Cavity Collapse Research Articles

Peering inside the peak ring of the Chicxulub Impact Crater—its nature and formation mechanism

The IODP‐ICDP Expedition 364 drilled into the Chicxulub crater, peering inside its well‐preserved peak ring. The borehole penetrated a sequence of post‐impact carbonates and a unit of suevites and clast‐poor impact melt rock at the top of the peak ring. Beneath this sequence, basement rocks cut by pre‐impact and impact dykes, with breccias and melt, were encountered at shallow depths. The basement rocks are fractured, shocked and uplifted, consistent with dynamic collapse, uplift and long‐distance transport of weakened material during collapse of the transient cavity and final crater formation.

Numerical investigation into cavitating flow around a NACA66 hydrofoil with DCM models

Unsteady cavitating flow is difficult to be predicted accurately with traditional RANS turbulence model, especially cavities shedding and evolution from sheet cavity to cloud cavity. In order to determine an appropriate numerical setup for accurate and reliable simulations of cavitating flow, the unsteady-state cavitating flow simulations are performed with the Zwart cavitation model accompanying with the DCM(Density correction model) model based on the RNG k-ε turbulence model after grid convergence test. The details about pressure distribution and cavities evolution around the hydrofoil show that the used models predict the cavities shedding frequency well, the pressure distribution along chord is quasi-periodic. Due to the dynamic of the shed cavities, periodic lift and drag coefficient are pretty clear with both positive and negative values. The cavities formation, breakup, shedding and collapse in a cycle are also presented.

A multi-technology analysis of the 2017 North Korean nuclear test

Abstract. On 3 September 2017 official channels of the Democratic People's Republic of Korea announced the successful test of a thermonuclear device. Only seconds to minutes after the alleged nuclear explosion at the Punggye-ri nuclear test site in the mountainous region in the country's northeast at 03:30:02 (UTC), hundreds of seismic stations distributed all around the globe picked up strong and distinct signals associated with an explosion. Different seismological agencies reported body wave magnitudes of well above 6.0, consequently estimating the explosive yield of the device on the order of hundreds of kT TNT equivalent. The 2017 event can therefore be assessed as being multiple times larger in energy than the two preceding North Korean events in January and September 2016. This study provides a multi-technology analysis of the 2017 North Korean event and its aftermath using a wide array of geophysical methods. Seismological investigations locate the event within the test site at a depth of approximately 0.6 km below the surface. The radiation and generation of P- and S-wave energy in the source region are significantly influenced by the topography of the Mt. Mantap massif. Inversions for the full moment tensor of the main event reveal a dominant isotropic component accompanied by significant amounts of double couple and compensated linear vector dipole terms, confirming the explosive character of the event. The analysis of the source mechanism of an aftershock that occurred around 8 min after the test in the direct vicinity suggest a cavity collapse. Measurements at seismic stations of the International Monitoring System result in a body wave magnitude of 6.2, which translates to an yield estimate of around 400 kT TNT equivalent. The explosive yield is possibly overestimated, since topography and depth phases both tend to enhance the peak amplitudes of teleseismic P waves. Interferometric synthetic aperture radar analysis using data from the ALOS-2 satellite reveal strong surface deformations in the epicenter region. Additional multispectral optical data from the Pleiades satellite show clear landslide activity at the test site. The strong surface deformations generated large acoustic pressure peaks, which were observed as infrasound signals with distinctive waveforms even at distances of 401 km. In the aftermath of the 2017 event, atmospheric traces of the fission product 133Xe were detected at various locations in the wider region. While for 133Xe measurements in September 2017, the Punggye-ri test site is disfavored as a source by means of atmospheric transport modeling, detections in October 2017 at the International Monitoring System station RN58 in Russia indicate a potential delayed leakage of 133Xe at the test site from the 2017 North Korean nuclear test.

A Method for Cavity Scale Estimation Based on Ground‐Penetrating Radar (GPR) Explorations: An Experimental Study

This study described the results of experiments comparing the cavity scales obtained from the GPR exploration with the direct excavation of the identified cavity scales. The first experiment was carried out on the actual roadway, and the additional experiment was carried out on the mock‐up site to prevent the cavity collapse under the ground. It was confirmed that the soil depth of the predicted cavity and the identified cavity was similar, but the predicted cavity scales by GPR exploration overestimated the longitudinal and cross‐sectional widths compared with the identified cavity scales. Based on the correlation between the cavity scales predicted by GPR exploration and the cavity scales identified in the mock‐up test, an empirical formula for estimating the cavity scales was proposed.

