# Forming Difficulty Evaluation for Curved Hull Plates Based on Grey Relational Analysis
## 3 Model for Evaluating the Forming Difficulty of Complex Curved Hull Plate
### Evaluation Process Design of Forming Difficulty for Complex Curved Hull Plates  
This paper conducts an evaluation method research based on the relationship between each influencing factor and the forming difficulty of complex curved hull plates. The relevant geometric parameter data can be obtained from the offset data. The data of process parameters and forming time are calculated based on the developed process parameter forecasting software [15]. This software has accumulated more numerical simulation and experimental data. It can calculate the forming process parameters according to the name of the plate, and some of the results have been applied in shipyards, which also shows the reliability of the data related to the forming process parameters obtained by the forecasting system. The process of evaluating the forming difficulty of complex curved hull plates is shown in Figure 9, and the steps are as follows:  
1. Extract the offset table file, plate file and plate seam file from the ship production design software TRIBON. Extract the plate thickness according to the plate part name and plate seam name. Determine the area enclosed by the plate edge. Combine the offset table file to calculate the discrete points within the polygon, and then calculate the date of the plate length and width. Calculate the radius of curvature at different locations along the length of the plate according to the three-point fitting method, and then calculate the distribution of deflection along the length of the plate according to the point-to-space curve distance formula.
2. According to the prediction system of outer hull plate forming parameters, the number of heating lines on both sides of the curved plate, the length of the heating line and the processing time corresponding to each heating line are calculated. Then the total number of heating lines, the difference of heating lines on both sides of the curved plate, heating lines pacing, the average heating speed and the total forming time as a reference sequence are calculated.
3. According to the data on the factors influencing the forming of curved plate obtained in steps (1) and (2), the correlation of each influencing factor with the difficulty of forming the curved plate are determined. The influencing factors are divided into two groups according to their correlation, which are those positively correlated with the forming difficulty of curved hull plates and those negatively correlated with the forming difficulty of curved hull plates.
4. According to the normalization method, the data of influencing factors are standardized. The correlation degree between each influencing factor and forming time is calculated according to the calculation formula of correlation coefficient and correlation degree.
5. According to the correlation between each influencing factor and the forming time, the weight coefficient of each influencing factor is calculated by the weight calculation formula. The coefficient matrix of the influencing factor weight is obtained.
6. According to the correlation between each influencing factor and the forming difficulty of the curved plate in step (3), the difficulty coefficient of each influencing factor can be calculated by means of the difficulty coefficient calculation formula. The matrix of difficulty coefficients of influencing factors is obtained.
7. Multiply the weight coefficient matrix of each influencing factor obtained from step (5) and step (6) with the difficulty coefficient matrix to obtain the evaluation result of the forming difficulty of curved hull plate.