## 5 Application of Calculating the Appropriate Temporary Piece Usage  
In order to investigate the proper temporary piece installation in the block assembly stage, a panel block model in the bottom area of the 81,000 DWT bulk carrier was selected as shown in Figure 19.  
The panel block finite element model was created, as shown in Figure 20, to examine the joint welding line in the hull width direction. The model is divided into two frames in the bow direction and four girders in the hull width direction, based on the joint welding line. The finite element model consists of a frame, girder, upper plate, bottom plate, and 20 longitudinal stiffeners. A strong-back and a temporary piece are also included. The distance between the strong-back and the temporary piece was applied through the field survey. There are 5 strong-backs and 39 pieces in the finite element model.  
The welding deformation analysis was performed with the purpose of identifying the deformation pattern of panel block joint welding according to the number of pieces and calculating the number of proper piece installations. Welding deformations were calculated for 39 pieces (simulation 1, current), 19 pieces (simulation 2), and 0 pieces (simulation 3). Figure 21 shows the final deformation for the simulation 1 upper plate. In the region between girders, displacement occurred in the direction opposite to the surface where the piece was installed.  
Figure 19: Panel block for simulation.  
Figure 18: Experimental and analysis results of joint welding deformations for panel block.  
Figure 22 shows the comparison of the displacements in the welding direction for each simulation. In all simulations, deformation rarely occurs in the girder region, and a relatively small difference of displacement occurs between longitudinal stiffeners in simulation 1 and simulation 2.  
Figure 21: Deformed shape of upper plate (simulation 1).  
Figure 20: Finite elements model of panel block: (**a**) upper plate and pieces and (**b**) whole model.  
As an example of calculated results, Figure 23 shows the angular deformation at y = 6600, for all three simulations. It can be seen that angular deformations are distributed along y-direction with each maximum displacement, as shown in Figure 22.  
Figure 23: Simulation results (displacement in x-direction y = 6600 mm).  
Figure 22: Simulation results (displacement in welding line direction x = 0 mm): (**a**) zone I; (**b**) zone II; (**c**) zone III; and (**d**) zone IV.  
In this study, the number of proper piece installations was calculated as follows, referring to the simulation result of Figure 22. First, the curve of the deformation result without using pieces (simulation 3) was set as the deformation limit. The appropriate number of pieces necessary to satisfy the deformation limit and to approach the current deformation curve (simulation 1) was determined. The result obtained when using 19 pieces (simulation 2) shows that, in this case, the deformation limit is not satisfied between the two longitudinal stiffeners regions (6600 mm \(<\) y \(<\) 7400 mm, 10,000 mm \(<\) y \(<\) 10,800 mm), as seen in Figure 22c,d. In other words, additional pieces are installed in these two areas. Therefore, in the case of the panel block model, a total of twenty-one pieces was determined to be the number of piece installations. Compared to the currently used number (simulation 1), a piece usage reduction of 46% can be expected. Additionally, in terms of weight reduction, the piece weight of approximately 34 kg could be reduced; moreover, the piece installation and removal time of approximately 450 min is expected to be reduced. Because a reduction in the number of pieces leads to a reduction of the external constraint force acting on the base plates, it is necessary that the welding residual stress decreases by a certain amount in both tension and compression.