Offshore oil and gas resources play a crucial role in supplementing the energy needs of human society. The crisscrossing subsea pipeline network, which serves as vital infrastructure for the storage and transportation of offshore oil and gas, requires regular inspection and maintenance to ensure safe operation and prevent ecological pollution. In-line inspection (ILI) techniques have been widely used in the detection and inspection of potential hazards within the pipeline network. This paper offers an overview of ILI techniques used in subsea pipelines, examining their advantages, limitations, applicable scenarios, and performance. It aims to provide valuable insights for the selection of ILI technologies in engineering and may be beneficial for those involved in pipeline integrity management and planning.

The wave glider is a new concept marine robot that can make use of wave energy to obtain thrust. Differ from the traditional unmanned vehicle, the wave glider consists of the floating body, the connecting tether, and the submerge glider. It can be regarded as a special catamaran structure. Therefore, the conventional kinetic model of the unmanned vehicle are inapplicable to the wave glider. In this paper, we propose a non-linear kinetic model of wave glider of six degrees of freedom based on three reference coordinate frames. The calculating formulas between the vertical liquid velocity and the system advance speed is derived by using the kinetic model. A method to design a glider wing structure under fixed wave speed in vertical direction was also presented. On the basis of the static stress analysis of the Glider wings, we compare different factors influencing the advance speed and optimize them by comparing the simulation results with the calculation results.

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 accurate prediction of vertical deformation (VD) in tidal flat terrains is crucial for their rational development and disaster warning. However, the high-precision and strong robustness prediction method of VD data in tidal flat terrain is still a great challenge due to the complex environmental conditions. In this study, VD data was collected over 7 consecutive days using Micro-Electro-Mechanical system (MEMS) sensor arrays deployed in a tidal flat. Particle swarm optimization (PSO)-optimized variational mode decomposition (VMD) is applied to decompose the acquired VD data for noise removal. The Fast Fourier Transform (FFT) and Spearman correlation coefficient analysis were employed to identify the inducing factors by comparing them with the decomposed VD. Four machine learning algorithms were evaluated to predict the trend and periodic components of VD, and the results showed that long short-term memory neural network (LSTM) outperformed the other three, achieving a root mean square error (RMSE) less than 0.15 and an R-squared ( R ² ) greater than 0.90. The proposed combined PSO-VMD-LSTM model effectively addresses the challenges of feature recognition, noise removal and deformation prediction of vertical deformation data in tidal flat terrains.

Sensor placement plays an important role in terrain deformation monitoring systems and has an essential effect on data collection. The difficulty of sensor placement entails obtaining the most adequate and reliable information with the fewest number of sensors. Most sensor placement schemes are currently based on randomized non-uniform sampling and probability statistics, such as structural modality and optimization methods, which are difficult to directly apply due to the randomness and spatial heterogeneity of terrain deformation. In this study, the placement conditions of two-dimensional non-uniform sampling with equal arc length were deduced for underwater terrain deformation monitoring based on the MEMS accelerometer network. In order to completely reconstruct the underwater terrain, the arc length interval of the sensors should be less than $\frac{1}{2\mathsf{\Omega }}$ ($\mathsf{\Omega }$ is the maximum frequency of the detected terrain). The maximum MRE and maximum RMSE were both less than seven percent in a terrain deformation monitoring experiment and a water tank test. The research results help technicians apply contact sensor arrays for underwater terrain monitoring.

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.