[Significance] With the rapid advancements in aerospace engineering technology, the performance requirements for aircraft are increasingly escalating. At present, there are numerous goals for aircraft utilization in military, transportation, and other sectors. Hypersonic aircraft, which operate under multiple operating conditions and across a wide velocity range, have become a hot research topic in many countries. A critical component of such high-performance aircraft is their power system. A high-performance aircraft must have a high-performance power system to match it. Existing mature power systems have limitations in terms of working conditions and performance. Therefore, the development trend has shifted toward combined power systems. Currently, prominent combined engines include rocket-based combined cycle (RBCC), turbine-based combined cycle (TBCC), air turborocket, and precooled engines. When considering factors like cost, performance, and safety, TBCC engines emerge as the most promising power system for hypersonic aircraft within the near space range of 20-100 km because of their flight envelope width, reusable, large unit thrust, and other advantages. Therefore, summarizing the key TBCC technologies and exploring their development path is crucial. [Progress] The United States, Japan, and the United Kingdom are pioneers in combined power research. These countries have achieved significant technical achievements, possess mature technologies, and have completed the entire research and development cycle for combined engine products. They are at the forefront of this field. In the future research and development strategy, the United States focuses on system-wide research of TBCC and RBCC technologies. Following the completion of the HYPR90 program, Japan has conducted an in-depth study into the precooled engine ATREX. Meanwhile, the UK continues its extensive research on SABRE, aiming to deploy it in future single-stage spacecraft. Other countries, such as Germany, Russia, and China, are also engaged in large-scale TBCC research, accumulating a large number of technologies to achieve breakthroughs from theory to engineering application in the future. In terms of TBCC key technologies, this paper analyzes and summarizes advancements in propulsion system technology and subsystem technology. For subsystems, current TBCC inlet forms are reviewed, with advanced mixed rectangular divergent and integrated multidimensional cross-sectional configurations being analyzed. The future direction points toward the development of 3D internal contraction inlets. The advantages and disadvantages of series and parallel exhaust systems are analyzed alongside the basic theory of the exhaust process, emphasizing the need for more theoretical support for exhaust systems. Numerous achievements in modal conversion control technology are listed, highlighting that future research should focus on integrating strongly coupled flight control with modal control technology. Regarding propulsion system technology, a comprehensive theoretical model for aircraft-engine integration is presented, pointing out the defects of the traditional separate design approach for aircraft and engines. This paper reviews the development of performance simulation and testing technologies domestically and internationally, suggesting that future assignments should involve developing sophisticated simulation software and building new test benches. [Conclusions and Prospects] The combined engine essentially integrates four types of engines: turbine, rocket, ramjet and precooled. This paper summarizes the key technologies of TBCC and explores their development routes while also providing three prospects for the future form of combined engines: combining new basic power forms, adopting new energy sources, and incorporating the external drive platforms.

[Objective] The atmosphere-breathing electric propulsion (ABEP) system has become a highly promising candidate for drag compensation in spacecraft operating in very low Earth orbit. To improve the inlet design of ABEP systems, this study performs a comprehensive numerical investigation of gas flows inside the inlet. The primary objective is to gain insight into the effects of the gas-surface interaction (GSI) model on the flow features, compression, and collection performances. [Methods] This paper explores ABEP inlet flows using the direct simulation Monte Carlo (DSMC) method. A typical altitude of 180 km in the upper atmosphere is considered, and four GSI accommodation coefficients (σ=1, 0.8, 0.5, and 0.2) are selected. The DSMC method simulates gas flows according to the motion of a cluster of simulation particles, where each particle represents a large number of real gas molecules. In the DSMC method, particle motions are computed deterministically, whereas intermolecular collisions are calculated statistically. Each simulation particle travels at a constant velocity until it collides with another simulation particle or a solid surface. In the event of an intermolecular collision, an appropriate molecular collision model is employed to compute post-collision velocities, and in the event of gas-surface collisions, a suitable GSI model is adopted to calculate the molecular velocity after reflection. In this work, the internal energy exchange is modeled using the Larsen-Borgnakke scheme. Further, the intermolecular collision is handled using the variable hard sphere model and the no time counter-collision sampling technique. The simulation is always evaluated as an unsteady flow, and a steady result is obtained as the large-time state of unsteady simulation. After achieving a steady flow, the simulation particles in each cell are sampled for a sufficient duration to decrease statistical scattering. All macroscopic field quantities (such as mass density, velocity, and temperature) and surface quantities (such as surface pressure, shear stress, and heat flux) are calculated based on these time-averaged data. [Results] Numerical results show that the distributions of gas pressure and mass flux are considerably affected by the GSI models. The lower the GSI accommodation coefficient, the higher the gas pressure and the larger the mass flux. Consequently, the GSI accommodation coefficients play a vital role in the compression factor and collection efficiency of the inlet. Furthermore, the decrease in the GSI accommodation coefficient from 1.0 to 0.2 leads to an increase in the compression factor and collection efficiency by a factor of 7 and 4, respectively. In addition, as the GSI accommodation coefficient decreases, the high-pressure region moves toward the ionization section, facilitating the ionization of neutral gas molecules. The following mechanism underlies this effect: after reflecting in a specular manner from the concave surface, the gas molecules congregate at the focus and enter the ionization section. [Conclusions] To improve the inlet design of an ABEP system, a combination of the geometric design and surface-material design should be adopted. A concave compression section should be employed, and at the same time, the inlet surface should be smoothened to decrease the GSI accommodation coefficient.

