最新刊期
卷 50 ， 期 5 ， 2018
- 摘要：Due to the diversity and complexity of mountain flood disasters, the research in key technical fields is still in the initial stage and cannot meet the actual needs of current mountain flood disasters. How to accurately forecast local heavy rainfall, develop a mountain flood monitoring technical system and a localized flood disaster prediction model, refine the dynamic warning indicators of mountain flood disasters, realize the transition from post-disaster relief to pre-disaster prevention, build a risk assessment platform, construct a mountain flood disaster prevention model, and improve mountain flood disaster warning and risk prevention capabilities are the frontiers and hot issues of current mountain flood disaster research, and the practical problems that must be faced in the construction of county-level non-engineering measures for mountain flood disaster prevention which strongly implemented by the country. Focusing on the above issues, the following three key research objectives are summed up. The first one is clarifying the dynamic process of mountain flood disasters, establishing a local rainstorm forecast model and a mountain flood dynamic simulation model. The second one is developing and constructing a multi-element monitoring technology and system for mountain flood, realizing real-time dynamic transmission and release of mountain flood disaster warning and risk assessment information, solving the problem of low accuracy of mountain flood peak flow forecast, short warning period and short-term emergency response. The last one is building a multi-level and multi-target dynamic early-warning and risk assessment platform for mountain flood disasters, refining the disaster prevention and mitigation mode of mountain flood disasters, and demonstrating and promoting that to the public. The following innovations will be achieved through the research. Starting from revealing the formation mechanism of small and medium-scale weather systems that induce flood, short-term near-storm forecasting techniques in mountainous areas is developed, the prediction accuracy of floods and torrential rains in mountainous areas is improved, and the warning period of mountain flood disasters is effectively extended. By researching multi-source remote sensing, radar, micro-nano sensing, intelligent recognition and other mountain rainwater monitoring data acquisition technology and integration of adaptive, practical and stable traditional technologies, a multi-element three-dimensional monitoring technology system for air and land integration is built, technological innovation and extend the mountain flood warning period is realized. Through the analysis of the response process of flood catastrophe process in mountainous areas, the formation process of rainstorm mountain floods and the dynamic mechanism of disasters are clarified, and the dynamic simulation model of mountain flood process based on rainfall prediction and dynamic monitoring of soil water content is constructed to improve the accuracy and reliability of mountain flood warning. Taking the migration process of mountain floods as the entry point, a multi-index warning model for mountain flood disasters is established, real-time dynamic grading warning technology for mountain flood disasters is developed, the warning period of disasters is effectively prolonged, and the aging time for emergency rescue responseis improved.关键词：mountain flood disaster;three-dimensional monitoring;dynamic warning;monitoring and warning information platform
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发布时间：2024-01-10 - 摘要：Acoustic emission (AE) is a transient emission of elastic energy due to the micro cracking of rock under loading and is widely used in the various tests of rock mechanics. By now, both parametric analysis and positioning analysis are the most frequently applied techniques in AE to describe the evolution of micro cracking in rock specimen under loading. However, micro cracking can be divided into two types, i.e. shear cracking and tension cracking. It is still an unexplored problem that whether AE signal can reveal the two cracking types. In order to solve this problem, direct tensile test, Brazilian split test and uniaxial compression test were carried out for the Baoxing marble, Sichuan province, China and all the AE waveform signals are recorded for the tests. The waveforms were further analyzed by Fast Fourier Transformation (FFT) to acquire their peak frequencies. Statistics showed that there exist predominant twin-peak frequencies for all the AE waveforms, which are independent of the testing methods and should reflect the inherent cracking property of the marble. Preliminary mechanical analysis indicated that the twin-peak frequencies are most likely the result of the two cracking types, the lower peak frequency is corresponding to the micro tension cracking, while the higher peak frequency to the micro shear cracking.关键词：marble;acoustic emission;twin-peak frequencies;tension or shear cracking;statistical analysis
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发布时间：2024-01-10 -
Stress Monitoring Techniques Based on the Twin Temperature Compensation Method of Digital CSIRO AI导读
摘要：The stress disturbance of surrounding rock is the direct factor causing the instability and failure of engineering.However, at present, there are no effective methods and techniques to obtain the stress disturbance of surrounding rocks. With the development of deep rock mechanics and mining theory, disturbance stress monitoring has become an important subject. Using the basic theory of CSIRO, this study put forward the twin temperature compensation, developed the stress monitoring techniques, and realized the real-time monitoring of rock mass disturbance stress in the engineering. Considering the great temperature effect of the environment, the unstable power supply and the small collection channel adjustment in the long-term monitoring, the collection system with function of data-connection is developed when the power is cut off and reconnected. Based on the technique of CSIRO cell basic theory and the complete temperature compensation method, the twin temperature compensation method was proposed to collect and measure circuits, and to calibrate the acquisition circuit. Considering the characteristics of stress monitoring environment, the strain gauge cloth plan of the rock mass close to excavating surface was designed, and based on the in-situ stress measurement principle, the measure strain and stress relationship formula was deduced. The improved circuit adjustment is used for measuring the wide range of the measurement channel, and the high precision thermistor is applied to monitor the measured temperature. Using the function of data-connection when the power is cut off, the monitoring data of the discontinuous conventional collecting circuit is overcome, and the measured 20 days of power failure in laboratory tests meet the requirement of measuring accuracy. According to the calibrated data in laboratory, the influence of temperature on the precision of monitoring system is effectively eliminated by the twin temperature compensation method. Aiming at the rock slope and underground chamber, different rock mass disturbance stress long-term monitoring systems are designed and developed. Field application test displays that, the rock mass disturbance stress long-term monitoring system fully reflects the advantages of power cut and twin temperature compensation. The results calculated by the relationship between strain and stress shows that the system can effectively monitor the rock mass disturbance stress.关键词：CSIRO cell;complete temperature compensation;long-term stress monitoring;twin temperature compensation;wireless transmission- 2772
