazard and vulnerability assessments, we generate risk maps for both day and night periods, providing valuable insights into spatial risk distribution dynamics. The findings underscore the importance of considering temporal variations in risk assessment and integrating demographic and structural factors into hazard analysis for informed decision-making in pipeline management and safety measures.

Turbulence generation in the transitional wake flow behind a sphere

Turbulence generation in the transitional flow in the wake behind a sphere is studied with numerical simulations. The filtered Navier–Stokes equation and the large eddy simulation method are employed as the governing equation and the numerical method, respectively. The ΩR̃ vortex identification method is used to trace the evolution of vortices in the wake flow. The energy gradient theory is used to analyze the spike formation in the wake flow. The simulation results show that the vortex structure in the wake flow is the type of hairpin vortices, which is similar to that in a boundary layer flow. Ejection and sweep motions exist around the hairpin vortices. There are two most unstable regions in the wake where turbulence “burst” is first produced, one is near the center of the vortex head and the other is between the two vortex legs. There is a high-pressure zone above the vortex head due to the decrease in the streamwise velocity, and a soliton-like coherent structure exists in this area. The mechanism of turbulence generation in the wake is the discontinuity of the streamwise velocity, which makes the Navier–Stokes equation be singular. This singularity leads to the formation of the “negative spike” in the streamwise velocity. The amplitude of the “negative spike” reaches up to 60% of the incoming velocity, which is close to the situation in a boundary layer flow on a flat plate. It is concluded that the mechanism of turbulence generation in the wake flow is the same as that in the boundary layer flow.

Synoptic weather patterns during fire spread events in Siberia

Several recent studies have indicated a strong relationship between extensive wildfires in Siberia and synoptic-scale weather processes. In this study, we used the concept of fire spread events to investigate the relationships between synoptic and surface-level weather conditions and extensive wildfires in Siberia during 2001–2022 using the MODIS and ERA5 reanalysis products. We analyzed the spatio-temporal features and seasonality of fire spread events in the region and found that most of them occurred in the central part of Eastern Siberia (ES) during the summer months, following the wildfire season in the region. A significant positive trend in the annual count of fire spread events was found in ES, coinciding with non-significant negative trends in cloud cover and precipitation and non-significant positive trends in air temperature and the fire weather index. Results show that in the ES region, which accounts for 46 % of the total number of considered events, the main driver of fire spread events is the formation of a positive geopotential height anomaly, which, based on the pattern of the meridional wind component, indicates the presence of an anticyclone above the area of fire spread events. The presence of a high-pressure zone causes a decrease in cloud cover over regions with fires, leading to increases in the amount of incoming solar radiation and surface air temperature and a decrease in precipitation. These conditions contribute to the drying of fuel and an increase in the overall fire hazard level, which in turn leads to an intensification of the combustion process, as evidenced by an increase in the radiative power of fires.

Farmers’ purchase intention and willingness to pay for certified sweetpotato seed under different disease pressure zones in Uganda

AbstractThe use of certified sweetpotato (Ipomoea batatas) seed (CSS) was reported to unlock the yield potential of the crop leading to an over 80% yield increase. Despite the availability of elements of a formal CSS system, uptake in Uganda has remained dismal. Interdependence between farmer knowledge, perceptions, and purchase behaviors (PBs) is not well understood in a way that could allow the design of meaningful policies and interventions. This study aimed at unveiling factors underlying PB through purchase intention (PI) and willingness to pay (WTP) by interviewing 289 farmers from Omoro and Mpigi districts in Uganda, representing the low and high virus disease pressure zones, respectively. A modified theory of planned behavior (TPB) incorporating awareness as independent and farmer innovativeness as mediating variables expounded the relationships. Data were collected on perceptions, knowledge, innovativeness, and PI using a five‐point Likert scale plus WTP as a price, subjected to descriptive and structural equation modeling analysis. Results indicated significant locational differences in most socioeconomic characteristics. Middle income, CSS information access, and farming experience of 7–30 years conferred more likelihood of high PI. Conversely, high PI, group membership, and being female and middle‐aged increased the likelihood of high WTP. The effects of attitude, perceived behavioral control, and awareness were significant in high disease zone, while subjective norm was significant across disease zones. PI significantly affects WTP in high disease zone (p = 0.000) but its effect is insignificant in low disease zone (p = 0.569). An interplay of socioeconomic, perception, and knowledge attributes influences CSS PB calling for social marketing strategies with location‐specific interventions.

