Flooding is the most prevalent and costly natural disaster in the world and building reservoirs is one of the major structural measures for flood control and management. In this paper, a framework ...was proposed to evaluate functions of reservoirs′ locations and magnitudes on daily peak flow attenuation for a large basin of China, namely Ganjiang River Basin. In this study, the Xinanjiang model was adopted to simulate inflows of the reservoirs and flood hydrographs of all sub-catchments of the basin, and simple reservoir operation rules were established for calculating outflows of the reservoirs. Four reservoirs scenarios were established to analyze reservoirs′ locations on daily peak flow attenuation. The results showed that: 1) reservoirs attenuated the peak discharges for all simulated floods, when the flood storage capacities increase as new reservoirs were built, the peak discharge attenuation by reservoirs showed an increasing tendency both in absolute and relative measures; 2) reservoirs attenuated more peak discharge relatively for small floods than for large ones; 3) reservoirs reduced the peak discharge more efficiently for the floods with single peak or multi peaks with main peak occurred first; and 4) effect of upstream reservoirs on peak attenuation decreased from upper reaches to lower reaches; upstream and midstream reservoirs played important roles in decreasing peak discharge both at middle and lower reaches, and downstream reservoirs had less effect on large peak discharge attenuation at outlet of the basin. The proposed framework of evaluating functions of multiple reservoirs′ storage capacities and locations on peak attenuation is valuable for flood control planning and management at basin scale.
A distributed rainfall-runoff model was developed to predict storm runoff from humid forested catchments. The model is physically based and takes into account the saturation excess overland flow ...mechanism and preferential subsurface flow. The watershed is discretized into a number of square grids, which then are classified into overland flow and channel flow elements based on water flow properties. On the overland elements, Infiltration, overland flow and lateral subsurface flow are estimated, while on channel flow elements river flow routing is performed. Lateral subsurface flow is calculated using Darcy’s law and the continuity equation, whereas overland flow and channel flow are modeled using a one dimensional kinematic wave approximation to the St. Venant equations. The model governing equations are solved by an implicit finite difference scheme. While using process-based equations and physically meaningful parameters, the model still maintains a relatively simple structure. Most of the model parameters can be derived from digital elevation models (DEMs), digital soil and land use data, and the remainder of the parameters that are comparatively sensitive can be determined by model calibration. The model is tested using nine storm events in the Jiaokou watershed, a sub-basin of Yongjiang River in Zhejiang Province, China. Of these storms, one storm is used for calibrating the model parameters and the remaining eight storms are used to verify the model. When judged by the model efficiency coefficient (
R
2), volume conversation index (VCI), absolute error of the time to peak (Δ
T), and relative error of the peak flow rate (
δP
max), acceptable results are achieved. Sensitivity analysis shows that the model is sensitive to saturated hydraulic conductivity (Ks), Manning’s roughness coefficients (
n) and the initial soil moisture content.
In this study, a GIS based simple and easily performed runoff routing approach based on travel time was developed to simulate storm runoff response process with consideration of spatial and temporal ...variability of runoff generation and flow routing through hillslope and river network. The watershed was discretized into grid cells, which were then classified into overland cells and channel cells through river network delineation from the DEM by use of GIS. The overland flow travel time of each overland cell was estimated by combining a steady state kinematic wave approximation with Manning’s equation, the channel flow travel time of each channel cell was estimated using Manning’s equation and the steady state continuity equation. The travel time from each grid cell to the watershed outlet is the sum of travel times of cells along the flow path. The direct runoff flow was determined by the sum of the volumetric flow rates from all contributing cells at each respective travel time for all time intervals. The approach was calibrated and verified to simulate eight storm runoff processes of Jiaokou Reservoir watershed, a sub-catchment of the Yongjiang River basin in southeast China using available topography, soil and land use data for the catchment. An average efficiency of 0.88 was obtained for the verification storms. Sensitivity analysis was conducted to investigate the effect of the area threshold of delineating river networks and parameter
K relating channel velocity calculation on the predicted hydrograph at the basin outlet. The effects of different levels of grid size on the results were also studied, which showed that good results could be attained with a grid size of less than 200
m in this study.
