Abstract:

Abstract: Fluid topology optimization is a breakthrough technology, which has broad application prospects in aerospace, automotive, electronic chips and other fields, however, the design of complex structure is difficult to process through the traditional manufacturing technology. With the development of additive manufacturing (3D printing) technology, it could provide an effective way to further expand the application and research of fluid topology optimization, which would of great significance for realizing the structural lightweight, dynamic optimization, safety optimization and performance improvement of related industrial equipment, and implementing the national strategy of “energy conservation and consumption reduction, carbon peak and carbon neutralization”. With the help of the literature metrology tool VOSviewer, were classified and summarized the literature related to fluid topology optimization in the Web of Science database were classified, comprehensively and the theoretical system, solution methods, optimization methods, and engineering applications of fluid topology optimization were expounded systematically, and the related problems were discussed. First of all, compared with solid topology optimization, fluid topology optimization involved more fields, more diverse flow regime characteristics, and more complex mathematical models, so it was more difficult to solve, took longer to calculate, and required more computing resources, which was the main factor restricting the engineering application of fluid topology optimization. Secondly, the three links and key technologies of fluid topology optimization were systematically described: representation method of design variable, CFD model and solution method, topology optimization model and solution method, and the characteristics and application scenarios of existing technologies were analyzed. At the same time, several application scenarios of fluid topology optimization, such as electronic chip heat sink, aircraft, automobile and heat exchanger, were briefly described. Finally, the development trend of fluid topology optimization was predicted and summarized. It was suggested that the multidisciplinary topology optimization research on turbulence, conjugate heat transfer, fluid-solid-heat coupling, fluid-solid-heat-mass coupling should be further strengthened; the research of topology optimization based on multi-objective function should be expanded; the deep combination with artificial intelligence should be further strengthened, more robust and mature intelligent CFD solver and intelligent optimization solver, and even intelligent software of fluid topology optimization should be developed.

Abstract: With the increasingly severe urban waterlogging situation, It was difficult for rainwater management with rainwater pipe network and other grey infrastructures for terminal rapid drainage to solve the problem of urban waterlogging fundamentally. And combining the green, grey and blue infrastructure organically could besides on ensuring that urban floods were effectively solved, systematically solve multi-scale problems such as water pollution and water shortage. Based on the concept of green-grey-blue infrastructure integration, this study reviewed the comprehensive evaluation of urban stormwater system status, the optimization of urban stormwater system, and urban flood control and drainage scheduling. In terms of urban stormwater system assessment, the performance assessment of low impact development system with green infrastructure as the main body and the performance assessment of urban stormwater pipe network system with gray infrastructure as the main body were reviewed. In terms of urban stormwater system optimization, the optimization of design parameters and layout of green infrastructure and the optimization of plan layout and pipe diameter depth of gray infrastructure such as pipe network was reviewed; in terms of urban flood prevention and drainage scheduling, the study of urban flood prevention and drainage was reviewed. In urban flood control and drainage scheduling, the research on urban flood control and drainage scheduling methods and urban flood control and drainage scheduling systems were also reviewed.

Abstract: Although plenty of studies have been carried out, waterlogging in urban areas is common. The frequent happening of flood inundation in urban underground spaces has great threat to the sustainable development of city and the life and property security of citizens. Firstly, according to the flooding events in urban underground spaces around the world, the basic information and characteristics of flood disasters in urban underground spaces were introduced in this study. The characteristics of flood disasters in underground spaces were analyzed from four aspects, including inundation development, rescue condition, invasion pattern, and damage feature. Then, the major scientific problems of flood control in urban underground spaces were raised from three aspects, i. e. factors, carriers, and defenders, based on which the difficulties, vulnerabilities, and poor executions were summarized and discussed. The influences on flood preventing of designed rainfalls, physical property and non-structural measures were concluded. Next, with an overview of related studies, studies on flood control in urban underground spaces were divided into two types, one based on flood control in urban areas and the other focused on features of underground spaces, both of which were analyzed in detail. Finally, an outlook of academic study and technical improvement on prospective flood control in urban underground spaces was conducted, as a scientific perspective to the development of sustainable societies and resilient cities.

