The construction of happy rivers and lakes is a significant initiative to expedite ecological civilization construction and a crucial task for the river-lake chief system at present and in the future. Taking the construction of a happy river and lake project in Zhongqu, Tibet as a case study, we outline 15 key tasks of the Zhongqu project from three aspects: river system governance, improvement of river management capacity, and support for the development of the watershed region. Subsequently, in comparison with the work plan for evaluating the effectiveness of happy-river-and-lake construction, we analyze the effectiveness of the Zhongqu project from seven perspectives: safety, ecology, livability, intelligence, culture, development, and public satisfaction. Given the unique geographical location, climatic conditions, topography, ecological environment, and cultural customs in the Zhongqu watershed, we discuss the challenges and propose corresponding solutions and suggestions. The pilot exploration of constructing happy-river-and-lake project for the Zhongqu River offers a theoretical foundation and technical reference for similar projects on the plateau.
The Wuhu-Yuxi reach, one of the vital links between cities in the Yangtze River Delta urban area, is located in the lower reaches of Yangtze River. Understanding the evolution of the Wuhu-Yuxi reach under new hydro-sedimentary conditions provides theoretical support for future flood control and river regulation. Observed field data for the Wuhu-Yuxi reach was analyzed to understand the altered flow-sediment regime and erosion-deposition features after the operation of the Three Gorges Reservoir (TGR). Results reveal that the Wuhu-Yuxi reach has remained generally stable. The riverbed is mainly subject to scouring, with the heads of sandbars eroded and retreating. Erosion on convex banks and deposition on concave banks have emerged in the sharp-bend section and the multi-braided section due to the development of the right sub-branch of upstream Qianzhou bar upstream which leads to an increased diversion ratio, and the mainstream chute cutoff resulted from the prolonged duration of medium-low water levels. Short sub-branches have also developed in the multi-braided section because the diversion ratio of the left sub-branch in the multi-braided section of Chenjiazhou bar has increased, which in turn intensifies the scouring of the Chenjie and Caojie waterways.
Curved slopes in natural river channels are highly susceptible to erosion, posing a significant challenge for river management. To address this issue, a comparative study was conducted on the protective effects of sand-and-gravel rip-rap bags of different shapes against erosion based on the concept of ecological slope protection. First, a geometric model of the curved-channel bed was constructed according to the actual river structure. Then, the CFD-DPM method was employed to analyze the bank-protection effects of rectangular, hemispherical, and semi-cylindrical bags placed on the concave bank of the curved channel. Results revealed that under a flow velocity of 0.5 m/s, among the three shapes of protection bags, rectangular bags bring about the least pressure on the concave bank, while semi-cylindrical bags obstruct the largest amount of sediment particles, leading to the smallest Reynolds number of particles and the minimum average particle velocity, 9% lower than that in the model without protection bags. In conclusion, rectangular rip-raping bags offers better protection for the adjacent concave bank, while semi-cylindrical bags provide the most effective sand-blocking function.
To reveal the formation and evolutionary patterns of typical meandering river morphology in the main stream of the Tarim River, this study used remote-sensing images and overlaying techniques to summarize the types of planform changes in the river boundaries of the middle reach of Tarim River from Wusiman to Aqike over the past decade. Moreover, integrating measured cross-sections and hydrological data, river regime analysis was employed to evaluate the stability of river cross-sections at different times. The results are as follows: 1) The planform geometric evolution of the middle reach from Wusiman to Aqike can be categorized into four single patterns (positive shift, negative shift, extension, and contraction) and four combined patterns (positive shift plus extension, positive shift plus contraction, negative shift plus extension, and negative shift plus contraction). Among them, the positive shift plus extension pattern is the most prevalent in the study reach. 2) Morphological parameters, namely the offset degree and widening degree, along with their calculation methods, were proposed to depict the main types of planform evolution in river channels. Annual discharge was found to be the primary factor influencing the offset degree, followed by the annual sediment transport and bedload discharge. Flood was identified as the key factor affecting the widening degree. 3) In recent years, the hydraulic geometric relation coefficient has increased, suggesting an enhanced longitudinal stability of the riverbed. Meanwhile, the transverse stability of the riverbed has also improved along the study reach. This research offers significant reference for flood control engineering and river channel regulation of meandering rivers in the middle reach of the Tarim River.
