最新刊期
卷 53 ， 期 2 ， 2021
- 摘要：The Wenchuan strong earthquake caused the mountain to break, and triggered a large number of landslides to accumulate in the slopes and channels. This provided a huge amount of loose solid sources for the formation of debris flows, which greatly reduced the threshold rainfall for the initiation of debris flows, and sharply increased the frequency of outbreaks, which became the main type of secondary disasters. Under the effect of multiple debris flows, the debris flow dam will be partially or completely filled-up, and the function of disaster mitigation has been reduced. However, there is inadequate research on the effects of sediment deposits behind the dam on the debris flow dam disaster reduction. In this study, based on the weakly compressible smooth particle flow (SPH), the Drucker−Prager (DP) criterion and the Herschel−Bulkley−Papanastasiou (HBP) rheological model are used to simulate the dynamic process of the interaction between the debris flow and the sediments behind the dam. The proposed method is verified by a flume experiment. On this basis, the model is further used to simulate the dynamic process of the Hongchungou debris flow disaster under sediments behind the dam. The research results show that the deceleration rate of debris flow through the dam is 31.6% under the condition of empty reservoir, the half storage conditions is 16.4% and 6.5% for full reservoir conditions. The sediments reduce the peak clipping effect of the dam, which significantly reduces the blocking effect. At the same time, the sediments behind the dam changes the dynamic response of the debris flow dam. Under the empty storage the debris flow shows the processes of dam hitting, climbing, and siltation, however the full storage shows the debris flow entrained by the siltation body passing the dam. In addition, the peak impact force at the bottom of the dam under the half-reservoir condition is reduced by 13.25% compared to the empty reservoir condition, and the peak impact force at the top of the dam under the full-reservoir condition is 1.75 times compared to the empty reservoir condition. The research results can provide a basis for debris flow dam design.关键词：debris flow;check dam;deposition behind the dam;impact dynamic proces
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发布时间：2024-01-10 - 摘要：Hydrological model has been widely used in flash flood warning. The traditional performance criteria of hydrological model focus on the accuracy of prediction, and the errors on both sides of the true value are supposed to be the same when these criteria are used, which often cause false warning and miss warning with the same probability. In the practical prevention and control of flash flooding, the life safety is of primary consideration. Therefore, the casualties caused by miss warning are much more serious than the economic losses caused by false warning. Based on the principle of reducing miss warning, the temporal difference of flood warning, a new performance criterion coupling the time for immediate evacuation, the time for preparing evacuation and the time of disaster occurrence, was proposed. Taking the floods in Guanshanhe river since 1975 as an example, TOPMODEL model, TVGM model and Xin’anjiang model were used to simulate floods based on the temporal difference of flood warning and the traditional criteria, and then the flood warning results were compared with the measured data. It shows that the results of the temporal difference of flood warning and the traditional indices are very different. By using the traditional criteria, TVGM model would be chosen, while TOPMODEL is actually the best model by the criterion of temporal difference of flood warning. As TVGM model causes more miss warnings but has the highest accuracy according to the traditional criteria, which doesn’t satisfy the requirements of flash flood warning. Therefore, the effectiveness and reliability of flash flood warning can be improved by using the criterion of the temporal difference of flood warning, which would be more suitable for flash flood warning.关键词：flash flood disaster;hydrological model;the temporal difference of flood warning;flash flood warning;Guanshanhe basin
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发布时间：2024-01-10 -
Experimental Study on the Loading Capacity of Suspended Section of Underwater Crossing Pipeline AI导读
摘要：Underwater traversing pipelines are prone to being exposed and suspended due to natural or man-made factors during the year-round service, which makes the pipeline partially or completely exposed to the water flow. In the meanwhile, the stress state of the pipeline changes or even breaks, seriously threatening the safety of the pipeline and the ecological health of the river. In order to study the loading capacity of the water flow force on the suspended section exposed by the flow passing through the underwater pipeline, a physical model experiment was carried out to explore the influence of four hydrodynamic conditions on the loading capacity of the pipeline when the flow rate, flow angle, pipe diameter and clearance ratio are constant. The experimental results indicated that the pipeline is partially under pressure, partially under tension on the water-facing surface, but pulled on back-water surface, whereas the pressure value at the midpoint of the pipeline towards the water surface is the largest. The tension on the top of the pipe is about 1.05 ~ 1.25 times of that on the bottom of the pipe. The pressure value of each point on the surface of pipeline is positively correlated with velocity, pipe diameter and pipe flow angle, but negatively correlated with clearance ratio. The pressure separation point moves forward with the increase of the velocity, the angle of the pipe flow, and the diameter of the pipe, but moves backward with the increase of the gap ratio. The vertical rising force per unit length of the pipeline is 1/10 to 1/20 of the horizontal drag force, both of which increase with the increase of flow velocity, pipe flow angle, and pipe diameter, but decrease with the increase of the gap ratio. According to the test data, combined with the multiple regression model fitting, the calculation formula of the horizontal drag force and rising force of the unit length pipeline was obtained, and the calculation result of the formula was basically consistent with the test result, which also had good generality in practical engineering examples. The research results will provide a certain theoretical reference for the wiring design, erosion protection and operation management of underwater crossing pipelines.关键词：underwater crossing pipeline;loading capacity;surface point pressure;horizontal drag force;vertical rising force- 1722
