Air Bubble Curtain Research Articles

Underwater sound from rotary oscillator and pile driving construction activities - I-205 Bridge over the Willamette River - I-205 Abernethy Bridge, Oregon

The Oregon Department of Transportation (ODOT) is conducting construction work in the Willamette River that involved the installation of piles through the water. There is a potential for impacts to wildlife, primarily fish, due to high noise levels. The project added piers to the existing bridge that consist of 12-foot diameter pile casings and drilled shafts. These casings are installed through rotary-oscillation drilled shafts that extended well below the water. These piles extend 200 feet below the river bottom. A large rotary oscillator was required to install the casings, which was supported on temporary platforms constructed in water. The platforms were supported by hollow 36-inch diameter steel piles. Underwater sounds from rotary oscillators have not been measured extensively in the past. This paper describes the underwater sound levels and characteristics of drilling large diameter casings deep through the substrate using the rotary oscillator. Measurements were also conducted for impact pile driving sounds from installation of the 36-inch diameter piles. The sound measurements evaluated the effectiveness of air bubble curtains meant to reduce sound from impact pile driving and meet permit requirements to minimize exposure of fish to harmful sound levels.

A three-dimensional model of an air bubble curtain in offshore pile driving

A three-dimensional model of an air bubble curtain in offshore pile driving

Air bubble curtain improves the welfare of captive rainbow trout fry and fingerlings

Fish welfare is becoming a priority for the fish farming industry. The search for practical, easy-to-implement methods to promote farmed fish welfare is therefore essential. Environmental enrichment aims to improve the psychological and physiological needs of a captive animal by increasing the complexity of its environment. During previous studies, we observed that fish seemed to be positively affected by short diffusions of air bubbles. In this study, we evaluated the effects of an innovative enrichment strategy consisting of introducing into the tank at the earliest stages of life, a pipe generating a curtain of air bubbles. Using rainbow trout (Oncorhynchus mykiss) as a captive fish model, we compared the short- (∼7 weeks) and long-term (∼21 weeks) effects of this bubble curtain diffused for one hour four times a day (Bubble condition) to a standard condition without bubbles (Control) on fish growth, aggressive and abnormal behaviors, as well as on fish motivation to access a bubble curtain, their emotional responses and their learning abilities. We found that bubble diffusion decreased aggressive and abnormal behaviors during diffusions in both the short-term and the long-term experiments. In the long-term experiment, this decrease was also observed during feedings and neutral periods when no bubble was diffused. Bubbles were found to be attractive for young Control fish (bubble-naive fish) subjected to a motivation test in the short-term experiment. When subjected to the emotional reactivity test, Bubble fish seemed less fearful, exhibiting a lower maximum velocity than Control fish in the long-term experiment only. However, the other behavioral parameters measured during this test, appetite and plasma cortisol levels were similar between treatments, irrespective of the experimental period. The latency to consume the reward observed in the spatial learning test in the long-term experiment was decreased in Bubble fish compared with Control fish, showing enhanced learning abilities in fish that experienced bubbles for 21 weeks. Growth parameters and fin erosion index did not differ between treatments. We conclude that repeated bubble diffusions act as an environmental enrichment for fish, combining physical, occupational, and sensory enrichment via the tactile stimulations provided by the air bubbles. This type of enrichment had a positive impact on the behavior of farmed rainbow trout in the long term, and would make it possible to integrate the notion of “positive welfare” into fish farms, while guaranteeing easy technical maintenance.

A multi-physics approach for modelling noise mitigation using an air-bubble curtain in impact pile driving

Underwater noise from offshore pile driving has raised significant concerns over its ecological impact on marine life. To protect the marine environment and maintain the sustainable development of wind energy, strict governmental regulations are imposed. Assessment and mitigation of underwater noise are usually required to ensure that sound levels stay within the noise thresholds. The air-bubble curtain system is one of the most widely applied noise mitigation techniques. This paper presents a multi-physics approach for modeling an air-bubble curtain system in application to offshore pile driving. The complete model consists of four modules: (i) a compressible flow model to account for the transport of compressed air from the offshore vessel to the perforated hose located in the seabed; (ii) a hydrodynamic model for capturing the characteristics of bubble clouds in varying development phases through depth; (iii) an acoustic model for predicting the sound insertion loss of the air-bubble curtain; and (iv) a vibroacoustic model for the prediction of underwater noise from pile driving which is coupled to the acoustic model in (iii) through a boundary integral formulation. The waterborne and soilborne noise transmission paths are examined separately, allowing us to explore the amount of energy channeled through the seabed and through the bubble curtain in the water column. A parametric study is performed to examine the optimal configuration of the double bubble curtain system for various soil conditions and pile configurations. Model predictions are compared with measured data. The model allows for a large number of simulations to examine different configurations of a single bubble curtain and a double big bubble curtain.

