最新刊期
卷 51 ， 期 5 ， 2019
- 摘要：Tibetan Plateau is one of the districts with the most susceptible geo-environments. The district is characterized by its complex geology, strong endogenic and exogenic geological processes as crustal uplift, high in-situ stresses, earthquakes, repeating ground freeze and thaw, intensive precipitation etc., frequent landslides and chained disasters. Landslides have become a serious problem affecting the construction of major engineering project as Tibet-Sichuan railway line and regional hydropower stations, and also menacing the safety of local residents and their living facilities. On October 10th and November 3rd, 2018, landslides, damming the upper reach of Jinsha River at Baige village, are two typical cases. However, for the research of major landslides in Tibetan Plateau, theoretically it’s not quite clear that how they happen and what is their catastrophic mechanism; technically it is still under development that how to effectively recognize and control the disasters in advance. That is, current theory and technique cannot provide efficient support for pre-disaster control and post-disaster relief works. The three-river area (Jinsha River, Lancang River and Nu River) is located on the southeast edge of Tibetan Plateau and is characterized by complex geology, strong endogenic and exogenic geological processes and frequent landslide disasters, making it selected as the key area for investigation. Multidisciplinary endeavor will be used in the investigation, starting from the genesis mechanism of landslides, revealing the evolution of the chained disasters, then suggesting techniques for early recognition and risk control of landslide disasters. Through solving the scientific problems of major landslides in Tibetan Plateau such as the coupling mechanism of endogenic and exogenic processes, the dynamic mechanism of the disaster and its chains, and the technical challenges as remote sensing-based early recognition and monitoring, kinematic process-based risk evaluation and control techniques, the project finally demonstrates the application of the above theory and techniques by typical case histories of disaster reduction.关键词：Tibetan Plateau;landslide;high-speed and long runout landslide;landslide dam;catastrophic mechanism;control measure
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发布时间：2024-01-05 - 摘要：Two adjacent buildings connected by a corridor bridge were retrofitted with the base isolation technology. Considering different seismic wave incidence angles, this paper calculated seismic responses of the buildings under bidirectional earthquakes using the time history analysis method. Earthquake inputs were selected following the GB50011—2010 code for seismic design of buildings, considering both design and rare intensity levels. The isolation layer consisted of lead-rubber bearings (LRB) and ordinary-rubber bearings (LNR). To solve the potential induced by the dynamic characteristic difference of the adjacent buildings, a base-isolation-with-damper (BID) model was adopted with supplemented viscous dampers, seismic responses of which were compared with the traditional base-isolation (BI) model. The research shows that, the seismic wave incidence angle can affect the building collision risk, especially under rare earthquakes. Supplemented dampers can effectively coordinate the asynchronous motion of adjacent buildings and reduce the risk of seismic collision.关键词：base isolation;adjacent building;collision;seismic wave incidence angle;damper
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发布时间：2024-01-05 - 摘要：Floods encountered by a reservoir project during operation and management period are mainly determined by the volume of rainstorm and the previous flood volume of the river. For small watersheds, the latter plays a minor role which can be ignored. For large and medium watersheds, the latter has a greater impact and thus should be paid attention to. Based on the total probability formula the concept of quantificational characterizing this influence of flood frequency distribution of the annual maximum time period flood volume whose condition is previous flood volume is proposed, and the calculation formula is given. Two calculation methods for the manage-flood based on previous flood volume are established, i.e., the direct method and the indirect method. The paper divides the previous flood volume of the river into two states: less water and more water. The direct method is based on the measured flood data, and the conditional distribution of less water and more water is deduced by the principle of single variable frequency calculation principle. The direct method is simple and practical, but it requires more data. In the indirect method, the Copula function is first used to describe the two dimensional joint distribution of the maximum period flood volume of annual (such as annual maximum seven days flood volume) and the previous flood volume of the river. The key of this method is the choice of Copula function. By analyzing the correlation charts of the maximum period flood volume of annual and the previous flood volume of the river, the Clayton–Copula function is selected to deduce the conditional distribution. The indirect method can be used in lack of data, but the shortcoming is that the appropriate Copula function should be selected, and the calculation is more complicated. Finally, the proposed direct method and indirect method were applied to the calculation of channel flood in Zagunao River. The results showed that the overall benefit of the reservoir was higher than that of the original operation that fixed the limits water level of reservoir in flood period.关键词：manage-flood;total probability formula;conditional distribution;previous flood volume
