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- Mialon, Bruno, et al.
(författare)
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Validation of numerical prediction of dynamic derivatives : The DLR-F12 and the Transcruiser test cases
- 2011
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Ingår i: Progress in Aerospace Sciences. - : Elsevier BV. - 0376-0421 .- 1873-1724. ; 47:8, s. 674-694
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Forskningsöversikt (refereegranskat)abstract
- The dynamic derivatives are widely used in linear aerodynamic models in order to determine the flying qualities of an aircraft: the ability to predict them reliably, quickly and sufficiently early in the design process is vital in order to avoid late and costly component redesigns. This paper describes experimental and computational research dealing with the determination of dynamic derivatives carried out within the FP6 European project SimSAC. Numerical and experimental results are compared for two aircraft configurations: a generic civil transport aircraft, wing-fuselage-tail configuration called the DLR-F12 and a generic Transonic CRuiser, which is a canard configuration. Static and dynamic wind tunnel tests have been carried out for both configurations and are briefly described within this paper. The data generated for both the DLR-F12 and TCR configurations include force and pressure coefficients obtained during small amplitude pitch, roll and yaw oscillations while the data for the TCR configuration also include large amplitude oscillations, in order to investigate the dynamic effects on nonlinear aerodynamic characteristics. In addition, dynamic derivatives have been determined for both configurations with a large panel of tools, from linear aerodynamic (Vortex Lattice Methods) to CFD. This work confirms that an increase in fidelity level enables the dynamic derivatives to be calculated more accurately. Linear aerodynamics tools are shown to give satisfactory results but are very sensitive to the geometry/mesh input data. Although all the quasi-steady CFD approaches give comparable results (robustness) for steady dynamic derivatives, they do not allow the prediction of unsteady components for the dynamic derivatives (angular derivatives with respect to time): this can be done with either a fully unsteady approach i.e. with a time-marching scheme or with frequency domain solvers, both of which provide comparable results for the DLR-F12 test case. As far as the canard configuration is concerned, strong limitations for the linear aerodynamic tools are observed. A key aspect of this work are the acceleration techniques developed for CFD methods, which allow the computational time to be dramatically reduced while providing comparable results.
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- Stackelberg, Otto, et al.
(författare)
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Lifestyle and Risk of Screening-Detected Abdominal Aortic Aneurysm in Men
- 2017
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Ingår i: Journal of the American Heart Association. - 2047-9980. ; 6:5
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Tidskriftsartikel (refereegranskat)abstract
- Background-Modifiable lifestyle-related factors associated with risk of abdominal aortic aneurysm (AAA) are rarely investigated with a prospective design. We aimed to study possible associations among such factors and comorbidities with mean abdominal aortic diameter (AAD) and with risk of AAA among men screened for the disease. Methods and Results-Self-reported lifestyle-related exposures were assessed at baseline (January 1, 1998) among 14 249 men from the population-based Cohort of Swedish Men, screened for AAA between 65 and 75 years of age (mean 13 years after baseline). Multivariable prediction of mean AAD was estimated with linear regression, and hazard ratios (HRs) of AAA (AAD >= 30 mm) with Cox proportional hazard regression. The AAA prevalence was 1.2% (n=168). Smoking, body mass index, and cardiovascular disease were associated with a larger mean AAD, whereas consumption of alcohol and diabetes mellitus were associated with a smaller mean AAD. The HR of AAA was increased among participants who were current smokers with >= 25 pack-years smoked compared with never smokers (HR 15.59, 95% CI 8.96-27.15), those with a body mass index >= 25 versus <25 ( HR 1.89, 95% CI, 1.22-2.93), and those with cardiovascular disease (HR 1.77, 95% CI, 1.13-2.77), and hypercholesterolemia (HR 1.59, 95% CI 1.08-2.34). Walking or bicycling for >40 minutes/day (versus almost never) was associated with lower AAA hazard (HR 0.59, 95% CI 0.36-0.97) compared with almost never walking or bicycling. Conclusions-This prospective study confirms that modifiable lifestyle-related factors are associated with AAD and with AAA disease.
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