《1 Engineering research fronts》

1 Engineering research fronts

《1.1 Trends in top 10 engineering research fronts》

1.1 Trends in top 10 engineering research fronts

The top 10 engineering research fronts in the field of civil, hydraulic, and architectural engineering are summarized in Table 1.1.1. These fronts cover a variety of disciplines, including structural engineering, construction materials, transportation engineering, architecture, HVAC, municipal engineering, surveying and mapping engineering, and hydraulic engineering. The following research fronts were recommended by experts: “smart city and smart basin integrated sensing based on geospatiotemporal big data,” “coupling response mechanisms of offshore engineering structures and seabed foundation systems under the action of wind, waves, currents, and earthquakes,” “urban spatial analysis and optimization methods based on big data,” “ventilation theory for adaptive thermal comfort and indoor air quality,” and “multiscale prediction of dynamic hazard evolution for underground engineering.” The five remaining fronts were identified using the co-citation clustering method applied to the top 10% of highly cited papers, and they were confirmed by experts. Table 1.1.2 presents annual statistical data on the core papers published between 2014 and 2019 that are relevant to these top 10 research fronts.

(1)  Smart city and smart basin integrated sensing based on geospatiotemporal big data

Integrated sensing is an important foundation for the realization of smart cities and smart basins. In smart cities and smart basins, ubiquitous smart sensors achieve the comprehensive perception of physical cities and physical watersheds and detect the core system of urban operations and watershed management in real time, thereby seamlessly connecting digital cities and digital watersheds with physical cities and physical watersheds. The real- time geospatiotemporal big data are then used to provide users with intelligent services. Developing trends in this research front include: 1) construction methods for the

《Table 1.1.1》

Table 1.1.1 Top 10 engineering research fronts in civil, hydraulic, and architectural engineering

《Table 1.1.2》

Table 1.1.2 Annual number of core papers published for the top 10 engineering research fronts in civil, hydraulic, and architectural engineering

integrated sensing infrastructure systems of smart cities and smart basins to realize the large-scale interconnection of monitoring resources and the coordination of multi-source heterogeneous sensing resources; 2) city and basin sensing methods based on integrated sensing infrastructure; and 3) integrated management and real-time analysis methods for the geographic spatial-temporal big data of smart cities and smart basins. Between 2014 and 2019, 36 core papers relevant to this research front were published. These papers received 924 citations, with an average of 25.67 citations per paper.

(2)  Coupling response mechanisms of offshore engineering structures and seabed foundation systems under the action of wind, waves, currents, and earthquakes

Offshore engineering structures such as harbor wharfs, breakwaters, oil production platforms, submarine pipelines, sea-crossing bridges and tunnels, and offshore wind power foundations confront severe operating environments and high safety risks. Under the action of winds, waves, currents, and earthquakes, the pore water pressure increases, and the effective stress decreases in the foundation of the seabed, which can lead to the strength-weakening and liquefaction of the seabed soil. At the same time, the action of waves and currents can scour the seabed foundation. Moreover, structural movements under the action of dynamic loads can also cause changes in the pore water pressure and effective stress in the seabed soil, complicating the bearing capacity of the seabed foundation. The coupling response mechanisms of offshore engineering structures and seabed foundation systems under the action of wind, waves, currents, and earthquakes are thus a key issue for the safety and durability of offshore engineering structures. The main problems to be solved include the following: 1) the mechanism and evolution law of the strength-weakening and liquefaction of different seabed foundations (gravel, sand, soft clay, etc.) under the action of different periodic cyclic loads such as waves, earthquakes, and structural motion; 2) elastoplastic constitutive models that consider the processes of strength- weakening, liquefaction, and excess pore pressure dissipation and consolidation after the liquefaction and re-liquefaction of seabed soil under the action of cyclic loads; 3) scouring models of different seabed foundations that account for seepage effects under the action of waves and currents; 3)  coupled numerical models and efficient and reliable numerical simulation methods for the nonlinear dynamic analysis of cyclic load–marine structure–seabed foundation systems; and 5) basic theory and experimental technology for physical model tests to investigate the bearing capacity of cyclic load–marine structure–seabed foundation systems. Between 2014 and 2019, 40 core papers relevant to this research front were published. These papers received 1271 citations, with an average of 31.78 citations per paper.

