This paper briefly discusses Digital Terrain Modeling (DTM) techniques. Then, by presenting applications of DTM to Route Optimisation and Presweeping, it is suggested that over-engineering, normally introduced as safety factors to allow for limitations in the mapping of seabed topography, could be reduced with consequent savings In capital costs Similarly, it is shown that DTM-enhanced engineering techniques can be applied to trend monitoring of Pipeline Survey data, and that this approach can reduce rectification and its associated operating costs Indeed, if DTM-enhanced engineering IS applied through the life of a pipeline, this can have additional benefits at the end of life The paper closes with a discussion of future developments.
All operators and offshore contractors are continually striving for two things
reduction in costs, and
improvement in safety
In many ways it might appear that these two aims are mutually exclusive However, by applying DTM techniques to enhance subsea engineering, it is possible to reduce overall costs while maintaining and even improving the level of safety These aims are achieved through a better comprehension of the operating environment
Unlike the civil engineer on land, the subsea engineer cannot step back and observe the lay of the land, or the details of the location of a subsea structure The range and field of view of a subsea video camera is very limited so that it is not possible to reference one feature to another, or to appreciate gradients of the sea floor. The real time output of echo sounders and sonars does not generally give an adequately comprehensive picture This is not a limitation if the seabed is flat but, in an area of rugged terrain, the subsea engineer must rely on visualization techniques The resulting unknowns have been compensated for by the application of safety margins or factors In this way safety has been maintained, but almost certainly at the expense of over engineering.
However, this deficiency can be mitigated by the ability to visualise the subsea environment by graphical models The value of this approach depends upon two main criteria the quantity and quality of the input data, and the agility and speed with which these can be assembled into a usable graphical form, and then manipulated. The use of a Digital Terrain Model to visualize the seabed means that submarine pipelines can be designed much more accurately and subsequently monitored throughout then lives Indeed, it is possible to consider five stages In the life of a submarine pipeline
design,
installation,
operating life,
life extension, and
abandonment
This paper demonstrates how DTM techniques can be utilised to enhance engineering during all these stages
The Admiralty Chart can be seen as a form of seabed terrain model It shows depths and contours and the positions of seabed hazards It also presents information on the seabed material It IS actually quite limited, however, so far as seabed modeling IS concerned because, until very recently, depths were obtained from single readings taken at intervals along survey lines whose positional accuracy was limited
