## 4 Numerical Simulation of Temperature Field of Spatial Grid Structure
### Comparative Analysis of Numerical Results and Test Results  
The solar temperature field of the test model was subject to the numerical simulation. Through the comparative analysis, the accuracy of the numerical simulation method of the structural non-uniform temperature field was verified by comparison with the measured data. Figure 10 shows the comparison between the numerical simulation results and the measured data of the solar temperature field at representative moments. The comparison of the temperature distribution showed that the numerical results have a distribution law similar to that of the measured results, and the extreme temperatures are also relatively similar. The temperatures of the top chords were almost the same. The temperature of the internal bottom chords was slightly lower than that of other chord members affected by the shadowing of the top members. The temperature of the web member was significantly lower than that of the chord member and the web members in different space angles were also significantly different. Due to the effects of the reflected radiation, the test temperatures of the peripheral bottom chords were higher than the numerical results. The maximum temperature of the structure model appeared at node position in the numerical results, which is mainly because the welding ball node had a larger surface area and was more evenly radiated by sunlight.  
Figure 9: Shadow distribution of the spatial grid structure model at representative moments. Black boxes indicate cross plate supports.  
Figure 11 compares the temperature field simulation value and the measured value at the representative measuring points, including the top and bottom chords and web members. From the results, the numerical results of each measuring point match with the measured results and the temperature variation trends throughout the day are the same. The numerical results at night were similar to the measured results, and the maximum temperatures of the day appear were also similar, but the numerical simulation results were slightly larger than the measured results.  
Figure 10: Temperature distribution of the spatial grid structure model. Black boxes indicate cross plate supports.  
Figure 12 is the all-day average error rate curve of the top and bottom chords and web members at all measuring points. From the results, the simulated temperature of each member at night has a small discrepancy when compared with the measured result, and the maximum error rate is only 3.6%. Except for the sunrise and sunset moments, the error rates of the simulated and the measured values at daytime are also maintained at a low level with an average error rate of 5.3%. The average error rate of the web member is slightly larger than that of the chord member. At sunrise and sunset, because the intensity of solar radiation and the environmental temperature both vary significantly, the error rates increase, with a maximum value of 21%. Besides, the simulated temperature is the result after the thermal equilibrium, but the measured result is the directly measured temperature at the measuring moment. In summary, the simulated temperature field distribution matches well with the measured result, which proves that this numerical simulation method is reliable and effective.  
Figure 11: Comparison between the simulation value and the measured value at the measuring point. Red and black lines indicate the simulated and measured results, respectively.