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发布时间：2024-01-10 - 摘要：In order to research the time-dependent deformation and failure properties of damage surrounding rock in the process of excavation and under continuous complex loading, a marble was initially damaged by preloading, and uniaxial aging damage compression test combined with acoustic emission and crack propagation analysis were conducted on original damage marble, comparative study on triaxial creep test between initial damage marble and complete one was executed. The results shows that initial damage marble has no apparent stress peaks under uniaxial aging damage compression, keeping stress constant when near to failure, the ring strain amplitude is much greater than the growth of axial strain. Synchronous acoustic emission monitoring revealed that volumetric strain inflection points is the forerunner of the initial damage damage occurred. Both axial and radial strains of initial damage marble are greater than the complete marble under triaxial creep test. Volumetric strain analysis showed that the initial damage marble appears volumetric dilatation at the beginning of the load. With the increase of confining pressure complete marble still come up shear brittle failure, while the initial damage marble transform from brittle to ductile, finally presented the "X" type conjugate shear ballooning failure. The results strongly suggested that the deformation and failure of damaged marble are different from the complete one, which could also provide important guiding significance for the theoretical analysis and the long-term stability of large cavities.关键词：original damage marble;complete marble;creep experiment;uniaxial compression;time-dependent deformation and failure
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发布时间：2024-01-10 - 摘要：The trend of linearization of land transportation makes the cross-section tunnel inevitable, which is the main accident section of tunnel lining deformation and destruction. Basic parameter like width and dip angle are important for judging the stability of tunnel with fault. The influence of fault dislocation on the cross-section tunnel and its destroy characteristics were researched by combining in-situ monitoring data with numerical simulation. Engineering background was the tunnel located in western China where the basic seismic rupture is Ⅷ degree. The deformation and failure mechanism of the cross-section tunnel where the width of one fault is 20 m, dip angle is 70°and the width of another is 8 m, dip angle is 65° were analyzed based on the measured data. The effects of fault dislocations of different fault widths (10 m, 20 m, 40 m) and dip (65 °, 75 °, 85 °) on the deformation and failure of cross-fault tunnels were further explored by ABAQUS. The influence mechanism of the change of fault width and inclination on the stress, strain and displacement of tunnel lining were revealed. The results showed that under the influence of fault dislocation, the displacement, strain and maximum principal stress of the tunnel lining are less affected by the width of the fault and greatly affected by the fault dip angle. The variation of fault width and dip angle has little effect on the displacement of lining in tunnels across the fault, and changing trend of displacements of dome, arch waist and arch of tunnel are almost the same. The increase of roughness of the structural surface of the surrounding rock decreases the change of displacement but the affect is small. The range of variation of the lining strain of the cross-fault tunnel are less affected by the width and inclination of the fault, but the strain of the tunnel lining gradually increases as the fault width increasing and the dip decreasing. By analyzing the stress characteristics of tunnel linings under different combinations of width and inclination, it was found that the smaller the fault width and the larger the inclination angle, the smaller the affected area of the lining, the more dangerous the tunnel lining. The results are expected to provide reference and guidance for the construction of cross-fault tunnel.关键词：strike-slip fault;tunnel;numerical simulation;in-situ monitoring;scope of influence;influence characteristics
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发布时间：2024-01-10 - 摘要：Disked core is one of the typical performance of high geostress environment in deep engineering area, and its morphological features can reflect the stress intensity and direction to some extent. Relying on the world's deepest (2 400 m) Jinping underground laboratory, field work was carried out and the disked core of different holes and direction were recorded in detail. Based on blue light no-contact LED scanning technology, coordinate data of rupture surface and side in three dimensions were obtained accurately. Detailed morphology of rupture surface and side of core was reconstructed. The shape of disked core and distribution of small rock step were studied through scanning technology. Studies of different type of disked core and theirs fractal dimension on different directional profiles were done. Combined with the numerical model, the stress in different locations of core residual roots which may result in disked core was learned in depth. The results showed that rupture surface has four morphological types, among which small rock step appears at periphery of the core and the rock shows asymmetric thickness. The position of the maximum fractal dimension is the same as the direction of component part of maximum principal stress. Crack propagation can be divided into two situations. The direction of fissure is divided into radial and axial direction. The first mode of destruction produces the core with asymmetrical thickness. The second mode of destruction produces a lamp-like rupture surface and the phenomenon of small rock step appears on periphery of the section. The first mode showed that crack would propagate along the direction of larger geostress under three unequal geostress. The second explored the reason of disked core under combined effect of rotation of drill and geostress. These results reflected the stress mechanism of disked core which will be useful for distinguishing the cause of disked core and identifying the geostress environment.关键词：disked core;fractal dimension;damage;stress mechanism;fracture morphology
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发布时间：2024-01-10 - 摘要：Taking the Jiaojia landslide in Heifangtai area as the geological archetype, we study the deformation and failure characteristics and the mechanism of instability of the slope under the condition of continuous enrichment of groundwater. To simulate the irrigation water quickly recharging into the groundwater through the concentrated channel, we arrange the drainage baffle and temporary water tank at the rear of the centrifugal model. It is designed to reproduce the whole process of deformation and failure of a loess landslide induced by the enrichment of groundwater. Additionally, the real-time monitoring and analysis of the pore water pressure, the change of the earth pressure and the deformation and evolution characteristics of the slope are conducted. The results show that a series of parallel steep tension cracks are induced at the top of the landslide, resulting in the plastic flow of the slope body. It is caused by the softening of the bottom of loess layer, the suffusion erosion and the uneven settlement of the loess slope. The rear wall of this kind of landslide is often of straight shape. The local shear dilatation deformation of the soil caused by the enrichment of groundwater leads to the continuous and sharp increase of the pore water pressure, and ultimately induces the sudden destruction of such landslides, with the failure characteristics similar to high-speed mud flow. Generally speaking, the failure mechanism of the loess landslide induced by the enrichment of groundwater is as follows: traction creep-half slope and trailing edge rupture-locking section progressive slip shear-slip belt piercing and high speed crushing failure.关键词：heifangtai;enrichment of groundwater;centrifuge model test;loess landslide
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发布时间：2024-01-10 -
Experimental Study on Optimization of Flow Concentration Time Parameter in Mountainous Watershed AI导读
