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For simulating fluid transients in pipelines with moving water-air interface, a one-dimensional Lagrangian particle model with second-order accuracy in both space and time is proposed. In this model, the meshless smoothed particle hydrodynamics (SPH) is used to approximate the spatial derivatives in the waterhammer equations, and the symplectic leap frog scheme is used for time integration. The nonlinear convective terms – which are mostly neglected in classical water hammer – are taken into account. The details of the Lagrangian particle method, boundary condition treatment and artificial viscosity for remedy of numerical oscillations due to shocks are presented. Two typical cases including transient flow with entrapped air pocket and rapid pipe filling are simulated and the results are validated against available experimental and numerical solutions, which has wide applications for flow simulation in drainage networks. To test the shock capturing ability of the developed model, the classical water hammer problem is also simulated and good agreement with the theoretical solution is obtained. It is shown that the proposed Lagrangian particle model is capable of solving waterhammer equations with moving boundaries and that it has high potential for multiphase transient flows.

Visual and pressurized pipeline systems with single- and multi-undulation layouts were used to study experimentally and analyze theoretically the transient characteristics of water-air two-phase flow during water fillings in undulation pipelines based on the combination action analyses of both the communicating pipe and the gravity of the water-air two-phase flows in the descending pipe. For the single undulation pipeline, the complex two-phase flow-pattern evolutions including full pipe flow and stratified flow for low, medium, high water-filling velocity cases, respectively, lead to a great difference in transient pressure, flow pattern and the water-filling duration. Especially for low and medium water-filling velocity cases, the hydraulic theories related to hydraulic drop and hydraulic jump were employed to investigate the entrapped air pocket evolutions in the descending pipe, and the mechanism of negative pressure at the top of the undulation pipes was analyzed. For the same multi-undulation pipeline, due to the different elevations of the three undulation points along flow direction, namely three different types of pipeline layout, high-medium-low case (high elevation undulation point, medium one, and low one), low-medium-high and high-low-medium ones, their water-filling durations are significantly different, i.e., approximately 80.02 s, 227.34 s and 617.78 s. Meanwhile, there are significant differences in flow patterns in water filling, namely larger entrapped air pockets in three descending pipes for the high-medium-low case, entrapped air pockets in the first two descending pipes and open channel stratified flow in the last one for low-medium-high case, some bubbles in three descending pipes for the high-low-medium case.

The traditional one-dimensional (1D) model often fails to accurately predict the dynamic pressure response of large offline air pockets during transients, due to a lack of comprehensive understanding of the underlying mechanisms of transient interaction with offline air pockets. This study investigated dynamic behavior and energy dissipation of offline air pockets through experiments and numerical models. Experimental pressure responses were predicted using a 1D-3D coupling model, which presented superior performance compared to traditional 1D model. The 1D-3D coupling model was further utilized to investigate the air-water interface, internal energy and turbulence distribution of offline air pockets. The results reveal that the stability of the air-water interface depends on the decelerating distance of the jet in offline tube, explaining the instability phenomenon with lower water levels observed in experimental snapshots. The internal energy pattern suggests different energy dissipation mechanisms compared to the inline air pockets. The distribution of turbulence intensity and effective thermal conductivity indicates significant additional energy dissipation at the inlet and outlet of offline neck. By incorporating a minor head loss term for offline neck into traditional 1D model, the pressure response aligns well with the results obtained from  1D-3D coupling model under different flow rates and air volumes.