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发布时间：2024-01-05 - 摘要：Breaching of the reservoir dams would pose great threats to the lives and property of people downstream. In China, more than 85% of failed dams are homogeneous cohesive earthen dams, meanwhile, over 50% of the failure caused by overtopping-induced breach. Therefore, it has great significance to deeply study the overtopping breach mechanism of the homogeneous cohesive earthen dam, so as to improve the prediction accuracy of the breach hydrograph, and to provide theoretical and technical support to the emergency rescue following dam breach. The mechanism of the breach evolution in the three-dimensional space for homogeneous cohesive dam due to overtopping failure was studied according to the large scale model tests, after which a numerical model for overtopping-induced dam breach is developed. The forming position of the headcut is determined by the dam configuration and characteristics of the overtopping flow, and the breach flow discharge is calculated using the broad-crested weir formula. Then a backward erosion formula which considers the physical and mechanical properties of the dam materials is adopted to simulate the migration of headcut, while the mechanical analysis is utilized to judge the collapse of the dam body upstream of the headcut. The erosion coefficient of dam material is introduced, and the erosion rate equation of dam material is established by analyzing the flow shear stress and the critical shear stress of dam material. The erosion rate equation is then used to simulate the breach development of dam crest and downstream slope. In addition, the limited equilibrium method is adopted to model the instability of the side slope of breach, and the sliding surface is assumed to be a plane. Moreover, the model can consider incomplete and base erosion, as well as one- and two- sided breach. Three large scale model tests for homogeneous cohesive dam due to overtopping failure with detailed measured data are chosen to validate the proposed model. The comparison of measured and calculated data indicated that the relative errors of peak breach flow, final breach average width, and time to peak are all within ±25%. In addition, the calculated breach hydrograph is in accordance with the measured one. In summary, the case studies verify the rationality of the proposed model.关键词：homogeneous cohesive dam;overtopping;breach mechanism;numerical simulation
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发布时间：2024-01-05 - 摘要：Scouring below the check dam is a doomed consequence after the upstream reservoir is fully deposited by debris. With the boulders crashing and debris flow scouring, apron, auxiliary dam or submerged dike which is commonly used as an erosion-control below the dam is gradually damaged. In the meantime, a scoured pit is formed and expanded, causing exacerbated headward erosion to the foundation of the dam, and easily inducing a toppling failure to the dam. In order to solve this problem, this paper puts forward an application of small caliber steel pipe piles to reinforce the foundation of check dam and prevent it from scouring by debris flow. The principle is that the small caliber steel pipe piles are embedded in the debris deposit at the front side of the dam toe, and the cement slurry is also injected into the pipe piles, to penetrate into the loose debris between the piles and bond the pipe piles and the debris deposit together. Through these steps, a consolidation body with a stronger anti-scour ability is formed, preventing the dam foundation from the headward erosion by debris flow and ensuring its safe running. By means of theoretical analysis and laboratory test, 4 key parameters of embedding location, pile depth, spacing between piles and layout arrangement are determined for the technical method design. Finally, an engineering project is carried out in the Yongjiagou debris flow valley in Mianzhu City, validating that this technical method has a good reinforcing effect. It is hoped that this will provide a reference for the erosion-control design for check dams in the future or for the rehabilitation and reinforcement in the maintenance stage.关键词：debris flow;check dam;scouring below dam;small caliber steel pipe piles;reinforcement
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发布时间：2024-01-05 - 摘要：The prediction of hydrometeorological extreme elements is valuable for preventing natural disasters, controlling and reducing losses. However, the methods for analyzing hydrological frequency are based on a large amount of data, and the studies on hydrological frequency analysis cannot be made in data scarcity regions. This paper builds a Gumbel hydrological frequency analysis model in situations when insufficient data are available, and proposes a new method of parameter estimation (maximum entropy estimation, MEE) for Gumbel distribution. The maximum entropy estimation requires only the lower and upper bounds of hydrology variables. The main steps of the Gumbel hydrological frequency analysis model are as follows: Firstly, the entropy of Gumbel distribution is defined. Secondly, an optimization model is built to estimate the parameters of Gumbel distribution based on the maximum entropy principle. Finally, a K–S goodness of fit test is made for Gumbel distribution model. The experiments of the hydrological frequency analysis of the maximum daily precipitation at the Yellow River were performed to validate the effect of MEE. All the experiments showed that the performance of the maximum entropy estimation was nearly identical to those of the conventional methods of parameter estimation which requires a large amount of data. Furthermore, thirty-three simulations were performed to validate the reliability of MEE in situations when insufficient data were available. The simulations show that the MEE has the following potentials: The performance of three parameter estimation methods are almost identical when the sample size is greater than 25. However, the MEE performs the best and the maximum likelihood estimation performs worst where the sample size is less than 15. Moreover, the MEE is not sensitive to the accuracy of the minimum value but sensitive to that of the maximum value.关键词：insufficient data;distribution entropy;maximum entropy estimation;data range;maximum daily precipitation
