Abstract:In order to calculate beam-column joints’ importance index in steel frame structure, an importance index calculation method was proposed. Firstly, equivalent resistance reduction coefficient was defined to quantify the influence of failure of joints on structure’s behavior. Then, equivalent failure probability coefficient was defined to quantify the failure probability of joints. Finally, based on Technique for Order Preference by Similarity to an Ideal Solution (TOPSIS Decision Method), considering equivalent resistance reduction coefficient and equivalent failure probability coefficient, a calculation method of beam-column joints importance index was proposed. The results of a four-story steel frame structure showed that this method could quantify joints’ importance and supply basis for inspection and appraisal of in-service steel structures.

Abstract:To reasonably predict safety-based dynamic reliability of the existing bridge girder system, the dynamic extreme stress data at the dangerous monitored points was adopted to build Bayesian dynamic vine- Copula model(BDVCM) through combining vine-Copula technique with Bayesian recursive processes about dynamic linear models(DLM), further, with first order second moment (FOSM) method, dynamic reliability of the bridge girder system considering time-variant nonlinear correlation of failure modes at the multiple dangerous monitored points was predicted. The dynamic monitored extreme stress data at five sections from a bridge girder was provided to illustrate the proposed model and method. The results show that predicted dynamic reliability of the bridge girder with considering the time-variant nonlinear correlation of failure modes at the multiple dangerous monitored points is bigger than that without considering the time-dependent nonlinear correlation of failure modes. It is illustrated that the predicted results without considering the time-variant nonlinear correlation of failure modes at the multiple dangerous monitored points are conservative.

Abstract:This paper proposed a novel method, which named the drilled core method, to test the basic mechanical properties of brick masonry before and after reinforcement. The method can be popularized to evaluate the effect of brick masonry reinforced by various mortar surface. An auxiliary loading device was designed to test the compressive strength and interface shear strength of core samples. Strength tests of 315 core samples and 54 standard brick masonry parts were successfully completed by using auxiliary loading device. After that, the interfacial shear strength tests under four different surface treatment conditions were completed to verify the feasibility for evaluating the interfacial shear strength after reinforcement. The compressive strength test results indicate that the compressive strength of core samples correlates strongly with the standard brick masonry parts. Before reinforcement, the correlation coefficient of compressive strength between core samples and standard brick masonry parts is suggested as 2.13 for MU7.5, 2.25 for both MU10 and MU15. After reinforcement, the correlation coefficient is suggested as 3.26 for all the masonry strength grade. The interfacial shear strength test results show that the interfacial shear strength between the strengthened surface layer and the brick masonry is less affected by mortar and block strength grade, but mainly by different treatment methods of brick masonry surface. All the test results show that, it is feasible to test the basic mechanical properties of brick masonry structure before and after reinforcement by using the proposed drilled core method for brick masonry structure.

Abstract:In the paper, the real buildings within a range of 1.8km×8.0km in a central area of Shanghai along the direction of WNW near Tongji University were reconstructed by scale models. The influence of the urban terrain features, the differences between far and near terrains and the distance between the starting position of the terrain and the observation location on mean wind profiles and wind field characteristics were discussed with wind tunnel experiments. Results showed that the gradient wind height is on the increase, until the wind profile becomes steady, with the increase of the distance between the starting position of the terrain and the observation location; the wind profile is influenced by terrain features greatly; the ground roughness exponents of the urban district in Shanghai are estimated as 0.50 to 0.75, which is far greater than the corresponding value 0.30 in the load code for the design of building structures in China. The value of ground roughness exponent of the urban district of large cities presented by the load code for the design of building structures should be increased.

Abstract:The extreme pressures and non-Gaussian feature of pressures are essential problems in the wind resistance design of the main structure and the surrounding structure, but the flow mechanism hasn’t been clarified yet. The non-Gaussian feature of wind pressure under the influence of the wind angle has been investigated using large eddy simulation (LES) at the Reynolds number of 22 000, and the relationship between the non-Gaussian region and the average field are analyzed. Flow mechanisms of extreme wind pressure are discussed based on instantaneous flow structure. The results show that the non-Gaussian region located at the rear corner and leeward side of the square cylinder, and there has not shown non-Gaussian feature at separation bubble region. The intermittent attachment vortex at rear corner creates extreme wind pressures on the surface of the square cylinder, which is closely related to the Karman vortex in the wake of the square cylinder. The extreme wind pressures on the leeward side of the square cylinder are caused by the cyclotron action of the Karman vortex in the wake of the square cylinder, and the positions of extreme wind pressures will change with the movement of Karman vortex.