With the access of large-scale wind power stations and solar power stations, wind energy and solar energy affect the safe and stable operation of the power system due to the lack of prediction accuracy. This paper presents an optimal scheduling method for the hydro-wind-solar complementary system based on standby flow. First, the standby flow is set according to the available water of each hydropower station based on the inflow. Then, the optimal scheduling model based on standby flow is developed. The objectives of this model are to maximize power generation and minimize the variance of residual load. Standby flow serves to mitigate the impact of inaccurate wind and solar energy predictions. Finally, a case study is conducted on the cascade hydropower station and connected wind and solar power stations along the lower Yalong River. Results show that compared with the scenario without standby flow, the power generation efficiency of the multi-energy complementary system with standby flow in typical wet month (June) and typical dry month (December) increases by 0.08% and 1.97%, respectively; and the variance of residual load decreases by more than 40%. In conclusion, setting standby flow can balance the power supply and demand of the power system while ensuring power generation efficiency, thereby guaranteeing the safe and stable operation of the power system.
To analyze the impacts of land use and climate change on flood season runoff in tropical island regions, we selected the middle and lower reaches of the Nandu River basin in Hainan, a tropical river area, as the study area. We employed the SWAT model to simulate flood season runoff changes under different scenarios. Results indicate that, under the land use change scenario, converting cropland or planted forest land to natural forest land in the watershed reduces both the average monthly runoff and its variance during the flood season. Conversely, converting planted forest land to cropland increases these two parameters. The runoff generation capacity of cropland is larger than that of planted forest land and natural forest land in descending order. Under the climate change scenario, the average monthly runoff and its variance during flood season in the basin are directly proportional to rainfall and inversely proportional to temperature. Particularly, the flood season average monthly runoff changes at Longtang Station are more susceptible to climate change. In the integrated scenario, compared with the base period, the increment of average monthly runoff and its variance due to climate change significantly outweighs the decrease caused by land use change. Longtang Station shows higher sensitivity to climate change.
China’s first-generation global land surface reanalysis CRA monthly precipitation products offer a new boundary information source for basin hydrological analysis. Taking station observations in the Yangtze River Basin as a reference, we assessed the applicability of CRA products from aspects of temporal evolution, spatial distribution, and drought identification ability. The results reveal that CRA data can effectively capture the interannual variations and monthly distribution of areal precipitation in the Yangtze River Basin. The multi-year average precipitation derived from CRA data is only 1.2% lower than the observed data. The correlation coefficients of monthly data all exceed 0.9. Nevertheless, the efficiency coefficients during the main flood season (July and August) are below 0.9, slightly lower than those in other months. The applicability of CRA products shows significant spatial heterogeneity. The mainstream of the Yangtze River from Yibin to Hukou has the best applicability with minimal spatial variation within this region, while the Minjiang and Tuojiang Rivers has the lowest applicability with remarkable spatial variability. CRA data tend to underestimate the precipitation in high-value areas and overestimate the precipitation in low-value areas. Nonetheless, CRA products display strong capabilities in identifying various levels of drought events on an intra-annual scale. These findings provide a reference for analyzing and enhancing the accuracy of CRA products, facilitating their application in basin hydrology.
Analyzing the spatiotemporal evolution characteristics of water use structure in core areas is crucial for optimizing water resources management and promoting the coordinated development of social economy and ecological environment. We employed the methods of information entropy, Lorentz curve, Gini coefficient, and location entropy, which mutually corroborated and complemented each other from different perspectives, to uncover the spatiotemporal evolution and spatial distribution characteristics of the water use structure in the Guanzhong region of China over the past decade. Findings indicate that from 2012 to 2021, the overall water use structure in the Guanzhong region evolved towards greater balance, and the spatial distribution disparity of water use structure gradually diminished. Nevertheless, spatial distribution differences existed among various types of water use, particularly in ecological environment and urban public water use. Moreover, significant disparities were observed in the water use structure among cities (districts) in the Guanzhong region. The water use structures of the Xixian (west Xianyang) New District and Xi’an City were the most balanced, whereas that of Weinan City was the most unbalanced. These results are largely consistent with the actual situation, offering valuable references for optimizing water resources allocation and scientifically planning the water use structure in the Guanzhong region.