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发布时间：2024-01-05 - 摘要：To obtain a thorough understanding of the controlling effect for debris flow mitigation by herringbone water-sediment separation structure (HWSSS), systematic experimental researches was conducted. First, based on the characteristic of HWSSS, theoretical analyses on the substance and energy regulation functions and related evaluating parameters were proposed. The results show that the HWSSS exerts different sieving functions to different grain size classes of the sediments. The coarse sediment (diameter larger than grid opening width D) separation ratio was within the range of 0.8~1.0. The fine sediment (diameter smaller than grid opening width) separation ratio can be well expressed by a power function with the relative grid opening width (D/dfm). The empirical formulas for calculating the total sediment separation rate by single structure (Pt) and multiple structure system (Pt(k)) were both developed. Generally, the separated sediments by HWSSS had a good sorting property, providing a possibility for the construction reuse. The density and velocity of discharged fluent, with smaller average diameter of solid particle and less sediment volume, were decreased. The theoretical calculation formula for the debris flow density after HWSSS regulating was also developed and verified by test data. All results are of great use in optimal design for HWSSS and developing series HWSSS system for debris flow mitigation.关键词：debris flow;check dam;herringbone water-sediment separation structure;grain size distribution;sediment separation rate
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发布时间：2024-01-05 - 摘要：The randomness of hydraulic fracturing on the lining of pressure tunnel threatens the safe operation of the deep buried pressure tunnel. In order to simulate the process of random hydraulic fracturing of the pressure tunnel lining with internal water pressure accurately, regarding concrete lining as two phase medium, using the commercial software ABAQUS and MATLAB, combined with the user material subroutine secondary development, a random hydraulic fracturing model was established with internal water exosmosis of the pressure tunnel lining based on the random assignment theory of mechanical parameters of the cohesive element. The priority task is to improve the constitutive relationship of traditional pore pressure cohesive element through the secondary development of ABAQUS user material subroutine, and the improved cohesive element was put forward to simulate the weak phase such as the initial default in the lining. Weibull distribution was recommended to describe the randomness of the mechanical parameters of the weak phase, while the strong phase of lining was simulated by solid pore pressure element, the mean value of mechanical parameters of the concrete was taken for the strong phase. The seepage-stress-fracturing coupling analysis model of pressure tunnel lining was proposed, which regards internal water pressure as body force. MATLAB was used for pre-processing and post-processing of the model. Taking a large-scale physical model test as an example, the whole process of hydraulic fracturing of the pressure tunnel lining was simulated using this model. The results showed that the lining of the pressure tunnel inevitably cracked and leaked out under high internal water pressure. The crack distribution of lining was sparse and random. The reinforcement stress of cracked lining increased first and then retract, which was closely related to the internal water pressure. Internal water exosmosis improved the stress condition of lining. The proposed model can well simulate the stochastic hydraulic fracturing characteristics of the pressure tunnel lining with internal water pressure well, and the calculation results of fracture distribution and reinforcement stress were in good agreement with the measured results of the model test. A reliable method for the hydraulic fracturing analysis of the pressure tunnel lining was provided.关键词：pore pressure cohesive element;pressure tunnel;hydraulic fracturing;weibull distribution;random assignment;hydro–mechanical coupling
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发布时间：2024-01-05 - 摘要：Landslide dams induced by strong earthquake in gullies are the important material source of debris flow hazards. Due to the intermittence of seasonal rainfall and the particularity of the gully topography, the eroding process of a landslide dam in the gully is obviously different from that of a landslide dam in the river channel. Taking the Yindongzi landslide dam as an example, the eroding characteristics of such dams were investigated. Based on years of on-site geological surveys and theoretical analysis, several results were found as follows: 1) The Yindongzi landslide dam suffered from the confluence erosion on the dam surface and a serial of eroding effects derived from the water flow or debris flow in the breach, including undercut erosion, lateral erosion and headcut erosion. 2) The huge height difference in transverse direction caused the initial breach of the Yindongzi landslide dam to occur on the side of dam and the direction of the lateral erosion induced by the water flow or debris flow in the breach was unidirectional. Under the joint action of this lateral erosion and the undercut erosion, the height of breach slope was gradually increased and the stability of dam was reduced. 3) The difference of soil strength in the upstream and downstream of Yindongzi landslide dam led to the different effects of confluence erosion on the dam surface. As the soil strength in the downstream was relatively low, the dam surface in this area was divided by two large cutting gullies and the integrity of dam was affected. 4) The special material structure of Yindongzi landslide dam led to a slow development of headcut erosion to the upstream and the eroding progress of the dam in downstream and upstream was inconsistent. With the combined action of various erosion effects, the height of breach slope in the downstream of the Yindongzi landslide dam was large and had a poor integrity. It is, therefore, likely to fall into instability and to form a secondary landslide. The secondary landslide will cause a large amount of loose material to enter the newly formed gully, providing a source of material for debris flow activity.关键词：landslide;landslide dam;debris flow;overtopping failure;lateral erosion;undercut erosion;headcut erosion
