一种适合低水头的拱洞型消能工的数值研究

采用VOF(volume of fluid)方法,模拟了低水头建筑物的泄水过程,通过慈溪龙山排涝出海闸工程实例对模型精确性进行校核,在此基础上提出一种新型拱洞型消能工,并与普遍采用的SAF(saint antony falls)型和原模型消能工的消能效果进行对比,结果表明,拱洞型消能工能进一步降低下泄水流的流速及水流深度,提高消能率,更有利于低水头建筑物的消能防冲。本文提出的拱洞型消能工,为低水头泄水建筑在选择消能防冲设施时提供了更多的选择。     

大石峡水利枢纽工程的泄水消能设计研究

大石峡水利枢纽工程是典型的高坝大库工程,泄水消能建筑物受地形地质条件影响,布置较难,具有水头高、超高流速、消能难、运用复杂等特点。针对工程开发任务、运用情况、坝型和地形地质条件,进行了泄水建筑物的方案比较、详细论证和研究,将泄水及引水发电系统集中于凸岸布置;泄水建筑物包括岸边溢洪道、中孔泄洪洞、放空排沙洞及生态放水孔,下游设置“护岸不护底”的联合消力塘。经过整体水工模型试验验证,泄水消能建筑物布置合理,运行安全。通过总结坝高250 m 级的大石峡水利工程泄水消能设计与研究,对超高坝的泄水工程设计有较好的借鉴作用。     

我国沿海生态植被消波研究进展

为对我国沿海生态植被消波研究进行综述,首先以消波植被作为切入点,分析了植被的刚度、分布以及非均匀性对消波效果的影响;进而,以水动力输入条件为切入点,综述了不同波浪情况下生态植被消波研究方法的异同;最后,将传统防波堤与生态植被消波进行对比,探讨二者在海岸条件、消波机制、生态效益、后期维护等方面的差异。认为消波植被刚度、分布、非均匀性等问题可以作为后续研究的方向,同时可尝试将防波堤消波与生态植被消波相结合,兼顾防灾减灾和生态保护的功能。     

The Competitive Impact of International Trade: The Case of Import Liberalization of the Japanese Oil Product Market

This paper analyzes the competitive impact of the recent import liberalization of the Japanese oil product market. In response to the import liberalization in March 1996, not only did the market price of gasoline decline sharply but also its domestic production kept rising and did not decline relative to imports. Moreover, its price fell substantially before the actual liberalization of the import. This paper demonstrates both theoretically and empirically that the theory of implicit cartel can explain such features of the impact of import liberalization very well. The paper also identifies the significantly positive welfare impact of such liberalization due to the expansion of supply in a market with a large tax wedge between price and cost and, possibly more importantly, due to the transformation of competitive conduct from unproductive investment for cartel-rent shifting into price cuts. J. Japan. Int. Econ., December 1999, 13(4), pp. 397–423. Hitotsubashi University; and Keio University. Copyright 1999 Academic Press.Journal of Economic Literature Classification Numbers: L40, F12, K21.     

Restoring native vegetation in a Eurasian water-milfoil dominated plant community using the herbicide triclopyr

In an effort to evaluate the selective control of the exotic weed Eurasian water milfoil (Myriophyllum spicatum L.) and to assess the recovery and restoration of the native submersed plant community, a 6-ha river and 4-ha cove plot were treated with the herbicide triclopyr at application rates of 2·5 and 1·75 mg/l, respectively, in the Pend Oreille River, WA, in August 1991. Water exchange half-lives within the plots were measured using rhodamine WT dye (river, t_1/2=20 h; cove, t_1/2=52 h), and triclopyr dissipation rates were also calculated (river, t_1/2=19 h); cove, t_1/2=53 h). Triclopyr concentrations were below the proposed potable water tolerance level (0·5 mg/l) within the river treatment plot by 3 days after treatment (<0·01 to 0·41 mg/l), and 675 m downstream of that plot by 1 day after treatment (<0·01 to 0·47 mg/l). Following the cove treatment, triclopyr residues ranged from 0·12 to 0·29 mg/l by 7 days after treatment, and from<0·01 to 0·06 mg/l as close as 150 m downstream from the plot. Eurasian water milfoil biomass was reduced by 99% in the treated plots at 4 weeks post-treatment, remained low one year later (river treatment, 28% of pretreat levels; cove treatment 1% of pre-treat levels) and was still at acceptable levels of control at two years post-treatment (river treatment, 47% of pre-treat levels; cove treatment, 24% of pre-treat levels). The four-week post-treatment efficacy results verified triclopyr concentration/exposure time relationships for controlling Eurasian water milfoil developed under laboratory conditions. Non-target native plant biomass increased 500–1000% by one year post-treatment, and remained significantly higher in the cove plot at two years after treatment. Native species diversity doubled following herbicide treatment, and the restoration of this robust community delayed the re-establishment and dominance of Eurasian water milfoil for three growing seasons. ©1997 John Wiley & Sons, Ltd.     

