A method for the measurement of hydrodynamic oil films using ultrasonic reflection

The measurement of the thickness of an oil film in a lubricated component is essential information for performance monitoring and control. In this work, a new method for oil film thickness measurement, based on the reflection of ultrasound, is evaluated for use in fluid film journal bearing applications. An ultrasonic wave will be partially reflected when it strikes a thin layer between two solid media. The proportion of the wave reflected depends on the thickness of the layer and its acoustic properties. A simple quasi-static spring model shows how the reflection depends on the stiffness of the layer alone. This method has been first evaluated using flat plates separated by a film of oil, and then used in the measurement of oil films in a hydrodynamic journal bearing. A transducer is mounted on the outside of the journal and a pulse propagated through the shell. The pulse is reflected back at the oil film and received by the same transducer. The amplitude of the reflected wave is processed in the frequency domain. The spring model is then used to determine the oil film stiffness that can be readily converted to film thickness. Whilst the reflected amplitude of the wave is dependent on the frequency component, the measured film thickness is not; this indicates that the quasi-static assumption holds. Measurements of the lubricant film generated in a simple journal bearing have been taken over a range of loads and speeds. The results are compared with predictions from classical hydrodynamic lubrication theory. The technique has also been used to measure oil film thickness during transient loading events. The response time is rapid and film thickness variation due to step changes in load and oil feed pressure can be clearly observed

A new approach for the measurement of film thickness in liquid face seals

Face seals operate by allowing a small volume of the sealed fluid to escape and form a thin film between the contacting parts. The thickness of this film must be optimized to ensure that the faces are separated, yet the leakage is minimized. In this work the liquid film is measured using a novel ultrasonic approach with a view to developing a condition monitoring tool. The trials were performed in two stages. Initially tests were based on a lab simulation, where it was possible to compare the ultrasonic film thickness measurements with optical interference methods and capacitance methods. A direct correlation was seen between ultrasonic measurements and capacitance. Where ultrasonic and optical methods overlap, good correlation is observed; however, the optical method will not record film thickness above 0.72 m. A second set of trials was carried out, where the film thickness was monitored inside a seal test apparatus. Film thickness was successfully recorded as speed and load were varied. The results showed that while stationary the film thickness varied noticeably with load. When rotating, however, the oil film remained relatively stable around 2 m. During the normal operation of the seal, both sudden speed and load changes were applied in order to initiate a seal failure. During these events, the measured film thickness was seen to drop dramatically down to 0.2 m. This demonstrated the ability of the technique to predict failure in a face seal and therefore its aptitude for condition monitoring

Oil film measurement in polytetrafluoroethylene-faced thrust pad bearings for hydrogenerator applications

There is a growing trend in the replacement of the babbit facing in thrust pad bearings with a composite polytetrafluoroethylene (PTFE) surface layer. The PTFE-faced bearings have been shown to allow a greater specific pressure, reduce thermal crowning, and, in some cases, negate the need for an oil-lift (jacking) system. These designs of bearing require new methods for the measurement of oil film thickness both to assist in their development and for plant condition monitoring. In this work, an ultrasonic method of oil film measurement is evaluated for this purpose. An ultrasonic transducer is mounted on the back face of the thrust pad. Pulses are generated and transmitted through the pad material, bonding interlayer, and PTFE surface layer. The proportion of the wave that reflects back from the oil film layer is determined. This is then related to the oil film thickness using a series of calibration experiments and a spring stiffness model. In practice, the reflected signal is difficult to distinguish, in the time domain, from other internal reflections from the pad. Signals are compared with reflections when no oil film is present and processing is carried out in the frequency domain. Experiments have been performed on a full size PTFE-faced thrust pad destined for a hydroelectric power station turbine. The instrumented pad was installed in a test facility and subjected to a range of loading conditions both with and without oil lift. Although there were some problems with the robustness of the experimental procedure, oil films were successfully measured and used to study the effect of the oil-lift system on film formation. © IMechE 2006

The influence of clearance on friction, lubrication and squeaking in large diameter metal-on-metal hip replacements

