Modelling wake effects in large wind farms in complex terrain: the problem, the methods and the issues

Computational fluid dynamic (CFD) methods are used in this paper to predict the power production from entire wind farms in complex terrain and to shed some light into the wake flow patterns. Two full three-dimensional Navier–Stokes solvers for incompressible fluid flow, employing k − ϵ and k − ω turbulence closures, are used. The wind turbines are modeled as momentum absorbers by means of their thrust coefficient through the actuator disk approach. Alternative methods for estimating the reference wind speed in the calculation of the thrust are tested. The work presented in this paper is part of the work being undertaken within the UpWind Integrated Project that aims to develop the design tools for next generation of large wind turbines. In this part of UpWind, the performance of wind farm and wake models is being examined in complex terrain environment where there are few pre-existing relevant measurements. The focus of the work being carried out is to evaluate the performance of CFD models in large wind farm applications in complex terrain and to examine the development of the wakes in a complex terrain environment

CFD modelling of wind farms in complex terrain

Modelling of entire wind farms in flat and complex terrain using a full 3D Navier–Stokes solver for incompressible flow is presented in this paper. Numerical integration of the governing equations is performed using an implicit pressure correction scheme, where the wind turbines (W/Ts) are modelled as momentum absorbers through their thrust coefficient. The k–ω turbulence model, suitably modified for atmospheric flows, is employed for closure. A correction is introduced to account for the underestimation of the near wake deficit, in which the turbulence time scale is bounded using a general “realizability” constraint for the fluctuating velocities. The second modelling issue that is discussed in this paper is related to the determination of the reference wind speed for the thrust calculation of the machines. Dealing with large wind farms and wind farms in complex terrain, determining the reference wind speed is not obvious when a W/T operates in the wake of another WT and/or in complex terrain. Two alternatives are compared: using the wind speed value at hub height one diameter upstream of the W/T and adopting an induction factor-based concept to overcome the utilization of a wind speed at a certain distance upwind of the rotor. Application is made in two wind farms, a five-machine one located in flat terrain and a 43-machine one located in complex terrain

Simulation of wind farms in flat and complex terrain using CFD

Use of computational fluid dynamic (CFD) methods to predict the power production from wind entire wind farms in flat and complex terrain is presented in this paper. Two full 3D Navier–Stokes solvers for incompressible flow are employed that incorporate the k–ε and k–ω turbulence models respectively. The wind turbines (W/Ts) are modelled as momentum absorbers by means of their thrust coefficient using the actuator disk approach. The WT thrust is estimated using the wind speed one diameter upstream of the rotor at hub height. An alternative method that employs an induction-factor based concept is also tested. This method features the advantage of not utilizing the wind speed at a specific distance from the rotor disk, which is a doubtful approximation when a W/T is located in the wake of another and/or the terrain is complex. To account for the underestimation of the near wake deficit, a correction is introduced to the turbulence model. The turbulence time scale is bounded using the general “realizability” constraint for the turbulent velocities. Application is made on two wind farms, a five-machine one located in flat terrain and another 43-machine one located in complex terrain. In the flat terrain case, the combination of the induction factor method along with the turbulence correction provides satisfactory results. In the complex terrain case, there are some significant discrepancies with the measurements, which are discussed. In this case, the induction factor method does not provide satisfactory results

Prevalence of high blood pressure and associated factors among adolescents and young people in Tanzania and Uganda.