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发布时间：2024-01-10 - 摘要：The loose deposited soils in the mountainous area of western China are usually widely graded and weakly consolidated. Upon rainfall infiltration, the fine particles within these soils are prone to migrate in the pores formed by those coarse particles, which changes the soils’ hydro-mechanical characteristics and destabilizes the slope. In order to study quantitatively the intrinsic evolution law of this rainfall-induced seepage-erosion coupled process within deposited soils and its influence on the slope stability, the fine particle migration phenomena observed within unsaturated deposited soil slopes in both the slope and pore scales were analyzed. Based on the mixture theory, a seepage-erosion coupled model capable of capturing the fine particle migration process within unsaturated soils was proposed. This model was then implemented into a finite element code, and was used to simulate the rainfall-induced seepage-erosion coupled process within a one-dimensional unsaturated soil column. Combined with the infinite slope model, the influences of erosion-induced soil permeability, water retention capacity and strength changes on the rainfall infiltration process as well as on the slope stability were analyzed quantitatively. Through numerical simulation, the intrinsic shallow slope failure mechanism, trigged by the formation of a relatively impermeable layer due to the fine particle migration-induced local change of soil permeability, was explained. It was pointed out that both the water retention capacity and shear strength of the deposited soils will be weakened due to the loss of fine particles, which will accelerate the rainfall-induced seepage-erosion process within the slope, and hence accelerate its failure process. In view of the fact that the changes of soil permeability, water retention capacity and strength due to the seepage-erosion coupled process are all adverse to the slope stability, it is therefore suggested that special attention should be paid to the fine particle migration effect when evaluating the stability of deposited soil slopes under rainfall infiltration.关键词：deposited soil;rainfall infiltration;internal erosion;fines migration;slope stability;modeling
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发布时间：2024-01-10 - 摘要：Comparative evaluations of failure probability were conducted with respect to an in-service wind turbine under earthquakes and wind loads. Firstly, to obtain the hazard curves under earthquakes and wind loads for a specific region where the wind turbine was built, hazard probability analyses were performed based on the special lifetime of this wind turbine. Then, to obtain structural fragility curves under earthquakes and wind loads, a blade-tower finite element model was established by shell and beam elements in a commercial finite element software and multiple sets of time histories were selected or generated based on the target seismic response and wind spectra. Numerous incremental dynamic analyses under material and geometric nonlinearity were conducted, respectively. Finally, according to the results of hazard and fragility analyses and the law of total probability, failure probabilities of the wind turbine under the two different disasters were compared. Results showed that the issue of conservative calculations was avoided by the hazard analysis based on the specific lifetime of wind turbines. On the account of the controllable pitch installed on the wind turbine, wind-resist responses under operational conditions were similar. Additionally, the failure probability of the wind turbine under wind loads was larger compared with the probability under earthquakes. On the one hand, the wind turbine was a long-period structure whose frequency was located at a point in the descending range of the seismic response spectrum; therefore, earthquake response was relatively low due to the short-period dynamic loads. On the other hand, the wind-rich areas were typically selected as the sites for wind farms, enlarging the probability of strong wind conditions and improving the failure probability under wind loads. The conducted investigations in this paper, considering the special lifetime of the wind turbine, guides the development of the multi-hazard probability evaluation in the wind turbine field.关键词：wind turbine;finite element;hazard analysis;fragility analysis;earthquake;wind load
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发布时间：2024-01-10 - 摘要：Due to the randomness of seismic waves and the complexity of geological structure, the seismic dynamic response characteristics of rock slopes become very complicated. Taking a rocky bank slope of a bridge across the Jinsha River as an example, the propagation characteristics of seismic waves in rock slope were studied by using finite element method (FEM), and the influence of different types of structural planes on the dynamic response characteristics of slopes was analyzed. Shaking table model test was used to verify the numerical results, and the dynamic deformation failure evolution law and failure mechanism of the slope were deeply investigated. The propagation characteristics of seismic waves in rock slope were studied by using FEM, and the dynamic deformation evolution law and failure mechanism of the slope were analyzed. The results showed that weak structural plane had a great influence on the wave propagation characteristics of slopes. In the wave propagation process, structural plane caused local amplification effect in the slopes. Under the same conditions, the dynamic amplification effect of the slopes is as follows: block slope > bedding slope > anti-dip slope. Slope elevation, surface microtopography and structural planes had a great influence on the dynamic amplification effect of slopes. The dynamic amplification coefficient of the slopes increased with the elevation, and the variation of the slope surface microtopography resulted in the phenomenon of local amplification at the platform area. The amplification effect in the block slope was mainly concentrated on the surface slope above the topmost bedding structural plane. Under the action of earthquake, the dynamic amplification effect of the block slope increased with the increase of the seismic intensity. The evolution process of dynamic deformation of the block slope mainly included three stages: elastic deformation, plastic deformation and sliding failure. Weak structural plane had a controlling effect on the seismic failure mode of massive slope, and the topmost structural plane was the potential sliding surface, and its seismic failure mode was split—slip—overturning failure.关键词：weak structural surface;rock slope;wave propagation characteristics;dynamic response;deformation evolution law;earthquake
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发布时间：2024-01-10 -
