Floating Offshore Wind Turbines Oscillations Damping.

This article deals with the modelling and control of oscillations that appear on floating offshore wind turbines (FOWT). First, these offshore wind energy systems, located in deep waters, are described and the modeling approach is presented. Secondly, the traditional structural control strategies based on tuned mass-damper (TMD) systems for oscillations reduction are complemented with a passive mechanism called inerter in order to improve the performance of the structural controller. This work is based on a previous work by the authors in which the inerter was located in parallel to an existing TMD in the nacelle of the FOWT. In this work, the inerter is located between the tower and the barge and results are compared to those obtained previously showing better performance. The results here presented are promising in terms of oscillations damping, both in amplitude and frequency, and constitute preliminary results of the ongoing current research of the authors

Modelling and control of floating offshore wind turbines

This tutorial deals with the modeling and control of floating marine wind turbines. First, these offshore wind energy systems, located on the high seas, in deep waters are described; some modeling approaches are discussed. The power control of these turbines is presented in detail, explaining the different types of control that seek to maximize the energy. The issue of unstable dynamics that can appear in the floating platform due to the wind turbine rotor control is highlighted, something that other types of offshore and onshore turbines do not share. An example shows the reduction of vibrations by applying structural control strategies; results prove that a passive device that is complemented with a mechanism called inerter eliminates the oscillations of the floatin

From local to global control

In this paper the authors study the problem of the existence of multiple local operating points in control systems. In particular, they consider a method of going from local to global control, i.e. given a number of local, linearized systems, from which global system do they come, and, can global controllers be determined in this case

Helicopter flap/lag energy exchange study

This paper presents a study on the energy exchange taking place on articulated helicopter main rotor blades. The blades are hinged, and the flap/lag modes are highly coupled. These dynamical couplings existing between the two degrees of freedom are clearly identifiable as the nonlinear terms that appear in the equations of motion are key to understand the energy exchange process. The work here conducted is carried out using VehicleSim, a multibody software specialized in modelling mechanical systems composed by rigid bodies. A spring pendulum system is also studied in order to examine its nonlinear behaviour and to establish existing analogies with the rotor blade nonlinear dynamics. The nonlinear couplings of both systems are compared to each other, and commensurability condition is analysed by means of short-time Fourier transform methods as well as the flap and lag amplitudes spectrum. Simulations are carried out, and the obtained results show clear analogies in the energy exchange process taking place in both systems. The stability of these modes is also studied using Poincare’ map method

Optimización heurística con criterios de error de control TMD en turbinas marinas flotantes

Among the current deployment of renewable energy systems, floating wind turbines are a promising resource. They take advantage of the wind at deep seas, where it reaches higher and more constant speed. However, being located in deep waters they are subject to heavy loads, caused mainly by waves and wind. To reduce the vibrations in the structure, passive control devices can be used, which come from civil engineering. But its design and tuning are not a simple task due to the diverse goals that coexist in the application of these passive control systems. In this work the use of different methods of signal analysis for the optimization of TMD devices (Tuned Mass Damper) is explored through genetic algorithms. Various error criteria have been applied for the optimization in order to obtain a greater reduction of vibrations in the various elements of the floating turbine

Introduction to the special section "Techniques of stability of fuzzy control systems"

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Dynamical analysis of a duolever suspension system

The authors investigate the dynamical behaviour of a Duolever type of suspension on a standard sports motorcycle. The paper contains the modelling aspects of it, as well as the optimization process followed in order to obtain the suspension parameters and geometry arrangements. Head angle, wheelbase and normal trail are studied as indicators of the handling properties of the suspension system. Matlab optimization toolbox was used to design a mathematical model of a duolever front suspension system which keeps its normal trail constant during the full suspension travel. By using VehicleSim software, non-linear simulations were performed on motorcycle model that includes a duolever suspension. By a quasi-static variation of the forward speed of the motorcycle, the time histories of the system's states were obtained. The corresponded root locus to the linearized model were plotted and compared to those of the original motorcycle model without duolever system. A modal analysis was performed in order to get a deeper understanding of the different modes of oscillation and how the duolever system affects them. The results show that whilst a satisfactory anti-dive effect is achieved with this suspension system, it has a destabilizing effect on pitch and wobble modes

Iterative lead compensation control of nonlinear marine vessels manoeuvring models

This paper addresses the problem of control design and implementation for a nonlinear marine vessel manoeuvring model. The authors consider a highly nonlinear vessel 4 DOF model as the basis of this work. The control algorithm here proposed consists of a combination of two methodologies: (i) an iteration technique that approximates the original nonlinear model by a sequence of linear time varying equations whose solution converge to the solution of the original nonlinear problem and (ii) a lead compensation design in which for each of the iterated linear time varying system generated, the controller is optimized at each time on the interval for better tracking performance. The control designed for the last iteration is then applied to the original nonlinear problem. Simulations and results here presented show a good performance of the approximation methodology and also an accurate tracking for certain manoeuvring cases under the control of the designed lead controller. The main characteristic of the nonlinear system's response is the reduction of the settling time and the elimination of the steady state error and overshoot

Suppression of Burst Oscillations in Racing Motorcycles

Burst oscillations occurring at high speed and under firm acceleration are suppressed with a mechanical steering compensator. Burst instabilities in the subject racing motorcycle are the result of interactions between the wobble and weave modes under high-speed cornering and firm-acceleration conditions. Under accelerating conditions the wobble-mode frequency decreases, while the weave mode frequency increases so that destabilizing interactions occur. The design analysis is based on a time-separation principle, which assumes that bursting occurs on time scales over which speed variations can be neglected. Therefore, under braking and acceleration conditions linear time-invariant models corresponding to constant-speed operation can be utilized in the design process. The inertial influences of braking and acceleration are modelled using d’Alembert-type forces that are applied at the mass centres of each of the model’s constituent bodies. The resulting steering compensator is a simple mechanical network that comprises a conventional steering damper in series with a linear spring. This network is a mechanical lag compensator

Iterated Nonlinear Control of Ship's Manoeuvring Models

This paper addresses the control design for a nonlinear vessel manoeuvring model. The authors consider a highly nonlinear vessel 4 DOF model. The proposed control algorithm consists of a combination of an iteration technique that approximates the original nonlinear model by a sequence of linear time varying (LTV) equations whose solution converge to the solution of the original nonlinear problem and, a lead compensation design in which for each of the iterated linear time varying systems, the controller is optimized at each time on the interval. The control designed for the last iteration is then applied to the original nonlinear problem. Simulations results show good performance of this approximation methodology and accurate tracking for certain manoeuvring cases under the control of the designed lead controller. The main characteristic of the nonlinear system's response are the reduction of the settling time and the elimination of the steady state error and overshoot