Drag on a kayak

[Kim1991]

Hi,

I need to determine the drag on a kayak. I have a model of the kayak and an approximate weight for the kayak+athlete. The kayak moves at 8 m/s in one direction. How would I model that in multiphysics? I'm not sure how to get the kayak to sit at the correct height in the water (which is related to the weight) as of course it wont be completely submerged.

Any help would be much appreciated.

Kim

[rhinterhoeller]

I can't help you on the multiphysics aspect of your problem but the flotation bit is relatively simple.

You're dealing with Archimedes principle here.  The mass of water that is displaced by the kayak is equal to the mass of the kayak.  The way to calculate this in IV is:

1. Model the kayak as a solid (you can skip any details that will stay above the waterline).
2. Assign a property with the density of water (I think 'default' uses that but don't take my word for it).
3. Sketch a line along the mid plane of the boat at you're best guess for where the kayak will float (dimension it so that you can change the immersed depth and the pitching angle).
4. Split the above-water portion away.
5. Have IV calculate the mass and centre of gravity.  In this case you have calculated the buoyancy and centre of buoyancy for the kayak as immersed.
6. If you're systematically adjust the immersion depth and pitch until the buoyancy and centre of buoyancy match the mass and centre of gravity of the loaded kayak.  You should be able to do this in 5 or 10 iterations.

Regards,

Richard

[S.LI]

Not sure your final simulation goal.

For just finding the deepness, I think you can try MES model with hydrostatic loads.

1.) pick the surface (usually the bottom of your boat), and apply hydrostatic loads with an appropriate water density. About the point on fluid surface, please input the best value you can estimate.

2.) apply gravity loads.

3.) make sure the load curve shape is constant for both of the two loads.

4.) maybe a little bit other constraints needed to keep the posture of your boat.

5.) start the simulation.

Then the simulation will find the deepness. According to my simulation, finally, you will see the boat oscillates at a deepness, since there is no damping introduced here. 

About the velocity, you can also apply it in MES as an initial velocity. To keep it constant, you might need apply other forces according to your model.

[Joey.X]

The drag force on kayak comes from following contributions for transient analysis

(a) Force of wave, this may dominate in drag force for surface boat/vehicles,  kayak should be in this category.

(b) Fluid dynamics force from submerged parts under water (No wave considered)

(c) Gravity/buoyancy force, depending coordinate used, these forces may have components in drag force.

ASIM counts (b) and (c) if using Multiphysics fluid-mechanical coupling analysis, however, the force of wave needs free-surface and 6-DOF features which are the not-supported features in ASIM.