Hello,
I am trying to use the linear finite element method combined with the Newmark method to calculate the dynamic response of a floating frame system. I don't want to use the modal superposition method in this code. So I build an equation of Md2x/dt2+Kx=F directly where F presents the external force. The stiffness matrix is established from the Euler beam.
The origin frame structure is a square that has a side length of 15 m and the cross-section of it is a circle whose diameter is 0.7m. A constant force of 1000N is set on the lower side of the square frame. When I set one of the points as a fixed point, the code seems to run well as shown in Fig.1.
However, when I make the frame a floating one, the beams start to deform unexpectedly as shown in Fig. 2. The length of the beam becomes much larger than 15 m. I think the stiffness is strong enough for such a structure as it hardly deformed in the fixed scenario.
I wonder if there must be a fixed point or if something else should be considered in solving the dynamic response of such a floating frame system.
Thank you for your reply.
The "finite element method" is one that by necessity must replace the classical "infinite element method" in the dynamic region and does not fit with the usual straight-line method - because a line element must be able to bend to capture all types of movements.
Sorry - I cannot convey a better linguistic explanation - because such explanations must be avoided if one is to capture living artistery.
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