Lecture Slides: Lecture Mechanics

1Challenge the future

P-L-3

Mechanics

The Modelling Team Department of Design Engineering

Faculty of Industrial Design EngineeringDelft University of Technology


Contents

• Systems

• Key components of Mechanical Systems

• Spring

• Damper

• Mass-Spring-Damper Systems

• Applications in product design


Aim

KnowledgeKnowledge

InsightInsight

CommunicationCommunication

To develop a basic understanding of the properties of mass-spring-damper system and its applications in product designs

To demonstrate that such a system might be modeled so as to provide useful data for designs

To communicate with experts in their professional languages

1

2

3


Systems


Repetition: What is a system?

System consists of a set of interacting or interdependent system components (or sub-systems)

System

-Structure & interconnectivity-Boundary-Input & Output-Surroundings


Example of a system

Tyre

Saddle

Tyre

…

Courtesy of http://www.cycle9.com/carrboro-chapel-hill-store/batavus-bicycles-lets-go-dutch/Courtesy of http://www.batavus.nl


System response

Boundary

Inputs Outputs

Courtesy of http://www.batavus.nlCourtesy of http://reviews.mtbr.com/blog/tag/Cycle-Solutions/

Velocity in the vertical direction

Displacement in the vertical direction


System response

Boundary

Inputs Outputs

Courtesy of http://www.batavus.nlCourtesy of http://www.utilitycycling.org/2009/08/cycling-services/




What are components of the bike’s model?

Tyre

Saddle

Tyre

Courtesy of http://www.batavus.nl


Components - Spring


Component - Spring

Ref. http://en.wikipedia.org/wiki/Spring_(device)

A spring is an elastic object used to store mechanical energy

Spring

2 m

eter

s 40

0 N

2 m

eter

s 40

0 N


Model a spring

Courtesy of http://en.wikipedia.org/wiki/Spring_(device)


Rehearsal: Bungee jumping

Courtesy of http://www.youtube.com/watch?v=sriUfHuHSXY


Components

Spring

Human.

Air.

► Earth Bungee jumping system


Cause-effect

Spring

Inertia force Stretchthe spring

Pull the person back

GravityMass of the person Air friction

Slow down the motion

Effect

Cause

0 =0

101

000


Modelling using Maple®


The solution


The solution

Displacement

Acceleration

Velocity


The solution

The amplitude is getting smaller,

Why?

Displacement

Acceleration

Velocity


Is it different? - Trampoline

Courtesy of http://www.youtube.com/watch?v=pSazagYBCM8


Components

Spring

Human.

Air.

► Earth Trampoline system


Cause-effect

Spring

Inertia force Stretchthe spring

Push the person back

GravityMass of the person Air friction


Effect

Cause

0 0 0 =0

101

000


The solution


The solution

Displacement

Acceleration

Velocity


The solutionThe amplitude is also getting smaller. The

same reason?

SpeedDisplacement Acceleration


Bungee jumping vs Trampoline

0 =0

0 0 0 =0

Bungee jumping

Trampoline


Components - Damper


Component - Damper

A damping elements resists relative velocity across them

Damper

Courtesy of http://en.wikipedia.org/wiki/Shock_absorber

Shock absorber with internal reservoir.

The components are:A - rod,B - the piston with seals,C - the cylinder,D - oil reservoir,E - floating piston,F - air chamber.


Model a damper


Case study: The slow closing toilet seat

Courtesy of http://www.youtube.com/watch?v=tBK1rewI8vQ


System components

The toilet seat


Cause-effect

Damper

Inertia moment The lid goes down

Slow downthe motion

GravityMass and

geometry of the lid

Effect

Cause

/2=0


Solving the model


The solution

/2/2

Angular displacement

Angular acceleration

Angular velocity


The mass-spring-damper system



Courtesy of http://www.taiwan-bicycle.com.tw/Pd_Detail.asp?FKindNO=F000004&SKindNO=S000671&ItemNo=I00002896



Courtesy of http://www.taiwan-bicycle.com.tw/Pd_Detail.asp?FKindNO=F000004&SKindNO=S000671&ItemNo=I00002896

ElasticityYoung's ModulusPoisson's RatioAnisotropy

Damping Coefficient

Spring Damper

Regarding material



Courtesy http://www.airliners.net/photo/Airbus-Industrie/Airbus-A380-861/1169635/L/


Case study: The skateboardThe movement in the vertical direction

Courtesy of http://skateboardingmagazine.com/blog/2009/02/01/the-worlds-largest-skateboard/

Designer:

Rob Dyrde

The World largest skateboard


System components

The skateboard

Spring

DamperAir

EarthPerson

NeglectNeglect

Neglect, why?Neglect, why?


System

Damper

Inertia force Drag themass back


SpringMass of the board

Effect

Cause

=0


Solution

Displacement

Acceleration

Velocity

The step


DiscussionC=50

K=1000 K=100 K=10

DisplacementDisplacement

VelocityVelocity

AccelerationAcceleration


Discussion

K=100

C=200 C=50 C=0.1

DisplacementDisplacement

VelocityVelocity

AccelerationAcceleration


Consider human also as a spring and a damper, can we model the shock to the head?

21 1 2

1 1 1 2 12

( ) ( ) ( )( ( ) ( )) ( ) 0d x t dx t dx tm k x t x t cdt dt dt

22 1 2 2

2 1 1 2 1 2 2 22

( ) ( ) ( ) ( ) ( )( ( ) ( )) ( ) ( ( ) ( )) ( ) 0d x t dx t dx t dx t dy tm k x t x t c k x t y t cdt dt dt dt dt


The natural frequency

2

2

( ) ( ) ( ) 0d x t dx tm c kx tdt dt

0km

2cmk

22

0 02

( ) ( )2 ( ) 0d x t dx t x tdt dt


The damping ratio


Resonance


Case study: Tacoma Narrow bridge

Courtesy of http://www.youtube.com/watch?v=P0Fi1VcbpAI


Interpret the response of a step function

Sett

ling

time

band

Mp St

eady

-sta

te

erro

r

22

0 0( ) ( )2 ( ) step

d x t dx t x t fdt dt

max

ss

ss

xAx x

22

ln

ln

A

A

21n

pt


Interpret the response - 2Example: If we know the response of a mass-spring-damper system regarding a step function F(t), can we extract parameter c and k from the response?

From definitions

Maximum overshoot ratio

max

ss

ss

xAx x

Damping ratio

22

ln

ln

A

A

Natural frequency21

n

pt

Maximum overshoot ratio

max

13.28

1.3723

ss

p

xt

x

Response

2.686A

Damping ratio0.3

Natural frequency1n

0km

2

cmk

Suppose m=1kg

1 kg/m, 0.6 Ns/mk c

m

k

c

x(t)

F(t)


Industrial applications


The pogo-stick

Courtesy of http://connect.in.com/pogo/photos-1-1-1-9ed7a7cecf4cb85de07b7f05697bfe43.html

Question?Where is

the damper?


The suspension systems (ref/auto.howstuffworks.com/)

Courtesy of http://auto.howstuffworks.com/car-suspension4.htmAI


The door closer (ref. /www.usbuildersupply.com)

Courtesy of http://www.usbuildersupply.com/index.php/hardware-basics/door-closer-overview/


Thank You!

Lecture Slides: Lecture Mechanics

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