Free Ascent Research Articles

Advancements in the Understanding of Single‐Bubble Dynamics: Integrated Experimental and Simulation Studies

Because of wake instability, bubbles always ascend along an unstable path, which is not considered when simulating their movement in steel refining and continuous casting systems. Utilizing the 3D shadow image method, a quantitative characterization of the bubble trajectories is conducted to establish a bubble path oscillation model considering the zigzag lateral movement of bubbles due to asymmetric wake shedding. This model is incorporated into a rectilinear bubble motion model within the Lagrangian framework and then used to simulate the free ascent of single bubbles within the 2.15–2.55 mm range. The predicted bubble ascent velocities and trajectories agree well with the experimental. The spatial position, velocity, acceleration, forces, volume swept by bubbles, and bubble residence time are discussed. The results shown that the dominant force in the horizontal direction is the lateral force, followed by the drag and virtual mass force. Compared to the rectilinear path model, the volume swept by bubbles with initial diameters of 2.15, 2.25, 2.34, 2.45, and 2.55 mm in this model increases by 30.8%, 32.0%, 34.0%, 31.5%, and 29.6%, respectively. These findings help accurately predict the path of bubbles and also may contribute to a better understanding of bubble dynamics in bubble metallurgy and clean steel production.

A Study on the Influence of Unsteady Forces on the Roll Characteristics of a Submarine during Free Ascent from Great Depth

The maximum diving depth of modern submarines has always been increasing. Although this has been useful and in some cases necessary, it usually comes with some risks. For instance, when a submarine encounters an emergency situation that requires immediate ascent from great depths, the situation becomes more dangerous, especially due to its rolling characteristics. To investigate the effect of unsteady forces during free ascent motion of submarines at great depths on submarine rolling, in this study, the SST-DDES model combined with the overset grid technique was used for the numerical simulation of a submarine free ascent. Water tank experiments for free ascent were conducted to validate the numerical approach, which confirmed the reliability of the numerical method. Following this, the CFD method was employed to conduct an initial exploratory investigation into the free ascent motion of deep-submergence submarines. The free ascent motion of submarines at great depths under five different degrees of freedom combinations was studied. The computational results indicated that submarines are more prone to roll over during free ascent at great depths. At a depth six times the length of the submarine, the maximum roll angle underwater reaches 22.8°. In addition, unsteady rolling moments, lateral forces, and yawing moments have a significant effect on submarine rolling, intensifying the tendency to roll. Furthermore, it was observed that the vertical hydrodynamic attack angle β is related to the rolling stability of the submarine, such that a moderate decrease in β is beneficial for the rolling stability. The numerical calculation method and preliminary research findings can provide theoretical support for controlling the ascent motion of real submarines.

Effects of different simulated submarine escape depths by free ascent in animal models.

Objective: If a damaged submarine cannot be rescued in time, it is necessary to carry out a submarine escape by free ascent. Decompression illness is the greatest threat to the safety of submariners. The maximum depth at which a safe escape can be carried out is unknown. This study intends to explore the maximum safe escape depth by observing the effects of simulated submarine escape at different depths on animal models. Methods: We evaluated pulmonary function indexes, blood gas values, blood cell counts, the myocardial enzyme spectrum, coagulation parameters, and proinflammatory cytokine levels in rats, electrocardiographic activity in rabbits after simulated 150-m, 200-m, 220-m, and 250-m submarine escape by free ascent. Results: An escape depth of 150m did not cause significant changes in the indicators. An escape depth of >200m led to pulmonary ventilation and gas diffusion dysfunction, hypoxemia, myocardial ischemia, and activation of the fibrinolytic and inflammatory systems. The magnitudes of the changes in the indicators were proportional to escape depth. Conclusion: An escape depth of 150m in animal models is safe, whereas escape at > 200m can be harmful.

Analytical presentation of the separation of dense suspension for the extraction of amber

New devices were developed to increase the extraction of amber, especially with the size less than 5 mm, which can not be extracted at the present time. They are made on the basis of a hydraulic spiral classifier using vibration and bubbling with air bubbles. Analytical formulas are needed to calculate such devices, in first, for free motion of particles, then the constrained motion, and then to determine the effect of vibration and bubbling on the speed. This article discussed the first part of the problem – hydrodynamics of free movement of amber and quartz particles in a mixture of amber sand-clay rocks with water. The technique and formulas of calculation of kinematic viscosity and speed of movement are given. The dependences of the kinematic viscosity and the speed of free deposition of quartz and free ascent of amber on the density of the suspension for particles size less than 5 mm are obtained. The non-linear character of the dependence of the speed of ascent of amber from the density of the suspension is set. The results obtained are the basis for the calculation constructional parameters and technological characteristics of the hydraulic classifiers of new construction.