Implications of Geo-stress Tensor Characteristics in Optimizing the Azimuth of Underground Cavern AI导读
摘要：High stress is the controlling factor that influencing the deformation mechanism and stability of surrounding rock mass of deep-seated underground caverns. Stress relief and deviatoric stress state are the main mechanical effects induced due to excavation in rock masses where in situ stress exists. Tensorial nature of in situ stress and the intersection angle between longitudinal direction and major stress determine the magnitude of stress relief and the anisotropic level of induced stress. A general formula was derived for the magnitude of stress relief due to excavation. Thus, the variation law of the magnitude of stress relief was studied as intersection angle between the cavern axis azimuth and maximum principal stress direction varies. An index called “contribution degree” was purposed to quantify the contributions of different principal stress components to the magnitude of stress relief by excavation, and then to ascertain the dominant one. In order to study the variation characteristic of deviatoric stress state, the variation of the characteristics of stress ellipses with the intersection angle between cavern axis and maximum principal stress direction were illustrated graphically in combination with quantitative data. The method has been applied to the underground powerhouse of Jinping fist stage hydropower station. The results showed that when the longitudinal axis of underground caverns parallel to the major stress in horizontal plane, the magnitude of stress relief reached minimum. However, minimizing stress relief and deviatoric level at the same time was difficult. The study showed that due to the complexity caused by tensorial nature, in general case, it was the composition characteristics of geostress tensor that determined how and to what extent the geostress would affect the deformation and stability of surrounding rock mass of underground openings. Therefore, attention should be paid to the comprehensive analysis of the spatial characteristics of the geostress tensor.关键词：rock mechanics;underground opening;in-situ stress;projection stress ellipses on three characteristic planes;selection of longitudinal direction of underground cavern;underground powerhouse of Jinping fist stage hydropower station- 1758
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发布时间：2024-01-10 - 摘要：Researches show that the slurry with quick lime as admixture is well compatible with earthen sites, and adding the micro-lime piles into this slurry can better eliminate shrinkage differentiation phenomenon of the slurry-soil interface. In order to explore the reinforcement effect and mechanism under the synergy of pile-slurry, fissure grouting of indoor earthen sites was carried out under single grouting technology and pile-slurry synergistic reinforcement technology with the width-diameter ratio of 1.5, 2.0, 2.5 and 3.0 (ratio of crack width to lime pile diameter). After curing for 63 days, the macro-properties (penetration resistance, density, liquid plastic limits and particle composition) of equidistant soil on both sides of the fissures were tested. Then the reinforcement effects of the soil on both sides of fissure were qualitatively and quantitatively analyzed by scanning electron microscopy, the specific surface area, cation exchange capacity and pore relative change rate of soil (Pr). The results showed that the reinforcement effect was better than that of single grouting when the width-diameter ratio was less than 2.5. The effect of soil reinforcement increased first and then decreased as the width-diameter ratio increases, and was the best when width-diameter ratio equaled to 2.0, and was weaker than that of single grouting when the width-diameter ratio was more than 3.0. The essence reflected by the results was that the compaction and agglomeration of soil on both sides of fissures caused by the expansion and ion migration of lime pile and slurry were not a simple linear superposition, but when the width-diameter ratio was more than 2.0, the slurry would obviously inhibit the compaction and agglomeration of the lime pile.关键词：fissure of earthen sites;pile-slurry synergy;width-diameter ratio;expansive compaction;ion migration
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发布时间：2024-01-10 - 摘要：The elasto-plastic stress-strain constitutive relation with double yield surfaces of expansive soil improved by lime and flyash was studied based on the ellipse-parabola constitutive model. Firstly, a series of the triaxial consolidated drained shear tests of the expansive soil improved by lime and flyash under wetting-drying cycles were conducted to obtain the test curves of deviatoric stress q and axial strain ε1, shear strain εs, and the test curves of bulk strain εv and axial strain ε1, respectively. Secondly, the expressions between the parameters of the ellipse-parabola constitutive model and wetting-drying cycles were fitted based on the triaxial test results. Finally, a modified ellipse-parabola constitutive model which can reflect the effect of wetting-drying cycles was proposed by introducing the factors of wetting-drying cycles. The study obtained conclusions as follows: 1) The stress-strain relationships between q and ε1 were strain hardening, and the relationships between q and εv were shrinkage under wetting-drying cycles, and the test curves of q–ε1、q–εs were hyperbola, respectively. 2) The deviatoric stress q decreased and the bulk strain εv increased under the wetting-drying cycles. The effect under wetting-drying cycles reduced the resistance of shear and compression of expansive soil treated by lime and flyash significantly. 3) The bulk yield surface was ellipse shape and the shear yield surface was parabola shape in the p–q stress plane. The bulk yield surface shrunk gradually to the origin of coordinates, and the shear yield surface degraded gradually to p coordinate in p–q stress plane, respectively. The effects of the first 9 wetting-drying cycles on the double yield surfaces were more obvious, and then the changes of double yield surfaces with wetting-drying cycles decreased gradually. 4) The constitutive model with double yield surfaces introduced the factors of wetting-drying cycles could quantitatively reflect the influences of wetting-drying cycles on the stress-strain relation of expansive soil improved by lime and flyash, and the evolutions of ellipse-parabola double yield surfaces. The proposed stress-strain constitutive equation could well predict the stress-strain relationship of expansive soil improved by lime and flyash under wetting-drying cycles.关键词：expansive soil improved by lime and flyash;wetting-drying cycle;ellipse-parabola constitutive model;stress-strain relation with double yield surfaces
