The seasonal variation characteristics of the water quality of the Jinpen Reservoir and the impacts of rainfall runoff on the reservoir were investigated. Water quality monitoring results indicated that, during the st...The seasonal variation characteristics of the water quality of the Jinpen Reservoir and the impacts of rainfall runoff on the reservoir were investigated. Water quality monitoring results indicated that, during the stable stratification period, the maximum concentrations of total ni- trogen, total phosphorus, ammonia nitrogen, total organic carbon, iron ion, and manganese ion in the water at the reservoir bottom on September 6 reached 2.5 mg/L, 0.12 mg/L, 0.58 mg/L, 3.2 mg/L, 0.97 mg/L, and 0.32 rag/L, respectively. Only heavy storm runoff can affect the main reservoir and cause the water quality to seriously deteriorate. During heavy storms, the stratification of the reservoir was destroyed, and the reservoir water quality consequently deteriorated due to the high-turbidity particulate phosphorus and organic matter in runoff. The turbidity and concentrations of total phosphorus and total organic carbon in the main reservoir increased to 265 NTU, 0.224 mg/L, and 3.9 mg/L, respectively. Potential methods of dealing with the water problems in the Jinpen Reservoir are proposed. Both in stratification and in storm periods, the use of measures such as adjusting intake height, storing clean water, and releasing turbid flow can be helpful to safeguarding the quality of water supplied to the water treatment plants.展开更多
The maximum normal impact resultant force(NIRF)is usually regarded as the sum of the static earth pressure of the dead zone and the dynamic impact pressure of the flowing layer.The influence of the interaction between...The maximum normal impact resultant force(NIRF)is usually regarded as the sum of the static earth pressure of the dead zone and the dynamic impact pressure of the flowing layer.The influence of the interaction between the flowing layer and dead zone on the impact force is ignored.In this study,we classified two impact models with respect to the pileup characteristics of the dead zone.Then,we employed the discrete element method to investigate the influences of the pileup characteristics on the impact force of dry granular flow on a tilted rigid wall.If the final pileup height is equal to the critical value,the maximum NIRF can be estimated using a hydrostatic model,because the main contribution to the maximum NIRF is the static earth pressure of the dead zone.If the final pileup height is less than the critical value,however,the particles in the dead zone are squeezed along the slope surface by the impact ofthe flowing layer on the dead zone,and because of shear effects,the flowing layer causes an entrainment in the dead zone.This results in a decrease in the volume of the dead zone at the moment of maximum NIRF with increases in the slope angle.As such,the maximum NIRF mainly comprises the instant impact force of the flowing layer,so hydro-dynamic models are effective for estimating the maximum NIRF.Impact models will benefit from further study of the components and distribution of the impact force of dry granular flow.展开更多
In this paper, ANSYS/LS-DYNA dynamic analysis software was used to establish finite element truss models with six trusses. The models with impact loads aimed to simulate the scenarios that structures were crashed by h...In this paper, ANSYS/LS-DYNA dynamic analysis software was used to establish finite element truss models with six trusses. The models with impact loads aimed to simulate the scenarios that structures were crashed by heavy truck. By changing the crashed position, the impact load intensity and structure height-span ratio, the models could give out the structural performance, including the stress, strain and other impacts in different scenarios. Besides, considering the component failure, this paper analyzed the possibility of structural progressive collapse. Results for the load cases from below indicate that it will be more destructive if impact load is arranged on 3rd side pillar and progressive collapse will occur if pillar fails after crashed.展开更多
