Study on an indirect measurement method for near-field shock waves in underwater explosions based on the principle of a constant cross section shock tube

To address the technical challenge of directly measuring near-field shock waves from large-yield underwater explosions, this paper proposes an indirect measurement and inversion method based on the principle of one-dimensional controllable attenuation of shock waves inside a constant cross section shock tube. At the theoretical level, a theoretical model for the one-dimensional attenuation of shock waves inside a constant cross section tube was established based on the method of characteristics. On this basis, an explicit inversion algorithm was derived to calculate the original shock wave parameters at the tube inlet from the attenuated shock wave parameters measured inside the tube, providing a theoretical basis for data inversion. Proof-of-principle experiments were conducted to verify the effectiveness of the method. Results show that the proposed measurement structure can convert the near-field shock wave with high amplitude and short pulse width captured at the tube inlet into a measurable signal with lower amplitude and longer pulse width, thereby significantly reducing the requirements for sensor measurement range and shock resistance. The inversion results based on the method of characteristics agree well with reference values, confirming the reliability of the theoretical inversion method. Furthermore, to address the susceptibility of free-field shock wave measurements to boundary-reflected wave interference in high-pressure enclosed environments, the feasibility of achieving decoupled measurement of the direct wave by exploiting the multiple reflection effect of the tube wall in the proposed measurement structure is discussed. This study provides a feasible technical pathway for reliably measuring near-field shock waves from large-yield underwater explosions.