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发布时间：2024-01-10 - 摘要：Subjected to complex loads, such as wave, earthquake and traffic loads, the corresponding stress states of the foundation soil are complicated. The simultaneous variations of the deviatoric stress and principal stress direction occur in practical engineering. However, there are few studies on properties of natural soft clay under combined principal stress rotation, which means that when the principal stress axis rotates, the deviatoric stress increases continuously, and the average principal stress and the medium principal stress coefficient remain unchanged. In order to study the deformation characteristics of saturated natural soft clay under combined principal stress rotation, the torsional shear tests of natural soft clay were carried out based on the hollow cylinder apparatus (HCA). The influence of different inclined consolidation and intermediate principal stress on the deformation and pore pressure of natural soft clay under combined principal stress rotation were discussed. The results showed that the deformation behavior and pore water pressure accumulation of tested samples were significantly influenced by the intermediate principal stress coefficient b. The compressive deformation was dominated in the axial direction when b equaled to 0 or 0.5, and extensive deformation was dominated under b equaled to 1.0. The generation of axial, circumferential and torsional deformation was different obviously, while the radial deformation was almost the same, the value of radial stain was approximate 0 when b equaled to 0.5. The corresponding major principal stress angles to the maximum value of pore water pressure were different under different inclined consolidation conditions. The change of stress and strain was not synchronous with the increase of the azimuth of deviator stress and principal stress, i.e., there was an obvious non-coaxial behavior.关键词：soft clay;combined principal stress rotation;inclined consolidation;intermediate principal stress;deformation;pore pressure
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发布时间：2024-01-10 -
Upper Bound Limit Analysis of Limit Support Pressure for Shield Excavation Face in Composite Ground AI导读
摘要：With the further development and utilization of underground space, the geological conditions faced by shield tunneling are more complex and diverse. When the shield tunnels in the composite strata, due to the differences in mechanical properties between the strata, it is easy to cause instability and damage due to improper determination of the supporting force of the excavation surface, which will bring negative impacts to the projects. It is difficult to determine the support pressure of the excavation face due to the stiffness differences between the upper and lower strata, when the shield tunnel passes through the composite strata. Based on the combined logarithmic helix failure model utilized as the instability model of the shield excavation face in the composite strata, the upper limit expression of the limit support force of shield excavation face in the composite strata was derived by using the upper bound theorem of limit analysis. The optimal solution of the ultimate support force was obtained by linear optimization technology, and the rationality of the combined logarithmic spiral failure mode was verified by comparing with the existing literatures. At the same time, the influence of different parameters on the ultimate support force and the critical failure mode were discussed, and the schematic diagram of the critical sliding surface was presented. The results showed that when the internal friction angle and cohesion of the upper stratum were fixed, the ultimate support force decreased with the increase of the internal friction angle and cohesion of the lower stratum. With the increase of the diameter of the tunnel, the ultimate support force increased significantly. The depth coefficient was defined as the ratio of the depth of the upper stratum to the diameter of the tunnel. The smaller the depth coefficient was, the more sensitive the ultimate support force was to the variations of the shear strength parameters of the stratum. But for a single stratum, the change of depth coefficient has no effect on the ultimate support force. The conclusions had a certain guiding significance for the practical engineering.关键词：shield tunnel;composite strata;upper bound limit analysis method;stability of excavation face- 1418
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发布时间：2024-01-10 - 摘要：In order to realize the resource utilization of the sewage sludge ash (SSA) in the concrete, the effects of adding the 0, 1%, 3% and 5% SSA on the workability, compressive strength and splitting strength of the ordinary Portland cement concrete (OPC) and recycled aggregate concrete (RAC) were studied. The results showed that adding SSA and using recycled coarse aggregate would reduce the workability of concrete. The more SSA added, the greater the degree of slump declined. When the dosage of SSA was 1%, 3% and 5%, the slump of ordinary concrete decreased by 20%, 24% and 28%, respectively, and that of recycled concrete decreased by 0, 25% and 67%, respectively. The compressive strength and splitting tensile strength of concrete mixed with SSA increase with age. The addition of 3% SSA promoted the compressive strength of OPC, and the compressive strengths at 7 d, 14 d and 28 d increased by 14.12%, 12.97% and 9.09%, respectively. The addition of 1% and 5% SSA had an adverse effect on the compressive strength of OPC. The addition of SSA increased the 7 d compressive strength of RAC, but it did not increase the 28d compressive strength of RAC significantly. Compared with the concrete without SSA, the average 7 d splitting strength of the OPC and the RAC with SSA decreased by 19.17% and 15.53% on average. Compared with the control group, the 28 d splitting strength of OPC with 1% and 3% SSA increased by 2.27% and 3.19%, respectively, while the RAC with 3% SSA increased by 18.72%. It can be seen that SSA with an amount of 3% could improve the compressive strength and splitting strength of OPC and RAC, which was a better amount. Different amounts of SSA had significantly improved the 0～7 d compressive strength of RAC. The microstructure analysis showed that the utilization of SSA in the RAC improved the utilization rate of SSA, which made the early strength of RAC with SSA increase obviously. When the amount of SSA was large, the excess SSA reduced the uniformity of concrete and affected strength development, resulting in no significant increase in compressive strength at 28d.关键词：recycled aggregate concrete;sewage sludge ash;compressive strength;splitting strength;microstructure
