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CAESAR II Users Guide

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CAESAR II Version
12

Example 1

Nodes 5, 10, and 15 define a cantilever pipe leg that is part of an offshore production platform. The dynamic load as a function of time is equal to a half sine wave. The waveform is the same for all three nodes, but the maximum dynamic load on node 5 is 5030 lb., on node 10 is 10,370 lb., and on node 15 is 30,537 lb. Three force sets are built for this problem. One has the dynamic loads acting in the X direction. The second has the dynamic loads acting in the Z direction. The third has the dynamic loads acting simultaneously in the X an Z directions. The force spectrum input data is:

X DIRECTION HALF SINE WAVE/CURRENT LOADING

Force

Direction

Node

Force Set #

5030

X

5

1

10370

X

10

1

30537

X

15

1

Z DIRECTION HALF SINE WAVE/CURRENT LOADING

Force

Direction

Node

Force Set #

5030

Z

5

2

10370

Z

10

2

30537

Z

15

2

X AND Z DIRECTION WAVE/CURRENT LOADING

Force

Direction

Node

Force Set #

5030

X

5

3

5030

Z

5

3

10370

X

10

3

10370

Z

10

3

30537

X

15

3

30537

Z

15

3

Example 2

A relief valve at node 565 is being investigated for different reactor decompression conditions. The maximum load for the first condition is 320 kips in the X direction. The maximum load for the second decompression condition is 150 kips in the X direction. The third decompression condition maximum load is 50 kips. Three different maximum force sets are defined:

REACTOR DECOMP CONDITION 1

Force

Direction

Node

Force Set #

320000

X

565

1

REACTOR DECOMP CONDITION 2

Force

Direction

Node

Force Set #

150000

X

565

2

REACTOR DECOMP CONDITION 3 (MOST FREQUENT)

Force

Direction

Node

Force Set #

50000

X

565

3

Example 3

A startup shock wave passes through a single elbow system. Nodes in the piping model are 5, 10, and 15 as shown:

As the wave starts off between 5 and 10 there is an initial dynamic axial load on the anchor at 5. When the shock wave hits the elbow at 10, the axial load in the 5-10 elements balance the initial imbalance at node 5, and there become an axial imbalance in the 10-15 element. This shock load is modeled as two separate impacts on the piping system. The first is the dynamic anchor load at 5. If 5 is a flexible anchor then this load may cause dynamic displacements of the piping system and 5 will just be subject to the dynamic time history pulse due to the shock. Assume the anchor at 5 is a flexible vessel nozzle. The second shock load is the unbalanced dynamic pressure load in the 10-15 element that exists until the shock reaches the node 15. Friction losses in the line reduce the shock magnitude as it travels down the line. In the time the wave leaves the anchor at 5 until it encounters the bend at 10, there is a 50% drop in the pulse strength as shown:

This pressure drop was calculated using a transient fluid simulator. Between nodes 10 and 15 the pulse strength drops even further as shown:

The force spectrum loads are:

X DIRECTION LOAD ON FLEXIBLE ANCHOR AT 5

Force

Direction

Node

Force Set #

-5600

X

5

1

Z DIRECTION LOAD ON ELBOW AT 10

Force

Direction

Node

Force Set #

2800

Z

10

2