Accelerated Controller Tuning for Wind Turbines Under Multiple Hazards

During their lifecycle, wind turbines can be subjected to multiple hazard loads, such as high-intensity wind, earthquake, wave, and mechanical unbalance. Excessive vibrations, due to these loads, can have detrimental effects on energy production, structural lifecycle, and the initial cost of wind turbines. Vibration control by various means, such as passive, active, and semi-active control systems provide crucial solutions to these issues. We developed a novel control theory that enables semi-active controller tuning under the complex structural behavior and inherent system nonlinearity. The proposed theory enables the evaluation of semi-active controllers’ performance of multi-degrees-of-freedom systems, without the need for time-consuming simulations. A wide range of controllers can be tested in a fraction of a second, and their parameters can be tuned to achieve system-level performance for different optimization objectives

A Semi-Active Vibration Isolator For 3D Printing On Shipboard

In the recent years, additive manufacturing (AM) (aka 3D printing)-has become a viable alternative to traditional manufacturing due to its unique advantages, such as enabling the fabrication of complex geometries at reduced weight and costs as well as allowing on-site fabrication for maintenance and repair. One specific application area of the AM is the navy vessels. During extended voyages, the navy vessels likely require the convenience of on-site fabrication of the malfunctioned parts. However, the shipboard equipment suffers from a broad range of external excitations arising not only from the waves but also from the vessel’s engines, which poses a concern for the quality of the 3D printed parts. Thus, efficient vibration isolation systems are needed for quality production. To this end, in this study, a novel semi-active vibration isolation system called Magnetorheological-based Semi-Active Vibration Isolator (MR-SAVI for short) was proposed. A comprehensive design methodology for the MR-SAVI, including both analytical and simulation modeling, was presented. A sophisticated optimization program was created to find the optimal values of the significant design parameters. The results were discussed, and future recommendations were made for the fabrication and characterization of the device

A Fail-safe, Bi-Linear Liquid Spring, Controllable Magnetorheological Fluid Damper for a Three-dimensional Earthquake Isolation System

Building codes governing building design and construction require that loss of human life is not anticipated during a large, infrequently occurring earthquake. However, earthquake-induced damage to the building load carrying components, nonstructural components, including architectural and mechanical systems, and internal equipment or contents, is still expected in code compliant buildings. Recent earthquakes have shown that economic losses are dominated by damage to nonstructural components and contents. Seismic isolation systems, which consist of layers of rubber or friction bearings separating the building from its foundation, are effective in protecting buildings from damage due to horizontal ground shakings. However, recent realistic large-scale earthquake shaking tests have shown that nonstructural components and contents in isolated buildings are susceptible to damage from vertical motions. In this study, a fail-safe, bi-linear liquid spring, controllable magnetorheological (MR) damper is designed, built and tested. The device combines the controllable MR damping in addition to the fail-safe viscous damping and liquid spring features on a single unit serving as the vertical component of the building suspension system itself. The controllable MR damping offers an advantage in the case that the earthquake intensity might be higher than that of the design conditions. The bi-linear liquid spring feature provides two different stiffnesses in compression and rebound modes. The higher stiffness in the rebound mode can prevent a possible overturning of the structure during rocking mode of vibrations.The device can be stacked together along with the traditional elastomeric bearings that are currently used to absorb the horizontal ground motions. In the occasion of an earthquake, it is not only exposed to vertical excitations, but also large residual shear excitations. It has to pass these shear forces between the ground and isolated structure. The theoretical and simulation modeling to overcome this major challenge and achieve other system requirements are presented. In addition, a comprehensive optimization program is developed in ANSYS platform to achieve all design requirements. The fabrication and experimental procedures are discussed. The test results showed that the device performed successfully under the combined axial and shear loadings. To our knowledge, this is the first device that not only can provide large damping and spring forces, but can also operate simultaneously under combined axial and shear loadings. The test results are compared against the theoretical modeling, and the results are discussed

Modelling and design of a dual channel magnetorheological damper

© Cranfield UniversityA limitation with the current analytical models for predicting the performance of a magnetorheological (MR) damper is that they fail to capture the hysteretic variation of force versus velocity variation correctly. This can significantly underestimate the damper force and overestimate the dynamic range of the device. In this work a transient analytical fluid dynamics model is developed by using a combination of Laplace and Weber transform and Duhamel’s superposition of velocity boundary condition, to overcome these limitations. The solution of the system of nonlinear simultaneous equations, obtained by applying mass flow balance, velocity compatibility conditions and force equilibrium of Bingham plastic plug flow, gives the damper force. This method is shown to generate direct and inverse model of an MR device. The proposed model has been validated against a commercially available MR damper at low speed, to a range of test signals. The mean error using the above model has been shown to be 5% for all the test signals. This compares well with three conventional models which give; transient constant velocity model 35%, quasi static model 35% and phenomenological model 35%. The phenomenological model gives 10% mean error for a sinusoidal input signal. The application of the proposed analytical model has been demonstrated by the design of a novel dual channel damper. The design of the electromechanical components has been shown to be np-hard problem and the optimisation using genetic algorithm has been applied to minimise the volume and electrical time constant. The performance of the dual channel damper has been simulated for various combinations of values of shear yield stress for two channels. Compared to the conventional single channel damper the novel design is shown to give 30% higher damper force, 50% improved dynamic range and limits the effect of transients to within 10% of the damper force. The dual channel damper is an effective solution to resist the onset of turbulent flow in the channels up to 20m/s piston velocity

