Strain and acceleration signals are essential for accurate event recognition along submarine cables. However, concise identification still poses challenges for the prompt recognition and classification of anchor smashing and hooking events with multiple types of sensors and multiple locations. For these reasons, this paper proposes a hybrid model that combines convolutional neural networks-bidirectional long short-term memory (CNN-BiLSTM) and a convolutional block attention module (CBAM) to instantaneously identify and organise anchor smashing and hooking events. Eight different categories of data were selected as data samples and collected from multiple Fiber Bragg Grating (FBG) strain sensors and accelerometers at four different locations. The results demonstrated that the recognition best accuracy of the method could reach 98.95%. This method has a better identification rate than the existing schemes used for the same purposes, confirming the validity and reliability of the proposed hybrid model.

The deformation monitoring of terrain and shallow strata is important to the gas hydrate mining environment and the early warning of seabed instabilities. Due to the complexity of the deep-sea environment and the difficulty of the seabed operation, in-situ and high-precision deformation monitoring of terrain and shallow strata simultaneously are big challenges for existing observation methods. This paper describes the design and experimental research of a terrain and strata deformation monitoring system based on MEMS (Micro-electro mechanical system) sensor network (SN). The SN consists of a horizontal array and a vertical array containing multiple cascaded MEMS accelerometers. The pitch angle and roll angle of the monitoring node can be calculated through the three-axis components of the accelerometer in the gravity field. Then, a reconstruction model of the terrain and strata deformation was proposed based on the rotation matrix and the arc model. To evaluate the monitoring system and validate the reconstruction model, a field experiment was conducted on a tidal flat in Changzhi Island for one week. The deformation of the terrain and strata and the pore water pressure were measured and obtained. The results demonstrate the feasibility of the proposed system.

The buried depth of submarine cables is very important to avoid damage on the cable from dropping and dragging anchors. This study focused on the actual engineering needs of submarine power cable protection and laying construction. In order to investigate the buried depth protection index of submarine cable, physical model tests, theory analysis, and numerical simulations were conducted in this study. The effects of the bottoming velocity, dropping energy, and anchor mass on the anchor penetration depth were analyzed and investigated. The analytical model based on the impact and drag mechanism is presented to analyze the forces and energy on the anchor. The accuracy and reliable of the model test results are verified by the theory analysis and numerical simulation, indicating that the buried depth protection index of the submarine cable in the research area is recommended to be 3 m. The research results can provide guidance for operation of the submarine cable laying machine and submarine cable protection.

The anchoring and hooking of ships, bedrock friction and biological corrosion threaten the safety and stability of submarine cables. A hydraulic jet submarine cable laying machine manages to bury the submarine cables deep into the seabed, and effectively reduces the occurrence of external damage to the submarine cables. This machine uses a hydraulic jet system to realize trenching on the seabed. However, the hydraulic jet submarine cable laying machine has complicated operation and high power consumption with high requirements on the mother ship, and it is not yet the mainstream trenching method. In this paper, a mathematical model for the hydraulic jet nozzle of the submarine cable laying machine is established, and parameters that affect the trenching efficiency are studied. The effects of jet target distance, flow, angle and nozzle spacing on the working efficiency of the burying machine are analyzed by setting up a double-nozzle model. The results of the theory, numerical simulation and experiment show that the operational efficiency of the hydraulic jet submarine cable laying machine can be distinctly improved by setting proper jet conditions and parameters.

The data synchronous acquisition is crucial to the seafloor subsidence monitoring system for gas hydrate mining areas based on microelectromechanical sensors (MEMS). Because the independent and high-precision time reference sources on land cannot be used on the seafloor, especially in the deep sea, a relative time synchronization method based on input/output (I/O) and controller area network (CAN) bus was proposed to realize the internal time synchronization of the system. To demonstrate the feasibility of the proposed method, tests including the deformation test of the MEMS sensor array under high pressure, synchronous accuracy test, and landslide and collapse simulation tests were carried out. The synchronization method was performed once every 24 h, and the time drift was reduced to 0.38 ms from more than 30 ms, demonstrating that method can achieve consistent internal time of the system. The method does not require additional hardware devices and has adjustable accuracy.