Jet formation during the gas penetration through a thin liquid layer

A free bubble reaching the liquid surface usually bursts and then forms a liquid jet with drops ejected. While bubble-mediated jetting is a topic widely studied, few investigations deal with the jet produced by a growing bubble. Here, we report and characterize a novel phenomenon, named periodic bubbling-bursting, that can develop when a continuous stream of gas penetrates through a thin liquid layer. This behavior is complex with a characteristic frequency and can be divided into three stages from bubbling to cavity collapse and jetting. We show that increasing the liquid layer thickness and gas velocity leads to a larger bubble. However, the effect is strongly coupled with the orifice diameter and a scaling law of the bubble rupture radius is derived. Subsequently, we demonstrate that the collapsing cavities exhibit shape similarity and deduce the dependence of pinch-off height and opening angle of the conical cavity on the bubble rupture radius and liquid layer thickness. This enables us to disentangle three different neck-pinching mechanisms at play in pinch-off. Accordingly, gravity shapes the cavity and participates in the capillary wave selection that strongly modulates the jet formation. With increasing layer thickness, the jet first becomes fat and small and then ends up thinner and higher, detaching more and smaller droplets. We present a simple scaling law for the jet velocity which involves the liquid layer thickness to the power 1/2. Finally, a phase diagram for jet breakup and no breakup is built with respect to the initial Weber and Bond numbers.

Estimation of the probability of karst cavities collapse under technogenic cyclic loads below the fatigue limit

The paper deals with the phenomenon of fatigue formation in soils over karst cavities under cyclic loading near the fatigue limit. A method is proposed for determining the stress state of the integumentary earth arising during the considered technogenic cyclic loads. Currently, the assessment of the possibility of karst cavities collapse is performed on the basis of static models, without taking into account the dynamic technogenic load. Especially in the case of slow cyclic loads of low intensity, which do not directly lead to collapse of the soil above the karst cavities. However, these actions change the bearing capacity of soils that are not taken into account at the exploration stage and are not laid in the project documentation for the construction of facilities in karst-dangerous areas. A technique for estimating pre-crisis states based on joint processing of active geoelectric and seismoacoustic geodynamic control signals is proposed.

Cavities "Pit Number" and micro-jets impingements

Cavitation pits and erosion were obtained using the rotating disk device, where a steel disk with cavitation inducers and specimens fixed on it rotates inside a water chamber to provide the cavitating flow. These pits were observed with the aid of a scanning electronic microscopy. Micro-jets resulting from cavity collapse cause damages to solid surfaces. Because they are caused by the micro-jets, these pits are approximate circular. The exponent named pit number was calculated using the pit counting, that is the number of pits by area and by time unit. The influence of flow velocity was also analyzed here, and how greater is the flow velocity, how greater is the pit counting calculated. It was also calculated the distance from the collapsing cavity to the wall, considering a conic micro-jet.

An energy conservative method to predict the erosive aggressiveness of collapsing cavitating structures and cavitating flows from numerical simulations

A new technique is proposed in this study to assess the erosive aggressiveness of cavitating flows from numerical flow simulations. The technique is based on the cavitation intensity approach by Leclercq et al. (2017), predicting the instantaneous surface impact power of collapsing cavities from the potential energy hypothesis (see Hammitt, 1963; Vogel and Lauterborn, 1988). The cavitation intensity approach by Leclercq et al. (2017) is further developed and the amount of accumulated surface energy caused by the near wall collapse of idealized cavity types is verified against analytical predictions. Furthermore, two different impact power functions are introduced to compute a weighted time average of the impact power distribution caused by the cavity collapses in cavitating flows. The extreme events are emphasized to an extent specified by a single model parameter. Thus, the impact power functions provide a physical measure of the cavitating flow aggressiveness. This approach is applied to four idealized cavities, as well as to the cavitating flow around a NACA0015 hydrofoil. Areas subjected to aggressive cavity collapse events are identified and the results are compared against experimental paint test results by Van Rijsbergen et al. (2012) and the numerical erosion risk assessment by Li et al. (2014). The model is implemented as a runtime post-processing tool in the open source CFD environment OpenFOAM (2018), employing the inviscid Euler equations and mass transfer source terms to model the cavitating flow.