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发布时间：2024-01-05 - 摘要：In prefabricated shear wall structures, the reliable connection between prefabricated components is the concerning focus. In order to avoid the tedious post-pouring process of horizontal joints during construction, a new type of connection method of precast concrete shear wall horizontal joint is proposed and its seismic performance was studied. The seismic performance of the cast-in-place monolithic shear wall was analyzed by establishing a refined finite element model, and the reliability was verified by comparing with the test results. Hereby the finite element model of the precast specimens with new connection method and the same size cast-in-place integral shear wall was established, and the seismic performance of the precast specimens was analyzed by considering the axial compression ratio and aspect ratio, respectively. The results show that the ultimate bearing capacity of precast concrete shear wall YZ–3 under forward loading is 3.3% higher than that of XJ–3 and the reverse loading is 5.4%, The ultimate load of model YZ–1 is 4.8% higher than that of the model XJ–1. Obviously, the bearing capacity of precast concrete shear wall is higher than that of cast-in-place shear wall under the same condition, and the bearing capacity of the prefabricated shear wall increases more obviously with the increase of the axial compression ratios; with the decrease of aspect ratio, compared with model YZ–2, the ultimate bearing capacity of the models YZ–4 and YZ–5 is increased by 44.2% and 79%, respectively, and the initial stiffness is increased by 18.0% and 47.1%, respectively. Therefore, the bearing capacity of precast concrete shear wall becomes stronger with the decrease of aspect ratio, while the initial stiffness becomes larger gradually, and the ductility of the precast model is better than that of monolithic shear wall, and the seismic performance is basically similar. The new connection method can transfer the stress of steel bar effectively and can be used as a reliable connection way.关键词：precast concrete shear walls;horizontal joint;bearing capacity;bolt connection;axial compression ratio;height-width ratio;seismic performance
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发布时间：2024-01-05 - 摘要：The completely weathered granite is easy to disintegrate and destroy when it meets water, and often induces geological disasters such as water inrush and mud inrush under the engineering disturbance. To realize effective design of grouting reinforcement parameters for completely weathered granite, this paper investigated the law of three factors, namely, grouting pressure, initial water content and clay content, to the anti-disintegration characteristics and compressive strength of completely weathered granite after grouting by response surface method, and the fitting equations were obtained. The results show that the order of grouting pressure, initial water content and clay content on anti-disintegration characteristics and compressive strength is grouting pressure < initial water content < clay content and grouting pressure < clay content < initial water content. There is a positive correlation between grouting pressure and reinforcement effect, but when the grouting pressure reached 1.5 MPa, the increment of compressive strength and anti-disintegration characteristics decreased. The effect of grouting reinforcement increased first and then decreased with the increase of initial water content and clay content, the optimal value of initial water content and clay content is 16% and 24%, respectively. The interaction among grouting pressure, initial water content and clay content was analyzed, and a design criterion for grouting parameters was proposed. According to the initial water content and clay content, completely weathered granite can be divided into the low pressure grouting zone (0.5～1.0 MPa), medium pressure grouting zone (1.0～2.0 MPa) and high pressure grouting zone (2.0～3.0 MPa). The research results can be used to guide the design of grouting reinforcement parameters in this stratum through engineering field verification, and the criterion can be applied to evaluate the effect of grouting reinforcement in this stratum.关键词：completely weathered granite;response surface method;disintegration characteristics;compressive strength;grouting parameter design
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发布时间：2024-01-05 - 摘要：In order to study the mechanical properties of the four-sided simply supported two-way laminated slab with shear keys, the test of the laminated slab was carried out and the feasibility of the finite element simulation method was verified based on the experimental results. By simulating the loading process of the laminated slab with different parameters, the distribution law of shear force of shear key and the influence factors on mechanical properties of laminated slab were analyzed, and the simplified calculation equations of yield bending moment and yield displacement were established. The results showed that a secondary concrete pouring phenomenon existed between the precast base plate and the shear key, between the precast base plate and the cast-in-place concrete. However, it still had a good integrity. Under the vertical uniform load, the shear key showed a brittle failure. Only when the number of shear keys in failure reached a certain extent could the laminated slab be failed. When the joint surface was set to the frictional contact mode, the yield load of the laminated slab increased and the yield displacement decreased with the increase of the number of rows of shear key, the number of columns and the cross-sectional area. When the three factors above increased to a certain extent, the influence was no longer obvious. For the two-way laminated slab with a certain number of shear keys, the strength grade of the concrete of the cast-in-place layer and shear key, and the friction coefficient of joint surface had little influence on the bearing capacity of the laminated slab. The simplified calculation equations established for the yield bending moment and yield displacement of the laminated slab with shear keys can be referenced in engineering.关键词：laminated slab;shear key;four-sided simple support;mechanical properties;influence factor
