Railtech 2015 | Noise & Vibrations

Pedro Alves Costa

Prediction and mitigation of railway vibrations. Potentialities and

challenges of numerical modelling

1. Introduction

1. Introduction

Growth of world population

Demands for the development of efficient

mass transportation systems

Environmental demands for the reduction of air

pollution

Development of efficient networks of rail transport in urban areas (metropolitan,

suburban rail networks, etc ..)

“Managing urban areas has become one of the most important development challenges of the 21st century.”

John Wilmoth Director of UN DESA’s

Railway traffic in urban

environment

Noise & Vibrations

Annoyance of inhabitants

Demand for mitigation measures

1. Introduction

1. IntroductionOutline of the problem: from the source to the receiver

1. Train-track dynamic interaction 2. Track – (tunnel) – ground interaction 3. Ground wave propagation 4. Soil-structure interaction (building) 5. Dynamic response of the building

through vibrations (1-80Hz) e re-radiated noise (16-250 Hz).

Challenge: The prediction by a simple and efficient way, but not simplistic, taking into account the main constrains of the problem.

Prediction approaches1. Introduction

Empirical models

1. Allow the inclusion of effects that are difficult to quantify;

2. Very useful when dealing with cases that are similar to the ones previously analyzed.

Numerical approaches

1. Very useful in the development of sensitivity analysis;

2. They are complex and sometimes e x t r e m e l y d e m a n d i n g f r o m computational point of view.

Hybrid approaches

1. Experimental assessment of transfer functions

2. Numerical evaluation of source functions

Verbraken et al, 2011

2. Numerical modelling of vibrations due to traffic

1 – Rail receptance on the moving reference frame

2 – Train-track dynamic loads

2.5D FEM- IEM2.5D FEM- PML

3 –

Gro

und

impe

danc

e2 Numerical modellingSub-structured approach

2.5 D approach2 Numerical modelling

Presupposes: linear response of the system; invariability of the domain along the development direction

Advantages: reduction of the computational effort

Drawbacks: it is not possible to include non-linear behaviour of the elements; it is not possible to include inhomogeneity along development direction

Train-track interaction

0.7 0.9 1.1 1.3 1.5 1.70

20

40

60

80

100

120

140

160

Unsprung Mass [-]

Incr

ease

Max

. Run

ning

RM

S [%

]

Rail3.5 m7 m15 m22.5 m

For vibration analysis the most relevant property of the rolling-stock is the unsprung mass.

Vehicle simplified model

2 Numerical modelling

Colaço, A., P. Alves Costa and D. Connolly, The influence of train properties on railway ground vibrations. Structure and Infrastructure Engineering, 2015. doi: 10.1080/15732479.2015.1025291. Alves Costa, P., R. Calçada and A. Cardoso, Influence of train dynamic modelling strategy on the prediction of track-ground vibrations induced by railway traffic. : Journal of Rail and Rapid Transit 2012. 226(4): p. 434-450.

Soil-structure interaction

The inertial forces generated in the structure give rise to an incremental wave-field

b0

bs uuu Δ+=

sb

sb

s

fffuK

−=

=Δ

( ) bbb2bb fuMCiK =−+ ωω

Impedance of the foundations

Substructuring

Different techniques for the s imu la t i on o f d i s t i nc t domains

2 Numerical modelling

3. Validation examples

10-1 100 101100

101

102

103

Fr (%)

Qt

8

2

31

4

5

6

7

9

4

13

0

21

14

20

16

15

14

1,5

3,0

4,5

6,0

7,5

9,0

10,5

12,0

Solo areno-argiloso,

Solo com matéria orgânicaSolo argiloso de

com intercalações

13,5

z (m) Descrição N (SPT)

material de aterro

de cor cinzenta

de solo arenoso

Solo argiloso de cor

fragmentos de calcáriocastanha com

Case study of Carregado

100 200 300 400

0

5

10

15

20Cs (m/s)

Dept

h (m

)

CH 2CH 1Average values

500 1000 1500 2000 2500

0

5

10

15

20Cp (m/s)

Dept

h (m

)

CH 2CH1Average values

3. Validation examples

Alves Costa, P., R. Calçada and A. Silva Cardoso, Track–ground vibrations induced by railway traffic: In-situ measurements and validation of a 2.5D FEM-BEM model. Soil Dynamics and Earthquake Engineering, 2012. 32(1): p. 111-128.

