Underwater Bubble Research Articles

A new experimental methodology to assess the wall pressure generated by a high-voltage underwater Spark-generated bubble

Abstract A new experimental methodology and test system is proposed to assess the wall pressure due to the high-voltage underwater Spark-generated bubble. In the methodology, a Hopkinson bar is used as the sensing element and the pressure signal is obtained based on the strain wave signal. Two main improvements are added to make this method detect the pressure loading due to the bubble collapse. The bubble in the experiments is formed by a discharge of 1500 V 1000 μ F . From the results of the experiments conducted in this paper, the proposed methodology and test system can be used to detect the pressure signal successfully, giving another way to obtain and study the wall pressure due to the underwater bubble collapse.

The annoying dripping tap

The surface of a pool of water hit by a falling drop acts like an acoustic speaker driven by a pulsating underwater bubble.

Bubble dynamics and its applications

Bubbles have very important applications in many fields such as shipbuilding engineering, ocean engineering, mechanical engineering, environmental engineering, chemical engineering, medical science and so on. In this paper, the research status and the development of the bubble dynamics in terms of theory, numerical simulation and experimental technique are reviewed, which cover the underwater explosion bubble, airgun bubble, spark bubble, laser bubble, rising bubble, propeller cavitation bubble, water entry/exit cavitation bubble and bubble dynamics in other fields. Former researchers have done a lot of researches on bubble dynamics and gained fruitful achievements. However, due to the complexity of the bubble motion, many tough mechanical problems remain to be solved. Based on the research progress of bubble dynamics, this paper gives the future research direction of bubble dynamics, aiming to provide references for researches related to bubble dynamics.

Controllable micro-/nanostructures on titanium surface induced by femtosecond laser for underwater air bubble manipulation

Bubbles exist widely in nature and industrial process. The research on bubbles has attracted the attention of many scientists due to the importance of practical application and a large number of studies on bubbles have been carried out since last century. In some cases, the gas in water is often in the form of bubbles, and these bubbles will have some adverse effects on the surface wettability. However, the presence of underwater bubbles also has beneficial effects on natural organisms and human beings. Therefore, it is necessary to study the surface construction of superaerophobicity or superaerophilicity and the manipulation of bubbles. A series of multiscale metallic micro-/nanostructures have been fabricated on typical titanium surface with different morphological features by using self-developed femtosecond laser scanning processing system, which can be controlled through parameters such as laser power, scanning time and scanning intervals. On this basis, the reversible wetting characteristics of multiscale micro-/nanostructures and underwater air bubble manipulation were experimentally investigated by using strategies such as ultraviolet light exposure and heating. The tuning mechanism of reversible wettability was clarified from the perspective of interface chemistry. The research results show that: the original titanium surface wettability has been amplified by multiscale micro-/nanostructures induced by femtosecond laser ablation and solid-liquid contact angle changed to 1° from 48°, being superhydrophilic and bubble contact angle changed to 156° from 136°, being superaerophobic, with bubble sliding angle only being 2° and an extremely low bubble adhesion force. However, under the condition of auxiliary heating, solid-liquid contact angle increased gradually to be superhydrophobic, with liquid sliding angle only being 8°, the surface adhesion force dropping sharply and underwater bubble contact angle rising gradually. The liquid contact angle on the multiscale micro-/nanostructures gradually decreased after the exposure of superhydrophobic surface under the ultraviolet lamp and finally the reversible tuning of superhydrophobic to superhydrophilic could be realized. Furthermore, there is a trend that the reversible tuning characteristics of the liquid contact angle and the bubble contact angle show the opposite way, which is closely related to the moving mechanism of the solid-liquid-gas contact line. The surface micro-/nanostructures with tunable bubble affinity and wettability are prepared by combining the femtosecond laser micromachining technology and the cutting-edge bubble manipulation technology. At the same time, the chemical mechanism of the underwater affinity and wettability of the bubble is studied. The theoretical model of the wettability of the bubble is established and the potential application of the bubble collection is explored so as to solve the problem of the manipulation of the bubble in the aqueous medium. Through our research, the inspirations will be found for the operation of bubbles in industrial production and daily life, which is of great value for dealing with a series of problems caused by bubbles and driving the generation of new bubble manipulation topics. The research results of this paper are also of great significance to the design and fabrication of micro-/nanostructures on typical metal surface and improving the application of metallic surface with reversible wetting characteristics in the fields of underwater bubble manipulation and collection and sewage treatment.

