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A new k- ϵ model is introduced that is consistent with Monin-Obukhov similarity theory (MOST). The proposed k- ϵ model is compared with another k- ϵ model that was developed in an attempt to maintain inlet profiles compatible with MOST. It is shown that the previous k- ϵ model is not consistent with MOST for unstable conditions, while the proposed k- ϵ model can maintain MOST inlet profiles over distances of 50km. Copyright © 2016 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

In this paper, the impact of atmospheric stability on a wind turbine wake is studied experimentally and numerically. The experimental approach is based on full-scale (nacelle based) pulsed lidar measurements of the wake flow field of a stall-regulated 500 kW turbine at the DTU Wind Energy, Risø campus test site. Wake measurements are averaged within a mean wind speed bin of 1 m s−1 and classified according to atmospheric stability using three different metrics: the Obukhov length, the Bulk-Richardson number and the Froude number. Three test cases are subsequently defined covering various atmospheric conditions. Simulations are carried out using large eddy simulation and actuator disk rotor modeling. The turbulence properties of the incoming wind are adapted to the thermal stratification using a newly developed spectral tensor model that includes buoyancy effects. Discrepancies are discussed, as basis for future model development and improvement. Finally, the impact of atmospheric stability on large-scale and small-scale wake flow characteristics is presently investigated. Copyright © 2015 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

The newly developed k- ε- f P eddy viscosity model is applied to double wind turbine wake configurations in a neutral atmospheric boundary layer, using a Reynolds-Averaged Navier-Stokes solver. The wind turbines are represented by actuator disks. A proposed variable actuator disk force method is employed to estimate the power production of the interacting wind turbines, and the results are compared with two existing methods: a method based on tabulated airfoil data and a method based on the axial induction from 1D momentum theory. The proposed method calculates the correct power, while the other two methods overpredict it. The results of the k- ε- f P eddy viscosity model are also compared with the original k- ε eddy viscosity model and large-eddy simulations. Compared to the large-eddy simulations-predicted velocity and power deficits, the k- ε- f P is superior to the original k- ε model. Copyright © 2014 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

The recently developed k- ϵ- f P eddy-viscosity model is applied to one on-shore and two off-shore wind farms. The results are compared with power measurements and results of the standard k- ϵ eddy-viscosity model. In addition, the wind direction uncertainty of the measurements is used to correct the model results with a Gaussian filter. The standard k- ϵ eddy-viscosity model underpredicts the power deficit of the first downstream wind turbines, whereas the k- ϵ- f P eddy-viscosity model shows a good agreement with the measurements. However, the difference in the power deficit predicted by the turbulence models becomes smaller for wind turbines that are located further downstream. Moreover, the difference between the capability of the turbulence models to estimate the wind farm efficiency reduces with increasing wind farm size and wind turbine spacing. Copyright © 2014 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

An improved k- ϵ turbulence model is developed and applied to a single wind turbine wake in a neutral atmospheric boundary layer using a Reynolds averaged Navier-Stokes solver. The proposed model includes a flow-dependent C μ that is sensitive to high velocity gradients, e.g., at the edge of a wind turbine wake. The modified k- ϵ model is compared with the original k- ϵ eddy viscosity model, Large-Eddy Simulations and field measurements using eight test cases. The comparison shows that the velocity wake deficits, predicted by the proposed model are much closer to the ones calculated by the Large-Eddy Simulation and those observed in the measurements, than predicted by the original k- ϵ model. Copyright © 2014 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Objective: Police officers experience many traumatic events over the course of their career, often resulting in posttraumatic stress disorder (PTSD) and associated psychological distress. Studies have investigated the efficacy of interventions aimed at reducing symptoms of PTSD experienced by police officers, but lacking are studies investigating the impact of PTSD on positivity, a construct we define as a latent variable estimated using self-report measures of optimism, gratitude, self-compassion, and mindfulness. The present study carried out a path analysis of a model testing the hypothesis that PTSD would be associated with increased psychological distress and decreased positivity, both of which influence well-being. The model also evaluated associations between constructs that could be modified through interventions to increase well-being-associations between posttraumatic growth, social support, physical activity and psychological distress, positivity, and well-being., Method: Police officers ( n = 506) completed an online survey that included self-report measures of the constructs included in the model being tested., Results: The model tested produced fit indices of root mean square error of approximation (RMSEA) = .089; comparative fit index (CFI) = .960; Tucker-Lewis index (TLI) = .93; standardized root mean square residual (SRMR) = .041 and R ² = .79. Results found that neither PTSD or psychological distress had a direct effect on well-being. Psychological distress indirectly influenced well-being by lowering levels of positivity, while positivity was associated with higher scores on the measure of well-being., Conclusions: The implication of the results is that interventions aimed at enhancing positivity could be expected to improve well-being in police officers and offering traditional therapies together with positivity enhancing therapies may have additional benefits over either alone. (PsycInfo Database Record (c) 2023 APA, all rights reserved).