摘要：The flood response process under heavy rains is extremely complicated due to steep slopes and variable vegetation coverage in mountainous area and the runoff convergence time in the slope has become a key parameter in flood process simulation. The most widely used flow concentration time formula at present is T = L0.6 n0.6 i–0.4 S –0.3, where T is the flow concentration time, L is the slope length, n is the roughness, i is the effective rainfall intensity and S is the slope. The current studies generallyly use a constant index of rainfall intensity to characterize runoff convergence time while few study considers the slope and vegetation abundance effects. In this work we conducted a series of indoor experiments to study overland flow concentration under different slopes and vegetation coverage conditions. In addition, the variation rules of runoff convergence time parameters are analyzed as well. The results show that the fitting value of rain intensity index represented for the impact of rain intensity on confluence time is about –0.40 on the 45° and 30° slope, which is consistent with frequently-used results of previous research. However, when it comes to the 15 ° and 5 ° slopes, the fitting values of rain intensity index turn into –0.30 and –0.25 respectively, which is slightly larger than that used in the common approaches. The further investigation under conditions with vegetation suggests that rain intensity index changes obviously with the existence of vegetation: while on slopes of 45°, 30°and 15°, the average fitting value of rain intensity index falls to –0.63 when vegetation coverage is 50% or above, significantly less than the theoretical value of –0.4; the mean value of rain intensity index in 20% coverage is about –0.37, almost the same as that in vegetation-free situation. In addition, rain intensity index under 5° slope condition for different vegetation coverage is relatively stable at values between –0.30 and –0.25.关键词：mountainous watershed;artificial rainfall;flow concentration time;rainfall intensity index- 2122
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发布时间：2024-01-10 - 摘要：Membranes play load-transferring roles between steel spiral cases and surrounding concrete in hydroelectric power plants. However, membranes are routinely recognized as linear-elastic materials in current engineering practices. The two most commonly-used membrane materials, i.e. the PU cork and PE foam, are chosen as the current study subjects. Cyclic compression-resilience tests were performed for the two materials with a lever-type consolidometer. The specimens were cut out with cutting rings and the cutting rings provide lateral confinement for the specimens in compression. The maximum pressure is 1.0 MPa with a loading/unloading interval of 0.1 MPa. Each loading/unloading cycle thus consists of 20 gradations. Then the HYPERFOAM model in conjunction with the MULLINS EFFECT option was employed to model the non-linear responses of the two materials in a single loading-unloading cycle based on the ABAQUS code. The specimen was modeled in line with its dimensions with CAX4 axisymmetric solid elements. The UNIAXIAL TEST DATA option was used to obtain the parameters for the HYPERFOAM model directly from the experimental stress-strain data. The strong evidence of the nonlinearity and irreversibility of the compressive behavior of both materials is found. The significant permanent set upon removal of the applied load was observed for both materials. The numerical simulation results fit well with the non-linear responses of the two materials in a single loading-unloading cycle. This study highlights the need to consider the non-linear compressive behavior of membrane materials in the structural design of spiral case structures. The presented simulation procedure based upon the ABAQUS code is practicable for the numerical description of the non-linear compressive behavior of membrane materials. To avoid as far as possible the potential adverse effects of permanent set on structural performance of spiral case structures, it is suggested that membrane materials should undergo sufficient duration and cycles of precompression before field service. The compressive stress-strain curves of membrane materials used for design purposes should be obtained on specimens that have undergone precompression.关键词：spiral case;membrane;nonlinearity;permanent set;compression test;numerical simulation
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发布时间：2024-01-10 - 摘要：Plastic hinge length is an important parameter when the elastic-plastic analysis is carried out on a structure and it has an important influence on the analysis result. The calculation method for the plastic hinge length is mainly the equivalent plastic length method at present and the plastic hinge length is calculated based on the deformation of a structure. While the plastic hinge length has a close relationship with the energy dissipation of a structure, but it is not considered in the equivalent plastic hinge length method. And the plastic hinge length should not be a constant and it should vary with the loading level of a structure. However, the empirical equation used to calculate the plastic hinge length only give the final length of the plastic hinge at present, and do not provide the relationship between the plastic hinge length and the loading level. Thus, it would lead to the reduction of analysis accuracy when this kind of plastic hinge length is adopted. Hence,a plastic hinge length calculation method based on energy dissipation for the reinforced concrete beam-column joint was established, and the influence of the loading level at the beam end on the plastic hinge length was taken into account. Comparison with the analysis result, it was found that the plastic hinge length calculated by the method proposed in this paper agrees well with the range of the plastic development. At last, the relationship between the plastic hinge length and the rotation at the beam end, the reinforcement ratio as well as the effective depth of the cross section was established by means of analysis of the 18 first-grade frame joints.关键词：plastic hinge length;energy dissipation;frame joint;finite element
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发布时间：2024-01-10 - 摘要：The fish collecting and luring facility was the key component of high-dam fish-crossing facilities. The fish-passing efficiency of fish passing facilities was determined by the hydraulic conditions near the inlet. In order to find out the areas where the hydraulic conditions of the inlet of the fish luring facility were satisfied, this paper took a high dam project as an example. According to the related survey results, seven kinds of over-fishing objects were identified, and two kinds of hydraulics conditions that met the requirements of the fish luring inlet were proposed, i.e., the flow range was 0.41~1.00 m/s and the turbulence energy range was 0~0.04 m2/s2. The three-dimensional numerical simulations were conducted by using the standard k-ε turbulence model and the VOF method to track the free surface of the water, simulating 1 km long river downstream of the tailrace tunnel under different operational condition of generator sets during the fish crossing seasons. The simulation aimed to study the turbulence energy and velocity in the river. The numerical model was verified by the physical model test with the model scale of 1:50. The results showed that under different operational conditions of generator sets, there existed an upstream fish passage channels along left side of bank with the turbulence energy less than 0.04 m2/s2 on all conditions, and according to the distribution of flow velocity, the areas of the passage channel meeting the flow rate conditions were respectively 35 732, 22 659 and 12 201 m2, respectively. According to the study, it was found that there was a 1 354 m2 area in the left bank that satisfies both hydraulics conditions of turbulence energy and flow velocity. This area was suitable for arranging the inlet of the fish collecting and luring facility.关键词：high-dam fish-crossing;fish collecting and luring facility;the location of entrance;turbulent numerical simulation;VOF method