APPLICATION OF LINER SYSTEMS WELLABLE ELASTOMERIC PACKERS FOR WELL CONSTRUCTION

The application of liner systems featuring swellable elastomeric packers in well construction has emerged as a groundbreaking development within the oil and gas industry. This technology, which will be discussed in detail in this paper, addresses critical wellbore challenges, providing an in-depth exploration of its advantages and the transformative effects it has on well construction. Swellable elastomeric packers, a key component of these liner systems, play a pivotal role in overcoming various wellbore obstacles. Their unique design allows them to expand when in contact with wellbore fluids, establishing a robust and reliable seal. This characteristic renders them adaptable to a diverse array of applications, showcasing their versatility. These packers are particularly instrumental in creating a barrier between different geological formations or production zones within a well. By expanding and isolating specific zones, they effectively prevent undesirable fluid flow between them. This not only optimizes reservoir management but also enhances overall production efficiency. In addition to their zonal isolation capabilities, swellable elastomeric packers contribute significantly to the integrity of well casings. Acting as an additional protective layer, they guard against corrosion, high-pressure zones, and other challenges encountered in harsh downhole conditions. This protective function becomes especially crucial in ensuring the longevity and reliability of wells subjected to demanding environments. For wells prone to sand production, the deployment of swellable packers proves invaluable. These packers isolate and stabilize sand-prone zones, mitigating the ingress of sand and preserving productivity. Often overlooked in well completion design is the preparation for abandonment. The incorporation of blind pipe sections with swellable packers along the horizontal section of the liner in the new completion procedure has become an effective tool for safely and efficiently shutting down horizontal wells. A noteworthy advantage of liner systems with swellable packers is their cost-effectiveness in providing zonal isolation and ensuring casing integrity. By reducing reliance on traditional cementing methods, these systems offer economic solutions without compromising performance. Their adaptability allows for customization to specific wellbore needs, making them compatible with various completion techniques and wellbore configurations. In conclusion, the incorporation of liner systems featuring swellable elastomeric packers marks a significant leap forward in well construction technology. The versatility and effectiveness of these packers address critical wellbore challenges, providing solutions that optimize reservoir management, enhance production efficiency, and contribute to the overall integrity of oil and gas wells. The purpose of this article was to examine samples and establish the conditions for their application. Keywords: liner systems, swellable elastomeric packers, well construction, zonal isolation, swelling rate, liner hanger.

Aerodynamic Analysis of Low-Pressure Axial Fans Installed in Parallel

Abstract Ducted rotor-only low-pressure axial fans play an integral role in automotive thermal management. The tightly packed under-hood region and down-stream heat-exchanger shape limit the fan diameter. In order to circumvent this limitation, multiple cooling fans of small diameters are tightly packaged and placed in parallel. Currently, there is limited scientific work, that study the aerodynamics of low-pressure axial fans when installed in parallel. This work aims to quantify the aerodynamic performance and the flow-field as a result of installing low-pressure axial fans in parallel through computational fluid dynamics (CFD). Publicly available experimental data from Friedrich-Alexander University is used for the validation of the numerical setup. Three-dimensional, full-annulus, unsteady Reynolds-averaged Navier-Stokes (URANS) analysis has been performed for both a single-fan and two-fans installed in parallel and their respective aerodynamic performance has been compared for the operation condition identified as the best efficiency point in experiments. Only small differences are observed in the overall aerodynamic performance of the two-fans in parallel compared to a single-fan. A circumferential nonuniformity in the form of a local high-pressure zone at the inlet of the fan is observed when the two-fans are placed in parallel. The resulting circumferential nonuniformity is quantified, both in space and time. A strong correlation is found between the pressure fields of the two-fans installed in parallel.

