Will param W3 effect transient analysis?

Altair Forum User

when i m doing a direct transient analysis, I don't understand what is the use of Param W3 since we already have the uniform structural damping define. I read from another forum that it is conversion factor from structural damping to viscous damping base on frequency interest. But the in the transient analysis, will it effect the displacement result in any way?

Altair Forum User

HI, 

 

W3 converts structural damping to equivalent viscous damping 

 

 Generally, in transient analysis the proper selection of the damping value becomes less important for very short duration events, such as crash impulse or a shock blast. The specification of the damping value becomes more important for long duration loadings (such as earthquakes) and is critical for loadings (such as sine dwells) that continually add energy into the system.

Altair Forum User

Altair Forum User said:

HI, 

 

W3 converts structural damping to equivalent viscous damping 

 

 Generally, in transient analysis the proper selection of the damping value becomes less important for very short duration events, such as crash impulse or a shock blast. The specification of the damping value becomes more important for long duration loadings (such as earthquakes) and is critical for loadings (such as sine dwells) that continually add energy into the system.

When you say the specification of the damping value, which value of damping value are yo refer to? Param G or the Ge value base on the material? In a case of applying viscous damping ( CVISC) as a element in the model, how do I differentiate the use of each damping value? I'm just a bit lost in different type of damping ratio we can apply and how it will affect the result of the analysis. 

Altair Forum User

Hi @wen li tang

 

Please see the image below for W3 from OptiStruct help and the equation will give you idea how the G/CVISC will be used. 

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Ruben Elices

Hi everyone,
Reading this post, I still don't understand how should we calculate the value of "W3". Could anyone shed some light on this?

W3 is the frequency of interest (rad/unit time) for converting overall structure damping to 
viscous damping. It is clear that if you have an harmonic loading, W3 should be the frequency of that input signal. However, how do you choose the "fequency of interest" if your input is, for instance, an acceleration that increases linearly over time and then suddenly stops?

Thanks!

Rajashri_Saha

Ruben Elices said:

Hi everyone,
Reading this post, I still don't understand how should we calculate the value of "W3". Could anyone shed some light on this?

W3 is the frequency of interest (rad/unit time) for converting overall structure damping to 
viscous damping. It is clear that if you have an harmonic loading, W3 should be the frequency of that input signal. However, how do you choose the "fequency of interest" if your input is, for instance, an acceleration that increases linearly over time and then suddenly stops?

Thanks!

Hi Ruben,

I just found that your asked question is unanswered.

You can calculate this as w3=2*Pi*(1st Natural frequency). You can get the 1st natural frequency value from Modal Analysis.

Thanks

Rajashri