Swimming Flashcards
Oscillatory movement?
Repetitive movemnt
How do you move in water?
By using appendages or body surface for thrust and using the active transfer of momentum to the surrounding water
What is the equation for momentum?
Mass x velocity
How to determine the amount of thrust generated?
The rate at which the animal transfers it’s momentum to the surrounding water
What is the equation for thrust?
M x velocity/time
What is drag in water?
Fish are resisted by the movement if flow past it’s own body
What does drag represent?
The rate at which momentum is lost
What is inhertia?
Ability to accelerate/ deccelerate mass
What is friction drag?
Drag forces that depend on the viscosity of water. Viscous interaction of fluid layers that are sheared as they pass the body
What is pressure drag?
Pressure exerted by the liquid on the body. Velocity is faster at the front of the body then the back. Loss of energy is due to energy not being returned as is passes
What is friction drag affected by?
Small animals
What is pressure drag affected by?
Large animals
What is pressure gradient?
Pressure gradient is developed from the front and back of the animals due to flow separation
What is sheared?
The relative deformation or sliding parallel layers of a fluid
What is viscosity?
A measure of resistance fluid has of being sheared
What happens when the more fluid is being sheared?
Higher the viscosity
What is the equation for viscosity?
Stress x time
What is Reynolds number?
Relationship between frictional and inhertial forces
What is the equation for Reynolds number?
Density do the fluid=p × l x velocity/ viscosity
What happens when Reynolds number is equal?
Characteristics are the same
What happens when Re number is low?
Viscous forces dominate
What happens when Reynolds number is high?
Inhertia forces dominate
What is drag coefficient?
Measure of the drag force to the predicted drag force
Due to the density of water what happens to animals?
Encounter much higher levels of dra and swim slower
What do streamline shapes do?
Reduce drag by reduces the amount of energy lost at the wake
What do streamlines represent and how can they be seen?
The see fluid particles at different locations within a flow field and by adding dye/ buoyant particles
Why do streamlines never flow symmetrically?
Due to viscosity
What is free stream?
The speed of water away from the object
Is the velocity of the free stream the same as the velocity of the fish?
Yes
What is no slip condition?
Where the water on the body is stationary and has 0 velocity
What is flow separation?
Due to energy being lost during pressure drag
What is caused during flow separation?
Vortecies
What are vortecies?
Rings of circulation that form due to difference in pressure and friction drag
What is unsteady flow?
Flow that changes overtime
What happens at moment at high re?
Inhertia forces dominate and pressure drag. Better to have a streamlined body
What is the taper?
Long body shape
What Is undulatory swimming?
Waves of bending that travel down the body axis. Waves form an angle of direction
What are lateral forces?
Swinging back and forth
What are the backward forces?
Summed to generate net propulsion force and causes the body to go forward
What is carangiform swimming?
Undulatory swimming in fish.
How to enhance thrust?
Have a larger caudal fin
How to Reduce drag using caudal fin?
Moving it slowly
What shape do caudal fins have?
Lunate shape
What is the angle of attack?
A shallow angle that encounters the oncoming flow
What does the angle of attack do?
Induces the asymmetric flow and causes velocity of flow differential on either side of the hydrofoil
How to create lift?
Net force perpendicular to direction of flow exerts a low pressure on the fin when moving causing a uplift forces. Also cancels out drag
What are most fish tail shapes like?
Symmetrical due to drag propulsion and lift
What is a hecterocorcal tail?
Used by sharks. Lift is achieved by the reduction of the ventricle lobe and the extension of the dorsal.
What is pectoral fin?
Fins on either side of the body used for rowing.
How is the pectoral fin used?
Changed the projected area of the fin in relative with the oncoming flow. This alters the drag produced by the strokes
During the propulsive stroke what is the position of the fin?
The fin is projected back with it orientated perpendicular to it’s movement this maximizes drag and the reaction thrust force
What is the fin movemnt during recovery stroke?
Rotated parallel to flow so the projected area is minimized so drag is low.
How can fin movements be seen?
PLV particle image velocimetry which visualise flow using a laser generated light sheet that illuminates the thin plave of water
How can pectoral fins generate thrust by lift?
By moving fins downwards with respect to the oncoming flow. A lift force is produced that has a forward component that overcomes drag
What is drag based propulsion for
Slow moving
What is lift based propulsion for?
Fast
What are undulating fins?
Used by sea horses. Lateral undulations that are propelled as a traveling wave down the fish.
What is jet based propulsion?
Eject a bolus of water at high velocity from a body cavity
How is the water filled in the cavity?
Muscles lined walls encloses a fluid filled chamber
How is the fluid jetted out?
Contraction of the circumferential muscle fibres decrease the diameter of the chamber and jet the fluid out
How does the cavity re fill with water?
Antagostic band of muscles allows the cavity to expand
How is jet propulsion most effective?
When the mass of fluid is more rather then the acceleration
What moves at low re?
Single celled organisms. Viscous forces dominate
How do low re animals achieve thrust?
Because viscous shearing of the fluid is the sole mechanism thrust is achieved by changing the shape of their propulsors to maximize and minimise drag depending on the stroke
What is cillate?
Seen in low re animals and there propulsors maximise drag and minimise drag
What is flagellates
Another method uses by low re animals where they take advantage of lelical and propagated bending waves
Where is flagella swimming seen?
In eukorytate and prokaryotes. Cellular projections that consists of microtubules linked together by various protein. Dyein.
Where is cillia swimming seen?
In sponges. Hundred of short cillia beat together. Slide with the flow by extending and bending the cillia
When is it possible to swim at intermediate re?
Depending on what speed you are going. Waterboatman use hairy appendages for drag based propulsion.
What is air water interface?
Dolphins in counter surface tension and waves which produce further drag.
What is air water intesurface
Dolphins in counter surface tension and waves which produce further drag.
How is it easy to pass through intersurface
By moving slowly through the waves
What is planing and how is it achieved?
Moving through the waves. Seen in birds. Must produce more acceleration
How can animals stride on water surface?
Animals use surface tension to generate Force equal to or greater than their own weight in order to walk on water.
How is it possible to run on water at a large size?
Take advantage of the mass density of water which exerts a reactive Force when accelerated rapidly.
What do lizards use to run on water?
Webbed feet and air cavity allows foot to be picked up from water.
