• ISSN 0258-2724
  • CN 51-1277/U
  • EI Compendex
  • Scopus
  • Indexed by Core Journals of China, Chinese S&T Journal Citation Reports
  • Chinese S&T Journal Citation Reports
  • Chinese Science Citation Database

2020 Vol. 55, No. 2

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Smoothness Estimation of Super-large Bridges in Railway Line Based on Fitting Railway Plane and Profile
WANG Ping, GAO Tianci, WANG Xin, YANG Cuiping, WANG Yuan
2020, 55(2): 231-237, 272. doi: 10.3969/j.issn.0258-2724.20180295
[Abstract](721) [FullText HTML] (513) PDF 1112KB(83)
Abstract:
Reasonable evaluation of the flexural deformation of long-span bridges is the basic precondition of guaranteeing service stability and comfort of trains. Considering the limitations of the current evaluation index, the deflection-span ratio, such as the effects of deflection on railway plane and profile being ignored, a new methodology that uses the least-square method to fit the deformation curve into the standard railway line in plane and profile first and then evaluates the smoothness of railway super-large bridge by the Code for Design of Railway Line, was proposed. This method was applied to the engineering example of Wufeng Mountain super-large bridge for validation. Results show that under the worst load conditions of system vibration, the minimum radii of the vertical curve and plane circular curve are 29.3 km and 54 km, respectively, which conform to specification requirements. Setting up a vertical arch can neutralize the vertical deformation to some extent, and is beneficial to keep the regularity of track. The proposed method could evaluate the deformation of bridges properly from the aspect of railway smoothness and is applicable to instruct the design of long-span bridges and ensure the safety of railway operation.
Static Behavior and Key Influencing Factors of Double-Cable Suspension Bridge
ZHANG Qinghua, ZHANG Ying, CHENG Zhenyu, KANG Jiping, HE Jing
2020, 55(2): 238-246. doi: 10.3969/j.issn.0258-2724.20170908
[Abstract](674) [FullText HTML] (341) PDF 1133KB(24)
Abstract:
Double-cable suspension bridge system is one of structural systems suitable for long-span multi-tower suspension bridges. In order to study the mechanical properties of the bridge system, the finite element method is used to analyze its static behavior and the effect of key design parameters. First, the main design parameters of a double-cable multi-tower suspension bridge are determined according to a typical single-cable multi-tower suspension bridge, and finite element models of the two types of suspension bridges are established. Based on the models, the vertical stiffness values of the two suspension bridges are then compared. Finally, the influence of key design parameters such as the ratio of side to main span, stiffness of middle tower, dead load distribution ratio, and rise-span ratio on the total unbalanced force of the main cable, vertical displacement at top tower, and the maximum mid-span deflections of the main beam are studied. The results show that compared with the single-cable bridge, the double-cable bridge can effectively improve the vertical stiffness of the bridge system and greatly reduce the total unbalanced force of the main cable. Reducing the ratio of side to main span has little effect on the vertical stiffness of the double-cable bridge and the total unbalanced force of the main cable. On the contrary, increasing the middle tower stiffness can improve the vertical stiffness of the double-cable bridge significantly, but simultaneously resulting in a large increase in the unbalanced force of the main cable. When the dead load distribution ratio ranges from 1.0 to 2.0, the displacement at middle tower top and mid-span deflections of main beams are smaller in the double-cable bridge. In addition, decreasing the rise-span ratio of top cable or increasing the rise-span ratio of bottom cable can significantly improve the vertical stiffness of the double cable bridge, and thus effectively reduce the maximum mid-span deflections of the main beam and the displacement at the middle tower top.
Direct Identification of Coefficients of Rational Function Approximation for Self-Excited Aerodynamic Forces
WU Bo, WANG Qi, LIAO Haili, LI Yulin
2020, 55(2): 247-255. doi: 10.3969/j.issn.0258-2724.20180593
[Abstract](592) [FullText HTML] (362) PDF 840KB(27)
Abstract:
The identification of coefficients of a rational function is the precondition for flutter analysis of long-span bridges based on rational function approximation. The number of lag terms of rational functions has a large influence on the identification accuracy. The coefficient identification of rational function approximation in existing methods are generally based on one lag term, which easily causes distortion problems in both aerodynamic description and coefficients and thus further affects the accuracy of flutter predictions. This paper proposes a direct identification algorithm of rational function coefficients by considering multiple lag terms, according to the principle that the self-excited aerodynamic force of sinusoidal signals is equal to the rational function in time domain and using the least square fitting method.. Then, the forced vibration test of a thin flat plate with harmonic vibration is carried out to characterize the self-excited forces, and the proposed algorithm is used to identify the coefficients of the rational function with different number of lag terms. Influences of the number of lag terms on the accuracy of self-excited aerodynamic force reconstruction and critical flutter wind speed calculation are analyzed. The accuracy of the algorithm is validated by comparing the critical wind speeds obtained from free vibration wind tunnel tests with those from flutter analysis using the identified coefficients. Results show that the calculated values of critical flutter wind speeds are in good agreement with the tested values, which verifies the effectiveness and accuracy of the proposed algorithm. Compared with the existing identification methods of rational function coefficients, the proposed identification method takes both efficiency and accuracy into account, and can be widely used in coefficient identification of rational function approximation for self-excited forces of bridge girders.
