scholarly journals Enhanced drag of a sphere settling in a stratified fluid at small Reynolds numbers

2009 ◽  
Vol 632 ◽  
pp. 49-68 ◽  
Author(s):  
KING YEUNG YICK ◽  
CARLOS R. TORRES ◽  
THOMAS PEACOCK ◽  
ROMAN STOCKER
Keyword(s):  
Time Lapse ◽  
Reynolds Numbers ◽  
Stratified Fluid ◽  
Buoyancy Frequency ◽  
Aquatic Environments ◽  
Fluid Viscosity ◽  
Vertical Fluxes ◽  
Small Reynolds Numbers ◽  
Density Interfaces ◽  
Time Lapse Photography

We present a combined experimental and numerical investigation of a sphere settling in a linearly stratified fluid at small Reynolds numbers. Using time-lapse photography and numerical modelling, we observed and quantified an increase in drag due to stratification. For a salt stratification, the normalized added drag coefficient scales as Ri0.51, where Ri = a3N2/(νU) is the viscous Richardson number, a the particle radius, U its speed, ν the kinematic fluid viscosity and N the buoyancy frequency. Microscale synthetic schlieren revealed that a settling sphere draws lighter fluid downwards, resulting in a density wake extending tens of particle radii. Analysis of the flow and density fields shows that the added drag results from the buoyancy of the fluid in a region of size (ν/N)1/2 surrounding the sphere, while the bulk of the wake does not influence drag. A scaling argument is provided to rationalize the observations. The enhanced drag can increase settling times in natural aquatic environments, affecting retention of particles at density interfaces and vertical fluxes of organic matter.

scholarly journals Effects of dead conspecifics, hunger states, and seasons on the foraging behavior of the purple urchin Heliocidaris crassispina

2020 ◽  
Author(s):  
Dominic Franco C. Belleza ◽  
Yuuki Kawabata ◽  
Tatsuki Toda ◽  
Gregory N. Nishihara
Keyword(s):  
Foraging Behavior ◽  
Field Experiments ◽  
Prey Species ◽  
Sea Urchins ◽  
Time Lapse ◽  
Aquatic Environments ◽  
Feeding Rates ◽  
Avoidance Behaviors ◽  
Time Lapse Photography

ABSTRACTTrophic cascades exerts a powerful effect between predator and prey relationships in an ecosystem. In aquatic environments, the signals associated with predators and predation are used by prey as a cue to avoid encountering predators when foraging for food. These cues are powerful enough to control prey populations and indirectly protect primary producers. We evaluated the effects of cues associated with predation on the purple urchin, Heliocidaris crassispina and examined effects of hunger state and season using time-lapse photography, we conducted a series of manipulative and in situ behavior experiments to determine foraging behavior patterns which demonstrate behavior modification. The results suggest that starved urchins were less sensitive to predation cues when compared to normally fed urchins. Field experiments indicated that 70% of fed urchins fled when exposed to a predation cue (presence of a dead urchin), whereas all starved urchins remained regardless of the cue, supporting the results from the laboratory using the dead urchin and algae treatment cues. Sea urchin activity and feeding rates were lower in winter-spring than in summer-autumn. We suggest that hunger state has a large influence over the behavioral-response of sea urchins, while also being affected by season due to metabolic control. In general, starvation overrides predator avoidance behaviors and exposes prey species to higher risks of predation.

Swimming sheet in a density-stratified fluid

2019 ◽  
Vol 874 ◽  
pp. 210-234 ◽  
Author(s):  
Rajat Dandekar ◽  
Vaseem A. Shaik ◽  
Arezoo M. Ardekani
Keyword(s):  
Wave Amplitude ◽  
Perturbation Expansion ◽  
Eddy Diffusivity ◽  
Reynolds Numbers ◽  
Stratified Fluid ◽  
Mixing Efficiency ◽  
Swimming Velocity ◽  
Aquatic Environments ◽  
Regular Perturbation ◽  
Swimming Efficiency

In this work, we theoretically investigate the swimming velocity of a Taylor swimming sheet immersed in a linearly density-stratified fluid. We use a regular perturbation expansion approach to estimate the swimming velocity up to second order in wave amplitude. We divide our analysis into two regimes of low ($\ll O(1)$) and finite Reynolds numbers. We use our solution to understand the effect of stratification on the swimming behaviour of organisms. We find that stratification significantly influences motility characteristics of the swimmer such as the swimming speed, hydrodynamic power expenditure, swimming efficiency and the induced mixing, quantified by mixing efficiency and diapycnal eddy diffusivity. We explore this dependence in detail for both low and finite Reynolds number and elucidate the fundamental insights obtained. We expect our work to shed some light on the importance of stratification in the locomotion of organisms living in density-stratified aquatic environments.

Pulsatile pipe flow pseudoplastic materials; The flow enhancement for Re ≪ 1

1983 ◽  
Vol 48 (6) ◽  
pp. 1579-1587 ◽  
Author(s):  
Ondřej Wein
Keyword(s):  
Small Parameter ◽  
Pipe Flow ◽  
Quantitative Estimation ◽  
Reynolds Numbers ◽  
Power Law Model ◽  
Viscosity Function ◽  
Small Reynolds Numbers ◽  
Title Problem ◽  
Flow Enhancement ◽  
Method Of Small Parameter

Solution of the title problem for the power-law model of viscosity function is constructed by the method of small parameter in the region of small Reynolds numbers. The main result of the paper is a quantitative estimation of the values of Re, when the influence of inertia on flow enhancement may be quite neglected.

scholarly journals Force distribution on a slender body close to an interface

1981 ◽  
Vol 24 (1) ◽  
pp. 27-36 ◽  
Author(s):  
J.R. Blake ◽  
G.R. Fulford
Keyword(s):  
Reynolds Numbers ◽  
Plane Wall ◽  
Slender Body ◽  
Force Distribution ◽  
Immiscible Liquids ◽  
Flat Interface ◽  
Small Reynolds Numbers ◽  
Rigid Plane ◽  
Limiting Case ◽  
Analytical Expressions

The motion of a slender body parallel and very close to a flat interface which separates two immiscible liquids of differing density and viscosity is considered for very small Reynolds numbers. Approximate analytical expressions are obtained for the distribution of forces acting on the slender body. The limiting case of a rigid plane wall yields results obtained previously.

The Mechanism of Cell-division

1953 ◽  
Vol s3-94 (28) ◽  
pp. 369-379
Author(s):  
M. M. SWANN
Keyword(s):  
Carbon Monoxide ◽  
Cell Division ◽  
Sea Urchin ◽  
White Light ◽  
Time Lapse ◽  
Psammechinus Miliaris ◽  
Energy Store ◽  
Time Lapse Photography

1. Developing eggs of the sea-urchin Psammechinus miliaris were subjected to carbon monoxide inhibition, which was controlled by changing from green to white light. The behaviour of the eggs was recorded by time-lapse photography. 2. If inhibition is applied before the eggs enter mitosis, their first cleavage is delayed by a time which is roughly equal to the period of the inhibition. 3. If the inhibition is applied when the cells have already entered mitosis, they complete mitosis and cleave with little or no delay, but their second cleavage is delayed by a time which is roughly equal to the period of the inhibition. 4. It is suggested that the necessary energy for the second mitosis and cleavage is being stored up during the first mitosis and cleavage, and that this energy store operates like a reservoir which is continually being filled but siphons out when it is full. Once the energy has siphoned out, it carries mitosis and cleavage through, even though the reservoir is not filling up because of carbon monoxide inhibition.

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