Abstract:To solve the problems of one-sided evaluation method, single index and incomplete system of the current asphalt pavement mixing field quality state, and provide a sound evaluation and prediction system, on the basis of grey model theory and the analysis of grey system characteristics of mixing plant quality management, a grey model analysis program was developed, with the quality management index system constructed, and the weighting method of index weight analyzed. In the present study, the construction method of index evaluation feature vector is proposed, the reference correlation coefficient of characteristic data sequence analyzed, and the method of quality evaluation and ranking defined. Through the analysis of grey system characteristics of mixing plant quality management, we established the grey model analysis program. Combined with specific examples, we construct the quality management index system, and analyze the weighting method of index weight. This paper puts forward the construction method of index evaluation feature vector. In this paper, the reference correlation coefficient of characteristic data sequence is analyzed, and the method of quality evaluation and ranking is defined. Through the comparative analysis of resolution coefficient, the authors believes that a reasonable value of resolution coefficient can improve the discrimination of evaluation objects. By studying the influence of the discrimination coefficient parameter of grey model on the evaluation result of quality state, it is found that the discrimination coefficient ρ can be used as the index of discrimination control, especially in the case involving reward and punishment and performance score measurement. This method can significantly improve the scientificity and operability of quality management evaluation of asphalt pavement mixing plant. This paper enriches the technical methods of pavement engineering quality management.

Abstract:To predict the viscoelastic responses of fiber-reinforced polymer matrix composites with imperfect interface in the time domain, the effects of viscoelasticity of polymers on the macroscopic/mesoscopic properties of composites are studied on the basis of the micromechanics model. According to the elastic-viscoelastic correspondence principle, a viscoelastic property evaluation method of composites based on the homogenization theory is developed. The boundary value problem and the materials′ homogenization constitutive equation are introduced into the Laplace domain, and then the macro/meso responses of the materials are transformed into the time domain by Zakian′s method with relatively stable performance, thus avoiding the step-by-step iteration of the viscoelastic constitutive with integral form. Different from the classical phenomenological theory and other numerical methods, the present work adopts the Trefftz concept that employs the complete elastic solutions with unknown coefficients to represent the internal trial displacement/stress fields. A spring model with stiffness is introduced to describe the interfacial damage, combined with the functional orthogonality of the analytical expression of fiber/matrix, and the accurate simulation of the interface was realized. Finally, the periodic boundary conditions are applied to the cells by the periodic variational principle, and the macroscopic homogenization constitutive is established to predict the macroscopic properties of materials. The results show that the proposed method can not only realize the efficient prediction of the long-term properties of composites, but also restore the local stress redistribution within unit cells to illustrate the effect of macroscopic modulus degradation.

Abstract:To describe and predict the vehicles′ two-dimensional movements under heterogeneous traffic environments (such as off-ramps), this research firstly proposes the concept of virtual boundary field (VBF). The influence of VBF on driver behaviors is analyzed from a microscopic point of view. The VBF model hence is established. A two-dimensional IDM (intelligent driver model) model that considers the VBF is constructed which takes the surrounding vehicles into account. The proposed model is capable of describing and predicting the two-dimensional trajectories of vehicles. To calibrate the parameters in VBF, the dynamic time wrapping (DTW) is employed as the objective. The PSO (particle swarm optimization) is used to optimize the location of VBF. The validation results show that the trajectories prediction error is about 3.1%-8.2% for Mirror traffic data, and is 3.8%-28.2% for NGSIM data, and the proposed model is capable of describing and predicting the lateral and lateral two-dimensional motion of conventional vehicles in mixed traffic flow environments on ramps. The proposed model can be used to provide basic information for the trajectories planning of autonomous vehicles in mixed traffic flow.

