How Multilayered Feathers Enhance Underwater Superhydrophobicity.

During the operation of water-filled pipelines, air can get trapped in the primary water flow in the form of air trapped pockets or moving bubbles. Consequently, entrained air may change the liquid-filled-pipeline system’s transient response significantly. It could have either a beneficial or a detrimental effect on pressure oscillations. The effect is dependent on the spatial dimensions and other physical properties of the pipeline system, the amount, the location of the air pocket(s), and the nature of the transient excitation. This paper provides an overview of modeling the rigid and elastic water columns in a hydraulic pipeline system with an entrapped air pocket. It presents one-dimensional analytical and numerical solutions for the transient filling of the pipeline system, with the numerical model based on the method of characteristics (MOC). The research aims to analyse the effects of water column elasticity under varying system parameters. Simulation results indicate that higher air pocket pressures are achieved in the rigid column model and that the effects of water column elasticity are most pronounced with a small air length ratio and a high initial pressure difference between the reservoir and the air pocket.

CHAPTER 12 - THERMAL INSULATION

Wave impact pressure on vertical walls under breaking waves of various types

Wave impacts on a solid deck in transient wave groups

Entrapped air pockets reduce flood conveying capacity of a surcharged drainage tunnel, and could be released explosively as geysers from vertical dropshafts. Nevertheless, the impact of dropshaft inflow on air pocket expulsion has hitherto not been fully understood. In this work, experiments was performed on a simplified drainage system consisting of a dropshaft with inflow. An air pocket was introduced into the tunnel; its dynamics in the dropshaft was measured with a high speed camera and pressure transducers. A heuristic analysis on the kinematics of the air pocket showed that when the dropshaft inflow is greater than a critical flow dependent on the dropshaft diameter, the increased compression leads to stronger air pocket expulsion, as spewing and/or ejection of air-water mixture. Observed occurrence of the phenomena generally agrees with the prediction. © 2022 American Society of Civil Engineers.

The phenomenon studied in this work is that of an air pocket entrapped by a free surface water wave inside a rectangular tank at a high filling level. The wave, which is a gravity wave, is caused by forced horizontal motion which is constructed in a particular way, in order to entrap an air pocket as it approaches the upper left corner of the tank. As the wave touches the roof, the air is compressed and starts to oscillate. The oscillations resemble, to some extent, the free oscillations of an underdamped mass-spring system, where the mass is related to the generalized added mass effect of the water pressure associated with the air pocket oscillations. The stiffness is due to the compressibility of the air. The reason for the damping or, more generally, the decay of the air pocket oscillations is less understood. Air leakage has been proposed as one possible reason for this decay. In this work, the role of air leakage is found not to be the reason for the decay of the air pocket oscillations, because it is not present during major parts of the impact. However, by drilling holes in the roof of the tank, the effect of leakage during the oscillations is proven to cause decay. To explain the physical source of the decay of the oscillations, damping due to heat transfer to and from the air pocket is investigated through an analytical one-dimensional steady-state model. The damping due to heat transfer is observed to play an important role. The obtained understanding of the mechanisms causing the decay of the air-pocket impact at the upper corner is believed to be relevant to other types of impacts, particularly the entrapment of air pockets on walls by breaking waves.

ABSTRACTThe aim of this research is to assess the maximum transient pressures in a rapidly filling water pipeline containing entrapped air. A three-dimensional computational fluid dynamics model is used to simulate the rapid filling process and to describe the maximum transient pressures for a given range of initial conditions (i.e. air pocket size and initial pressure differences). Results are compared with experimental data. The air pocket size that leads to the highest maximum pressure (critical air pocket size) has been obtained for each initial pressure difference. Two types of behaviours have been identified at the maximum compression of the air pocket: air compression preserving a clear air–water interface and total air compression with the collapse of the air–water interface. The former typically occurs for small air pockets combined with low initial pressure differences, whereas the latter occurs for large air pocket sizes with high initial pressure differences.

