Best practice of using air-bubble curtains as part of complex fish protection structures

Приведены результаты исследований работы комплексных рыбозащитных сооружений с использованием воздушно-пузырьковых завес. Дано описание механизма работы комплексных рыбозащитных сооружений и принципа работы воздушно-пузырьковой завесы. На основе гидравлического расчета разработана методика проектирования и применения воздушно-пузырьковой завесы в составе комплексных рыбозащитных сооружений. Приведены результаты исследований по оценке функциональной эффективности построенных комплексных рыбозащитных сооружений. Комплексные рыбозащитные сооружения, имеющие в своем составе запани и воздушно-пузырьковые завесы и работающие в эрлифтном режиме, достаточно эффективно защищают молодь рыб. При правильно подобранных параметрах работы оборудования и выбранном створе размещения сооружений, с учетом гидравлических и технических особенностей водозабора, их эффективность гарантированно превышает нормативные значения. The results of studying the operation of complex fish protection structures with the use of air-bubble curtains are presented. A description of the operating mechanism of complex fish protection structures and the principle of operation of the air-bubble curtain is given. On the basis of a hydraulic calculation, a method for designing and using an air-bubble curtain as part of complex fish protection structures has been developed. The results of estimating the functional efficiency of the built complex fish protection structures are presented. The complex fish protection structures that include debris deflectors and air-bubble curtains and operate in an air-lift mode, effectively protect fish fry. Provided the operating parameters of the equipment and the selected alignment of the structures with account of the hydraulic and technical features of the water intake have been correctly chosen, their efficiency is guaranteed to exceed the standard values.

Research on the influence of bubble curtains on shock wave fields of the underwater explosion

Shock waves, which derive from explosions, generate reflected and refracted waves when propagating in the layered medium with various acoustic stiffness. Depending on the acoustic characteristic of each layer of the medium, properties of reflected and refracted waves will increase or decrease pressures/stresses at the investigated point of medium, compared to influences of explosive shock waves (incident waves) propagated in a homogeneous and isotropic medium. Based on this mechanical physical property, scientists have studied a diversity of solutions decreasing effects of explosive shock waves in various medium such as rock and soil, water, air. However, currently there have not been any comprehensive theoretical studies on the reduction in intensity of the underwater explosion shock wave when interacting with bubble curtain. By using the analytical method and the virtual explosive method, the paper presents the propagation rule of new waves formed when the underwater explosion shock wave interacts with the bubble curtain. The results showed that the more the thickness of the bubble curtain or the higher the bubble content or the longer the distance from the explosive to the curtain, the weaker the intensity of the shock wave when passing through the curtain.

An ensonified bubble curtain blocks 4 species of invasive carp in a laboratory flume but also deters other fish, while sound alone is less effective overall and does not target carp

Four species of invasive carp from Asia are advancing up the Mississippi River through its locks and dams and threatening to damage to its ecosystems. It has been hypothesized that sensory stimuli could be projected into locks to block the movement of these carp. Sound has garnered attention because carp are hearing specialists, so they might be targetable. A recent study demonstrated that when a broadband cyclic sound was projected into an air curtain to create an ensonified bubble curtain (EBC), it was especially effective at blocking bighead and common carp and less effective at blocking a native species that lacked hearing specializations, while sound alone was generally less effective. However, whether an EBC might be similarly and uniquely effective at blocking all species of carp, and what its effects might be on other fishes in general, has not yet been addressed. To answer these questions, this study examined the responses of 10 species of fishes including 4 carps, 2 native hearing specialists, and 4 native non-specialists in a darkened laboratory flume while either a cyclic sound was played on its own or projected into an air curtain. The EBC blocked all 4 carps 9297% of the time without habituation, but 5 native fish were also partially blocked. In contrast, sound alone only blocked 2 carps and affected the other fishes in ways not related to their hearing abilities. An EBC appears well suited to blocking carp invasions, especially if native fish movement is a secondary concern.

Study on the Propagation Law of Water Hammer Wave in Underwater Blasting and the Reducing Effect of Air Curtain on Water Hammer Wave

The harmful effects (water hammer wave, flying stone, and broken quality of concrete) produced in the process of underwater drilling and blasting are the key factors affecting the safety of underwater drilling and blasting. In fact, the harm caused by the water hammer wave is the most significant. As a consequence, it is of great significance to study the propagation law of water hammer waves. Based on the background of the cofferdam demolition project at the inlet section of Shibishan Central Canal in Ningguo City, China, a three-dimensional numerical model was established based on Coupled Eulerian–Lagrangian (CEL) method. Besides, the propagation law of water hammer waves at different water depths with different millisecond times was studied. Meanwhile, the reduction effect of the water hammer wave at different positions of the bubble curtain was analyzed. The results showed that, in the direction of the minimum resistance line of the charge, the attenuation law of the water hammer wave is accorded with the Cole formula and attenuated exponentially. The attenuation speed of the water hammer wave increased at first and then decreased with the increase of the millisecond time. In addition, the attenuation rate of the peak pressure was the fastest when the millisecond interval 30 ms was used. The attenuation of the water hammer wave at different water depths decreased at first and then decreased with the increase of water depth. The attenuation law of the water hammer wave decreased linearly with the increase of the distance between the bubble curtain and the charge. The research results can provide particular guiding significance for similar on-site construction.

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.