Current Issue : April - June Volume : 2018 Issue Number : 2 Articles : 5 Articles
Computational and analytical studies of degradation of wind turbine blade materials at\nthe macro-, micro-, and nanoscale carried out by the modelling team of the Section Composites and\nMaterials Mechanics, Department ofWind Energy, DTU, are reviewed. Examples of the analysis of\nthe microstructural effects on the strength and fatigue life of composites are shown. Computational\nstudies of degradation mechanisms of wind blade composites under tensile and compressive loading\nare presented. The effect of hybrid and nanoengineered structures on the performance of the\ncomposite was studied in computational experiments as well....
To monitor wind turbine vibrations, normal behaviour models are built to predict tower\ntop accelerations and drive-train vibrations. Signal deviations from model prediction are labelled as\nanomalies and are further investigated. In this paper we assess a stochastic approach to reconstruct\nthe 1 Hz tower top acceleration signal, which was measured in a wind turbine located at the wind\nfarm Alpha Ventus in the German North Sea. We compare the resulting data reconstruction with\nthat of a model based on a neural network, which has been previously reported as a data-mining\nalgorithm suitable for reconstructing this signal. Our results present evidence that the stochastic\napproach outperforms the neural network in the high frequency domain (1 Hz). Although neural\nnetwork retrieves accurate step-forward predictions, with low mean square errors, the stochastic\napproach predictions better preserve the statistics and the frequency components of the original signal,\nretaining high accuracy levels. The implementation of our stochastic approach is available as open\nsource code and can easily be adapted for other situations involving stochastic data reconstruction.\nBased on our findings we argue that such an approach could be implemented in signal reconstruction\nfor monitoring purposes or for abnormal behaviour detection....
A wind-tunnel investigation was carried out to characterize the spatial distribution of the\nintegral time scale (Tu) within, and in the vicinity of, two model wind farms. The turbine arrays\nwere placed over a rough wall and operated under high turbulence. The two layouts consisted\nof aligned units distinguished only by the streamwise spacing (Ã?â?xT ) between the devices, set at\nfive and ten rotor diameters dT (or Sx = Ã?â?xT/dT = 5 and 10). They shared the same spanwise\nspacing between turbines of 2.5dT; this resulted in arrays of 8 Ã?â?? 3 and 5 Ã?â?? 3 horizontal-axis turbines.\nHotwire anemometry was used to characterize the instantaneous velocity at various vertical and\ntransverse locations along the central column of the wind farms. Results show that Tu was modulated\nby the wind farm layout. It was significantly reduced within the wind farms and right above them,\nwhere the internal boundary layer develops. The undisturbed levels above the wind farms were\nrecovered only at ââ?°Ë?dT/2 above the top tip. This quantity appeared to reach adjusted values starting\nthe fifth row of turbines in the Sx = 5 wind farm, and earlier in the Sx = 10 counterpart. Within the\nadjusted zone, the distribution of Tu at hub height exhibited a negligible growth in the Sx = 5 case;\nwhereas it underwent a mild growth in the Sx = 10 wind farm. In addition, the flow impinging the\ninner turbines exhibited Tu/Tu\ninc < 1, where Tu\ninc is the integral time scale of the overall incoming\nflow. Specifically, Tu ââ? â?? Ã?²Tu\ninc at z = zhub, where Ã?² < 1 within standard layouts of wind farms, in\nparticular Ã?² ââ?°Ë? 0.5 and 0.7 for Sx = 5 and 10....
A shallow-water equation (SWE) is used to simulate earthquake-induced water waves in this study. A finite-difference method is\nused to calculate the SWE. The model is verified against the models of Sato and of Demirel and Aydin with three kinds of seismic\nwaves, and the numerical results of earthquake-induced water waves calculated using the proposed model are reasonable. It is also\ndemonstrated that the proposed model is reliable. Finally, an empirical equation for the maximum water elevation of earthquakeinduced\nwater waves is developed based on the results obtained using the model, which is an improvement on former models....
This paper investigates the characteristics of surface waves propagating on a grounded\nanisotropic dielectric slab. Distinct from the existing analyses that generally assume that the fields of\nsurface wave uniformly distribute along the transverse direction of the infinitely large grounded slab,\nour method takes into account the field variations along the transverse direction of a finite-width slab.\nBy solving Maxwell�s equations in closed-form, it is revealed that no pure transverse magnetic (TM)\nor transverse electric (TE) mode exists if the fields are non-uniformly distributed along the transverse\ndirection of the grounded slab. Instead, two hybrid modes, namely quasi-TM and quasi-TE modes,\nare supported. In addition, the propagation characteristics of two hybrid modes supported by the\ngrounded anisotropic slab are analyzed in terms of the slab thickness, slab width, as well as the\nrelative permittivity tensor of the anisotropic slab. Furthermore, different methods are employed to\ncompare the analyses, as well as to validate our derivations. The proposed method is very suitable\nfor practical engineering applications....
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