Another perfect sailing day, but still on the DL for another 4 weeks. G. mentioned wanting to filter out the chop input to the flap, so I added chop to the stability model to see the effect. The plot above is the work ( drag times distance ) for the foils in the case of a 3 ft wave and a 3ft wave with 0.5 ft chop. Vertical axis in ft-lbs (1 ft-lb = 1.35 Joules), horizontal in feet. The spike represent the extra work due to response to the chop by the flap.
It does seem like filtering out the high-frequency could be a good idea....all the extra work has to be slowing the boat down. But any filter will slow the response (e.g. to sharp waves) down so there will be some optimization.
There was one question about the work in the chop ( green line) case, so I plotted with a better scale. The wave and chop start at 200 ft. Before that, the work in the green/blue cases are the same. After the chop starts, the work by the flap responding to the chop is taking more energy out of the boat.
This model has some simplification so it is really not good for predicting absolute performance like the one Alan posted in Doug Culnane's website. I just ran this case to get an idea of the energy going into the response to chop, which ideally the control system would ignore.
Just need to figure out a way to implement filters without op-amps and batteries.
why does green line start higher and finish lower?
ReplyDeleteReposted the graph so you can see the two lines start at the same place. Green line is higher at the exit due to the extra work by the induced drag due to response to the chop, I guess. This model is a linear one so the forces are not accurate ( e.g. no stall) but maybe it gives some direction.
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