Nastran 2024 Dynamic setup for half sine

[scratchy]

How do you set up a half sine loading in the dynamic setup box ?

I have the half sine setup in the loading table data... But can not seem to input the correct data into the dynamic box. It seems to give me an additional point or / and not finish on zero load. See attached...

[John_Holtz]

Hi @scratchy 

If I understand your question, you want to know how to enter the Dynamics Setup input so that the analysis runs for exactly 0.0033 seconds and not a microsecond longer.

First, the analysis will always have a step after the final duration. I suggest that you extend the load curve so that the load behaves the way you want it to be after the theoretical duration. That is, do you want the load to be zero in the milliseconds after 0.0033 duration or something else.

On the Dynamics Setup dialog, normally the duration is important and the time step size is less important. I suggest the "Cycle Dependent Term" should be set to Time Step. Then you can enter the duration (=0.0033 seconds) and number of steps, and the initial time step size will be calculated.

John

[scratchy]

Looks like there seems to be a residual force there even at zero load...

Both versions tried ie 3.3 ms - zero load with 3.63 ms -0.309 load and 3.3 ms - zero load with 3.63 ms - zero load

[John_Holtz]

Hi,

I think we need a lot more information about what you are doing, and maybe even the model.

Since the analysis is some type a transient analysis, the stress and reaction forces do not have to be zero when the applied force is zero. A load applied over 0.0016 seconds sounds like an impact type of load, so the model will vibrate after the load is removed. The question is, why is the result so close to zero when it should be much larger!

John 

[scratchy]

I am using a non linear transient response...... What is the difference to a direct transient response.... Which one should be first choice... Thanks

[John_Holtz · Accepted solution]

Nonlinear includes large displacement effects, such as

• large displacement and rotation
• the stiffness changing due to the displacements
• direction of loads changing due to the displacements
• nonlinear material properties.

Direct transient is a linear analysis and is limited to small displacement because none of the above effects are included. Also, direct transient is limited to bonded contact. See Faces with separation contact held together in a linear analysis in Nastran (autodesk.com).

As for which analysis you should use, start with the analysis type that gives the answers required in the least amount of time. A linear analysis will be a faster solution since there is no convergence required.

John

[scratchy]

John.... Many Thanks