最新刊期
卷 51 ， 期 1 ， 2019
- 摘要：As an important space carrier to participate in global competition, the Guangdong−Hong Kong−Macao Greater Bay area is facing the pressure from the energy demand and environment protection. Developing geothermal resources is an effective way to solve the problem. In this paper, the possibility of geothermal development in Greater Bay area was reasoned, based on the analysis of regional geotectonic, stratigraphic lithology and geothermal field. Considering deep ground temperature, rock thermal physical parameters and terrestrial heat flow, geothermal water resource and hot dry rock resource were quantitatively assessed through raster units. Further, high potential geothermal zones were distinguished. Results show that: 1) the intersected fault structures and widely distributed granite in the Greater Bay area provide a favorable geological environment for the storage and formation of geothermal resource, which is verified by the measured terrestrial heat flow; 2) the computing results indicates that temperature would be over 70 ℃ at depth of over 1.3 km and 168.81～233.61 ℃ at depth of 5 km, showing a high potential of geothermal resource; 3) The estimate geothermal resources in the Greater Bay area amount to 5.83×1017 kJ within the depth of 5 km. It is equivalent to the thermal value of standard coal of 5.94×109 t and can reduce the emission of CO2 by 4.04×109 t, when recovery rate is set at 30%. 4) The area of high potential geothermal resources is mainly distributed along the northeast deep fault, i.e. in Foshan, Zhongshan, Jiangmen, Shenzhen and Hong Kong, where the unit geothermal resource potential is equivalent to standard coal of 5.19×105 t per square kilometer, and should be taken as key area for geothermal prospecting and exploitation.关键词：Guangdong−Hong Kong−Macao Greater Bay area;geothermal resources;geological environment;potential assessment;raster unit
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发布时间：2024-01-05 - 摘要：In October 10th and November 3rd 2018, two landslides happened successively on the right bank of the upper reaches of Jinsha River, which dammed the river at Baige village, Jiangda county, Tibetan Autonomous Region. The dammed lakes and their breaching flood brought about severe disaster to local residents and their production and life facilities along the river. Based on the field investigation immediately after the slides and other related materials, a systematic analysis is made on the formation and process of the slides in the paper. Results show that: 1) the " 10·10” slide is a high position, high shear crack, high speed and incomplete wedge slide and its volume is around 107 m3; 2) geologically the slide is situated in the suture zone of Jinsha River and the bedrock is Xiongfeng gneiss group of Proterozoic, which is characterized by multiphase repeated deformation and metamorphism and is severely mylonitized and altered; 3) the sliding area can be vertically divided into 3 zones of anti-sliding zone, major sliding zone and hauling zone, which are separated roughly at elevation 3 500 m and 3 000 m, respectively. The major sliding zone is of wedge shape cut by two well-developed structural planes, the anti-sliding zone is of tetrahedron shape formed by two undeveloped structural planes, while the hauling zone is completely weathered earth mass mixed with clumped and heavily fractured rock; 4) the slide has two sliding directions of S80°E in the major sliding zone and N70°E in the anti-sliding zone and the elevation of shear crack is around 2 950 m above sea level; 5) the power driving the slide is mainly from the gravity of the wedge in the major sliding zone and the developing process of the slide is the progressive failure of the comparatively intact rock mass in the anti-sliding zone under the gravity of the major sliding zone; 6) the sliding process can be divided into 6 steps. Firstly the major sliding zone and the anti-sliding zone begins, secondly the support-losing hauling zone starts up, thirdly the first started mass collides with the left bank of the river (the bank in Sichuan Province) at high speed, then moves up the slope for around 95 m and laterally to form the debris-scouring zone, fourthly the first started mass moves downward and collides with the mass from the hauling zone above the river and the merged mass punches the river water to form high-speed sandy water jet, resulting in jet-scouring zones on the both banks, fifthly the downslope of the landslide dam fails, resulting in the secondary landslide and finally the punch-induced misty rain leads to the flush of the dam surface; 7) the " 11·3” landslide is the local failure of the earth mass in the hauling zone due to the progressive disintegration of the fractured rock mass acting as retaining wall and its volume is around 3×106 m3; 8) there still exist badly deformed mass in the hauling zone and the estimated volume is 5.5×106 m3, so further sliding and damming risk is big and feasible control measures should be taken.关键词：Jinsha River;Baige landslide;high-speed landslide;formation mechanism;formation process;landslide dam;dammed lake
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发布时间：2024-01-05 - 摘要：In order to find out the damage evolution rule of the concrete with initial damage caused by early freezing under the coupling of freeze-thaw cycle and sulfate erosion, initial damage to concrete specimens by freezing and thawing them at the 7th and 14th day during the preparation of concrete specimens was carried. Based on this, different initial damage degree on macro performance and internal structure was researched. Then according to the principle of damage mechanics, the dynamic modulus of elasticity and compressive strength were defined as damage variables, by regression fitting analysis of damage process of variable, and the damage evolution equation of different initial damage specimen caused by early freeze-thaw was established in corrosion and freezing environment. The results indicated that two kinds of concrete specimens with different initial damage are affected by early freeze-thaw in the decay process of their mechanical properties and their form are " lead effect”, which is closely related to the degree of initial damage. At the same time, the comparison and analysis of the change process of ultrasonic pulse propagation velocity and internal defect zone of concrete inferred that early freeze-thaw accelerates the propagation speed of cavity and crack, and the initial value of macroscopic mechanical properties of concrete and the ability of resisting salt and freezing in later stage are affected. The dynamic modulus of elasticity and the damage evolution equation of compressive strength can be used as a general formula for the attenuation of mechanical properties of concrete with similar damage degree, which can provide a theoretical basis for evaluating the service status and predicting the life of structures in similar environments. At the same time, the damage relationship between dynamic modulus of elasticity and compressive strength can be deduced from each other, which can reduce the limitation of data acquisition due to the shortage of instruments.关键词：concrete;freeze-thaw cycle;sulfate erosion;early freeze-thaw;initial damage;damage evolutional law
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发布时间：2024-01-05 - 摘要：Myrids of intensive structure clusters have been built in big cities and small towns due to the rapid development of urbanization. The dynamic interaction between soil and structure cluster is different from the dynamic interaction between a single structure and soil. The influence law of the dynamic interaction between soil and structure cluster on the response of superstructure was studied in this paper, and the results can be utilized in the seismic design of superstructure considering cluster effect. In addition, the cluster effect was first presented in this paper. According to an accomplished shaking table test of soil and buildings, a finite element model involving the shaking table test was established to study the influence laws of the cluster effect on the responses of structures. Davidenkov foundation model was used to simulate the nonlinearity of soil in the finite element model. Based on verifying the accurate of the finite element model, cluster effect was studied to extend the research of SSCI, including soil properties, structure spacing and structure number. Last, the mechanism of SSCI was studied based on the laws of the displacement. The laws and the parametric influences on the soil and structure cluster interaction were fully summarized. The results are listed as follows: Under earthquake excitation, the structures in different locations had different responses, which involves the cluster effect of SSCI. Cluster interaction reduced the acceleration responses of structures, while velocity might be larger or less than that of the single building, relating with the earthquake input and the structure location. The displacement of the central building reduced, but these of the surrounding structures along the vibration increased, and the farthest buildings from the center had the largest displacements. The maximum absolute value of the influence factor of the cluster effect for on the displacement reached 770.794%. The building number was the most significant factor that affected the cluster effect in the SSCI system. The cluster interaction constantly reduced when the structure spacing increased and disappeared. When the clear spacing was larger than as 1.32 times as the size of the building foundation size, and the cluster effect becomes weak. It can be seen from the above results that the dynamic interaction between soil and structure cluster has a significant influence on the dynamic response of superstructure. In the seismic design of superstructure, the cluster effect of the dynamic interaction between soil and structure cluster cannot be ignored.关键词：cluster effect;soil and structure cluster interaction (SSCI);shaking table test;finite element method;ANSYS;Davidenkov foundation model
