The directory in which this program is run contains a number of sample
parameter files that you can use to reproduce the results presented in this
section. If you do not specify a parameter file as an argument on the command
-line, the program will try to read the file "parameters.prm" by default, and
-will execute the two dimensional version of the code. As explained before, if
+line, the program will try to read the file "`parameters.prm`" by default, and
+will execute the two dimensional version of the code. As explained in
+the discussion of the source code, if
your file name contains the string "23", then the program will run a three
dimensional problem, with immersed solid of co-dimension one. If it contains
the string "3", it will run a three dimensional problem, with immersed solid of
@endcode
However, as the error message already states, the code that triggers the
-exception will also generate the specified file ("parameters.prm" in this case)
+exception will also generate the specified file ("`parameters.prm`" in this case)
that simply contains the default values for all parameters this program cares
about (for the correct dimension and co-dimension, according to the whether a
string "23" or "3" is contained in the file name). By inspection of the default
@endcode
The rationale behind creating first `parameters.prm` file (the first time the
-program is run) and then a `output/parameters_22.prm` (every other times you
-run the program), is because you may want to leave most parameters to their
+program is run) and then a `output/parameters_22.prm` (every time you
+run the program with an existing input file), is because you may want
+to leave most parameters to their
default values, and only modify a handful of them, while still beeing able to
-reproduce the results and inspect what parameters where used for a scpeficic
-simulation.
+reproduce the results and inspect what parameters were used for a specific
+simulation. It is generally good scientific practice to store the
+parameter file you used for a simulation along with the simulation
+output so that you can repeat the exact same run at a later time if necessary.
+Another reason is because the input file may only contain those
+parameters that differ from their defaults.
For example, you could use the following (perfectly valid) parameter file with
this tutorial program:
@code
set Velocity degree = 3
end
@endcode
-
and you would run the program with Q3/Q2 Taylor-Hood finite elements, for 101
steps, using a Nitsche penalty of `10`, and leaving all the other parameters to
-their default value. You could then inspect all the other parameters in the
+their default value. The output directory then contains a record of
+not just these parameters, but indeed all parameters used in the
+simulation. You can inspect all the other parameters in the
produced file `parameters_22.prm`.
+
<h3> Two dimensional test case </h3>
The default problem generates a co-dimension zero impeller, consisting of a
-rotating rectangular grid, where the rotation is for half a second in one
-direction, and half a second in the opposite direction, with constant angular
-velocity equal to $\approx 2\Pi rad/s$. Consequently, the impeller does half a
-rotation and returns to it's original position. The following animation
+rotating rectangular grid, where the rotation is for half a time unit in one
+direction, and half a time unit in the opposite direction, with constant angular
+velocity equal to $\approx 2\pi \frac{\text{rad}}{\text{time unit}}$. Consequently, the impeller does half a
+rotation and returns to its original position. The following animation
displays the velocity magnitude, the motion of the solid impeller and of the
tracer particles.
Cycle 3:
Time : 0.006, time step: 0.002
Solved in 121 iterations.
+
...
+
Cycle 499:
Time : 0.998, time step: 0.002
Solved in 199 iterations.
We see that, generally, the tracer particles have somewhat returned to their
original position, although they have been distorted by the flow field. The
following image compares the initial and the final position of the particles
-after 1s of flow.
+after one time unit of flow.
<p align="center">
<div class="img" align="center">
To play around a little bit, we complicate the fictitious domain (taken from
https://grabcad.com/library/lungstors-blower-1), and run a co-dimension one
simulation in three space dimensions, using the following
-"parameters_23.prm" file:
+"`parameters_23.prm`" file:
@code
subsection Stokes Immersed Problem
+---------------------------------+-----------+------------+------------+
@endcode
-showing how the solver is taking most of the solution time in three dimensions,
-and that the particle motion and Nitsche assembly remain under control.
+Now, the solver is taking most of the solution time in three dimensions,
+and the particle motion and Nitsche assembly remain relatively
+unimportant as far as run time is concerned.
<p align="center">
<div class="img" align="center">
well for Nitsche penalization, and we should come up with a better
preconditioner if we want to aim at larger problems. Moreover, a checkpoint
restart strategy should be implemented to allow for longer simulations to be
-interrupted and restored, as it is done for example in the tutorial step-69.
+interrupted and restored, as it is done for example in the step-69 tutorial.
projects / dealii.git / commitdiff