vibration control in marine applications

7/31/2019 vibration control in marine applications

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STUDY OF VIBRATION

AND ITS CONTROL FORMARINE APPLICATIONS

K.S.SAJIKUMAR

ASST. PROF. IN MECHANICAL

ENGINEERING

CET

SIVAPRASAD K.S.

MD1107

MACHINE DESIGN

CET

Guided by Presented by


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CONTENTS

Introduction Vibration in Marine Systems

Study of Vibration in Marine

Vibration Control Smart Spring Mounting System

Resonance Control using Selective Damping

Conclusion

References


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INTRODUCTION

What is Vibration?

Crew discomfort, fatigue and increased

maintenance cost

Produces acoustic noise and signatures


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VIBRATION IN MARINE

SYSTEMS

Steady-state vibration

Hull

Propulsion system

Unbalance of propellers, shafts andmachineries

Hydrodynamic forces

Local structures, machinery etc.

Vibrating hull

Unbalanced machinery and equipment


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Contd

Transient vibrations

Slamming

Shocks generated by air blasts and

underwater explosions


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A crew vessel


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STUDY OF VIBRATION IN

MARINE

Vibration Response of Ship Hull

Structure

Natural frequency high

Due to stiffening components

A detailed frequency response analysis

required

Time consuming

Only engine room and full length kneel is

considered


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Contd

Input mobility of engine room due to

different excitations are analyzed

FEA model containing only major stiffnesscomponents

FEA model with hull and deck plates

included

Finite beam

Infinite beam


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Contd

Only major stiffness components

Finite element models of half engine room(a) stiffness

components only


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Contd

Includes both stiffness components and

the hull and deck plates

Finite element models of half engine room (b) hull and

deck plates included


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OUT OF PLANE FORCE

EXCITATION

Out-of-plane force input mobilities of the engine bed and the

corresponding finite and infinite beams


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INPLANE FORCE

EXCITATION

In-plane force input mobilities of the engine bed and the

corresponding finite and infinite beams


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TORTIONAL MOMENT

EXCITATION

Torsional moment input mobilities of the engine bed and

the corresponding finite and infinite beams


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BENDING MOMENT

EXCITATION

Bending moment input mobilities of the engine bed and

the corresponding infinite beam


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VIBRATION CONTROL

Passive and Active vibration control

Passive

Not efficient at low frequency

Activeo Global performance less impressive

o High cost


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PASSIVE APPROACH

Support mounted machinery raft on a

set of resilient mounts

Force transmission of an ideal and real structure


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Contd

Not practicable

Large no. of mounts required

Difficulty in specifying the stiffness

accurately


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SMART SPRING

MOUNTING SYSTEM

Hybrid active/passive system

Uses electromagnet combined in

parallel with passive elements

Both local and global control strategy

adopted


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Contd


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Contd

+ + + + Where

diag 2 ,

obtained by the transform ,Where V is an orthonormal matrix of

eigenvectors of


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MachineryRaft

Displacements

Filter OutRigid Body

ModalVelocities

CalculateRigid BodyResponseFunctions

CalculateLocal Demand

Forces

Improvement due to a Smart Spring mounting system

Schematic diagram of the global control process


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CONTROL SYSTEM

DEVELOPMENT

Schematic diagram of a Smart Spring local control system

12 () + () + () ,

=


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Modal output and measured force


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RESULTS

Actuator response for low-frequency disturbance and constant demand


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Actuator response for low-frequency disturbance and saw-tooth demand


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Active and passive mount response


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RESONANCE CONTROL

USING SELECTIVE DAMPING

More vibration sources

Secondary vibration paths that short

circuit the mounts

Selective Damping reduces vibration

in receiving structures


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Point acceleration power to broad-band excitation-uncontrolledand controlled


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Far-field acoustic power to broad-band excitation-uncontrolled

and controlled


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CONCLUSION

Vibration in marine structures is a very

significant problem

A brief study of the causes of vibration

and its characteristics has been done

Smart Spring machinery mounting

system could reduce the vibration to

certain extend Selective Damping that controls

vibration in the receiving structure


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Contd

Smart Spring mounting system along

with Selective Damping reduces the

vibration to a greater extend


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REFERENCES

1. S.Daley, F.A.Johnson, J.B.Pearson, R.Dixon (2004).

Active vibration control for marine applications, Control

Engineering Practice 12 (2004) 465-474

2. Tian Ran Lin, Jie Pan, Peter J.OShea, Chris

K.Mechefske (2009). A study of vibration and vibrationcontrol of ship structures, Marine Structures 22 (2009)

730-743

3. Crede, C.E., Harris C.M. (1961). Shock and Vibration

Handbook Vol. 3, McGraw Hill, New York: Wiley.

4. Frank DeBord, Jr., Willaim Hennessy and Joseph

McDonald (1996). Measurement and analysis of

Shipboard Vibrations, Los Angeles Section Meeting


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vibration control in marine applications