shock & vibration: case study - luxea · 2017-12-06 · shock & vibration: case study for...
TRANSCRIPT
Shock & Vibration:
Case Study
For Northrop Grumman Information Systems
LX Course: 3rd Quarter 2011
The presentation material is a proprietary property of Luxea & Dunamis Inc.
Contact the company for appropriate distribution.
Luxea Inc. / Dunamis Tech Inc.
2 The presentation material is a proprietary property of Luxea & Dunamis Inc. Contact the company for appropriate distribution.
Rack on Isolators – Pulse Shock, K
Luxea Inc. / Dunamis Tech Inc.
3 The presentation material is a proprietary property of Luxea & Dunamis Inc. Contact the company for appropriate distribution.
Live meeting number:
1-877-740-2201
Pass code: 9702761
SCHEDULE
Week Topic/Case Study HW
1 Overview and Introduction
2 Review of Shock & Vibration for Electroincs I
3 Case I: Transportation random vibration
4 Case II: Rack on isolators – pulse shock
5 Case II: Rack on isolators – pulse shock, K
6 Case II: Rack on isolators – multi-DOF and
7 Case II: Rack on isolators – drop shock
8 Case II: Rack on isolators – random vibration
9 Case III: Chassis/PCB – shock
10 Case III: Chassis/PCB –random vibration
11 Case IV: Transit Case Analysis – MIL-HDBK-304
12 Case V: Transit Case Analysis – Nonlinearity
CLASS NOTES & SOFTWARE
• LuxCalc Tools v1.2.3 is available for download from NG ESL server.
• Class notes will be posted on Fridays downloadable from Luxea.com site.
www.luxea.com/seminars
Create an account to access the files and blog access.
In the name field, start with “NG” before your name, e.g., name: NG Keith Yi
Privilege level is given to course registrants within 24 hours.
HOMEWORK
• Homework description is included in the class notes.
• Answer is posted every Thursday pm.
• Discussions and comments are encouraged through Luxea HW blog
www.luxea.com/blog
Best comments/discussion/review will be selected bi-weekly for a prize.
Blog
Announcements
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Accessing Class Notes
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• Login after the privilege is given.
• Move the mouse over to Services – Seminar.
• When Seminar lectures is displayed, click it.
Test Case II – Equipment Rack Shock Isolation Analysis
Problem Statement
A rack equipment is to be isolated from shock.
It is exposed to 40g 11 ms saw tooth pulse.
Limit the transmitted load to payload to 20 g.
Isolators
x
y
z
Rack frame
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Isolators
Data and Assumptions
Data and Assumptions
The payload weight = 774 lbs
The rack structure is significantly stiffer than isolators.
Modal damping coefficient = 0.15
IDC M16-540-18 isolators (four on top and four at the base)
Analysis Task - stiffness
How to represent the isolator K’s into the model K1.
What’s the effect of rack frame stiffness (qualitative assessment)?
How about the non-linear K?
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Isolator Modeling
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Springs in Parallel
K1 K2
21 KKKeq
Springs in series with fixed ends
21 KKKeq
K1
K2
m1
Springs in parallel – common deflection at each spring
Springs in series – common force at each spring
212121 KKKKFFF
FKKK
F
K
F
2121
21
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Springs in Series
21
111
KKKeq
K1
K2
Isolator Specifications
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Shear/Roll
K = 470 lb/in
Bottom-out = -3.5 in
K = 1200 lb/in
Bottom-out = 1.75 in
K = 300 lb/in
Bottom-out = 3.5 in
Tension Compression
Estimate the expected deflection range.
Use different K for shock and vibration.
Check for g and max.
K in Vertical Direction
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• Isolators in tension and compression
• The slope is K.
• K’s are additive.
• The blue is used in previous analysis, and the red in current analysis.
• K in tension is more dominant (K variation in tension has more effect).
Compression (K=470 lb/in)
1.75 in
Tension (K=1200 lb/in)
1.75 in
Exercise – Build K Table for LuxCalc
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Roll & shear
Tension
Compression
Deflection (in)
Combined Force (lbs)
0.00 0
0.10 820
0.25 1540
0.88 5949
1.75 13280
Responses – Linear K from Last Week
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Max allowable isolator deflections: Tension = 1.75 in
Keq = 4 (470 + 1200) = 6680 lb/in
Max displacement = 1.173 in
Max 10.6 g
LuxCalc Input
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Load-deflection table
Nonlinear
selection
Add table rows.
Responses – Nonlinear K
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Max displacement:
1.116 vs. 1.174 in Max acceleration:
12.7 g vs. 10.6 g
Since the stiffness in tension is significantly larger, the acceleration response is expected to be
more influenced by the tension K. The maximum acceleration is increased from 10.6 g in constant
K case to 12.7 g using nonlinear K model. The corresponding maximum displacement is
decreased from 1.174 inch to 1.12 inch.
Summary
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Combination of K’s into model K1
Series or parallel (opposite of resistors)
Non-linear K effect
Better or worse than linear approximation?
Higher K higher fn higher g
Depends on K near maximum deflection
Response curve to 40 g saw-tooth
shock with 15% damping
A (g)
fn / fp
Increasing fn or p (or decreasing fp)
Homework 5
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Nonlinear effect for lateral shock
Linear assumption of K = 300 x 8 = 2400 lb/in
Nonlinear response comparison – build K table and run.
Roll & shear
40 g 11 ms saw-tooth shock
Luxea Inc. / Dunamis Tech Inc.
18 The presentation material is a proprietary property of Luxea & Dunamis Inc. Contact the company for appropriate distribution.
Rack on Isolators – & Multi DOF
Case Study II
Equipment Rack System
Shock and vibration analysis of an equipment rack system –
effect and 2 DOF case
Shock pulse and drop shock per
MIL-STD-810F
Random vibration per MIL-STD-
810F
One and two DOF models,
various parameter effects
Use of LuxCalc Tools for quick
evaluations
This case study demonstrates the
influence of various parameters.
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