最新刊期
卷 49 ， 期 6 ， 2017
- 摘要：Abstract:In order to slove the problem that the representative particle size method is difficult to accurately quantify the roughness of the gravel bed surfaces (GBS), the statistical theory was introduced to study the roughness properties of natural GBS. A series of loose-stacked GBS were prepared by using particles with different size and composition. Based on the analysis of the laser scanning data of the above GBS and the existing test results, the relationship between the statistical parameters of bed roughness and particle size was discussed, and the elevation variation characteristics of gravel bed profiles (GBP) and GBS was analyzed. The results showed that the frequency distribution of bed elevation had a negative skewness, the curve shape was steeper than the normal distribution, and the kurtosis Ku is greater than 3 which belongs to high narrow peak. The standard deviation σz increased with the increase of the median particle size d50, and the skewness Sk decreased with the increase of d50. In the case of the same particle size d50, the standard deviation σz and skewness Sk of unworked GBS were less than that of water-worked GBS, but there was no significant difference in kurtosis Ku. The one-dimensional structure function of GBP satisfied the variogram spherical model, whose parameters included the range, nugget and abutment value. The range showed a trend of first decrease and then increased with the increase of d50 and σz, and nugget and abutment value increase with the increase of d50 and σz. The trend couied be fitted with second order polynomial curves. The distribution pattern of two-dimensional structure function was closely related to sampling scale hx and hy. When hx, hy and d50 were equivalent, the distribution of the two-dimensional structure function was close to the circular shape and the rough GBS was isotropic, with the distribution law of the structural function being consistent with that of the water-worked GBS. With the increase of hx and hy, the complexity of the distribution of the two-dimensional structure function was enhanced obviously. The structure function values of different quadrants were different, and there was no longer the distribution law of the water-worked GBS and the rough GBS was anisotropic.关键词：gravel bed surfaces;roughness properties;statistical parameters;structure function
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发布时间：2023-11-14 - 摘要：Abstract:The change of the relationship between rivers and lakes affected by the Three Gorges Reservoir has been a major focus in recent years.The backflows from the Yangtze River to the Poyang Lake is the main feature of the relationship,and its variation characteristics and occurrence conditions are still controversial.The hydrological data since 2003 of the Jiujiang,Balijiang and Datong hydrological station located in the Yangtze River and the Duchang,Kangshan and Hukou hydrological station located in the Poyang Lake were used.The relationship between the Yangtze River and the Poyang Lake after the operation of the Three Gorges Reservoir was analyzed from the aspects of water level,flow rate,inter-annual variation and annual distribution of runoff.The internal mechanism of the backflows from the Yangtze River to the Poyang Lake based on the basic law of energy balance was discussed and the theoretical formulas were deduced.The results showed that: 1) Poyang Lake had the characteristics of both river channel and lake.The characteristics transforms from river channel to Lake when the water level of Duchang station was above 15 m.The lake characteristics was presented when the water level of Kangshan station was above 17 m;2) The backflows from the Yangtze River to the Poyang Lake occued mainly in the flood season from July to September.In the total days of backflows,41.6 %,24.8 % and 28.8 % belonged to July,August and September respectively.The intensity of backflows was weakened to a certain extent by the flood control operation after the 175 m deep experimental impoundment of the Three Gorges Reservoir.3) The conditions of water level of Yangtze River were higher than that of Poyang Lake,large floods in the Yangtze River,and total inflow of the Poyang Lake receding or remaining stable were necessary for the formation of backflows.Furthermore,the magnitude and duration of the backflows mainly depended on the Yangtze River flood peak.The proposed methods and conclusions can provide a reference for further understanding the relationship between rivers and lakes and their interaction with each other,and provide scientific evidence for the comprehensive management of the Poyang Lake.关键词：Three Gorges Reservoir;Poyang Lake;relationship between river and lake;backflows from river to lake
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发布时间：2023-11-14 - 摘要：Abstract:With the increasing operation of hydropower stations, a refined generation dispatch model becomes more urgently needed for the precise control of cascade hydropower stations under deterministic runoff, such as rules extraction by simulation operation under long series runoff, optimal dispatch level evaluation of historical operation process, and etc. However, most of the studies on refined generation dispatch model focused on the refined description of transform relationships between hydropower and electric energy or hydraulic connection between cascade hydropower stations. The time scale of dispatch model, which is another important factor affecting the accuracy of dispatch model, was short of attention. The time scale of dispatch model affects theaccuracy of dispatch model in a complex way. This paper attempted to discover the influence between time scale and the accuracy of dispatch model by both theoretical analysis and case study. The control variable method and progressive analytical method were used to uncover the key factors which affect the accuracy of dispatch model and to analyze its influence rule qualitatively. The case study of cascade hydropower stations downstream of the Jinsha River has been conducted to analyze influence between time scale and the accuracy of dispatch model by these factors. With modeling analysis in different inflow conditions and water level control strategies, we have uncovered key factors which affect the accuracy of dispatch model quantitatively. Then we proposed a multiple time-scale generation dispatch model for accurate description of the dispatch problem. The simulation results show that the theoretic results proposed in this paper is sound. Moreover, the proposed model has a better performance on both accuracy and efficiency compared with other models, which means that this model can be used for historical operation evaluation and dispatch rules extraction of cascade hydropower stations downstream of the Jinsha River.关键词：downstream Jinsha River;multi time-scale;cascade dispatch model;model accuracy analysis;?
