Master Thesis - OUFTI-1

5.4 Modal analysis
This analysis will allow to predict the global dynamic behavior of OUFTI-1.
In this analysis, the CubeSat is modeled using exactly the same strategy as in section
5.2. Only the static loads and the boundary conditions are removed to obtain the behavior
of OUFTI-1 in "free-free" boundary conditions. This type of study allows to obtain a rst
idea of its behavior in real life conditions in a simple way. In addition, the results can
be used to realize a model updating. Indeed, this conguration has the advantage that
it does not introduce additional unknowns about the boundary conditions. So, the model
updating can be performed more accurately. However, these conditions are really dicult
to simulate during an experimental test and some approximations must be done (but it is
not the topic that we want to develop here).
5.4.1 Results
It was decided to compute the ve rst modes of OUFTI-1. Their natural frequencies
are listed in Table 5.8.
Modes (mm) Natural frequencies (Hz)
1 325.51
2 333.92
3 343.27
4 368.63
5 377.29
Table 5.8: Five rst natural frequencies of OUFTI-1 in hard-mounted conguration
It can be noted that all these frequencies turn around a value of 350 Hz. This is due to
the fact that each of these modes excites only the electronic cards of OUFTI-1 (and their
xations).
These results prove that OUFTI-1 respects the ESA requirement on the natural frequencies:
"The Cubesats shall not have structural modes at frequencies lower than 120 Hz
in hard-mounted conguration".
Now, the rst two modes will be described (the following ones present the same behavior
and so, it does not have a great interest to analyze them):
• The rst mode of OUFTI-1, which corresponds to a natural frequency of 325.51 Hz,
is presented in Figure 5.12.
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