Shield-Roof Interaction in Longwall Panels: Insights from Field Data and Their Application to Ground Control

The shield-roof interaction as mining proceeds in longwall panels remains unclear, hindering the further increase of longwall productivity. To uncover the mechanisms of shield-roof interaction, using our self-developed Status of Shield and Roof IntelliSense (SSRI) system, we investigated the effects of idle time, retreating rate, setting pressure, yielding, and shearer’s cutting, as well as neighboring shields’ advance on the spatial-temporal evolution of leg pressure and leg closure of shields. Our results show that the shield-roof interaction is not only dependent on the shield capacity, but also collectively determined by the time-related factors, the geological condition, the setting pressure, yielding characteristics, and mining method. Understanding the shield-roof interaction in longwall panels enables us to apply the SSRI system for ground control in longwall coal mines. Early warning of severe roof weighting can be achieved by establishing a warning model based on the decision tree algorithm. Apart from this, we can also assess the working condition of yield valve and diagnose fluid leakage of shield cylinder using the SSRI system. Finally, we propose the research prospects on shield-roof interaction in longwall panels to achieve a more reasonable determination of shield capacity, prediction of roof fall and coal wall spalling, and self-adaptive control of the shield.

Experimental and Numerical Analysis of Hybrid 3kW Ocean Wave-Power Generation System Subjected to Regular and Irregular Wave Forces

In particular of coastal area, needs of ocean energy development have emerged with global demands on non-pollution energy. Although there are several types of wave-power generation systems, such as an attenuator and an overtopping device, these have problems related to frequent damages or limited applicable area. This study is concerned with development of a new hybrid wave-power system, which is expected to provide higher power efficiency than the previous system, and experimental and numerical estimations on performance of the new system. The proposed wave power absorber is composed of a generator embedded in the floating shield cylinder, pendulum plate to accelerate rotation of generator, self-dynamic positioning devices, and a support column to fix the entire power generation system to the seabed. To determine major design parameters and to conduct a specific concept design of the proposed power generation system, hydrodynamic tests of the floating shield cylinder were carried out. The cylinder was scaled with a scale factor 0.12. Several test specimens were fabricated to examine effects of the following physical characteristics on the system performance: draft depth of the cylinder, diameter of the cylinder, longitudinal projective area of the cylinder, a number of blades attached on the cylinder, blade length. Each specimen was subjected to 8 regular and 4 irregular wave loads for 5 minutes; an extreme water wave condition was also included. In the hydrodynamic tests, rotation numbers of the cylinder per a minute were measured. Although consistent patterns of the angular velocity of the cylinder was not observed from the experimental results, the results showed that the ratio of draft depth to diameter mainly effects on the angular velocity of the cylinder, and that the cylinder quickly rotates at the crest of an incident wave while it inversely and slowly rotates at the through. Furthermore, to supplement the above tests and to analyze mechanical behaviors of the support system, numerical simulations of the system were also conducted. To calculate water pressure on the cylinder and the support column, the commercial computational program ANSYS AQWA was used. The distribution and the magnitude of the predicted water pressure were then mapped into the finite element model of the cylinder and the support structure to examine the structural responses and stability against overturning.