Large diameter metal-on-metal bearings (MOM) are becoming increasingly popular, addressing the needs of young and more active patients. Clinical data has shown excellent short-to-mid-term results, though incidences of transient squeaking have been noted between implantation and up to 2 years post-operative. Geometric design features, such as clearance, have been significant in influencing the performance of the bearings. Sets of MOM bearings with different clearances were investigated in this study using a hip friction simulator to examine the influence of clearance on friction, lubrication and squeaking. The friction factor was found to be highest in the largest clearance bearings under all test conditions. The incidence of squeaking was also highest in the large clearance bearings, with all bearings in this group squeaking throughout the study. A very low incidence of squeaking was observed in the other two clearance groups. The measured lubricating film was found to be lowest in the large clearance bearings. This study suggests that increasing the bearing clearance results in reduced lubricant film thickness, increased friction and an increased incidence of squeaking

An online survey of postmenopausal women to determine their attitudes and knowledge of the menopause

OBJECTIVE: To explore postmenopausal women's attitudes and knowledge of the menopause. STUDY DESIGN: An online survey to evaluate women's attitudes and knowledge of the menopause, promoted via social media. In this study, only the data from 829 women who identified as postmenopausal were analysed. MAIN OUTCOME MEASURES: Quantitative and qualitative data. RESULTS: Regarding women's attitudes towards the menopause before they went through it, 18.0% were accepting of it, 15.8% were dreading it and 5.1% were looking forward to it. 38.1% of women felt that the menopause was difficult, 24.6% felt it was very difficult and 20.7% felt it was fine. 94.1% of women had never been taught about the menopause at school, and 49.0% did not feel informed at all about the menopause. More than 60% started looking for information regarding menopause as their symptoms started. The qualitative thematic analysis of the participants' responses produced six themes: the need for education, knowledge and understanding of symptoms, why is getting treatment so difficult, feelings and attitudes towards the menopause, the impact of menopause on a woman's life, the importance of the media - are they getting it right. CONCLUSION: Women's lack of education and their healthcare professionals' lack of adequate training on the menopause means that women enter this critical life stage uneducated and unsupported. It is vital that everyone is taught about the menopause and that general practitioners receive proper training. The negative narrative of menopause needs to be re-addressed to normalise the menopause and give postmenopause women hope

Childless by circumstance – using an online survey to explore the experiences of childless women who had wanted children

Childlessness is increasing globally. This study aimed to explore the experiences of childless women who had wanted children. An online survey study was promoted through social media to recruit women aged ≥46 years who were childless by circumstance. The survey remained open for 15 days. In total, 303 survey responses were collected, 176 of which were complete surveys. In total, 15.3% (27/176) of women who had wanted children reported that they had not tried to have children, most commonly due to the lack of a partner (40.7%, 11/27). Of the 139 women who had tried to have children, 70.5% (98/139) had used calendar-based menstrual cycle tracking methods to identify their fertile window, and many had undergone fertility checks including hormone tests (75.5%, 105/139) and ultrasound scans (71.2%, 99/139). A significant proportion of women had experienced a miscarriage (40.2%, 56/139). Many women had decided not to have any fertility treatment (43.2%, 60/139). For those who did, the majority had tried in-vitro fertilization (74.6%, 59/79). The most common reason that women gave for stopping fertility treatment was due to emotional reasons (74.7%, 59/79). When asked how women felt now about their childlessness, the most common issues identified were unhappiness (85/158, 54%), acceptance (43/158, 27%) and happiness (30/158, 19%). There should be more support for unsuccessful fertility patients and other childless women, and more emphasis should be placed upon fertility education in order to ensure that women are better informed about fertility issues

A survey of women's experiences of using period tracker applications: Attitudes, ovulation prediction and how the accuracy of the app in predicting period start dates affects their feelings and behaviours

