To solve the problem of local remeshing in multi-body separation numerical simulation of flight vehicle with unstructured mesh, a method for the construction of local remeshing regions was proposed based on element neighbouring indices. Firstly, the mesh quality was checked by the element radius ratio and the remeshing regions were marked. Secondly, the remeshing regions were extended by the neighboring indices of mesh elements. Finally, the around elements of the non-two manifold sides were marked for ensuring the boundary definition of remeshing regions which satisfied two sides manifold criterion. The numerical experiment of a separation simulation was conducted by the proposed method. In this simulation, the local remeshing was operated successfully for 16 times, and the average of the overall remeshing element radius ratio was improved above 0.71. The calculation results and comparative analysis of the wind tunnel experimental data shows that, the trajectory and motion of the separation were calculated accurately in the numerical experiments. It is verified that the proposed unstructured remeshing process is effective.

Element-sizing fields are necessities for guiding the generation of high-quality meshes used in finite element analyses and smoothness of this field heavily affect the element quality of the resulting mesh. A new algorithm was proposed to smooth the element-sizing fields. Based on the H-variant proposed by Borouchaki, et al. (BOROUCHAKI H, HECHT F, FREY P J. Mesh gradation control. International Journal for Numerical Methods in Engineering, 1998,43(6):1143-1165), some basic geometric concepts and a theory that aimed at analyzing the smoothness of 2D element-sizing fields quantitatively was established in this paper. The rule of the reasonable sizing transition for 2D area was achieved. Based on this rule, an improved algorithm from Borouchaki sizing-correcting method defined on unstructured background meshes was designed. This algorithm adjusted the size values attached on a small set of background mesh nodes to ensure the output of a well graded size field. Finally, mesh examples were given to validate the proposed theory and algorithm. Compared with other smoothing methods, the proposed algorithm in this paper can help get meshes with better quality.