Decreased Incidence of Pulmonary Barotrauma After Discontinuation of Emergency Free Ascent Training.

Because a significant association between training to perform emergency free ascent (EFA) and the occurrence of pulmonary barotrauma (PBT) was demonstrated in 2006, the Belgian Underwater Federation (BUF) decided to discontinue this procedure. An evaluation was needed 10 yr after the implementation of this change. All medical records with a diagnosis of PBT that occurred in Belgium from November 2006 to September 2016 were prospectively collected. Data on the proportion of in-water skills training dives were obtained from BUF. A total of 5 cases of PBT were identified, significantly down from 34 cases in the previous 10-yr period. Of those cases, four occurred during training dives (two during ascent training). Analysis of the case files furthermore showed that two should have been medically disqualified from diving. Compared with the retrospective cohort (1995-2005), incidences are significantly reduced from 0.83 to 0.078/10,000 training dives and from 3.33 to 0.11/10,000 ascent-training dives; concomitantly, the incidence of PBT in nontraining dives also was reduced (from 0.0042 to 0.0014×10-4/10,000 dives), possibly because less divers undertake the EFA procedure in case of a technical incident and have learned to solve the problem differently. Discontinuation of emergency free ascent training was associated with a reduction in the incidence of PBT in the 10-yr follow-up period. We observed a significant decrease of PBT during training dives, confirming the hypothesis that EFA training in its previous form did not contribute significantly to diving safety.Lafère P, Germonpré P, Guerrero F, Marroni A, Balestra C. Decreased incidence of pulmonary barotrauma after discontinuation of emergency free ascent training. Aerosp Med Hum Perform. 2018; 89(9):816-821.

Simulation of Ascent Rule for the Individual Escape Suit

During the individual escape, free ascent is the only way to decompression. While the men are situated in the deep pressure, the velocity of ascent, the time of getting to balance become the most important factors for escape. The paper use mathematical methods, consult the hydrodynamics parameter which educed by experiment, simulate the ascent rule while the men are in the individual escape suit, and calculate the ascent velocity, acceleration, balance time of different weight, and compare the simulation result with the experiment , which can prove the veracity of simulation.

Pulmonary Barotrauma in Divers During Emergency Free Ascent Training: Review of 124 Cases

Experience from treating diving accidents indicates that a large proportion of divers suffering from pulmonary barotraumas (PBT) or arterial gas embolism (AGE) were engaged in training dives, specifically emergency free ascent (EFA). We tried to verify this relationship and to calculate, if possible, the risk associated with normal recreational dives, training dives, and EFA training dives. All diving accidents treated at the Centre for Hyperbaric Oxygen Therapy (Brussels, Belgium) from January 1995 until October 2005 were reviewed. Data on the average number of dives performed and the proportion of in-water skills training dives were obtained from the major Belgian dive associations. A total of 124 divers were treated, of whom 34 (27.4%) were diagnosed with PBT. Of those, 20 divers (58.8%) had symptoms of AGE. In 16 of those, EFA training exercise was deemed responsible for the injury. The association between EFA training and PBT proved to be very significant, with an odds ratio of 11.33 (95% confidence interval: 2.186 to 58.758). It was possible to calculate that a training dive (0.456 to 1.36/10,000) carries a 100 to 400 times higher risk, and an ascent training dive (1.82 to 5.46/10,000 dives) a 500 to 1500 times higher risk for PBT than a non-training dive (0.0041 to 0.0043/10,000 dives). This study confirms a significant association between EFA training dives and the occurrence of PBT.

Buoyant balaenids: the ups and downs of buoyancy in right whales.

A variety of marine mammal species have been shown to conserve energy by using negative buoyancy to power prolonged descent glides during dives. A new non-invasive tag attached to North Atlantic right whales recorded swim stroke from changes in pitch angle derived from a three-axis accelerometer. These results show that right whales are positively buoyant near the surface, a finding that has significant implications for both energetics and management. Some of the most powerful fluke strokes observed in tagged right whales occur as they counteract this buoyancy as they start a dive. By contrast, right whales use positive buoyancy to power glides during ascent. Right whales appear to use their positive buoyancy for more efficient swimming and diving. However, this buoyancy may pose added risks of vessel collision. Such collisions are the primary source of anthropogenic mortality for North Atlantic right whales, whose population is critically endangered and declining. Buoyancy may impede diving responses to oncoming vessels and right whales may have a reduced ability to manoeuvre during free ascents. These risk factors can inform efforts to avoid collisions.