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发布时间：2024-01-05 - 摘要：Based on the technical principle of gob-side entry retaining formed by advanced roof cutting, this study takes non-pillar mining in deep working face of Chengjiao coal mine as the research background, and comprehensively uses methods of mechanics analysis, numerical calculation and field measurement to investigate the control countermeasures of surrounding rock in deep gob-side entry retaining formed by cutting roof. The roof of gob-side entry retaining induced by cutting roof formed a cantilever beam above the roadway and the pressure on the roadside support body was reduced. The broken expand gangue formed by cutting the roof filled the goaf good, which reduced the displacement of roof sinking by about 50%. It should be noted that the side roof of gob area is the key part for surrounding rock deformation in roof cutting roadway and needs to be intensively supported. Note that the plastic zone of solid coal rib in deep roof cutting roadway is large and the shallow bolt bearing layer can be anchored in the stable coal body in the elastic zone using the anchor coal rib support technology. The pressure of deep roof cutting roadway has a fast speed and is very fierce after mining, leading to the damage of single prop in the roadway. Utilizing the hydraulic supporter with high resistance as the temporary support can resist deep strong dynamic pressure and the impact load. The roadside rigid block gangue experienced compression bending failure due to its inability to adapt to the large deformation. In order to have consistent deformation with the roof and floor, the roadside block gangue in deep roof cutting roadway should achieve a certain vertical sliding deformation. The support technology combining gob-side roof constant resistance large deformation bolt, contractible U section steel block gangue, entry-in hydraulic support and solid coal side anchor rope was proposed, and the industrial field tests were conducted. The field monitoring results show that the surrounding rock of deep gob-side entry retaining formed by cutting roof is basically stable about 290 m behind the working face and all of the indexes after roadway stabilization can meet the operational requirements of next coal mining face.关键词：deep;gob-side entry retaining by cutting roof;advance presplitting roof by shaped charge blasting;control countermeasures;engineering test
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发布时间：2024-01-05 - 摘要：The mechanical properties of the soil-structure interface are of great significance for the study of the interaction system between soil and structure. The properties of surrounding soils and the surface roughness of the structure are important factors affecting the mechanical properties of the contact surface. To investigate the influence of surface roughness of concrete structure on shear behavior of soil-structure interface, a series of large scale direct shear tests were performed for interfaces between different soil types (red clay, sand and gravelly soil) and concrete. The surface roughness was changed by prefabricating different numbers of regular semicircular grooves on the concrete surface, and the surface roughness of the concrete was quantitatively evaluated by sand filling method. Based on the results of tests, the influence of surface roughness on shear stress-shear displacement curves and shear strength parameters of different types of interface were discussed. The test results indicated that three types of shear stress versus shear displacement curves were observed for interface between different soils and concrete, including strain softening for red clay-concrete interface, perfect plasticity for sand-concrete interface and strain hardening for gravelly soil-concrete interface. The shear strength of different types of interface increased obviously with increasing roughness. But the benefit of surface roughness was weakened under a higher normal stress. A clear linear relationship between interfacial shear strength and normal stress was observed under different roughness conditions, indicated that the shear failure of interface agreed well with the Mohr–Coulomb strength criterion. The increasing roughness could remarkably increase the apparent cohesion of interface, but had little influence on internal friction angle of interface.关键词：soil types;roughness;interface;shear failure;large scale direct shear test
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发布时间：2024-01-05 - 摘要：As the real and three-dimension monitoring method, microseismic monitoring can be utilized to evaluate engineering rockmass stability and offer early security warning to people. However, affected by the complicated engineering site conditions, microseismic signals are usually mixed with some noises, which would influence the subsequent microseismic analyses. To reduce noise based on local mean decomposition (LMD) and singular value decomposition (SVD), a new LMD–SVD denoising method was proposed. This new method firstly decomposed noisy microseismic signals by LMD to obtain a series of product functions (PF) from low frequency to high frequency distribution. By calculating the correlation coefficient (CC) between the original signal and each PF component, boundary PF component between the effective signal and noise was obtained. The PF component (components) before the boundary component is(are) eliminated to achieve the first step of noise reduction. Subsequently, in order to further reduce residual noise existing in the LMD decomposition results, SVD method was introduced and corresponding singular value order was determined by utilizing percent of contribution to total energy (PCTE) to complete the second step of noise reduction. Final denoised signal would be obtained through the above denoised processes. In the simulation experiments of this study, empirical mode decomposition (EMD), LMD, LMD–SVD were respectively taken to reduce noise existing in a noisy Ricker wavelet. The results of signal-to-noise ratio (SNR), waveform and spectrogram before and after noise reduction presented that LMD–SVD was a better method for noise reduction compared with other two methods. In addition, the proposed LMD–SVD method was applied to denoise noisy microseismic signals collected from microseismic monitoring system of the underground powerhouse on the left bank of Baihetan Hydropower Station. The denoised results show that LMD–SVD can effectively remove high frequency noise existing in the microseismic signals and facilitate subsequent microseismic analysis works.关键词：microseismic signal denoising;local mean decomposition;singular value decomposition;correlation coefficient