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发布时间：2024-01-05 -
Improvement of Watershed Subdivision Method for Large Scale Regional Distributed Hydrology Model AI导读
摘要：Watershed subdivision is an important basic work of distributed hydrological model, which is related to the accuracy of basin hydrological simulation and prediction. In the process of watershed subdivision in large-scale and complicated terrain area, the traditional method has some shortcomings in accurately describing the spatial extent of the study area, determining the outlet of the basin, and extracting the river network of the inflow area, which commonly uses a single catchment area threshold to extract the river network and divide the watersheds based on surface runoff and flow model. Consequently, a watershed subdivision method, using stem-branch topological codification, was proposed based on automatic recognition of the outlets of basin and the fusion of river network with variable catchment area thresholds. The method mainly includes the determination of basin outlets, the determination of the maximum and minimum catchment area thresholds, the multi-threshold virtual river network integration and watershed subdivision and coding. Taking China as an example, 25 174 watersheds were divided, with an average area of 381 km2, a maximum area of 5 512 km2 and a minimum area of 4 km2. The coincidence degree between the simulated area and the actual area reached 99.92%. While using the traditional method, the number of watersheds was 21 768, and the average area was 434 km2, and the coincidence degree was only 98.5%. Moreover, the results were compared with the actual water systems and the current basin of China to verify the applicability of the method. The program is realized through programming that is fast and efficient. It takes into account the computational efficiency of the model and the accuracy of watershed subdivision, which lays a good foundation for developing distributed hydrological model in large scale region and helps to better serve the management of hydrology and water resources in the region, especially at the national macro level.关键词：watershed subdivision;large scale region;basin outlet identification;multi-threshold virtual river network integration- 2204
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发布时间：2024-01-05 - 摘要：Most of the riverbeds in the mountainous area are composed of pebble sediment with a wide size distribution, and the riverbed slope changes obviously. Affected by sediment supply and water flow, the erosion and deposition processes in different river reach are complex and changeable, and the retrogressive deposition and flash flood occurs frequently. In order to analyze the influence of sediment supply on the riverbed deformation and water level change in mountainous rivers, the process of retrogressive deposition of gravels in a typical mountainous river is simulated based on the CFD−DEM coupling method, and the calculated results are compared with the flume test data. The calculation results show that once sediment is deposited in the downstream due to the slope of river bed becoming gentle, it will rapidly spread to the upstream, which will lead to a wide range of river bed rise. Besides, the initial position of deposition, the rate of deposition and the thickness of deposition are related to the concentration of sediment, the velocity of water flow and the particle size. The decrease of the flow rate and the increase of the intensity of sediment supply will result in a faster rate of the retrogressive deposition and the thinner thickness of river bed. Furthermore, the sediment deposition in the mountainous river may lead to a significant rise in the water level along the channel. In the front of the deposition, the water level increases most sharply. As the development of the retrogressive deposition, the water level at this position will fall slightly and tend to be stable. The results demonstrate that sediment supply conditions play important roles in the deformation of rivereds and the occurance of flow-sediment disasters in mountainous rivers. This provides a theoretical basis for revealing the mechanism of the disasters caused by flood and sediment.关键词：mountainous river;sediment supply;sediment deposition;channel deformation;CFD−DEM coupling
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发布时间：2024-01-05 - 摘要：The horseshoe vortex (HV) is formed at the upstream of a vertical cylinder when flow passes the cylinder and it is responsible for the local scouring at the base of the cylinder. Extensive works had been carried out to investigate the characteristics of HV in open channel flow with high Reynold number and large flow depth. However, it was difficult to measure HV experimentally in low Reynold number and shallow flow depth, in view of limitation of experimental technology. To capture HV accurately in shallow water flow, a high resolution and high frequency particle image velocimetry (HR-PIV) was employed in present study. Subsequently, the flow fields upstream of the cylinder were captured by HR-PIV in 6 experimental groups with shallow flow depth. The separation points of each groups were obtained by analyzing the characteristics of time-averaged flow fields. The HV was calculated by λci criterion where λci represented the swirling strength of vortex. Then the locations of HV were obtained in accordance with the maximal swirling strength point. In addition, the radius of HV was calculated by superposition of Oseen vortex and pure shear model. The results showed that within a low cylinder Reynolds number (ReD) where ReD<5 000, as the increase ofReD, the location of separation point and HV were rapidly approaching the cylinder simultaneously, whereas the HV moved rapidly towards the flume bed, while the radius of HV decreased and the swirling strength increased. Under shallow water flow conditions and the cylinder diameter keeping constant, as the increase of flow depth, the locations of separation point moved towards upstream; HV moved towards upstream and free surface, simultaneously, while the radius of HV increased. Theses HV parameters in the present flow conditions were larger than those in open channel flows. Derived from previous works, it was found that the separation point and HV would display a different manner as ReD became lager. When 5 000<ReD <8 000, the separation point was still rapidly moving downstream while HV remained stable as increasing ReD. While ReD>8 000, the separation point was slowly moving downstream and HV still remained stable. The research results can provide a basis and reference for engineering design for preventing local scouring at the base of cylinder.关键词：flow around cylinder;horseshoe vortex;particle image velocimetry;shallow water flow;low Reynolds number
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发布时间：2024-01-05 - 摘要：The projection of surface runoff in the context of climate change is important to the rational utilization and distribution of water resources. This study conducted a case study in Fu River basin. A basin scale hydrological model was built based on macroscale processes of surface runoff and water-energy balance. This model can describe the quantitative relationship among climatic factors, underlying surface and surface runoff. Driven by hypothetical climatic scenarios and climate change dataset provided by CMIP5, the climate change impacts on surface runoff in the Fu River basin can be addressed. The results showed that: 1) Compared with other distributed hydrological models, the hydrological model in this study uses fewer parameters and has simpler calculation methods, which was good at simulating annual surface runoff. 2) The surface runoff was less sensitivity to climate change in the Fu River basin, i.e., the increase of only 1 °C in temperature might result in a surface runoff decrease of 3.6% to 6.3% and a 1% precipitation increase might result in a streamflow increase of 1.7% to 1.9%. 3) The temperature across the Fu River Basin was projected to increase by 1.1 to 2.6℃ from 2020 to 2050, as compared to that from 1961 to 1990. But the uncertainty existed among the projection results of precipitation. The surface runoff was expected to decrease by 10% to 11% without considering the climate change projected by GFDL-ESM2M, which was much different from those predicted by other GCMs.关键词：climate change;surface runoff;water-energy;Fu River basin
