Probabilistic structural analysis to quantify uncertainties associated with turbopump blades

A probabilistic study of turbopump blades has been in progress at NASA Lewis Research Center for over the last two years. The objectives of this study are to evaluate the effects of uncertainties in geometry and material properties on the structural response of the turbopump blades to evaluate the tolerance limits on the design. A methodology based on probabilistic approach was developed to quantify the effects of the random uncertainties. The results indicate that only the variations in geometry have significant effects

Probabilistic analysis of bladed turbine disks and the effect of mistuning

Probabilistic assessment of the maximum blade response on a mistuned rotor disk is performed using the computer code NESSUS. The uncertainties in natural frequency, excitation frequency, amplitude of excitation and damping are included to obtain the cumulative distribution function (CDF) of blade responses. Advanced mean value first order analysis is used to compute CDF. The sensitivities of different random variables are identified. Effect of the number of blades on a rotor on mistuning is evaluated. It is shown that the uncertainties associated with the forcing function parameters have significant effect on the response distribution of the bladed rotor

Probabilistic Design and Analysis Framework

PRODAF is a software package designed to aid analysts and designers in conducting probabilistic analysis of components and systems. PRODAF can integrate multiple analysis programs to ease the tedious process of conducting a complex analysis process that requires the use of multiple software packages. The work uses a commercial finite element analysis (FEA) program with modules from NESSUS to conduct a probabilistic analysis of a hypothetical turbine blade, disk, and shaft model. PRODAF applies the response surface method, at the component level, and extrapolates the component-level responses to the system level. Hypothetical components of a gas turbine engine are first deterministically modeled using FEA. Variations in selected geometrical dimensions and loading conditions are analyzed to determine the effects of the stress state within each component. Geometric variations include the cord length and height for the blade, inner radius, outer radius, and thickness, which are varied for the disk. Probabilistic analysis is carried out using developing software packages like System Uncertainty Analysis (SUA) and PRODAF. PRODAF was used with a commercial deterministic FEA program in conjunction with modules from the probabilistic analysis program, NESTEM, to perturb loads and geometries to provide a reliability and sensitivity analysis. PRODAF simplified the handling of data among the various programs involved, and will work with many commercial and opensource deterministic programs, probabilistic programs, or modules

Probabilistic evaluation of uncertainties and risks in aerospace components

This paper summarizes a methodology developed at NASA Lewis Research Center which computationally simulates the structural, material, and load uncertainties associated with Space Shuttle Main Engine (SSME) components. The methodology was applied to evaluate the scatter in static, buckling, dynamic, fatigue, and damage behavior of the SSME turbo pump blade. Also calculated are the probability densities of typical critical blade responses, such as effective stress, natural frequency, damage initiation, most probable damage path, etc. Risk assessments were performed for different failure modes, and the effect of material degradation on the fatigue and damage behaviors of a blade were calculated using a multi-factor interaction equation. Failure probabilities for different fatigue cycles were computed and the uncertainties associated with damage initiation and damage propagation due to different load cycle were quantified. Evaluations on the effects of mistuned blades on a rotor were made; uncertainties in the excitation frequency were found to significantly amplify the blade responses of a mistuned rotor. The effects of the number of blades on a rotor were studied. The autocorrelation function of displacements and the probability density function of the first passage time for deterministic and random barriers for structures subjected to random processes also were computed. A brief discussion was included on the future direction of probabilistic structural analysis

Factors Affecting Online Streaming Subscriptions

As digital media continues to expand, competition between cable television and online streaming services increases. Acquiring customers today takes more than just advertising; it requires tailoring business objectives to the needs and wants of consumers. Numerous studies have examined the connection between the adoption of cable and online media, and key variables such as cost, ease of use, and social trends. In this study, we explore a number of factors which consumers consider when choosing cable television and online streaming options. Sample data was collected through a survey questionnaire at a large public university. Multivariate regression models were developed to identify factors affecting each option. Both models showed statistical significance. The regression model for cable TV showed additional purchase, social trend (negative), cost and customer service factors were statistically significant. In contrast to the cable TV, only social trend and available options were significant in the regression model for online streaming. Media options were marginally significant. With respect to demographics, gender played no clear role while age showed marginal impact in choosing online streaming over cable television

Probabilistic structural analysis methods for space transportation propulsion systems

Information on probabilistic structural analysis methods for space propulsion systems is given in viewgraph form. Information is given on deterministic certification methods, probability of failure, component response analysis, stress responses for 2nd stage turbine blades, Space Shuttle Main Engine (SSME) structural durability, and program plans.

