Element Time Step

The default time step calculation used by Radioss is the element time step.

For one finite element, the element time step can be written as:(1)
Δ t E l e m e n t = l c c MathType@MTEF@5@5@+= feaagKart1ev2aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq=Jc9 vqaqpepm0xbba9pwe9Q8fs0=yqaqpepae9pg0FirpepeKkFr0xfr=x fr=xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaeuiLdqKaam iDamaaBaaaleaacaWGfbGaamiBaiaadwgacaWGTbGaamyzaiaad6ga caWG0baabeaakiabg2da9maalaaabaGaamiBamaaBaaaleaacaWGJb aabeaaaOqaaiaadogaaaaaaa@4305@
Where,
l c
The element’s characteristic length, whose calculation depends on the element type being used and is described in Finite Elements of the User Guide.
c MathType@MTEF@5@5@+= feaagKart1ev2aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbwvMCKf MBHbqefqvATv2CG4uz3bIuV1wyUbqedmvETj2BSbqefm0B1jxALjhi ov2DaebbnrfifHhDYfgasaacH8srps0lbbf9q8WrFfeuY=Hhbbf9v8 qqaqFr0xc9pk0xbba9q8WqFfea0=yr0RYxir=Jbba9q8aq0=yq=He9 q8qqQ8frFve9Fve9Ff0dmeaacaGacmGadaWaaiqacaabaiaafaaake aacaWGJbaaaa@39BF@
Speed of sound in the material, which can be expressed as c = E ρ MathType@MTEF@5@5@+= feaagKart1ev2aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq=Jc9 vqaqpepm0xbba9pwe9Q8fs0=yqaqpepae9pg0FirpepeKkFr0xfr=x fr=xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaam4yaiabg2 da9maakaaabaWaaSaaaeaacaWGfbaabaGaeqyWdihaaaWcbeaaaaa@3A99@
ρ
Material density
E MathType@MTEF@5@5@+= feaagKart1ev2aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbwvMCKf MBHbqefqvATv2CG4uz3bIuV1wyUbqedmvETj2BSbqefm0B1jxALjhi ov2DaebbnrfifHhDYfgasaacH8srps0lbbf9q8WrFfeuY=Hhbbf9v8 qqaqFr0xc9pk0xbba9q8WqFfea0=yr0RYxir=Jbba9q8aq0=yq=He9 q8qqQ8frFve9Fve9Ff0dmeaacaGacmGadaWaaiqacaabaiaafaaake aacaWGfbaaaa@39A1@
Young's modulus

For every simulation cycle, each element’s characteristic length and sound speed are used to calculate the critical time step of every element in the model. The time step calculation occurs at the same time as the internal force calculation. To ensure stability, the simulation’s cycle time step is found by multiplying the minimum time step of all the elements by a scale factor (default is 0.9). The scale factor is needed to ensure that the simulation remains stable if there is a sudden change in the model stiffness.

The element time step method is applied for the entire model using:
  • /DT
  • Δ T sca Δ T min
Where,
Δ T sca
Scale factor for the element time step
Δ T min
Minimum time step that activates specific actions listed in /DT