This study selects the Qingshui River Basin, the largest first-order tributary of the Yellow River in Ningxia, as the research area. It comprehensively considers the co-development of water resources, socio-economic, and water environment subsystems in this basin. By applying the system dynamics method, we established a system dynamics model of the Qingshui River Basin using Vensim software and set up five different scenarios. Based on historical data from 2006 to 2020, we employed the entropy weighting-TOPSIS method to predict the dynamic changes in water resources carrying capacity under these five scenarios from 2021 to 2030 so as to identify the optimal solution for enhancing the basin’s water resources carrying capacity. Results indicate that the water resources carrying capacity of the Qingshui River Basin remains inferior under the status-quo continuation scenario. The economic-priority, agricultural-priority, and environmental-priority scenarios can only partially alleviate the pressures on socio-economic development, water resources supply and demand, and the water environment. In contrast, the comprehensive and coordinated scenario can comprehensively improve the evaluation indicators of water resources carrying capacity, meeting the requirements for promoting the basin’s sustainable development. This study offers a reference for water resources management and planning in the Qingshui River Basin.
Water level prediction for the Three Gorges-Gezhouba cascade hydropower stations is crucial for their safe and stable operation and overall benefits. Nevertheless, due to the combined effects of multiple factors, such as the complex transformation between dynamic and static storage-capacity calculations and the unsteady flow downstream of the stations, traditional methods struggle to accurately predict short-term water levels. When the stations perform peak-shaving and frequency-regulation tasks under complex operating conditions, there is a risk of violating scheduling regulations and opening the gates, which may lead to engineering safety hazards and economic losses. In this study, we employed the Long Short-Term Memory (LSTM) deep-learning method to develop an ultra-short-term water-level prediction model for the Three Gorges-Gezhouba Hydropower Stations. We utilized water-level, inflow, and output data to forecast the ultra-short-term water-level processes of the stations. Subsequently, we analyzed the prediction accuracy of the model using data from peak-shaving scenarios. The results show that the model exhibits high overall accuracy, stability, and adaptability, and maintains stable prediction accuracy under different peak-shaving conditions. However, the prediction results tend to be homogenized at extreme water levels. The average error of 24-hour water-level prediction for the upstream of the Three Gorges and Gezhouba is less than 0.05 m. These findings can offer technical support for the refined scheduling of cascade hydropower stations.
Biological activated carbon (BAC) filters that have been in service for an extended period (over 7 years) may encounter a decline or even a complete loss in the removal efficiency of organic compounds. To investigate the removal efficiency of organic compounds in long-serving BAC filters and propose targeted operational optimization strategies, we selected a 12-year-old BAC filter at the LC water treatment plant (WTP) in City Z as our research subject. We analyzed its operational performance by evaluating the total organic carbon (TOC) removal efficiency and explored optimization strategies from the aspects of ozone (O3) dosage and backwashing methods. The results revealed that the LC WTP experienced significant fluctuations in the organic compound removal efficiency, with a high risk of ineffectiveness. Biodegradation is the primary mechanism for organic compound removal in long-serving BAC filters, accounting for approximately 67%, while adsorption only contributes 33%. When the specific O3 dosage ranged from 0.36 to 0.52 mg O3/mg TOC, the BAC filter at the LC WTP performed relatively well. Either too low or too high O3 dosage was unfavorable for enhancing the performance of long-serving BAC filters. At the LC WTP, the TOC levels in the effluent from both the surface and upper layers of the BAC filter increased before backwashing. Backwashing with water containing 0.5 mg/L of effective chlorine can improve the performance of long-serving BAC filters.
Water turbidity is a crucial indicator of aquatic environment as it directly reflects water quality. Taking Liangzi Lake as the research object, this paper utilized Aqua MODIS remote sensing data from 2003 to 2021 on the Google Earth Engine (GEE) remote sensing cloud computing platform to invert the water turbidity of the Liangzi lake and analyze its spatiotemporal variation characteristics. Results indicate the following: (1) Liangzi Lake features higher water turbidity in winter and spring than in summer and autumn, with turbidity exceeding 30 NTU in winter and spring and below 20 NTU in summer and autumn.(2) The water turbidity of Liangzi Lake has gradually decreased in recent years. Before 2011, the average water turbidity was approximately 30 NTU, with significant spatial variation. Areas close to land had a higher turbidity of about 50 NTU compared to the average. After 2011, the average water turbidity gradually decreased to about 25 NTU, with areas close to land experiencing a notable decrease to approximately 30 NTU. (3) The water turbidity of Liangzi Lake is correlated with land cover types within the Liangzi Lake Protected Area, with the green area having the greatest impact with a correlation coefficient of -0.63. Larger green areas correspond to lower turbidity. Over the past ten years, the overall water turbidity of Liangzi Lake has decreased from 30 NTU to 25 NTU, a reduction of 16.67%, indicating significant achievements in the management and improvement of Liangzi Lake.
