Free Internet Rowing Model (FIRM)

Discussion in 'Software' started by Leo Lazauskas, Oct 30, 2014.

  1. NoEyeDeer
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    NoEyeDeer Senior Member

    Haven't done any more modelling, but have a question for Leo.

    At the start of the manual it lists good and daft ways to try and use this app. What I'm interested in is how the differences in stroke length and boat speed will influence optimal catch and release angles, as well as torso angles, for a fixed seat boat compared to a scull.

    My question is, would it be reasonable to attempt to use FIRM to get quantitative comparisons for these details?
     
  2. Leo Lazauskas
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    Leo Lazauskas Senior Member

    If you exert the same force over a longer stroke then, yes, you
    will cover more distance for each stroke, but you will do more work.
    A better comparison would be to look at the mean hull speed per stroke
    for the same "impulse". If you increase stroke length in the model,
    decrease the maximum force so that the area under the curve is the
    same.
    Kleshnev has grappled with the same issue in his August 2014
    newsletter:
    http://www.biorow.com/RBN_en_2014_files/2014RowBiomNews07.pdf

    Changing the torso angle will change the boat acceleration, but it
    will have little or no effect on mean hull speed.

    Version 2.30 will be released in a couple of days.
    Old anthro.csv files will need to be changed to include radii of
    gyration of limb segments. Standard values for these will be included
    in the example files.
     
    Last edited: Nov 16, 2014
  3. NoEyeDeer
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    NoEyeDeer Senior Member

    With the torso angles and catch/release angles I was mainly wondering if FIRM could give insights on optimums, or if that's not an appropriate use of the app.

    What I'm thinking is that past certain torso angles you're likely to become biomechanically inefficient, so there would be a useful limit on torso angles. This is probably more the case towards the catch where (if rowing fixed seat) you're basically trying to pick up a load from touching your toes, if you see what I mean.

    The other thing is that any lift force at the catch, which seems to be trendy among scullers, is likely to largely dependent on the square of the boat speed. That means slower fixed seat boats may be more efficient with shorter catch angles. I don't know if this is actually the case, but it seems plausible and is something I would be interested doing comparative modelling for, if this is an appropriate usage of FIRM.

    Shortening the stroke is probably going to mean less variation in hull speed, but OTOH more energy chewed up throwing your torso, arms and oars around, so there will be trade-offs there too.


    I saw your grumbles about the source of data being retired Air Force personnel. TBH this is pretty much ideal from my perspective, since data for aging white blokes is what I need for myself. :D
     
  4. Leo Lazauskas
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    Leo Lazauskas Senior Member

    FIRM might give you some insights into how the mean hull speed and
    instantaneous propulsive acceleration varies with catch angle and torso
    angles. I suspect you would be better off looking at how to improve the
    mid-drive, where most power is generated.

    I think there is too much emphasis on the lift force generated by the blades.
    Firstly, it occurs for a very short time near the catch, when blades are close
    to the surface. Secondly, there is also an attendant drag that goes with that
    lift. Many people think that lift comes with no penalty.

    That's right. It is a very complex system. I will try to explicitly calculate "internal" power losses at some stage.
    In one reference I saw a few years ago there were 17 definitions of rowing "power"!

    They are probably Ok for oldish, smaller men. Fighter pilots tend to be short
    wiry types. I doubt that there are many 2m tall, 100 kg fighter pilots.

    I read that the differences in segment masses and CM location can be as
    much as 15%-20%, but fortunately it doesn't make quite as much difference
    to hull speed and acceleration predictions.

    There are many new techniques for estimating limb masses, CM, and other
    quantities. Pinning a severed limb and swinging it like a pendulum to estimate
    its radius of gyration is not for the faint-hearted I imagine.
     
  5. NoEyeDeer
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    NoEyeDeer Senior Member

    Just read that. Makes sense, as far as it goes, but doesn't mention the fact that if you shorten the stroke, you'll probably also be increasing the stroke rate. So in that case you wouldn't need to hold WpS constant. All that would matter would be mean speed for a given power output over the course (including allowances for internal losses at the different stroke rates).
     
