|
How can I use Stress Profiles in ALTA 7 PROs 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 dont 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.
|
