Abstract:The C¹ continuous Bell triangular element is adopted in this paper to investigate the mechanism of flexoelectricity. The plane strain boundary value problem of a cylindrical tube is solved， and the asymmetry of flexoelectric structure is used for creating piezoelectricity without using piezoelectric materials. In the numerical examples， the accuracy and convergence of the Bell element are verified， the influence of the intrinsic length on the response of the flexoelectric structure in gradient elasticity theory is then studied， and the size effect of flexoelectricity is also analyzed. This paper can provide a basis for the analysis of flexoelectricity and the design of flexoelectric structures.

Abstract:The periodic stepped section phononic crystal beam is studied. Based on the theoretical derivation， the structural design function of the expected band gap is realized by establishing the reinforcement learning model framework. A method to determine the edge state frequencies from the perspective of eigenmode is proposed， and the accuracy of this method is verified by the transmission and reflection analysis of the whole structure and semi structures， based on which， the robust transmission characteristics of the designed edge state for elastic waves are tested. The reinforcement learning design scheme and the eigenmode analysis method of edge states proposed make the design and analysis process of edge states of phononic beams simple， and help promote the research of designing edge states to realize the accurate regulation of elastic waves.

Abstract:When broadband elastic waves propagate in a graded structure， the waves of different frequency components will stop propagating forward and have energy accumulation at different positions of the structure， which is called elastic wave rainbow trapping. Mode conversion refers to the phenomenon in which the polarization of elastic waves changes during propagation. The use of rainbow trapping to achieve mode conversion of elastic waves is an emerging research direction in the field of wave manipulation. In order to achieve bidirectional mode conversion of flexural wave and longitudinal wave through rainbow trapping， a beam with graded pillars is proposed in this paper. The band structures of the subunits are solved by adopting the transfer matrix method， and their correctness is verified by using the finite element method. According to the band structures of the subunits， the mechanism of the flexural-longitudinal wave rainbow trapping and its mode conversion is explained from the perspective of wave number change. The flexural-longitudinal wave rainbow trapping is verified by finite element frequency domain simulation. The bidirectional mode conversion of flexural wave and longitudinal wave when flexural-longitudinal wave rainbow trapping occurs is verified by finite element time domain simulation.

Abstract:Based on electromechanical coupling metamaterials， a low-frequency vibration reduction approach for cylindrical shell constructions is proposed in this paper. A reduction method for the electromechanical coupling system is put forward， and the reduction model is corrected， using the modal synthesis approach. The wave resistance characteristics of the bandgap in the finite-length electromechanical coupling metamaterial cylindrical shell are studied， and the regulation law of the inductance and resistance parameters to the bandgap characteristics is analyzed. Two optimum circuit parameter design strategies are provided for low-frequency vibration reduction applications. Finally， the first three resonances are tuned using the double-layer ring strengthened cylindrical shell as the study object. The numerical simulation results reveal that the first three resonance peaks have a vibration suppression effect of over 25dB， proving that the low-frequency vibration reduction approach proposed in this paper can effectively suppress the low-frequency vibration of cylindrical shell structures.

Abstract:Circumferential ultrasonic guided waves feature the excellent potential of rapid screening and characterizing multilayered composite cylindrical structures， whilst the key to achieving these is to extract their dispersion relations. The traditional approaches for solving dispersion equations are only applicable for isotropic single-layer annulus， which however， are difficult or even impossible to solve guided waves in anisotropic multilayered annuli. This paper develops a semi-analytical finite element （SAFE） approach to compute circumferential guided waves based on elastodynamics， via COMSOL Multiphysics coefficient PDE（partial differential equation） platform. The method and associated results are cross validated by the dispersion curves reported in the literature， and are then applied to two typical engineering cylindrical structures. The proposed approach has manifested itself by extendable applications in industry， as it potentially allows for the computation of circumferential guided waves in multilayered composite annuli with arbitrary material properties， arbitrary number of layers， and arbitrary circumferential cross-sectional shapes.

Abstract:The application of carbon fiber reinforced thermoplastic composites， co-curing with embedded metal inserts， is one of the effective methods to realize high-performance lightweight and intelligent design of structures in important engineering fields such as aerospace and automobile. It can effectively avoid the loss in the mechanical properties caused by the drilling of composites and local stress concentration by fiber discontinuity. In this paper， the metal insert was embedded in carbon fiber/PA6 prepreg. The co-cured composites were prepared by the hot-press process. The effects of two different structural forms of continuous and discontinuous fibers around the embedded component on the mechanical behaviors of the composites were investigated. With the aid of the ultrasonic testing technology， the damage and failure modes of intelligent connection structures were analyzed. The influence of the local fiber structure on the mechanical properties and failure behaviors of composites was simulated by adopting the finite element method. The results show that the local fiber structure around the embedded metal inserts has a neglectable influence on the mechanical properties of carbon fiber reinforced thermoplastic composites， but causes different failure modes in composites.