Underwater bubble low frequency source for Arctic acoustic tomography, navigation, and communication

Arctic acoustic tomography requires a broadband source in the frequency range of 5–100 Hz. To meet this requirement, Teledyne Marine suggests applying a seismic source, recently developed for the Marine Vibrator Joint Industry Project. The source is considered to be less harmful for marine inhabitants and gives more precise and higher resolution imaging of the subsurface formations and structures. The coherent source is based on the application of an underwater, gas filled bubble resonator covered by an elastic membrane. The membrane supports high volume displacement. The sources are not sensitive to cavitation and to coupling effects. The fluid dynamics and acoustics of a spherical resonator are defined by the Rayleigh-Plesset equation. The buoyancy deforms the shape of a real bubble from spherical. The 3D simulation and experiments have shown that a cylindrical form is a practical engineering solution. It performances similar to a spherical bubble, keeps its shape and can be towed with a high speed. The Q-factor of a practical bubble resonator is ~10. Two systems are considered to cover a wide frequency band: a tunable resonator and a broadband multi-resonance system. The research proved that the bubble sound source is a practical solution for a frequency below 100 Hz.

A study of bubble collapse pressure pulse waves from small scale underwater explosions near the water surface

Explosive detonators have been used to study the effect of proximity of the water surface on the pressure wave generated by the collapse of an underwater explosive bubble. Transducers at four different depths recorded the pressure pulse, and a low resolution high speed video camera was used to observe the overall dynamics of the bubble. The detonators were fired at selected depths (z) within the range of 6.0–161.3 cm, corresponding to dimensionless depth (γ) values of approximately 0.3–9.0 where γ = z/Rmax, and Rmax is the maximum radius of the bubble during its first pulsation. Analysis of the recorded pressure waves was complicated by the superposition of the emitted wave with its reflection from the water surface. Despite this difficulty there was clear evidence of a dependency of the peak pressure (Pmax) and impulse (I) of the emitted wave on γ. The pressure pulse generated by the deeper events (γ > 3.4) did not appear to be strongly influenced by the water surface, exhibiting only a weak dependence on γ. However, Pmax and I decreased markedly for shallower detonations in the range γ ≈ 1.6–2.8. Imaging results showed that this decrease was associated with migration of the bubble away from the surface during its collapse. A markedly different behaviour was observed when γ was decreased further to 1.1. It was found that although the bubble was still repelled from the surface and I continued to decrease, Pmax increased dramatically. Details of the pulse and imaging results suggested a more complex bubble collapse behaviour at this depth. For shallower values of γ (<0.6) the bubble did not collapse and appeared to breach the water surface and ingest additional gas from the atmosphere.

Research on the estimate formulas for underwater explosion bubble jet parameters

The underwater explosion bubbles have significant applications in the military, but the characteristics of bubble jet near a solid wall are still not very clear. Due to convenience and high efficiency, the boundary integral method is used to study the characteristics of bubble jet in this paper. The shape of bubble jet is simplified to a cylindrical shape when the jet impacts on the opposite surface, so the characteristics of bubble jet are characterized by three parameters, including the cylindrical width (diameter), the cylindrical height and the jet velocity. By adjusting the charge weight W, the detonated depth H and the stand-off distance parameter γ (γ=(H−h)/Rm, where h is the depth of solid wall, and Rm is the maximum bubble radius), the relations of the bubble jet width, height and velocity with them are explored, where three appropriate mathematical models are selected. Finally, based on the least square method, three estimate formulas for bubble jet width, height and velocity are obtained, which have good accuracy to predict the bubble jet width, height and velocity when W = 50–1000 kg, h = 50–500 m and γ = 0.65–1.5. The purpose is to provide a reference for computing the damage of the bubble jet to structures in engineering.

Numerical study on the interaction between underwater explosion bubble and a moveable plate with basic characteristics of a sandwich structure

The dynamics of an underwater explosion bubble interacting with a moveable plate with basic characteristics of a sandwich structure are investigated numerically using boundary element method. The response of sandwich structures is assumed to be a moveable plate with a given velocity profile. The influence of the plate velocity profile, the standoff distance and the scale of the plate on the bubble behaviors are discussed. Within the scope of discussions, the bubble volume and period are a decreasing function of the maximum crushing velocity, the core compression, and the plate dimension, and an increasing function of the standoff distance. Three different regimes of bubble behaviors are distinguished: (1) jet directing towards the plate; (2) the bubble splitting into multiple bubbles or oscillating spherically without jet; (3) jet directing away from the plate. The results indicate that the sandwich plate which can provide larger deformation and larger maximum deformation velocity is beneficial for altering the jet direction to direct away from the plate.