Fe-6.5wt%Si alloy possesses excellent electromagnetic properties, including high resistivity, low iron loss, high magnetic permeability, and almost zero magnetostriction coefficient, making it an ideal core material for low-noise and low-iron-loss applications. However, the higher silicon content promotes the formation of ordered phases B2 and D03, which significantly increases the material’s brittleness. Traditional rolling processes are inadequate for producing Fe-6.5wt%Si alloy thin ribbons. Planar Flow Casting, on the other hand, has a high cooling rate, which can suppress the formation and growth of ordered phases in high-silicon steel, reduce the material’s brittleness, and produce Fe-6.5wt%Si alloy thin ribbons. However, Fe-6.5wt%Si alloy ribbons produced by Planar Flow Casting have gaps on the as-cast surface and micro-roughness defects on the free surface at small scales. Simulation results indicate that the gap on the as-cast surface is caused by the formation of air-pocket due to the entrapment of gas into the puddle. The presence of air-pocket can affect the heat transfer between the melt and the cooling roll, consequently influencing the fluid velocity and causing fluctuations on the free surface, and even leading to fracture of the thin ribbon. The wetting behavior of the melt on the cooling roll surface influences the entrainment of air-pocket, and favorable wetting conditions can reduce the entrainment of air-pocket, thereby improving the surface quality of the alloy thin ribbon.

Air pockets can become trapped at high points in pipelines with irregular profiles, particularly during service interruptions. The resulting issues, primarily caused by peak pressures generated during pipeline filling, are a well-documented topic in the literature. However, it is surprising that this subject has not received comprehensive attention. Using a model developed by the authors, this paper identifies the key parameters that define the phenomenon, presenting equations in a dimensionless format. The main advantage of this study lies in the ability to easily compute pressure surges without the need to solve a complex system of differential and algebraic equations. Numerous cases of filling operations were analysed to obtain dimensionless charts that can be used by water utilities to compute pressure surges during filling operations. Additionally, it provides charts that facilitate the rapid and reasonably accurate estimation of peak pressures. Depending on their transient characteristics, pressure peaks are either slow or fast, with separate charts provided for each type. A practical application involving a water pipeline with an irregular profile demonstrates the model’s effectiveness, showing strong agreement between calculated and chart-predicted (proposed methodology) values. This research provides water utilities with the ability to select the appropriate pipe’s resistance class required for water distribution systems by calculating the pressure peak value that may occur during filling procedures.

The air is trapped in spillways, pipelines, conduits, and channels which leads to air-water flow and the accumulation of air bubbles that can form large air pockets. These air pockets can cause significant structural failures due to the dynamic consequences they induce. Consequently, this paper investigates the incidents and events that occur due to air pocket formation and measures and strategies to mitigate these issues. The investigation was conducted independently based on a literature review. The literature review focused on interpreting the mechanisms involved in the production of air bubbles and air pockets in pipelines. The research comprehensively examined all occurrences and adverse outcomes associated with the formation of air pockets, including the slug flow phenomena, air entrainment, and air blowout incidents. Moreover, this study reviewed all measures and strategies to mitigate the consequences resulting from air bubbles, such as slug flow management, air management techniques, air pocket explosion, and air entrainment. The results of the literature review showed a lack of predictions of air pocket consequences. Furthermore, the majority of the research conducted relies on prior datasets, observations, and experimental tests. However, these studies are unable to adequately demonstrate the limitations associated with the occurrence of air pockets in hydraulic structures. This is mostly owing to the challenges and constraints in managing the boundary conditions within physical models. Also, all experimental studies addressed the air pocket formation only in pipelines, and there was a lack of studies on the consequences of air pockets in hydraulic structures such as spillways and tunnel systems. Additionally, there was a lack of studies that address CFD techniques using developed software such as ANSYS; these techniques have proven their abilities to predict several consequences caused by air pockets. CFD techniques can simulate any complex problem correlated to air pocket events. This study can address air pocket consequences in any hydraulic structure: Morning Glory spillways, key piano spillways, and drop shaft spillways. Furthermore, this technique can adopt various parameters and extend measures and strategies to mitigate air pocket formation in hydraulic structures. The paper recommends the use of the CFD technique for further studies in the field of air pocket mitigation. Also, as a result of spillway structures, especially Morning Glory spillways, the paper recommends executing further research to predict consequences resulting from air pockets in hydraulic structures and investigate more remedial strategies to mitigate these consequences.