Abstract: In order to explore the impact of extreme rainstorms on urban waterlogging characteristics and emergency response capacity, a urban waterlogging model for a certain area in Jinshui District of Zhengzhou city, was developed based on InfoWorks ICM model, and the drainage capacity and waterlogging characteristics of urban pipe network with extreme rainstorm were analyzed. Application with ArcGIS network analysis module, the emergency reachable range and response time of public security, medical treatment and fire protection departments were evaluated to determine the whole city′s emergency response capacity. The results showed that the drainage capacity in the study area was lower wholly, and the proportion of pipes with drainage capacity less than 3 a was 50. 15%, which were mostly distributed in the middle and south and could not meet the drainage standard of 3 ~ 5 years in important areas. Meanwhile, the inundation area was closely related to the drainage capacity and the underlying characteristics. The accumulated water showed the distribution characteristics of more in the south and less in the north under the larger standard of waterlogging control such as 20 a and 100 a, while more water area appeared in the north and near the river with “7·20” rainstorm. The emergency service department with higher emergency vehicle wading ability owned higher emergency response ability in extreme rainstorm, the fire department had the highest response ability in 100 a and “7·20” rainstorm scenarios, and the reachable area in 10 min accounted for 78% and 36%, respectively. Moreover, the joint multi-department regulation could effectively improve the emergency response capability. For example, compared with the best department( he department with the largest proportion of reachable range with the same time threshold) , the emergency reachable area of joint multi-department regulation increased by 16%, 7%, and 4%, respectively in 5, 10, and 15 min with the 100 year rainstorm.

Abstract: Recently, the global climate has sharply changed, which led to frequent floods. The specific high-intensity and extreme rainfall, and the consequent flood events occurred in the urban areas have seriously damaged the safety and property of residents.There was a torrential rainfall event happened in Zhengzhou on July 20th, 2021,which caused the most serious urban pluvial flood disaster since 1949 in China. Many studies have been done to explore the cause and mechanism of formation as well as the characteristics of the serious rainstorm，in order to improve the urban flood prevention and control. This paper analyzed the relevant studies of urban waterlogging systematically, especially focused on the Zhengzhou “7·20” Torrential Rain waterlogging disaster. Three contents were discussed, including: 1) the return period, spatial-temporal distribution and formation mechanism of the storm event 2) the shortcomings of drainage and waterlogging prevention infrastructure, as well as the weakest li＜x＞nk effect of emergency facilities 3) the main problems existing in urban flood emergency management 4) risk management and urban planning considering flood situation. The results show that the rainstorm in Zhengzhou has the characteristics of extreme and difficult to predict, and the single-day and cumulative precipitation both exceed the historical extreme values. Due to the coupling and comprehensive influence of typhoon, topography and "rain island effect", the heavy precipitation weather process was caused. Zhengzhou "7·20" pluvial disaster exposed the obvious shortcomings of drainage and waterlogging prevention infrastructure and construction in Zhengzhou city. There are bottlenecks in the river defense system. And inadequate emergency facilities and management capacity. ba＜x＞sed on the above problems, it is necessary to appropriately adjust the waterlogging prevention and control standards, strengthen the flood risk management and planning and construction control measures, build the engineering system of external flood waterlogging and prevention and control, and strengthen the intelligent dispatching and emergency command and decision-making ability of urban flood.

Abstract: To solve the difficult tradeoff between security requirements and resource cost in radio frequency identification (RFID) triple authentication protocol, a PUF-based high-security lightweight RFID triple authentication protocol (PHL-RTAP) was proposed. Physical unclonable function (PUF) was utilized to authenticate the tag identity for protecting the tag from physical cloning attacks and reducing the tag cost, meeting the demand of resource-constrained RFID system. The quadratic residual algorithm was adopted to secure the reader data privacy. Random numbers were introduced to resist replay attacks and ensure the anonymity and untraceability of tags and readers. The PHL-RTAP could realize a complete triple authentication between server, reader and tag, and expand the scale of readers and tags in RFID systems according to different requirements, so that it was suitable for large-scale tag RFID system. Security analysis showed that PHL-RTAP could effectively resist various malicious attacks such as tracking attacks, replay attacks, physical cloning attacks and desynchronization attacks. BAN logic analysis and AVISPA tool were used to verify the security of the protocol. Compared with recent protocols, PHL-RTAP could make up for the security defects of similar RFID protocols, and has low resource costs such as computing cost, tag storage cost, and communication cost. PHL-RTAP could achieve both high security and lightweight, and was suitable for resource-constrained RFID triple authentication scenarios.

Abstract: Real datasets often contain categorical and numerical attributes, and categorical attributes can be divided into ordinal and nominal attributes. Datasets with both categorical and numerical attributes can be called heterogeneous-attribute data. To solve the problem that the existing distance metrics of heterogeneous-attribute data can not distinguish ordinal attributes in the categorical attributes resulting in missing information and poor clustering effect, a new subspace clustering algorithm based on distance metric was proposed. Firstly, this study summarized the existing progress of distance metric of heterogeneous-attribute data and the solutions to distinguish ordinal attribute. Then the distance formulas were defined for the attribute values of ordinal, nominal, and numerical attributes from the perspective of their natural characteristics. Subsequently, a dynamic weighting scheme was proposed to weight different attributes according to their contributed inter-and intra-cluster distances during clustering. Finally, the distance formula and dynamic weighting scheme were combined to form the distance metric applicable to heterogeneous-attribute data, and a subspace clustering algorithm for heterogeneous-attribute data was thus proposed. Because the algorithm unified the distance metric of heterogeneous-attribute data and could search clusters in subspace, it could achieve good clustering effect on heterogeneous-attribute data. Experimental results on 11 real data sets showed the effectiveness of the algorithm.