The Sound Produced by a Dripping Tap is Driven by Resonant Oscillations of an Entrapped Air Bubble

This paper details an investigation into the characteristic ‘plink’ sound produced by water droplets impacting a liquid surface, such as those falling from a dripping tap. Modern high-speed video and audio capture techniques have been applied to this problem for the first time. Previous literature investigating the underwater sound produced has been validated, with the key sound producing feature both above and below the water confirmed to be the entrainment of a small underwater air bubble. Recorded sound frequencies have been shown to align with the theoretical natural oscillation frequency of the entrained bubble, confirming this to be the driver of the characteristic ‘plink’ sound. For the first time these oscillations of the entrained bubble have been directly observed on video footage. An investigation into the effect of underwater reverberation showed that the airborne sound field is not simply the underwater field propagating through the water-air interface, as had previously been assumed. An alternative hypothesis is that the oscillating bubble induces oscillations of the water surface itself, giving a more efficient mechanism by which the underwater bubble drives the airborne sound field. A model for this new hypothesis produces good agreement with experimental data.

Simulations of the dynamics and interaction between a floating structure and a near-field explosion bubble

The simulation of the interaction between a surface ship with a near-field underwater explosion bubble is performed using the three-dimensional (3D) boundary integral method for simulating the physical process of the bubble coupled with the finite element method for calculating the structural response in conjunction with the doubly asymptotic approximation for handling the fluid-structure interaction problem. An indirect procedure is proposed solely for investigating the effect attribute to the free surface elevation on the bubble dynamics and the structural response through a comparison of two different 3D boundary integral numerical methods. The present model is validated by comparing the numerical simulation results with the experimental data. For a near-field explosion, the results indicate significant effects due to the free surface elevation on the bubble dynamics and transient response of the ship hull, including modification of the bubble pulsation period and the pressure distribution on the wet surface, which is the key initiator of the destructive action. The transient structural response characteristics including the global and local response of the hull ship subjected to an underwater explosion bubble are investigated in detail and the related mechanism behind the phenomena are also analyzed.

An Integrated Janus Mesh: Underwater Bubble Antibuoyancy Unidirectional Penetration.

Gas bubbles are a powerful tool with applications in particle visualization, spacers, actuation pistons, and pressure sensors. Controlling the transportation of bubbles in the liquid phase is a challenge that needs to be solved in many industrial processes, such as in the pipe transportation of fluids, the corrosion of ocean vessels, and the control of foaming processes. There are few existing materials capable of the antibuoyancy unidirectional transportation of bubbles. Here, a Janus superwetting mesh is fabricated by integrating aerophilic (AL) and superaerophobic (SAB) surfaces. The resulting composite mesh achieves underwater bubble antibuoyancy unidirectional penetration. In aqueous solution, bubbles pass through the mesh from the SAB side to the AL side, but are blocked from passing through in the opposite direction. This Janus mesh can be considered to be a bubble diode, so is convenient for use in underwater bubble unidirectional transportation. This work may promote the development of advanced materials for gas bubble directional transportation and separation in aqueous media.

Numerical investigation on global responses of surface ship subjected to underwater explosion in waves

Transient fluid-structure interaction (FSI) has always been a challenging problem in ship mechanics. Underwater explosion and its highly nonlinear impact on nearby structures are more complicated. In this paper, the global responses of a surface ship subjected to an underwater explosion in waves are numerically investigated considering the nonlinear coupling between the fluid and structure solvers. The fluid field is modeled with the boundary element method (BEM), while the potential decomposition theory is adopted to take the surface waves into account. The global responses of the ship structure are modeled with the mode superposition method. Then a FSI model is established using the mode decomposition method of the acceleration potential to consider the interaction. An underwater explosion experiment is carried out to validate the numerical model, which shows good agreement between the numerical and experimental results. With the presented model, the interactions between a ship and an underwater explosion bubble both in still water and waves are simulated. The dynamics of the ship global responses and the influence of the waves are analyzed which shows noteworthy nonlinearity.

Switchable Underwater Bubble Wettability on Laser-Induced Titanium Multiscale Micro-/Nanostructures by Vertically Crossed Scanning.

