Re: UDL assigned to piping model

Query:-1
1.)As per the snap attached below, please note that there are 2 heat exchangers. I have modeled them as pipe elements filled with water.

2.)After that I calculated the weight of the heat exchanger modeled in CAESAR-II and compared it with actual operating weight provided by the heat exchanger manufacturer.

3.)To ensure that correct weight is used in CAESAR-II, The difference between CAESAR-II model and actual operating weight is added to heat exchanger model by defining a UDL for the weight difference.

4.)The UDL is defined only for the heat exchangers and not for the rest of the piping.

5.) Still when I activate the color coding tab, I see that UDL is highlighted for the piping also. Can you please clarify the reason. Refer the snap below for reference.


Query:-2
1.)I have modeled the Heat exchanger supports as rigid elements and have provided the restraints as per fixed and sliding saddles.

2.)Ideally the operating weight provided by the heat exchanger manufacturer should match with the loads taken. By the saddle supports in CAESAR-II.

3.)If we take a look at the restraint summary for the operating load case W+T1+P1+U1+F1; it does not match. What is the reason for the same.

Uniform loads are a "carry forward" property. Unless you reset your uniform load to zero, the input following your heat exchanger will have the heat exchanger's uniform load.

Hello Dave,

Thank you for your reply.

So, as per your response I should not use UDL to make up the difference in
the weight of the heat exchanger. If not so then how can I ensure that the
heat exchanger modeled on CAESAR-II shall have the same weight as that given by the manufacturer. Which of the following approach is more correct / viable:-

1.) Play around with the fluid or materiel density to match up the operating weight of the heat exchanger.
2.) Play around with the thickness of the elements used to model the
heat exchanger

Awaiting your expert advice.

Thank you in advance.

Also request you to reply to my Query-2 posted in my 1st post

Step 1) Copy your CAESAR file and delete everything but the vessel. Run the input checker, and it'll tell you how much your caesar model of your vessel weighs and its center of gravity.

Step 2) Find actual weight of vessel and actual center of gravity of vessel.

Step 3) Calculate the difference in weight, and locate the point in CAESAR where applying this mass will result in the CAESAR reported mass and COG match actual mass and COG. You can do so using either a force or a downward-oriented rigid element with mass.

Note 1: If you end up with false reports of overstress in the vessel, then you may distribute the mass.

Note 2: This recommendation is for static analysis only. Additional caution may be warranted on dynamic analysis.

My preference for this would be the addition of a small dummy rigid element of the correct weight (mass) at the CG, as Michael suggests above.

The concentrated force will work also. The UDL method will work as long as you set the magnitude back to zero on the first pipe element following the exchanger. There are two problems with both the Force and UDL methods. First you have to be sure to add "F1" or "U1" to all of the static load cases that contain the "W" primitive. Second, neither "F1" or "U1" will transfer into dynamics if you intend to do further analysis. The additional dummy rigid is the safest way to go.

I personally suggest you DO NOT call the exchanger body rigid, it's not. Vessels are just large diameter pipes, and if you ever go vertical you would want to see wind deflections. Therefore you shouldn't indicate that vessels are rigid.