Experiments on the short-term development of sine-generated meandering rivers

This paper presents recent works on the simulation of short-term development of sine-generated meandering river in laboratory conditions. The influences of initial system parameters on the evolution process of rivers are investigated, including control over channel sinuousness, channel width and dominant discharge, eventually leading to different results of planforms. Measurements on the bank-line, flow field, bed topography and sediment transport rate were carried out. Braided rivers are easy to produce using non-cohesive sediments in floodplains, whereas environmental temperatures and humidities could influence the fluvial process by their effects on material cohesion. Channelized rivers were obtained in the “High Flow” conditions and the river corridor width was proven to be mainly connected with initial channel sinuousness and water discharge. Sickle-shaped and bamboo leaves-shaped sandbars were formed in the channels during the transformation process of meandering to braiding, the stability degree of sandbars reflects the adaption of channel morphology to hydrodynamic condition. Quantitative analysis confirms the formation of free steady bars, which manifests the free response as a downstream oscillation of the perturbation. Damping length is mainly affected by dominant discharge, channel width is the secondary factor, and channel sinuousness is the weakest factor. The wavelength of steady bars approximately equals to half of the initial streamwise wavelength. Sediment transport rate tends to increase with the increasing of channel sinuousness but stops growing due to the excessive increase of flow route and flow friction. The experiment results could be useful for verifying river pattern discriminant functions and offer a basis for further study on the morphological evolution of large-scale natural rivers, such as Yangtze River.     

Effect of water content on the mechanical properties of an artificial porous rock

Bulletin of Engineering Geology and the Environment - Water content significantly affects the mechanical properties of porous rocks, for which both clay content and rock microstructure have been...     

Dislocation climb in Mo5SiB2 during high-temperature deformation

During high-temperature compression tests on intermetallic Mo₅SiB₂, the dislocation microstructures vary with increasing temperature and strain rate. At 1400 °C, an increasing tendency exists for slip planes to be of an unexpected type (e.g., {143) and {523)) as a function of the decreasing strain rate and increasing strain that originates from a dislocation climb. As the temperature increases to 1600 °C, the internal strain rate of 6.07 × 10^− 3 s^− 1 from the dislocation climb at 4% strain exceeds the applied value of 1.67 × 10^− 3 s^− 1, and thus, the climb mainly controls the plastic strain, as evidenced by a strength that is lower than that at 1200 °C under the same conditions.     

Effects of tantalum on austenitic transformation kinetics of RAFM steel

The RAFM (reduced activation ferritic/martensitic) steels containing different tantalum contents (0 wt.％,0.027 wt.％,0.073 wt.％) were designed and cast.Differential scanning calorimetry and optical microscopy were employed to explore the influence of tantalum content on the austenitic transformation of RAFM steels.The austenitic transformation kinetics was described by a phase-transformation model.The model,involving site saturation nucleation,diffusion-controlled growth and impingement correction,was established based on the classical Johnson-Mehl-Avrami-Kolmogorov model.The phase-transformation kinetics parameters,including D0 (pre-exponential factor for diffusion) and Qd (activation energy for diffusion),were calculated by fitting the experimental data and the kinetic model.The results indicated that the average grain size is decreased with the increase of tantalum.The values of Ac1 and Ac3 (onset and finish temperature of austenitic transformation,respectively) are increased by increasing the tantalum content.The increase of tantalum caused the decrease of D0.However,Qd is increased with the increase of tantalum.In addition,as a carbides forming element,tantalum would reduce the carbon diffusion coefficient and slow down the austenitic transformation rate.     