  6. Leo Lazauskas
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    Leo Lazauskas Senior Member

    Maybe that's why impulse isn't used very often. :)
    For me the shapes of the curve are interesting, and how they vary between
    rowers in multiple crews.

    If you are really interested in power, then you can get some idea using FIRM.
    Oar handle power is handle force X OHCE distance from pin X angular velocity
    squared.
    You can get power of body segments using their weights and speeds.
    I haven't thought much about internal losses yet. I have been looking at a
    variety of "bio-energetic" models which could be fun to implement at some
    stage, e.g. having small "tanks" to simulate anaerobic and aerobic capacities.

    Version 2.30 was released yesterday.
    Old anthro.csv input files will need to be changed to include radii of gyration.
    Examples use "standard" estimates for those radii.

    I've also included two more (real) rowing shells so users can compare
    performance, and use them as the basis for their own designs.
    (Fixed seat rowing is still very crude because I don't have any on-water data
    to work with).

    Late edit:
    Old main input files will also need to be changed to include wind speed and direction.
     
  7. NoEyeDeer
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    NoEyeDeer Senior Member

    As soon as I can, I'll see about getting you some fixed seat data. It'll take me a while to get anything useful though. However, next year I'm going to try and set up comparisons between my new boat and the Herreshoff/Gardner boat, including test runs with the same person rowing each boat alternately. I want to get a good indication of how the real world performance with the same "engine" stacks up against the Michlet predictions. This should be useful information for future fixed seat designs.
     
  8. Leo Lazauskas
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    Leo Lazauskas Senior Member

    That will be an interesting exercise for you!
    One day I should try to get some of my acquaintances to fix the seats
    on their boats for one or two runs and record (at 100Hz) the gate forces,
    oar angles, hull velocity and acceleration. That's all I really need.

    Incidentally, the "internal power losses" you mentioned in a previous
    post seem to be independent of stroke rate. See:
    Hofmijster, Mathijs,
    "Mechanics and energetics of rowing",
    PhD Thesis, VU University, 2010,
    http://hemus.nl/maand/2010/mechanics_rowing.pdf
     
  9. NoEyeDeer
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    NoEyeDeer Senior Member

    Interesting read. I noticed this down on page 37:

    It's also clear that athletes can't sustain the higher stroke rates for long, which implies something is being lost somewhere and that these losses increase at higher stroke rates.
     
  10. Leo Lazauskas
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    Leo Lazauskas Senior Member

    I also wonder how those very high rates would affect their longevity as athletes.
    You'd think that very high stroke rates must increase wear and tear on some
    joints.

    There are a variety of possibilities: increased drag due to surge; losses at
    the oarblade; compressing the chest cavity at a rate that is out of phase
    with the best regime for breathing and oxygen uptake, etc etc.
     
  11. NoEyeDeer
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    NoEyeDeer Senior Member

    Yeah I was thinking of the last one too, since breathing is very important for rowing. Well, important for continuing to live too. :D
     
  12. Leo Lazauskas
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    Leo Lazauskas Senior Member

    In my youth I used to think that about drinking too. I also noticed that doubling the drinking rate caused my knee joints to buckle earlier. That's science.
     
  13. NoEyeDeer
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    NoEyeDeer Senior Member

    I had a theory that the reason they try to make sure you're smart before letting you into university is because of the number of brain cells that will be slaughtered by student drinking games. Need to have some left at graduation time.
     
  14. Atkinsopht
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    Atkinsopht New Member

    Leo:
    I too have been looking at FIRM.
    Do you know how to contact the author?
    I can find no name or contact information.
    Hope you are well and Happy New Year.
    Bill Atkinson
     

  15. Leo Lazauskas
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    Leo Lazauskas Senior Member

    A few bugs that have corrected in version 2.31 which will be released
    early in 2015.

    1. The FIRM window is incorrectly titled FIRM v2.21. This is just a
    minor over-sight.

    2. Radii of gyration are referenced to the segment CM. The heading of
    Table 1 is ambiguous. This has been corrected in version 2.31.

    3. Average air and hydro drag power calculations shown on the main
    screen and in summary.csv are incorrect. They are actually drag
    averages in Newtons. No other calculations are affected. This has
    been corrected in Version 2.31.
     
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