Experimental investigation of an active slat for airfoil load alleviation

This article discusses the utilisation of an active slat concept to reduce turbulence induced fluctuating loads on an airfoil. The performance of the active slat is tested in the wind tunnel under different complex inflows 3 created by an active grid resulting into variations in the angle of attack. Different open loop control strategies are developed to mitigate the load fluctuations on the airfoil. The aerodynamics around the airfoil is changed by actively moving the trailing edge of the slat. It is observed that the active slat concept is able to alleviate load fluctuations on the airfoil for inflow angle fluctuations of different scales

Wind Energy and the Turbulent Nature of the Atmospheric Boundary Layer

Wind turbines operate in the atmospheric boundary layer, where they are exposed to the turbulent atmospheric flows. As the response time of wind turbine is typically in the range of seconds, they are affected by the small scale intermittent properties of the turbulent wind. Consequently, basic features which are known for small-scale homogeneous isotropic turbulence, and in particular the well-known intermittency problem, have an important impact on the wind energy conversion process. We report on basic research results concerning the small-scale intermittent properties of atmospheric flows and their impact on the wind energy conversion process. The analysis of wind data shows strongly intermittent statistics of wind fluctuations. To achieve numerical modeling a data-driven superposition model is proposed. For the experimental reproduction and adjustment of intermittent flows a so-called active grid setup is presented. Its ability is shown to generate reproducible properties of atmospheric flows on the smaller scales of the laboratory conditions of a wind tunnel. As an application example the response dynamics of different anemometer types are tested. To achieve a proper understanding of the impact of intermittent turbulent inflow properties on wind turbines we present methods of numerical and stochastic modeling, and compare the results to measurement data. As a summarizing result we find that atmospheric turbulence imposes its intermittent features on the complete wind energy conversion process. Intermittent turbulence features are not only present in atmospheric wind, but are also dominant in the loads on the turbine, i.e. rotor torque and thrust, and in the electrical power output signal. We conclude that profound knowledge of turbulent statistics and the application of suitable numerical as well as experimental methods are necessary to grasp these unique features (...)Comment: Accepted by the Journal of Turbulence on May 17, 201

The challenge of comprehensively mapping children's health in a nation-wide health survey: Design of the German KiGGS-Study

<p>Abstract</p> <p>Background</p> <p>From May 2003 to May 2006, the Robert Koch Institute conducted the German Health Interview and Examination Survey for Children and Adolescents (KiGGS). Aim of this first nationwide interview and examination survey was to collect comprehensive data on the health status of children and adolescents aged 0 to 17 years.</p> <p>Methods/Design</p> <p>Participants were enrolled in two steps: first, 167 study locations (sample points) were chosen; second, subjects were randomly selected from the official registers of local residents. The survey involved questionnaires filled in by parents and parallel questionnaires for children aged 11 years and older, physical examinations and tests, and a computer assisted personal interview performed by study physicians. A wide range of blood and urine testing was carried out at central laboratories. A total of 17 641 children and adolescents were surveyed – 8985 boys and 8656 girls. The proportion of sample neutral drop-outs was 5.3%. The response rate was 66.6%.</p> <p>Discussion</p> <p>The response rate showed little variation between age groups and sexes, but marked variation between resident aliens and Germans, between inhabitants of cities with a population of 100 000 or more and sample points with fewer inhabitants, as well as between the old West German states and the former East German states. By analysing the short non-responder questionnaires it was proven that the collected data give comprehensive and nationally representative evidence on the health status of children and adolescents aged 0 to 17 years.</p

Pressure-based lift estimation and its application to feedforward load control employing trailing-edge flaps

This experimental load control study presents results of an active trailing-edge flap feedforward controller for wind turbine applications. The controller input is derived from pressure-based lift estimation methods that rely either on a quasi-steady method, based on a three-hole probe, or on an unsteady method that is based on three selected surface pressure ports. Furthermore, a standard feedback controller, based on force balance measurements, is compared to the feedforward control. A Clark-Y airfoil is employed for the wing that is equipped with a trailing-edge flap of x/c=30% chordwise extension. Inflow disturbances are created by a two-dimensional active grid. The Reynolds number is Re=290 000, and reduced frequencies of k=0.07 up to k=0.32 are analyzed. Within the first part of the paper, the lift estimation methods are compared. The surface-pressure-based method shows generally more accurate results, whereas the three-hole probe estimate overpredicts the lift amplitudes with increasing frequencies. Nonetheless, employing the latter as input to the feedforward controller is more promising as a beneficial phase lead is introduced by this method. A successful load alleviation was achieved up to reduced frequencies of k=0.192.DFG, 218736457, Experimentelle Untersuchung von Strömungskontrollmethoden zur Lastkontrolle an Windkraftanlagen mittels einer Forschungswindkraftanlage im WindkanalDFG, 414044773, Open Access Publizieren 2021 - 2022 / Technische Universität Berli

