## 2 Methodology
### Simplification of Experimental Interference Factors  
A lubricating oil system is composed of many components; its internal structure is complex, the flow path is variable, and the system operation state is closely related to environmental conditions. In order to improve the efficiency of modeling and the feasibility of simulation calculation under the premise of maintaining reasonable accuracy of the model, this paper makes some necessary simplifying assumptions on the system, aiming to highlight the dominant influencing factors and avoid modeling redundancy and the waste of simulation resources. In this study, we ignored the influence of external environmental temperature and ship operating conditions on the internal flow characteristics of the lubrication system. This process is based on the following considerations: In most actual operation conditions of marine ships, the lubricating oil system is equipped with temperature adjustment and pressure adjustment devices. There is a certain non-steady-state process in the early stage of the system, but after entering the steady state, the temperature of the lubricating oil is usually controlled in a relatively constant range (such as 60 \({}^{\circ}\)C-80 \({}^{\circ}\)C), so that the influence of the viscosity change on the flow field tends to be stable. Therefore, considering the fluid physical property disturbance caused by environmental factors is less sensitive to the model results, and ignoring its influence, will not significantly weaken the simulation accuracy but can significantly improve the simplicity of modeling. Inertia loss caused by lubricating oil flow in the pipeline is also not considered in detail in the model. This is because the influence of the inertia term is mainly reflected in the high-speed start and emergency stop stage, the lubrication oil system mostly runs in the steady flow mode, and the pressure fluctuation range is small. The contribution of the inertia term to the total pressure drop is very small, which is far lower than the proportion of the along resistance and the local resistance term, so it can be ignored in the steady-state analysis. In addition, the loss caused by evaporation or small leakage at the interface during the flow of the lubricant is omitted. Although this kind of loss is common in the actual system, its volume flow rate is in the order of magnitude inferior to the overall circulating flow rate of the system (usually less than 1% of the total flow rate), and it has little impact on the system pressure, flow rate, and oil supply stability. Therefore, it is reasonable to ignore these edge loss terms to ensure modeling efficiency and avoid introducing unnecessary noise factors. Regarding the structural complexity of pipelines, only the local flow resistance caused by pipe segments with bending angles greater than 30\({}^{\circ}\) is modeled in this paper, and microbends smaller than this threshold are treated as equivalent straight pipe segments. This is based on the engineering empirical law of fluid dynamics that the local drag coefficient of a small-angle elbow is very low, and its contribution to the system pressure drop can be almost ignored. The neglect treatment can simplify the node definition of the pipeline network and the calculation process of the impedance matrix, thereby greatly improving the simulation efficiency. Although in practical application lubricating oil may be mixed with trace moisture or solid particle impurities due to aging equipment, lax sealing, a harsh external environment, and other reasons, the influence of such factors has not been considered in the simulation modeling of this study. The entry of moisture and mechanical impurities is usually random, and its concentration, particle size distribution, and entry time are difficult to accurately quantify.