Analyse und aktive Dämpfung von durch Netzeinbruch verursachten Schwingungen am Antriebsstrang einer Windenergieanlage (WEA) mit DFIG

Wind turbines with doubly fed induction generators (DFIG) are most popular in the wind branch since years. However, this kind of turbines exhibits a high sensibility to grid faults. Furthermore, oscillations will be induced and transferred to the drive train because of grid faults, which results in large loads to the mechanical components. Due to the coupling with the elastic rotor blades the oscillation frequencies will be changed and extra vibrations will be induced. This feature will be more strengthened with the application of longer and more elas-tic rotor blades. This paper studies the vibrations in the drive train of 5MW DFIG turbine through simulations. Two dominate frequencies of the torsional vibration can be extracted, which is the result of the interaction of flexible rotor b lades and the drive train. According to the frequencies and physical parameters the equivalent model of the drive train can be derived, with which the model-based active vibration damping can be developed. The active damper is designed with the LQG algorithm, which consists of a LQR controller and discrete Kalman Filter. With this concept the oscillations in the drive train, which in our case mainly induced by the grid fault, can be effectively suppressed by the generator control

Nanostrukturierung durch lokale Konzentration von Laserstrahlung mit Hilfe der Nahfeldsondentechnik Abschlussbericht

Available from TIB Hannover: F97B1721+a / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEBundesministerium fuer Bildung, Wissenschaft, Forschung und Technologie, Bonn (Germany)DEGerman

Nonlinear Propagation of Spin Waves in Microscopic Magnetic Stripes

Demidov VE, Jersch J, Rott K, Krzysteczko P, Reiss G, Demokritov SO. Nonlinear Propagation of Spin Waves in Microscopic Magnetic Stripes. PHYSICAL REVIEW LETTERS. 2009;102(17): 177207.We have studied experimentally with high spatial and temporal resolution propagation of intense spin waves in microscopic Permalloy stripes. We show that the nonlinearity of the spin system of metallic magnetic films together with microscopic-scale confinement effects lead to an anomalous nonlinear magnetic dynamics, such as a nonlinear spatial self-modulation of spin waves characterized by the repulsive nonlinearity. This phenomenon appears to be densely connected with the nonlinear damping in the system. We find that both of these effects develop synchronously on the nanosecond temporal scale

Growth hormone and connective tissue in exercise

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Mapping of localized spin-wave excitations by near-field Brillouin light scattering

Jersch J, Demidov VE, Fuchs H, et al. Mapping of localized spin-wave excitations by near-field Brillouin light scattering. APPLIED PHYSICS LETTERS. 2010;97(15): 152502.We report on the experimental study of the spatial characteristics of high-frequency spin-wave modes localized at the edges of micrometer-size in-plane magnetized permalloy ellipses. Using a near-field Brillouin light scattering technique, we have mapped the modes with the spatial resolution of few tens of nanometers. We show that the width of the localization area strongly depends on the applied magnetic field and reduces to about 85 nm for high fields. We also demonstrate that the existing theoretical models do not appropriately describe spatial characteristics of the modes. (c) 2010 American Institute of Physics. [doi:10.1063/1.3502599