Numerical investigation on the unsteady cavitation shedding dynamics over a hydrofoil in thermo-sensitive fluid

Cavitation shedding is of a great practical interest since the unsteady flow features can induce significant fluctuations around the body where cavitation occurs, especially in thermo-sensitive fluid. The present paper numerically studies the unsteady cavitating flows over a NACA0015 hydrofoil in thermo-sensitive fluid of fluoroketone with special emphasis on the cavitation shedding dynamics. Comparisons between numerical predictions and available experimental data are performed to validate the numerical framework and help us further understand the physical feature. The results show that the predicted cavity evolution and pressure distribution are in good agreement with the experimental data. It is observed that the cavitating flows over the hydrofoil undergo more complex unsteady periodic evolution, including the cavity formation, growth, break-off, collapse and shedding. Two propagation patterns of the re-entrant flow appear along the chordwise direction and the spanwise direction, which are responsible for the unsteady cavity evolution. Note that the temperature distribution around the hydrofoil is closely related to the cavity evolution. The temperature around the hydrofoil undergoes a strong evolution that is contributed by the local evaporation and condensation processes. Meanwhile, the thermal effects on cavitating flows are associated with temperature-dependent physical properties of the fluid media. Interestingly, compared to the isothermal cavitation, thermal effects suppress the intensity of cavitation and show a potential to reduce the pressure pulsation peak. Furthermore, there is a strong interaction between the complex vortex structure and cavitation evolution. In one typical cycle, the rotation effect and the shear effect co-dominate the cavity growth, break-off and shedding of the unsteady cavitating flows.

Benign syringomyelia with the abortive type of the course

Syringomyelia is a chronic disease with progressive cavitation and clinical presentations of spinal cord injury. The paper describes clinical cases of a rare benign variant of syringomyelia with spontaneous cavity collapse. The peculiarity of the described clinical cases is childhood-onset of the disease, lack of progression and/or development of myelopathic symptoms, and signs of syringomyelia cavity collapse according to magnetic resonance imaging findings. The authors designate this childhood-onset variant of the disease as abortive. The tendency towards collapse in the cavity in these patients may be due to a single pathogenetic mechanism, which is of interest for a further investigation.

Causes of post-installation penetration of jack-up spudcan foundations in clays.

This paper examines possible causes of additional spudcan settlement after preloading using both centrifuge model tests and small strain finite element analysis, in which spudcan settlement due to cavity collapse, consolidation settlement and settlement due to cyclic loading are incorporated. Back-analyses of seven jack-up rigs in the Gulf of Mexico show that even complete cavity collapse could only explain part of the measured additional settlements in the majority of the cases. Small strain finite element analyses also show that spudcan consolidation settlement is likely to account for even less of the additional settlement than cavity collapse in the sites considered. On the other hand, centrifuge model tests show that large amplitude cyclic rocking has a very significant effect on spudcan settlement, even if half of the preload has been removed. However, this effect cannot be explained by the exceedance of the yield envelope since the loading combination had not exceeded the yield envelope. One possible explanation is the stiffness and strength degradation of the soil under cyclic loading. In view of this, a conservative approach is recommended in instances where large amplitude cyclic rocking, such as that arising from storm loading, is expected shortly after preloading. The presence of lattice legs is found to reduce the spudcan settlement during large amplitude cyclic rocking.

Cavitation Erosion Performance of Steel, Ceramics, Carbide, and Victrex PEEK Materials

Abstract Cavitation erosion has to be taken into consideration during material selection in many industrial sectors, e.g., offshore, marine, and oil and gas, in which components operate under severe working conditions. The cavitation erosion equipment, located at the University of Southampton, uses a vibratory apparatus to compare, rank, and characterize the cavitation erosion performance of materials. This article highlights some of the results obtained from industrial research (consultancy) work employing a Hielscher UIP1000hd 20 kHz ultrasonic transducer (Hielscher Ultrasonics GmbH, Teltow, Germany). The transducer is attached to a titanium horn to induce the formation and collapse of cavities in a liquid, creating erosion (material loss) of the specimen undergoing testing. The results from erosion cavitation testing (in accordance with ASTM G32-16, Standard Test Method for Cavitation Erosion Using Vibratory Apparatus (Superseded)) of two commercially available steels are presented herein and are shown to have less resistance to cavitation when compared to polyether(ether ketone), ceramic, and carbide materials. These materials are presented, along with Nickel 200, which was used to normalize the results. A plot of cumulative erosion versus exposure time was determined by periodic interruption of the test.

