Abstract:

The performance of radial spherical plain bearing joints is investigated in this paper， based on the engineering background of steel roof renovation of Shanghai Stadium. First， tests on bearing capacity and rotational performance of the joint were performed under vertical compressive force. Both the ultimate bearing capacity and the strain intensity development feature were grasped. A method for calculating rotational friction coefficient and its value of the joint were proposed. Next， finite element numerical analysis was conducted using ABAQUS to further study the damage mode and mechanical behavior of the joint. It is found that the radial spherical plain bearing joint has good load carrying capacity and rotation performance under compressive condition， and achieves the function of fully hinged space node of steel structures.

Abstract:

To fulfill modular design and post-earthquake function recovery for reinforced concrete shear walls， a novel precast reinforced concrete shear wall with replaceable self-centering energy-dissipation components （RSECs） is proposed in this paper. This novel type of shear wall （named NPRW shear wall） mainly composes of RSECs， bottom blocks， and prefabricated wall panels， where each part is connected by high-strength bolts. When the structural wall is subjected to earthquakes， the RSECs dissipate most of the seismic energy and reduce residual deformation for convenient replacement after earthquakes. The design method of the NPRW shear wall is introduced， in which the design process is based on the conventional shear wall design. A finite element model of the NPRW shear wall is established to simulate the seismic performance of novel shear walls and the accuracy of the numerical model is verified by comparing with the experimental results. For three conventional shear walls design examples， the corresponding NPRW shear walls are designed based on the proposed design process， followed by numerical simulation and comparative analysis between the novel and conventional shear walls. The results indicate that the novel NPRW shear wall designed using the proposed method has similar bearing capacity and lateral stiffness， and exhibits good energy-dissipation capacity， and self-centering capability， which meet the design goal.

Abstract:

Conventional shield tunneling requires the construction of launching and receiving shafts， which limits its applicability in densely built-up urban areas with restricted construction space. Ground penetrating shield technology （GPST） overcomes this limitation by enabling shield launching and receiving directly at the ground surface without working shafts. Taking the GPST tunnel project beneath West Gaoqing Road in Shanghai as the engineering background， this paper meticulously documents and analyzes ground deformation across different overburdens （from shallow to ultra-shallow） encountered by the shield. Subsequently， it discusses the underlying mechanisms and evaluates the control techniques. The results show that when the overburden thickness is less than 0.4 times the tunnel diameter， the tunneling-induced surface heave exceeds 40 mm， and mitigation measures are required. Grouting volume and grouting pressure are identified as the key factors governing ground deformation during GPST construction. The combined application of partial-span reinforcement and surcharge loading provides a noticeable mitigation effect， whereas the full-span reinforcement together with surcharge loading achieves optimal outcomes.

Abstract:

Taking the deep soft soil subgrade project of the South Extension of Wanhuan West Road as the background， the K₀-MCC model was embedded into the finite element software ABAQUS through secondary development of a UMAT subroutine to establish a finite element model of deep soft soil subgrades considering soil anisotropy. Settlements， pore water pressures， and horizontal displacements caused by subgrade filling were calculated. The model’s validity was verified by comparison with field-measured data. The settlement and deformation mechanisms of deep soft soil subgrades were analyzed. Furthermore， by comparing the effectiveness of cement-mixed piles and prestressed pipe piles in controlling settlement， reinforcement methods suitable for deep soft subgrades were proposed. The results indicate that the initial stress anisotropy of the soil and stress-induced anisotropy have significant effects on the settlement and deformation of soft soil subgrades. The settlement during the two-stage surcharge of the deep soft soil subgrade reached 0.337 m， while the consolidation settlement occurring during the construction interval after the first surcharge was only 0.005 m. Within one year after the surcharge， as excess pore water pressure dissipated and the subgrade continued to bear load， settlement further developed， reaching a total of 0.366 m， with settlement generated during surcharge construction accounting for 92 % of the total. After subgrade filling， settlements were larger at shallower depths and closer to the subgrade center. Compared with cement-mixed piles， prestressed pipe pile reinforcement is more effective in controlling construction settlement of deep soft soil subgrades， particularly in terms of total and long-term settlement control.