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发布时间：2024-01-05 - 摘要：The relationship between stage and discharge caused by flood fluctuation shows a clear loop curve and most of the current researches are based on plain rivers. Due to larger river-bed slope, bigger size of sediment the difficult flow characteristics affected by many factors, some assumptions used are inconsistent so that the result is not very accurate. Therefore, this paper, considering the differences of river bed morphology and sediment particle size between mountain rivers and flat rivers, introduces new parameters of equations about river grade and sediment size and reintroduces the new stage–discharge relationship based on Saint–Venant equations. The results of examples application show this method can better fit the actual data of stage–discharge of the cross-sections in mountain rivers and plain rivers. When adapting the line, this method only need to make some corrections to the parameters according to the actual situation, which is more convenient to modify and has good practicality, high precision and strong adaptability.关键词：mountain rivers;stage–discharge relationship;loop-rating curve;diffusion wave;mathematical model
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发布时间：2024-01-05 - 摘要：Helical gear is an important element of mechanical equipment. The accurate calculation of meshing stiffness and the stability analysis of the transmission system have important practical significance. Based on the change rule of tooth contact line of helical gear, the change law of mesh stiffness about single gear pair in unit length and the ISO calculation method of mesh stiffness, a kind of approximate method was put forward for calculating the mesh stiffness of helical gear and used to study effects of the structural parameters of helical gear on mesh stiffness fluctuation. A dynamic model of helical gear transmission which included the change rule of mesh stiffness obtained from the analysis was established and solved by using multi-scale method. The influence of the loads and meshing stiffness fluctuation of helical gear on the primary resonance was analyzed. The results showed that the calculation method of meshing stiffness could be used to determine the meshing stiffness fluctuation rule of helical gear quickly and accurately. By applying the meshing stiffness fluctuation obtained to study the dynamic characteristics of helical gear transmission, some more accurate variation rules of primary resonance caused by meshing stiffness fluctuations and load fluctuation were gained. When other parameters remained unchanged, the increase of the static load and meshing stiffness fluctuate could improve the primary resonance stability accordingly. But larger static loads resulted in higher primary resonant frequencies and very small meshing stiffness fluctuations could cause the primary resonance unstable under the condition of high-frequency excitation. The amplitude of primary resonance increased with the load fluctuation and the stability of helical gear transmission deteriorates. Through the proposed calculation method of meshing stiffness and the dynamic analysis of helical gear transmission by multi-scale method, the general characteristics of helical gear transmission had been revealed more universally.关键词：mesh stiffness;helical gear;primary resonance;nonlinear
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发布时间：2024-01-05 - 摘要：The ability of mechanical equipment to work normally in the expected service environment is usually reflected by operational reliability. Traditional methods for evaluating operational reliability of mechanical equipment are often based on a large number of historical samples. However, traditional methods are difficult to accurately evaluate the actual operation status of mechanical equipment without historical samples and its future performance degradation trend effectively. The normalized EEMD information entropy and relevance vector machine with combined kernel function were constructed to evaluate and predict the operation reliability of mechanical equipment. Firstly, the vibration signals of mechanical equipment during the operation process were collected, and the vibration signals were decomposed by the ensemble empirical mode decomposition method (EEMD). Several intrinsic mode functions (IMF) components were obtained, and their relative energy and normalized EEMD information entropy were calculated to construct characteristic indicators to characterize the operation status of mechanical equipment. Secondly, the operational samples of mechanical equipment were used to train the relevance vector machine, and particle swarm optimization algorithm was used to optimize the weights and kernel function parameters in the RVM. Finally, the constructed operation state characteristic indicators were input into the relevant vector machine to predict the performance degradation trend for mechanical equipment. The results of evaluation and prediction of rolling bearing operation state showed that the proposed method can fully extract the characteristic information reflecting rolling bearing operation state, and the prediction method of operation reliability also fully takes into account the historical regularity of the rolling bearing performance degradation. Compared with single kernel function relevance vector machine and other intelligent prediction models, the combined kernel relevant vector machine improves the accuracy and robustness of rolling bearing operation state prediction, and provides a novel mode for mechanical equipment operation state evaluation and performance degradation prediction in engineering application.关键词：combined kernel;relevance vector machine;information entropy;operation condition;mechanical equipment