Abstract:To apply the thermal comfort into the optimization of building arrangement, a variables design method based on Kmeans clustering was proposed. Then, it was combined with numerical simulation, genetic algorithm and universal thermal climate index(UTCI) to implement the building arrangement optimization on Matlab. Finally, the building arrangements with centralized type, decentralized type and edge flow type water displacement were optimized respectively. The results showed that after optimizing, a reduction of 0.1~0.6°C of UTCI was observed. It is alsoconcluded that in the moderate heat stress, the increasing of wind speed is the key of thermal comfort improvement.

Abstract:Reliable live load value is the prerequisite for reliability design of civil engineering buildings. Traditionally, building live loads are investigated by means of indoor objects sampling and weighing. This method has many problems such as low efficiency, high labor cost, long duration, limited samples, poor timelines in reflecting indoor items change and difficulty in weighing large items. Inspired by the big data concept, this paper proposes a new research method for investigating indoor sustained live loads. Through the multi-source heterogeneous data such as photos, videos, identification codes, and voices, combined with internet resources, the weight of objects in the building is obtained by means of object detection, image retrieval, voice or text recognition. After the detailed introduction of the implementation method, further case studies show that the use of big data technology can achieve efficient and convenient building live load survey, and build a new load research paradigm

Abstract:According to the problems of space closure, low illumination and high diving risk in tunnel, the cognitive model (namely ACT-R) was introduced to model the cognitive and action in the cognition and control behavior of vehicle driving in tunnel, and the virtual reality technology was used to establish 3D tunnel and its related traffic facilities and landscape model. Secondly, combined with SCANeRTM studio cockpit, a virtual reality (VR) tunnel driving test environment was established. The feasibility of tunnel traffic facilities and landscape evaluation technology based on virtual augmented reality was verified by experiments. It is proved by experiment that track spike, contour mark and tunnel reflector, can improve the field of driver’s vision, relieve the driving pressure in the tunnel, and make the driver drive in a more relaxed state. As a result, they can improve the safety of driving in the tunnel.

Abstract:Aiming at the problems of slow convergence and small noise reduction of the active control system for vehicle interior road noise. Considering the noise-weighting characteristics, the Normalized Filter Weighted-x Least Mean Square (NFWXLMS) algorithm for vehicle interior road noise active control based on off-line reconstruction of secondary path is proposed. On the premise of not increasing the computational complexity of the control system, the convergence speed and noise reduction of the system can be effectively improved. Based on Simulink simulation, the convergence and noise reduction of the NFWXLMS algorithm and the Normalized Filter-x Least Mean Square (NFXLMS) algorithm are compared. The results show that the new algorithm can effectively improve the convergence and enhance the noise reduction of the system. Finally, the road test of the system based on the two algorithms is carried out, and the results show that the noise reduction of the system has been significantly improved.

Abstract:Lithium-ion battery is an electro-thermo-mechanical coupling system. It is of great significance to study the mechanical properties during the charging and discharging processes. According to Linear Variable Differential Transformer (LVDT), the static stress properties at different states and the dynamic stress properties under different charging and discharging currents of single-cell Lithium-ion pouch battery are measured and analyzed. The effects of current, state of charge, historical operating conditions and other factors on the stress change of the battery are studied. Through goodness analysis of fit test and significance validation, a reliable multivariate regression model of stress properties is established. The research shows that there is a monotonous relationship between static stress and state of charge; dynamic stress is generated during the charging and discharging process, and as the charging current becomes larger, the dynamic stress will increase accordingly. The established battery stress model can well describe the stress changes of the battery at different charging phases and under different currents.

Abstract:The mass, cumulative quantity and micro-morphology of particulate matters from a China Ⅵ gasoline direct injection(GDI) vehicle during Worldwide Harmonized Light Vehicles Test Cycles (WLTC) have been researched experimentally. The results showed emission factors of particulate mass (PM) and particulate number (PN) were both lower than the regulation limits; The cumulative amount of particulate matters varied in three stages, which was significantly higher in the first 300s, the last 300s and 600～800s. The PN was much more when engine was started under cold condition; the accumulation from first 300s had been over the total amount of hot-engine operation. Particulate matters were mainly formed by basic carbon particles whose shapes were irregular. The basic carbon particles were composed of many microcrystalline carbon layers, the inner core was disordered while the outer shell was ordered; When basic carbon particles overlapped, some formed large particles and others formed large carbon particles. The characteristic parameters of basic carbon particles were all unmoral distribution, similar to the GDI engine; The distribution of basic carbon particles diameter, carbon crystal length and carbon crystal curvature were relatively concentrated and the values were all lower than test results of the engine bench.

