planner / VPM-B patches

[Robert C. Helling]

> On 18 Aug 2015, at 14:47, Davide DB <dbdavide at gmail.com> wrote:
> 
> 
> I'm seeing some great discrepancy on multilevel and repetitive dives.
> Really I don't know if it's a DP bug.
> 
I guess, we will find out with a few more programs added.

> My question: does it make sense testing a bounce dive as 10'@100m. I
> think it's like play dice. isn't it?

So maybe we should not take that sheet to literal. I just added another dive with an hour bottom time at 100m to give uns an example of a deep long dive.

> 
> it worth copying here an excerpt of DP user manual about repetitive
> dives (I'm under the impression it was very experimental...)
> 
> Repetitive Dives
> 
> DecoPlanner allows the user to plan repetitive dives over any period.
> The theory behind repetitive dives is based on Bühlmann’s pulmonary
> shunt model. During a surface interval, gas elimination is delayed due
> to the pulmonary shunt mechanism; the gas loading remains higher than
> a normal set of calculations would conventionally calculate.
> Accordingly, on repetitive profiles, it will mean either less no-stop
> time or longer deco time.
> DecoPlanner runs gas-loading calculations for all the compartments on
> a continuous basis, which may cover days or even weeks! The gas
> loading is calculated and updated within a mission and are calculated
> according to what the diver is doing (surface interval or diving).
> At the end of the first dive of a mission (i.e. after all
> decompression), each compartment will have a certain loading of helium
> and nitrogen. Generally, after oxygen decompression, the fast
> compartments will be completely empty of helium and nitrogen and they
> will on-gas with nitrogen during the surface interval! The slowest
> compartment, 635 minutes for nitrogen, takes over two and a half days
> to completely off-gas, so any repetitive dive will halt that process.
> Until a better implementation of the pulmonary shunt model is
> developed, DecoPlanner behaves as if the surface interval is at one
> metre, breathing 21% (i.e., air), and as such the tissues never clear
> completely; once a surface interval of three to four hours is exceeded
> the penalty on the subsequent dive is the same whether the diver waits
> four or 24 hours.

This sounds to me like they are describing how to treat repetitive diving of a traditional diffusion (e.g. Buehlmann) model, except that „completely empty“ should be true only for a somewhat liberal interpretation of the word „completely“ and not like a bubble model.

> 
> Repetitive VPM
> 
> [Adapted from an original document written by Yount, Maiken, Baker]
> 
> At the start of a first dive, if the diver has not been diving for a
> few weeks, the radial distribution of gas nuclei or “bubble seeds” in
> the body is assumed to be pristine. In other words, the radial
> distribution is the same in all tissue compartments and has its
> long-term equilibrium values.
> During ascent or decompression on the first dive, the supersaturation
> gradients in each compartment may be relaxed (increased) by the VPM
> dynamic critical volume algorithm to allow Nactual versus Nsafe number
> of bubbles to form. This causes dispersion in the radial distribution
> of gas nuclei across the various tissue compartments.
> To compensate on a repetitive dive, the VPM adjusts the minimum
> initial radius of gas nuclei in each compartment by an amount
> proportional to the dispersion that took place on the previous dive.

I must admit: I cannot make much sense of the prose these people write, in particular I find it very hard to turn that into code/formulas.

Best
Robert

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