1. Yoshiyuki Obuchi NAOJ / Mechanical Engineering shop Dec. 29th 2016
Modal analysis report - Payload assembly frame
Yoshiyuki Obuchi
NAOJ / Mechanical Engineering shop
Dec. 29th 2016

2. Motivation
To determine if the payload assembly frame is stiff enough to hold the WAB suspension, natural frequencies of the frame was calculated and some stiffening options were explored to meet the 100Hz of requirement.

3. Analysis model Total of four cases were calculated. Case1 Bare model
WAB suspension
dummy mass 3kg
stiffener
Case1
Bare model
Case2
Partially reinforced
Case3
Fully reinforced X Y Z
Case4
Anchored

4. Analysis conditions -Contact condition all mating surfaces are bonded
fixed
-Contact condition
all mating surfaces are bonded
-Load condition
no load
-Constraint condition
four interface points are fixed in six DOF

5. Results Natural frequency and mode shape Mode No. Case1 Case2 Case3
1st
24 / Global
37 / Global
59 / Global
64 / Local
2nd
26 / Global
40 / Global
84 / Local
3rd
44 / Global
78 / Global
88 / Local
4th
68 / Global
87 / Local
5th
80 / Global
107 / Global
122 / Local
6th
119 / Global
100 / Global
See backup slides for detail.

6. Summary　
Payload assembly frame was not stiff enough to hold the WAB suspension.
X shaped stiffeners worked nicely but the 1st mode frequency is still way below 100Hz of requirement.
In Case4, adding anchor to the basement greatly helped to improve the frequency. Local vibration modes below 100Hz can be eliminated with minor modification.
We may also need to discuss if we can put such a stiffeners while maintaining an accessibility to the payload.

7. Backup (Case1)　
1st 24Hz
2nd 26Hz
3rd 44Hz
4th 68Hz
5th 80Hz
6th 119Hz

8. Backup (Case2)　
1st 37Hz
2nd 40Hz
3rd 78Hz
4th 87Hz
5th 88Hz
6th 100Hz

9. Backup (Case3)　
1st 59Hz
2nd 64Hz
3rd 88Hz
4th 88Hz
5th 107Hz

10. Backup (Case4)　
1st 64Hz
2nd 84Hz
3rd 88Hz
4th 88Hz
5th 122Hz