## 6 Stress Analysis of the Bare Tower Subjected to Solar Radiation Variation
### Analysis of Stress Variation in Temperature Difference at All Times  
There are generally two methods for finite element simulation software to calculate thermal stress in the model, that is, the direct coupling method. To save the calculation time of the model, the indirect coupling method is mainly adopted to simulate the change in the thermal stress of the main tower. The specific process is as follows:  
1. The general heat transfer conductance analysis of the main tower model is carried out to obtain the temperature results of the node element at the required position at each moment;
2. In the construction phase analysis, the heat conduction result is determined as the thermal load;
3. Extract the corresponding node temperature value as a specific load to apply the forced temperature boundary conditions;
4. Simultaneously calculate the heat conduction analysis and construction phase analysis, and check the required temperature difference stress in the post-processing window. Through calculation, the temperature difference stress of measuring points on each side of the outer wall and inner wall of the 12 th column changes from time to time and are plotted in Figures 12 and 13, where tensile stress is positive and compressive stress is negative. As can be seen, during the solar sunshine period from 6:00 to 18:00 in the daytime, the thermal stress decreases gradually with the increase of the temperature of the outer tower wall, while during the night, the thermal stress increases with the decrease of temperature, and the maximum tensile stress is 1.3 MPa at about 23:00. The thermal stress trend of the inner tower wall is opposite to that of the outer tower wall. During the period from 6:00 to 18:00 when the temperature of the inner tower wall is lower than that of the outer tower wall, the thermal stress keeps increasing, and the maximum tensile stress of the western inner tower wall is 2.7 MPa at 18:00. This phenomenon indicates that the maximum tensile stress occurs in the inner part of the tower wall under the action of positive temperature difference. Under the action of negative temperature difference, the maximum tensile stress will be generated outside the tower wall. Figure 12: Time variation of temperature difference stress at measuring points on the outer wall. As can be seen from Figure 14, under the action of positive temperature difference on the tower wall, the area of tensile stress is mainly concentrated on the inner tower wall; the maximum value is located at the corner where the tower wall intersects, and the range of tensile stress is mainly diffused vertically along the tower wall. The reason could be attributed to the principle of heat expansion and cold contraction: the temperature of the outer wall increases due to solar radiation, hence heat expansion is supposed to happen; however, the outer wall is constrained by the inner wall of which the temperature is less changed, which leads to the compressive stress in the outer wall and tensile stress in the inner wall (see Figure 14). At 14:00, 16:00, and 18:00, the stress reaches 2.3 MPa, 2.8 MPa and 2.7 MPa, respectively, and the local stress is relatively large, which conforms to the characteristics of short-term rapid change. As can be seen from Figure 15, under the action of negative temperature difference on the tower wall, the area of tensile stress is mainly concentrated on the outer tower wall. The maximum value is located in the upper part of the western outer tower wall, and the range of tensile stress is mainly diffused along the center of the tower wall to both sides. The reason could be attributed to the principle of heat expansion and cold contraction: the temperature of the inner wall is less changed while the temperature of the outer wall decreases rapidly due to the heat conductivity and lack of solar radiation, which leads to the compressive stress in the inner wall and tensile stress in the outer wall (see Figure 15). The stress at 3:00 and 7:00 reaches 0.1 MPa and 1.3 MPa, respectively.