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发布时间：2024-01-10 - 摘要：When the flow rate of the tributary is large, the water exchange between main stream and tributary is complex and the interconnections is obvious. In order to explore the characteristics of water temperature stratification in both the main and branch reservoirs and hydrodynamics near the junction, a laterally 2-D water temperature model is developed, which is verified by the water temperature data of the Jinping Ⅰ Reservoir. The simulation shows good agreement with the observation on the vertical water temperature of the main and branch reservoirs and the temperature of discharged water. The water stability coefficient is used to analyze the spatial and temporal characteristics of reservoir temperature, which shows that temperature is stably-stratified in Jinping Ⅰ reservoir. In the fluctuating backwater area of the main reservoir, temperature is well-mixed vertically from June to September, but it is strongly stratified from October to February of the next year. The stratification intensity of the branch reservoir was stronger than that of the main reservoir, and the stratification was gradually weakening in longitudinal direction when approaching the conjuction. Meanwhile, due to the large flow rate of the tributary of Jinping Ⅰ Reservoir, the backward flow from main to branch reservoir shows obvious seasonal changes. The backward flow mainly occurred from June to July with a small Froude number, and the stratification of density current was obvious. During the flood season, with the flow rate and Froude number increasing, the tributary flow is mainly discharged from the upper and middle layers of the reservoir, and there is less backward flow from the main reservoir. During the dry season, owing to the slow velocity and weak stratification in the reservoir, the water exchange between the main and branch reservoir is not obvious. There is no obvious backward flow when the water level falls down.关键词：JinpingⅠ;reservoir water temperature;branch reservoir;stratified density flow
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发布时间：2024-01-10 - 摘要：The static drill rooted nodular pile is a kind of composite pile foundation by inserting the prefabricated nodular pile into the cemented soil. The FEM models of the PGPN (pre-bored grouting planted nodular) pile under compression and tension were established using ABAQUS, and the reliability of the model was verified by comparing the calculated load-displacement curves with the field test results. The axial bearing characteristics of the pile were analyzed by using numerical calculation method. The results show that the bearing characteristics of the PGPN pile under compression are better than that of pile under tension. The nodes along pile shaft can be closely combined with the surrounding cemented soil and that nodes do not bear the load from the soil directly. The cemented soil along the pile shaft only transfers the shear stress between pipe pile and soil. When S=60 mm, the pipe pile tip resistance accounts for 25.8% of the total pile tip resistance for pile under compression, and it accounts for 16.6% of the total pile tip resistance for pile under tension, which is less than the load borne by enlarged cemented soil pile base. When the nodular pile length ratio increases from 0 to 0.375, the ultimate bearing capacity of the pile under compression increases from 3 045 kN to 6 173 kN, and the ultimate bearing capacity of the pile under tension increases from 1 910 kN to 2 441 kN. At the same time, the enlarged pile base resistance increases significantly. However, when the length ratio is increased from 0.375 to 0.625, the ultimate bearing capacity, total pile shaft capacity, pipe pile tip resistance and enlarged pile base resistance are not improved obviously.关键词：pre-bored grouting planted nodular pile;compressive pile;uplift pile;bearing characteristics;nodular pile length ratio
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发布时间：2024-01-10 - 摘要：In order to solve the brick masonry structures’ problems such as the low level of earthquake fortification, non-standard construction and energy-wasting features of wall materials in masonry structures, a new-type assembly autoclaved fly ash brick masonry walls suitable for masonry building was proposed . Firstly, four new-type assembly reinforced concrete blocks including tie column block, ring beam block cleaning block and half brick block were constructed, which have the advantages that they can be used as both wall material and formwork, so as to meet the requirement of no-template construction process. Secondly, the axial compression test of autoclaved fly ash brick short columns was carried out to analyze the failure mode and deformation characteristics and the constitutive parameters such as compressive strength, elastic modulus and stress-strain curves were obtain. Finally, the seismic performance of assembly autoclaved fly ash wall restrained by ring beam and construction column was analyzed by numerical simulation method from three aspects-ultimate bearing capacity, stiffness degradation and displacement ductility. The results showed that this autoclaved fly ash brick’s constitutive relationship has a simple form, and is in good agreement with the test data. The constructional column and ring beam under prefabricated construction measures and cast-in-situ construction measures have influence on the seismic performance of the common brick masonry wall and autoclaved fly ash brick masonry wall. The bearing capacity and stiffness value of the assembly masonry walls and the cast-in-place masonry walls are no different. But the displacement ductility of the assembly masonry walls is better than that of the cast-in-place masonry wall. The stiffness degradation rate and displacement ductility of autoclaved fly ash brick walls are similar to that of the common brick masonry walls. But the bearing capacity of the autoclaved fly ash brick walls is larger than that of the common brick masonry walls. And the assembly autoclaved fly ash brick masonry wall has better seismic performance than the common brick masonry wall. The new-type masonry structure is simple and widely applicable. The research results can solve the main problems faced by masonry structures and are beneficial for autoclaved fly ash to be used in masonry buildings.关键词：new-type assembly reinforced concrete blocks;autoclaved fly ash brick wall;axial compression test;seismic performance;construction technology
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发布时间：2024-01-10 - 摘要：Around the stability problem of homogeneous ground embankment, a new method for non-slice calculation of safety factor and the determination of the critical sliding surface of embankment slope is proposed. The range of three dimensional independent variables which determine the position of circular sliding surface is given. By taking the landslide body as the research object and using it as the integral domain, the non-slice integral limit equilibrium analysis is carried out, and the function expression of the safety factor is deduced. Based on the extreme condition of binary function, the critical sliding surface position can be directly determined without searching by combining finding the minimum value by lowering the dimension with the iterative calculation. The calculation program is compiled and the proposed method and the slice method are compared by two examples of homogeneous soil slope and embankment slope, and the results show that the safety factor of the same sliding surface is 0.68% smaller than that of M-P method; the deviation of the critical sliding surface position obtained by this method and slice method which strictly satisfying the limit equilibrium condition + traditional search method is small; the minimum safety factor of the embankment slope corresponding to the critical sliding surface is 0.87% higher than that of the M-P method + traditional search method; when the limit equilibrium condition is strictly met, the safety factor is not sensitive to the distribution of normal stress at the bottom of slip surface.关键词：homogeneous ground embankment;safety factor;non-slice method;limit equilibrium;critical sliding surface
