The Initial Conditions icon bar offers the option: Secondary Region from Material Point  , which can be used to define a new region that will be initialized differently from the default initialization.

This option is critically useful when you have regions that are disconnected from each other. In internal combustion engine simulations, it is very common that the simulation domain includes engine cylinder, intake and exhaust manifolds or ports that are disconnected, because the intake and exhaust valves are often closed at the beginning. In this case, you must use this option to define a secondary region from material point for each disconnected region and specify their initial conditions respectively.

Creating a new Initialization will add an item to the Initial Conditions tree and open an Editor panel to configure the initial conditions of that region. Figure 3.25: New Secondary Region from Material Point shows part of the panel. Here, you need to specify a Location for the Material Point. This is an extra material point different from the default Material Point under Mesh Controls (See Mesh Controls for Automatic Meshing). This new material point must sit inside the watertight surfaces, and touch a cell inside the secondary region.

Figure 3.25: New Secondary Region from Material Point

Once a secondary region is created, then the Initialization Order must be correctly set. Initialization order is used by the meshing library internally and its purpose is as follows: after the simulation starts, when disconnected regions become connected due to boundary motions, the initialization order determines which region should be used in assigning properties in newly created cells. The order (from smaller index to larger index) should generally follow the direction of the flow.

For example, in a four-stroke engine, when new cells are created by the movement of an intake valve, those cells should be initialized from the intake port, and not from the cylinder. It is required that the initialization order of the intake port should be lower than the Initialization order of the cylinder. Similarly, the Initialization order of the cylinder should be lower than the Initialization order of the exhaust port.

So, the initialization order for a four-stroke engine should be:

The following tutorials provide examples of initializing four-stroke engines using New Secondary Region from Material Point:

In a two-stroke engine with side ports that are uncovered by the piston motion, sliding port interfaces separate the engine cylinder from the intake and exhaust ports. Initialization order should be:

The following tutorials provide examples of initializing two-stroke engines using New Secondary Region from Material Point:

The following tutorial provides a usage of New Secondary Region from Material Point in a non-engine case, where regions are disconnected by an injector pintle closure:

In the unusual case that no stationary location exists that stays inside the watertight surface throughout the entire simulation, the material point location can be set to translate along with a moving boundary surface. Use the Translate Material Point with Boundary Motion option on the Initial Conditions panel to specify the boundary that should have paired movement with the material point.

You must specify a Region Type for the new secondary region. For more information, refer to Assigning Region Types.

The panel allows specifying constant or spatially varying initial conditions of several solution variables for this secondary region. For details, refer to Initialization Panel.

The Initial Conditions icon bar offers the option: Secondary Region from Sub-volume  , which can be used to define a new region that will be initialized differently from the default initialization. Using this option requires creation of user-defined sub-volumes under the Geometry node. See Sub-Volumes for more information and how to specify them.

This option is useful when you want to initialize a region that is connected to other region(s), and you want specific initial conditions to apply for this region only. In an engine simulation, this option is typically used to define a subchamber or prechamber attached to an engine cylinder.

Initialization Order is important when using sub-volumes for initial conditions. The rule is that sub-volumes must be given a lower initialization order (which means higher priority) compared to the material point regions. Most often, the material point regions refer to the Default Initialization. So, setting initialization order to 1 for the sub-volume and 2 for the default initialization would work.

You must specify a Region Type for the new secondary region. For more information, refer to Assigning Region Types.

The panel allows specifying constant or spatially varying initial conditions of several solution variables for this secondary region. Refer to Initialization Panel for details.

A secondary region created either by material point or sub-volume requires a Region Type specification. The Region Type is used to activate or deactivate certain physical models and to control certain output reporting, mainly in internal combustion engine simulations.

You can accept the default RegionType or assign another type to the secondary region:

Region ID is an index used to denote different initialization items in the Workflow tree. As shown in Figure 3.26: Examples of initialization items under Initial Conditions, the first initialization item listed in the Workflow tree ("Default Initialization") receives region ID = 1, the second initialization item ("One Secondary Region") is given region ID = 2, the third item ("Another Secondary Region") is given region ID = 3, and so on.

Figure 3.26: Examples of initialization items under Initial Conditions

Region ID is a spatially resolved variable (see Table 3.3: Spatially resolved variables that are eligible output to the solution file in Spatially Resolved Panel). You may use this variable to check the scope of the default initialization region and any secondary regions defined in the project.