When I use the
"Save Log of Simulations" feature in
BlockSim 7 and calculate the average of all the
individual results, why isn’t that value identical to
the results from a single set of simulations using the
To understand this question
and the reason why the results are not identical,
suppose you are interested in the
reliability/maintainability performance for a system and
you want to use simulation to estimate useful metrics,
such as the mean availability and the total expected
downtime after 1000 hours of operation.
model the system in
BlockSim and then use the General
tab of the Maintainability/Availability Simulation
window to run 100 simulations for the specified mission
time (1000 hours), the Simulation Results Explorer will
display a variety of metrics obtained by calculating the
average of the results from the 100 separate simulation
runs. Furthermore, if you specify a "seed" that will be
the starting point for the random number generation, the
simulation routine will draw from a single stream of
randomly generated numbers for the series of 100
simulations. Therefore, the results will be reproducible
if you perform the exact same set of simulations again,
using the same seed, for the exact same diagram.
As an example, Figure 1 shows the settings and some
results from a basic simulation analysis.
Figure 1: The settings for a single set of 100
simulations, along with the Mean Availability and Total
Downtime metrics estimated for 1000 hours of operation.
Now suppose that you want to perform a more
in-depth exploration that will help you to analyze the
variability within the simulation results. For that
purpose, you can use the Save Log of Simulations option,
which is available in
BlockSim 7.0.2 or higher. With this option, you
still specify the number of simulations and seed on the
General tab (let’s assume they are the same as in
Figure 1) and then you also specify some additional
inputs on the Display/Other Settings tab, as shown in
The additional settings for using the "Save Log of
Simulations" feature include: a) a value by which to
increment the seed for each individual simulation, b)
the results that will be displayed in the log and c) the
path/filename for the log file.
With the settings
shown in Figures 1 and 2, BlockSim will perform one
simulation using a seed of 1, then a second simulation
using a seed of 11 (1 + 10 = 11), and so on until the
utility has performed 100 separate simulations. Figure 3
shows a portion of the log file generated for this
example. As you can see, the first data row shows the
Mean Availability and Total Downtime obtained from the
simulation performed with seed=1, the next row shows the
results from the simulation with seed=11, and so on.
Figure 3: Portion of the
log of simulation results, where each row represents the
simulation performed using the specified seed.
Although both of these techniques will provide results
based on 100 simulations of the diagram, the values will
not be identical because the simulations will draw from
different streams of randomly generated numbers.
With the basic simulation approach described first,
all 100 simulations will draw from a single stream of
randomly generated numbers where the seed=1.
Whereas, with the "Save Log of Simulations" method, the
first simulation will utilize a stream with seed=1, the
second simulation will utilize a stream with seed=2, and
Therefore, if you were to compute the
average of all 100 of the individual availability (or
downtime) results shown in the log, it would not be
identical to the comparable result displayed in the
Simulation Results Explorer. This is not cause for
concern because there will always be variability in the
results obtained via simulation. The range of values
generated by the "Save Log of Simulations" feature will
allow you to explore how significant that variability
might be for any particular analysis.
Can I configure Xfmea 5/RCM++ 5 to give a particular
user access to some projects but not others?
Yes. In Xfmea 5 or
RCM++ 5 when you
are working with an Enterprise database or with a
Standard database with login security enabled, the
Access Group feature makes it possible to provide each
user account with different types of access for
different projects in the database. For example, you may
want to grant a user read/write access to all projects
in the "Department A" and "All Departments" groups,
read-only access to all projects in the "Department B"
and "Department C" groups and no access to projects in
the "Confidential" group. There are three steps to use this
functionality. (Note that only users with the
Admin access level in the database can perform these
steps. In the steps below these individuals are referred to as "authorized users.")
- An authorized user can choose File
> Database Setup > Define Access Groups to open the
Define Access Groups window and define the categories
that are used within the database to differentiate the
different types of access that can be granted to users.
- To restrict
a user’s access based on group, an authorized user can
choose File > Database Setup > Manage Users to open the
Manage Users window. Open the user record, set the
Access Level to By Access Group and then set the
permission level (User, View or None) for each group.
To restrict access to a project based on group,
authorized users can select the project and then choose
Project > Project Properties to open the Project
Properties window. On the Access tab, click
the Restrict access to project by selected user access
groups option and select which access group(s) the
project belongs to.