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====== Channelflow Tutorial ====== | ====== Channelflow Tutorial ====== | ||
- | |||
- | ===== Intro ===== | ||
So you've installed channelflow. Now what? Well, computational fluid | So you've installed channelflow. Now what? Well, computational fluid | ||
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of my own research. Probably the best way to get started with | of my own research. Probably the best way to get started with | ||
channelflow is to step through a few examples of run-of-the-mill | channelflow is to step through a few examples of run-of-the-mill | ||
- | calculations using these utilities. If you want to get right to these | + | calculations using these utilities. |
- | examples, skip to Section 3. | + | |
- | + | ||
- | + | ||
- | ===== Overview of channelflow utility programs ===== | + | |
- | + | ||
- | Here's a list of current channelflow utilities. The first three | + | |
- | are taken out of alphabetical order because they're featured in | + | |
- | Section 3, Example Calculations. | + | |
- | + | ||
- | ^ program name ^ purpose ^ | + | |
- | | randomfield | build a random initial velocity field, save to disk | | + | |
- | | couette | integrate an initial condition, save results to disk | | + | |
- | | fieldprops | print out norms, symmetries, geometrical data of a stored field | | + | |
- | | makemovie | extract slices of fields in order to make a movie | | + | |
- | | addfields | compute sum a_n u_n and store result to disk | | + | |
- | | arnoldi | compute the eigenvalues and eigenfunctions of eqbs and orbits | | + | |
- | | ascii2field | convert a file of ASCII data to a channelflow FlowField | | + | |
- | | changegrid | change the discretization or box size of a field | | + | |
- | | field2ascii | convert a channelflow FlowField to a file of ASCII data | | + | |
- | | fieldplots | extract a number of 2D slices of the 3D field, good for plots | | + | |
- | | findorbit | compute an equilibrium or periodic orbit of plane Couette | | + | |
- | | L2Dist | compute the L2 distance between two fields | | + | |
- | | L2IP | compute the L2 inner product | | + | |
- | | makebasis | construct an orthonormal basis from a set of fields | | + | |
- | | makeheatmode | construct a field that decays in time according to Laplace eqn | | + | |
- | | makestokesmode | construct a stokes eigenfunction of laminar equilibrium | | + | |
- | | perturbfield | add random perturbations to a given field | | + | |
- | | projectfields | project a set of fields onto a given basis | | + | |
- | | projectseries | project a sequence of fields onto a given basis | | + | |
- | | seriesprops | compute statistics on a sequence of data | | + | |
- | | symmetrize | find the phase shift of a field that optimizes symmetries | | + | |
- | + | ||
- | 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 -vdt -dt 0.02 -ts sbdf4 u0.ff | + | |
- | + | ||
- | + | ||
- | "Options" (e.g. -opt1 value) are used to reset default values | + | |
- | of parameters. For options, the first two columns in the built-in | + | |
- | help give the short and long form of the option (e.g. -ts and | + | |
- | --timestepping), the third column indicates the type of parameter | + | |
- | expected (e.g. real, int, bool, string), and the fourth gives the | + | |
- | the default value. For example, "couette -dt 0.02 -ts cnab2" sets | + | |
- | the time stepping method to 2nd order Crank-Nicolson Adams-Bashforth | + | |
- | with dt=0.02. | + | |
- | + | ||
- | "Flags" simply turn on boolean options that would otherwise be set | + | |
- | to false. For example, calling "couette -vdt" turns on variable-dt | + | |
- | timestepping, which adjusts dt at fixed intervals to keep the CFL | + | |
- | number within bounds. For flags the third and fourth columns of | + | |
- | built-in help are left blank. | + | |
- | "Arguments" always come after all options and flags. Arguments usually | + | Please refer to [[:docs#utilities|Utilities]] and [[docs:utils:options|Utility Options]] |
- | specify the filenames of binary velocity fields that the utility will | + | for a detailed guide of individual utilities and their options. You can also run any |
- | load and operate on. Most channelflow programs have one required | + | utility with a ''-h'' or ''--help'' option to get a brief description of the |
- | argument (e.g. "couette u0.ff") some two (e.g. "L2Dist u0.ff u2.ff"). | + | utility's purpose and options, e.g |
- | Others take a variable number of arguments (e.g. makebasis u0 u1 u2"). | + | |
- | Unfortunately it's difficult to document variable-number arguments | + | |
- | properly in the four-column option system, so variable-number arguments | + | |
- | are usually documented with a "usage: line right after the description | + | |
- | of the utility's purpose. | + | |
- | So, as you read work through the Example Calculations, you can run the | + | <code> |
- | suggested command with a --help option to clarify what the options are | + | couette --help |
- | doing and what other options are possible. | + | </code> |
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===1. Generate an initial condition and examine its properties === | ===1. Generate an initial condition and examine its properties === | ||
- | gibson@akbar$ randomfield -Nx 48 -Ny 35 -Nz 48 -lx 0.875 -lz 0.6 -m 0.20 u0.ff | + | gibson@akbar$ randomfield -Nx 48 -Ny 33 -Nz 48 -lx 2 -lz 1 -m 0.20 u0.ff |
This command generates a no-slip, divergence-free velocity field with | This command generates a no-slip, divergence-free velocity field with | ||
- | random spectral coefficients on a 48 x 35 x 48 grid, on [0, 2pi] x | + | random spectral coefficients on a 48 x 33 x 48 grid, on [0, 2pi] x |
[-1, 1] x [0, pi], with magnitude 1/V \integral_V |u|^2 dx = 0.2. The | [-1, 1] x [0, pi], with magnitude 1/V \integral_V |u|^2 dx = 0.2. The | ||
field is a perturbation from the laminar flow --by default, velocity | field is a perturbation from the laminar flow --by default, velocity | ||
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couette -T0 0 -T1 400 -o data-LBp01 LBp01ef1 | couette -T0 0 -T1 400 -o data-LBp01 LBp01ef1 | ||
- | couette -T1 0 -T1 400 -o data-LBm01 LBm01ef1 | + | couette -T0 0 -T1 400 -o data-LBm01 LBm01ef1 |
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mkdir basis-UBtrans | mkdir basis-UBtrans | ||
- | cd basisUBtrans | + | cd basis-UBtrans |
Download an equilibrium solution of plane Couette flow from the | Download an equilibrium solution of plane Couette flow from the |