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发布时间：2024-01-10 - 摘要：The study on the shear characteristics and soil migration law of clay-cement soil interface is important to deeply understand the bearing and deformation behaviors of cement-soil piles and walls. A series of direct shear tests for clay-cement soil interfaces with different roughness were performed to study the mechanical properties of the interfaces in terms of the shear strength, shear failure law and deformation behavior. The test results showed that the shear failure of the interface followed the Mohr-Coulomb strength criterion. The friction angle of the clay-cement soil interface increased with the increasing roughness, while the growth rate then gradually slowed down. The cohesion of the clay-cement soil interface varied similarly to that of the clay. In addition, the curves of the normal strain versus shear displacement for the clay-cement soil interfaces exhibited a shear contraction pattern, where the magnitude of the shear contraction increased with the increasing normal stress and interface roughness. The normalized effective coefficient (Es) of the interface strength increased with the increasing roughness, and the Es became larger than 1.0 as the roughness R exceeded 1.0 mm, indicating that the shear strength of the clay-cement soil interface was improved and became larger than that of the clay itself due to the existence of “passive resistance”. Moreover, the curves of the shear displacement versus shear stress under different normal stresses and roughness experienced an exponential relationship, from which a unified exponential model was established to describe the relationship among the roughness, shear stress, shear displacement, normal stress, friction angle and cohesion of the interface. Besides, the shear failure zone gradually spread from the shear forward direction to the shear rear as shearing. The research results are helpful in revealing the mechanical behavior of cement-soil interfaces and can also provide references and guidance in the design of cement-soil piles and walls.关键词：interface;shear behavior;roughness;clay;cement soil;direct shear test
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发布时间：2024-01-10 - 摘要：Fiber-reinforced polymer (FRP) has been widely used in concrete reinforcement projects. The bonding performance between the FRP and concrete influences the reinforcement effect well. Numerous studies were conducted on the bond strength of FRP externally bonded concrete, and a lot of empirical models were developed, while there were few empirical models of the bond strength of FRP near-surface-mounted (NSM) concrete. In order to accurately predict the bond strength between near-surface-mounted FRP and concrete, the gene expression programming (GEP) method was employed to develop a bond strength prediction model of NSM FRP bonded to concrete, and a specific calculation formula was established. The model was developed using six parameters including the concrete compressive strength, bond length, groove depth-to-width ratio, FRP axial rigidity, FRP tensile strength and epoxy tensile strength. The predicted values calculated by the proposed formula agreed well with the experimental values, indicating that the model was reliable. Through the sensitivity analysis of the model, it was found that the GEP model can reflect the internal relationship between bond strength and single factor, i.e., the bond strength increased with the increase of the bond length, concrete compressive strength, the groove depth-to-width ratio and FRP axial rigidity. The GEP model was compared with the empirical model and the wavelet neural network model. Six statistical indicators were selected to evaluate the prediction performance of these models. It can be found that the accuracy of the GEP model and the wavelet neural network model was high, and the errors were low where the coefficients of determination were 0.793 and 0.787, respectively. In general, the accuracy of the GEP model was slightly better than the wavelet neural network model, and the accuracy of the two models was much higher than the empirical models.关键词：bond strength;gene expression programming;fiber-reinforced polymer;concrete;prediction model
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发布时间：2024-01-10
HYDRAULIC & CIVIL ENGINEERING
- 摘要：In order to make efficient use of network resources, balance the energy consumption of network topology, eliminate redundant links between network topology, reduce node loads, and extend the life cycle of network of the maximum, in this paper a topology optimization algorithm for wireless sensor networks (PGOSG) was designed based on the concept of potential game and optimal stiffness sub-graph, which considers the residual energy of nodes, the load of nodes and the redundancy of network topology links. First, according to the power change of communication between nodes, the power set of nodes was constructed as the strategy set of the game, and the potential-game function was constructed with the goal of balancing energy consumption by using the potential game theory, which converges to the Nash equilibrium point, and then constructs the preliminary network topology structure. Second, taking advantage of the fact that the number of global links with the optimal rigid graph is small and does not damage the network topology, an optimal rigid sub-graph was used to eliminate redundant links between to the network topology layer by layer to obtain the final network topology. The network topology, link communication quality, network robustness and the network life cycles of PGOSG algorithm were analyzed by the simulation experiments, and compared with the existing DEBA algorithm. The simulation results show that: in the topology, PGOSG algorithm eliminates redundant links to the network communication links, and reduces the load of some nodes in the network. In terms of energy consumption balance, PGOSG algorithm formulates node data forwarding rules, effectively utilizes network resources, balances node energy consumption and avoids redundant forwarding between nodes in the game stage. Therefore, the algorithm proposed in this paper can eliminate redundant links in the network, reduce the node load and link weight, and prolong the network lifetime.关键词：redundant links;wireless sensor networks;potential-game;optimal rigid sub-graph;network topology
