Exact Solution of Unsteady Flow of Viscoelastic Fluid in a Pipe with Fractional Maxwell Model

The unsteady flow of viscoelastic fluid in a cylindrical pipe was investigated using the fractional Maxwell model. Two special cases of unsteady pipe flow were expressed. The first is start-up flow, and the second is oscillating flow. The exact solution of start-up flow under a constant pressure gradient was obtained by using the theories of Laplace transform and Fourier-Bessel series for fractional derivatives. The exact solution of oscillating flow was obtained by utilizing the separation of variables.     

济南黄河隧道超大直径盾构端头冻结加固技术

始发和接收段为盾构隧道施工过程中的重要风险源,特别是在富水地层中的防水措施十分关键。冻结法已普遍被应用于处理盾构始发和接收段止水加固的问题。依托济南黄河隧道工程,对超大直径泥水平衡盾构端头冻结技术进行总结。对工程地质和周边管线等实际情况进行具体分析,计算单个洞门接收和始发的需冷量后选择合适的冻结设备,并进行盐水循环和清水循环设计;通过始发段测温孔的设置和按时间分布记录的数据,分析了加固处的降温速率和冻结壁发展情况;从冻结帷幕厚度和冻土平均温度等指标对冻结效果进行评估;最后对冻结中可能遇到的冻胀、融沉、设备故障和洞门破除等风险进行评估,并给出相应的处理方法。以上得到的数据和结论可为以后工程中的冻结加固方向提供参考。     

内燃机内流动的研究

较系统地从流动试验测试手段和装置、流动数值模拟3个方面叙述了目前该领域内研究的现状和发展趋势。对内燃机几种重要的流动形式的形成及其对内燃机性能的影响进行了归纳,特别是将燃油射流形成的流动作为重要的流动形式之一进行了论述;总结了内燃机流动试验研究的几种测试手段和装置;介绍了几种流动数值模拟软件及其特点。     

一种新型汽车减振器优化设计方法研究

在对磁流变液减振器理论模型进行分析的基础上,确定了影响磁流变液减振器性能的结构参数。将磁流变液的非线性磁特性与非牛顿流体力学性能相结合,建立了以降低磁流变液减振器响应时间常数、增加其调节比为目标函数的优化模型。根据优化结果,研制了一种新型车用磁流变液减振器,并进行了验证试验。     

电控液驱风扇冷却系统及其在工程机械上的应用

开发了一种电控液驱风扇冷却系统,解决了工程机械的过热和过冷问题。采用比例溢流阀调节液驱系统的流量和压力,从而调节风扇转速以达到改变系统的散热量。此系统已应用于工程机械并进行现场试验,该工程机械冷却系统包含发动机冷却液散热器、变矩器油散热器和液压油散热器,在作业过程中3个冷却器中的冷却介质始终都维持在最佳温度,采用此冷却系统可提高发动机的经济性,即降低油耗,减小噪声,易布置等特点。     

交流传动内燃机车变流器与牵引电机联合冷却系统研究

随着交流传动内燃机车布局空间条件的日趋恶化,机车上大型零部件及电机的分体式冷却布局方式和传统冷却塔结构型式已显露出很大的局限性,为此,提出了一种新型通风冷却布局方案,即将风冷部件(牵引电机或主发电机)和水冷部件(变流柜的变流模块)的冷却系统进行有机结合,充分利用各环节冷却温度的需求差异,对发热设备进行有效冷却。这种集成布置充分缩减了机车两大部件的通风冷却装置在机车上的布局空间,优化了机车的整体布置,同时还降低了机车辅助功率,提高了机车效率。     

Constructal design of tree-shaped microchannel disc heat sink with wavy walls北大核心CSCD

［Objective］To meet the efficient thermal management needs of electronic devices such as ships and underwater vehicles, this study focuses on the constructal design of a tree-shaped microchannel disc heat sink with wavy walls. ［Method］A design prototype of the heat sink with wavy walls is first proposed. Based on constructal theory, the amplitude and wavelength of the wavy walls are designed under the constraints of fixed heat sink volume and fixed microchannel volume by maximizing the comprehensive performance evaluation criteria (PEC) while considering both heat transfer and flow pressure drop. ［Results］The results show that the wavy walls increase the heat transfer surface areas and generate vortices in their cavities, effectively reducing the maximum temperature. When the inlet Reynolds number is fixed at 700, 900 or 1100 respectively, the maximum temperature is reduced by 13.5 K by increasing the amplitude of the wavy walls, while the pressure drop increases significantly; and the maximum temperature is reduced by 4.7 K by reducing the wavelength of the wavy walls, while the pressure drop increases slightly. There are optimal amplitudes that raise the comprehensive performance evaluation criteria to extreme values for given larger wavelengths, while the comprehensive performance evaluation criteria increase monotonously as the amplitude increases for given smaller wavelengths. ［Conclusion］Wavy walls can significantly improve the thermal performance of tree-shaped microchannel disc heat sinks, and the use of constructal design can realize optimal geometric constructs with optimal comprehensive performance evaluation criteria. © 2023 Authors. All rights reserved.     

耙吸挖泥船环保阀溢流效果试验与数值分析

通过计算流体动力学数值模拟与模型试验相结合的方式，对耙吸挖泥船环保阀减少空气进入溢流筒的机理和作用进行相关研究。将模型试验与数值模拟的结果进行对比，验证气液两相流数值模型的准确性。进行不同进口流量、不同环保阀角度时的计算，获得进口流量、泥舱内液面高度、环保阀角度之间的相关性数学描述，据此建立环保阀的控制策略。建立叠加式溢流筒的数值模型，分析其在减少溢流上的效果。