Breathing volumes and gas exchange during simulated rapid free ascent from 100 msw

The crew of a disabled submarine can be rescued by means of free ascent through the water to the surface. Pulmonary gas exchange was studied during simulated rapid free ascent in subjects standing immersed to the neck in a pressure chamber. The pressure was rapidly increased to 1.1 MPa [100 meters seawater (msw)] followed by decompression at 0.03 MPa/s (3 msw/s). Effective inspired tidal volume, as estimated by an Ar dilution method, fell gradually to zero during decompression from 20 to 0 msw. Directly determined expired tidal volumes were increased up to two to three times at the time of return to surface pressure compared with pre- and postdecompression volumes. End-tidal PCO2 was increased on compression and fell to a nadir of 3.4 kPa (25 Torr) at the time of return to surface pressure. Thus, intrapulmonary gas expansion caused simultaneous inspiratory hypoventilation and expiratory hyperventilation. If O2-enriched gas is to be used to reduce the risk of decompression sickness, it should be administered early during decompression to alter the intrapulmonary gas composition. The time course of arterial PCO2 changes as reflected by end-tidal values during short-lasting compression/decompression would act to promote inert gas supersaturation in the brain.

Gait characteristics of children during free ascent climbing performances

The purpose of this study was to examine the characteristics of children's climbing performances with an emphasis placed on determining the appropriate dimensions of climbing apparatus as shown by the gait patterns adopted by the users. Seventy-two male and female children were selected and assigned to one of eight groups according to their age. The population comprised children whose ages ranged between 1.5 and 5.5 years with groups designated every 6 months (total eight groups). Each subject performed three trials consisting of an ascent of a 1.83 X 1.83 m climbing structure. The wooden climbing frame incorporated a regular matrix of handholds/footholds with a between rung difference of 0.15 meters. On command, the subjects climbed from a target area centered at the bottom of the frame to the top where the parent or guardian was located to offer encouragement. all trials were filmed using one 16 mm motion-picture camera. A large mirror placed in the field of vision permitted the recording of both the rear and lateral views. The temporal and displacement characteristics of a representative gait cycle for each subject were analyzed. The results provided little evidence to indicate either an age related or overall preferred consistent climbing gait. However, the most common method of ascent (38.92%) involved an order of peripheral segment movement of the right leg followed by right arm then left leg followed by left arm. A statistical analysis utilizing analysis of variance procedures with Newman Keuls post-hoc evaluation ( p<0.05) conducted on the temporal characteristics of a gait cycle during a trial by each subject revealed: (1) that both the absolute contact and airborne times for the upper and lower limb segments were greater for the subjects between 1.5 and 2.5 years than for the subjects between 4.5 and 5.5 years, (2) that there existed an age dependent systematic decrease in the relative contact times for the lower limb segments, (3) that the age dependent decreases in the absolute lower limb airborne times were relatively greater than the corresponding decreases in the contact times with a significant linear trend being recorded. While the preferred horizontal spacing was found to be approximately 0.15 meters for all subjects, the preferred inclined spacing between consecutive handholds/footholds was found to be age dependent.

An unusual case of air embolism precipitated by decompression.

THE occurrence of air embolism during submarine escape training has been very infrequent. In 67,000 ascents from depth in the Escape Training Tank at New London during the past five years, only 7 cases have occurred. One of these, which terminated fatally, has previously been reported.1 The current technic for individual escape from a submerged submarine is called buoyant-assisted, free ascent. The person escaping enters a special isolated compartment, which is then flooded from the sea to about chest level. With compressed air the pressure within the compartment is increased to equal the outside sea pressure. The escape hatch can . . .

Light-Weight Refractometer

This paper describes a seven-pound device that indicates changes in the refractive index of a gas. Because it is capable of detecting refractivity fluctuations that are as small as one part per million, it is useful in studying the irregularities in the refractive index of the troposphere that are important in short radio-wave transmission. The refractometer is self-contained, so that it may be used in controlled or in free ascent through the atmosphere. The device is essentially a high frequency oscillator whose frequency is governed by the capacitance of an air sensing condenser. Special provision is made for reliable operation over the wide range of temperatures normally found in the troposphere.

Principles and Technique of Free Ascent in Submarine Escape

Principles and Technique of Free Ascent in Submarine Escape