Morison’s Equation

Question 1

What is Morison’s Equation for total force per unit length on a body?

Answer 1

f = C_D·(½ ρu|u|D) + C_M·ρ·(πD²/4)·(∂u/∂t)

Where:

C_D: drag coefficient
C_M: inertia coefficient
u: fluid velocity
∂u/∂t: fluid acceleration

Question 2

What does Morison’s Equation represent?

Answer 2

It combines the drag and inertia force contributions on slender structures in oscillatory flow.

Question 3

n Morison’s Equation, the modulus sign ∣u∣ ensures the drag force is always in the direction of the _______.

Answer 3

flow

Question 4

True or False: Morison’s Equation accounts for wake effects and pressure recovery.

Answer 4

False – it assumes undisturbed flow (slender body assumption).

Question 5

What is the Keulegan-Carpenter (KC) number?

Answer 5

KC = (U·T) / D

Where:

U = characteristic velocity
T = wave period
D = diameter of the body

Question 6

What does the KC number represent?

Answer 6

The displacement of fluid relative to body size over a wave cycle — important in predicting dominant forces.

Question 7

Match KC value with dominant force:

KC > 20 →
KC < 5 →
5 < KC < 20 →

Answer 7

• Drag-dominated
• Inertia-dominated
• Mixed influence (both drag and inertia significant)

Question 8

For large KC, the fluid moves a large distance, forming a ______ wake.

Answer 8

low-pressure

Question 9

True or False: At small KC, flow separation is more significant than at large KC.

Answer 9

False – separation is limited at small KC due to low fluid displacement.

Question 10

How is KC linked to drag/inertia ratio?

Answer 10

(drag forces) / (inertia forces) = (u²·D) / (D²·∂u/∂t) = (U·T)/D = KC