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发布时间：2024-01-10 - 摘要：Under cyclic loading of the train, the cumulative deformation of the subgrade will be produced, which causes the track irregularity and affects the comfort and safety of the train. In this paper, the cumulative deformation of grading macadam filter for railway subgrade under cyclic loading is studied by large dynamic triaxial tests. The tests were carried out to study the effects of cyclic loading time, confining pressure and cyclic stress ratio on accumulated deformation of grading macadam material. Based on the experimental results, a mathematical model that can reflect the development pattern of the cumulative deformation of grading macadam material is proposed. The tests show: 1) With the increase of cyclic stress ratio, the number of cycles required for the cumulative deformation achieves stability increases gradually. When the cyclic stress ratio is constant, the influence of confining pressure on the number of cycles required for stability is not obvious. The larger the confining pressure is, the larger the final cumulative deformation is. 2) Under the same confining pressure, the larger the cyclic stress ratio is, the more number of cycles are needed for stability and the larger the final cumulative deformation of the grading macadam material is. 3) The larger the confining pressure is, the larger the cumulative deformation is. The larger the cycle stress ratio is, the larger the final cumulative deformation is. When the cyclic stress ratio reaches 0.4, the accumulative deformation law is no longer valid for the stable type. The influence of cyclic loading time, confining pressure and cyclic stress ratio on the cumulative deformation of grading macadam material was obtained through experiments. According to the characteristic of stable type’s cumulative deformation curve, a mathematical formula for predicting the cumulative deformation of grading macadam material is proposed. The rule of stable type’s cumulative deformation of grading macadam filter is revealed. It provides a basis for accurate prediction and control of post-construction settlement of railway subgrade.关键词：graded gravel;large-scale dynamic triaxial test;cyclic loading;cumulative deformation
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发布时间：2024-01-10 - 摘要：Due to the time limitation of creep tests in laboratories, the derived stationary creep rate is usually 5 to 50 times as large as it measured in-situ. Estimation of the long-term stationary creep rate from creep experiments with a short duration is a difficulty issue in salt mechanics. Based on the existing theoretical research on the creep behavior of rock salt, a new constitutive model was proposed to solve the above problem. By combining the advantages of two typical rock salt creep constitutive models of Lubby2 and IfG-G&S, a new Lubby2_Ⅰ-Ⅱ model was developed. This new model can describe the automatic transform of the rock salt behavior from the transient creep into the stationary creep, and be further developed into a creep damage model. Based on the experimental data of the rock salt in Jintan, Jiangsu, the parameters of the above three creep models were determined. In addition, the stationary creep rate and deformation were calculated by using the obtained parameters, and then compared with the experimental data and the convergence of the rock salt cavern in Jintan. The results showed that the Lubby2_Ⅰ-Ⅱ model can not only describe the creep experimental curve of the salt sample well, but also estimate the back analyzed long-term stationary creep rate of the rock salt in Jintan much better and more reliable. This good agreement confirms the reliability of the Lubby2_Ⅰ-Ⅱ model for estimating the long-term stationary creep rate from short-term laboratory experimental data.关键词：creep of rock salt;constitutive model;stationary creep rate;Lubby2;IfG-G&S;Lubby2_Ⅰ-Ⅱ model
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发布时间：2024-01-10 - 摘要：With the growing popularity of cloud storage, it become more and more important to ensure the safety and availability of data. However, data corruption is inevitable. Therefore, to efficiently detect the damaged data is an urgent issue. The LT codes-based cloud storage scheme and the rank-based skip list cloud storage scheme bring high communication and computation cost to data user. To address these problems, a LT code-based two level distributed binary tree cloud storage scheme was proposed in this paper. The scheme improved the efficiency of detecting damaged data blocks by constructing two level distributed binary tree structure of detection data and generating aggregation labels via BLS signature. At the same time, based on the coding property of LT code, the updated data block was used in exclusive or operation. The dynamic update of the data was realized and the data update of the cloud server can be verified, so as to solve the problem of fast and accurate detection of the damaged data and the data dynamic update. It also has a better overall performance. Compared with the original LT code-based detecting damaged data scheme, our experimental results showed that our approach has the same storage cost but lower communication and computational cost. Compared with the RS code-based updating dynamic data scheme, our experimental results showed that our approach has the same storage and communication cost but lower computational cost.关键词：cloud storage;LT code;BLS signature;dynamic update
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发布时间：2024-01-10 -
Research on McEliece and Niederreiter Public-key Cryptosystem Algorithm Based on Quantum BCH Codes AI导读
摘要：In order to resist the security threat of quantum computing attacks to the traditional cryptosystem, a class of McEliece public-keycryptosystems was designed in this paper, based on the fact that no quantum computing algorithm can attack the McEliece public-key cryptosystem within polynomial time. Three types of algorithms for generating quantum BCH codes were presented. The first one was general quantum BCH code generation algorithm, the second one was special symmetric quantum BCH code generation algorithm, and the third one was special asymmetric quantum BCH code generation algorithm. Based on the asymmetric quantum BCH codes generated in this paper, the quantum McEliece public-key cryptosystem and the quantum Niederreiter public-key cryptosystem were designed, and the encryption and decryption processes of the two public-key systems were given in detail. The proposed cryptosystems not only retained the advantages of the post-quantum computation, but also can encrypt and decrypt in quantum states. The basic field has been extended to the arbitrary finite field. The computational complexity theory, data structure and algorithm model of the two public-key cryptosystems were analyzed. The exponential time and space complexity were obtained, and the results of resisting the attacks of Shor and Grover algorithms were also obtained. Finally, with the structural characteristics of quantum BCH codes, a classical Niederreiter signature system was designed, which has the ability of resisting quantum attacks.关键词：CSS construction;quantum BCH codes;public-key cryptosystem on error correcting codes;post-quantum attacks;digital signatures- 3115
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发布时间：2024-01-10 - 摘要：In order to solve the problem of low detection efficiency and low accuracy caused by feature redundancy in current network intrusion detection technology, an improved Grey Wolf Optimizer algorithm integrated with Cuckoo Search was applied to feature selection for network intrusion detection, which aimed at reducing the feature redundancy and improving the performance of network intrusion detection. First, the Levy flight mechanism in the Cuckoo Search algorithm was adopted to disturb the position of three grey wolves with the best fitness values, which avoided the local optimum in the process of searching the optimal solution. Then, the updating mechanism of the Grey Wolf Optimizer algorithm was utilized to update the location information of grey wolves, ensuing these wolves could gather in the direction of their prey. Finally, the location of the grey wolf group was randomly updated according to the predetermined probability value. Hence, the grey wolf group could randomly jump out of the local optimum in the process of continuous approximation of the prey, which improved the global-search ability of the Grey Wolf Optimizer algorithm in feature selection for network intrusion detection. The NSL-KDD dataset in network intrusion detection was used for the verification, and the Grey Wolf Optimizer algorithm, the Cuckoo Search algorithm and the traditional Information Gain algorithm were compared in the experiments from the viewpoint of feature selection. The experimental results showed that, when applying the improved Grey Wolf Optimizer algorithm integrated with Cuckoo Search to feature selection for network intrusion detection, it could achieve good results in both the classification accuracy and the selection of feature subsets. In summary, the improved Grey Wolf Optimizer algorithm integrated with Cuckoo Search had a relatively significant improvement in the ability of global search, and its application in feature selection could effectively improve the performance of network intrusion detection.关键词：network intrusion detection;feature selection;Grey Wolf Optimizer algorithm;Cuckoo Search algorithm
