scholarly journals Plankton reach new heights in effort to avoid predators

2012 ◽  
Vol 279 (1739) ◽  
pp. 2786-2792 ◽  
Author(s):  
Brad J. Gemmell ◽  
Houshuo Jiang ◽  
J. Rudi Strickler ◽  
Edward J. Buskey
Keyword(s):  
Water Surface ◽  
High Speed ◽  
Energetic Cost ◽  
Initial Kinetic Energy ◽  
Liquid Environment ◽  
Predator Prey ◽  
Viscous Forces ◽  
Field Recordings ◽  
Perceptive Field ◽  
Important Food Source

The marine environment associated with the air–water interface (neuston) provides an important food source to pelagic organisms where subsurface prey is limited. However, studies on predator–prey interactions within this environment are lacking. Copepods are known to produce strong escape jumps in response to predators, but must contend with a low-Reynolds-number environment where viscous forces limit escape distance. All previous work on copepod interaction with predators has focused on a liquid environment. Here, we describe a novel anti-predator behaviour in two neustonic copepod species, where individuals frequently exit the water surface and travel many times their own body length through air to avoid predators. Using both field recordings with natural predators and high-speed laboratory recordings, we obtain detailed kinematics of this behaviour, and estimate energetic cost associated with this behaviour. We demonstrate that despite losing up to 88 per cent of their initial kinetic energy, copepods that break the water surface travel significantly further than those escaping underwater and successfully exit the perceptive field of the predator. This behaviour provides an effective defence mechanism against subsurface-feeding visual predators and the results provide insight into trophic interactions within the neustonic environment.

Splash formation by spherical drops

2001 ◽  
Vol 427 ◽  
pp. 73-105 ◽  
Author(s):  
LIOW JONG LENG
Keyword(s):  
High Resolution ◽  
Quantitative Data ◽  
Water Surface ◽  
High Speed ◽  
Scaling Laws ◽  
Capillary Wave ◽  
Water Drop ◽  
Qualitative And Quantitative ◽  
High Resolution Images ◽  
The Impact

The impact of a spherical water drop onto a water surface has been studied experimentally with the aid of a 35 mm drum camera giving high-resolution images that provided qualitative and quantitative data on the phenomena. Scaling laws for the time to reach maximum cavity sizes have been derived and provide a good fit to the experimental results. Transitions between the regimes for coalescence-only, the formation of a high-speed jet and bubble entrapment have been delineated. The high-speed jet was found to occur without bubble entrapment. This was caused by the rapid retraction of the trough formed by a capillary wave converging to the centre of the cavity base. The converging capillary wave has a profile similar to a Crapper wave. A plot showing the different regimes of cavity and impact drop behaviour in the Weber–Froude number-plane has been constructed for Fr and We less than 1000.

Whitecap coverage measurements in laboratory modeling of wind-wave interaction in presence of induced wave breaking

2021 ◽  
Author(s):  
Alexander Kandaurov ◽  
Yuliya Troitskaya ◽  
Vasiliy Kazakov ◽  
Daniil Sergeev
Keyword(s):  
Wave Breaking ◽  
Water Surface ◽  
High Speed ◽  
Wind Wave ◽  
Wave Train ◽  
Side Wall ◽  
Channel Cross Section ◽  
Whitecap Coverage ◽  
Wave Channel ◽  
Manual Processing

