为分析不同的定轨策略对卫星定轨精度的影响,利用全球分布的近80个国际GNSS服务组织(International Global Navigation Satellite System Service, IGS)跟踪站连续观测数据和多种定轨策略确定了GNSS卫星的精密轨道。将IGS最终精密星历...为分析不同的定轨策略对卫星定轨精度的影响,利用全球分布的近80个国际GNSS服务组织(International Global Navigation Satellite System Service, IGS)跟踪站连续观测数据和多种定轨策略确定了GNSS卫星的精密轨道。将IGS最终精密星历作为参考轨道,结果表明, GPS卫星单天解定轨结果在径向、切向和法向均优于9 cm,GLONASS卫星单天解定轨结果在径向、切向和法向优于10 cm。此外,不同的定轨策略对轨道精度的影响或改善量级不同。结果表明,选择合适的光压模型等对轨道精度改善细微,而准确的先验大地测量参数以及基准一致性改正对轨道的改善可达1~2 cm。择优选取各个解算策略后通过多天轨道弧段叠加后GPS和GLONASS卫星的定轨精度分别提高了10.9%和8.1%。展开更多
The thermal conductivity of methane hydrate is an important physical parameter affecting the processes of methane hydrate exploration,mining,gas hydrate storage and transportation as well as other applications.Equilib...The thermal conductivity of methane hydrate is an important physical parameter affecting the processes of methane hydrate exploration,mining,gas hydrate storage and transportation as well as other applications.Equilibrium molecular dynamics simulations and the Green-Kubo method have been employed for systems from fully occupied to vacant occupied sI methane hydrate in order to estimate their thermal conductivity.The estimations were carried out at temperatures from 203.15 to 263.15 K and at pressures from 3 to 100 MPa.Potential models selected for water were TIP4P,TIP4P-Ew,TIP4P/2005,TIP4P-FQ and TIP4P/Ice.The effects of varying the ratio of the host and guest molecules and the external thermobaric conditions on the thermal conductivity of methane hydrate were studied.The results indicated that the thermal conductivity of methane hydrate is essentially determined by the cage framework which constitutes the hydrate lattice and the cage framework has only slightly higher thermal conductivity in the presence of the guest molecules.Inclusion of more guest molecules in the cage improves the thermal conductivity of methane hydrate.It is also revealed that the thermal conductivity of the sI hydrate shows a similar variation with temperature.Pressure also has an effect on the thermal conductivity,particularly at higher pressures.As the pressure increases,slightly higher thermal conductivities result.Changes in density have little impact on the thermal conductivity of methane hydrate.展开更多
基金supported by the National Natural Science Foundation of China(51106163)the National Basic Research Program of China (2009CB219504)the Joint Funds of NSFC with the Government of Guangdong Province(U0933004)
文摘The thermal conductivity of methane hydrate is an important physical parameter affecting the processes of methane hydrate exploration,mining,gas hydrate storage and transportation as well as other applications.Equilibrium molecular dynamics simulations and the Green-Kubo method have been employed for systems from fully occupied to vacant occupied sI methane hydrate in order to estimate their thermal conductivity.The estimations were carried out at temperatures from 203.15 to 263.15 K and at pressures from 3 to 100 MPa.Potential models selected for water were TIP4P,TIP4P-Ew,TIP4P/2005,TIP4P-FQ and TIP4P/Ice.The effects of varying the ratio of the host and guest molecules and the external thermobaric conditions on the thermal conductivity of methane hydrate were studied.The results indicated that the thermal conductivity of methane hydrate is essentially determined by the cage framework which constitutes the hydrate lattice and the cage framework has only slightly higher thermal conductivity in the presence of the guest molecules.Inclusion of more guest molecules in the cage improves the thermal conductivity of methane hydrate.It is also revealed that the thermal conductivity of the sI hydrate shows a similar variation with temperature.Pressure also has an effect on the thermal conductivity,particularly at higher pressures.As the pressure increases,slightly higher thermal conductivities result.Changes in density have little impact on the thermal conductivity of methane hydrate.