[Objective] With advancements in modern flight vehicle design, an increased demand for maneuverability is observed, often requiring flight vehicles to operate under conditions involving a high angle of attack and large rudder angle. However, the prevalent linearized model of flight vehicle longitudinal dynamics in aerospace engineering is primarily tailored for launch vehicles, relying on assumptions such as small angle of attack and control surface deflection. Consequently, establishing a linearized model of flight dynamics applicable under conditions of the high angle of attack and large rudder angle is necessary. [Methods] This paper uses the small perturbation method to establish a linearized model of the rigid-flexible coupling flight dynamics for flight vehicles, which is then compared and analyzed with the commonly used model in aerospace engineering. Initially, the vector-form flight dynamic equations are projected onto the specified coordinate system, resulting in matrix-form scalar equations. Subsequently, the general linearized form of the dynamic equations in matrix form is derived, and the equation coefficients for the longitudinal dynamic model are obtained. High-precision linearization of the nonlinear expressions for inertia forces and moments owing to control surface deflection is performed, yielding linearized expressions that accurately describe the influence of the perturbation in the angle of attack and rudder angle on these forces and moments. A rigid-flexible coupling multibody system comprising a flexible body and rigid rudder is used as an example to compare simulation results of the linearized model derived in this paper, the traditional linearized model, and the original nonlinear model under the high angle of attack and large rudder angle, verifying the high simulation accuracy of the proposed model. [Results] By comparing the coefficients of the dynamic equations derived in this paper with those in the commonly used model in aerospace engineering, we observe that when the angle of attack and the rudder angle are considered small, the coefficients of the dynamic equations obtained in this paper can be simplified to match those of the commonly used model in aerospace engineering. However, unlike the commonly used model in aerospace engineering, the linearized expressions for inertia forces and moments owing to control surface deflection in this paper include not only the increments of control surface deflection acceleration but also the increments of the rudder angle and angle of attack. Simulation results indicate that the linearized model derived in this paper produces results close to those of the nonlinear model than those of the traditional linearized model. [Conclusions] When the angle of attack and the rudder angle are small, the simulation results of the simplified linearized models are relatively close to those of the linearized model derived in this paper. However, under the high angle of attack and large rudder angle, a considerable discrepancy is observed between the simulation results of the linearized models that treat the angle of attack or rudder angle as small quantities and the linearized model derived in this paper. In such cases, treating the angle of attack or rudder angle as small quantities may lead to substantial errors. The research presented in this paper offers a high-precision linearized model that can be used for the guidance and control system design of a flight vehicle.

[Objective] Asteroid research has become a focal point of scientific inquiry in recent years. These celestial bodies have drawn significant scientific and economic interest and pose a potential threat to the Earth's safety. This study addressed the challenges in tracking and analyzing small asteroids or those with limited observational data. These asteroids often have significant errors in their ephemeris information, which makes it difficult for impactors to capture them accurately using only these data. The challenge is compounded when the asteroid remains outside the camera's field of view after adjustments based on the ephemeris positions. Therefore, an efficient and rapid search strategy must be adopted to adjust the camera's direction, ensuring that the asteroid is viewed. [Methods] This research is based on China's inaugural asteroid impact mission. The focus is on the final-stage target search strategies for asteroids with small diameters but significant orbit determination errors, employing optical cameras. A critical challenge in this mission is the high relative speed between the impactor and the target asteroid. This speed necessitates the completion of the entire approach and final impact within approximately 4 000 s. Thus, the search strategy must be time-efficient to fit within these strict temporal constraints. Moreover, the camera used in this mission has certain operational limitations due to the parameters involved. For example, a camera cannot capture images during impactor maneuvering. Furthermore, the captured images must be processed autonomously by the impactor's onboard computer to facilitate autonomous navigation. The camera must operate under the principle of minimal imaging, constrained by the requirement of adequate coverage area to minimize the computational load on the onboard computer and reduce the overall search time. To address these operational challenges, a scanning search strategy is designed to maximize the area covered by each imaging instance. This strategy is developed by considering two critical constraints. First, the total search duration must be less than one-tenth of the entire approach phase, which translates to less than 400 s. Second, the imaging interval must be greater than 0.5 s. The proposed strategy can effectively cover target areas of varying sizes by adjusting the number of searches. This study provides a detailed analytical expression for the achievable area coverage with varying numbers of searches. In addition, a method for recursive calculation is proposed for different field-of-view positions. This methodology is crucial to ensure the adaptability and efficiency of the search strategy in real-time scenarios. Numerical simulation techniques are applied to validate the effectiveness of the proposed search strategy. These simulations are critical for testing the strategy under various conditions and assessing its feasibility and reliability. [Results] The results of these simulations were highly encouraging. The search strategy achieved a 100% success rate, with a maximum duration of 356.2 s and an average duration of 98.3 s. The shortest duration recorded for a single search was approximately 1.5 s. [Conclusions] These results are particularly noteworthy because they demonstrate the strategy's compatibility with the performance of the camera, the computational power of the onboard computer, and maneuvering time constraints.