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发布时间：2024-01-05 -
Study on the Anchoring Performance and the Installation Parameters for the Large-tonnage CFRP Cable AI导读
摘要：The anchoring problem of large-tonnage CFRP cable for the long-span cable-stayed bridge and the special installation problems caused by long-cables were studied. The nonlinear model of the anchorage system with variable stiffness of load transfer component (LTC) and the installation system of stayed cable had been established by finite element simulation. The performance of the LTC was optimized, including the elastic modulus, the length, the internal taper and the thickness at loading end and the interfacial friction coefficient, and its strength was evaluated. For cable installation, the key parameters was studied, including the correction angle, the difference of cable force at two ends of the cables and the deformation of the cables, and the installation parameters of steel cable and CFRP cable with the length of 1 085 m was compared. The results show that the stress concentration in anchor zone is reduced by the variable stiffness of the LTC. Based on the material requirements of each part, the design parameters of anchorage system of CFRP cable with 15 000 kN are obtained. The steel sleeve needs a length of 1 000 mm, a diameter of 424 mm, a wall thickness of 40 mm and an internal taper of 5° by 45# high-strength structural steel; the radius of load transfer material at loading end is 40 mm, and the elastic modulus of each section ranges from 1 to 2 GPa (LTC-1), 4 to 7 GPa (LTC-2), 15 to 25 GPa (LTC-3), and 30 to 40 GPa (LTC-4). The selection of load transfer materials for each section is a mixture of resin and quartz sand (LTC-1 and LTC-2), polymer mortar or high performance concrete (LTC-3 and LTC-4). The installation correction angle, the difference of cable force in both ends of the cable and the deformation of the cable are obtained for the cable installation. The difference of CFRP and steel cable in anchoring force between the main tower and the main girder, CFRP cable of the longest is 1/6 of that of steel cable. The relationship between anchorage correction angle and the cable length is positively correlated, and the correction angle for CFRP cable is only 1/4 than that of steel cable. Compared with steel cable, the CFRP cables have smaller sag, and the correction angle is reduced by 1°, which benefits the cable installation.关键词：large tonnage;CFRP cable;numerical method;anchor system;installation parameters- 2713
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发布时间：2024-01-05 - 摘要：The manage-flood is very important for flood control safety and economic effectiveness of reservoir engineering. There are two approaches which can be used to calculate the manage-flood at present, i.e., one is based on Copula functions, and the other is based on the principle of total probability. The latter can be divided into direct method and indirect method. The direct method based on the principle of total probability is explored in this article. The flood data for calculation of manage-flood have been divided into three condition:Sufficient data condition, relatively sufficient data condition and insufficient data condition. For sufficient data conditions, the length of flood data series in main flood season is greater than 30 years and the length of flood data series in pre-main flood season and post-main flood season is no less than 20 years, respectively; For relatively sufficient data condition, the length of flood data series in main flood season is greater than 30 years and the length of flood data series in non-main flood season is no less than 20 years; For insufficient data condition, the length of flood data series in main flood season is greater than 30 years and the length of flood data series in non-main flood season is less than 20 years. The calculating methods of manage-flood for three flood data conditions have been presented based on the principle of total probability in this paper. For sufficient data condition, the mathematical expect formula of total probability has been adopted with frequency analysis; for relatively sufficient data condition, the mathematical expect formula of total probability with combined data in non-main flood season was applied; for insufficient data condition, the back calculation approach was presented, and the formula of manage-flood based on the principle of total probability has been suggested. The case studies for calculating of manage-flood in different flood data conditions have been given for different basins. The comparison of the suggested method to the method of Copula function has been discussed. The results have showed that the suggested method is better than the method of Copula function, and the designed value of manage-flood is reasonable.关键词：division of flood period;manage-flood;total probability;Copula function;flood frequency
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发布时间：2024-01-05 - 摘要：Bonded steel plate has attracted extensive attention in the field of reinforced concrete structure, but the durability study of reinforced structure is rarely involved, especially the durability study of the coupling action of load and hydrothermal environment. In order to explore the durability and damage mechanism of reinforced concrete beams strengthened with bonded steel plates under the coupling action of load and hydrothermal environment, a steel plate bonded concrete reinforced with 7 bonded steel plates r was tested under hydrothermal environment. Considering the coupling action of no-load, static load and alternating load with hydrothermal environment respectively, the aging test was conducted in 15 days and 30 days under high temperature and humidity conditions. Finally, the mechanical test was performed to obtain failure mode, deflection, strain of steel plate and steel bar under the coupling action of different load and environment. After long term load and hydrothermal environment coupling, the mechanical properties of the reinforced structure was studied, as well as the damage of durability. Results showed that the mechanical properties of the reinforced beams with no load action were degraded after 15 days and 30 days. And the strengthened beams under the static load were more obvious. Especially for reinforced beams under the action of alternating load, the mechanical properties of the beams were most significantly degraded. Alternating load and hydrothermal action made the mechanical performance of reinforced beams decrease and the ultimate strength, flexural behavior and ultimate strain of steel plate were decreased by 17.26%, 17.21% and 41.92%, respectively, compared with the reference beam. The coupling of load and hydrothermal environment had an effect on the stress in beams, while did not have any significant effect on failure pattern. And the failure modes of reinforced beams under the coupling action of load and hydrothermal environment were divided into three stages of concrete cracking, crack development and steel plate peeling failure. The penetration of hydrothermal corrosion medium into reinforced concrete beams and bonding interface caused damage to durability and this effect was aggravated under the action of load.关键词：bonded steel plate;reinforced concrete beam;the coupling action of load and hydrothermal environment;durability
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发布时间：2024-01-05 - 摘要：Push-out failure is easy to happen in stud shear connector with small length-diameter ratio of stud. At present, the bearing capacity of push-out failure mode is usually determined by test. In order to extend the application of finite element analysis, the compression strain of concrete near the stud end was taken as a control variable to judge whether the push-out failure happens. Firstly, ABAQUS software was used to create finite element model of standard push-out test. The results were compared with both the reference and design codeand the correctness of finite element model was verified. Then, the influences of length and diameter of stud on bearing capacity were analyzed combined with the method of analyzing the push-out failure. Lastly, the calculation formula of bearing capacity with push-out failure was given. Results showed that the tie constraint between stud and concrete was the upper limit of stiffness for surface-to-surface interaction. Push-out failure was prone to happen with lower concrete strength and it was unsafe to just restrict the length-diameter ratio of stud larger than four to avoid pull-out failure in design code. The degree of increase of bearing capacity caused by the diameter of stud was not affected by concrete strength. When the diameter of stud increased from 13 mm to 22 mm with an increment of 3 mm, the bearing capacity increased by 42%, 31% and 35%, respectively. Eurocode4 was suggested to be followed for design when the diameter of stud was larger than 16 mm, because the value calculated from Code for Design of Steel Structure was a little large. The judgment method and calculation formula of bearing capacity proposed for push-out failure were reasonable and verified by calculated value of design code.关键词：composite structure;shear connector;pull-out failure;bearing capacity;finite element method
