Case Studies
Vancouver, B.C. - June 2002
Crest of a Wave Reaches the Forward
Legs of a Platform
Data visualisation is a key component in postprocessing results from Sandwell's
numerical models. Tecplot quickly allows them to represent large quantities
of data in a form that can be understood easily. This layout shows how
the platform disturbs the water surface in its vicinity. This helps determine
how high the deck of the platform should be located so it is not impacted
by wave crests.
About the Engineer
Dr. Sundar Prasad works for Sandwell
Engineering, Inc. in Vancouver, Canada. He is a Senior Analyst in
the Coastal
and Ocean Engineering Group. The primary focus of his work at Sandwell
is to provide their structural engineers with data on the effects of ocean
wave interaction with offshore and coastal structures such as oil platforms
and breakwaters. Typically, this involves the use of both numerical and
experimental methods, depending on the complexity of the problem.
Numerical Methods
Numerical methods have the advantage of lower cost, increased flexibility,
and faster turnaround times from problem definition to results. Since
their needs are very specific, and are not fully addressed by commercially
available software, Sandwell has written their own in-house Wave3D code
to model wave interaction with large offshore platforms. The accuracy
of the code has been verified against results from experimental tests
in wave basins.
Wave Interaction with a Tension Leg Platform
Our plot of the month represents a number of ways in which results from
a simulation of wave interaction with a tension leg platform can be visualised.
A wave of 12.8 m height with a period of 9.9 seconds was generated within
Wave3D. The large plot shows an instant in the simulation when the crest
of the wave reaches the forward legs of the platform.
Shown in the bottom left of the layout are color contours of the maximum
water surface that was reached during the course of the simulation (usually
consisting of about eight to ten waves passing by the platform). It is
clear that for the chosen wave direction, the region just forward of the
gap between the front legs sees amplification of the wave crests.
Dr. Prasad's group also needs to determine the forces experienced by the
platform in waves. The bottom right plot displays the maximum hydrodynamic
pressure reached during the simulation on the body of the platform. This
information allows structural engineers to determine how the hull plates
(and internal structural bracing components) on the platform will perform
under different operating conditions.
How They Do It
Sandwell's Wave3D has specific subroutines written to write files in a
format that can be directly read into Tecplot. All the data in the plot
is based on four-node quadrilateral finite-elements. The data is supplied
to Tecplot as a list of node numbers and X, Y, s coordinates and connectivity
data for the elements. In the case of the pressure contours, a pressure
is also associated with the location of a node on the platform model.
The data is imported as an ASCII file into Tecplot which then generates
a plot based on a predefined layout. Dr. Prasad has several layouts depending
on the nature of the data in the plot.
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