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发布时间：2024-01-10 - 摘要：In order to solve the problem of optimal anchor node layout in indoor positioning system, an anchor node layout method was proposed in this paper by deploying anchor nodes to achieve the minimum positioning error. Based on the multi-measurement positioning algorithm, for the problems of irregular measurement area, difficulty in calculation and so on, a combination of geometric analysis and experimental analysis was used to study the relationship between positioning error and the layout of anchor nodes. The positioning error of double-anchor nodes was accurately calculated by the geometric area relationship, and a new error upper limit estimation method was proposed for node positioning error. This error upper limit reflected the position of the anchor node and the error at the anchor node. The maximum error between any two anchor node layouts was compared and the three-dimensional distribution of errors was presented. Then, in this paper, DUPSO (dissipative uniform search particle swarm optimization) algorithm was introduced, a new multi-anchor node spatial layout optimization algorithm was proposed, and an optimal layout that can minimize the maximum positioning error was found. In order to verify that the algorithm of this paper is applicable to the solution of various rules, irregular environments and the optimal layout of different number of anchor nodes, the optimal layout of anchor nodes and different numbers of anchor nodes in different environments and the layout of different anchor nodes were simulated, and the layout methods of different anchor nodes were compared. The experimental results showed that with the optimal layout of the anchor nodes, the indoor positioning system can obtain higher positioning accuracy. The layout optimization algorithm presented in the paper is universal, feasible and effective in practice.关键词：anchor nodes layout;layout optimization;multi-measurement positioning;error upper limit estimation
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发布时间：2024-01-10 - 摘要：Inter-contact time between different node pairs in opportunistic crowd sensing networks is different, which results in different makespan of tasks when the tasks are taken by different nodes. In order to minimize the average makespan of tasks, an online multi-task assignment algorithm based on prediction (OTAP) was proposed and implemented. Based on the real mobility trace datasets, the distribution of the inter-contact time between nodes was analyzed and a subroutine for discovering the contact law between nodes was developed. Relying on the prediction for inter-contact time between nodes, each time the node responsible for task execution was assigned the most amount of task that could be accomplished before the next contact with the task allocator. Using four different real mobility trace datasets, the performance of OTAP was verified and analyzed by ONE simulator. Experiment results showed that OTAP outperformed the existing algorithm NTA on the average makespan of tasks by 50.49%, 45.34%, 32.71% and 32.23% individually on the four different datasets. Completion ratio of tasks was also improved on two mobility datasets.关键词：opportunistic crowd sensing;multi-task assignment;online algorithm
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发布时间：2024-01-10 - 摘要：In order to prevent from leaving the monitoring area due to the water flow and have restricted mobility, the underwater sensor nodes are usually connected with anchors fixed in the bottom. However, most of previous studies do not consider about this important property. In this paper, a restricted floating localization (RFL) algorithm was proposed based on the mobile characteristics of underwater nodes. A restricted floating node model was firstly established according to the activity law of the underwater nodes under the action of gravity, buoyancy, water impulse, and cable tension. Then, a mobile beacon was used to assist localization. It moves along a straight trajectory in the deployment area, changes its direction and broadcasts its position information over a period of time. The mobile beacon’s position information and the underwater node’s moving rule were used by RFL makes to deduce the position of anchor. In order to reduce the estimation error, the median value was taken by multiple calculations. Then, the node localization process with the assist of anchor and mobile beacon’s position information was completed. The anchor position error, the influence of anchor on node localization and node localization error in RFL algorithm were analyzed by simulation, and the RFL algorithm was compared with the existing algorithms (such as TL, MFLA and LSLS). Simulation results showed the average localization error of RFL was 49.6% of TL, 44.8% of MFLA and 32.1% of LSLS, and the maximum error and minimum error were smaller than TL, MFLA and LSLS. In conclusion, RFL has higher accuracy and stability than the existing algorithms. It is simple, feasible and highly practical.关键词：underwater sensor network;restricted floating;localization;anchor;mobile beacon
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发布时间：2024-01-10 - 摘要：Collaborative filtering algorithm is one of the most widely and successfully used recommendation algorithm. Traditional collaborative filtering algorithm only considers the positive correlation nearest neighbors while ignore the influence of negative correlation nearest neighbors when predicting item rating, which has caused problems like low accuracy and low diversity. In order to resolve these problems, based on positive correlation and negative correlation neighbors a collaborative filtering algorithm is proposed. Firstly, the algorithm computes the similarities and Coefficient of Variation between users and sorts the neighbors according to the similarities which were modified by the Coefficient of Variation. Secondly, the positive nearest neighbors and the negative nearest neighbors are selected based on dynamic weight value α and threshold value β, then item ratings are predicted based on the positive nearest neighbors and the negative nearest neighbors respectively. Finally, the last prediction result is acquired by combining predicting ratings based on the positive nearest neighbors and the negative nearest neighbors with weight. The experiments are tested on the MovieLens with three metrics, and the result show that this approach is achieved great improvement of the accuracy and diversity of recommendation effectively.关键词：collaborative filtering;positive correlation nearest neighbors;negative correlation nearest neighbors
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发布时间：2024-01-10 - 摘要：In order to solve the problem of high delay, low efficiency and complex features extraction in the traditional website phishing detection methods, a hybrid algorithm model using LSTM and the random forest was proposed. The model was composed of URL context feature extraction and hybrid features classification. Firstly, a 128-step deep network structure according to the Recurrent Neural Network was built. The experiment data was collected from the open source community, including phishing URLs and benign URLs. The URL data was encoded to a series of sequences with local features by natural language processing technology. The experiment feature sets were composed of the character context features of the URL sequence extracted by LSTM network and non-character sequence features in the traditional detection methods. Secondly, in order to get the best split point of each feature,phishing URLs recognition model was constructed by Random Fores. Then, the URL characters were chosen as the input source.On the one hand, the character sequence feature dimension of the random forest was reduced. On the other hand, in combination with the non-sequential features, the problem of the single detection rule of LSTM algorithm was avoided. In order to verify the validity of the model, a comparison experiment of our model with random forest algorithm and LSTM algorithm was designed, and the time cost of different LSTM training scale was further analyzed. The experiments demonstrated that the hybrid algorithm model provided an accuracy rate of 98.52%, surpassing single LSTM neural network and a single random forest by 3% and 7%. Meanwhile, when LSTM and hybrid model increased the same magnitude of accuracy, the latter had a smaller time cost.The experiment showed that the hybrid model overcame the efficiency problem of the traditional recognition model in feature extraction and recognition. Thus, the hybrid algorithm was suitable for rapid detection undera large of phishing attacks.关键词：Long short-term memory;recurrent neural networks;random forest;phishing attack detection
