DPV/Sea Scooter problems anyone?

[victorzamora]

Thrust values from Flow Simulation in Solidworks? What we did was create a plane that enabled us to get volumetric flow through it. We backed out an Eulerian derivation of mass flowrate through the plane to determine thrust.
I believe Solidworks can give you "thrust" numbers if you create a disk with a forced flow velocity exiting it. A bigger simulation volume will give you more accurate numbers.

Having said that, the easiest, cheapest way to get Solidworks to give you the most accurate numbers is to send the CAD model off to a custom machining firm and build your own DPV, buy 3 "high end" DPV's, a lake, and a full slew of divers and testing equipment and perform a full slew of tests in fresh water. Then, buy enough salt blocks to raise the salinity in your new lake to ocean levels and repeat. Then dead sea levels, and repeat. This latter method will be the least like to cause suicidal thoughts.

 

[Jon Nellis]

Time to resurrect this thread I think. It's been 7 months since I've posted and I've finally designed and built a prototype DPV using waterjet propulsion. Took me a while and some, well acutally, a lot of advice from my supervisor to build this beast. However, although I'm getting the results I want using Flow Simulation from SolidWorks, I struggling to find a practical way of calculating the thrust of the unit. Does anyone have any ideas of getting about this?

From what I've seem of SWFS you won't be able to simulate this, since some of the parameters you need to define are the same one you are looking for. i.e. the spinning impeller can't generate a mass flow based on its rotational velocity in a duct without entering an inlet and/or exit mass flow for the duct, which are the values you are looking for. Not to mention, you can only input rotational speed, which assumes infinite torque from the motor. Just because you have, for example, a 4000rpm motor, does not mean that it will actually spin that fast under the load of the impeller.

Your best bet is to get it wet. If you don't have the electronics water proofed yet, use a long shaft between the motor and jet section and hang it in a pool from a load cell with the motor out of the water. Unfortunately, jet style thrusters have been proven to not be as power efficient as ducted propellers in low speed thrust. They are better at keeping things out of the rotating parts, but all the extra ducting and higher boundary layer speed differentials create significant frictional losses.

Cheers,
Jon

 

[Matthew Yung]

From what I've seem of SWFS you won't be able to simulate this, since some of the parameters you need to define are the same one you are looking for. i.e. the spinning impeller can't generate a mass flow based on its rotational velocity in a duct without entering an inlet and/or exit mass flow for the duct, which are the values you are looking for. Not to mention, you can only input rotational speed, which assumes infinite torque from the motor. Just because you have, for example, a 4000rpm motor, does not mean that it will actually spin that fast under the load of the impeller.

Cheers,
Jon

Thrust values from Flow Simulation in Solidworks? What we did was create a plane that enabled us to get volumetric flow through it. We backed out an Eulerian derivation of mass flowrate through the plane to determine thrust.
I believe Solidworks can give you "thrust" numbers if you create a disk with a forced flow velocity exiting it. A bigger simulation volume will give you more accurate numbers.

Yep, I probably should have mentioned that first. I got the values of the water velocity that was travelling through the water tunnel by adding a rotational field around the impeller. Using the results, I put them into a formula which gave me a theoretical value for thrust. Since I wasn't able to determine the mass flow rate or the velocity flow rate of water, I used "Total Pressure" at 10m below depth for the inlets and outlets. The simulation showed results close to what I was expecting, but after reading your comments, it seems I may be off...