Background： Measurements of tree heights and diameters are essential in forest assessment and modelling. Tree heights are used for estimating timber volume, site index and other important variables related to forest ...Background： Measurements of tree heights and diameters are essential in forest assessment and modelling. Tree heights are used for estimating timber volume, site index and other important variables related to forest growth and yield, succession and carbon budget models. However, the diameter at breast height （dbh） can be more accurately obtained and at lower cost, than total tree height. Hence, generalized height-diameter （h-d） models that predict tree height from dbh, age and other covariates are needed. For a more flexible but biologically plausible estimation of covariate effects we use shape constrained generalized additive models as an extension of existing h-d model approaches. We use causal site parameters such as index of aridity to enhance the generality and causality of the models and to enable predictions under projected changeable climatic conditions. Methods： We develop unconstrained generalized additive models （GAM） and shape constrained generalized additive models （SCAM） for investigating the possible effects of tree-specific parameters such as tree age, relative diameter at breast height, and site-specific parameters such as index of aridity and sum of daily mean temperature during vegetation period, on the h-d relationship of forests in Lower Saxony, Germany. Results： Some of the derived effects, e.g. effects of age, index of aridity and sum of daily mean temperature have significantly non-linear pattern. The need for using SCAM results from the fact that some of the model effects show partially implausible patterns especially at the boundaries of data ranges. The derived model predicts monotonically increasing levels of tree height with increasing age and temperature sum and decreasing aridity and social rank of a tree within a stand, The definition of constraints leads only to marginal or minor decline in the model statistics like AIC An observed structured spatial trend in tree height is modelled via 2-dimensional surface fitting. Conclusions： We demonstrate that the SCAM approach allows optimal regression modelling flexibility similar to the standard GAM but with the additional possibility of defining specific constraints for the model effects. The longitudinal character of the model allows for tree height imputation for the current status of forests but also for future tree height prediction.展开更多
泥石流为含有大量泥沙与石块的固液两相混合物,对于山区基础设施安全威胁巨大。在当前的防灾工程中,防护结构常被用于拦截泥石流。然而,目前对泥石流与防护结构的相互作用机理仍缺乏认识。为此,采用耦合的光滑粒子流体动力学(smoothed p...泥石流为含有大量泥沙与石块的固液两相混合物,对于山区基础设施安全威胁巨大。在当前的防灾工程中,防护结构常被用于拦截泥石流。然而,目前对泥石流与防护结构的相互作用机理仍缺乏认识。为此,采用耦合的光滑粒子流体动力学(smoothed particle hydrodynamics,SPH)和离散单元法(discrete element method,DEM)数值模型模拟了水槽试验中含有石块的泥石流运动,其中SPH模拟泥石流中的黏性流体,DEM模拟泥石流中的石块,分析了泥石流对刚性防护结构的冲击过程及冲击力。模拟结果表明,随着水槽倾角由0°依次增长为8°、15°、24°、30°,峰值冲击力增长倍数依次为2.59、4.75、8.88、11.45,倾角越大其峰值冲击力的增长率越大;而随着流体体积的增大,其峰值冲击力增长率也逐渐变大,相较V=0.024 m 3分别增长了0.79倍、1.64倍、3.20倍和4.56倍,但是稳定下来的静态冲击力基本与体积的变化成正比,而石块粒径对峰值水面高程的影响更显著。研究成果为泥石流防护结构的强度设计提供了理论支撑。展开更多
基金supported by the National Science and Technology Pillar Program(Grant No.2012BAC04B02)the National Natural Science Foundation of China(Grant No.51478378)
文摘The seasonal variation characteristics of the water quality of the Jinpen Reservoir and the impacts of rainfall runoff on the reservoir were investigated. Water quality monitoring results indicated that, during the stable stratification period, the maximum concentrations of total ni- trogen, total phosphorus, ammonia nitrogen, total organic carbon, iron ion, and manganese ion in the water at the reservoir bottom on September 6 reached 2.5 mg/L, 0.12 mg/L, 0.58 mg/L, 3.2 mg/L, 0.97 mg/L, and 0.32 rag/L, respectively. Only heavy storm runoff can affect the main reservoir and cause the water quality to seriously deteriorate. During heavy storms, the stratification of the reservoir was destroyed, and the reservoir water quality consequently deteriorated due to the high-turbidity particulate phosphorus and organic matter in runoff. The turbidity and concentrations of total phosphorus and total organic carbon in the main reservoir increased to 265 NTU, 0.224 mg/L, and 3.9 mg/L, respectively. Potential methods of dealing with the water problems in the Jinpen Reservoir are proposed. Both in stratification and in storm periods, the use of measures such as adjusting intake height, storing clean water, and releasing turbid flow can be helpful to safeguarding the quality of water supplied to the water treatment plants.
