Yolanda Vidal

A modified Chua chaotic oscillator and its application to secure communications

A new modification to the Chua oscillator is proposed.Bifurcation diagrams, Poincare map and the Lyapunov exponents are presented.An application to secure communications is presented.A synchronization scheme based on the modified oscillator is proposed.System simulations are performed for analysis. In this paper, a new modified Chua oscillator is introduced. The original Chua oscillator is well known for its simple implementation and mathematical modeling. A modification of the oscillator is proposed in order to facilitate the synchronization and the encryption and decryption scheme. The modification consists in changing the nonlinear term of the original oscillator to a smooth and bounded nonlinear function. A bifurcation diagram, a Poincare map and the Lyapunov exponents are presented as proofs of chaoticity of the newly modified oscillator. An application to secure communications is proposed in which two channels are used. Numerical simulations are performed in order to analyze the communication system.

Force‐derivative feedback semi‐active control of base‐isolated buildings using large‐scale MR fluid dampers

The combination of passive and active schemes has been increasingly considered in the structural control com munity as a promising way to design efficient smart hybrid base isola tion systems for seismic protection. This paper considers a hybrid system in which an active feedback control law is derived to b e applied in parallel with a passive isolation device. The ac tive control uses the restoring force supplied by the passive isolator as the main feedback signal. This paper can be divided in two mai n p rts: in the first one, the paper presents the theoretical formulat ion nd stability analysis in the active control strategy; i n the second part, a set of numerical simulations is performed when the force is supplied in a semi-active way to validate and discuss the effi ci ncy of the approach in a more realistic scenario. Moreover, the p erformance of the proposed semi-active control algorithm i s compared with passive-off, passive-on and clipped-optimal control lers. The proposed control scheme reduces the base displace ment without increasing the floor accelerations.

An Experimental Realization of a Chaos-Based Secure Communication Using Arduino Microcontrollers

Security and secrecy are some of the important concerns in the communications world. In the last years, several encryption techniques have been proposed in order to improve the secrecy of the information transmitted. Chaos-based encryption techniques are being widely studied as part of the problem because of the highly unpredictable and random-look nature of the chaotic signals. In this paper we propose a digital-based communication system that uses the logistic map which is a mathematically simple model that is chaotic under certain conditions. The input message signal is modulated using a simple Delta modulator and encrypted using a logistic map. The key signal is also encrypted using the same logistic map with different initial conditions. In the receiver side, the binary-coded message is decrypted using the encrypted key signal that is sent through one of the communication channels. The proposed scheme is experimentally tested using Arduino shields which are simple yet powerful development kits that allows for the implementation of the communication system for testing purposes.

Fault detection in base-isolation systems via a restoring force observer

This paper proposes a fault detection method for hysteretic base-isolation systems. One of the key contributions of this work is a Lyapunov-based restoring force observer that leads to the design of a robust fault detection scheme. The different fault types considered are stiffness and damping variations in the system. The proposed fault estimation method provides a direct estimate of the size and severity of the fault, which can be important in many civil engineering applications. A design procedure is described, and nonlinear simulation results are presented to demonstrate the applicability of the proposed method.

Smart Structural Control Strategies for Offshore Wind Power Generation with Floating Wind Turbines

In recent years, wind energy is the fastest growing clean and renewable energy source in the world. However, most of the wind farm development has been limited to the land space and shallow water regions. Recently, several European countries (including Spain), USA and Japan started to plan floating offshore wind farms. In June of 2009, the first floating offshore wind turbine (Hywind) of the world was installed by Statoil-Hydro and Siemens on the coast of Karmoy, near the port of Bergen, Norway. In general, floating offshore wind farms are considered to be more difficult to design and install. However, in deep waters they are less sensitive to the space availability, noise restriction, and visual pollution, among others. Moreover, the wind power generation is more effective due to that floating offshore wind farm are exposed to a much stronger and steadier wind field.

Power regulation of wind turbines using torque and pitch control

Power generation control in variable-speed variable-pitch horizontal-axis wind turbines operating at high wind speeds is considered in this work. A torque and pitch control strategies are proposed, implemented and validated using the National Renewable Energy Laboratory wind turbine simulator FAST (Fatigue, Aerodynamics, Structures, and Turbulence) code. Numerical results show that the proposed controllers are effective for power regulation. The performance of the contributed controllers is compared to some state-of-the-art methodologies showing its improvements.

UPDATED LAGRANGIAN FORMULATION FOR CORRECTED SMOOTH PARTICLE HYDRODYNAMICS

Smooth Particle Hydrodynamics (SPH) are, in general, more robust than finite elements for large distortion problems. Nevertheless, updating the reference configuration may be necessary in some problems involving extremely large distortions. If a standard updated formulation is implemented in SPH zero energy modes are activated and spoil the solution. It is important to note that the updated Lagrangian does not present tension instability but only zero energy modes. Here an stabilization technique is incorporated to the updated formulation to obtain an improved method without mechanisms.

Locking in the incompressible limit: pseudo-divergence-free element free Galerkin

Locking in finite elements has been a major concern since its early developments and has been extensively studied. However, locking in mesh-free methods is still an open topic. Until now the remedies proposed in the literature are extensions of already developed methods for finite elements. Here a new approach is explored and an improved formulation that asymptotically suppresses volumetric locking for the EFG method is proposed. The diffuse divergence converges to the exact divergence. Since the diffuse divergence-free condition can be imposed a priori, new interpolation functions are defined that asymptotically verify the incompressibility condition. Modal analysis and numerical results for classical benchmark tests in solids and fluids corroborate this issue.

Hardware in the Loop Wind Turbine Simulator for Control System Testing

This chapter illustrates how to set up an inexpensive but effective Hardware-in-the-Loop (HIL) platform for the test of wind turbine (WT) controllers. The dynamics of the WT are simulated on the open-source National Renewable Energy Laboratory WT simulator called FAST (Fatigue, Aerodynamics, Structures, and Turbulence), which emulates all required input signals of the controller and reacts to the controller commands (almost) like an onshore real turbine of 5 MW. The dynamic torque control system runs on an open hardware Arduino microcontroller board, which is connected to the virtual WT via USB. In particular, the power generation control in the full load region for variable-speed variable-pitch wind turbines is considered through torque and pitch control. The HIL proposed platform is used to characterize the behavior of the WT in normal operation as well as in fault operation. In particular, a stuck/unstuck fault is modeled and the behavior of a proposed chattering torque controller is analyzed in comparison to a baseline torque controller.

Experimental study of semiactive VSC techniques for vehicle vibration reduction

Abstract Semiactive vehicle suspension with magnetorheological dampers is a promising technology for improving the passenger comfort of a ground vehicle. In this work we consider the problem of vibration suppression in suspension systems of an experimental platform called semiactive suspension system (SAS). The system under study is equipped with a magnetorheological damper which is used as a semiactive nonlinear device. Three different variable structure controllers are proposed and experimentally tested. Experimental results show that the vibration of the suspension system is well controlled with the semiactive VSC. Furthermore, it is found that the implementation of the controllers implies a better performance than the use of a purely passive device. Despite the performance of all the controllers is comparable, the one based on the updating term yields the best results among them all.