Query: active articulated tip blade

title: Articulated blade tip devices for load alleviation on wind turbines
abstract: This paper investigates the load alleviation capabilities of an articulated tip device, where the outermost portion of the blade can rotate with respect to the rest of the blade. Passive, semi passive and active solutions are developed for the tip rotation. In the passive and semi passive configurations tip pitching is mainly driven by aerodynamic loads, while for the active case the rotation is obtained with an actuator commanded by a feedback control law. Each configuration is analyzed and tested using a high fidelity aeroservoelastic simulation environment, by considering standard operative conditions as well as fault situations. The potential benefits of the proposed blade tip concepts are discussed in terms of performance and robustness.

title: Wind tunnel investigation of the effects of blade tip geometry on the interaction of torsional loads and performance for an articulated helicopter rotor
abstract: The Langley transonic dynamics tunnel was used to determine the degree of correlation between rotor performance and the dynamic twist generated by changes in blade tip geometry using an articulated rotor with four different tip geometries at advance ratios of 0.20, 0.30 and 0.35. Based on the data obtained, it is concluded that: (1) there appears to be no strong correlation between blade torsion loads and rotor performance prediction; (2) for a given rotor task at each advance ratio investigated, both the azimuthal variation of torsional moment and the mean torsional moment at 81% radius are configuration dependent; (3) reducing the nose down twist on the advancing blade appears to be more important to forward flight performance than increasing the nose down twist on the retreating blade; (4) the rotor inflow model used was important in predicting the performance of the adaptive rotor; and (5) neither rigid blade solidity effects, inflow environment, nor blade torsion loads can be used alone to accurately predict active rotor performance.

title: AEROELASTIC CONTROL OF HELICOPTER BLADE SAILING IN UNSTEADY FLOW USING SMART MATERIALS
abstract: This paper analyzes the unsteady flow response of a helicopter blade sailing control system using two different smart materials strategies involving shape memory alloy (SMA) and magnetorheological damper (MRD) The aeroelastic analysis focuses on the performance of a proposed semi active controller with respect to the reduction of blade flapping vibrations in articulated rotors during engagement shipboard operations. The designed control yields gust load alleviation by increasing the stiffness/damping of the flapping motion. The simulation results show that the proposed SMA/MR aeroelastic controller can yield tunnel strike suppression and significant reduction in upward blade tip deflections at the unsteady wind over deck conditions of interest.

title: The floating wind turbine system
abstract: Having a floating wind turbine tower structure of the system, the column structure comprises at least one structure extending from the stabilizing arm column and using the position of the rotatable mounting of the holding means to facilitate Deepwater anchored to the seabed. By providing a variable buoyancy system for a wind turbine tower itself and stabilization arm integral buoyancy chamber. Comprising means for adjusting the buoyancy pump system to assist transportation, installation, repair and removal. The wind turbine rotor is downwind of the tower structure to allow the wind turbine to follow the wind direction in the absence of active yaw drive system case. And a support tower arm structure is designed to stabilize the following manner by means of buoyancy, gravity and wind tether tension balance: the wind makes the top of the support tower is inclined to provide greater clearance between the support tower and the rotor blade tip. The larger gap convenience articulated rotor hub to reduce dynamic loads structural damage. The main components of the turbine may be assembled and transported to the coast offshore installation site.

title: Design, Fabrication and Testing of an Active Camber Rotor Blade Tip
abstract: This paper presents a morphing blade design for wind turbine application with flexibility in chord wise bending while providing sufficient stiffness to carry the aerodynamic loads. The NACA64 profile is selected for the camber morphing blade demonstrator. A corrugation concept is chosen because it is relatively easy to manufacture and provides sufficient stiffness to resist deformation due to the aerodynamic loads (through the provision of effective stringers) while providing the required flexibility for chord wise bending. A mechanical actuation mechanism is employed to achieve the desired morphing angle and increase the stiffness of the morphing airfoil section to resist aerodynamic loading. The design of a morphing blade demonstrator is presented together with the manufacturing process. Finally, an experimental study is conducted where the morphing angle is measured for increasing actuation load and compared with FE analysis showing good agreement between the experimental results and results from the finite element analysis in addition to achieving the desired morphing angle.

