Gerhard Ersdal

Bio: Gerhard Ersdal is an academic researcher from Petroleum Safety Authority Norway. The author has contributed to research in topics: Performance indicator & Audit. The author has an hindex of 10, co-authored 37 publications receiving 291 citations. Previous affiliations of Gerhard Ersdal include University of Stavanger & Norwegian Petroleum Directorate.

Green Water on Norwegian Production Ships

Abstract: Green water events have made local damage on Norwegian production ships in sea states significantly lower than the 100-year sea states. These incidents have occurred both in the bow area, amidships and aft. Both analyses and model testing demonstrate a significant amount of green water on the deck structures in the 100-year wave situations. There is no general agreement on how to calculate the waves entering the deck of the ship, nor how well the wave height and the freeboard exeeedance are correlated. The model tests show a large scatter when relating green water wave height and the corresponding freeboard exceedance. Significant modifications have been made on the production ships, such as raised forecastle and installation of wave-breaking walls. Operational restrictions have also been introduced, including restrictions to personnel access in green water zones and storage limitations. This paper describes the Norwegian requirements to air gap and green water. A description of the five production ships in Norway and the green water incidents are included. The status of the methods for evaluating the green water phenomenon as well as precautions taken to prevent further incidents, are also described.

Experience And Risk Assessment of FPSOs In Use On the Norwegian Continental Shelfi Descriptions of Events

Abstract: With this paper we will summarize the operational experience of FPSOs in Norwegian waters as seen from the regulatory point of view. Reported incidents, challenges and lessons learnt in the years after the first production vessel came on stream will be described, and utilized in an assessment of risk. At the end of 2000, five production vessels are in operation on the Norwegian Continental Shelf. Norne FPSO has been on location in the Haltenbanken region since 1997. Petrojarl Varg has been on location in the North Sea since 1998. Asgard A has been on location in the Haltenbanken region since 1998. Balder FPU and Jotun A has been on location in the North Sea since 1999. In addition, there are three floating storage units; Polysaga, Njord B and Asgard C. Totally these vessels represent more than nineteen years of offshore experience.

New Standard for Assessment of Structural Integrity for Existing Load-Bearing Structures-Norsok N-006

Abstract: An increasing number of platforms in the Norwegian continental shelf are reaching their design life. For various reasons these platforms will require an assessment of their structural integrity. When performing these assessments the engineer is faced with tasks where little guidance is found in design standards, for several reasons. The two most important being: 1) The analyses that is performed in a typical assessment of existing structure is often applying very advanced techniques and methodology that seldom is used in design of new structures, as the cost of doing advanced analysis is relatively low compared to replacement of an existing structure, but relatively high compared to moderate additions of e.g. steel in the design of a new structure. 2) Design standards are based on theories, methods and experience for structures in a given design life (e.g. fatigue design and corrosion protection design). When this design life is extended, sound methods for ensuring that the structures are still sufficient safe is needed. Such methods will normally be “condition based design”, where inspection, maintenance and repairs are included in the assessment in integrated way. Such methods are not given in normal design standards. For these reasons a new NORSOK standard is developed that gives recommendation on how to deal with the specific aspects that engineers meet when performing assessments of structures in general, but also specifically for assessment for life extension. The standard is named “Standard for Assessment of Structural Integrity for Existing Load-bearing Structures” and is issued as a NORSOK standard and given the number N-006 [1]. The topics that are covered in the standard include: Shut down and unmanning criteria for platforms not meeting ordinary requirements, specific issues for determination of ultimate capacities by use of non-linear methods, cyclic capacity checks, fatigue life extension, requirements to in-service inspection etc. The paper describes the background and the content of the new standard and it presents examples of recommendations given. The role of the new standard in the Norwegian regulatory system is shown.Copyright © 2009 by ASME

On the Risk of Structural Failure On Norwegian Offshore Installations

Abstract: The purpose of this paper is to review the worldwide historical structural failure data in the 1990s on offshore structures, and compare this with the present risk analyses of Norwegian offshore structures. The paper describes an overview of registered accidents to offshore structures based on the databases WOAD and CODAM. The accident data is given for fixed platforms, jack-ups and for floating platforms. Estimates of risk level in annual frequencies and PLL values are given for each platform type. The paper concludes that: • The risk connected to mari ne operations and structures give a significant contribution to the total risk. • The historical risk to marine operations and structures is significant higher than the results from risk analyses. • Neither component nor system based reliability analyses of structures give adequate descriptions of the real risk connected to structures. • Human errors are probably the dominating cause of accidents connected to structural failure.

Background for New Revision of DNV-RP-C203 Fatigue Design of Offshore Steel Structures

Abstract: The DNV-RP-C203 Fatigue Design of Offshore Steel Structures is being used by a number of different companies for fatigue assessment of different types of structures. This has resulted in questions to DNV about background for the different sections in the document. It is therefore important that the basis for this document is open to the industry. Quite a lot of the background material has also been published earlier at conferences and in journals. In some situations it has been found that the content can be improved to better suite the industry. The document is presented in an electronic version making revisions easy. Therefore it has been revised several times since the last official presentation of a revision in 2005. The present paper gives an overview of the most significant changes made in the document since the 2005 revision. Some of these changes are already included in the present version of DNV-RP-C203. The remaining changes will be included in a revision dated 2010.Copyright © 2010 by ASME

Additive manufacturing of metallic lattice structures: Unconstrained design, accurate fabrication, fascinated performances, and challenges

Abstract: Lattice structures, which are also known as architected cellular structures, have been applied in various industrial sectors, owing to their fascinated performances, such as low elastic modulus, high stiffness-to-weight ratio, low thermal expansion coefficient, and large specific surface area. The lattice structures fabricated by conventional manufacturing technologies always involve complicated process control, additional assembly steps, or other uncontrollable factors. Furthermore, limited types of unit cells can be used to construct lattice structures when using conventional processes. Fortunately, additive manufacturing technology, based on a layer-by-layer process from computer-aided design models, demonstrates the unique capability and flexibility and provides an ideal platform in manufacturing complex components like lattice structures, resulting in an effective reduction in the processing time to actual application and minimum of material waste. Therefore, additive manufacturing relieves the constraint of structure design and provides accurate fabrication for lattice structures with good quality. This work systematically presents an overview of conventional manufacturing methods and novel additive manufacturing technologies for metallic lattice structures. Afterward, the design, optimization, a variety of properties, and applications of metallic lattice structures produced by additive manufacturing are elaborated. By summarizing state-of-the-art progress of the additively manufactured metallic lattice structures, limitations and future perspectives are also discussed.