6.2. Converting to a New Unit System

When converting to a new system of units, you have to specify the current system as well as the new one. Here, and only here, Ansys Polydata assumes by default that the current system of units is the MKS system, although this is without any influence on the data you have entered. It is only when you specify a change in the system of units that the numerical values of the material data will be altered.

If you want to change to a new unit system (for example, if you want to change from MKS to CGS), or keep the current system of units but change the unit just for one quantity (for example, use Fahrenheit for temperature instead of Kelvin), follow the steps below.

Important:  You should be particularly careful to ensure that the length unit you use is the same as the one used when you generated the mesh. If the mesh length unit is not appropriate, you can use Ansys Polyfuse to scale the mesh. See Translating, Rotating, and Scaling a Mesh for details.

  1. Select Change System of Units in the Material data menu.

      Change System of Units

    Ansys Polydata will show a menu that includes the currently assumed or selected units for length, mass, time, temperature, and electric current.

  2. Specify the system of units that you are currently using. By default, the current system is MKSA + Kelvin unit for temperature. If you have been entering inputs using a different unit system (for example, if you have been entering values based on a mass unit of grams instead of kilograms), you need to modify the current system to ensure that your past inputs are converted properly to the new unit system.

    1. Select Define current system of Units

        Define current system of Units

      (Note that this menu item is called Modify current system of Units if you have selected it before.)

      The new menu presents a set of common systems of units. Select the system that corresponds to your system of units. The standard systems are:

      •   American #1, using inch, pound, second, Ampere and Fahrenheit units

      •   American #2, using feet, pound, second, Ampere and Fahrenheit units

      •   Metric #1, using millimeter, gram, second, milliAmpere and Celsius units

      •   Metric #2, using centimeter, gram, second, Ampere and Celsius units (CGSA + Celsius)

      •   Metric #3, using meter, kilogram, second, Ampere and Celsius units (MKSA + Celsius)

      •   Metric #4, using meter, kilogram, second, Ampere and Kelvin units (MKSA + Kelvin, the default system)

    2. If none of the options corresponds to your case, select each quantity to be modified and choose its correct unit.

    3. When you are done defining units, select Upper level menu and review the current system of units. Your current system of units will be named user defined system in the comment part of the menu if it does not correspond to a standard system. If you want to return to a standard system, then select it in the menu.

  3. Specify the system of units to which you want to convert your inputs (and continue to use for subsequent inputs after the conversion).

    1. Select Define new system of Units.

        Define new system of Units

      (Note that this menu item will be called Modify new system of Units if you have selected it before.)

      The new menu presents the same set of common systems of units as described above. If one of the common systems corresponds to your system, then select it.

    2. If none of the options corresponds to your case, select each quantity to be modified and choose its unit.

    3. When you are done defining units, select Upper level menu and review the new system of units. Your new system of units will be named user defined system in the comment part of the menu if it does not correspond to a standard one. If you want to return to a standard system, then select it in the menu.

  4. Convert from the current system of units to the new system.

      RUN

    Ansys Polydata will convert the units, and open a separate window to report the progress and any errors or other messages. In particular, old and new values for the material parameters are displayed, and a warning is issued in connection with any data that have not been modified due to the change in units.

  5. Press the Return key on your keyboard to close the window. Ansys Polydata will then ask you to confirm that you want to change to the new unit system.

  6. Click Yes to accept the new unit system (or click No to return to the original system of units).

The new system is now the current system. All future inputs to Ansys Polydata will be in the new unit system.