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发布时间：2024-01-10 - 摘要：In order to resolve the problem that the existing Retinex algorithm for the image processed could not achieve the enhancement of color and detail at the same time, and the enhancement of detail easily produced halo, noise amplification, color distortion, etc., a haze image enhancement algorithm based on the fusion strategy of Retinex model was proposed. Firstly, the color enhancement was achieved in HSV space, and the reflection component without color distortion was obtained according to the luminance component. Secondly, in the RGB space, the fast bilateral filter was used to preserve the detail of the image. On the basis of obtaining the reflection component, the original part and the color recovery factor were introduced to realize the detail enhancement. Finally, the processed image was weighted and fused in the RGB color space and then the dehazed image was obtained. The haze image which was dehazed by the proposed algorithm and the existing algorithm could obtain different dehazing results. The dehazed image obtained by the proposed algorithm increases the detail information, and there is no obvious color distortion and halo phenomenon, and the information entropy of the processed image is improved. This algorithm has shorter computation time and good operability. According to the experimental results and evaluation criteria, the proposed algorithm could achieve a good effect of detail enhancement on the basis of reducing color distortion.关键词：haze image;Retinex model;color distortion;image enhancement
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发布时间：2024-01-10 - 摘要：In order to solve the problems of rotor over-current and fault-ride-through (FRT) and improve the performance of the doubly-fed induction generator wind power generation system (DFIG-WPGS), the based on variable damper (BVD) strategy was proposed. The negative feedback control based on virtual crowbar resistance and inductance was used in the BVD control method. The virtual variable resistance and inductance circuit was introduced in the DFIG rotor side. The virtual variable resistance was positively related to faulty PCC voltage amplitude. In the BVD control method, a damper was introduced in DFIG rotor current control loop to limit the overcurrent. The BVD control method could effectively control the rotor current in the fault process of DFIG-WPGS.The FRT simulation results of DFIG-WPGS as deep drop fault appeared in PCC voltage were showed as follows. In the BVD control method, the DC boost voltage of the AC excitation power supply was smaller than that of the vector control method. At the moment of PCC voltage drop fault, the overcurrent amplitude of the DFIG rotor was smaller. The amplitude of the rotor current during the fault process was greater, which was more conducive to DFIG power control. The effectiveness of the BVD control method was further validated by the experimental results. While improving the FRT performance of DFIG-WPGS, the BVD control method could not only effectively suppress DC side overvoltage of the AC excitation power supply, but also suppress the DFIG rotor overcurrent. The proposed BVD control method is practical in engineering applications.关键词：doubly-fed induction generator wind power generation system;power generation;wind power;electric power plants;fault-ride-through;based on variable damper
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发布时间：2024-01-10 -
Experimental Study on Mechanical and Physical Properties of New Straw Fiber Solid Concrete Brick AI导读
摘要：In order to take advantage of agricultural residues, a new type of wall material with good comprehensive properties was developed. The mix proportion of straw fiber reinforced concrete was studied. The mechanical and physical properties of new straw fiber solid concrete brick (NSFCB) and general solid concrete brick (GCB) were studied. The compressive strength of straw fiber reinforced concrete was tested. Compression tests on the largest face, flexure tests, heat insulation tests and dry shrinkage tests of solid bricks were respectively carried out. The compressive stress-strain curves and early dry shrinkage ratio-time curves of bricks were analyzed by function fitting. The results showed that the effects of calcium chloride and kaolin on strengthening the strength of straw fiber reinforced concrete were obvious. The compressive strength on the largest face and flexural strength of NSFCB were respectively reduced by 28.5% and 6.8% due to straw fiber. However, the ratio of flexural strength to compression strength of NSFCB was improved 30.5%, and it was better than GCB in the ductility. The improved rational fraction was sufficiently suitable for the compression stress-strain test curves of brick, and adjusted coefficient of determination was almost close to 1. NSFCB was outstanding in heat insulation performance, and the average thermal conductivity was decreased by 18.9%. The drying shrinkage ratio of NSFCB changed little after 7 days, and dry shrinkage performance of NSFCB was good. Early dry shrinkage ration-time test curve of NSFCB that fitted by hyperbolic function possessed a high fitting degree, and there was no significant difference in population distribution.关键词：solid concrete brick;straw fiber;mechanical property;physical property- 2327
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发布时间：2024-01-10 - 摘要：Extremely low cycle fatigue (ELCF) properties of pressure vessel steel Q345R steel with torsional pre-strain were investigated. The fatigue tests were conducted on a MTS 809 servo-hydraulic material testing machine. The tests were run under uniaxial tension-compression loading with total lateral strain control. The ELCF behaviors, such as cyclic stress response characteristics, cyclic stress-strain relationships, and the fatigue life were investigated. The fatigue lives were processed by Weibull double parameters probability function, and the results revealed good linear correlations between the fatigue lives and the confidence level in the double logarithmic coordinate. The strain-life data from the axial tests were used to derive suitable Hollomon and Coffin-Manson parameters for the test material. And the fatigue life prediction models were obtained. Moreover, the relationship between the plastic strain energy and the cycles was calculated and the cyclic toughness was analyzed. The scanning electron microscope (SEM) micrographs revealed that compared to the material without pre-strain, the fracture of the torsional pre-strained material has more cavities, voids and secondary cracks.关键词：Q345R steel;torsional pre-strain;extremely low cycle fatigue(ELCF);fatigue toughness;microcosmic fracture mechanism
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发布时间：2024-01-10 -
Study on Solidification Effect of Heavy Metal by Tailings Cementation and Discharging Technology AI导读
