Numerical Modellings of Properties of the Summer Quasi-Stationary Circulation Systems and Their Monthly Variations

An ocean-atmosphere and land-air coupled numerical model system is used to study the basic properties and the monthly time variations of the summer quasi-stationary circulation systems. It is found that either at the upper or at the lower levels of the atmosphere, the circulation patterns have a two-wave structure in the zonal direction at the mid and high latitudes of the Northern Hemisphere. Such a structure of circulation is totally matchable to that of the land-sea distribution there. It is proved, hence, that the land-sea distributive pattern is the fundamental cause for the summer quasi-stationary circulation pattern. The topography in the globe is the secondary factor for circulation systems. The circulation centres of the quasi-stationary systems are always located in certain areas due to the thermodynamic contrast between land and sea.From the time evolutions of the circulation systems it is seen that the change is larger at the beginning period of the time integration, it is because of using the zonally averaged mean fields as the initial values of the model. As long as the basic simulated pattern of circulations reaches the state similar to that of the real climatic fields resulting from the coeffects of the land-sea distribution and the topography, the circulation systems modelled will change slowly and tend to a quasi-stationary state. Therefore, the time integration does not need to last for a very long time, if the purpose of numerical modellings is to test sensitivities of some factors influencing the climate, 20 model days may be enough for sensitive experiments.

电厂循环水系统凝汽器水锤两阶段关阀防护

火电厂循环水系统凝汽器的安全、可靠运行是火电厂稳定运行的最基本保证。为确保火电厂循环水系统安全运行,选择合适的防护措施是十分必要的。通过对水泵和凝汽器等边界条件的处理,建立了某火电厂循环水系统过渡过程的数学模型。结合实际工况,进行了各种快、慢两阶段关闭蝶阀方案的计算。结果表明:采用快、慢两阶段关闭蝶阀的优化方案可有效解决事故停泵过程中凝汽器压力过低和水泵倒转转速过大的矛盾,对防止凝汽器处产生弥和水锤有一定效果。分析了各工况的计算结果,对凝汽器的水锤防护及系统的运行方案提出了建议,数值模拟结果可为同类的工程布置设计和安全运行提供借鉴。

巴音河河床硬质化对地下水循环模式的影响研究

在西北干旱区,人类活动通过大型水利工程、农业引水灌溉等方式在不同程度上影响和改变着天然状态下的地下水循环模式,并引发一系列的次生灾害。以青海省德令哈市巴音河为例,选取山前冲洪积和冲湖积平原为研究区,利用MODFLOW软件沿河流方向建立地下水流的剖面二维数值模型,划分地下水流系统,分析相同径流量条件下河床硬质化对地下水循环模式的影响作用。结果表明河床硬质化改变了河流对地下水的补给机制,极大地影响了局部地下水流系统,使得地下水位整体下降,溢出带位置下移约800 m,且地下水出现了集中排泄现象。

火电厂循环水系统冷却塔高位布置水锤数值模拟

火电厂循环水系统布置受地形特征影响有时需要采用冷却高位布置方案,循环水系统水泵扬程低、流量大,冷却塔高位布置方案能否成立主要取决于系统的水锤压力大小。结合工程实例采用特征线方法,给出了循环水系统水锤数值模拟的基本方程以及水泵、凝汽器和冷却塔等相关设备的边界方程,模拟了高位布置方式下循环水系统内的水锤压力变化,论述了高位布置方式时减小系统水锤压力的工程措施。研究成果和讨论对实际工程应用具有参考意义。

池式钠冷快堆事故余热排出系统一回路仿真研究

池式钠冷快堆事故余热排出系统采用了非能动工作原理,依靠液态钠及空气的自然对流排出堆芯余热。为研究事故工况下余热排出系统一回路的换热能力,基于FORTRAN语言,建立堆芯单通道及盒间流模型,采用全隐二阶迎风差分格式及改进的欧拉法离散求解,对事故余热排出系统一回路系统进行数值模拟,并对全厂断电事故进行仿真计算验证。结果表明:该程序能较好地反映事故余热排出系统瞬态变化过程,并可达到超实时仿真。

火电厂循环水系统高位集水池水面波动数值模拟研究

针对火电厂循环水系统高位集水池在水泵启动及事故停泵过程中的水面波动现象,利用CFD软件采用VOF方法,通过UDF给定瞬态边界条件,对某电厂流道承压式与流道开敞式两种设计方案的高位集水池,在3台泵同时启动及同时事故停泵过程中的水面波动现象进行了数值模拟。计算结果表明,启动工况及事故工况下,流道开敞式的钟形进水流道由于增加了钟形吸水室的自由水面面积,较流道承压式的肘形进水流道更能减弱对高位集水池段的水面扰动。在重点考虑高位集水池段在水泵启动及事故停泵过程中水面波动的情况下,建议采用流道开敞式的循环水泵房布置形式。