<p>Whitecap coverage were retrieved from high-speed video recordings of the water surface obtained on the unique laboratory faculty The Large Thermostratified Test Tank with wind-wave channel (cross-section from 0.7×0.7 to 0.7×0.9 m<sup>2</sup> at the end, 12 m fetch, wind velocity up to 35 m/s, U<sub>10</sub> up to 65 m/s). The wind wave was induced using a wave generator installed at the beginning of the channel (a submerged horizontal plate, frequency 1.042 Hz, amplitude 93 mm) working in a pulsed operation (three periods). Wave breaking was induced in working area by a submerged plate (1.2×0.7 m<sup>2</sup>, up to 12 depth, AOA -11,7°). Experiments were carried out for equivalent wind velocities U<sub>10</sub> from 17.8 to 40.1 m/s. Wire wave gauge was used to control the shape and phase of the incident wave.</p><p>To obtain the surface area occupied by wave breaking, we used two Cygnet CY2MP-CL-SN cameras with 50 mm lenses. The cameras are installed above the channel at a height of 273 cm from the water surface, separated by 89 cm. The image scale was 302 μm/px, the size of the image obtained from each camera is 2048x1088 px<sup>2</sup>, which corresponds to 619x328 mm<sup>2</sup> (the long side of the frame along the channel). The shooting was carried out with a frequency of 50 Hz, an exposure time of 3 ms, 250 frames were recorded for each wave train. To illuminate the image areas to the side of the measurement area, a diffuse screen was placed on the side wall, which was illuminated by powerful LED lamps to create a uniform illumination source covering the entire side wall of the section.</p><p>Using specially developed software for automatic detection of areas of wave breaking, the values of the whitecap coverage area were obtained. Automatic image processing was performed using morphological analysis in combination with manual processing of part of the frames for tweaking the algorithm parameters: for each mode, manual processing of several frames was performed, based on the results of which automatic algorithm parameters were selected to ensure that the resulting whitecap coverage corresponded. Comparison of images obtained from different angles made it possible to detect and exclude areas of glare on the surface from the whitecap coverage.</p><p>The repeatability of the created wave breakings allows carrying out independent measurements for the same conditions, for example the parameters of spray generation will give estimations of the average number of fragmentation events per unit area of the wave breaking area.</p><p>The work was supported by the RFBR grants 21-55-50005 and 20-05-00322 (conducting an experiment), President grant for young scientists МК-5503.2021.1.5 (software development) and the RSF grant No. 19-17-00209 (data processing).</p>

Visual Observation of Fragmentation Behavior on Molten Material Jet Surface in Coolant

2008 ◽  
Author(s):  
Yuta Uchiyama ◽  
Yutaka Abe ◽  
Akiko Fujiwara ◽  
Hideki Nariai ◽  
Eiji Matsuo ◽  
...  
Keyword(s):  
Water Surface ◽  
High Speed ◽  
Internal Flow ◽  
Core Material ◽  
Generation Process ◽  
High Speed Camera ◽  
Sodium Coolant ◽  
Molten Material ◽  
Fragmentation Behavior ◽  
Jet Breakup

For the safety design of the Fast Breeder Reactor (FBR), it is strongly required that the post accident heat removal (PAHR) is achieved after a postulated core disruptive accident (CDA). In the PAHR, it is important that the molten core material is solidified in sodium coolant which has high boiling point. Thus it is necessary to estimate the jet breakup length which is the distance that the molten core material is solidified in sodium coolant. In the previous studies (Abe et al., 2006), it is observed that the jet is broken up with fragmenting in water coolant by using simulated core material. It is pointed out that the jet breakup behavior is significantly influenced by the fragmentation behavior on the molten material jet surface in the coolant. However, the relation between the jet breakup behavior and fragmentation on the jet surface during a CDA for a FBR is not elucidated in detail yet. The objective of the present study is to elucidate the influence of the internal flow in the jet and fragmentation behavior on the jet breakup behavior. The Fluorinert™ (FC-3283) which is heavier than water and is transparent fluid is used as the simulant material of the core material. It is injected into the water as the coolant. The jet breakup behavior of the Fluorinert™ is observed by high speed camera to obtain the fragmentation behavior on the molten material jet surface in coolant in detail. To be cleared the effect of the internal flow of jet and the surrounding flow structure on the fragmentation behavior, the velocity distribution of internal flow of the jet is measured by PIV (Particle Image Velocimetry) technique with high speed camera. From the obtained images, unstable interfacial wave is confirmed at upstream of the jet surface, and the wave grows along the jet-water surface in the flow direction. The fragments are torn apart at the end of developed wave. By using PIV analysis, the velocity at the center of the jet is fast and it suddenly decreases near the jet surface. This means that the shear force acts on the jet and water surface. From the results of experiment, the correlation between the interfacial behavior of the jet and the generation process of fragments are discussed. In addition, the influence of surface instability of the jet induced by the relative velocity between Fluorinert™ and coolant water on the breakup behavior is also discussed.

