Nautilus DIVE PLANNER Version 1.0 사용자 설명서
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VERSION 1.0
VERSION 1.0
VERSION 1.0
VERSION 1.0
VERSION 1.0
Comparison of the VPM to Conventional
Decompression Procedures
Decompression Procedures
A major difference between the VPM and standard
supersaturation algorithms is that the VPM programs use
an iterative procedure to calculate a decompression
schedule. In each step of the iteration, a new decompression
schedule is calculated. The total decompression time is then
fed-back into the calculation to revise the critical gradients
(SUB PNEW in the BASIC Programs), and a more liberal
schedule is produced. Maybe this should be called the
“IGBM” —the increased gradient bubble model ;*) This
process of updating the ascent repeats until the
decompression time converges to what supposedly
corresponds to the formation of the maximal allowable
amount of free gas. The first and last schedules produced
for a short dive are often quite different. This results from
the contribution of both the magnitude of the growth gradient
+G and the time that the gradient acts to drive bubble growth.
After a short dive, the tissues will off gas rapidly to circulation.
Hence, because the time that the gradient acts is small, the
magnitude of G can be increased by allowing shorter and
shallower stops.
supersaturation algorithms is that the VPM programs use
an iterative procedure to calculate a decompression
schedule. In each step of the iteration, a new decompression
schedule is calculated. The total decompression time is then
fed-back into the calculation to revise the critical gradients
(SUB PNEW in the BASIC Programs), and a more liberal
schedule is produced. Maybe this should be called the
“IGBM” —the increased gradient bubble model ;*) This
process of updating the ascent repeats until the
decompression time converges to what supposedly
corresponds to the formation of the maximal allowable
amount of free gas. The first and last schedules produced
for a short dive are often quite different. This results from
the contribution of both the magnitude of the growth gradient
+G and the time that the gradient acts to drive bubble growth.
After a short dive, the tissues will off gas rapidly to circulation.
Hence, because the time that the gradient acts is small, the
magnitude of G can be increased by allowing shorter and
shallower stops.
VPM tables handle the in and out gassing of dissolved gas
in tissues the same way as conventional neo-Haldane
calculations do. That is, parallel compartments with
exponential half-times ranging from minutes to hours are
used to model the uptake and elimination of inert gas by the
body. This is and off gassing is handled symmetrically in all
of my programs. The divergence of the VPM from
conventional calculations is in the details of how a diver’s
ascent is controlled. Rather than setting limits on the maximum
pressure ratio/difference between gas dissolved in tissues
and ambient pressure (supersaturation), ascents are limited
by controlling the volume of gas that evolves in the body
due to the inevitable formation of bubbles. As long as this
volume is kept smaller than a certain “critical volume,” it is
presumed that a diver’s body has the ability to tolerate the
bubbles. If the volume of bubbles exceeds the critical volume,
the diver is at risk of a pain-hit or worse. The volume of the
gas in bubbles is related to the product: (number of bubbles)
x (Gradient) x (growth time). The number of growing bubbles
in tissues the same way as conventional neo-Haldane
calculations do. That is, parallel compartments with
exponential half-times ranging from minutes to hours are
used to model the uptake and elimination of inert gas by the
body. This is and off gassing is handled symmetrically in all
of my programs. The divergence of the VPM from
conventional calculations is in the details of how a diver’s
ascent is controlled. Rather than setting limits on the maximum
pressure ratio/difference between gas dissolved in tissues
and ambient pressure (supersaturation), ascents are limited
by controlling the volume of gas that evolves in the body
due to the inevitable formation of bubbles. As long as this
volume is kept smaller than a certain “critical volume,” it is
presumed that a diver’s body has the ability to tolerate the
bubbles. If the volume of bubbles exceeds the critical volume,
the diver is at risk of a pain-hit or worse. The volume of the
gas in bubbles is related to the product: (number of bubbles)
x (Gradient) x (growth time). The number of growing bubbles
is set by the maximum compression encountered on a dive.
This crushing pressure is related to the deepest depth of the
dive as well as the descent rate and gas mixture. All of the
programs on this site directly relate pCrush to the maximum
depth. The gradients and bubble growth time are controlled
by the ascent schedule, with the surface explicitly considered
the last decompression stop.
This crushing pressure is related to the deepest depth of the
dive as well as the descent rate and gas mixture. All of the
programs on this site directly relate pCrush to the maximum
depth. The gradients and bubble growth time are controlled
by the ascent schedule, with the surface explicitly considered
the last decompression stop.
Rather than using tens or hundreds of arbitrary of
parameters to generate ascent schedules, the main result
parameters to generate ascent schedules, the main result
of the VPM is the replacement of the ascent-limiting
matrix of M /a-b values with only four constants,
corresponding to measurable physical and physiological
quantities. In the BASIC programs, they are found in
SUB DIVEDATA. The minimum bubble radius excitable
into growth ro = r
matrix of M /a-b values with only four constants,
corresponding to measurable physical and physiological
quantities. In the BASIC programs, they are found in
SUB DIVEDATA. The minimum bubble radius excitable
into growth ro = r
o
, the skin tension of bubble nuclei
gamma =
γ , the nuclear crushing tension gc = γ
c
, and
the maximum tolerable volume of bubbles, which is
proportional to lambda =
proportional to lambda =
λ. For the hour-long time
scales treated by this program, the nuclear regeneration
time (see Yount’s eq. 2) is essentially infinite, and hence,
not used. From these constants, critical gradients G are
formed in SUB DIVEDATA on the first iteration and then
in SUB PNEW on subsequent iterations. The critical
gradients limit ascents because they are directly related to
the rate of bubble-growth by the diffusion equation.
time (see Yount’s eq. 2) is essentially infinite, and hence,
not used. From these constants, critical gradients G are
formed in SUB DIVEDATA on the first iteration and then
in SUB PNEW on subsequent iterations. The critical
gradients limit ascents because they are directly related to
the rate of bubble-growth by the diffusion equation.
Reference: Eric Maiken
http://www.decompression.org/maiken/
VPM_Background.htm
VPM_Background.htm
The appendix of: D.E. Yount, D.C. Hoffman, On the Use
of a Bubble Formation Model to Calculate Diving
Tables. Aviation, Space, and Environmental Medicine,
February, 1986.
of a Bubble Formation Model to Calculate Diving
Tables. Aviation, Space, and Environmental Medicine,
February, 1986.
NAUTILUS incoporates the Variable Permiability Model
into its portfolio of Decompression Models.The user will
have control over the values used for Gamma, Lambda,
and M yielding what NAUTILUS designates as VPM-x
into its portfolio of Decompression Models.The user will
have control over the values used for Gamma, Lambda,
and M yielding what NAUTILUS designates as VPM-x