## 2 System Modeling
### Co-Simulation Platform Based on LabVIEW and AMESim
#### 2.3.1 Simulation Model Based on AMESim
It can be seen from Figure 6 that when different numbers of branches are connected in parallel, the pressure of the main pipe is inversely proportional to the opening of the pipe load simulation valve, and it conforms to the regulation law of the ball valve. That is, when the opening of the ball valve is between 80% and 100%, the pressure change is relatively gentle. There is little difference between the main pipe pressure value in the simulation model and the experiment, and the simulation and experiment have good consistency. Figure 6 shows that the flow of the main pipe is proportional to the opening of the pipe load valve, which also conforms to the regulation law of the regulating ball valve. Moreover, the increment of the main flow from three channels to four channels in parallel shows an increasing trend with the increase of the opening of the pipe load valve. It should be noted that when the pipe load valve opening is greater than 60%, the flow of the four-channel main pipe in parallel is greater than the range of the flowmeter (20 m\({}^{3}\)/h), and there is no test value temporarily. However, from the comparison between the simulation value and the experimental value of the main flow of the three-channel pipe in parallel, it can be seen that the simulation model is also consistent with the test bench data sample. Therefore, it can be considered that the simulation model based on AMESim can replace the testbed for subsequent research when the multi-channel confluent water supply is constant. Figure 6: Constant flow performance verification: (**a**) Main pipe pressure under different pipe loads; (**b**) Main pipe flow under different pipe loads. The control process of the multi-channel concentrated water supply system is an unsteady flow state for the main pipe pressure, that is, when the main control valve on the main pipe changes or the control ball valve on the channel changes, the flow state in the main pipe is not stable, and the main pipe pressure changes with time. The model based on AMESim not only needs to have a high degree of consistency with the research platform in the steady state of the system, but more importantly, the simulation model also needs to have a good dynamic consistency with the research platform when the system state changes. From Figure 7a, it is evident that when the switching time and switching sequence of the two channels are different, the fluctuation of the main pipe pressure will also change. Compared with the simulation model, the main pipe pressure before and after the switching is different. This is because the switching of two centrifugal pumps and channels cannot be exactly the same, resulting in different pressure values of the main pipe before and after the switch. From Figure 7b, we see that when the three channels are connected in parallel, the opening time of the main control valve is 5 s, and the pressure on the main control valve increases gradually with the opening of the main control valve. There is a difference between the simulated value and the test value when it is turned on. This is because there is a certain initial pressure at the beginning of the research platform, but the overall trend is the same, and the experimental value and the simulated value have a high degree of consistency after the turn-on. In a word, although the results of the experiment and the simulation model under constant flow and unsteady flow have certain errors, the overall trend is the same. It can be considered that the simulation model is a reproduction of the research platform, and the simulation model can be used for system control research.