[Objective] With the continuous advancement of the informationization of air traffic control (ATC) in civil aviation, the ATC system currently acts as a hub supporting the efficient and safe operation of the aviation transportation industry. In this process, a large volume of business data is generated and processed within the ATC system that needs to be exchanged across different domains with external entities or organizations to meet the growing demands of informatization. However, data security, real-time processing, and efficiency issues have become increasingly prominent, posing bottlenecks to the further development of the ATC system. Driven by the promotion of informationization of the ATC system, the application subsystems within the civil aviation ATC system have gradually become fragmented, forming multiple information silos. This not only hinders the effective circulation of information but also limits the overall operational efficiency of the ATC system. Therefore, facilitating information sharing and system integration has become a critical task in the current phase of informationization. The exchange of information across industries, business domains, and organizations is a key aspect of achieving these goals. The process of cross-domain information exchange is considerably more complex than simply transmitting information from one place to another, involving multiple stages such as information storage, metadata registration, user identity authentication, and access control. Moreover, cross-domain information exchange also faces many challenges, including data heterogeneity, platform heterogeneity, distribution, autonomy, and security. This study aims to address these challenges by proposing a model for the automatic classification of multisource heterogeneous ATC operational data security to enhance data management, ensure security, promote information sharing, and facilitate business collaboration within the civil aviation ATC system. [Methods] Herein, first, a dataset is constructed to facilitate the classification of the ATC operational data security. Representative data from various operational categories are selected, and 13 key security attributes are identified to design the data security classification. Five security levels are established based on relevant laws and regulations pertaining to data security and the characteristics of the civil aviation ATC operational data. Subsequently, an automatic classification model is developed based on the AdaBoost algorithm with the classification and regression tree (CART) as the base classifier, considering the unique characteristics of the ATC operational data. [Results] Experimental results demonstrate the effectiveness of the proposed automatic classification model. A comparative analysis of the proposed model against other machine learning algorithms reveals that the proposed model achieves the highest accuracy rate, reaching 95.5%. Thus, the proposed model successfully classifies multisource heterogeneous ATC operational data according to their security attributes, enabling the formulation of tailored security strategies and access control mechanisms for different data security levels. [Conclusions] This proposed model considerably enhances the data management capabilities of the civil aviation ATC system, ensures data security, promotes information sharing, and facilitates business collaboration within the system. Thus, this study provides a robust framework for addressing the challenges associated with data security and integration in complex operational environments, laying a foundation for further advancements in civil aviation ATC informationization.

[Objective] The design of Chinese high-speed railway tunnels, characterized by their high arched ceiling and large sections, presents unique challenges in terms of heat and mass transfer behaviors. These architectural features significantly influence the dynamics of smoke movement, resulting in distinctive patterns of longitudinal flow and temperature distribution of smoke during a fire, which differ markedly from those observed in conventional highway tunnels. [Methods] To investigate the specifics of smoke flow dynamics, this study embarked on full-scale fire experiments conducted within the Baijiashan tunnel of the Yuxiang high-speed railway between Chongqing and Qianjiang. These experiments were instrumental in capturing critical data on flame height and longitudinal distribution of smoke temperature under various fire scenarios. Building on this empirical foundation, the study analyzed the combustion stages and calculated the longitudinal smoke velocity for each fire scenario examined. [Results] Previous literature has highlighted that the heat release rates in full-scale experiments were calculated based on the equivalent diameter of fire sources, with values of 0.38, 1.01, and 2.52 MW, respectively. It was observed that as the heat release rate increased, there was a corresponding significant uptick in the longitudinal velocity of the smoke. Within the confines of a high-speed railway tunnel, the vertical temperature distribution of fire smoke exhibits a distinct top-hat pattern. This characteristic distribution remains consistent farther from the fire source. Furthermore, this study delineates the boundary between one-dimensional shooting flow (Region II) and critical flow (Region III) within the context of a Chinese high-speed railway tunnel, identified as x/H ≈3.85 based on experimental data. The study also probes into the suitability of existing models for predicting the longitudinal flow and temperature distribution of fire smoke in long, narrow spaces such as high-speed railway tunnels. It was found that owing to the extended length of one-dimensional shooting flow (Region II), models that assume constant smoke thickness fall short in accuracy within this region. [Conclusions] This study revealed that despite the larger net height and cross-sectional area of high-speed railway tunnels compared to those of conventional railway tunnels, the heat release rate of the fire source critically influences the speed at which smoke spreads longitudinally. Moreover, the evolution of vertical temperature distribution is determined by the convective heat transfer coefficient beneath the ceiling and the ceiling jet thickness. As the smoke spreads, the smoke velocity evolution, along with the convective heat transfer coefficient and ceiling jet thickness, gradually stabilizes. This stabilization contributes to the stable top-hat temperature profile observed vertically. Leveraging Froude scaling, a new model for the longitudinal attenuation of smoke temperature rise in Region III of a Chinese high-speed railway tunnel has been developed and validated for x/H ≥3.85. The insights gained from this work enrich the experimental research on the characteristics of longitudinal smoke flow in Chinese high-speed railway tunnels. Moreover, the field data obtained on the longitudinal flow and temperature distribution of fire smoke offers theoretical support for evaluating how the longitudinal spread of fire smoke affects personnel evacuation strategies in Chinese high-speed railway tunnels.

