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Large-area Photogrammetry Based Testing of Wind Turbine Blades
No full textAn optically based sensing system that can measure the displacement and strain over essentially the entire area of a utility-scale blade leads to a measurement system that can significantly reduce the time and cost associated with traditional instrumentation. This paper evaluates the performance of conventional three dimensional digital image correlation (3D DIC) and three dimensional point tracking (3DPT) approaches over the surface of wind turbine blades and proposes a multi-camera measurement system using dynamic spatial data stitching. The potential advantages for the proposed approach include: (1) full-field measurement distributed over a very large area, (2) the elimination of time-consuming wiring and expensive sensors, and (3) the need for large-channel data acquisition systems. There are several challenges associated with extending the capability of a standard 3D DIC system to measure entire surface of utility scale blades to extract distributed strain, deflection, and modal parameters. This paper only tries to address some of the difficulties including: (1) assessing the accuracy of the 3D DIC system to measure full-field distributed strain and displacement over the large area, (2) understanding the geometrical constraints associated with a wind turbine testing facility (e.g. lighting, working distance, and speckle pattern size), (3) evaluating the performance of the dynamic stitching method to combine two different fields of view by extracting modal parameters from aligned point clouds, and (4) determining the feasibility of employing an output-only system identification to estimate modal parameters of a utility scale wind turbine blade from optically measured data. Within the current work, the results of an optical measurement (one stereo-vision system) performed on a large area over a 50-m utility-scale blade subjected to quasi-static and cyclic loading are presented. The blade certification and testing is typically performed using International Electro-Technical Commission standard (IEC 61400-23). For static tests, the blade is pulled in either flap-wise or edge-wise directions to measure deflection or distributed strain at a few limited locations of a large-sized blade. Additionally, the paper explores the error associated with using a multi-camera system (two stereo-vision systems) in measuring 3D displacement and extracting structural dynamic parameters on a mock set up emulating a utility-scale wind turbine blade. The results obtained in this paper reveal that the multi-camera measurement system has the potential to identify the dynamic characteristics of a very large structure
Photogrammetry and Optical Methods in Structural Dynamics - A Review
No full textIn the last few decades, there has been a surge of research in the area of non-contact measurement techniques. Photogrammetry has received considerable attention due to its ability to achieve full-field measurement and its robustness to work in testing environments and on testing articles in which using other measurement techniques may not be practical. More recently, researchers have used this technique to study transient phenomena and to perform measurements on vibrating structures. The current paper reviews the most current trends in the photogrammetry technique (point tracking, digital image correlation, and target-less approaches) and compares the applications of photogrammetry to other measurement techniques used in structural dynamics (e.g. laser Doppler vibrometry and interferometry techniques). The paper does not present the theoretical background of the optical techniques, but instead presents the general principles of each approach and highlights the novel structural dynamic measurement concepts and applications that are enhanced by utilizing optical techniques
Transport of Sessile Droplet in Porous Medium with Evaporation and Chemical Reaction
No full textThe dynamic of a sessile droplet spread of a wetting Newtonian fluid into a porous substrate in the presence of evaporation and chemical reaction is considered. The function for capillary pressure is found to be different from the classic Leverett-udell function. The evaporation and chemical reaction are fully coupled with the porous media flow with impact on the continuity, momentum, and energy equations. The multiphase and multi-component Navier-Stokes equations for sessile droplets in a porous medium going through phase change and chemical reaction are solved explicitly on a finite difference mesh and the results are validated with laboratory and open air experimental data. The Runge-Kutta fourth order method is used to integrate the governing equations in time. In the model, chemical reactions are allowed among all phases; solid, liquid, and vapor. The local properties are functions of the species or phases that are present therefore, varying in time. Pesticides and any chemical that is released into the environment can evaporate and may also enter a chemical reaction with other pre-existing chemicals or simply moisture in the environmental substrates. The technique is proven to be very accurate and robust with widespread applications in defense, environmental safety, pharmaceuticals, and medical fields
