problem with running transient analysis

[bluesyd]

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

 

[bluesyd]

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

 

[yusf]

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