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发布时间：2023-11-14 - 摘要：Abstract:As cascade power stations are constructed and operated,more concerns are attracted to their negative impact on fish from supersaturated total dissolved gas (TDG) generated by high dam spilling.The supersaturated TDG dissipates very slowly in natural rivers,even more slowly in reservoirs.Generally the spilling flow with high TDG saturation level exists from the upstream cascade's stilling basin to the downstream cascade's forebay.The fishway,which is an important facility to recover the non-continuity of the river,is a region of fish gathering.The TDG supersaturation flow in the fishway,which uses the water in reservoir as replenishment,is harmful for fishes.To explore the transportation and dissipation of TDG in the fishway,the experimental studies of different flow rates were conducted in a T shape fishway channel.The numerical simulations were performed according to the experimental conditions to obtained dissipation rate of different cases.The results revealed that water depth affected the disspation rate significantly.The dissipation rate of TDG decreased with the increase of water depth in fishway.No clear relations were found between TDG dissipation rate and mean velocity,turbulence and turbulent dissipation rate.Furthermore,it showed that the TDG dissipation rate in fishway was obviously higher than that in channel without clapboards,because the clapboards rose the residence time for flow and TDG in the flow dissipated adequately.The research provides scientific basis of the exploration of negative impact to fish in TDG supersaturation flow in fishway,and provides new ideas and reference for the research of the mitigation measures for the problem.关键词：supersaturation;total dissolved gas;dissipation coefficient;fishway
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发布时间：2023-11-14 - 摘要：Abstract:The geometric parameter of width-depth ratio plays an important role in three-dimensional characteristics of water flow in curved channels.Considering that bends with small width-depth ratio (< 5) widely exist in mountain rivers and artificial channels,the Acoustic Doppler Velocimeter (ADV) was employed to measure distributions of velocity in a U-shape bend with three different width-depth ratios of 1.5,2.0 and 3.0,respectively.Based on the measurements,the transverse gradient of water surface,transverse flow circulation,redistribution of velocity,turbulence intensity,and bed shear stress were investigated to analyze the structure of water flow.The experimental results demonstrated that as the increase of width-depth ratio:1) flow dynamic axis moved to concave bank earlier,which resulted in main streamline with low inlet velocity flows along the convex bank until the export of bend,while that with large inlet velocity moved to concave bank earlier;2) the locations of fluctuation of transverse velocity moved forward,which corresponded to 120° section,90° section and 60° section,respectively,in these three working conditions;3) the locations of secondary circulation on the surface of concave appeared in advance which were 120° section,60° section and 30° section,respectively,and both the strength and the range of secondary circulation increased;4) the bed shear stress increased.It should be noted that the shear stress was larger between inlet section and top section of the bend,and the location of the strongest shear stress appeared in the first half of the bend,which could infer that sediment erosion in this position was strong.The shear stress corresponding to the convex bank was larger than that of the concave bank after the top of the bend.The results could effectively describe the structure of water flow in small width-depth ratio conditions,and provide references for the sediment scouring and silting in the bend.关键词：bend flow;transverse of water surface;transverse circulation;redistribution of velocity;turbulence intensity;bed shear stress
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发布时间：2023-11-14 - 摘要：Abstract:Rock salt is a globally recognized ideal medium for energy storage.Due to the special characteristics of Chinese rock salt,e.g.,thin depth,high impurity content and containing many insoluble interlayers,the horizontal cavern is more suitable for the underground energy storage in China.In order to ensure the safety of the cavern and to maximize the total storage volume,a new storage form of the horizontal cavern with two wells under constant internal pressure was proposed.The two wells,which were used to inject and extract brine and natural gas respectively,were evenly arranged in a rotating cavern.During natural gas extraction/injection,brine was injected into/extracted from the cavern,so that the internal pressure was maintained at its constant maximum level.Based on the actual geological structure and mechanical parameters of the salt rock in Jintan,a numerical model of the new horizontal cavern was established,and then a simulation was carried out with the finite difference software FLAC3D.The feasibility and safety of the storage form were studied from four aspects:stability,tightness,usability and blowout analysis.Besides,the operation of the traditional gas storage was also simulated for comparison.The results showed that,the new storage form could meet all aspects of safety requirements,and its performance was significantly better than that of the traditional gas storage.In addition,the new storage form had some other advantages,such as good economic efficiency,flexibility,strong ability of peak regulation,good ability to cope with blowout,low cost of the unit volume,making full use of salt layer and so on; thus,the new storage form is demonstrated to be quite suitable for China's rock salt.关键词：underground gas storage;horizontal cavern with two wells and constant internal pressure;thin-layered rock salt;numerical simulation