Abstract:In order to explore the operation rules of the mixed traffic flow consisting of human-driven vehicles (HDVs) and connected and autonomous vehicles (CAVs), this paper studies the impact of different managed lane setting strategies on the traffic flow of urban expressways. First, on the basis of the coupling relationship between car-following and lane selection probability of different types of vehicles, the evolution mechanism of expressway capacity was quantitatively described under different managed lane setting strategies. Then, the variation pattern of vehicle delays was analyzed using the SUMO simulation platform under mixed traffic flow conditions. Finally, the influence of different managed lane setting strategies on the collision risk of vehicles was investigated by analyzing the vehicle lane changing types and gaps. Results showed that the capacity reached the maximum value when the CAV penetration rate was less than 30% or more than 80% and HDVs were restricted to general purpose lanes. Bus and CAV lanes should be considered when the CAV penetration rate was between 30% and 80%. The average delay on the roadway was the lowest and almost unrelated to the CAV penetration rate when bus and CAV lanes were designed but their right-of-way was not restricted. The risk of vehicle collisions increased when managed lanes were provided only for CAVs or high-occupancy vehicles (HOVs). These results indicate that CAV penetration rate is an important factor for development of a reasonable managed lane setting strategy, and has significant influence on the capacity of the road section with managed lanes. The average delay of road sections and the collision risk between vehicles in the traffic flow are mainly influenced by the managed lane setting strategy.

Abstract:In order to study the effects of surrounding rock void of the tunnel bottom on dynamic response characteristics of the heavy-duty railway tunnel under the hydro-mechanical coupling effect. The method of combining field test and numerical simulation was adopted. Taking the vertical displacement, pore water pressure, and vertical dynamic stress as evaluation indicators, the dynamic response law of water-rich tunnel bottom structure under different cavity shapes (ellipse, cosine and rectangle) was analyzed. A practical void shape has been proposed, and the threshold value of the tunnel bottom surrounding rock void in the water-rich tunnel was determined. The results show that with the increase of the void width, the dynamic response of the tunnel bottom structure increases continuously, and the dynamic response changes intensify when the void width exceeds a certain value, this phenomenon is especially obvious in the void area. Among the three void shapes, the rectangular void has the largest dynamic response, followed by the elliptical void, and the cosine void is the smallest. Among them, the elliptical void is the most realistic. The dynamic response of the base under this void is 4.2 times that of the case without void, and the threshold value of surrounding rock void of the tunnel bottom is 0.6 m. The research results can provide a basis for the safety of water-rich heavy-duty railway tunnels and the treatment of voiding diseases.

Abstract:In recent years, the rapid changes in the water transportation industry have also led to the frequent occurrence of ship-bridge collisions. Although the bridge collision prevention facilities currently used can resist the impact of ships, there is still a lack of reproduction and quantitative analysis of the whole process of ship-bridge collisions. In order to map the relationship between impact force and impact depth of ship bow under large deformation and reproduce the collision process of ship bridge. Firstly, a large mass horizontal impact test device is used to carry out several successive cumulative collision tests on the reduced size bow model of 500 DWT without bulbous bow. Secondly, LS-DYNA, a large finite element analysis software, was used to build a refined reduced bow model, and the simulation analysis of multiple consecutive cumulative collisions was carried out by restart function, and compared with the test results. Test and simulation results show that with the accumulation of the number of impacts, the peak single impact force and the accumulated impact deformation of the reduced-scale ship bow model are gradually increased, while the increment of each impact deformation and the impact time are gradually decreased. There is a basic correspondence between the deformation of collision damage to the ship bow structure and the absorbed energy.

Abstract:In order to investigate the structural response of CRTS Bi-block ballastless track system on continuous bridge under dynamic train load, and predict the fatigue life of the ballastless track structure on the bridge, based on the principle of bridge-rail interaction and train-track-bridge coupling dynamics, a (40+64+40)m continuous bridge of Nanchang-Jingdezhen-Huangshan high speed railway is taken as the research object, the refined simulation model of continuous beam bridge-ballastless track system considering the nonlinear constraints between bridge, bearing and abutment, shear nail, baseplate, elastic cushion, track plate, fastener and rail is established by using the finite element method. The dynamic response characteristics of coupling system and the longitudinal force distribution law of CWR are studied, and the structural fatigue characteristics of ballastless track laid on continuous beam bridge are analyzed. The results show that: the maximum compressive stress of rail under temperature load appears at both ends of continuous beam, and the maximum tensile stress appears in the middle of bridge span. The maximum tensile stress of rail under vertical load appears near the pier of continuous beam bridge, and the maximum compressive stress appears in the middle of bridge span. Under the action of braking load, the maximum tensile and compressive stress of rail appear near the bridge pier. The longitudinal force of the rail is controlled by the temperature load, and the maximum stress is 143.1 MPa, meeting the specification requirements; Under the action of dynamic train load, the maximum tensile and compressive stress of rail on simply-supported bridge and continuous bridge are equivalent. The maximum tensile stress of track plate appears near the limit groove in the middle span of continuous beam bridge, the tensile stress at the bottom surface of track plate is greater than that at the top surface. The maximum tensile stress of the baseplate occurs near the main pier of the continuous beam bridge, the tensile and compressive stress at the top and bottom surface of the baseplate are basically the same. Under the action of dynamic train load, the service life of the most vulnerable part of the rail is about 27.1 years, and there will be no fatigue failure to track plate and baseplate during service.

