最新刊期
卷 51 ， 期 2 ， 2019
- 摘要：Under the combined impacts of climate change and human activities, water resources, environment and ecological problems of China’s rivers and lakes interweave and overlap. As the largest freshwater lake in China, the Poyang Lake region and its five major tributaries are facing serious problems, including the reduction of water quantity, soil erosion, shoreline shrinkage and deterioration of aquatic habitat, whereas the current research level and key technologies cannot meet the requirements of ecological priority and green high-quality development. How to integrate resources, ecology, environment and other constraints into water conservancy project planning, construction and operation, clarify the impact of water conservancy projects on the ecological environment of rivers and lakes and the evolution trend of ecosystems under this influence, put forward technical measures to mitigate their effects, and meet the needs of human society and health to water ecosystem, are the forefront and hot issues of current ecological water conservancy theory system research and key technology research and development, but also the inevitable requirements of promoting the construction of national ecological civilization and the implementation of the Yangtze River protection. Aiming at the above problems, the characteristic factors of ecological water conservancy in the Poyang Lake region and its five major tributaries and its response mechanism to the development and utilization were distinguished and analyzed; the technical system of integrated ecological water conservancy for the land, bank and water was studied and developed; the integrated management technology and planning design scheme of ecological water conservancy were put forward and engineering demonstration was carried out, and the construction mode and monitoring and evaluation system of river and lake ecological water conservancy were constructed. Through the research of multi-disciplinary intersection, point combination, theory and practice, the interreaction mechanism of the characteristic factors of ecological water conservancy in rivers and lakes was revealed, and the monitoring and evaluation index system of coupling engineering, resources, environment and ecology was put forward to realize the theoretical innovation; a series of key technologies for agricultural water-saving pollution control and soil protection in red soil hilly and dry slopes and key technologies for hydraulic engineering assisted repair of damaged aquatic habitats were developed to realize technological innovation; solutions for comprehensive controlling system of river and lake ecological water conservancy were proposed, including planning guidelines, design guidelines, governance techniques, monitoring indicators, evaluation methods and construction models, to achieve integrated innovation.关键词：ecological water conservancy;ecological environment of rivers and lakes;monitoring and evaluation system;Poyang Lake region and its five major tributaries
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发布时间：2024-01-05 - 摘要：With the continuous development of urbanization plain of China, the real-time flood simulation and forecasting has become the main research content and important technical support for flood management in urbanization plain. The dynamic inversion of hydrodynamic parameters is one of the difficulties in real-time flood simulation and forecasting. Based on prior knowledge of rive roughness, this paper explored an efficient dynamic inversion technique for estimating river roughness parameters. Firstly, based on the continuity and slowness of spatial variation of river roughness, a prior knowledge that used smoothness matrix representing spatial variation of roughness was proposed. Then, taking the prior knowledge as a soft constraint condition, and combining with the extended Kalman filter algorithm for real-time correction of nonlinear dynamic system, a robust dynamic inversion model of river network roughness parameters in urbanization plain was developed. Through an example analysis, the influences of weight of roughness smoothness item, initial roughness estimation and station number on dynamic inversion results were systematically examined. The results show that: 1) the stability and spatial inversion characteristics of river roughness parameters can be effectively controlled by adjusting weight of roughness smoothness item; 2) the inversed roughness values of channels near stations tend to be true, and the ones of channels far from stations tend to be smooth in spatial distribution; 3) the inversed roughness values ofchannels near stations are less affected by the initial roughness estimation, while the ones of channels far from stations are more affected by the initial roughness estimation; 4) the more accurate the initial roughness estimation and the more the number of stations, the smaller the systematic error of inversed roughness, the smaller the amplitude of fluctuation adjustment at the beginning of dynamic inversion, and the better the inversion effect. The proposed model can be effectively applied to the dynamic inversion of river roughness parameters in urbanization plain.关键词：plain river network;dynamic inversion of roughness;prior knowledge
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发布时间：2024-01-05 - 摘要：With the operations of the Three Gorges Dam and its upstream cascade reservoirs, sediment load in the middle and lower reaches of the Changjiang River has decreased sharply, and the long-term and long-distance riverbed erosion has been extending towards the Estuary. Understanding the controlling factors of morphological processes and future evolution trend of the Changjiang Estuary is a major question for estuarine evolution and regulation. Using GIS techniques, morphological evolution of the Changjiang Estuary (Xuliujing to Hengsha) since 1997 were quantitatively analyzed, and the evolution trends till 2030 and 2050 were predicted by a well calibrated and validated numerical model (Delft3D). The results indicated that the study area shows overall erosion with significant local changes in 1997—2015. The erosion gradually increases as the sediment discharge decreases sharply, and the net erosion volume in 2010—2015 is as high as 75 million m3. Erosion mainly occurs at deep channel lower than 10 m, while the shallow shoals are dominated by accretion. Model predictions indicated that the study area would maintain strong erosion in 2015—2030 under present sediment supply condition (125 million t/a) and the erosion may decrease in 2030—2050 due to the increased resistance of river bed erosion. However, strong erosion still occurs under extremely low sediment supply (100 million t/a) with conversion from accretion to erosion at shallow shoals. Under the combined natural and human impacts, estuarine evolution processes are complex, and the evolution trend could be an important guidance to the integrated regulation of the Changjiang Estuary.关键词：morphological evolution;fluvial sediment decline;numerical modeling;evolution trend prediction;Changjiang Estuary
