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901.
902.
为全尺寸反射面的实际成型提供理论依据,本文通过建模仿真重点分析了外蒙皮装配偏差、自重及成型和使用温度差对反射面工作面型面精度(R. M. S)的影响。结果表明,当外蒙皮装配偏移量在0.5mm内时,其反射面工作面理论R. M. S值的变化量为0.47μm;在成型放置状态下,反射面11 kg自重其工作面理论R. M. S值变化量为0.55μm;反射面夹层结构的成型和使用温度差110℃,反射面工作面的理论R. M. S值变化量为17.79μm。 相似文献
903.
904.
基于瞬时频率估计的双曲调频信号检测技术 总被引:1,自引:0,他引:1
基于双曲调频信号的特征分析,提出了一种新的HFM信号检测方法——周期斜率方差检测器。根据不同信噪比下周期斜率方差的概率密度,给出了该检测器的二元假设检验模型,并对比了相同条件下该检测器与匹配滤波器的性能。仿真结果表明,周期斜率方差检测器是一种恒虚警概率检测器,在较低信噪比下可有效检测双曲调频信号,并对多普勒失配有很好的适配性。 相似文献
905.
A self-sensing test method for the temperature of piezoelectric stack,based on the high correlation between the static capacitance and the stack temperature,is proposed in order to construct a self-sufficient methodology of temperature measurement. Firstly,a theoretical model of static capacitance of the piezoelectric stack under preload was set up,and the influence of preload on the static capacitance was analyzed. Secondly,the correctness of the model was verified by static capacitance test experiments under various preloading conditions. Finally, the temperature measurement experiments at low-temperature stage for two kinds of piezoelectric stacks,namely the lowtemperature-resistant piezoelectric stack and conventional piezoelectric stack, were conducted under various preloading conditions using a polynomial fitting method. The results,which validate the accuracy of the test method,show that the maximum temperature deviations of the two kinds of piezoelectric stack are 3.9 ℃ and 2.8 ℃,respectively,when the preload force is close to the specified value. The test method uses the piezoelectric stack itself as a temperature sensor,which does not require additional equipment for temperature sensing,so that the space and equipment cost could be economized. And the test for static capacitance is concise and convenient,which indicates that in the cooling process,a concise and efficient test of the temperature of the piezoelectric stack could be realized so as to grasp the current temperature change in time. 相似文献
906.
针对树脂基防隔热复合材料高温条件下复杂的热/力/化学的多场耦合问题,从高温性能预报模型、高温响应求解方法和高温试验测试三方面进行了论述。详细介绍了研究树脂基防隔热复合材料高温响应相关的热解动力学模型、材料高温热物性及力学性能演化表征方法、材料高温响应模型的求解方法以及表征材料高温响应的多种高温试验测试手段。对上述研究方法的发展进行了评述,并对未来发展趋势进行了展望。本文有助于相关研究人员认识和发展树脂基复合材料在高温下的热力响应分析方法,也可供工程技术人员对这类材料的防隔热性能和高温承载性能进行研究。 相似文献
907.
The aging behavior of softening composite solid propellant was investigated by measuring its mechanical and ballistic prosperities during prolonged storage at elevated and room temperatures. Accelerated aging was conducted at 65 °C for 231 days while the normal aging was performed at 25 ± 3 °C and relative humidity less than 50% for 8 years. The mechanical properties were obtained from uniaxial tensile tests for the aged propellant specimens while the ballistic properties were determined from static firing tests of subscale motors aged for 112 days at 65 °C. The mechanical results show that the maximum tensile strength and Young's modulus initially increase and subsequently decrease with increasing aging time, while the maximum tensile strain generally increases with increasing aging time. The ballistic properties like burning rate show a small change which cannot affect the ballistic performance. The experimental results show that the changes in the mechanical properties are significant during the aging period, but the burning rate does not undergo significant changes. From this study, it is observed that the propellant ages through a combination of reactions like post-cure, oxidative cross-linking, chain scission, and hydrolysis. The chain scission and the hydrolysis effect are the most significant process, which makes the propellant soft and extendible. The observed aging mechanism has been modeled using an exponential function with two terms which can describe the complex behavior of the aging. By applying Arrhenius equation,the activation energy values were obtained based on the propellant mechanical properties. The shelf life of this propellant formulation at 25 °C is predicted to be 13 years using the modulus as failure criteria and control parameter. 相似文献
908.
Acoustic metasurface has attracted increasing attention due to the ability of manipulating the transmitted and reflected phase of waves to generate various acoustic functionalities with planar layer of sub?wavelength structure.We design an acoustic metasurface with a semi?closed and nested slotted tube array,and it possesses the capacity of modulating the reflected phase with sub ? wavelength thickness(about λ/23). The reflected phase shifts can be obtained from 0 to 2π by different rotation angles of internal slotted tubes. The theoretical results agree well with the numerical results by a finite element method. The results show that some excellent wavefront manipulations are demonstrated with the phase array by using acoustic metasurface such as anomalous reflection and sub?wavelength flat focusing. The design may offer a path for acoustic manipulation and promote the potential applications of acoustic metasurface in low frequency noise control,acoustic imaging and cloaking. 相似文献
909.
910.
讨论了漂浮基空间机器人在轨捕获目标卫星过程的碰撞动力学建模,以及捕获操作结束后空间机器人与卫星混合体的稳定控制问题。首先采用多刚体动力学建模方法并结合空间机器人捕获目标卫星过程中的碰撞动力学特性,建立了漂浮基空间机器人在轨捕获漂浮卫星过程的动力学模型,并在此基础上计算出完成捕获操作后空间机器人与目标卫星混合体关节的运动速度。然后针对卫星及空间机器人系统惯性参数均是未知的复杂情况,应用上述模型、神经网络控制理论和Lyapunov稳定性理论,设计了空间机器人与卫星混合体在捕获过程碰撞冲击影响下稳定运动的高斯径向基函数神经网络控制方案,以达到对捕获卫星的有效控制。此外,高斯径向基函数神经网络控制方案具有不需要测量和反馈载体位置、移动速度与加速度的显著优点。系统数值仿真证实了上述控制方案的有效性。 相似文献