The Dynamic Failure Behaviour of High-Pressure Zones during Medium-Scale Ice Indentation Tests

Results from medium-scale ice-crushing dynamic tests are presented in this paper based on a series of indentation experiments on confined ice samples using spherical indenters to simulate high-pressure zones (hpzs) with areas on the order of 103–104 mm2. The effects of ice temperature, interaction speed, indenter size and structural compliance on failure behaviour and associated structural dynamics have been studied. Observed failure behaviour consisted of a combination of continuous crushing extrusion and intermittent spalling, both of which were highly dependent on test conditions. Overall, the effects of the studied conditions on ice failure behaviour and associated interaction dynamics were found to be similar to the results reported from previous small-scale experiments, suggesting scale independence of the mechanisms that dominate ice failure behaviour. In general, warmer ice and smaller contact areas are associated with continuous extrusion with intermittent spalling, resulting in smoother peak pressures, while colder ice and larger contact areas tend to result in fracture-dominated behaviour with sharp peaks and substantial load drops. Ice temperature was also found to significantly influence interaction dynamics, with colder ice showing larger amplitude and longer duration dynamic activity, and higher peak pressures. Interaction speed was observed to primarily affect dynamic aspects of ice–structure interactions, with faster tests leading to higher failure frequencies. Similarly, structural compliance was found to mainly impact failure frequency, as well as the extent of load drops, with compliant structures tending to produce more significant load drops following failure. Overall, these experiments have helped enhance our understanding of compressive ice failure and contribute to improved models for dynamic ice–structure interactions.

Numerical study on hydraulic characteristics of rotating stepped dropshafts in deep urban tunnels.

As an important component of the deep tunnel drainage system for dealing with urban waterlogging, the rotating stepped dropshaft has been proposed due to its small air entrainment. However, the hydraulic characteristics inside the shaft still need to be fully studied. In this study, the flow patterns, water velocity, and pressure in the rotating stepped dropshaft under different flow rates and geometric parameters were studied using a three-dimensional numerical model. The results show that increasing the central angle of the step and reducing the step height can both reduce the terminal velocity. A theoretical formula for predicting the terminal velocity was established and well validated. The connection between the shaft and the outlet pipe poses a severe threat to the structural safety due to alternating positive and negative pressures. Wall-attached swirling flow generates a circular high-pressure zone at the bottom of the dropshaft and the larger the flow rate, the greater the pressure gradient at the center of the bottom. By using the momentum theorem and considering the impact pressure range of the swirling flow, the shaft bottom pressure can be predicted reasonably well.

Research on the Temperature and Thermal Stress of the Roll Quenching Process of Thin Plates

The roll quenching process can be approximated as a high-pressure jet impinging on a high-temperature moving steel plate. The process can greatly improve the strength and overall mechanical properties of the steel plate. However, the cooling uniformity and other factors lead to the problem of poor plate shape after quenching. It is found that in the roll quenching process, the roller conveyor speed has a large influence on the temperature field and stress field. This paper establishes a roll quenching mechanism model, iterates the convective heat transfer coefficient on the steel plate surface through the inverse heat transfer method, and performs a numerical simulation. Through the numerical simulation of the roll quenching process in the high-pressure zone of the steel plate, the temperature and equivalent force change rule of the transient of each position of the steel plate in the thick direction are obtained. It is found that the plate does not reach its maximum value when it is in the quenching zone, but there is some hysteresis that becomes more pronounced as it gets closer to the core. These findings are valuable for regulating the roll-hardening process and maintaining optimal strip surface quality in industrial production environments.

Research on the inflation process of underwater parachute by numerical simulation and model test

In order to meet the application requirements of the underwater parachute, the underwater inflation performance of a drag parachute is investigated based on numerical simulation and water tank test. A method for simulating the inflation process of underwater parachute based on Arbitrary Lagrangian Eulerian (ALE) method is proposed. The variation of axial force in the numerical simulation exhibits a similar trend to that observed in the model test, and the discrepancy of value between them is relatively insignificant. The purpose of this paper is to provide a basis for the evaluation and design of underwater parachutes for underwater applications. The effects of parameters such as permeability and flow velocity on the inflation performance are discussed in detail, and the analysis is carried out for parameters such as axial force and structural deformation. The results show that the high-stress zone and high-pressure intensity zone of the underwater parachute were found to be mainly concentrated in the center of the canopy and the joint. It can be observed both in model test and numerical simulation that, during the inflation process, vortexes are generated inside and outside the canopy. After the inflation shape of the canopy has stabilized under steady flow, lateral forces are generated on the parachute due to asymmetric vortex shedding, which cause the parachute to rotate around the axis.

