## 4 Feature Prediction and Full-Condition Simulation
### Anti-Surge Prediction and Full-Condition Simulation of ATF System  
The characteristics of the anti-surge valve are deeply simulated. For the actual ATF system, the situations with surge risk are mainly concentrated in small flow conditions and overpressure ratio operation during start-up or shutdown. In general, excluding human factors, overpressure ratio operation is less likely. Artificially closing the supply valve 3\(\mu\) as described in Section 4.1 rarely occurs. However, in starting and stopping conditions, the system should gradually increase the flow rate from 0 kg/s to the design flow rate. Proper use of anti-surge valve 4\(\mu\)s is required during this period. In the virtual space of the BPNN-MDSG digital twin, the anti-surge characteristics of the system are studied by practical simulation tests. Figure 16 shows the valve opening in the unit start-up condition without surge valve 4\(\mu\)s. During compressor start-up, minimal power demand results in low blade loading and system-wide low-flow conditions. This necessitates maintaining inlet valve 1\(\mu\) at approximately 10% opening. The system does not start the gas service at start-up, so the opening of the gas supply valve 3\(\mu\)s is 0. Initially, the discharge valve is fully open. As the compressor power slowly increases, the discharge valve is gradually reduced to less than 10%, and the system runs at a small flow rate. When the compressor speed reaches the design speed, the inlet valve gradually opens and slowly increases the blade load. After 100 s, according to the gas supply demand, adjust the inlet valve 1\(\mu\) and the downstream gas supply valve 3\(\mu\)s to obtain different gas pressures, and the system works normally. Figure 17 shows the dynamic prediction results of the ATF compressor system mass flow rate and pressure under the above start-up conditions. Although the actual valve operation tried to establish a low power balance during start-up and tried to avoid the occurrence of surge under low flow, the system surge was still caused by the small inlet flow in 0-80 s. Compared with the surge characteristics of the overpressure ratio in Section 4.1, the vibration frequency is higher and the amplitude is smaller when starting. The reason is that the frequency and amplitude characteristics of the surge are affected by the network of the ATF compressor system. The surge at start-up is caused by the upstream incoming flow  
Figure 16: Valve opening in start-up condition without surge protection. being too small, and the surge in Section 4.1 is caused by the downstream departing flow being too small. The dominant cavity causing the surge is different between the two. The former is more urgent to release the high-pressure area of the downstream cavity, while the latter is more urgent to recover the low-pressure area of the upstream cavity. In this system, the volume of the upstream pipe network is 29.15 m\({}^{3}\), which is much smaller than the downstream pipe network volume of 121.28 m\({}^{3}\). The larger the volume, the slower the downstream high-pressure release and the slower the upstream low-pressure recovery. The longer it takes to complete a vibration cycle. In the prediction of the starting working condition as shown in Figure 17, the work capacity of the compressor at low power is not balanced with the system pressure, the flow rate of the incoming compressor is too low, and the system enters surge. Upon start-up completion at approximately 80 s, valve 1# (inlet) is opened to augment the flow rate. This increases compressor power consumption, balances inlet-outlet flow-pressure parameters,  
Figure 17: Mass flow (**a**) and pressure (**b**) of start-up condition without surge protection: (**a**) Flow forecast result. (**b**) Pressure prediction result. and suppresses surge conditions. Subsequent coordinated valve adjustments enable stable gas delivery operations across varying discharge pressures.