Investigation of LNG Underwater Release and Combustion Behavior on Water Surface

2021 ◽  
Vol 73 (04) ◽  
pp. 35-36
Author(s):  
Chris Carpenter
Keyword(s):  
Wind Tunnel ◽  
Water Surface ◽  
High Speed ◽  
Volume Flow Rate ◽  
Flame Temperature ◽  
Pressure Gauge ◽  
Water Line ◽  
Accidental Release ◽  
Combustion Behavior ◽  
Offshore Technology

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper OTC 30646, “Experimental Investigation of LNG Underwater Release and Combustion Behavior on the Water Surface,” by Yixiang Zhang, Jianlu Zhu, and Youmei Peng, China University of Petroleum, et al., prepared for the 2020 Offshore Technology Conference, originally scheduled to be held in Houston, 4-7 May. The paper has not been peer reviewed. Copyright 2020 Offshore Technology Conference. Reproduced by permission. Most liquefied natural gas (LNG) is transported by ship, creating opportunities for potential hazards to surrounding devices and the environment. Nevertheless, few studies have examined the characteristics of LNG underwater leakage and subsequent vapor flame. The paper considers transportation safety and risk evaluation for LNG, with emphasis on accidental release and vapor flame. Introduction The cryogenic nature of LNG, with a boiling point of -162°C, raises safety concerns with regard to vaporization gas hazards and the potential for pool fires. According to the literature devoted to LNG accidental release and spill, three puncture positions have been proposed: Category I, where the leakage point is above the water line; Category II, where the point is at or close to the water line; and Category III, where the point is below the water line. A need exists to investigate LNG underwater leakage and combustion behavior for risk assessment. This work focuses on experimental research of the dynamic behavior of LNG jet release under water and the immediate burning on the water surface using three orifices and different crosswinds. The main points of investigation include the following: - Liquid-rising process and microbehavior in the orifice - Flame geometry on the water surface under crosswinds - Flame-temperature distribution on the water surface Experimental Setup Experimental Facilities. Experiments were conducted in a rectangular tank measuring 1000 mm long, 500 mm wide, and 500 mm high, which was placed in a wind tunnel. The nozzles have diameters of 1, 3, and 5 mm in the middle of the discharge pipe. An inline cryogenic flow-meter with a measuring range of 0.06 - 0.6 m3/h was used to regulate the volume flow rate with an accuracy of 1.5 %. The pressure measurements were performed by a pressure gauge with a range from 0 to 4 MPa placed on the end of the discharged pipeline. The LNG jets were re-leased vertically into the bulk water at a depth of 0.6 m. Images were recorded using a high-speed video camera system. Experimental Conditions. The window was closed when LNG was released, and the discharged gas was quickly diffused from the wind tunnel. The temperature in the room was 17±1°C and 14±0.5°C in water. The relative humidity was approximately 50%. All tests were conducted three times.

scholarly journals The Hydrodynamics of High Diving

Proceedings ◽  
2020 ◽  
Vol 49 (1) ◽  
pp. 73
Author(s):  
Thibault Guillet ◽  
Mélanie Mouchet ◽  
Jérémy Belayachi ◽  
Sarah Fay ◽  
David Colturi ◽  
...  
Keyword(s):  
Water Surface ◽  
High Speed ◽  
Water Entry ◽  
Air Cavity ◽  
Initial Height

Diving consists of jumping into water from a platform, usually while performing acrobatics. During high diving competitions, the initial height reaches 27 m. From this height, the crossing of the water surface occurs at 85 km/h, and as such it is very technical to avoid injuries. Major risks occur due to the violent impact at the water entry and the formation and collapse of the air cavity around the diver. In this study, we investigate experimentally the dynamics of the jumper underwater and the hydrodynamic causes of injuries in high dives by monitoring dives from different heights with high-speed cameras and accelerometers in order to understand the physics underlying diving.

scholarly journals Hydroelastic effects during the fast lifting of a disc from a water surface

