What is 'soft spring'
What is 'soft spring'
(OP)
Greetings all
In the context of FEA, what is 'soft spring'?
When is it switched on and what sort of values are used
Many thanks
Regards
Ed Clymer
Resinfab & Associates
England
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RE: What is 'soft spring'
Other than that, is it possible that they are describing a very compliant spring as opposed to a very stiff spring (the compliant spring having a very low stiffness constant 'k', the very stiff spring having a very high stiffness constant 'k')? Perhaps all they are describing is a pillow foundation rather than a hard concrete foundation?
RE: What is 'soft spring'
I hope this link will help you :
http://c
Soft Spring
For such a spring the incremental force f required to produce additional incremental deformation u decreases as spring deformation increases.
Hard Spring
The incremental force required to produce a given displacement becomes increaseingly greater as the spring is deformed.
Regards
Torpen
RE: What is 'soft spring'
Either way, not applicable to linear FEA
Cheers
Greg Locock
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RE: What is 'soft spring'
RE: What is 'soft spring'
http://c
seems to suggest that "softening spring" and "soft spring" are synonymous, doesn't it? Perhaps that's just a little sloppiness in the descriptions on the link.
What does "3-2-1 method of minimal supports" mean?
RE: What is 'soft spring'
The 3-2-1 method:-
This involves choosing three reasonably well separated points that define a plane (i.e. not three points in a straight line!) Any convenient plane will do, but for the sake of argument let’s use the XY plane. The first point is restrained in all three translational directions.
Now any single object has six degrees of freedom, three in translation and three in rotation, commonly known as rigid body motions since no internal strain energy is involved. What this first point of restraint does is reduce the number of remaining degrees of freedom to the three rotations. The second point is carefully chosen at a Y offset from the first and thus shares the same X and Z coordinates. The second point is restrained in the X and Z directions only. There now remains just a single unrestrained freedom, rotation about the Y axis. The third point is restrained in the Z direction only and thus knocks out this final freedom.
Of course there are many variations that can be used instead, a similar approach can be applied to any of the global planes, or if there is no convenient global plane available then a local axes system will suffice.
However it is achieved the number of supports in a 3D model must equal six for a minimal support condition, any less and the structure is under supported and is insoluble, any more and the structure is over constrained.
When used correctly, the supports prevent rigid body motion without applying any restriction to the deformation of the part and thus will not react any load so long as a fully balanced set of loads and moments has been applied.
This approach allows the FE analyst to mimic a stress engineers free body diagram where all the applied loads have been sketched in. Assuming all loads are applied as realistic pressure distributions, then a very clean set of results is obtained, completely free of artificial stress concentrations.
Limitation - static linear analysis only.
RE: What is 'soft spring'
RE: What is 'soft spring'
RE: What is 'soft spring'
If the thing you are modeling isn't symmetric, then it is usually much more difficult to figure out the boundary constraints. Symmetric or not, you still have to restrict those 6 degrees of freedom.
RE: What is 'soft spring'
3 + 2 + 1 = 6
The minimum set of supports necessary to prevent all rigid body motions, but in a way that allows for full unrestricted deformation of the model.
The simplest test of these supports is to let the model expand with a uniform temperature applied throughout, the FE solver will report back to give displacements with zero stress.
Of course if planes of symmetry exist, then it is best practice to make use of them, otherwise the 3-2-1 approach is quite simple to apply.