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发布时间：2024-01-05 - 摘要：Gravity currents encountered in both natural environment and engineering applications have important influence on industrial production and life. In this paper, two high-speed digital cameras (one is from the top view and the other one is from the side view) were employed to obtain the three-dimensional motions of lock-exchange gravity current through a large number of repetitive experiments, i.e. these experiments were carried out under the same conditions. The front location, speed, height, and angles of the gravity current and their uncertainties were analyzed, and the effects of three-dimensional current motions on these uncertainties were investigated. The images from the top-view show that the density current head positions across the flume are different, indicating the presence of the three-dimensional motions in gravity current. The results show that the gravity current is composed of lobes and clefs, and the three-dimensional patterns of current motions from the lateral diffusion and the friction from the wall may be the cause of the uncertainty for current motions. The front location, speed, height, and angles of gravity current follow normal distributions at the selected time. The uncertainties of these parameters were measured by the coefficient of variation (COV). For the front locations, the COV values decreases rapidly in the initial stage, and decreases below 6% slowly in the subsequent stage. The COV values for the front speed also rapidly reduces and then maintains a near constant value, approximately equal to 5%. Based upon the experimental results, the uncertainty for the front location or speed of gravity currents due to the three-dimensional gravity current motions will be approximately 5%～6% of the averaged front location or current speed, which can be used as a reference value for future individual measurement.关键词：gravity current;three-dimensional effect;repetitive experiments;uncertainty
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发布时间：2024-01-05 - 摘要：Two 1/3.5 reduced scale one-story 1 × 2 bay reinforced concrete (RC) flat plate sub-structures were fabricated and static progressive collapse tests in the scenario of a side column loss were carried out on them. Progressive collapse performance such as collapse failure modes and mechanism was investigated and the influence of diagonal constructional slab bottom reinforcement (DCSBR) on the progressive collapse performance of RC flat plate structures was discussed. Experimental results showed that, after punching failure happened in the joint region of the removed column, bending-shear failure was observed in the joint regions of adjacent corner column and side column successively. Arc-shaped cracks on the slab top and radial cracks on the slab bottom distributed around the removed column appeared during loading. Load carried by the removed side column was mainly transmitted along the short slab span to the adjacent column in the residual structures. Comparing with the specimen without DCSBR, the crack load, the first peak load and the ultimate collapse resistance of the specimen with DCSBR improved by 78.3%, 32.3% and 50.7%, respectively. The maximum value and fluctuation range of the dynamic increase factor (DIF) of load reduced obviously for the specimen with DCSBR. The analysis showed that tensile membrane action was one of the most important working mechanisms against collapse in flat plate structures. When static method was used to analyze the collapse performance of flat slab structures, DIF of load should be greater than 1.16 and less than 2.0. DCSBR can be used as an efficient constructional method to improve the collapse resistance of weak regions in flat plate structures. Finally, the collapse resistance calculation model of flat slab structures in the scenario of a side column loss was presented based on the experimental results, and the comparison of calculations with experiments indicated that the calculation model can be used to assess collapse resistance of flat plate structures in the scenario of a side column loss.关键词：flat plate;progressive collapse;failure mode;working mechanism;membrane action
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发布时间：2024-01-05 - 摘要：The geological processes, including earthquake, engineering excavation, weathering, erosion and transport caused a large number of loose accumulation bodies. The stone content in these loose accumulation bodies were different, and the instability induced by rainfall leaded to geological disasters including landslides and debris flows, which seriously threaten the production and living of local residents and the operation of large projects. It is thus crucial to conduct the model tests of different stone content and rainfall intensity using the large scale model platform, and to analyze the influence of stone content and rainfall intensity on the deformation and instability of loose accumulation. The results showed that the evolution of volume water content could be divided into four stages during the rainfall process of loose accumulation. The moisture content almost remained unchanged in stageⅠ, and then increased rapidly in stageⅡ. In stage Ⅲ, the moisture content reached its peak value, and then lightly decreased; after this, the moisture content increase slowly in stage Ⅳ. The larger the rock content, the smaller the volume moisture content of the same rainfall intensity and time, and the earlier the tensile failure occurs at the back edge. The smaller width of the corresponding tensile failure, the shorter duration of the slope failure continues. When the rainfall duration was same, the greater the rainfall intensity, the greater the volume moisture content is. The higher the rainfall intensity, the higher the volume moisture content of the loose accumulation body. Under different rainfall intensities, the volume moisture content of loose accumulation body varies with each other. The stability influence of rainfall intensity on loose accumulation body was more obvious. The greater intensity of rainfall, the main tensile cracks of loose deposits were smaller, and the main tensile cracks time, the maximum crack width, and the instability of the maximum displacement cumulative rainfall duration decreased more significantly. The results would provide references for predicting the instability and calamity in loose accumulations during disaster area.关键词：loose accumulation;stone content;rainfall intensity;instability
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发布时间：2024-01-05 - 摘要：Rock-burst is a serious threat to the construction safety of deep tunnels, which causes huge economic loss and staff casualties. The evolution process of rock-bursts is accompanied by a series of micro-seismic events. Analyzing and processing these characteristic parameters about the microfracturing such as size, time, space, energy, volume, etc, which is helpful to understand the fracture mechanism of rock mass, and provides a theoretical basis for the study of rock-burst disaster. In this research, theoretical analysis combined with micro-seismic monitoring were used. Based on the hundreds of immediate rock-bursts (including immediate strain structure slip rock-bursts and immediate strain rock-bursts), with different types and intensities, occurred in four deep headrace tunnels at Jinping-Ⅱ hydropower station in Sichuan province, China. The self-similarity characteristic and fractal behavior of micro-seismic volume distributions during the dynamic evolution process of such rock-bursts were studied. The achieved results are as follows: The volume distribution of micro-seismic events during the development of immediate rock-bursts shows great self-similarity, the value of correlation coefficient are all greater than 0.97. For different types of immediate rock-bursts, the daily volume fractal dimension increases during the evolution of immediate rock-bursts, and they totally increase up to a certain threshold value before the rock-burst occur. The volume fractal dimension values on each day were between 0.8 and 0.1 for the evolution of immediate strain structure slip rock-bursts, but those of immediate strain rock-bursts were between 0.4 and 1.3, and both of them are greater than 1.0 when the rock bursts. The micro-seismic energy fractal dimension can be used as a significant guideline to build up a warning system and reduce the risk of rock-bursts during construction under high in-situ stress condition.关键词：micro-seismic;self-similarity;fractal;strain−structure slip rock-burst;strain rock-burst
