In the underground space development of residential areas, outdoor thermal environments at the pedestrian level greatly depend on the ground greening configuration, which is in turn affected by the overburden thickness of the underground space (OTUS). However, few studies have considered the effects of OTUS on the ground greening configuration and the further effects of the ground greening configuration on the outdoor thermal environment. This study aimed to provide insights into the design of OTUS for improving outdoor thermal environments. Two residential areas with row and enclosed layouts in Nanjing, China, were numerically studied using the computational fluid dynamics (CFD) simulation software ENVI-met. Outdoor thermal environments in the two residential areas, which had the same greening coverage rate, were simulated under different OTUSs and ground green configurations. The results indicate that to create a comfortable outdoor thermal environment, the OTUS should be designed to satisfy the requirement for planting small trees. If this requirement cannot be adequately satisfied, individuals can also set up tree wells or add soil on top of underground structures to plant small trees, and establish an OTUS that can satisfy the requirement of planting large shrubs in other areas.
The development of urban underground space can increase the green area of a city and have a positive impact on urban microclimate. However, the negative impacts of urban under-ground space development on the urban microclimate are rarely considered and analyzed. In this study, we focus on analyzing the impact of the development of underground commercial streets under determinant urban form on urban microclimate using outdoor CO concentrations as the evaluation index. In this regard, it was possible to quantitatively evaluate the influences of various development factors (e.g., development intensity of underground commercial streets; location and height of shaft exhaust; and various ground-greening configurations of transverse and vertical trees, large and small shrubs, and grasses) on the outdoor CO concentration. The results showed that higher development intensity increases outdoor CO concentration and its range of effects. Properly increasing the height of shaft exhausts, choosing a dispersed layout for shaft exhausts, and planting large shrubs on the ground in the development area of underground commercial streets can effectively reduce the impact of underground commercial street development on urban air quality.
Reasonable design of the overburden thickness of underground space (OTUS) can influence the outdoor thermal environment by affecting the ground plant communities. To optimize the design of the OTUS for improving the outdoor thermal environment, this study summarized the influence mechanism of the OTUS on the outdoor thermal environment and proposed a framework of the optimization design of underground space overburden thickness. A typical row layout residential area in Nanjing, China, was taken as the research object on which to perform a numerical study of the influence of plant communities formed by two types of plant collocations (a middle- and low-level plant collocation and a middle- and high-level plant collocation) on the outdoor thermal environment (airflow field, air temperature, relative humidity and thermal comfort) under three different ratios of trees to shrubs (2:3, 1:2, and 1:3), and to provide suggestions regarding the design of the OTUS according to the designer’s requirements. The conclusions were summarized as follows: (1) If a designer wants to enhance outdoor ventilation, the OTUS should be designed to satisfy the requirements for the middle- and low-level plant collocations and the overburden thickness of the 2/5 underground space development area should be set to 80~100 cm, the overburden thickness of the other 2/5 area should be set to 45~60 cm and the overburden thickness of the remaining 1/5 area should be set to 30~45 cm. (2) If a designer wants to reduce air temperature, increase relative humidity, and improve outdoor thermal comfort, the OTUS should be designed to satisfy the requirements for middle- and high-level plant collocations and the overburden thickness of the 1/4 underground space development area should be set to 80~100 cm, and the overburden thickness of the remaining 3/4 area should be set to 45~60 cm.
Urban power supply network plays a vital role in maintaining the city operation. The vulnerability of power supply network in the face of events has been one of significant concerns. This study presents a new methodology and framework for “dose-response” vulnerability assessment of urban power supply network. This framework can explore the vulnerability of power supply network under two types of events: random type and intentional type. It also integrates a new metric that calculates the vulnerability of power supply network in both structural dimension and functional dimension. Taking the power supply network of a city in east China as an example, network vulnerability under different types of events was assessed, and the “dose-response” interrelationships between network performance and event scale under different types of events were thoroughly discussed. The results demonstrated that power supply network was more vulnerable to intentional events in both dimensions. For intentional events, power supply network was more vulnerable to degree-based attack than to betweenness-based attack. After that, the redundancy coefficient α of power supply network was optimized. The conclusion and some suggestions for future research were given in the end.
The outdoor thermal environment of the underground parking system of a residential area in Nanjing, China is simulated using ENVI-met software for three planning schemes in which underground space is not used, partly used, and fully used. The scale of underground space development is found to affect the outdoor thermal environment. The quality of the outdoor thermal environment is best when the underground space is fully used. Compared with the situation where underground space is not used, the partial use of underground space reduces the wind speed by up to 0.09 m/s, reduces the air temperature by up to 0.5 °C, and increases the relative humidity by up to 3%, whereas the full use of underground space decreases the wind speed by up to 0.33 m/s, reduces the air temperature by up to 1.1 °C, and increases the relative humidity by up to 5%. The use of underground space is shown to improve the ecological environment of the residential area and enhance the quality of the outdoor thermal environment.
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