Abstract:Based on the unsteady simulation results, proper orthogonal decomposition (POD) was used to analyze the unsteady wake of fastback DrivAer automotive model. The comparison between improved delayed detached-eddy simulation (IDDES) results and the experimental data verifies the effectiveness of simulation method. The POD results of wake recirculation region show that the energy contribution of the first two modes is 12.39% , 6.78% and 5.61% respectively.The spectrum analysis indicates that the first two modes correspond to the same low-frequency quasi-sequential flow structure with a dominant frequency of 0.216(30Hz). Phase analysis show that they have a temporal phase shift of 0.455π. The phase average of the vorticity reconstruction field based on the first two modes reveals that quasi-sequential flow structure is found to be dominated by the periodic motion of the shear layer on the underside of the wake. The first 273 POD modes (93% of the energy) can reconstruct the original flow field well and greatly reduce the degree of freedom.

Abstract:The velocity distribution profiles of annular synthetic jet were identified by experimental method and the optimum heat dissipation distance was obtained by parametric study. By combining it with LED headlamp, the heat dissipation effect of the synthetic jet on LED headlamp was confirmed by the experimental method. Based on large eddy simulation, the flow field and temperature field of the component were solved, and the distribution of temperature and heat transfer coefficient was clarified while verifying the validity of the simulation method. POD method was used to analyze the flow field and convective heat transfer coefficient on the surface of aluminum substrate. The results indicated that the distribution characteristics of convective heat transfer coefficient and thermal control effect of synthetic jet are mainly determined by the large-scale eddy of the flow field.

Abstract:Active grille shutter can control vehicle front-end opening area, thereby the fuel economy will be improved. The control of grille angle and fan speed under different vehicle driving conditions is a difficulty in the research of active grille shutter. Firstly, the accuracy of both computational fluid dynamics simulation and engine cooling system one-dimensional model were verified by wind tunnel tests and numerical simulation separately. Secondly, an approximate model considering the AGS angle, cooling fan speed, vehicle speed and drag coefficient, cooling air velocity was constructed by optimal Latin hypercube sampling and neural network fitting method, and then the model was input to the cooling system model. According to the real-time engine cooling demand, the AGS angle which can both meet the cooling requirements and minimum drag coefficient was chosen out. Finally the fuel reduction ratio of 0.6%~0.7% could be achieved under different ambient temperatures.

Abstract:How to improve the accuracy of load shedding under the premise of ensuring real-time performance is an important problem. Sparsity is a widespread feature of the big data stream. Therefore, we propose two load-shedding methods of the big data stream with sparsity in two scenarios. In the normal business scenario, we model the big data stream with the high dimensional space. Then we propose a load shedding method based on centrifugation, which uses the elastic distance to measure the distance of data. In the anomaly-monitoring scenario, we analyze the feature of the big data stream and propose a load shedding method based on equivalence class, which uses the combined similarity to divide the data set into equivalence classes. The combined similarity was composed of processing behavior similarity and data similarity to measure the difference between data. Repeated test results show that the two load shedding methods in this paper can significantly improve the accuracy compared with the conventional load shedding methods.

Abstract:In order to solve the problem that the unbalance of neutral-point voltage and output current harmonics cannot be effectively controlled at the same time, a multi-objective optimal control strategy for three-level traction inverter based on particle swarm optimization was proposed in this paper. Firstly, a mathematical model of harmonic suppression and neutral-point voltage balance control was established. Then the multi-objective optimization model was built with the idea of penalty function. The object function of the optimum problem was to minimize the total harmonic distortion rate of the output currents. And the key constraint was to make the neutral-point voltage fluctuation as small as possible. Finally, the PSO algorithm was applied to solve the optimum problem, and the goal of suppressing the output current harmonics and reducing the neutral-point voltage fluctuation was achieved. Simulation and experimental results verify the effectiveness of the proposed multi-objective optimal control strategy.