Based on the mechanism experiments conducted for the spillway of the Lianghekou hydropower station, this study investigates the variation tendencies of the flow regime, dynamic pressure, air vent cavities, wind speed, and aeration concentration under three types of aeration thresholds. The applicability of formulas for calculating cavity length, gas-water ratio, and water content ratio to the studied project are analyzed, and the derived conclusions could be employed for further investigation on Lianghekou hydropower station and other similar hydraulic projects. Research findings indicate that aeration in the water flow becomes more pronounced with the increasing of spillway discharge, and several hydraulic indicators increase simultaneously, including the root mean square of time-averaged pressure and fluctuating pressure, aeration rate, cavity negative pressure, and cavity length. At a given discharge, the air concentration increases along the spillway, and the vertical distribution of aeration concentration displays successively C-shaped, S-shaped, and I-shaped patterns. According to the research findings, we recommend that Shi Qisui’s formula for cavity length, Chen Zhaohe’s formula for gas-water ratio, and Hall’s formula for water content ratio are most suitable for the estimations of the present study.
To support precise measurement and control of water volume in irrigation area, this study investigated the influence of diversion outlet on the flow pattern in front of control gate, as well as the variation laws of flow coefficient and head loss of trapezoidal control gate under different slopes and water diversion angles. We observed the flow pattern at diversion outlet and analyzed the causes, and further established the flow formula for trapezoidal control gate by using dimensional analysis method and calculated the head-losses based on 495 groups of discharge tests under different water diversion conditions. The discharge tests involved different gate openings and water heads with three slopes (m=1.5, 1.75, and 2) and five water diversion angles (θ=30°, 45°, 60°, 75°, and 90°). Results revealed that a backwater area was formed in front of the control gate. The coefficient of determination of the flow formula was R2=0.934, and the average relative error of the flow was 2.83%. Relative head loss decreased as the relative opening of the control gate increased. The results demonstrated high accuracy of the proposed flow formula for trapezoidal control gate, which offers a basis for flow measurement in trapezoidal channels in irrigation areas.
Natural vibration frequency is a crucial parameter in the seismic design of reinforced soil retaining walls. To date, there is no consensus on the calculation methods for the natural vibration frequency of non-monolithic reinforced soil retaining walls. This paper reviews seven existing methods for calculating the natural vibration frequency. Taking the modular reinforced soil retaining wall (hereinafter referred to as the modular type) and the composite gabion geogrid reinforced soil retaining wall (hereinafter referred to as the composite type) as research subjects, we assess the effectiveness of these existing calculation methods by comparing the accuracy coefficient and the absolute percentage error between the measured and calculated results. The analysis reveals that the natural vibration frequencies of the modular and composite models are generally consistent at different heights. Wu Yongsheng’s calculation method shows the closest agreement with the actual measurements. Ghanbari’s method can more effectively mitigate the influence of parameter changes on the analytical calculation, thus demonstrating stronger adaptability. Xu Peng’s method has certain advantages in terms of accuracy and adaptability, with a wider application scope. In seismic design, we recommend that engineers evaluate the natural vibration frequency of the reinforced soil retaining wall before and after construction and consider the horizontal displacement of the panels as an indicator to measure the structural damage state.
A series of through-diffusion tests were carried out to explore the diffusion and adsorption behaviors of Cu2+ in bentonites modified with hydroxypropyl methylcellulose (HPMC). The test results were compared with those of untreated bentonite. Pollute V7.0 was employed to quantitatively evaluate the impact of HPMC on the performance of bentonite in intercepting Cu2+. The diffusion test results indicated that when the HPMC content reached 2% and 5%, the capacity of bentonite adsorbing Cu2+ decreased by 40% and 46%, respectively, while the diffusion coefficient of Cu2+ dropped by 7% and 34%, correspondingly. The results from Pollute V7.0 demonstrated that adding 2% and 5% HPMC to sodium bentonite enhanced the performance of bentonite for adsorbing Cu2+ by factors of 1.34 and 2.03, respectively. Overall, the findings of this study offer valuable information for assessing the performance of HPMC-modified bentonite.
