Just sharing….

I noticed that for wind/wave, we have to create nodes at the same elevation that we are giving in wind /wave pr Vs Elevation table. (see below Mail).
So when occasional load/stress is high, make sure there is a node! And check manually.

In big models, it is better to mark elevation on iso’s at the level, where there is pressure change as per wind/wave load table and introduce a node at that elevation.

[b]Please update in next version / add in caesar manual. [/b]

Regards
Krishnabharathi




--------------------------------------------------------------------------

From: Loren Brown [mailto:lbrown@coade.com]
Sent: September 6, 2007 11:35 PM
To: Shawn Zhong; Krishnabharathi V
Subject: RE: wind loads regarding



Caesar II interpolates the wind pressure for the elevation that you are at. It averages the pressure of the From and To Node and then uses that result to calculate a constant force that applies to the entire element. If your wind pressure changes with elevation then adding nodes will change your results.


Regards,



Loren A. Brown
Senior Engineer
COADE Engineering Physics, Inc.
12777 Jones Rd., Suite 480
Houston, TX 77070
(281) 890-4566
Lbrown@coade.com
http://www.coade.com






---------------------------------------------------------------------------

From: Shawn Zhong
Sent: Thursday, September 06, 2007 9:19 AM
To: Krishnabharathi.V@
Cc: Loren Brown
Subject: RE: wind loads regarding


I think you will obtain more accurate results if you add the nodes where the wind load profile changes. I think CAESAR calculates wind load for each element, and if the wind profile applied on that element is not linear, CAESAR may take approximation. It may take me some time to dig it out, but I will let you know later.



Regards,

Shawn Zhong

COADE, Inc.

12777 Jones Rd, Suite 480

Houston, Texas 77070

281-890-4566

http://www.coade.com

Let me clarify something I said in the above e-mail. Caesar II calculates the wind pressure at each node by linear interpolation of your nodal elevation in the wind pressure vs. elevation table. It applies P*D*L/2 to the node (assuming the wind is orthogonal to the pipe). So if a node is common to two elements it will have a force from half the length of each element applied to it.

Just see comparison with a node at centre of the pipe and without a node.

Pipe length=10000mm
OD=469.8mm
Material= (306)API-5L X65
Node 10 Anc
Node 20 guide
I applied wave load(Morrison eqn) in terms of wind pr.

Withoutnode @ the centre of the pipe:

Total force calculated by Caesar (“x” ) : Fx=26338N (@10) + 17640N (@20 = 46978N

Withnode @ the centre of the pipe:

Total force calculated by Caesar (“x”) Fx=33554 N (@10) + 25168 (@20 = 58722N

Difference in load on support/tie-in riser with node and with out node = 58722-46978= 11744N (around 1197Kgf will make big
Difference is support design , hope you agree )

Hence I feel it should be added in Caesar manual, the importance of creating a node at the elevation mentioned in Wind table.

Expecting ur comments.

Regards
Krishnabharathi

create a caesar model, same as above for a small discussion.
Node 10 to 20 Pipe length Dy=10000mm
OD=469.8mm
Material= (306)API-5L X65
Node 10 Anc
Node 20 guide
Global cooridinate @node 10 = 0.0
windshape factor=1.0

Loren A. Brown / give ur comments:

I checked in a model that Caesar applying not average pressure(mentioned by you), it is applying maximum pressure for the whole element, if there is not a node at the point where there is change in elevation.

Wind table used:
Pressure(N/m2) Elevation(m)
10000 0.0
20000 5.0
20000 10.0

Pipe OD=469.8mm (0.469m)
Length = 10000mm (10m)

Area = DL = 0.469 * 10 = 4.698 m2

For discussion at centre of the pipe(5m), applying different pr. ( Area / 2 = 4.698 / 2 = 2.349 m2)
**********************************************************
WITHOUTNODE:

CAESAR RESULT: Fx=58676+35279 = 93955N

Manual check = P * A = 20000 N/m2 * 4.698 m2 = 93960 N (ok matching with Caesar result) <<< note Caesar is taking maximum pressure (20000 N/m2) and applying for Whole element length of 10m.

**********************************************************
WITH NODE @ the centre of the span :

CAESAR RESULT: Fx=48223+33988 = 82211N

Manual check:

For 0 to 5m height:

2.349 m2 * 15000 N/m2 = 35235 N

For 5 to 10m height:

2.349 m2 * 20000 N/m2 = 46980 N

Total force = 35235 + 46980 = 82215 N (ok matching with Caesar result) <<< note Caesar is taking average pressure(15000 N/m2) for for 0m to 5m and remaining 5m (5m to 10m elevation) it is 20000 N/m2 > only when there is a node.

Sorry, we've been a little busy around here. I stand corrected:

Caesar II takes the midpoint of the pipe element and calculates the pressure from the table at that point, then uses this over the entire element. So, if your pressure is changing you may want to add some nodes.