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发布时间：2024-01-05 - 摘要：Concrete gravity dam response under strong ground motions has a profound impact on the safety assessment and damage failure mode of structures. In this paper, the endurance time analysis (ETA) method was used to generate endurance time accelerations (ETAs), calculate and analyze the probability density evolution process and failure probability of damage evaluation factors subjected by the Koyna ground motion ETAs. The Koyna gravity dam finite element model was established, and the dynamic response and damage process of dam under ETAs was simulated. The plastic dissipation energy, damage dissipation energy, damage volume and normalized damage volume as damage evaluation factors were used. Based on the probability density evolution theory, the generalized probability density evolution model was set. The probability density curves varied with ETA history under different damage evaluation factors were calculated. Selecting two typical moments as moderate damage and severe damage evaluation criterion and combining probability density curves with failure probability, probability curves under different damage evaluation factors and different damage evaluation criterion were compared to realize failure probability analysis and evaluation of dam under different peak ground acceleration. Previous studies showed that damage evaluation index obeys the normal distribution which is just a kind of assumption and no detailed basis. According to the present research, the probability density distribution of damage evaluation index results is similar to normal distribution and has certain deviation compared with PDE method. The studies shows that probability density evolution process based on ETAs has high computation efficiency and precision. Compared with the results of normal distribution, the results of PDE are closer to the true probability distribution. It can be more conservative to represent failure probability of dam when using plastic dissipation energy and damage dissipation energy as damage factors under different ground motion intensity.关键词：concrete gravity dam;ETA;damage evaluation factor;probability density evolution;failure probability
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发布时间：2024-01-05 - 摘要：After a long time operation, a conventional earth rockfill dam (e.g. homogeneous dam or core wall dam) may suffer from a lot of dam diseases such as dam-break, overtopping, landslides and leakage. On the basis of a large number of practices of rebuilding and strengthening the medium and small-sized dams, a new type of dam, a longitudinal reinforced rockfill dam, is proposed. This new type of dam has triple functions of seepage control, stress resistance and deformation resistance. It also has significant advantages in both construction material selection and construction technology when compared to a conventional earth rockfill dam. Based on the theoretical research and successful practice of the new dam construction technology by placing rigid structures (also called longitudinal reinforcements) in conventional rockfill dams, the factors of safety against overtopping compared with that of the unreinforced rockfill dams was briefly analyzed in this paper. The hydraulic process of the overtopping is presented, during which the downstream material is washed away and forming a scour hole in the dam. The progressive development of the scour hole will change the stress distribution of the reinforced body. Eventually the reinforced body will reach a state in which it is subjected to the pressure from the upstream when the toe zone is empty. The advantage of this new dam is that it changes the conventional overtopping failure mode to the progressive scour hole development mode, therefore delays the dam breaking, and provides time for repair and evacuation. The longitudinal reinforced rockfill dam has important and broad applications in the construction of new dams or strengthening of existing rockfill dams.关键词：new type of dam;longitudinal reinforced rockfill dam;safe operation;overtopping failure;depth of scour;mechanical strength
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发布时间：2024-01-05 - 摘要：Composite wall in the cold-formed thin-walled steel structure house has a good shear performance. When the double-layer composite wall is applied, the weak part is located at the floor connection, which becomes the failure under reciprocating loads. Considering the axial pressure of different walls and different types of anchor bolts, a total of 9 double-storey wall in three groups were tested for shearing performance. The research results showed that the energy consumption and ductility of the wall are worse than the single wall. The out-of-plane instability of the joints along the floors or buckling failure of the floor beams often occur, and the construction of the floor joints is the key to the bearing of structures. The effect of the inner layer of the strip on the shear capacity of the double wall is not obvious. The out-of-plane displacement occurs at the floor joint, the stiffness and bearing capacity will suddenly drop, and the random out-of-plane instability will increases with the increase of the axial pressure. It is not obvious to improve the out-of-plane stability of the wall only by using struts to increase the vertical compressive capacity of the floor. Double-nuts anti-pulling bolt has obvious effects on improving the bearing capacity of the wall. It was suggested that this kind of anchor bolt could be used at the floor connection of such multi-storey buildings, which can effectively improve the shear resistance of walls.关键词：cold-formed steel thin-wall panel;cyclic load;model test;shear capacity;failure mode
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发布时间：2024-01-05 -
Analytical Solution for Rheological Consolidation of Soft Clay with Threshold Hydraulic Gradient AI导读
