Hiroyuki Kajiwara

LPV techniques for control of an inverted pendulum

The authors present a comprehensive application of linear fractional transformation and polytopic control techniques to the control of an arm-driven inverted pendulum, The particular interest of this application lies in the fact that all ingredients of the design problem have to be taken into account; from the specifications up to the constraints inherent to real-world implementations. In this context, it has been shown that currently available synthesis methodologies, such as μ and LPV techniques, may fail to provide acceptable answers, A major obstacle is undoubtedly the implementation constraint that puts hard limitations on the controller dynamics, These limitations are generally difficult to handle within the usual formulation of LPV control techniques. It has been shown that a suitable extension of these techniques including LMI region constraints on the closed-loop dynamics can overcome this difficulty. When implementable, it has been observed that LPV controllers outperform fixed μ controllers both in robustness and performance. These observations were confirmed by simulations but more importantly by a number of records on the physical experiment.

Development of an ROV operated both as towed and self-propulsive vehicle

Abstract A remote-operated vehicle (ROV) developed for investigations of the sea bottom over a wide area can be operated as both a towed and a self-propulsive vehicle. Called DELTA, the shape is similar to that of a delta-wing aircraft. The vehicle has two propellers and weight shift apparatus as actuators. The paper describes the design of the control system for the vehicle. Non-linear motion equations of the towing cable and DELTA are discussed, followed by a description of the LQI control system and robust control based on H∞ control. Depth control performance was improved by the robust controller. Some successful experimental results are shown.

LPV technique for rotational speed control of wind turbines using measured wind speed

In the paper, we apply LPV (linear parameter varying) control methodology for the rotational speed control problems of wind turbines. Our goals are extracting maximum power in the region below the rated wind speed and maintaining the rated power in the region over the rated wind speed. Effectiveness of the LPV control is shown by means of numerical simulations, compared with results by conventional controls

Wide-Range Stabilization of an Arm-Driven Inverted Pendulum Using Linear Parameter-Varying Techniques*

The purpose of the paper is to demon- strate the ability of LPV (Linear Parameter Vary- ing) control techniques to handle difficult nonlin- ear control problems. The focus in this paper is on the wide range stabilization of an arm-driven in- verted pendulum. Two different LPV control tech- niques are used to design nonlinear controllers that achieve stabilization of the pendulum over the max- imum range of operating conditions while providing time- and frequency-domain performances. The mer- its of each of these techniques are investigated and the improvements over more classical LTI (Linear Time-Invariant) control schemes such as #<» or y, controllers are discussed. A particular emphasis is put on the real-time implementation of these con- trollers for the inverted pendulum experiment. It is shown that suitable multi-objective extensions of the standard characterization of LPV controllers allow to cope with sampling rate implementation constraints. Finally, a complete validation of the proposed LPV controller structures is carried out through a set of realistic nonlinear simulations but also by means of physical experiment records.

Development of a DES toolbox and its application to a robot-gait planning

The paper presents a discrete-event-system toolbox that we developed and its application to gait planning of a six-leg robot. It is shown that K/sup /spl dagger/C/ operation can generate a non-conservative gait.

A Coupled Aero-Hydrodynamic Simulator for Offshore Floating Wind Turbines

Offshore floating wind turbines (OFWTs) are expected as the future of wind energy. However, the analysis of OFWTs is much more complicated than that of fixed-bottom wind turbines. The simulators currently in use, based on the classic blade element momentum (BEM) theory, will be inadequate while used on OFWTs because of the unsteady motions induced by wind and waves. Thus, simulators with advanced approaches are of necessity for analyzing OFWTs. In this work, a coupled aero-hydrodynamic simulator in MATLAB/Simulink is developed, for simulating the response and aerodynamic performance of OFWTs under wind and waves in the time domain. For aerodynamics, the code uses an unsteady BEM model or the free vortex wake method (FVM) to calculate the aerodynamic loads and performance of the wind turbine. For hydrodynamics, a linearized classic marine hydrodynamic model, based on the frequency-dependent parameters obtained from the code of WAMIT, is employed to calculate the hydrodynamic loads of the platform by solving the hydrostatic, diffraction and radiation problems with fluid-memory effect. Furthermore, Morison’s equation and the strip theory are applied to calculate the nonlinear viscous drag for improving the quality of the model. Finally, a series of cases with different wind and wave conditions is tested on a sample model combining “NREL offshore 5-MW baseline wind turbine” with “OC3-Hywind platform”. The results show that the simulator is able to predict the response and aerodynamic performance of OFWTs under wind and waves. Moreover, the FVM is more suitable for analyzing the aerodynamic performance of OFWTs than the unsteady BEM model because of its higher fidelity and less limitations.Copyright

