1.2.4. Units Syntax

The default units system for Tdyn is the International System (IS). They are:

  • Time in seconds (s)

  • Lengths in meters (m)

  • Masses in Kilograms (kg)

  • Forces in Newton (N)

A derived unit is Pascal (Pa), where \(Pa=N/m^2\)

These units can be changed in several parts of the program. Every window that asks for data for constraints, loads or properties has a field to choose the units for that window. The chosen units are only applicable in the data attached to it in the same window.

The units in which are expressed the coordinates of the geometrical model are chosen in the General data window:

Tdyn Data > Simulation data > Units > Geometry units

Other predefined units that can be chosen are:

  • Forces: Kilogram-force (kp)

  • Lengths: centimeter (cm), millimeter (mm)

Different units can be selected using “More Units” option in the unit selection-box. A selection window is opened and selected units are inserted to create new ones:

../../../_images/more_units.png

Fig. 1.19 Unit selection-box.

These units can also be edited by selecting “Edit mode>Edit field” option in the unit selection-box. In edition mode new units can be written. After writing new units, they can be checked by selecting “Edit mode>check” option, if an edited unit is correctly written it will be signalled in green colour, if the new unit is wrongly written it will be signalled in red colour. Different operations can be inserted by selecting “Edit mode>Insert”.

Result units can be expressed as:

N-m-kg where:

  • Displacements are in m

  • Velocities are in m/s

  • Accelerations are in m/s2

  • Strengths are in N/m or N·m/m

  • Stresses are in Pa= N/m2

N-mm-kg where:

  • Displacements are in mm

  • Velocities are in mm/s

  • Accelerations are in mm/s2

  • Strengths are in N/mm or N·mm/mm

  • Stresses are in N/mm2

Kp-cm-utm where:

  • Displacements are in cm

  • Velocities are in cm/s

  • Accelerations are in cm/s2

  • Strengths are in Kp/cm or Kp·cm/cm

  • Stresses are in Kp/cm2

KN,m,Mpa where:

  • Displacements are in m

  • Velocities are in m/s

  • Accelerations are in m/s2

  • Strengths are in kN/m or kN·m/m (kN=103 N)

  • Stresses are in Mpa=106 Pa

Note that the units in this system does not form a compatible system.