Real-Time Quality Monitoring and Control of Highway Compaction

Compaction quality affects the long-term performance of highways, and thus is important in the highway construction. The current practice for compaction quality control primarily relies on the monitoring of rolling parameters such as rolling passes, speed and vibration of rollers, and lift thickness. Soil samples are randomly collected to evaluate the compactness. This practice is subject to two main limitations. First, the compaction monitoring and measurement are not always comprehensive since limited samples are manually collected. Second, compaction information cannot be disseminated to owners, supervisors, contractors, and operators in timely fashion. In this study, intelligent compaction (IC) technology is leveraged to monitor and control highway compaction quality. A new measure of compaction quality, compaction power per unit volume (E), is created and used with other IC measurement values such as compaction meter value (CMV) to achieve more reliable monitoring and assessment. Field experiments were conducted. The results demonstrated that the integration of CMV and E in the regression model leads to a higher coefficient of determination than that of using only CMV or E. A real-time monitoring system is developed, which not only evaluates the compaction quality of the entire area, but also synchronizes the compaction information among owners, supervisors, contractors, and operators in real-time. As such, this system cultivates an integrated “operator–contractor–supervisor–owner” quality control mechanism, which can improve the current highway compaction practice.     

Accuracy assessment of ultra-wide band technology in locating dynamic resources in indoor scenarios

The use of Ultra-Wideband (UWB) technology in reporting the real-time location of resources (workers and equipment) is shown to be effective in improving the current safety monitoring practices. Since many site accidents occur when workers are struck by moving equipment or enter hazard-prone areas, it is important to evaluate the accuracy of the UWB RTLS in estimating the location of dynamic resources on construction sites. In this paper, the effects of variables, such as “speed” and “heading”, on the accuracy of the estimated location of dynamic tags are investigated. It is shown that the accuracy is inversely proportionate to the speed of the tag, the number of tags being tracked and the complexity of the path on which the tag is moving. A novel approach to defining “danger zones” on construction sites is also proposed through which the feasibility of using static tags to define the boundaries of forbidden areas on site is validated. The findings of this study indicate the applicability of UWB in locating dynamic resources on construction sites.     

Shape optimization of bi-directional flow passage components based on a genetic algorithm and computational fluid dynamics

The inlet/outlet is an important part of a water conveyance system in a pumped storage power station (PSPS). Its hydraulic characteristics are directly related to the operation and economic benefit of the PSPS. Frequent changes between inflow and outflow operations pose significant challenges in the design of the inlet/outlet diffusion segment shape. In this study, an effective optimization method, including three-dimensional parametric modelling, computational fluid dynamics and a genetic algorithm, is introduced and coupled to the design of the diffusion segment shape. The hydraulic characteristics of bi-directional flow, including the head loss, velocity uneven distribution and uneven discharge distribution, are selected as the objective function in the optimization method. Using this method, the recommended shape of the inlet/outlet is studied and its hydraulic characteristics are discussed. The results indicate that the optimized inlet/outlet has better performance.     

Microstructure evolution of CMAS glass below melting temperature and its potential influence on thermal barrier coatings

CaO–MgO–Al₂O₃–SiO₂ (CMAS) deposition significantly degrades the performance of thermal barrier coatings (TBCs). In this study, the microstructure evolution of CMAS glass at temperatures below its melting point was investigated in order to study the potential influence of temperature on the applicability of CMAS glass in TBCs. The CMAS glass fabricated in this study had a melting point of 1240 °C, became opaque, and underwent self-crystallization when the temperature reached 1000 °C. After heat treatment at 1050 °C, diopside and anorthite phases precipitated from the glass; at a higher temperature (1150 °C), diopside, anorthite, and wollastonite were formed as the self-crystallization products. An increase in the dwelling time resulted in the transformation of diopside to wollastonite and anorthite. At 1250 °C, all products formed a eutectic microstructure and melted. The results indicate that even at low temperatures, CMAS glass underwent microstructure evolution, which could influence the coating surface and stress distribution when deposited on TBCs.     

母线洞对地下洞室群施工期风流行为的影响研究

基于CFD技术，采用标准k-ε湍流模型，分别建立地下洞室群风流场单相流模型和CO扩散混合模型。对施工期通风风流行为进行三维数值模拟，分析了母线洞贯通前后主厂房的风流场分布和厂房内不同位置CO浓度分布随时间的变化趋势。结果表明：母线洞贯通后使得主厂房内低速涡旋区增大，造成厂房底部施工工作面附近风流场紊乱，在工作面附近区域形成污染物滞留区。这易导致主厂房和主变室之间形成污风循环，对安全施工造成影响。