> On 18 Aug 2015, at 14:47, Davide DB <[email protected]> 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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