Design and Analysis of a Novel Air Bubble Curtain for Mixing and Aeration in Process Vessels

This article focuses on designing and analyzing a new method for mixing in process vessels. We propose using an air bubble curtain to accomplish the desired mixing. The air bubble curtain used in this study is made of an empty pipe with several holes through which air is pumped, which in turn produces a swarm of bubbles that causes pseudo-turbulent mixing in the tank filled with a liquid solution. A uniform distribution of bubbles within the tank was assured by maintaining a see-saw movement of the air bubble curtain. Mixing inside the tank was quantified by measuring the salt concentration in a laboratory model tank (30 cm × 30 cm × 30 cm) and a pilot-scale tank (200 cm × 100 cm × 100 cm). The optimal flow rates of air and the mixing time in both tanks that can achieve complete mixing were obtained from the experimental results. The proposed air bubble curtain can be of potential use in wastewater treatment, biotechnology, and aquaculture where turbulent mixing is required with minimum energy dissipation per unit mass.

Theoretical analysis and experimental investigation of air-bubble-stream-induced water circulation

Air-bubble curtain is an amount of air injected vertically into a water body. The generation of such a flow and the lack of a continuous interface cannot be described by a smooth mathematical function. Therefore, a two-phase flow model is introduced. A numerical model for the concurrent flow of buoyant bubbles continuously flowing into a 2D water field, and the water flow (generated by the bubbles), is formulated and solved. The two-phase flow model consists of the 2D Navier equations for the water phase (continuous phase) and of the active Lagrangian particles for the simulation of the air bubbles (discrete phase). The coupling of the two phases is done through the continuity and the momentum equilibriums. The numerical solution by explicit second-order Finite Differences (FD) scheme leads from a cold start to steady flow conditions, resolving for the water velocities vector field and the air bubbles’ concentration distribution. The flow configuration is repeated in laboratory conditions, and the velocity field is measured by the particle image velocimetry (PIV) technique. In this work, the numerical two-phase flow model and the hardware aspects of our measurement device are analyzed, followed by the comparison of the numerical and experimental results. This empowers the validity and credibility of the algorithm introduced. Finally, interesting conclusions are drawn regarding the operational use of the model.

Experimental evaluation of two-layer air bubble curtains to prevent seawater intrusion into rivers

Abstract The seawater intrusion (SWI) into rivers can lead to many negative consequences, especially on agricultural activities and live ecosystems in upstream areas of rivers. One solution to prevent SWI is using air bubble curtains (ABCs). The objective of this study is to investigate the optimal location of ABCs and airflows. To this end, several tests with different flow and salinity rates were performed and effect of ABC location on SWI investigated. The results show that, when the ratio of seawater to freshwater densities increased from 1.006 to 1.010, the ratio of saline wedge tip velocity to seawater velocity, airflow to seawater discharge ratio for first and second ABCs are raised 60, 58, and 70%, respectively. Also, when the Froude number (Fr) > 0.031, seawater density changes do not significantly affect the process of SWI. Besides, results of the study show that the closer the ABC is to the river downstream, the higher the airflow rates required. In addition, the optimal value of air bubbles for controlling SWI depends on the density of seawater, where more airflow is required to control denser flows. Finally, the regression equations to predict the SWI parameters based on flow properties were derived.

