Environmental vibrations and ground-structure interactionby Philippe JEAN

General concepts

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MEFISSTOEnvironmental vibrations and ground-structure interaction

CSTB’S TOOL TO TACKLE ENVIRONMENTAL VIBRATIONS

ISSUES

> Predicts vibration and structure-borne noise in buildings

> Tunnels and multilayer grounds

> Ground-structure interaction

A CUTTING-EDGE CALCULATION METHOD

> Hybrid BEM/FEM formulation

> Vibration propagation calculated in 2.5D

> Structure-borne noise calculated by 3D modal coupling

EASE OF USE

> Generation of open files (text, GMSH)

> A Scilab package for pre- and post-treatment

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2.5D modelling

AN APPROACH WELL-ADAPTED TO RAIL APPLICATIONS

> Geometry defined in a 2D cut… (perpendicular to the rail)

> … but excitation defined in 3D (a set of points)

> 2.5D result obtained by integration over a set of 2D results

A NECESSARY APPROACH (COMPARED TO FULL 2D) …

… AND SUFFICIENT (COMPARED TO FULL 3D)

> Simplified geometry definition and meshing (2D)

> Much smaller CPU time

> Captures main physical phenomena

MEFISSTOEnvironmental vibrations and ground-structure interaction

P. Jean, C. Guigou, M. Villot, A 2,5D BEM Model for Ground-Structure Interaction, Building Acoustics,11(3), 1-17 (2004)

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Hybrid FEM/BEM method

FEM : FINITE ELEMENTS

> Field described using a discretization of the entire domain

> Adapted to finite domains only

> Can handle with complex and/or thin structures

BEM : BOUNDARY ELEMENT METHODS

> Description using the domain boundaries only

> Can handle infinite domains (ground layers)

FEM/BEM APPROACH

> Can easily handle all cases!

> For the end-user, just a switch (BEM/FEM) for each domain

MEFISSTOEnvironmental vibrations and ground-structure interaction

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Structure-borne noise calculationORIGINAL APPROACH 2D 3/4

> Post-treatment of 2.5D calculations

> Reconstruction of 3D acoustic volumes (finite depth)

> Calculation of the acoustic pressure field using SEA-like radiation

or modal coupling

> Approach validated against full 3D calculation

MEFISSTOEnvironmental vibrations and ground-structure interaction

2.5D geometry 3D geometry

P. Jean, A 2,75D Model for the Prediction of Noise Inside Buildings Due To Train Traffic, Acta Acust United Ac 104, 1009-1018 (2018)

Applications

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Urban train impact on future building

➢ Acquisition of the architectural data

and ground layers (geotechnical

study)

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Urban train impact on future building

➢ Source identification

• On site measurements➢ Different distances from track

➢ Measurement of the three components

• Mefissto calculation on initial site

• Tuning (damping factor, injected force

level…)

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Urban train impact on future building

2D vertical velocity level @ 50 Hz

➢ Calculation of the vibration

field for the future building

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Urban train impact on future building

➢ Impact of different isolation solutions

Initial (no solution) Screen Decoupling

Resilient

layer

level

Validations

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Comparison with 3D FEM

Tunnel – ground transfer case

Vibration levels at

surface

3D

FEM

2.5D model3D model

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Tunnel mobility

Tunnel mobility

➢ Impact force in the middle of the apron in a tunnel

➢ Measured mobility at several distances down the tunnel

(along the z-axis) and weighted average

➢ Effective mobility: ratio between velocity response [m/s] and

force density [N/m1/2]x

y

z

Eff

ecti

ve m

ob

ilit

y

[ m

.s-1

/ (N

.m-1

/2)]

Calculation

Measurement

E. Augis, M. Villot, P. Jean, C. Gallais, P. Ropars, C. Guigou-Carter. Vibration emission from railway lines in tunnel – part 1: characterization. In

Proceedings of ICSV23 in Athens (2016)

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Tunnel mobility

Tunnel mobility

➢ Impact force in the middle of the apron in a tunnel

➢ Measured levels on apron and on transverse wall

x

y

z

E. Augis, M. Villot, P. Jean, C. Gallais, P. Ropars, C. Guigou-Carter. Vibration emission from railway lines in tunnel – part 1: characterization. In

Proceedings of ICSV23 in Athens (2016)

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Ground-structure interaction

Ground-structure transfer function

➢ Difference of vertical vibration level

at different points

➢ Impact force on surface

How to set up a calculation ?