(3)  Urban spatial analysis and optimization methods based on big data

With the development of Internet technologies, the paradigm of urban spatial analysis is being transformed by the emergence of new big data that are geo-referenced, such as cell phone data, public transport tap-in/out data, and social media check-ins. The advantages of this type of data include its large size, fine resolution, and wide coverage. These data record various human behaviors across time and space with a new level of precision, thereby forming new pipelines for us to observe, perceive, and interpret cities and their transformation. Spatial analysis and optimization based on urban big data are frontiers in urban studies and practices. The institutes leading the relevant research are located in the West in developed countries or districts, such as the United States, the United Kingdom, and the European Union, and in rapidly developing countries and areas, such as China. Developed countries typically maintain more comprehensive research systems and networks with the solid establishment of theory, methods, and applications, whereas rapidly developing countries, particularly China, are notable for the large size of their urban big data, which is attributable to their large populations, optimism toward new technologies, and good software and hardware facilities. Between 2014 and 2019, 58 core papers relevant to this research front were published, and these papers received 2461 citations, with an average of 42.43 citations per paper.

(4)  Ventilation theory for adaptive thermal comfort and indoor air quality

The concept of ventilation theory for adaptive thermal comfort and indoor air quality refers to the idea that when a person is in a naturally ventilated environment, the thermal acceptability of his or her body increases due to its thermal adaptation. Because natural ventilation can provide better indoor air quality, a balance can be achieved between energy conservation and comfort. The main research directions in this front include: 1) the physiological and psychological mechanisms of human thermal adaptability in building environments; 2) effects and prediction models for thermal comfort caused by exposure experiences and thermal adaptation; 3) indoor air quality assessments in naturally ventilated environments and passive building environments; and 4) design methods for naturally ventilated environments and passive building environments. This research front has maintained a high level of activity in recent years. Extensive field surveys have been conducted in various climate zones worldwide, enriching adaptive thermal comfort theory and improving the prediction accuracy of human thermal comfort in naturally ventilated buildings. Natural ventilation, artificial airflow, and personalized comfort equipment have been used to replace traditional air conditioning and heating equipment in specific seasons and spaces in order to reduce the dependence of buildings on traditional energy and to integrate human development with nature. Between 2014 and 2019, 544 core papers relevant to this research front were published, and these papers received 16 740 citations, with an average of 30.77 citations per paper.

(5)   Multiscale prediction of dynamic hazard evolution for underground engineering

At present, the construction of underground structures is developing rapidly. Many of these structures are large in scale and may encounter complex geological environments as well as hazard threats induced by strong earthquakes, active fault zones, and seismic liquefaction. Such threats pose a serious challenge to the science and technology of disaster prevention and mitigation in geotechnical and underground engineering. The multiscale prediction of dynamic hazard evolution for underground engineering is based on a combination of interdisciplinary subjects, including geotechnical earthquake engineering, structural dynamics, and multiscale science, and on the construction of multiscale dynamic analysis models that cover the macro- and meso-space scales and time effect scales. The aim is to reveal not only the integral dynamic response characteristics of underground structures at the macro-scale but also the dynamic damage mechanisms of critical joints at the meso- scale when subjected to strong earthquakes. The ultimate goal is to realize the multiscale prediction of the entire process of dynamic hazard evolution for underground engineering under high seismic intensity and adverse site conditions and thus to provide a scientific basis and technical support to improve disaster prevention and mitigation for underground structures. The main research directions in this front include: longitudinal seismic design theory for long and large tunnels, multiscale analysis methods for massive nonlinear seismic responses in underground structures, physical experimental simulations of the effects of strong earthquakes and non-uniform seismic spatial variations, dynamic response analysis of complex underground structures with sharp stiffness transitions, and dynamic hazard simulations for underground engineering in adverse sites, such as liquefaction sites and active fault zones. Trends suggest that future developments will include: the damage mechanisms of underground engineering under strong earthquakes and design countermeasures, seismic mitigation technologies and structural measures for underground structures, and rational and unified performance-based concepts for the seismic design of underground structures. Furthermore, optimizing the combination of seismic countermeasures and mitigation measures and adapting them to the seismic response characteristics of underground engineering under complex and adverse geological conditions remains one of the most challenging and urgent problems in this front. Between 2014 and 2019, 93 core papers relevant to this research front were published, and these papers received 2297 citations, with an average of 24.70 citations per paper.

