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.

Transportation Random Vibration

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 – drop shock

6 Case II: Rack on isolators – random vibration

7 Case II: Rack on isolators – multi-DOF and nonlinear effect

8 Case III: Chassis/PCB – shock

9 Case III: Chassis/PCB – random vibration

10 Case IV: Transit Case Analysis – MIL-HDBK-304

11 Case V: Transit Case Analysis – Nonlinearity

12 Summary and Closing

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.

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

4

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• “Untrusted Website” message appears.

Click “Click here to proceed” button at the bottom per NG webmaster’s instruction.

The screen will appear until the site is established.

Announcements – cont’d

Problem Statement

The package had been qualified

to MIL-STD-810F truck vibration.

Alternative transportation

proposed: C5 & C130 aircrafts

Can we show that the air

transportation is acceptable?

Use of LuxCalc Vibration for

comparisons

Various input spectra result in

surprising results

Transportation Random Vibrations

NG package responses to various MIL-STD-801F transportation

random vibrations are to be compared.

1. Review all transportation-related (non-operational) specifications

and identify the environment to be evaluated.

• Temperature, humidity, altitude, shock and vibration

• Only the random vibration is affected.

2. Compare and understand the input random vibration spectra –

Truck, C5 and C130

• PSDin vs. frequency

• Input grms

• Estimate the system’s fundamental natural frequency

Evaluation Process

Evaluation Process – cont’d

3. Identify the qualified subassembly and the critical component of

interest.

4. Evaluate the response of the subassembly.

• Calculate and compare its response to the various random

spectra.

• Compare the vibration spectra between C130, C5 and

Truck transportations from MIL-STD-810F.

Category 7 (jet air) Category 8 (propeller)

Category 4 (truck)

Qualified to

Proposed

Random Vibration Spectra

• Frequency range

• Input grms

• PSDinput at fn

• Multiple natural frequencies?

0.1 g2/Hz

0.01 g2/Hz

0.015 g2/Hz

0.003 g2/Hz

Approximate system natural frequency, fn

Random Vibration Curve Comparison

Parameters of interest

• Upper structure – rigid payload protected by isolators

• Lower structure – stiff steel framed pallet

• The package system above the isolators was qualified as the subassembly.

• The upper package system has electronics inside.

• Lower pallet is structurally stiff and of less interest.

Rigid payload with m2 = 19,500 lbs

Rigid steel pallet structure with m1 = 5,900 lbs

Assumed K1 = 10e6 lb/in

Multiple isolators with

combined K2 = 500,000 lb/in

Modeling Decision

m2 = 19,500 lbs

m1 = 5,900 lbs

K2 = 500,000 lb/in

Mass: m1 and m2 are given.

Effect of 1 and K1 should be studied along

the analysis process.

Input Parameter Considerations

• Below isolator - pallet: m1 = 5,900 lbs, K1 = 10e6 lb/in

• Above isolator - payload: m2 = 19,500 lbs, K2 = 5e5 lb/in

• Model damping: I = 15%, II = 5%,

Damping

2 is provided by the isolator manufacturer.

1 is selected based on experience (1~10%)

Stiffness

K2 is provided by the isolator manufacturer.

K1 is selected so that fI and fII are well separated.

Typical Damping Ratios

System Viscous Damping

Metals (in elastic range) <0.01

Continuous Metal Structures 0.02 to 0.04

Metal Structure with Joints 0.03 to 0.07

Aluminum / Steel Transmission Lines ≈0.0004

Small Diameter Piping Systems 0.01 to 0.02

Large Diameter Piping Systems 0.02 to 0.03

Auto Shock Absorbers ≈0.30

Rubber ≈0.05

Large Buildings during Earthquakes 0.01 to 0.05

Prestressed Concrete Structures 0.02 to 0.05

Reinforced Concrete Structures 0.04 to 0.07

V. Adams and A. Askenazi, Building Better Products with Finite Element Analysis, OnWord Press, Santa Fe, N.M., 1999.

• Below isolator - pallet: m1 = 5,900 lbs, K1 = 10e6 lb/in

• Above isolator - payload: m2 = 19,500 lbs, K2 = 5e5 lb/in

• Model damping: I = 15%, II = 5%,

m1 = 19,500 lbs

m2 = 5,900 lbs

K2 = 500,000 lb/in

2

1

LuxCalc Input

• Input grms = 1.136

• Response grms = 1.066

• Peak PSD at fI = 0.190 g2/Hz

Truck PSD

Truck

Response to Truck Vibration

• Input grms = 2.875

• Response grms = 0.966

• Peak PSD at fI = 0.1268 g2/Hz

C130 PSD

C130 Aircraft

Response to C130 Aircraft Vibration

• Input grms = 2.111

• Response grms = 0.357

• Peak PSD at resonance (fI) = 0.038 g2/Hz

C5 PSD

C5 Aircraft

Response to C5 Aircraft Vibration

• Comparison of three transportation mode responses

Response Curve Comparison

Truck C130 Aircraft C5 Aircraft

Response Comparison

• Comparison of three transportation mode responses

Response Curve Comparison

Response Curve Comparison

• Input grms is higher in C-130 and C5 vibrations than the truck’s

spectra.

•The important parameters are response grms and PSDin at

resonance – both parameters are lower in both aircraft

transportations.

• It is concluded that the air transportation via C130 or C5 are likely

to cause less severe vibration loads for the package.

Truck C-130 C-5

Input grms 1.194 2.875 2.111

Response grms (1 ) 1.066 0.966 0.357

PSD at resonance 0.190 0.127 0.038

Case Study I – Summary and Conclusions

Case Study I – Summary and Conclusions

Luxea Inc. / Dunamis Tech Inc.

21 The presentation material is a proprietary property of Luxea & Dunamis Inc. Contact the company for appropriate distribution.

Shock & Vibration: Case Study

Homework 3.1

1. Register in luxea.com with “NG” in the name field.

2. Download and install LuxCalc 1.2.3 from NG ESL server.

3. Repeat the random vibration analysis with a SDOF model, ignoring

the pallet below the isolators.

4. Repeat the analysis by varying 1 and K1. What conclusions can you

draw from this exercise on the effect of 1 and K1?

23