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, Available online , doi: 10.16516/j.gedi.issn2095-8676.****.**.***
Abstract:
Introduction The topside module of an offshore step-up station usually has numerous tube-I section joints with complicated structure, which cannot be checked by general structural design software. Hence, a feasible checking design method and refinement of stiffener schemes are in need. Method A simplified model based on typical tube-I section joints of the topside module of an offshore step-up station was established, and five stiffener schemes were designed for it. Based on the finite element software simulation method, three typical displacement loading conditions, i.e., axial compression displacement, in-plane rotation, and out-of-plane rotation, were applied to analyze the plastic zone development and failure modes of the five stiffener schemes. For the longitudinal stiffener scheme selected, the effective stress section of the stiffener was assumed based on existing codes, and a simplified calculation method for stiffener stress check under complicated loads was proposed. The results were examined using the finite element method. Result The results show that the unstiffened tube-I section joint cannot satisfy the design principle of ‘strong joint and weak member’, and it is necessary to take stiffening measures such as stiffeners. The longitudinal stiffener scheme performs better in terms of bearing capacity and economical efficiency. Longitudinal stiffeners are essential for the shearing capacity of beam webs, while the transverse stiffeners cannot enhance shearing capacity. Finite element analysis indicates that the stress distribution is consistent with the assumption of the simplified calculation method, and the simplified calculation method predicts higher stress levels than the finite element results, which means the proposed simplified calculation method is feasible and safer. Conclusion The longitudinal stiffener scheme is a better stiffening scheme for the joint. The proposed simplified calculation method can be adopted to check the longitudinal stiffener scheme efficiently.
, Available online
Abstract:
Introduction At present in China, the ships near offshore wind power platforms are mainly monitored by means of the ship AIS system and remote cameras. Such means lacking information technology often require a lot of manpower and material resources. In order to effectively warn the ships near the offshore wind power platform, this paper analyzes the urgent problems to be solved that are encountered in the current offshore ship identification, and proposes an offshore ship fusion recognition algorithm that combines the improved Faster-RCNN network and ship AIS system. Method First, improvement suggestions were proposed for three aspects of the Fast-RCNN model, and the structures such as the backbone network and the loss function were adjusted. Second, the ships in the pictures taken by the remote cameras were detected by the improved Faster-RCNN network, and the results were supplemented and corrected in combination with the relevant information from the ship AIS system. Finally, the verification sets were tested according to the optimal model saved in the model training process, and each model was evaluated using the indicators of precision, recall and average precision (AP). Result The Faster-RCNN model inference speed and accuracy for different feature extraction networks and classification loss functions are improved greatly. The ability of offshore wind power platforms to monitor ships is improved. The offshore ship information was processed and the navigation trajectory was obtained in combination with the ship AIS system, realizing the detection of the ships in the pictures taken by the remote cameras. Conclusion Experiments show that the feature extraction network and the replacement of the classification loss function of the traditional Faster-RCNN can effectively improve the detection accuracy of the network in the ship recognition task, and the ship trajectory can be effectively obtained by integrating the ship AIS system.
, Available online
Abstract:
Introduction With the steady progress of the carbon peaking and carbon neutrality goals, more and more distributed renewable energy is connected to the power grid. Among them, in economically developed coastal areas with heavy power load, vigorously developing offshore wind power has become a hot field of wide concern for scholars at home and abroad. However, the inherent intermittency of wind power generation, especially when the offshore wind farm is actively disconnected from the main grid during typhoons, can adversely affect the receiving-end grid. Method In order to realize the friendly access of offshore wind power during typhoon, considering the advantages of hydrogen energy storage such as high storage efficiency, low emission and wide application, this paper proposed a collaborative control method between offshore wind farm and hydrogen management system (HMS). On the one hand, during the period of typhoon approaching, this method could maximize the use of wind energy for power generation under normal operation. On the other hand, when the typhoon passed through and the offshore wind farm was gradually disconnected from the grid, the hydrogen energy system released electric energy to alleviate the active power drop of the wind farm and solve the problems such as the ramp rate in the operation of the traditional wind turbine generator systems, so as to reduce its adverse impact on the receiving-end grid and effectively smooth the volatility of the offshore wind power output. This paper firstly introduced the physical modeling method and control model of offshore wind farm and hydrogen energy system in detail, and explained the collaborative control strategy between them according to the typhoon period. Result Finally, simulation results show that the proposed method enables the offshore wind farms to be more flexible and friendly to meet the grid-connected operation during typhoons. In addition, the hydrogen energy storage system can maximize the use of wind energy for power generation under normal operation, Conclusion and control the hydrogen energy system to release electric energy during typhoons to solve the problems such as the ramp rate of the traditional wind turbine generator systems, so as to reduce its adverse impact on the receiving-end grid.
, Available online
Abstract:
Introduction This work aims to select the optimal wind-measurement instrument to satisfy observational requirements of Airborne Wind Energy System (AWES). Method Observation campaign between wind lidar and wind profiler radar was carried out on an AWES demonstration project location. Data acquisition rate, vertical profile characteristics and temporal variation characteristics of both instruments were compared and analyzed. Result The results show that the data acquisition rate of wind lidar decreases to less than 0.4 with altitude rising to 3 km, while the wind profiler radar can maintain above 0.98, revealing better observational adaptability. The vertical profiles of wind speed and direction, as well as the day-by-day and multi-day fluctuation characteristics are consistent in both instruments and can be verified by the reanalysis data and the contemporaneous radiosonde data of high-altitude meteorological stations. Statistical indicators like median, extreme deviation and standard deviation of the wind lidar observations are closer to and better correlated with the reanalysis data, while extreme deviation and standard deviation of the wind profiler radar observations are larger overall. Therefore, the wind-measurement accuracy of wind profiler radar is not as good as that of wind lidar. Conclusion This work suggests that wind-measurement instrument should be reasonably selected and wind measurement schemes should be scientifically set up at different stages of AWES power plant project according to the climatic conditions of the project location.
