Understanding the interaction between groundwater and surface water in permafrost regions is essential to study flood frequencies and river water quality, especially in the high latitude/altitude basins. The applicati...Understanding the interaction between groundwater and surface water in permafrost regions is essential to study flood frequencies and river water quality, especially in the high latitude/altitude basins. The application of heat tracing method,based on oscillating streambed temperature signals, is a promising geophysical method for identifying and quantifying the interaction between groundwater and surface water. Analytical analysis based on a one-dimensional convective-conductive heat transport equation combined with the fiber-optic distributed temperature sensing method was applied on a streambed of a mountainous permafrost region in the Yeniugou Basin, located in the upper Heihe River on the northern Tibetan Plateau. The results indicated that low connectivity existed between the stream and groundwater in permafrost regions.The interaction between surface water and groundwater increased with the thawing of the active layer. This study demonstrates that the heat tracing method can be applied to study surface water-groundwater interaction over temporal and spatial scales in permafrost regions.展开更多
High-quality solidification microstructure during directional solidification relies on precise temperature gradient control, so accurate calculation of the temperature field is critical. In this study, a 3D transient ...High-quality solidification microstructure during directional solidification relies on precise temperature gradient control, so accurate calculation of the temperature field is critical. In this study, a 3D transient global heat transfer model of directional solidification by the Bridgman method based on the finite difference method is developed. The radiation heat in this model is calculated by the discrete transfer method, and a modified method of external surface area for irregular geometric models is proposed to reduce the zigzag shape caused by finite difference grids. Considering the radiative heat transfer between any surface elements of all materials in the directional solidification furnace, a dynamic ray tracing algorithm is developed to simulate the entire process of directional solidification. Then, the simulated results are compared with the theoretical results and experimental results, respectively. Finally, based on the present model and method, the simulation program developed is applied to the directional solidification of actual castings. The simulated results are in good agreement with the experimental results, which indicate that the model and method developed in this study is effective and practical.展开更多
In order to ensure the safety of fluid flow in deep-water submarine pipelines,a safe and energy-saving built-in skin effect electric heat tracing technology was adopted as the thermal management strategy.The magnetic ...In order to ensure the safety of fluid flow in deep-water submarine pipelines,a safe and energy-saving built-in skin effect electric heat tracing technology was adopted as the thermal management strategy.The magnetic field distribution of built-in skin effect heating system is analyzed based on the mechanism of built-in skin effect heating system,so as to obtain the equivalent circuit model of built-in skin effect electric heating system.Meanwhile,heating power is introduced as an intermediate variable to establish the relationship between power supply frequency and built-in skin effect heating temperature.Aiming at the skin effect electric heating system,an Active Disturbance Rejection Control(ADRC)method is proposed macroscopically based on Hammerstein model.Firstly,the parameters of Hammerstein model are identified and optimized using the auxiliary model and standard particle swarm optimization algorithm.Then,the ADRC controller of linear link is designed,and the required heating temperature is used to solve the intermediate variable heating power.Finally,inversion calculation is applied in the nonlinear link to solve the required power frequency,so as to achieve the purpose of efficient heating and verify the feasibility and effectiveness of control strategy through simulation.展开更多
Electron cyclotron resonance heating （ECRH） is one of the main auxiliary heating schemes for the HL-2A tokamak. Routinely, the ohmic heating can provide a heating power about 300-450 kW in this device （ estimated f...Electron cyclotron resonance heating （ECRH） is one of the main auxiliary heating schemes for the HL-2A tokamak. Routinely, the ohmic heating can provide a heating power about 300-450 kW in this device （ estimated from that the total toroidal current is about 300 kA while the totoidal voltage is 1-1.5 V）. The total power for the ECRH now is 1 MW and in future 2 MW.展开更多
基金supported by the National Natural Science Foundation of China(41690141,41671067)the second Tibetan Plateau Scientific Expedition and Research Program(STEP)(2019QZKK0605)+1 种基金the Fundamental Research Funds for Central Universities(lzujbky-2019-40)CAS"Light of West China"and the State Key Laboratory of Cryospheric Science,CAS(SKLCS-ZZ-2020).
