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#16
 
 
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You've bombed out the freeloaders on turkey and booze and seen them off the premises; it's 2am and the house is quiet, and the wife and kids don't know you are using their computers to run your programs in parallel. Nerd heaven! All the best for the holidays, Leo. 

#17
 
 
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I'll meet you in Nerd heaven (hopefully not too soon) Nerdy holidays for you Uli 
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#20
 
 
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The fact that max. Tcb and the max. Bwl do not occur at the same section may also be a design factor. If so, since the Delft series neglect this factor, all our VPPs could be at err at this point. Maybe top designers understood this long ago and have exploited it in rules like IMS or ORC. 
#21
 
 
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Please keep in mind, that the program is a byproduct of my optimization program. I am only interested in the wetted part of the hull. In my optimization process computing speed is more important than second order effects on the resistance. Keuning shows that bow flare has an effect at large trim and on added resistance in waves. The effect of large trim would be taken care of in my VPP, because I calculate the input parameters for the Delftregression from the hull in the heeled and trimmed attitude. The effect of bow flare on added resistance would disappear unnoticed because Gerritsma's formula for added resistance does not care about bow flare. If the updated version of UliLines with more control over the topsides at the bow is of any help to you, I can try to speed up my work and release the update asap. Uli 
#22
 
 
Interpolating with NURBS or other spline formulations. can lead to oscillations. Try a simple experiment. Create a series of lines which are parallel and planar. Move one line so that it is no longer planar with the others. Now use those lines as input for a NURBS surface. The surface will have waves.
__________________ David Cockey 
#23
 
 
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Interesting to hear that you use coefficients derived from the (static) heeled & trimmed hull as Delft regression input (in the upright formulas?)... do all modern VPPs work that way? As I recall, my (ancient) VPP uses always the upright coefficients, and corrects residuary resistance with an added drag factor due to heel. 
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Uli 
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Uli 
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__________________ David Cockey 
#27
 
 
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See www.orc.org/minutes/ITC%202012.pdf , I a waiting for ORC VPP2013 documentation to be published to learn more. Seems they no longer use delft series upright with a bunch of parameters. Only a dynamic waterline length, LVR (DLR the other way), and BTR (beam/dratft ratio). And they use heeled hull parameters, not uprigh hull parameters with heel correction. BTW, does anyone know how LSM (second moment length) are computed ? There are some clues on page 21 chapter 4.2.2.4. http://www.orc.org/rules/ORC%20VPP%2...ion%202012.pdf What I am missing is where is zero x stem or stern, and what unit (meter, feet). And how is LSM0 is computed. Is it a recursive computation, since depth correction for section does include LSM0 term ? Thanks. 
#28
 
 
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John C. Clements "Ship Lines Using ConvexityPreserving Rational Cubic Interpolation", J. of Ship Research, Vol. 35, No. 1, March 1991, pp. 2831 presents an algorithm for the determination of the weights (called Tau in the paper). The paper also contains a Fortranprogram that can be used. 
#29
 
 
Remmlinger, thanks for the reference. I'll have to obtain a copy and read it. Another approach is to use ordinary/nonrational cubic Bsplines and select the number of intervals and parametarization based on preserving convexity and/or minimizing/eliminating waviness. This is in contrast to the usual approach of basing the number of intervals and parametarization directly on the interpoating points, and then determining the splines (nonrational or rational) using the previously determined intervals and parametarization. I don't know but wouldn't be surprised if someone has pursued this or a similar concept and published something. I was part way there about twenty five years ago but then dropped it when it was no longer needed. Unfortunately I can't find my notes from that time.
__________________ David Cockey 


#30
 
 
You may find these up your alley then: "Application of a realcoded genetic algorithm for the fitting of a ship hull surface through a single nonuniform Bspline surface", Le TH., Kim DJ. JMST Vol 16, No.2 2011. and "Surface intersection in geometric modeling of ship hulls", Ventura M., Guedes Soares C., JMST, Vol 17, No.1 2012. 
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