Poseidon CCR dives: Nitrogen loading

[Robert C. Helling]

On 05 Nov 2014, at 17:37, Willem Ferguson <willemferguson at zoology.up.ac.za> wrote:

Willem,

> 1) This patch has an unintended consequence: The ending cylinder pressure for the diluent cylinder (as seen on the equipment tab) is changed to reflect that of the ending pressure of the oxygen cylinder. The diluent cylinder index for the Poseidon diluent is the dreaded and infamous 1. We hardcode the cylinder IDs here while reading in the dive log because it is very specific to the Poseidon. In addition, even though these specific two cylinders have already been assigned to enum values of oxygen and diluent respectively, we are in the process of setting up the cylinders, so we cannot already use the functions that use these enum values.
> So:  dive->cylinder[1].sample_end.mbar for this sample dive has a value of 141, that of the oxygen cylinder. The correct ending value for this variable is 137. I have carefully looked around the code around line 600 in file.c but cannot see the cause of this problem. Run the code with and without your patch and see the difference.
> 

This is weird. For some reason the pressures for the O2 cylinder are shown even when the gas name is “Air”. Have to investigate this further.

> 2) A question just to improve my understanding of the code. If the explicit_first_cylinder() result is diluent, does this mean that the deco requirements are calculated for the gas in the diluent cylinder? In this case the diluent is air, but the displayed ceilings do not (at first sight) appear to be shallower than that for air dives to the quivalent depths. For instance, if I simulate the sample dive as an air dive using the planner, the dive extended to 70 min for sufficient deco. So if the ceilings reflect the pn2 values at the various depths as actually calculated at each point on the profile, why does it matter whether one starts with cylinder 0 or cylinder 1?


It means that air is handed to fill_pressures as gasmix (for which then the inert gas pressures are adopted according to the set point). So it should do the correct thing. If you gave it O2 then the gas output would always be pure O2 (and thus no deco obligation).

Best
Robert

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Robert C. Helling     Elite Master Course Theoretical and Mathematical Physics  
                      Scientific Coordinator                                   
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