Hydrodynamics: Drag

Question 1

Drag

Answer 1

Resistance of motiom through fluid – proportional to V^2

Question 2

3 Types of Drag

Answer 2

Form Drag
Friction Drag
Induced Drag

Question 3

Form Drag

Answer 3

Displace amount of water equal to animals largest frontal area (influenced by shape)
Minimum drag occurs when teardropped shape
Minimum drag when maximum depth positioned 36% between head and tail (usually corresponds with boundary between contractor and diffuser zone)
Minimum drag when width is ~25% maximum length

Question 4

Friction Drag

Answer 4

Proportional to SA – larger SA more drag
High speed results in transverse folds which increase friction/drag
Minimize drag with tight elastic surface – uncommon in fishes
scales can reduce transverse folds

Question 5

Ontogeny of scale development

Answer 5

Most fish start scaless
Begin to cover whole body with cycloid scales
The development of ctenoid scales on bottom
Then slowly develop on the rest of the body
These ctenoid scales will cover the whole body except for the head which retains cycloid scales

Question 6

How do ctenoid teeth decrease drag

Answer 6

peaks and valleys cause vortices
Act as ball bearings to help them slide
Keep boundary layer close to the body

Question 7

Swordfish Hydrodynamics

Answer 7

Sword is bumpy: ensure turbulence in boundary layer and reduce boundary layer separation in diffuser zone

Question 8

Use of mucous to reduce drag

Answer 8

60% reduction of drag when covered in mucous
lowers viscosity in the boundary layer
Increase micro vortices in boundary layer

Question 9

Induced Drag

Answer 9

motion of body and fins
fins are depressed
grooves for fins
oscillatory swimming mode

Question 10

What makes up most of drag?

Answer 10

Friction drag
90% of drag is friction drag

Question 11

Zone 1

Answer 11

Frontal rudders, balancing, lifting surfaces
Anterior to center of mass
held against body during swimming
Produce drag – turning/slowing
Resistance of fin proportional to velocity squared
Juveniles have proportionally large fins

Question 12

Capacity to turn

Answer 12

Center of mass
Center of longitudinal projection

Question 13

Dynamic stability

Answer 13

This is highest when center of gravity is anterior to center of longitudinal projection

Question 14

Dynamic instability

Answer 14

This is required to turn
Sailfish use dorsal fin to move center of longitudinal projection anterior
Hump in spawning salmon does the same thing

Question 15

Zone 2

Answer 15

Stabilizer keels
create transverse forces posterior to COM, prevent deflection of the body
sub-carangiform: dorsal fin near end of the propolsive wave
Thunniform: have dorsals posterior for increased stability

Question 16

Zone 3

Answer 16

Propulsive organs, lifting surface
primary propulsion, stabilize when coasting and rudder
Dorsal and anal used for propulsion are symmetric
Finels on high speed fishes control boundary layer