We investigated the effect of high hydrostatic pressure on the normal grain growth in 2‐D aluminium foils. The time dependence of the mean grain area was obtained. It was shown that normal grain growth takes place both at atmospheric pressure and under high hydrostatic pressure. The grain growth rate decreases by a factor 1.3 under high pressure. The activation volume for grain growth was 0.13 of the atomic volume. It was shown that high pressure strongly influences the ratio oflow angle boundaries and general boundaries at the early stages of secondary recrystallization.

Transient flows in stormwater systems can lead to damaging and dangerous operational conditions, as exemplified by geysering events created by the uncontrolled release of entrapped air pockets. Extreme rain and associated rapid inflows may result in air pocket entrapment, which causes significant changes in flow conditions and potentially geysering. Stormwater geysers have been studied in different experimental and numerical modeling studies, as well as from limited data gathered within real systems. However, there is still no complete understanding of geysering events, as stormwater system geometries vary considerably. Most past studies involved releasing air from an intermediate shaft, in which a significant fraction of the entrapped air may bypass the release. This work advances the understanding of geysering by considering uncontrolled air release through an upstream shaft or manhole. In such cases, the entire air pocket is released upon reaching the shaft, worsening the occurrence of geysering. Pressure and water level measurements were performed for various combinations of initial water pressure, trapped air pocket volume, and vertical shaft geometries, indicating the higher severity of these geysering events. The results obtained also corroborate previous studies in that the measured pressure heads were lower than the grade elevation. Future studies should include larger-scale testing and the representation of this geometry using CFD.

The phenomenon studied in this work is that of an air pocket entrapped by a free surface water wave inside a rectangular tank at a high filling level. The wave, which is a gravity wave, is caused by forced horizontal motion which is constructed in a particular way, in order to entrap an air pocket as it approaches the upper left corner of the tank. As the wave touches the roof, the air is compressed and starts to oscillate. The oscillations resemble, to some extent, the free oscillations of an underdamped mass-spring system, where the mass is related to the generalized added mass effect of the water pressure associated with the air pocket oscillations. The stiffness is due to the compressibility of the air. The reason for the damping or, more generally, the decay of the air pocket oscillations is less understood. Air leakage has been proposed as one possible reason for this decay. In this work, the role of air leakage is found not to be the reason for the decay of the air pocket oscillations, because it is not present during major parts of the impact. However, by drilling holes in the roof of the tank, the effect of leakage during the oscillations is proven to cause decay. To explain the physical source of the decay of the oscillations, damping due to heat transfer to and from the air pocket is investigated through an analytical one-dimensional steady-state model. The damping due to heat transfer is observed to play an important role. The obtained understanding of the mechanisms causing the decay of the air-pocket impact at the upper corner is believed to be relevant to other types of impacts, particularly the entrapment of air pockets on walls by breaking waves.

