It is one of the most effective ways to use laboratory long air gap discharges for investigating the fundamental process involved in the lightning strike.During the 1960s and the 1970s,the electro-geometrical method(E...It is one of the most effective ways to use laboratory long air gap discharges for investigating the fundamental process involved in the lightning strike.During the 1960s and the 1970s,the electro-geometrical method(EGM)and the rolling sphere method were developed base on the breakdowncharacteristics of negative long spark discharges,which have been widely used to design the lightning shielding system of transmission lines and structures.In recent years,the scale of the power facilities is increased dramatically with the rising of power grid's voltage level.The impact of upward connecting leader launched from those large-scale facilities on the lightning shielding performance cannot be neglected;otherwise,the validity of the EGM in the lightning shielding design of EHV and UHV transmission lines will be challenged.The research evolutions on the lightning striking distance,the lightning simulation experiments and the positive upward connecting leader process by using laboratory long sparks are reviewed and discussed in this paper.展开更多
Based on mineral component and in-situ vane shear strength of deep-sea sediment, four kinds of simulative soils were prepared by mixing different bentonites with water in order to find the best simulative soil for the...Based on mineral component and in-situ vane shear strength of deep-sea sediment, four kinds of simulative soils were prepared by mixing different bentonites with water in order to find the best simulative soil for the deep-sea sediment collected from the Pacific C-C area. Shear creep characteristics of the simulative soil were studied by shear creep test and shear creep parameters were determined by Burgers creep model. Research results show that the shear creep curves of the simulative soil can be divided into transient creep, unstable creep and stable creep, where the unstable creep stage is very short due to its high water content. The shear creep parameters increase with compressive stress and change slightly or fluctuate to approach a constant value with shear stress, and thus average creep parameters under the same compressive stress are used as the creep parameters of the simulative soil. Traction of the deep-sea mining machine walking at a constant velocity can be calculated by the shear creep constitutive equation of the deep-sea simulative soil, which provides a theoretical basis for safe operation and optimal design of the deep-sea mining machine.展开更多
文摘It is one of the most effective ways to use laboratory long air gap discharges for investigating the fundamental process involved in the lightning strike.During the 1960s and the 1970s,the electro-geometrical method(EGM)and the rolling sphere method were developed base on the breakdowncharacteristics of negative long spark discharges,which have been widely used to design the lightning shielding system of transmission lines and structures.In recent years,the scale of the power facilities is increased dramatically with the rising of power grid's voltage level.The impact of upward connecting leader launched from those large-scale facilities on the lightning shielding performance cannot be neglected;otherwise,the validity of the EGM in the lightning shielding design of EHV and UHV transmission lines will be challenged.The research evolutions on the lightning striking distance,the lightning simulation experiments and the positive upward connecting leader process by using laboratory long sparks are reviewed and discussed in this paper.
基金Project(51274251)supported by the National Natural Science Foundation of China
文摘Based on mineral component and in-situ vane shear strength of deep-sea sediment, four kinds of simulative soils were prepared by mixing different bentonites with water in order to find the best simulative soil for the deep-sea sediment collected from the Pacific C-C area. Shear creep characteristics of the simulative soil were studied by shear creep test and shear creep parameters were determined by Burgers creep model. Research results show that the shear creep curves of the simulative soil can be divided into transient creep, unstable creep and stable creep, where the unstable creep stage is very short due to its high water content. The shear creep parameters increase with compressive stress and change slightly or fluctuate to approach a constant value with shear stress, and thus average creep parameters under the same compressive stress are used as the creep parameters of the simulative soil. Traction of the deep-sea mining machine walking at a constant velocity can be calculated by the shear creep constitutive equation of the deep-sea simulative soil, which provides a theoretical basis for safe operation and optimal design of the deep-sea mining machine.