To optimize the electroosmotic method, we investigated the consolidation effect of soft soil under various potential gradients and conducted a comprehensive analysis of energy consumption. Six groups of potential gradients (1.00, 1.25, 1.50, 1.75, 2.00, 2.25 V/cm), denoted as V1 to V6, were set up. We comprehensively analyzed the optimal potential gradient for electroosmotic reinforcement of soft soil by comparing the drainage ratio, contact resistance, and average energy-consumption coefficient during electroosmosis, along with the water content, bearing capacity, and shear strength after electroosmosis. The results indicate that, except for V1 and V2, there were negligible differences in the drainage ratio and final water content of the soil after electroosmosis. However, in the later stage of power-on, the contact resistances of V1, V3, and V6 increased by 15.76, 25.65, and 35.39 times respectively, and the average energy-consumption coefficients increased by 5.07, 6.12, and 10.98 times respectively. The soil strength of all groups increased with the rise of the potential gradient. Specifically, the average bearing capacity of the V1-V6 soils increased by 2.79-4.89 times, and the average shear strength increased by 5.7-12.2 kPa. This is mainly because the soil can consolidate rapidly under a high potential gradient. Therefore, without considering energy consumption, the optimal potential gradient ranges from 2.00 to 2.25 V/cm. However, when energy-saving is taken into account, the optimal potential gradient lies between 1.50 and 2.00 V/cm.
The aim of this research is to reveal the influence of spatial form parameters and other factors in soil nail design on the three-dimensional stability of deep foundation pits in silty clay. A deep foundation pit in a silty clay area in Hebei was taken as the engineering background. Based on the response surface method, Plackett-Burman and Box-Behnken experiments were designed. MIDAS-GTS and Design-Expert were used to establish experimental models. The influence of various parameters on the safety of soil nail support in deep foundation pits of silty clay and the applicability of optimization schemes were analyzed through numerical simulation and monitoring data. Results show that the impact of each parameter on the safety of the pit in the silty clay area, in descending order of significance, is as follows: soil nail length, slope angle of excavation, soil nail spacing, soil nail inclination, and soil nail diameter. In the combined effect of support parameters, the soil nail length and spacing have the greatest impact on the safety factor. The predictive model established by the response surface method can provide the best optimization scheme. The optimization scheme shifts the soil slip surface backward, reducing the maximum horizontal displacement of the foundation pit from 9.33 mm to 5.42 mm and the maximum vertical settlement from 16.9 mm to 11.8 mm, providing a reference for the design of soil nail support for this type of foundation pit.
Reasonably and accurately determining the mechanical parameters of surrounding rock is crucial for the stability analysis of surrounding rock and the design of supporting structures during the construction of underground water-sealed storage caverns. Based on the engineering geological characteristics of underground water-sealed storage caverns, an intelligent inversion method for the mechanical parameters of surrounding rock during construction is proposed for the equivalent continuous medium model. First, the constitutive model of the cavern rock mass is determined via laboratory and numerical tests. Then, the mechanical parameters of the constitutive model are estimated using the Hoek-Brown strength criterion and other methods, and the sensitivity of each parameter to the deformation and relaxation of the surrounding rock is analyzed. Based on these analyses, an orthogonal test scheme for the parameters to be inverted is designed. Finally, an intelligent inversion model for the mechanical parameters of the surrounding rock is constructed using samples obtained from numerical simulations and an evolutionary neural network model. Comprehensively estimating the initial value ranges of the mechanical parameters of the surrounding rock for different classes of rock mass basic quality can avoid large deviations in inversion results caused by the wide optimization range of intelligent algorithms. Sensitivity analysis of the mechanical parameters to the deformation and relaxation of the surrounding rock can reduce the number of inversion parameters. The proposed intelligent inversion method is applied to a typical underground water-sealed storage cavern project in Shandong Province. Results show that the relative errors of the settlement of the peripheral rock vault, the maximum displacement of the cavern circumference, the internal deformation, and the average depth of relaxation are all less than 10%, meeting the precision requirements of engineering applications. Therefore, the proposed intelligent inversion method exhibits high feasibility and reliability through practical application and can serve as a reference for similar projects.
