There is no "lift"!

Shall we discuss oar efficiency here or in the oar efficiency thread?

 

I'm not trying to highjack this thread and turn it into an efficiency thread. It's just that I think there is a parallel in that jehardiman's assertion seems to require momentum theory to hold and the same has also been asserted for the efficiency formula. In various places and in various language, Leo, jehardiman, myself, and several of the authors of the papers referenced in the "oars" thread have mentioned that getting straight at the problem as directly as possible is desirable when trying to evaluate an entire system.

Unfortunately, if you want to play around with component optimization, you are forced to deal with the bits and bobs of the mechanism. But once a change has been made and all of the component's new parameters decided, go back and evaluate the entire mechanism using the most direct method. This is where global optimization should be pursued.

Some quotes along this line of thinking- since most of us would prefer to quoted rather than slandered

Jeh's opening post in this thread.

My post in response to TSpeer's post, #33 and #34 in the Oars thread.

The opening paragraph from here - http://www.atkinsopht.com/row/bladefcy.htm

 

If by "momentum theory" you mean the approximation using a number of simplifications for the theoretical limit of efficiency of a propeller which is frequently referred to as "actuator disk theory", then I don't currently see how it is directly relevant to an oar.

It's possible to draw a control volume around an oar and apply the momentum integral equation to that volume. By itself that doesn't produce anything which is directly useful. There may be some simplifications and approximations which can be used to result in an approximate theory for oar efficiency.

I'm currently working on a post in the oar efficiency thread about the efficiency of rowing based on the motion of the oar and hydrodynamic force on the blade. But it does use simple vector component analysis, not the momentum integral equation.

 

I agree.

<edit> Since I am not an NA and don't play one on tv, I am probably being a bit loose with my reference to Momentum Theory. I didn't take any classes in it and don't have any canonical knowledge. I am using it in the sense that changes in the internal energy of the system can be ignored and time factors such as phase shifts are negligible. Once time is brought into play, one ought to be prepared to deal with internal energy, and that necessitates dealing with the position, velocity, and acceleration of everything inside the control volume. Momentum theory, to me, is an approximation that lets us ignore accelerations, and time in general. An independent entity represents momentum and time is vanquished.

 

Just added a related post in http://www.boatdesign.net/forums/hy...lsive-efficiency-oars-47468-4.html#post641798

 

Calm down.

I do know a lots about fluid mechanics and I can challenge anyone here in that field. However, I do know very little about rowing, yes.

Cheers

 

It's very, very well understood that lift and drag are components of a single force vector in a given coordinate system. Forces are decomposed into components because it's actually useful to know how much of a force is in a given direction. (Sometimes they are decomposed for little reason because someone is following the tradition blindly, but it's not a tradition based on misunderstanding or without good reason.)

It's still as real as any other force.

 

You should see the hornet's nest I stirred up when, unaware of this thread, I started a new thread on a very closely aligned subject.


Enjoy!