Influence of Thermal Conductivity on Temporal and Spatial Distributions of Temperature Filed in Cold Region Tunnel
SUN Keguo, LI Si, XU Weiping, XIAO Zhifei, LI Haobo, XU Yuping
2020, 55(2): 256-264, 289. doi: 10.3969/j.issn.0258-2724.20180530
[Abstract](806) [FullText HTML] (615) PDF 2018KB(22)
Abstract:
The temperature field of a tunnel in cold region is crucial to its antifreezing design, and the thermal conductivity of the supporting structure and surrounding rock has a significant effect on the temporal and spatial distributions of the temperature field. Taking a highway tunnel in cold region as the prototype calculation model, methodologies including theoretical derivation, field measurement and numerical simulation are used to study the influence of thermal conductivity on the temporal and spatial distributions of tunnel temperature filed. Results show as follows: At any time the temperature of each point in the variable temperature circle decreases with the growth of thermal conductivity of the supporting structure; and the larger the thermal conductivity of the supporting structure, the smaller the temperature reduction rate at the same position. At any time the temperature of supporting structure increases with the growth of thermal conductivity of surrounding rock, but the temperature variation of surrounding rock is characterized by regionalization. That is, the surrounding rock can be divided into zones Ι and Ⅱ. As the thermal conductivity of the surrounding rock increases, the temperature in zone Ι increases, while the temperature in zone Ⅱ decreases. What’s more, the slope and intercept of the boundaries between zones Ι and Ⅱ are greater at a larger time scale. The research results can provide references for the antifreezing design and route selection of tunnels in cold regions.
Lining and Surrounding Rock in Non-circular Tunnel Based on Complex Variable Method
LI Yansong, CHEN Shougen
2020, 55(2): 265-272. doi: 10.3969/j.issn.0258-2724.20180243
[Abstract](627) [FullText HTML] (331) PDF 1257KB(26)
Abstract:
A complex variable method is presented of stress and displacement problems for a non-circular deep tunnel with a certain given boundary conditions at infinity. Firstly, in order to overcome the complex problems caused by non-circular geometric configurations and the lining supports, optimal design method are used to determine coefficients of the conformal mapping function. Secondly, The problem of the multiply connected region is overcome by Power series complex function method, which determine stress and displacement within tunnel lining and within surrounding rock. The coefficients in the stress functions are determined by complex variable method. Finally, the complex variable method is validated by FLAC finite difference software through an example. Both the complex variable method and the numerical simulation obtain the similar results of the stress concentration and the minimum radial displacement occurs at a similar place of tunnel. It is demonstrated that the complex variable complex variable method is reliable and reasonable. Under deep buried conditions, the complex variable method does not need to establish models and mesh according to different burial depth and working conditions. Only mapping function and boundary conditions are required for the calculation. The complex variable method overcomes the problems of inaccuracy and slow calculation caused by meshing dimension and other problems in software calculation. And it also provides another way for solving non-circular tunnel excavation problems in the range of elasticity in a fast and accurate way.
Meso-mechanical Effect of Track Slab Rebar Corrosion
SU Chengguang, LIU Dan, ZHAO Pingrui, LIU Xueyi
2020, 55(2): 273-281, 289. doi: 10.3969/j.issn.0258-2724.20190321
[Abstract](615) [FullText HTML] (280) PDF 2141KB(11)
Abstract:
To explore the effect of rebar corrosion on double-block ballastless track slab concretes, a meso-scale mechanical model of track slab concretes was built to study the mechanical properties and damage modes of the slabs with different rebar diameters, spacing and cover thicknesses, the effect of train and temperature loads on the mechanical property of reinforced concrete track slabs with corrosion was analyzed. The results show that the cracking mode of track slabs induced by rebar corrosion mainly depends on the thickness of rebar cover but rarely relies on the diameter or spacing of rebar. In the event the internal cracks of the slabs connect together, the expansion displacement of rebar increases with the increase of the rebar spacing. When the cover thickness is 60 mm and the rebar spacing is 120 mm, the rebar corrosion displacement of 61.2 μm would result in the internal coalescence cracks. The train load has little effect on the slabs with corrosion crack, and may make the stress on the slabs tend to be uniform. The temperature cooling of 30 °C and the negative temperature gradient may cause the further significant increase of the tension damages of slabs with corrosion, at the same time it may cause the coalescence cracks through along the horizontal and vertical directions of slabs. The temperature rise of 30 °C and the positive temperature gradient barely have effect on the damages of the track slabs with corrosion.