[Objective] Recently, extreme precipitation has increased globally. Waterlogging disasters caused by rainfall have endangered people's lives and caused property losses. As the cell of the city, the community is the fundamental unit to resiliently withstand disasters. However, stress testing in the community resilience field is still in its infancy, and little research exists on relevant theoretical and technical frameworks. Therefore, this paper uses a rainstorm waterlogging disaster as an example to study the community resilience stress test method and provides application cases. [Methods] The community resilience stress test stimulates and assesses community resilience in response to various emergency events. Herein, the resilience curve method is used to calculate community resilience. This paper presents a specific community resilience stress test method for rainstorm waterlogging disasters. First, using the historical rainstorm disaster data and rainstorm intensity formula, 12 extreme rainfall scenarios were designed according to the 2 dimensions of hourly rain intensity and rainfall duration, covering 30-200 mm hourly rain intensity. Second, based on InfoWorks Integrated Catchment Modeling, this paper constructs a community rainstorm waterlogging hydrodynamic model. This study conducted the community rainstorm waterlogging measurement experiment in the rainy season. The monitoring data obtained are used for parameter calibration and validation of the hydrodynamic model. Then, this paper presented a resilience evaluation method focusing on engineering resilience. The system performance of community rainstorm waterlogging is defined by the proportion of inundated areas. The system performance of a drainage network is defined by the fullness of the drainage network. Community waterlogging resilience was calculated using these two types of system performance. Resilience is expressed using the area of the concave portion of the system performance curve of community rainstorm waterlogging. The termination time of the integral is calculated as the time when the system performance of the drainage network returns to 1. [Results] Using the community J in Beijing as an example, this paper conducted a stress test on the community's waterlogging resilience under 12 different extreme rainfall scenarios, based on the results of hydrodynamic simulation. The results show that community resilience is less affected by rainfall duration and positively correlated with hourly rainfall intensity under rainstorm waterlogging disasters. Under the extreme rainfall scenario of 200 mm/h, about 44% of the community was flooded, and the maximum water depth was nearly 1 m. About 95% of drainage pipes are overloaded. It takes 5.7 hours to fully restore the drainage capacity of the network. Waterlogging spots of varying severity in this community are observed. This paper provides targeted suggestions on how to improve community resilience under rainstorm waterlogging disasters for five main waterlogging-prone spots. [Conclusions] This paper proposes a stress test method for community resilience to waterlogging and analyzes the evolution process of resilience and risk tolerance of community J from two perspectives: drainage capacity of pipe network and inundated area of the community. This method provides a quantitative assessment of community resilience. The test results can be used for monitoring and investigating rainstorm waterlogging risk in community institutions and government departments. These results are conducive to preventing and resolving disaster risks in advance.

[Objective] The primary aim of this research is to address the critical issue of potential fires arising from fuel spillage on hot surfaces. This work is vital owing to the inherent risks associated with such scenarios, particularly in industrial environments where accidental contact between flammable liquids and hot surfaces can lead to disastrous outcomes. A comprehensive understanding of the evaporation patterns and heat transfer mechanisms of fuel droplets on heated surfaces is imperative for mitigating these fire hazards. [Methods] By undertaking this investigation, the goal is to provide valuable insights that can inform safety protocols, design considerations, and risk assessment strategies in various industries dealing with flammable substances. Glass heating substrates serve as the foundation for the investigations, allowing us to simulate real-world scenarios in which fuel droplets come into contact with hot surfaces. To maximize the infrared transmittance of the glass, we increase the transmittance film on the quartz glass to 93%-96%. This study encompasses a range of representative fuels, including acetic acid, ethanol, acetone, ethyl acetate, n-heptane, and cyclohexane, to ensure a comprehensive understanding of the diverse fuel properties. In experimental analysis, we employ state-of-the-art infrared imaging technology in conjunction with a robust volume estimation method. This combination of tools enables us to precisely observe and measure the evaporation behavior of the selected fuel droplets. [Results] This study had yielded innovative and noteworthy results that significantly contributed to the current body of knowledge in this field. Unique thermal patterns on the surfaces of different fuel droplets were observed, providing a detailed understanding of the evaporation process. Hydrothermal waves (HTWs) and Bénard-Marangoni (B-M) cells were identified on acetic acid and ethanol droplets, representing a novel finding with implications for the broader understanding of thermal dynamics on liquid surfaces. A particular highlight was the identification of a previously unreported double-vortex thermal pattern on the surface of cyclohexane droplets. This discovery added a layer of complexity to the existing literature, highlighting the complexity and diversity of thermal behaviors in the context of fuel evaporation on heated surfaces. It founded that the contact angle exhibited minimal variation, generally staying within a range of 10 degrees for all six fuels. Consequently, when evaluating the droplet volume using the volume estimation method, it became clear that the liquid was not significantly influenced by changes in the contact angle, and such variations didn't affect the primary results. [Conclusions] In conclusion, this research illuminates the intricate interplay between fuel droplets and hot surfaces, providing crucial insights for fire prevention strategies and safety measures. The observed thermal patterns, including the novel double-vortex pattern, provide a deeper understanding of the underlying mechanisms governing fuel evaporation. This knowledge is instrumental in refining safety protocols, designing effective preventive measures, and informing future research in the broader field of fire safety and risk management. The findings of this investigation underscore the need to consider specific fuel properties and surface characteristics when developing targeted safety strategies for industries dealing with flammable substances. In the future, the goal is to integrate these insights into practical applications, potentially enhancing the safety and resilience of industrial processes involving flammable liquids.

