Abstract:The stochastic Fourier spectrum provides a physical based perspective for fluctuating wind simulation. To properly model the probability density function of the elemental variables, the basic physical meaning of the elemental variables is elaborated and the statistical distributions of them are identified from the measurements. It is revealed that the statistical distribution of the cutoff wave number displays an obvious bimodal pattern; the power spectrum density derived from the fitted distribution of the original identifications deviates from the Kaimal spectrum evidently in the low and middle frequency band. Besides, the identifications of the cutoff wave number are eminently characterized by a clustering phenomenon, based on which the kmeans cluster analysis is utilized to reveal the underlying structure of the data set. It is pointed that the cluster characteristic of the fluctuating wind speed sample is closely related to the above abnormal phenomenon. Finally, the distribution modeling for the cutoff wave number is conducted for the reasonably selected measurements based on the cluster results.

Abstract:When implementing a highly nonlinear stressstrain model to solve boundaryvalued problems, one of the major challenges is how to reduce the accumulative error and to maintain the effectiveness of the numerical integration. In general, the conventional explicit algorithm tends to have a lower computational efficiency and a higher accumulative error. In order to deal with these challenges, this paper proposes an improvedexplicit algorithm combining with the cuttingplane method, in which the Dormand and Prince RungeKutta method is used instead of the forward Euler. Using the highly nonlinear SANICLAY model for structured clay as an example, the convergence, the computational efficiency, and the accuracy of three algorithms, namely the conventional explicit algorithm, the improvedexplicit algorithm, and the implicit algorithm, are compared via numerical simulations of single element tests. Finally, the improvedexplicit algorithm is applied to the multielement calculation of tunnel excavation. Compared with the implicit algorithm, the conventional explicit algorithm has a lower computational efficiency and a higher accumulative error. The improvedexplicit algorithm can greatly improve the computational efficiency and accuracy.

Abstract:The 3D laser scanning technology was introduced for the first time to acquire the global deformation of the inner surface of segmental lining during prototype loading test on the quasi-rectangular shield lining with a large crosssection. Based on the experimental data, the deformation and the effective transverse rigidity ratio of the lining structure were analyzed. The values of the deformation characteristics and the effective transverse rigidity ratios of the segmental lining in both vertical and horizontal directions in the dead weight and design state were determined as well. The variation of deformation and the effective transverse rigidity ratios with the burial depth and lateral earth pressure coefficient were obtained. The variation of deformation and effective transverse rigidity ratios with the buried depth in the limit failure state were shown to follow a doublelinear pattern. Finally, shellspring models were established to compare the similarities and differences of the deformations and effective transverse rigidity ratios between the quasirectangular and circular tunnels in detail, and the significant influence of the deadweight on the overall structural stiffness was revealed.

Abstract:The damping properties of concrete members are closely related to concrete aggregate characteristics. Replacing natural sand and crushed stone with different recycled aggregates (RA), the first damping ratio of suspension beam of recycled aggregate concrete (RAC) in elastic stage was tested by using the free vibration attenuation method, and the relationship between damping ratio and concrete strength/elastic modulus was analyzed. Moreover, the RAC pore structure and interfacial transition zone (ITZ) characteristics were investigated by using the nitrogen adsorption method and scanning electron microscopy (SEM), and the damping mechanism was discussed. The results show that the damping ratio of RAC beams increases significantly, when compared with that of natural aggregate concrete (NAC) beams, and the damping ratio increases with the decrease of concrete strength and elastic modulus. The effect of aggregate property, especially the aggregate surface modification, on the concrete damping property is noteworthy. The total pore volume and average pore diameter of RAC are larger than those of NAC, and the ITZs in RAC are weaker. Therefore, the sliding and friction in ITZs and the flexible cushion action of pores result in more energy dissipation in RAC beams.