Structural stability analysis of spherical bubble clusters in acoustic cavitation fields

The upwelling growth and evolution of spherical bubble clusters appearing at one-quarter wavelength from the water surface in ultrasonic cavitation fields at frequencies of 28 kHz and 40 kHz are studied by high-speed photography. Due to the interactions among bubbles, the stable bubble aggregation occurs throughout the rise of the bubble cluster, whose vertical pressure difference leads to a more significant spreading in the upper part of the cluster in the standing-wave field. At 28 kHz, the rising speed is about 0.6 m/s, controlled by the primary acoustic field. After a violent collapse of the bubble clusters, the aggregating structure begins to hover near the water surface. The size and stability of the structure are affected by the frequency and pressure of the primary acoustic field. If two clusters are close to each other, the clusters deviate from the spherical shape, even trailing off, and eventually merge into a single bubble cluster. By considering the influence of water-air boundary, based on the mirror principle, a spherical bubble cluster model is developed to explore the structure stability of the clusters, and the modified dynamics equations are obtained. The effects of driving acoustic pressure amplitude, bubble number density, water depth, and bubble equilibrium radius on the optimal stable radius of the spherical bubble cluster are numerically analyzed by using the equivalent potentials at 28 kHz and 40 kHz. The results show that the optimal stabilizing radius of spherical bubble cluster is in a range of 1–2 mm, and it tends to decrease slightly with the increase of the driving acoustic pressure and bubble number density. It is worth noting that the nonlinearity is enhanced by increasing acoustic pressure, which may promote the stability of the cluster structure. The smaller the unstable equilibrium radius, the easier it is to grow, and the stable size at 40 kHz is slightly smaller than that at 28 kHz. Generally, spherical clusters first appear in a high-pressure region and then move to a low-pressure region. If the acoustic pressure drops below a certain critical value, bubble clusters disappear. The theoretical analysis is in good agreement with the experimental observation. The analysis of the growth and structural stability of spherical bubble cluster is helpful in understanding the behavioral modulation of bubbles.

Stapled Anastomosis Versus Hand-Sewn Anastomosis With Mucosectomy for Ileal Pouch-Anal Anastomosis: A Systematic Review and Meta-analysis of Postoperative Outcomes, Functional Outcomes, and Oncological Safety.

This systematic review and meta-analysis aimed to compare outcomes between stapled ileal pouch-anal anastomosis (IPAA) and hand-sewn IPAA with mucosectomy in cases of ulcerative colitis and familial adenomatous polyposis. This systematic review and meta-analysis was performed according to the Preferred Reporting Items for Systematic Review and Meta-analysis) guidelines 2020 and AMSTAR 2 (Assessing the methodological quality of systematic reviews) guidelines. We included randomized clinical trials (RCTs) and controlled clinical trials (CCTs). Subgroup analysis was performed according to the indication for surgery. The bibliographic research yielded 31 trials: 3 RCTs, 5 prospective clinical trials, and 24 CCTs including 8872 patients: 4871 patients in the stapled group and 4038 in the hand-sewn group. Regarding postoperative outcomes, the stapled group had a lower rate of anastomotic stricture, small bowel obstruction, and ileal pouch failure. There were no differences between the 2 groups in terms of operative time, anastomotic leak, pelvic sepsis, pouchitis, or hospital stay. For functional outcomes, the stapled group was associated with greater outcomes in terms of seepage per day and by night, pad use, night incontinence, resting pressure, and squeeze pressure. There were no differences in stool Frequency per 24h, stool frequency at night, antidiarrheal medication, sexual impotence, or length of the high-pressure zone. There was no difference between the 2 groups in terms of dysplasia and neoplasia. Compared to hand-sewn anastomosis, stapled ileoanal anastomosis leads to a large reduction in anastomotic stricture, small bowel obstruction, ileal pouch failure, seepage by day and night, pad use, and night incontinence. This may ensure a higher resting pressure and squeeze pressure in manometry evaluation. The protocol was registered at PROSPERO under CRD 42022379880.

