Measuring and Calculating the Dynamic

Response of Simple Structures

AOE 3054

E. Nikolaidis

Outline

1 Introduction

2 Analysis of Dynamical Behavior of Structures

3 Dynamic Testing of Structures

4 Summary/Concluding Remarks

1 Introduction

• a. Dynamic loading

Dynamic means time varying

Examples:

• Aircraft wing-gust loads

• Offshore platform-waves

• Car on rough pavement

• Earthquake loads

Terminology

• Vibration: ?

b. Static versus dynamic analysis

Static• Constant load,

response• No inertia

forces

Dynamic• ?• Inertia forces

c. Steps in a dynamical investigation

• Design

• Analysis

• Testing/correction of model

• Redesign

2 Analysis of Dynamical Behavior of Structures

• Define ? model

• Derive ? model

• Solve for dynamical behavior

3 Dynamical Testing of Structures

Why dynamical testing:

• ?

• ?

• Full-scale structure

• Reduced scale physical models (use in early design stages)

Frequency response function

Basic property of linear systems: Sine in-Sine out

Scos(t) ?

Beam that can be modeled as a SDOF

system

Observations

=0 then ?

• At resonance:

Amplitude ratio=Q=AK=1/2Phase angle= ?

• For frequencies of excitation much higher than natural frequency the response amplitude is close to zero

• Example: Large space structures

4 Summary/Concluding Remarks

• Dynamic loading

• Steps in dynamical investigation

• Test

Motivation

Examples