On the dynamics of the Furuta pendulum

The Furuta pendulum, or rotational inverted pendulum, is a system found in many control labs. It provides a compact yet impressive platform for control demonstrations and draws the attention of the control community as a platform for the development of nonlinear control laws. Despite the popularity of the platform, there are very few papers which employ the correct dynamics and only one that derives the full system dynamics. In this paper, the full dynamics of the Furuta pendulum are derived using two methods: a Lagrangian formulation and an iterative Newton-Euler formulation. Approximations are made to the full dynamics which converge to the more commonly presented expressions. The system dynamics are then linearised using a Jacobian. To illustrate the influence the commonly neglected inertia terms have on the system dynamics, a brief example is offered.Benjamin Seth Cazzolato and Zebb Prim

Active control of structural sound radiation using a spatial control method with multiple structural sensors

This paper introduces a method to control structural sound radiation using multiple structural sensors. Tonal radiation from a vibrating arbitrary structure is considered in this paper. Based on the estimation of the vibration profile of a noise radiating structure, spatial signals that represents radiated pressure field can be generated. These spatial signals can also be spatially weighted to control radiated noise at some far-field regions more than at others. Numerical studies on a simply-supported plate were performed which demonstrate the ability of the proposed method to control sound radiation that is spatially weighted over certain regions in the far-field.Dunant Halim and Ben S. Cazzolat

A model-based method for damage detection with guided waves

Abstract not availablePouria Aryan, Andrei Kotousov, Ching-Tai Ng and Benjamin Cazzolat

A generalized approach to modal filtering for active noise control - Part II: Acoustic sensing

Copyright © 2002 IEEEFor pt. I see ibid., vol.2, no.6, p.577-89 (2002). Scaling laboratory-sized active noise control systems into industrial-sized implementations is a difficult exercise. Problems relating to sensing system design account for some of the difficulty. In the first part of this paper, an alternative approach to sensing system design was presented where acoustic radiation patterns are decomposed using fundamental acoustic quantities, rather than structural modal based quantities. In this paper, the approach is tackled in the acoustic domain instead of structural vibration. The technique has been simulated in the time and frequency domains using acoustic sensors and implemented experimentally.Simon G. Hill, Scott D. Snyder, Ben S. Cazzolato, Nobuo Tanaka and Ryoji Fukud

Linear and nonlinear hydrodynamic models for dynamics of a submerged point absorber wave energy converter

Available online 18 December 2019This study compares the response of a submerged CETO-shaped point absorber wave energy converter using linear, partially-nonlinear, pseudo-nonlinear, and fully-nonlinear methods to model hydrodynamic effects. Linear potential flow models calculate hydrodynamic parameters to represent the fluid-structure interaction; typical dynamic models apply these parameters without pose-dependence. The partially-nonlinear method evaluates excitation forces at different poses to introduce a pose-dependent excitation force; in addition to the excitation force, the pseudo-nonlinear method calculates hydrodynamic coefficients using linear potential flow methods and includes pose-dependence through interpolating pre-calculated parameters to represent the radiation force. The fully-nonlinear CFD model is a numerical wave tank validated against published data. The applicability of linear-based methods has been explored by comparing the motion, force, and power of the system under various operating conditions against the fully-nonlinear results. It was expected that for low amplitude waves results tend towards the linear results; however, for both low amplitude waves and increased submergence depth, linear methods provided poor representations of the nonlinear CFD results. Geometric nonlinearities were insufficient to capture all the nonlinear behaviour. A frequency-dependent nonlinearity was identified in the water above the buoy resonating. For such submerged point absorbers, linear methods do not adequately represent the influential nonlinear effects.Benjamin W. Schubert, William S.P. Robertson, Benjamin S. Cazzolato, Mergen H. Ghayes

Horizontal stability of a quasi-zero stiffness mechanism using inclined linear springs

Negative stiffness mechanisms have seen renewed attention in recent years for their ability to reduce the resonance frequency of a structure without impeding their load-bearing ability. Such systems are often described as having quasi-zero stiffness when the negative stiffness is tuned to reduce the overall stiffness of the system as close to zero as possible without creating an instability. The system analysed in this work consists of a vertical spring for load bearing, and two symmetric inclined springs which behave with a snap-through effect to achieve negative stiffness. While this structure has been analysed extensively in the literature, generally only the stiffness in the vertical direction has been considered in the past. Here, the horizontal stiffness is assessed as well, and it is shown that it is possible to achieve quasi-zero stiffness in both directions simultaneously if the spring stiffnesses and pre-loads are chosen appropriately. Attention is paid to the tuning required in order to set the equilibrium point at a position which is arbitrarily close to having quasi-zero stiffness while avoiding issues arising from mechanical instability.William S. P. Robertson, Ben Cazzolato, and Anthony Zande

Analytic magnetic fields and semi-analytic forces and torques due to general polyhedral permanent magnets

Date of current version December 20, 2019This article outlines an algorithm which analytically calculates the magnetic field produced by a general polyhedral permanent magnet with any number of faces and arbitrary face orientations, then uses the algorithm to semi-analytically calculate the force and torque on a second general polyhedral magnet. The algorithm is validated against both the literature and finite element simulations using cuboids and dodecahedra. It is then used to model a basic two-magnet repulsive system, where it is shown that frustum magnets can produce a larger force per unit volume than cuboidal magnets. The shape of the frustums is optimized to maximize the force between them at a given separation distance, showing a considerable increase in force when compared with cuboidal magnets with the same volume. This article shows that there is scope to improve the performance of magnetic systems by using novel magnet shapes and presents an algorithm which can be used for this optimization process.James L. G. O'Connell, William S. P. Robertson, and Benjamin S. Cazzolat

An optimal arrangement of mooring lines for the three-tether submerged point-absorbing wave energy converter

Abstract not availableN.Y. Sergiienko, B.S. Cazzolato, B. Ding, M. Arjomand