High pressure oxygen turbopump bearing cage stability analyses

The low service life of the high pressure oxygen turbopump (HPOTP) bearings used in the space shuttle main engine was examined by use of the Battelle "BASDAP' bearing computer stability model. The dynamic instability of the bearing cage resulted in excessive wear and eventual failure of the unit. By maintaining a cage/race clearance of no more than 0.25 millimeters (0.010 inches), ball/pocket clearance of no less than 0.54 millimeters (0.025 inches), dynamic balancing of the cages, and maintaining adequate lubricant films between the balls and races, cage instability and subsequent bearing degradation can be reduced

Cage stability analysis for SSME HPOTP bearings

A numerical model of cage motion (CAGEDYN) was used to analyze the stability of bearing cages in the Space Shuttle main engine (SSME) high pressure oxygen turbopump (HPOTP). The stability of existing bearing geometries, as well as perturbations of these geometries, was analyzed for various operating conditions. Results of the analyses show that some combinations of operating parameters, exacerbated by the sparse lubrication that exist in the HPOTP bearings, can cause unstable cage oscillations. Frequencies of cage oscillations were predicted by the CAGEDYN numerical model by Fourier analysis of predicted cage motions. Under conditions that cause unstable cage motion, high frequency oscillations were predicted that could cause premature cage failures

Evaluation of feasibility of measuring EHD film thickness associated with cryogenic fluids

The feasibility of measuring elastohydrodynamic (EHD) films as formed with a cryogenic (LN2) fluid is evaluated. Modifications were made to an existing twin disk EHD apparatus to allow for disk lubrication with liquid nitrogen. This disk apparatus is equipped with an X-ray system for measuring the thickness of any lubricant film that is formed between the disks. Several film thickness experiments were conducted with the apparatus which indicate that good lubrication films are filmed with LN2. In addition to the film thickness studies, failure analyses of three bearings were conducted. The HPOTP turbine end bearings had experienced axial loads of 36,000 to 44,000 N (8,000 to 10,000 lb). High continuous radial loads were also experienced, which were most likely caused by thermal growth of the inner race. The resulting high internal loads caused race spalling and ball wear to occur

Investigation of instability, dynamic forces, and effect of dynamic loading on strength of cages for the bearings in the high pressure oxygen turbopumps for the space shuttle main engine

Experiments were performed to determine the effect of cyclic loading on bearing cage strength. A long term working tensile load of approximately 1300 N (300 lbs) was found to be the likely maximum. Higher loads caused a decrease in cage tensile strength after the 125,000 cycle testing period. Poisson's ratio in compression was found to be highly dependent upon the direction of the fiberglass plies. At room temperature the value was 0.15 with the plies and 0.68 across the plies. At -196 C (-321 F), the value with the plies was 0.20. The results of the analyses conducted have again demonstrated the critical need for improved lubrication in the high pressure oxygen turbopump bearings. Lubricant films with low shear strength and low friction coefficients promote cage stability and decrease ball/cage forces during marginal operating conditions. The analysis of the effect of combined bearing loads on ball/cage loads has identified a radial load of 3600 N (800 lbs) as the maximum for the current clearance of the balls and cage pockets. Liquid oxygen impinging on the cage in the direction of rotation was found to enhance cage stability

Measurements of elastohydrodynamic film thickness, wear and tempering behavior of high pressure oxygen turbopump bearings

The reusable design of the Space Shuttle requires a target life of 7.5 hours for the turbopumps of the Space Shuttle main engine (SSME). This large increase from the few hundred seconds required in single-use rockets has caused various problems with the bearings of the turbopumps. The berings of the high pressure oxygen turbopump (HPOTP) were of particular concern because of wear, spalling, and cage failures at service time well below the required 7.5 hours. Lubrication and wear data were developed for the bearings. Since the HPOTP bearings operate in liquid oxygen, conventional liquid lubricants cannot be applied. Therefore, solid lubricant coatings and lubricant transfer from the polytetrafluorethylene (FTFE) cage were the primary lubrication approaches for the bearings. Measurements were made using liquid nitrogen in a rolling disk machine to determine whether usable elastohydrodynamic films could be generated to assist in the bearing lubrication

