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How can I use Stress Profiles in ALTA 7 PRO’s Monte Carlo and
SimuMatic utilities?
ALTA 7 PRO offers
the cumulative damage life-stress model, which allows you to
analyze data with up to eight stress levels that vary with time.
This model is used in conjunction with Stress Profiles, which
describe the relationship of stress to time.
Like all life-stress models in
ALTA, the cumulative damage model can also be used in the Monte
Carlo utility, which allows you to generate data based on the
life-stress model, distribution, parameters, and stress levels
that you specify, or in the SimuMatic utility, which allows you
to perform a large number of reliability analyses on data sets
that have been created using Monte Carlo simulation.
To use this option in either
utility, simply
select Cumulative Damage from the Model drop-down
list on the Model page, then specify a number
from 1 to 8 in the Number of Stress Columns field. To apply Stress Profiles to the points that will
be generated, right-click the cells in Stress columns in the
Spreadsheet area of the Monte Carlo or SimuMatic window and
select from the available Stress Profiles, as shown next.
Note that the
Stress Profiles field, which appears when the cumulative
damage model is selected, allows you to manage the Stress
Profiles available in the project without exiting the Monte
Carlo or SimuMatic utility. The Stress Profile
icon beside the field allows you to edit the Stress Profile
currently selected in the drop-down list or, if Add New
is selected, create a new Stress Profile and add it to the
drop-down list.
For data generated by
the Monte Carlo utility, once the Standard Folio containing the
data has been created, you can also use a Stress Profile for the
use stress value for any stress by clicking the Set Use
Stress link on the Main page of the Standard Folio Control
Panel. In the Use Stress Level window that appears, select the
Profile checkbox and then select a Stress Profile from
the drop-down list, as shown next.
Why don’t my results exactly match the ones in the BlockSim and RENO
training guides, even when I use a "seed" for the simulation?
As you may be aware, results
obtained through repeated simulations of the same
BlockSim diagram or
RENO flowchart will exhibit some variability. The use of a seed in
simulation forces the software to use the same sequence of
random numbers in each simulation, resulting in repeatability.
However, you need to be aware that when you use a seed, the same
stream of random numbers is utilized for all simulations that
begin with the same seed, but the order of the
utilizations of the stream will depend on the order in which
objects were added to the diagram or flowchart. The random numbers are
assigned based on an internal ID number assigned upon creation to each block,
in a BlockSim diagram, or construct/definition, in a
RENO flowchart. Note
that you can select to display these internal IDs in the
diagram/flowchart by selecting the Show Block ID option on the
Appearance page of the Diagram/Flowchart Options window.
This means that two identical
diagrams/flowcharts that are simulated with the same seed may
return different results if the objects in both
diagrams/flowcharts were not added in exactly the same order. For example, two people may have
BlockSim projects containing
identical diagrams using blocks A and B. If A
was created before B in one diagram, A will take the first random value from
the stream and B will take the second. If the other person created the same diagram but created B before
A, B will take the first random value from the stream and A will
take the second, thus yielding potentially different answers,
even though both persons may have used the same seed in
simulation. Note that this type of variability should be
expected in analyses performed using simulation and that, as the number of simulations increases,
this difference will be less significant.
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