DNV Software's revolutionary Sesam computer program for structural analysis was a vital key for what turned out to be a rapid development of Norway's offshore industry. It is 40 years since SESAM-69 was released.

“Sesam contributed an enormous amount to the development of the Norwegian oil industry, more than people realize,” says DNV Software managing director Elling Rishoff. “It was a small piece of the puzzle, but it was a very important piece.”

Big size - small brain! The Univac 1108 is hoisted into DNV.	DNV invested heavily in desktop computing.	Laptop: Flexible works station	Notification on the spot

The story of Sesam starts in 1956, when professor Ray W. Clough of University of California at Berkeley spent a sabbatical year at the Norwegian Ship Research Centre in Trondheim. Clough was working on a new method for finding approximate solutions of partial differential equations and integral equations in the analysis of structures, the finite element method (FEM). This was long before FEM was generally viewed as an acceptable method, even before the term ‘finite element method’ was coined by Clough himself.

Clough’s visit was the beginning of a lasting link between UC Berkeley and the Norwegian Institute of Technology (NTH). Visits to Norway by John H. Argyris of University of Stuttgart and Professor J.R. Pauling of University of California at Berkeley, both pioneers in FEM, also helped in creating a FEM expertise at NTH and DNV.

DNV had been using FEM for a few years when NTH student Pål Bergan attended professor Ivar Holand’s first FEM class in 1966. Before long he was working on a first, general-purpose finite element computer program for his dissertation. The program was named Sesam. Bergan intended it to have a wide span of practical applications through flexible input and output. The first work was done on a Univac 1107 computer with 64kb of memory.

Pioneers
Until this time, ship design was based primarily on empirical methods, and strength calculations were done in an analytical manner. But with the building of supertankers, designs were getting so complicated that empirical methods were insufficient. DNV soon realised that it needed a more powerful FEM program than the ones being used. By 1968, Bergan’s work in Trondheim caught the eye of DNV’s Trond Vahl, Eivald Røren and CEO Egil Abrahamsen.

DNV, represented by Per Otto Araldsen, bought Sesam from Bergan in 1968 for the equivalent annual salary of a research assistant, NOK 30,000 (roughly USD 4,000). The purchase of Sesam proved to be a turning point for DNV, and also for the Norwegian shipping industry.

DNV immediately budgeted 36 manyears on the development of the program, an unprecedented effort at a time when the average project might have two or three employees working on it. The DNV team added the important multi-level superelement technique to Sesam. It was only later that the ‘explanation’ of the name Sesam was invented: SuperElement Structural Analysis Modules.

In 1969 the first version of the program, SESAM-69 was commercially released. By that time the American program Nastran, created with support from NASA, was also on the market. In the late 1960s Boeing used Nastran for an analysis with 64,000 degrees of freedom. Most people in the industry were impressed by that, until 1970, when Per Otto Araldsen and Eivald Røren attended an FEM seminar at Wright-Patterson Air Force Base in Ohio, and presented the most recent Sesam analysis.

SuperElement
Using SESAM-69, the Norwegians had done an analysis of the oil tanker Esso Norway with 420,000 degrees of freedom, comparing the results with physical measurements.

“All the FEM pioneers were there,” says Araldsen, noting that many of them were from Boeing. “There wasn’t a soul there from the maritime industry. They viewed us as slightly odd,” he says. But when he presented the analysis of a structure ten times the size of their jumbo jets, it got their attention. “They reacted with shock,”
says Araldsen. “They thought we were making it up. They couldn’t believe that this came from Norway, a very small country.”

This was Sesam’s real breakthrough. Sesam used the SuperElement technique that was missing in Nastran. Although the largest analyses today have up to eight million degrees of freedom, an analysis of close to half a million is still seen as fairly substantial. Almost four decades ago, it would take up to a couple of weeks to process to analyse half a million degrees of freedom. It was also necessary to ensure that each superelement was analysed in less than twelve hours to process.