INTRODUCTION: Using an online survey, the aim of this study was to ask women about their real-life experiences of using period tracker apps, their attitudes towards using their app, the information the app provided regarding ovulation and how the accuracy of the app in predicting period start dates affects their feelings and behaviours if their period comes earlier or later than predicted. METHODS: This mixed-methods observational study was conducted by an online survey of 50 multiple-choice and open-ended questions. The survey was generated with Qualtrics XM® and promoted via social media. It was open to any person who had used a period tracker. RESULTS: From 375 total responses, 330 complete responses were obtained, giving a completion rate of 88.0%. Respondents were aged between 14 and 54, with a mean age of 26.0 (±7.81). When asked what was the best thing about using the app, 29.7% (98/330) of respondents selected 'To know when I'm ovulating'. Respondents were asked if their period ever started earlier than the app predicted; 54.9% (189/330) said it had and 72.1% (238/330) said it had started later than predicted. When asked how they felt if their period arrived earlier or later than expected, thematic analysis of periods starting earlier revealed four themes: feeling unaffected, being frustrated/unprepared, feeling anxious/stressed and feeling confused/intrigued. Thematic analysis when their period arrived later revealed six themes: anxious/concerned about pregnancy, disappointed about pregnancy, seeking advice/informing healthcare professionals, thoughts about menopause, feeling unaffected and being better prepared. CONCLUSION: Period trackers need to be clearer on their intended use and reliability, especially for period due date and ovulation. Qualitative analysis shows the impact of inaccurate predictions on aspects of the users' health. This study calls for period tracker app companies to update their apps to provide transparency to their users about their intended use and capabilities

An online survey of UK women's attitudes to having children, the age they want children and the effect of the COVID-19 pandemic

STUDY QUESTION: What are women's views on having children, including the age they want to have them and other influences such as the coronavirus disease 2019 (COVID-19) pandemic? SUMMARY ANSWER: Women's views on having children, at their preferred age of 30 years, included their maternal urge and concerns about their biological clock and stability, while 19% said COVID-19 had affected their views. WHAT IS KNOWN ALREADY: Women globally are delaying the birth of their first child, with the average age of first birth approaching 32 years in some countries. The average age women have their first child in the UK is 30.7 years and over 50% of women aged 30 years are childless. The fertility rate stands at 1.3 in several European Union countries. Some people are not having their desired family size or are childless by circumstance. It is essential to understand people's attitudes to having children in different countries to identify trends so we can develop educational resources in an age-appropriate manner. STUDY DESIGN, SIZE, DURATION: We conducted an anonymous, online survey of multiple choice and open-ended questions. The survey was live for 32 days from 15 May 2020 to 16 June 2020 and was promoted using social media. PARTICIPANTS/MATERIALS, SETTING, METHODS: A total of 887 women from 44 countries participated in the survey. After filtering out women who did not consent, gave blank or incomplete responses, and those not in the UK, 411 responses remained. From the data, three areas of questioning were analysed: their views on having children, the ideal age they want to have children and the effects of the COVID-19 pandemic. Qualitative data were analysed by thematic analysis. MAIN RESULTS AND THE ROLE OF CHANCE: The average age (±SD) of the women who completed the survey was 32.2 years (±5.9), and they were mainly heterosexual (90.8%) and 84.8% had a university education. One-third of women were married/in a civil partnership (37.7%) and 36.0% were cohabitating. In relation to their views on having children, the main themes identified were: the maternal urge, the ticking of the biological clock, why did no one teach us this?, the need for stability and balance in their life, pressure to start a family and considering other ways to have a family. When asked 'In an ideal world, at what age approximately would you like to have had or have children?' a normal distribution was observed with a mean age of 29.9 (±3.3) years. When asked 'What factors have led you to decide on that particular age?' the most frequent choice was 'I am developing my career'. Three themes emerged from the qualitative question on why they chose that age: the need for stability and balance in their life, the importance of finding the right time and life experiences. The majority of women felt that the COVID-19 pandemic had not affected their decision to have children (72.3%), but 19.1% said it had. The qualitative comments showed they had concerns about instability in their life, such as finances and careers, and delays in fertility treatment. LIMITATIONS, REASONS FOR CAUTION: The survey was promoted on social media only and the women who answered the survey were highly educated. WIDER IMPLICATIONS OF THE FINDINGS: The women surveyed ideally want children at age 30 years but there are obstacles in their way, such as the need to develop their career. Global tailored fertility education is essential to ensure people make informed reproductive choices. In addition, it is essential for supportive working environments and affordable childcare to be in place in every country. STUDY FUNDING/COMPETING INTEREST(S): J.C.H. is founder of www.globalwomenconnected.com and Reproductive Health at Work, and author of the book Your Fertile Years. This project was funded by the Institute for Women's Health, UCL. TRIAL REGISTRATION NUMBER: N/A