Wind turbine rotor blade monitoring using digital image correlation: a comparison to aeroelastic simulations of a multi-megawatt wind turbine

Optical full-field measurement methods such as Digital Image Correlation (DIC) provide a new opportunity for measuring deformations and vibrations with high spatial and temporal resolution. However, application to full-scale wind turbines is not trivial. Elaborate preparation of the experiment is vital and sophisticated post processing of the DIC results essential. In the present study, a rotor blade of a 3.2 MW wind turbine is equipped with a random black-and-white dot pattern at four different radial positions. Two cameras are located in front of the wind turbine and the response of the rotor blade is monitored using DIC for different turbine operations. In addition, a Light Detection and Ranging (LiDAR) system is used in order to measure the wind conditions. Wind fields are created based on the LiDAR measurements and used to perform aeroelastic simulations of the wind turbine by means of advanced multibody codes. The results from the optical DIC system appear plausible when checked against common and expected results. In addition, the comparison of relative out-of-plane blade deflections shows good agreement between DIC results and aeroelastic simulations.Ministry of Science and Culture of Lower Saxon

External and Turbomachinery Flow Control Working Group

Broad Flow Control Issues: a) Understanding flow physics. b) Specific control objective(s). c) Actuation. d) Sensors. e) Integrated active flow control system. f) Development of design tools (CFD, reduced order models, controller design, understanding and utilizing instabilities and other mechanisms, e.g., streamwise vorticity)

HIV/AIDS, Food Supplementation and Livelihood Programs in Uganda: A Way Forward?

BACKGROUND: Over the last decade, health, nutrition and policy experts have become increasingly aware of the many ways in which food insecurity and HIV infection negatively impact and reinforce one another. In response, many organizations providing HIV care began supplying food aid to clients in need. Food supplementation, however, was quickly recognized as an unsustainable and incomplete intervention. Many HIV care organizations therefore developed integrated HIV and livelihood programs (IHLPs) to target the root causes of food insecurity. METHODS AND FINDINGS: We conducted a qualitative study using in-depth interviews with 21 key informants who worked at seven organizations providing HIV care, food aid, or IHLPs in Kampala, Uganda in 2007-2008 to better understand the impact of IHLPs on the well-being of people living with HIV and AIDS (PLWHAs) and the challenges in transitioning clients from food aid to IHLPs. There was strong consensus among those interviewed that IHLPs are an important intervention in addressing food insecurity and its adverse health consequences among PLWHAs. Key informants identified three main challenges in transitioning PLWHAs from food supplementation programs to IHLPs: (1) lack of resources (2) timing of the transition and (3) logistical considerations including geography and weather. Factors seen as contributing to the success of programs included: (1) close involvement of community leaders (2) close ties with local and national government (3) diversification of IHLP activities and (4) close integration with food supplementation programs, all linked through a central program of HIV care. CONCLUSION: Health, policy and development experts should continue to strengthen IHLPs for participants in need. Further research is needed to determine when and how participants should be transitioned from food supplementation to IHLPs, and to determine how to better correlate measures of food insecurity with objective clinical outcomes so as to better evaluate program results

Flaps for Wind Turbine Applications: First Results of the Experimental Investigations

PO.ID C005 • Trailing edge flaps → high potential for dynamic load reduction for wind turbines • Flaps at wings → known as significant sound source • Experimental set-up to study blade flap acoustics • Sound source localization by beamforming method • First results show: (1) Significant sources at flap side edges (2) Flap deflection affects source power Abstract Identification of flap side edge noise for different flap deflection angles

Thermo-mechanical stress in tubular solid oxide fuel cells: Part II - Operating strategy for reduced probability of fracture failure

A spatially discretised thermo-electrochemical model is developed to calculate the temperature distribution in a tubular solid oxide fuel cell (SOFC). This is used in a mechanical model to compute the distribution of thermo-mechanical stress in the ceramic membrane-electrode assembly of the cell. The resulting risk of fracture failure is determined by means of Weibull analysis. Part I of this work covers the dynamic operating properties of the SOFC and the time scale of material creep in its ceramic components. This work, Part II, deals with the risk of fracture failure related to transient operating scenarios, discusses its dependency on the operating conditions and derives a low-risk operating strategy. Contrary to the common perception, thermal gradients are found to have little impact on thermo-mechanical stress in the studied SOFC. Failure-relevant stress levels arise merely due to thermal mismatch of the ceramic layers. Regarding the operating strategy, the dynamics of changes in operating conditions are of minor importance for the resulting risk of failure, while operating strategies aiming at a constant mean cell temperature prove to be advantageous. The consideration of material creep is shown to be essential for a sound analysis of thermo-mechanical stress and risk of fracture in the investigated SOFC

Thermo-mechanical stress in tubular solid oxide fuel cells: Part I - transient operating behaviour and the relevance of material creep

A spatially discretised thermo-electrochemical model is developed to calculate the temperature distribution in a tubular solid oxide fuel cell (SOFC). Model validation is accomplished based on the operating data from a demonstration plant. Using a mechanical model of the ceramic membrane-electrode assembly, the distribution of thermo-mechanical stress is calculated from the temperature profile. The resulting risk of fracture failure, being one of the crucial life-limiting factors of SOFC, is determined by means of Weibull analysis. The methodology and results are presented in two parts: Part I covers the dynamic operating properties of the SOFC and the time scale of material creep in its ceramic components. Part II deals with the risk of fracture failure related to transient operating scenarios, discusses its dependency on the operating conditions and derives a low-risk operating strategy. The dynamic operating behaviour is found to be dominated by the large thermal inertia of the solid cell components. An analysis of the creep relaxation indicates a significant relief of mechanical stress in the electrodes within a few hours of operation. This justifies a novel assumption regarding the stress-free state in the mechanical analysis of the fuel cell, which significantly increases the plausibility of the resulting risk of fracture failure

Piezo-Electric Actuation of Rotor Blades in an Axial Compressor

An actuation method for the experimental investigation of compressor rotor blade vibrations is demonstrated. Three blades of the first compressor stage in a two-stage low-speed axial-flow compressor have been equipped with piezo-electric actuators, i.e. macro fiber composites (MFC). For measuring the actuated blade vibrations, strain gages are used. The control system which has been developed within this project allows to pre-set a vibration amplitude of the blade tip. The transmission of the actuation voltage of up to 1000V into the rotor is accomplished by a slip ring. A slip ring is also used for transmitting the strain gage signals. The tests in the rotating machine show that the forces induced by MFCs are large enough to cause sufficiently strong vibrations. The signal quality of the data transmission via slip ring is high enough to operate the control unit that allows actuating the rotor blades up to a pre-defined vibration amplitude when matching the lower eigen modes of the blades