I'm at the helm of the Bluefin training vessel bringing vital supplies of hot chocolate to
a research team stranded somewhere off the coast of Tasmania.
If anything were to go wrong then there are a million dollars’ worth of boat, research
equipment, and of course hot chocolate that I’m liable for.
Or would be liable for if this were an actual boat.
This is the Centre for Marine Simulation at the University of Tasmania.
It's in this very room where they train pilots to operate in some of the most difficult
and technical situations in the world.
And today we're going to find out how it works.
When you’re trying to replicate the real world inside a computer, the best place to
begin is the real world.
This is the actual Bluefin vessel safely moored at Beauty Point.
For most of us the hardest thing about getting into a new hire car is setting up the Bluetooth.
This is because all cars handle pretty much the same.
There is a very high amount of friction between the road and the car tires and, on
top of that, the ratio of engine power to vehicle mass is pretty high.
Not so with a boat.
First of all there is very low resistance between the water and the ship’s hull.
And, although the engines are massive on this sort of boat, their power is quite small
as compared with the enormous mass of the ship.
Combined with high inertia, due to this mass, and the effect of wind and wave forces this
makes precise steering really difficult.
Ships won’t just travel in a straight line either but will heave, yaw, surge, roll, sway,
and pitch their way across the sea.
How all these unique forces interact with each other in order to produce the vessel’s
unique sailing signature makes simulating it both incredibly important but also very
difficult to achieve.
In order to create our simulations, we need a lot of data.
Rather than waiting for the ocean to produce the right sort of conditions in order to test
our theories, the engineers at the Australian Maritime College decided to skip out the middleman
and make their own ocean.
I’m inside what's called the model test basin.
At one end we have a series of paddles, but I like to think of them as keys on a piano
with which we hope to replicate the symphony of the seas.
If we have them all move together - as they’re doing now - then they’ll push
on the water in the same way to produce a plane wavefront of uniform frequency.
This is the simplest type and is really good for testing out theories.
If we were to instead play each of these paddles individually and use some real life
data we can almost exactly replicate what it's like to be on the ocean.
At 35 metres by 12 metres the model test basin is huge, but since it's only about 800 mm
deep it's not quite large enough for us to test the actual Bluefin ship in.
For that I’m going to introduce to you our third - and in my opinion favourite- Bluefin
model of the day.
This is a 1:20 scale exact replica of the real Bluefin ship.
This means that for every 1 mm on the model we have 20 mm in real life.
It’s also remote controlled.
By scaling wave height by the same factor we can see how the boat responds to a variety
of sea states as it conducts a few different maneuvers.
By using the same tracking system as movie studios use to make CGI characters we can
track the motion of the boat to a high level of precision.
As we saw with our Engineering Europe series,
a ship is stable if it’s centre of buoyancy is directly above its centre of mass.
When we introduce waves we complicate the situation by dynamically changing the centre
of buoyancy.
Compared with its equilibrium position, this incoming wave will submerge more of the
bow and less of the stern.
This means we have more of the lift up front and less out the back; pushing the centre
of buoyancy further forward than the center of mass.
This torque causes the ship to pitch upwards.
As the wave continues to pass through it becomes level before pitching the other way.
If we increase the wavelength we can have a much smoother ride since the differences
in buoyancy for each part of the hull will cancel each other out.
You can artificially adjust what frequency of wave your boat is experiencing - and get
a smoother ride - by adjusting the angle and speed with which you encounter these waves.
However, to more rigorously analyse speed, we’re going to have to make a new model.
A few years ago part of my summer research job was to create some very similar models
as to these ones for a large resources company.
As it turns out, this is actually a far more complex task than it might first appear.
On this small scale even very minute differences between the model and real world will result
in massive differences in the sorts of forces and behaviours that we’re measuring.
On top of that, you’ve also got to replicate the overall density as well as the moment
of inertia because if not then they’re just going to behave like completely different
vessels.
These models are built in-house at a cost of between $5,000 (AUD) and $60,000 (AUD).
You can paint them either yellow or pink in order to get the best view of the fluid
properties going on.
I think you can guess why they went for yellow.
For longer sections of travel we have a towing tank.
At one end we have a wave generator allowing us to produce any sort of sea state that we
want.
And here is the carriage.
It moves along the 100 metre towing tank through which we drag along the boat.
You can see here we’ve created a positive feedback loop where the wavelength of the
wave is equal to the length of the boat.
The passengers would not be having a good time.
Since the researchers conducting this particular experiment only cared about heave and pitch
we reduce the degrees of freedom and measure forces by using these two cylindrical extenders.
We’ve done the tests and collected our data but you’ve probably noticed that the motion
looks a little bit strange; it’s going much faster than we’d expect in the real world.
Let's imagine a 10 metre tall ship and its 10 cm high 1:100 scale model.
Now, for whatever reason, something is dropped from the top mast and into the sea
below.
Assuming a spherical cow in a vacuum, a little bit of high school physics should tell
us it will take 1.4 seconds for the real object to fall 10 metres but only 0.14 seconds to fall 10 cm.
Remember, we've only changed the scale of the ship.
Gravity remains constant.
To make them match we slow down the recording.
Specifically by the square root of the scale factor.
That is 10 for the 1:100 spherical cow and 4.47 for the 1:20 Bluefin.
At this scale things look much more realistic and significantly more cool.
This same technique is used in old-school disaster movies where they make a small scale
model of the explosion, film it, then play it back in slow motion.
I’m back at the Marine Simulation Centre.
This is their tugboat model which allows crews to test really complex maneuvers which
require both the tugboat as well as the actual vessel in order to operate correctly.
This gives them a really hands-on practical experience of how to use a boat.
On top of them having two different crews
which can operate together, the actual boat physics and how the simulations work is incredibly
accurate because of all those tests we ran earlier.
For example if I do a massive turn immediately
the boat takes some time to respond.
Just because of how the different forces operate, because of our momentum, and the
ship conditions.
With enough measurements from towing tanks, test basins, and of course ship trials the
team here can simulate almost any vessel in any condition in the world.
When you see a boat come into port doing a particularly complex maneuver or operating
on the high seas, you can be certain that at least one person aboard spent a very good
deal of time in this simulator.
I meanwhile should probably get back to my Antarctic research team; they’ll be wanting
their hot chocolate any day now.
Until next time, this has been James Dingley from the Atomic Frontier.
Keep Looking Up.
Huge thanks to everyone from the University of Tasmania who made this video possible and,
in particular, to Tom, Richard, and Nick.
Next episode we’re going to go visit one of the world’s most unique robots.
See you then.