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发布时间：2024-01-10 - 摘要：In order to explore the evolution law of pocket switched network (PSN), the link prediction which is a part of network behavior prediction problem in PSN was studied in this paper. PSN has lots of features such as node mobility, intermittent connection and high latency. The challenges of link prediction are the opportunistic connection and the time-varying topology. The key to obtain high-quality link prediction is how to obtain the attributes of nodes comprehensively. A link prediction method was proposed in the paper, which is based on learning automaton and firefly algorithm (FA-LP). The learning automaton was employed to cluster nodes adaptively so as to complete the community division of the network. The node community attribute influence coefficient and mobile behavior influence coefficient were defined to construct the similarity index which reflects the community attributes, node mobility and intermittent connection between nodes. After fusing the index with CN, RA, AA, etc., a similarity vector of node pairs was achieved. Taking the advantages of analyzing time series of autoregressive integrated moving average model, the evolution law of the vector sequence was extracted. The binary classifier optimized by firefly algorithm was constructed to predict the connection of node pairs at the next moment. The experimental results on INFOCOM2006 and MIT datasets show that the proposed method has better accuracy and better stability than the ones of RBM and week estimators.关键词：pocket switched network;link prediction;learning automata;firefly algorithm
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发布时间：2024-01-10
INTERNET OF THINGS
- 摘要：Distributed optical sensing (DAS) has the advantages of continuous distribution information retrieval, less environmental impact and low cost. In this paper, a method of vehicle trajectory extraction using DAS system was proposed, which provides the basis for the realization of whole time-space traffic state detection in smart highway environments. First, the free fiber core in the highway communication fiber and the DAS detection equipment based on Φ-OTDR were used to collect the ground vibration signal for the driving vehicles in real-time. Then, the vibration signal was transformed into time–frequency domain channel by channel by S transform to accumulate the energy in the frequency interval where the vehicle vibration signal was located, and the vibration energy of all channels was accumulated to form a spatiotemporal two-dimensional vibration energy response. Finally, the multiple enhanced vehicle trajectories were transformed into multiple singular points in the range–velocity domain by Radon transform, so the vehicle trajectories are separated and extracted unsupervised by extracting singular points in the range–velocity domain. The proposed vehicle trajectory extraction method was verified and tested in the real expressway environment of two-way three lanes. The experimental results showed that compared with the method based on wavelet, the vehicle trajectory is more obvious after being processed by this S transform based algorithm. Meanwhile, compared with the method based on Hough transform, more local peaks is accumulated and clustered in Radon domain. Therefore, it is easier to separate multi-vehicle trajectories with the proposed method.关键词：distributed acoustic sensing (DAS);S transform;Radon transform;vehicle trajectory extraction
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发布时间：2024-01-10
INFORMATION ENGINEERING
- 摘要：To study the heat and mass transfer characteristics of hydrogen desorption process in metal hydride hydrogen storage reactor, a two-dimensional axisymmetric mathematical model for metal hydride reactor was established. The reactor was filled with composite compacts made of Ti0.95Zr0.05Mn1.55V0.45Fe0.09 alloy and expanded natural graphite. The validity of the model was verified by the experimental data in literature. The effects of heat transfer fluid temperature, mean fluid velocity and hydrogen delivery pressure on the hydrogen desorption process were investigated, and the hydrogen desorption characteristics were compared at the optimal and baseline sets of the operating parameters. The kinetics characteristics of the hydrogen desorption reaction were analyzed at the optimal sets of the operating parameters. The simulation results showed that the heat transfer performance is better near the heat exchanger tube wall, where the hydrogen desorption reaction proceeds more quickly. When the temperature increases from 313.15 K to 353.15 K, the hydrogen desorption time decreases from 17100 s to 6700 s. Increasing the mean velocity can accelerate the hydrogen desorption process, but its strengthening effect is limited. When the flow rate of heat transfer fluid exceeds 3 m/s, the enhancement effect of increasing the mean fluid velocity is not obvious due to the contact thermal resistance between the metal hydride bed and the wall of the heat transfer tube becomes the main thermal resistance in the overall heat transfer process. The optimal operating parameters are as follows as: the hydrogen delivery pressure of 0.3 MPa, the temperature of heat transfer fluid of 353.15 K, and the mean velocity of heat transfer fluid of 3 m/s. Compared with the baseline set of the operating parameters, the hydrogen desorption reaction time is shorten by about 56%, and hence the optimization of the operating parameters can significantly improve the dehydrogenation rate of the reactor. The hydrogen desorption process of the Ti0.95Zr0.05Mn1.55V0.45Fe0.09 alloy is mainly controlled by hydrogen pressure only in the first 4 s, while the whole reaction process is mainly controlled by the heat transfer process.关键词：metal hydride;hydrogen storage;reactor;hydrogen desorption;numerical simulation
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发布时间：2024-01-10 - 摘要：Zingiberaceae is a large family of the perennial herbaceous plants, members of which have attracted continuous phytochemical interest due to their culinary uses as well as their biological and the pharmaceutical activities. Stahlianthus involucratus is a tropical Zingiberaceae plant and its rhizomes have long been used in traditional medicine to treat inflammation, pain, and fever. In order to clarify the action mechanism of Stahlianthus involucratus and its further development and utilization, systematic study of the chemical composition of Stahlianthus involucratus is of great significance. Previous phytochemical investigations on this species resulted in isolation of cadinane dimers, sesquiterpenoids. In order to further study the chemical constituents of Stahlianthus involucratus, different column chromatographic techniques such as semi-preparative high perfrmance liquid chrmatgraphy and the column chromatography were used to separate and the purify chemical constituents from ethyl acetate fraction and n-hexane fraction of 75% ethanol extract of Stahlianthus involucratus, and the structures of monomer compound were elucidated by mass spectrometry and NMR. Eleven compounds were separated and purified, which were identified as: stigmastern (1), 2–hydroxy–1,2–bis[5–(hydroxymethyl)–2–furanyl]ethenone (2), (Z)–2–acetoxy–5–ethylidene–2–methyl–3–methylenehexanedioic acid (3), hexanedioic acid, 2–(acetyloxy)–5–ethylidene–2,3–dimethyl–, [R–[R*,S*–(Z)]]–(9CI) (4), hexanedioic acid, 5–ethylidene–2–hydroxy–2,3–dimethyl–, [R–[R*,S*–(Z)]]–(9CI) (5), 1,4-dihydroxy–2–methylbenzene (6), 2–ethyl–2–butenoic acid (7), 2–furoic acid (8), (2E)–3–(4–hydroxyphenyl)–2–propenoic acid (9), senecio-nan-11,16-dione (10), Seneciphyllinine (11). Among these compounds, compound 3 was a new natural product and the others were known compounds. Compound 3 was obtained as a white amorphous powder. Its molecular formula was established as C12H16O6 by mass spectrometry at m/z 279.0841 ([M+Na]+). The relationship of C–H can be determined by13C NMR spectrum and HSQC experiments. Combined with the COSY spectrum, the structure of the compound can be inferred. According to chemical shift of the C–2 olefin proton in the1H NMR spectrum data, it can be inferred that the olefin between C–2 and C–3 is ofZ–isomerism. Herein, compound 3 was named as (Z)–2–acetoxy–5–ethylidene–2–methyl–3–methylenehexanedioic acid.