Vehicle-Guideway Coupling Vibration Comparative Analysis for Maglev Vehicles While Standing Still
WANG Keren, LUO Shihui, MA Weihua, CHEN Xiaohao, ZOU Ruiming
2020, 55(2): 282-289. doi: 10.3969/j.issn.0258-2724.20170891
[Abstract](620) [FullText HTML] (340) PDF 1250KB(27)
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In order to study the vehicle-guideway coupling vibration characteristics of the two kinds of low-speed maglev trains with three suspension frame and the second suspension installed in the end and middle of the suspension frame respectively, the vertical vehicle-guideway coupling vibration dynamic model was established according to Newton’s second law. Firstly, the coupling relationship between the vehicle body and the suspension frame of the two kinds of maglev trains was analyzed through the dynamic equation, then the dynamic characteristics of the two kinds of maglev trains were studied respectively when the initial angular displacement of 0.09 degrees was existed, and finally the difference of the work of the second suspension on the suspension frame of the two kinds of maglev trains was studied, respectively. The results show that compared with the maglev train with the secondary suspension installed at the end of the suspension frame, the maglev train with the secondary suspension installed at the middle of the suspension frame has less coupling between the vehicle body and the suspension frame. When there is an initial angular displacement of 0.09 degree in the suspension frames of the two kinds of maglev trains, the maglev train with the secondary suspension installed at the middle of the suspension frame has smaller vehicle body displacement, vertical vibration acceleration of the vehicle body, vibration displacement of the track beam and suspension gap fluctuation compared with the maglev train with the secondary suspension installed at the end of the suspension frame. The maximum value of vehicle body displacement, vertical vibration acceleration of the vehicle body, vibration displacement of the track beam and suspension gap fluctuation of the maglev train with the secondary suspension installed at the middle of the suspension frame is about 0.005 mm, 0.004 m/s2, 0.004 mm and 0.005 mm respectively, and the maglev train with the secondary suspension installed at the end of the suspension frame is about 0.023 mm, 0.02 m/s2, 0.021 mm and 0.02 mm respectively. Compared with the maglev train with the secondary suspension installed at the end of the suspension frame, the maglev train with the secondary suspension installed at the middle of the suspension frame has less work of the secondary air spring on the suspension frame, only 50% of the former.
Functional Relationships between Sound Powers Radiated from Noise Sources of High-Speed Train and Its Speed
ZHU Ziwei, LI Muxiao, CHENG Gong, SHENG Xiaozhen
2020, 55(2): 290-298. doi: 10.3969/j.issn.0258-2724.20180023
[Abstract](812) [FullText HTML] (336) PDF 1478KB(42)
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To solve the problem that the existing logarithm empirical formula cannot satisfactorily fit the relationship between the sources contribution rate and the speed, the microphone array was used to identify the external sound sources of a high-speed train at different speeds. Dividing the train surface into sub-regions with the location of the known main noise sources, the relationship between sound power level and its contribution rate of main noise sources sub-region and train speed were analyzed quantitatively. Then, according to the characteristic of different kinds of noise sound powers increment rate with speed, the new fitting formula was established based on the existing logarithm empirical formula. Finally, the new formula was verified on the noise data of different train. The results show that when the train runs at 350 km/h, radiated noise from the lower region of railway system dominate the total radiated noise, which account for more than 70%. The sound power of the rising pantograph region is significant in the local region as well, which account for more than 50%. With the speed increase, the contribution rate of lower region decrease and the pantograph regions increase, and each regions change rapidly first and then slowly, finally become stable. Using the advanced fitting method, the fitting degrees of sound power level and sound power contribution rate with speed in the source regions of the train are all above 0.9.
Seismic Behavior of Energy-Saving Block & Invisible Multi-ribbed Frame Composite Walls with Different Opening Positions
LI Shengcai, LIN Qiang, GUO Lin
2020, 55(2): 299-309. doi: 10.3969/j.issn.0258-2724.20180793
[Abstract](612) [FullText HTML] (327) PDF 1234KB(15)
Abstract:
In order to study the failure modes and seismic performance of energy-saving block & invisible multi-ribbed frame composite wall (EBIMFCW) in terms of hysteretic behavior, stiffness degradation, ductility, energy dissipation capacity, etc., low cyclic reversed loading tests were conducted on six test specimens of EBIMFCW designed in a scale of 1/2 and manufactured with varied opening positions. First, the test results of the specimens were compared and analyzed to determine their failure modes and hysteretic behaviors. Then, the stiffness degradation of each specimen was analyzed using the tangent stiffness calculation method and compared with others, the yield displacement was determined by the graphic method, and the displacement ductility coefficient was calculated using a formula to judge the ductility of each specimen. Finally, the energy dissipation capacity of specimens was studied using the equivalent viscous damping coefficient. Results show that under the horizontal low cyclic reversed loading, a shear-compression failure often occurs to the EBIMFCW with appropriate reinforcement and the failure process can be divided into elastic, elastoplastic and failure stages. The shape of hysteretic loop curve of specimens is relatively full, suggesting that the wall with holes has good seismic performance. Besides, the skeleton curve of the wall with a central opening is descending more slowly and the wall has better seismic performance than those with a non-central opening; a closer opening position to the wall center results in a more favorable contribution of the wall stiffness in the elastoplastic stage and thus a bigger deformation ability of the wall. In addition, the ductility coefficients of the six specimens are all greater than 3, meeting the requirements of the seismic design code; when the opening position is closer to the wall center, the specimen has a better ductility, a larger equivalent viscous damping coefficient, and better energy dissipation performance. Based on the test data, the allowable deformation values of the wall under different performance targets are determined, which provides a theoretical basis for design of EBIMFCWs.