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发布时间：2023-11-14 - 摘要：Abstract:In order to investigate the in-plane stability of steel supporting structure with corrugated webs under the pressure of surrounding rocks,a model experiment was carried out to study the stability behavior,displacement and strain developments of U-shaped steel supporting structure with corrugated webs.The results showed that the ultimate failure mode was global asymmetric buckling,the deformation of the two sides of the support was outward along the radial direction,and the deformation of right side was larger than that of left side.Plastic deformation occurred only in the flange at the crown of the top arc and the web of the corner arc.The finite element model was verified by comparing the experimental results with that of finite element analysis.On this basis,the parametric numeric analysis on elastioplastic buckling behavior of corrugated steel webs was conducted by finite element method.The results showed that the corrugated steel webs were not sensitive to the initial imperfection,while the web height,the web thickness and the flange thickness were sensitive factors to the bearing capacity of elastic-plastic stability.When the slenderness ratio is small,the symmetric instability or antisymmetric instability may occur.When the slenderness ratio is large,the support will develop the antisymmetric instability.With the increase of slenderness ratio,the elasto-plastic buckling coefficient ks increases.Under the same boundary conditions and load conditions,the ultimate stability capacity of the steel support with corrugated webs is more than twice as much as that of the H-shaped steel support for mining with the same weight.关键词：corrugated web;stability capacity;U-shaped support;model experiment;slenderness ratio
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发布时间：2023-11-14 - 摘要：Abstract:In order to solve the issues during the construction of the water-soluble single well bedded rock salt cavern,including the long trough period,the complex stripping tube process etc.,the technology of the water-soluble cavity for double well with horizontal well spacing was studied.A similar experimental platform was proposed to establish a physical method.The characteristics of the flow field and concentration field of the water - soluble cavity in the well spacing were discussed,which revealed the relationship between the cavity expansion and the flow field in double well water soluble cavity.The results showed that the cavity flow field was divided into four regions:the boundary eroded area,the floating plume area,the convective diffusion area,and the bottom saturated zone.And different regions influenced each other.The floating plume area was the key area to drive the flow field of the cavity,and the corresponding flow field model was established according to the flow field characteristics of the plume.According to the macroscopic flow characteristics,the convective diffusion was divided into strong diffusion region and weak diffusion region;the boundary dissolution region had a significant effect on the cavity expansion of the double well water soluble cavity.The tracer characteristics of the saturated zone were not obvious while the concentration stratification shows the opposite.By comparing and analyzing the results of double well cavity and single well cavity model,it was found that the process of double well water soluble cavity could be beneficial to the construction of salt hole.The study provides a theoretical basis for the application of water well in the well spacing,which is of great significance to optimize the construction of salt cavern gas storage.关键词：bedded rock salt;water dissolving cavity;flow field;well spacing;double wells
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发布时间：2023-11-14 - 摘要：Abstract:In order to reveal the mechanism for the influence of the snowmelt infiltration on the non-equilibrium flow and stability of residual slope,the instability reason of a residual soil slope induced by snowmelt in Fujian Province was analyzed based on the unsaturated seepage model and the non-equilibrium flow model.Then,the influence laws of different diameters,distances,bending ratios and the lengths of macropores on moisture field and safety factor of the slope were also obtained based on non-equilibrium flow model.The results showed that non-equilibrium flow had a greater impact on the slope stability than that of considering unsaturated seepage.The theory of non-equilibrium flow could be adopted to reasonably interpret the instability mechanism of a residual slope induced by the snowmelt.With the increasing of the macropore diameter,the pore water pressure and the moisture exchange capacity between macropore domain and matrix domain would increase,but the priority conduction of water flow and stability for slope would decrease;the conduction route of water would be extended and water accumulation in the macropore would be decreased with the increasing of the length of the macropore.The length of the macropore played a certain part in the safety factor of slope.The bending ratio of the macropore had little influence on water content and safety factor of slope.There was a critical distance for the macropore distances which could lead to minimum safety factor of slope.The preferential flow of macropores would be restricted if the distance between macropores was too large,and the mutual superposition of non-equilibrium flow would decrease the pore water pressure in deep layer if the distance between macropores was too short.Therefore,the influence of non-equilibrium should be paid more attention for the instability of slope with macropore induced by snowmelt in the short-term frozen zone,especially in the distance between macropores and the length of macropore.关键词：residual soil slope;short-term frozen zone;snowmelt;non-equilibrium flow;stability