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Input dataBUILDING

> An architectural cut in DWG/DXF format or a simple description

➢ Clean up the file to keep relevant domain boundaries

➢ Define the different domains

GROUND

> Some data regarding the ground layers (geotechnical report)

➢ Find layer depths and type of materials (soft ? organic ? sandy ?)

➢ Get some typical parameters values (e.g. in provided database) and tune them to fit measurements if

possible

SOURCE

> Some data regarding the source

➢ Measured vibration levels (recommended)

➢ Force density (N2/m per third-octave)

MEFISSTOEnvironmental vibrations and ground-structure interaction

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Model dataGEOMETRY

> Can be generated using the Scilab package from a DXF file

DOMAINS

> Calculation method: BEM or FEM

> Material parameters: density, Young’s modulus, Poisson’s ratio, damping coefficient

SOURCES AND RECEIVERS

> Position of point sources (2 components in 2D - 3 components in 2,5D)

> Receivers points or zones (can include acoustic volumes)

TYPE OF RESULTS

> Calculation of the velocity field or structure-borne noise (acoustic volumes)

> Results: spectral values or maps (GMSH format)

MEFISSTOEnvironmental vibrations and ground-structure interaction

Demo

Mefissto in practise

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Mefissto in practiseCORE: TWO HIGHLY-OPTIMIZED EXECUTABLE FILES

> mefissto : runs 2D and wavenumber calculations

> integre_kz : 2.5D wavenumber integration

A SCILAB PACKAGE FOR PRE-TREATMENT AND POST-

TREATMENT

> Developed within a free numerical calculation environment:

Scilab/GMSH

> Pre-treatment: writes geometry from DXF, checks input files,

checks meshes

> Run calculations: possibility to parallelize over frequencies

> Post-treatment: reads output files, plots, third-octave

integration…

MEFISSTOEnvironmental vibrations and ground-structure interaction

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Provided documentation

USER MANUALS

> Starter guide and modeling guide (in progress)

> Scilab package functions description

> A set of documented examples with input files and results

> A comprehensive description of Mefissto input file format

MATERIAL DATABASE

> Provides typical values of material parameters,

for ground layers and structures

MEFISSTOEnvironmental vibrations and ground-structure interaction

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Short term evolution

MODULE FOR SOURCE CALCULATION: VIBRAFER1

> Simplified model of train track system

> Input: train unsprang mass, train speed, track component

parameters, rail unevenness

> Output: injected force spectrum (input to Mefissto)

MEFISSTOEnvironmental vibrations and ground-structure interaction

1 M. Villot, E. Augis, C. Guigou-Carter, S. Bailhache, C. Gallais, P. Jean. Vibration emission from railway lines in tunnel – part 2 : prediction. In ICSV23 in Athens (2016)

Get MEFISSTO

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Get MEFISSTO

Full purchase : 19 500 € excl tax

➢ Life-time license for 1 computer

➢ 2 days initial technical training by MEFISSTO experts

➢ Free maintenance for 1 year

➢ Free remote technical support for the 1st year : 16 hours maximum

Maintenance and technical support after 1 year of acquisition :

1 950 € excl tax / year

➢ Software maintenance including update

➢ Remote technical support : 8 hours maximum / year

SOFTWARE ACQUISITION

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IN-HOUSE EXPERT CONSULTING OR SUBCONTRACTING

Get expertise around MEFISSTO

Subcontracting : from 2 500 € to 10 000 € excl tax per analysis

> varies depending on the study purpose and

input data

➢ Various input data:

❖ 2D vertical cuts

❖ Soil description

❖ Vibration measurements / force density

➢ Type of results:

❖ Vibration levels

❖ Structure-borne noise levels

❖ 2D maps of vibration levels

Contact : Alexandre JOLIBOIS

alexandre.jolibois@cstb.fr / +33 6 66 63 17 02

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Merci pour votre attention