It is possible to create laminates, composed of plies with spatially varying fiber orientation, which have stiffness properties that vary as a function of position. Previous work had modeled such variable stiffness laminae by taking a reference fiber path and creating subsequent paths by shifting the reference path. We introduce a method where subsequent paths are truly parallel to the reference fiber path. The primary manufacturing constraint considered in the analysis of variable-stiffness laminates was limits on fiber curvature, which proved to be more restrictive for parallel-fiber laminae than for shifted-fiber laminae. The in-plane responses of shifted-and parallel-fiber variable-stiffness laminates to applied uniform end shortening were determined. Both shifted and parallel-fiber variable-stiffness laminates can redistribute the applied load, thereby increasing critical buckling loads compared to traditional straight-fiber laminates. The primary difference between the two methods is that parallel-fiber laminates are not able to redistribute the loading to the degree of the shifted fiber; this significantly reduces the increase in critical buckling load for parallel-fiber variable-stiffness laminates over straight-fiber laminates. (Author) Abstract Using advanced manufacturing techniques it is possible to create laminates, composed of plies' with spatially varying fiber orientation, which have stiffness properties that vary as a function of position. Previous work had modeled such variable stiffness laminae by taking a reference fiber path and creating subsequent paths by shifting the reference path. This paper introduces a method where subsequent paths are truly parallel to the reference fiber path. The primary manufacturing constraint considered in the analysis of variable stiffness laminates was limits on fiber curvature which proved to be more restrictive for parallel fiber laminae than for shifted fiber. The in-plane responses of shifted and parallel fiber variable stiffness laminates to applied uniform end shortening were determined. Both shifted and parallel fiber variable stiffness laminates can redistribute the applied load thereby increasing critical buckling loads compared to traditional straight fiber laminates. The primary differences between the two methods is that parallel fiber laminates are not able to redistribute the loading to the degree of the shifted fiber. This significantly reduces the increase in critical buckling load for parallel fiber variable stiffness laminates over straight fiber laminates.
The Barkhausen noise amplitude was measured under conditions of biaxial stress in steel pipe for the case of a magnetic field noncoaxial with the stress axes. The stress axes for stresses σ1 and σ2 were orthogonal to each other. In particular, σ1 was the axial stress and σ2 was the hoop stress. Various angles were used for the field direction, along with various stress magnitudes, both compressive and tensile. The stress σ2 was always tensile, but σ1 was both compressive and tensile. A model for this biaxial stress situation, based on the Sablik–Jiles magnetomechanical model, was formulated. Using a model for the Barkhausen noise deriving from the Alessandro et al. model, the Barkhausen noise power maximum amplitude was computed for various field angles and stresses σ1 and σ2. The numerical results from this model calculation agreed qualitatively with many features of the experimental results. Thus, one found both numerically and experimentally that with field direction at small angles from the σ1 axis, the Barkhausen noise amplitude increased as the stress σ1 was increased from negative to positive. At large angles (generally greater than 45°), the reverse was true and the Barkhausen noise amplitude decreased as stress σ1 was increased. Also, the curves for the various angles tended to intersect when σ1 was set equal to σ2. Differences between numerical and experimental results are discussed, and suggestions are made for further improvement of the modeling.
Locating internal corrosion damage in gas pipelines is made difficult by the presence of large uncertainties in flow characteristics, pre-existing conditions, corrosion resistance, elevation data, and test measurements. This paper describes a preliminary methodology to predict the most probable corrosion damage location along the pipelines, and then update this prediction using inspection data. The approach computes the probability of critical corrosion damage as a function of location along the pipeline using physical models, for flow, corrosion rate, and inspection information as well as uncertainties in elevation data, pipeline geometry and flow characteristics. The probabilistic methodology is based on the internal corrosion direct assessment (ICDA) methodology. The probability of corrosion damage is the probability that the corrosion depth exceeds a critical depth times the probability of the presence of electrolytes such as water. Water is assumed present at locations where the pipeline inclination angle is greater than the critical angle. The corrosion rate is defined to be a linear combination of three candidate corrosion rate models with separate weight factors. Monte Carlo simulation and the first-order reliability method (FORM) implemented in a simple spreadsheet model are used to perform the probability integration. Bayesian updating is used to incorporate inspection information (e.g., in-line, excavation, etc.) and update the corrosion rate model weight factors and thereby refine the prediction of most probable damage location. This provides a systematic method for focusing costly inspections on only those locations with a high probability of damage while allowing future predictions to better reflect field observations.
With the expected introduction of wind turbine facilities for the generation of electricity to the US Outer Continental Shelf (OCS) waters, there is a need to evaluate how the long term operations of these facilities can be ensured through Integrity Management (IM) activities, particularly inspections. There is a long operational history of IM in the Gulf of Mexico, offshore California and Alaska, and around the world for fixed and floating oil and gas platforms. Both prescriptive and Risk- Based Inspection (RBI) methodologies have been established and implemented. This experience provides a foundation for implementing similar integrity management programs for offshore wind turbine facilities. This paper describes a guidance document developed to assist operators and regulators in developing IM programs for offshore wind farms, the incorporation of existing guidance for subsea structures, above-water structures and access systems, along with guidance from subject matter experts regarding critical inspection areas, inspection techniques, and inspection intervals that are unique to wind turbine facilities. This work was funded by the US Department of the Interior, Minerals Management Service (MMS). Development Approach An integrity management program is designed to ensure the safe and efficient operations of a facility over its service life. It is comprised of three primary activities:Inspection activitiesContinuous monitoring activitiesEngineering evaluation and data management This basic framework has been used extensively with offshore oil and gas platforms worldwide. Coupling this with inspection and monitoring practices unique to wind turbine facilities (both onshore and offshore) provides a basis for developing guidelines for an offshore wind turbine integrity management program. These guidelines and the approach used in their development are documented in MMS TA&R Project 627, " Inspection Methodologies for Offshore Wind Turbine Facilities?? [1]. Information from regulatory standards, industry recommended practices, and subject matter experts was used to divide a typical offshore wind turbine facility into specific systems and structures with similar inspection scope, frequency and approach. The highlighted critical inspection locations were coupled with practical inspection realities (e.g., what can be accessed and how can areas be inspected) important to developing a successful integrity management program. This paper provides an overview of the MMS TA&R Project 627 [1] including:Description of a typical offshore wind turbine facilityPotential failure modes and inspection techniquesRecommended integrity management guidelines
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