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发布时间：2024-01-05 - 摘要：In order to perfect the salt expansion theory of coarse-grained saline soil and explore the influencing factors and mechanism of the salt−frost heaving force, 96 groups of coarse-grained sulphate saline soil samples are prepared artificially then indoor model tests have been carried out by self-designed test device. Test results showed that the sensitive range of temperature on the salt−frost heaving force is −0.2℃～−1.0℃. The salt content had no influence on the rules that the salt−frost heaving force increasing with temperature and determines the maximum salt−frost heaving force together with water content. For samples with same void ratio, the increasing water content led to an increased amount of the salinity which resulted in the maximum salt−frost heaving force. When the salt content kept constant, however, the increase of water content caused the decrease of maximum salt−frost heaving force. The maximum salt−frost heaving force achieved the maximum and minimum values when the void ratio was 0.58 and 0.55, respectively, which was related to the crystallization position of salt in the soil frame. Furthermore, based on the test results, a mathematical expression of frost heaving limit depth of coarse-grained sulphate saline soil is given by the hierarchical synthesis method, which is expected to provide guidance for the quantitative evaluation and design of salt−frost heaving deformation of coarse-grained sulphate saline soil.关键词：coarse-grained;sulphate saline soil;salt−frost heaving force;limit depth
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发布时间：2024-01-05 - 摘要：Cohesive force is an important mechanical parameter of cohesive soil, and the density and void ratio of soil are important factors affecting its cohesion, but the cohesion force of cohesive soil is difficult to estimate, while its density and void ratio have changed. With the theory of molecular attractive forces between solids, the functional relationship between soil cohesion and its dry density or void ration was analyzed. To establish the conceptual model of pore structure in cohesion soil, the uniform cohesive soil was simplified into a combination of soil particles and pores, in which the soil particles are connected into a whole by molecular attractive forces, and the soil cohesion was simplified into the resultant force of molecular attractive forces per unit area. On the base of the conceptual model, the relationship between soil particle spacing and soil void ratio was built, and the influence of void ratio on soil particle spacing was analyzed. According to the theory of molecular attractive forces between solids established by Lifshitz, the functional relationship between soil cohesion and its dry density or void ration was established, and a mathematic method for calculating the cohesive force of uniform soil was derived. The calculation results of the cohesive force were compared with that of the direct shear test, and the rationality of the proposed method was verified. The results showed that, the soil particle spacing is positively correlated to void ratio, as the void ratio increasing, its influence on soil particle spacing gradually decreases. The cohesion force of uniform soil is positively correlated to dry density, and negatively correlated to void ratio. At the same time, the effect of dry density on cohesive force is more significant with its increase.关键词：cohesion force;void ratio;soil particle spacing;molecular attractive force;direct shear test
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发布时间：2024-01-05 - 摘要：Deterioration of fracture characteristics for concrete under acid rain attack was investigated by laboratory-accelerated corrosion tests, three-point bending (TPB) tests and scanning electronic microscopy (SEM). Elastic modulus, initial cracking load and maximum load of the corroded concrete with different corrosion periods were obtained and the deterioration of fracture toughness was analyzed. The corrosion depth increases with corrosion duration under simulated acid rain environment. The observation by scanning electron microscopy showed that the microstructures of crack tip are porous and loose due to acid corrosion, and many crisscross cracks appear at corrosion layer, which make the corresponding resistance stresses to crack propagation decrease. The experimental results of three-point bending tests showed that initial cracking load and maximum load of the corroded specimens increase in the initial stage of immersion, and decrease with the increase of immersion time. Beyond that, the deterioration of initial cracking load is accelerated with the increase of corrosion degree. The fracture toughness of concrete increases with corrosion time at the initial stage and then decreases, and the lower the pH value is, the shorter the duration of the strengthening phase is. Under the impact of acid corrosion, physical and chemical properties of the concrete change significantly around the crack tip, which is the main factor that results in the decrease of the mechanical properties for concrete. Also, the curves of fracture toughness versus corrosion depth were obtained in this study.关键词：concrete;three-point bending;electrometric method;scanning electronic microscopy;fracture toughness;corrosion depth
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发布时间：2024-01-05 -
Experimental Investigation on Flow Velocity Distribution in Mountain Rivers with Coarse Sediment Bed AI导读
摘要：In mountain rivers with coarse sediments, the ratio of water depth to sediment diameter (h/d) is relatively small especially under the condition of shallow water depth. Therefore, the vertical velocity distribution along the river cannot be described accurately with traditional logarithmic or logarithmic-wake law. In this paper, flume experiments were carried out with two kinds of sediments (glass beads d=1.4 cm and pinpong d=4 cm) to test the influence of coarse sediment on vertical velocity distribution under different h/d. In the presence of coarse sediment bed, one of the problems encountered is how to determine the reference level y0. For practical purpose, the present study assumes that y0 does not varies with h/d, namely, y0=0.2d. The measured data were first converted to dimensionless and then compared to theoretical results calculated by logarithmic-wake law. In addition, the coefficient B and another wake coefficient Π in in logarithmic compensation formula were calibrated to fit for the measured data. The results indicate that when the value of h/d is small, the coefficient B decreases with the increase of h/d while the wake coefficient Π presents an opposite trend; when the value of h/d becomes larger, both B and Π tend to a constant. Finally, a modified logarithmic-wake law is derived to describe the velocity distribution in mountain river flows with small h/d. The modified model agrees well with the experimental data conducted in the present laboratory flume. Furthermore, it also has a good adaptability to riverbed with coarse sediments.关键词：coarse sediment bed;shallow submerge degree;vertical velocity distribution;logarithmic-wake law- 2308
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发布时间：2024-01-05 - 摘要：Floodplain vegetation has an important influence on the flow and sediment transport and river bend migration, especially when flood overflows the main channel. The influence of dense floodplain vegetation on the height of secondary current cell and the position of the center of the cell was investigated through physical experiments in which the artificial grass was deployed on the floodplain to simulate floodplain vegetation. The experimental results indicated that the floodplain vegetation affected the height of secondary current cell most significantly at cross-over sections. The height of the cell was equal to the bankfull level in the non-vegetated channel, but was equal to the sum of the bankfull level and the canopy height. The floodplain vegetation increased the bankfull level equivalently. In a meandering bend, the influence of vegetation on the height of secondary current cell reduced gradually, and then was negligible at the apex section. Based on experimental observations, a method for predicting the position of secondary current cell was proposed and verified using the data from a different source, indicating that this method was capable of accurately predicting the position. Finally, the relation between the relative intensity of secondary current cell and the ratio of main channel discharge and total discharge was discussed. Regardless of whether vegetation was fixed on the floodplain or not, the maximal discharge ratio occurred at apex section in all scenarios. As the main channel depth increased, the difference between the ratios in non-vegetated channel and vegetated channel was reduced. When the main channel depth was close to or smaller than the sum of canopy height and bankfull level, the characteristics of secondary current cell along a meandering reach in the channel with overbank flows would be similar to those in a channel with inbank flows.关键词：meandering compound channels;vegetation;secondary flows;predictive method;main channel conveyance capacity