Abstract:In this paper， ABAQUS was adopted to simulate the mechanical properties of high strength steel （HSS） flange-welded web-bolted connections in fire. Based on the validated numerical model， parametric analysis of HSS flange-welded web-bolted connections was conducted. It is shown that： as the temperature increases， M_max， M_y and K_ini of the connections decrease correspondingly. Compared with the connections made of higher strength steel matched with thin beam-column flange and web， the connections made of lower strength steel matched with thick beam-column flange and web can obtain a similar plastic bending bearing capacity and rotational capacity， thus realizing the optimal design of connections.

Abstract:The existing member importance calculation methods of spatial latticed shell structures only analyze the influence of the damage or failure of a single member on the total structure， without considering the random damage and interaction of members. To solve these problems， this paper introduces the elementary effects method into member importance analysis for the first time， and the new elementary effect is defined for spatial latticed shell structures. Meanwhile， members are divided into importance members and general members， and the two-stage decision method combining trail calculation and formal calculation is proposed to improve the calculation efficiency of determining importance members. Besides， the importance ranking method based on the technique for order preference by similarity to an ideal solution （TOPSIS decision method） is proposed to determine the relative importance ranking of important members. In summary， the member importance analysis method based on the improved elementary effects method is proposed. To reduce the calculation budget of the improved elementary effects method， a modified radial sampling strategy is proposed. The analysis results of the Kiewitt shell numerical model shows that compared with existing methods， random sampling based on the important members determined by the proposed method can effectively reduce the estimation error of the ultimate bearing capacity of the shell structure.

Abstract:The carbonation reaction of recycled aggregate and carbon dioxide could improve the properties of recycled aggregate and fix carbon dioxide at the same time. This paper clarifies the importance of carbon sequestration in cement-based materials for carbon neutralization and summarizes the mechanism of carbonation modification of recycled aggregates. Based on the Fick’s law， the carbon sequestration model in the three stages of original concrete service， recycled aggregate stacking， and recycled concrete service was established， and a case study was conducted. Moreover， the carbon reduction contribution model of recycled aggregate carbonation was established， and the annual carbon reduction accounting was performed for different carbonation methods of recycled aggregates， based on the estimated amount of recycled aggregate produced in China from the year 2020 to 2060. The results show that accelerated carbonation approaches could release the huge carbon reduction potential of recycled aggregates， which is an important measure to promote carbon neutrality.

Abstract:This paper aims to study the solidification and stabilization effect of cement-based composite cement curing agent on mixed contaminated soil with a high level of Cd and Zn， to explore whether there is synergy or antagonism between Zn and Cd， and to Compare the difference of curing effect between mixed contaminated soil and single contaminated soil. The cement-based composite cement curing agent includes cement， lime， fly ash， and montmorillonite. Four tests including the unconfined compressive strength test， the toxic leaching test， the X-ray diffraction（XRD） analysis ，and scanning electron microscope（SEM） test were performed. These tests can study mixed contaminated soil strength characteristics and leaching toxicity at different curing agent contents. In addition，this paper also investigats the relationship between the pH value and leaching toxicity and the solidification difference between the mixed contaminated soil and the single contaminated soil Moreover， it analyzes the composition and morphology of the solidified products by XRD and SEM， and then analyzes curing mechanism. The results prove that the strength of solidified products can be improved by using quicklime， fly ash， sepiolite， and montmorillonite instead of the same amount of cement. There is no antagonism between Zn²⁺ and Cd²⁺， and the existence of Cd²⁺ can help the fixation of Zn²⁺. The leaching concentration of heavy metal ions decreases significantly with the increase of leaching solution pH value. Compared with the samples with poor curing effect， the samples with good curing effect have more acicular， reticular， and other relatively dense structures.

Abstract:This paper proposes a quantitative physical evaluation system for 15-minute community-life circles based on multi-source urban big data. Measurements from both life service and health safety were conducted. Taking the four high-density mega-cities， i.e.， Beijing， Shanghai， Shenzhen and Wuhan as representative cases， surveys and interviews were performed， followed by empirical analyses. The results demonstrated that the four cities have different emphases on the construction of public service facilities， in which Shanghai has the highest level of community-life circle construction. Aimed at solving the problem of community-life circles within the four cities， optimization suggestions such as comprehensively improving facility coverage， exploring differentiated development paths， establishing safe and continuous transportation networks， and constructing a nested system of community prevention and control facilities were proposed， which may provide important support for further planning integration and improvement of public service quality in high-density cities.

Abstract:In order to explore in depth the significant factors affecting the traffic risk of bridge sections of freeway， this paper taking traffic order index （TOI） as dependent variable， and identifies the relationship between TOI and traffic characteristics， road attributes， and external environment. Based on the safety evaluation model， the Plots of individual conditional expectation （ICE） were applied to discover the contributing factors to traffic risk of bridge sections of freeway. The results indicate that compared with the gradient boosting decision tree model， the random forest（RF） models is more accurate for traffic safety risk evaluation. In addition， among the influencing factors， congestion is an important traffic flow factor affecting the safety risk of bridge sections. Under low visibility and adverse weather conditions， traffic risks are higher. The upstream and downstream of the river-crossing bridge are considered high-risk corridors in the bridge sections of the freeway. This paper can provide new ideas and methods for traffic safety risk evaluation and discovery of contributing factors to traffic risks of bridge sections， which is helpful for the traffic management department to accurately implement management.

