The objective of this research is to develop an accurate and reliable procedure to measure the second order harmonic of a Lamb wave propagating in a metallic plate. There are two associated complications in measuring these nonlinear Lamb waves, namely, their inherent dispersive and multimode natures. To overcome these, this research combines a time-frequency representation with a hybrid wedge generation and laser interferometric detection system. The effectiveness of the proposed procedure is demonstrated by characterizing the inherent material nonlinearity of two different aluminum plates whose absolute nonlinearity parameters are known from longitudinal wave measurements.

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An accurate mathematical model is indispensable for simulation and control of a micro helicopter. The nonlinear model in this work is based on the rigid body motion where all external forces and moments as well as the dynamics of the different hardware elements are discussed and derived in detail. The important model parameters are estimated, measured or identified in an identification process. While most parameters are identified from test bench measurements, the remaining ones are identified on subsystems using the linear prediction error method on real flight data. The good results allow to use the systems for the attitude and altitude controller design.

Purpose -The purpose of this paper is to describe the design and prototype implementation of the "Cable Crawler", a mobile teleoperated robot for the inspection of high-voltage power lines which rides on the topmost ground cable. By not being limited to just moving from mast to mast, it implements an innovative mechanism that allows for crossing a set of mast tops as well as smaller obstacles autonomously. Design/methodology/approach -After a brief overview of the state-of-the-art for this application, the basic concept of the robot is presentedwhich basically consists of a chassis and six motorized rubber-coated rollers, two in a horizontal position to take the weight and four vertical ones. The four vertical rollers are pressed onto the wire by springs, which guarantees slip-less propulsion in difficult situations. The detailed design of the most challenging components is presented, as well as the successful tests with the prototype. Findings -The feasibility of the concept is proven with a prototype implementation and successful test results. Practical implications -With a mass of 58 kg and only six drives, it consequently follows the industry's wish to have a robust, easy to maintain and rather cheap solution. Regarding the fields examined by the robot, the project concentrated on the detection of trees growing into proximity of the wires. Future work will mainly stress in further reducing the robot's mass and in facilitating its transport to the mast by the workers. Originality/value -The presented prototype allows for moving on the topmost ground cable of high-voltage power-lines and to passively roll over mast tops and smaller obstacles. With these properties, it is able to inspect long distances of cables in an autonomous way and by using a relatively low-cost and robust robot.