Framework and baseline examination of the German National Cohort (NAKO)

The German National Cohort (NAKO) is a multidisciplinary, population-based prospective cohort study that aims to investigate the causes of widespread diseases, identify risk factors and improve early detection and prevention of disease. Specifically, NAKO is designed to identify novel and better characterize established risk and protection factors for the development of cardiovascular diseases, cancer, diabetes, neurodegenerative and psychiatric diseases, musculoskeletal diseases, respiratory and infectious diseases in a random sample of the general population. Between 2014 and 2019, a total of 205,415 men and women aged 19–74 years were recruited and examined in 18 study centres in Germany. The baseline assessment included a face-to-face interview, self-administered questionnaires and a wide range of biomedical examinations. Biomaterials were collected from all participants including serum, EDTA plasma, buffy coats, RNA and erythrocytes, urine, saliva, nasal swabs and stool. In 56,971 participants, an intensified examination programme was implemented. Whole-body 3T magnetic resonance imaging was performed in 30,861 participants on dedicated scanners. NAKO collects follow-up information on incident diseases through a combination of active follow-up using self-report via written questionnaires at 2–3 year intervals and passive follow-up via record linkages. All study participants are invited for re-examinations at the study centres in 4–5 year intervals. Thereby, longitudinal information on changes in risk factor profiles and in vascular, cardiac, metabolic, neurocognitive, pulmonary and sensory function is collected. NAKO is a major resource for population-based epidemiology to identify new and tailored strategies for early detection, prediction, prevention and treatment of major diseases for the next 30 years. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1007/s10654-022-00890-5

Prevalence, determinants and spectrum of attention-deficit hyperactivity disorder (ADHD) medication of children and adolescents in Germany: results of the German Health Interview and Examination Survey (KiGGS)

Objective: To investigate the prevalence, determinants and spectrum of attention-deficit hyperactivity disorder (ADHD) medication and its associations with socioeconomic status (SES), health-related behaviour and living conditions. Design: Observational cross-sectional study. Setting: Germany. Participants: Representative population-based sample of non-institutionalised youth aged between 0 and 17 years (n=17 450) and examined between 2003 and 2006. Main outcome measure: Prevalence and spectrum of ADHD medication (Anatomical Therapeutic Chemical (ATC) code N04BA) measured by standardised computer-assisted personal interview (CAPI) on drug use. Results: The overall prevalence of ADHD medication (stimulants including atomoxetine) was 0.9% (95% CI 0.7% to 1.1%). Boys used these drugs (1.5%, 1.2% to 1.8%) five times more than girls 0.3% (0.2% to 0.5%). The highest prevalence rates were for boys aged 6–10 years (2.3%, 1.7% to 3.1%S) and 11–13 (2.7%, 2.0% to 3.7%). Boys from families with no immigration background used ADHD medication almost 6 times as frequently as boys with an immigration background (1.7% vs 0.3%). Multivariate analysis (binary logistic regression) showed boys (OR 5.16, 95% CI 3.15 to 8.47), 11-year-olds to 13-year-olds (2.24, 1.28 to 3.49), children in large cities (2.18, 1.13 to 4.22), children with no immigration background (3.06, 1.34 to 6.99), and children with only a good (vs excellent) parent-rated health status (1.91, 1.18 to 3.08) being more likely to be using ADHD medication. A visit to the doctor in the last month or last quarter was associated with a higher probability for ADHD medication (3.18, 1.29 to 7.95 and 3.59, 1.45 to 8.90, respectively). Conclusions: Results show prevalence rates of ADHD medication use for the German child and adolescent population that are considerably lower than published prevalence rates from the USA, but comparable with those of western European and Scandinavian countries. Lower use rates in rural versus urban regions may point to differential healthcare access. The inverse association of ADHD medication use with immigration status suggests potentially restricted access to healthcare services for immigrants or may reflect culture-specific differences in attitudes towards symptoms of ADHD

Diseño y optimización de un generador de flujos rotacionales

In this thesis, a rotating flow generator device is developed with the aim to contribute in future wind flow research. The whole process of optimization, in which different blade configurations were tested to get a flow deviation as close as possible to the theoretical maximum value, is explained. The effect on the main flow of different shapes, lengths and numbers of blades was measured with a DANTEC X-Wire in order to get the velocity in both components of the X-Y plane. Once the optimization of the device was achieved, a characterization of the flow while increasing the rotational speed is shown to prove the efficiency of the device. Finally, some recommendations and improvements are exposed for later uses of the device.<br /