Abstract: In order to cope with the unstable conditions of single sensor for life detection in the fields and disaster areas, a life search method was proposed based on multi-sensor information fusion. Firstly, ResNeXt networks with different structures were constructed to extract features with different dimensional information. Deep features of audio Mel-scale Frequency Cepstral Coefficients were extracted using a one-dimensional ResNeXt network, and deep features of the infrared images were extracted using a two-dimensional ResNeXt network. Secondly, the two high-dimensional features were fused by dimensionality reduction using discriminant correlation analysis (DCA) to take into account the correlation and category of different features in order to obtain richer environmental information, thus improving the life search accuracy. Finally, the fused features were fed into a support vector machine classifier for decision making in life recognition. A bimodal dataset of audio and images with correlation was created and the proposed method was experimentally compared and analyzed in this dataset to evaluate the search performance of the proposed method. The experimental results demonstrated that the proposed method could outperform other traditional methods in feature extraction and feature fusion, and the multi-sensor fusion recognition accuracy could reach 98. 7%, which proved that the method could effectively improve the accuracy of human detection in special scenes, and the performance of multi-sensor fusion based human detection was higher than that with single sensor.

Abstract: Network node embedding is mapping nodes in a network to a low-dimensional vector representation, so that vector space-based learning methods can be directly applied to handle downstream tasks such as link prediction. Most of the existing network node embedding models were for unsigned networks and could not be directly used to deal with signed networks (usually need to be converted into unsigned networks for processing, thus discarding a lot of valuable information embedded in the positive and negative signs on the edges).A node embedding model (SNEDA)based on graphical neural networks was proposed that could directly deal with symbolic networks. Based on structural balance theory and status theory, the paths between nodes were divided into 20 different motif structures according to the direction and the positive and negative information on the edges. A network propagation model was designed with two levels of attention mechanism, which could capture the contribution and influence of different neighboring nodes to the vector representation of node i by node-level attention mechanism when aggregating the direct neighboring information of node i, and captured the vector representation of different motif to node i by path-level attention when aggregating the second-order and higher-order neighboring information of node i. A two-level attention mechanism was introduced to integrate different contributions and influences at the node level and path level, which could it not only improve the time efficiency of the algorithm but also make the final vector representation of node i more beneficial to improve the prediction accuracy of the downstream link prediction task. Through experiments conducted on four real social network datasets, the SNEDA model improved the AUC and F1 metrics by about 3.1% and 1.1%, respectively, compared with the benchmark model, and the results showed that the network representation obtained by the model could improve the accuracy of link prediction.

Abstract: To avoid the simulation error caused by the consistent solid-liquid energy transfer rate in the boiling heat transfer LB( lattice Boltzmann) model, different energy transfer rates of solid and liquid are successfully distinguished by tentatively introducing the physical parameters λ, cp of solid and liquid into the temperature relaxation time τ T , as a result, a novel solid-liquid conjugate boiling heat transfer LB model is proposed in this paper. After verifying the accuracy, stability and rationality of the model, boiling heat transfer at different wettability surfaces are simulated by the solid-liquid conjugate model and the original pseudo-potential model. The results show that the unintentional neglection of different heat transfer capacities of solid and liquid regions in the original pseudo-potential model leads to the appearance of large low-density phase transition region around the bubble root. The existence of low-density phase transition region produces additional interphase forces and greatly changes the wall contact angle of bubbles. However, the solid-liquid conjugate heat conduction model realized characterization of different thermophysical properties of solid and liquid regions by introducing a temperature relaxation time function. The low-density phase transition region only appears in a very small range and at very low level, the actual bubble wall contact angles obtained by the conjugate heat transfer model are closer to the setting bubble contact angle. For other wettable surfaces except superhydrophilic surfaces, the maximum relative error of the actual contact angle obtained by the conjugate heat transfer model is 8. 6%, which is 9. 8% lower than that of the original pseudopotential model. The solid-liquid conjugate boiling heat transfer LB model can more accurately describe the actual microscopic process of boiling heat transfer.