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发布时间：2024-01-05 - 摘要：NDVI (normalized difference vegetation index) can reflect the changes of vegetation growth. It has been widely used to monitor multi-scale vegetation growth conditions. Based on MODIS remote sensing data, the time series of NDVI from 2001 to 2015 in Zoigê area were reconstructed by filtering software TIMESAT, and three key vegetation growth properties were extracted: The start of vegetation growth period, the length of vegetation growth period and the maximum NDVI value. The key climatic factors affecting the vegetation growth period were analyzed. The results showed that: 1) The average start time of vegetation growth period increased, and the average length of vegetation growth period prolonged, while and the maximum NDVI values had no significant changes from 2001 to 2015. 2) The average vegetation growth properties had no obvious regular pattern of change in spatial distribution.As the elevation increased, the start of vegetation growth period postponed, the length of vegetation growth period shortened visibly, and the maximum of NDVI did not change obviously. 3) Temperature is the main factor that impacted vegetation growth period in Zoigê area. Increasing accumulated temperature in April and May could advance the start time of vegetation growth period. The average length of vegetation growth period would be longer with the higher accumulated temperature in September and October. The increase of accumulated temperature from the start time of growth period to the time of the maximum NDVI also increased the maximum value of NDVI. 4) The correlation between NDVI and SPI was not significant. Therefore, the vegetation in Zoigê area had low dependence on precipitation. The findings showed the changes of vegetation growth period in Zoigê area and their response to climate over the past 15 years. The methods used in this paper can provided a useful tool for remote sensing monitoring of vegetation characteristics at large scales.关键词：remote sensing;normalized difference vegetation index(NDVI);vegetation growth period;accumulated temperature;standardized precipitation index(SPI)
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发布时间：2024-01-05 - 摘要：In online community question answering (CQA), many raised questions under go long response time and lack high quality answers. There is a realistic need to measure the community users’ professionalism degree on a specific problem. To date, previous methods based on link analysis or text analysis focused on only the professional metrics of community and topic, and did not fully investigate the question granularity. To address this issue, the concept of user professionalism based on question granularity in CQA was defined, and a prediction method for user professionalism based on question granularity was proposed, including a measurement method and a prediction model. Based on the community users’ evaluation mechanism of answering qualities, the prediction method established professional metrics of users on the question granularity. Integrating together the user bias, the problem bias and the latent feedback of the question set that users answered, a model on problem granularity based on matrix factorization is constructed to predict how professional the user is in answering questions. By using the question–answer (QA) dataset under topics of Internet in Zhihu, comparative experiments with two mainstream methods were conducted. The results showed that the proposed measurement method of evaluating the degree of user professionalism is effective, and the prediction model has higher prediction accuracy.关键词：community question answering;question granularity;user professionalism;matrix factorization;prediction model
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发布时间：2024-01-05 - 摘要：In order to solve the influence maximization problem in evolving social network, a dynamic influence maximization algorithm based on the linear threshold model was proposed in this paper. The goal of influence maximization was to mine out the top k most influential seed users and maximize the spread of influence through them. An algorithm called LTDIM was proposed based on the linear threshold model. Specially, firstly, the formal definition of dynamic influence maximization problem was given and the initial seeding method based on alive edge path was proposed. Then, according to the analysis of various network topology changes, an incremental seeds updating algorithm was presented. Finally, to further improve the time efficiency, two pruning strategies DP (degree pruning) and IIP (influence increment pruning) based on nodes degree and influence increment were devised. Experiments on the eight network snapshots of four real social networks evaluated the algorithm performance in terms of running time and influence spread. Experimental results demonstrated that compared with the state-of-the-art static heuristic algorithms, the algorithms proposed in the paper can achieve a great deal of speedup in running time while maintaining matching performance in terms of influence spread.关键词：dynamic social networks;influence maximization;linear threshold model;pruning strategy
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发布时间：2024-01-05 - 摘要：Aiming at the problems of data sparseness of user item ratings and low recommendation accuracy in traditional collaborative filtering recommendation methods, an improved hybrid recommendation approach based on user interest ratings filling was proposed. Firstly, the users’ preference to the item types was analyzed, and the user interest ratings were calculated. Afterwards, the operation of matrix filling was performed. Then the impact of users’ subjective ratings differentiation and the item’s own quality were considered, and the traditional Pearson correlation coefficient was improved. Based on the filled ratings matrix, users’ similarity and items’ similarity were computed, to predict ratings from the perspective of users and items respectively. Moreover, the weighted sum of two predicted ratings was calculated further to perform the hybrid recommendation. Finally, experiments were carried out on the Movielens100k dataset. The filling effect of user interest ratings matrix was analyzed firstly, and then the proposed approach, traditional collaborative filtering recommendation methods, and previous methods in the literature were compared and analyzed. The results show that the proposed matrix filling method can effectively alleviate the effect of data sparseness, and the filling effect is better than traditional ratings matrix filling methods. Furthermore, our improved hybrid recommendation approach (IHRIRF) has better recommendations than traditional collaborative filtering recommendation method HCRF as well as WPCC method.关键词：collaborative filtering;data sparseness;rating differentiation;hybrid recommendation;Pearson correlation coefficient
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发布时间：2024-01-05 - 摘要：In order to solve problems of heavy rendering loads and unstable frame rates caused by huge data and rich details of large terrain in flight simulation, a terrain modeling method based on Tessellation was proposed. The key idea of the method is to build a view-dependent multi-resolution LOD structure of terrain based on geometry clipmaps. Firstly, several Tessellation control points, which are able to express structures and all states of geometry clipmaps by index groups, were generated in CPU and stored in vertex cache. Then, index points were generated in index cache by each level of geometry clipmaps according to Tessellation control points in vertex cache and transferred from CPU to GPU. Secondly, adaptive triangle patches were generated by GPU tessellation shader according to index points in GPU. In update phase of rendering cycle, states switching of geometry clipmaps was did by simply replacing index points in changing regions. Finally, ‘cracks’ caused by different resolutions between adjacent levels were eliminated by modifying outer tessellation level factor of shared edges between levels, which can generate triangle patches from inside to outside at shared edges of outer level corresponding to the inner level. The experimental results showed the proposed method can make full use of new features of the latest graphics cards. It is able to decrease data transmission from CPU to GPU while achieves the balance of rendering loads, and improves the rendering efficiency and real-time frame rate stability during terrain navigation. The proposed method of crack eliminating is simple and effective, which ensures the real degree of details of large terrain and meets the requirements of stable real-time terrain rendering in flight simulation.关键词：flight simulation;tessellation;geometry clipmaps;GPU;terrain modeling