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发布时间：2023-11-14 - 摘要：Abstract:For researching the rockburst proneness of Beishan granite under different stress state,servo Test System was used in this study.The stress-strain curves of Beishan granite under different confining pressures were obtained,and the loading process was controlled by axial pressures and circumferential deformation.It was mainly focused on the energy evolution of rocks in the process of failure,and the results proved that both the total energy and elastic energy increased with increasing confining pressure when rock failure.Variable quantity of total energy and elastic energy from peak stress to residual stress increased with increasing confining pressure.The effect of the energy storage coefficient and the energy releasing coefficient on the rock failue were analysed,and a new rock burst proneness index was performed based on the energy storage and releasing coefficient,which not only represented energy change characteristics but also expresses the rockburst proneness under different stress states.It was thusused to research the rockburst proneness under different stress states,and the result showed that the rockburst proneness increased with increasing confining pressure.Specifically,when the confining was less than 10 MPa,the effect of confining on rockburst proneness was weakened;when the confining pressure exceeded 10 MPa,the effect on rockburst proneness sharply increased;thereafter,as the confining continues to increase,the effect was gradually decreased.关键词：Beishan granite;strain energy;class Ⅱcurve;stress state;rock burst proneness
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发布时间：2023-11-14 - 摘要：Abstract:Recently,as the structure damage of slope lining occurred,experimental investigation on the difference between the mean pressures and the fluctuating pressures on the back and front sides of slope lining plate is carried out based on the Wudongde Hydroelastic model.The most adverse operating condition is simulated when the water stop and drainage facilities partially and totally invalid,respectively.Results showed that both the seepage pressure and the instantaneous fluctuating pressure contribute to the uplift force which causes the damage of the slope lining plate.The seepage pressure induced by the water level was different between the back and front side of slope lining plate,and it was mainly affected by the wave surface elevation in cushion pools. Therefore,we studied the space and probability distribution of the wave surface elevation.Experimental results showed that the wave elevations near the water entry were higher than those near the slope protection with similar reference number as the water entry.Moreover,as the reference number increased (or decreased) from the water entry,the water elevation gradually decreased (or increased).Inspired by the studies of ocean wave statistics,Gram-Charlier series distribution was adopted to describe the probability density distribution of the wave surface elevation.According to the data fitting,Gram-Charlier series distribution was more consistent with the actual situation than Normal distribution.It was considered that the fluctuating pressures acting on the front and back sides of the slope lining plate obey the normal distribution.Both the stochastic process in which the random variables obey Gram-Charlier series distribution and two mutually independent Gaussian stochastic processes contributed to the destruction of slope lining plate.Comprehensively considering the load characteristics and the failure mechanism,the applicability and the probable error for the traditional safety monitoring index of cushion pool were analyzed.关键词：slope lining plate;failure mechanism;wave surface elevation in cushion pool;Gram-Charlier series distribution;safety monitoring index
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发布时间：2023-11-14 - 摘要：Abstract:A large number of landslides and collapses are often triggered by earthquake,but little attention has been paid to the risk assessment of glacier lake outburst under coaction of earthquake and ice avalanches.To investigate the characteristic of hydrodynamic pressures under coaction of earthquake and ice avalanches,experimental analysis of hydrodynamic pressures were conducted under separate earthquake action and ice avalanches action,respectively.The ice block sliding into the reservoir was added during the process of earthquake simulated by shaking table,the characteristic of combined hydrodynamic pressures caused by earthquake and ice avalanches were then observed.The results show that the seismic hydrodynamic pressures were decreased from the bottom to the top,which was in good agreement with Westergaard's briefly solutions.However the hydrodynamic pressures caused by ice avalanches were increased from the bottom to the top.Meanwhile the effect of the volume,the sliding block velocity and initial water depth were considered to study the characteristics of the hydrodynamic pressures,and an empirical equation was obtained to predict the maximum pressure loads acting on the dam.The hydrodynamic pressure distribution curves under coaction of earthquake and ice avalanches were approximately equal to the superposition of separate earthquake and ice avalanches actions,but the combined values were smaller than the superposition values,and the estimation method of maximum hydrodynamic pressure was proposed.关键词：earthquake;glacier lake outburst;ice avalanches;shaking table;combined hydrodynamic pressures
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发布时间：2023-11-14 - 摘要：Abstract:Human mobility has regularity.It has theoretical significance and realistic needs to build mobility models of human movement.Previous models were usually based on the assumption that human mobility is scalable and did not take into account the times of trips and influence of infrastructure network.To address these problems,by analyzing passengers' traveling data sets of civil aviation,the following characteristics of passengers' traveling were found:the trip distances of passengers are not scale-free,the trip number of times is anisotropic,and passengers' movements have different trends along with different numbers of trip times.In order to describe the characteristics of passengers' travelling data,a passenger mobility model based on potential trip purpose (PMMPTP) was proposed.Firstly,the model considered that passengers' travel has relationship with the economic factors of destination cities,and a method for calculating the selection probability of a city was proposed.Secondly,the exploration and return mechanism of passengers' travelling was taken into account.Then,a method for calculating the probability that passengers explore new airports and return to the historic airports was proposed.The simulation experiments firstly simulated the travel characteristics of civil aviation using PMMPTP model and then tested the validity of the model by predicting the throughput of airport and airline.The results showed that the model can fit the actual data of civil aviation travel,and effectively solve the problem of modeling low frequency passenger's trips.关键词：civil aviation passengers;the distribution of trip number;potential trip purpose;the characteristics of trip;mobility model