0 50 100 150 200 2500

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1x 10-8

Frequency (Hz)

Rece

ptan

ce (m

/N)

H2 - ExperimentalH0 - ExperimentalH - Numerical

41.52541.55041.57541.60041.62541.65041.67541.70041.725-0.01

-0.005

0

0.005

0.01

Location (km)Un

even

ness

(m)

Instrumented cross-section

CL

NaturalGround

Concrete sleepers

Ballast

Subballast

0.22 m

0.35 m

0.55 m

1.25 m3.50 m

UIC60 railRailpad

// 0.60 mBallast: E=97 MPa, ν=0.12

ρ=1590 kg/mξ=0.061

3

Subballast: E=212 MPa, ν=0.20

ρ=1910kg/mξ=0.04

3

Railpad: k=600 kN/mm c=22.5 kNs/mm

3. Validation examplesCase study of Carregado

3. Validation examplesCase study of Carregado

Infinite elements

A.B.- White et al

-3 -2.5 -2 -1.5 -1 -0.5 0 0.5 1-12

-10

-8

-6

-4

-2

0

2x 10-4

Time (s)

Disp

lacem

ent (

m)

-4 -3 -2 -1 0 1 2 3 4-0.06

-0.04

-0.02

0

0.02

0.04

0.06

Time (s)

Velo

city

(m/s

)

Rail Sleeper

3. Validation examplesCase study of Carregado

Infinite elements

White et al

d=22.0 m

-4 -2 0 2 4-5

0

5x 10-4

Time (s)

Velo

city

(m/s

)

-4 -2 0 2 4-5

0

5x 10-4

Time (s)

Velo

city

(m/s

)d=15.0 m

-4 -2 0 2 4-4

-2

0

2

4x 10-3

Time (s)

Velo

city

(m/s

)

d=3.5 m

Rai

lway

Tra

ckFr

ee-fi

eld

0 50 100 1500

0.5

1

1.5

2

2.5

3x 10-5

Frequency (Hz)V

eloc

ity (m

/s/H

z)

d=22.0 m

0 50 100 1500

0.5

1

1.5

2

2.5x 10-5

Frequency (Hz)

Vel

ocity

(m/s

/Hz)

d=15.0 m

0 50 100 1500

0.5

1

1.5 x 10-3

Frequency (Hz)

Vel

ocity

(m/s

/Hz)

d= 3.5 m

Case study presented by Fernandéz 2014 (measurements - CEDEX, 2002)

3. Validation examplesRailway tunnel in Madrid

5 10 15 20 25-6

-4

-2

0

2

4

6x 10-4

Tempo (s)

Velo

cidad

e (m

/s)

ExperimentalNumérico

0 20 40 60 80 1000

1

2

3

4

x 10-4

Frequência (Hz)

Veloc

idade

(m/s/

Hz)

NuméricoExperimental

100 101 10240

50

60

70

80

90

Frequência (Hz)

Veloc

idade

(dB

- ref

. 10-8

m/s)

VC-D

VC-E

VC-C

VC-B

Equipamento - VC-A

5th floor

Time (s) Frequency (Hz) Frequency (Hz)

Velocity (m/s)

Velocity

Velocity

5 10 15 20 25-6

-4

-2

0

2

4

6x 10-4

Tempo (s)

Veloc

idade

(m/s)

ExperimentalNumérico

0 20 40 60 80 1000

1

2

3

4

x 10-4

Frequência (Hz)

Velo

cidad

e (m

/s/H

z)

NuméricoExperimental

100 101 10240

50

60

70

80

90

Frequência (Hz)Ve

locida

de (d

B - r

ef. 10

-8 m

/s)

Equipamento - VC-A

VC-C

VC-B

VC-E

VC-D

7th floor

Time (s) Frequency (Hz) Frequency (Hz)

Velocity (m/s)

Velocity

Velocity

3. Validation examplesRailway tunnel in Madrid

Lopes, P., J. Fernández Ruiz, P. Alves Costa, L. Medina Rodríguez and A. Silva Cardoso, Vibrations inside buildings due to subway railway traffic. Experimental validation of a comprehensive prediction model. Science of the Total Environment 2015. (10.1016/j.scitotenv.2015.11.016).

4. Mitigation measures

4. Mitigation measuresClassification

i) Improve the track maintenance; ii) Changes on rolling stock; iii) Introduction of resilient elements in the track:

•Pads; Under-sleeper pads; Ballast mats. •Floating slab systems

M i t i g a t i o n m e a s u r e s c a n b e implemented at different locations:

• At the receiver;

• At the source.

• Along the propagating path; Trenches; wave barriers, etc.

Reduction of the unsprung mass

Improvement of the geometrical quality of the track

4. Mitigation measures

Bombardier BogiesColaço, A., P. Alves Costa and D. Connolly, The influence of train properties on railway ground vibrations. Structure and Infrastructure Engineering, 2015. doi: 10.1080/15732479.2015.1025291.

