We have seen various topics such as force
exerted by a jet on vertical flat plate, force
exerted by a jet on stationary inclined flat plate, force
exerted by a jet on stationary curved plate, force
exerted by a jet on a hinged plate, force
exerted by a jet on a curved plate, force
exerted by a jet of water on a series of vanes and force
exerted by a jet of water on a series of radial curved vanes in
our recent posts.
Case
I –
Propulsive
force exerted on the ship, F = ρ a (V + u) x V
Case
II –
Now we will see here the basics of jet propulsion of
ships with the help of this post. Before going to study the basics of jet
propulsion of ships, we must have information about the principle of jet propulsion.
We have already discussed the principle of jet
propulsion, in our previous post, where we have discussed the following terms
as mentioned here.
- Jet Propulsion definition
- Jet propulsion of a tank with an orifice
- Condition for maximum efficiency
- Equation for maximum efficiency
Now it’s time to discuss the basics of jet
propulsion of ships, so let us take one cup of coffee and read this post.
Jet propulsion of ships
As we know that Jet propulsion means the propulsion
or movement of the bodies such as ships, aircraft, rocket etc., with the help
of jet. The reaction of the jet, coming out from the orifice provided in
the bodies, is used to move the bodies.
We will be interested here to study the movement of
ships with the help of jet. A ship will be driven through water on the basis of
principle and application of jet propulsion.
A jet of water, which is discharged at the back of
ship, will exert a propulsive force on the ship. Ship will have centrifugal
pumps which will withdraw water from the surrounding area from sea. This water
will be discharged through the orifice, provided at the back of ship, in the
form of jet.
Hence the reaction of jet, coming out at the back of
the ship, will propel the ship in the opposite direction of the jet.
There will be two way through which centrifugal pump will take water from surrounding sea
Through inlet orifices, orifices which are at right angles
to the direction of motion of the ship
Through inlet orifices, orifices which are facing
the direction of motion of the ship
Case
I –
Jet
propulsion of the ship when inlet orifices are at right angles to the direction
of motion of the ship
Following figure, displayed here, indicates a ship
which is having the inlet orifices at right angles to the direction of motion
of the ship.
Propulsive
force exerted on the ship, F = ρ a (V + u) x V
Work done per second, W = ρ a (V + u) x V x u
Where,
V = Absolute velocity of jet of water coming at the
back of the ship
u = Velocity of the ship
Vr = Relative velocity of jet with
respect to jet = (V + u)
Case
II –
Jet
propulsion of the ship when inlet orifices are facing the direction of motion
of the ship
Following figure, displayed here, indicates a ship
which is having the inlet orifices facing the direction of motion of the ship.
In this case, the expression for propelling force
and work done per second will be identical as we have seen in case I i.e. when orifices
are at right angles to the direction of motion of the ship.
Energy supplied by the jet in case II will be different.
Do you have any suggestions? Please write in comment
box.
We will see another topic i.e. Introduction to hydraulic machines, in the subject of fluid mechanics, with the help of our next
post.
Reference:
Fluid mechanics, By R. K. Bansal
Image courtesy: Google
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