Study On Thermal Conductivity Of Composite Wall By The Extended Finite Element Method

With the booming of construction industry, natural resources are decreasing andthe environmental pollution is more and more serious. How to reduce the impact of theconstruction industry on the environment has been a widespread community concern.Recent years, green building is rising. As a key part of the green building, thecomposite wall insulation system has attracted much attention. The study on thermalconductivity of the composite wall has become a hot issue in the field of buildingenergy-saving and material science. In the present thesis, the extended finite elementmethod (XFEM) is developed to investigate the very problem. And under the studybackground of a severe cold region in the northern, to have numerical simulationanalysis about composite wall that containing different insulation materials. The mainresearch work and achievements are as follows:(1) The domestic and international developments and applications of greenbuilding are comprehensively reviewed. The concepts and functions of composite wallare provided. And the paper indicated the need for research and development ofcomposite wall. In addition, the frequently used research methods for heat conductionproblem in composite wall are described together with their main features.(2) The basic theory of thermal conductivity and the basic idea of the XFEM arebriefly introduced. The governing equation and associated boundary conditions arepresented for two-dimensional steady heat conduction analysis. The differences andsimilarities between the conventional finite element method (FEM) and the XFEM arelisted. The article highlighted the advantages of the extended finite element method indealing with the issue about the discontinuity, and the significance of using theextended finite element method to analysis the problems about composite wall heatconduction.(3) The XFEM formulations for steady heat conduction problem are derived. Thearticle elaborated the implementation steps about the extended finite element methodto solve the problem of heterogeneous material thermal conductivity, including thecalculation of the level set function, the distinguishing of the improved node and unit,the selecting of improved function, cell decomposition, and numerical integration. Thecorresponding flowchart and some important details are provided. Based on Fortran95,the XFEM codes for heat conduction problem are developed. To verify the feasibilityand accuracy of the proposed method, several typical problems in heterogeneous materials are tested and the computed results agree well with those by the FEM.(4) Following the above work, the thermal conductivity of an engineeringcomposite wall is studied by the proposed method. The influence of four insulationmaterials on the thermal conductivity of the composite wall is systematically examinedand the corresponding conclusions are drawn. Research results can provide somereferences for selecting green energy-saving building insulation materials.