SiC含量对Ti3SiC2/SiC复合材料性能的影响

采用反应热压烧结法制备了Ti3SiC2/SiC复合材料,针对SiC含量对该复合材料致密化程度、力学性能以及应力.应变行为的影响进行了研究.结果表明:(1)随着SiC含最的增加,试样难于致密,试样需要在更高的温度才能达到较高的致密度;(2)随SiC含量的增加,Ti3SiC2/SiC复合材料弯曲强度和断裂韧性提高,但SiC含量达到50%时,由于复合材料含有较多的孔洞,使强度和断裂韧性降低;(3)Ti3SiC2/SiC复合材料在常温下表现为非脆性断裂.     

液体中心式气液同轴离心式喷嘴火焰振荡特性

气液同轴离心式喷嘴在特定的结构和工况下极易发生自激振荡,为了探究自激振荡对燃烧过程的影响,针对液体中心式气液同轴离心式喷嘴,开展了氧气和酒精的可视化燃烧试验研究.基于非接触光学观测方法同步获得了喷雾与火焰的动态结构,研究了缩进长度及喷注工况对火焰的动态特性、自激振荡特性以及燃烧效率的影响.研究发现,随着喷嘴缩进长度的增...     

考虑连接刚度的导弹固有特性分析

导弹的动力分析是导弹设计中的一个重要环节,工程中常用非均匀梁作为动力分析的简化模型显然不够精确。本文采用了按照导弹实际尺寸建立的三维模型,而且动力模型中在舱段连接处引进了虚梁元,以考虑导弹舱段连接刚度的影响,进行固有特性分析。计算结果表明考虑舱段连接刚度后的固有特性计算值与实际值比较吻合。本文采用的方法对导弹进行动力分析时可推荐应用。     

基于群论的空间可展开结构自由度分析

为了开发构型新颖、生命力强、便于运输和储藏的空间可展开结构，使其满足所处环境的时间、空间等苛刻条件，适应特殊任务的实际需求，亟需开展空间可展开结构的自由度及折展性能分析。由于现有可展结构多具有一定的对称性，基于群论方法，从对称学角度解析结构可动的本质，提出判别对称体系可动性的充分条件。根据几何约束性质，运用矩阵理论和变分原理，推导了可展结构中典型构成单元的位移协调矩阵。利用对称子空间，推导了机构位移模态、自应力模态的对称表示，并以闭合环形可展开结构为研究对象，开展了结构自由度分析。研究工作有助于新型空间可展开结构的研发与设计，为可展结构及其衍生结构的进一步研究与应用提供了理论基础。     

考虑移动目标不确定行为方式的轨迹预测方法

针对现有方法难以预测出符合飞行移动目标不确定行为方式轨迹的问题,提出基于逆强化学习的飞行移动目标轨迹预测方法,通过学习目标行为偏好以及模拟目标行为决策过程的方式预测目标的移动轨迹。首先基于深度神经网络建立目标的行为决策模型与行为偏好模型,然后通过最大熵逆强化学习方法交替地学习模型参数。为了有效地学习目标的不确定行为特征,采用监督学习的方法学习出目标示例轨迹概率分布模型,用于指导目标行为偏好模型的训练以及初始化目标行为决策模型,同时通过对目标行为偏好模型进行预训练的方式提高其训练质量。仿真结果表明,提出的飞行移动目标轨迹预测方法可通过学习到的目标行为决策模型较为准确地模拟目标的行为方式,预测的目标轨迹分布与真实的目标轨迹分布在Kullback Leibler(KL)散度下的相似度可达0.24。     

基于流的遥感图像超分辨率重建

为了提高遥感图像超分辨率重建的质量，提出了一种基于流的遥感图像重建算法。首先，在Glow模型的基础上引入改进后的RRDB架构用于低分辨率图像特征提取，通过构建更多层和连接以提升训练的稳定性。然后，以一种纯数据驱动的流模型来训练分布的参数，通过最大化负的对数似然的方法进行优化，得到该算法的损失函数。实验证明该模型在网络训练过程中能够快速达到稳定收敛的状态，且具有很强的泛化能力。用重建出的图像质量对比SRCNN、SRGAN、ESRGAN，经过测试后发现，提出的算法远远优于SRCNN算法，与其他算法相比也有明显优势。重建出的图像不仅在指标上有所提升，例如与SRCNN相比，PSRN和SSIM分别提升了15%和40%，且人眼观察时有更高的清晰度，高频细节更为丰富。     