Introduction of resilient elements4. Mitigation measures

Mola(rigidez da manta)

Massa(massa da laje)

Suporte rígido(invert do túnel)

Spring (mat, bearings, etc

Track support

It enables a reduction of t h e e n e r g y t h a t i s transferred from the track to the support.

0 fn fcut0

1

2

3

Frequência

Fato

r de

am

plific

ação

da

forç

a

Frequency

Load amplification factor

0 20 40 60 80 100 120-1

-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8

1x 109

Frequency (Hz)

Dyna

mic

stiffn

ess (

N/m

)

Real - non isolatedImag - non isolatedReal - k=0.025 N/mm3 (mat beneath the subbalast)Imag - k=0.025 N/mm3 (mat beneath the subbalast)Real - k=0.025 N/mm3 (mat beneath the ballast)Imag - k=0.025 N/mm3 (mat beneath the ballast)

The introduction of the mat changes considerably the dynamics of the train-track system.

4. Mitigation measuresIntroduction of resilient elements

Alves Costa, P., R. Calçada and A. Silva Cardoso, Ballast mats for the reduction of railway traffic vibrations. Numerical study. Soil Dynamics and Earthquake Engineering, 2012. 42(0): p. 137-150.

0 20 40 60 800

1

2

3

4

5

6

7x 10-5

Frequency (Hz)Ve

locity

(m/s/

Hz)

Softer matWithout mat

-4 -2 0 2-1.5

-1

-0.5

0

0.5

1

1.5x 10-4

Time (s)Ve

locity

(m/s)

Softer matWithout mat

100 101 102-10

-5

0

5

10

15

20

25

Frequency (Hz)In

sertio

n los

s (dB

)

Mat beneath ballastMat beneath subballast

100 101 102-10

-5

0

5

10

15

20

25

Frequency (Hz)

Inse

rtion

loss (

dB)

Mat beneath ballastMat beneath subballast

d=7.5 m d=15 m

5. Mitigation measuresIntroduction of resilient elements

A detailed design is mandatory in order to a v o i d l a r g e r p e a k v i b r a t i o n l e v e l s i n nearby buildings!

101-15

-10

-5

0

5

10

15

20

25

30

Frequency (Hz)

Inse

rtion

Loss

(dB)

softer matintermediate matstiffer mat

Lopes, P., P. Alves Costa, M. Ferraz, R. Calçada and A. Silva Cardoso, Numerical modeling of vibrations induced by railway traffic in tunnels: From the source to the nearby buildings. Soil Dynamics and Earthquake Engineering, 2014. 61-62: p. 269-285.

Trenches and wave barriers4. Mitigation measures

Track modeled with FEM

Soil-track surface discretized with BEM

Open or in-filled Trench: interior modeled with FEM; soil-trench surface discretized with BEM

Train simulated by a multi-body approach

Soil modeled with BEM

Most influent parameters

Depth

Filling material

4. Mitigation measuresTrenches and wave barriers

In the case of stiff barriers t h e r e i s i n t e r f e r e n c e b e t w e e n t h e g r o u n d dispersion curves and bending dispersion curves of the barrier. Coulier et al, 2014; Barbosa & Alves Costa, 2015

Barbosa, J., P. Alves Costa and R. Calçada, Abatement of railway induced vibrations: Numerical comparison of trench solutions. Engineering Analysis with Boundary Elements, 2015. 55(0): p. 122-139.

Complex dynamic response in layered ground

4. Mitigation measuresTrenches and wave barriers

5. The challenges

5. The challengesThe introduction of the uncertainty in the modelling procedures

The reality is is not deterministic. The assessment of uncertainty sources and the stochastic analysis of the predictions are key aspects to obtain reliable results.

The holistic approachRailway vibrations, railway noise and maintenance operations are interrelated aspects that should be analyzed taking into account na holistic approach. Efficient numerical modelling techniques are relevant tools for the achievement of that goal.

The transfer of knowledge from academia to engineering practiceSeveral efficient numerical approaches have been developed in academia environment during the latter years. However, the transfer of these techniques to engineering practice is something that needs to be improved. Numerical approaches are useful tools for the support in the design of vibration mitigation measures.

Centre of Competence in Railways

University of Porto | Faculty of Engineering

Faculty of Engineering

CSF – Centro de Saber da FerroviaCentre of Competence in Railways

DEC

DEMec DEEC

Civil

Mechanical Electrical/Computer

C4R – Capacity for Rail

In2Rail - Innovative Intelligent Rail

iRail – Doctoral Programme

PFP – Portuguese Railway Platform

PFP – Portuguese Railway Platform

Thank you for your attention Pedro Alves Costa ____________________ Assistant Professor Faculty of Engineering University of Porto Portugal

Email: pacosta@fe.up.pt mobile: 00351 962934245