Frequency-sweep examination for wave mode identification in multimodal ultrasonic guided wave signal

This article has been made available through the Brunel Open Access Publishing Fund.Ultrasonic guided waves can be used to assess and monitor long elements of a structure from a single position. The greatest challenges for any guided wave system are the plethora of wave modes arising from the geometry of the structural element which propagate with a range of frequency-dependent velocities and the interpretation of these combined signals reflected by discontinuities in the structural element. In this paper, a novel signal processing technique is presented using a combination of frequency-sweep measurement, sampling rate conversion, and Fourier transform. The technique is applied to synthesized and experimental data to identify different modes in complex ultrasonic guided wave signals. It is demonstrated throughout the paper that the technique also has the capability to derive the time of flight and group velocity dispersion curve of different wave modes in field inspections. © 2014 IEEE

EAC-1A: A novel large-volume lunar regolith simulant

The European Astronaut Centre (EAC) is currently constructing the European Lunar Exploration Laboratory (LUNA), a large training and operations facility to be located adjacent to EAC at the DLR (German Aerospace Centre) campus in Cologne, Germany. With an estimated representative lunar testbed area of approximately 660 m(2), a large volume of lunar regolith simulant material is needed for this purpose. In this study, a basanitic sandy silt from a quarry located in the Siebengebirge Volcanic Field is evaluated as a large-volume source of material. The focus of this project has been to conduct a physical and chemical characterisation of the fine-grained material to be used in LUNA;the European Astronaut Centre lunar regolith simulant 1 (EAC-1A). The physical characterisation tests undertaken include sphericity, density measurements, cohesion and static angle of repose, with mineralogical investigations via petrographical analysis with optical microscope and SEM, XRF, XRD and DSC measurements. The results of the EAC-1A tests are compared to published data on existing widely used lunar regolith simulants, namely JSC-1A, JSC-2A, NU-LHT-3M, DNA and FJS-1

Investigation of ultrasonic guided waves interacting with piezoelectric transducers

"(c) 2015 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other users, including reprinting/ republishing this material for advertising or promotional purposes, creating new collective works for resale or redistribution to servers or lists, or reuse of any copyrighted components of this work in other works."Ultrasonic Guided Waves (UGW) can be used to inspect and monitor a structure from a single test location. Piezoelectric transducers are commonly dry-coupled with force to the surface of the waveguide in order to excite UGWs. These UGWs propagating within the waveguide will interact and reflect from known features, thus possible damage could be detected. In this paper the interaction of UGWs with piezoelectric transducers is reported and investigated. An Finite Element Analysis (FEA) approach has been used to conduct a parametric study in order to quantify the effect of the waveguide diameter on the guided wave response. Laboratory experiments are carried out to measure the effect of the force on the dry-coupled piezoelectric transducers and the corresponding guided wave response including reflections and mode conversions. A test rig is used to apply and measure the force on the piezoelectric transducers. For verification, a 3-Dimensional Laser Doppler Vibrometry (3D-LDV) scan is performed on the waveguide in order to quantitatively identify the modes of interest. The conclusions reached this paper, particularly with respect to the quantification of the wave mode properties, lead to useful recommendations which can contribute to field inspection scenarios

Design and Analysis of Multicast-Based Publisher/Subscriber Models over Wireless Platforms for Smart Grid Communications

As the challenges associated with delivering reliable electrical power in the world are increasing, the mixture of 'fast response time' and 'distributed data sources' may cause scalability issues with the traditional approach that mostly uses centralized communication infrastructure. Due to tremendous demand growing in the future, the centralized approach will become less efficient. Therefore, this paper presents multicast-based Publisher/Subscriber communication models based on IEC-61850 standard for the smart grids. Models are proposed with regards to digital substations indicating the use of the emerging digital communication standards offered by IEC-61850 over typical Wireless Local Area Network. Simulation models are developed using the OPNET simulator. Therefore, the dynamic performance issues of the smart grid could be studied conveniently during the planning stage in advance of field trials

Wave mode discrimination of coded ultrasonic guided waves using two-dimensional compressed pulse analysis

Ultrasonic guided waves testing is a technique successfully used in many industrial scenarios worldwide. For many complex applications, the dispersive nature and multimode behavior of the technique still poses a challenge for correct defect detection capabilities. In order to improve the performance of the guided waves a 2-D compressed pulse analysis is presented in this paper. This novel technique combines the use of pulse compression and dispersion compensation in order to improve the signal-to-noise ratio and temporal-spatial resolution of the signals. The ability of the technique to discriminate different wave modes is also highlighted. In addition, an iterative algorithm is developed to identify the wave modes of interest using adaptive peak detection to enable automatic wave mode discrimination. The employed algorithm is developed in order to pave the way for further in-situ applications. The performance of Barker-coded and chirp waveforms are studied in a multimodal scenario where longitudinal and flexural wave-packets are superposed. The technique is tested in both synthetic and experimental conditions. The enhancements in signal-to-noise ratio and temporal resolution are quantified as well as its ability to accurately calculate the propagation distance for different wave modes

Performance evaluation of smart metering infrastructure using simulation tool

Future smart grids will require existing distribution networks to support novel distribution management system functionalities. Millions of smart meters will be deployed in the UK in near future. Vast amounts of data from such meters and other intelligent electronic devices (IEDs) in distribution network substations will require high speed communications. Such data will have to be concentrated at the local level before being transmitted to the control centre through different communication media. The performance of the underlying communication media should be evaluated to assure the required level of performance guarantees from the distribution network operators (DNOs) during the data transmission. Initially, an OPNET based Power Line Communication (PLC) simulation was verified using available experimental test results. Then a simulation study consisting of smart meters, concentrators and PLC links was used to evaluate the transmission time between local concentrators and smart meters for varying data sizes. Greater number of smart meters consumed higher bandwidth. This limitation was studied by varying the number of smart meters and concentrators connected to the PLC medium. The successful transmission rate for each configuration was also evaluated to confirm how many smart meters manage to send all the data to the concentrator within a specified time limit. Several other scenarios were used to evaluate the performance of the smart metering infrastructure