An algorithm is presented to adapt the coefficients of an array of FIR filters, whose outputs are linearly coupled to another array of error detection points, so that the sum of all the mean square error signals is minimized. The algorithm uses the instantaneous gradient of the total error, and for a single filter and error reduces to the "filtered x LMS" algorithm. The application of this algorithm to active sound and vibration control is discussed, by which suitably driven secondary sources are used to reduce the levels of acoustic or vibrational fields by minimizing the sum of the squares of a number of error sensor signals. A practical implementation of the algorithm is presented for the active control of sound at a single frequency. The algorithm converges on a timescale comparable to the response time of the system to be controlled, and is found to be very robust. If the pure tone reference signal is synchronously sampled, it is found that the behavior of the adaptive system can be completely described by a matrix of linear, time invariant, transfer functions. This is used to explain the behavior observed in simulations of a simplified single input, single output adaptive system, which retains many of the properties of the multichannel algorithm.

A multiple error LMS algorithm and its application to the active control of sound and vibration

Oscillating-water-column wave energy converters and air turbines: A review

The wave energy is having more and more interest and support as a promising renewable resource to replace part of the energy supply, although it is still immature compared to other renewable technologies. This work presents a complete analysis of the wave energy technology, starting with the characterisation of this global resource in which the most suitable places to be exploited are showed, and the classification of the different types of wave energy converters in according to several features. It is also described in detail each of the stages that are part in the energy conversion, that is, from the capture of the energy from the waves to the extraction of a proper electrical signal to be injected to the grid. Likewise, existing offshore energy transmission alternatives and possible layouts are described.

Review of wave energy technologies and the necessary power-equipment

The sustainable development of the offshore wind and wave energy sectors requires optimising the exploitation of the resources, and it is in relation to this and the shared challenge for both industries to reduce their costs that the option of integrating offshore wind and wave energy arose during the past decade. The relevant aspects of this integration are addressed in this work: the synergies between offshore wind and wave energy, the different options for combining wave and offshore wind energy, and the technological aspects. Because of the novelty of combined wave and offshore wind systems, a comprehensive classification was lacking. This is presented in this work based on the degree of integration between the technologies, and the type of substructure. This classification forms the basis for the review of the different concepts. This review is complemented with specific sections on the state of the art of two particularly challenging aspects, namely the substructures and the wave energy conversion.

/pdf/a-review-of-combined-wave-and-offshore-wind-energy-36d9gm4j19.pdf

A review of combined wave and offshore wind energy

Electro-rheological (ER) fluids are now regarded as one of the most versatile of the materials available for building smart structures and machines. In principle, ER fluids promise an elegant means of providing continuously variable forces for the control of mechanical vibrations. In practice, the development of industrial devices has been hampered by the unavailability of suitable ER fluids. Prompted by recent advances in ER fluid development this paper provides a comprehensive survey of ER devices for vibration control. The key modes of operation are identified and progress towards a unified approach to visualizing the macroscopic behaviour is summarized before presenting a comprehensive survey which includes contributions to the identification of ER fluid dynamics and the application of feedback control. The discussion of results includes some thoughts on future trends.

https://iopscience.iop.org/article/10.1088/0964-1726/5/4/011/pdf

Applications of electro-rheological fluids in vibration control: a survey

Ocean waves are a huge, largely untapped energy resource, and the potential for extracting energy from waves is considerable. Research in this area is driven by the need to meet renewable energy targets, but is relatively immature compared to other renewable energy technologies. This review introduces the general status of wave energy and evaluates the device types that represent current wave energy converter (WEC) technology, particularly focusing on work being undertaken within the United Kingdom. The possible power take-off systems are identified, followed by a consideration of some of the control strategies to enhance the efficiency of point absorber-type WECs. There is a lack of convergence on the best method of extracting energy from the waves and, although previous innovation has generally focused on the concept and design of the primary interface, questions arise concerning how best to optimize the powertrain. This article concludes with some suggestions of future developments.

https://journals.sagepub.com/doi/pdf/10.1243/09576509JPE782

A review of wave energy converter technology

This paper presents a computationally fast and efficient least-squares method to minimize the vibration of any general rotor-bearing system by the application of external control forces. The D-optimality concept is used to optimize the force locations. The proposed method provides a wide range of statistical information, and the sensitivity of the optimum response to changes in the control forces. Magnetic bearings can be applied to implement the open-loop adaptive vibration control strategies outlined in the paper. These components can also be used to inject a multi-frequency test signal as required for identi­fication studies.

Vibration control of multi-mode rotor-bearing systems

This paper develops the authors' earlier work on vibration control of multi-mode rotor-bearing systems. It shows how a single magnetic actuator can be used to estimate system characteristics and apply the optimum control force needed to minimize synchronous vibration. In the application considered here, a rotor is supported on oil-film bearings. The algorithm determines the optimum control force without prior knowledge of the bearing or rotor characteristics or the distribution of out-of-balance forces. A rig is described and used to illustrate the application of the theoretical work.

Active vibration control of flexible rotors: an experimental and theoretical study

A method of online fault identification in rotor/magnetic bearing systems is presented using wavelet analysis. A filter bank approach is taken to identify the discrete time wavelet coefficients of the rotor displacement signals. From artifacts present in the discrete time wavelet series associated with specific faults, it is shown that it is possible to identify both the onset time and the fault type. This method is demonstrated for simulations of a flexible rotor/active magnetic bearing assembly during auxiliary bearing contact and direct synchronous forcing for a range covering flexible critical speeds. Experimental validation was performed on a flexible rotor/active magnetic bearing facility undergoing sudden rotor unbalance, resulting in rotor orbits with and without auxiliary bearing contact. Artifacts associated with both the sudden mass loss and the rotor/bearing contact are identified.

Fault identification in rotor/magnetic bearing systems using discrete time wavelet coefficients

We introduce an adaptive variable bias current control scheme to minimize the energy consumption of magnetic bearings without altering the dynamic performance. We developed analytical expressions for the optimum bias current settings for both differential and unidirectional modes of operation as a function of the orbit size and the desired bearing stiffness. The orbit size is measured in situ by a recursive Fourier coefficient calculation. The analytical results are presented in normalized variables, and hence can be applied to any size and type of magnetic bearing. Both zero and nonzero static load cases are considered. We show analytically that, under variable bias current operation, the differential mode provides better energy efficiency and stiffness capacity than the unidirectional mode. We present the energy consumption data obtained experimentally on a flexible rotor magnetic bearing rig. The data show that, with the proposed variable bias current approach, a significant energy saving can be obtained without deterioration of dynamic performance

M. N. Sahinkaya

Papers

A review of wave energy converter technology

Vibration control of multi-mode rotor-bearing systems

Active vibration control of flexible rotors: an experimental and theoretical study

Fault identification in rotor/magnetic bearing systems using discrete time wavelet coefficients

Variable Bias Current in Magnetic Bearings for Energy Optimization