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发布时间：2024-01-05 - 摘要：Tensegrity mechanisms are new type mechanism consist of a set of compressive components (rigid rods) and continuous tensile components (ties). The benefits of tensegrity mechanisms in comparison with conventional ones include low mass, small inertia force, good flexibility and foldable. According to configuration principle of tensegrity structure, a 4–SPS type tensegrity mechanism under actuated was designed, which consist of a top platform, a base one and 4 elastic chains (springs) and 4 rigid driven chains (prismatic actuators). The vector equations were deduced from position relation of the mechanism, and the static equilibrium equation also was obtained include the quality of the rigid components. Due to the existence of unconstrained degree of freedom of the mechanism under actuated, analysis of this type of mechanism was more challenging and complicated in comparison with conventional mechanism. Positional positive and negative solution were analyzed through simultaneous minimum potential energy equation and position equation, and the numerical solutions of which also were acquired by using vriable step search method. Finally, velocity and acceleration equations of the mechanism were deduced under the condition of equilibrium, also, motion graphs are drew according to the equations.关键词：tensegrity;parallel mechanism;kinematic;static equilibrium
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发布时间：2024-01-05 - 摘要：Pipelines will be seriously corroded by crude oil and natural gas in the long-term transportation. AC potential drop technology can be used to monitor the inner wall of oil or gas pipelines. The core of the method is based on the distribution of alternating current meeting with skin effect in the metal component. Different crack defects have different effects on the distribution of osmotic current field and change the measured voltage value. Therefore, corrosion can be monitored by monitoring the change of voltage value. However, this monitoring method can only monitor the crack defects in the fixed direction, and the accuracy of solving a crack at random position is low. The Angle between the direction of electrode wire and crack should be greater than 45°. An innovative method was proposed called multidirectional AC potential drop, which made the angle between the direction of crack and electrode wire from 0°～90.0° to 67.5°～90.0°. The simulation in finite element analysis software and experimental results showed that the values of the ratio of voltage were exponential along with crack depths by using multidirectional AC potential drop technology. The proposed method can more accurately monitor the random crack corrosion, which enriches and develops the inspection of pipelines.关键词：AC potential drop technology;skin effect;multidirectional current;crack detection
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发布时间：2024-01-05 -
Group Secret Key Extraction Scheme Based on Received Signal Strength in Cognitive Radio Networks AI导读
摘要：To secure the communications in cognitive radio networks (CRNs), a group secret key extraction scheme based on received signal strength (RSS) was proposed. This scheme employed relay nodes to extract a group secret key in the chain topology. Be more specific, nodes other than the head and the tail were considered as relay nodes, of which the RSS measurement of each adjacent pair was extracted. Then, each RSS measurement was quantified referring to predetermined thresholds to ensure the randomness of the generated key which was multiple RSS measurements related. Finally, the gray code was utilized to encode the quantified RSS measurements. In this paper, MATLAB was used to simulate the process of users establishing group secret key in Gaussian channel. By setting different levels of noise, the signal-to-noise ratio (SNR) varied from 0 dB to 30 dB. The results showed that the bit inconsistency rate increased with the number of nodes in the group and decreased with the increase of SNR. At the same time, the key generation rate of the proposed scheme under different conditions was analyzed by numerical analysis. It showed that the group secret key rate varied with the number of nodes in the group and SNR, which was opposite to the bit inconsistency rate. The proposed scheme outperforms contemporary ones with higher extraction efficiency and a lower communication cost as well.关键词：cognitive radio networks;received signal strength;group secret key- 2294
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发布时间：2024-01-05 - 摘要：Large scale 3D scene reconstructions are usually realized via merging local depth maps with heavy computational burden, so that the accuracy of local 3D data will affect the accuracy and the efficiency of scene reconstruction. To tackle this problem, in this paper, an image selection method to improve the computation efficiency and accuracy of 3D reconstruction was proposed. To improve the efficiency, a reference image selection method based on bit operation was proposed. Specially, a minimum calibrated images subset covering all three-dimensional points of the scene was selected as the reference image set, then an evaluation function of neighbor image selection was defined according to the scale evaluation factor, the angle between two camera main optical axes and the angle between 3D points and camera main optical axes. In implementation of the neighbor image selection algorithm, the method firstly removed most of the neighbor image candidates by the overlapping rate of reference image and candidates, and then sorted the remaining candidates by the evaluation indicator with descending order. Effective reference images selection can greatly reduce the amount of depth map calculation in multi-view 3D reconstruction of large scene, while effective adjacent images selection took into account the reconstruction accuracy and integrity. The proposed method was compared with another two methods and the COLMAP algorithm on two public data sets with ground truth and two data sets collected from real outdoor scenes. Experimental results demonstrated that the proposed method saved computing time by 53%～59%, improved the completeness by 4%～6% and the accuracy by 4%～7% in contrast to the other two image selection methods. Besides, the proposed method saved computing time more than 16%, improved the completeness by 3% and the accuracy about 2.7% in contrast to the state-of-the-art COLMAP method. Experimental results on multiple data sets demonstrated the effectiveness of the proposed method.