Abstract:In order study the calculation method for flexural capacity of high strainhardening ultrahigh performance concrete (UHPC) Tbeams, a fourpoint loading experiment of five girder specimens was conducted and the loaddeflection curve of reinforcement and high strain strengthening UHPC was drawn. The Tbeam failure process was divided into the elastic stage, the fracture development stage, and the loadtofailure stage. Different from common concrete, when the force of high strainhardening UHPC beam reach the ultimate load carrying capacity, the relationship between stress and strain of UHPC of compressive region is still linear. Meanwhile, since the contribution of UHPC tensile strength of tensile region to flexural capacity, after UHPC cracking, should be considered, an equivalent rectangular stress coefficient β of UHPC of tensile region is proposed. The calculation method for flexural capacity of reinforced UHPC Tbeams is deduced, based on the flat section assumption. This method is compared with the foreign calculation method and the accuracy of each method is analyzed. The results show that the calculated value of the proposed method fits the test value well, providing reference for theory analysis and structural design of reinforced UHPC T-beams.

Abstract:In order to solve the problem of mistuing of tuned mass damper (TMD) and overcome the difficulty to adjust the frequency of TMD during normal using, a selfadjusting TMD was proposed. The selfadjustable TMD was generated by a tank instead of solid mass, using a servo control system to start the drive to change the mass of (TMD) and spontaneously adjust the frequency of TMD to main structure near the natural frequency of vibration, under the special harmonic excitation. The vibration reduction effects with or without this selfadjustable device under freedom vibration and forced vibration were set to investigate the effect on improving the previous TMD based on the equivalent damping ratio, the peak value of acceleration, and rootmeansquare. The results indicate that the selfadjustable TMD has a good convergence and could increase the equivalent damping ratio of the structure. The selfadjustable TMD has good vibration tuned effects for the various excitation conditions.

Abstract:Seismic responses of girder bridges may vary due to different structural systems and foundation types. In this regard, based on typical threespan girder bridges in liquefiable river valleys, three 2dimensional finite element models considering soilstructure interaction were built, including simply supported girder bridge with pile group foundations, continuous girder bridge with pile group foundations, and simply supported girder bridge with pileshaft foundations. Nonlinear time history analyses were performed to investigate the seismic response properties of these bridges. Postearthquake deformations of the soil and bridge, pile deformations, column drift ratios, bearing displacements, and expansion joint deformations were investigated to reveal the impact of soil liquefaction on seismic responses of these three types of bridges. The numerical results show that soil liquefaction significantly increases the unseating potential of the simply supported girder bridge with pile group foundations. For abutments of continuous girder bridge, unseating or abutmentdeck collision potentials are generally increased. In contrast, seismic responses of the simply supported girder bridge with pileshaft foundations are rarely influenced by soil liquefaction.

Abstract:In order to study the factors such as the joint position, unbonded prestressed tendons, shear keys affecting the shear performance of precast segmental bridge pier with grouted splice sleeve, quasistatic tests of four precast segmental bridge piers and one castinplace concrete pier were conducted. The damage development and failure mode of models were discussed. Their shear performance was summarized by analyzing hysteresis curves, ultimate shear capacity, displacement capacity. The shear performance of precast segmental bridge pier was compared with the castinplace concrete specimen. The experimental results show that the failure mode of precast segmental bridge pier with grouted splice sleeve was bendingshear failure. The precast segmental bridge pier has a good displacement capacity and energy dissipation which is similar to the shear performance of castinplace specimen. Adding unbonded prestressed tendons in the center of the section increases the shear bearing capacity and reduces the residual deformation.

Abstract:A novel high performance fiber reinforced concrete ultrahigh toughness concrete (UHTC) is expected to have promising applications in civil engineering due to its outstanding ductility. A series of fatigue tests were conducted on 3 continuous decks to study the fatigue properties of UHTC used as the structural joints in bridge continuous decks with different steel reinforcement ratios. The test results show that the UHTC specimens exhibit a significant multicracking behavior and good ductile failure characteristics under the fatigue load. The fatigue life of the UHTC continuous deck is more than three times that of the ordinary RC continuous deck at the same stress level. Under fatigue loading, the presence of UHTC can effectively reduce the increase of plastic strain in steel reinforcement, decrease the bending stiffness degradation, and improve the fatigue life of continuous deck structure.