Abstract:In order to quantify the capacity of stay cables to resist construction errors during installation and hence improve the constructability of cable-stayed bridges in industrialized construction processes, an interval inversion framework for mining the performance of assembly tolerance was proposed. The lower bound of interval reliability index was used to describe the extreme interference of multi-source uncertainty, and the inversion process was solved as a multi-objective optimization problem with reliability constraints. A decoupling prediction algorithm based on machine learning was developed, with the direct mapping of the worst-case reliability index realized by integrating finite element calculation, reliability boundary prediction, and surrogate models. The fault-tolerant planning for the cable stretching process of a real-scale cable-stayed bridge was carried out. Results show that when uncertainties were reasonably quantified, the maximum allowable tension errors of target cables ranged from 217.4 to 317.3 kN, with an anti-error rate of 7.29% to 12.98%. The interval inversion method proposed in this paper avoids the huge computational effort required by multi-loop nested optimization. On the premise of ensuring structural reliability and design optimality, the compatibility and controllability of the on-site tensioning process can be effectively improved.

Abstract:To investigate the bond properties of polyvinyl alcohol fiber reinforced engineered cementitious composites (PVA-ECC) and basalt fiber reinforced polymer (BFRP) bars, the surface form of BFRP bars (wrapped ribbed, sandblasted wrapped ribbed), anchorage length ( 5d, 7d, 9d ), diameter (8,0, 12 mm), thickness of PVA-ECC protective layer (0,5, 5,5 mm) and PVA-ECC strength (C50, C80) are taken as parameters, and 28 bond anchorage specimens of PVA-ECC and BFRP bars were designed and manufactured by pull-out test. By observing and analyzing the failure mode, bond strength and bond-slip curve of each specimen, the influence of various factors on the bond performance of PVA-ECC and BFRP bars were explored. Finally, by analyzing the applicability of the existing constitutive model, the bond-slip constitutive model of BFRP bars and PVA-ECC were established with reference to the test results. The results show that the specimens with smaller protective layer thickness (5 mm) are prone to fracture failure, and the bond strength is only 39.59% of that of normal specimens. Sandblasting on the surface of BFRP bars could increase the maximum average bond stress. With the decrease of anchorage length, the bond strength between BFRP bars and PVA-ECC increase gradually. Keeping the relative rib height unchanged while increasing the diameter of BFRP bars could avoid the negative effects of increasing the diameter of BFRP bars on the bond properties. When the strength of PVA-ECC increases from 50.5MPa to 81.3MPa, the bond strength increases by 45.53%. Avoiding the smaller protective layer thickness of BFRP bars or increasing the diameter of BFRP bars while keeping the relative rib height unchanged could ensure that PVA-ECC and BFRP bars exhibit sufficient bond strength.