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发布时间：2023-11-14 - 摘要：Abstract:The accuracy and efficiency of multi-view stereo matching are seriously hindered by the scale of the image datasets and the wide variety of matching information.To address this issue,in this paper,a fast semiglobal optimizing method based on GPU was proposed for depth map calculation with parallel computing technology applied.First,the matching cost of single image was computed by the plane sweep method on CPU. Second,the matching costs were aggregated by using semiglobal optimizing method executed on GPU in parallel.The core module included two strategies:1) by aggregating the cost in each direction globally and parallelly,the utilization rate of the multi-cores of the GPU was increased;2) The computation on each single pixel was assigned to different threads and computed in parallel.To alleviate the constraint of limited bandwidth,the data reuse of GPU had also been taken into consideration.Then,the filtering on GPU was proposed to remove the outliers and enhance the image.Finally,the consistency of the 3D point projections on every image was used as a constraint for outlier detection and optimization.The proposed method had been tested on multi-group datasets.Experiments showed that the proposed method achieved as high as 22.41 times and 9.13 times speedup compared to two-threaded and eight-threaded implementation on a multi-core CPU system respectively,while also preserving similar quality.Compared with other algorithms of depth map calculation on tested datasets,the proposed method always achieved as fast as more than 5 times speedup in the reconstruction process.Compared with other algorithms on several datasets via open source pointcloud comparison software (CloudCompare),the proposed method could effectively improve the accuracy and integrity of the reconstruction results.关键词：3D reconstruction;plane sweep;depth map;parallel semiglobal optimization;GPU;filtering
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发布时间：2023-11-14 - 摘要：Abstract:In order to overcome the storage loss and capacity degradation issues of the batteries in wireless sensor network,a communication model of battery storage loss and capacity degradation was established for maximizing the throughput within each wireless sensor life cycle.The optimization problem was firstly transformed into a convex problem.Then,the power control strategy,which is simultaneously related to the current harvesting energy level,the battery energy level,and the channel gain,can be directly obtained through the convex optimization analysis.Next,a dual power threshold algorithm was presented to deal with the problems of battery storage loss and capacity degradation,and optimize the average system throughput.Afterwards,a charge-discharge management policy was proposed to restrain decay rate of the battery capacity.The proposed policy is able to optimize and estimate both of the life cycle and the battery discharge space of the wireless sensor.Simulation results demonstrated that compared with the adaptive directional water algorithm,the presented dual power threshold algorithm is capable of avoiding frequent charge-discharge operations,thus reducing the storage loss of the harvesting energy,optimizing the average throughput and the life cycle,and finally promoting the total throughput within each life cycle.关键词：energy harvesting;wireless sensor;storing inefficiency;battery degradation;Rayleigh fading
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发布时间：2023-11-14 - 摘要：Abstract:Echo state network (ESN) is an important method for time series prediction.However,the overfitting problem is likely to occur when the training data contain noise or outliers.To solve this problem,an ESN model based on smoothly clipped absolute deviation (SCAD) penalty function was proposed in this paper.Different from the traditional methods,such as ridge regression,L1 norm penalty,wavelet denoising and other methods added into the ESN model,the SCAD penalty function was used to select the variables of the ESN model.Specially,to meet the variable sparseness,the small coefficients are set to zero.And the large coefficients are taken as constants,which can well solve the over-fitting problem of ESN and satisfy approximate unbiased estimation.For the nonconvex optimization problem of SCAD penalty function,the local quadratic approximation (LQA) solution was presented in the paper,and the enormous computational complexity of the least angle regression (LQR) method for solving the SCAD penalty function was overcome.Then,the particle swarm optimization (PSO) is used to quickly determine the hyperparameters selection of smoothly clipped absolute deviation-echo state network (SCAD-ESN) model.The proposed method overcame the blindness of the conventional methods using the experience to select the hyperparameters,which is blind and difficult to determine the global optimum.Finally,the chaotic system simulation and network traffic simulation showed that,compared with the conventional models,the model can effectively reduce the test error and overcome overfitting problem.关键词：chaotic time series prediction;echo state network;smoothly clipped absolute deviation penalty;particle swarm optimization