2019 ◽  
Vol 869 ◽  
pp. 726-751 ◽  
Author(s):  
P. Vega-Martínez ◽  
J. Rodríguez-Rodríguez ◽  
T. I. Khabakhpasheva ◽  
A. A. Korobkin
Keyword(s):  
Water Surface ◽  
High Speed ◽  
Hydrodynamic Force ◽  
Early Stage ◽  
The Body ◽  
Plate Motion ◽  
Elastic Behaviour ◽  
Simple Extension ◽  
Wetted Area ◽  
Water Exit

Here we report the results of an experimental study where we measure the hydrodynamic force acting on a plate which is lifted from a water surface, suddenly starting to move upwards with an acceleration much larger than gravity. Our work focuses on the early stage of the plate motion, when the hydrodynamic suction forces due to the liquid inertia are the most relevant ones. Besides the force, we measure as well the acceleration at the centre of the plate and the time evolution of the wetted area. The results of this study show that, at very early stages, the hydrodynamic force can be estimated by a simple extension of the linear exit theory by Korobkin (J. Fluid Mech., vol. 737, 2013, pp. 368–386), which incorporates an added mass to the body dynamics. However, at longer times, the measured acceleration decays even though the applied external force continues to increase. Moreover, high-speed recordings of the disc displacement and the radius of the wetted area reveal that the latter does not change before the disc acceleration reaches its maximum value. We show in this paper that these phenomena are caused by the elastic deflection of the disc during the initial transient stage of water exit. We present a linearised model of water exit that accounts for the elastic behaviour of the lifted body. The results obtained with this new model agree fairly well with the experimental results.

scholarly journals Snap-jaw morphology is specialized for high-speed power amplification in the Dracula ant, Mystrium camillae

2018 ◽  
Vol 5 (12) ◽  
pp. 181447 ◽  
Author(s):  
Fredrick J. Larabee ◽  
Adrian A. Smith ◽  
Andrew V. Suarez
Keyword(s):  
High Speed ◽  
Muscle Power ◽  
Element Analysis ◽  
Predator Prey ◽  
Mantis Shrimp ◽  
Power Amplification ◽  
Form Function ◽  
Function Relationship ◽  
Relationship Of ◽  
Insight Into

What is the limit of animal speed and what mechanisms produce the fastest movements? More than natural history trivia, the answer provides key insight into the form–function relationship of musculoskeletal movement and can determine the outcome of predator–prey interactions. The fastest known animal movements belong to arthropods, including trap-jaw ants, mantis shrimp and froghoppers, that have incorporated latches and springs into their appendage systems to overcome the limits of muscle power. In contrast to these examples of power amplification, where separate structures act as latch and spring to accelerate an appendage, some animals use a ‘snap-jaw’ mechanism that incorporates the latch and spring on the accelerating appendage itself. We examined the kinematics and functional morphology of the Dracula ant, Mystrium camillae , who use a snap-jaw mechanism to quickly slide their mandibles across each other similar to a finger snap. Kinematic analysis of high-speed video revealed that snap-jaw ant mandibles complete their strike in as little as 23 µsec and reach peak velocities of 90 m s −1 , making them the fastest known animal appendage. Finite-element analysis demonstrated that snap-jaw mandibles were less stiff than biting non-power-amplified mandibles, consistent with their use as a flexible spring. These results extend our understanding of animal speed and demonstrate how small changes in morphology can result in dramatic differences in performance.

The Effect of Viscosity Ratio on the Hydrodynamics of Separation From an Oil-Coated Particle

2014 ◽  
Author(s):  
Sasan Mehrabian ◽  
Nima Abbaspour ◽  
Markus Bussmann ◽  
Edgar Acosta
Keyword(s):  
Oil Sands ◽  
High Speed ◽  
Oil Spills ◽  
Viscosity Ratio ◽  
Solid Particles ◽  
Water Separation ◽  
Viscous Forces ◽  
Coated Particle ◽  
Oil Water ◽  
Maximum Separation

