Dear Coade Members,

I request the Coade member to confirm the example modeling of Spring can support with friction attached with this topic is right or wrong. The modeling is as per Coade Newletter Oct-1996.

If there is any error, i request the member to provide the solution of it.

Yes this "appears" correct. However, please e-mail your jobfile to techsupport@coade.com, so we can work with the real file.

Dear Richard Ay,
Please tell me what paldex have done is right or not?
I think it is right.

But paldex's "Hanger Node = 170 Hanger Connecting Node = 180" is not consistent with what was stated in Coade Newletter Oct-1996. It should be "Hanger Node = 180 Hanger Connecting Node = 170" per COADE Mechanical Engineering News in February, 1996.

llljq,

Yes you're right, the hanger and CNODE are flipped. We'll check the jobfile when it shows up.

Hi Richard

I'm trying to put the spring can in suction line of boiler feed water pump.
when I analysizing the system with this spring can all loads on the suction of pump are OK but vertical movement in spring can node is less than 1 mm (0.5 mm)meanwhile when I put +y restraint instead of spring can the loads on the pump suction shooting up.
I just wanted to know in this kind of situation can I analyse the system with spring can and put the rigid shoe in isometric instead of can because of small vertical movement?.

Regards,
Mahmoud

We need to see the model to see what is going on. In general, no you can't switch out restraint types. Something else is going on here.

Dear llljq,

From your reply, what i understood is, you are saying that the model what i attached is as per Coade newsletter Oct. 1996 and the modeling should be as per newsletter feb. 1996.

If so, from my point of view, the modeling as per Oct. 1996 is the final and correct modeling. But the model what you have attached is as per newsletter feb. 1996. Please confirm this.

Dear Richard Ay,

The concept of using CNODE for the spring can and other cases such as CNODE for pumps nozzle connection and equipment nozzles are not elucidate.

My requirement is “How the CNODE has an effect in reducing the loads at the pump nozzle?” & “How the CNODE will have an effect in case of spring can?” Also in case of WRC 297, the use of CNODE is something like a software setup (i.e.) if you provide the CNODE connection, the flexibility will be automatically inserted for WRC 297.

As per Coade Newsletter Feb. 1996, page-16 – Modeling Spring can with friction in Caesar-II, in last paragraph it is given as “This modeling technique can also be applied to situations where the shoe or trunnion slides on top of a bolted spring can.” My understanding is that, in this case the friction value (Mu) must be entered at the node 10 to take an account of friction effect and remove at node 20 for non sliding foundation condition. Is this is right or wrong.

Also, if the foundation is non-sliding for the spring can then the friction (mu) value at node 20 must be left blank and the remaining part shall be modeled as same as Coade Newsletter Feb. 1996. Am I right?

My final conformation is that, the only difference between modeling of spring can with friction and without friction is only the addition of friction (mu) value and leaving blank of friction (mu) value at the node 20. Is this is right or wrong.

Please confirm these issues.

It has no effect, other than to put the node in the Restraint report, which some users find easier to locate the loads.


Maybe, it depends what degrees of freedom you associate between the node and the CNODE.


Yes, CAESAR II inserts the flexibilities between the nozzle node and the CNODE. You can then do other things with the CNODE - like displace it or continue modeling the equipment.


Yes you would have to include friction effects at the sliding interface.


If there is no sliding, defining mu is not necessary.


If you're not going to deal with friction, then you can simply define the hanger at the desired node and you're done. You don't need any of the other elements or restraints. These were necessary only to include friction (because a spring hanger is just a point with a stiffness and a vertical preload - there is no length or influence from other DOFs).

Dear paldex,
you are right. It should be modeled as per Oct. 1996 (the final and correct modeling).

But as per latest CAESAR II Applications guide(Please refer the attachment)

MANI's attachments is a picture from CAESAR II On-line documentation-Application Guide. The topic is "Modeling Spring Cans with Friction".

Yes, The attachment shows the topic “Model of Spring Can with friction". as per COADE Newsletter February 1996 but correct one should be as per October 1996.

I remain mystified as to why we would WANT to model friction on a spring support.

There is a clearance between the spring coil OD and the can liner ID. If the movement of the pipe is less than this number, the movement is going to be accommodated by a lateral deformation of the spring. If the movement of the pipe is more than this number, the spring is going to rub against the iside of the can and something is eventually going to give.

It's probably right to model a spring can this way, but you should put a gap on the CNODE equal to the internal clearance for the spring and redesign your piping system if the gap closes.

Exactly... I concur with CraigB's interpretation. Modeling spring can with friction might be the right way to interpret spring coil contact with spring can shell, but, proper interpretation should be observed. Say, for springs with rod hangers... your spring coils might not touch the shell due to pipe movements because of the rod hanger lenght, therefore you need to do simple triangular calculation as to get displacement at spring hanger location...