3.1. General Situation
To understand a research field, it is necessary to break down and analyze the overall situation, such as the publication time, number of publications, and publication trends, to help researchers quickly grasp the research trends in this field and pave the way for a further, in-depth understanding in stages.
3.1.1. Overall Number of Publications
The publication-trend chart was drawn based on the number of sample studies that was found in the CNKI database and WOS database (
Figure 1). As shown in
Figure 1, the domestic literature on wave-energy policy began to be published in 1992, earlier than the international literature on wave-energy policy, which was published starting in 1996. From the post and on the basis of an analysis of the annual average number, looking at the total domestic output over nearly 30 years, the total number of published studies equaled 35, with an annual average of 1.17. Over 26 years, the international community published 667 papers, with an annual average of 25.65. Both at home and abroad, the annual total that was identified presents an obvious gap, indicating that Chinese scholars lack interest in wave-energy policy research. The emphasis on wave-energy policy research is not enough, and this could also indicate that the wave-energy policy-system construction is not complete. An analysis from the perspective of the overall trends shows that the wave-energy policy research at home and abroad started at the end of last century. In 2004, it attracted more attention from scholars, with the international number presenting an obvious growth trend, with a faster research and development speed than the domestic total. There is still great room for improvement in the research on wave-energy policy in China.
3.1.2. Information about the Author and the Institution
To conduct in-depth research in a research field, one should first pay attention to the academic achievements of the core authors. According to Price’s law, the number of core authors can be calculated using the following formula [
32].
MP represents the minimum number of published papers by the core authors, and NPmax represents the cumulative number of published papers by the authors with the most papers within the research period. If a stable core group of authors accounts for 50% of the total number of papers, it can be considered that a core group of authors was formed in this field. The degree of cooperation between the authors of academic research is also an important index by which to judge the progress of academic research. A single author’s research ability is limited, so he cannot cover all branches of the discipline, and a good scientific-research-cooperation relationship is conducive to the maturity of the discipline system.
In China, Citespace is used to visually analyze authors. From the perspective of core authors, it was found that Wang J published the most documents, with a total of four papers. According to the calculation formula, the MP value is 1.5; that is, for two or more papers, an author can be regarded as the core author in the field of wave-energy policy research in China (as shown in
Table 1). According to the search for “Wang J” and “Ma CL” on CNKI, the key author Wang J focuses on the development, utilization, and industrialization of marine energy. Ma CL, the core author, focuses on technical fields such as ocean-energy generation and wave-energy development and utilization. From the perspective of author cooperation, the density value of the atlas of co-authors of domestic wave-energy policy research is 0.0399, which is lower than the normal level of 0.1. In the atlas (
Figure 2), the connection is short and the density is low. Wang J, Ma CL, and Wang HF of the National Oceanographic Technology Center of the State Oceanic Administration are the leaders of wave-energy policy research. However, the authors of the overall wave-energy policy research did not form a close academic-cooperation group, which reflects that wave-energy policy researchers are relatively independent.
As shown in
Figure 3, the number of nodes of domestic cooperative institutions is N = 33, the number of connections is E = 17, and the network density is D = 0.0322, indicating that only 32 domestic institutions have published articles on wave-energy policy in domestic journals, and the links between the institutions are not close. Looking at the number of published institutions (see
Table 2), there is a significant gap in the number of published institutions, and the research institutions focusing on wave-energy policy are mainly concentrated in marine-research centers at the national level. Among them, the National Oceanographic Technology Research Center published 10 papers and the National Oceanographic Information Research Center published 3 papers, accounting for 37% of the total number of published papers in China. These two institutions are the backbone of wave-energy policy research.
Based on comprehensive
Figure 4 and
Figure 5, high-level wave-energy policy research is lacking and the scientific research cooperation is low. A sufficient amount of attention to this issue is required to strengthen the cooperation of wave-energy policy research exchanges, share and synchronize resources and achievements, and increase the level of wave-energy policy research in our country as soon as possible.
Internationally, Liu Y is the scholar with the largest number of published literature on wave-energy policy in WOS. According to the calculation formula, the MP value is 1.83, which means that for two or more published papers, Yang can be regarded as the core author in the field of international wave-energy policy research. There are 73 core authors in the field of international policy and environmental studies. In terms of the number of articles published by institutions, Australian Natl Univ published the most papers—10—followed by the Chinese Academy of Sciences and Tsinghua University with eight papers, whereas Heriot Watt Univ, Univ Edinburgh, and Univ Exeter published seven papers each. The overall publication volume of influential international institutions is much higher than that of domestic institutions.
Citespace was used to create a visual analysis of international authors and institutions. As shown in
Figure 4, the density of the map of co-authors of foreign wave-energy policy research is 0.0052 (<0.1), but the authors Liu Y, Dalton G, Wang Y, Liu X, and Wang Z obviously formed a cooperative network, which is conducive to resource-sharing and discipline integration, and promotes the deep integration of wave-energy policy research.
Figure 5 shows the cooperation network of international research institutions. The number of nodes is N = 394, the connection is E = 413, the network density is D = 0.0053, and cooperation between institutions is not obvious. Australian Natl Univ, which has the largest growth rings, published the most papers and is surrounded by a dense network of connections, suggesting that the organization formed a circle of collaboration on wave-energy policy.