Abstract:

Under the background of urban stock renewal， it is essential to strategically allocate limited funds and resources to existing rail transit station areas with higher potential returns. Scientifically identifying stations with renewal potential is critical for promoting urban spatial integration and structural optimization. From the perspective of sustainable development of rail transit passenger flow， this paper argues that station areas with renewal potential should possess both the capacity for passenger flow growth and the potential to stimulate surrounding vitality. To effectively detect changes in passenger flow–heat interaction types， it employs multi-source data， taking 408 metro stations in Shanghai as case studies. Explainable machine learning models are developed for the years 2019， 2021， and 2023 to identify the driving and limiting factors of station passenger flows. Based on this， station area passenger flow–heat interaction types are classified into four main categories and eight subcategories. The spatial Markov chain method is then applied to analyze the transition patterns of these interaction types from 2019 to 2021 and from 2021 to 2023. In addition， it explores the positive and negative spillover effects from neighboring station areas. Moreover， it proposes a method to pre-assess the renewal potential of station areas from the passenger flow-heat interaction perspective， providing a scientific foundation and policy suggestions for the urban renewal of existing rail transit stations.

Abstract:

To address the difficulty of quantitatively planning rail transit network structures in practical applications， a quantitative planning method for urban rail transit network structure based on potential corridor search is proposed. Based on a summary of the fundamental characteristics of rail transit network structures， potential rail transit corridors are searched by combining the concept of the depth-first search （DFS） graph traversal algorithm with a full-path search algorithm. Subsequently， a set of potential network structure schemes is generated by matching potential corridors one by one to form network structures. The potential network structure schemes are evaluated and screened through a preliminary model split under each potential network structure and an objective function that minimizes total social cost， ultimately yielding an optimal set of network structure schemes. The method is implemented and validated through a case study， and the results demonstrate that the proposed method is feasible and effective， with strong engineering application value.

Abstract:

A two-dimensional tread braking thermo-mechanical coupled finite-element mathematical model is established that balances computational accuracy and efficiency， integrating the high accuracy of strong thermo-mechanical coupling with the high efficiency of weak coupling. The effects of track gradient， vehicle load and axle load， initial emergency-braking speed， emergency-braking deceleration， and ambient temperature on the maximum tread temperature and peak thermal stress of the wheel are investigated. The results show that for every 3 ‰ increase in track gradient， the maximum wheel-tread temperature increases linearly by approximately 4.15 °C， while the maximum thermal stress increases linearly by about 8.18 MPa. For each 1 t increase in axle load， the maximum temperature increases linearly by approximately 7.19 °C and the maximum thermal stress by about 14.29 MPa. For every 10 km·h?1 increase in initial braking speed， the maximum temperature increases approximately linearly by about 31.21 °C and the maximum thermal stress by about 59.77 MPa； meanwhile， the time required to reach the maximum temperature and stress increases nonlinearly with speed. When the deceleration increases by 0.2 m·s?2， the maximum temperature increases approximately linearly by about 16.12 °C and the maximum thermal stress by about 31.67 MPa， while the time to reach the maximum temperature decreases nonlinearly. As ambient temperature decreases， the maximum tread temperature shows a downward trend， whereas its influence on the maximum thermal stress is relatively small. These findings provide quantitative data support and technical reference for thermal safety evaluation and optimized design of train operations on long and steep gradients.

