Welcome to this video where I will be showing you how to extract boundary
condition independent reduced order models in Simcenter Flotherm 2019.1
Reduced Order Modeling is an approach to derive
a dynamic compact thermal model from a thermal simulation model.
A model is BCI if it predicts temperature in space and time with the same level of accuracy
regardless of the thermal environment in which it is placed. A BCI-ROM will enable extremely fast
transient solutions while retaining high accuracy in all situations. The BCI ROM extraction method
in Simcenter Flotherm is an extension of the FANTASTIC method. For more information on this
method, refer to the validation documents on Support Center and the following literature.
Here is conduction only model with two sources, and ambient attributes attached to all faces.
To export a BCI-ROM select project, export project,
BCI-ROM. In the BCI-ROM preferences dialog box define a requested acceptable relative error.
The default value of 0.001 is recommended for most applications. The HTC range sets
the heat transfer coefficient range that is exercised for all ambient
attributes attached at a model, either through the solution, the main faces,
or through cutouts. The default range of 1 to 10,000 W/m^2K is used for Delphi
model generation in Simcenter Flotherm PACK, and is well suited for package level applications.
Navigate to a folder and click save. The solver runs in order to create the export files. The
Thermal Netlist rate BCI-ROM export progress dialog box is displayed, showing a percentage
progress bar. Note that a CFD solution is not created. When the export has finished,
an info message is displayed. The reduced order model is exported in the form of a zip file
which contains start.mtx, matrices defining the ROM, report.ROM, a brief report of the
result of the extraction process including achieved relative error. ROM_parameters.m,
a script compatible with mathematical programming tools such as MATLAB and GNU Octave, that provides
a means to set variables of interests when solving the BCI-ROM in these tools. Now we'll move on to
solving the extracted BCI-ROM in MATLAB. Unzip this folder and place the BCI-ROM in
the desired location for solving. The solver harness available from Support Center contains
several scripts that are used to solve the BCI-ROM and produce plots of the results.
The main script that drives all the Simcenter Flotherm version 19.1 is called ROM_start.m
This is the starting point for all BCI-ROM solves, and the only file in the solver
harness that requires modification. The key setting in ROM_start.m is the project to be
solved. The path to the folder containing the BCI- ROM files should be specified as in the example
shown. Note the relative paths are supported. Within the BCI-ROM open ROM_parameters.m
This is a script file used by the BCI-ROM solver harness to set the following parameters for the
ROM solve. Duration of the transient, heat transfer coefficient values for each ambient
attribute, ambient temperature for each ambient attribute and initial temperature,
power as a function of time for each heat source. When Simcenter Flotherm creates
the ROM_parameters.m file during BCI-ROM extraction,
it will include several values from the original model. The heat transfer
coefficients for the attached ambience, the power dissipation for each heat source,
the global ambient temperature is written as temperature for all ambient attributes
and the initial simulation temperature. Note; if transient variations of power are defined
in the Simcenter Flotherm model these are not included in the ROM_parameters.m file.
They can be added however as per the instructions in the ROM_parameters file. More detailed
information on these settings can be found in the BCI-ROM solver harness PDF available in the
download from Support Center. Save the changes to the ROM_start and ROM_parameters
file. To solve, run the ROM_start file. The ROM solver harness is configured to
create four charts by default following ROM solve completion. 1: probe temperature versus time. The
probe temperatures are centroid temperature for every heat source in the Simcenter Flotherm
model, and temperatures for every monitor point in the Simcenter Flotherm model. 2: Surface
Heat Flows versus time. Each curve on this chart is the heat moving through the collection
of faces associated with the ambient attribute in the Simcenter Flotherm model. A curve for
the total heat flow is also included. 3: Mean Surface Temperature versus time. Each curve on
this chart is the average surface temperature for the collection of faces associated with an
ambient attribute in the Simcenter Flotherm model. 4: Source Power versus time. Each heat source in
the Simcenter Flotherm model is represented with a curve in this chart. Note; these default charts
are defined in the ROM_plot_probe file. This file can be modified to customize
this behavior if desired. The temperature and heat flow data are written to CSV files in the folder
containing the BCI-ROM files. The file names are probe.csv and hflows.csv
The full result set is available in the MATLAB workspace named 'out', following a ROM solve as well. Stored in the
'out' workspace are the following fields which can be copied into other tools if desired for further
analysis or plotting. t_hat x steps, y_hat, a vector in
the ROM space used during the extraction process, T_hat probe temperatures,
hflux surface heat flows, Tstar mean surface temperatures and sources, heat source power dissipation.
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