Abstract:To solve the problem of high energy consumption during asphalt pavement construction, compaction tests were conducted using a vibratory roller on an asphalt mixture, and the relationship between the degree of compaction and the number of rolling passes was obtained. Asphalt paving tests were conducted on the mixture with a paver, and the relationship between the degree of compaction during paving and the vibration frequency of the paver was identified. Based on the above research findings, calculation models were developed to determine the number of rollers, the working power of the paver and the roller, and the overall energy consumption of paving and rolling process related to the compaction degree of paving. The model analysis shows that the high density of asphalt mixture paving layer can be achieved by adjusting vibration frequency of the paver. The power consumption of the paver is slightly increased, yet the rolling workload of rollers can be greatly reduced, thereby significantly reducing the overall energy consumption. The results show that by using the proposed energy-saving technology, the vibration frequency of the paver is increased from 10 Hz to 35 Hz, with the compaction degree of paving increased from 0.800 to 0.901, and the total energy consumption of the paving and rolling process reduced by 30.4%, producing a significant effect on energy saving and emission reduction.

Abstract:In order to identify the weak units in the complex goaf group, taking the goaf of an underground limestone mine as an example, through the construction of the discrete vibration mechanics model and the analysis of the related influence factors of the strain change, a damage mode identification method for weak units is innovatively proposed. The screening process is given, and its reliability is verified from two aspects: calculation examples and practical engineering application. The research results show that the screening index of natural frequency and strain mode can accurately identify the weak units in the goaf group. Both single-body and double-body unit damage will cause the natural frequency discrimination index I_M(k) of the goaf group to be greater than 0, and the value of strain modal discrimination index I_N(x) of the damaged area will be obviously convex. With the degree of damage increasing, the value of I_M(k) and the peak value ofI_N(x) peak value are getting bigger and bigger. Under only B1 damage conditions, the higher-order I_M(k) is more sensitive than the lower-order to reflect the degree of damage, and the fourth-order index recognition effect is better; Under only Z6 damage conditions, the second and fourth-order I_M(k) recognition effect is better excellent. Under B1 and Z6 damage conditions, I_M(k) is more sensitive to the changes of B1 damage degree than Z6, and the second-order I_M(k) recognition effect is better. The results have opened up a new direction for the quantitative evaluation of the safety of the underground goaf group.

Abstract:In order to quantify the impact of depot capacity on the operation of rolling stocks in urban rail transit and make appropriate decisions on the capacity design of depots in the planning stage, this paper investigates the depot capacity design in the conditions of multiple depots, service lines, and turn-back stations under a single line. First, a mixed-integer linear programming model was established for different operation phases of rolling stocks considering departure modes, with the deadhead mileage as the optimization objective. Then, the proposed model was validated by a case study of Guangzhou Metro Line 13. Finally, the effects of arrival and departure directions, departure capacity, and turn-back operations on the deadhead mileage and capacity design under different departure modes were discussed. Results showed that the cost-saving design of depot capacity could be quickly obtained by the proposed model. Additionally, the arrival and departure directions as well as the departure capacity had impact on the capacity design, and the extent of the impact varied depending on departure modes. While the turn-back operations affected the capacity design only in the case of uniform departure mode. The results in this paper provide a new method for the design of depot capacity, which can be used to support the decision of urban rail transit depot planning in practice.

Abstract:To resolve the problem of heavy self-weight, easy cracking and low load-bearing capacity of ordinary concrete poles, on the basis of centrifugal molding process, the optimal mix ratio of coarse aggregate UHPC was designed by adjusting the centrifugal speed, acceleration and time. Six UHPC annular poles with coarse aggregate were made by variable speed centrifuge, thus enhancing the production efficiency. The failure mode, crack resistance and bearing capacity were investigated by four-point bending static loading with steel fiber content and reinforcement ratio as parameters. The test results show that the failure mode of the pole can be divided into three stages: elasticity, crack development and failure. With the increase of steel fiber content, the number of main cracks of the pole gradually decreases, while the number of minor cracks increases accordingly. Steel fiber hindered the development of cracks to a certain extent, and its flexural capacity increased by 42.6%. With the increase of reinforcement ratio, the number of main cracks of the pole is not much different, but the length and width of the cracks are obviously reduced. The resistance to deformation is strengthened, and the flexural bearing capacity is increased by 63.8%. The calculation results of flexural bearing capacity of RPC pole is close to the experimental value, but relatively safe and conservative. However, with the increase of reinforcement ratio and steel fiber content, the theoretical calculation value is closer to the experimental value.The calculation method of the flexural bearing capacity of the activated powder concrete pole is similar to that of the test results.