关键词：multi-view 3D reconstruction;depth map;image selection;reconstruction accuracy;computational efficiency
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发布时间：2024-01-05 - 摘要：To achieve the engineering application of the low temperature denitration catalyst, it is necessary to study how to futher improve its activity and sulfur resistance. Activated carbon supported Ce–Mn catalyst with Sn doping was prepared. The effect of Sn on the structure and properties of catalyst was studied. The influence of structural property change on denitration performance and sulfur resistance of catalyst was studied. The crystalline phase structure, surface element composition, texture property, surface acidity and redox property of catalyst were characterized by means of XRD, XPS, N2 adsorption–desorption, NH3–TPD and H2–TPR techniques respectively. The activity and sulfur–resistance of catalyst for NH3 selective catalytic reduction was investigated in fixed bed reactor. The result showed that the structure and properties of catalyst was significantly affected by the doping of Sn. The doped Sn increased the crystallinity and reduced the specific surface area which led to decreased dispersity of active components. The reduction of adsorption oxygen and Ce3+ content was also reduced which induced the decline of redox performance. The number of medium-strong acid sites decreased while strong acid sites increased. The low temperature activity of the catalyst reduced, but the sulfur resistance was improved significantly. With the increase of Sn content from 0 to 1.5%, the light-off temperature for the conversion of NO raised 135 ℃, the NO conversion descended 20%～40% in whole range of test temperature. The activity of catalyst with 0.5% Sn doping was only decreased 13% after reaction 340 minutes at 150 ℃ and 100 μL/L SO2, which was significantly lower than catalyst without Sn. While at 210 ℃, the activity increased slightly with increase of reaction time. The reduction of low temperature activity of the catalyst was related to the decrease of redox property and dispersity of the active component, while the improvement of sulfur resistance was related to the increase of surface acidity.关键词：activated carbon;catalyst;Sn doping;performanc
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发布时间：2024-01-05 - 摘要：The composite condensate expansion materials is a new type of mine filling material. The effects of the admixture dosage on the compressive strength, non-solid phase volume ratio, expansion ratio and strength loss rate of the multiphase condensate expansion filling materials were studied by single factor test and random test method. Based on a large number of test data obtained by random test method, the effect of material properties under multi-factor combined action was studied by 3D visual model analysis. Polynomial approximation method was used to establish a multivariate nonlinear regression model corresponding to different types of filling performance. The results showed that with the increase of SAP content, the compressive strength and water resistance of the filling body decreased gradually. With the increase of GPA content, the strength of the filling body decreased gradually, the expansion rate of the filling slurry increased significantly, and the water resistance of the filling body decreased gradually. The content of GPA has the greatest influence on the 3 d compressive strength; the volume fraction of non-solid phase is mainly affected by the content of SAP, and the expansion rate of multi-phase condensate expansion material is mainly affected by the content of GPA. The strength loss rate is mainly affected by HA content.关键词：hemihydrate phosphogypsum;random test;composite admixture;multivariate nonlinear regression analysis;3D data visualization
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发布时间：2024-01-05 - 摘要：In order to realize the recycling of municipal solid waste glass, the various strengths and deformation indexes of C30 and C50 strength grades waste glass powder concrete (WGPC) were studied according to the standard test method by replacing cement with waste glass powder in different dosages. It showed that when the amount of waste glass powder was between 25%～30%, the decrease in compressive strength of C30WGPC was the largest, reaching 21.7%. The replacement of cement by C30 WGPC could be within 0～25% and the optimal blending amount of C50 WGPC could be greater than 25%. The waste glass powder incorporation improved the concrete brittleness and the concrete brittleness would increase with the strength grade increasing. The relationship between axial compression strength and cubic compressive strength of C50WGPC could be used to approximately calculate by the conversion of ordinary concrete. In addition, the WGPC elastic modulus formula was suitable for calculating the ordinary concrete elastic modulus and the Poisson ratio of WGPC was not much different from the ordinary concrete. The test results show that the waste glass powder can be used to test the concrete with higher strength grade and provide the basic parameters for the WGPC engineering application.关键词：WGPC;compressive strength;splitting tensile strength;elastic modulus;Poisson ratio
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发布时间：2024-01-05
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