The mechanisms of jetting, vortex sheet, and vortex ring development in asymmetric bubble dynamics

Bubble dynamics near a rigid boundary at Reynolds numbers of O(10–100) exhibit significant viscous effect, associated with ultrasonic cavitation and cavitation damage. We study this phenomenon experimentally using high-speed photography of spark-generated bubble oscillation in silicone oils, whose viscosity is about three orders larger than water. Comparing to bubbles in water, bubble surfaces in silicone oil are more stable and thus more cycles of oscillations may be observed and studied. Additionally, we investigate this phenomenon numerically using the volume of fluid method. We propose a non-reflective boundary condition, reducing the computational domain's dimensions tenfold based on the far-field asymptotic behavior. This paper pays particular attention in the mechanism for the bubble jetting, the vortex sheet, and the vortex ring development. Initially, a stagnation point at the bubble center moves away from the wall owing to asymmetric bubble expansion, leaving the bubble around the moment the bubble reaches its maximum volume. During this process, a vortex sheet forms inside the bubble. As the vortex sheet approaches the bubble interface, it transfers momentum to the gas–liquid interface, influencing the flow near the bubble wall. The high-pressure zone at the stagnation point drives the distal bubble surface to collapse first and fastest subsequently. This asymmetric collapse generates circulation around the bubble's side cross section, leading to the development of a vortex ring within the bubble gas at the outer rim of the decaying vortex sheet. The vortex ring, with its core inside the bubble gas, functions like a bearing system in accelerating the jet.

Prediction of the slurry pressure and inversion of formation characteristics based on a machine learning algorithm during tunnelling in a fault fracture zone

The reasonable setting of the slurry pressure is very important for the safety of shield tunnel construction. In view of the common geological problems of high water pressure and multiple fracture zones in water conveyance tunnels in China, the instability mechanism of the shield excavation face in these formations remains unclear. In this paper, based on the Pearl River Delta Water Resources Allocation Project, various machine learning algorithms are introduced, and the predicted values of the slurry pressure obtained with different machine learning algorithms are evaluated and compared. The optimal machine learning algorithm suitable for this project is determined. Then, using this algorithm, considering the influence of the fault fracture zone, the concept of the formation influence coefficient is proposed, which is used as the input of the prediction model. The influences of the formation coefficient distribution and the influence width of the fracture zone on the accuracy of slurry pressure prediction are examined. Finally, based on this model, the slurry pressure of nearly 100 groups is predicted and verified. The results show that (1) if the influence of the fault fracture zone is considered and a reasonable influence width of the fault fracture zone can be determined, the mean absolute error (MAE) of the predicted slurry pressure is much higher than that of the predictions without considering the fault fracture zone, and the prediction accuracy can be improved by approximately 25%; (2) when the formation influence coefficient is obtained via the method of the theoretical distribution and the influence width of the fault fracture zone is 17 rings, the prediction accuracy of the slurry pressure reaches the optimal value; and (3) through on-site refined investigation, it can be determined that the influence width of the fault fracture zone is 19 rings. The research results of this paper can provide an effective method for setting the shield slurry pressure under high-water pressure conditions in the fault fracture zone.

Mine pressure behavior law of isolated island working face under extremely close goaf in shallow coal seam

In order to study the mining pressure characteristics of the shallow buried coal seam with the same silo working face under the very close mining void zone and the overlying coal rock body, the theoretical analysis is used to determine whether the open-cutting eye bearing layer belongs to the mining under the very close mining void zone or not, based on the numerical simulation of FLAC3D and on-site measurement of the working resistance at the end of the cycle of the working face's hydraulic bracket, It is proposed to divide the mining stress of the working face based on the advancing length of the working face, that is, the high-pressure zone, the transition zone and the low-pressure zone. The results of the study show that: FLAC3D software was used to analyze the stress intensity of the “C” island working face when it was mined back to 50 m, 100 m, 150 m, and 180 m (one time “square”), and the simulation results were imported into the Origin software, which was used to analyze the stress intensity of the working face. The simulation results were imported into Origin software, and the influence range of mining stress was divided into four areas: high-stress area, stress transition area, low-stress area, and "square" stress concentration area. According to the on-site measurement of the working resistance at the end of hydraulic support cycle, the initial pressure step of the working face under the overlying coal rock body is 48.9–55.7 m, with the peak value of 38 MPa, the cycle pressure step is 9.0–23.3 m, with the peak value of 36 MPa, and the dynamic load factor of the working face is 1.14–1.16; relative to the overlying coal rock body, the average decrease of the cycle pressure step is nearly 10% and the average increase of dynamic load factor is 1.14–1.16; compared with that under the overlying coal rock body, the average decrease of the cycle pressure step is nearly 10% and the average increase of dynamic load factor is 1.14–1.16. Compared with the overlying coal rock body, the average decrease of the cycle pressure step under the overlying mining zone is nearly 10%, the average increase of the dynamic load factor is 20%, and there is no obvious regularity and periodicity in the direction of strike, and the working face is divided into three parts along the direction of strike: high-pressure zone, transition zone, and low-pressure zone. Therefore, in the process of mining under the overlying coal rock body, we should strengthen the roadway peripheral rock support and roof and floor management, which is of guiding significance to the mining of similar working faces and mine safety production.

