How persistent are hysteresis patterns between suspended sediment concentration and discharge at different timescales?

ABSTRACT

This study was conducted to characterize the hysteresis of suspended sediment concentration (SSC) at different timescales for the Educational and Research Forest Watershed of Tarbiat Modares University, Iran. Hysteresis loops were developed between flow discharge and SSC using data for (i) the whole period, (ii) seasonal, (iii) monthly and (iv) storm-event timescales. The data were collected on an hourly basis at daily and storm-event scales from October 2007 to July 2008. The SSC hysteresis for all the events in the whole study period showed a clockwise pattern, with a flushing behaviour pointing to sudden changes in sediment sources. The results further reveal that the study watershed behaves differently from the viewpoint of hysteresis patterns, with different conditions of dilution and flushing between SSC and flow discharge at different timescales. These result from the complex varying effect of governing conditions on the watershed.     

风急流对吕宋海峡黑潮路径变异的影响及其动力机制

为研究风急流对吕宋海峡处黑潮路径的影响,本文使用1.5层约化重力浅水模式,设置了与吕宋海峡跨度相接近的缺口宽度,考虑西边界流在西边界缺口处当处于迟滞过程的临界状态时,其路径受风急流影响的动力机制,并初步探讨了在实际海陆边界条件下,实际风急流对黑潮路径的影响。结果显示,理想情况下,当西边界流处在由入侵流态到跨隙流态转变的临界状态时,西风、南风以及西南风风急流可以激发西边界流由入侵流态转变为跨隙流态。当西边界流处在由跨隙流态向入侵流态转变的临界状态时,北风、东风以及东北风风急流可以激发西边界流由跨隙流态转变为入侵流态,并且在风急流消失后西边界流不能再恢复到初始流态。实际情况下,冬季风急流有利于黑潮入侵南海,夏季风急流有利于黑潮跨越吕宋海峡,这和理想情况下的模拟结果以及实际观测结果相一致,这对进一步研究南海北部的上层环流以及南海的质量、能量输送有重要意义。     

部分预制型钢混凝土梁抗震性能试验研究

为探究部分预制型钢混凝土梁的抗震性能,进行了7个部分预制型钢混凝土梁试件的拟静力试验,研究了试件的裂缝开展过程、破坏形态、承载能力、延性、耗能能力和刚度退化情况,探究预制截面模式、剪跨比和后浇混凝土强度等对其抗震能力的影响。结果表明:地震作用下,该7个试件力学性能较好,剪跨比是影响试件抗震性能的首要要素,剪跨比大的试件耗能能力强,型钢约束部分混凝土可以提高试件的耗能能力,截面模式和后浇混凝土强度对抗震性能影响不大。     

我国东北地区某些荒芜土地的景观生态建设

我国东北地区荒芜土地的主要问题是:①土地自然生产力得不到充分发挥;②土地退化。本文根据景观生态学关于人与自然共同创造的思想及生物控制共生与自然界等级组织理论,主张在东北区域的沙地上建立林、草、田复合生态系统,在沙垅间长洼地上节节修筑沙坝,控制7—8月暴雨径流,再按不同生境种植水稻、芦苇及红麻,既适应环境,又提高生产力。     

台站用百叶箱内外气温比对与分析

用双通道自动测温表对台站用的百叶箱内外气温进行了同步比对测量与分析。指出自然通风时，百叶箱对箱内气温变化产生一定程度的滞后和热辐射作用。滞后作用较明显。     

基于相关函数理论的动模量和阻尼比计算新方法

基于相关函数理论,提出一种新的计算动三轴试验动模量和阻尼比的方法。假设土体为黏弹性体,采用自相关函数分析应力、应变波形的平均幅值,进而计算动模量;采用互相关函数分析应变滞后于应力时程波形的相位差,进而计算阻尼比。利用饱和珊瑚砂、南京细砂和原状粉质黏土的不排水应变控制分级循环加载试验数据,分析结果表明：动模量和阻尼比计算的相关函数法对不同土样具有普适性;应变幅值小于1×10?4时,相关函数法计算动模量及阻尼比的精度明显优于传统的滞回圈法;应变幅值大于1×10?3时,土体呈现强非线性特性,应力-应变滞回圈不对称,相关函数法计算的阻尼更为可靠。     

Formulation of a three‐dimensional constitutive model for unsaturated soils incorporating mechanical–water retention couplings

Wheeler, Sharma and Buisson proposed an elasto‐plastic constitutive model for unsaturated soils that couples the mechanical and water retention behaviours. The model was formulated for isotropic stress states and adopts the mean Bishop's stress and modified suction as stress state variables. This paper deals with the extension of this constitutive model to general three‐dimensional stress conditions, proposing the generalized stress–strain relationships required for the numerical integration of the constitutive model. A characteristic of the original model is the consideration of a number of elasto‐plastic mechanisms to describe the complex behaviour of unsaturated soils. This work presents the three‐dimensional formulation of these coupled irreversible mechanisms in a generalized way including anisotropic loading. The paper also compares the results from the model with published experiments performed under different loading conditions. The response of the model is very satisfactory in terms of both mechanical and water retention behaviours. Copyright © 2013 John Wiley & Sons, Ltd.     

Convection in a rotating,laterally heated annulus transition to lower symmetry

Abstract

The radial temperature differences at which the transition from lower symmetry to the wave regime and the transition from the wave regime to lower symmetry occur have been measured for rotation rates ≦2rad/sec. It was found that the temperature differences at which the transitions occur differ for a fixed rotation rate, depending on whether the radial temperature difference is either increased or decreased with time. There is hysteresis in the transition at lower symmetry.     

A novel hysteresis model in unsaturated soil

This study presents a novel hysteresis model based on van Genuchten's soil‐moisture relationships. The proposed model yields a series of closed‐form relationships in which two shape factors α and η are determined from the main drying and wetting curves. Experimental and literature‐cited data were used to assess model accuracy. The proposed model was also compared with the Scott and KP models. Analytical results indicate that the present model is simple, accurate and effective in constructing the series of wetting and drying scanning curves. Notably, the proposed model outperforms the Scott and KP models in terms of model accuracy. Moreover, the novel model eliminates the pumping effect and has perfect closure at scanning curve reversal points. Copyright © 2004 John Wiley & Sons, Ltd.