关键词：zingiberaceae;stahlianthus involucratus;chemical constituent
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发布时间：2024-01-10 - 摘要：To solve the problem that it takes a long time to cultivate granular sludge under single load or gradually increasing load and the removal of pollutants is unstable. An alternative change of influent carbon-nitrogen loading was proposed to study the formation process of aerobic granular sludge (AGS) and the removal effect of pollutants. Cultivated AGS by influent—aeration—sedimentation—drainage (S1) and influent— aeration—anoxia—aeration—anoxia—aeration—sedimentation—drainage (S2), and the morphological changes, sedimentation performance and pollutant removal situation during the formation of granular sludge were compared and analyzed. Results showed that the average particle size of the reactor (S1) was 0.5 mm on Day 84 and the reactor (S2) on Day 78. At the Day 115, the average particle size of the sludge in two reactors was 0.85 mm and 0.97 mm.S1 and S2 mass concentration of the MLSS is 4.940, 5.895 g/L and SVI in the reactor is 80, 46 mL/g, mature AGS was more conducive to the growth of microorganisms, maintained higher biomass and sedimentation performance.The removal effect of COD and NH4+–N under two operating modes changed slightly, and the removal effect of TN and PO43––P was significantly different. The removal rates of COD, NH4+–N, TN, and PO43––P in S1 operation mode were 90.0%, 99.7%, 74.5% and 85.0% spectively, while were 94.0%, 99.9%, 94.35%, 95.0%, respectively, in S2, and 4.0%, 0.2%, 19.9% and 10.0% higher than that in S1. The aerobic granular sludge with larger particle size and better pollutant removal performance Could be cultivated in reactor (S2) with intermittent aeration.关键词：aerobic granular sludge;load alternation;operation mode;removal rate
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发布时间：2024-01-10
CHEMICAL ENGINEERING & MATERIAL ENGINEERING
- 摘要：To further investigate the influence of internal components on separation characteristics of a gas–liquid separation unit in a new skid-mounted device with gas–liquid separation and flash distillation, based on standardk–ε turbulent model and Eulerian/Eulerian approach, the CFD method was performed to establish a numerical simulation model of flow characteristic on the separation chamber to improve it’s simulation efficiency. The simulation results were compared with the experimental measurements to verify the accuracy of the model, and the internal components’ structural parameters were optimized. The analysis of the influence of communicating pipes, demister, deflector, baffle plate on separation efficiency, showed that the number and location of communicating pipes can lead the fluid in the separation chamber disturbance. With the thickness of the demister increasing, the trapping effect of the droplets is enhanced, while the diameter of which has little influence upon separation efficiency. The deflector mainly affects the velocity of the inlet fluid, when it’s depth and angle changed, the separation ability changed significantly. The baffle, mainly rectifing the fliud flow, has little effect on the separation effect. Through the optimization of internal components’ structure on the separation chamber, liquid in separation chamber can be discharged smoothly into the cylinder, and also avoid the cylinder air lock when the number of communicating pipes are more than two and distribute in the liquid and gas regions of the separation chamber, respectively. The separation efficiency of gas–liquid separation unit will reach 98% when the demister at a thickness of 60 mm to 120 mm. When the deflector at an angle of 90° to 135° and a depth of 385 mm to 647 mm, the slow flow in liquid regions of separation chamber leads to the drainage smooth, and the separation efficiency can be improved. The above results will provide theoretical guidance for the optimization and design of structural parameters on gas-liquid separation unit in a new skid-mounted device with gas-liquid separation and flash distillation.关键词：skid-mounted device with gas–liquid separation and flash distillation;flow field;structure optimization
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发布时间：2024-01-10 - 摘要：During the movement of the ball screw mechanism (BSM), the friction and wear between the balls and raceway cause the accuracy to deteriorate and reduce its accuracy retention. For the asymmetry of the contact area of the helical raceway of the high-speed BSM, there is a big error in the calculation of the contact geometry and relationship between the screw and the nut raceway by using the traditional Hertzian contact theory. Based on the minimum excess principle, a method was proposed to analyze and calculate the normal contact stress between the ball and the raceway of the high-speed BSM. Firstly, a BSM coordinate system was established based on the Frenet-Serret coordinate conversion formula to geometrically describe the contact between the ball and the raceway at the contact point, and then re-gridded by a two-dimensional interpolation algorithm to facilitate subsequent contact mechanics analysis; the contact area and control equation between the ball and raceway were discretized to improve the accuracy of numerical calculations. To solve the complex computational solution of the contact problem and the slow convergence, the contact problem was transformed by applying the variational fraction principle. The polar value problem was solved by using the conjugate gradient method for cyclic iteration to achieve fast convergence and improve the computational efficiency of the contact problem numerical solution, solving the contact stress distribution between the ball and the raceway. Since the calculation of the contact surface deformation was equivalent to the convolution between the