(6)  Nano-engineered concrete materials in civil engineering

The need for concrete materials that meet increasingly strict requirements is being expressed in modern civil engineering; however, traditional single- or multi-performance impr- ovements at the macro-scale can barely meet this need. Multi- scale micro-nano-structure regulation and function upgrades are one of the feasible ways to improve the performance of concrete materials for modern civil engineering. Nanomaterials enable the nano-optimization of cementing gels to regulate the micro-nano-structure of concrete materials. Chemical coordination and hybridization with cement-based materials can be realized by doping organic functional groups. Moreover, nonreactive nanoparticles can regulate the early hydration progress of cement to refine its molecular structure, while some nanoparticles with reactive surface properties can be used as strong nano-bridges to coordinate and complex with cementing gels. The nano-regulation and optimization of cementing gels can significantly improve the toughness and durability of concrete materials with very low dosages. Moreover, introducing nanomaterials can provide traditional concrete materials with new functions for performance optimization. Through doping or surface infiltration, some nanomaterials can equip concrete materials with electrical conductivity and self- cleaning abilities. Piezoelectric nanoparticles can introduce intelligent perception to concrete materials, while physicoch- emical self-healing can be initiated by nano-functionalized healants in concrete materials. Nanomaterial-based functional improvements in concrete materials can thus meet the integrated structural and functional requirements of modern civil engineering. Theoretical analysis and numerical simulation are critical to achieving designable nano-engineered concrete materials. Nanomaterial- based optimization strategies for concrete materials can be established through computational chemistry at the nano-scale. Big data-based modeling can contribute to the elaboration of the effects of nanoparticles on concrete materials. In this way, the top-level design and rational doping theory of high-performance and multifunctional nano- engineered concrete can be achieved. Theoretical analysis, numerical simulation, and nano-dispersion technologies should be combined in order to realize nano-regulation, nano- functionalization, and nano-design in concrete. Between 2014 and 2019, 74 core papers relevant to this research front were published, and these papers received 3995 citations, with an average of 53.99 citations per paper.

(7) Urban planning and design to reduce the urban heat island effect

In urban development, the temperature of the urban surface and canopy is higher than that of nearby rural areas. This phenomenon is called the urban heat island effect. The heat island effect is influenced by many factors including the urban morphology, land surface, air pollution, and anthropogenic heat. In the context of global climate change, the heat island effect further exacerbates abnormal weather phenomena, such as heat waves, and health risks to urban populations such as respiratory distress and heat stroke, resulting in adverse effects on urban climate and human comfort. Research on health-and-comfort oriented urban planning and design has been emphasized in international academic papers. The research on urban heat islands and microclimates involves the research fields of architecture, urban planning, and landscapes. The main technical measures are usually categorized as meso-scale or micro-scale. At the meso-scale are urban wind corridor planning analyses based on land use and development intensity, quantitative studies of the heat island effect based on high-resolution remote sensing technology, and green space ecological planning to mitigate the urban heat island using geographic information systems. At the micro-scale are the application of computational fluid dynamic technology for wind and heat simulation to optimize urban space planning and architectural design research and park or green space and urban street tree landscape designs to improve human comfort and mitigate heat risks. The urban block grid fineness method is a key technology for addressing the resolution reduction of the meso- and micro- scales. Other measures applied to urban heat islands include urban climate strategies, the innovation of sustainable urban developments, urban morphology, green design for heat risk management, and the prediction of the impact of urban development intensity on pollution diffusion and the energy consumption of urban agglomerations. Between 2014 and 2019, 188 core papers relevant to this research front were published, and these papers received 6975 citations, with an average of 37.10 citations per paper.

(8)   Performance evolution and durability design principles for materials and structures on highways and for track engineering

Pavement material and structures are damaged by repetitive traffic loads and cyclic environmental disincentives and then deteriorate gradually over their in-service life. The concepts of behavioral evolution and durability-based design principles for pavement materials and structures refer to the evolution of pavement structures and materials and the development of fundamental design theory and methodology for durable pavement design. The main research areas in this front include: 1) using multi-scale theoretical analysis, numerical simulations, and experimental tests (both laboratory and field) to reveal the in-service behavioral evolution of pavement materials and structures and quantitatively describing their performance; 2) using modifiers to improve the durability of pavement materials; 3) considering the real stress/strain state of structures and the bimodular properties (different compression-tension properties) of materials to develop more accurate pavement design procedures; 4) developing more reliable pavement structure design models based on monitoring the long-term performance of pavement; and 5) optimizing pavement structures and conducting preventive maintenance to enhance the durability and service life of pavement. Potential research prospects include: 1) investigating the behavioral evolution of pavement materials and structures under the coupled effects of multiple factors based on the long-term performance monitoring and accelerated pavement testing; 2) developing highly efficient modifiers to improve the binder-aggregate interface bonding and the overall mechanical properties of pavement materials; and 3) developing a harmonious analysis of the mechanical properties and the structural mechanical responses of pavement materials based on the in-service behavior of pavement material and structure. Between 2014 and 2019, 56 core papers relevant to this research front were published. These papers received 1584 citations, with an average of 28.29 citations per paper.

