论文部分内容阅读
为了增加大口径望远镜次镜支撑结构第一阶固有频率,采用施加有预紧力的八根钢索取代原有的四翼梁结构。文中首先根据Euler-Bernoulli梁理论将此次镜支撑结构简化为一个由质量点和梁组成的简化模型并使用变分法得出系统固有频率表达式以及系统第一阶固有频率;然后以1.23 m望远镜为例,计算得出预紧力为20 000 N时系统第一阶固有频率为18.9 Hz与有限元仿真软件ANSYS得出的17.8 Hz相比误差为6%,证明了简化的可行性与理论的正确性。最后通过分析次镜室质量不变的情况下,不同主镜口径下预紧力与次镜支撑结构第一阶模态的关系,得出对于1.23 m望远镜,施加70 000 N的预紧力即可以使一阶模态达到34 Hz,对于2 m、4 m口径的望远镜,通过调节预紧力,可以将一阶频率控制在20 Hz以上的结论。文中的方法可以用于类似结构的动力学特性计算;同时这种结构具有较高的抗扭转刚度,并能够有效减轻次镜支撑结构的重量,对于大口径光学系统的设计有很好的指导意义。
In order to increase the natural frequency of the first order of the secondary mirror support structure of the large-aperture telescope, the original four-spar structure was replaced by eight steel cables with pre-tightening force. In this paper, we first simplify the mirror support structure into a simplified model consisting of mass points and beams according to the Euler-Bernoulli beam theory and derive the natural frequency of the system and the first natural frequency of the system by using the variational method. Then, Taking the telescope as an example, the first natural frequency of the system is 18.9 Hz when the pre-tension is 20 000 N, and the error is 6% compared with the 17.8 Hz obtained by the finite element simulation software ANSYS. It proves the feasibility and simplification of the theory Correctness Finally, by analyzing the relationship between the secondary lens constant and the prestressing force of the primary mirror and the first-order mode of the secondary mirror support structure, it is concluded that for the 1.23 m telescope, a preload of 70 000 N The first-order mode can reach 34 Hz. For 2 m and 4 m telescopes, the first-order frequency can be controlled above 20 Hz by adjusting the pre-tightening force. The method in this paper can be used to calculate the dynamic characteristics of similar structures. At the same time, this kind of structure has high torsional stiffness and can effectively reduce the weight of secondary mirror support structure, which is of great guiding significance for the design of large-aperture optical system .