检索结果-南通市图书馆

Adaptive algorithm for estimating excavation-Induced displacements using field performance data

在线全文

学校读者我要写书评

暂无评论

Underground Space 2020年第2期5卷 115-124页

作者： Haijian Fan Gangqiang Kong transportation Engineer Texas Department of TransportationUSA college of Civil and transportation Engineering Hohai UniversityNanjingJiangsu ProvinceChina

Empirical models provide a practical way to estimate the displacements induced by ***,there are uncertainties associated with the predictions of empirical models owing to:(a)the imperfect knowledge of the model and(b)the uncertainties of the input *** uncertainties of these models can be characterized by a bias factor which is defined as the ratio of the actual displacement to the predicted *** bias factors associated with the C&O method and the KJHH model are evaluated using the Bayesian method and a database of 71 excavations in *** improve the predictions of the maximum displacement,an adaptive algorithm is proposed using field performance *** performance of the proposed algorithm is demonstrated by an example in which excavation-induced displacements are generated by finite element method in normally consolidated *** example shows that the developed algorithm can significantly improve the predictions by incorporating the field performance data.

关键词： Excavation Displacement prediction Bayesian updating Model bias

Threshold values of traffic flow for the provision of exclusive bus lanes

维普期刊数据库评论

在线全文

维普期刊数据库

学校读者我要写书评

暂无评论

Journal of Beijing Institute of Technology 2013年第3期22卷 342-349页

作者：孙锋王殿海马东方金盛 college of transportation Jilin University college of transportation Shandong University of Technology college of Civil Engineeringand Architecture Zhejiang University

A simulation network model was established using VISSIM software and verified by the T- test. The model took into consideration the road conditions, pedestrian crossing, traffic composi- tion, bus stops and traffic signal. The operating characteristics of buses and cars under different flow conditions were studied using the simulation model, and the speed-flow models of buses and cars were established based on the simulation results. Finally, the threshold values of traffic flow for the provision of exclusive bus lanes was determined with the target of optimal travel benefits （per capi- ta） , which would provide a basis for the planning and design of exclusive bus lanes on urban roads.

关键词： public transportation exclusive bus lane traffic management speed-flow model

Moisture effect on compressive behavior of concrete under dynamic loading

在线全文

学校读者我要写书评

暂无评论

Journal of Central South University 2014年第12期21卷 4714-4722页

作者：周继凯丁宁 college of Civil and transportation Engineering Hohai University

The effect of moisture content upon compressive mechanical behavior of concrete under impact loading was studied. The axial rapid compressive loading tests of over 50 specimens with five different saturations were executed. The technique "split Hopkinson pressure bar"(SHPB) was used. The impact velocity was 10 m/s with corresponding strain rate of 50 s-1. The compressive behavior of materials was measured in terms of stress-strain curves, dynamic compressive strength, dynamic increase factor(DIF) and critical strain at a maximum stress. The data obtained from test indicate that both ascending and descending portions of stress-stain curves are affected by moisture content. However, the effect is noted to be more significant in ascending portion of the stress-strain curves. Dynamic compressive strength is higher at lower moisture content and weaker at higher moisture ***, under nearly saturated condition, an increase in compressive strength can be found. The effect of moisture content on the average DIF of concrete is not significant. The critical compressive strain of concrete does not change with moisture content.

关键词： concrete split Hopkinson pressure bar high strain rate compressive behavior moisture content

Study of heat treatment parameters for large-scale hydraulic steel gate track

在线全文

学校读者我要写书评

暂无评论

Water Science and Engineering 2013年第4期6卷 423-432页

作者： Ping-zhou CAO Guang-zhong LIU Kai WU college of Civil and transportation Engineering Hohai University

In order to enhance external hardness and strength, a large-scale hydraulic gate track should go through heat treatment. The current design method of hydraulic gate wheels and tracks is based on Hertz contact linear elastic theory, and does not take into account the changes in mechanical properties of materials caused by heat treatment. In this study, the heat treatment parameters were designed and analyzed according to the bearing mechanisms of the wheel and track. The quenching process of the track was simulated by the ANSYS program, and the temperature variation, residual stress, and deformation were obtained and analyzed. The metallurgical structure field after heat treatment was predicted by the method based on time-temperatuxe-transformation （TTT） curves. The results show that the analysis method and designed track heat treatment process are feasible, and can provide a reference for practical projects.

关键词： steel gate track heat treatment parameter residual deformation numerical simulation

Damage Processes of Polypropylene Fiber Reinforced Mortar in Different Fiber Content Revealed by Acoustic Emission Behavior

在线全文

学校读者我要写书评

暂无评论

Journal of Wuhan University of Technology(Materials Science) 2018年第1期33卷 155-163页

作者：王岩 CHEN Shijie XU Zhengzheng LIU Shaojun HU Hongxiang college of Civil and transportation Engineering Hohai University

The performances of the cement-based materials can be improved by the incorporation of polypropylene fiber, but the damage processes become more complex with different fiber contents at the same time. The acoustic emission（AE） technology can achieve the global monitoring of internal damage in materials. The evolution process of failure mode and damage degree of polypropylene fiber reinforced mortar and concrete were analyzed by measuring the AE energy, RA value, AF value and b value. It was found that the cement matrix cracked on the initial stage, the cracks further developed on the medium stage and the fibers were pulled out on the last stage. The matrix cracked with minor injury cracks, but the fiber broke with serious damage cracks. The cumulative AE energy was proportional to the polypropylene fiber reinforced concrete and mortar＇s ductility. The damage mode and damage degree can be judged by identifying the damage stage obtained by the analysis of the AF value.

