Improving scheduled maintenance by missing data reconstruction: A double-loop Monte Carlo approach

This article describes a Monte Carlo-based approach for reconstructing missing information in a dataset used by General Electric for reliability analysis, which contains data coming from field observations at inspection of gas turbine components. The approach is based on a combination of maximum likelihood estimation technique to estimate the failure model parameters, Fisher information matrix to estimate the confidence intervals on the estimated parameters, and a double-loop Monte Carlo approach to estimate the missing equivalent starts (i.e. data of turbine state without the relative equivalent starts). The proposed methodology reduces the uncertainty in the estimation of the parameters of the turbine. The results of the application of the novel approach to a real industrial dataset are discussed along with a sensitivity analysis for the quantification of the robustness of the methodology to deal with different sizes of datasets

Mechanical Analysis of the Nb3Sn Dipole Magnet HD1

The Superconducting Magnet Group at Lawrence Berkeley National Laboratory (LBNL) has recently fabricated and tested HD1, a Nb3Sn dipole magnet. The magnet reached a 16 T field, and exhibited training quenches in the end regions and in the straight section. After the test, HD1 was disassembled and inspected, and a detailed 3D finite element mechanical analysis was done to investigate for possible quench triggers. The study led to minor modifications to mechanical structure and assembly procedure, which were verified in a second test (HD1b). This paper presents the results of the mechanical analysis, including strain gauge measurements and coil visual inspection. The adjustments implemented in the magnet structure are reported and their effect on magnet training discussed

On Compton Imaging

AbstractOn Compton ImagingbySara MattafirriDoctor of Philosophy in Engineering-Nuclear EngineeringUniversity of California, BerkeleyProfessor Stanley G. Prussin, Co-Chair Professor Kai Vetter, Co-ChairProfessor Jasmina Vujic Professor Steven ConollyThe feasibility of producing an image of radioactivity distribution within a patient or confined region of space using information carried by the gamma-rays emitted from the source is investigated. The imaging approach makes use of parameters related to the gamma-rays which undergo Compton scattering within a detection system, it does not involve the use of pin-holes, and it employs gamma-rays of energy ranging from a few hundreds of keVs to MeVs. Energy range of the photons and absence of pin-holes aim to provide larger pool of radioisotopes and larger efficiency than other emission imaging modalities, such as single photon emission computed tomography and positron emission tomography, making it possible to investigate larger pool of functions and smaller radioactivity doses.The observables available to produce the image are the gamma-ray position of interaction and energy deposition during Compton scattering within the detection systems. Image reconstruction methodologies such as backprojection and list-mode maximum likelihood expectation maximization algorithm are characterized and applied to produce images of simulated and experimental sources on the basis of the observed parameters.Given the observables and image reconstruction methodologies, imaging systems based on minimizing the variation of the impulse response with position within the field of view are developed. The approach allows imaging of three-dimensional sources when an imaging system which provides full 4 &pi view of the object is used and imaging of two-dimensional sources when a single block-type detector which provides one view of the object is used. Geometrical resolution of few millimeters is obtained at few centimeters from the detection system if employing gamma-rays of energy in the order of few hundreds of keVs and current state of the art semi-conductor detectors; At this level of resolution, detection efficiency is in the order of 10^-3 at few centimeters from the detector when a single block detector few centimeters in size is used. The resolution significantly improves with increasing energy of the photons and it degrades roughly linearly with increasing distance from the detector; Larger detection efficiency can be obtained at the expenses of resolution or via targeted configurations of the detector.Results pave the way for image reconstruction of practical gamma-ray emitting sources

Kinetics of phase growth in Nb3Sn formation for heat treatment optimization

The kinetics of growth and superconducting properties of Nb{sub 3}Sn are investigated as a function of the heat treatment (HT) duration and temperature for Internal Tin and Powder-in-Tube strands at 650, 700 and 750 C. For all times and temperatures, the Nb{sub 3}Sn layer thickness is measured, the critical current at 4.2 K is tested as a function of magnetic field, and the upper critical field is evaluated. Results of the layer critical current density are also shown as a function of HT duration and temperature

A double-loop Monte Carlo approach for Part Life Data Base reconstruction and scheduled maintenance improvement

International audienc

Semi-Markov Model for the Oxidation Degradation Mechanism in Gas Turbine Nozzles

International audienc

Comparison of Weibayes and Markov Chain Monte Carlo methods for the reliability analysis of turbine nozzle components with right censored data only

International audienc

Optimization of Superconducting Focusing Quadrupoles for the High Current Experiment

The Heavy Ion Fusion (HIF) program is progressing through a series of physics and technology demonstrations leading to an inertial fusion power plant. The High Current Experiment (HCX) at Lawrence Berkeley National Laboratory is exploring the physics of intense beams with high line-charge density. Superconducting focusing quadrupoles have been developed for the HCX magnetic transport studies. A baseline design was selected following several pre-series models. Optimization of the baseline design led to the development of a first prototype that achieved a conductor-limited gradient of 132 T/m in a 70 mm bore, without training, with measured field errors at the 0.1% level. Based on these results, the magnet geometry and fabrication procedures were adjusted to improve the field quality. These modifications were implemented in a second prototype. In this paper, the optimized design is presented and comparisons between the design harmonics and magnetic measurements performed on the new prototype are discussed