(9)  Formation mechanisms and changing trends of extreme hydrologic events

Extreme hydrologic events are hydrologic events that occur with a small probability of occurrence but a strong impact in a particular region and within a certain time scale, for which the hydrological variables deviate significantly from their normal values. Extreme hydrologic events are multi-dimensional nonlinear systems that are influenced by climate, underlying surfaces, human activities, and other factors. Their formation mechanism is therefore highly complex. In recent years, the intensity and frequency of extreme hydrologic events caused by global climate change have increased, and the consequently increased risk of flood and drought has become a major challenge for humans. The formation mechanisms and changing trends of extreme hydrologic events under the impact of global change have become top issues in current research. Main research trends include: 1) the impact of the interaction of climate–vegetation–hydrology–human activity on extreme hydrologic events; 2) trend detection, changing attributes, and future scenarios of extreme hydrologic events given the impacts of natural climate variability and human activities; 3) climate–hydrologic bidirectional coupling models and multi-scale extreme hydrologic process simulations in changing environments; and 4) risk assessment of, multi- dimensional regulation of, and comprehensive responses to extreme hydrologic events. In the future, the formation mechanisms and changing trends of extreme hydrologic events in complex environments should be investigated via a multi-disciplinary approach based on climate, hydrology, geography, management, etc., using three-dimensional total factor monitoring and scientific experiments, multi- source data fusion and assimilation, ensemble simulation of physical models with artificial intelligence (AI), and other new technologies. Between 2014 and 2019, 238 core papers relevant to this research front were published. These papers received 9287 citations, with an average of 39.02 citations per paper.

(10)   Catastrophic effects of deep energy exploitation and regulation of its mechanical behavior

The rapid development of human society has produced a growing demand for energy. With improvements in all types of technical engineering systems, the exploitation of energy resources has gradually reached the deep part of the earth. In recent years, the exploitation of shale gas, hot dry rock, coalbed methane, and combustible ice have seen an upsurge. However, deep rock masses are found in complicated geological environments with high temperature and high stress, and their mechanical behaviors are more complex than those of shallow rock masses. Affected by coupled fluid–thermal–chemical–mechanical effects, the key parameters of deep rock masses, including their mechanical strength, deformation mechanisms, and permeability characteristics, are not well explained by traditional theories. Meanwhile, catastrophic problems, such as rock bursts, induced seismicity, large deformations of soft rocks, and wall instabilities in complex strata, occur frequently in deep mining. Catastrophic mechanisms thus require further investigation. To better explore the effects of deep energy mining disasters and further improve the control of the mechanical behaviors of deep rock masses, the following research aspects should be given special attention: the multi-field coupling mechanisms of complex fractured rock masses; the mechanisms, processes, and evaluation of deep, dynamic disasters; the physical and mechanical properties, deformation, and failure characteristics of deep rock masses; and the influence of deep, complex structures on the physical and mechanical properties of rock masses. Between 2014 and 2019, 105 core papers relevant to this research front were published. These papers received 3319 citations, with an average of 31.61 citations per paper.

《1.2 Interpretations for three key engineering research fronts》

1.2 Interpretations for three key engineering research fronts

1.2.1 Smart city and smart basin integrated sensing based on geospatiotemporal big data

Integrated sensing is an important foundation for the realization of smart cities and smart basins. In smart cities and smart basins, ubiquitous smart sensors realize the comprehensive perception of physical cities and physical watersheds and detect the core system of urban operations and watershed management in real time, thereby seamlessly connecting digital cities and digital watersheds with physical cities and physical watersheds. The real-time geospatiotemporal big data are then used to provide users with intelligent services. With the development of smart cities and smart basins, urban and basin sensing has gradually developed from isolated online sensing to multi-network integrated sensing.

