In high-voltage (HV) insulation, electrical trees are an important degradation phenomenon strongly linked to partial discharge (PD) activity. Their initiation and development have attracted the attention of the research community and better understanding and characterization of the phenomenon are needed. They are very damaging and develop through the insulation material forming a discharge conduction path. Therefore, it is important to adequately measure and characterize tree growth before it can lead to complete failure of the system. In this paper, the Gaussian mixture model (GMM) has been applied to cluster and classify the different growth stages of electrical trees in epoxy resin insulation. First, tree growth experiments were conducted, and PD data captured from the initial to breakdown stage of the tree growth in epoxy resin insulation. Second, the GMM was applied to categorize the different electrical tree stages into clusters. The results show that PD dynamics vary with different stress voltages and tree growth stages. The electrical tree patterns with shorter breakdown times had identical clusters throughout the degradation stages. The breakdown time can be a key factor in determining the degradation levels of PD patterns emanating from trees in epoxy resin. This is important in order to determine the severity of electrical treeing degradation, and, therefore, to perform efficient asset management. The novelty of the work presented in this paper is that for the first time the GMM has been applied for electrical tree growth classification and the optimal values for the hyperparameters, i.e., the number of clusters and the appropriate covariance structure, have been determined for the different electrical tree clusters.
The investigations of flow-induced vibration have been around for decades to solve many engineering problems related to structural element. In a hindsight of advancing technology of microelectronics devices, the implementation of flow-induced vibration for energy harvesting is intrigued. The influence of downstream flat plate to flow-induced vibration experienced by a square cylinder is discussed in this study to surpass the limitation of wind energy due to geographical constraints and climate change. The mechanism of flow-induced vibration experienced by a square cylinder with downstream flat plate is numerically simulated based on the unsteady Reynolds Navier-Stokes (URANS) flow field. The Reynolds number, Re assigned in this study is ranging between [Formula: see text]-[Formula: see text] and the mass damping ratio designated for the square cylinder is [Formula: see text] = 2.48. The influence of three different flat plate lengths [Formula: see text], 1 and 3 is examined. Each case of different flat plate is explored for gap separation between the square cylinder and the plate in the range [Formula: see text]. Based on the numerical findings, the configuration of cylinder-flat plate with length [Formula: see text] has shown the highest potential to harvest high energy at comparatively low reduced velocity.
This study examined the mean and turbulent wind speed distribution within the canopy height of a tropical urban campus based on a representative geometry model via wind tunnel experiments. The vertical wind profiles were analysed around two high-rise buildings, Menara Razak (MR) and Residensi Tower (RT) at both wind directions (22.5° and 202.5°). To examine the influence of high-rise buildings on strong wind, the collected data of mean wind speed (u), root mean square (urms), and skewness (SK) were analysed. Effects of the wind direction, building layout or arrangement and building geometry under the canopy height were also examined. The results show that the building layout influenced the wind distribution within the target site, and the approaching wind flow direction also influenced the wind flow interaction with the building. The height of the target building (H) influenced the distance traveled by the vortices in the wake flow. For the MR and RT cases, the vortices could be affected up to a minimum distance of H and 1.5H, respectively. The study demonstrates that the building layout significantly influences the distribution of wind speeds within the canopy height of a tropical urban campus.