Operating under jet splashing conditions can increase the capture efficiency of scoops

Scoops are used in aero-engines to capture oil and direct the oil flow for the lubrication of bearings, where a direct oil injection is not effective or possible. The design of scoops focuses on the capture of oil to aim for the highest capture efficiency. The operating conditions are usually chosen such that splashing of the oil jet against the outer side of scoops is avoided. In this paper it is shown that some degree of splashing may be beneficial and results in an increase of the scoop capture efficiency. An analytical approach is presented to describe the range of operating conditions at which the jet is aimed to hit a specific fixed point on the outer or inner scoop contour. These operating conditions are introduced as splashing and capture conditions, respectively, and described in terms of a dimensionless velocity ratio and the jet angle. A “splashing criterion” is introduced to describe the operating conditions at which the jet is aimed to hit the rear side of the scoop. A “capture criterion” is introduced to describe the operating conditions at which the jet is aimed to hit the scoop tip. The basic assumption in this paper is that the best scoop capture efficiency is correlated to the splashing criterion and not to the capture criterion. The correlation is confirmed by a series of experiments on a scoop, performed at different jet angles and a range of velocity ratios. From the match of the correlation curve with the experiments, it is concluded that the best scoop efficiency is obtained when the jet is aimed to splash on the outer scoop contour at a point near the rear side. It could be proven that this splash point does not change with the jet angle. The fact that this point of “best efficiency” remains a fixed splashing point on the scoop contour may be helpful in the design of scoops

Rapid filling of pipelines with the SPH particle method

The paper reports the development and application of a SPH (smoothed particle hydrodynamics) based simulation of rapid filling of pipelines, for which the rigid-column model is commonly used. In this paper the water-hammer equations with a moving boundary are used to model the pipe filling process, and a mesh-less Lagrangian particle approach is employed to solve the governing equations. To assign boundary conditions with time-dependent (upstream) and constant (downstream) pressure, the SPH pressure boundary concept proposed recently in literature is used and extended. Except for imposing boundary conditions, this concept also ensures completeness of the kernels associated with particles close to the boundaries. As a consequence, the boundary deficiency problem encountered in conventional SPH is remedied. The employed particle method with the SPH pressure boundary concept aims to predict the transients occurring during rapid pipe filling. It is validated against laboratory tests, rigid-column solutions and numerical results from literature. Results obtained with the present approach show better agreement with the test data than those from rigid-column theory and the elastic model solved by the box scheme. It is concluded that SPH is a promising tool for the simulation of rapid filling of pipelines with undulating elevation profiles. Keywords: Rapid filling of pipelines; Undulating elevation profile; SP

Dynamic Behaviour of Air Valves in a Large-Scale Pipeline Apparatus

[EN] This paper describes an experimental programme on the dynamic behaviour of air valves performed in a large-scale pipeline apparatus. Dynamic flow tests were performed at large (full) scale, since previous quasi-steady flow tests at small scale did not lead to realistic results. Investigations in a large-scale pipeline apparatus lead to a better understanding of the physical processes associated with the dynamic performance of air valves. Float type air valves of nominal diameter of 50 and 100 mm were tested in geometrically similar 200 and 500 mm test sections, to allow for the assessment of dynamic scale effects and the development of dimensionless parameter groups and dynamic scale laws. The approach in the determination of the dynamic performance of air valves was to measure their response to flow acceleration/ decelerations, which are imposed upon the valve. In this way, the air valve behaviour following events like system start-up, pump trip and pipe rupture is simulated. Key results of the dynamic flow tests, including air release tests (valve slam) and column separation tests (effect of air valve on surge suppression), are presented and discussed.The authors gratefully acknowledge the support of the European Commission for their funding of the Transnational Access to Major Research Infrastructure activity within the Improving Human Potential (IHP) Programme.Bergant, A.; Kruisbrink, A.; Arregui De La Cruz, F. (2012). Dynamic Behaviour of Air Valves in a Large-Scale Pipeline Apparatus. Strojniški vestnik ¿ Journal of Mechanical Engineering. 58(4):225-237. doi:10.5545/sv-jme.2011.032S22523758

