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Physics Simulation
Simcenter STAR-CCM+ can model a wide range of physics phenomena including fluid mechanics, solid mechanics, heat transfer, electromagnetism, and chemical reactions. Scenarios with multiple time scales can be solved within the same simulation.
Mesh Motion and Adaption
Many simulations that involve motion or geometry change require you to move or deform the mesh. Other simulations require localized mesh adaption in order to achieve an accurate solution.
Overset Meshes
Overset meshes are used to discretize a computational domain with several different meshes that overlap each other in an arbitrary manner. They are most useful in problems dealing with large motions as well as optimization studies where a geometry can be enclosed in an overset region and set to different positions.
Overset Mesh Workflow
The general workflow for using an overset mesh involves the steps outlined below.
Choosing the Time Step Size for Unsteady Overset Simulations
The time step size of an overset simulation depends on the mesh size.

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Physics Simulation
Simcenter STAR-CCM+ can model a wide range of physics phenomena including fluid mechanics, solid mechanics, heat transfer, electromagnetism, and chemical reactions. Scenarios with multiple time scales can be solved within the same simulation.
- Defining Physics Workflow
  Simcenter STAR-CCM+ contains a wide range of physics models and methods for the simulation of single- and multi-phase fluid flow, heat transfer, turbulence, solid stress, dynamic fluid body interaction, aeroacoustics, and related phenomena. These physics models are all selected using a physics continuum.
- Setting Up Physics
  This section provides information on how to set up physics models in STAR-CCM+.
- Running Physics Simulations
  This part of the documentation describes preparation and procedures for running a Simcenter STAR-CCM+ simulation.
- Motion
  In general, motion can be defined as the change in position of a body with respect to a certain reference frame.
- Space
  The primary function of the Space models in Simcenter STAR-CCM+ is to provide methods for computing and accessing mesh metrics. Examples of mesh metrics include cell volume and centroid, face area and centroid, cell and face indexes, and skewness angle.
- Time
  The primary function of the time models in Simcenter STAR-CCM+ is to provide solvers that control the iteration and/or unsteady time-stepping.
- Mesh Motion and Adaption
  Many simulations that involve motion or geometry change require you to move or deform the mesh. Other simulations require localized mesh adaption in order to achieve an accurate solution.
  - Overset Meshes
    Overset meshes are used to discretize a computational domain with several different meshes that overlap each other in an arbitrary manner. They are most useful in problems dealing with large motions as well as optimization studies where a geometry can be enclosed in an overset region and set to different positions.
    - Overset Hole Cutting
      The overset hole-cutting procedure is essentially a cell marking procedure. The hole in one region, mostly in the background region, is virtual because no cells are actually removed. They are deactivated and have no part in the solution process. This procedure takes place when the overset interfaces are initialized, and also in each time-step when mesh changes due to motion (for unsteady simulations). See also: GUID-EA52A744-93FD-4F99-B007-064BDFCAA8BF.html.
    - Overset Mesh Interfaces
      An overset mesh interface couples one overset region with the background region or another overset region.
    - Adaptive Mesh Refinement for Overset Meshes
      The Adaptive Mesh Refinement (AMR) technique includes a built-in adaptive criterion for overset meshes. This criterion provides adaption for matching the cell size between lower prioritized regions and higher prioritized regions.
    - Overset Gap Treatment
      When the wall boundaries of moving bodies approach each other, small gaps can occur between the wall boundaries. In many applications they require special treatment.
    - Advanced Overset Concepts
      Some overset applications especially involving complex geometry and motions require advanced treatment to assemble regions connected by overset interfaces.
    - Overset Mesh Workflow
      The general workflow for using an overset mesh involves the steps outlined below.
      - Setting up Overset Regions
        A typical overset simulation consists of one or more overset regions that overlap the background region. However, you can have multiple overlapping overset regions without a background region if necessary.
      - Generating Overset Meshes
        A critical factor in successfully applying overset meshes is to have similar sized and enough cells across the overlapping zone between background and overset regions. This overlapping zone must contain at least 4–5 cell layers in both background and overset meshes.
      - Creating Overset Interfaces
        An overset mesh interface couples one overset region with the background region or another overset region.
      - Setting up Overset Topology
        Automatic overset topology is activated by default. This option is applicable to most situations. Only for specific situations, the topology algorithm fails and you must select the appropriate overset topology method. Refer to Overset Topology for typical application scenarios.
      - Setting up Prism Layer Shrinkage
        If you expect moving bodies in your overset simulation to closely approach another body or wall, you can activate prism layer shrinkage to morph the cells in the small gap that forms. By default, only prism cells at wall boundaries are shrunk. See also: Prism Layer Shrinkage and Prism Layer Shrinkage Reference.
