API 650 Rotation

Rotation of Shell of a tank calculated as per API 650 gives theta, the same is implemented in nozzle (API 650) which is reflected in Error Report .

My query is Figure P-1 of API 650 considers anticlockwise rotation as negative, however I believe Caesar (Rx entered as vector in Node XX) considers clockwise rotation as negative.

Should we convert the sign of nozzle rotation from error report while feeding as a displacement vector?

It have nothing to do with clockwise or anticlockwise (only by chance).
Rotation will be downward. If the nozzle is oriented like in the API figure, then the rotation is by chance anticlockwise. If it was 180 degrees rotated it would be clockwise. Sign is related to the axis orientation and nozzle orientation.

Regards,

Thanks Danb,
Of course, nozzle rotation sign depends on Elevation from Tank bottom and orientation of nozzle with respect to axis.

In the attached image below,

Let us take a case of Outlet nozzle which is at low elevation from tank bottom.
The theta value shown in error report is -1.21 deg (example: shown in attached image)
however in while feeding input of this rotation as a vector, the value should be entered as Rx= +1.21 deg and not as -1.21 deg
Generally it may be missed while feeding as an input vector.

This was my query!


Thanks

Exactly what I said.

You enter +1.21 because X axis is oriented as in your sketch.

Caesar considers clockwise rotation as +, but you should looking where the arrow is pointing.

Regards,

One should look at the deflected shape and/or animation in the output graphics to confirm pipe is deflecting as expected.

Danb - you said c2 considers clockwise rotation as +.

This isn't necessarily true. c2 uses the "right hand rule" to determine postive/negative rotation. Using your right-hand, put your thumb on the axis, pointing to the arrow head. The direction your fingers curl is positive rotation.

You are right. Actually I was saying this thinking that I'm the one that turn around and looking where the thumb is pointing (fingers curl clockwise). My english is not so good.

Best regards,

Stressguy81,

You are looking at a wrong picture. You should look at the one on the left. You will notice that the rotation is in accordance with the left figure coordinates system. If your nozzle have the same coordinate orientation you can maintain the sign, if not, you have to change.

The figure that you attached is for Rotation under a radial force.

Regards,

Danb,

Speaking of Caesar coordinates,
In our case radial is represented by +Z and hence the thumb faces along +X
It is known that CAESAR II uses the "right hand rule" to determine positive/negative rotation.
Hence the nozzle rotation which is downwards will yield a Rx=+1.21 deg (In this specific case, not necessarily always!).

If the same nozzle had been facing along -Z, the rotation to be fed in Caesar would be Rx=-1.21 deg.

I presume your are taking to image what I have attached below, This image shows the axis orientation and presuming API also uses a "right hand rule" to determine positive/negative rotation it would match with our second case (i.e,) Nozzle is oriented along -Z and will yield a Rx=-1.21 deg.

Coordinate matching can always be done, it would be generally missed by a stress analyst thinking the error report shows rotation w.r.t Nozzle axis modeled in Caesar, and this was the concern.

I do understand now what you want to point out.
Well, it is the stress engineer responsibility to make sure that displacements are inserted correctly. Caesar offer you a small calculator that is in accordance with API 650 figure and formula and do not automatically adjust coordinates.

With 5.3 will not be necessary to do this because from 5.3 presentation I understand that you can import the rotation so it will solve also this problem.

Regards,