关键词： polypropylene fiber different content mortar concrete acoustic emission damage processes

Experimental Study on Tensile Behavior of Cement Paste, Mortar and Concrete under High Strain Rates

在线全文

学校读者我要写书评

暂无评论

Journal of Wuhan University of Technology(Materials Science) 2015年第6期30卷 1268-1273页

作者：陈徐东 SHAO Yu XU Lingyu CHEN Chen college of Civil and transportation Engineering Hohai University

Effects of the strain rate on cement paste, mortar and concrete were studied. A modified SHPB testing technique with fl attened Brazilian disc（FBD） specimen was developed to measure the dynamic tensile stress-strain curve of materials. A pulse-shaped split Hopkinson pressure bar（SHPB） was employed to determine the dynamic tensile mechanical responses and failure behavior of materials under valid dynamic testing conditions. Quasi-static experiments were conducted to study material strain rate sensitivity. Strain rate sensitivity of the materials was measured in terms of the stress-strain curve, elastic modulus, tensile strength and critical strain at peak stress. Empirical relations between dynamic increase factor（DIF） and the material properties were derived and presented.

关键词： tensile behavior cement-based materials experimental study split Hopkinson pressure bar

Transport path optimization algorithm based on fuzzy integrated weights

在线全文

学校读者我要写书评

暂无评论

Chinese Physics B 2014年第11期23卷 672-677页

作者：侯远达徐肖豪 college of Computer Science and Technology Tianjin University Military transportation Department Military transportation University college of Air Traffic Management Civil Aviation University of China

Natural disasters cause significant damage to roads, making route selection a complicated logistical problem. To overcome this complexity, we present a method of using a trapezoidal fuzzy number to select the optimal transport path. Using the given trapezoidal fuzzy edge coefficients, we calculate a fuzzy integrated matrix, and incorporate the fuzzy multi- weights into fuzzy integrated weights. The optimal path is determined by taking two sets of vertices and transforming undiscovered vertices into discoverable ones. Our experimental results show that the model is highly accurate, and requires only a few measurement data to confirm the optimal path. The model provides an effective, feasible, and convenient method to obtain weights for different road sections, and can be applied to road planning in intelligent transportation systems.

关键词： fuzzy integrated weights ovtimization vertices

Discrete Element Modeling of Asphalt Concrete Cracking Using a User-def ined Three-dimensional Micromechanical Approach

在线全文

学校读者我要写书评

暂无评论

Journal of Wuhan University of Technology(Materials Science) 2011年第6期26卷 1215-1221页

作者：陈俊 college of Civil and transportation Engineering Hohai University

We established a user-defined micromechanical model using discrete element method （DEM） to investigate the cracking behavior of asphalt concrete （AC）. Using the ＂Fish＂ language provided in the particle flow code in 3-Demensions （PFC3D）, the air voids and mastics in asphalt concrete were realistically built as two distinct phases. With the irregular shape of individual aggregate particles modeled using a clump of spheres of different sizes, the three-dimensional （3D） discrete element model was able to account for aggregate gradation and fraction. Laboratory uniaxial complex modulus test and indirect tensile strength test were performed to obtain input material parameters for the numerical simulation. A set of the indirect tensile test were simulated to study the cracking behavior of AC at two levels of temperature, i e, -10 ℃ and 15 ℃. The predicted results of the numerical simulation were compared with laboratory experimental measurements. Results show that the 3D DEM model is able to predict accurately the fracture pattern of different asphalt mixtures. Based on the DEM model, the effects of air void content and aggregate volumetric fraction on the cracking behavior of asphalt concrete were evaluated.

关键词： discrete element method asphalt concrete cracking behavior three-dimensional simulation micromechanics

Effects of System Pressure and Heat Flux on Bubble Nucleation and Growth

在线全文

学校读者我要写书评

暂无评论

Chinese Journal of Mechanical Engineering 2015年第5期28卷 964-970页

作者： QIU Chao ZHANG Huichen transportation Equipments and Ocean Engineering college Dalian Maritime University

Characteristics of bubble nucleation and growth are critical for its application. It is affected by several factors including viscosity, surface tension and temperature. However, the effect of pressure on bubble nucleation and growth has been underreported, although it processes significant effect on above characteristics. In this work, a micro copper electrode is etched on a slab covered with copper to produce bubble on the surface by current input. The nucleation time of bubble is measured under different heat flux and system pressures. The nucleation and growth processes are recorded with a high speed camera in order to discuss the effects of heat flux and system pressure on bubble characteristics. The experiment results indicate that the micro electrode with higher heat flux produces more thermal energy, which makes the time of bubble nucleation shorter and the speed of bubble growth faster. Higher system pressure causes the increase of the critical nucleation temperature and also baffles the bubble nucleation and growth. Bubble growth includes the stages of rapid growth and dynamic equilibrium, with the speed being from fast to slow. In the former part of rapid growth, heat flux plays a dominant role in bubble growth. While the effect of system pressure on bubble growth becomes significant in the latter part of rapid growth. Both the nucleation time and bubble growth agree well with the theoretical analysis. The obtained results help to accurately control bubble nucleation and growth required in different application.

关键词： bubble nucleation system pressure heat flux