docs:utils:couette
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docs:utils:couette [2009/02/13 08:45] gibson |
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| - | ====== couette ====== | ||
| - | |||
| - | ''couette'' integrates plane Couette or channel flow from a given initial condition and save velocity fields to disk at a regular interval. (It should probably be called ''integrate''; I might change it to that in the next release.) | ||
| - | |||
| - | ====== main options ====== | ||
| - | |||
| - | <code> | ||
| - | -T0 --T0 <real> default == 0 start time | ||
| - | -T1 --T1 <real> default == 100 end time | ||
| - | -dt --dt <real> default == 0.03125 timestep | ||
| - | -dT --dT <real> default == 1 save interval | ||
| - | -ts --timestepping <string> default == sbdf3 timestepping algorithm | ||
| - | -nl --nonlinearity <string> default == rot method of calculating nonlinearity, | ||
| - | -o --outdir <string> default == data/ output directory | ||
| - | -R --Reynolds <real> default == 400 Reynolds number | ||
| - | -c --channel channelflow instead of plane Couette | ||
| - | -b --bulkvelocity hold bulk velocity fixed, not pressure gradient | ||
| - | -P --dPdx <real> default == 0 value for fixed pressure gradient | ||
| - | -U --Ubulk <real> default == 0 value for fixed bulk velocity | ||
| - | <flowfield> (trailing arg 1) initial condition | ||
| - | </code> | ||
| - | |||
| - | [[docs:utils:couette:alloptions|Complete option list]] | ||
| - | |||
| - | ===== time intervals ===== | ||
| - | |||
| - | The integration starts at ''t=T0'' and saves data at times ''t = T0 + n dT'', exactly. The ''dt'' | ||
| - | value is //approximate//. Channelflow actually rounds ''dt'' to the closest integral divisor of ''dT'' | ||
| - | so that the save interval is exactly what you asked for. Data is saved to disk in files named ''u0.ff, u1.ff, u2.ff, ...'' if ''t'' takes on integer values or filenames with four-digit precision if ''t'' otherwise, e.g. ''u0.000.ff, u0.125.ff, u0.250.ff, ...''. The integration stops when ''t = T0 + n dT > T1.'' | ||
| - | |||
| - | ===== timestepping ===== | ||
| - | |||
| - | The ''-ts'' or ''--timestepping'' sets the finite-difference time stepping algorithm. It takes the following | ||
| - | values | ||
| - | |||
| - | ^value^ %%O(dt^n)%% ^algorithm^ | ||
| - | |''cnfe1''| 1 |Crank-Nicolson Forward Euler| | ||
| - | |''cnab2''| 2 |Crank-Nicolson Adams-Bashforth| | ||
| - | |''smrk2''| 2 |Spalart-Moser Runge-Kutta| | ||
| - | |''sbdf1''| 1 |Semi-implict Backwards Differentiation| | ||
| - | |''sbdf2''| 2 |Semi-implict Backwards Differentiation| | ||
| - | |''sbdf3''| 3 |Semi-implict Backwards Differentiation| | ||
| - | |''sbdf4''| 4 | Semi-implict Backwards Differentiation| | ||
| - | |||
| - | ===== nonlinearity ===== | ||
| - | |||
| - | The ''-nl'' or ''--nonlinearity'' specifies the method for calculating the | ||
| - | nonlinearity u⋅∇u in the Navier-Stokes equation. | ||
| - | |||
| - | ^ value ^ ^method^ | ||
| - | | ''rot'' | (∇×u)×u |rotational| | ||
| - | | ''conv'' | u⋅∇u |convection| | ||
| - | | ''div'' | ∇⋅(uu) |divergence| | ||
| - | | ''skew'' | (u⋅∇u + ∇⋅(uu))/2 |skew-symmetric| | ||
| - | | ''alt'' | |alternating between ''conv'' and ''div''| | ||
| - | |||
| - | ===== mean constraints ===== | ||
| - | |||
| - | ====== Usage examples ====== | ||
| - | |||
docs/utils/couette.txt · Last modified: 2010/02/02 07:55 (external edit)
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