摘要：The influence of a threshold gradient of water flow in soft clays on consolidation behavior has been gradually recognized. However, the consolidation theory with consideration of a threshold hydraulic gradient and rheological characteristics has rarely been reported in the literature so far, and especially the analytical solution for this problem has never been studied. In view of the deficiency in consolidation theories, the governing equation for one-dimensional consolidation of the clay with consideration of the threshold gradient and rheological characteristics is developed on the basis of Terzaghi’s theory for one-dimensional consolidation. An analytical solution for the governing equation is obtained by the method of Laplace transform. The analytical solutions for one-dimensional consolidation derived so far considering either a threshold gradient or a rheological model are all special cases of the solution derived herein. Based on the solution proposed in this study, the influences of the threshold hydraulic gradient and different rheological models on consolidation behavior are investigated. The results show that the influences of the ratio of the threshold gradient (i0) and the thickness of clay layer (H) to the load (q0) on consolidation behavior with consideration of rheological characteristic do not evidently change comparing to that under consideration of linear elastic model. The larger R is, the longer it takes for the moving boundary to reach the bottom of the layer, and the larger the ultimate value of excess pore water pressure is, and the smaller the ultimate average degree of consolidation is. Moreover, the condition that the moving boundary reaches the bottom of the layer differs with that with no consideration of rheological characteristic. If the same parameters of different rheology models are adopted, the dissipation curves of excess pore water pressure and the variation of moving boundary with time under different rheology models are almost same at the early stage of consolidation. At the late stage of consolidation, the difference between dissipation curves of excess pore water pressure different rheological models is so little that the influence of different rheological models on the result can be ignored.关键词：soft clay;threshold hydraulic gradient;moving boundary;rheological consolidation;analytical solution- 1901
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发布时间：2024-01-05 -
Stability Analysis on Shallow Layer Failure of Soil Slope Based on Unsaturated Soil Strength Theory AI导读
摘要：Based on unsaturated soil strength theory, a discriminant equation is established for the critical failure state of soil element in slope, and a combined failure mode of " upper and lower edge parallel slope curved surface” for soil slope is proposed, which includes three sliding regions composed of the tension zone at upper edge, the main slide zone in middle and the squeeze zone at lower edge. It is demonstrated that the failure surface morphology of the upper and lower edge sliding mass coincides with the logarithmic spiral. A new stability analysis method is established for unsaturated soil slope based on the limit equilibrium theory. The results shows that the relationships between landslide depth zw and main slide zone length L2 are better reflected using this combined failure mode of " upper and lower edge parallel slope curve”. The stability of shallow soil slope decreases and tends gradually to the results of infinite slope stability with increase of the main slide zone length L2. For saturated soil slope, the effects of internal friction angle and slope angle on slope stability are very little, but the influence of cohesion is significant. For unsaturated soil slope, the slope stability is reduced apparently as cohesion and internal friction angle decreases and slope angle increases. As the soil slope is in critical state (i.e. safety factor FS=1.0), the sliding surface of potential landslide gradually migrates to the shallow layer with the increase of soil saturation. It indicates that the soil slope with rising saturation caused by rainfall is more prone to shallow failure. Compared with the traditional infinite length slope stability analysis method, for a finite length soil slope, this combined failure stability analysis method is more reasonability and accuracy because of the consideration of the mechanical effects of upper and lower edge zone.关键词：unsaturated soil strength theory;soil slope;shallow layer failure mode;stability analysis;logarithmic spiral- 2286
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发布时间：2024-01-05 - 摘要：In order to calculate the rock-socketed depth of rock-socketed piles, the failure characteristics of rock outside piles and the horizontal force and bending moment on the top of bedrock should be taken into account. According to horizontal ultimate bearing characteristics of rock-socketed pile, a simplified analysis model of rock-socketed depth calculation was established. Based on the Hoek–Brown strength criterion and static balance principle, a theoretical calculation formula of rock-socketed depth of rock-socketed piles was deduced with the consideration of horizontal force and bending moment at the top of bedrock. Comparison and analysis of an engineering example showed that values of rock-socketed depth calculated by theoretical formulas are closer to the method of codes. And then the influences of horizontal load, pile diameter, rock uniaxial compressive strength and rock mass rating indexRMR on rock-socketed depths were discussed. The results showed that the rock-socketed depth increases linearly with the increase of horizontal force, non-linearly with the increase of bending moment, and decreases non-linearly with the increase of pile diameter, rock uniaxial compressive strength and rock mass rating index RMR. At the same condition, when pile diameter increases from 1.0 m to 2.0 m and 3.0 m, rock-socketed depth decreases by 32% and 44%, respectively. When rock uniaxial compressive strength increases from 15 MPa to 30, 45 and 60 MPa, rock-socketed depth reduces by 44.4%, 59.7% and 67.6%, respectively. When the value of rock mass rating index RMR increases from 30 to 45, 60 and 75, rock-socketed depth reduces by 48.9%, 72.3% and 84.2%, respectively. Rock mass rating index RMR has a significant effect on rock-socketed depth. If the value of rock mass rating index RMR is more than 85, the rock-socketed depth will less than 1.0 m. When determining the optimum rock-socketed depth of actual rock socketed piles, the strength and quality of rocks and pile diameters should be considered comprehensively.关键词：pile foundation;rock-socketed depth;horizontal load;Hoek–Brown strength criterion;ultimate bearing capacity