Abstract:In order to reasonably set the rigid layer depth in pavement structure and improve the rationality of backcalculated modulus, the fullscale test track was used to measure the layerbylayer deflection basins at each structural layer of pavement using falling weight deflectometer(FWD), the influences of rigid layer depth and stress level on the layerbylayer backcalculation modulus of subgrade were analyzed, and a setting method for the rigid layer depth based on the consistency of subgrade modulus was developed. The results of the case study show that, compared with the stress level, the effect of the rigid layer depth on the subgrade backcalculated modulus is significant. The relationship between the setting depth of the rigid layer and the pavement equivalent thickness is exponential. The comparison with other setting method of rigid layer depth show that the method developed in this paper can significantly improve the consistency of the layerbylayer backcalculated modulus of subgrade and drastically reduce the coefficient of variation from more than 13% to 6.9%.

Abstract:Based on vehicletrack coupling dynamics and wheelrail rolling contact analysis, a rail wear prediction model was developed combining the material wear theory and the corresponding calculating program was written, which can quantitatively predict the distribution and development of rail wear. In view of the significant effect of discrete grid density of wheelrail contact patch on the prediction model, the influencing mechanism of the factor was analyzed from the perspectives of contact force distribution, wear distribution and so on. The reasonable grid density of contact patch was discussed. The research results show that the grid density does not affect the correctness of calculated results, but sparse grid causes many sharp shape changes in the creeping force and wear distributions. Increasing the grid density can improve the precision and smoothness of wear distribution, but the computation cost increases dramatically. When the grid density increases to 20×20, the change of rail wear rate tends to be stable. Continuing increasing the density does not bring about obvious improvement. Therefore, a grid density of 20×20 is suggested in the prediction model, which can achieve a high computation efficiency and accuracy.

Abstract:Carsharing is a new but controversy mobility service in China. The government is unable to determine the appropriate policy direction since the impacts of carsharing on traffic system is not yet clear. However, this problem was addressed based on transaction and user data from the largest carsharing company, EVCARD, in Shanghai. Descriptive statistics was used to analysis carsharingtrip amount and demand spatiotemporal distribution. Multiple linear regression and binary logistic regression were developed to draw characteristics of highfrequency users and users travelling at peak hours, respectively. The results show that most carsharingtrips and peakhour travels occur at the outskirt of city. The travels within the central area of the city have no commuting characteristics. Meanwhile, there are no similar features between highfrequency users and peakhourtrip users, and sometimes, there are even opposite features. Therefore, it is concluded that the carsharingtrip has no significant negative impact on traffic congestion in Shanghai.

Abstract:By using wind tunnel test and numerical simulation, the aerodynamic drag performance of a nearground fishshaped bluff body originated from ostracion cubicus was studied. The results indicate that the nearground bluff body is actually low aerodynamic drag, whose characteristic is determined by the large boattailing angle of the model and the relatively simple vortex structure in the wake. Compared with the CD, Cp and wake structure captured by the simulation and test, the most accurate prediction for the aerodynamic performance is achieved by using the SST turbulence model.

Abstract:Based on the wind tunnel test data of aerodynamic performance of MIRA vehicle body, the iteration step, time step, and grid scheme were researched when large eddy simulation was adopt to solve the obviously transient flow field with large separation structure around bluff body near ground. Meanwhile, the simulation accuracy of three subgrid scale turbulence models was studied using the comparative analysis method. Finally, the solving strategy of large eddy simulation was proposed which is applicable for the simulation of aerodynamic performance of notchback vehicle.

Abstract:Different from optimization study of the single performance of turbocharger impeller, this paper takes the compressor isentropic efficiency, the impeller maximum stress, and the impeller maximum deformation as the optimization objective. Based on ANSYS Workbench, the turbocharger compressor flowthermalsolid multiphysics coupling simulation model was established. Using the orthogonal matrix method and the 2k method, the key design parameters of the compressor were studied. The radial basis function and nondominated sorting genetic algorithm II were applied to solve the global optimization problem. Finally, the optimal scheme of impeller structure design were obtained. The results show that the most significant decrease is the impeller maximum deformation of 28.09%, the impeller maximum stress is decreased by 16.34%, and the compressor isentropic efficiency is increased by 2.83%.