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发布时间：2023-11-14 - 摘要：Abstract:Physical-layer security has become a critical technique in current wireless networks.The existing conventional physical layer security techniques,e.g. artificial-noise-aided transmit beamforming,do not apply well to multicast transmission from large multicast user and eavesdropper user numbers.To address this problem,an enhanced secure multicast algorithm based on user clustering scheme was proposed.Firstly,the multicast users with close channel vectors were divided into a cluster and different clusters were served on different channels.Secondly,a heuristic joint power allocation and beamforming design algorithm based on this user clustering scheme were proposed to maximize the globally achievable secure multicast rate.Finally,to reduce the overall computation complexity,the new searching method was put forward to solve power allocation and beamforming design jointly.Simulation results showed that the enhanced secure multicast algorithm can support a much higher secure transmission rate than conventional secure multicast (CSM) schemes,and the proposed joint power allocation and beamforming design algorithm outperform existing CSM schemes with the ergodic searching method greatly in terms of computation complexity.关键词：physical-layer security;multicast;beamforming;artificial noise
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发布时间：2023-11-14 - 摘要：Abstract:In order to solve the problem that the current vulnerability assessments do not give enough consideration to the interaction among grids,an evaluation approach of interconnected district grid vulnerability was presented based on tie-line groups energy transmission.First,the inherent hierarchical structure and operational characteristics in the current district interconnected power grids were expounded.The features of black box data and the external grid dependence of the actual power systems were indicated.Then,the rationality of district grid vulnerability assessments based on tie-line groups energy transmission was analyzed.Secondly,the drawbacks of the two inherent vulnerability evaluation indices,i.e. node structure and branch load rate with weak macroscopic feature,were corrected by introducing two new indices,disturbance resistance and horizontal load rate indices.These two new indices focus on power disturbance and power exchange,which were not considered in the previous vulnerability assessment papers.And,an evaluation indices system suitable for actual power system was established.Then,the method of variation coefficients was used to evaluate the vulnerability of interconnected power grid based on tie-line groups energy transmission mode.Finally,the effectiveness of the evaluation was verified by the IEEE57 node system.关键词：vulnerability;district power grid;tie-line groups;transmission mode
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发布时间：2023-11-14 - 摘要：Abstract:In order to inhibit the harmful chaos of permanent magnet synchronous motor (PMSM),the model of PMSM was transformed to a generalized Hamilton model with some nonlinear disturbance.Then a disturbance compensator and a tracking controller were designed from its Hamilton model.Next a disturbance compensator with adjustable gain matrix was designed for the nonlinear disturbance in the generalized Hamilton model,and the system with the disturbance compensator was proved to have the asymptotic stability by Lyapunov stability theorem.After fixing the Hamilton energy function with freely choosing the desired equilibrium,the tracking controller with undetermined coefficient matrix was designed with the method of modified interconnect and damping control,and the undetermined coefficient matrix was a modified matrix with an expected structure.To improve the adaptive ability of the system,grey wolf optimizer (GWO) was applied to find the best adjustable gains of the disturbance compensator and the optimal coefficients of expecting correction matrix for the tracking controller.The wolf position vector was composed of adjustable gain parameters and the undetermined coefficients of the correction matrix,and the iterative process of GWO was a purposeful optimization one.To verify the validity of the above-controlled method,several contrast experiments were designed from the change of desired output,the load disturbance,as well as the a-axis and d-axis voltage disturbance.The experimental results showed that the chaotic phenomena of the system are suppressed,the system could follow the expected output well and have better capacity in resisting load disturbances and voltage disturbances.The validity of grey wolf optimizer algorithm in assisting the controllers' parameters on the basis of the optimized objective function,which improves the adaptive ability of the system,was also proved by the experimental results.关键词：permanent magnet synchronous motor;chaos;Hamilton system;grey wolf optimizer;tracking control;disturbance compensation
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发布时间：2023-11-14 - 摘要：Abstract:Pilger cold rolling technology,as the most important technical means of cold-rolled seamless metal tube,has the characteristics of high material utilization,large cross sectional deformation and high machining accuracy 304 stainless steel rolled by LG-60 pilger mill was taken as the object of study and a numerical simulation model was established.With metallographic microscope,scanning electron microscope and X ray diffractometer,the evolution of the organization in the process of cold rolling steel was analyzed from the different deformation segments of the pipe.The results showed that the technological parameters can meet the requirements of plastic deformation of the tube.But in the rolling process,it is likely to form cracks or other defects during rolling.Therefore,key parameters such as rolling force,tube equivalent stress and residual stress during cold rolling simulation of pilger were analyzed and obtained.The optimal process parameters based on feed volume,back angle and Q value were obtained.It was also found that a large amount of dislocations were produced in the sample during the rolling process.The grain was broken and the size decreased.In the process of rolling,there was the transformation of austenite phase to alpha-martensite phase.关键词：cold rolling;process parameters;numerical simulation;microstructure;evolution
