### 3.3.2. Continuing the History

In some circumstances where you choose to read initial conditions from a file, you need just an approximate initial guess for the main solved variables (particularly velocity and pressure) to get your run started. However, in many circumstances you might want to continue as smoothly as possible from a previous run, particularly if you are running a single transient case that has to be stopped and restarted, perhaps to enable a new mesh to be used, or to enable the geometry to change at a particular time (for example, when a valve opens).

The setting that controls this choice is the Continue History From check box. This setting can be made on any panel which allows the specification of an Initial Values file. (If the CFX-Solver is being started from the command line, then the `-continue-from-file` or the `-continue-from-configuration` can be used to turn on the Continue History From setting.)

If you want to use an initial guess for your new run, then you can choose to clear (turn off) the Continue History From check box. (If the CFX-Solver is being started from the command line then the Continue History From setting will be off if all the Initial Values Files are specified using the `-initial-file` and `-initial-configuration` arguments.)

If you want to have the smoothest possible run continuation from a previous run, then you should select (turn on) the Continue History From check box. If you have just a single Initial Values file, then the history must be continued from this file. If you have multiple Initial Values files, then the history can be continued from only one file, which you must select.

The setting of the Continue History From check box has various effects that are tabulated in more detail below. In general, the aim of this setting is to provide as smooth a restart as possible, given the contents of the existing results file and the setup of the new CFX-Solver Input file.

Continue History From check box | Cleared (off)[a] | Selected (on)
--- | --- | ---
Variables | Excluding Mesh Displacement (described below), only principal variables and solver-internal derived variables that are under-relaxed or have a recursive definition are copied/interpolated. For example, mass flow integration point data will not be copied/interpolated. In general, this option should be switched off only if a rough initial guess is required. | All principal variables and dependent variables will be copied to make the run continuation as smooth as possible if the source domain and target domain have the same mesh. If the source domain and target domain have different meshes, only principal and solver-internal derived variables that are under-relaxed or have a recursive definition are interpolated. Particle database, particle tracks and particle sources will be copied/interpolated, if appropriate. Depending on the similarity between the mesh/topology/physics in the CFX-Solver Input file and Initial Values File(s), data on GGI interfaces, faceset data and element-set data may also be copied from the Initial Values File for use in the new run. More details can be found in Interpolating from a Single File.

Initial Values File containing Mesh Displacements

If the Mesh Deformation Option (on the Interpolator tab; see Interpolator Tab in the CFX-Pre User's Guide) is set to `Automatic` or `Use Latest Mesh`, then the CFX-Interpolator will compare the mesh in the Solver Input File with the final mesh in the Initial Values File. If they are the same then the all relevant variables (not including mesh displacement, mesh velocity or final mesh) are copied from the Initial Values File to the Solver Input File; otherwise the variables are interpolated.

Setting the Mesh Deformation Option to `Use Initial Mesh` makes the CFX Interpolator check whether the mesh in the Solver Input File matches the initial mesh in the Initial Values File instead. If these meshes match, then the variables are copied (including mesh displacements and mesh velocities) from the Initial Values File rather than interpolated. This could result in unexpected behavior because it results in variables being copied from nodes in the Initial Values File to the equivalent nodes in the Solver Input File without taking proper account of their temporal derivatives in a second order backward Euler transient scheme. However, this can be the desired behavior for a minority of analyses such as mesh motion with `Specified Displacement` or `Specified Location`.

If the Mesh Deformation Option (on the Interpolator tab; see Interpolator Tab in the CFX-Pre User's Guide) is set to `Automatic` or `Use Initial Mesh`, then the CFX Interpolator will compare the mesh in the Solver Input File with the initial mesh in the Initial Values File. If the meshes are the same, then the relevant variables (including mesh displacements and mesh velocities) are copied from the Initial Values File to the Solver Input File; otherwise variables (not including mesh displacement or mesh velocity) are interpolated.

Setting the Mesh Deformation Option to `Use Latest Mesh` makes the CFX-Interpolator check whether the mesh in the Solver Input File matches the final mesh in the Initial Values File instead. If these match then the variables (not including mesh displacement or mesh velocity) are copied from the Initial Values File rather than interpolated. However, this can be the desired behavior if a smooth restart is desired and the Solver Input File mesh matches the Initial Values File final mesh.

Iteration/Timestep Counter | The new run will start from an `Outer Iteration` (steady-state) or `Timestep` (transient) of zero. The CEL variables `Accumulated Timestep`, `Accumulated Coupling Step` and `Accumulated Iteration Number` will be equivalent to `Current Timestep`, `Current Coupling Step` and `Current Iteration Number`, respectively. | The new run will start from the `Outer Iteration` (steady-state) or `Timestep` (transient) at which the previous run finished. The CEL variables `Accumulated Timestep`, `Accumulated Coupling Step` and `Accumulated Iteration Number` will not be equivalent to `Current Timestep`, `Current Coupling Step` and `Current Iteration Number`, respectively, but instead will continue to accumulate from the previous run (in the Initial Values File).
Monitor Data | The new run does not contain monitor data from the previous run. | The new run contains the monitor data from the previous run. This data will be plotted by default whenever the new run is monitored in the CFX-Solver Manager (although it can be excluded by using the Monitor Properties dialog box and setting the Timestep Range Option to `This Run Only`).
Particle Tracks | The new run does not contain any Lagrangian particles (or their tracks) from the previous run, although the particle sources to the fluid(s) from the previous run will be available. | Particle tracking will continue from the particles in the previous runs, particle tracks will be available from the previous run, and particle sources to the fluid(s) will be available. Some limitations apply: for details, see Using an Initial Values File that Contains Particles.
Run History | The new run does not contain any history relating to the existence of a previous results file nor its associated transient files. | If the results of the new run are loaded into CFD-Post with the setting Load Complete History as a single case/separate cases selected, then CFD-Post will be aware of the existence of the Initial Values File and all of its associated transient and files.
Transient Statistics | Transient statistics from the previous run are not used or available. | Transient statistics continue to accumulate from the Initial Values File into the new run.
[a] This does not apply if Use Mesh From is set to `Initial Values`. See Using the Mesh from the Initial Values File for details.

Note: Regardless of whether the Continue History From check box is selected or cleared, the following rules apply:

- If the initial values file contains results from a time transformation run, and the target solver input file is not a time transformation run, then the interpolator will only copy or interpolate values reconstructed from the Fourier coefficients. Variables without Fourier data will be skipped. This rule applies regardless of whether there is an interpolation mapping object defined.

- If the initial values file contains Fourier data from a transient blade row simulation, and the source passage is replicated (that is, Total Num. Instances is greater than 1), the interpolator will only interpolate values that are reconstructed from the Fourier coefficients. Variables without Fourier data will be skipped.

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