Study of an air bubble curtain along a wall in water and radiated noise mitigation

The injection of air bubbles into the liquid phase of a freestream flow has several impacts on the flow structure, which depends on the volume and size of the bubbles. This work experimentally investigates the characteristics of air bubble injection into freestream flow using three different injector models. The effects of the bubble curtain on the sound wave attention are studied. A wide range of air injection rates from 2 to 50 standard liters per minute is injected into the freestream water at Froude numbers (Fr) of 50.5, 70.7, and 90.9. The injector model is placed on the sidewall, which is where the bubble curtain is generated. High-speed cameras and an image processing technique are used to visualize and quantify the projected void fraction (PVF) of air bubbles. The sound measurement system consists of two hydrophones. The first hydrophone projects sound waves at discrete frequencies ranging from 17 to 50 kHz, and the second receives the transmitted sound waves. The bubble PVF is observed to increase with the air injection rate as the Froude number increases. There is no significant increment in the thickness of the bubbly curtain when the air injection rate or Froude number increases. The different air injector models produce various air bubble flow patterns, and model II provides the highest PVF. The bubble curtain greatly suppresses sound waves at all frequency ranges. However, the sound attenuation rate varies along the frequency range. The insertion loss increases depending on the PVF of the bubbles, freestream velocity, and frequency range. At a high Froude number of 90.9, the increased air injection rate does not affect the insertion loss. Model II has a relatively higher insertion loss rate at frequencies >26 kHz.

Investigation on factors affecting the performance of the air bubble curtain in preventing the penetration of salinity

Investigation on factors affecting the performance of the air bubble curtain in preventing the penetration of salinity

Experimental Investigation of Air Bubble Curtain Effects on Water Wave Field

This paper studies the effects of an air bubble curtain on surface water waves. Water particle velocities and free surface elevations were measured simultaneously at two cross-shore locations downstream of the air bubble curtain. Measurements were carried out for regular waves using different air bubble curtain configurations. Free surface elevations were measured using resistive gauges and the instantaneous velocities were acquired using an Acoustic Doppler Velocimeter (ADV). The characteristics of the free surface elevation time series, velocity field and turbulence are analyzed and discussed. The free surface elevation was found to be attenuated by the air bubble curtains. The phase averaged velocity profiles also depict the effect of the air bubbles in the flow field by generating milder longitudinal velocities (u) and by increasing the transverse component of the velocity (w). The increase in the turbulence intensity and the different energy spectrum produced by the air bubble curtain is also observed. The experimental results indicate that the thickness of the air bubble curtain and the total air flow rate affects the wave field.

Analysis of underwater shock wave attenuation by air bubble curtain based on bubble shape

Bubble curtain is an important means to protect underwater explosion shock wave. It is of great significance to study the mechanism and technical parameters of bubble curtain for safety and application of underwater blasting. By using high-speed photography technology and video framing processing technology, indoor small underwater bubble curtain model is photographed and analyzed. It is found that the gas curtain is highly discontinuous and inhomogeneous in both the formation process and the interaction process with the underwater explosion shock wave. The gas and liquid are mixed in the air curtain area, and the interface contour is complex and diverse. Air displacement will directly affect the quality of the air bubble curtain. The larger the air displacement, the better the continuity and quality of air curtain. On this basis, consider the influence of bubble shape, interface, and gas-liquid coexistence , programming is carried out through the APDL language that comes with the LS-Dyna finite element software. By setting the variation range of bubble diameter and the minimum difference between bubble diameters, a certain number of bubbles of different diameters are randomly placed to simulate the distribution of bubbles in the real air curtain. The air curtain quality under different gas source pressure can be simulated by changing the number of bubbles in the set air curtain area. It is found that this method can more truly reflect the protection mechanism of air curtain in the protection process of shock wave. Comparing the protective effect of air curtain with different bubble numbers on the same shock wave, it shows that with the increase of bubble number in unit area, the protective effect is more obvious. However, when the number of bubbles reaches a certain number, the overall continuity and stability of the air curtain are basically fixed, and the protection effect tends to be stable.

Research on the plume stability of air bubble curtains under low transverse flow velocity environment in dredging engineering

Air bubble curtain anti-fouling systems, which meet both the environmental standards of suspended solids diffusion and navigation requirements, have unique advantages in environmental dredging technology. Through the bubble plume formed by dense bubble hole jets, the bubble curtain blocks the material exchange between the designated area and other areas in the water to prevent the diffusion of suspended pollutants and protect the water environment. The protection efficiency of the bubble curtain is determined by the fusion of the bubble flow in the rising process and the stability of the plume under the action of a cross flow. The feasibility of a bubble curtain in field engineering is evaluated in this paper. Using two fluid models, the time-varying process of bubble fusion and migration in a bubble plume is analyzed. The dynamic behavior characteristics of the bubble plume are obtained, and the factors influencing the stability of the bubble plume are quantitatively described. The results show that the turbidity of the water body decreases in front of and behind the bubble curtain, which proves that the bubble curtain system is practical in dredging engineering. The number, size range and median value of bubbles in the flume are related to the ventilation pressure and pipe structure. There are three different phenomena in the half-width of the bubble plume at different heights. With the general linear model, it is concluded that the fusion height of the bubble plume is the most sensitive to the change in the bubble tube hole spacing and that the migration characteristics of the bubble plume are most significantly affected by the air flow at the bubble hole. The mechanical analysis of the plume stability shows that the Weber number is the most important parameter affecting the failure of the bubble curtain.

