ABSTRACT
Power cables consist of insulation, padding and sheathing, which are highly susceptible to ignition. Power cables are an important factor affecting fire risk in urban utility tunnels (UUTs). In this paper, the combustion characteristics of four types of power cables (YJV, ZR-YJV, ZR-VV, and ZR-PE) in UUTs were investigated using a cone calorimeter. In this paper, laboratory experiments were conducted to investigate the combustion characteristics of power cables with two different parameters including two heat fluxes (35 kW/m2 and 75 kW/m2) and two sheath thicknesses (3 mm and 5 mm). The effects of heat release rate (HRR), effective heat combustion (EHC), optical density index (ODI) and smoke production rate (SPR) on ignition and combustion were investigated. The results showed that ZR-VV power cables have lower TTI, lower average HRR, lower EHC, higher MLR, and lower SEA than YJV and ZR-YJV power cables.With a conical calorimeter and heat flux of 35 kW/m2, the HRR of the power cables increased within 200 s, while for ODI, the total smoke output of ZR-YJV cables was minimized. Heat flux has a significant effect on HRR, SPR and EHC of ZR-PE cable. Sheath thickness has little effect on HRR, SPR and EHC of ZR-PE cables. In addition, one of the most important parameters, the ignition time, which depends on the composition and structure of the cable, was identified. Finally, the effect of external heat flux is complex and depends on the combustion characteristics of the power cable. Laboratory tests provide useful information for understanding the combustion behavior of power cables, including heat release rate, effective thermal burn, optical density index, and smoke production.
ABSTRACT
Thermal infrared imaging is less affected by lighting conditions and smoke compared to visible light imaging. However, thermal infrared images often have lower resolution and lack rich texture details, making them unsuitable for stereo matching and 3D reconstruction. To enhance the quality of infrared stereo imaging, we propose an advanced stereo matching algorithm. Firstly, the images undergo preprocessing using a non-local mean noise reduction algorithm to remove thermal noise and achieve a smoother result. Subsequently, we perform camera calibration using a custom-made chessboard calibration board and Zhang's camera calibration method to obtain accurate camera parameters. Finally, the disparity map is generated using the SGBM (semi-global block matching) algorithm based on the weighted least squares method, enabling the 3D point cloud reconstruction of the object. The experimental results demonstrate that the proposed algorithm performs well in objects with sufficient thermal contrast and relatively simple scenes. The proposed algorithm reduces the average error value by 10.9 mm and the absolute value of the average error by 1.07% when compared with the traditional SGBM algorithm, resulting in improved stereo matching accuracy for thermal infrared imaging. While ensuring accuracy, our proposed algorithm achieves the stereo reconstruction of the object with a good visual effect, thereby holding high practical value.