Modeling hydrodynamic cavitation in venturi: influence of venturi configuration on inception and extent of cavitation

Hydrodynamic cavitation (HC) is useful for intensifying a wide variety of industrial applications including biofuel production, emulsion preparation, and wastewater treatment. Venturi is one of the most widely used devices for HC. Despite the wide spread use, the role and interactions among various design and operating parameters on generated cavitation is not yet adequately understood. This article presents results of computational investigation into the cavitation characteristics of different venturi designs over a range of operating conditions. Influence of the key geometric parameters such as the length of venturi throat and diffuser angle on the inception and extent of cavitation is discussed quantitatively. Formulation and solution of multiphase computational fluid dynamics (CFD) models are presented. Appropriate turbulence and cavitation models are selected and solved using a commercial CFD code. Care was taken to eliminate the influence of numerical parameters like mesh density, discretization scheme, and convergence criteria. The computational model was validated by comparing simulated results with three published data sets. The simulated results in terms of velocity and pressure gradients, vapor volume fractions and turbulence quantities, and so on, are critically analyzed and discussed. Diffuser angle was found to have a significant influence on cavitation inception and evolution. The length of the venturi throat has relatively less impact on cavitation inception and evolution compared to the diffuser angle. The models and simulated flow field were used to simulate detailed time–pressure histories for individual vapor cavities, including turbulent fluctuations. This in turn can be used to simulate cavity collapse and overall performance of HC device as a reactor. The presented results offer useful guidance to the designer of HC devices, identifying key operating and design parameters that can be manipulated to achieve the desired level of cavitational activity. The presented approach and results also offer a useful means to compare and to evaluate different designs of cavitation devices and operating parameters. © 2018 American Institute of Chemical Engineers AIChE J, 65: 421–433, 2019

Bubble Bursting: Universal Cavity and Jet Profiles.

After a bubble bursts at a liquid surface, the collapse of the cavity generates capillary waves, which focus on the axis of symmetry to produce a jet. The cavity and jet dynamics are primarily controlled by a nondimensional number that compares capillary inertia and viscous forces, i.e., the Laplace number La=ργR_{0}/μ^{2}, where ρ, μ, γ, and R_{0} are the liquid density, viscosity, interfacial tension, and the initial bubble radius, respectively. In this Letter, we show that the time-dependent profiles of cavity collapse (t<t_{0}) and jet formation (t>t_{0}) both obey a |t-t_{0}|^{2/3} inviscid scaling, which results from a balance between surface tension and inertia forces. Moreover, we present a scaling law, valid above a critical Laplace number, which reconciles the time-dependent scaling with the recent scaling theory that links the Laplace number to the final jet velocity and ejected droplet size. This leads to a self-similar formula which describes the history of the jetting process, from cavity collapse to droplet formation.

Transgastric Endoscopic Cystogastrostomy in a Patient With Gastric Sleeve Anatomy

