## 2 Methodology
### Material Properties and Boundary Conditions  
In Chapter 2.1, modeling simplification for numerical analysis of heat transfer was described. This chapter defines the boundary conditions of the simplified model and the thermophysical properties of the solid, which is a heat transfer medium. The heat transfer mechanism of this numerical analysis model is as follows. The heat generated from the heat panel passes through the upper part of the mold and reaches the spar-cap interface. After that, the heat released from the mold is conducted to the spar-cap through a process of receiving thermal resistance due to contact between solids. The heat that has passed through the spar-cap is transferred from the spar-cap surface into the air, and convection heat transfer proceeds. The air warmed by convection transfers heat to the outside of the control volume. Along with this, irradiation is performed on the spar-cap surface, and finally heat is transferred to the outside of the control volume. The factor that determines the heat flux transferred from the solid to the fluid is the heat transfer coefficient \(h\) in Equation (3). Then, the method of realizing radiation is performed via the VF method of Equation (5). From the model's point of view, convection and radiation do not require complicated assumptions of boundary conditions and thermophysical properties for calculation. However, the spar-cap and its mold need to make some assumptions about thermophysical properties and boundary conditions. In order to perform a heat transfer simulation, it is necessary to determine information about the boundary conditions and thermophysical property values of the target model. It is difficult to copy the actual heat transfer mechanism as it is for the boundary conditions and physical property values applied to the simulation. In particular, the method of simulating the composite material curing process causes problems to be considered from a microscopic point of view and problems to be considered from a macroscopic point of view. The schematic diagram in Figure 4 shows how to solve this problem by distinguishing between macroscopic and microscopic heat transfer. Figure 4a, which is based on the y-z plane of Figure 2a, is a schematic cross-sectional view of the macroscopic heat transfer process. This figure shows how the heat generated by the heat panel is transferred to the spar-cap surface and is released out of the system by the action of radiation and convection heat transfer. This heat transfer system shows that there is no inflow of air and that the heat generated by the heat panel simply goes out as with convection or radiation. Since this method has limitations in achieving the microscopic  
structure of the composite and the boundary of the mold contact surface, a method was devised to implement the model as it is through several assumptions. First is the contact heat transfer between the mold and the spar-cap. When heat is transferred from the mold to the spar-cap, there is thermal resistance due to contact. The following assumptions were made in order to apply the contact interface \(h_{r}\) to the heat transfer simulation via Equation (4). Looking at Figure 4b, a thinly coated epoxy on the spar-cap bottom face is present at a constant thickness between the spar-cap and the mold. In order to obtain \(h_{r}\) that determines the heat flux on the contact surface between the mold and the spar-cap, the thermal conductivity \(k_{r}\) of the epoxy shown in Table 1 and an arbitrary thickness \(\delta=1\) mm are substituted into Equation (4). The second is a method of simplifying the microscopic fiber structure of a composite material and replacing it with one physical characteristic. The grid size of the FRP macro size model and the micro size model is very difficult to implement in one simulation