Irrigated area is the basic data required for effective agricultural water conservation, yet traditional survey and statistical methods no longer meet current monitoring needs. In this research, GF-1 and Sentinel-2 satellite images were fused to construct the sample spectrum of crop growth period. Based on the pixel-scale spectral matching method, the crop planting structure and actual irrigated area of Zaohe irrigation district in Suqian City, Jiangsu Province from 2017 to 2022 were synergistically extracted. Results show that the main planting pattern in Zaohe irrigation district is rice-wheat rotation. From 2017 to 2022, the actual irrigated area was 85.11 km2, 91.91 km2, 103.65 km2, 95.85 km2, 97.72 km2 and 88.24 km2. respectively. Validation using sample points and a confusion matrix yielded an overall accuracy of 89.71% and a Kappa coefficient of 0.80, indicating higher accuracy and better extraction effects compared to existing products like IrriMap_Syn and IWMI products. This method is suitable for extracting the irrigated area in south China, and can provide technical and data support for the daily supervision of management departments and the optimization of water resource allocation.
The Three Gorges Reservoir (TGR) area features a large number of tributaries, but the lack of basic hydrological station monitoring leads to the scarcity of hydrological and water-resources information for these tributaries, affecting regional water resource management and flood control safety. To address this issue, we selected 20 typical tributaries in the TGR area, among which 18 are ungauged, to build 3D digital river models for these tributaries by self-developed remotely-sensed hydrological station technology along with satellite and unmanned aerial vehicle (UAV) remote-sensing data. Based on this model, we calculated the river discharges, relative water levels, water-surface widths, and other information from January 2016 to July 2023 for the monitoring sections. Results revealed that: 1) The cross-sections of 20 typical tributaries in the TGR area display U-shape, demonstrating mountainous characteristics. The remotely-sensed hydrological station technology demonstrates high accuracy in calculating ungauged tributary discharges in the TGR area, with the average Nash-Sutcliffe efficiency coefficient (NSE) and coefficient of determination (R2) reaching 0.74 and 0.76, respectively. 2) During the study period, the relative water levels of the tributaries changed minimally. The percentages of months with monthly relative water-level fluctuations below 1.2 m in the upper, middle, and lower tributaries of the reservoir were 93.1%, 86.8%, and 87.4% respectively. 3) The average discharges of typical ungauged tributaries were generally stable. However, trend analysis indicated that the discharges of 13 ungauged tributaries have being decreasing, suggesting an overall downward trend in tributary discharges in the reservoir area. 4) The 20 tributaries have abundant annual average and total discharges, with the annual average inflow reaching 16.475 billion m3, accounting for approximately 4.8% of the total annual inflow of the reservoir area, offering substantial water resource support for regional economic development.
To explore the mechanical properties of ultra-high performance concrete (UHPC) with different steel fibers under uniaxial tension, we designed ten sets of uniaxial tensile tests on dog-bone-shaped UHPC specimens. We investigated how the aspect ratio (37, 50, 64, 65), dosage (2%, 3%, 4%), shape (end-hooked and curved), and forming methods(mixing and slurry) of steel fibers affect the tensile strength, stress-strain curves, tensile toughness, and failure process of UHPC. Results reveal that as the aspect ratio of hooked steel fiber rises, the tensile strength of UHPC increases by 6.54%-9.37%, and the residual strength ratio in the strain-softening segment grows by 5.00%-38.30%. When the volumetric dosage of end-hooked steel fiber increases from 2% to 3% and 4%, the tensile strength, peak strain, and residual strength ratio in the strain-softening segment of UHPC increase, along with an enhancement in tensile toughness. Compared with specimens formed by the mixing method, those formed by the slurry method with end-hooked steel fibers show no significant change in strength, but the peak strain increases by 53.61%-91.96%. The stress-strain curve of UHPC with curved steel fibers demonstrates strain-hardening characteristics, and its failure process involves the propagation of multiple cracks. In comparison to specimens with end-hooked steel fibers of the same aspect ratio, UHPC with curved steel fibers exhibits a 19.41-19.96-fold increase in peak tensile strain and an 18.00%-70.03% increase in the residual strength ratio in strain-softening segment. This indicates that the toughening effect of curved steel fibers is superior to that of end-hooked steel fibers. By using the hardening index and the residual strength ratio in the strain-softening segment, we can comprehensively evaluate the strain-hardening characteristics before peak axial-tensile strain and the axial-tensile toughness after peak in UHPC.