The endoscopic cystogastrostomy has become the standard for management of walled-off pancreatic fluid collections (PFC). However, altered gastric anatomy, such as the gastric sleeve, can present a challenge to endoscopists. As a result, patients with altered gastric anatomy may be referred for surgery, rather than endoscopic intervention. However, surgery is associated with increased costs and length of stay. Here, we report a successful transgastric necrosectomy/ PFC drainage. A 70 year old man with a history of sleeve gastrectomy in 2009 for obesity presented with necrotizing gallstone pancreatitis and subsequent peri- pancreatic fluid collection. After conservative management, the patient was discharged to home, only to present six weeks later with recurrent pancreatitis and poor oral intake. A CT of the abdomen showed an 8 cm pancreatic pseudocyst compressing the gastric sleeve. On upper endoscopy, gastric sleeve anatomy was noted without obstruction. Endoscopic ultrasound (EUS) showed a large 8 cm x 7 cm walled off necrosis adjacent to the stomach with approximately 50% necrosis. Using electrocautery, the hot Axios system (Boston Scientific) was used to access the necrotic collection from the antrum, approximately 3 cm proximal to the pylorus. This site was chosen to avoid intervening vessels seen more proximally and in surrounding areas. Cystogastrostomy was successfully performed with balloon dilation of the stent and placement of pigtail stents. Repeat EGD/EUS one month after Axios placement showed intact gastric anatomy and complete collapse of the prior necrotic fluid collection cavity. To our knowledge, no case reports have been published to date describing a transgastric approach to cystogastrostomy in patients with gastric sleeve anatomy. Endoscopists may shy away from this patient population due to concerns for decreased working space, increased intraluminal pressure and possible disruption of the suture line. One case report notes pseudocyst drainage via the duodenum in a gastric sleeve patient due to the above mentioned concerns. While concerns exist about the feasibility of necrosectomy in post gastric sleeve anatomy, this case shows that transgastric cystogastrostomy can be successfully and safely performed in patients with altered gastric anatomy, such as sleeve gastrectomy. Given the decreased maneuverability, more distal sites, such as the gastric antrum, may be most amenable to the procedure.1408_A.tif Figure 1: Axios stent in the distal gastric wall in post- sleeve gastrectomy anatomy.1408_B.tif Figure 2: 8 cm x 7 cm walled off necrosis adjacent to the stomach.

Roles of distal aspartate and arginine of B-class dye-decolorizing peroxidase in heterolytic hydrogen peroxide cleavage

Dye-decolorizing peroxidases (DyPs) represent the most recently classified hydrogen peroxide–dependent heme peroxidase family. Although widely distributed with more than 5000 annotated genes and hailed for their biotechnological potential, detailed biochemical characterization of their reaction mechanism remains limited. Here, we present the high-resolution crystal structures of WT B-class DyP from the pathogenic bacterium Klebsiella pneumoniae (KpDyP) (1.6 Å) and the variants D143A (1.3 Å), R232A (1.9 Å), and D143A/R232A (1.1 Å). We demonstrate the impact of elimination of the DyP-typical, distal residues Asp-143 and Arg-232 on (i) the spectral and redox properties, (ii) the kinetics of heterolytic cleavage of hydrogen peroxide, (iii) the formation of the low-spin cyanide complex, and (iv) the stability and reactivity of an oxoiron(IV)porphyrin π-cation radical (Compound I). Structural and functional studies reveal that the distal aspartate is responsible for deprotonation of H2O2 and for the poor oxidation capacity of Compound I. Elimination of the distal arginine promotes a collapse of the distal heme cavity, including blocking of one access channel and a conformational change of the catalytic aspartate. We also provide evidence of formation of an oxoiron(IV)-type Compound II in KpDyP with absorbance maxima at 418, 527, and 553 nm. In summary, a reaction mechanism of the peroxidase cycle of B-class DyPs is proposed. Our observations challenge the idea that peroxidase activity toward conventional aromatic substrates is related to the physiological roles of B-class DyPs.

Assisted reproductive techniques in mares.

A wide variety of assisted reproductive techniques (ARTs) are available to aid in managing aspects of equine reproduction. Embryo recovery and transfer can be used to obtain more than one foal per mare per year, and to obtain foals from mares that cannot carry a foal to term. Oocyte recovery and either transfer to the oviduct of an inseminated recipient mare (oocyte transfer), or intracytoplasmic sperm injection (ICSI) and embryo culture can be used to obtain foals from mares with some types of subfertility, such as problems of the tubular tract. ICSI can be used to obtain foals when sperm number or quality is low. Because of its ease of use for the mare owner and efficiency, oocyte recovery and ICSI is being used in some cases for management of normally fertile mares and stallions. Oocytes can be recovered from live mares by the referring veterinarian, and shipped overnight to a laboratory for ICSI, without any decrease in oocyte or embryo viability. In case of unexpected death of a mare, ovaries or oocytes can be transported to the ICSI laboratory for production of embryos. Embryos produced both in vitro and in vivo can be biopsied to determine their genetic makeup before they are transferred. Equine embryos can be vitrified successfully; collapse of the blastocoele cavity allows efficient vitrification of expanded blastocysts. In contrast, cryopreservation of unfertilized equine oocytes still has low success. Genetics of valuable animals can be preserved via nuclear transfer (cloning) and several commercial companies offer this service clinically.

