lsdyna application of hourglass

Altair Forum User

Hi 

 

I have a basic understanding of hourglass which defines a viscosity property, but how can I apply this property when a rigid wall is going to crash a hollow tube?

 

 

 

Regards,

Altair Forum User

Hi Thomas,

 

hourglass isn't a property, it is a effect that occurs when elements are under integrated. It isn't wanted.

 

Typically you have elements (e.g. shells), which have only one integration point at the middle of the element (but normally more then one through the thickness, e.g. 3 ore 5).

Think about a deformation of a quad, push the upper edge together und the lower edge, by the same amount, apart. Mirror this element at the short edge and the shape of this two elements looks like a hourglass :-)

For explicite code, this deformation happens without any usage of energy. Thats very dangerous, since you have a lot of deformations, but without any change of energy balance.

For that, there are a lot of features to prevent this modes. E.g. small forces in the opposite direction of the possible shape, but sum of forces = 0.

 

If you are using e.g. PSOLIDX->ISOLID, than here is commented:

 

1 - Standard 8-node solid element, 1 integration point.  Viscous hourglass formulation with orthogonal and rigid deformation modes compensation (Belytschko).

 

That means 1 integration point = under integrated = hourglass is possible, but they prevent it trough some Belytschko stuff.

 

 

Hopefully this helps a little bit.

 

Regards,

Mario

Altair Forum User

Thomas,

In HyperMesh, you can define the *CONTROL_HOURGLASS options and values in the control cards.

Cheers,

Eric