Vidar Ahjem

Combining Goal Models, Expert Elicitation, and Probabilistic Simulation for Qualification of New Technology

New technologies typically involve innovative aspects that are not addressed by the existing normative standards and hence are not assessable through common certification procedures. To ensure that new technologies can be implemented in a safe and reliable manner, a specific kind of assessment is performed, which in many industries, e.g., the energy sector, is known as Technology Qualification (TQ). TQ aims at demonstrating with an acceptable level of confidence that a new technology will function within specified limits. Expert opinion plays an important role in TQ, both to identify the safety and reliability evidence that needs to be developed, and to interpret the evidence provided. Hence, it is crucial to apply a systematic process for eliciting expert opinions, and to use the opinions for measuring the satisfaction of a technologys safety and reliability objectives. In this paper, drawing on the concept of assurance cases, we propose a goal-based approach for TQ. The approach, which is supported by a software tool, enables analysts to quantitatively reason about the satisfaction of a technologys overall goals and further to identify the aspects that must be improved to increase goal satisfaction. The three main components enabling quantitative assessment are goal models, expert elicitation, and probabilistic simulation. We report on an industrial pilot study where we apply our approach for assessing a new offshore technology.

Development of Time Domain Model for Synthetic Rope Mooring Systems

Mooring of offshore structures in very deep water has been made possible through the use of lines made of fibres of synthetic material. The mechanical behaviour of synthetic ropes is considerably more complex than that of steel wire rope and chain, due to the visco-elastic and visco-plastic properties of the synthetic material. In particular, the gradually developing permanent increase in rope length will affect the offset and motion of the moored structure and make its characteristics change from one storm to the next.For design and analysis of offshore mooring systems incorporating synthetic ropes it is valuable to have good models that can be used for response simulation in the time domain. The paper describes the development of a time domain model for synthetic rope. The model structure and the values of the parameters are determined from experimental data using a system identification technique. The resulting model is implemented in an existing computer program for analysis of mooring and riser systems. In particular, the permanent elongation of the synthetic rope appears to be well represented.Copyright

New Methods for Qualification Assisted Innovation Applied to a Practical Example

New technologies typically involve innovative aspects that are not addressed by existing normative standards and hence are not assessable through common certification procedures. To ensure that new technologies can be implemented in a safe and reliable manner, a specific kind of assessment is performed, which in many industries, e.g. the energy sector, is known as Technology Qualification (TQ). TQ aims at demonstrating with an acceptable level of confidence that a new technology will function within specified limits. DNV is currently developing a new method with application to Technology Qualification, drawing on the concept of assurance cases, based on a combination of function analysis originating from Value Engineering and argumentation logic used in safety cases. The method enables improved definition of the technology and where to focus when building confidence in it.The method uses ‘Function Analysis’ that is structured towards what the system does instead of what it is. The focus on the functions encourages exploration of alternative ways by which the functions can be provided. Focus on functions draws attention to the system as a whole rather than each part the system consists of. This helps avoiding interface problems and may prove vital in an innovation process.When the functions have been identified, one can proceed with analysing how a technical solution provides those functions. Those elements of the technical solution that represent proven technology can be dealt with by the conventional engineering processes and need not be included in the technology qualification process. Those elements assessed as new (or novel) are taken forward in the technology qualification process. This assessment is based both on the novelty of the function itself, the technical solution implementing it and the intended use of the technology in its intended environment. Confidence is demonstrated by first stating the goal of the qualification effort. Such a claim can be formulated as “The […] technology is fit for […]”. Then this goal is broken down into sub-goals. This is repeated till the lowest level claims can be directly justified by hard evidence. As an aid to overview and simplicity, such an argument structure (assurance case) can be presented graphically. The graphical assurance case can be readily communicated, reviewed and updated to reflect the needs and concerns of all stakeholders.An on-going joint industry project for certification requirements to Deepwater Deployment and Recovery Systems will benefit from this improved method for qualification assisted innovation.Copyright