Dual Purpose Tunable Vibration Isolator Energy Harvester: Design, Fabrication, Modeling and Characterization

This dissertation is focused on design, fabrication, characterization, and modeling of a unique dual purpose vibration isolation energy harvesting system. The purpose of the system is to, simultaneously, attenuate unwanted vibrations and scavenge kinetic energy available in these vibrations. This study includes theoretical modeling and experimental work to fully characterize and understand the dynamic behavior of the fabricated dual purpose system. In the theoretical study, both numerical (Runge-Kutta) and analytical (Harmonic Balance Method, HBM) methods are used to obtain the dynamic behavior of the system. The system features a combination of mechanical and electromagnetic components to facilitate its dual functionality. The system consists of a magnetic spring, mechanical flat spring, and dampers. The combination of negative stiffness of the magnetic spring with positive stiffness of the mechanical spring results in lowering the cut off frequency of the system. Lowering the cut off frequency improves the device’s ability to operate in a wider range of frequencies. Results from dynamic measurements and model simulation confirm the ability of the device to function in both vibration isolation and energy harvesting modes simultaneously. The dual-purpose device is able to attenuate vibrations higher than 12.5 [Hz]. The device also produces 26.8 [mW] output power at 1g [m/s2] and 9.75 [Hz]. Performance metrics of the device including displacement transmissibility and energy conversion efficiency are formulated. Results show that for low acceleration levels, lower damping values are desirable and yield higher energy conversion efficiencies and improved vibration isolation. At higher acceleration, there is a trade-off where lower damping values worsen vibration isolation but yield higher conversion efficiencies

Distributed real-time hybrid simulation: Modeling, development and experimental validation

Real-time hybrid simulation (RTHS) has become a recognized methodology for isolating and evaluating performance of critical structural components under potentially catastrophic events such as earthquakes. Although RTHS is efficient in its utilization of equipment and space compared to traditional testing methods such as shake table testing, laboratory resources may not always be available in one location to conduct appropriate large-scale experiments. Consequently, distributed systems, capable of connecting multiple RTHS setups located at numerous geographically distributed facilities through information exchange, become essential. This dissertation focuses on the development, evaluation and validation of a new distributed RTHS (dRTHS) platform enabling integration of physical and numerical components of RTHS in geographically distributed locations over the Internet.^ One significant challenge for conducting successful dRTHS over the Internet is sustaining real-time communication between test sites. The network is not consistent and variations in the Quality of Service (QoS) are expected. Since dRTHS is delay-sensitive by nature, a fixed transmission rate with minimum jitter and latency in the network traffic should be maintained during an experiment. A Smith predictor can compensate network delays, but requires use of a known dead time for optimal operation. The platform proposed herein is developed to mitigate the aforementioned challenge. An easily programmable environment is provided based on MATLAB/xPC. In this method, (i) a buffer is added to the simulation loop to minimize network jitter and stabilize the transmission rate, and (ii) a routine is implemented to estimate the network time delay on-the-fly for the optimal operation of the Smith predictor.^ The performance of the proposed platform is investigated through a series of numerical and experimental studies. An illustrative demonstration is conducted using a three story structure equipped with an MR damper. The structure is tested on the shake table and its global responses are compared to RTHS and dRTHS configurations where the physical MR damper and numerical structural model are tested in local and geographically distributed laboratories.^ The main contributions of this research are twofold: (1) dRTHS is validated as a feasible testing methodology, alternative to traditional and modern testing techniques such as shake table testing and RTHS, and (ii) the proposed platform serves as a viable environment for researchers to develop, evaluate and validate their own tools, investigate new methods to conduct dRTHS and advance the research in this area to the limits

NSF/ESF Workshop on Smart Structures and Advanced Sensors, Santorini Island, Greece, June 26-28, 2005: Structural Actuation and Adaptation Working Group

This document is a result of discussions that took place during the workshop. It describes current state of research and development (R&D) in the areas of structural actuation and adaptation in the context of smart structures and advanced sensors (SS&AS), and provides an outlook to guide future R&D efforts to develop technologies needed to build SS&AS. The discussions took place among the members of the Structural Actuation and Adaptation Working Group, as well as in general sessions including all four working groups. Participants included members of academia, industry, and government from the US and Europe, and representatives from China, Japan, and Korea