## 2 Overall Layout and Structural Design
rubber and plastic aggregate material are inserted in parallel, filling the slot and squeezing up each other to form an airtight contact slit between the two sealing blocks. The sealing blocks are flexible enough to allow the strut to pass through the slit (see Figure 2b). Furthermore, observed on the probe, the probe-moving calibration facility with an enclosed chamber, compared with wind-tunnel-like calibration rigs, has a uniform flow coming to the probe with four side walls moving at the same speed as the uniform flow, thus the incoming flow has better uniformity and no side wall boundary layers exist, hence no side wall interference resulting from the boundary layers is produced. The complete motion process of the moving carriage that bears a hot wire probe can be divided into three stages: acceleration stage, constant-speed stage, and deceleration-to-stop stage. The constant-speed stage is used for hot wire calibration. The total length of the three stages was estimated to be 9.26 m. Considering the safety distance margin for the carriage motion at both ends and the carriage parking space, the total length of the enclosed chamber was suggested to be 9.4 m. In view of the limited space to accommodate the facility and the manufacturing cost, the cross-section size of the enclosed chamber was selected as 0.8 m wide and 0.6 m high (see Figure 2).The enclosed chamber is supported over the carriage by 20 propping pillars which stand on a mounting platform and are fixed on it by bolts. The outer surface of the chamber bottom wall has a vertical distance of 303 mm to the top surface of the carriage, and a distance of 595 mm to the top surface of the mounting platform (see Figures 2a and 3). In the space below the enclosed chamber and above the mounting platform, two parallel guide track pedestals and two parallel guide tracks are arranged. The pedestals are welded on the top of the mounting platform, and the two guide tracks are laid and fixed on the two pedestals, respectively. The moving carriage is placed on the guide tracks by embedding sliding blocks (fixed to the lower face of the carriage) into the slots of the tracks,  
Figure 3: The assembly of the mechanical structure system. 1. Water intake pipes; 2. Enclosed chamber; 3. Water return pipes; 4. Synchronous belt; 5. Mounting platform; 6. Synchronous pulley; 7. Guide track; 8. Chamber propping pillars; 9. Guide track pedestal; 10.Moving flat plate carriage; 11. Steam (moist air) pipes; 12. Recirculating dehumidifier; 13. Humidifier; 14. Constant-temperature water tank; 15. Temperature and humidity control cabinet; 16.Driving motor; 17. Recirculating heating/refrigerating machine. to ensure that the carriage only moves horizontally along the lengthwise direction of the guide tracks without jumping up and down or wagging sideways (Figure 3). In Figure 3, most components of the mechanical structure system can be seen, e.g., the enclosed chamber, the pillars supporting the chamber, the mounting platform, the guide track pedestals, the guide tracks, the synchronous pulley, the synchronous belt, the moving flat plate carriage, and the driving motor, etc. Some devices of the temperature and humidity control system can also be found in Figure 3, which are the constant-temperature water tank, the recirculating heating/refrigerating machine, the water intake and return pipes, the humidifier, the dehumidifier, the humidification/dehumidification steam (moist air) pipes, and the control cabinet of the temperature and humidity control system, etc.