We conducted a cross-sectional study among school/college students in Tanzania and Uganda to determine the prevalence of high blood pressure (BP) and associated factors. Participants were classified to have high BP if they had pre-hypertension or hypertension. Interviews were done using the WHO STEPS instrument. Using data from both countries (n = 1596), the overall prevalence of high BP was 40% (95% CI: 37-42). The prevalence of pre-hypertension was 29% (95% CI: 26-31) and that of hypertension was 11% (95% CI: 10-13). High BP was independently associated with obesity (aOR = 6.7, 95% CI: 2.2-20.0), male sex (aOR = 3.2, 95% CI: 2.4-4.4), and among males aged above 20 years (aOR = 5.5, 95% CI: 2.9-10.5). Consumption of fruits/vegetables was associated with decreased odds for high BP (aOR = 0.7, 95% CI: 0.50-0.98). The increasing burden of pre-hypertension across age groups could explain the early onset of hypertension and cardiovascular diseases (CVDs) among young African adults. There is a need for longitudinal studies to explore the drivers of pre-hypertension in East African adolescents

Parents' Psychological and Decision-Making Outcomes following Prenatal Diagnosis with Complex Congenital Heart Defect: An Exploratory Study

UNLABELLED: Background. Parents with a fetus diagnosed with a complex congenital heart defect (CHD) are at high risk of negative psychological outcomes. Purpose. To explore whether parents' psychological and decision-making outcomes differed based on their treatment decision and fetus/neonate survival status. Methods. We prospectively enrolled parents with a fetus diagnosed with a complex, life-threatening CHD from September 2018 to December 2020. We tested whether parents' psychological and decision-making outcomes 3 months posttreatment differed by treatment choice and survival status. Results. Our sample included 23 parents (average Age[years]: 27 ± 4, range = 21-37). Most were women (n = 18), non-Hispanic White (n = 20), and married (n = 21). Most parents chose surgery (n = 16), with 11 children surviving to the time of the survey; remaining parents (n = 7) chose comfort-directed care. Parents who chose comfort-directed care reported higher distress (x¯ = 1.51, s = 0.75 v. x¯ = 0.74, s = 0.55; Mdifference = 0.77, 95% confidence interval [CI], 0.05-1.48) and perinatal grief (x¯ = 91.86, s = 22.96 v. x¯ = 63.38, s = 20.15; Mdifference = 27.18, 95% CI, 6.20-48.16) than parents who chose surgery, regardless of survival status. Parents who chose comfort-directed care reported higher depression (x¯ = 1.64, s = 0.95 v. x¯ = 0.65, s = 0.49; Mdifference = 0.99, 95% CI, 0.10-1.88) than parents whose child survived following surgery. Parents choosing comfort-directed care reported higher regret (x¯ = 26.43, s = 8.02 v. x¯ = 5.00, s = 7.07; Mdifference = 21.43, 95% CI, 11.59-31.27) and decisional conflict (x¯ = 20.98, s = 10.00 v. x¯ = 3.44, s = 4.74; Mdifference = 17.54, 95% CI; 7.75-27.34) than parents whose child had not survived following surgery. Parents whose child survived following surgery reported lower grief (Mdifference = -19.71; 95% CI, -39.41 to -0.01) than parents whose child had not. Conclusions. The results highlight the potential for interventions and care tailored to parents' treatment decisions and outcomes to support parental coping and well-being. HIGHLIGHTS: Question: Do the psychological and decision-making outcomes of parents differ based on their treatment decision and survival outcome following prenatal diagnosis with complex CHD?Findings: In this exploratory study, parents who decided to pursue comfort-directed care after a prenatal diagnosis reported higher levels of psychological distress and grief as well as higher decisional conflict and regret than parents who decided to pursue surgery.Meaning: The findings from this exploratory study highlight potential differences in parents' psychological and decision-making outcomes following a diagnosis of complex CHD for their fetus, which appear to relate to the treatment approach and the treatment outcome and may require tailoring of psychological and decision support

Protocol for ADDITION-PRO: a longitudinal cohort study of the cardiovascular experience of individuals at high risk for diabetes recruited from Danish primary care.