The ablation characteristics of 2.5D SiC/SiC composites under ultra-high temperatures were studied using an oxy-acetylene torch flame. The results showed that the ablation region macroscopic ...morphology could be divided into three regions according to the distribution characteristics of SiO2. The linear ablation rate decreased linearly with time and the mass ablation rate was 160 mg/s. The ablation behaviour was dominated by sublimation and mechanical exfoliation. The ablation fracture of the fibre underwent three processes: Necking, fracture, and stable retreat, resulting a needle-like structure under the competing effects of gas diffusion and thermochemical reactions.
•The liner ablation rate of PIP-2.5D SiC/SiC was 53.87 µm/s at 60 s of ablation.•The SiC fibre ablation fracture showed needle-like structure.•The SiO2 was attached to the fibre surface in ‘ribbons’ and ‘skeletons’.
Plain-woven SiC/SiC Z-pinned joints were prepared using chemical vapour infiltration. The oxidation behaviours and failure mechanism were investigated using push-out tests before and after oxidation. ...Microstructural analysis indicated that the degree of oxidation of the pin near the surface was more severe than that in the middle region. Internal damage was monitored using an acoustic emission (AE) system. Pattern recognition was introduced to study the evolution of failure during the test. Combined with the failure morphology, all AE signals were labelled as matrix cracking, fibre–matrix debonding, matrix peeling, and fibre break. The results suggest that the failure mechanism of the Z-pinned joints under axial loading is dominated by fibre–matrix debonding and matrix cracking.
•The degree of oxidation of the Z-pinned joints decreased from the end sides of the pin to the middle region.•The oxidation behaviors of the Z-pinned joints are dominated by the consumption of the PyC interphase and generation of SiO2.•The weak and strong bonding between fibre and matrix results in different fracture morphology.•The microscopic failure mechanism of Z-pinned joints under push-out loading is dominated by fiber/matrix debonding and matrix cracking.
•The ablation mechanism of SiC/SiC composites under 1800°C gas environment was revealed.•SiC fibers were the conical tip under the action of thermochemistry and thermomechanics.•SiO2 nanowires formed ...on SiC substrate in edge region by high-temperature gas.•Ablation gas products destroy the continuity of SiO2 and reduce the ablation resistance of the material.
An oxyacetylene torch tested the ablation of SiC/SiC composites at 1800℃. According to the distribution of ablation product silica, the morphology could be divided into three regions. The fibers in the oval central region were ablated and broken, and the fracture surface is the conical tip. The silica liquid film in the transition region plays a role in resisting the ablation of the material. However, the generation of airflow channels destroys the liquid film's continuity and reduces the material's ablation resistance. Bean sprouts-like nano-sized silica was grown on the surface of the dome-top SiC matrix in the marginal region.
To clarify the role of the coating interface geometry and thermally grown oxide (TGO) layer in the failure of environmental barrier coatings (EBCs) and to further understand the cracking and spalling ...mechanisms of coatings, in this study, the thermomechanical properties of the multilayer coating system (Yb2SiO5/Yb2Si2O7/Si), the morphology of the coating interface and the influence of the oxide layer on the local stresses during cooling were considered based on a random rough interface geometry model. The results showed that the rough geometry increased the magnitude of residual stresses at the interface and that the stress distribution away from the interface was less affected than the coating without roughness. The cracks on the outer surface of the Yb2SiO5 layer initiate in the valley region and spread with a stress value independent of the TGO thickness, and this failure may occur by cracking under tensile stress. The overall stress intensity at the TOP/EBC interface was lower than that at the upper surface of the TOP layer. The presence of TGO increased the magnitude of residual stresses in the BC and EBC layers, which caused cracks at the TGO/BC and TGO/EBC interfaces to occur at opposite locations. The phase change of the TGO layer from β-cristobalite to α-cristobalite cause a rapid increase in the overall level of coating stress, which may be a direct factor in coating failure. The calculation results provide a theoretical basis for the coating design and manufacturing process.