Abstract:This paper provides a calculation method for backward analysis of concrete self-anchored suspension bridges considering creep effects. In view of the need for analyzing creep effect of concrete self-anchored suspension bridges, a calculation method for backward analysis on the basis of concrete creep mechanism is proposed. Firstly, the structural state of the concrete self-anchored suspension bridge at a known time is viewed as the analysis basis, introducing the retrogressive creep coefficient of concrete, and the creep effect analysis is conducted through the retrogressive creep coefficient to obtain the structural state at loading age. Then, the creep effect analysis is carried out using the creep coefficient. The structural internal force and deformation state of the concrete self-anchored suspension bridge at any time can be obtained. The key to the whole analysis process is the analysis of the internal force state of the structure at the loading age. The engineering example verification shows that the process of concrete creep effect regression analysis is convenient and concise, resulting in an accurate and effective analysis. Applicable to the analysis of concrete structure creep effect regression, including concrete self-anchored suspension bridges, the approach plays a guiding role for the design optimization and construction process control of concrete structures, thus providing a new research method for analyzing concrete creep effect.

Abstract:The LCL-type grid-connected inverter with inverter-side feedback is widely used in practical applications. However, the system stability can be affected by the digital control delay which changes the system phase-frequency characteristics. Therefore, this paper proposes a phase lead compensation based on an adaptive notch filter (ANF). Firstly, the phase lag caused by the control delay is compensated by the phase lead of the notch filter, which avoids the system phase crossing -180° at the resonance frequency; thus, the system stability and its robustness to weak grids are improved. Secondly, the system resonance frequency is estimated by the ANF algorithm, and the notch frequency is dynamically adjusted according to the estimated value; hence, the stability range of the resonance frequency is extended, which enhances the adaptability of the system to LCL parameters variations. Finally, the proposed method is verified by experiments, and the results show that the grid-connected inverter based on the ANF scheme has good stability. Moreover, compared with the traditional notch scheme, the proposed scheme has better robustness to the grid impedance and the LCL parameters variations; thus, it is more conducive to the control of LCL-type grid-connected inverters in weak grids.

Abstract:In order to solve the health evaluation problem of self-validating pneumatic actuators, a data-driven method was proposed. A prediction model was constructed using relevance vector machine (RVM) regression based on the normal working data of actuators. The residual feature was obtained as the event set by subtracting the actual output of the actuator from the predicted results. The target countermeasure set was established as consisting of four evaluation indexes of health, sub-health, marginal failure, and failure. The normal distribution function and the semi-trapezoidal function were selected as the membership functions to build the benchmark models that express the performance degradation degree of the actuator. The weight distribution models of local health degree and comprehensive health degree were established by using the analytic hierarchy process, grey relation algorithm, and entropy method. Finally, the least squares support vector machine was used to determine the health level. Results show that the method realized the overall and partial health assessment of pneumatic actuators, which is more practical and can reflect the performance status of self-validating pneumatic actuators.

Abstract:To solve the maneuvering control problem, a new adaptive sliding mode control combined with thrust vector is proposed, and a closed-loop optimal control allocation system is built to realize the optimal allocation of aerodynamic rudder and vector nozzle ensuring stable maneuvering flight of the near space vehicle. To cope with the complex uncertainty in the maneuvering flight environment, a new adaptive sliding mode controller is designed to relax the limit of uncertainty boundedness assumption of the typical adaptive sliding mode control, and obtain the expected control torque to ensure the stable tracking of attitude angle. Control allocation is the key to maneuver flight control because there are many control inputs for the near-space vehicle with thrust vector technology. To ensure the stability and safety of maneuvering flight, an optimal closed-loop optimal control distribution system was designed to improve the distribution performance from the perspective of stability. The expected control torque is accurately and stably distributed to actuators, completing the coordinated control of the aerodynamic rudders and the vector nozzles, and achieving the stable tracking of the reference command by the attitude angle during the maneuvering flight. The simulation results verify the effectiveness of thrust vector technology for expanding the range of attitude angles in the horizontal and vertical directions of near space vehicles, and prove that the designed controller can ensure flight attitude stability under the influence of complex uncertainties.