Unit System
Introduction
Defining engineering problems with units brings clarity to a problem, especially when shared with or reviewed by peers, solving problems involving multiple physics, etc. This is particularly important to solve problems that involve multiple domains (physics). For example, when there is interaction between multiple physics (flow, thermal, electrical and structural) in a problem, defining physical entities with units will ensure the data shared between the different physics is handled correctly. Structural engineers prefer to work in milli-meters for distance whereas CFD (Computational Fluid Dynamics) engineers like to use meters. When transferring models between the two engineers, proper scaling is necessary. SimLab allows users to set consistent units by selecting one of several predefined unit sets. One can choose not to use the unit system.
Units in SimLab
When SimLab is launched,the units “MMKS (mm kg N C s)” enabled by default while creating a new database.
It posts the below startup message which will indicate the customers about the default units.
- Consistent unit systems:
- Inconsistent unit systems:
Users can also set the default modelling units using “Enable units for new database” in File | Preferences | Applications | Options.
User can also change the units in current database using bottom right corner of the application.Once modeling is started, user cannot enable / disable unit system.
Current display unit system is shown at bottom right corner in SimLab.
Based on current display unit system, it displays the unit along with the value in qualified editbox.
If user enters the value in another unit. Conversion will happen automatically to the current display unit system.
If the current display system is MMKS (Pressure unit - MPa) and user given unit in MKS (Pressure unit- Pa), it converts the Pascal value to Megapascal automatically. Script captures the units based on current display unit system.
Default solver deck export unit systems in SimLab:
Solver decks exported/solved from SimLab solutions will be exported in consistent unit systems.
| Default solver deck export unit systems | Solutions |
|---|---|
| MPA (mm t N s) | Structural Implicit |
| MKS (m kg N s) | Flow and EM (Molding, SPH, Electronics Thermal Management, Fluid flow, Electromagnetics, Electrostatics) |
| MMGNMS (mm g N ms) | Explicit/Drop test |
User can specify the desired consistent unit system for exporting solver deck for Solutions, by changing the “Unit system” in “Format and execute options.”
When importing files such as solver input file, results file, etc., SimLab will ask for the units in which these files are defined. After importing these files, the displayed values will relect the values in the current display unit system. If the unit system is not enabled, the imported file units will not be asked.
Rules when using unit system in SimLab
User can work in one of two modes, one with unit system enabled and the other without.
- The user should not mix files created in the two modes. Database and scripts created with unit system OFF should be used only with SimLab with unit system OFF.
- The working behavior will be same as previous versions when unit system is disabled.
- Once a model is imported or created (database is not empty anymore), the units option will be frozen.
- Databases created in previous versions do not support units. When these databases are opened the units system will be disabled and cannot be changed.