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发布时间：2024-01-05 - 摘要：In order to alleviate premature convergence in traditional differential evolution algorithms, a differential evolution algorithm based on sharing learning strategy (SLDE) was proposed and the concepts of sharing-individual (SI) and sharing learning factor were introduced in SLDE. The sharing-individual covers the whole population, while the superior individuals guide the promising searching direction, the inferior individuals maintain the population diversity in the evolution process. By learning from the sharing-individual, information exchange was achieved among the whole population to avoid missing information of individuals, which helps the algorithm jump over the trap of local optimal solution and improve the local and global exploration capability. Meanwhile, the evolutionary information of individuals was made full of use in SLDE, and the sharing learning factor was self-adaptively adjusted according to the distance of fitness value of individual and the optimal fitness value, in order to alleviate the randomness and blindness from the random individuals and enhance the searching ability. A total of 22 Benchmark test functions with different properties were used for performance test comparison with seven state-of-the-art DE variants. The experimental results showed that SLDE has strong ability to escape from local optima, significantly reduce the evolutionary generations and greatly improve the convergence precision, convergence speed and stability. The overall global optimization performance of SLDE is much better than other improved DE algorithms.关键词：differential evolution;sharing learning;sharing-individual;sharing learning factor;self-adaptiveness
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发布时间：2024-01-05 - 摘要：In order to estimate the change trend of aircraft taking off and landing separation in case of low visibility, improve the efficiency of runway use and reduce flight delay, an aircraft taking off and landing separation model in airport category Ⅱ operation was proposed. Firstly, the taking off and landing operation procedures under the category Ⅱ operation were analyzed to detail the process of aircraft taking off, landing, lining up and vacating runway. Secondly, a taking off and landing model was established based on the category Ⅱ operational regulations. Then, the cellular structure was defined, the rule of avoiding deceleration and the condition of vacating runway were introduced, and a cellular automata model of aircraft taxing was defined. Finally, the control rules were abstracted as constraint conditions and the taking off and landing separations were quantified. An example of Urumqi airport was used to verify the simulation. The change trends of taking off and landing separation and separation standard deviation were obtained through computer numerical simulation by setting different values for parameters such as the ratio of aircraft type, the ratio of landing and taking off, the length of the critical area and the time of vacating. The experiments demonstrated that in categoryⅡoperation, the separation was large, with a peak of 228.6 s. The capacity for landing and taking off were only 60% and 90% of the normal operation conditions. The peak of separation standard deviation was 74 s, which was 1.64 times of normal situation. The vacating position was the main factor for the increase of continuous landing separation. Results showed that the model could quantify the influence of key factors on the taking off and landing separation. The simulation results are in line with the actual operation, and provides theoretical foundation for improving efficiency in categoryⅡoperation.关键词：air traffic management;cellular automaton;taking off and landing separation;computer numerical simulation
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发布时间：2024-01-05 - 摘要：Inverted planetary roller screw (IPRS) is a kind of linear transmission mechanism which has advantages of high load carrying capability, long fatigue life, high transmission accuracy and low noise. Due to these advantages, it has wide application prospect in the fields of aerospace, weapon equipment, CNC machine tools and petrochemical industry. Up to the present, there is little research about this mechanism. Therefore, a model was derived to calculate load distribution, axial deformation and contact fatigue life. Firstly, surface equation of screw, roller and nut was established. Based on Surface meshing theory, the meshing points of the roller with the screw and nut in a pitch were derived respectively. According to the surface equations and the location of contact points, an accurate method to calculate the elastic deformaion between the meshing surface was derived. Secondly, A model of IPRS’s load distribution was obtained based on the geometric relationships between Hertz deformation, thread deformation and axial deformation. Based on its load distribution condition and motion principle, a fatigue life model was deduced using Lundberg–Palmgren equation. Then, a program was compiled in the MATLAB Environmet to calculate load distribution axial deformation and contact fatigue life. By comparing calculationg result with the expriments, the load distribution and axial deformation model was verified. The influence of the key parameters on the performance of IPRS was analyzed and the following results were derived. The load distribution was mainly influenced by the number of teeth, the number of rollers and the helix angle, and increased with the increases of these three factors. The axial stiffness was mainly influenced by the number of teeth, the number of rollers, the helix angle and the outer diameter of the nut, and increased with the increases of the number of rollers and the outer diameter of the nut, increased first and then decreased with the increase of the number of teeth and the helix angle. The contact fatigue life was mainly influenced by the number of teeth, the number of rollers, the contact angle and the radius of thread profile, and increased with the increases of the number of teeth, the number of rollers and the radius of thread profile, decreased with the increase of contact angle.关键词：inverted planetary roller screw;load distribution;axial deformation;stiffness;contact fatigue life
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发布时间：2024-01-05 - 摘要：With the wide application of the aerostatic spindle in the ultra-precision machining process, the requirements for the kinematic precision of the spindle are increasing. It is necessary to predict and improve the precision of the spindle motion accurately. Based on the nonlinear dynamic characteristics of the aerostatic bearing, the vibration characteristics and prediction model of the aerostatic spindle were studied, and the influence of the nonlinear dynamic characteristic analysis on the spindle rotary precision was explored. Firstly, the dynamic flow model of the gas film of the aerostatic journal bearing was established, the nonlinear dynamic stiffness and damping coefficients were obtained by the perturbation method. The gas film was used as the spring-damping system to build the bearing-rotor system, and the dynamic vibration model of bearing-rotor system was established by dynamic analysis. Then nonlinear dynamic parameters were introduced into the vibration model, and the curve of the radial runout error, the deflection error and the total error of radial vibration were obtained by solving the model with MATLAB. The frequency domain analysis were conducted on the vibration signal. Finally, Rotation Error Measurement experimental of spindle was performed to inspect the results of vibration error analysis. From the dynamic analysis of the aerostatic journal bearings, the dynamic stiffness and dynamic damping of the bearing are all nonlinear, and the dynamic stiffness increases with the increase of eccentricity, and the dynamic damping decreases. From the vibration analysis of the bearing-rotor system, the following conclusions can be obtained. 1) The nonlinear analysis has an obvious influence on the deflection error, but the influence on the radial runout error is not obvious. It shows that the nonlinear analysis mainly affects the deflection error of the spindle and thus affects the total radial error. 2) The maximum amplitude of the deflection error is basically stable when the fixed value analysis is analyzed, while the maximum amplitude of the deflection error has an increase process and tends to be stable at the time of nonlinear analysis, and the maximum amplitude of the nonlinear analysis is obviously larger than the amplitude of the constant value analysis. 3) The total radial error of the nonlinear analysis and the constant value analysis is basically the same at the beginning of the gas supply, but with the increase of time, the maximum amplitude under the nonlinear analysis is larger than the maximum amplitude under the constant value analysis, which shows that the nonlinear analysis has no obvious effect on the error of radial runout and the deviation angle when the gas supply is started. When the gas supply is stable, the nonlinear dynamic stiffness and dynamic damping will obviously affect the vibration amplitude of the rotor. 4) From the frequency domain, the resonance frequency at the maximum amplitude of the nonlinear analysis is 964 Hz, and the resonance frequency at the maximum amplitude of the constant value analysis is 986 Hz, and the nonlinear analysis reduces the resonance frequency at the maximum amplitude. 5) When the frequency is higher than 1 500 Hz, the amplitude change of the rotor is very small, which shows that the vibration of the rotor is more stable when the frequency is greater than 1 500 Hz, and the vibration frequency of the gas film is not easy to resonate with the natural frequency. Experimental results indicated that the error of radial rotation error of the spindle based on nonlinear analysis is reduced by 1.43% to 6.54% compared to the constant value analysis. Therefore, the coupled vibration analysis of the bearing-rotor system can be achieved by applying the gas film as the spring-damping system to the rotor. The introduction of nonlinear dynamic characteristic parameters of bearing realizes the effect of bearing dynamic performance on spindle dynamic vibration. Based on nonlinear dynamic characteristics, the vibration analysis of the bearing-rotor system can more accurately analysis and predict the radial vibration error of the aerostatic spindle.关键词：aerostatic journal bearing;bearing-rotor system;nonlinear analysis;vibration error