A study on torsional vibration reduction for variable-speed variable-pitch wind turbines

As the size of the wind turbines increases, the structural loads causing fatigue stress on mechanical components become more dominant. Torsional vibration reduction in drive-train helps to reduce the stress and avoid potential resonances with power grid system. In this study, a new approach based on disturbance observer and band-pass filter is proposed. The design of the parameters leads to solve a constrained optimization problem. The stability of the system can be guaranteed by the constraint conditions. The effectiveness of the proposed method is confirmed via simulations and experiment.

Combined FIV and VIV Effects on a Cantilevered Pipe Discharging Fluid in Deep Waters

To avoid or mitigate global warming, several ocean carbon capture and storage concepts have been proposed. One of the recent approaches is to dispose carbon dioxide via a fixed vertical cantilevered pipe onto the seabed in deep waters. Due to a high aspect ratio and flexibility of such long pipe conveying fluid with fixed-free end conditions and external hydrodynamic loading caused by currents, the pipe may experience large-amplitude 3-D vibrations leading to structural failure. Hence, it is essential to understand and investigate the pipe nonlinear dynamic behaviors subject to combined flow-induced vibration (FIV) and vortex-induced vibration (VIV). In this study, the 3-D nonlinear equations of a cantilevered pipe discharging fluid in the sea are analyzed using a Galerkin-based multi modal approach combined with a finite difference Houbolts integration scheme. Particular attention is paid to the combined effects of FIV and VIV on the dynamic response of the cantilevered pipe in water. To model the fluctuating lift and drag forces associated with VIV, the two dimensional wake oscillators distributed along the pipe are adopted. Numerical simulations in the FIV case of a pipe discharging fluid in the air are first validated with experimental results in the literature to justify the mathematical models and numerical approaches. Modal convergence analysis is also performed. Results in the combined FIV and VIV cases are then highlighted in order to show the effects of cross-flow and in-line VIV when compared with the pure FIV case. The effects of geometric nonlinearities, the coupling/interaction of multi modes and the space-time modifications of pipe responses and trajectories are highlighted. It is hoped that the numerical observations and findings obtained from this study could be verified by experimental studies which are presently lacking in the literature.

Sliding-Mode Control System Design for an Experimental Model With Resonance-Free SWATH

Given an experimental model with a resonance-free SWATH, the paper represents successful experimental results of sliding-mode control applied to the pitch control loop, which indicate its effectiveness in regular-wave disturbance rejection compared with the case of using PD control only.Copyright

VIV analysis of a cantilevered pipe discharging fluid with a nozzle in the sea

Abstract Vortex induced vibration (VIV) should be taken into account for the vibration analysis of a cantilevered marine riser. This paper is dedicated to the VIV for the nonlinear vibration analysis of a cantilevered pipe discharging fluid with a nozzle at sea. In this study, three dimensional (3-D) motion equations are derived based on modified Hamilton Principle in a rigorous way. The Morison formula is used to calculate the external fluid-induced static drag force and viscous damping forces in the in-line (IL) and cross-flow (CF) directions. A double-van der Pol oscillator model is adopted employing a set of calibrated wake coefficients in Facchinetti et al. (2004) for the VIV effect. A new hydrodynamic force model is proposed considering the coupling effect of IL and CF motions. The mathematical model together with proposed solution methods are validated after comparisons with experimental results.