To tackle the high carbon emissions issue resulting from doubling the cement dosage in ultra-high performance concrete (UHPC), a low-carbon ultra-high performance concrete (LC-UHPC) was developed by replacing a large proportion of Portland cement with granulated blast furnace slag, fly ash, and silica fume. Eleven groups in a total of 154 specimens were fabricated with three factors, namely, cement replace ratio, steel fiber volume content, and water-binder ratio taken into account. Through cube compression tests at different ages, flexural tests, and uniaxial compression tests, the mechanical properties of LC-UHPC, including failure patterns, basic strength, and deformation capacity, were analyzed. Based on the test results, a mathematical equation for the stress-strain curve under uniaxial compression was derived. Results indicated that the LC-UHPC displays shear failure mode under uniaxial compression. Moreover, the addition of steel fibers significantly enhances the mechanical properties of LC-UHPC. Compared with conventional UHPC, up to 70% of the cement in LC-UHPC can be replaced, and its 28-day compressive strength can reach 149.09 MPa. The established axial stress-strain equation can accurately predict the mechanical responses of LC-UHPC under uniaxial compression. This equation provides valuable insights for studying the mechanical properties of LC-UHPC and the design of related structural components.
Manifold method based on independent covers is a novel approach for numerically solving partial differential equations. By constructing approximate functions, it generates a “partitioned series solution” for partial differential equations. This method not only achieves the main functions of the finite element method (FEM) and other numerical techniques but also outperforms them in certain aspects, such as mesh generation flexibility and computational stability. However this also means that its calculation formulas and program design are different from existing methods. This paper reviews the major research outcomes in solid computation in recent years, and summarizes a set of simple and general calculation formulas in which the shape function of the local approximation function is expressed as the product of the Partition of Unity (PU) function, coordinate transformation matrix, and series matrix. The shape function and its derivatives under various scenarios are discussed in details. Different matrices and the time integration method are also given. These formulas can be applied to solve the differential equations of motion in elasticity, conduction equations, and wave equations, covering one-to-three-dimensional steady-state and transient analyses, along with three types of boundary conditions. They offer features such as high-order series, arbitrary mesh shapes, accurate boundary geometric simulation, precise application of essential boundary conditions, and local analytical series near the crack tip. Utilizing these formulas, a general program for the new method can be developed.
Based on the general calculation formula of the manifold method based on independent covers presented in the previous article, we provide the flowchart of the calculation program. First, we summarize the integration methods for various geometric shapes (such as partitions, stripes, and boundary faces) that may appear in one- to three-dimensional spaces. On this basis, we develop integration programs according to simplex geometric elements of points, lines, faces, and bodies. This approach ensures the universality for any mesh shape. Next, we propose a programming strategy that separates the integration module from the integrand function module. The arbitrary combination of these two modules endows the program with extensibility and the potential to achieve universality in solving partial differential equations. Moreover, the universality of series is realized through the determination of series formulas, corresponding coordinates, coordinate transformation matrices, and series matrices. In addition, all calculation parameters can be input via formulas using user subroutines, thus achieving universality of input parameters. Ultimately, with relatively less program code, we can conduct one- to three- dimensional steady-state and transient analyses of the differential equations of motion in elasticity, conduction equations, and wave equations, including one to three types of boundary conditions.
Based on the general calculation formulas and programming methods proposed in the previous two articles, we conduct a comprehensive validation across one- to three-dimensional problems. These involve the displacement field, temperature field, seepage field, sound field, electrostatic field, and potential flow field by solving the differential equations of motion in elasticity, the conduction equation, and the wave equation (covering both steady-state and transient analyses). The provided examples demonstrate the distinctive characteristics of the manifold method based on independent covers. These features include the ability to handle meshes of any shape and connection, the accurate simulation of geometric boundaries, the precise application of essential boundary conditions, high-order series approximation, and the use of analytical series near crack tips. Finally, we summarize the entire article and propose a new term “series manifold element (series element)”.