Abstract: In order to improve the rationality of the planning and layout of electric vehicle (EV) charging stations and avoid the situation of high investment and low efficiency, a planning method of EV charging station that considered users′ dynamic charging demand was proposed. Firstly, the starting and ending points of user were obtained by using the travel theory, start and end point (origin-destination,OD) matrix method; a dynamic traffic road network model with time-varying traffic congestion was constructed. The Dijkstra algorithm was improved to plan the EV travel path, considering the real-time changes of ambient temperature and vehicle speed. Based on the influence of mileage and power consumption, a charging station selection model considering the dynamic charging needs of users was established; then, the M/M/c queuing theory method was used to configure the capacity of charging stations. The cost of construction, operation and maintenance of charging stations and the economic losses of EV users (including the sum of time loss and power loss) was minimized as the objective function, and a charging station planning model was established. Finally, taking the actual road conditions in the main urban area of a city as the planning area, the model was solved by iterative arrangement optimization combined with particle swarm algorithm. The results showed that the locations of the six planned charging stations in the area were evenly distributed, which could reduce the cost of users′ charging journeys. And the optimal configuration number of charging piles could ensure charging satisfaction while minimizing the total economic cost of charging stations. The proposed planning method was reasonable and effective.

Abstract: Taking 21700 lithium ion battery pack as the research object, the finite element simulation was carried out by controlling the changes of battery spacing, convective heat transfer coefficient, and Phase Change Material ( PCM) thermal conductivity of lithium battery with different arrangement. The effects of cell spacing, convective heat transfer coefficient and PCM thermal conductivity on the temperature field of different battery arrays Rectangular, Quadrilateral, and Hexagonal Arrangement with phase change BTMS were studied. The results showed that when the battery spacing was 4 mm and 6 mm, the three had approximate maximum temperature, and when the battery spacing was 2 mm and 1 mm, the maximum temperature of the Rectangular Arrangement was the largest, for example, the maximum temperature rise of the Rectangular Arrangement was 105. 86% and 108. 25% of the Quadrilateral Arrangement and Hexagonal Arrangement, respectively. However, the temperature differences of the three components tended to decrease with the increase of the spacing. With different convective heat transfer coefficients, the maximum temperature of Rectangular Arrangement was always the largest while that of Quadrilateral Arrangement was the smallest. With the increase of convective heat transfer coefficient, the temperature difference among the three showed a trend of increasing. With the increase of the thermal conductivity of PCM, the maximum temperature of the three gradually decreased with a decreasing rate. With the five different thermal conductivity of PCM, the average maximum temperature rise of Rectangular Arrangement was 105. 31% and 106. 02% of that of Quadrilateral Arrangement and Hexagonal Arrangement, and the temperature difference of latent heat storage stage of the three decreased. In the sensible heat stage, the temperature difference between Rectangular Arrangement and Hexagonal Arrangement was not affected, but the temperature difference of Quadrilateral Arrangement increased continuously. Considering the highest temperature and temperature difference, the Hexagonal Arrangement lithium battery pack had the best thermal performance with PCM thermal management.

Abstract: Based on the electrocaloric effect, a novelty refrigeration device with a ribbon electrocaloric module made of electrocaloric material P(VDF-TrFE-CFE) ternary polymer was proposed. In the device, the ribbon electrocaloric module was driven by a driving wheel and moved sequentially pass through electrodes, hot end, and cold end. In this way, the EC module would undergo four stages of electrocaloric effect. Continuous cooling could be achieved at the cold end. A numerical simulation study of a cooling unit of the structure was carried out, and the effects of the polarization time, length, movement speed, temperature span and applied electric field strength of the electrocaloric module on the cooling performance were investigated. The results showed that the polarization time of the electrocaloric module was essential to obtain a stable cooling power density(CPD). The CPD increased with the increase of the length of the electrocaloric module and its motion speed, decreased with the increase of the temperature span at both ends. It also showed a strong positive correlation with the electric field strength. The optimal COP/COPc values existed for different electric field strengths. The cooling power density of a cooling unit reached 6.61 W/cm at a temperature span of 3 K and an electric field strength of 160 MV/m.

Abstract: In order to protect paper and solve the problem of bacterial drug resistance, in this study, carboxymethyl cellulose and berberine were used as raw materials to prepare berberylated carboxymethyl cellulose (BBR-DCMC) through schiff base reaction. The single factor experiment and response surface method were used to optimize the preparation process, and disk AGAR diffusion method was used to determine the antibacterial activity. The results showed that when the mass ratio of dialdehyde carboxymethyl cellulose and modified berberine was 7 ∶15, reaction temperature was 39. 0 ℃ , and pH was 5. 0, the optimum synthetic conditions was obtained. And the model established by the response surface method was true and reliable. Besides, BBR-DCMC had good antibacterial and antifungal properties against bacteria and molds. The minimum inhibitory concentration of the product against Staphylococcus aureus and Escherichia coli were 0. 2 mg / mL, the minimum inhibitory concentrations against Aspergillus niger and Candida albicans were 0. 4 mg / ml. This research provided some theoretical guidance for the protection of paper cultural relics.