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发布时间：2023-11-14 - 摘要：Abstract:Aimed at the problems of bigger engaging angle of cycloid-pin gear,lower reliability of turning arm bearing and higher uniform position precision of pinwheel,the composite cycloid,that has a relatively strong controllability in geometry,was utilized to establish the internal tooth profile of small tooth difference planetary drive (STDPD),then a new high-performance STDPD with composite cycloid internal tooth profile (CCITP) was proposed.Based on the geometry principle of traditional cycloid pinwheel drive,the geometrical design method of CCITP was presented,and the impacts of c2 on geometrical shape and curvature were analyzed.Using kinematic conjugate theory of gear meshing,the profile equation of CCITP,the meshing equation of conjugate gear drive,the conjugate profile equation with small tooth difference and action line equation were established.The analysis of meshing boundary properties based on parameter transformation was conducted.According to the mathematic princple that singularity appeared on conjugate profile,the judgement equation for determining whether undercutting occurred or not was derived.Meshing properties including action line,contact ratio,pressure angle,induced normal curvature and sliding ratio of this new gear drive (TNGD) were investigated,sensitivity analysis methods on induced normal curvature and sliding ratio in certain meshing range were put forward.The results indicated that meshing boundary point existed on composite cycloid internal profile,furthermore the effective theoretical methods of both the transition-curve geometry design of internal tooth dedendum and the non-undercutting design of conjugate profile were provided on account of meshing boundary model and undercutting judgement equation.Meanwhile,the analysis result of action line and contact ratio showed that the multi-teeth meshing property of TNGD could be carried out.When the tooth number,eccentricity,tooth height and internal tooth distribution circle of TNGD were determined,c2 was the only gear parameter that really could impact the pressure angle,induced normal curvature and sliding ratio.The minimum and average of planet gear pressure angle decreased with c2,the impacts of c2 on induced normal curvature and sliding ratio were classified into non-sensitive and sensitive ranges in one meshing cycle.The impacts in non-sensitive range could be ignored,while both the average of induced normal curvature and the amplitude and average of sliding ratio in sensitive range were decreased with c2.Compared with the traditional cycloid drive having the same parameters,the advantages on pressure angle,induced normal curvature and sliding ratio of TNGD were shown.Accordingly,better meshing performances in multi-tooth meshing,force transmitting,lubrication,capacity and anti-wear were achieved.Therefore,a certain effect in engineering application of TNGD was showed.关键词：planetary drive with small tooth difference;conjugate principle;geometric characteristic;meshing property
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发布时间：2023-11-14 - 摘要：Abstract:Aimed at the problem that the existing models of hydraulic damper with pressure relief valve consider different factors and have different forms,a unified dynamic model was presented for hydraulic damper with pressure relief valve internal and external by analyzing the effects of oil mixed with gas and oil compressibility,valve port dynamic flow force,valve port discharge coefficient and equivalent area,and string pipeline resistance on equivalent damping and damping force peak.The theoretical results of equivalent damping and damping force peak were compared with the test data while some hydraulic damper with 1, 9 and 26 mm excitation amplitude.The results showed that the errors of equivalent damping are -9.994 5 %,0.672 4 % and -2.757 2 %, respectively. and the errors of damping force peak respectively are -0.457 4 %,1.973 3 % and -4.074 9 %.The model accuracy has been validated by the results of errors.Furthermore,the analysis results of influence factors showed that oil elastic modulus is sensitive to air percentage in low pressure,it descends rapidly with air percentage increasing,and oil elastic modulus has great influence on equivalent damping and damping force peak,especially with small excitation amplitude. Valve port dynamic flow force has large effect on damping force peak while pressure relief valve opening,but has little effect on equivalent damping. The simplification of valve port discharge coefficient and equivalent area almost have no influence on equivalent damping and damping force peak and the pipeline resistance and oil compressibility of pipeline have slight influence on equivalent damping and damping force peak.关键词：hydraulic damper;pressure relief valve;modeling factors;equivalent damping;damping force peak
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- 3765
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发布时间：2023-11-14 - 摘要：Abstract:Abrasive belt grinding is one of the important means to improve the accuracy and quality of free-form surface.Aiming at the shortcomings in the efficiency and accuracy in the process of belt grinding of free-form surface,based on the characteristics of abrasive belt grinding,a trajectory planning method for abrasive belt grinding free surface was proposed by machining accuracy control.First,the radius of curvature of grinding interference and fabrication tolerance of the grinding wheel width were deduced,thus with the analysis of grinding wheel and machining surface points principal curvature, the processing requirements were optimized by genetie algoviyhm double out to meet to free surface error,and the contact wheel size parameters of no curvature interference processing requirements was obtained.Then,based on the principal curvature direction of the machining points,the adaptive strip-width maximization planning of the machining path was realized,and algorithm for the compliant treatment of the surface distortion in grinding head axial potential oscillating were studied,finally the grinding path which has the space stability and meet the grinding wheel contact point was gotten.Finally the processing of the experiment was verified by the trajectory planning method of a certain type of aero-engine blade the surface with CNC abrasive belt grinding machine.The results showed that the blade profile accuracy by using the method of trajectory planning after grinding can better meet the corresponding tolerance requirements,and the surface quality and accuracy of blade profile were improved,and the validity and practicability of the grinding path planning for free-form surfaces were verified.The method can be expected in control of machining error,solves the problem of contact local interference problems caused by improper selection of parameters of grinding wheel size,and the efficiency and accuracy of abrasive belt grinding can be effectively improved.关键词：free-form surface;strip-width maximization machining;adaptive;trajectory planning;abrasive belt grinding
