## 4 Results and Analysis
### Technical Theme Content Evolution  
According to the theory of technology life cycle and combining the change in patent applications per year of unmanned ship technology from 2013 to 2022, Figure 8 shows the fitted curve of year and annual patent applications. The development of unmanned ship technology is categorized into the following three phases. * In the embryonic stage (2013-2015), the number of annual patent applications in unmanned ships began to increase, and the annual growth rate increased slowly, indicating that the technology in unmanned ships was gradually developing. * In the rapid development stage (2016-2019), the number of annual patent applications in unmanned ship technology increased rapidly, and the annual growth rate was relatively high, indicating that the technology in unmanned ships was developing rapidly. * In the stable development stage (2020-2022), the annual number of patent applications in the unmanned ship field technology was at a high level, and the annual growth rate was low, indicating that after the rapid development stage of the unmanned ship field technology, unmanned ship technology technology was still evolving. Based on the technology life cycle theory and annual fluctuations in patent applications for unmanned ship technology, we categorize the development of unmanned ship technology into three stages: embryonic, rapid development, and stable development. Table 4 shows the subject content obtained by LDA training on patent data at each stage. In the embryonic stage of technological research in unmanned ships, there are fewer patent applications and fewer technical topics of concern in the first stage. In the rapid development stage of technological research in unmanned ships, the number of patent applications is gradually increasing, and the number of technical topics of concern rises in the second stage. In the steady development stage of technological research in unmanned ships, the number of patent applications and technical topics of concern has gradually stabilized in the third stage. The cosine similarity between technical topics at each stage is calculated using Formula (3). To improve the accuracy of topic association, the similarity threshold T needs to be designed. If the threshold between two topics is less than T, the correlation between the two topics is considered insufficient. This study invalidates the topic association when the similarity is less than 0.3. Figure 8 shows that the correlation between the two technical topics is stronger. The more comprehensive the connection line between each technical topic, the stronger the correlation between the two technical topics. Figure 8: Fitting curve of the number of patents for unmanned ship technology. All technical themes of unmanned ships are related in three stages, showing an evolutionary relationship of division, inheritance, and integration in Figure 9. Each research direction gradually becomes stable and concrete, and the research depth gradually increases. The technical topics of remote control (A-Topic 0, B-Topic 7, C-Topic 7) and hull structure (A-Topic 5, B-Topic 4, C-Topic 6) have always been hot technologies in the field of unmanned ships. Autonomous navigation and attitude control technology topics only exist in the first stage (A-Topic 3, A-Topic 1) and the second stage (B-Topic 12, B-Topic 5). These two technologies are gradually maturing, and their research interest is declining. However, autonomous navigation technology mainly splits positioning technology (C-Topic 12), making the research more detailed. Some technologies are inherited and developed based on previous technologies, such as water quality/water area detection (A-Topic 2, B-Topic 3, C-Topic 9), and surveying and mapping technology (A-Topic 4, B-Topic 14, C-Topic 11).