The acoustic signals of the drill pipe of a seafloor drill present weak features under noise interference such as marine environmental noise and the mechanical vibration of the seafloor drill. Accurately extracting the features of the weak acoustic signals of a drill pipe under a strong background noise is an effective means of realizing wireless acoustic communication for a seafloor drill. However, the existing short-time Fourier transform and wavelet transform methods have the defects of fixed window length, wavelet basis function, and decomposition layers, which lead to the inability to accurately extract the weak acoustic signal features of a drill pipe. To overcome these challenges, this study investigates the application of S-transform (ST) in the weak acoustic signal feature extraction of a seafloor drill pipe based on its fundamental principles. Firstly, a time-frequency analysis of the drill pipe’s acoustic signal using ST is conducted, which yields the distribution of the signal across the time and frequency axes. Secondly, singular value decomposition (SVD) is applied to mitigate the noise within the time-frequency matrix. Finally, the noise-reduced time-frequency matrix is analyzed to extract the subtle features of the acoustic wave present within the signal. In order to more accurately assess the differences between the different time-frequency analysis methods in the extraction of weak acoustic wave signals, short-time Fourier transform, wavelet transform, and ST are used to extract the weak acoustic wave characteristics of the drill pipe, respectively. The results show that the ST-based method can effectively improve the accuracy of weak acoustic wave signal feature extraction and provide strong support for reliable transmission of cone penetration test data from the seafloor drill.

This study investigates the impact of expanding and reducing deformation ratios on the performance of L360 straight-seam welded pipes formed by the JCO process for offshore oil and gas transportation. The Split Hopkinson Pressure Bar (SHPB) experimental technique was used to examine the stress/strain relationships, yield strength, and compressive strength of the pipe materials subjected to high strain rates. The results indicated that the impact performance of the pipes significantly improves with both expansion and reduction processes, demonstrating an enhancement effect of deformation. The impact of yield strength and compressive strength increases with higher expansion ratios, reaching maximum values of 1009 MPa and 847 MPa, respectively, at an expansion ratio of 1.2%. At a reduction ratio of 0.8%, the impact yield strength increased by 64% and the compressive strength by 14%. These findings not only provide theoretical support for optimizing the expansion and reduction processes and their associated equipment but also have direct and significant practical implications for enhancing the performance and safety of offshore oil and gas transmission pipelines, thereby contributing to the advancement of the field.

In cone penetration test (CPT) based on submarine drilling rigs, encountering harder soil layers requires drill-bit rotation. During this process, the flow noise generated by seawater flushing the drill bit propagates along the drill pipe with the detection signal, leading to signal distortion. To improve the accuracy of the received signal and mitigate the impact of flow noise on CPT results, numerical simulation software (Fluent 18.0) was employed to investigate the flow-noise characteristics within the drill-bit borehole during seawater flushing. The effects of key parameters on flow noise are analyzed, and structural optimization to reduce flow noise is conducted. The findings reveal that the noise in the drill-bit flow channel increases as the inlet flow velocity increases. When the flow velocity increases from 10 to 20 m/s, the maximum noise value increases by nearly 30 dB. Similarly, as the rotational speed of the drill pipe increases from 500 to 1500 rpm, the maximum noise value increases three-fold. Furthermore, increasing the inclination angle of the guide hole appropriately reduces the fluid noise in the drill-bit flow channel. For instance, increasing the inclination angle from 0 to 30° reduces the maximum noise by 18.75%. It is important to note that under different flow velocities and rotational speeds, the flow noise is primarily concentrated in the low-frequency band. These results offer valuable insights for the low-noise flow-field optimization design and have significant implications for enhancing the accuracy of wireless acoustic CPT signal reception.

To address the inherent limitations of traditional resonant underwater sound sources—specifically their excessive size and the sharp decline in sound pressure level (SPL) at frequencies below resonance—a blade-type extremely low frequency (<30 Hz) underwater sound source system was developed. The structure of the system and the principles of its coupled rotational and oscillatory motions are elucidated. The kinematic equations of the blade oscillation driven by a combined crank-connecting rod-slider-connecting rod-rocker mechanism are established, and the effects of the impeller rotational speed and the blade oscillation speed on the SPL are analytically evaluated. The prototype was tested in both air and underwater environments. The experimental results show that the blade-type sound source can emit acoustic waves of extremely low frequency ranging from 2 Hz to 7 Hz, with the fundamental frequency of the acoustic waves perfectly aligned with the blade oscillation frequency. Increasing rotational speed more strongly affects the SPL of harmonics, while changing the oscillation frequency has a greater effect on the fundamental. Notably, a steady increase in the SPL in this paper is maintained even when the oscillation-to-rotation frequency ratio exceeds 2, while the existing blade sound source gradually decreases when the ratio exceeds 1/2. With blade dimensions as small as 13 cm in length and 9 cm in width, the SPL at 10 Hz reaches 131.77 dB (re 1 μPa), highlighting its potential for high-performance acoustic radiation applications at an extremely low frequency.