[Objective] Multisource fire accidents frequently occur in tunnels, and their combustion characteristics are complex, influenced by both the parameters of the source itself and air entrainment and thermal feedback of adjacent fire sources. The combustion characteristics of multisource fires are related to the size, fuel type, and spacing of neighboring sources. In a dual-source fire in a tunnel, adjacent dual sources may compete for air, leading to flame merging. During flame merging, special flame phenomena occur, such as flying fire and fire whirlwinds, increasing the probability of fire spread and the degree of danger. Thus, building a reduced-size tunnel model to systematically analyze the evolution mechanism of multisource fire behavior is necessary. [Methods] Herein, we built a 1∶6-scaled tunnel model and conducted scaled experiments to investigate the dynamic evolution characteristics of restricted symmetric dual-source fire in natural ventilation tunnels under different fire source spacings. We studied the combustion rate, flame morphology, flame fusion, and ceiling temperature distribution. In particular, the ceiling temperature was further divided into near- and far-fire-source regions. We aimed to reveal the evolution of an asymmetric entrainment mechanism involving flame tilting and the fusion of a restricted symmetric dual-source fire in a tunnel. In addition, we constructed a quantitative model for the highest temperature rise of symmetrical dual-source fires under different fire source spacings and lateral offset distances. Thus, the dynamic characteristics of the tilting or even fusion of a restricted symmetric dual-source fire were elucidated. [Results] This study found that the mass loss rate, heat release rate, and flame height of the fuel were negatively correlated with the lateral offset distance and fire source spacing. When the dimensionless distance between the fire sources (S/D) was less than or equal to 1, flame fusion occurred, and a peak temperature occurred below the ceiling. As the distance between fire sources increased, the maximum temperature distribution transitioned from a “single peak” to a “double peak”. When the S/D≥4, the two fire sources essentially burned independently, and the peak number of the maximum temperature curve changed to 2. The dimensionless maximum temperature rise in the near-fire-source region exhibited an exponential decay relationship with the dimensionless lateral offset distance. A prediction model for the maximum temperature rise in the near-fire-source region was established and verified through comparison with experimental data from previous study and this study and numerical simulation results. [Conclusions] This study provides basic data to further elucidate the combustion mechanism of dual-source fire in tunnels under different lateral offset distances. Moreover, this study offers a theoretical basis for smoke control and emergency rescue during multisource fires in tunnels.

[Objective] In this paper, we proposed a new method to enhance the flexural performance of reinforced concrete (RC) beams, improve construction efficiency, and reduce the wet work at the reinforcement site. This method involves reinforcing RC beams with prestressed carbon textile reinforced concrete (P-TRC) plates connected to the RC beams using nails. [Methods] The proposal is underpinned by a four-point bending test conducted on P-TRC plates RC beams. The test results led to the development of a calculation formula for the height of the compression zone in beams reinforced with P-TCR plates in different modes, such as cracking, yielding, tensile failure, and compression failure. [Results] These calculations consider the strain hysteresis of the carbon fiber fabric, which is caused by nail bending. Furthermore, the formula to calculate the bending bearing capacity of the reinforced beam's tension zone under different failure modes was obtained from moment balance. This paper also introduces the stress mechanism of the nail as a reinforcing layer. When traditional layer paving methods are used to reinforce the RC beam, the adhesion between the reinforcing layer and the RC beam relies heavily on chemical adhesion, the frictional resistance between the old and new concrete, and the mechanical occlusion force of the joint surface. However, quantifying the shear performance index of the reinforcing layer proves challenging, and it is difficult to guarantee the failure mode of the reinforcing layer. If peeling or detachment occurs in the reinforcement beam, it could easily lead to a failure in the reinforcement effect. Conversely, when a nail is used for reinforcement, the nail bears the shear capacity of the reinforcement layer. The shear bearing capacity of the nail gradually tends to decrease from the pure bending section of the reinforced beam to the bending and shear section of the same. Under the action of the concentrated force couple formed by the load and the support reaction, the nail in the bending shear section undergoes normal tension. This normal tensile force is generated by the frictional force between the nail and the concrete. By controlling the number, size, and shear strength of nails, the shear performance index of the reinforcing layer can be quantified. Consequently, the P-TRC plate only experiences a failure mode of tensile failure. Additionally, this paper proposes a calculation formula for the midspan deflection of the beam reinforced with a P-TRC plate during normal use, considering the elongation of the reinforcement at the bottom of the beam. Moreover, through experimental procedures, a theoretical calculation formula for the maximum midspan deflection of the beam reinforced with P-TRC plates is proposed. [Conclusions] To validate the calculation formula for the bending bearing capacity and deflection of the reinforced beam, the flexural capacity and mid-span deflection curve of the normal cross-section of the beam reinforced with P-TRC plates under six different working conditions was calculated and compared with the test value. The results show that the theoretical and experimental values of the beam reinforced with P-TRC plates are consistent. This suggests that the presented calculation method holds significant value as a reference for guiding actual engineering design.