Abstract:

To investigate the relationship between the characteristics of trackside noise and the geometric defects of the wheel tread in subways， it is necessary to accurately locate the spatial position of the wheel-rail noise source of the moving train. A noise source localization method based on the coherence of trackside signal environment is proposed. First， acoustic signals are collected by deploying sensor arrays. Then， the time difference of arrival （TDOA） calculation method for trackside acoustic time-domain signals was optimized using the Euclidean norm. Finally， the feasibility of this improved moving sound source localization method was verified by comparing it with traditional methods. The results demonstrate that the proposed method achieves better error stability at speeds below 60 km·h^－1. Regarding the localization range， the method performs well within a predicted angle range of θ < 59.5°. The proposed method achieves high-precision localization of moving point sound sources for signals with a signal-to-noise ratio （SNR） above 40 dB.

Abstract:

The hyporheic zone is a place where river water and groundwater frequently interact， whose internal nitrogen cycle is of great significance for maintaining the ecological health of rivers. Taking tidal rivers in the Shanghai as the research object， the seasonal variations in inorganic nitrogen concentrations in groundwater in the riparian hyporheic zone and their key driving factors were investigated using on-site monitoring， sampling tests and statistical analysis. The results show that ammonia nitrogen （NH??—N） and nitrate nitrogen （NO??—N） concentrations were significantly higher during the hyporheic flow （HF） net inflow period than those during the HF net outflow period， while nitrite nitrogen （NO??—N） concentration was extremely low. With increasing distance from the river， the dominant form of inorganic nitrogen shifted from NO??—N to NH??—N， and NH??—N concentration initially increased and then decreased while NO??—N concentration gradually decreased. The key factors influencing the changes in inorganic nitrogen concentrations in groundwater in the hyporheic zone were hyporheic exchange flux， Eh， and pH during the HF net inflow period ， and Eh and hyporheic exchange flux during the HF net outflow period. The function of hyporheic zone in tidal riverbanks tends to be a nitrogen sink during the HF net inflow period and a nitrogen source during the HF net outflow period.

Abstract:

Nitrogen， as a critical nutrient for crop growth， has raised sustainability concerns in agricultural systems due to soil-groundwater pollution caused by excessive application. This review begins with an elaboration of nitrogen transport-transformation processes in crop root zone soil-water systems， followed by a systematic analysis of numerical simulation theories governing its subsurface migration. Particular emphasis is placed on critical evaluation of advancements and persistent limitations in current modeling approaches. Building on the current research landscape， three pivotal development trajectories are explored， including quantitative characterization of multi-process interaction mechanisms， accurate acquisition of data and information， and systematic integration of advanced modeling methodologies. Finally， future research directions are proposed for nitrogen migration-transformation simulation in crop root zone soil-water systems.

Abstract:

Advanced oxidation processes （AOPs） based on peroxides such as persulfate and peracetic acid have become a research hotspot in water environment treatment in recent years， and they have high efficiency for the degradation of new pollutants such as polycyclic aromatic hydrocarbons （PAHs） in soil and groundwater environments. Meanwhile， carbon-based materials， as electron shuttles in emerging peroxide activation systems， have also attracted extensive attention due to their high specific surface area， abundant functional groups， diverse modification methods， and advantages of low cost and minimal secondary pollution in water environment remediation. Carbon-based materials readily induce non-radical pathways during the catalytic activation of peroxides， and the direct electron-transfer non-radical mechanism has received far less scholarly attention than pathways involving singlet oxygen or high-valent metal-induced oxidation. This electron-transfer process is closely related to metastable intermediates formed between carbon-based materials and peroxides. Therefore， this paper describes the direct electron transfer mechanism of activated peroxides of carbon-based materials in different dimensions based on related studies， and summarizes the possible adsorption active sites and influencing factors of this mechanism， so as to provide a theoretical foundation for research in related fields. Finally， the characterization methods of the electron transfer process （electrochemical method， chemical quenching method） are introduced， and the current problems and future development prospects of the system are proposed， hoping to provide feasible ideas and methods for the deeper research and wider application of the system.

