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341.
342.
《中国航空学报》2021,34(2):301-317
The paper presented topology optimization of 2D and 3D Nanofluid-Cooled Heat Sink (NCHS). The flow and heat transfer problem in the NCHS was treated as a single-phase nanofluid based convective heat transfer model. The temperature-dependent fluid properties were taken into account in the model due to the strong temperature-dependent features of nanofluids. An average temperature minimum problem was studied subject to the fluid area and energy dissipation constraints by using the density method. In the method, the design variable is updated according to the gradient information obtained by an adjoint based sensitivity analysis process. The effects of the energy dissipation constraint, temperature-dependent fluid properties and nanofluid characteristics on optimal configurations of NCHS were numerically investigated with following conclusions. Firstly, branched flow channels in the optimal configuration increased with the rise of the allowed energy dissipation. Secondly, temperature-dependent fluid properties were significant for obtaining the appropriate optimal results with best cooling performance. Thirdly, heat transfer performances of optimal configurations were enhanced by reducing the nanoparticle diameter or increasing the nanoparticle volume fraction. Fourthly, the optimal configuration for nanofluid had better cooling performance than that for its base fluid. 相似文献
343.
《中国航空学报》2021,34(5):27-38
Studies show that different geometries of a Variable Cycle Engine (VCE) can be adjusted during the transient stage of the engine operation to improve the engine performance. However, this improvement increases the complexity of the acceleration and deceleration control schedule. In order to resolve this problem, the Transient-state Reverse Method (TRM) is established in the present study based on the Steady-state Reverse Method (SRM) and the Virtual Power Extraction Method (VPEM). The state factors in the component-based engine performance models are replaced by variable geometry parameters to establish the TRM for a double bypass VCE. Obtained results are compared with the conventional component-based model from different aspects, including the accuracy and the convergence rate. The TRM is then employed to optimize the control schedule of a VCE. Obtained results show that the accuracy and the convergence rate of the proposed method are consistent with that of the conventional model. On the other hand, it is found that the new-model-optimized control schedules reduce the acceleration and deceleration time by 45% and 54%, respectively. Meanwhile, the surge margin of compressors, fuel–air ratio and the turbine inlet temperature maintained are within the acceptable criteria. It is concluded that the proposed TRM is a powerful method to design the acceleration and deceleration control schedule of the VCE. 相似文献
344.
345.
空间科学任务协同设计过程优化 总被引:2,自引:0,他引:2
为了对概念设计阶段空间科学任务协同设计过程进行合理规划, 减少设计反馈, 降低系统耦合度, 提出了设计结构矩阵(DSM)过程建模和遗传算法(GA) 过程优化算法. 该方法采用DSM对空间科学任务设计活动序列进行建模, 通过DSM描述设计活动间的信息依赖关系, DSM上三角之和代表该设计活动序列设计反馈次数; 将 DSM对应的设计活动序列视为染色体, 采用GA进行序列优化, 最小化设计反馈次数. 通过过程优化算法获取最佳设计活动序列, 优化设计过程, 降低系统耦合度. 空间科学任务实例分析结果表明, 该方法能够有效应用于空间科学任务协同设计的过程建模和过程优化, 指导设计过程的制定. 相似文献
346.
To simulate the different lunar phases and ensure continuous adjustability of the radiant brightness, a new broad spectrum light and frosted glass were applied and designed in the optical system for lunar simulator with the shapes and radiance being able to be adjusted. According to the engineering demand and index requirements of the optical system, three major design aspects are addressed, including the high reliability and maintainability for broad-spectrum light, heat dissipation in lunar simulator for long working hours, and bearing of the main frame under different working conditions. By designing a reasonable machine structure, and through the structure itself with the matrix arrangement of 48 axial flow fans, an effectively cooling air duct is established. Deformation and temperature were calculated by the finite element software ANSYS. The results showed that the displacement deformation reached 0.33mm and stress deformation reached 0.02MPa at the temperature of 20℃; when the main frame was in the temperature field between 20℃ and 65℃, the maximum displacement deformation reached 13.30mm and maximum stress deformation is 97.90MPa, and the amount of this deformation is very small in considering of the mechanical structure dimensions and weight of the lunar simulator. 相似文献
347.
针对目前高轨GPS信号可用性差及定位精度低的特点, 对GPS/北斗组合系统的 高轨卫星定位技术进行研究, 对比分析了单GPS系统与GPS/北斗组合系统的卫 星可见性和几何精度因子. 结果表明, GPS/北斗组合系统比单GPS系统的卫星可 见性好, 且定位精度高. 同时通过提出在星载接收机上采用高精度原子钟, 可实现三星定位, 降低对接收机的技术要求. 相似文献
348.
为实现对星敏感器光谱探测能力的测试和标定, 研制了一套可模拟恒星光谱的地面标定系统, 要求其光谱模拟精度优于10%. 采用光谱分布可控、光强可调的模拟照明系统作为地面标定系统的核心器件来模拟恒星光谱变化, 设计高成像质量准直光学系统使模拟星图成平行光出射, 在光学系统出瞳处产生星图, 完成具有恒星光谱信息的高精度星图模拟. 进而利用Lighttools建立标定系统的光谱仿真模型, 仿真结果表明恒星光谱模拟精度优于10%. 相似文献
349.
太阳帆航天器以两姿态角作为轨道控制输入时, 其轨道动力学方程具有非仿射非线性特性. 通过人工平动点处线性化获得的线性系统可完成太阳帆航天器轨道保持控制器的分析与设计. 由于线性近似模型为有误差模型, 存在近似有效范围约束, 表现为轨道高度约束和姿态角幅值约束. 本文研究了姿态角幅值约束对线性近似模型有效性的影响, 通过计算给出满足近似误差要求的姿态角幅值约束. 当控制输入存在幅值约束时, 控制器轨道修正能力受到束缚. 通过研究姿态角幅值约束下的最大允许入轨误差, 设计了最大允许入轨误差下线性二次型调节器(LQR)用于轨道保持控制, 并将控制器应用于太阳帆日地三体系统非线性模型中, 实现了日地人工L1点Lissajous轨道最大允许入轨误差的控制收敛和良好精度下的轨道保持控制. 相似文献
350.