[Objective] With the rapid development of informatization and digitization, it has become challenging for traditional 2D design methods to meet the requirements of tight time limitations and lifecycle modeling management. In addition, the manual assignment of model properties is complicated and time-consuming for designers. To improve the inefficiency and inconvenience of manual retaining design and to enrich incomplete information generated using existing BIM software. [Methods] This paper summarizes the boundary condition and process of deploying retaining according to specification and studies the delivery requirements of BIM information and the challenges of traditional design software. Then, an intelligent algorithm for deploying a retaining wall is proposed, with which the condition for placing the retaining wall can be checked at each station along the path. The automatic matching of retaining types and heights, bottom slope smoothing, and merging of different segments are also achieved. A retaining software plug-in is redeveloped based on the OpenRoads Designer of the Bentley platform for validation and application. National standard drawings and subgrade retaining structures are embedded in the system, guaranteeing the structural security of the wall. The continuous highway is discretized into station sequence, and a dichotomy is used to rapidly find the most suitable height on each section, considering the flap width and buried depth requirements. To optimize the construction cost, the location of the retaining wall is filtered by the side slope height along the highway. Various types of retaining walls contained in the software can be selected by custom priority. The subgrade retaining walls are divided into different parts based on length and bottom slope restriction. The bottom edges of the generated segments are finally readjusted to a linear or stair-stepping state, and the height of each section is recalculated based on the measurements. Thus, the one-click intelligent design of subgrade retaining is completed. [Results] Several products were obtained by the system, which were summarized as follows: (1) Plan, elevation, and cross-section drawings of each retaining segment, including graphic shapes and size dimensions. (2) Engineering quantity sheets containing detailed items. (3) 3D retaining models attached with information in the level of details 3.0. The output provided accurate results, fulfilled industrial requirements, and could be further used in construction, operation, and maintenance process management. The method was validated by a practical highway project with a length of 13.4 km. The comparisons of the results with HintCAD (a popularly used software on highways) were summarized as follows: (1) Deviation was less than 6% on the total retaining length, gravel inverted filter layer, geotextile, and earthwork volume owing to the ignorance of geology and environmentally sensitive areas and terrain-calculation difference between 2D and 3D methods. (2) The error of average retaining height and concrete volume is less than 12%, which was caused by manual and conservative bottom handling methods. (3) The precision accuracy was completely accepted table for engineering projects in the preliminary design stage. (4) The calculated results could be further modified by users to fulfill the design intent. [Conclusions] Thus, this method offers a better option for retaining design and deployment and considerably improves design efficiency, 3D visualization, and property information compared with the current design approach, which contributes to 3D forward design in railway and highway projects.

[Objective] Wet spray concrete is an important initial support method in new Austrian tunneling method construction. However, the production of harmful substances, such as dust and chloride, during construction remains a serious threat to the health of workers. At present, much research has been on the sources of dust and dust control measures in wet spray technology, whereas scarce research was on dust generation in wet spray concrete until 2023, and there is insufficient understanding of the dust generation mechanism. [Methods] In this study, concrete with different flowabilities was prepared by changing the polycarboxylate superplasticizer (PCE) dosage in the wet spray concrete mixture. A self-constructed multidimensional test platform for jet flow was used to perform flowability and spray tests on fresh concrete with different flowabilities. This work coupled the theories of jet fragmentation and surface oscillation to examine the jet fragmentation process and dust production characteristics of wet spray concrete, investigating its dust generation mechanism. The flowability tests characterized the concrete’s flowability using slump and plastic viscosity. The jet tests primarily included capturing wet spray concrete jets using a high-speed camera and computer vision tools, such as OpenCV, to process the images, including grayscale conversion, noise reduction, sharpening, binarization, morphological operations, and contour extraction. The spread angle of the jet was measured to evaluate its coherence. In addition, MATLAB was used to examine the size of concrete droplets splashed on the side plate lightbox in the experimental chamber to calculate dust concentration and particle size distribution during the wet spraying process, which was compared with the results of a laser dust analyzer. [Results] According to the jet states, the jet flow cycle was classified into primary, intense, and ending stages. The initial and ending stages did not form stable jets, whereas the intense stage demonstrated less variation in jet morphology and high levels of jet fragmentation and atomization, considerably impacting the dust concentration. For the initial and ending stages, the PCE dosages of 1.00%, 1.10%, 1.15%, and 1.20% led to relatively stable jets with minimal fragmentation. The PCE dosages of 1.25%, 1.30%, and 1.35% mainly had primary fragmentation, and a PCE dosage of 1.40% had