×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

problem with running transient analysis

problem with running transient analysis

problem with running transient analysis

(OP)
Hi all,
I'm trying to run a transient analysis using Patran/Nastran. I've been trying to follow one of the MSC tutorial without much success. Please refer to the following link for the pdf version of the tutorial.
http://www.mscsoftware.com/support/online_ex/Nastran/DynAnal.cfm (tut3: direct transient response analysis)

The main problem I've got is when I tried to create the time dependent pressure/force, instead of giving me a numerical value such as -1 for pressure and 50 for force, I got a value of '0' displayed on the screen. I've followed every step shown on the exercise and yet I could not get the right magnitude showing up on my model.

I then decided to ignore the problem and assumed that it was just a display issue and went on to run the analysis. The analysis ran okay and then I imported the result file into Patran to view the data. This is when I realise it was more than a display problem.

Instead of getting a decaying sinusoidal curve as shown on page 3-22 of the tutorial, I got a curve with no negative values. It seems to me that the negative part of the sine wave had been flipped into the positive region though the magnitude of the curve appeared to be correct. So if you could imagine instead of having a trough followed by a crest as a shown in Figure 3.3 on page 3-22 of the tut, I had 2 crests. I still had alternating crests and troughs between t=0.008 and t=0.04s(after the input force was stopped). It was still showing a decaying pattern but with all the values above the 0-axis.

I know it's hard to picture what I've just said and I'd appreciate it if someone could tell me how I can upload a picture or a file to the forum(that is if it is allowed). And if you could understood what I just described, can you please tell me what I did wrong? Your help will be greatly appreciated!

Thanks,

anne

RE: problem with running transient analysis

(OP)
Hi All,

I've just realised that I was displaying just the magnitude in the result file and that's why all the values were showing to be positive. I changed it z component which is the vertical vibration direction and the final results looked the same as those showing in the tutorial. However, I still have the problem displaying the force/pressure correctly on the model. I'm still not able to display the vector arrows with the right magnitude. I guess it's problem just a display issue because the final results from the analysis were still valid. However, I'd like to know if any of you know how I can fix this problem. I'd prefer to be able to visualise the correct loads on the model.

thanks!

anne

RE: problem with running transient analysis


hi


what you must do is just going in Loads/BCs menu and then selecting plot/marker option as well as all load case under assigned loads and typing  the value of  let say 0.0041 under Dynamic Value part for time/freq.
thats all..you can change above value but it should be between upper and lower bounds

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources