9 - Wave Forces

Question 1

What is the inertial force ?

Answer 1

The integral of the pressure over the surface area of body.

Question 2

What 2 components is the pressure made up of ?

Answer 2

The hydrostatic and dynamic pressure.

Question 3

What is the drag force ?

Answer 3

The integral of the tangential stress over the area.

Question 4

The equation of force contains a value of u, multiplied by and absolute value of u, why is this?

Answer 4

So that it shows the force can be negative or positive.

Question 5

What is the interaction force?

Answer 5

The presesence of a body alters the linear situation, so the linear theory is not fully adequate to describe problem. Interaction force includes effect of the structure

Question 6

What is Newton’s second law?

Answer 6

F = ma

Question 7

F = ma, what does it also equal?

Answer 7

density * volume * dv/dt

Question 8

For this equation: density * volume * dv/dt. What does each of the elemetns mean?

Answer 8

Volume : volume of displaced water (volume of structure)
Velocity of body = velocity of displaced water

Question 9

What is the meaning of Ca in Ca * density * volume * dv/dt?

Answer 9

Mass coefficient

Question 10

If the cyclinder has a diameter very small (smaller than wavelength), why is the drag force dominant?

Answer 10

Small D compared to wavelength, meaning that it will leave a wake behind it. The pressure from linear theory doe not change a lot around the cylinder.

Question 11

For a very large diameter cylinder, why is the inertia force dominant?

Answer 11

The pressure from the linear theory varies a lot around it. Speed coming from different directions, no wake

Question 12

What happens in a wake ?

Answer 12

There is a pressure drop.

Question 13

If a body is much larger than the wavelength ( 4,5 times), what does this tell you about the wave crests?

Answer 13

There is multiple wave crests acting on it at one time.

Question 14

For a small diameter, what would you desribe about the distance it travels compared to the diameter?

Answer 14

S / D»_space; 1

Question 15

For a large diameter cyclinder, what would you describe about the horizontal distance travelled ?

Answer 15

S / D «_space;1

Question 16

How is the interaction force estimated, if it isn’t ignored ( for small - medium sized cyclinders?

Answer 16

Using the added mass approach.

Question 17

If the diameter of a cyclinder is extremly big, how is the interaction force estimated ?

Answer 17

By a method that considers full interaction, e.g. sea wall

Question 18

What is the Keulugen-Carpenter number?

Answer 18

Kc = u * T / D

Question 19

If Kc > 25, what does this mean?

Answer 19

The drag force is dominant

Question 20

If 5 < Kc < 25, what does this mean?

Answer 20

Both drag force and intertia force are important

Question 21

If Kc < 5, what does this mean?

Answer 21

Inertia force is dominant.