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发布时间：2024-01-05 - 摘要：The free water accumulated at the contact surface between pavement and subgrade appears to flow at high speed and form pumping effect due to variation of air pressure, which results in scouring subgrade and damaging pavement. In order to treat this problem, the influencing factors, the change law and mechanism of the anti-erosion performance of three typical cement concrete semi-rigid base materials (suspended dense structure, skeleton dense structure, skeleton-gap structure) were systematically analyzed by indoor scouring experiments and the project example of Baohan highway in Qinba mountain area. The result showed that the anti-erosion performance of the three semi-rigid bases was increased with the increase of cement content and strength grade, and curing time. It was unfavorable to improve anti-erosion performance of the semi-rigid bases when the water content and compaction were too high or too low, so that the water content and compactness were strictly control in practical engineering. The erosion resistance of the semi-rigid bases was greatly affected by its structural type. In view of the actual situation of the project, it was suggested that the skeleton dense structure should be adopted preferentially by the engineers.关键词：road engineering;anti-erosion performance;model experiments;cement stabilized macadam base;influencing factors
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发布时间：2024-01-05 - 摘要：Vegetation has significant effects on overland flow velocity and plays an important role in sediment transportation on a slope. The land coverage is an important factor to affect the roughness of the slope. The previous researches have focused on a relatively small range of vegetation coverage. To reveal the relationship between vegetation coverage and overland flow velocity, a series of flume experiments are carried out by using artificial grass to study quantitatively the characteristics of the overland flow velocity under different vegetation coverage. The experiments are set under the conditions of 9 different vegetation coverage from 0 to 80%, 3 slope gradients (10°,20°,25°) and 6 flow discharge (0.286～1.058 L·s–1), which are 162 groups in total. The result shows that the velocity along the slop changes from increase to decrease with the increase of the vegetation coverage. The discharge has a great effect on velocity when the coverage is less than 30% and has small effect when the coverage is more than 30%. The vegetation coverage is introduced in the velocity formula of overland flow, using the common form e–x in the growth model to reflect the influence of vegetation on slope roughness. Applying the nonlinear regression to the experiment data, the parameters k, a, b, c are determined as 10.06, –1.71, 0.22, 0.4 respectively. The formula obtained matches well with the measurement ( R2=0.96). Applying the formula to the lab experiments in other literatures, the results agreed with the experiment data reasonably well (R2=0.73). It seems that the formula has good adaptability to laboratory tests, although its applicability to field conditions needs further testing.关键词：overland flow;ground vegetation;vegetation coverage;velocity
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发布时间：2024-01-05 - 摘要：For the limitations of the boundary condition under instantaneous constant load in traditional sand-drained consolidation theory, the three-dimensional consolidation equation of sand-drained ground was solved based on the continuous drainage boundary. And the analytical solution considering the effects of smear and well resistance was obtained. Then, the rationality of the solution was verified by degenerating and comparing the analytic solution with the existing research results. Finally, the excess pore water pressure and average consolidation degree of sand-drained ground under continuous drainage boundary conditions were analyzed according to the analytical solution. The results showed that the continuous drainage boundary condition realizes the whole process from impermeable to completely permeable by changing the value of interface parameter b, which compensates for the shortcoming of traditional boundary. In terms of the excess pore water pressure, the drainage capacity of ground surface is reduced with the decrease of the value of b. Therefore, the excess pore water pressure exists at the top surface of the ground, and the smaller the b is, the greater the excess pore water pressure is. Meanwhile, the pore pressure increases with the enhancing distance from the sand-drained at the same plane. As for the consolidation degree, the average consolidation degree of the ground decreases with the decrease of b. So, the consolidation rate of the ground may be overestimated under the complete drainage condition of the traditional consolidation theory. Moreover, the consolidation rate of the foundation would be significantly reduced with the decrease of the permeability coefficient in the smear area and the sand well. Therefore, the disturbance to the soil of the well wall should be reduced and the seepage capacity of the vertical drainage should be increased to weaken the smear effect and the well resistance. In addition, the rates of settlements and consolidation will be underestimated if the vertical seepage is ignored, although the radial seepage is dominant in sand-drain.关键词：continuous drainage boundary;sand-drained ground;smear effect;well resistance;interface parameter
