Prediction of the state of roof collapse is a big challenge in tunnel engineering, while the limit analysis theory makes it possible to derive the analytical solutions of the collapse mechanisms. In this work, an exac...Prediction of the state of roof collapse is a big challenge in tunnel engineering, while the limit analysis theory makes it possible to derive the analytical solutions of the collapse mechanisms. In this work, an exact solution of collapsing shape in shallow underwater tunnel is obtained by using the variation principle and the upper bound theorem based on nonlinear failure criterion. Numerical results under the effect of river water and supporting pressure are derived and discussed. The maximum water depth above the river bottom surface is determined under a given buried depth of shallow cavities and the critical depth of roof collapse is obtained under a constant river depth. In comparison with the previous results, the present solution shows a good agreement with the practical results.展开更多
Uranium enrichment determination by non-destructive assay is an important method in authenticating the nuclear warhead or uranium component in deep nuclear reduction verifications.In this paper,the feasibility of appl...Uranium enrichment determination by non-destructive assay is an important method in authenticating the nuclear warhead or uranium component in deep nuclear reduction verifications.In this paper,the feasibility of applying the high-energy photon interrogation to determine the uranium enrichment is studied.Simplified models are presented which were simulated by particle Monte Carlo transport code.The results indicate that the relation curves of the released neutrons and the enrichment of uranium objects are almost linear.For a uranium object of a given shape,the uranium enrichment can be obtained with the relation curves,which could be got in advance by calibration experiments or simulations.展开更多
基金Foundation item： Project（2013CB036004） supported by the National Basic Research Program of China Project（51178468） supported by the National Natural Science Foundation of China Project（2013zzts235） supported by Research Foundation of Central South University, China
文摘Prediction of the state of roof collapse is a big challenge in tunnel engineering, while the limit analysis theory makes it possible to derive the analytical solutions of the collapse mechanisms. In this work, an exact solution of collapsing shape in shallow underwater tunnel is obtained by using the variation principle and the upper bound theorem based on nonlinear failure criterion. Numerical results under the effect of river water and supporting pressure are derived and discussed. The maximum water depth above the river bottom surface is determined under a given buried depth of shallow cavities and the critical depth of roof collapse is obtained under a constant river depth. In comparison with the previous results, the present solution shows a good agreement with the practical results.
文摘Uranium enrichment determination by non-destructive assay is an important method in authenticating the nuclear warhead or uranium component in deep nuclear reduction verifications.In this paper,the feasibility of applying the high-energy photon interrogation to determine the uranium enrichment is studied.Simplified models are presented which were simulated by particle Monte Carlo transport code.The results indicate that the relation curves of the released neutrons and the enrichment of uranium objects are almost linear.For a uranium object of a given shape,the uranium enrichment can be obtained with the relation curves,which could be got in advance by calibration experiments or simulations.