轴流压气机静子角区分离流动的DDES数值研究

为进一步加深对压气机静子角区分离流动非定常性和湍流特性的认识,以某台用于低速模拟的多级低速轴流压气机的第3级改型静子为研究对象,采用延迟脱落涡模拟(DDES)方法进行详细的数值研究.结果表明:压气机静子角区分离流动受到叶片几何参数和来流条件的综合影响;通道涡是引起静子角区分离的主要涡系结构,其发展过程伴随着大小尺度发簪...     

Experimental study on flow excursion instability of supercritical hydrocarbon fuel in scramjet regenerative cooling parallel channels

Flow instability of supercritical hydrocarbon fuel is a crucial issue in scramjet regenerative cooling structure. In this study, flow excursion instability and flow distribution in parallel tubes were experimentally studied for supercritical fluids. Two types of flow excursion occur in a single tube. Type I and Type II excursions, and they are corresponding to decreasing and increasing flow rate respectively. They can trigger flow maldistribution between parallel tubes and the hysteresis phenomenon of flow distribution. The effects of system parameters, including inlet temperature, system pressure, and heat flux, on flow distribution were analyzed. In addition, the relationship between flow excursion and the pseudo-critical interval proposed in the literature was established according to the heated tube outlet temperature at the onset of flow instability. Finally, the flow excursion instability boundary was obtained using two dimensionless parameters. These experimental results can provide helpful insight on the mechanism of Scramjet regenerative cooling.     

Trailing-edge shock loss control with self-sustaining synthetic jet in a supersonic compressor cascade

To effectively reduce the loss of strong shock wave at the trailing edge of the supersonic cascade under high backpressure, a shock wave control method based on self-sustaining synthetic jet was proposed. The self-sustaining synthetic jet was applied on the pressure side of the blade with the blow slot and the bleed slot arranged upstream and downstream of the trailing-edge shock,respectively. The flow control mechanism and effects of parameters were investigated by numerical simulation. The res...     

Effect of hygrothermal aging on moisture diffusion and tensile behavior of CFRP composite laminates

Carbon Fiber Reinforced Polymer (CFRP) composites are widely used in aircraft structures, because of their superior mechanical and lightweight properties. CFRP composites are often exposed to hygrothermal environments in service. Temperature and moisture can affect the material properties of composites. In order to make clear the moisture diffusion behavior and the properties degradation of composites, the TG800/E207 composite laminates with four stacking sequences [0]₁₆, [90]₁₆, [±45]_4s, and [(+45/0/0/–45)_s]_s are designed and manufactured. Moisture absorption tests are carried out at 80 ℃, 90 %RH. It is shown that the moisture absorption curves of composite laminates present a three-stage. A modified Fickian model was proposed to capture the diffusion behavior of TG800/E207 composite laminates. The relationships among the non-Fickian parameters, the environmental parameters and the stacking sequences of CFRP were correlated and compared. Results showed that the modified Fickian curve is sensitive to the diffusivity of Stage I and Stage II. Compared with unaged specimens, the maximum tensile stress for [0]₁₆, [90]₁₆, [±45]_4s, and [(+45/0/0/–45)_s]_s decreased by 14.94 %, 28.15 %, 11.96 %, and 26.36 %, respectively. The strains at failure for [0]₁₆, [90]₁₆, [±45]_4s, and [(+45/0/0/–45)_s]_s decreased by 55.38 %, 62.65 %, 46.41 %, and 31.71 %, respectively. The elastic modulus for [0]₁₆, [90]₁₆, [±45]_4s, and [(+45/0/0/–45)_s]_s increased by 90.93 %, 94.57 %, 49.22 %, and 8.22 %, respectively. [90]₁₆ sample has the minimum saturated moisture content and the maximum strength degeneration.