Abstract:

The automated mooring system of a vessel is subject to large operational loads and requires fast wave-compensation motions. When a full-degree-of-freedom parallel mechanism is used as the mooring device， a large number of hydraulic cylinders are needed as actuators. Due to the high loads and large quantity of cylinders， stringent requirements are imposed on the flow rate and power capacity of the hydraulic system. To address this issue， a low-degree-of-freedom 2UPU-2SPU parallel unit is proposed. By installing one such unit at both the bow and stern of the ship， a dual parallel mechanism configuration is formed that meets the requirements of automated mooring. A comprehensive analysis and optimization of the workspace， kinematic behavior， and mechanical performance of the proposed mechanism are conducted. Screw theory is employed to analyze the motion characteristics of the 2UPU-2SPU parallel unit. Based on the transmission and constraint characteristics of motion and force， a high-quality workspace is defined to avoid transmission singularities and constraint singularities. The regular high-quality workspace volume index， global transmission/constraint indices， and global stiffness performance indices of the mechanism unit are derived. Taking these three categories of indices as objective functions， dimensional optimization is conducted using the SPEA2 multi-objective optimization algorithm. Furthermore， in accordance with preferences for dynamic and static performance， the analytic hierarchy process （AHP） is applied to select solutions with superior overall performance. The proposed mooring system explicitly considers installation constraints and coordinated combined motion. The unit mechanisms can be installed on the quay primarily through an anchor-bolt system， facilitating practical deployment.

Abstract:

To address the challenges of the non-position sensing algorithm in response speed， dynamic stability and calculation time of high-speed permanent magnet synchronous motor under low speed conditions， a new high-frequency injection down-order estimation method is proposed. By reducing the integration link of the position observer and the use of the bandpass filter， the phase delay of the rotor is reduced， and the dynamic response and algorithm efficiency of the system are improved. Moreover， the steady-state error is eliminated by introducing the feedforward compensation of the rotor’s phase angle position， realizing error-free tracking. The experimental results demonstrate that the proposed method achieved a rotor position estimation error of 5.7 ° under steady-state conditions at 300 r·min^-1， which is only ?31 % of that of conventional methods. Additionally， the settling time during dynamic conditions is reduced by ?30 %?， and the computational time of the algorithm decreases by ?18 %?. The proposed method exhibites advantages such as ?fast response， stable dynamics， and reduces computational load， meeting the requirements for rapid and reliable startup in high-speed motor systems.

Abstract:

The large nephrite deposit recently discovered in Luodian， Guizhou Province represents a major breakthrough in the exploration history of nephrite in China. Previous studies have shown that this deposit has obvious particularity and difference compared with other known nephrite deposit， both domestically and internationally. To reveal the new genetic type of the deposit， this paper analyzes the source of Si and Ca essential for mineralization. By integrating the geological characteristics of the mining area with the sources of metallogenic materials and the physicochemical conditions of mineralization， the deposit’s genesis was determined， and a metallogenic model was established. This provides a scientific basis for the rational exploitation of the Luodian nephrite deposit and supports mineralization prediction， exploration， and development of nephrite deposits in neighboring areas.

Abstract:

Snowball options are path-dependent exotic derivatives with embedded barrier structures， whose payoff profiles hinge on the price trajectory of the underlying asset over the full lifespan of the contract. Within the classical Black-Scholes model framework， this paper constructs a partial differential equation （PDE） model for the valuation of snowball options under continuous monitoring conditions. By integrating financial replication techniques and PDE-solving theories， an explicit pricing formula is derived. The computational efficacy of this closed-form solution is further evaluated through systematic comparisons with numerical methodologies， namely the finite difference method and Monte-Carlo simulation. Additionally， drawing on real-world market parameters， the paper probes into the impacts of key determinants， such as volatility and barrier levels， on option prices. The findings provide viable methodological guidance for the practical pricing of snowball options， and supplement the pricing analytics of relevant structured products under continuous monitoring scenarios.