Construct and Application of LM-CDBN Deformation Prediction Model for Supertall Buildings
QIU Dongwei, WANG Tong, DUAN Mingxu, LUO Dean, WANG Laiyang
2020, 55(2): 310-316. doi: 10.3969/j.issn.0258-2724.20180293
[Abstract](651) [FullText HTML] (324) PDF 731KB(18)
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In order to improve the prediction accuracy of supertall building deformation, the method of adjusting the weight and threshold in the conditional deep belief network (CDBN) model was improved. The LM (Levenberg-Marquardt) algorithm was used as a weighting method to construct the LM-CDBN network model. This method was applied to the deformation prediction of a 298 m supertall building. Then, the model was fully evaluated in terms of training error, goodness of fit, and prediction stability. Finally, the prediction results of LM-CDBN model, deep belief network (DBN) model, extreme learning machine (ELM) and unscented Kalman filter-support vector regression (UKF-SVR) were compared. The result shows that the prediction performance of LM-CDBN was 32%, 55% and 24% higher than three other models respectively. LM-CDBN model improves in the information extraction stability and generalization ability of solving nonlinear problems in time-varying systems.
Theoretical Model and Performance Tests of Rotational Eddy Current Dampers with Cable
XUE Songtao, BAN Xinlei, XIE Liyu, YU Bilong
2020, 55(2): 317-322. doi: 10.3969/j.issn.0258-2724.20170802
[Abstract](802) [FullText HTML] (460) PDF 1499KB(23)
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A novel rotational eddy current damper with cable is proposed, which is composed of inerter, spring and damping elements. In order to validate the mechanism for vibration mitigation, a mechanical model of a single-layer frame equipped with the damper is built. A series of vibration tests are carried out in terms of the frame, inerter and eddy current damper to analyze the impacts of air gap dimension between the conductor plate and permanent magnet, the material and thickness of the conductor plate on additional damping ratio. The conductor plates used in the tests include copper plates with the thickness of 5 mm or 10 mm, iron plate with the thickness of 5 mm, and a composite plate made up of a 5 mm thick copper plate and a 5 mm thick iron plate. In the vibration test, the conductor plates of different materials work in the air gaps of 10 mm, 20 mm, 30 mm, 40 mm. The test results show that the iron plate is added after the copper plate, and the damping is increased to 1.9 times and 1.4 times when the copper plate and iron plate are used alone. The air gap is a critical factor affecting the eddy current damping. When the air gap increases, the damping ratio will decrease rapidly. Adjusting the air gap dimension is the most effective and easiest method to change the damping ratio. The maximum damping ratio provided by the damper is 15.40%, which proves that it has a strong energy dissipation ability.
Experimental Study on Seismic Performance of RC Columns Made of Ultra-High-Strength Materials
SHAO Jiabang, ZHAO Hua, ZHAO Shichun, SUN Yuping
2020, 55(2): 323-331. doi: 10.3969/j.issn.0258-2724.20180453
[Abstract](571) [FullText HTML] (302) PDF 2256KB(9)
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As recent strong earthquakes have revealed, the excessive deformation of the traditional ductile structures under mega-earthquakes far more than design intensity makes the structures hard to be repaired after earthquakes. To assure sufficient resilience of concrete columns, i.e., stable response and small residual deformation under mega-earthquakes, low-bond and ultra-high-strength (UHS) prestressed concrete (PC) strands rather than deformed reinforcing barsare adopted as the longitudinal reinforcing bars. To verify this method, pseudo-static tests were conducted for five 1/3-scale concrete columns with asquare section of 250 mm × 250 mm, height of 1 000 mm, shear span ratio of 2.0, and axial load ratio of 0.25. The steel amount of UHS PC strand and confinement configuration of transverse reinforcement were experimental variables. Test results indicate that when low-bond and UHS PC strands was used aslongitudinal reinforcement, the lateral resistance of concrete columnskept increasing trend before the drift level reached 3.5%, which effectively reduced residual deformation and limited residual drift below one-fifth of the corresponding peak drift. It is also indicated that carbon fiber reinforced polymer wrapping prevents stripping of concrete cover and further reduces the residual deformation after large deformation of concrete columns.
Mechanical Behavior of Intercalation Plate Joints of Concrete-Filled Steel Tubular Wind Turbine Tower
WEN Yang, CAI Junqing, CHEN Mingjun
2020, 55(2): 332-342. doi: 10.3969/j.issn.0258-2724.20180273
[Abstract](719) [FullText HTML] (323) PDF 1161KB(10)
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In order to understand mechanical behavior of intercalation plate joints of concrete-filled steel tubular wind turbine tower, static test of four split-type nodes was carried out, and finite element nonlinear analysis of parameters expansion was carried out by ABAQUS. Effect force distribution of the gusset plate and equivalent stress distribution in cone were analyzed by change the thickness of the gusset plate and the height of the spherical column. The results show that failure modes include buckling failure mode, inclusion slip failure mode, and spherical column shear failure mode, which depend on the thickness of the gusset plate, the holding force of the inclusion, and the height of the spherical column. The gusset plate is the weak part of the node, which varied with the thickness of the gusset plate and the height of the spherical column, the high stress zone concentrate at the intersection between lower part of the gusset plate and the spherical column. If brace buckling failure do not occur, the spherical column at the same height, the thickness of the gusset plate is no more than 12 mm (n ≤ 12 mm), the bearing capacity of the node increases with the gusset plate thickness, when the gusset plate thickness is larger than 12 mm (n > 12 mm), with the increase of the gusset plate thickness, the increase of the node bearing capacity slows down significantly. when the gusset plate thickness is the same, the sphere cylinder height is no more than 90 mm (h ≤ 90 mm), the bearing capacity of the node obviously increases with the increase of the ball column height, when the sphere cylinder height is larger than 90 mm (h > 90 mm), the bearing capacity of the node slows down with the increase of the sphere cylinder height obviously. It suggests that the gusset plate thickness is no more than 12 mm （n ≤ 12 mm）, the ball column height is no more than 90 mm （h ≤ 90 mm） is more reasonable for such nodes in actual engineering design.
