The introduction of the IACS Common Structural Rules (CSR) in April 2006 has implied a revolution in class society software. The new requirements introduced a major shift toward more extensive design calculations to fulfil both the prescriptive scantling requirements and mandatory strength assessment using finite element analysis.
Key challenges
Efficient software is essential both for ship designers and classification societies for productivity and quality. Ship design is an iterative process starting with a design specification from which a capacity plan and preliminary key drawings are developed. These first scantlings are experience-based, and through the early design process an extensive amount of calculations are to be carried out to settle the final scantlings and produce class drawings complying with the classification society’s rule requirements. Efficient tools are essential to optimise the design and reduce the risk of costly design modifications later in the process. With today’s high steel cost and the need to place steel orders early in the process, it is even more critical to determine the final scantlings at an early stage.
The classification societies have the same need for software in the approval phase to verify the designs according to their rules. With shorter design and building schedules due to increased productivity at the yards, the pressure on timely approval is high and efficient rule calculation software is essential for the approval
engineers. When the Common Structural Rules for tankers and bulk carriers were implemented, the shipbuilding industry had to cope with two completely new design standards. Whilst the rule development over the past ten to fifteen years can be characterised as a slow evolution, the introduction of Common Structural Rules represented a revolution. With the new rules, tougher strength requirements were introduced and more extensive finite element analyses were made mandatory to prove the hull strength. All of a sudden, the designs that yards had developed for years were out-dated and had to be reassessed, redesigned and documented for compliance with the new rules. In parallel with the introduction of the Common Structural Rules, the newbuilding market has been booming, and order books are filled up for the next years. Existing yards improve their production lines and new yards are established to cover the market demand for newbuildings. The high activity, combined with completely new design standards for tank and bulk vessels, has resulted in a gap between available structural design competence and shipping industry needs.
The classification societies had to build competence in using and understanding the new rules based on the knowledge developed by the key personnel participating in the rule development. The same competence is needed in the design offices and shipyards seeking more support and assistance from the classification societies to develop new designs. In addition, the rules were not fully mature, and the list of questions, answers and common interpretations is significant and still increasing. The Common Structural Rules for tankers and the Common Structural Rules for bulk carriers represent two very different standards and aproaches, which complicates the picture. Rule harmonisation is on the agenda, but when and how is still an open question. In this context, software covering both the prescriptive and direct strength requirements of the Common Structural Rules is developed, chasing the same competence on the new rules and structural design as both the design offices and classification societies hull approval units.
Development premises
Early delivery of Nauticus Hull software supporting the Common Structural Rules has been the main development premise for DNV to facilitate design and approval from day one of the new rule regime. Nevertheless, Nauticus Hull should continue to cover the needs for hull strength software in the design and approval of all other ship types according to the DNV Rules.
To meet these design premises, the development of Nauticus Hull has been based on the existing platform, building on the already strong position in the market and proven tools such as Section Scantlings. Our ambitions are high, and Nauticus Hull shall continue to be positioned as the world’s leading class software.
Our innovation
The Nauticus Hull program has already undergone some major upgrades in order to accommodate the need for software according to the new rules.
In January 2006, DNV was the first company to officially launch a complete software solution according to the Common Structural Rules for tankers. With the Nauticus Hull April 2006 release, DNV was again first, this time to release software covering the IACS Rules for both tankers and bulk carriers. Through the releases in 2007, new tools and improved functionality has been added.
A key requirement from ship designers when contributing in the development of the software has been to focus on cutting the total design and approval time, and not focusing only on reducing modelling and input time. In particular, new tools have been developed to make finite element analysis more efficient from modelling and load generation to automated post-processing, code-checking and reporting.
The traditional finite element modelling and analysis programs are being replaced by GeniE, a third-generation Computer Aided Engineering (CAE) tool based on concept technology developed by DNV Software. The development of GeniE has been driven and motivated by the industry’s need for more efficient tools for modelling and design iterations. By introducing concept technology, GeniE allows engineers to focus on the overall structural design rather than nodes and elements.
From a GeniE model, representing the actual structure, different models can be derived depending on the purpose of the analysis. For hydrodynamic analyses the GeniE model will generate a panel model and mass model, while for a structural analysis the GeniE model will generate a finite element model and capacity model. By offering design, modelling, analysis and result evaluation features within the same user interface, GeniE supports the need for fast design iterations. Combined with strong features for 3D visualisation, this significantly reduces the time spent on modelling and documentation through the design process.
Nauticus Hull in 2007 is built on Brix Foundation, with Brix Explorer as the main entry point to all the Nauticus Hull applications. Through Brix Explorer, all relevant files and data for each job are gathered into one database providing a complete overview of tasks carried out and enabling sharing of common ship data by the different programs. By building Nauticus Hull on the Brix platform, the Nauticus Hull applications can also be integrated with other Brix applications such as Brix Project Manager and Brix Workflow Manager.
Prepared for the future
With the 2007 releases of Nauticus Hull, the basic functionality to cover the scope of the Common Structural Rules is in place; future releases will focus on enhancements and improvements. A new tool for defining the arrangement and tank plan is currently under development and in the next release a result scanning functionality will be implemented based on Section Scantlings.
In GeniE, the automated load and corrosion addition generation in place for bulk carriers will be extended to cover both CSR Tank and DNV Rules. Automated buckling and yield checks as included in the 3D modeller today will also be implemented in GeniE, both for the Common Structural Rules and the DNV Rules.
Nauticus Hull interfaces with Nauticus Early Design and other software used in the early design process software such as NAPA will also be further developed to facilitate improved quality and productivity of the design process. Combined with Brix functionality for knowledge and work process management, Nauticus Hull is well prepared for the future.