Based on the analysis of the advantages and disadvantages of existing surface flattening algorithms, this paper proposes a free‐form surface flattening algorithm that minimizes geometric deformation by combining the advantages of the geometric flattening method and the mechanical energy flattening method to address the problems of many iterations, large changes in convergence, and weak visualization of deformation. The point cloud surface is meshed using the triangular slice search method, and the 3D surface mesh is wrapped around the surface using geometric mapping relationships. The initial correction and deformation analysis of the ring flatten graphic are carried out according to the average flattening error, and a global geometric deformation energy model is established to obtain the energy‐minimizing unfolding conditions and optimize the initial flattening graph by iterative optimization. The verification of the algorithm shows that the algorithm is general, has good robustness, high flattening accuracy, and visualizes the flattening deformation. The method is suitable for some design occasions of machining, such as the flattening calculation of automobile outer cladding parts and sheet metal parts. It is especially suitable for the flattening calculation of ring‐like parts, and is a good guide for the design calculation and stamping process of sheet‐metal‐like parts.
Surface sediments were collected from the Yangtze River Estuary (YRE) in to analyse the seasonal and spatial distributions of acid-volatile sulphide (AVS), simultaneously extracted metals (SEM) and the sediment toxicity. An optimised method was used for the AVS and SEM analysis and the results showed that the seasonal variations of AVS were positively correlated with changes in water temperature and the position of higher AVS was relatively fixed. The average of SEM was gradually increased from May 2012 to February 2013 and there were abnormally high values of SEM Cu and SEM Ni in the YRE. Concentrations of the five SEM components were in the following order: Cd < Pb < Cu ≈ Ni < Zn. The correlations among the concentrations of the five metals suggested that these metals in the sediments of the YRE did not have stable anthropogenic and/or natural origin. The mean values of AVS and SEM in the YRE were closer to those in the Huanghe Estuary and were lower than those in the Pearl River Estuary. The results of two sediment toxicity assessments showed that the sediments of most areas in the YRE had potential sediment toxicities, especially the Ni and Cu contamination.
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