Effect of Casting Defects on Mechanical Properties of Steel Structures with Cast Steel Joints
YAN Huadong, GONG Weijia, JIN Hui
2020, 55(2): 343-349, 371. doi: 10.3969/j.issn.0258-2724.20180081
[Abstract](638) [FullText HTML] (309) PDF 867KB(8)
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In order to study the influence of the grade size and position distribution of casting defects on the static and fatigue properties of steel castings, firstly, a three-dimensional solid steel truss model with cast steel joints was built by Solidworks, and the size and location of casting defects on the cast steel joints were determined based on the published literature; then, the truss structures containing different casting defects were subjected to static loading, and the stress distribution and displacement distribution of the structure were analyzed to determine the influence of casting defects on its static strength and static stiffness; finally, the truss structures with different casting defects were subjected to equal amplitude fatigue loading, and the local fatigue life of the model was obtained through the modified S-N curve of the cast steel joint to clarify the effect of casting defects on it fatigue performance. The results show that when the different positions of the cast steel joints contain casting defects with the same size, the maximum difference in maximum stress of different models is 11.7%, the fatigue life of the different models differs by two orders of magnitude. When the same position of the cast steel joint contains casting defects of different sizes, the maximum difference in maximum stress of different models is 1.7%, the fatigue life of the different models differs by one orders of magnitude. In spite of the different positions of the cast steel joints contain casting defects with the same size or the same position of the cast steel joint contains casting defects of different sizes, there is no significant effect for the overall and local displacement distribution of the structure. When the distribution of casting defects in the cast steel joint changes, the rate of change of maximum stress between different models is 8.8%, the fatigue performance between different models is inferior to the model that only contains one casting defect.
Bubble Model Based Grid Generation and Grid Size Control over Free-Form Surface
WANG Qisheng, GAO Boqing, WU Hui
2020, 55(2): 350-356. doi: 10.3969/j.issn.0258-2724.20180210
[Abstract](546) [FullText HTML] (267) PDF 1253KB(9)
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To generate triangular grids with regular shapes and adaptive sizes over free-form surfaces, an automatic grid generation method is presented on the basis of a bubble dynamic model. Grid nodes were first decorated on the discretized surface according to certain rule, and were regarded as elastic bubbles. The inter-bubble forces and the forces from surface adsorption were introduced. The motion control equations of bubbles were established. Then, the equilibrium state of the bubble system was acquired by the numerical simulation algorithm. Finally, the centers of balanced bubbles were connected into a triangular grid by an extended Delaunay method. In the bubble model, the size of a bubble is determined by the relative radius function. And the control of the grid size is realized by adjusting the bubble size. Through the relative radius function factoring in the distance from each bubble center to selected points or curves, the curvature of reference curves or the surface and so on, the method can generate triangular grids with edges adapted to the surface features. Six cases have demonstrated that the grids generated by the proposed method have regular shapes and adaptive sizes, with their shape quality indexes all higher than 0.97. The method provides the convenience for the design of grid structures.
Dynamic Displacement Response of Pavement Structure under Moving Vehicle Load
ZHANG Xianmin, KONG Weibin, LIU Xiaolan
2020, 55(2): 357-363. doi: 10.3969/j.issn.0258-2724.20170137
[Abstract](547) [FullText HTML] (418) PDF 998KB(30)
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In order to study the dynamic displacement response law of pavement structure under driving load, a finite element model (FEM) of pavement structure is established by the theory of elastic layered system. Applying the random dynamic load of a vehicle to the FEM, the variation of vertical dynamic displacement in the structural test area is analyzed with changing thickness and modulus of the pavement layer, and a mathematical model of relationship between the peak dynamic displacement of the test area and parameters of the pavement structure layer is proposed to characterize the dynamic response of the pavement structure. Results of FEM calculations show that the peak dynamic displacement of the pavement test area decreases with an increase in the soil matrix modulus; what's more, the peak dynamic displacement is more sensitive to the soil matrix modulus than to other pavement layer parameters, and the mathematical relationship between them is logarithmic. Meanwhile, the peak dynamic displacement of the pavement test area is approximately linear with the thicknesses of the surface layer and the base layer, and is approximately logarithmic with the thickness of the subbase layer. However, the dynamic displacement curves of the test area with different surface layer moduli, base layer moduli and base layer moduli almost coincide, implying that they are not the main influencing factors of the dynamic displacement. The obtained results provide a basis for the detection of pavement bearing capacity.
