Eli5: How do they effectively test scale models of giant ships in water? Doesn’t the water behave differently in the small vs large scale?

Question

Eli5: How do they effectively test scale models of giant ships in water? Doesn’t the water behave differently in the small vs large scale?

In: Physics

Answer 1

There is alot of calculations that go into it. Unfortunately I forgot alot from my Naval Architecture class but you use the Reynolds number and Froudes number.

Using Froudes number you can build a relationship between the scale models speed and the designed speed of the vessel. This often means that the scale speed is not a linear relationship because the goal of the model is to have turbulent flow to have measurable effects from the wake.

This is the equation used with V equal to velocity and g equal to force of gravity (9.81m/s) and L is length. Froudes number should be constant for a vessels hull shape so you just need to make them equal to each other.
Fn = (V/g√L)

This is the best of my memory but if i remembered properly you can use froudes when you have a higher reynolds number for the model meaning you have turbulent flow on the model because that helps simulate the waves for a full scale vessel