Sleipner A is an offshore drilling platform in the North Sea. Such platforms are constructed on shore in two parts, a concrete base and the platform itself. These are then mated in a deep water area near shore (a fjord typically) and then floated out to the desired position in the North Sea. Thus the concrete base has a number of large buoyancy cells allowing it to float. The process of mating the platform to the base is the most critical part of this process. During mating, the concrete base is lowered, so that the support pillars are just under water, allowing the platform to be properly positioned over it. At this time, the buoyancy cells are deeper than they will ever be, and thus subject to the highest water pressure they will ever see. The cells must thus be designed with this in mind. On August 23, 1991 while the original concrete base for Sleipner A was being lowered for mating, it sprang a leak and sank, causing a seismic event registering 3.0 on the Richter Scale, and an economic loss of about 700 million dollars.

So what went wrong? It seems that the concrete base structure was designed using a well known and quite sophisticated finite element algorithm and code, and one that had been successfully employed before in this same type of application. There was great trust placed in this particular algorithm and code, and a sophisticated design was produced. Later investigation, using a different finite element algorithm, showed however that the algorithm used initially made a poor finite element approximation of a critical area in the cluster of cells, resulting in an underestimate of stresses by about 50% and a design in which the cell walls were too thin in critical places.

After the original base sank, the operator was faced with an economic loss of production of about a million dollars a day. And they no longer trusted the computer analysis. So what could they do to get this project moving? What they did was to make a decision "to proceed with the design using precomputer sliderule era techniques" [8]. The resulting design was not as sophisticated as the first, and reportedly somewhat more costly to build, but it did not sink. One of the investigative reports later concluded with a simple lesson [8], namely that "relatively simple hand calculations ... should always be done, both to check the computer results and to improve the engineers' understanding of the critical design issues." This is a point that many of us make in teaching the senior design class in which students may make extensive use of simulation packages. However, in my experience this is a point that does not take easily with students and has to be repeatedly pounded in.

These two examples suggest that, without good algorithms and software, putting too much trust in computing power may be downright dangerous. Perhaps more importantly, these examples show we must always keep in mind that, no matter how powerful the computer or sophisticated the software, results must be viewed with sound engineering judgement.