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发布时间：2024-01-05 - 摘要：The spatiotemporal effects of deformations of rocky tunnels are significant during the construction. Stress release coefficient method is not applicable to study the deformations of rocky tunnels because of the limited advance knowledge of the quantitative connection between the stress release rate and the parameters associated with the construction process and the surrounding rock properties. In order to investigate spatiotemporal deformations of rocky tunnels during construction, the combination model of Burgers body and Drucker–Prager criterion is applied to characterize the mechanical properties of surrounding rock. The closed-form solutions of tunnel’s deformation are derived by using the correspondence principle of elasticity–viscoelasticity and the non-associated flow rule. The displacement release coefficient method is introduced to describe spatiotemporal deformations of the surrounding rock during the construction of rocky tunnels. The maximum short term radial displacement corresponding to plane strain analysis of a tunnel cross section has the similar function formations as the Manh solutions. Moreover, the present solutions reduce to the Park solutions when the time effect is neglected. The correctness and effectiveness of the present solutions are verified by comparing the previous numerical/analytical solutions and the present solutions. Finally, spatiotemporal deformations curves of rocky tunnels, which includes creep characteristic curve of tunnel, radial distribution curve of tunnel’s deformation and longitudinal deformation profile of tunnel, are analyzed with considering the effects of different parameters, such as cohesive, internal friction angle, dilation angle and retardation time. The results show that the deformation of tunnel nonlinearly increases with the increase of time and longitudinal distance, but decreases as the depth of surrounding rock increases. The deformation of tunnel is the nonlinear decreasing function of cohesive and internal friction angle as well as the radius of plastic zone. The dilation of rock increases the deformation of tunnel. Besides, the retardation time determines the time history of tunnel’s deformation. Effects of incorporated parameters on spatiotemporal deformations of rocky tunnels are consistent with their physical meanings. Displacement release coefficient method successfully describes the spatiotemporal deformations of rocky tunnels, which provides the theoretical guidance for the construction of rocky tunnels.关键词：rocky tunnel;construction process;time effect;spatial effect of tunnel face;displacement release coefficient method;analytical solution
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发布时间：2024-01-05 - 摘要：In order to analyze the effects of periodic factors and trend factors on the displacement of earth-rockfill dam, and grasp the cause and trend of displacement change better, the change rule and prediction method of periodic component and trend component in displacement of earth-rockfill dam were studied. HP filter was used to decompose measured displacement sequence into trend term and periodic term. MLR prediction model was established for the trend term and SARIMA prediction model was established for the periodic term, which is MLR–SARIMA model for displacement prediction of earth-rockfill dam. MLR–SARIMA model highlighted the prediction advantages of MLR model on trend data and SARIMA model on periodic data, and it only needed measured displacement data to carry out the prediction analysis. After the HP filter decompose, the trend displacement had a slow growth trend, and the annual amplitude decreased from 1.42 mm to 0.51 mm. It was shown that the trend displacement of earth-rock dam caused by aging factor decreased year by year and tended to be stable. The periodic displacement had a significant annual periodicity. This was due to the annual periodic changes of water level and temperature. The annual amplitude was about 7.00 mm. The displacement of the earth-rockill dam was mainly caused by periodic displacement.The change rule was consistent with the general earth-rockfill dam. The results showed that the HP filter can be used to extract the trend and periodic terms in displacement data of earth-rockfill dam. The prediction results of MLR–SARIMA model were accurate, the relative error was small, within 5%, theRMSE, MAPE and AMAPE evaluation index of the model were both better than single SARIMA model. It was shown that the MLR–SARIMA model highlighted its advantages in predicting trend and periodicity data, which can be applied to prediction of horizontal displacement of earth dam.关键词：earth-rockfill dam;MLR–SARIMA model;displacement prediction;HP filter
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发布时间：2024-01-05 - 摘要：The vertical plug is a new way to dissipate water energy, in which the flow can be regarded as a submerged jet, and the construction leads to the high velocity and pressure on the wall. In order to explore the wall pressure distribution at the impinging zone and offer some scientific evidence for structural and hydraulic design, based on a spillway project, the characteristics of the wall pressure is analyzed by theoretical derivation, experimental test and numerical simulation under the condition of submerged jet with different flow rate. The results indicate that the measured pressure on the bottom axes agrees well with the numerical one, and both results have good agreement with the theoretical curve when the ratio of the distance between the test point and largest pressure point and the length of half maximum pressure is less than 1, but they are much larger than the theory when it is more than 1. The pressure gradually tends to the theoretical curve with the increasing of distance between press-slope and the center of the jet. The half-pressure length, which does not depend on the position of press-slope at the impacting zone downstream when the distance is 2.35 times larger than the jet diameter, is nearly equal to 0.3 times the diameter of the jet. Furthermore, the pressure of the top and side wall is decreasing when approaching to the center of the jet.关键词：vertical plug;submerged jet;wall pressure;half-pressure length;numerical simulation
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发布时间：2024-01-05 - 摘要：Water depth ratio between upstream and downstream plays an important role on dam-break flow. In the past studies, few researches were conducted when the water depth ratio was greater than 0.5, and most of the studies didn’t have enough series and discussed little about the upstream reservoir. In this paper, an experimental study was conducted by using wave probe on a large scale flume (length 18 m, width 1 m, height 1.09 m) for the instantaneous dam-break flow at the initial water depth ratio of 0 to 0.9, and new phenomena have been found. The experiment found that when downstream is dry, the water depth in the wavefront area of the dam-breaking flow will have a significant raise, and the wavefront velocity will be obvious lower than the Ritter’s solution. When the water depth ratio is greater than 0.3, extra negative waves will appear near the gate after a period of time, and these waves have different characteristics compared to negative wave linked to the upstream hydrostatic area. When the water depth ratio is greater than 0.5, waves appears in the downstream which cannot be considered as steady. Among them, the first wave peak is the highest and remains almost unchanged during the evolution. However, these waves have a trend to return stable and the stable water depth has a good agreement with Stoker’s solution. Within the experimentally observed range, the average velocity of the first extra negative wave increases under the same water depth ratio, as well as the first wave in the downstream. In addition, as the water depth ratio increases, the average velocity of the first extra negative wave becomes larger, while the first wave in the downstream decreases. It is found that the characteristic of instantaneous dam-break flow is very similar through the comparison of various hydraulic factors between different upstream headwater but in same initial water depth ratio.关键词：dam-break flow;initial water depth ratio;hydraulic characteristics;extra negative wave;wave velocity
