珊瑚砂振冲密实加固响应室内模型试验研究

随着海洋岛礁工程的大力推进,吹填珊瑚砂地基的密实加固问题开始备受关注。利用自主研发的室内振冲器开展了珊瑚砂饱和砂土地基的室内振冲模型试验研究,深入分析了振冲过程中动孔隙水压力、水平动土压力等动参量的响应规律,探讨了振冲后沉降变形、相对密实度的变化特征。结果表明：松散珊瑚砂地基的密实度在经过两次双点振冲反复加固后均提升至中密。其中相对密实度在振冲点位处的提升效果较其余位置更为明显,并且中层或深层区域的加固效果优于表层区域。在超孔隙水压力方面,其最大值出现在振冲珊瑚砂地基过程中的贯入阶段,并且在留振开始时出现衰减现象。珊瑚砂地基在振冲器上拔过程中超孔隙水压力发生断崖式下跌。在第2次贯入时,超孔隙水压力比的峰值较首次出现显著下降。超孔隙水压力比等值线云图表明,振冲过程中的超孔隙水压力比等值线呈现平行分布。珊瑚砂浅层水平土压力随振冲器的贯入与拔出均呈现增加态势,深层水平土压力则呈现减少态势。     

Numerical Study on Tidally Induced Cross-Frontal Mean Circulation

An analytical solution for a circulation across a tidal front obtained by Dong, C., Ou, H-W., Chen, D., &; Visbeck, M. (2004 Dong, C., Ou, H-W., Chen, D., &; Visbeck, M. (2004). Tidally induced cross-frontal mean circulation: Analytical study. Journal of Physical Oceanography, 34, 293–305. doi: 10.1175/1520-0485(2004)034<0293:TICMCA>2.0.CO;2[Crossref], [Web of Science ®] , [Google Scholar]). Tidally induced cross-frontal mean circulation: Analytical study. Journal of Physical Oceanograph, 34, 293–305) suggests that the cross-frontal circulation can be decomposed into four parts: frontal cell, Ekman cell, Bernoulli cell, and Stokes drift. This study examines the analytical solution thoroughly using a two-dimensional numerical model solving primitive Navier-Stokes equations. The direct comparison between the numerical and the analytical models of three cases (winter tidal front, summer tidal front, and no front) with the same configurations demonstrates that the analytical solution captures the major features of the cross-frontal circulation. A series of numerical experiments are applied to study the sensitivity of the cross-frontal circulation to physical variables: tidal intensity, horizontal topography scale, frontal strength, and vertical eddy viscosity. The ratio of the tidal excursion distance to the topographical scale is crucial to the Ekman cell in the homogenous ocean. With a greater density gradient, both the Bernoulli and Ekman cells are enhanced. Assumptions made in the analytical model are also examined. The uniform eddy viscosity and linearization in the analytical model could overestimate the bottom flow in the Ekman cell and underestimate the Bernoulli cell in the shallower region, respectively. The influence of the internal tide on the cross-frontal circulation is discussed.     

A minimal model of the Atlantic Multidecadal Variability: its genesis and predictability

Through a box model of the subpolar North Atlantic, we examine the genesis and predictability of the Atlantic Multidecadal Variability (AMV), posited as a linear perturbation sustained by the stochastic atmosphere. Postulating a density-dependent thermohaline circulation (THC), the latter would strongly differentiate the thermal and saline damping, and facilitate a negative feedback between the two fields. This negative feedback preferentially suppresses the low-frequency thermal variance to render a broad multidecadal peak bounded by the thermal and saline damping time. We offer this “differential variance suppression” as an alternative paradigm of the AMV in place of the “damped oscillation”—the latter generally not allowed by the deterministic dynamics and in any event bears no relation to the thermal peak. With the validated dynamics, we then assess the AMV predictability based on the relative entropy—a difference of the forecast and climatological probability distributions, which decays through both error growth and dynamical damping. Since the stochastic forcing is mainly in the surface heat flux, the thermal noise grows rapidly and together with its climatological variance limited by the THC-aided thermal damping, they strongly curtail the thermal predictability. The latter may be prolonged if the initial thermal and saline anomalies are of the same sign, but even rare events of less than 1% chance of occurrence yield a predictable time that is well short of a decade; we contend therefore that the AMV is in effect unpredictable.     