Study of the Sound Escape with the Use of an Air Bubble Curtain in Offshore Pile Driving

Underwater noise pollution generated by offshore pile driving has raised serious concerns over the ecological impact on marine life. To comply with the strict governmental regulations on the threshold levels of underwater noise, bubble curtains are usually applied in practice. This paper examines the effectiveness of an air bubble curtain system in noise reduction for offshore pile driving. The focus is placed on the evaluation of noise transmission paths, which are essential for the effective blockage of sound propagation. A coupled two-step approach for the prediction of underwater noise is adopted, which allows us to treat the waterborne and soilborne noise transmission paths separately. The complete model consists of two modules: a noise prediction module for offshore pile driving aiming at the generation and propagation of the wave field and a noise reduction module for predicting the transmission loss in passing through an air bubble curtain. With the proposed model, underwater noise prognosis is examined in the following cases: (i) free-field noise prediction without the air bubble curtain, (ii) waterborne path fully blocked at the position of the air bubble curtain while the rest of the wave field is propagated at the target distance, (iii) similarly to (ii) but with a non-fully blocked waterborne path close to the seabed, and (iv) air bubble curtain modeled explicitly using an effective medium theory. The results provide a clear indication of the amount of energy that can be channeled through the seabed and through possible gaps in the water column adjacent to the seabed. The model allows for a large number of simulations and for a thorough parametric study of the noise escape when a bubble curtain is applied offshore.

Acoustic insertion loss by a bubble layer for the application to air bubble curtain and air masker

Acoustic insertion loss by a bubble layer for the application to air bubble curtain and air masker

Modelling of wave transmission through a pneumatic breakwater

A theoretical approach is derived to study interaction of linear water waves with an air bubble curtain used as a pneumatic breakwater. Modelling of wave transmission through an aerial barrier is a complex task due to a need to cover processes associated with wave-current interaction, effects of two-phase flows, wave damping, etc.. An initial boundary-value problem is solved by applying an efficient eigenfunction expansion method and a time-stepping procedure. The derived semi-analytical solution is used to study the effect of basic parameters of the model on wave dissipative properties of the pneumatic breakwater. Results show that wave damping by the breakwater is mainly affected by an air flow rate. The increased air discharge results in higher velocities of ascending bubbles and increases aerial barrier width. This leads to a substantial reduction of transmitted wave heights, especially for waves of intermediate length and short waves. In order to verify the applicability of the presented theoretical approach, laboratory experiments are conducted in a wave flume for different wave regimes and pneumatic breakwater characteristics. The analysis of a wave transmission coefficient calculated numerically and measured in the laboratory confirms that the derived model can be used for a certain range of wave conditions.

Noise reduction by the application of an air-bubble curtain in offshore pile driving

Underwater noise pollution is a by-product of marine industrial operations. In particular, the noise generated when a foundation pile is driven into the soil with an impact hammer is considered to be harmful for the aquatic species. In an attempt to reduce the ecological footprint, several noise mitigation techniques have been investigated. Among the various solutions proposed, the air-bubble curtain is often applied due to its efficacy in noise reduction. In this paper, a model is proposed for the investigation of the sound reduction during marine piling when an air-bubble curtain is placed around the pile. The model consists of the pile, the surrounding water and soil media, and the air-bubble curtain which is positioned at a certain distance from the pile surface. The solution approach is semi-analytical and is based on the dynamic sub-structuring technique and the modal decomposition method. Two main results of the paper can be distinguished. First, a new model is proposed that can be used for predictions of the noise levels in a computationally efficient manner. Second, an analysis is presented of the principal mechanisms that are responsible for the noise reduction due to the application of the air-bubble curtain in marine piling. The understanding of these mechanisms turns to be crucial for the exploitation of the maximum efficiency of the system. It is shown that the principal mechanism of noise reduction depends strongly on the frequency content of the radiated sound and the characteristics of the bubbly medium. For piles of large diameter which radiate most of the acoustic energy at relatively low frequencies, the noise reduction is mainly attributed to the mismatch of the acoustic impedances between the seawater and the bubbly layer. On the contrary, for smaller piles and when the radiated acoustic energy is concentrated at frequencies close to, or higher than, the resonance frequency of the air bubbles, the sound absorption within the bubbly layer becomes critical.

