3,746 research outputs found
Structural damage detection using cross correlation functions of vibration response
No full textStructural damage detection methods based on vibration responses are appealing for a variety of reasons such as their potential to observe damage from sensors placed remote from an unknown damage site. Of particular interest to the authors is online damage detection in which changes in the structure can be flagged up in an automated fashion by permanently installed transducers. In a previous paper by the authors, the inner product vector (IPV) was proposed as a damage detection algorithm which uses cross correlation functions between response measurements. Implicitly assumed in the formulation is that the response quantity is that of displacement resulting from white noise excitation. In this paper, the IPV technique is first reviewed and then generalised to address velocity and acceleration response to band pass white noise excitation. It is shown that the IPV is a weighted summation of the mode shapes, and the effect of some particular measurement noise on the IPV can be adaptively eliminated in the calculation of IPV. Then, the damage detection method based on changes in the IPV is proposed. Finally, damage detection experiments of shear frame structure, honeycomb sandwich composite beam and aircraft stiffened panel are presented to illustrate the feasibility and effectiveness of the proposed method<br/
Structural health monitoring of constrained tapered beam-like structures using natural frequencies and nodal points
No full textThe integrity and safety of beam-like structures are dependent in part on their boundary conditions which can vary with time due to damage or aging. Structural health monitoring of such structures should therefore include attention to boundary conditions. Where the boundary conditions can be represented by a lumped spring then the identification of associated stiffness parameter values may be a means to quantifying the integrity of the support. This paper investigates such a method for identifying the equivalent translational and rotational stiffness of a constrained tapered beam-like structure. An analytical model of a beam of tapered width and thickness is adopted as a simplified representation of a tower-like structure. The model is used to explore in what scenarios natural frequencies and/or nodal points might be sufficiently sensitive to changes in support conditions to be measurable indicators of damage. The method is evaluated by Monte Carlo simulations for a numerical example where the severity of noise can be controlled
Voice Compression and Communications: Principles and Applications for Fixes and Wireless Channels
No full textUp-to-date, expert coverage of topics in wireless voice communications Voice communication is the most important facet of mobile radio service. Even when the predicted surge of wireless data and Internet services becomes a reality, voice will remain the most natural means of human communication. Voice Compression and Communications details issues in wireless voice communications and treats compression, channel coding, and wireless transmission as a joint subject. Part I covers background material, whereas Part II provides detailed information on both proprietary and standardized analysis-by-synthesis codecs, including the speech codecs of virtually all existing wireline-based and wireless systems. Parts III and IV discuss mainly research-based wideband, audio, as well as very low-rate schemes likely to find their way into future standards. Voice Compression and Communications describes fundamental concepts in a non-mathematical way early in the book for those with only a background knowledge of signal processing and communications. More advanced readers will find detailed discussions of theoretical principles, future concepts, and solutions to various specific wireless voice communications problems
Large deflection of a simply supported beam
No full textThe large deflection of a simply-supported beam loaded in the middle is a classic problem in mechanics which has been studied by many people who have implemented different methods to determine the solution, such as analytical exact solutions and the finite element method. The problem is investigated again here but the Galerkin method is used to obtain an approximate force-deflection characteristic of the beam. It is shown that the beam can be modelled with a Duffing-type stiffness with hardening nonlinearity. The exact solution and that from the finite element method are used to validate the results. The accuracy of the results and the suitability of the Sine function to model the deflected shape of the beam in the Galerkin method are investigated.The large deflection of a simply-supported beam due to a pure bending moment is also investigated. The exact solution is obtained and the results are used to describe the behaviour of the beam
Inspection of electrical wires for insulation faults and current surges using sliding temperature sensor based on optical Microfibre coil resonator
No full textWe present a compact and robust temperature sensor based on an optical microfiber coil resonator packaged around a Teflon tube. The probe can efficiently slide along electrical wires to map the local temperature for locating insulation faults and reporting high current surges. A temperature responsivity of 95 pm/°C up to ~80 °C was demonstrated. This sensor is potentially low cost and simple to fabricate, making it attractive for domestic and industrial applications
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