Influence Of Structure Length Research Articles

A unified dynamic analysis method for kilometre-scale ultra large spacecraft based on dynamic stiffness method

Ultra-kilometre and super-flexible spacecraft are the important development trends in the future. Classical multi-body dynamics and structural dynamics analysis theory have some limitations in dynamic modelling and solution of large deformation structures. In this paper, an improved dynamic stiffness method (DSM) is proposed to deal with the dynamical modelling and solution of ultra-kilometre spacecraft. The method retains the high accuracy and efficiency of the original DSM in dealing with continuous dynamical systems and breaks through the limitations of the original method in dealing with large deformation structures by introducing equivalent linearization techniques. Results show that the modal frequencies and mode shapes in this paper agree well with finite element solutions, and the maximum deviation is less than 1%; Besides, with the increase of spacecraft length, the structure has entered the nonlinear stage from the linear stage, the fundamental frequency of the structure will be lower than 0.001Hz, and the influence of structure length, density, and the mass of additional cabins on natural frequencies is less significant than that in linear stage. The proposed dynamic analysis framework can be further employed in the dynamic response and vibration control problems of super large spacecraft.

Detailed analysis of the influence of structure length on pulse propagation through finite-size photonic crystal waveguides

We present a detailed analysis of the influence of the finite length of a photonic crystal (PhC) waveguide on its final response to pulses propagation. The analyzed PhC waveguide is accessed by conventional dielectric waveguides and the lack of a perfect coupling between them produces reflections at the interfaces, leading to the appearance of several output pulses at the end of the PhC waveguide. If the length of the PhC waveguide is short enough these repetitions overlap and the parameters that define the total output pulse (mainly amplitude, temporal width, time delay and group velocity) vary significantly. An oscillatory behavior of these parameters is observed when the length of the PhC waveguide is modified. A theoretical model has been used to achieve each cavity generated pulse at the output of the PhC waveguide. The unique parameters needed for these calculations are the propagation constant of the PhC waveguide and the transmission and reflection coefficients at each interface. Numerical simulations based on the eigenmode expansion method are used to obtain these parameters. The time and resources required to calculate the output pulse with this method are significantly reduced in comparison with FDTD simulations and the results are proved to be quite accurate.