Civil Engineering Reference
In-Depth Information
As a guide, the global axis system should be orientated as noted below. The
origin should be at the center of the platform or structure at chart datum, MSL
or mud line, as determined by the project.
x axis points toward platform east
●
y axis points toward platform north
●
z axis points vertically upward
●
Note: The axes convention may differ for each project.
Joint numbers are assigned by the engineer. Allowing the program to automati-
cally assign joint numbers should not be permitted. It is important to follow a strict
numbering system when creating or editing a model. This allows easier interpreta-
tion and use of the analysis results. An example of modeling is shown in
Figure 3.18
.
Joint Coordinates
To facilitate the checking process when using software, the joint coordinates are
always input and presented using a single set of units (i.e., m or ft). Take care to
avoid using dual units (m/cm or ft/in), which is the usual mistake.
Figure 3.19
presents the structure geometry with node, tubular element and pile modeling.
Offshore structure fixed platforms usually have a sliding connection
between the structure elements that should be considered in the modeling,
and the two most common cases are:
Jacket piles are welded off at the top of the jacket and guided within the legs
by spacers, as shown in
Figure 3.20
.
●
Conductors are restrained horizontally but not vertically by conductor
frames, as shown in
Figure 3.21
.
●
401
403
400 series numbers
300 series numbers
301
303
202
201
203
200 series numbers
100 series numbers
101
103
FIGURE 3.18
Node modeling to enhance quality assurance.
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