Abstract:In order to study the basic principle and the reasonable length of auxiliary lanes， the original trajectory data of vehicles in the two-lane exit auxiliary lane section are extracted by using unmanned aerial vehicle (UAV） video and the YOLOv3 target detection algorithm， and the microscopic lane change characteristics and speed distribution features of vehicles are obtained by Kalman filtering and Frenet coordinate system conversion. The modified hyperbolic tangent function lane change model was used to fit the lane change trajectory， and the goodness of fit for left and right lane change was 97.48 % and 97.62 %， respectively. According to the vehicle operation and microscopic lane change characteristics of the road section， a two-lane exit auxiliary lane length calculation model was established， and the auxiliary lane was divided into the right lane change section， the reaction section， the waiting section， and the left lane change section. The study shows that the most important influencing factor in the length of the exit auxiliary lane is the lane change length， which is positively related to the driving speed. Compared with the Route Specification， the calculation principle of the minimum length of the auxiliary lane is clarified， and the scope of the auxiliary lane is defined， which provides reference for flexible application in design.

Abstract:In response to the needs of collaborative production of multiple workshops， the collaborative scheduling problem of multiple flexible workshops was studied， and an order decomposable collaborative robust scheduling method was proposed. First， collaborative scheduling solution was given. Then， a two-level decision tree production order distribution model was designed， in which the first level was used to select the distribution strategy， and the second one was used to split production order. In the first level， a genetic algorithm-based tardiness detection method was designed to improve the accuracy of workshop capacity evaluation， meanwhile， the new order insertion was regarded as a dynamic scheduling process， and scheduling robustness was enhanced through chromosome level selection. In the second level， a upper and lower bound criteria for production order decomposition was proposed based on linear programming. Finally， a benchmark case and some production cases were used to test the method proposed. The test results show that the method is feasible and effective， which can be used as a reference for practical application in enterprises.

Abstract:Nowadays， the electro-hydraulic brake system （EHB） adopts the master cylinder pressure sensor as feedback for pressure control under normal braking conditions， while ignoring the difference in pressure between the master and the wheel cylinder. Therefore， first， through the solenoid valve test bench， the forward and reverse throttling characteristic of the inlet valve of the hydraulic control unit （HCU） in the fully open state is tested. After that， the pressure volume （PV） characteristic of the wheel cylinder is tested by the brake test bench. Based on the above， a dynamic model between the pressure of the master cylinder and the wheel cylinder under non-limiting conditions is established， and the accuracy of the model is verified by real test data. The wheel cylinder pressure estimated by the above model rather than the master cylinder pressure sensor is adopted as the feedback and introduced into the master cylinder pressure control algorithm of the EHB without changing the original control algorithm. Based on the classical control theory， the rapidity and stability of the new control system is analyzed. Finally， real vehicle test of pressure control is conducted. The results show that under the same target step condition， the response speed of the wheel cylinder pressure and vehicle deceleration is increased by about 12 %， thereby shortening the braking distance under emergency braking conditions. In addition， since the estimated wheel cylinder pressure is smoother than that of the master cylinder without overshoot， the new control system runs more smoothly during the rapid pressurization process， significantly improving the noise， vibration， and harshness （NVH） performance. Finally， real vehicle tests under multiple conditions indicate that the new control system is stable.

Abstract:At present， the research on traffic marking extraction is insufficient for refined segmentation of traffic markings with rich semantic information. This paper proposes an algorithm to refine traffic marking semantic segmentation based on mobile laser scanning. The algorithm first extracts road surface from the point cloud， then transforms the surface into a raster image according to intensity information， so as to extract traffic markings through binary processing， based on which， all traffic markings are roughly divided into two categories by rectangularity filtering， and different semantic segmentation strategies are applied for recognition. Finally， the refined semantic information of 10 kinds of symbolic and non-symbolic traffic markings is obtained. A study was conducted by 8 groups of urban road point cloud data acquired in Shanghai， China， whose results demonstrate that the proposed workflow and method can achieve a Precision， recall， and F of 96.04 %， 96.92 %， and 96.48 %， which provides more abundant semantic information for a high-precision map.

Abstract:Point cloud registration is an important issue in the intelligent processing of point cloud data. It is also the key to applying point clouds in smart cities， autonomous driving， and 3D reconstruction. To solve the problem of low efficiency and poor robustness of existing point cloud registration methods， an automatic point cloud registration algorithm based on kernel correlation neural network is proposed. First kernel correlation of each point in point cloud is calculated by using several point kernels. Then the point cloud information is coded through multi-layer perceptron， and point correspondence is generated based on the coded feature vector to calculate the transformation parameters. Finally， the registration result is optimized through iteration. Using the Bunny， Dragon， Happy， Elephant， Horse in the 3D scanning model library of Stanford University， the algorithm proposed in this paper and other algorithms such as iterative closest point （ICP） are compared. The experiment shows that the algorithm proposed can achieve an accurate registration of different object point clouds， with a better accuracy and efficiency. It has a good stability even in the presence of noise and different density in the point cloud data.