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发布时间：2024-01-05 - 摘要：In order to address the problem that the traditional differential privacy preservation scheme is distributed layer by layer by half of the remaining privacy budget, i.e., equal ratio allocation of privacy budget, and when it is applied to the decision tree, the privacy budget allocated to the top layer is too small, the random noise is too large, and the classification accuracy is affected with the increase of the height of decision tree, a scheme of equal-arrival privacy budget allocation based on decision tree height difference was proposed, which combined differential privacy protection preservation with mainstream decision tree C4.5 classification algorithm. The Laplace mechanism and the exponential mechanism can ensure the security of the decision tree. This scheme utilized the MapReduce framework of the big data Hadoop platform, and the main program performed parameter configuration of MapReduce and outer loop. When executed to each node, the main program passed the statistical task of the dataset attribute to the Mapper class. The Reducer class received the statistical result of the Mapper class. The Laplace mechanism was used to add random noise. The noise-added result was returned to the main program for calculation the information gain rate. The main program used the exponential mechanism to select the best subdivision scheme. The recursion process stopped until the number of samples was 0. The experiment used the car data set of UCI database to test, and compared classification results of two schemes under different privacy budgets. Experiment showed that this scheme can satisfy differential privacy with acceptable classification accuracy reduction, and improve the classification accuracy under the same privacy budget compared to the traditional privacy budget allocation. For the car data set, the algorithm can balance the security and effectiveness of the data set when the privacy budget was 0.7 or 0.8. Therefore, the scheme of equal-arrival privacy budget allocation based on decision tree height difference can improve classification accuracy to a certain extent. It can be practically applied to decision tree classification.关键词：classification;decision tree;differential privacy;big data
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发布时间：2024-01-05 - 摘要：The charging location data generated by electric vehicles frequently accessing charging piles for charging are of great significance for optimizing the arrangement of charging piles and guiding the electric power dispatching. However, charging location data are private information for vehicle users. In order to prevent the leakage of the privacy of these users, it is urgent to explore a way of private charging location data aggregation. Therefore, a local differential privacy technology is adopted to preserve the charging location data of electric vehicles. A partition-based privacy preservation charging location data aggregation method is proposed by introducing Bayesian randomized multiple dummies algorithm. The method employs the Bayesian randomized multiple dummies algorithm to design a local obfuscation algorithm for locally perturbing a vehicle’s charging location. Then, the private location aggregation method for charging location data with the characteristics of sparseness and small size samples is designed by combining reconstruction algorithm of the randomized multiple dummies algorithm. At the same time, under the premise of ensuring the level of privacy preservation, the whole location domain is divided to narrow the privacy location domain, thereby further improving the utility of aggregation result. The privacy analysis of the proposed method is given. Finally, experimental results on four different synthetic datasets, namely, uniform distribution, normal distribution, peak distribution and random distribution, as well as the public Gowalla dataset are carried out. The experimental results show that the proposed method is superior to the existing randomized projection matrix based private aggregation method in terms of utility under the same privacy level.关键词：electric vehicles;charging location;local differential privacy;privacy preservation
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发布时间：2024-01-05 - 摘要：In order to solve the problem that locality preserving projection hashing can results in the poor expression of image feature and lower retrieval efficiency when it is applied in image retrieval, a novel image retrieval method based on hashing combining principal component analysis (PCA) with locality preserving projection (LPP) is proposed. Firstly, the sample is reduced dimension with PCA, a random matrix is introduced to make rotation of the PCA transformational matrix. The original sample is projected into the PCA transformational matrix and the reduced-dimension PCA sample is achieved. Meanwhile, the similarity structure between samples is taken into account. The reduced-sample is mapped with LPP. On these basis, the projection matrix is constructed with a random matrix. Finally, the original sample is projected into the projection matrix and the hash coding is achieved. The presented method can keep the local and overall similarity structure of the samples because of the application of PCA and LPP. Furthermore, the quantization error between codes is reduced by introducing of random rotation, thus improving the efficiency of image retrieval. Experiments show that the proposed method can achieve better performance compared with other traditional methods.关键词：image retrieval;hashing;principal component analysis (PCA);locality preserving projection (LPP)
