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4 Structure and Mechanism Technology of Lunar Lander
Different from stress analysis, the establishment of the stability analysis model
was not very concerned with the stress concentration area. And it was concerned with
the areas where compressive stress and shear stress was relatively serious. Because
the model of stress analysis had been able to get the deformation mode relatively
accurately, there was no need to consider mesh refinement as a whole. However, in
the local area where compression stress and shear stress were serious, it was still
possible to refine the mesh further more so as to ensure that there were enough units
to accurately represent the instability waveform. Otherwise, the unit mesh was too
sparse, causing the structure to stiffen relative to other regions, resulting in inaccurate
calculation results.
In the stress analysis model of complex structure, spring element was usually used
to simulate the local connection. When the stability analysis as carried out, the spring
element couldn’t provide the differential stiffness, so other suitable units were used
in the local connection where the instability waveform was greatly affected.
The results of stability analysis were greatly influenced by boundary conditions.
Although the boundary condition was the same as stress analysis, it was necessary
to draw lessons from past analysis experience and test results. The determination
of boundary conditions was mainly based on engineering experience. In addition,
the subjective judgment of the rationality of the instability waveform could check
whether the boundary conditions were accurate.
It was worth noting that the stability analysis results obtained from the finite
element method as a linear eigenvalue might be more deviations from test results,
especially for plate and shell structure. This was mainly due to the geometric defects
and material defects in the structure manufacture process and the uneven load.
The stability analysis of the Chang’E-3 lunar lander during the development
process was carried out. Because the stability coefficient of the analysis was greater
than 3 and it was local instability, the model which was exactly the same as static
analysis (including load and boundary condition) was used in the stability analysis.
4. Frequency Response Analysis
The frequency response analysis was the response analysis of the spacecraft under the
sinusoidal excitation condition. The response analysis results under different sinusoidal frequency excitation could be plotted as the curve of the frequency response
curve.
Frequency response analysis includes analysis of acceleration, displacement,
stressed, load (force) and etc. The purpose of frequency response analysis was:
(1) to obtain structural stressed and load at connection pointed under the sinusoidal
load, to guide and verify the structure design and parameter design, to verify the
dynamic strength of the structure; (2) to obtain the acceleration response of each part
under the sinusoidal load, and to judge the secondary structure, large parts and so
on. The frequency coupling of spacecraft with secondary structure and large parts
was used to evaluate the stiffness design rationality of secondary structure and large
components, which provided the basis for the establishment of the sine vibration
environment conditions of equipment onboard the lunar lander.
4 Structure and Mechanism Technology of Lunar Lander
Different from stress analysis, the establishment of the stability analysis model
was not very concerned with the stress concentration area. And it was concerned with
the areas where compressive stress and shear stress was relatively serious. Because
the model of stress analysis had been able to get the deformation mode relatively
accurately, there was no need to consider mesh refinement as a whole. However, in
the local area where compression stress and shear stress were serious, it was still
possible to refine the mesh further more so as to ensure that there were enough units
to accurately represent the instability waveform. Otherwise, the unit mesh was too
sparse, causing the structure to stiffen relative to other regions, resulting in inaccurate
calculation results.
In the stress analysis model of complex structure, spring element was usually used
to simulate the local connection. When the stability analysis as carried out, the spring
element couldn’t provide the differential stiffness, so other suitable units were used
in the local connection where the instability waveform was greatly affected.
The results of stability analysis were greatly influenced by boundary conditions.
Although the boundary condition was the same as stress analysis, it was necessary
to draw lessons from past analysis experience and test results. The determination
of boundary conditions was mainly based on engineering experience. In addition,
the subjective judgment of the rationality of the instability waveform could check
whether the boundary conditions were accurate.
It was worth noting that the stability analysis results obtained from the finite
element method as a linear eigenvalue might be more deviations from test results,
especially for plate and shell structure. This was mainly due to the geometric defects
and material defects in the structure manufacture process and the uneven load.
The stability analysis of the Chang’E-3 lunar lander during the development
process was carried out. Because the stability coefficient of the analysis was greater
than 3 and it was local instability, the model which was exactly the same as static
analysis (including load and boundary condition) was used in the stability analysis.
4. Frequency Response Analysis
The frequency response analysis was the response analysis of the spacecraft under the
sinusoidal excitation condition. The response analysis results under different sinusoidal frequency excitation could be plotted as the curve of the frequency response
curve.
Frequency response analysis includes analysis of acceleration, displacement,
stressed, load (force) and etc. The purpose of frequency response analysis was:
(1) to obtain structural stressed and load at connection pointed under the sinusoidal
load, to guide and verify the structure design and parameter design, to verify the
dynamic strength of the structure; (2) to obtain the acceleration response of each part
under the sinusoidal load, and to judge the secondary structure, large parts and so
on. The frequency coupling of spacecraft with secondary structure and large parts
was used to evaluate the stiffness design rationality of secondary structure and large
components, which provided the basis for the establishment of the sine vibration
environment conditions of equipment onboard the lunar lander.