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gtspring2009:schedule:chflow1 [2009/01/20 08:16]
gibson 		gtspring2009:schedule:chflow1 [2010/02/02 07:55] (current)
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 Today is about using predefined channelflow utility programs to do calculations. Today is about using predefined channelflow utility programs to do calculations.
  
 +The utilities plus Matlab form a crude interactive system for CFD. 
  
 ===== Important concepts ===== ===== Important concepts =====
- 
- 
 ==== FlowField ==== ==== FlowField ====
  
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 </​latex>​ </​latex>​
  
-so that they have Dirichlet boundary conditions and form a vector space. +so that they have Dirichlet boundary conditions and form a vector space. The Matlab visualization 
- +scripts add the laminar flow back on by default.
- +
-==== Channelflow utilities ==== +
- +
-FlowFields are binary file representations of velocity fields. +
- +
-Channelflow utilities are programs that operate on FlowField files or directories +
-of FlowField files saved at regular intervals. +
- +
-Examples: +
-^ utility ^ action ^ +
-| fieldprops ​   | print out properties of field: norms, symmetries, etc. | +
-| fieldplots ​   | extract 2D slices of a velocity field for plotting ​    | +
-| addfields ​    | compute u' = sum a_n u_n and save to disk              | +
-| couette ​      | integrate an initial condition, save results to disk   ​| ​  +
-| seriesprops ​  | compute statistics of saved fields ​                    | +
-| makebasis ​    | Gram-Schmidt orthogonalize a set of fields ​            | +
-| projectseries | project saved data onto basis set                      | +
-| findorbit ​    | compute equilibria, traveling waves, periodic orbits ​  | +
-| arnoldi ​      | compute eigenvalues of solutions via Arnoldi iteration | +
- +
-The utilities are stand-alone command-line programs that are run from +
-the Unix shell. You can get brief built-in help information ​on each +
-utility ​by running it with a -h or --help option. For example, running +
-"​couette --help"​ produces +
- +
-  gibson@akbar$ couette --help +
-  couette : +
-        integrate an initial condition and save velocity fields to disk. +
- +
-  options : +
-    -T0       ​--T0 ​          <​real> ​  default ​== 0       start time +
-    -T1       ​--T1 ​          <​real> ​  ​default == 100     end time +
-    -vdt      --variabledt ​                              ​adjust dt for CFL +
-    -dt       ​--dt ​          <​real> ​  ​default == 0.03125 timestep +
-    -dtmin ​   --dtmin ​       <​real> ​  ​default == 0.001   ​minimum time step +
-    -dtmax ​   --dtmax ​       <​real> ​  ​default == 0.05    maximum time step +
-    -dT       ​--dT ​          <​real> ​  ​default == 1       save interval +
-    -CFLmin ​  ​--CFLmin ​      <​real> ​  ​default == 0.4     ​minimum CFL number +
-    -CFLmax ​  ​--CFLmax ​      <​real> ​  ​default == 0.6     ​maximum CFL number +
-    -ts       ​--timestepping <​string>​ default == sbdf3   ​timestepping algorithm +
-    ... +
-     ​-p ​       --pressure ​                               print pressure grad +
-    <​flowfield> ​     (trailing arg 1)                    initial condition +
- +
-The built-in help gives a brief description of each utility'​s purpose +
-and a list of its command-line options and arguments. Channelflow +
-utilities are invoked at the command line with syntax like +
- +
-   ​utility -opt1 value -opt2 value -flag1 arg3 arg2 arg1 +
- +
-or concretely +
- +
-   ​couette -T0 0 -T1 400 -vdt -dt 0.02 -ts sbdf4 u0.ff +
- +
-Utilities often store data at regular intervals dT into a output directory, specified with  +
--T0, -T1, and -dT, and -o options. E.g.  +
- +
-   ​couette -T0 0 -T1 400 -dt 0.02 -dT 2.0 -o data/ u0.ff +
- +
-integrates the flow from t=T0 to t=T1 with timestep dt=0.02 and stores a time series of  +
-velocity fields at intervals dT=2.0 in the ''​data/''​ directory. The velocity fields have  +
-filenames  +
- +
-  data/​u0.ff +
-  data/​u1.ff +
-  etc. +
- +
-where the label is the time t = T0 + n dT. If T0 or dT is not an integer, the label is rounded  +
-to three decimal places. +
- +
-For utilities that //read// time series of velocity fields, you need to specify the same  +
-(or compatible) time intervals. For the most part, the default dT=1 is a good, simple interval.  +
- +
-Reynolds number defaults to 400. +
- +
-Most utilities save their command-line arguments into a file ''​utilityname''​.args for future reference. +
- +
-===== Example calculations ===== +
- +
-==== Computing a 1d unstable manifold ==== +
-    +
-The Nagata (1990) "​lower-branch"​ equilibrium has a one-dimensional unstable manifold. +
-Here we compute the unstable manifold by integrating two 1d trajectories  +
- +
-<​latex>​ +
-u_{\pm}(x,​t) = f^t(u_{LB} \pm v_{LB}), t \in [0, \infty] +
-</​latex>​ +
- +
-using several channelflow utilities:  +
- +
-  * ''​fieldprops''​ +
-  * ''​arnoldi''​ +
-  * ''​addfields''​ +
-  * ''​couette''​ +
-  * ''​seriesprops''​ +
-  * ''​makebasis''​ +
-  * ''​projectseries''​ +
-\\ +
-\\ +
-1. Download the solution from the [[http://​www.channelflow.org/​database|channelflow database]]  +
- +
-   wget http://​channelflow.org/​database/​a1.14_g2.5_Re400/​LB.ff +
- +
-\\ +
-\\ +
- +
-2. Examine the properties of the lower-branch solution with ''​fieldprops''​ +
- +
-   ​fieldprops -g uLB +
-\\ +
-\\ +
-3. Plot the LB with "​fieldplots"​ and matlab script "​plotbox"​ (bad  +
- +
-   ​fieldplots -o plot uLB +
-    +
-then within Matlab, ''​plotbox('​LB'​)''​. +
-\\ +
-\\ +
- +
-4. Compute the eigenfunctions with ''​arnoldi''​ (skip this?) +
- +
-   ​arnoldi --flow LB.ff +
- +
-This produces eigenfunctions ''​ef0.ff,​ ef1.ff,''​ ... and a file of eigenvalues ''​lambda.asc''​. +
-\\ +
-\\ +
-5. Perturbation along the unstable manifold with ''​addfields''​ +
- +
-  addfields 1 uLB  0.01 uLBef1 ​ uLBp01ef1 +
-  addfields 1 uLB -0.01 uLBef1 ​ uLBm01ef1 +
-\\ +
-\\ +
-6. Integrate the perturbations with ''​couette''​ +
- +
-   ​couette -T0 0 -T1 400 -o data-uLBp01ef1 uLBp01ef1 +
-   ​couette -T0 0 -T1 400 -o data-uLBm01ef1 uLBm01ef1 +
-\\ +
-\\ +
-7. Produce input vs dissipation curves for perturbations with ''​seriesprops''​+
  
-   ​seriesprops ​-T0 0 -T1 400 -d data-uLBp01ef1 -o ivd-uLBp01ef1  +**Note: I moved the rest of this class tutorial into the ** [[docs:​tutorial|channelflow tutorial]]. //John Gibson 2009-01-29//
-   ​seriesprops -T0 0 -T1 400 -d data-uLBp01ef1 -o ivd-uLBm01ef1 ​+
gtspring2009/schedule/chflow1.1232468175.txt.gz · Last modified: 2009/01/20 08:16 by gibson

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