Currently, the major research topics concerning smart city and smart basin integrated sensing include: (1) Construction methods for integrated sensing infrastructure systems of smart cities and smart basins, such as 1) new technologies for the large-scale interconnection of monitoring resources between cities and river basins, including mass sensor network communication, heterogeneous sensor access, sensor network resource management, sensor network service composition, streaming data mining analysis, and geographic information interoperability; and 2) new collaborative methods for multi-source heterogeneous sensing resources, such as sensor information modeling, observation capability evaluation, collaborative monitoring, data fusion of point and surface observations, and on-demand focused services; (2)   City and basin sensing methods based on integrated sensing infrastructure, including 1) multi-scale comprehensive perception indices, common technology and standard systems, seamless spatial perception methods of urban agglomeration and watershed surface elements; 2) multi-scale intelligent light field video imaging and analysis methods; 3) fine scene space-time perception and online monitoring methods; and 4) the multi-scale synthesis of city and watershed sensing service methods; and (3)   The integrated management and real-time analysis of geographic spatiotemporal big data from smart cities and smart basins, including integrated expression methods of multi-source real-time geographic information, fusion and organization methods for real-time geographic information, flexible service methods for real-time geographic information, and deep mining methods for geographic spatial-temporal big data.

As shown in Table 1.1.1, between 2014 and 2019, 36 core papers concerning “smart city and smart basin integrated sensing based on geospatiotemporal big data” were published, with each paper being cited an average of 25.67 times. The top five countries in terms of output of core papers on this topic are China, the United States, Malaysia, Iran, and Australia (Table 1.2.1). China is one of the most active countries, having published 27.78% of the core papers. The five countries with the highest citations per paper were South Korea, the United States, Turkey, Malaysia, and Switzerland. The papers published by Chinese authors were cited 19.80 times per paper on average, which indicates that there is an opportunity for improvement by Chinese scholars on this front. As illustrated by the international collaborative network depicted in Figure 1.2.1, close cooperation was observed among the most productive top 10 countries.

The five institutions that published the most core papers were Chinese Academy of Sciences (China), China Institute of Water Resources and Hydropower Research (China), Canik Basari University (Turkey), the National University of Malaysia (Malaysia), and the University of Hong Kong (China) (Table 1.2.2). The top two institutions in terms of widely cited publications are the Chinese Academy of Sciences and the China Institute of Water Resources and Hydropower Research. Both institutions are leaders in the application of AI techniques for urban flood warning and catchment flood forecasting to prolong the leading time and increase the forecasting accuracy. As illustrated in Figure 1.2.2, the ten most productive institutions have conducted collaborative studies in this regard.

《Table 1.2.1》

Table 1.2.1 Countries with the greatest output of core papers on “smart city and smart basin integrated sensing based on geospatiotemporal big data”

《Figure 1.2.1》

Figure 1.2.1 Collaboration network among major countries in the engineering research front of “smart city and smart basin integrated sensing based on geospatiotemporal big data”

《Table 1.2.2》

Table 1.2.2 Institutions with the greatest output of core papers on “smart city and smart basin integrated sensing based on geospatiotemporal big data”

《Figure 1.2.2》

Figure 1.2.2 Collaboration network among institutions in the engineering research front of “smart city and smart basin integrated sensing based on geospatiotemporal big data”

As shown in Table 1.2.3, the five most active countries in terms of paper citations were China, Iran, the United States, Vietnam, and Australia. The top five institutions in terms of citations of core papers were Ton Duc Thang University (Vietnam), Duy Tan University (Vietnam), University of Tehran (Iran), University of Tabriz (Iran), and the University of Southern Queensland (Australia) (Table 1.2.4). China ranked first in terms of the quantity of core papers produced and the number of citations of core papers, indicating that Chinese researchers pay close attention to this topic.

Summarizing the above statistical data, in terms of research trends concerning “smart city and smart basin integrated sensing based on geospatiotemporal big data,” compared with their foreign counterparts, Chinese scholars have performed well and are gradually becoming leaders in the field.

1.2.2 Coupling response mechanisms of offshore engineering structures and seabed foundation systems under the action of wind, waves, currents, and earthquakes

Offshore engineering structures such as seaport wharfs, breakwaters, oil production platforms, submarine pipelines, cross sea bridges, subsea tunnels, and offshore wind power foundations confront severe operating environments and elevated safety risks. Under the action of wind, waves, currents, and earthquakes, the pore water pressure increases,

《Table 1.2.3》

Table 1.2.3 Countries with the greatest output of citing papers on “smart city and smart basin integrated sensing based on geospatiotem- poral big data”

《Table 1.2.4》

Table 1.2.4 Institutions with the greatest output of citing papers on “smart city and smart basin integrated sensing based on geospatiotemporal big data”

and the effective stress decreases in the foundation of the seabed. This can lead to the strength-weakening and liquefaction of the seabed soil. At the same time, the action of waves and currents can scour the seabed foundation. In addition, structural movements under the action of dynamic loads can also change the pore water pressure and effective stress in the seabed soil, complicating the bearing capacity of the seabed foundation. The coupling response mechanisms of offshore engineering structures and seabed foundation systems under the action of wind, waves, currents, and earthquakes are key issues for the safety and durability of offshore engineering structures.