Separating oil from solid particles is of great importance in many industrial processes including the extraction of bitumen from oil sands, and the remediation of oil spills. The usual approach is to separate the oil from the solid by introducing another liquid (e.g. water). Separation is often assisted by fluid mixing, and chemical addition. Yet while oil-water-particle separation has been well studied from a chemical standpoint, little research has taken into account the effect of hydrodynamics on separation. In this work, the separation of oil from a single oil-coated spherical particle falling through an aqueous solution was evaluated as a function of viscosity ratio. Solvents were used to modify the viscosity of the oil. The experiments were recorded using a high-speed camera and post-processed using the MATLAB image-processing toolbox. A CFD model has also been developed to study this phenomenon. The results indicate that when viscous forces are strong enough, the oil film deforms, flows to the back of the sphere, and forms a tail that eventually breaks up into a series of droplets due to a capillary wave instability. When the viscosity ratio is small (i.e. the oil is less viscous than the solution), a thin tail forms quickly, the growth rate of the instability is high, and hence the tail breaks very quickly into smaller droplets. When the viscosity ratio is high (i.e. the oil is more viscous), more time is required for the deformation/separation to initiate, and the tail is thicker and breaks more slowly into larger droplets. It was observed that when the viscosity ratio is close to 1, the rate of separation is increased and maximum separation is achieved.

scholarly journals Controlled impact of a disk on a water surface: cavity dynamics

2009 ◽  
Vol 633 ◽  
pp. 381-409 ◽  
Author(s):  
RAYMOND BERGMANN ◽  
DEVARAJ VAN DER MEER ◽  
STEPHAN GEKLE ◽  
ARJAN VAN DER BOS ◽  
DETLEF LOHSE
Keyword(s):  
Particle Image Velocimetry ◽  
Water Surface ◽  
High Speed ◽  
Particle Image ◽  
Boundary Integral ◽  
Infinite Cylinder ◽  
High Speed Imaging ◽  
Image Velocimetry ◽  
Minimal Radius ◽  
Surface Cavity

In this paper we study the transient surface cavity which is created by the controlled impact of a disk of radius h0 on a water surface at Froude numbers below 200. The dynamics of the transient free surface is recorded by high-speed imaging and compared to boundary integral simulations giving excellent agreement. The flow surrounding the cavity is measured with high-speed particle image velocimetry and is found to also agree perfectly with the flow field obtained from the simulations.We present a simple model for the radial dynamics of the cavity based on the collapse of an infinite cylinder. This model accounts for the observed asymmetry of the radial dynamics between the expansion and the contraction phases of the cavity. It reproduces the scaling of the closure depth and total depth of the cavity which are both found to scale roughly as ∝ Fr1/2 with a weakly Froude-number-dependent prefactor. In addition, the model accurately captures the dynamics of the minimal radius of the cavity and the scaling of the volume Vbubble of air entrained by the process, namely, Vbubble/h03∝(1 + 0.26Fr1/2)Fr1/2.

Mechanics of Immersed Particle Collisions

1999 ◽  
Vol 121 (1) ◽  
pp. 179-184 ◽  
Author(s):  
Roberto Zenit ◽  
Melany L. Hunt
Keyword(s):  
High Speed ◽  
Control Volume ◽  
Particle Diameter ◽  
Digital Camera ◽  
Pressure Profile ◽  
Stokes Number ◽  
Elastic Collision ◽  
Initial Kinetic Energy ◽  
Fluid Inertia ◽  
Particle Collisions

The present work investigates the mechanics of particle collisions submerged in a liquid using a simple pendulum experiment. Particle trajectories for different particles in water are measured using a high-speed digital camera and the magnitude of the collision is recorded using a high-frequency-response pressure transducer at the colliding surface. The particle deceleration occurs at distances less than half a particle diameter from the wall. The measured collision impulse increases with impact velocity and particle mass. Comparisons are drawn between the measured pressures and the predictions of basic impact mechanics assuming a perfectly elastic collision. A control-volume model is proposed that accounts for the fluid inertia and viscosity. When a particle approaches a planar surface or another particle, the fluid is squeezed prior to contact, reducing the initial kinetic energy and decelerating the particle. The pressure profile is integrated over the surface of the particle to obtain a force that is a function of the initial particle Reynolds number, Reo, and the ratio of the densities of the particle and fluid phases, ρp/ρf. The model predicts a critical Stokes number at which the particle reaches the wall with zero velocity. Comparisons between the proposed model and the experimental measurements show qualitative agreement.

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