By comparing the number of publications published by CNKI and WOS institutions, the number of publications published by Chinese Academy of Sciences and Tsinghua University ranks second and third among WOS institutions, but no literature from these institutions can be found in the domestic CNKI database. This also indicates that Chinese wave-energy policy has not had a large-scale impact on domestic academic journals, and the next step should be to guide institutions that contribute to wave-energy policy to strengthen domestic academic cooperation.
3.3. Research Context
To further analyze the evolution of each keyword, the time graph generated by Citespace was used to describe the duration and development trend of hot topics in the field of wave-energy policy research. The horizontal axis represents the time axis, the right vertical column represents keyword clustering under the LLR algorithm, each node in the horizontal axis represents a research topic, the number of node circles is proportional to the frequency of the occurrence of corresponding keywords, and the lines between nodes represent the connection between different keywords.
In the keyword-evolution graph of the CNKI database, N = 103, E = 249, Q = 0.7269 > 0.5, and S = 0.9269 > 0.7; in the keyword-evolution graph of the WOS core-set database, N = 503, E = 1662, Q = 0.6.83 > 0.5, and S = 0.7014 > 0.7. The timeline division structure is, therefore, reasonable.
In the CNKI database, as shown in
Figure 12, the nodes on the horizontal-axis timeline show two characteristics: first, there are more node circles in the early stage and fewer node circles in the late stage; second, the distribution of nodes in the early stage is scattered and the distribution of nodes in the late stage is concentrated, indicating that the overall research trend in wave-energy policy changed from comprehensive to refined. In the figure, only nodes with the keywords “marine energy” and “renewable energy” are obvious, whereas the other nodes are not prominent, indicating that domestic wave-energy policy-research hotspots are not prominent, policy guidance is insufficient, and the policy coverage is not complete [
50]. From the perspective of the timeline evolution of the theme word “#0 ‘ocean energy',” combined with our country’s wave-energy policy-development practice, the wave-energy policy in our country underwent an initial research-development stage, a policy-linkage stage of multi-organizations, and the construction stage of the policy system. The wave-energy policies of our country are constantly being explored to promote the development of our country’s wave-energy industry and gradually increase the level of ocean-energy technology through policy guidance. With the support of relevant policies, the development and utilization of wave energy has entered a rapid development period [
40].
Figure 13 shows that foreign wave-energy policy research can be roughly divided into three stages. The first stage is the preliminary exploration stage, from approximately 1996 to 2004. In this research stage, the number of nodes is small, but the nodes are prominent. Taking the node “renewable energy” in cluster #2 and “impact” in cluster #7 as symbols, the research focus of this stage should be the initial exploration of wave energy as renewable energy and the background of policy generation. The second stage is the substantial progress stage, from approximately 2005 to 2012. In this research stage, the number of nodes increases, and important nodes are prominent. “Wave energy” in cluster #2, “system” in cluster #3, “policy” in cluster #4, “climate change” in cluster #5, “model” in cluster #6, “management” in cluster #7, and “energy” in cluster #8 are hotspots. These hotspots are closely connected with each other, indicating that international scholars carried out a series of studies on these hot topics. The third stage is the comprehensive deepening stage, from approximately 2013 to 2022. In this research stage, the number of nodes surges, mainly focused on the time axis of cluster #0, cluster #1, cluster #2, cluster #3, and cluster #4. Based on the breakthrough in wave-energy technology, the research in this stage focuses on resource integration, resource allocation, energy capture, energy consumption, and other aspects to promote the comprehensive construction of a wave-energy policy system [
51]. For further analysis, the largest cluster #0, “energy harvesting” (
Figure 14), and the longest timeline cluster #2, “wave-energy harvesting” (
Figure 15), were included. Cluster #0, “energy harvesting,” appeared for the first time in 2013, and important nodes include “optimization” (37, 2013), “energy harvesting” (19, 2016), “resource allocation” (16, 2018), and “resource management” (14, 2020). The number on the left of the brackets represents the cumulative occurrence times of keywords, and the year on the right represents the year of keyword emergence. By extracting the annual distribution map of keywords, important keywords in cluster #0 are shown to be on the rise, showing the key field for future research. Cluster #2, “wave energy,” appeared for the first time in 1996, and the keyword “renewable energy” was used in the initial research, indicating that foreign wave-energy policy-system frameworks take renewable energy as the starting point, and important nodes include “renewable energy” (74, 1996), “wave energy” (50, 2009), and “performance” (25, 2015). This clustering research has lasted for more than 20 years. The annual distribution map of keywords shows that the keywords “renewable energy” and “performance” show a downward trend, whereas “wave energy” shows a slight upward trend, indicating that wave-energy policy research will remain a hot topic in the future.
In this paper, the literature on wave-energy policy in the CNKI database and the WOS core collection was visualized and analyzed by Citespace. From the perspective of literature publication, policy hotspots, and policy-development context, it can be seen that the overall quantity and quality of wave-energy policy research are on the rise. However, there is still a significant difference between domestic and foreign development speed. Compared with domestic wave-energy policy research, foreign countries have shown a certain cooperation network and domestic and foreign research hotspots have a certain convergence, but the domestic hotspot scope is relatively narrow and there is still room for expansion. Therefore, this study needs to further analyze the textual content of domestic wave-energy policies, explore the policy orientation at the national level, form an interactive effect from policy implementation and theoretical research, and effectively solve the practical problems in the development and utilization of wave energy.