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>chris, > >as i understand it, you are using wienke's critical gradients to limit >tissue supersaturation on repetitive dives (this is of course where the >reduced gradient bubble model takes over from yount's varying >permeabillity model). Close, but not quite. What we use is a customized model wienke developed for us to calculate dynamic critical gradients that vary throughout the course of the dive. Thus as you watch the tissue window you will see the gradients are in a state of constant flux, responding to the ever changing status of the dive. These critical values are affected by several factors. 1. Which dive this is in a series. (how many dives you have made) 2. Duration of last surface interval. (micro bubble nucleation probability) 3. Depth of last dive. (possible deeper than previous dive) 4. Diver Workload. (modifies ongassing/offgassing, and thermal production) 5. Diver Thermal status (relative heat loss at current point in dive). 6. Total number of days diving. (bubble stress from multi-day dives) 7. Diver Fitness ( a general physical condition rating, including previous DCS). 8. Water Temp. 9. Compartmental Status (ongassing vs. Offgassing) > >also, i wasn't too clear on the nature of your algorithm--the vpm and full >rgbm require itterative calculations to converge on a schedule (rather >than giving aschedule on the first go-through as buhlmann,etc). do you >use look-up tables with wienke's chi-s to reduce the allowable gradients >or does abyss really do a full-blown bubble calculation? > None of the above. Though we are looking into building a fully itterative version into V2.00 The three current algoriths in Abyss are Buhlmanian in nature, and thus are Not itterative. Bruce is working on some new code for us right now. Exactly how that will pan out is not yet known. But I suspect we will have a NON-Buhlman algorithm available in V2.00 next year. >do you use decap M-s for the first dive or wienke's gradients? > Neither. We start out with our own "a/b, or Ms", and then initiate the variations/modifications based upon the nature of the dive. With both the Halftime and the a/b values, Abyss is modifying them throughout the dive. I think we currently have 2,048 halftimes and 25,344 a/b values that Abyss has access to over the course of a dive. >if you >use vpm gradients, and yount/hoffmann's algorithm, you get the deep >stops. did your user interface originally supress these stops (due to >unpopularity) before you added the soft-switch? When we released V1.00 Abyss had the deepstops in it. But the majority of the users did not want them. So we changed the code to remove them from the calculations. This generally resulted in the loss of 2-3 1 minute stops. What I plan on adding back will look at your current depth, the first required deco stop, the gradient change in allowable compartmental pressures, and then determine a series of short deep stops to reduce the rate of increase in the compartments resulting from the decrease in ambient pressure durring hte ascent. Problem is, as soon as we introduce the deeper stops, the shallower stops begin to change as a result of the extra ongassing/offgassing <G>!! Christopher M. Parrett, President, Abysmal Diving Inc. Makers of ABYSS, Advanced Dive Planning Software. 6595 Odell Place, Suite G. Boulder CO, 80301 Ph, 303-530-7248, Fx, 303-530-2808 ftp://abysmal.com/users/abysmal http://www.emi.net/boynton/abyss/abyss.html
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