Dag McGeorge

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.

Science and Technology of Bolt-Adhesive Joints

This chapter addresses bolt-adhesive joints to transfer both loads and moments. All our examples are taken from maritime applications. Experience has shown that bolt-adhesive joints in the maritime industry are not designed for hybrid action where one joining method improves the performance of the other. Rather they are used in a fail-safe-mode where one joining method takes over should the other fail. Three different applications will be discussed: (1) composite superstructures and composite to steel joints on large ocean going vessels, (2) adhesive bonding of windows, also known as “direct glazing” and (3) cellular sandwich concept for large ocean going ships such as bulk carriers. The sandwich is composed of two steel faces and a lightweight concrete core.

Bonded patch repairs for metallic structures – A new recommended practice

Bonded patch repairs are an efficient repair method for corroded or cracked metal structures, if welding is inconvenient. Avoiding the fire hazard of welding is a major reason for using patch repairs, but it can also be reduced distortions of the metal parts, protecting heat sensitive materials or equipment near the repair such as cables and so on. The lack of guidelines for performing such repairs has been a major hindrance for using this technology. A new recommended practice ‘Design, Fabrication, Operation and Qualification of Bonded Repair of Steel Structures’ has been published addressing: when a repair can be applied, which failure mechanisms need to be addressed, which material properties are needed, fabrication-related issues and in-service inspection. This paper will give a brief introduction to the document and its application areas.

Strength of bonded overlap composite joints in marine applications

Abstract: This chapter deals with methods for predicting the strength of overlap composite joints for marine applications such as ships and offshore structures. Failure loads obtained experimentally are presented and compared with theoretical predictions. Capacity estimates provided by traditional strength of materials approaches do not agree with the experiments, but results obtained using a recently developed inelastic fracture-based analysis method represent the measured strength values well.

Carcass Tearing in Flexible Pipes

This paper presents a novel model of carcass tearing in flexible pipes. The model is based on a simple parameterization of the pipe design in terms of isotropic layers, together forming the composite pipe structure. The model allows evaluations of interfacial shear stresses between the inner pipe layers, as well as axial normal stress and strain levels in response to gravitational and thermal loading.Interfacial slip of a given interface, i.e. axial sliding of adjacent layers relative to each other, is accounted for by introducing a maximal possible value of the interfacial shear stress for a given interface, amounting to a static friction capacity. The model shows how a cut-off of the shear stress at the shear stress capacity implies an interfacial slip, which is followed by a significant increase in axial strain of the carcass layer.Detailed quantitative results of the model are presented for a particular 11.5 inch K-carcass riser design. In order to improve engineering practice, an analytical expression of the governing shear stress is derived in terms of the gravitational and thermal loads. This analytical expression is easily applied for particular design evaluations.The model directs attention to critical design parameters related to the carcass tearing failure mode and thereby supports continued safety in the design and operation of flexible pipes from a carcass tearing perspective.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

New Standard for Design of Free Fall Lifeboats

A new standard for site-specific design of free fall lifeboats has been developed, aiming at providing for sufficiently safe lifeboat designs. The objective has been to develop a standard that follows the same reliability-based safety philosophy and design principles as those implemented and used for design of conventional fixed and floating offshore structures. The standard is intended to cover all aspects involved in the design process for a free fall lifeboat, providing requirements that shall be met in design as well as guidance on how to meet these requirements. The following aspects are covered: Safety philosophy and design principles, metocean conditions, loads, materials, structural design, operational requirements, occupant safety and comfort, model testing and full scale testing, installation, equipment, and qualification of lifeboat concepts. The new standard is published both as an OLF Guideline by the Norwegian Oil Industry Association OLF and as a DNV Offshore Standard, DNV-OS-E406, by Det Norske Veritas. The paper presents the highlights of the new standard with emphasis on topics which are critical for design of free fall lifeboats, first of all structural safety, human safety and comfort, and headway.© 2009 ASME