高重力坝防冲建筑物体型参数对水力特性的影响

高重力坝防冲建筑物体型参数的选取决定了泄洪消能水流的水力特性,从而影响水电站的安全运行。采用水工模型试验的方法,研究了防冲建筑物体型参数对水流的水力特性影响规律。研究结果表明：水垫塘长度的减小,使塘内淹没冲击射流的扩散空间减小、冲击区的紊动增强,导致塘内底板时均压强谷值减小、脉动压强均方根峰值增大、底板安全风险增大;二级消力池池长的减小,使出池临底流速增大、下游冲刷风险增大;二道坝高度的降低,导致水垫塘底板沿程时均压强减小、脉动压力均方根峰值增大、底板安全风险增大,同时导致二级消力池内水跃收缩断面水深增加、跃首区临底流速降低、紊动强度降低、脉动压力均方根峰值减小,但出池临底流速增大。     

考虑底摩阻损耗的波浪传播与衰减计算的边界元法

边界元法在势流计算中具有使问题降低一维的优点。为了将边界元法与基于粘性流体理论的底部波能损耗结合起来,本文采用一种包含底摩阻系数的底部边界条件,可以在考虑底摩阻损耗的情况下计算极平缓岸坡上波浪的传播与衰减。数值结果得到了物模实验数据的验证。     

台阶式溢洪道相对消能率与相对佛汝德数关系研究

台阶式溢洪道是目前研究的热点,台阶消能率和佛汝德数是重要的水力参数。将台阶式溢洪道佛汝德数与对应光滑溢洪道佛汝德数对比,引入相对佛汝德数的概念,准确地反映由于台阶的存在对水流佛汝德数的改变值。通过对0.5,1.0,2.0 m 这3个不同台阶高度,坡度为38.66°的台阶式溢洪道进行试验研究,探讨了相对佛汝德数和相对消能率之间的关系。结果表明非均匀流流态下相对佛汝德数和相对消能率表现出良好线性关系,相关系数为0.992 7~0.998 9。单宽流量不同,相对佛汝德数和相对消能率对应直线的斜率明显不同,其斜率随单宽流量加大而增大;而台阶高度变化对相对佛汝德数和相对消能率线性关系的直线斜率影响很小。     

BSC框架下MRCTM闭环供应链整体绩效的熵值评估法

针对MRCTM闭环供应链模式特点,在BSC框架下,构建了一套闭环供应链绩效评价指标体系;并运用复杂性科学的熵理论与耗散结构理论,探讨了闭环供应链绩效的耗散结构模型并予以分析评价,丰富了闭环供应链的绩效评价理论和方法。     

东山拦河闸下游消能工加固改造研究

东山水利枢纽拦河闸下游消力池遭受破坏,且下游河道河床下切、水位明显降低,严重影响工程的安全运行。为了解决工程存在的问题,拟在已破坏的消力池改造的基础上,在其下游修建二级消力池。根据拦河闸加固改造工程设计的闸址下游河道水位与流量关系资料,对拦河闸加固改造的下游两级消力池体型和消能特性进行分析和水力计算,提出了消力池的布置方案。研究提出的加固改造两级消力池方案经水力模型试验验证是合理的,其成果可供类似工程设计参考。更多还原