文摘The maximum normal impact resultant force(NIRF)is usually regarded as the sum of the static earth pressure of the dead zone and the dynamic impact pressure of the flowing layer.The influence of the interaction between the flowing layer and dead zone on the impact force is ignored.In this study,we classified two impact models with respect to the pileup characteristics of the dead zone.Then,we employed the discrete element method to investigate the influences of the pileup characteristics on the impact force of dry granular flow on a tilted rigid wall.If the final pileup height is equal to the critical value,the maximum NIRF can be estimated using a hydrostatic model,because the main contribution to the maximum NIRF is the static earth pressure of the dead zone.If the final pileup height is less than the critical value,however,the particles in the dead zone are squeezed along the slope surface by the impact ofthe flowing layer on the dead zone,and because of shear effects,the flowing layer causes an entrainment in the dead zone.This results in a decrease in the volume of the dead zone at the moment of maximum NIRF with increases in the slope angle.As such,the maximum NIRF mainly comprises the instant impact force of the flowing layer,so hydro-dynamic models are effective for estimating the maximum NIRF.Impact models will benefit from further study of the components and distribution of the impact force of dry granular flow.
文摘In this paper, ANSYS/LS-DYNA dynamic analysis software was used to establish finite element truss models with six trusses. The models with impact loads aimed to simulate the scenarios that structures were crashed by heavy truck. By changing the crashed position, the impact load intensity and structure height-span ratio, the models could give out the structural performance, including the stress, strain and other impacts in different scenarios. Besides, considering the component failure, this paper analyzed the possibility of structural progressive collapse. Results for the load cases from below indicate that it will be more destructive if impact load is arranged on 3rd side pillar and progressive collapse will occur if pillar fails after crashed.
文摘Background： Measurements of tree heights and diameters are essential in forest assessment and modelling. Tree heights are used for estimating timber volume, site index and other important variables related to forest growth and yield, succession and carbon budget models. However, the diameter at breast height （dbh） can be more accurately obtained and at lower cost, than total tree height. Hence, generalized height-diameter （h-d） models that predict tree height from dbh, age and other covariates are needed. For a more flexible but biologically plausible estimation of covariate effects we use shape constrained generalized additive models as an extension of existing h-d model approaches. We use causal site parameters such as index of aridity to enhance the generality and causality of the models and to enable predictions under projected changeable climatic conditions. Methods： We develop unconstrained generalized additive models （GAM） and shape constrained generalized additive models （SCAM） for investigating the possible effects of tree-specific parameters such as tree age, relative diameter at breast height, and site-specific parameters such as index of aridity and sum of daily mean temperature during vegetation period, on the h-d relationship of forests in Lower Saxony, Germany. Results： Some of the derived effects, e.g. effects of age, index of aridity and sum of daily mean temperature have significantly non-linear pattern. The need for using SCAM results from the fact that some of the model effects show partially implausible patterns especially at the boundaries of data ranges. The derived model predicts monotonically increasing levels of tree height with increasing age and temperature sum and decreasing aridity and social rank of a tree within a stand, The definition of constraints leads only to marginal or minor decline in the model statistics like AIC An observed structured spatial trend in tree height is modelled via 2-dimensional surface fitting. Conclusions： We demonstrate that the SCAM approach allows optimal regression modelling flexibility similar to the standard GAM but with the additional possibility of defining specific constraints for the model effects. The longitudinal character of the model allows for tree height imputation for the current status of forests but also for future tree height prediction.
文摘泥石流为含有大量泥沙与石块的固液两相混合物,对于山区基础设施安全威胁巨大。在当前的防灾工程中,防护结构常被用于拦截泥石流。然而,目前对泥石流与防护结构的相互作用机理仍缺乏认识。为此,采用耦合的光滑粒子流体动力学(smoothed particle hydrodynamics,SPH)和离散单元法(discrete element method,DEM)数值模型模拟了水槽试验中含有石块的泥石流运动,其中SPH模拟泥石流中的黏性流体,DEM模拟泥石流中的石块,分析了泥石流对刚性防护结构的冲击过程及冲击力。模拟结果表明,随着水槽倾角由0°依次增长为8°、15°、24°、30°,峰值冲击力增长倍数依次为2.59、4.75、8.88、11.45,倾角越大其峰值冲击力的增长率越大;而随着流体体积的增大,其峰值冲击力增长率也逐渐变大,相较V=0.024 m 3分别增长了0.79倍、1.64倍、3.20倍和4.56倍,但是稳定下来的静态冲击力基本与体积的变化成正比,而石块粒径对峰值水面高程的影响更显著。研究成果为泥石流防护结构的强度设计提供了理论支撑。