The dynamic behaviour of check valves in pipeline systems

A semi-empirical method is developed to describe the dynamic behaviour of check valves in pipeline systems. The method is based on parameterized valve models and dimensionless valve characteristics, which may be obtained from experiments. The check valve is considered as a black box with certain input and output characteristics. The check valve closure and associated pressure surges are the dominant phenomena. Undamped check valves may be considered as a special case of damped check valves. Much attention is paid to the description of the hydrodynamic (fluid) forces on the internal, moving valve elements. These elements may be considered as translating or rotating bodies with (at least) one plane of symmetry. The equations of motion for the constrained, unsteady motion of such a body in an unconfined, unsteady fluid flow are based on the dynamical theory of Kirchhoff, extended to an unsteady fluid flow. The equivalent equations for a body in a confined fluid are based on Lagrange's method of generalized coordinates. A general (dimensionless) valve equation of motion is developed, which is valid for most of the existing check valve types. Basic differential equations are derived for the transient flow in a pipe with constant initial flow deceleration. The equations are applied to describe the check valve closure under reflection free and reflecting boundary conditions in the form of dimensionless, analytical equations. The theory is based on conventional waterhammer theory. The pipe and valve equations are coupled via the integral form of the momentum equation. The uncoupled and coupled, (dimensionless) pipe and valve equations show formally which (dimensionless) variables and valve, system and fluid parameters are relevant to the dynamic behaviour of check valves in pipeline systems. In that sense they are used in a dimensional analysis to develop (dimensionless) valve characteristics and dynamic scale laws. Based on the dimensionless valve characteristics, models for undamped and damped check valves are developed and implemented in the waterhammer computer code CVWP (Check Valve Waterhammer Program). Experiments are performed in the test facility at Delft Hydraulics to measure several valve characteristics of weakly and strongly damped check valves. The dynamic scale laws are validated by means of numerical simulations. The valve models are validated against experimental data. The study has been performed within the Check Valve Research Project (CVRP)

Sleep duration and incidence of obesity in infants, children and adolescents : a systematic review and meta-analysis of prospective studies

Study Objective: To assess the prospective relationship between sleep and obesity in a paediatric population. Methods: We performed a systematic search using PubMed, Embase, Web of Science and Cochrane (up to 25th September 2017). Included studies were prospective, had follow-up >1 year, had duration of sleep at baseline, and measures of incidence of overweight or obesity and/or changes in body mass index (BMI) z-score and BMI during follow-up. We extracted relative risks or changes in BMI z-score or BMI and 95% confidence intervals (CI) and pooled them using a random effect model. Results: Forty-two studies were included but, as there was significant heterogeneity, results are presented by age strata. Short sleep was associated with a greater risk of developing overweight or obesity in infancy (7 Studies, 14 738 participants, RR: 1.40; 95% CI 1.19 to 1.65; p<0.001), early childhood (8 Studies, 31 104 participants, RR: 1.57; 1.40 to 1.76; p<0.001), middle childhood (3 studies, 3 005 participants, RR: 2.23; 2.18 to 2.27; p<0.001) and adolescence (3 studies, 26 652 participants, RR: 1.30; 1.11 to 1.53; p<0.002). Sleep duration was also associated with a significant change in BMI z-score (14 studies, 18 cohorts, 31 665 participants) (mean difference -0.03; -0.04 to -0.01 per h sleep; P=0.001) and in BMI (16 studies, 24 cohorts, 24 894 participants) (mean difference -0.03 kg/m2; -0.04 to -0.01 for every h of increase in sleep; P=0.001). Conclusions: Short sleep duration is a risk factor or marker of the development of obesity in infants, children and adolescents

Intervention characteristics associated with a reduction in fear of falling among community-dwelling older people: A systematic review and meta-analysis of randomized controlled trials

