Hourglass
Altair EmployeeAnswers
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Hi Sandeep,
Hourglass is weird modes of deformation that occur in under integrated elements and no stresses will be produced. This can affect solution accuracy by varying the structure’s true response. This leads to inaccurate stress, strain and deflection results. For an under-integrated element, displacements and forces may exist for each node of the element. If sum of all these forces and displacements give null strain and stress on the integration point of the element then that element fails to calculate stiffness for certain mode of deformation. At this stage we say element has entered into hourglass. Soon after this as element failed to calculate stiffness the element will behave weirdly. Fully integrated solids and shells do not hourglass.
Meanwhile, I suggest you to go through the RADIOSS ebook (Pages 31 and 32) where hourglassing is well explained with figures and videos. Please download your free ebook copy from http://www.altairuniversity.com/free-ebooks-2/free-ebook-crash-analysis-with-radioss-a-study-guide/
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We have to check hourglass energy for under-integrated elements ?How much it should be ?
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Hi,
Create output blocks for each component and from the time history file plot the hourglass energy for each component so that user can easily trace the component which is responsible for high hourglass energy in the model.
The normal value for hourglass energy is 10% to 15% of the total energy when using under integrated elements.
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Hi ,
If i am using ISolid1 for brick elements in radioss, how can i control the hourglass energy?
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Hi,
You will have to use Isolid 14 or 24 for controlling hourglass in solid elements.
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Hi George,
i have tried Isolid 24 and found some element severe deformation and ISolid 14 is very expensive. So i am thought of using ISolid 1 to check the bric element behavior.
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will Isolid=14 suits for tetra elements?
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Altair Forum User said:
will Isolid=14 suits for tetra elements?
No, it will applicable for Hexa elements only.
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