### 2.5.2. Restart Details

Restarting a run should have little effect on the convergence history and no effect on the final results. Additional information regarding several types of restarts is presented below.

- Runs Using Mesh Adaption

- Runs After Physical Model or Solver Parameter Changes

- Runs After Topology or Mesh Changes

- Multi-Configuration Simulations

#### 2.5.2.1. Runs Using Mesh Adaption

Restarting a run that uses mesh adaption has no effect on the final results. If the maximum number of adaption steps has been specified, then CFX-Solver determines how many adaption steps were completed in the initial run when determining how many adaption steps remain.

#### 2.5.2.2. Runs After Physical Model or Solver Parameter Changes

You may change CCL settings before continuing from a previously generated CFX-Solver Results file. This is, however, not handled as a restart. For this case, the previously generated results file is first read into CFX-Pre, settings are modified, and a new CFX-Solver Input file is written. Note that this file contains the updated CCL as well as the final mesh and mesh adaption parameters from the previous run. A new run is then defined using:

- The newly generated file as the Solver Input File,

- The previously generated results file in an Initial Values definition.

Tip: On the details view of Initialization in CFX-Pre, set the initial conditions for the variables contained in the old results file to Automatic. This will ensure that they will be restarted.

Changing the fundamental physics of an analysis, such as the fluids and/or materials involved, is not recommended. Do not change the reference pressure.

Note: If a run that requires the wall scale to be calculated is restarted, and a wall scale-related setting was changed (for example, a free slip wall changed to a no-slip wall), the wall scale will not automatically be recalculated if its calculation was terminated in a previous run. To force it to be recalculated, set the expert parameter `ignore solve flag on restart` to true. For details on expert parameters, see CFX-Solver Expert Control Parameters in the CFX-Solver Modeling Guide.

Additional information on initial conditions is available in Initialization in the CFX-Pre User's Guide and Reading the Initial Conditions from a File in the CFX-Solver Modeling Guide.

#### 2.5.2.3. Runs After Topology or Mesh Changes

If you make changes that affect the way that the mesh is defined, or that affect the way that the physics CCL relates to the topology of the mesh that is stored in the solver input file, such as:

- Changing the underlying geometry

- Recreating the mesh with different parameters, mesh controls, or inflated boundaries

- Adding a new physics location or removing an existing physics location such as a domain (DOMAIN), subdomain (SUBDOMAIN), boundary condition (BOUNDARY), or domain interface (DOMAIN INTERFACE)

- Changing the name of any subdomain or boundary condition, including the default boundary condition

- Changing the locations of the physics, for example, by modifying the locations of domains, subdomains, boundaries, or domain interfaces

...then you can continue the run as described in Runs After Physical Model or Solver Parameter Changes. Note that such changes cannot be made at the time the run is started, by using the CFX-Solver’s `-ccl` command line argument. Instead, such changes must be incorporated into a solver input file using CFX-Pre, and you must set, on the Initial Values tab, Use Mesh From to `Solver Input File`.

Note that changing the type of boundary condition is possible with the `-ccl` command line argument.

#### 2.5.2.4. Multi-Configuration Simulations

Multi-configuration simulations may only be restarted from a multi-configuration results (.mres) file. The simulation will continue from the final simulation step contained in the specified results file as follows:

- If all active configurations in that simulation step completed successfully, then the new run will begin with the next simulation step.

- If all active configurations in that simulation step failed to complete successfully, then the new run will attempt to complete the final simulation step and execute the configurations that are still active. This occurs if the simulation is stopped prematurely.

Care is required when CCL changes are made before continuing a multi-configuration simulation. This is because CCL is propagated (that is re-used) from the multi-configuration results (*.mres) and most recently created configuration results (*.res) files. In particular:

- Global CCL changes (for instance, `LIBRARY`, `SIMULATION CONTROL` contents including `EXECUTION CONTROL`, etc…) must be applied to the multi-configuration results file.

- Configuration specific CCL changes (such as `FLOW` contents) must be applied to the most recently generated configuration results files.

Important: Previously created configuration results (*.res) files are required for accurate CCL propagation (as noted above) and to resolve configuration dependent initial values, as defined in Run Definition Tab in the CFX-Pre User's Guide. Paths to these results files are stored and re-used when restarting multi-configuration simulations, and these paths are relative to the working directory. For example, the stored path for the first run of the configuration name `Configuration1` corresponding to the multi-configuration results file named mySim_001.mres is: mySim_001/configuration1_001.res.

Use of relative paths enables the directories (and files) for a multi-configuration simulation to be transferred to another working directory (for example, on another file system) to perform a restart. Restarts are not possible if the required directories (and files) have not been transferred to the desired working directory.

Note: If a restart is performed using a specific configuration’s result file (for example, configuration1_001.res), then only that configuration will continue execution, but the multi-configuration simulation will not continue.

If you use results that were generated by a multi-configuration run as the initial values for another run, then CFX-Solver Manager may use the original multi-configuration workspace name and state for the new run and show the new run as part of the original multi-configuration run if the original is also being monitored.

Release 18.2 - © ANSYS, Inc. All rights reserved.