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KONG Qiao-ling MA Jie State Key Laboratory of Ocean Engineering Shanghai Jiaotong University Shanghai China 《船舶与海洋工程学报》2007,6(4)
The phase change characteristic of the power source of an underwater glider propelled by the ocean's thermal energy is the key factor in glider attitude control. A numerical model has been established based on the enthalpy method to analyze the phase change heat transfer process under convective boundary conditions. Phase change is not an isothermal process,but one that occurs at a range of temperature. The total melting time of the material is very sensitive to the surrounding temperature. When the temperature of the surroundings decreases 8 degrees,the total melting time increases 1.8 times. But variations in surrounding temperature have little effect on the initial temperature of phase change,and the slope of the temperature time history curve remains the same. However,the temperature at which phase change is completed decreases significantly. Our research shows that the phase change process is also affected by container size,boundary conditions,and the power source's cross sectional area. Materials stored in 3 cylindrical containers with a diameter of 38mm needed the shortest phase change time. Our conclusions should be helpful in effective design of underwater glider power systems. 相似文献
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Activity-based models of travel demand have received considerable attention in transportation planning and forecasting in recent years. However, in most cases they use a micro-simulation approach, thereby inevitably including a stochastic error that is caused by the statistical distributions of random components. As a consequence, running a transport micro-simulation model several times with the same input will generate different outputs, which baffles practitioners in applying such a model and in interpreting the results. A common approach is therefore to run the model multiple times and to use the average value of the results. The question then becomes: what is the minimum number of model runs required to reach a stable result? In this paper, systematic experiments are carried out using Forecasting Evolutionary Activity-Travel of Households and their Environmental RepercussionS (FEATHERS), an activity-based micro-simulation modelling framework currently implemented for the Flanders region of Belgium. Six levels of geographic detail are taken into account. Three travel indices – average daily activities per person, average daily trips per person and average daily distance travelled per person, as well as their corresponding segmentations – are calculated by running the model 100 times. The results show that the more disaggregated the level, the larger the number of model runs is needed to ensure confidence. Furthermore, based on the time-dependent origin-destination table derived from the model output, traffic assignment is performed by loading it onto the Flemish road network, and the total vehicle kilometres travelled in the whole Flanders are subsequently computed. The stable results at the Flanders level provides model users with confidence that application of FEATHERS at an aggregated level requires only limited model runs. 相似文献
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介绍了直接数字频率合成技术以及分析其杂散误差,对相位截断误差和幅度量化误差进行了傅立叶级数分析研究。文章最后还简单介绍了几种改善杂散误差的方法。 相似文献
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基于相移变压器的双桥整流器研究 总被引:1,自引:0,他引:1
叶满园 《华东交通大学学报》2006,23(2):82-85
提出了一种采用相移变压器的双桥12脉冲整流器拓朴结构,对其工作原理进行了具体的介绍,并且分析了相移变压器的功能以及消谐原理.最后对这种拓扑结构进行了仿真和实验研究,结果表明这种整流器系统具有优良的工作性能,具有很高的实际应用价值. 相似文献
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桥梁监测系统中复杂结构的静力应变传感器优化配置方法 总被引:4,自引:0,他引:4
在桥梁结构状态监测评估系统中,传感器优化配置问题是监测信息经济可靠的关键,也是业内广泛关注的热点问题之一。本文以复杂桥梁结构为研究对象,提出了一套基于关心截面插值拟合误差最小准则的传感器优化配置方法,并通过实例介绍了该方法的优化步骤及验证了其有效性。 相似文献
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为研究寒区隧道围岩在持续低温作用或冻融循环作用过程中,考虑岩体相变过程中多相体各组分变化引起的岩石热学参数差异对围岩温度场时空变化规律的影响,利用已有岩体未冻水含量研究成果,进一步推导不同孔隙率下岩体的热学参数计算公式。基于多孔介质模型建立考虑相变过程的围岩温度场计算模型,分析考虑潜热时不同孔隙率下围岩冻结缘的空间形态变化规律,及相变过程对温度场的影响。研究结果表明: 1)饱和岩体孔隙率越高,对岩体整体热学参数影响越大; 2)低温持续作用围岩时,冻结缘向围岩深处移动并不断变宽,其宽度与其深度呈线性关系; 3)饱和围岩孔隙率对冻结缘移动速度影响较大,但对其宽度基本无影响; 4)由于相变潜热,岩体在冻融循环过程中围岩温度时程曲线出现不对称阶梯状形态,且其阶梯形状宽度与围岩孔隙率呈正相关; 5)冻融循环过程中,升温及降温过程中冻结缘临近岩体温度梯度存在差异引起的传热效率不同直接导致升温、降温时程曲线的不对称性特征出现; 6)沿硐室围岩径向向外,各处围岩体的温度时程函数与加载的温度函数存在着振幅衰减和相位滞后的现象,且岩体孔隙率越高该现象越明显。 相似文献