We present here a kind of novel multiscale TiO2 square micropillar arrays on titanium sheets through vertically crossed scanning of femtosecond laser. This multiscale micro-/nanostructure is ascribed to the combination of laser ablation/shock compression/debris self-deposition, which shows superaerophobicity in water with a very small sliding angle. The laser-induced sample displays switchable bubble wettability in water via heating in a dark environment and ultraviolet (UV) irradiation in alcohol. After heating in a dark environment (0.5 h), the ablated titanium surface shows superaerophilicity in water with a bubble contact angle (BCA) of ∼4°, which has a great ability of capturing bubbles in water. After UV irradiation in alcohol (1 h), the sample recovered its superaerophobicity in water and the BCA turns into 156°. The mechanism of reversible switching is believed as the chemical conversion between Ti-OH and Ti-O. It is worth noting that our proposed switching strategy is time-saving and the switch wetting cycle costs only 1.5 h. Then we repeat five switching cycles on the reversibility and the method shows excellent reproducibility and stability. Moreover, laser-induced samples with different scanning spacing (50-120 μm) are fabricated and all of them show switchable underwater bubble wettability via the above tunable methods. Finally, we fabricate hybrid-patterned microstructures to show different patterned bubbles in water on the heated samples. We believe the original works will provide some new insights to researchers in bubble manipulation and gas collection fields.

Underwater Superaerophobic and Superaerophilic Nanoneedles-Structured Meshes for Water/Bubbles Separation: Removing or Collecting Gas Bubbles in Water.

Water/bubbles separation has great practical significance, which can avoid the harm caused by underwater bubbles or cleverly collect useful gas bubbles in water. Here, a Cu(OH)2‐nanoneedles‐structured rough copper mesh is fabricated by a one‐step chemical reaction. The original rough mesh shows superhydrophilicity in air and superaerophobicity in water. The underwater superaerophobic mesh has great anti/removing‐bubbles ability in water. In contrast, the rough mesh switches to superhydrophobicity in air and superaerophilicity in water after further being modified with fluoroalkylsilane. The underwater superaerophilic mesh can absorb bubbles and allow bubbles to pass through the mesh. Based on the superhydrophilic/superaerophobic mesh and the superhydrophobic/superaerophilic mesh, a strategy to remove gas bubbles from the water pipe is proposed, and an in‐water bubbles‐collection device is also designed. It is believed that these two kinds of mesh will have more applications in controlling the behavior of underwater bubbles.

Reversible switch between underwater superaerophilicity and superaerophobicity on the superhydrophobic nanowire-haired mesh for controlling underwater bubble wettability

Controlling the underwater bubble wettability on a solid surface is of great research significance. In this letter, a simple method to achieve reversible switch between underwater superaerophilicity and underwater superaerophobicity on a superhydrophobic nanowire-haired mesh by alternately vacuumizing treatment in water and drying in air is reported. Such reversible switch endows the as-prepared mesh with many functional applications in controlling bubble’s behavior on a solid substrate. The underwater superaerophilic mesh is able to absorb/capture bubbles in water, while the superaerophobic mesh has great anti-bubble ability. The reversible switch between underwater superaerophilicity and superaerophobicity can selectively allow bubbles to go through the resultant mesh; that is, bubbles can pass through the underwater superaerophilic mesh while are fully intercepted by the underwater superaerophobic mesh in a water medium. We believe these meshes will have important applications in removing or capturing underwater bubbles/gas.

Effect of crossflow velocity on underwater bubble swarms

We investigate the effect of crossflow velocity on submerged bubble plumes or swarms by employing the use of high-speed photography and an image-processing method to measure bubble rise velocities. Particle image velocimetry (PIV) was used to accurately determine the crossflow freestream velocity as well as boundary layer information. We varied the gas flow rates from 2 to 25 L/min. This range exceeds those of previous studies we could find in the open literature which were mostly less than 5 L/min and involved isolated bubbles. Combined with the crossflow velocities, this resulted in the investigation of a wide range of flow conditions providing a database of 36 experimental data points and constitutes a substantial addition to the bubble swarm/crossflow literature. Because our experiments involved larger gas flow rates than previously reported, we had to develop a digital image-processing algorithm using standard functions in Matlab to measure swarm rise velocities, and angles of inclination under crossflow. Results were validated against reported data at similar experimental conditions. It was established that increasing freestream velocity strongly suppressed bubble rise velocities and resulted in bubble breakup. Relationships for predicting rise velocity and inclination angle were derived as non-dimensional functions of the crossflow velocity, fluid properties and inlet gas flow rates. These showed good agreement with the current as well as reported experimental data.

Numerical investigation of an underwater explosion bubble based on FVM and VOF

Dynamics of the underwater explosion (UNDEX) bubble in a free field is numerically investigated in the present paper using a compressible two-phase flow solver. The finite volume method (FVM) is adopted for discretization of the Navier-Stokes equations. The volume of fluid (VOF) method is utilized to capture the bubble-water interface. Validation is carried out against the Gilmore model for a spherical bubble and an experiment for the aspherical UNDEX bubble subjected to buoyancy. The bubble expansion, collapse, high-speed liquid jet and the rebounding are well predicted. Meanwhile, the propagating pressure waves can be clearly captured. The pressure and velocity fields within and surrounding the bubble are described in detail. For the UNDEX bubble subjected to strong buoyancy effect, the jet impacts on the opposite side in a small region rather than at a single point. Splitting of some tiny bubbles can be observed in the jet impact area. The toroidal bubble undergoes splitting and coalescence subsequently. Additionally, non-uniform distribution of the velocity of the gas in the bubble could be observed almost in the entire bubble life while the pressure field inside the bubble is quite uniform. Lastly, the jet dynamics as well as the migrating behaviors of the bubble under the effect of buoyancy is carefully investigated.