Social-ecological and regional adaptation of agrobiodiversity management across a global set of research regions

To examine management options for biodiversity in agricultural landscapes, eight research regions were classified into social-ecological domains, using a dataset of indicators of livelihood resources, i.e., capital assets. Potential interventions for biodiversity-based agriculture were then compared among landscapes and domains. The approach combined literature review with expert judgment by researchers working in each landscape. Each landscape was described for land use, rural livelihoods and attitudes of social actors toward biodiversity and intensification of agriculture. Principal components analysis of 40 indicators of natural, human, social, financial and physical capital for the eight landscapes showed a loss of biodiversity associated with high-input agricultural intensification. High levels of natural capital (e.g. indicators of wildland biodiversity conservation and agrobiodiversity for human needs) were positively associated with indicators of human capital, including knowledge of the flora and fauna and knowledge sharing among farmers. Three social-ecological domains were identified across the eight landscapes (Tropical Agriculture-Forest Matrix, Tropical Degrading Agroecosystem, and Temperate High-Input Commodity Agriculture) using hierarchical clustering of the indicator values. Each domain shared a set of interventions for biodiversity-based agriculture and ecological intensification that could also increase food security in the impoverished landscapes. Implementation of interventions differed greatly among the landscapes, e.g. financial capital for new farming practices in the Intensive Agriculture domain vs. developing market value chains in the other domains. This exploratory study suggests that indicators of knowledge systems should receive greater emphasis in the monitoring of biodiversity and ecosystem services, and that inventories of assets at the landscape level can inform adaptive management of agrobiodiversity-based interventions.     

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用拟准检定法和岭估计解算病态污染方程

针对法方程呈现病态且观测值受到污染而不严格服从正态分布的情况 ,探讨运用拟准检定法抗御粗差 ,用岭估计改善法方程的病态性。拟准检定法是根据真误差与观测值的确定关系式 RΔ =- RL求解真误差估值Δ。在 A或 ATA病态的情况下 ,直接求 R是不稳定的。对 A作奇异值分解计算 R,可避免对病态矩阵直接求逆。由于 R是秩亏的 ,通过附加“拟准观测真误差估值范数极小”的条件来求解真误差估值。拟准检定法与岭估计两者的结合 ,一般情况下有效地剔除了粗差 ,而且改善了方程的病态性 ,计算简单、快捷 ,结果比较理想。     

A three-point method for estimating wave reflection of obliquely incident waves over a sloping bottom

A three-point method for estimating wave reflection is proposed to account for monochromatic oblique incident waves propagating over a sloping beach. The amplitudes of reflected wave and incident wave are separated using wave amplitudes measured at three fixed wave gauges with a distance. The applicability of the theory is verified by comparing the simulated results with the available theoretical, numerical and experimental results for the estimation of wave reflection. The sensitivity is also tested to provide a more accurate prediction of the reflection coefficient.     

A new smooth hysteretic model for ductile flexural‐dominated reinforced concrete bridge columns

A new smooth hysteretic model is proposed for ductile, flexural‐dominated reinforced concrete bridge columns. Four columns designed per modern seismic codes were tested using monotonically increasing and variable‐amplitude cyclic loading protocols and ground motion loading to develop the model. Based on the test results, hysteretic rules for damage accumulation and path dependence of reloading were constructed. For damage accumulation, unloading stiffness degradation is correlated with the maximum displacement and hysteretic energy dissipation, while reloading stiffness degradation is set equal to the unloading stiffness degradation. Pinching severity is related to the residual displacement in the direction opposite to the loading direction. Strength deterioration is correlated with the damage index and does not occur until the damage index reaches a threshold, after which the deterioration is proportional to the increase of the damage index. For path dependence of reloading, reloading paths are classified into primary paths and associate paths. The primary paths are those that start from a residual displacement that is equal to or larger than the previous maximum one. The associate paths are those that do not belong to primary paths and tend to be directed towards certain points. Reloading without load reversal is assumed to be linear. Comparison with the results of pseudo‐dynamic tests using three consecutive ground motions showed that the proposed model closely matched the test results. Copyright © 2017 John Wiley & Sons, Ltd.     

太湖流域高度城镇化地区畅流活水多目标调度决策研究

随着城市化进程的加快,高污染负荷、弱水动力条件、强人工干预导致的平原河网地区河道水质恶化、生态衰退已成为制约城市高质量发展的瓶颈之一。结合太湖流域高度城镇化地区水文水动力特性,构建了水动力-水质耦合模型,模拟了不同情景下河网水动力与水质情况。统筹考虑水质改善、水动力提升、经济成本等多目标,建立了活水调度多目标决策体系,基于模糊层次分析法确定评价体系水质改善、水动力提升与经济成本指标层权重分别为0.390、0.345、0.265,为各指标层设计对应的要素层,并利用模糊综合评价法进行评价。结果表明,针对不同调度情景下水质改善、水动力提升及经济成本等多目标的决策,利用多目标调度决策方法可有效确定效果最佳的工程调度情形。太湖流域高度城镇化地区区域性控制工程对畅流活水效果的影响要远大于锡山区控制工程,运东大包围城市防洪工程调度模式对研究区活水效果的影响最大。比选出的最优活水方案实现的研究区活水效果为水质达标率82%,水质平均提升率31%,Ⅲ类水断面占比61%,平均流速0.10 m/s,较优流速占比39%,滞水率32%。相较于传统的单指标或多指标简单比较的决策方法,多目标调度决策方法更具有综合性、...