Dynamic response of a pump-turbine runner during turbine's mode starting up

With an increase in head and rotational speed, pumped storage units, particularly the runner, experience higher pressure and centrifugal force. In this study, a combination of the 1D method of characteristics (MOC), 3D computational fluid dynamics (CFD) as well as computational structure dynamics (CSD) was employed to examine the dynamic response of a pump turbine runner during turbine's mode starting up. A detailed analysis of the transient characteristics during this process was conducted. Initially, the high-pressure zone concentrated on the pressure surface of the runner's inlet side. However, this zone gradually expanded over time and shifted to the suction surface. The time-frequency of pressure pulsation showed significant low-frequency and second harmonic frequency components. Different monitoring points exhibited different sensitivities to rotational speed and torque. It can be assumed that runner's blade stress is proportional to the square of the rotational speed. The sensitivity of blade stress related to runner speed and torque provides important results and analysis. P2 is the most sensitive to changes in rotational speed, while P1 is the most sensitive to changes in torque. These findings enhance our understanding of the dynamic behavior of the RPT runner and contribute to potential improvements in design and operation.

Numerical Study on Cavitating Flow-Induced Pressure Fluctuations in a Gerotor Pump

Using the RNG k-ε turbulence model and a full cavitation model, this study numerically simulated cavitating flow-induced pressure fluctuations in a gerotor pump and analyzed the relationship between cavitating flow and pressure fluctuations. The results demonstrate that, as the inlet pressure decreases, the cavitation phenomenon in the gerotor pump intensifies, and the cavitation range in the rotor increases. Some of the vapor even spreads into the oil inlet groove, leading to high vapor content in the chamber that is in contact with the oil inlet groove. The pressure fluctuation characteristics of the flow field in the pump exhibit evident periodic changes. Under different cavitation conditions, the pressure fluctuation amplitude at the monitoring point decreases with increasing inlet pressure, whereas the main frequency of pressure fluctuation remains unaffected by cavitation conditions. The pressure fluctuation amplitude is the strongest at point O1 of demarcation between the low-pressure and high-pressure zones in the chamber, and the volume between the oil inlet groove and the oil outlet groove serves as the main vibration source in the rotor pump. To ensure the stable and efficient operation of the gerotor pump, it is recommended to operate it at a larger NPSH.

Investigating the Role of Fluids in the Source Parameters of the 2013–2014 Mw 5 Matese Seismic Sequence, Southern Italy

Abstract We investigate the variability of Brune stress drop (Δσ), apparent stress (τa), and Savage–Wood radiation efficiency (ηsw=τa/Δσ), in the 2013–2014 Mw 5.0 earthquake sequence that struck the Matese area in the southern Apennines range of Italy. The sequence is clustered in a relatively small crustal volume in the 13–22 km depth range, which is greater than that of background seismicity and normal-faulting sequences that occurred under the range axis, usually located in the first 15 km of the crust. We find high Savage–Wood radiation efficiency values for most of the analyzed earthquakes located in a narrow crustal volume, with values ranging from well above the self-similarity value to very high values as high as 0.55. In addition, a large variability in radiation efficiency (up to 90%) is observed for two similar magnitude events at different depths. Previous studies reported seismic evidence of fluid involvement in the nucleation process of the Matese earthquakes. By integrating our results with crustal geophysical data published recently, we propose that most of the earthquakes characterized by high values of ηsw are nucleated within high pore pressure zones located in the crystalline midcrust of Adria. We reckon that high pore pressure fluids of deep origin played a role in the rupture process and were responsible for the mixed shear-tensile sources inferred from the analysis of the S-wave/P-wave spectral amplitude ratio for most of 2013–2014 earthquakes.