The dynamic responses of seabed foundations and their coupling effect with structures are core problems in the coupling response mechanisms of offshore engineering structures and seabed foundation systems under the action of wind, waves, currents, and earthquakes. There are three types of response models for seabed foundations: the Laplace, diffusion, and Biot consolidation equations. Both the Laplace and diffusion equations assume that the soil skeleton is not deformable and consider the pore fluid to be either incompressible or compressible. The coupling effect between the soil skeleton and pore fluid is not considered in either model. The Biot consolidation equation assumes that the soil skeleton is deformable, the pore fluid is compressible, and the fluid motion satisfies Darcy’s law. Moreover, it considers the acceleration of both the soil skeleton and the pore fluid. Although the coupling effect of the soil skeleton and pore fluid are considered in the Biot consolidation equation, the constitutive model of the seabed soil is limited in the elastic range. In modelling the coupling response mechanisms of offshore engineering structures and seabed foundation systems under the action of wind, waves, currents, and earthquakes, most methods apply various dynamic actions on the structure as loads and do not consider the response effect of the seabed foundations under dynamic actions.

The main topics to be addressed in this field include the following:

(1)  The mechanisms and evolution of the strength-weakening and liquefaction of different seabed foundations (gravel, sand, soft clay, etc.) under the action of different periodic cyclic loads such as waves, earthquakes, and structural motions;

(2)   An elasto-plastic constitutive model that accounts for the processes of strength-weakening, liquefaction, and excess pore pressure dissipation and consolidation after the liquefaction and re-liquefaction of different types of seabed soil under the action of cyclic loads;

(3)   Scouring models of different seabed foundations that consider seepage effects under the action of waves and currents;

(4)   Coupled numerical models for the nonlinear dynamic analysis of cyclic load–marine structure–seabed foundation systems and efficient, reliable numerical simulation methods; and

(5)  Basic theory and experimental technology to test physical models to investigate the bearing capacity of cyclic load–marine structure–seabed foundation systems.

As listed in Table 1.1.1, between 2014 and 2019, 40 core papers concerning “coupling response mechanisms of offshore engineering structures and seabed foundation systems under the action of wind, waves, currents, and earthquakes.” On average, each paper was cited 31.78 times. The top five countries in terms of core-paper output were China, Australia, Denmark, the United Kingdom, and the Netherlands (Table 1.2.5). China was the most active country in this front, producing 57.50% of the core papers. The top five countries in terms of the average number of citations per paper were the Netherlands, the United States, Denmark, the United Kingdom, and Mexico. In terms of core-paper citations, papers published by Chinese authors were cited 26.87 times per paper on average, indicating that researchers in China are gradually gaining attention. As illustrated by the international collaborative network depicted in Figure 1.2.3, relatively close cooperation was observed between China, Australia, and the United Kingdom.

As listed in Table 1.2.6, the five institutions publishing the highest number of core papers were Griffith University (Australia), Technical University of Denmark (Denmark), Hohai University (China), Chinese Academy of Sciences (China), and Shanghai Jiao Tong University (China). In recent years, researchers from Griffith University have conducted in-depth, systematic studies on the dynamic responses of seabed foundations under the action of waves and currents, while researchers from the Technical University of Denmark have

《Table 1.2.5》

Table 1.2.5 Countries with the greatest output of core papers on “coupling response mechanisms of offshore engineering structures and seabed foundation systems under the action of wind, waves, currents, and earthquakes”

conducted research on seabed scouring around pipelines and vertical circular cylinders under the action of waves and currents. As illustrated in Figure 1.2.4, the top 10 institutions have cooperated closely.

The five countries with the most citations of core papers were China, the United Kingdom, Australia, Norway, and the United States (Table 1.2.7). The five institutions with the most citations of core papers were Hohai University (China), Shanghai Jiao Tong University (China), Griffith University (Australia), Technical University of Denmark (Denmark), and Ocean University of China (China) (Table 1.2.8). China ranked first in terms of both the number of published core papers and the number of citations of core papers, indicating that Chinese researchers have paid close attention to this research front.

