Animal - Section B - Locomotion 1 (Fish) Flashcards
What is the Reynolds number?
Density of the medium
x
velocity
x
linear dimension (length vs width)
/
viscosity of the water
Locomotory costs in water are relatively low but are afected by a number of factors, what are they?
- Lift
- Thrust
- Weight
- Drag
What kind of animals tend to have the higher reynolds number?
Larger animals have higher reynolds numbers because they are larger and faster.
(Reynolds number is a dimensionless number used in fluid mechanics to indicate whether fluid flow past a body or in a duct is steady or turbulent)
Describe Pressure drag
The force required to overcome the inertia of the water molecules in in order to push them out of the way - varies with fluid density, velocity and the fish’s shape (streamlined or chunky)
What kind of animals tend to have the higher reynolds number?
larger animals have higher reynolds numbers because they are larger and faster.
What are the 3 types of drag?
- Pressure drag
- Frictional drag (viscous drag)
- Wave drag
Define viscosity
The viscosity of a fluid is the measure of its resistance to gradual deformation, sheer stress or densile stress. For liquids it corresponds to the informal concept of thickness. For example:
‘Honey has a higher viscosity than water’
Large fast swimmers cannot prevent drag by they can lessen its effects. How?
Surface compliance - instead of having a rigid body surface, soft and rubbery is better such as whale blubber allows the body to flex which dampens out turbulence.
Small projections - on the skin or scales create lots of small disruptions as apposed to big disruptions. Disrupts boundary layer which creates little turbulance instead of large (dimples on a golf ball, shark denticles)
Slime - (Mucus) reduces viscosity of the water in the boundary layer
(just 1% slime reduces friction by 60%)
Oscillation - of the fish’s tail pushes water back which helps to cancel the pressure drag in the fish’s wake.
What does the heteroceral tail of shark do?
It causes an upward directed force posteriorly that rotates the body around the centre of mass.
(Tails of fast swimming sharks such as the Mako and Great white have a much more even shaped tail)
The best body shape for encouraging laminar flow has a maximum thickness of around _.__ of body length.
- 0.25 of body length
- depth & width of body approx 1/4 of total length.
Large animals such as birds, whales, dolphins are very well ___________ in order to reduce the ____ on their body as they move through the medium
A. Streamlined
B. Drag
Describe wave drag
A fish swimming near the surface loses energy by making waves
What are the two types of swimming in fishes?
-Undulatory (eels, rays)
Have high relative surface area (thin, flat or long bodies) increasing viscous drag, Slow swimmers but can swim backwards, high manouverability.
-Oscillatory (Tuna, Mako)
Tail movement can only power you forward
Wake vortices by oscillatory swimming can assist schooling fishes which is why fish all swim slightly ______
A. offset
The aspect ratio is the span of the
span of the tail vs chord (thickness of the chord)
Low Reynolds numbers are associated with _______ flow
High Reynolds numbers are associated wuth _________ flow
A. Laminar (no turbulance)
B. Turbulent
Describe Frictional drag (viscous drag)
The boundary layer is a velocity gradient from the fish’s surface to the surrounding water - depends on fluid viscosity, surface area of the fish and velocity.
The fastest swimmers have ____ bodies with hig ______ ratio tails
A. Stiff
B. Aspect
