On Tue, Feb 07, 2017 at 08:47:41AM +0100, Robert Helling wrote: > Hi, > > > On 06 Feb 2017, at 19:30, Robert Helling <[email protected]> wrote: > > > > a no progress report: I guessed it’s the max_ambient_pressure but now I > > know, it is not. Tonight, I will not have further time to look into this > > (we have visitors), so if someone else wants to give it a try: There are a > > few other state variables of VPM-B, all defined as global variables in > > deco.c. I would next try max_crushing pressure (by resetting this between > > dives and see if this makes the deco almost independent of the day. In > > Buehlmann, one can see, that the difference in saturation is only minimal). > > > > I think I understand this now. This is a „feature“ of the VPM-B model. (For > some background on this model see http://euve10195.vserver.de/wp/?p=27 > <http://euve10195.vserver.de/wp/?p=27> or the German version > http://euve10195.vserver.de/wp/?p=46 <http://euve10195.vserver.de/wp/?p=46>) > > One of the state variables of this model is the „crushing radius“ (here > r_reg) defined by > > 2(γc−γ)rreg=pmax+2(γc−γ)rcrit > which enters the calculation of the allowed gradient (at least in the first > iteration) as > > G0=2γγcγc–γrreg. > > If you are doing repetitive diving, this is tracked between dives and since > p_max (the maximal over pressure during the dives) enters the maximal depth > encountered is relevant for the deco. Your first dive has a depth of 60m so > it sets this variable also for the second dive which is only 40m. Thus, > according to these formulas, it allows for a bigger gradient which means it > is more liberal with respect to over pressure in the tissues which results in > shorter deco. > > And no, I don’t think this makes sense. But it is the model. It is not the > first oddity of this model we come across. > > As far as Subsurface is concerned, I guess we should leave it as is (after > all, people want „the real model“, if we would change the behaviour of > Subsurface we would break with the original Baker code and people will hate > us for this). > > Thanks for finding this out. Once I have a bit more time, I will write about > this in my blog.
We should link to your posts from our page... Or maybe add them to our page (with your permission). I think that would be quite useful to have. Thanks for the explanation! /D _______________________________________________ subsurface mailing list [email protected] http://lists.subsurface-divelog.org/cgi-bin/mailman/listinfo/subsurface
