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Abstract The transportation of hydrogen is a weak link in the large‐scale development of the hydrogen energy industry. Injecting hydrogen into the natural gas pipeline network for transportation is an efficient way to achieve the large‐scale, long‐distance, and low‐cost transportation of hydrogen. Hydrogen can lead to hydrogen embrittlement in natural gas pipelines and cause safety incidents if hydrogen and natural gas are not mixed uniformly. Therefore, it is necessary to study the blending process and blending uniformity of hydrogen and natural gas. In this study, a three‐dimensional model of the hydrogen‐injected natural gas pipeline was constructed. The effects of hydrogen injection inlet and turbulator configuration on the mixing process of hydrogen and natural gas were investigated using a computational fluid dynamics approach. The results show that increasing the number of hydrogen injection inlets shortens the distance L98% of uniform mixing of hydrogen and natural gas. Increasing the radial distance r from the initial hydrogen mixing positions to the center of the pipeline will shorten the distance for uniform gas mixing in the pipeline. The addition of turbulator configurations in the pipeline significantly reduces the distance to uniform gas mixing. Changing the distance Lturb from the turbulator to the initial mixing position further shortens the distance between hydrogen and natural gas mixing uniformly. The results of this study provide a reference for the structural design of the hydrogen–natural gas mixing pipeline and the gas distribution state during the mixing process.

Hydrogen-blended natural gas transportation can effectively solve the problem of wind and photovoltaic energy curtailment and reduction of greenhouse gas emission, and realize the low-cost transportation of hydrogen in large scale, so it becomes an important way to achieve the "double carbon" goal. However, the risk of hydrogen embrittlement will be brought by blending hydrogen to the existing natural gas pipeline system and relevant transportation facilities. Therefore, the mechanism of hydrogen embrittlement was analyzed based on the structural composition of hydrogen-blended natural gas transportation system. Meanwhile, investigation was performed for the hydrogen embrittlement of the pipelines, welds, valves, compression devices, storage units and terminals of the hydrogen-blended natural gas transportation system. On this basis, countermeasures for prevention of hydrogen embrittlement were put forward. Then, the prospect and development of hydrogen-blended natural gas transportation system were forecast. Generally, the research results could provide reference for the large-scale and market-oriented development of hydrogen-blended natural gas transportation in China, and the improvement of research and development of pipeline hydrogen transportation technology and equipment, further accelerating the safe development of hydrogen economy.

Geosynchronous orbit satellite is usually the first early warning equipment to catch ballistic missile launches in actual combat. However, the detection information it provides is lack of dimension, which makes the traditional target guidance method hard to be directly applied on the target guidance for low-orbit satellite. Aiming at this point, this paper studies the target guidance method for low-orbit satellite by geosynchronous orbit satellite. First, based on the altitude constraint of infrared radiation during the launch and active flight of the ballistic missile, the azimuth and pitch detection ranges of the infrared sensor of the low-orbit satellite are calculated with the guidance of one geosynchronous orbit satellite. Then, the detection distance of the infrared sensor of the low-orbit satellite is modeled and calculated, which leads to a successful target detection for the low-orbit satellite. Finally, the effectiveness and accuracy of this method are verified through a numerical simulation experiment.