Research On Path Designing Of Underwater Vehicles For Subsea Pipeline Inspection

As the exploitation of global land natural gas and oil has gradually entered the middle and late stages,the difficulty of energy exploration and development on the land has increased,and the rich marine resources have increasingly highlighted the huge development potential.Subsea pipelines,as a main means for transporting natural gas and oil resources to land,are susceptible to damage due to the influence of complex and unstable marine environmental factors.They are normally laid in shallow waters with complex submarine topography and environment.Consequently,regular inspections of subsea pipelines have a high socio-economic value.Autonomous Underwater Vehicle(AUV)provides an important technical support for ocean observation and detection,which has the features of continuous and stable operation,high efficiency and low cost.It is usually equipped with acoustic or optical sensors for environmental perception,so as to realize the perception of local environmental targets,path planning and decision-making.Through the fusion of multi-sensor data and supported by built-in computing and processing systems,it is empowered with a variety of functional forms and the ability of understanding and perceiving the environment.The paper studies the processing method of underwater acoustic image,subsea pipeline inspection and dynamic local path planning.Furthermore,a system for subsea pipeline inspection and collision-free tracking was established in the paper.The main research contents of this paper are as follows:1.The architecture of the subsea pipeline inspection and collision-free tracking system was designed,analyzed and constructed the Forward Looking Sonar(FLS)system.According to the degree of abstraction of the data structure in the system,the instruction information transmitted in the subsea pipeline inspection and collision-free tracking system is divided into four parts,including the data collection part,the image processing part,the environmental information fusion part and the decision planning part.2.Due to the refraction by water column,the scattering of sound waves,the uneven seawater quality,or the flowing seawater,patch noise will be introduced.In order to accurately identify and distinguish obstacles and noises,an improved Otsu algorithm based on traditional threshold segmentation algorithms,such as K-means,Otsu,AMF(Adaptive Median Filtering),was proposed in the paper,.The extended echo and background clutter are separated correctly,and the contour of the target image was kept relatively complete.In addition,the paper proposed an obstacle suppression method for a small area,which reduces the complexity of the algorithm.3.Considering that the subsea pipeline may be fund partially buried and bent in the tracking process.Based on the Hough transform,three types of points were selected as key points.Then,the least square method was adopted to realize curve fit of them.The fitting results satisfy the requirements for pipeline tracking accuracy.4.When performing subsea pipeline inspection,the original image of forward-looking sonar contains a lot of false information and noise.Denoising of the image was performed based on the adaptive threshold denoising method of Curvelet transform.Experimental results show that the algorithm can effectively reduce false information and regional interference,and improve the accuracy and real-time performance of pipeline detection and collision-free tracking systems.5.In order to achieve the shortest and smoothest path design for obstacle-free collisions,a path planning algorithm was proposed to achieve real-time update of the AUV’s velocity at the expense of less steering.Finally,the basic principles of the Kalman prediction model was analyzed,and a discrete Kalman filter was designed to estimate the state of linear moving dynamic obstacles,so as to reduce the false alarm rate for obstacles.6.The sea trial experiments show that the proposed algorithms can meet the real-time and continuity requirements for the tracking system,which are also feasible and effective for the tasks of subsea pipeline inspection and collision-free tracking.Consequently,the proposed algorithm is feasible and effective.