Abstract:The cold start tests of a direct inject turbocharged diesel engine with a low compression ratio of 14.25 were conducted respectively at an altitude of 0, 3 000, and 4 500 m at different coolant auxiliary heating temperatures of 20, 30, 40, 50 and 60 ℃, as well as using intake heating auxiliary, by utilizing the plateau environment simulation test bench, to study the influence of coolant heating temperature and intake heating on its start performance of the diesel engine under different altitude conditions. The results indicate that the afterburn cycle with a poor work ability and the misfire cycle with negative work appear more and more frequent at a higher altitude in the cold start of a low compression ratio diesel engine, which caused the reduction of combustion work capacity, the extension of startup time, and the deterioration of starting performance with elevation increasing. When started under conditions of heating coolant or intake air, the number of afterburn and misfire cycle was significantly reduced during startup, then the power ability were resumed and the engine starting performance were improved. However, the occurrence probability of afterburn and misfire cycle could not be further reduced when the temperature of the coolant reached a certain degree such as 40 ℃, and a further higher coolant temperature will not be effective for improving the starting performance. Compared with intake heating, coolants heating auxiliary can both increase the temperature at the end of the compression process and reduce the friction resistance during start process at the same time, then obtain more better improvement for cold starting of low compression ratio diesel engine.

Abstract:The vehicle fuel preheater is an important and effective means to improve operating condition during cold engine starting. A conclusion is reached that the fuel preheater improves operating efficiency of the engine effectively through a series of tests and analyses. A more efficient way to improve operating efficiency of fuel preheater is to install spoiler in the combustion chamber. In this paper, the CFD software is used to simulate the preheater combustion chamber installed spoiler. The temperature distribution, CO distribution, and O2 distribution of the combustion chamber are obtained at different spoiler locations and different spoiler sizes. The comparative analysis indicate that the optimal spoiler diameter is 70 mm, compared with the nonspoiler design, and the fuel preheater efficiency is increased by 17%. The optimal position of the spoiler is 80 mm from the bottom, and the efficiency of the fuel preheater is 11.4% higher than the original design in which the spoiler is 60 mm from the bottom spoiler.

Abstract:The information of diesel spray in a stable hot coflow (300—673 K) is recorded with a highspeed camera and a laser diffraction instrument. The results show that as the coflow temperature increases, the spray penetration decreases and a peak spray angle appears. When the coflow temperature is equal to 300 K, the Sauter mean diameter of the droplets is between 10 μm and 20 μm and slightly increases along the axis. Dv90 decreases by 17% from 20 mm to 40 mm in the axial distance. The size distribution parameters decrease along the radius. The uniformity of the droplet sizes becomes better as the axial/radial distance increases. The Sauter mean diameter increases from 15 μm to 24 μm and the uniformity increases as the coflow temperature increases from 300 K to 673 K, owing to the fast evaporation of small droplets.

Abstract:The performance of Atkinson gasoline engine was simulated and analyzed based on the 1D engine model at working condition of the part load of 3 000 r?min-1. The results show that with the increase of EGR rate or LIVC, the engine fuel consumption is increased in the case that the throttle position, airfuel ratio, and ignition timing keep unchanged. In order to improve the Atkinson engine fuel economy，the united simulation model of MATLAB and GTpower was set up in the wide open throttle working condition. The values of EGR rate, LIVC, ignition timing, and airfuel ratio were iteratively optimized by using a redesigned genetic algorithm. The fuzzy clustering method was adopted to analyze all the previous generations for obtaining the best fuel consumption and the corresponding control parameters at different load points.

Abstract:The design method of a twodimensional dynamic vibration absorber based on acceleration is proposed, and a twodimensional dynamic vibration absorber is designed to absorb the bouncing and pitching vibration. Aimed at the requirement of low dynamic stiffness for the installation of twodimensional dynamic vibration absorber, a high static stiffness low dynamic stiffness vibration absorber is designed for the installation of twodimensional dynamic vibration absorber by using the negative stiffness characteristic of disc spring. The vertical nonlinear dynamic model of highspeed EMU is established, and the effect of twodimensional dynamic vibration absorber on vehicle vibration is analyzed. The results show that the twodimensional dynamic vibration absorber can effectively reduce the bouncing and pitching vibration of car body, and improve the running stability.