Modal & direct frequency analysis
Altair EmployeeFrom the frequency response analysis of a flat plate, I have couples of questions:
1. why do we only constrain dof3?
2. is there a specific direction of the dynamic loaded is applied? when I view my result, it seems like the direction of deflection is mainly in Y- axis.
3. If I'm doing a frequency response analysis on an face of a optimize shape, can I follow the tutorial to perform the same analysis?
4. I also applied Modal and Direct analysis on the same model, but they provide me different result. Can you explain why is that?
Answers
-
Hi
By giving dof 3 using load type drea you are not constraining it, you are rather giving the excitation in z direction. You are getting different results in what aspects?? amplitudes, frequency or deformation pattern?
0 -
Altair Forum User said:
Hi
By giving dof 3 using load type drea you are not constraining it, you are rather giving the excitation in z direction. You are getting different results in what aspects?? amplitudes, frequency or deformation pattern?
ok what if i want to do excitation in the x or y direction?
well I'm having the displacement to be different in both analysis, is that common?
Also how can you analysis the natural frequency of the model? is there any tutorial that i can follow?
0 -
I think the decision on direction of load is rather practical than theoretical.
You can run a normal mode analysis to get natural frequencies. There are tutorials available on OptiStruct help.
0 -
Altair Forum User said:
I think the decision on direction of load is rather practical than theoretical.
You can run a normal mode analysis to get natural frequencies. There are tutorials available on OptiStruct help.
thanks. I think I found what I'm looking for.
I have two more question:
1. what is the difference between direct and modal analysis.
2. In my model, I will need to apply viscous damper, I tired to look for information of how to do that but I couldnt find any, will you able to help me out?
0 -
Altair Forum User said:
Hi
By giving dof 3 using load type drea you are not constraining it, you are rather giving the excitation in z direction. You are getting different results in what aspects?? amplitudes, frequency or deformation pattern?
so, if i want to excite the model in the X or Y direction, I would have to Use DOF1 or 2, load type Darea is that correct?
0 -
Altair Forum User said:
so, if i want to excite the model in the X or Y direction, I would have to Use DOF1 or 2, load type Darea is that correct?
Yes, for x excitation you will use dof1.
0 -
Altair Forum User said:
Yes, for x excitation you will use dof1.
thank you!
I'm currently trying to apply dynamic load on a optimize shape and analysis the displacement of the model. The model is similar to a cantilever beam, dynamic load will be added on the top corner of the structure. What kind of load type should I use? SPCD or DAREA? I'm having trouble understanding their function in HM and the result I using DAREA isnt realistic. I follow the transient analysis of bracket tutorial to do set up my analysis.
0 -
Altair Forum User said:
Yes, for x excitation you will use dof1.
This is a model that I set up to run transient analysis, if you can help me take a look at it that will be very helpful. The goal of this analysis is to analyze the model with viscous damping apply to model and compare the displacement with and without viscous damping. The model is created by topology optimization. The shape is simulating a lateral system of a structure. I have done the analysis with static loading on the model and now I want to try it with dynamic loading. The contain file shows a dynamic loading in the X-direction apply to the structure and displacement is collected. However, i m not sure if the model is set up correctly and have no idea how to apply viscous damping as a material element damping in the model. I'm totally stuck on it right now.
0 -
Hi
Conversion of structural damping to viscous damping will be purely based on the frequency interest, for that you may run normal mode analysis prior to dynamic analysis. while specifying frequency of interest in PARAM,W3 make sure frequency unit is radian per time.
0 -
Further,
PARAM,W3 is used to convert structural damping to viscous, where W3 is the frequency of interest (Operating frequnecy) in radians per unit time.
0 -
Altair Forum User said:
Further,
PARAM,W3 is used to convert structural damping to viscous, where W3 is the frequency of interest (Operating frequnecy) in radians per unit time.
if i want to apply viscous damping as material in certain area of the model, how will I model it?
0 -
Hello Mr Prakash,
therefore if i want to use PARAW W3, in a transient response analysis, i need to know which natural frequency in particular? Can i choose the first natural frequency or i need other information to estimate it ?
Therefore can you explain me the differences between PARAM G and consequentely PARAM W3, and the use of TABDMP card ?
best regards !
0 -
Hi Rescue,
W3 is not the natural frequency, its the frequency at which you have designed to operate the system.
Direct trans response analysis needs PARAM W3 along with PARAM G. (PARAM G used alone has no effect on system for direct trans resp)
TABDMP is used in case of modal transient (damping as a tabular function of natural frequency).
0