“They couldn’t take much longer than that,” says Aanund Berdal, principal technical support engineer. “The computers back then used to crash on average every twelve hours; if you had a superelement analysis that took too long, chances are you wouldn’t get it through.”

	Concrete gravity structure, built by Andoc for Shell and intended for the Dublin Field in the North Sea, being towed out from Rotterdam bound for Stord, Norway.
Sesam proved to be the best solution for designing the huge Condeep structures. The Troll platform is the largest gravity-based concrete structure ever to be built and installed offshore.	SESAM-69: The Finite Element Method (FEM) helps solve advanced mathematical problems with limited computer capacity by use of the super-element technique.

Sesam goes offshore
On 23 December 1969, a new discovery of oil and gas was announced in Norway; Ekofisk turned out to be the largest oil field in the history of the North Sea. Sesam was exactly what was needed to be able to design the required megastructures. In the following years, Sesam became the industry standard for analysing offshore structures. The program was used on the Ekofisk tank and several Condeep concrete platforms. Of the 30 concrete platforms in the North Sea, nearly all have been analysed using Sesam.

In the late 1970s, it was clear that new developments in engineering called for a completely new version of Sesam. The original program was retired; the new Sesam saw the light of day in the early 1980s. It introduced interactive graphic geometry modelling with automatic finite element mesh generation, as well as interactive graphic post-processing capabilities. This version was the one that was used on structures such as the huge fixed Troll A platform (the largest structure moved by man) and Heidrun (the first concrete tension-leg floating platform). Sesam became established as the most comprehensive tool for design and analysis of offshore applications.

The development in the 1980s added hydrodynamic analysis capabilities to Sesam including transfer of hydrodynamic loads to the subsequent structural analysis. That version of Sesam also covered analysis of jacket structures, by far the most common offshore platform. Sesam now emerged as a fully general-purpose analysis tool for all kinds of offshore structures.

Brevik FE model of Frigstad D90 Semi

Forging ahead
In 1991 yet a development phase was initiated. “We saw the need to create a completely new architecture,” says Sesam product manager Ole Jan Nekstad. “At our initiative, several oil and engineering companies were asked to give input on, what the new generation of Sesam should look like.”

In 1994 the program development started, lasting until 1999. The goal was to establish the analysis tool for the next millennium. The high-level concept modelling technique was introduced together with a design-oriented and unified user interface. Moreover, analysis features for mooring systems and flexible risers were added to the already extensive range of Sesam analysis capabilities.

Since the turn of the century, the focus has been on strengthening GeniE as Sesam’s new modeller and introducing the new graphical user interface in the hydrodynamic programs HydroD and DeepC. Says Nekstad: “The success of GeniE, HydroD and DeepC also depends on the continuous enhancements of the core Sesam programs such as Sestra and Wadam. During the past two decades, Sesam has grown to become a worldwide system for strength assessment of offshore and maritime structures – we are proud to have most of the key players in the industry as our customers.

Half a century of innovation
“Today, after more than 50 years of innovation, DNV is for the first time in a position where we use the same modeller for offshore and maritime structures,” says Elling Rishoff. “We’re using the same modeller for tankers, semi-submersibles, jackets, topsides and FPSOs. This lets our customers use their employees in a flexible manner between offshore and maritime.” As for the future development of Sesam, the plans are already taking shape. “We will use the strength of GeniE to become a serious player in the jacket and modifications market. We will improve our technology so that our customers will be able to work on loads, response, panel and frame construction, all with a focus on sustainable engineering. This is where DNV Software will be unique.

“Another important focus area is the development of Proban integrated with GeniE – providing a new era of construction reliability,” says Rishoff.

DNV Software will also open up systems, so that our computer-aided engineering (CAE) solutions will be easily integrated with the computer-aided design (CAD) systems that are currently in use in the marine industry.

From the start in 1969, Sesam has grown to become a market leader and the preferred structural design analysis tool for marine industry worldwide. Four decades of innovation and proud service has brought Sesam and DNV to the forefront of marine software development. “We will continue this work and remain a leader of technological advancement,” says Rishoff.

Author: Kaia Means, MediaMix