应我校williamhill威廉希尔官网赵军明教授邀请，法国科学院院士、索邦大学教授Olivier Pinoneau将于2025年4月15日至4月17日前来交流并作学术报告，届时将进行“温室气体辐射传输”、“变折射率的大气温度影响”、“自开发多物理场有限元软件”三个主题内容的介绍，欢迎感兴趣的师生参加。
主讲人：Olivier Pinoneau
主讲专家简介：Olivier Pinoneau，法国索邦大学教授，法国科学院院士，曾担任法国国家科研中心(CNRS)、法国国家空间研究中心(CNES)、索邦大学、法国核废料管理委员会(CNE)、法国兴业银行基金会、芬兰国家超级计算中心(CSC)等多个国际研究机构的科学委员会成员(scientific board)，曾代表法国科学院出席欧洲科学院科学咨询委员会(EASAC)，于2003 年当选法国科学院院士。主要研究领域为应用数学、计算机科学和应用的交叉方向，著有 6 本书，发表超过300篇研究论文，是开源多物理场有限元仿真软件FreeFEM++的发起人。
讲座时间地点：2025年4月15日10:00—12:00 节能楼212会议室
讲座摘要：
Computing Earth’s Greenhouse Effect
In this talk we shall address the problem of computing the effect of greenhouse gases(GHG) on the temperature of our Earth atmosphere.
Starting from the change in the extinction and scattering coefficients due to GHG we analyse the Vector Radiative Transfer Equations for Earth’s atmosphere. Using a method similar to ray tracing coupled with a matrix size reduction called H-matrices and with an iterative method called Iterations on the Source we have been able to compute the radiative transfer in 3D in a valley near the Mont-Blanc for complex absorption coefficients measured by the Gemini.
The computations show that CO2 increases the temperature near the ground but cools it at high altitude (as measured). The 3D computations are compared with a simpler 1D model which can be enriched to account for the non-spherical shapes of the molecules of the GHG via an added term in the scattering matrix.
聚焦温室气体(GHG)对地球大气温度的影响，基于GHG引起的消光与散射系数变化，分析地球大气的矢量辐射传输方程。结合光线追踪、矩阵降维及源项迭代方法，模拟勃朗峰附近山谷的三维辐射传输，结果表明二氧化碳会使地面附近的温度升高，但在高海拔地区反之。最后对比三维模型与改进的一维模型，可通过在散射矩阵中添加修正项反应GHG分子的非球形形状。
讲座时间地点：2025年4月16日10:00—12:00 节能楼312会议室
讲座摘要：
Computing an Atmosphere with Varying Refractive Index
This talk will present our numerical studies of the impact of a varying refractive index on temperature in a stratified atmosphere, with particular emphasis on greenhouse gases (GHG) such as CO2 and clouds.
Varying concentrations of GHG and the presence of clouds are modelled by their effects on absorption and scattering coefficients in given ranges of frequencies. The study shows that the numerical method is capable of reproducing small changes due to GHG and the influence of refraction from clouds.
Clouds have a refractive index close to air and varying smoothly, included in the VRRTE, but at the ocean-air interface the Fresnel conditions need to be applied for which the numerical implementation will be also discussed.
Temperature variations are at the core of the present study. Iterations on the source are used to adjust the temperature to reach thermal equilibrium. Convergence and monotony are analysed as in the reference literature.
通过数值方法探讨分层大气中变化折射率对温度的影响。模拟不同浓度的温室气体和云的对吸收和散射系数的影响，研究表明，该数值方法能够高精度复现由于温室气体和云折射引起的微小变化，云的折射率与空气接近且变化平滑，但在海洋-空气界面处需应用菲涅尔条件。最后通过源项迭代的方法实现热平衡，并分析算法的收敛性和单调性。
讲座时间地点：2025年4月17日10:00—12:00 节能楼212会议室
讲座摘要：
A High Level MultiPhysics FEM Software
The FreeFem project was started in the 90’s by Dominique Bernardi and myself to ease teaching and prototyping algorithms to solve Partial Differential Equations(PDE). Then Fr´ed´eric Hecht inserted his advanced automatic mesh generator; after 2005 he took the leadership and we rewrote everything using Lex and Bison.
Top priority was given to the user interface to define the PDE and hide the technical parts of the numerical methods. We tried to be at the highest possible level, nearest to the mathematical statements.
For nonlinear, time dependent, multiphysics systems of PDE, it is the responsibility of the user to specify the scheme. By comparison to its commercial competitor COMSOL1, FreeFem++ is deliberately primitive for graphics but it is interfaced with paraview and others; on the other hand FreeFem++ does things that COMSOL cannot do. It runs on Mac OS, Windows, Linux and supercomputers in parallel with perfect scaling. FreeFem++ has also the best open source module for mesh adaptivity in 2D and 3D.
介绍报告人和其他研究人员开发的一款多物理场有限元软件。该软件兼顾先进的自动网格生成器和友好的用户界面，同时支持paraview等可视化软件接口。应用于非线性、时变和多物理场偏微分方程(PDE)系统，用户只需专注PDE的定义，无需深入了解数值方法的技术细节。与其商业竞争对手COMSOL相比，FreeFem++具备完美拓展性，可以在Mac OS，Windows，Linux和超级计算机并行运行；拥有最好的开源模块，可用于2D和3D网格自适应。