文摘Understanding the interaction between groundwater and surface water in permafrost regions is essential to study flood frequencies and river water quality, especially in the high latitude/altitude basins. The application of heat tracing method,based on oscillating streambed temperature signals, is a promising geophysical method for identifying and quantifying the interaction between groundwater and surface water. Analytical analysis based on a one-dimensional convective-conductive heat transport equation combined with the fiber-optic distributed temperature sensing method was applied on a streambed of a mountainous permafrost region in the Yeniugou Basin, located in the upper Heihe River on the northern Tibetan Plateau. The results indicated that low connectivity existed between the stream and groundwater in permafrost regions.The interaction between surface water and groundwater increased with the thawing of the active layer. This study demonstrates that the heat tracing method can be applied to study surface water-groundwater interaction over temporal and spatial scales in permafrost regions.
基金financially supported by the National Nature Science Fund Projects of China(Nos.51475181 and 51605174)
文摘High-quality solidification microstructure during directional solidification relies on precise temperature gradient control, so accurate calculation of the temperature field is critical. In this study, a 3D transient global heat transfer model of directional solidification by the Bridgman method based on the finite difference method is developed. The radiation heat in this model is calculated by the discrete transfer method, and a modified method of external surface area for irregular geometric models is proposed to reduce the zigzag shape caused by finite difference grids. Considering the radiative heat transfer between any surface elements of all materials in the directional solidification furnace, a dynamic ray tracing algorithm is developed to simulate the entire process of directional solidification. Then, the simulated results are compared with the theoretical results and experimental results, respectively. Finally, based on the present model and method, the simulation program developed is applied to the directional solidification of actual castings. The simulated results are in good agreement with the experimental results, which indicate that the model and method developed in this study is effective and practical.
文摘In order to ensure the safety of fluid flow in deep-water submarine pipelines,a safe and energy-saving built-in skin effect electric heat tracing technology was adopted as the thermal management strategy.The magnetic field distribution of built-in skin effect heating system is analyzed based on the mechanism of built-in skin effect heating system,so as to obtain the equivalent circuit model of built-in skin effect electric heating system.Meanwhile,heating power is introduced as an intermediate variable to establish the relationship between power supply frequency and built-in skin effect heating temperature.Aiming at the skin effect electric heating system,an Active Disturbance Rejection Control(ADRC)method is proposed macroscopically based on Hammerstein model.Firstly,the parameters of Hammerstein model are identified and optimized using the auxiliary model and standard particle swarm optimization algorithm.Then,the ADRC controller of linear link is designed,and the required heating temperature is used to solve the intermediate variable heating power.Finally,inversion calculation is applied in the nonlinear link to solve the required power frequency,so as to achieve the purpose of efficient heating and verify the feasibility and effectiveness of control strategy through simulation.
文摘通过焊接热模拟研究了在超大线能量下焊接时Al元素、Mg元素和Ti元素含量对EH36高强船板钢热影响区粗晶区组织、性能的影响规律,采用Thermo-Calc热力学计算与SEM,EDS测试相结合的方法揭示了Al元素、Mg元素和Ti元素含量与母材中氧化物类型、尺寸、数量及粗晶区相变的关系.结果表明,Al_(2)O_(3)无法诱导针状铁素体相变,当Al元素质量分数低于0.005%时,钢中可形成Mg元素、Ti元素或其复合氧化物,可促进粗晶区针状铁素体相变.Mg元素和Ti元素联合添加时,当Mg元素质量分数由0.0042%降低为0.0013%,氧化物类型由MgO转变为Mg_(2)TiO_(4),经统计20个视场内的氧化物数量由408个提高到503个,平均直径由1.37μm减小到1.10μm,显著提高了非均匀形核的比表面积,抑制了晶界铁素体的形成,使t8/5=300 s时粗晶区热模拟试样-20℃冲击吸收能量由43 J提升到127 J.
文摘Electron cyclotron resonance heating （ECRH） is one of the main auxiliary heating schemes for the HL-2A tokamak. Routinely, the ohmic heating can provide a heating power about 300-450 kW in this device （ estimated from that the total toroidal current is about 300 kA while the totoidal voltage is 1-1.5 V）. The total power for the ECRH now is 1 MW and in future 2 MW.
