Spring Results appear incorrect

[roy7BB24]

Hi all

I had some dramas with springs in a recent project, and decided to set up a simple model to ensure these things are behaving as intended. 

See above photo of the simulation I've set up, loads and dimensions provided in the FBD attached

 These are the generated results, no errors or warnings. The only major point of concern is that blue line that goes from the spring base to space somewhere. This isn't an intended part of the model, I'm not sure why its there. 

I've attached the FBD and the model below. The primary cause for concern here is there is a 40N reaction in the x direction (horizontal) at the pin constraint, and a -40N in the X direction in the base the spring is attached to. There is also no reaction in the TY direction (vertical) for the spring base, which should in theory be equal and opposite to the applied load. Lastly, I noticed a 1000Nm Reaction in the MZ direction for the spring base, which once again shouldn't be there. 

If someone could explain these results and why this doesn't match a theoretical result it would be much appreciated

Kind Regards

Roydon Mackay

 

[John_Holtz · Accepted solution]

Hi Roydon,

The line (that stretches to the origin) is a bug in the display. It is not affecting the results. See Dummy line visible while viewing results for model with connector in Inventor Nastran.

The results are wrong because the input of the spring stiffness is wrong. K1 is not in the axial direction; K1 is in the X direction (based on the coordinate system set for the spring). K2 is the stiffness in the Y direction. You need to enter a stiffness for all 6 directions. See How to enter spring stiffness in Nastran.

The moment is shown because it is correct based on the input set on the dialog. You probably want to change the input so that you get the moment calculation you want. See Moment results on SPC Summation dialog not as expected in Inventor Nastran.

John

[roy7BB24]

Roger that, what a rookie error. I didn't have the advanced options expanded, and it only showed the one stiffness box, and I thought I could just enter an axial stiffness for the spring. I've corrected that and the results now make sense. I've run through a few more trials and they also seem to be working as intended. Back on track, Thanks John