Assessing the underwater acoustics of the world's largest vibration hammer (OCTA-KONG) and its potential effects on the Indo-Pacific humpbacked dolphin (Sousa chinensis).

Anthropogenic noise in aquatic environments is a worldwide concern due to its potential adverse effects on the environment and aquatic life. The Hongkong-Zhuhai-Macao Bridge is currently under construction in the Pearl River Estuary, a hot spot for the Indo-Pacific humpbacked dolphin (Sousa chinensis) in China. The OCTA-KONG, the world's largest vibration hammer, is being used during this construction project to drive or extract steel shell piles 22 m in diameter. This activity poses a substantial threat to marine mammals, and an environmental assessment is critically needed. The underwater acoustic properties of the OCTA-KONG were analyzed, and the potential impacts of the underwater acoustic energy on Sousa, including auditory masking and physiological impacts, were assessed. The fundamental frequency of the OCTA-KONG vibration ranged from 15 Hz to 16 Hz, and the noise increments were below 20 kHz, with a dominant frequency and energy below 10 kHz. The resulting sounds are most likely detectable by Sousa over distances of up to 3.5 km from the source. Although Sousa clicks do not appear to be adversely affected, Sousa whistles are susceptible to auditory masking, which may negatively impact this species' social life. Therefore, a safety zone with a radius of 500 m is proposed. Although the zero-to-peak source level (SL) of the OCTA-KONG was lower than the physiological damage level, the maximum root-mean-square SL exceeded the cetacean safety exposure level on several occasions. Moreover, the majority of the unweighted cumulative source sound exposure levels (SSELs) and the cetacean auditory weighted cumulative SSELs exceeded the acoustic threshold levels for the onset of temporary threshold shift, a type of potentially recoverable auditory damage resulting from prolonged sound exposure. These findings may aid in the identification and design of appropriate mitigation methods, such as the use of air bubble curtains, “soft start” and “power down” techniques.

The use of an air bubble curtain to reduce the received sound levels for harbor porpoises (Phocoena phocoena)

In December 2005 construction work was started to replace a harbor wall in Kerteminde harbor, Denmark. A total of 175 wooden piles were piled into the ground at the waters edge over a period of 3 months. During the same period three harbor porpoises were housed in a marine mammal facility on the opposite side of the harbor. All animals showed strong avoidance reactions after the start of the piling activities. As a measure to reduce the sound exposure for the animals an air bubble curtain was constructed and operated in a direct path between the piling site and the opening of the animals' semi-natural pool. The sound attenuation effect achieved with this system was determined by quantitative comparison of pile driving impulses simultaneously measured in front of and behind the active air bubble curtain. Mean levels of sound attenuation over a sequence of 95 consecutive pile strikes were 14 dB (standard deviation (s.d.) 3.4 dB) for peak to peak values and 13 dB (s.d. 2.5 dB) for SEL values. As soon as the air bubble curtain was installed and operated, no further avoidance reactions of the animals to the piling activities were apparent.

エアバブルカーテン (A.B.C.) による成層破壊の基礎的研究

エアバブルカーテン (A.B.C.) による成層破壊の基礎的研究

Fouling control using air bubble curtains: protection for stationary vessels

There is an increasing need by the marine industries for effective non-toxic control of fouling. One of the major limitations of new fouling release coatings is that they cannot protect structures whilst stationary and will not release certain fouling organisms when vessels are operating at low speeds. This is a major problem for slow or infrequently moving vessels and for vessels docked in tropical waters where fouling pressure is extreme. This paper describes novel technology (provisional patent # 2008905482) to protect vessels whilst stationary using air bubble curtains. The results of several panel tests and one hull patch trial demonstrate that this technique is a simple, cost-effective means to complement fouling release coatings whilst vessels are in dock