Turbine Rotors Whirl After Dynamically Stable Designs Are Updated

LecturePg. 91-98.The problem of steam turbine rotor whirling following uprating of a stable design and the measures taken to define the problem and implement a solution are described. Nearly identical units installed at several of Union Carbide's process plants exhibited different symptoms of minor instability after rerating. The newest unit, rerated before installation, began to exhibit signs of not-so-minor instability following a very stable and successful startup. The deceptive symptoms, temporary corrective action, final diagnosis of the problem, including field testing, are discussed

Distortion Of Speed Changer Housings And Resulting Gear Failures

PaperPg. 7-14.Gear case distortion due to thermal effects has caused unique and costly failures at several of Union Carbide's process plants. The unusual nature of these failures has prompted us to make an in-depth logical investigation considering the most obvious as well as the not so obvious reasons for failure. Diagnosis indicates that distortion of the housing due to temperature variations, including changes in ambient and the design of the internal lubrication and gear mesh cooling spray, is more significant than previously suspected. Several examples illustrating the problems and their solutions, including the field mechanical and optical measurement methods, are discussed

Guidelines For Performance Testing Centrifugal Compressor

PaperPg. 169-171.Performance testing of centrifugal compressors in the field is generally a compromise at best, and shop testing before delivery to the site is usually preferred. There are circumstances that dictate or suggest that the aerodynamic performance be tested after installation in the field why field testing is sometimes required or in some cases preferred, the objectives of the test, and a brief description of the procedures used to achieve the objectives are presented. Detailed enumeration of the test instrumentation and the data recorded has not been included, but reference is made to various test codes for such detail

Fatigue Failures Of Compressor Impellers And Resonance Excitation Testing

LectureThe similarity of failures of impellers in centrifugal compressors soon after initial startup and failures of impellers in other compressors after about seven years of successful operation and the test programs to define the problems are described. Early failure of an impeller in a turbine driven air compressor followed by other failures in parallel constant speed process compressors installed at another Union Carbide process plant indicated resonance or response at known excitation frequencies. However, fatigue failure of an impeller without a known source of excitation soon after initial start-up was followed by an identical failure about four years later in the same constant speed machine. Concurrently, an impeller failed by fatigue in a turbine driven process compressor after about seven years of satisfactory operation. These failures led to extensive testing and quality control programs at several manufacturers’ plants for both new equipment and replacement impellers plus a revitalized series of field tests to identify the excitation sources. Shaker testing and field testing were effective in determining that, while the resonant frequencies and modal patterns may not correspond with any known source of excitation, the fluid flow at various load and speed conditions can excite a resonance and lead to failure. Both the shop and field testing, including corrective action, are discussed

Passive range of motion functional magnetic resonance imaging localizing sensorimotor cortex in sedated children

OBJECT: In this study, the authors examined whether passive range of motion (ROM) under conscious sedation could be used to localize sensorimotor cortex using functional MR (fMR) imaging in children as part of their presurgical evaluation. METHODS: After obtaining institutional review board approval (for retrospective analysis of imaging data acquired for clinical purposes) and informed consent, 16 children underwent fMR imaging. All 16 had lesions; masses were found in 9 patients and cortical dysplasia was found in 4; the lesions in 3 patients were not diagnosed. Passive ROM was performed during blood oxygen level-dependent MR imaging sequences. Three of the patients also performed active motor tasks during the fMR imaging study. All patients were evaluated using passive ROM of the hand and/or foot; 3 patients were evaluated for passive touch of the face. In 9 cases, intraoperative electrocorticography (ECoG) was used. Five of the patients underwent intraoperative ECoG to evaluate for seizure activity. Four patients had intraoperative ECoG for motor mapping. Five of the patients had subdural grids placed for extraoperative monitoring. RESULTS: In 3 cases, the active and passive ROMs colocalized. In 4 patients ECoG was used to identify motor cortex, and in all 4 motor ECoG yielded results consistent with the passive ROM localization. Thirteen of 16 children have undergone resection based on passive ROM fMR imaging findings with no unanticipated deficits. CONCLUSIONS: These preliminary data suggest that passive ROM fMR imaging can accurately detect functional hand, leg, and face regions of the sensorimotor cortex in the sedated child. This extends current extraoperative mapping capabilities to patients unable or unwilling to cooperate for active motor tasks

A digital pediatric brain structure atlas from T1-weighted MR images

Human brain atlases are indispensable tools in model-based segmentation and quantitative analysis of brain structures. However, adult brain atlases do not adequately represent the normal maturational patterns of the pediatric brain, and the use of an adult model in pediatric studies may introduce substantial bias. Therefore, we proposed to develop a digital atlas of the pediatric human brain in this study. The atlas was constructed from T1-weighted MR data set of a 9-year old, right-handed girl. Furthermore, we extracted and simplified boundary surfaces of 25 manually defined brain structures (cortical and subcortical) based on surface curvature. We constructed a 3D triangular mesh model for each structure by triangulation of the structure’s reference points. Kappa statistics (cortical, 0.97; subcortical, 0.91) indicated substantial similarities between the mesh-defined and the original volumes. Our brain atlas and structural mesh models (www.stjude.org/brainatlas) can be used to plan treatment, to conduct knowledge and model-driven segmentation, and to analyze the shapes of brain structures in pediatric patients

PET-CT of the Normal Spinal Cord in Children

Rationale and Objectives: The aim of this study was to assess the correlation between age and spinal cord metabolic activity in children using positron emission tomography-computed tomography. Materials and Methods: The cohort included 128 children imaged from January 2003 through April 2007, excluding those with spinal disease. Using axial images, the fluorodeoxyglucose activity in the pons and three cervical, three thoracic, and two lumbar spinal cord levels was subjectively graded as minimal, moderate, or intense. From regions of interest at each level, the maximum standardized uptake value was determined. Patients were grouped by age: group 1, \u3c5 years; group 2, ≥5 to \u3c10 years; group 3, ≥10 to \u3c15 years; and group 4, ≥15 to \u3c22 years. Subjective grade and standardized uptake values were compared at each level and for each level between age groups. The α level was set at 0.0046 on the basis of Bonferroni\u27s correction for multiple comparisons. Results: There were 16 patients in group 1, 19 in group 2, 33 in group 3, and 60 in group 4. Subjective grades and standardized uptake values were higher in the pons, midcervical, and low thoracic areas than elsewhere in all age groups. Subjective grades significantly increased with age in the cervical and thoracic cord (P \u3c .0005). Standardized uptake values in the pons and all cord levels significantly increased with increasing age (P ≤ .0008). Conclusions: In children, the metabolic activity of the spinal cord increases with age. On positron emission tomography, the cord can appear intensely avid in the midcervical and low thoracic areas. © 2009 AUR