Data availability statement: data can be viewed at: https://osf.io/v89an/?view_only=8711c954c6b746428cec4d06ef5cfd08.A correction has been published: The Gerontologist, Volume 62, Issue 10, December 2022, Page e629, https://doi.org/10.1093/geront/gnac131Supplementary data: Supplementary data are available online at https://academic.oup.com/gerontologist/article/61/6/e269/5817811#supplementary-dataCopyright © The Author(s) 2020. Background and Objectives: Fear of falling (FoF) is associated with decreased physical functioning and an increased fall risk. Interventions generally demonstrate moderate effects and optimized interventions are needed. Intervention characteristics, such as setting or delivery method may vary. We investigated which overarching intervention characteristics are associated with a reduction in FoF in community-dwelling older people. Research Design and Methods: A systematic review and meta-analysis of randomized controlled trials (RCTs) in community-dwelling older people without specific diseases was performed. Associations between intervention characteristics and standardized mean differences (SMD) were determined by univariate meta-regression. Sensitivity analyses were performed. Results: Data on 62 RCTs were extracted, 50 intervention groups were included in the meta-analysis. Most intervention characteristics and intervention types were not associated with the intervention effect. Supervision by a tai chi instructor (SMD: −1.047, 95% confidence interval [CI]: −1.598; −0.496) and delivery in a community setting (SMD: −0.528, 95% CI: −0.894; −0.161) were—compared to interventions without these characteristics—associated with a greater reduction in FoF. Holistic exercise, such as Pilates or yoga (SMD: −0.823, 95% CI: −1.255; −0.392), was also associated with a greater reduction in FoF. Delivery at home (SMD: 0.384, 95% CI: 0.002; 0.766) or with written materials (SMD: 0.452, 95% CI: 0.088; 0.815) and tailoring were less effective in reducing FoF (SMD: 0.687, 95% CI: 0.364; 1.011). Discussion and Implications: Holistic exercise, delivery with written materials, the setting and tailoring potentially represent characteristics to take into account when designing and improving interventions for FoF in community-dwelling older people. PROSPERO international prospective register of systematic reviews, registration ID CRD42018080483.This study was funded by Maastricht University in The Netherlands. The authors received no specific further funding

Disentangling interventions to reduce fear of falling in community-dwelling older people: a systematic review and meta-analysis of intervention components

© 2021 The Author(s). Purpose: Fear of falling (FoF) is a common and debilitating problem for older people. Most multicomponent interventions show only moderate effects. Exploring the effective components may help in the optimization of treatments for FoF. Materials and methods: In a systematic review of five scientific literature databases, we identified randomized controlled trials with older community-dwelling people that included FoF as an outcome. There was no restriction on types of interventions. Two reviewers extracted information about outcomes and content of interventions. Intervention content was coded with a coding scheme of 68 intervention components. We compared all studies with a component to those without using univariate meta-regressions. Results: Sixty-six studies, reporting on 85 interventions, were included in the systematic review. In the meta-regressions (n = 49), few components were associated with intervention effects at the first available follow up after the intervention, but interventions with meditation, holistic exercises (such as Tai Chi or Pilates) or body awareness were significantly more effective than interventions without these components. Interventions with self-monitoring, balance exercises, or tailoring were less effective compared to those without these components. Conclusions: The identified components may be important for the design and optimization of treatments to reduce FoF.Implications for rehabilitation Fear of falling (FoF) is a common and debilitating issue among older people and multicomponent interventions usually show only small to moderate effects on FoF. This review and meta-analysis investigated 68 intervention components and their relation to intervention effects on FoF. Interventions with meditation, holistic exercises (such as Tai Chi), or body awareness are more effective than interventions without these components. Clinicians aiming to reduce FoF may recommend selected interventions to older people taking into account the current knowledge of intervention components.Maastricht University

OVER DE INHOUD VAN HET AMERIKAANSE BEGRIP „GENERALLY ACCEPTED ACCOUNTING PRINCIPLES”

OVER DE INHOUD VAN HET AMERIKAANSE BEGRIP "GENERALLY ACCEPTED ACCOUNTING PRINCIPLES