Numerical simulation of transient turbulent cavitating flows with special emphasis on shock wave dynamics considering the water/vapor compressibility

The objective of this paper is to investigate the compressible turbulent cavitating flows with special emphasis on shock wave dynamics, with the water/vapor compressibility taken into account. The simulations are performed by solving the compressible, multiphase unsteady Reynolds-averaged Navier-Stokes equations with Saito cavitation model and SST-SAS turbulence model. The compressibility of both the pure water and vapor is considered by employment of the Tait equation of state for water and ideal gas equation of state for vapor. Results are presented for a 3-D NACA66 hydrofoil fixed at α = 6° and σ =1.25 in partial cavitating flows. Cavity collapse induced shock wave formation and propagation, which is closely related to the compressibility characteristics of cavitating flows, are well predicted. Good performance has been obtained for both the cavity evolution process and cavitation induced pressure signals, especially the cavity collapse induced shock wave emission and its interaction with the attached cavity sheet. The pressure peaks in microseconds accompanying the shock wave are captured. The typical quasi-periodic sheet/cloud cavitation evolution is characterized by the following four stages: (1) the growth of the attached cavity sheet, (2) development of re-entrant flow and attached cavity sheet breakup, (3) attached cavity sheet rolling up and cavity cloud shedding, and (4) cloud cavity collapse, shock wave emission and propagation. The cloud cavity collapse induced shock wave dynamics is supposed to be the major origin of cavitation instabilities.

Modelling of hydrodynamic cavitation with orifice: Influence of different orifice designs

Hydrodynamic cavitation (HC) may be harnessed to intensify a range of industrial processes, and orifice devices are one of the most widely used for HC. Despite the wide spread use, the influence of various design and operating parameters on generated cavitation is not yet adequately understood. This paper presents results of computational investigation into cavitation in different orifice designs over a range of operating conditions. Key geometric parameters like orifice thickness, hole inlet sharpness and wall angle on the cavitation behaviour is discussed quantitatively. Formulation and numerical solution of multiphase computational fluid dynamics (CFD) models are presented. The simulated results in terms of velocity and pressure gradients, vapour volume fractions and turbulence quantities etc. are critically analysed and discussed. Orifice thickness was found to significantly influence cavitation behaviour, with the pressure ratio required to initiate cavitation found to vary by a factor of 10 for orifice thickness to diameter (l/d) ratios in the range of 0–5. Inlet radius similarly has a pronounced effect on cavitational activity. The results offer useful guidance to the designer of HC devices, identifying key parameters that can be manipulated to achieve the desired level of cavitational activity at optimised hydrodynamic efficiencies. The models can be used to simulate detailed time-pressure histories for individual vapour cavities, including turbulent fluctuations. This in turn can be used to simulate cavity collapse and overall performance of HC device. The presented approach and results offer a useful means to compare and evaluate different cavitation device designs and operating parameters.

Acoustically induced cavity cloud generated by air-gun arrays-Comparing video recordings and acoustic data to modeling.

For seismic air-gun arrays, ghost cavitation is assumed to be one of the main mechanisms for high-frequency signal generation. Ghost cavitation signals are weak for seismic frequencies (<300 Hz) and do not contribute to seismic reflection profiling. In the current experiment, the ghost cavity cloud is monitored by a high-speed video camera using 120 frames per second. This is, as far as the authors know, the first convincing photographic evidence of ghost-induced cavitation. In addition to video recording, acoustic signals were recorded with a sampling rate of 312.5 kHz using broadband hydrophones suspended 17 m below the array. The pressure drop around the source array is estimated using air-gun modeling followed by a phenomenological modeling of the growth and collapse of each vapor cavity. The cumulative effect of cavity collapses is modeled based on linear superposition of the acoustic signals generated by individual cavities. The simulated acoustic ghost cavitation signal and the corresponding cavity cloud show good agreement with the field data.