Swimming

Report
Physics of swimming
Physics of swimming
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not all fish swim
not all swimmers are fast or efficient
but - in order to swim fast, all fish have the same constraints
due to physics - thus fast fish tend to look similar
Physics of swimming
Properties of water as medium in which to move
• density - 830x greater than air
• viscosity – 70x greater than air
Physics of swimming
Properties of water as medium in which to move
• density - 830x greater than air
• viscosity – 70x greater than air
• lift – force exerted on object perpendicular to direction of flow (or movement)
- proportional to the area over which the pressure difference acts
lift
Physics of swimming
Properties of water as medium in which to move
• density - 830x greater than air
• viscosity – 70x greater than air
• lift
• drag – 830x greater than in air
- increases with speed of object or current
- due to separation of flow from object into turbulent flow
Physics of swimming
Properties of water as medium in which to move
• density - 830x greater than air
• viscosity – 70x greater than air
• lift
• drag – 830x greater than in air
- increases with speed of object or current
- due to separation of flow from object into turbulent flow
• boundary layer
- laminar or turbulent
Physics of swimming
Reynolds number (Re): ratio of inertial forces to viscous forces
Re = LVr/m
L = length of object
V = velocity of object
r = density of fluid
m = viscosity of fluid
Physics of swimming
Reynolds number (Re): ratio of inertial forces to viscous forces
Re = LVr/m
L = length of object
V = velocity of object
r = density of fluid
m = viscosity of fluid
flow changes to turbulent at Re ~ 2,000
turbulent flow is a consequence of
increasing speed
increasing length
(decreasing viscosity)
(increasing density of liquid)
boundary layer changes to turbulent as Re goes from 5x105-5x106
Physics of swimming
Reynolds number (Re): ratio of inertial forces to viscous forces
Re = LVr/m
L = length of object
V = velocity of object
r = density of fluid
m = viscosity of fluid
Examples of Re:
animal
whale
tuna
copepod
sea urchin sperm
speed
10 m/s
10 m/s
20 cm/s
0.2 mm/s
Re
300,000,000
30,000,000
300
0.03
Physics of swimming
for efficient swimming
avoid separation of boundary layer from surface
maximize laminar flow in boundary layer
Physics of swimming
for efficient swimming
avoid separation of boundary layer from surface
maximize laminar flow in boundary layer
minimize turbulent flow in wake
Physics of swimming
solutions:
streamline body (tapering):
aspect ratio of about 0.25
maximum thickness of body 1/3 from front (head)
b
a
Aspect ratio = a/b
Physics of swimming
solutions:
streamline body (tapering):
aspect ratio of about 0.25
maximum thickness of body 1/3 from front (head)
drag reduction - keep body rigid
Physics of swimming
solutions:
streamline body (tapering):
aspect ratio of about 0.25
maximum thickness of body 1/3 from front (head)
drag reduction - keep body rigid
slime layer to reduce frictional drag
rough surface (cteni) keeps boundary layer attached?
Australian Museum
Physics of swimming
Swimming modes
“kick and glide”
active - sustained for hours or days
burst - only for up to 30 secs
large fishes have greater difference between burst and active than small fishes
Physics of swimming
Swimming modes
“kick and glide”
active - sustained for hours or days
burst - only for up to 30 secs
large fishes have greater difference between burst and active than small fishes
Physics of swimming
active swimming accomplished using red muscle along sides of fish
- high myoglobin and mitochondrial enzymes
burst swimming with white muscle
- great contractile speeds, low endurance
BCF - body/caudal fin propulsion
anguilliform
entire body undulates
laterally flattened, elongated body
inefficient
Anguilliformes – moray eel
Perciformes – snake mackerel, etc.
subcarangiform
swim with posterior portion of body, less than one wavelength
tend toward truncate, rounded, or emarginate tails
head still yaws with motion of swimming
aspect ratio of tail ~1.5-2
cods, basses, trout, many others
Salmoniformes – rainbow trout
carangiform
less that half to one third of body flexes
generally narrow peduncle, flared and strongly forked or lunate tail
high aspect ratio tail (square of span/surface area) ~3.5
herrings, jacks, some scombrids
Perciformes – jacks (Carangidae)
thunniform
extremely stiff body, narrow peduncle, high aspect ratio tail (4-10)
large tendons to support muscular energy transmission to tail; stiffened tail
tunas, marlins, sailfishes, some sharks
Perciformes – tuna
(Thunnidae)
ostraciiform
only moves tail, rest of body rigid
boxfishes, porcupine fish
Tetraodontiformes – boxfish
(Tetraodontidae)
MPF - median/paired fin propulsion
rajiiform
undulate pectoral fins from front to back, with wing-like ‘flapping’
Rajiiformes – Rajidae
(manta ray)
didontiform
undulate pectorals for sculling and maneuvering
Tetraodontiformes - pufferfish
(Ostracidae)
labriform
oscillate pectorals for sculling and maneuvering
Perciformes – parrotfish (Labridae)
amiiform/gymnotiform
use undulatory waves of dorsal (Amia) or anal (Gymnotids) fins
also seahorses, with narrow-base dorsal
Amiiformes - bowfin
Gymnotiformes - knifefish
balistiform
use simultaneous motion of dorsal and anal fins - triggerfish
(used to some extent in eels, percids, flatfish)
Tetraodontiformes – triggerfish
(Balistidae)
tetraodontiform
both dorsal and anal fins
move together to each side
Tetraodontiformes – ocean sunfish (mola)
NON-SWIMMING LOCOMOTION
gliding above water - flying fishes
add to take-off propulsion by using tail lobe in water like propeller
may fly up to 400 m, as high up as 5 m
may add pelvic fins as secondary gliding surfaces
Scorpaeniformes – flying gunard
Other forms of nonswimming locomotion:
burrowing - eels, gobies, flatfish, rays
wriggling - eels
hitchhiking - remoras, lamprey
push-and-hold - gobies using pelvic disk; lamprey using oral disk
Other forms of nonswimming locomotion:
‘walking’ or climbing on pectorals - walking catfish, mudskippers
walking on bottom – sea robins using pectoral rays; batfish and
relatives walk on modified pelvics
Siluriformes – walking catfish
Perciiformes
(Gobiidae)
- mudskipper
Lophiiformes - batfish
Other forms of nonswimming locomotion:
‘walking’ or climbing on pectorals - walking catfish, mudskippers
walking on bottom - searobins using pectoral rays; batfish and
relatives walk on modified pelvics
Aulopiformes - tripod fish
Other forms of nonswimming locomotion:
leaping - mullets, tuna, sailfish - also salmonids moving upstream
Other forms of nonswimming locomotion:
jet propulsion - by forcible ejection of water out of gills by
operculum used as ‘assist’ to fast take-off by some percids,
sculpins
passive drift - larvae, sargassum fish
frogfish

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