Beam elements in LS-DYNA
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Hello everyone,
Computational Mechanics Forum
Mode Superposition Method
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We know that in Dynamic Analysis , to solve the equations of the form:
[M]{D2 X} +[C]{D1X}+[K]{X} = {R} ---------------- EQ.1
Where [M], [C],[K] are square matrices of mass, damping and stiffness matrices respectively.
D is derivative wrt time, {X}, {R} are the column matrices of displacement, external load respectevily.
We
use either direct step by step integration method or mode superposition
method. Both of them have advantages one over the other. Say, I am
[LS-DYNA] Attenuating vibrations of shell element after an explosion
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Hello!
The model I'm working on in LS-DYNA is a simple pyramid-shaped shell constrained along the bottom edges with all DOF taken. The material used is MAT_PIECEWISE_LINEAR_PLASTICITY. Above the model there's a LOAD_BLAST (Air burst) placed, which deforms the model after the explosion.
The issue is that the model seems to vibrate ininitely after the explosion, what can be seen on the attached images (first one shows the graph of "Rigid Body Displacement", second one shows close-up of the line within the yellow rectangle).
cauchy stress, first piola kirchoff stress, second piola kirchof stress
Some basic questions involving cauchy stress, first piola kirchof stress and second piola kirchof stress:
1) We know that Cauchy stress involved deformed areas-therefore this (Cauchy stress) has an obvious physical interpretation
2)Now, first piola kirchof stress is expressed as:
S = JF^-1 . sigma
where, J is the jacobian of the deformation gradient which physically is the measure of the volume change produced by a deformation.
F is the deformation gradient
sigma is Cauchy stress.
Principle of virtual work and conservation of linear momentum
I've been reading Prof.Bower's text on solid mechanics:
http://solidmechanics.org/text/Chapter2_4/Chapter2_4.htm#Sect2_4_1
Can anyone plz help me to understand how principle of virtual work is another form of conservation of linear momentum?
Mindlin's theory
I have modelled a base with concentic circles-that is circles of same centre and different radii.
Also, each circle has a different thickness.The largest thickness being 2000 mm.
Can I use Mindlin's plate elements for these plates (circles).I believe Mindlin's theory works for thick plates.Will a thickness of 2000mm cause any problem?
Generalised Displacement control (can track both snap through and snap back)
I've been programming geometric non-linear analysis of beams.I'm done with load control approch,displacement control approach (whih can track snap through NOT snap back)and generalised displacement control (which can track both snapm through and snap back).
Stability/Buckling analysis vs Geometric non-linearity
Can anyone point out some important conceptual differences between a non-linear analysis incorporating geometric-non linearity (be it using Total Lagrangian/Updated Lagrangian/ co-rotational formulation) and a stability (buckling) analysis.
Sorry for asking too fundmantal question
Snap back and snap through
Can anyone explain the difference betwen sap back and snap through with examples?
Please help