Swimming locomotion Flashcards
What is periodic (steady or sustained) swimming?
- Cyclic repetition of the propulsive movement
- Traversing large distances at more or less constant speed
What is transient (unsteady) swimming?
- Rapid starts, escape maneuvers and turns at the last millisecond to catch prey/avoid predators
What is body and caudal fin locomotion?
body bends into a backward-moving propulsive wave
What is Medial and paired fin swimming?
Undulatory or rowing motions of the fins to create thrust
in what three ways does the transfer of momentum from the fish to the surrounding water occur while swimming?
- Lift
- Drag
- Acceleration reaction
How is lift formed with regard to swimming
Pressure differential caused by asymmetries in the flow:
–> Pressure on one side of hydrofoil is greater than on the other
What is friction drag with reguard to fish?
Friction between fish and the boundary layer of water
- -> arises as a result of viscosity in the water in areas of flow with large velocity gradients
- -> depends on wetted surface area (Sw), speed and nature of boundary layer
How is pressure drag created by fish?
Distortion of flow around solid bodies and depends on their shape
How does a fish create the pressure drag called induced drag?
Fins generate vortices unrelated to thrust. Depends largely on the shape of fin
What is the acceleration reaction regarding fish?
The inertial force associated with accelerating the water surrounding a body or appendage
What does the acceleration reaction depend on?
- Acceleration
- changing velocity
- mass of the object
- the shape of the object
What is the acceleration reaction?
F= Drag of body + Inertia of added mass
Added mass = Volume of water accelerated with the body or appendage
How does the acceleration reaction respond to increasing velocity? Decreasing velocity?
Increasing velocity = inertial forces are in the same direction as drag
Decreasing = inertial forces are in opposite direction of drag
What are the two main forces of thrust production?
- Added mass
2. Lift-based (vorticity) method
How does the lift-based (vorticity) method work?
Tail creates awake that has reverse directional rotation to that of the von karmen street vortex trail. This generates thrust as a result.
What happens at low reynolds number?
Cd is high, viscosity dominates and there are few to no vorticies
What happens at high reynold number?
Cd decreases and inertia dominates. Vorticies create pressure drag but skin friction is lowered.
What does newtons third law mean with regard to fluid moving down?
The force imparted by fluid moving down is equal and opposite to the lift force
What is froude efficiency?
Power out / Power in = (Power supplied by the jet, paddle, etc) / (Power paid by the engine to supply the increase in momentum)
= 2V1 / (V2 + V1)
What is strouhals number?
(fA) / U
f = tail beat frequency
U = average forward velocity
A = wake birth
What is a normal strouhals number?
0.25 < St < 0.35
In an anguilliform swimmer, caudal elements generate more forward thrust for what two reasons?
- Tail moves farther:
- -> moves larger amounts of fluid
- -> F= ma
- -> Newton’s third law (equal and opposite reaction) - Tail elements push more directly forward. (vector points more directly towards direction of motion)
What limits the forward speed of anguilliforms?
The body wave moves faster than the forward swimming speed so to increase forward speed they must first increase wave propagation speed.
What are the advantages of anguilliform swimming?
Very maneurverable and better at acceleration from zero velocity than Thunniforms.
- Swim slower than carrangiforms and thunniforms
Summarize Anguilliform swimming (8)
- Body undulates from head to tail
- More than one wavelength on body
- More caudal elements contribute to larger thrust forces
- Lateral forces are large and tend to cancel each other out
- Body wave travels faster (V) than forward speed (U)
- Low efficiency if defined by U/V
- Froude efficiency may be quite high
- Most certainly speed is limited
Thrust and propulsive efficiency depend on what? (4)
- Aspect ratio of the caudal fin
- -> High aspect ratio fins lead to improved efficiency because they induce less drag per unit of lift or thrust produced - Shape of the caudal fin
- -> A sharp-curved leading edge is beneficial because delays boundary layer separation for high thrust values (allows high angle of attack) - Fin stiffness
- -> A higher degree of stiffness increases thrust generation capability - Oscillatory motions of the fin
- -> Struhal number
Why do caudal elements generate more forward thrust? (2)
- Tail moves farther
- > moves larger amount of liquid
- > F=ma
- > Newton’s 3rd law (equal/opposite reaction) - Tail elements push more directly forward (vector points more directly towards direction of motion)
how do anguilliform swimmers use a drag based form of forward motion?
->Fluid is accelerated down the eel’s body as it produces thrust
-> Drag along the eel’s body removes momentum from the fluid
These two effects cancel each other out and produce no net change in downstream fluid momentum as long as the eel is swimming steadily
*As drag decreases speed of fluid moving around eels body the pressure must increase (Bernoulli) which squeezes the eel forward
Summarize Caragniform swimming: (5)
- Undulations restricted to posterior third of body
- Thrust largely from stiff caudal tail
- Generally faster swimmers than anguilliforms or sub-caragniforms
- Turning and accelerating abilities are compromised due to stiff body
- Lateral forces are concentrated at the posterior , increases recoil (waggle) of the head
How do caragniform sharks recapture some of the energy of the passive vortices it’s body creates?