Evaluation of outer race tilt and lubrication on ball wear and SSME bearing life reductions

Several aspects of the SSME bearing operation were evaluated. The possibility of elastohydrodynamics (EHD) lubrication with a cryogenic fluid was analyzed. Films as thick as .61 microns were predicted with one theory which may be thick enough to provide hydrodynamic support. The film formation, however, is heavily dependent on good surface finish and a low bulk bearing temperature. Bearing dynamics to determine if the radial stiffness of a bearing which are dependent on bearing misalignment were analyzed. Four ball tests were conducted at several environmental conditions from an LN2 bath to 426 C in air. Surface coatings and ball materials are evaluated. Severe wear and high friction are measured for all ball materials except when the balls have surface lubricant coatings

Recognizing and managing a deteriorating patient: a randomised controlled trial investigating the effectiveness of clinical simulation in improving clinical performance in undergraduate nursing students

Aims To report the results of a randomised controlled trial which explored the effectiveness of clinical simulation in improving the clinical performance of recognising and managing an adult deteriorating patient in hospital. Background There is evidence that final year undergraduate nurses may lack the knowledge, clinical skills and situation awareness required to competently manage a deteriorating patient in hospital. The effectiveness of clinical simulation as an educational strategy to teach the skills required to recognise and effectively manage the early signs of clinical deterioration needs to be evaluated. Method This was a two centre, randomised, controlled trial with single blinded assessments. Data were collected in July 2013. Ninety- eight first year nursing students were randomised either into a control group where they received a traditional classroom lecture, or an intervention group where they received simulation training. Participants completed a pre and post- intervention objective structured clinical examination. General Perceived Self Efficacy and Self-Reported Competency scores were measured before and after the intervention. Student satisfaction with teaching was surveyed after the teaching intervention. Results The intervention group performed significantly better in the objective structured clinical examination after their simulation training. General Perceived Self Efficacy and Self-Reported Competency were not correlated with performance. There was no significant difference in the post intervention General Perceived Self Efficacy and Self-Reported Competency scores between the control and intervention group. The intervention group were significantly more satisfied with their teaching method. Conclusion Simulation based education may be an effective educational strategy to teach nurses the necessary skills to effectively recognise and manage a deteriorating patient

PTPN22 R620W minor allele is a genetic risk factor for giant cell arteritis

Published online 7 April 2016.Giant cell arteritis (GCA) is one of the commonest forms of vasculitis in the elderly, and may result in blindness and stroke. The pathogenesis of GCA is not understood, although environmental, infectious and genetic risk factors are implicated. One gene of interest is PTPN22, encoding lymphoid protein tyrosine phosphatase (Lyp), expressed exclusively in immune cells, which is proposed to be an 'archetypal non-HLA autoimmunity gene'. The minor allele of a functional PTPN22 single nucleotide polymorphism (rs2476601, R620W), which disrupts an interaction motif in the protein, was originally reported to be associated with biopsy-proven GCA in Spanish patients, with supporting data from three replicate Northern European studies. Recently, this observation was extended with additional patients and controls, and studies encompassing European, Scandinavian, UK and American patients. The aim of our study was to determine the association between PTPN22 rs2476601 (R620W) and biopsy-proven GCA in an Australian case cohort.Susan Lester, Alex W Hewitt, Carlee D Ruediger, Linda Bradbury, Elisabeth De Smit, Michael D Wiese, Rachel Black, Andrew Harrison, Graeme Jones, Geoffrey O Littlejohn, Tony R Merriman, Bain Shenstone, Malcolm D Smith, Maureen Rischmueller, Matthew A Brown, Catherine L Hil