secondary fragmentation. In the intense stage, the PCE dosages of 1.00%, 1.10%, and 1.15% mainly showed primary fragmentation, whereas the PCE dosages of 1.20%, 1.25%, 1.30%, 1.35%, and 1.40% primarily exhibited secondary fragmentation. The average dust concentration increased by 138% in the secondary fragmentation stage compared with the primary fragmentation stage. The particle size distribution of the dust decreased and then increased with increasing PCE dosage, with the smallest dispersion observed at 1.15% PCE (10.40-19.80 μm). As the PCE dosage increased, the frequency of small particle dust decreased, and the distribution of dust frequency approached uniformity while the particle size dispersion increased. The concrete mixture with the lowest dust concentration and most concentrated dust particle size distribution was identified as cement, water, fine aggregate, coarse aggregate, PCE (1.000 0∶0.370 0∶1.837 5∶1.562 5∶0.011 5). This work examined the mechanism of concrete jet fragmentation and dust production. Intense aerodynamic effects resulting from substantial velocity differences at the nozzle produced surface waves as the jet moved further, resulting in the detachment of surface concrete droplets and causing primary or secondary fragmentation and dust formation. At higher PCE dosages, a portion of free water adhered to the surface of the mixed material, producing a lubrication layer between the filled mixture and the delivery pipe during pumping. At the nozzle, the concrete aggregates and lubrication layer underwent primary and secondary fragmentation, producing small liquid droplets that collided and bonded to form dust.[Conclusions] This work investigated the dust generation mechanism and characteristics of wet spray concrete jets, classified the jet spray stage, and explored the mechanism of concrete jet fragmentation and dust generation. This offers valuable insights and references to dust reduction work in wet spraying; however, exploring the microlevel aspects of jet fragmentation in concrete with different flowabilities warrants further investigation, with several questions remaining to be answered in the future.

[Objective] Cable cranes are the main concrete transportation equipment used in arch dam construction. Productivity analysis of cable crane transportation is crucial for improving scheduling management, reducing operational costs, and controlling dam construction progress. However, the traditional manual recording method for analyzing cable crane productivity is time-consuming and labor-intensive. Moreover, existing monitoring methods, such as sensors and global navigation satellite systems, are susceptible to interference because of the challenging environment and complicated operating space at dam construction sites. Furthermore, they usually entail high installation and maintenance costs. Therefore, this study proposes an intelligent monitoring method based on visual tracking and pattern recognition for cable crane transportation in dam construction. [Methods] The proposed method initially tracks the process of cable crane transporting concrete using visual tracking technology to obtain the complete moving trajectory of crane buckets. Subsequently, it establishes a pattern recognition model to automatically identify the working states of cable cranes and calculate their productivity by analyzing the time-series features of the trajectory data. In the visual tracking of cable cranes, the main challenge is to address the similar appearance and occlusion problems of crane buckets. Therefore, we propose a new multiobject tracking framework by introducing a rematching mechanism based on tracklet features (segments of the entire object trajectory), which effectively reduces the occurrences of ID switches and enhances tracking accuracy. Additionally, You Only Look Once (YOLO) model is trained as the object detector of the tracking framework. Subsequently, trajectory data obtained by visual tracking is used as input for the pattern recognition model of cable crane working states, with the output being the pouring productivity. This pattern recognition model employs spline interpolation and Savitzky-Golay filters to solve the problems of missing values and noises in the trajectory data. A first-differential method is applied to statistically analyze the variation patterns of the trajectory data. This model can rapidly and accurately identify the working states and determine the key efficiency indicators of cable cranes. [Results] A testing experiment was conducted at an arch dam construction site to evaluate the monitoring performance using this approach. Experimental results are summarized as follows: 1) The proposed vision-based multiobject tracking method proves effective in detecting and tracking cable buckets in intricate construction scenes, thus achieving effective and complete tracking of moving trajectories of crane buckets; moreover, identity F1 score (IDF1) and multiple object tracking accuracy (MOTA) metrics reach 94.8% and 90.0%, respectively. 2) The proposed pattern recognition model can rapidly and accurately distinguish six working states in the cable crane transportation process, including horizontal transport, descent, unloading, ascent, horizontal return, and waiting for loading. 3) Key productivity indicators, such as duration of a single transporting cycle, number of transporting cycles, duration of each working state, and concrete pouring intensity, are accurately calculated and meet engineering management requirements. This also confirms the practicability, reliability, and accuracy of the proposed monitoring method. [Conclusions] Thus, this study successfully integrates vision-based tracking and pattern recognition technologies to develop an intelligent monitoring method, consequently achieving automatic and accurate calculation of cable crane productivity. Furthermore, it demonstrates a positive application effect at dam construction sites and provides innovative perspectives and technical support for construction management.