      - Setting up Overset Mesh Refinement
        In an overset simulation, you can use AMR mesh method to improve the interpolations at the overset interface if the initial mesh is not refined for the entire motion. See also: GUID-28A739CF-6DE2-4D87-B582-E390B522011C.html.
      - Choosing the Time Step Size for Unsteady Overset Simulations
        The time step size of an overset simulation depends on the mesh size.
      - Activating Load Balancing for Parallel Overset Mesh Simulations
        When running an overset mesh simulation in parallel on multiple cores, the traditional mesh-based domain decomposition can lead to imbalanced CPU loads across the parallel cores. This CPU load imbalance is due to the overset assembly process, which poses a substantial computational cost on the processors where the acceptor cells reside. Overset mesh load balancing rebalances the domain decomposition such that the acceptor cells are distributed most evenly across the parallel cores.
      - Enforcing Overset Mass Conservation
        Although mass is not strictly conserved in the vicinity of the overset interface, additional techniques are available that mitigate the imbalance. To enforce mass conservation for the overset grid method, you must select the appropriate conservation method.
      - Visualizing and Analyzing Solution
        Overset meshes are automatically created while running a simulation. Two mesh representations are available to visualize the mesh: volume mesh and overset mesh.
      - Troubleshooting Overset Mesh
        Several troubleshooting features are available for analyzing the quality of the overset mesh.
    - Setting up Overset Mesh with Fluid Film
      For certain applications, it is useful to combine overset mesh with fluid film.
    - Setting up Overset Mesh with Lagrangian Multiphase
      When combining overset mesh with Lagrangian two-way coupling, you are advised to activate the following overset interface properties:
    - Overset Modelling Scenarios
      Several overset setups are categorized according to region topology and motion with simplified real work applications.
    - Overset Mesh Methodology
      The overset methodology includes:
    - Overset Mesh Reference
  - Morphing
    The morpher motion allows you to account for the effect of moving boundaries on your analysis in a transient simulation.
  - Adaptive Mesh Refinement
    Adaptive Mesh Refinement (AMR) is a dynamic method that refines or coarsens cells based on adaptive mesh criteria as they query the flow solution. Solution quantities are automatically interpolated to the adapted mesh.
  - General Remeshing
    Simcenter STAR-CCM+ provides a remeshing model within a physics continuum that triggers remeshing when certain conditions are met. Built-in conditions are provided based on mesh quality checks, and you can also configure your own trigger on the remeshing solver.
- Materials
  Material models simulate substances, including various mixtures.
- Fluid Flow
  Many engineering design projects require you to predict the effect of flowing fluids on containing structures or immersed objects. While you can analyse simple scenarios with hand calculations, complex scenarios require you to apply numerical methods for accurate solutions.
- Viscous Flow
  Viscous Flow is a finite element approach for use with viscoelastic materials and other highly viscous non-Newtonian fluids, such as liquid plastics and rubber, dough and similar foodstuffs, molten glass, and mud. Viscoelastic materials resemble elastic materials, but also exhibit viscous effects, rebounding slowly from deformations.
- Passive Scalars
  Passive scalars are user-defined variables of arbitrary value, assigned to fluid phases or individual particles. They are passive because they do not affect the physical properties of the simulation. An intuitive way to think of passive scalars is as tracer dye in a fluid, but with numerical values instead of colors, and with no appreciable mass or volume.
- Heat Transfer
  Heat transfer is the study of energy in transit due to a temperature difference in a medium or between media. Heat transfer extends thermodynamic analysis through the study of the modes of energy transfer and through development of relations to calculate energy transfer rates.
- Species
  This chapter provides information about the chemical species models in Simcenter STAR-CCM+. A species model is activated whenever a multi-component liquid or multi-component gas is chosen from the Material model section of the Physics Model Selection dialog.
- Porous Media
  Simcenter STAR-CCM+ allows you to simulate the transport of a fluid or energy (e.g. heat, electrical charge) through porous materials using the concept that the action of the porous media can be represented using appropriate loss (or 'diffusion') coefficients.
- Adjoint
  The adjoint method is an efficient means to predict the influence of many design parameters and physical inputs on some engineering quantity of interest, that is, on the engineering objective of the simulation. In other words, it provides the sensitivity of the objective (output) with respect to the design variables (input).
- Fans and Blowers
  Simcenter STAR-CCM+ provides models for axial and radial fans where classical fan laws apply.
- Virtual Disk Model
  The virtual disk model is based upon the principle of representing propellers, turbines, rotors, fans, and so on, as an actuator disk. The actuator disk treatment is practical when you are concerned about the influence of the rotor/propeller behavior on the flow rather than knowing about the detailed interactions between the flow and the blades of the rotating device.
