「船体速度」は、実際には速度と長さの平方根の比です。物事をさらに混乱させるために、長さはフィート単位で、速度はノット単位です。これが定数1.34の発生方法です。(ProTip:二度と話さないようにしましょう!)
耐波性(Rw)フルード数(Fr)が約0.35で急激な上昇が始まります。その下に、Rw is usually small compared to the skin-friction
and other hydrodynamic drag components.
Now, for sake of example, let the wave resistance coefficient be defined as
Cw=Rw/(0.5ρU2S), where ρ is water density, U is ship speed,
and S is the (static) wetted surface area of the hull.
In deep water, Cw increases roughly like Fr to the 6th power.
The depth-based Froude number is Fh=U/gh−−√, where g is
gravitational acceleration, and h is water depth.
For finite depth water, Cw can increase almost like Fh to the 10th power
as Fh→1. Once through (the critical value) Fh=1, wave resistance
begins to decrease, and it can be lower than in deep water for the same
length-based Froude number (Fr).
Fh<1 is usually referred to as sub-critical; Fh>1 is super-critical,
and (roughly) 0.9<Fh<1.1 is trans-critical.
In the trans-critical regime, the hull also experiences forces and moments
that significantly change its attitude with respect to the undisturbed free-surface of water.
The trim and heave of a hull is known as "squat". This phenomenon is difficult
to predict accurately. It can have some effects on resistance but, more importantly, in
shallow water there is also a danger of the ship grounding against the sea-bed.
This can cause large losses of income, and there have also been fatalities attributed
to the phenomenon.
Wave patterns for finite depth are quite interesting...
fh080.gif
fh090.gif
fh099.gif
fh101.gif
fh110.gif
fh120.gif
As Fh enters the trans-critical regime, wave patterns change dramatically.
The angle of the V-shape opens out and becomes 90 degrees at Fh=1.
For sub-critical speeds, transverse waves (those perpendicular to the ship's
track) are apparent.
In super-critical flow, transverse waves disappear. (In short, they cannot keep
up with the ship).
DISCLOSURE: These patterns were made using my (free) program Flotilla.
More patterns can be found at:
www.cyberiad.net/wakeimages.htm