## 4 Simulation Study of De-Bonding Performance of Composite In Situ Separator
### Simulation Settings  
(1) Simulation Software Settings  
In this study, ANSYS Fluent 19.0 was selected for simulating and analyzing the internal flow field of the separator. However, the built-in discrete element functionality of Fluent was inadequate to support the dual-sphere particle model under investigation and to extract the loads on the NGH bonds between dual-sphere particles, failing to meet the research requirements. Therefore, this study simultaneously used the particle discrete element simulation software Altair EDEM 2018 coupled with Fluent to investigate the motion behavior of hydrate particles in the hydrocyclone field. In Fluent, the Reynolds Stress Model (seven equations), suitable for fluid rotation conditions, was chosen as the turbulence model. To couple with EDEM, the transient calculation method was used. The fluid material was seawater, with a density of 1025 kg/m\({}^{3}\) and a viscosity of 0.0017 Pa-s. The inlet was set as a velocity inlet, with an equivalent velocity of 10.03 m/s corresponding to an inlet flow rate of 4 m3/h. The outlet was set as a pressure outlet. In EDEM, sand particles were modeled as two spheres, each with a diameter of 0.6 mm, and the bonding between particles was established through an API, with a length of 0.06 mm, as shown in Figure 5. A particle factory was set up at the separator inlet to inject sand particles into the separator at a rate of 1000 particles/s, with a particle velocity of 10.03 m/s. During the post-processing of the simulation results, the loads on the bonds could be extracted to analyze whether GHBS particles could achieve de-bonding. In addition, Hertz-Mindlin (no-slip) was used as the particle-to-particle contact model; the Euler model was the time integration method; the mesh size was 0.9 mm; and the time step was 1.18 \(\times\) 10\({}^{6}\) s.  
(2) Coupling Method  
In the coupling of ANSYS Fluent 19.0 and EDEM, Fluent was run independently first to allow the flow field within the separator to reach a stable state, followed by coupling with EDEM. Calculations revealed that when the simulation time was no less than 3 s, further increases in the simulation time did not significantly impact the flow field within the separator. Therefore, the pre-simulation time for Fluent was set to 3 s. A two-way coupling method was used, along with a 20-fold Fluent Drag Law Particle Scale-Up Factor. As a result, the actual particle size of the sand particles in the simulation was 30 \(\upmu\)m. The reason for using the Fluent Drag Law Particle Scale-Up Factor was that the grid size in EDEM depends on the smallest particle size. Using the real particle size would result in a  
Figure 5: Weakly cemented GHBS particle model diagram. \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline
**Grid Sizes** & **1** & **1.2** & **1.4** & **1.6** & **1.7** & **1.8** & **2** \\ \hline Total Numbers of Grid Elements & 1,796,787 & 1,038,531 & 527,571 & 236,273 & 181,439 & 137,605 & 50,431 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Grid sizes and total number. grid number no less than 1\(\times\)1010, and the Particle Scale-Up Factory could greatly reduce the computational costs. (3) Reliability Verification  
To verify the reliability of the simulation model, calculations were performed using the same particle size and five inlet flow rates as in experiments reported previously [10]. The particle linear velocity and particle trajectory distribution obtained were compared with the experimental results. The results showed that the error between the simulation and the experiment did not exceed 10%, indicating that the computational model used in this study was reliable. (4) Simulation Scheme  
The helical flow channel enhanced the de-bonding performance primarily by restricting the axial movement speed of GHBS particles, making the pitch of the helical flow channel a major variable. In addition, the particle size significantly impacted the strength of the cementing bonds and their motion behavior.