Abstract:Focused on the influence of artificial island group on surrounding wa ve-current coupled hydrodynamics, a tidal current model and a wave model for Jingmeng Bay in Qinhuangdao, which had been well calibrated, were established to calculate the surrounding current and wave with the software MIKE21. Based on the analysis of hydrodynamic responses to artificial island group, some measurement points were selected to study the interaction between artificial islands. It can be founded that tidal current, due to resistance, guide and diversion functions by artificial islands, formed a large area of weak circulation between the Conch Island and shoreline, but it increased significantly in the inlet between the Lotus Island and Conch Island as well as the outer sea area of artificial island group. Current fields located in the three mentioned areas were largely affected by artificial islands, of which the Conch Island plays a controlling role. The changes of tidal current velocity, caused by artificial island group, were not satisfied with linear superposition of differences induced by each artificial island. However, the group influence on wave field is linearly summed by individual artificial island influence. The construction of artificial island group has advantageous in wave attenuation, but greatly weakens the tidal current in near-shore area.

Abstract:Based on the measured and related data from meteorological and hydrological stations in the Three-River Headwaters Region during 1956—2012, the variation characteristics of precipitation, temperature, NDVI (normal difference vegetation index) and runoff were analyzed by using the linear regression method, Mann-Kendall test method and Spearman test method. Moreover, the influences of climate and the underlying surface to runoff were analyzed by using the weighting factor method based on Budyko hypothesis. The results indicated that the annual precipitation showed a significant increase trend in the source region of the Yangtze River and Lancang River, and the annual mean temperature showed a significant warming trend in the Three-River Headwaters Region. The annual NDVI showed a significant increase trend in the source region of the Yellow River. In addition, the changing slopes of annual runoff in the source region of the Yangtze River, Yellow River and Lancang River were 6.54×108m3,—2.05×108m3 and 1.54 ×108m3 per 10 years, respectively, but these trends were not significant. The weighting factor method used in this study can not only accurately estimate the annual mean runoff, but also need not to assume that the climate and underlying surface changes have the same contributions to runoff changes. Overall, both climate and underlying surface showed a positive contribution to runoff changes in the source region of Yangtze River and Yellow River. However, in the source region of Lancang River, the underlying surface is positive contributing factor to runoff variations when the weighting factor (i.e., ) was 1.0, whereas it was a negative contributing factor when was 0.5 and 0. The contributions of climate change on runoff in the source region of the Yangtze River, Yellow River and Lancang River were 55.21%~92.85%, 52.47%~68.50%, and 89.91%~124.58%, respectively. Meanwhile, our results emphasized that the changes of runoff in the Three-River Headwaters Region were mainly affected by climate change. Precipitation is the main controlling factor of climate that influences runoff, and vegetation cover is the main controlling factor of underlying surface that influences runoff.

Abstract:The phenomenon of gravity current exists widely in natural environments and hydraulic engineering. In practical conditions, the obstacle is an effective mean to prevent the invasion of gravity current, so it is valuable and worthwhile to study the effects of obstacles on the dynamic characteristics of gravity current. In this paper, the lock-exchange experiments were carried out to compare the maximum diffusion height and head velocity of gravity current with different obstacle conditions, and the optimal obstacle layout for the engineering application can be therefore obtained. In addition, the velocity profiles in the upstream and downstream of the obstacles, the vorticity field of gravity current over the obstacles, and changes in the entrainment coefficient of gravity current along the channel were analyzed. The results show that for the optimal engineering layout scheme of consecutive obstacles is as follows: the first obstacle needs to be higher than the second obstacle, and the distance between two obstacles should be as large as possible, but the typical head shape of gravity current should not be restored before it meet the second obstacle. In the upstream of the first obstacle, the velocity profiles is disturbed and decreased, and the disturbed range is approximately equal to the height of the obstacle. In the downstream of the second obstacle, there are obvious wall region and jet region in the velocity profiles of the gravity current. Compared with the condition of no obstacle and single obstacle, the thickness of the gravity current flowing through the two obstacles decreases obviously. When the gravity current flows over obstacles, the current entrainment coefficient presents an "M" type distribution. The entrainment coefficient of gravity current over the second obstacle is greater than that in the first obstacle. The conclusion of the study can provide scientific basis for mitigating the hazards induced by gravity current and ensuring the safety of hydraulic infrastructures.