Mechanism of Polygonal Wear on Wheels of Electric Multiple Units on Lanzhou-Xinjiang Passenger Dedicated Line
ZHAO Xiaonan, CHEN Guangxiong, KANG Xi, ZHU Qi, ZHANG Sheng, LÜ Jinzhou
2020, 55(2): 364-371. doi: 10.3969/j.issn.0258-2724.20190027
[Abstract](751) [FullText HTML] (450) PDF 3214KB(27)
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Wheels of the electric multiple units (EMU) running on the Lanzhou-Xinjiang Passenger Dedicated Line have undergone severe polygonal wear because of the harsh environment. This wear increases the contact force between wheels and rails, affects the comfort of passengers, and even endangers train running. To deal with it, the models of the coupled friction and self-excited vibration for a wheelset-track-slab system are established on the basis of the wheel polygonal wear rules obtained by the long-term tracking and the frictional self-excited vibration principles. Then, the cause and development pattern of the wheel polygonal wear are studied by using the complex eigenvalue method. The results show that the frictional self-excited vibration caused by the saturated creep force between wheels and rails can easily result in the 15th−16th order polygonal wear on a straight line. Meanwhile, when the braking system is coupled with the wheelset-track system, at the unstable vibration frequencies of the power wheelset and un-power wheelset, the 23th−24th and 22th−23th order polygonal wear emerges. Finally, the increasing adhesion coefficient between the wheels and rails may account for the fact that the wheel polygonal wear develops faster in winter and spring than in summer.
Influence of Surface Feature Height of Deterministic Texture on Tactile Perception of Fingertip
LIU Taofeng, LI Yiyuan, LI Wei, ZHOU Zhongrong
2020, 55(2): 372-378. doi: 10.3969/j.issn.0258-2724.20180038
[Abstract](592) [FullText HTML] (287) PDF 1167KB(13)
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In order to reveal the basic mechanism and law of the tactile perception of human body, first of all, the influences of the surface feature height of deterministic texture on the fingertip skin friction behavior were studied through friction and wear analysis in mechanical physics. Secondly, by means of psychological test, the latent period and amplitude of P300, a cognitive component related to the friction behavior, were obtained. Finally, combining the test results of both, the relationship between skin friction behavior of fingertips and tactile perception was studied. The results show that the friction force is mainly composed of adhesive friction, hysteresis friction and interlock force when the finger skin is in contact with the deterministic texture surface with large roughness. There is a strong correlation between the tactile perception of finger skin and the friction effect. When the surface texture increase from 0.1 to 0.4, the skin deformation of fingertips increase from 2.356 to 2.941, the hysteresis friction and inter locking effect caused by skin deformation of fingers become more obvious. The samples with large texture feature height induce P300 with small latency, large peak and obvious perception, while the samples with small texture feature height are the opposite, which indicate that skin friction perception mainly depend on the hysteresis friction and interlocking effects directly related to skin deformation.
Leakage Analysis and Volumetric Efficiency of Symmetrical Multiple Output Gear Motors
WEN Desheng, WANG Shaopeng, TIAN Shanheng
2020, 55(2): 379-385. doi: 10.3969/j.issn.0258-2724.20180226
[Abstract](531) [FullText HTML] (311) PDF 888KB(15)
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In order to study the leakage and volumetric efficiency of a symmetrical multi-output geared motor, the geometric displacements of the internal and external motors under different connection modes were calculated based on the internal structure of the symmetric multi-output gear motor. The main leakage paths of the motor were analyzed. By establishing a mathematical model of the leakage, general expressions of leakage under different connections were summarized. At the same time, an experimental platform was built to test the volumetric efficiency of the symmetrical multi-output geared motor. The results show that when the inlet and outlet pressure of the motor increase from 0.9 MPa to 5.9 MPa, the volumetric efficiency of the internal motor decreases from 94.2% to 80.2%, and the volumetric efficiency of the external motor decreases from 92.5% to 73.6%. The efficiency drops from 88.8% to 63.2%, and the volumetric efficiency decreases from 86.0% to 62.7% during differential connection. When the pressure difference between the inlet and outlet is 5.9 MPa, the volumetric efficiency of the internal motor alone is 80.2%, and the volumetric efficiency of the motor is 62.7%.
Lane Detection Algorithm Based on Dilated Convolution Pyramid Network
TIAN Sheng, ZHANG Jianfeng, ZHANG Yutian, XU Kai
2020, 55(2): 386-392, 416. doi: 10.3969/j.issn.0258-2724.20181026
[Abstract](607) [FullText HTML] (285) PDF 963KB(24)
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In order to meet the accuracy and timeliness requirements of advanced driver-assistance system in lane detection, the improved ResNet50 network as the basic model to extract the features of the local laneline is proposed. Given that the dilated convolution can exponentially expand the receptive field, the dilated convolutional pyramid module is designed to completely extract the laneline features on different scales. The idea of anchor grid is proposed, by which the output is divided into a set of grids, and each grid is classified and analyzed by regression. After non-maximum suppression and other post-processes, a set of laneline marking points are output by the model. Experimental results show that if the model is tested with CULane multi-scene dataset and the intersection-over-union (IoU) threshold is 0.3, the comprehensive evaluation index F-measure reaches 78.6% and the detection rate reaches 40 frames per second. With similar evaluation indexes, the detection rate of the proposed model is much higher than that of the spatial convolutional neural networks (SCNN) model, and its detection performance in difficult scenes such as dazzle light and curve is more desirable.
