## 5 Conclusions  
This study investigates the mechanisms by which the geometric parameters of flow paths influence axial loads during fast transient response processes under existing sudden change boundaries, with particular emphasis on the effects of inertial forces within the cavity. Various single-cavity flow paths and cavity-tube combined flow paths are selected as research subjects. Utilizing a validated three-dimensional model based on experimental data, this research performs an in-depth analysis of the fast transient response processes under sudden change boundaries. From the perspective of inertial forces, and considering the relative gas mass changes within the cavity and the variations in the distribution of \(Ma\), this study analyzes and summarizes the mechanisms by which the inlet and outlet areas of the cavity, tube lengths, and cavity shapes affect the evolution of axial loads in the flow paths. The main research conclusions are as follows:  
(1) The variation of \(A/V_{Vessel}\)\({}^{\frac{2}{3}}\) directly affects the range of CIDZ within the cavity, influencing the magnitude of the inertial forces present. During the fast transient response process of the flow path under the sudden change boundary, an increase in \(A/V_{Vessel}\)\({}^{\frac{2}{3}}\) directly amplifies the influence of these inertial forces, leading to oscillations in the axial load response within the cavity, with both the oscillation period and amplitude gradually increasing. Furthermore, due to the influence of the inertial forces, a phase difference arises in the axial force oscillations at different end faces within the cavity, which enhances the oscillation of the axial force difference between the two end faces, thereby complicating the evolution of the axial load in the flow path. (2) For the cavity-tube flow path, changes in \(l_{1}/d\) primarily affect the equivalent CIDZ range and influence the duration of inertial forces within the cavity, while having minimal impact on the magnitude of these forces. When \(l_{1}/d\) falls within different ranges, the tube serves distinct functions in the flow path. Under the conditions established in this study, when \(l_{1}/d\leq 0.25\), the tube acts as an orifice in the flow path, and an increase in \(l_{1}/d\) reduces the impact of CIDZ on CIDZ, thereby diminishing the influence of inertial forces within the cavity. This results in a decrease in the amplitude of axial load oscillations within the cavity while increasing the phase difference in axial force oscillations at both ends, leading to greater discrepancies in axial forces between the two ends. Conversely, when \(0.25<l_{1}/d\), the tube functions as a conduit in the flow path, and an increase in \(l_{1}/d\) directly enlarges the equivalent range of EIDZ, thereby enhancing the influence of inertial forces within the cavity. This leads to an increase in the amplitude of axial load oscillations within the cavity and reduces the phase difference in axial force oscillations at both ends, resulting in smaller discrepancies in axial forces between the two ends. For the cavity-double tube flow path, changes in \(l_{2}/d\) primarily affect the volume of the flow path, reducing the influence of CIDZ on the flow path and consequently decreasing the axial load oscillation process within the cavity. (3) Whether in the cavity-single tube flow path or the cavity-double tube flow path, \(L/D\) primarily influences the phase of the axial load response process while also affecting the magnitude of the inertial forces within the cavity by limiting the axial and radial ranges of CIDZ. When \(L/D\) is small, it mainly restricts the axial range of CIDZ; as \(L/D\) increases, the limitation gradually shifts from the axial range to the radial range. In this study, when \(L/D\leq 0.78\) is present, the axial range of CIDZ is primarily constrained, and the increase in \(L/D\) has a minimal impact on the axial load oscillation process.