The present research is focused on the numerical crack coalescence analysis of the micro-cracks and cracks produced during the cutting action of TBM disc cutters. The linear elastic fracture mechanics(LEFM) concepts a...The present research is focused on the numerical crack coalescence analysis of the micro-cracks and cracks produced during the cutting action of TBM disc cutters. The linear elastic fracture mechanics(LEFM) concepts and the maximum tangential stress criterion are used to investigate the micro crack propagation and its direction underneath the excavating discs. A higher order displacement discontinuity method with quadratic displacement discontinuity elements is used to estimate the stress intensity factors near the crack tips. Rock cutting mechanisms under single and double type discs are simulated by the proposed numerical method.The main purposes of the present modeling are to simulate the chip formation process of indented rocks by single and double discs.The effects of specific disc parameters(except speed) on the thrust force Ft, the rolling force Fr, and the specific energy ES are investigated. It has been shown that the specific energy(energy required to cut through a unit volume of rock) of the double disc is less than that of the single disc. Crack propagation in rocks under disc cutters is numerically modeled and the optimum ratio of disc spacing S to penetration depth Pd(i.e. S/Pd ratio) of about 10 is obtained, which is in good agreement with the theoretical and experimental results cited in the literature.展开更多
The vertical thermohaline structure in the western equatorial Pacific is examined with a Gravest Empirical Mode(GEM)diagnosis of in-situ mooring measurements. The poor GEM performance in estimating deep thermohaline v...The vertical thermohaline structure in the western equatorial Pacific is examined with a Gravest Empirical Mode(GEM)diagnosis of in-situ mooring measurements. The poor GEM performance in estimating deep thermohaline variability from satellite altimetry confirms a lack of vertical coherence in the equatorial ocean. Mooring observation reveals layered equatorial water with phase difference up to 6 months between thermocline and sub-thermocline variations. The disjointed layers reflect weak geostrophy and resemble pancake structures in non-rotating stratified turbulence. A coherency theorem is then proved, stating that traditional stationary GEM represents in-phase coherent structure and can not describe vertically out-of-phase variability. The fact that stationary GEM holds both spatial and temporal coherence makes it a unique tool to diagnose vertical coherent structure in geophysical flows. The study also develops a non-stationary GEM projection that captures more than 40% of the thermohaline variance in the equatorial deep water.展开更多
文摘The present research is focused on the numerical crack coalescence analysis of the micro-cracks and cracks produced during the cutting action of TBM disc cutters. The linear elastic fracture mechanics(LEFM) concepts and the maximum tangential stress criterion are used to investigate the micro crack propagation and its direction underneath the excavating discs. A higher order displacement discontinuity method with quadratic displacement discontinuity elements is used to estimate the stress intensity factors near the crack tips. Rock cutting mechanisms under single and double type discs are simulated by the proposed numerical method.The main purposes of the present modeling are to simulate the chip formation process of indented rocks by single and double discs.The effects of specific disc parameters(except speed) on the thrust force Ft, the rolling force Fr, and the specific energy ES are investigated. It has been shown that the specific energy(energy required to cut through a unit volume of rock) of the double disc is less than that of the single disc. Crack propagation in rocks under disc cutters is numerically modeled and the optimum ratio of disc spacing S to penetration depth Pd(i.e. S/Pd ratio) of about 10 is obtained, which is in good agreement with the theoretical and experimental results cited in the literature.
基金supported by the National Basic Research Program of China (Grant No.2012CB417400)the National Natural Science Foundation of China (Grant Nos. 41576017 & U1406401)
文摘The vertical thermohaline structure in the western equatorial Pacific is examined with a Gravest Empirical Mode(GEM)diagnosis of in-situ mooring measurements. The poor GEM performance in estimating deep thermohaline variability from satellite altimetry confirms a lack of vertical coherence in the equatorial ocean. Mooring observation reveals layered equatorial water with phase difference up to 6 months between thermocline and sub-thermocline variations. The disjointed layers reflect weak geostrophy and resemble pancake structures in non-rotating stratified turbulence. A coherency theorem is then proved, stating that traditional stationary GEM represents in-phase coherent structure and can not describe vertically out-of-phase variability. The fact that stationary GEM holds both spatial and temporal coherence makes it a unique tool to diagnose vertical coherent structure in geophysical flows. The study also develops a non-stationary GEM projection that captures more than 40% of the thermohaline variance in the equatorial deep water.