Visual Fields at Presentation and after Trans-sphenoidal Resection of Pituitary Adenomas

Purpose: To evaluate visual field changes in patients with pituitary adenomas following trans-sphenoidal surgery. Methods: Eighteen patients with pituitary adenomas underwent a complete ophthalmic assessment and visual field analysis using the Humphrey Field Analyzer 30-2 program before and after trans-sphenoidal surgical resection at the Himalayan Institute of Medical Sciences over a one year period. Visual acuity, duration of symptoms, optic nerve head changes, pattern of visual field defects, and variables such as mean deviation and visual field index were compared. Results: Thirty-six eyes of 18 patients including 10 male and 8 female subjects with mean age of 35.1±9.9 years and histologically proven pituitary adenoma were included. Mean visual acuity at presentation was 0.29 logMAR which improved to 0.21 logMAR postoperatively (P = 0.305). Of 36 eyes, 24 (66.7%) had visual field defects including temporal defects in 12 eyes (33.3%), non-specific defects in 10 eyes (27.8%), and peripheral field constriction in 2 eyes (5.6%). Mean deviation of visual fields at presentation was -14.28 dB which improved to -11.32 dB postoperatively. The visual field index improved from 63.5% to 75% postoperatively. Favorable visual field outcomes were correlated with shorter duration of symptoms and absence of optic nerve head changes at presentation. Conclusion: Visual field defects were present in two thirds of patients at presentation. An overall improvement in vision and visual fields was noted after surgical resection. An inverse correlation was found between the duration of symptoms and postoperative visual field recovery, signifying the importance of early surgical intervention

A Path Difficult to Tread: Pure Autonomic Failure, A Case Report

Introduction - Pure autonomic failure is a rare disorder characterized by orthostatic hypotension, absence of a compensatory rise in heart rate, and abnormal autonomic functions. In most cases, supine hypertension is seen coupled with orthostatic hypotension, making the management of these patients a big challenge. We present the case of a 74-year-old gentleman, who presented to the ED with altered mental status for a day; weakness, and falls for 3 weeks. The patient had a past medical history of Hypertension, alcoholism, and REM sleep disorder. He was being treated for erectile dysfunction for the last 10 years and had a family history of Parkinson\u27s disease in his mother and sister. The patient was compliant with Lisinopril 40 mg, Amlodipine, and Rosuvastatin, Tamsulosin 0.4 mg. His blood pressure(BP) on presentation was ranging between 109/74-194/76 mm of Hg. Systolic BP dropped by 30mmHg after tilting the angle of the bed to 45 degrees for 1 minute with no change in HR and the patient became symptomatic in this position. Orthostatic vitals showed a dramatic drop in Systolic BP of \u3e80mmHg with no change in heart rate. MRA and MRI showed chronic microvascular changes. The Echocardiogram, Cortisol, and TSH levels were all normal. All anti-hypertensives were discontinued and supportive treatment was started with Midodrine, Droxidopa, and Pyridostigmine, thigh-high TED hose and abdominal binders at bedtime, and Nitroglycerin patch at night for hypertension. The patient was started on fludrocortisone as he continued to drop his BP by 80 mmHg on standing. The use of TED stockings and bed tilting improved the issue of uncontrolled supine hypertension at night. Conclusion- Treatment of autonomic dysfunction continues to be challenging. There are no definitive guidelines and management is largely individualized. Both pharmacological and non-pharmacological measures are used

Newspaper media framing of obesity during pregnancy in the UK: A review and framework synthesis

Two thirds of women report experiencing weight stigma during pregnancy. Newspaper media is powerful in framing health issues. This review synthesized UK newspaper media portrayal of maternal obesity. NexisUni was searched to identify newspaper articles, published January 2010 to May 2021, reporting content on obesity during pregnancy. Framework synthesis integrated quantitative and qualitative analysis of the content of articles. There were 442 articles included (59% tabloids and 41% broadsheets). Three overarching themes with interacting sub-themes were as follows: (1) Women were blamed for their weight, risks, and NHS impact. (2) Women were solely responsible for solving obesity, gendered from school age. (3) Women with obesity were a burden on individuals (e.g., themselves, their children, and health professionals), to society, and the NHS. Catastrophizing language framed the “problem,” “scale,” and “public health concern” of maternal obesity, emphasizing risk, and danger and was alarmist, aggressive, and violent as to elicit fear or devalue women. Articles platformed ‘expert’ voices rather than women's lived experiences. This review identified that UK newspaper media negatively frames and oversimplifies the topic of maternal obesity. Exposure to blaming and alarmist messaging could increase women's guilt, stigma, and internalized weight bias. The newspaper media should be harnessed to de-stigmatize maternal obesity and promote maternal well-being