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发布时间：2024-01-05 - 摘要：In engineering practice, the starvation may occur due to insufficient supply of lubricant in hypoid gears. Therefore, a starved elastohydrodynamic lubrication model for hypoid gears was developed with the consideration of contact geometry, surface roughness, inlet oil layer thickness, and arbitrary entrainment velocity vector of interface. Model validation was executed by means of comparison between the obtained numerical results and the available starved EHL data found from some previous studies. A comprehensive analysis for the effect of inlet oil supply condition on film thickness at engaging-in, engaging-out and pitch point was conducted in a wide range of operating conditions. In addition, the influence of speed on lubrication performance under different inlet oil supply condition was obtained. The results showed that the comparison between numerical and experimental results demonstrates a good agreement. It was indicated that the difference of film thickness among the three meshing point are getting smaller when the amount of lubricant in the inlet decreased. If the inlet oil layer thickness is reduced down to a certain value, the film thickness of the three meshing points would be the same. Besides, the speed has significant effect on the lubrication behavior. The film thickness gradually increases with the increase of the speed, if the speed keeps getting greater, the film thickness would remain constant under starved condition while the film thickness would keep rising under fully flooded condition.关键词：hypoid gears;starved lubrication;lubrication performance
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发布时间：2024-01-05 - 摘要：The push-rods oscillatory transmission with needle gears has the advantages of simple structure, convenient manufacturing and high machining precision. For this kind of transmission, the profile equation of movable tooth is the basis for tooth analysis and the key issue to guarantee the precision and stability of transmission. Different from the traditional way, where the profile equation is derived by enveloping and the profile curve is approximated by line, a new method for tooth profile equation derivation and simplification was proposed. The profile equation of movable tooth was deduced by the contact condition in the transmission process. Then the equation was simplified by Taylor expansion to facilitate the calculation in the research of tooth profile and meshing characteristics. Sequentially, to guide the rapid design of the transmission structure, an analytical discriminant to guarantee the transmission undistorted was established by the simplified equation. On these bases, the computational formula of transmission angle was derived and the influence of the main design parameters, such as surge wheel’s eccentricity and needle gear’s rotational radius, on the maximum transmission angle were analyzed. Analysis showed that the maximum transmission angle is positively correlated with surge wheel’s eccentricity, yet negatively with needle gear’s rotational radius. Furthermore, the error of simplified equation was analyzed and the result showed that the maximum horizontal and vertical coordinate errors are not exceeding ±0.06 μm. Thus, the accurate tooth profile equation could be replaced by the simplified equation. Finally, the three-dimensional model of the reducer with simplified tooth profile curve was designed and based on it, the fixed speed ratio transmission was verified by simulating. Simulation result showed that the error of speed ratio is about 0.007%. Consequently, the practicability of the simplified equation and the feasibility of oscillatory reducer with simplified movable tooth profile was validated by both theoretical analysis and simulation. The research results could be used as a theoretical basis for structural design and application.关键词：push-rod oscillatory transmission with needle gears;tooth profile simplified modeling;transmission angle analysis;error analysis
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发布时间：2024-01-05 - 摘要：Dry gas seal is one of the important sealing methods in shaft seal, especially for the devices with high sealing reliability requirements. Due to the designed relationship between the sealing gas film and the seal rings, the vibration of the floating ring is related to the change of the sealing gas film stiffness value. Therefore, the dynamic feature of floating ring system affects the reliability of the dry gas seal. A dynamic feature optimization method based on the particle swarm optimization and the projection pursuit was proposed. According to the working conditions, the pre-stressed modal analysis of the floating ring system was completed, and the accuracy of the modal analysis was verified by the spectrum analysis from experiment. The results of the experiment and analysis proved that it was necessary to optimize the dynamic feature of the floating ring system to improve the reliability of dry gas seal. The axial design parameters of the floating ring system were selected as the optimization parameter. Combining the response surface methodology with the Box–Behnken experiment design, the complete quadratic polynomial response surface models of optimization objective and constraint about optimization parameters were presented, respectively, which made the implicit relations explicit. With the natural frequency of the floating ring system as the objective function and the system static deformation as the constraint, the natural frequency reached to 142 Hz efficiently through the particle swarm optimization algorithm, increased 20% compared to the original natural frequency. Furthermore, the positive and negative relationship between the natural frequency and the optimization parameters was defined. Finally, the influence degree of optimization parameters on the natural frequency was obtained through the projection pursuit analysis. Based on the combination of the particle swarm optimization and the projection pursuit, the natural frequency of the floating ring system was increased above the given highest operating rotational speed 8 000 r/min (133 Hz).关键词：sealing reliability;particle swarm optimization;projection pursuit;dynamic feature optimization;parameters design
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发布时间：2024-01-05 - 摘要：In order to produce water efficiently and develop new membrane materials, plate and frame type membrane module was composed with biaxial stretch microporous membrane of PTFE, and vacuum membrane distillation system was set up to explore the desalination performance of NaCl solution. Orthogonal experiment was designed and the effect of feed temperature, flow rate, and concentration on water production were studied at 9 kPa absolute pressure degree on the one side of membrane. It was found that the temperature changed has the most significant influence on the membrane flux and the desalination rate changed slightly. With the increase of concentration, the membrane flux gradually decreases but the desalination rate increases. The increase of feed flow rate would increase the membrane flux, but no effect on the desalination rate. the flux has reaches 18.4 kg/(m2·h) at the conditions of 120 L/h feed flow rate and 40 g/L concentration when temperature at 60 ℃. More than 99.9% desalination rate and less than 5 μs/cm conductivity of produced water are found at different operation conditions. The process of mass transfer of vacuum membrane desalination was analyzed and coefficient of mass transferwas calculated by results of experiment. It was concluded that temperature is the important factor of coefficient of mass transfer and membrane flux because the coefficient of mass transfer increase linearly with it. Range analysis was developed and showed that temperature is the main influencing factor of the process. Repeated trials was studied and showed that the membrane remains stable running in the process of experiment. It was concluded that biaxial stretch microporous membrane of PTFE can be used for NaCl solution which concentration less than 80 g/L.关键词：biaxial stretch microporous membrane of PTFE;membrane distillation;desalination;coefficient of mass transfer
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发布时间：2024-01-05
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