[Objective] The self-inducing impeller reactor is a high-efficiency device for gas-liquid and gas-liquid-solid three-phase mixing. This innovative reactor offers several advantages over traditional stirred reactors, such as higher gas utilization, a simpler structure, easier operation, and superior heat and mass transfer performance. Its potential applications span a range of chemical processes, from foam flotation and bio-fermentation to hydrogenation, oxidation, alkylation, and halogenation reactions. Despite its promising capabilities, the development and scale-up of the self-inducing impeller reactor largely rely on empirical knowledge and experimental work. Therefore, there is a clear need for more fundamental research to gain a better understanding of the reactor mechanics and provide essential foundational data for its future application. [Methods] In this study, we designed and constructed a double-disk self-inducing impeller using 3D-printing. The effects of different speeds and immersion depth of the impeller on the critical impeller speed, gas holdup, and gas-liquid mass transfer performance were studied. The critical impeller speed, a key indicator of the reactor's gas dispersal capability, is defined by the minimum speed at which the first bubble appears. It is influenced by several factors, such as the impeller's shape, size, immersion depth, as well as liquid properties. [Results] The experimental results indicate that the critical impeller speed increases as the immersion depth of the impeller increases. Moreover, deviations were observed between the predicted critical speeds and those achieved during operation, which could be likely attributed to axial drifts in the critical speed. Increasing the speed of the self-inducing impeller was found to significantly improve both the gas holdup and the gas-liquid interfacial area within the system. Under the experimental conditions described in this work, the gas holdup varied from 0% to 10%, with bubble sizes ranging from 1 to 5 mm. An automated platform based on LabVIEW was established to measure the mass transfer coefficient of hydrogen in tetrahydrofuran, achieving optimal gas-liquid mass transfer coefficients between 0.08 to 0.17 s^-1 for a liquid volume of 1.2 L. Furthermore, a dimensionless correlation was fitted to predict the k_La for the self-inducing impeller reactor, offering valuable guidance for reactor scaling-up. The results show that fitting data closely aligns with the experimental data. Finally, we explored the kinetics of the progesterone hydrogenation reaction within a self-inducing impeller reactor and conducted simulations using the Dynochem software based on the experimental data. These simulations indicated that variations in the mass transfer coefficients, specifically at 0.08/s and 0.8/s, do not significantly affect the reaction outcomes. This observation suggests that the mass transfer rate greatly exceeds the reaction rate (R_rxn/R_mt<10%). [Conclusions] In summary, this study successfully established an online automated research platform for a self-inducing impeller reactor. This innovative platform facilitated the evaluation of the reactor performance, focusing on crucial parameters such as critical speed, power consumption, gas holdup, bubble size, and mass transfer coefficient. Additionally, experiments and simulations were conducted on a small scale, specifically focusing on a progesterone hydrogenation reaction. These investigations provided preliminary insights into the effective scale-up of the reactor, laying a solid foundation for further analysis and development.

[Objective] A centrifugal compressor is a key equipment in the gas diffusion isotope separation cascade at pressures below 5 000 Pa, and its performance affects the economics of the separation cascade. Currently, only a few studies have focused on the performance and internal flow characteristics of centrifugal compressors under negative pressure conditions (inlet pressure ≤101 325 Pa), especially when the inlet pressure is as low as 400 Pa. Additionally, in our experiments with the designed centrifugal compressor, an increase in inlet pressure improved the pressure ratio for the same inlet volume flow rate. Therefore, investigating the impact of the inlet pressure on the performance of centrifugal compressors is necessary. [Methods] Taking the Krain centrifugal impeller as the research object, the finite volume method is used to solve the three-dimensional Reynolds time-averaged Navier-Stokes (RANS) equations, and the ideal gas state and Spalart-Allmaras turbulence model equations are substituted into the RANS equations. A single flow channel calculation model, including the inducer, impeller, and vaneless diffuser, is meshed by 1.88 million hexahedral structural grids. The thickness of the first layer of the grid near the walls is 6 μm, and the y⁺ value in most calculation domains is set to be less 10, satisfying the grid independence verification. The boundary conditions are as follows: total pressure, total temperature, and velocity along the axis direction are given at the inlet, while the mass flow rate is provided at the outlet; all walls are no-slip adiabatic boundaries. The relative deviation between the calculated values of the verification case and experimental values is approximately 3%, indicating the accuracy and reliability of the calculation method. [Results] The numerical results were summarized as follows. (1) As the inlet pressure decreased, the total pressure ratio and total isentropic efficiency of the compressor first decreased slowly and then decreased rapidly. When the pressure was 400 Pa, performance was reduced by 10% compared with that at 101 325 Pa, and the range of stable operating conditions decreased. (2) The specific entropy increase in the compressor components gradually increased with decreasing inlet pressure, implying that the specific flow loss was improved. Among them, the specific entropy increase in the vaneless diffuser increased faster than the two other components. (3) The distribution of the specific entropy increase revealed that the decrease in the inlet pressure reinforced backflow and secondary flow losses at the impeller outlet, as well as boundary layer lossed on the hub and shroud side of the diffuser. (4) The flow characteristics showed that when the inlet pressure decreased to 400 Pa, the backflow velocity at the impeller outlet increased, and the backflow region expanded. In the vaneless diffuser, as the inlet pressure decreased, the gradient of the radial velocity on the hub side and that of tangential velocity on the hub and shroud sides decreased, indicating a thicker boundary layer. [Conclusions] The decrease in the inlet pressure increases the thickness of the boundary layer on the hub side of the vaneless diffuser and enhances backflow and secondary flow at the impeller outlet, increasing the boundary layer, backflow, and secondary flow losses and subsequently decreasing compressor performance. Therefore, during the initial design stage of negative-pressure centrifugal compressors, performance predicted using a one-dimensional performance model based on positive pressure is high and needs to be corrected.