Difference & application of constrain modes , attachment modes, normal/real modes
Difference & application of constrain modes , attachment modes, normal/real modes
(OP)
Usually i used to work with normal modes(real modes) . I observed there are few other modes in solution form called attachment modes , constrain modes, rigid body modes etc. What are they? Where we can apply them?





RE: Difference & application of constrain modes , attachment modes, normal/real modes
If you do want to model a structure 'free-free' you can add very soft springs to tie it to earth, which is roughly what we do when we test free-free.
Cheers
Greg Locock
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RE: Difference & application of constrain modes , attachment modes, normal/real modes
RE: Difference & application of constrain modes , attachment modes, normal/real modes
RE: Difference & application of constrain modes , attachment modes, normal/real modes
The attachement mode is used in response simulation (i.e. random vibration analysis) for the base excitation location.
The constraint mode is used in response simulation to apply distributes loads.
I can look for some papers for you to provide more details.
Marilyn Tomlin
RE: Difference & application of constrain modes , attachment modes, normal/real modes
When running the Response Simulation (RS) module with NX NASTRAN and NX Advanced Simulation the SEMODES-RS (SOL103) solution generates the following types of mode shapes for the structure:
• "Normal modes", representing the deformed shapes (eigenvectors) of the structure at specific natural frequencies (eigenvalues).
• "Attachment modes", representing the static deformation shape due to a unit static load applied at the location where an excitation force will be applied. Attachment modes are necessary for using the Mode Acceleration data recovery method.
• "Constraint modes", representing the static deformation due to a unit static displacement of a boundary degree of freedom (DOF). Constraint modes are necessary for using the Enforced Motion excitation type.
• "Distributed attachment modes", representing the structural behavior due to a dynamic load. They are required for calculating mode acceleration responses to distributed dynamic excitations.
NX Response Simulation (RS) is an Advanced Simulation solution process for use with NX Nastran. It allows you to evaluate the static or dynamic responses of a structural model subjected to various loading conditions. The software calculates these responses using modal approaches.
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Blas.
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RE: Difference & application of constrain modes , attachment modes, normal/real modes