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5.1 - Other Resistances - Coggle Diagram
5.1 - Other Resistances
Viscous Pressure Drag
Varies with
L/D ratio
Slender bodies
less form drag
too long body
increase frictional resistance
greater area
Submerged bodies
L/D BTW 5 and 7
Optimum
Form Resistance
Pressure distribution
on hull
Stern decelerates
Bow accelerates fluid
If non-viscous
Aft end
pressure higher than
static pressure
water moves forward
filling the aft
With viscosity
virtual lengthening
water does not move forward
increases resistance
Lower pressure
Separation Resistance
Separation of boundary layer
Generates eddies
particles start moving
foward
Frictional Resistance
Generates Boundary layer
particles close hull
same hull velocity
particles away
medium velocity
Momentum supplied
TO water, BY hull
in the boundary Layer
Wave-braking Resistance
irregular flow
ahead of bow
Due to flow separation
at free surface
Taylor
Taylor Instability Criterion
Free surface becomes unstable
Radius of curvature results in
centrifugal acceleration (\(\dfrac{V²}{R} \) )
greater than critical value
Avoid
Tangent to curve
of sectional areas at forward perpendicular be NOT too steep
Eddy resistance
All fricitonal Resistance
Around ship
Due to Eddy-making
Usually refers to
Disturbed streamlines
due to abrupt changes
sharp edges
appendages
Excludes
Tangentional skin friction
Form Resistance
Principal causes
Skin Friction
Viscous Pressure Drag
Separation Resistance
Ship Form Resistance
Higher than plank
Low speeds
Wave-making resistance
hardly occurs
Fr < 0,10
Free surface at STERN rises
Height \(\approx \dfrac{V²}{2g}\)