Entrapped air pockets can cause failure in water distribution systems if air valves have not been appropriately designed for expelling air during filling manoeuvres performed by water utilities. One-dimensional mathematical models recently developed for studying this phenomenon do not consider the effect of blocking columns inside water pipelines. This research presents the development of a mathematical model for analysing the filling process in a pipeline with an undulating profile with various air valves, including blocking columns during starting-up water installations. The results show how different air pocket pressure peaks can be produced over transient events, which need to be analysed to ensure a successful procedure that guarantees pipeline safety during the pressure surge occurrence. In this study, an experimental set-up is analysed to observe the behaviour of two blocking columns during filling by comparing the air pocket pressure pulses.

This paper focused on the sessile droplet freezing and ice adhesion on aluminum with different wettability （hydrophilic, com- mon hydrophobic, and superhydrophobic surfaces, coded as HIS, CHS, SHS, respectively） over a surface temperature range of -9℃ to -19℃. It was found that SHS could retard the sessile droplet freezing and lower the ice adhesion probably due to the interfacial air pockets （IAPs） on water/SHS interface. However, as surface temperature decreasing, some IAPs were squeezed out and such freezing retarding and adhesion lowering effect for SHS was reduced greatly. For a surface temperature of-19℃, ice adhesion on SHS was even greater than that on CHS. To discover the reason for the squeezing out of lAPs, forces applied to the suspended water on IAPs were analyzed and it was found that the stability of IAPs was associated with surface mi- cro-structures and surface temperature. These findings might be helpful to designing of SHS with good anti-icing properties.

Water utilities are concerned about the issue of pipeline collapses, as service interruptions lead to water shortages. Pipeline collapses can occur during the maintenance phase when water columns compress entrapped air pockets, consequently increasing the pressure head. Analysing entrapped air pockets is complex due to the necessity of numerically solving a system of differential equations. Currently, water utilities need more tools to perform this analysis effectively. This research provides a numerical solution to the problem of entrapped air pockets in pipelines which can be utilised to predict filling operations. The study develops an analytical solution to examine the filling process. A practical application is shown, considering a 600 m long pipeline with an internal diameter of 400 mm. Compared with existing mathematical models, the results of the new analytical equations demonstrate their effectiveness as a new tool for computing the main hydraulic and thermodynamic variables involved in this issue.

Background: Endometrial cancer is the most common disease of the female reproductive system. Vaginal cuff brachytherapy (VCB) has intrinsic advantages compared to external beam therapy when treated with radiation. A single-channel cylinder is a standard applicator in VCB. The present study aims to estimate a change in the dose to vaginal mucosa due to air pockets between the cylinder and vaginal mucosa by calculating with the Acuros BV algorithm and comparing it to the Task Group 43 (TG-43) algorithm. Materials and Methods: Patients who presented with air packets were included retrospectively. For each patient, three plans were created: the first plan used TG-43, the second plan used dose recalculation with Acuros BV, and the third plan was generated by re-optimization by Acuros BV. On the same axial computed tomography image, the point doses at the cylinder's surface and the displaced mucosa were recorded and the ratios were then estimated. Results: The average volume of air pockets was 0.08 cc (range of 0.01-0.3 cc), and 84% of air pockets displaced the vaginal mucosa by ≥0.2 cm. The average ratios of dose were 0.77 ± 0.09 (1 standard deviation [SD]) and 0.78 ± 0.09 (1 SD) for TG-43 and Acuros BV algorithms, respectively. Due to the air pocket, mucosa received a reduced dose by an average of 22.72% and an average of 23.29% for TG-43 and Acuros BV, respectively. The maximum displacement of mucosa and the ratio of doses were negatively correlated for both. In the Optimized Acuros BV plan, total dwell time increased by 1.8% but no considerable change in the dose ratios. Conclusion: The calculated dose of mucous membrane forced out of the cylinder surface by air pockets by the Acuros BV algorithm was nonsignificantly different from TG-43. Therefore, even in the presence of air pockets, the TG-43 algorithm for calculating the VCB dose is appropriate.