BACKGROUND: Screening programmes for type 2 diabetes inevitably find more individuals at high risk for diabetes than people with undiagnosed prevalent disease. While well established guidelines for the treatment of diabetes exist, less is known about treatment or prevention strategies for individuals found at high risk following screening. In order to make better use of the opportunities for primary prevention of diabetes and its complications among this high risk group, it is important to quantify diabetes progression rates and to examine the development of early markers of cardiovascular disease and microvascular diabetic complications. We also require a better understanding of the mechanisms that underlie and drive early changes in cardiometabolic physiology. The ADDITION-PRO study was designed to address these issues among individuals at different levels of diabetes risk recruited from Danish primary care. METHODS/DESIGN: ADDITION-PRO is a population-based, longitudinal cohort study of individuals at high risk for diabetes. 16,136 eligible individuals were identified at high risk following participation in a stepwise screening programme in Danish general practice between 2001 and 2006. All individuals with impaired glucose regulation at screening, those who developed diabetes following screening, and a random sub-sample of those at lower levels of diabetes risk were invited to attend a follow-up health assessment in 2009-2011 (n=4,188), of whom 2,082 (50%) attended. The health assessment included detailed measurement of anthropometry, body composition, biochemistry, physical activity and cardiovascular risk factors including aortic stiffness and central blood pressure. All ADDITION-PRO participants are being followed for incident cardiovascular disease and death. DISCUSSION: The ADDITION-PRO study is designed to increase understanding of cardiovascular risk and its underlying mechanisms among individuals at high risk of diabetes. Key features of this study include (i) a carefully characterised cohort at different levels of diabetes risk; (ii) detailed measurement of cardiovascular and metabolic risk factors; (iii) objective measurement of physical activity behaviour; and (iv) long-term follow-up of hard clinical outcomes including mortality and cardiovascular disease. Results will inform policy recommendations concerning cardiovascular risk reduction and treatment among individuals at high risk for diabetes. The detailed phenotyping of this cohort will also allow a number of research questions concerning early changes in cardiometabolic physiology to be addressed.RIGHTS : This article is licensed under the BioMed Central licence at http://www.biomedcentral.com/about/license which is similar to the 'Creative Commons Attribution Licence'. In brief you may : copy, distribute, and display the work; make derivative works; or make commercial use of the work - under the following conditions: the original author must be given credit; for any reuse or distribution, it must be made clear to others what the license terms of this work are

Flow and wakes in large wind farms in complex terrain and offshore

Power losses due to wind turbine wakes are of the order of 10 and 20% of total power output in large wind farms. The focus of this research carried out within the EC funded UPWIND project is wind speed and turbulence modelling for large wind farms/wind turbines in complex terrain and offshore in order to optimise wind farm layouts to reduce wake losses and loads

Relationship between expectation management and client retention in online cognitive behavioural therapy

Background: Engaging clients from the outset of psychotherapy is important for therapeutic success. However, there is little research evaluating therapists’ initial attempts to engage clients in the therapeutic process. This article reports retrospective analysis of data from a trial of online cognitive behavioural therapy (CBT) for depression. Qualitative and quantitative methods were used to evaluate how therapists manage clients’ expectations at the outset of therapy and its relationship with client retention in the therapeutic intervention. Aims: To develop a system to codify expectation management in initial sessions of online CBT and evaluate its relationship with retention. Method: Initial qualitative research using conversation analysis identified three communication practices used by therapists at the start of first sessions: no expectation management, some expectation management, and comprehensive expectation management. These findings were developed into a coding scheme that enabled substantial inter-rater agreement (weighted Kappa = 0.78; 95% CI: 0.52 to 0.94) and was applied to all trial data. Results: Adjusting for a range of client variables, primary analysis of data from 147 clients found comprehensive expectation management was associated with clients remaining in therapy for 1.4 sessions longer than those who received no expectation management (95% CI: -0.2 to 3.0). This finding was supported by a sensitivity analysis including an additional 21 clients (1.6 sessions, 95% CI: 0.2 to 3.1). Conclusions: Using a combination of qualitative and quantitative methods, this study suggests a relationship between expectation management and client retention in online CBT for depression, which has implications for professional practice. A larger prospective study would enable a more precise estimate of retention