- Turbulence
  Most fluid flows of engineering interest are characterized by irregularly fluctuating flow quantities.
- Transition
  The term transition refers to the phenomenon of laminar to turbulence transition in boundary layers. A transition model in combination with a turbulence model predicts the onset of transition in a turbulent boundary layer.
- Wall Distance
  Wall distance is a parameter that represents the distance from a cell centroid to the nearest wall face with a non-slip boundary condition. Various physical models require this parameter to account for near-wall effects.
- Radiation
  The Radiation Model is the gateway, or entry point to all of the radiation modeling capabilities of Simcenter STAR-CCM+. This section describes Simcenter STAR-CCM+’s radiation modeling.
- Aeroacoustics
  Aeroacoustics investigates the aerodynamic generation of sound.
- Reacting Flow
  Simcenter STAR-CCM+ provides a selection of models that you can use to simulate a wide range of reacting flow applications.
- Internal Combustion Engines
  In an internal combustion engine (ICE), for example a gasoline engine, the process of combustion takes place in a cylinder (or cylinders) within the engine. The working fluid is a fuel and oxidizer mixture (usually air), which reacts to form combustion products.
- Multiphase Flow
  Multiphase flow is a term which refers to the flow and interaction of several phases within the same system where distinct interfaces exist between the phases. Simcenter STAR-CCM+ considers flow options where phases coexist as: gas bubbles in liquid, liquid droplets in gas, and/or solid particles in gas or liquid, and/or (large scale) free surface flows.
- Dynamic Fluid Body Interaction
  Dynamic Fluid Body Interaction (DFBI) in Simcenter STAR-CCM+ allows you to simulate the motion of a 6-DOF body with the displacement and rotation resulting from the defined mechanical and multiphysics interaction (flow, DEM, solid stress, EMAG).
- Harmonic Balance
  Some unsteady flows have a regularly repeating flow pattern, that is, they are time-periodic. Consider the flow from a fan blade passing across the entrance to a duct. Measurements of the instantaneous flow just within the duct would show a regularly repeating pattern. If the flow disturbances are sufficiently large, and propagate to the end of the duct, measurements of the unsteady flow at any point within the duct show repeating patterns. Such time-periodic patterns can be expressed using Fourier series.
- Solid Stress
  Simcenter STAR-CCM+ allows you to model the response of a solid continuum to applied loads, including mechanical loads and thermal loads that result from changes in the solid temperature.
- Electromagnetism
  Simcenter STAR-CCM+ allows you to model engineering applications involving electromagnetic phenomena. Example applications are electric motors, electric switches, and transformers, which can be modeled based on the classical theory of Electromagnetism.
- Electrochemistry
  Electrochemistry is the study of chemical reactions which occur due to an imposed electrical charge, or a difference in electrical potential at a boundary between a conductor–such as a metal–and an electrolyte. Simcenter STAR-CCM+ provides models that allow you to simulate batteries, corrosion, etching, and other electrochemical reactions.
- Electric Circuits
  Electrical circuits are conducting loops of interconnected electrical components, such as batteries, power sources, resistors, and inductors.
- Plasma
  Plasma is a state of matter similar to a gas that is composed partially or completely of charged particles such as ions and electrons which are not bound to each other.
- Batteries
  You can simulate batteries in Simcenter STAR-CCM+ using battery cells and battery cycling procedures that are defined either directly in Simcenter STAR-CCM+, or in the external software package Simcenter Battery Design Studio.
- Casting
  Casting simulations are performed using transient multiphase simulations using the VOF model with solidification. Conjugate heat transfer is applied between the solidifying melt and the solid mold.
- Region Sources
  This section provides some guidelines on how to use region sources for some common problems.
- Cell Quality Remediation
  The Cell Quality Remediation model helps you get solutions on a poor-quality mesh. This model identifies poor-quality cells, using a set of predefined criteria, such as Skewness Angle exceeding a certain threshold. Once these cells and their neighbors have been marked, the computed gradients in these cells are modified in such a way as to improve the robustness of the solution.
- Guidelines for Applying Simcenter STAR-CCM+
  This part of the documentation provides guidelines on applying Simcenter STAR-CCM+ models to your applications.
- Common Solvers Reference
  In Simcenter STAR-CCM+, solvers compute the solution during the simulation run.

Choosing the Time Step Size for Unsteady Overset Simulations

The time step size of an overset simulation depends on the mesh size.

The time step should be set so that the overset mesh does not move in the overlapping zone within one time step more than:

The smallest cell in this zone when 1st-order Euler scheme for time integration is used.
Half the smallest cell size in this zone when the 2nd-order implicit time integration scheme is used.

If inactive cells become active without being first acceptor cells, there are no saved values for these cells at the last time step. Here Simcenter STAR-CCM+ applies an extrapolation scheme to initialize the previously uninitialized cells. See also: Initialization of Previously Uninitialized Cells.