09-27-2018 08:32 AM
Dear nx nastran users
I have 2 questions..
1.
I would like to know how to model the viscoelastic that changes the Young's modulus and loss factor
depending on the frequency.
In the NX documentation, in the Advanced Dynamic Analysis User's Guide there is an example carried out in the Nastran environment.
However, it is difficult to know how to perform it only by looking at that part.
2. Is sol103(Normal mode analysis) also applicable for viscoelastic?
I look forward to your advice.
09-27-2018 11:53 AM
2. SOL103 calculate linear normal modes, It can not handle with nonlinear materials.
09-27-2018 05:19 PM
Viscoelastic properties are specified on the Viscoelasticity tab on the isotropic material dialog. You need to select a Model, then enter the values for that model (see below).
Note that this is just defining material table data. Whether it is exported to a solver input deck or used by the solver during the analysis depends on the solver, analysis type and settings, etc.
10-02-2018 09:56 AM
Dear Jimb
Thank you for your reply. However, I am going to new post abot " How to use isotropic materiall property"
because I am unfamiliar with the application method.
If you have time, I would appreciate your advice.
10-02-2018 09:59 AM
Dear Karachun
Is it nonlinear that the modulus varies with frequency?
_
10-02-2018 04:58 PM
In Frequency response (SOL108 or SOL 111) you can vary E vs. Freq, but not E vs. strain (Stress-Strain curve). SOL103 ignore Frequency dependent properties, Stress-Strain curve, Damping and calculate only linear modes with linear assumptions like infinitesimal strain theory.
Describe here your physical problem, maybe we can reduce it to simple linear solution. At this point, it is look like you are asking xy problem
10-02-2018 09:41 PM - edited 10-02-2018 09:47 PM
Dear Karachun
Thank you for mentioning xy issue. It was a chance to look back at me.
What I would like to do ultimately is to calculate the Sound Transmission Loss(STL) of the EPDM rubber.
STL is an index of sound insulation performance and is defined as the ratio of the incident sound energy to the transmitted sound energy.
STL=10*log10(I_i/I_t) , I_i=I_incident sound energy, I_t=Transmitted sound energy
I have found that the STL of rubber may be very different( Frequency dependent young's Modulus VS Independent
See Fig.1 Ref.Investigation_of_Sound_Transmission_Loss_of_an_automotive_door_Sealing_system_by_using_FEA)
STL calculation process is as follows.
1.acoustic excitation --> 2.calculate Rubber response --> 3.Calculate Transmitted intensity(Vibro-acoustic Solver)
NX provides Acoustic excitation(named as "Distributed Acoustic Plane Waves") but I dont't have vibro-acoustic Solution. but anyway i have other vibro-acoustic programs - Virtual Lab and VAONE
Virtual Lab and VAONE required mode analysis results or Forced response by Acoustic excitation
so In my opinions, I have to solve normal mode by considering frequency dependent young's modulus.
Please let me know if I have any wrong idea.
10-02-2018 01:57 AM
Unfortunately I am not familiar with acoustic analysis. Check NX Nastran Acoustics User`s Guide, maybe you can find some answers here.
01-02-2019 11:31 AM
Dear @JimB and @Karachun I'm also interested in this topic, but this is my first time that I work with elastomers and frequency response (SOL108). Does someone can suggest a tutorial to learn on NX Nastran 12 about the usage of elastomer model (with module function of frequency) in frequency domain analysis (e.g. FRF of a steel structure with elastomers pad)?
01-17-2019 07:45 AM