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发布时间：2024-01-05 - 摘要：In order to predict the changing rule of pressure control performance of axial piston pump under oceanic environment, the pressure control system model of piston pump was established based on the underwater hydraulic oil viscosity–stiffness model. The system control performance was comprehensively analyzed from the aspects of stability, rapid response and control accuracy, and the results showed that if the variation factor was the viscosity, the parameters of the system phase margin, amplitude margin, rise time, and steady state were increased from the initial values of 59.4°, 8.77 dB, 0.045 s, and 3.4% to 138.4°, 23.4 dB, 0.28 s, and 7.4%, respectively. If the variation factor was stiffness, the parameters of the three characteristics were reduced from initial values to 42.6°, 23.4 dB, 0.038 s, and 1.2%, respectively.When considering the composite effects of viscosity and stiffness, the parameters of the three characteristics were increased from the initial values to 137.6°, 23.1 dB, 0.265 s, and 7.3% respectively. The analysis results showed that when the effects of viscosity and considering the comprehensive effects of viscosity–stiffness, the stability of the system increased with the increase of water depth, meanwhile the rapid response and control precision decreased with the increase of water depth. When considering the effects of stiffness, the changing trend of the three characteristics were quite opposite. It was pointed out that the control systems can be regarded as variable viscosity–dynamic stiffness control systems and variable viscosity–fixed stiffness control systems at the sea level of 0～1 000 m and 1 000～7 000 m, respectively. Finally, the experimental results further confirmed the results of the theoretical analysis.关键词：variable viscosity–dynamic stiffness model;control model;influence mechanism
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发布时间：2024-01-05 - 摘要：The mechanical seal of welded metal bellows is one of the important sealing methods in shaft seal, and the vibration characteristics of seal end face are a key factor in the amount of leakage and end face wear. Due to the lack of the theoretical research on the vibration displacement of the mechanical seal face of welded metal bellows, the influence of each working parameter on the end face vibration has not been analyzed. The geometric model of the face seal ring and the mathematical model of surface pressure and distribution moment under the polar coordinate were established. Based on the ring theory and numerical analysis method, the solution formula of the end face vibration displacement was deduced. Then, the special solution of the axial vibration and radial vibration displacement under different working conditions of the sealing face was solved by using MATLAB. The comparison of the results of special solutions of displacemen showed that the radial vibration displacement is larger than the axial direction under the same working conditions. A vibration test was designed for the radial direction. The displacement of the seal face was measured by using eddy current sensor, and the effects of medium pressure, working speed, load coefficient and compression amount on radial vibration displacement were studied. Experimental results showed that the working speed and compression have a serious impact on the radial vibration displacement, and the medium pressure and load coefficient have the same influence trends on the radial vibration displacement. With the increase of the working speed, the radial vibration displacement drastically increases. As the amount of compression increases, it increases slowly and then increases rapidly. With the increase of the medium pressure or the increase of the load factor, the radial vibration displacement decreases first and then increases. By comparing theoretical calculations with experimental results, the correctness of the mathematical model of the vibration displacement of the seal face was verified. The reasonable working parameters are listed as follow: The medium pressure is 0.4～1.4 MPa, the working speed is 1 500～2 500 r/min, the load factor K is 0.60～0.75, and the compression is 4～6 mm.关键词：mechanical seal;ring theory;face vibration;radial vibration displacement
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发布时间：2024-01-05 -
Effect of Multi-wedge on Sealing Performance in Mechanical Seal with Equilateral Triangular Dimples AI导读
摘要：The mechanism of how the geometric features of dimples work on the performance of mechanical seal with micro-dimple has been rarely studied, although the geometric design of dimples is one of the most important means for enhancing the performance. In order treat this problem, based on the multiphase flow cavitation model in fluent, the wedge effect theory and the numerical calculation were employed to develop a three-dimensional numerical model of the lubricant in mechanical seal with equilateral triangular dimples for studying the effect of the geometric features on the leakage rate and the load-carrying capacity at different orientation angles. Firstly, the fluid factor was calculated for the flow pattern check, and the grid independence test of film was conducted for determining the grid size. The simulation result was also compared with the reference in order to ensure the accuracy of calculation model. Secondly, the multi-wedge phenomenon was proposed based on the wedge effect theory and the analysis of pressure contours. The equilateral triangular dimple has three different wedges. The orientation angle changes the angles between each wedge and the rotational velocity of seal face, which determines the character and intensity of the wedges. The cooperation of the three wedge effects influences the pressure distribution, and then determines the sealing performance. Finally, the leakage rate and load-carrying capacity of the mechanical seal with equilateral triangular dimples were studied based on the multi-wedge phenomenon. The leakage rate is minimal when the orientation angle α=40° for the low pressure difference, and α=110° for the high pressure difference. The increase of velocity enhances the change trend of leakage rate. The load-carrying capacity decreases at first, and then increases when α∈[0°,120°], and is minimal when α=60°. With the increase of velocity, the load-carrying capacity increases when α∈[0°,40°] and α∈[100°,120°], but decreases when α∈[40°,100°].关键词：mechanic seal;equilateral triangular dimples;multi-wedge;leakage rate;load-carrying capacity- 2358