BeiDou Navigation Satellite System/Inertial Measurement Unit Integrated Train Positioning Method Based on Improved Unscented Kalman Filter Algorithm
CAI Xuan, WANG Changlin
2020, 55(2): 393-400. doi: 10.3969/j.issn.0258-2724.20170816
[Abstract](740) [FullText HTML] (298) PDF 958KB(34)
Abstract:
In order to improve the accuracy and continuity of train positioning, BeiDou satellite receiver and inertial measurement unit were employed to construct an on-board integrated positioning system. Given the nonlinearity and robustness in the information fusion estimation of mulit-sensor positioning, an improved unscented Kalman filter (UKF) algorithm was proposed by applying the equivalence of robustness to the standard UKF. With the equivalent transformation of noise covariance in the standard UKF algorithm, the filter gain was adjusted, such that the filtering algorithm has a strong ability to suppress gross errors in sensor observation. The improved UKF algorithm and the standard UKF algorithm were applied to the integrated positioning for simulation comparison. The results show that, the filtering accuracy of the improved UKF is slightly higher than that of the standard UKF under normal conditions; the filtering accuracy and stability of the improved UKF is significantly better than the standard UKF when sensor observations contain gross errors. The average estimation errors of north and east positioning are respectively decreased by 48.5% and 48.8%. The average estimation errors of north and east speed are respectively declined by 43.7% and 48.9%.
Application of Multi-Clause Synergized Deduction in First-Order Logic Automated Theorem Proving
CAO Feng, XU Yang, CHEN Shuwei, WU Guanfeng, CHANG Wenjing
2020, 55(2): 401-408, 427. doi: 10.3969/j.issn.0258-2724.20180800
[Abstract](576) [FullText HTML] (273) PDF 708KB(14)
Abstract:
First-order logic is an important branch in mathematical logic, and automated reasoning of its logical formula is one of the important research hotspots in the field of artificial intelligence. Most of the state of the art first-order logic automated theorem proving systems adopt binary resolution method. There are only two clauses involved, and therefore only a complementary pair of literals are eliminated during each resolution step. As a consequence, the resulted clause has many literals, which affects the deduction efficiency. In this paper, a multi-clause synergized deduction algorithm is proposed based on contradiction separation rule. This algorithm allows multiple clauses used in deduction, and is able to eliminate more than one complementary pairs. The clause of contradiction separation is controllable and usually has less literals, which can effectively improve the inference ability. This multi-clause synergized algorithm adjusts the deduction order of clauses according to two kinds of weights, effective deduction weight and ineffective deduction weight. Backtracking mechanism is used to search for an optimal path, and effectively plan the deduction path. The algorithm is applied to the international top prover－Eprover 2.1, and Conference on Automated Deduction 2017 competition theorems (FOF division) are set as the test object. Eprover 2.1 with multi-clause synergized deduction algorithm outperformed Eprover 2.1 and solved 8 theorems more than Eprover 2.1. It also solved 31 theorems out of the 110 theorems unsolved by Eprover 2.1, accounting for 28.2% of the total.
Energy Management Strategy of Hybrid Tram Based on Dynamic Degree of Hybrid
CHEN Weirong, SHI Fangli, DAI Chaohua, AN Qi, LIU Yubei, LIU Yang
2020, 55(2): 409-416. doi: 10.3969/j.issn.0258-2724.20181071
[Abstract](680) [FullText HTML] (293) PDF 1359KB(13)
Abstract:
In order to improve system efficiency and operational economy of hybrid tram, according to the relationship between dynamic degree of hybrid (DDOH) and system efficiency, a hybrid tram energy management strategy (EMS) based on DDOH online convex programming is proposed. Firstly, each component is modeled based on system parameters of the hybrid tram. Secondly, the online convex programming method is used to solve the problem, and the real-time optimal DDOH data of the system is obtained. Finally, the effect of DDOH on system efficiency is observed by RT-LAB real-time simulation platform under typical tram conditions. The results show that the relationship between DDOH and system efficiency fits a convex curve. The instantaneous efficiency is improved by 9.6% when we use DDOH online convex programming energy management strategy, compared to the situation using traditional energy-followed energy management strategy with same parameters. For a complete running circle, the power can be saved by 2 886.2 kJ, and the operational economy can be improved by 3.29%.
Data-Driven Based Remaining Useful Life Prediction for Proton Exchange Membrane Fuel Cells
ZHANG Xuexia, GAO Yuxuan, CHEN Weirong
2020, 55(2): 417-427. doi: 10.3969/j.issn.0258-2724.20180016
[Abstract](978) [FullText HTML] (436) PDF 560KB(113)
Abstract:
Proton exchange membrane fuel cell (PEMFC) is a power generation technology with promising application prospects. The prognosis for the remaining useful life of PEMFCs plays an important role in its commercial use. In this work, the degradation mechanism and output characteristics of PEMFCs are reviewed to explore how systems and environmental factors affect the degradation. Then, the status quo of data-driven based RUL prediction methods is summarized, while the neural network prognostics algorithms are highlighted. Furthermore, the sources of uncertainty in prediction algorithms are analyzed. Finally, the future research of RUL prediction is discussed, which focuses on the problems such as limited empirical data, lack of modeling transient processes, and being hard for online prediction. In particular, there remains many difficulties in the remaining useful life prediction of large-power PEMFCs..