摘要：In order to solve the problems of heavy metal pollution and tailings slope stability, tailings cementation and discharging technology were put forward. The pollutant source and heavy metal migration principle in tailings were analyzed. Results showed that heavy metal is mainly contained in leachate and bleeding water of tailings. Its diffusion depends on convection, molecular diffusion, and mechanical dispersion. The microstructure evolution was studied by electron microscopy and the result showed that the permeability coefficient decrease when cement is used. The cemented tailings soaked experiment was carried out. Results showed that with the increase of cement content, the anti-disintegration of cemented tailings is enhanced. When cement content is larger than 3%, the cemented tailing is no longer disintegration. The compression test also shows that 4% is the criticality content. Heavy metal content determination experimental results show that cement can hardly affect the content of heavy metals in bleeding water, but it can induce a decrease of the heavy metals in leachate water with the increase of cement content. When the cement content exceeds 3%, the amount of heavy metal decreases rapidly which can meet the national emission standards. In conclusion, the migration of heavy metals has a lot to do with the microstructure, permeability and anti-disintegration performance of the emissions. The larger the permeability is and the weaker anti-disintegration performance is, the more heavy metal leaching.关键词：tailings discharge;heavy metal;microstructure;percolate;cement content- 1817
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发布时间：2024-01-10 - 摘要：The study of crack propagation is the key and foundation of pressure vessels’ residual life prediction. In view of security assessment for pressure vessels with immerged cracks, based on the security attenuation path simulation, another calculation method is put forward to predict the residual life. First of all, the iterative calculation based on Paris fatigue crack growth formula is conducted to build the model of geometric correlation change in crack length and depth. Next, this correlation model is used to simulate the security attenuation path track of immersed crack defects in R6 evaluation diagram. The immersed crack change represented by path track can be divided into immersed crack phase and surface crack phase. Then the numerical integration method is adopted to get the residual track segment of security attenuation path in different phases, and the calculation model of immersed crack safety margin is built. This calculation model can show related dynamic safety margins for different sizes of crack defect, and reflect the safety degree of pressure vessels. After building the mechanical model of pressure vessels’ crack defect, the stress intensity factor of special crack point in finite element method is calculated. And weight function method is adopted to get the function formula of the stress intensity factor range K of crack defect. The function formula of fatigue circulation time N is calculate by Paris formula integral. Lastly, according to the model of geometric correlation change in crack length and depth, the fatigue circulation times of immersed cracks is calculated by means of integration.关键词：pressure vessel;buried crack;residual life;safety margin;weight function
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发布时间：2024-01-10 - 摘要：For a single or a small batch CNC turning cutting tool reliability estimation, the traditional reliability estimation methods large sample statistics-based is inefficient. Which are limited for some reasons, such as the difficulty for time-dynamic process description, inaccurate model and non-individual characteristics. In order to improve the precision and credibility of reliability assessment to the cutting tools under the condition of a single or a small batch sample, a new operation reliability estimation method based on singular value decomposition (SVD) transform and support vector space is proposed. Firstly, the vibration signals of the tool holder are acquired during the cutting process. The salient features closely related to the tool wear are extracted by wavelet packet decomposition, energy distribution and time-frequency statistic analysis. The SVD method is employed for the dimensionality reduction of high dimension feature data so as to reduce the computational complexity and the redundant component. Secondly, dimension reduced data are substituted into support vector space model to establish a hyper sphere. Then the relative distance between the sample points and the hyper sphere is calculated and used to describe the degradation of the tool. The semi normal function is further introduced to reflect the mapping relationship of the relative distance and the operation reliability of the tool. Two tools whose wear states are failure and normal are used as evaluation cases respectively. The data before and after dimension reduction are used to established the support vector hyper sphere space for reliability evaluation. The results show that dimensional data reduction can effectively reduce the deformation of the hyper sphere coming from the data dispersion. Finally, the unified data of multiple tools under the uniform failure threshold are used for reliability evaluation of the 1st tool. The results show that the changing trend of the tool's relative distance and running reliability are more obvious and whose volatility is reduced when the training data conditions are sufficient. Especially, at the end of tool wear, it is conducive to the accurate evaluation of the tool service performance. The proposed operational reliability assessment method is free from the dependence of the traditional reliability assessment method on large-sample statistical data, which enriches and develops the reliability evaluation theory.关键词：cutting tool;singular value decomposition;support vector space;operation reliability
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发布时间：2024-01-10 - 摘要：The processing quality of spiral groove on sealing ring has a significant effect on the performance of dry gas seal. In order to obtain high spiral groove processing quality and provide an effective guidance on spiral groove processing technology, Silicon carbide (SiC) ceramic materials and tungsten carbide (WC) cemented carbide materials, which are commonly used in dry gas seals, are selected to study the laser processing technology of spiral groove by LM-20 fiber laser marking machine. The influence of laser power, scanning velocity, filling spacing, repetition frequency, marking number and other parameters on spiral groove depth
${h_{\rm{g}}}$ ${h_{\rm{g}}}$ ${h_{\rm{g}}}$ 关键词：dry gas seal;spiral groove;laser beam machining;processing technology- 2476
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发布时间：2024-01-10 - 摘要：For patients with the upper limb dyskinesia,the rehabilitation exoskeletons are applied in the rehabilitation training of shoulder and elbow joint.Because of the floating property of the glenohumeral joint and the inevitable wear error,it is difficult to keep the axes of the exoskeleton aligning with human axes in real time.Besides,the additional forces/moments caused in the connection interface reduce the training effect and the wear comfort.To eliminate the additional forces/moments,an adaptive rehabilitation exoskeleton with the configuration 4R3P2R is proposed,and relevant inverse position analysis and the gravity balance optimization are completed for the exoskeleton.The configurations PPRRRP and PRRR are adopted in the exoskeleton for the glenohumeral joint and the elbow joint,respectively.The sub-chain PPRRRP and the glenohumeral joint form a 3-DOF human-machine chain with proper DOFs.Similarly,the sub-chain PRRR and the elbow joint form a plane 2-DOF human-machine chain.Based on the exoskeleton configuration,the kinematics model of the human-machine chain is established and the results of the inverse position are solved.The function relationship between the gravitational potential energy of the exoskeleton and the rotation angles of the upper extremity is derived at the any posture.The configuration analysis shows that the flexion/extension of the glenohumeral joint is driven by the second active joint.The driven torque of this active joint is dominated by the gravities of the rest joints.Hence,the gravity balance should be applied to the second active joint.In the given work space of the upper limb,a zero-free-length spring is added into the exoskeleton.The gravity balance model of the spring is established and the relevant parameters are optimized on account of the minimum change of the total potential energy in the exoskeleton.Furthermore,a numerical simulation of the gravity balance model is completed and the results show that the exoskeleton possesses better balance ability.关键词：upper limb rehabilitation;exoskeleton;configuration synthesis;human-machine compatibility;gravity balance
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发布时间：2024-01-10
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