《Figure 1.2.3》

Figure 1.2.3 Collaboration network among major countries in the engineering research front of “coupling response mechanisms of offshore engineering structures and seabed foundation systems under the action of wind, waves, currents, and earthquakes”

《Table 1.2.6》

Table 1.2.6 Institutions with the greatest output of core papers on “coupling response mechanisms of offshore engineering structures and seabed foundation systems under the action of wind, waves, currents, and earthquakes”

《Figure 1.2.4》

Figure 1.2.4 Collaboration network among major institutions in the engineering research front of “coupling response mechanisms of offshore engineering structures and seabed foundation systems under the action of wind, waves, currents, and earthquakes”

《Table 1.2.7》

Table 1.2.7 Countries with the greatest output of citing papers on “coupling response mechanisms of offshore engineering structures and seabed foundation systems under the action of wind, waves, currents, and earthquakes”

《Table 1.2.8》

Table 1.2.8 Institutions with the greatest output of citing papers on “coupling response mechanisms of offshore engineering structures  and seabed foundation systems under the action of wind, waves, currents, and earthquakes”

1.2.3 Urban spatial analysis and optimization methods based on big data

With the development of internet technologies, the paradigm of urban spatial analysis is being transformed by the emergence of new big data that are geo-referenced, such as cell phone data, public transport tap-in/out data, and social media check-ins. The advantages of this type of data include its large size, fine resolution, and wide coverage. These data record various human behaviors across time and space with a new level of precision, thereby forming new pipelines for us to observe, perceive, and interpret cities and their transformation. Spatial analysis and optimization based on urban big data are thus frontiers for urban studies and practices.

Three domains of urban studies are involved in this front. The first is urban observation based on human behavior data, which enables our understanding of the spatial characteristics of urban elements and improves the sensitivity of the statues of various urban sub-systems, such as populations, workplaces, public service, and transport. This domain has been well explored. The second domain is urban diagnosis and performance evaluation. On the basis of human behavior data, research in this domain evaluates urban performance, including commuting and the work–life balance, population distribution, and accessibility, in terms of urban sufficiency and equality. The output of such studies is strongly related to urban optimization. Most of these efforts, however, have not yet produced applications as they have focused on problem detection and methodological developments without a convergent form for applications. The third domain is the reformation of the relevant urban theory. This reformation has been enabled by the discovery and definition of new rules of urbanization with the intelligent simulation, integration, and prediction of urban systems and their transformation. Research in this domain is still limited, but it has been widely recognized as an essential direction.

A new era of urban science and research is now being encouraged by the availability of urban big data. The main focus of current efforts is to bridge research and practice using various emerging technologies for spatial analysis and optimization. The ultimate aim of such efforts is to facilitate smart cities with theoretical innovations of the new urban science.

The institutions leading the relevant research are located in the West in developed countries or districts, such as the United States, the United Kingdom, and the European Union and in rapidly developing countries and areas, such as China. Developed countries typically maintain more comprehensive research systems and networks with the solid establishment of theory, methods, and applications, whereas rapidly developing countries, particularly China, stand out for the large size of their urban big data due to their population size, optimism regarding new technologies, and good software and hardware facilities.

The world-leading institutions in this front include the Massachusetts Institute of Technology (e.g., Media Lab), University College London (e.g., the Centre for Advanced Spatial Analysis and Urban Dynamic Lab), Swiss Federal Institute of Technology in Zurich (e.g., Future City Lab), Alan Turing Institute, Google, Twitter, and Microsoft. The leading institutes in China include Tongji University (e.g., China Intelligent Urbanization Co-creation Centre for High-Density Regions), University of Chinese Academy of Sciences, Tsinghua University, Peking University, Alibaba, Tencent, Huawei, and Jingdong. Universities are the majority among these institutes because of their interdisciplinary advantage in incorporating urban planning, geography, computer science, geographical information science, etc., in a new urban science, which has led to their dominance in this research. As a complement to this research, technology companies utilize their data sources and advanced facilities for data storage, computation, and real-time applications via their internet platforms.

Thanks to the complementary advantages of diverse sectors, the forms of cooperation on this front vary greatly. The main types include multi-sector cooperation across many universities, governments, associations, and enterprises (e.g., China Intelligent Urbanization Co-creation Centre for High- Density Regions), cross-university cooperation (e.g., Alan Turing Institute), and institute–enterprise cooperation (e.g., CAUPD-Alibaba Future City Lab).