Experiments with the Underwater Bubble Low Frequency Sound Resonator

An infra-sound source with a resonator in the form of an underwater bubble made from an elastic material is a simple engineering solution. The elastic membrane supports high volume displacement and a large radiation aperture. The Rayleigh-Plesset equation defines the dynamics of a spherical bubble including surface tension and viscous effects. The shape of a large bubble deforms due to gravitational effects. Its internal pressure oscillations are comparable with the difference of gravity pressure and these effects are part of its dynamics. The real Q-factor of a practical bubble is smaller than theoretical. The underwater bubble resonator was studied experimentally in the pool and at the Woods Hole Oceanographic Institution’s dock. The research includes the 3D finite-element analysis and its comparison with the experimental data. The study gave the real values for the Q-factor, resonance frequencies and sound pressure levels. The experimental resonator has good performance with a maximum SPL 190 dB at the resonance frequency 6-12 Hz. It was shown that a cylindrical resonator can be towed with a speed of 8 knots. The research proved that this is a practical approach for a coherent low frequency sound source, which can find applications in a marine seismic survey.An infra-sound source with a resonator in the form of an underwater bubble made from an elastic material is a simple engineering solution. The elastic membrane supports high volume displacement and a large radiation aperture. The Rayleigh-Plesset equation defines the dynamics of a spherical bubble including surface tension and viscous effects. The shape of a large bubble deforms due to gravitational effects. Its internal pressure oscillations are comparable with the difference of gravity pressure and these effects are part of its dynamics. The real Q-factor of a practical bubble is smaller than theoretical. The underwater bubble resonator was studied experimentally in the pool and at the Woods Hole Oceanographic Institution’s dock. The research includes the 3D finite-element analysis and its comparison with the experimental data. The study gave the real values for the Q-factor, resonance frequencies and sound pressure levels. The experimental resonator has good performance with a maximum SPL 190 dB at the...

Effects of underwater bubble CPAP on very-low-birth-weight preterm newborns in the delivery room and after transport to the neonatal intensive care unit.

The development of less invasive ventilatory strategies in very-low-birth-weight (VLBW) preterm newborns has been a growing concern in recent decades. This study aimed to measure differences in the clinical progression of preterm newborns using two distinct periods in a university hospital: before and after using underwater bubble continuous positive airway pressure (ubCPAP). This is a retrospective study of VLBW preterm newborns with gestational ages less than or equal to 32 weeks admitted to the neonatal intensive care unit. The time series was divided into two groups: a pre-CPAP group ( n = 45) and a post-CPAP group ( n = 40). The post-CPAP group had fewer resuscitations, required fewer surfactant doses, spent fewer days on mechanical ventilation, and demonstrated less of a need for fraction of inspired oxygen > 30%. UbCPAP is an easy to use, minimally invasive, and effective ventilatory strategy for VLBW preterm newborns that can be used in environments with limited resources. Thus, adopting this simple strategy as part of a service organization and health policy can positively impact outcomes.

Simulation of bubble dynamics oscillating near a circular aperture made in a curved rigid plate using boundary element method

The dynamics of a spark-generated bubble oscillating near a circular aperture made in a curved rigid plate is investigated using boundary element method. The influences of the standoff distance and the aperture size on the bubble behavior are studied. Based on the relative value of these parameters, four distinct oscillation scenarios would be recognized: (I) two simultaneous (inward and outward) jets, (II) an inward jet directing towards the opening, (III) quasi or fully spherical oscillation without jet and (IV) an outward jet directing away from the opening. In the scenarios with jet, the jet can be formed in the first oscillation cycle or in the second expansion phase, depending on the standoff distance and opening size. A diagram is provided representing four distinctive regions distinguished by the mentioned four different oscillation scenarios. The results also indicate that the damage caused by an underwater explosion bubble to discontinuous structures might not be as serious as to non-perforated structures since the bubble jet would possibly not be formed or this jet is directed away from the opening. The effect of opening on the bubble dynamics might be utilized in the design of the protection tanks on vessel and other practical underwater structures.