Introduction

Simcenter STAR-CCM+ is a powerful multiphysics simulation software developed by Siemens Digital Industries Software This comprehensive tool enables engineers to model and analyze complex engineering problems involving various physical phenomena, including: Fluid flow, Heat transfer, Stress analysis, Particulate flow, Electromagnetics.

This article consists of a general overview of StarCCM+ on Qarnot including useful flags and parameters to use in Tasq.

To learn how to launch a simulation using StarCCM+ on Qarnot please read our Tutorial

Star CCM+ Profile

This section covers StarCCM+ profiles, which are necessary to run simulations with Star CCM+ on Qarnot. If you want to learn how to use StarCCM+ in your tasks, refer to our guide.

Below is a list of profiles and their descriptions:

Profile	Description
starccm-(yourcompany)	Star CCM+ on Qarnot cloud with preconfigured licenses informatoin
starccm-ssh-yourcompany	Connect to your cluster that runs Star CCM+ using an SSH connection

Be careful to ensure your star ccm+ profile has been created and is available.

Constants to use in StarCCM+ Profiles

When using StarCCM+ profiles on Qarnot, several constants must be configured to define the behavior of your task:

Constant	Default Value	Description
DOCKER_TAG	latest	Version of StarCCM+ to use
DOCKER_SSH		Your SSH key, if you want to connect to the tasq with ssh (not mandatory)
STARCCM_CMD	starccm+ -power -batch run your_sim_file.sim	Script that setup the cluster, and run user's command
STARCCM_PRECISION	mixed	Starccm precision to use if available. "mixed" or "double".
NO_EXIT	False	Set to 'true' to keep the cluster alive once your simulation is finished.
SETUP_CLUSTER_NB_SLOTS		Number of processes per node in the mpihost file

The NO_EXIT Constant

Function:
The NO_EXIT constant by Qarnot to control the behavior of the simulation application at the end of a process. When enabled (i.e. set to true), it prevents the simulation from terminating automatically upon completion of a batch process or when an error occurs.
Contexts for Use:
- Debugging: Keeping the session open after execution helps engineers inspect the simulation state, log files, and other diagnostic outputs.
- Extended Post-Processing: In cases where further analysis is required immediately after simulation completion, NO_EXIT ensures that the session remains active for additional operations.
Be careful:
- a simulation with NO_EXIT set to True need to be terminated manually

Important flags

This is a non exhaustive list of flags and parameters to consider when using Simcenter STAR-CCM+ on Qarnot cloud HPC Platform

Command Flags for Different Scenarios

When running simulations, various flags are used to optimize execution for different computing environments. Below are examples and detailed explanations of each flag.

Single-Node Execution flags

Command example:

starccm+ -batch mesh,run cylindre_complet_extrusion_both_demi_DP_reconstruit_init.sim -power

Explanation of Flags:

-batch
Executes the simulation in batch mode, meaning it runs without the interactive GUI. This is ideal for automated runs or when using VDI to streamline operations.
- You can specify several commands at the same time when launching a simulation on star CCM+, or example here we want to execute the meshing and simulation run
- If you want to just launch your simulation please only use run
- If you are familiar with StarCCM+ macro, you can use a macro file to start your simulation (<macro-file>.java)
- If you want to run your simulation step by step for debugging purpose, use step
-power
Enables power or high-performance mode for simulation execution, often optimizing resource usage for intensive computations.
mesh,run

Multiple-Nodes Execution flags

Running simulations on multiple nodes allows for parallel processing, significantly reducing computation time for large-scale simulations. By distributing tasks across several machines, you can leverage combined CPU and memory resources effectively. This approach is particularly beneficial when handling complex models that demand extensive computational power.

Command Example:

starccm+ -batch -mpi openmpi -mpiflags "--mca btl ^openib,tcp --mca pml ucx --mca osc ucx" -machinefile /job/mpihosts mesh,run cylindre_complet_extrusion_both_demi_DP_reconstruit_init.sim

Explanation of Flags:

-batch
Similar to the single-node case, this runs the simulation in non-interactive batch mode.
- You can specify several commands at the same time when launching a simulation on star CCM+, or example here we want to execute the meshing and simulation run
- If you want to just launch your simulation please only use run
- If you are familiar with StarCCM+ macro, you can use a macro file to start your simulation (<macro-file>.java)
- If you want to run your simulation step by step for debugging purpose, use step

{{alert type="info" content="The following flags should not be edited as they enabled to run your case on Qarnot's infrastructure"}}

-mpi openmpi
Specifies the MPI (Message Passing Interface) library to use—in this case, OpenMPI—for enabling parallel processing across multiple nodes.
-mpiflags
Allows passing additional options directly to the MPI runtime. The following flags help optimize data transfer between cluster’s nodes and improve performance. You should not need to edit them to use start running your simulation on Qarnot
- --mca btl ^openib,tcp: Excludes specific byte transfer layers (e.g., openib) and enforces the use of TCP.
- --mca pml ucx: Sets the point-to-point messaging layer to use UCX (Unified Communication X).
- --mca osc ucx: Configures the one-sided communication for collective operations using UCX.
-machinefile
Specifies a file that contains a list of hostnames or IP addresses of the nodes available for the simulation.
Usage Tips:
- Qarnot Scheduler automatically set the IP addresses of the node in /job/mpihosts so you don’t need to edit anything

Star CCM+ on Qarnot

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