BLUE rubber bleb nevus syndrome, a rare vascular malformation involving the gastrointestinal tract, may result in clinically significant acute and chronic bleeding.The bleeding is generally chronic and unremitting, with continual melena necessitating transfusion or surgical management.Definitive surgical management is frustrating because the lesions are usually multiple (often numbering in the hundreds) and may be found anywhere in gut derivatives from the mouth to the anus, most often in the small intestine.The length of the instruments available and the risks of incomplete removal and perforation limit endoscopic treatment such as sclerotherapy or laser photocoagulation as an alternative.[3][4][5][6] Case ReportAn 11-yr-old, 29.6-kg girl with blue rubber bleb nevus syndrome underwent simultaneous upper and lower endoscopy and exploratory laparotomy for resection of multiple vascular lesions.She had experienced gastrointestinal bleeding 2 weeks before admission.After intravenous premedication with midazolam, anesthesia was induced with propofol, fentanyl, and pancuronium.The trachea was intubated with a 6.0-mm cuffed orotracheal tube, and anesthesia was maintained with an air-oxygen mixture and 0.5-1.2%end-tidal isoflurane.Ventilation at a tidal volume of 320 ml and a rate of 9 breaths/min was controlled by a rising-bellows pneumatic anesthesia ventilator.Standard noninvasive monitors were used, and in addition, a radial artery line was placed.An infrared spectrometer was used (Datex Capnomac Ultima; Datex Medical Instrumentation, Tewksbury, MA), and end-tidal carbon dioxide and isoflurane concentrations were recorded.Approximately 3 h into the procedure, after laparotomy, esophagogastroduodenoscopy, and transoral proximal enteroscopy with manual assistance to advance the telescope and while undergoing colonoscopy (Olympus PCF-160-AL video colonoscope; Olympus America Inc., Melville, NY), the patient had a decrease in oxygen saturation to 88 -94%, a decrease in end-tidal carbon dioxide to 22 mmHg, and hypotension (51/31 mmHg; baseline, 93/43 mmHg).Simultaneously,

This paper introduces and experimentally verifies a self-regulating method for reducing the friction losses in large microchannels at high liquid pressures and large liquid flows, overcoming limitations with regard to sustainable liquid pressure on a superhydrophobic surface. Our design of the superhydrophobic channel creates an automatic adjustment of the gas pressure in the lubricating air layer to the local liquid pressure in the channel. This is achieved by pneumatically connecting the liquid in the microchannel to the air pockets trapped at channel wall trough a pressure feedback channel. When liquid enters the feedback channel it compresses the air and increases the pressure in the air pocket. This reduces the pressure drop over the air-liquid interface and increases the maximum sustainable liquid pressure. We define a dimensionless fluidic number, W F = P L D h /?cos?c, which expresses the fluidic energy carrying capacity of a superhydrophobic microchannel. We experimentally verified that our geometry can sustain several times higher liquid pressure before collapsing, and we measured better friction reducing properties at higher W F values than in previous works. This method could be applicable for reducing near-wall laminar friction in both micro- and macroscale flows.

Hybrid membrane system for desalination and wastewater treatment : Integrating forward osmosis and low pressure reverse osmosis

Impact of high water pressure on oil generation and maturation in Kimmeridge Clay and Monterey source rocks: Implications for petroleum retention and gas generation in shale gas systems

To solve the problem of fracturing due to high water pressure when pumping in the diversion tunnel, the mechanism of hydraulic fracturing (HF) in the tunnel under high internal water pressure is studied. A numerical model of HF considering water-rock interaction is established using the PFC2D discrete element simulation software. The HF mechanism of surrounding rock under high internal water pressure is studied, and the development process of hydraulic cracks is obtained. The influence of surrounding rock parameters on fracturing is analyzed and the law between principal stress and crack development is investigated. The high-pressure water injection test under different tunnel diameters is also carried out. Numerical test research shows that under the action of high internal water pressure, the surrounding rock at the cavity wall splits first, and the water entering the crack generates water pressure on the crack sidewall, which in turn generates tensile stress at the crack tip and further causes the crack expansion. The crack length is exponentially related to the internal water pressure. The high internal water pressure decays gradually with the crack extension distance and stabilizes when the crack extension reaches a certain length because the water pressure is less than the tensile strength of the surrounding rock. The fracturing results indicate that the process of HF damage is tensile types, and the increase of cohesion plays a suppressive role in crack opening, while the internal friction angle has little effect on the HF effect. The influence of principal stress on the HF result shows that the direction of HF is along the direction of major principal stress. The major principal stress promotes the cracking, while the minor principal stress inhibits the crack growth. By simulating the water injection test for different hole diameters of the diversion tunnel, it is found that the fracturing distance of the surrounding rock increases approximately linearly with the increase of the hole diameter. The test results can provide a basis for the design and construction of high-pressure tunnels such as pumped storage power plants.