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发布时间：2023-11-14 - 摘要：Abstract:The curvature relationship of the conjugate tooth surface of gear pair is the important parameter which is the characterization of gear transmission quality,and has a direct effect on the induced normal curvature,contact zone shape,contact property,lubrication,wear and tooth surface stress.Based on the deduced tooth surface equation of cylindrical gear with variable hyperbolic arc-tooth-trace (VH-CATT),its curvature expressions were deduced and its change regulations were studied. Firstly,based on the machining principle of the great cutter head,the tooth surface equations of VH-CATT gear were derived according to the transformation matrix of coordinates.According to the derived tooth surface equations,the principal curvature,gauss curvature,mean curvature and induced normal curvature of the VH-CATT gear were derived by using differential geometry and meshing theory.Based on the derived expressions,the tooth surface data,principal curvature,Gaussian curvature,mean curvature,induced normal curvature of the VH-CATT gear pair were simulated and analyzed by computer software.And the change regulations of the VH-CATT gear curvatures were obtained in the meshing process.It could be seen from the research results that the change trends of principal curvature of the concave tooth surface and convex tooth surface are consistent in the tooth line direction,but have the little differences.The principal curvatures gradually increase in the tooth profile direction,but the increase range is just the opposite,and the change trend of principal curvature is consistent with the convexity of profile.The Gauss curvature and mean curvature of the gear pair are very small,and the change range is also small in the meshing process,and no mutation occurs.It was proved that the tooth surfaces of VH-CATT gear pair are smooth and continuous.The main value of induced curvature is close to zero in the tooth line direction,and is the negative in the tooth profile direction.It was also proved that the interference phenomenon of gears don't occur in the meshing process.The research results of curvature,Showed that the VH-CATT gear drive has good performance and stable transmission.关键词：cylindrical gear with variable hyperbolic arc-tooth-trace(VH-CATT);tooth surface equation;principal curvature;gaussian curvature;mean curvature;induced normal curvature
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发布时间：2023-11-14 - 摘要：Abstract:A method of magnetic suspension that the robot is suspended by the amperage force of the energizing coil in the high voltage direct current (HVDC) magnetic field was proposed to solve the problem of slippage and wear of the traveling wheel of the arm-type inspection robot.The magnetic model of magnetic suspension was established and the relationship between magnetic suspension force and physical model parameters was analyzed theoretically.The model of magnetic suspension is simulated by COMSOL software.The results showed that the model can produce the suspension force in accordance with the theoretical calculation under different system parameters.Further,the influence of anti-vibration hammer on magnetic suspension force was also simulated and the results show that the effect of the anti-vibration hammer on the magnetic suspension force was very small.Finally,according to the proposed magnetic suspension model,the minimum magnetic system is designed and experimented.The experimental results showed that the magnetic suspension method proposed is feasible.关键词：HVDC;inspection robot;magnetic suspension;modeling;simulation
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- 4665
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发布时间：2023-11-14 - 摘要：Abstract:Q345 is a kind of ferrite and pearlite dual phase steel that is widely used on bearing force components in architectural structures and mechanical systems,the long term dynamic loading during their service life induces the fatigue fracture under the stress amplitude that far below the tensile strength of the material,which require the study of the fatigue failure of the material.The conventional fatigue test was carried out with the help of electromagnetic resonance fatigue test machine (140 Hz) to study the fatigue failure of Q345,the stress-life (S-N) curve of Q345 was collected in high cycle fatigue regime.The initiation and propagation of the cracks of Q345 under cyclic loading was studied by the scanning electron microscope (SEM),and the intrinsic dissipation energy during the fatigue failure of the material was investigated with the help of infrared camera additionally.The fatigue failure of low carbon steel Q345 under high frequency cyclic loading was induced by the micro cracks initiated from ferrites grains.The propagation of the micro cracks was influenced by the micro structure of the material,and apt to propagate along the ferrite grains and the grain boundaries,but could be easily hampered by the presents of pearlite grains in the crack tip.The presence of pearlite grains helped retard crack propagation,which made the fatigue crack tortuous.The variation of the temperature field was not distinct until the stress amplitude was higher than the fatigue limit in the high cycle fatigue regime,therefor,the fatigue limit can be quickly determined based on the temperature variation of the specimen surface under the cyclic loading.Furthermore,a model was established in thermodynamics framework to characterize the intrinsic dissipation energy of the material under high frequency cyclic loading, and the result showed that the relation between intrinsic dissipation energy of unit volume material and limited fatigue life loading presented to be nonlinearly.关键词：Q345;high cycle fatigue;ferrite;crack initiation;intrinsic dissipation energy
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发布时间：2023-11-14
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