Cruise Ship Disaster Wind Analysis

 

Zooming in, we get more detail on the mesh local to the ship. You will also notice an area of light blue higher speed air coming out of the middle portion of the ship. 

 
What is happening here, is since I didn’t make this CAD myself, I missed the fact that there were no windows in this ship CAD, just holes through the ship.  You can see in this image here the air moving through the ship where cabins should be.  Obviously this isn’t correct, so a corrected model was run with the holes sealed.  
 

 

 I also plotted velocity vectors with the velocity contours to see how the air was moving as it came toward the ship.

 

 

We can get a better feel for the airflow using streamline animations, like the 3 below showing different views of the same streamlines.

 

 Another good way of getting a feel for the extent of the low speed air is an isosurface, which is a 3D plot that connects points with the same value to make a surface.  Here I’m looking at anywhere that the airspeed is 15 miles/hr, a good amount slower than the 25 miles/hr wind.  You can see the extent of the air being slowed down, which gives an indication to the forces affecting the ship.

 

Similarly a surface pressure plot will show where the high pressure regions, which when added up over the entire surface provide the force on that object.

 

 

But of course what we really want is the actual values for the force and the torques.  FloEFD can output this into excel spreadsheet tables.  Below are the results from the second analysis with the cabin holes “sealed”. 

 

 My main surprise is how low the actual force was compared to the weight of the ship.  The ship weighs 256,480,000 lbs!  264,175 lbs of force is about 0.1% of the ship weight, yet it was enough to move the ship back to shore.  Granted, we didn’t include any ocean current/wave effects in this analysis, which may have played a part, but as there was no data for that, I couldn’t include this into the simulation.

 

The more I think about it though, the more I can see that the force shouldn’t be massive.  If it was, imagine how many docks would be crushed when a stiff wind blew in on a ship that was docked.  Also, unlike most things that we can reference when thinking about forces, a ship isn’t on solid ground.  There are no ground forces to resist this wind force.  Similar to those “World’s Strongest Man” competitions where men pull airplanes or 18 wheel transport trucks, the pulling force is small compared to the size of the object being pulled, which is possible because the tires on the objects.  Or how little tugboats can move ships much larger then they are.

 

In the end, what I take out of this analysis was that I was really surprised at the size of the wind wake behind the ship at about 1450 ft.  But more then that, I was amazed at the tiny amount of wind force that moved this massive boat to shore and saved so many lives that day.