By pushing against the vortices to generate thrust
Summarize Caragniform and Subcaragniform swimming: (3)
- Tend to be fusiform
- -> Increased body depth at 1/3 to 1/2 between head and tail
- -> decreased body depth at caudal peduncle - Waveform present on posterior half of body (subcaragniform) or posterior third of body (Caragniform)
- -> Lateral forces do not cancel (waggles head)
- -> Body depth increase behind head counters waggle
- -> Dorsal fin acts to reduce waggle of the head - Sharks can recapture some energy from drag producing vortices by pushing against passive vortices
- -> increase efficiency in the absence of a rigid body
What are tip vortices?
Induced drag coming off hydrofoil
Summarize thunniform swimming: (5)
- Tend to be fusiform
- -> Increased body depth at 1/3 to 1/2 between head and tail
- -> decreased body depth at caudal peduncle - Waveform restricted to caudal peduncle and caudal fin
- -> Lateral forces do not cancel (waggles head)
- -> Body depth increase behind head counters waggle
- -> Dorsal fin acts to reduce waggle of the head - Rigid body
- Body rigidity compromises maneuverability and acceleration
- Most efficient at high speeds (Thunniforms are the fastest swimmers)
How can Transient swimming performance be measured?
By the ratio of the minimum turning radius during fast starts to the length of the body
Turning radius/Body length
What is important for an acceleration specialist?
Acceleration reaction and Inertia
What are the design specifications for an acceleration specialist?
From a standing start must : Move a large volume of water quickly --> Increase body depth --> this generates large thrust Thrust must overcome inertia Acceleration reaction large (Important) --> Reduce any mass unnecessary for powering fast start
What does the vestibular system sense?
Direction and speed of movements
What does the vestibular system form the basis of?
The tail flip escape behaviour
What is the tail flip escape?
A response to a perceived risk.
Fish flick their tails and move laterally away from the signal or threat
Which cells conduct signals quickly? Large or small?
Large
What size are mauthner cells?
Large
What are the characteristics of fast start muscles?
Must have
1. High power output
2. Be fast
But don’t need to show much endurance
What are the characteristics of white muscle?
Fast Glycolytic
- -> High intrinsic velocity
- -> Fatigue quickly
- -> Lots of contractile machinery
- -> Few mitochondria
- ->Function anaerobically
- -> Convert glycogen to lactic acid
What are the characteristics of Pink muscle?
Fast oxidative glycolytic
What are the characteristics of Red Muscle?
Slow Oxidative
- -> Low intrinsic velocity
- -> Fatigue slowly
- -> More mitochondria
- -> Less contractile machinery
- -> Function aerobically
What type of muscle is good for slow steady swimming?
Red Muscle
What type of muscle is good for Fast Short swimming?
White Muscle
For organisms that do not use undulatory locomotion, thrust can be generated by what?
- Drag based-propulsion (rowing/undulating fins)
- Lift-based Propulsion (flapping)
- Jet propulsion
- Bacterial flagellum
What is propeller efficiency?
Useful power output/Total (muscle) Power input
how do amiiforms, gymnotiforms and balistiforms swim?
They use the same concept as the added mass method
- Pass undulatory wave down oscillating fin
- Increase amplitude towards tail (fish moves forwards)
- Increase amplitude towards head (fish moves backwards)
How do fish compensate for the upward force generated by the fin at the rear of the body that tends to pitch the body?
The fins are arranged at an angle relative to the body axis which reduces the upward component of force
What is a power stroke?
A high drag position
What is a recovery stroke?
A Low drag position
When do you get the best efficiency?
When the paddle is infinitely large but moves infinitely slow
Why is undulatory locomotion so efficient?
Dont have to have a recovery stroke
What does swimming involve?
- Lift
- Drag
- Acceleration reaction
Why are reynolds numbers higher for aquatic organisms than their aerial counterparts?
The kinematic viscosity of water is less than that of air
What is discontinuous thrust?
When you paddle on both sides at the same time
What is continuous thrust?
When you alternate paddling from side to side
What is a disadvantage of continuous thrust and how is it solved?
The side forces are unbalanced so a keel is needed to prevent this unbalance.
what does the acceleration reaction allow with reguards to a symmetrical stroke?
It allows it to generate thrust
How does one reduce their drag on a recovery stroke?
Reduce the surface area of the paddle
What are the mechanisms of thrust generation is a beetle?
- Creates high drag on power stroke but low drag on recovery stroke
- Move axis of oscillation towards the rear of the body
What is sculling?
The use of pectoral fins as paddles (drag-based)
What is Flapping?
The use of paddles as wings (Lift based)
What is the cost of Transport? (Equation)
Metabolic Power / Velocity = COT
How can you increase your speed while using medial and paired fins to swim?
Must increase the frequency of beating fins
When swimming it is cheaper to move __________ (Speed). Why?
Slower
- -> Cost to push through water is high
- -> Dont have to support body weight
When flying it is cheaper to move _______ (Speed). Why?
Faster
- -> Cause cost to push through air is low
- -> Must generate lift to support body weight
What types of drag must swimmers overcome?
Friction drag and Pressure drag
What is the most dominant force at high Re?
Pressure drag
Swimmers that use lift based mechanisms must also overcome what kind of drag?
Induced drag
Which is more important in the water, Lift or Thrust?
Thrust because of bouyancy
What types of drag must Fliers overcome?
Friction drag, pressure drag and induced drag
