Simulation of kite hydrofoil using Kangaroo???

I'm designing a kite hydrofoil similar to this...

I want to simulate the lift forces generated by the front wing and the rear wing with a view to understanding...
1. How stable is the system in terms of pitch forwards and backwards
2. What effect do the following have on the system...
   a) Angle of Attack (AOA) of the front wing
   b) AOA of the rear wing
   c) Position of the mast along the fuselage.
   d) Position of rider above the mast (distribution of weight between front and rear feet amd position of the mast between the feet).

So, in essence I want to model a 2 dimensional system as follows...

I would like to incorporate a coefficient of lift versus AOA for the front and rear wings.

Data for this can be found in text file format for example here for the Eppler 817 airfoil that I want to use... EPPLER817 DATA

I might need more info than this though???

Assume constant velocity???

Ultimately, the lift generated by the hydrofoil will equal the weight of the rider otherwise you would sink or jump forever upwards but the hydrofoil can generate more lift or less lift than the rider depending on its angle of attack. I could assume the wing can generate -1.0x to 1.5x the weight of the rider in lift?

The rear wing is usually approx 1/3 the size of the front wing. So perhaps assume 1/3 of the lift of the front wing although I will probably use a different airfoil section which will have different lift characteristics.

Assume the rider can shift weight forwards and backwards between front foot and rear foot to keep the foil level, but perhaps include a time lag or some means of indicating how stable the system is.

Ignore the water surface and assume the wings remain submerged.

I want to assess the difference between having an AOA on the front wing and no AOA on the rear wing versus no AOA on the front but a AOA that creates a downforce on the rear wing (Which is how they are normally configured I think). I believe the rear wing is alwasy trying to pitch the front wing upwards creating a greater AOA and hence more lift. The rider has to keep pressure on their front foot to stop the front wing stalling and control the lift to be equal to their weight.

My aim is to understand what parameters to use for front wing AOA, rear wing AOA and mast position to create a hydrofoil that is stable but not so stable that it takes a lot of effort to pitch it forwards and backwards. So I'm not looking for the most stable configuration, I'm looking to avoid something that is really unstable or requires (for example) the rider to put 100% of weight on one foot!

Is it possible to create a meaningful simulation of this with Kangaroo 1 or 2? I made a start... Not sure I've approached it in the right way and haven't attempted to add the coefficient of lift vs AOA feedback.

A video of kite hydrofoiling...

More info for those still reading...
Kite hydrofoils come in many shapes and sizes... there are high aspect ration wings for racing, low aspect wings for beginners / low speed. There seem to be many configurations of mast position, feet position over the mast, length of fuselage, size of front wing to rear wing etc etc.

I'm planning on CNC machining the front wing, fuselage and rear wing in one piece made up from bamboo. Then applying glass fibre or carbon fibre. I already have an aluminium mast and will make a board.

Attachments:

HYDRO_KANGAROO.gh, 17 KB

Replies to This Discussion

Permalink Reply by peter fotiadis on November 15, 2016 at 12:25am

Hmm ...

Still in the wrong side of things eh? he he > only wave windsurfing is the thing to do (and/or speed slalom).

Other that that: consider a classic spin out situation in windsurfing (tail breaks away > sideways > fin in peaces > Adios Amigos). By what means a "2d" simulation can handle that?

Other than that: FEA is a must when designing fins (or hydrofoils in general).

Other than that: Study Oracle Team (the greatest America's Cup racer of all times: THAT immortal race at SF bay ... blah. blah),

and of course that NZL 32 that started all that

Permalink Reply by martyn hogg on November 15, 2016 at 5:10am

I'm not trying to design the foil, just trying to understand how the front and rear foils balance.
If the balance is unstable, you pitch forward and backwards trying to balance your weight about the mast.

You should try one of these on your windsufferer board... Makes riding a challenge again in light winds and gives you that magic carpet ride you will never get on a conventional fin.

Permalink Reply by peter fotiadis on November 15, 2016 at 6:43am

Well... with the advance of electronics these days I guess that this could be another "reactive" design challenge like the new breed of 10ms reacting shocks [first shown in BMW S1000RR SP4] the likes of Ohlins Mechartonics or braking when cornering (impossible without Big Brother).

I.e, mastermind a movable fin system that can "adjust" in forces (in Oracle Team this balance is due to a very fast moving ballast [reaction time: 5ms]).

PS: A friend has a static Carafino thingy. Indeed is "airy" but in some remote sense that I don't like.

Permalink Reply by martyn hogg on November 15, 2016 at 11:17am

Yeah Carafino have been the pioneers for kite foils.
However, I want to make one and adhere to KISS principles so maybe I'll just make one and see what happens :-)

Permalink Reply by peter fotiadis on November 15, 2016 at 11:38am

Well ... since VW signed that recent agreement with Boeing > carbon would reach the masses quite soon (including AEC stuff).

Who would believe a decade ago that in 60 seconds you can make a CF automotive thingy:

http://zoltek.com/applications/automotive/

http://zoltek.com/wp-content/uploads/2015/09/60-Second-Cycle-Time.pdf

So do some Web search and make a DIY CF foil

Permalink Reply by martyn hogg on November 15, 2016 at 11:53am

Awesome... When I have a working prototype I'll be sure to invest!

Now, where was I... Oh yeah, what AOA to set my foils at... :|

Permalink Reply by martyn hogg on November 15, 2016 at 2:55pm

OK, so I'm a bit further with the Kangaroo...

Created a rigid body

Anchored the mast foot in X,Y and Z

Anchored all other points to XY Plane

Added forces at foot positions and wing positions.

Can't figure out what I'm doing wrong... any Kangaroo experts out there?

Attachments:

HYDRO_KANGAROO.gh, 26 KB

Permalink Reply by peter fotiadis on November 16, 2016 at 2:41am

My dear Watson

What has Kangaroo to do with all that? See (WIP) attached that later on will deliver the holly grail (forces et all).

Actually ... not ... since fluid dynamics and other "trivial" stuff are required for doing a proper foil ... but let's be brave and fool ourselves.

Using a teardrop board shape (for real men: utterly unforgiving and a "bit" handful to control) kinda like the notorious all times classic F2 265 (what a hand grenade was that !!!).

Attachments:

HydroFoil_K2_V1.gh, 120 KB
HydroFoil_K2_V1.3dm, 70 KB

Permalink Reply by peter fotiadis on November 16, 2016 at 3:16am

BTW: Kite apart ... the fact that any decent sail these days is designed having loose leech stuff in mind ... makes the foil/fin design far more complicated (since de-power in gusts is "addressed" ). And of course (blame: Outhaul/Sail profile/Batters/etc) the sail CoF is NOT were you expect it.

Permalink Reply by martyn hogg on November 23, 2016 at 5:19pm

I did this using Anenome in the end...

Bit of a headache getting all the angles and forces in the right direction and a lot of assumptions going on but it's a simple 2D simulation of the balance of lift forces for a kite hydrofoil.

Permalink Reply by Arthur Lara on August 18, 2017 at 8:02am