An analytical model of transducer array arrangement for guided wave excitation and propagation on cylindrical structures

Ultrasonic guided wave (GW) inspection is one of the non-destructive testing (NDT) techniques available for the engineering structures. Compared with other NDT techniques, guided waves can propagate a long distance with a relatively high sensitivity to defects in the structure. In order to increase the performance for pipe inspections to meet higher requirements under different conditions, the optimisation of piezoelectric transducer array design is still a need, as the technique is currently subject to a complex analysis due to wide number of guided wave modes generated. This can be done by optimising the transducer array design. In this paper, it is described an analytical mode of a set of piezoelectric transducer arrays upon torsional wave mode T(0,1) excitation in a tubular structure. The proposed analytical model for predicting signal propagation is validated by using finite element analysis in ABAQUS and three-dimensional laser vibrometer experiments for transducer array characterisations. The proposed analytical model works well and very fast for simulating transducer excitation and wave propagation along cylindrical structures. This will significantly reduce the complexity of guided wave analysis, enhancing effectively the structural health of structures and subsequently reducing the industry maintenance cost

Spatiotemporal Changes in Extreme Precipitation in China’s Pearl River Basin during 1951–2015

Precipitation is a key component of the hydrological cycle and one of the important indicators of climate change. Due to climate change, extreme precipitation events have globally and regionally increased in frequency and intensity, leading to a higher probability of natural disasters. This study, using the long-term APHRODITE dataset, employed six precipitation indices to analyze the spatiotemporal changes in extreme precipitation in the Pearl River Basin during 1951-2015. The Mann-Kendall (M-K) test was used to verify the significance of the observed trends. The results indicate that: (1) the interannual PRCPTOT showed a trend with an average positive increase of 0.019 mm/yr, which was followed by an increase in SDII, R95P, and RX1day, and a decrease in R95D and CWD; seasonal PRCPTOT also displayed an increase in summer and winter and a decrease in spring and autumn, corresponding to increases in R95P and SDII in all seasons. (2) The annual precipitation increases from the west to east of the basin, similar to the gradient distribution of SDII, R95P and RX1day, with the high R95D happening in the middle and lower reaches of the Xijiang River, but the CWD increased from the north to south of the basin. The seasonal spatial distributions of PRCPTOT, SDII, and R95P are relatively similar except in autumn, showing an increase from the west to east of the basin in spring and winter and a gradual increase from the north to south of the basin in summer, indicating that the Beijiang and Dongjiang tributary basins are more vulnerable to floods. (3) The MK test results exhibited that the Yunnan-Guizhou Plateau region in the upper reaches of the Xijiang River Basin became drier, and there was an increase in extreme precipitation in the Beijiang and Dongjiang river basins. The study results facilitate valuable flood mitigation, natural hazard control and water resources management in the Pearl River Basin

Effects of a finite size reflecting disk in sound power measurements

© 2018 Elsevier Ltd In practical sound power measurements in an anechoic room, a baffle sometimes has to be used to support the sound source under test so that the anechoic room can be used as a hemi-anechoic room by laying a reflecting plane. To understand the effects of a finite size reflecting plane on measurements quantitatively, this paper investigates the effects of a disk on sound power measurements by formulating an exact solution to the problem based on the spheroidal wave functions. Three practical measurement cases are considered and the correction terms for the cases are presented based on numerical simulations. Experiments are conducted to validate the analytical solutions and numerical results

UTSP: User-Based Two-Step Recommendation with Popularity Normalization towards Diversity and Novelty

© 2013 IEEE. Information technologies such as e-commerce and e-news bring overloaded information as well as convenience to users, cooperatives and companies. Recommender system is a significant technology in solving this information overload problem. Due to the outstanding accuracy performance in top-N recommendation tasks, two-step recommendation algorithms are suitable to generate recommendations. However, their recommendation lists are biased towards popular items. In this paper, we propose a user based two-step recommendation algorithm with popularity normalization to improve recommendation diversity and novelty, as well as two evaluation metrics to measure diverse and novel performance. Experimental results demonstrate that our proposed approach significantly improves the diversity and novelty performance while still inheriting the advantage of two-step recommendation approaches on accuracy metrics