title: Modelling and experimental validation of active and passive eddy current sensors for blade tip timing
abstract: To monitor the vibration of blades in rotating machinery, the contactless method called Blade Tip Timing (BTT) is widely used. blade vibration and clearance are important diagnostic features for condition monitoring, including the detection of blade cracks. To perform the BTT technique, optical sensors were widely used by industry due to their high accuracy, but the main drawback of these systems is their low tolerance to the presence of contaminants. To overcome this downside, eddy current sensors are a good alternative for health monitoring applications in gas turbines due to their insensitivity to contaminants and debris. This type of sensor has been used by many researchers, predominantly on the experimental side to investigate BTT systems and there is a lack of modelling to support the measurement system design. This paper fills the gap between experiments and modelling for the particular case of a blade rotating past eddy current sensors. Hence the novelty of this paper is the simulation of the BTT application using detailed quasi static finite element models of the electro magnetic field to estimate the outputs from active and passive eddy current sensors. A test rig composed of a bladed disk with 12 blades clamped to a rotating shaft was designed and manufactured in order to validate the proposed models with experimental measurements. Finally, a parametric study is presented to show the effect of the blade tip clearance and the rotational speed on the accuracy of the BTT measurement. This leads to better understanding of the sources of error in the time of arrival of the blades passing the sensor and hence insight into the blade vibration measurement accuracy.

title: Active Control of Wind Turbines Through Varying Blade Tip Sweep
abstract: In this research work an introduction to the concept of an actively controlled horizontal axis wind turbine through varying blade tip sweep, is presented. The concept refers to variable tip swept rotor blades, that have the ability to pivot collectively aft, about an axis located at the blade tips. Quantities to be controlled are power production and blade loads. The investigation is carried out with a modified Blade Element Momentum (BEM) model that takes into account variable tip swept rotor blades and the modifications are based on results from a lifting line theory based model. The simulations refer to the 5 MW NREL reference wind turbine that incorporates a suitable controller and preliminary results show beneficial behavior in all of the investigated areas.

title: Research on active disturbance rejection control method for turbine blade tip clearance
abstract: Blade tip clearance (BTC) is one of the key factors affecting the efficiency and reliability of high performance turbomachinery such as heavy duty steam turbines, aircraft engines and other gas turbo machines. The self adjusting ability of BTC according to the operation condition changing is important to meet the requirement of performance. In this paper, the principle and method of adjusting the BTC by controlling the axial displacement of the rotor were proposed and studied. The basic principle is that the BTC of the turbomachinery with a conical tail shroud will be affected by the axial displacement of rotor and thereby can be adjusted by controlling the axial position of rotor, which can be adjusted by the controllable oil pressure acting on the thrust bearing. To reach a higher control precision, lower noise and model perturbation, an adaptive quasi sliding mode control (AQSMC) algorithm based on the disturbance observer (DOB) was designed, and numerical and experimental investigations were carried out. The numerical simulation results show that this algorithm can not only effectively suppress the disturbance, but also, compared with the general reaching law, effectively reduce the chattering and transient high gain switching effect of the closed loop controller system and avoid the instability caused by the controller. Based on the DOB AQSMC algorithm, the BTC was stabilized within 2 s with no overshoot and no misalignment in the test rig, and this algorithm achieves a better control performance than the proportion integral differential (PID) algorithm. These achievements can be used to push forward the intelligent turbomachinery development.

title: Numerical study of potential application of active suction and blowing through blade tip perforation to reduction of helicopter rotor thickness noise

title: Interactive comment on "Articulated blade tip devices for load alleviation on wind turbines" by C. L. Bottasso et al
abstract: Thank you to the Associate Editor for the reviews of our paper "Articulated blade tip devices for load alleviation on wind turbines" We have revised and expanded the manuscript with respect to the original submission to accommodate as much as possible the reviewers' suggestions. We have also taken this opportunity to make several other small improvements to the text, and additions to the bibliography.