Free Vibration Characteristics of Multi-constrained Fuel Rod
LIU Pengliang, CHEN Biaosong, FAN Chenguang, LI Fei
2020, 55(2): 428-434. doi: 10.3969/j.issn.0258-2724.20180522
[Abstract](659) [FullText HTML] (217) PDF 1049KB(26)
Abstract:
In order to develop flow-induced vibration calculation program for nuclear fuel design, a theoretical method for analyzing multi-constrained fuel rod vibration is established based on beam theory and potential flow theory. Firstly, the vibration control equations in air and the overall stiffness matrix and mass matrix in dry modal are obtained through the multi-span continuous beam theory. Then the additional mass matrix in the wet modal is presented by considering the effect of axial flow and boundary conditions through the potential flow theory. Finally, Finally, the pressurized water reactor (PWR) fuel rod is used as an example. The theoretical analysis results about its natural frequencies and modes are obtained and the effects of spring stiffness and added mass coefficient on the natural frequency are explored. The results show that the theoretical analysis results are consistent with those calculated by the ANSYS. As the fuel rods are in bundle in the core and are surrounded by high-speed flow, its vibration frequency and mode are affected by axial fluid flow and rod boundary, but due to multi-constraints the vibration mode is seldom affected. The larger the tension and torsion spring stiffness, the higher the vibration frequencies of the fuel rod. The first natural frequency can be increased by 79.1% with the torsion spring increasing. The higher the additional mass coefficient, the lower the vibration frequencies of the fuel rod. The first natural frequency can be reduced by 18.2% as the additional mass coefficient increases. The ideal vibration characteristics can be obtained by optimizing the stiffness, which provides reference for the design of the grid.
Performance Analysis of Tri-state Boost Converter with Dynamic Reference Current Control
ZHOU Guohua, ZENG Shaohuan, ZHOU Shuhan, MAO Guihua
2020, 55(2): 435-441, 458. doi: 10.3969/j.issn.0258-2724.20180005
[Abstract](570) [FullText HTML] (228) PDF 1384KB(19)
Abstract:
To improve the efficiency, load range, and transient response performance of a tri-state boost converter operating in the pseudo continuous conduction mode (PCCM), the dynamic reference current (DRC) control was studied. First, the principles of the DRC controlled tri-state boost converter were analysed. Further, its conversion efficiency and load transient response performance were compared with those of the tri-state boost converter with constant reference current (CRC) control. Furthermore, their corresponding load range expressions were deduced. Finally, the theoretical analyses were verified by experiment. The results show that the efficiency of the DRC controlled tri-state boost converter in the light-load condition is improved by 14% compared with that of the CRC controlled tri-state boost converter. Moreover, the DRC controlled tri-state boost converter can operate in PCCM within full-load range. When the load is reduced and increased, the regulation time is decreased by 37.5% and 32.0%, and the voltage overshoot is decreased by 69.7% and 61.9%, respectively.
Hyperspectral-Based Corona Aging Evaluation for Composite Insulators
ZHANG Xueqin, GAO Runming, GUO Yujun, KANG Yongqiang, LI Yuansheng, WU Guangning
2020, 55(2): 442-449. doi: 10.3969/j.issn.0258-2724.20181062
[Abstract](573) [FullText HTML] (294) PDF 1177KB(19)
Abstract:
Composite insulators have been widely used in transmission lines due to good water repellency and hydrophobic migration. Corona discharges aggravate the aging of composite insulators. To this end, a method was proposed to evaluate the corona aging of composite insulators based on hyperspectral technology. Firstly, the new composite insulating silicone rubber sheet was subjected to corona aging, the Fourier infrared spectrum of the samples was analyzed, by which the samples were classified into six categories. Then, the reflection intensity at different bands on the surface of the silicone rubber sheet was obtained by using a hyperspectral imaging camera. Further, the characteristics of the original spectra lines was extracted by the principal component analysis (PCA). Finally, the support vector machines-insulator corona aging evaluation (SVM-CAE) model was established, and 60 sets of data were examined. The effects of different kernel functions on the accuracy of model evaluation were compared. The results of hyperspectral detection and evaluation show that, as the aging time increases, the high spectrum of samples under different aging times has obvious difference. With the increase of aging time, the spectral curves of silicone rubber insulation show a decreasing trend in 600 nm−900 nm bands. After the feature extraction by PCA algorithm, the model classification accuracy with polynomial kernel function was 93.333%.
Switching Scheme of Multi-mode Modulation Based on Selected Harmonic Elimination Pulse Width Modulation
YU Bin, SONG Wensheng, ZHAO Leiting, JIANG Wei, FENG Xiaoyun
2020, 55(2): 450-458. doi: 10.3969/j.issn.0258-2724.20180148
[Abstract](685) [FullText HTML] (280) PDF 1194KB(31)
Abstract:
In order to suppress the current and torque shock, a switching scheme of multi-mode modulation based on selected harmonic elimination pulse width modulation (SHEPWM) was proposed. Based on the basic principle of SHEPWM, the spectrum of phase voltage was analyzed. The relationship between current harmonics and modulation index was acquired with different switching angle numbers. Then, the switching process was abstracted as the first-order transient response of the fundamental circuit and harmonics circuits, and the mathematic model of the switching process was built. The mechanism of current shock during switching process was analyzed. Hardware-in-loop (HIL) experiments of two switching schemes were carried out on the RT-LAB HIL experimental platform. The results indicate that the main cause of the torque shock is the harmonic current amplitude step change during the switching process, and the harmonic currents amplitude keeps constant when switching at π/2 or 3π/2, so the phase current switches smoothly. The three phase currents can’t satisfy the phase requirement at the same time, so each phase switching at π/2 or 3π/2 separately can suppress the current and torque shock effectively.

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