As listed in Table 1.1.1, between 2014 and 2019, 58 core papers concerning “urban spatial analysis and optimization methods based on big data” were published, and on average each paper was cited 42.43 times. The top five countries in terms of core-paper output were China, the United States, Norway, Australia, and the United Kingdom (Table 1.2.9). As one of the leading research countries, China published 41.38% of the core papers on this research front. The top five countries in terms of the average number of citations per paper were the United Kingdom, Switzerland, Singapore, Norway, and the United States. On average, the papers published by Chinese authors received 49.54 citations per paper, which is slightly above the overall average. From the perspective of cooperation networks between countries (Figure 1.2.5), close cooperation has been observed among the most productive ten countries particularly between the United States and China.

The five institutions producing the most core papers on this front are Wuhan University (China), Norwegian University of Science and Technology (Norway), Sun Yat-Sen University (China), Peking University (China), and Arizona State University (USA) (Table 1.2.10). Wuhan University is the leader in the fields of spatial analysis with big data and the measurement, computation, and redefinition of urban structures and their transformation. The Norwegian University of Science and Technology is a pioneer in the research of environmental sensing and smart sustainable urbanization supported by the Internet of Things (IoT), information and communication technology, and other emerging technologies. From the perspective of cooperation network among the leading institutions (Figure 1.2.6), collaborative studies have been conducted by the top 10 most productive institutions on this front, except for the Norwegian University of Science and Technology.

The top five countries in terms of citations of core papers are China, the United States, the United Kingdom, Spain, and Australia (Table 1.2.11). The top five institutions in terms of

《Table 1.2.9》

Table 1.2.9 Countries with the greatest output of core papers on “urban spatial analysis and optimization methods based on big data”

《Figure 1.2.5》

Figure 1.2.5 Collaboration network among major countries in the engineering research front of “urban spatial analysis and optimization methods based on big data”

《Table 1.2.10》

Table 1.2.10 Institutions with the greatest output of core papers on “urban spatial analysis and optimization methods based on big data”

《Figure 1.2.6》

Figure 1.2.6 Collaborative network among major institutions in the engineering research front of “urban spatial analysis and optimization methods based on big data”

《Table 1.2.11》

Table 1.2.11 Countries with the greatest output of citing papers on “urban spatial analysis and optimization methods based on big data”

citations of core papers are Chinese Academy of Sciences (China), Wuhan University (China), Massachusetts Institute of Technology (USA), Sun Yat-Sen University (China), and Peking University (China) (Table 1.2.12). China ranked first in terms of the number of published core papers and citations of core papers, indicating that Chinese researchers have paid close attention to research performed on this front.

《2 Engineering development fronts》

2 Engineering development fronts

《2.1 Trends in top 10 engineering development fronts》

2.1 Trends in top 10 engineering development fronts

The top 10 engineering development fronts in the field of civil, hydraulic, and architectural engineering are summarized in Table 2.1.1. These fronts cover a variety of disciplines, including structural engineering, landscape and urban panning, transportation engineering, geotechnical and underground engineering, bridge engineering, construction materials, municipal engineering, hydraulic engineering, and geodesy and survey engineering. Among these development fronts, experts recommended the following: “planning and design technologies for public health emergency responses,” “deep-water detection of latent defects and treatment technologies for water conservancy projects,” “city information modeling,” “regulation methodologies for the properties and microstructures of cement-based materials used in extreme environments,” “regulable design of ultra- high-performance concrete,” “technology and equipment

《Table 1.2.12》

Table 1.2.12 Institutions with the greatest output of citing papers on “urban spatial analysis and optimization methods based on big data”

《Table 2.1.1》

Table 2.1.1 Top 10 engineering development fronts in civil, hydraulic, and architecture engineering

for leakage monitoring and in-situ repair for urban water supplies and drainage networks,” and “Earth observation and geospatial information processing technologies based on the blockchain.” The remaining topics were identified from patent maps and then confirmed by experts. Table 2.1.2 presents annual statistical data on patents published between 2014 and 2019 related to these top 10 development fronts.

(1)   Planning and design technologies for public health emergency responses

Urban planning and design can play a pivotal role in responses to public health emergencies involving space interventions since urban development has inevitable effects on human contact with infection sources, the mode of transmission and processes of infectious diseases, and the number of people who are susceptible via both ecological and social processes in the urban space. Although there are no wholly specific planning and design technologies for public health emergency responses, existing technologies for land use and urban ecology identification, the construction of the 3D urban physical space and environmental models, environmental pollution monitoring and assessment, etc. contribute to

《Table 2.1.2》

Table 2.1.2 Annual number of patents published for the top 10 engineering development fonts in civil, hydraulic & architecture engineering