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发布时间：2024-01-05 - 摘要：The fracture sectional raised height is an important aspect of the fracture sectional deformation degree and the degree of deformation of the drill pipe fracture is an vital basis for evaluating the shear performance of the shear ram blowout preventer (BOP), which is directly related to the recycling and efficiency of the drill pipe. In order to make a reasonable assessment of the raised height of drill pipe fracture section, based on the basic laws of kinematics, the motion equations of the shear ram were established and the construction parameters were comprehensively considered. After that based on the matrix form of the coordinate conversion formula and the theory of slip line, the theoretical prediction of the fracture sectional raised height of the drill pipe caused by the single shear point at any time and the final were derived. Then the position of fracture sectional raised height of the drill pipe was identified and the evaluation model of the fracture sectional raised height of the drill pipe caused by the single shear ram was established. The shearing experiment of shear CT90 coiled tubing was carried out with a shear ram blowout preventer, and the fracture data of the CT90 coiled tubing was acquired to verify the evaluation model. The results showed that the assessment model established in this paper is close to the height of the fracture elevation obtained by the shearing test. The relative error is within 10%, with high reliability and applicability. The impact of the critical structure parameters of the shear ram impact block and drill pipe, such as V-angle and edge chamfer, on the fracture sectional raised height of the sheared drill pipe was further analyzed. The study showed that with the increase of the V-angle, the drill pipe fracture sectional raised height increases, and with the increase of edge chamfering, the height of fractured of the drill pipe changes in a wave shape, and the troughs gradually increase. When the edge chamfering angle is 20°, the height of the drill pipe fracture bulge is minimum, and the drill pipe fracture sectional raised height increasies with the increase of the length of the shear point to the center point of the V-shaped angle. In the case of meeting well control requirements, when designing the shear ram, the edge chamfer of the impact block should be 20°. The smaller the V-angle, the better and shorten the length of the shear point to the V-shape as much as possible. The height of the fractured drill pipe increases with the increase of the drill pipe inner diameter and wall thickness in meeting the drilling and mining requirements, choosing smaller-diameter thinner-walled drill pipe.关键词：shear ram blow out preventer;drill pipe fracture section;raised height;shearing experiment
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发布时间：2024-01-05 - 摘要：Compared with traditional steel, magnesium alloy has many advantages such as small density, lightweight, high specific strength, high specific stiffness, good thermal conductivit and comprehensive performance and it has good application and broad prospects in petrochemical and information industry. However, it is poorly plastic at room temperature, which leads to cracks in the rolling process and affects their quality, therefore it is required to be solution-treated to improve its plasticity before processing. Taking into account this, the original grain structure of AZ31 magnesium alloy tube was obtained by metallographic experiment. Based on the thermodynamic mechanism of grain growth, the mechanism of curvature driving and the energy dissipation mechanism, a cellular automata model and three major grain evolution rules was established. And the grain evolution and edge number of AZ31 magnesium alloy at different temperatures and different times were studied. Finally, the microstructure with uniform grain distribution and hexagonal shape was obtained. Through the topological analysis of grain growth and grain size distribution statistics, it was found that the grain size is normally distributed at different temperatures and times, with hexagonal grains being the most. On this basis, the mathematical model of grain growth under the solid solution condition was established, and its grain size and final properties after solid solution were reasonably predicted and controlled. The analysis of the kinetics of grain growth showed that the growth index of magnesium alloy is 0.87. The correctness and rationality of the cellular automaton model were verified by experiments, which laid a foundation for studying the grain evolution of magnesium alloy during deformation.关键词：AZ31 magnesium alloy;cellular automata;solid solution;grain size
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发布时间：2024-01-05 - 摘要：In order to improve the flocculation ability of polyacrylamide (PAM), the organic montmorillonite (OMMT) was first prepared by the intercalation of methacrylatoethyl trimethyl ammonium chloride (DMC) into the interlayers of sodium montmorillonite (Na–MMT). X-ray diffraction (XRD) results showed that the interlayer space of Na–MMT is increased from 1.25 to 1.43 nm, which illustrated that DMC has intercalated into the interlayers of MMT. Then OMMT was introduced into the dispersion polymerization system of PAM W/W emulsion using gelatin as stabilizer to prepare PAM–MMT W/W emulsion. The microstructure of the emulsion was characterized through transmission electron microscope (TEM), and the result showed that the emulsion is a mixture of the polyacrylamide " crosslinked” by the MMT particles and PAM W/W emulsion. Effects of OMMT dosage, gelatin concentration, pH value and cationic monomer concentration on the properties of the PAM–MMT W/W emulsion were investigated, and the result showed that all the emulsion prepared under proper conditions have a good storage stability and re-dispersion ability in water. And the viscosity and flocculation ability both have a positive relationship with the OMMT dosage and gelatin concentration. When the pH value is at the isoelectric point (IEP) of gelatin, the emulsion has the lowest viscosity and best flocculation ability. With the increase of DMC concentration, the viscosity decreases, while the flocculation ability towards the kaolin suspension increases first and then decreases.关键词：dispersion polymerization;" water in water” emulsion;montmorillonite;gelatin
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发布时间：2024-01-05
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