influence coefficient matrix and the normal compressive stress, the two-dimensional convolution calculation, and the corresponding two-dimensional fast Fourier transform were used to solve the numerical solution of the contact problem. In numerical solutions, the main computational effort was focused on the computation of elastic deformations using the two-dimensional fast Fourier transform (FFT) technique Easy and fast calculation of elastic deformation in the contact area. Applying the minimum excess principle and Hertzian contact theory to solve the elastic contact stress distribution between a smooth ball and a plane, respectively, The results of the two calculation methods are compared, and the calculated values overlap well, which verifies the correctness of solving the contact stress distribution based on the principle of minimum excess; Based on the principle of minimum excess to analyze the influence of helix angle on the contact area and elastic deformation at the contact point of ball and raceway, and the results obtained by this method and Hertzian contact theoretical calculations for comparative analysis, as the BSM raceway helix angle increases, the error at the screw and ball contact point A is always greater than the error at the contact point of the nut and ball contact point B. The non-Hertzian solution contact stress peak at the contact point of the screw raceway and ball contact point A gradually becomes smaller, the non-Hertzian solution contact stress peak at the contact point of the nut raceway and ball contact point B gradually increases, and the stress peak at the contact point A is always greater than the peak at the contact point B. The non-Hertzian solution contact stress peak at the contact point of the nut raceway and ball contact point B gradually increases. The minimum excess principle non-Hertzian contact calculation method accurately calculates the stress distribution in the contact area of the ball and raceway and allows comprehensive and accurately calculate the width and depth of the wear zone of the raceway. Therefore, using the minimum excess principle non-Hertzian contact solution can improve the calculation accuracy of the contact stress distribution of the ball screw mechanism, and ensure the precision prediction retention of its accuracy.关键词：ball screw mechanism;contact stress;minimum excess principle;conjugate gradient method;Hertzian contact
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发布时间：2024-01-10 - 摘要：The continuously variable transmission (CVT) is an ideal solution of mechanical transmission. As the development of modern industry and vehicle technology, the CVT is expected to realize the adaptive shifting when the load changes. For the roller flat disk CVT, which is a kind of traction CVT that the output shaft is coaxial with the shifting direction of the shifting component, a screw-spring adaptive shifting mechanism (ASM) of load torque was proposed and the dynamic analysis was conducted. Firstly, the structure model of roller flat disk CVT with screw-spring ASM was described. Then, the kinematic model was established by using analytical method, the contact model was established with Hertz contact theory, and the dynamic model was conducted through the separation analysis method, respectively. Finally, the change regular of side-slip force between roller and flat disk, as well as the transformation law of roller during adaptive shifting of different load torque were mainly analyzed, and the effect of balance spring stiffness coefficient on shifting process was also studied. Simulation experiment was also carried out to verify the transformation law of roller during the adaptive shifting process. The results showed that: In the process of adaptive shifting, the side-slip force is basically constant when the side-slip coefficient is higher than 0.55; The adaptive shifting process is actually a vibration process, and the stiffness coefficient and the load variety could directly affect the dynamic response characteristics; When the initial load conditions are different, the same output load only affects the amplitude of the vibration, but there is no significant effect on the offset of the roller in the speed stabilization state. The simulation results of the transformation law during adaptive shifting process are consistent with the trend of the calculated results, but there is a clear difference between the stable time. The simulation results are closer to the actual situation.关键词：roller flat disk;traction continuously variable transmission;adaptive shifting;dynamic analysis;side slip force
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发布时间：2024-01-10 - 摘要：For the dry gas seal, the depth of spiral groove and the processing accuracy of groove bottom surface had a significant effect on the sealing performance, but there exist some challenges for the groove depth accurately controlling and the processing accuracy of the groove bottom surface. With the groove depth hg=10 μm and the groove bottom surface roughness Ra≤0.8 μm as the designing goals, an optimization study on the laser processing technology of the spiral groove dry gas seal was carried out. Four factors of marking number, laser power, filling spacing, and scanning velocity which significantly affect the groove depth hg and the groove bottom surface roughness Ra were chosen, and 12 levels were taken for each factor, the groove depth hg and the groove bottom surface roughness Ra under 12 sets of processing parameters were respectively obtained through uniform test. The mapping relationship between the process parameters and the groove depth hg, the groove bottom surface roughness Ra were established by using ACE non-parametric regression, and a large number of processing parameter samples were randomly generated based on the Monte Carlo Method. Three sets of processing parameters met the designing goals and their prediction were obtained through interpolation algorithms and sample screening. After the three sets of processing parameters were fine-tuned and tested, some experimental results corresponding to the three sets parameters were obtained. The experimental results indicated that the groove depth hg and the groove bottom surface roughness Ra under the three sets of parameters are well in line with the designing goals, and their prediction are the same with experimental values, indicating that the ACE method has a higher prediction accuracy. Finally, taking the processing efficiency and quality of the groove bottom as optimization goals, the spiral groove laser processing parameters which meet the design goals are obtained.关键词：dry gas seal;spiral groove;laser processing;optimization
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发布时间：2024-01-10
MECHANICAL ENGINEERING
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