A large density difference of a basin-type insulator in gas-insulated metal-enclosed switchgear (GIS) weakens its mechanical strength, which will threaten the safe and stable operation of GIS. In this article, an ultrasonic nondestructive testing method for density uniformity of GIS basin-type insulators was proposed. First, seven standard samples with different Al ₂ O ₃ content were tested by an ultrasonic testing system, and then a mapping relationship between density and ultrasonic velocity was established. Second, the uncertainty of the testing system was obtained, and the ultrasonic velocities of 192 positions in a 126 kV three-phase basin-type insulator were measured. Finally, the density distribution of the insulator was obtained based on the mapping equation of velocity-density, and a contour plot of density was established by the cubic spline interpolation. The results show that there was a positive linear correlation between the density of standard samples and the ultrasonic velocity, and the determination coefficient was 0.992. Notably, the expanded uncertainty of ultrasonic propagation time for detecting 45 mm-thick EP/Al ₂ O ₃ composites was only 0.0112 μs. The ultrasonic propagation time of detection positions in the insulator was from 31.0634 to 31.4708 μs and the difference was greater than 0.0112 μs, which illustrated that the testing system meets the requirements for detecting the density of the insulator. According to the contour plot of density, the density distribution of the insulator was shown clearly and efficiently. The density was higher at the bottom edge of the insulator and the upper part of the insert, whereas the density was smaller at the lateral upper part of the insulator and the lower part of the insert. Specifically, the maximum density of the insulator was 2.36 g/cm ³ and the minimum density was 2.25 g/cm ³ . The feasibility of nondestructive testing density by the ultrasonic method is verified, which provides a new method for density evaluation of GIS insulators.

Thermal stress of gas-insulated metal-enclosed switchgear (GIS) basin-type insulators weaken its mechanical properties, which will threaten the safe and stable operation of GIS. In this article, the simulation and experiment of thermal stress in a 252-kV GIS basin-type insulator were carried out. An acoustic-distance difference method based on the ultrasonic critical refraction longitudinal wave (ultrasonic $L_{\mathrm {CR}}$ ) and a measuring method for propagation depth of ultrasonic $L_{\mathrm {CR}}$ were proposed respectively: the variation of propagation depth in epoxy composites was measured by ultrasonic probes of different frequencies, and a mapping function between the propagation depth and detection frequency was established. The 2-MHz variable-angle ultrasonic probes were used to test the circumferential thermal stress below the surface of the 252-kV basin-type insulator, and the thermal stress simulation of the insulator was performed. The circumferential thermal stress at different positions of the insulator was obtained and then a contour plot of the stress was established by the cubic spline interpolation. The results showed that the propagation depth of ultrasonic $L_{\mathrm {CR}}$ in the subsurface of epoxy composites decreased exponentially with the frequency, the mapping relationship of depth-frequency had a good goodness of fit, and the coefficient of determination was as high as 0.988. The circumferential thermal stress at 9 mm below the surface of the insulator was tensile stress, which decreased first and then increased along the radial direction, showing as a V-shaped distribution. The experimental values were in good agreement with the simulation values, which verified the effectiveness of the proposed methods.

The multifactor accelerated aging test is an important means to predict the lifetime of gas-insulated switchgear (GIS) O-ring seals, while the leakage rate (LR) is a potential index for failure evaluation. This article proposed a three-factor accelerated aging test platform and a leakage test system (LTS) for GIS seal rings. The aging factors are thermal, mechanical compression, and pressured SF ₆ gas. The pressure aging vessel (PAV) can be filled with various gases to simulate the operating conditions of the GIS and age multiple samples simultaneously. During the aging process, leakage tests are conducted on flange pairs without disassembling and separating the seal rings. After the test, the aging can be continued so as to study the evolution of LR with aging time. In order to analyze the properties of leakage test and validate the platform, a three-factor accelerated aging and a traditional two-factor accelerated aging (thermal and compression) were conducted on GIS O-ring seals of EPDM material. Compression set (CS) and LR were tested. The result showed that a steady inherent LR F ₀ exists for the LTS. The LR rose linearly with accumulating time, allowing simplified calculation of LR. The three-factor aged samples had significantly smaller CS than those of the two-factor aged samples, indicating that the working condition of GIS with SF ₆ atmosphere significantly slows the aging rate of GIS seal rings. The findings proved that the three-factor accelerated aging test platform and LTS effectively simulate the operating conditions of GIS seal rings and evaluate their properties.

We present a new statistic signal strength model, called Exponential-Rayleigh (ER) model, for device-free (DF) target localization and tracking issues in this paper. It is a single target measurement model for radio frequency (RF) based on received signal strength (RSS) measurement in outdoor regions. The model is a non-linear function between RSS measurements and target motion state. It consists of three parts: the largescale exponential attenuation part, the small-scale Rayleigh enhancement part and the noise. Different from the proposed models, while reserving the large-scale attenuation, we mainly present the small-scale Rayleigh enhancement model in ER model. The Rayleigh part depicts the multi-path caused by single target so as to reduce the multi-path error. In the context of localization and tracking experiment using particle filter, we validate the effectiveness of ER model.

Wooden architectural heritage, an irreplaceable repository of cultural value, is highly vulnerable to factors such as component aging, biological infestations, and various forms of damage. Most current preservation methods primarily focus on salvage and repair after damage occurs, lacking the ability to predict changes in the structural components in advance. This study addresses this gap by constructing a digital twin behavioral model through the design of a TLSA-PSO prediction network grounded in the broader digital twin framework. Using typical ancient wooden architectural heritage in China as a case study, the validity and accuracy of the behavioral prediction model are verified. Additionally, a digital twin behavioral model visualization system is developed to display the prediction results. Experimental outcomes demonstrate that the behavioral prediction model can accurately forecast the behavioral changes of architectural heritage, achieving a goodness of fit of 0.99. This makes preventive protection of architectural heritage feasible.

To obtain high‐precision measurement data using vehicle‐borne light detection and ranging (LiDAR) scanning (VLS) systems, calibration is necessary before a data acquisition mission. Thus, a novel calibration method based on a homemade target ball is proposed to estimate the system mounting parameters, which refer to the rotational and translational offsets between the LiDAR sensor and inertial measurement unit (IMU) orientation and position. Firstly, the spherical point cloud is fitted into a sphere to extract the coordinates of the centre, and each scan line on the sphere is fitted into a section of the sphere to calculate the distance ratio from the centre to the nearest two sections, and the attitude and trajectory parameters of the centre are calculated by linear interpolation. Then, the real coordinates of the centre of the sphere are calculated by measuring the coordinates of the reflector directly above the target ball with the total station. Finally, three rotation parameters and three translation parameters are calculated by two least‐squares adjustments. Comparisons of the point cloud before and after calibration and the calibrated point clouds with the point cloud obtained by the terrestrial laser scanner show that the accuracy significantly improved after calibration. The experiment indicates that the calibration method based on the homemade target ball can effectively improve the accuracy of the point cloud, which can promote VLS development and applications.