Modelling of the tapping machine for finite element ...

J. Negreira / ICA 2016 / Buenos Aires, 6th September 2016

Modelling of the tapping machine for finite element

prediction tools – Preliminary parametric studies

Juan Negreira, Delphine BardDivision of Engineering Acoustics,

Lund University (Sweden)


Silent Timber Build

Design indicators: human

response to floor vibrations

Computer prediction tools: foresee

performance and structural

modifications during design phase

AIMS:

• Cost and time savings for industry

• Vibroacoustic comfort


Introduction (I)

• Multi-storey wooden buildings allowed in 1994

– Many advantages

– Main disadvantages

» Disturbing vibrations

» Variability

• Sound transmission

– Airborne

– Structure-borne


Introduction (II)

• Current ISO standards (Sweden: 50–3150 Hz)

– Identical for light / heavy constructions

– Low frequencies out of the scope

» AkuLite Statistical analyses (objective parameters & subjective ratings)

– Impact: lower limit 20 Hz

• Vibroacoustic comfort is sought research needed in:

– Human perception of floor vibrations

– Prediction tools

» Structural modifications during design phase

– Inexpensive, not time-consuming

ISO tapping machine

A. Homb (2005)


Impact sound prediction tools

1. Excitation sources

2. Vibroacoustic transmission

3. Human perception

Research question:

Can the ISO tapping machine be implemeted in

predictive tools in a time-efficient and accurate way?


Objective and method

• Objective: guidelines for modelling ISO tapping machine (FEM)

− Need for simplified guidelines

• Method:

− Parametric studies

» Relative differences between modelled results

• Research limitations:

− Interaction floor/hammers not accounted for (yet)

Simple Cumbersome- +

Accuracy???


Overview

Equivalent?


FE-model

• Dimensions: 1200 x1200 mm2

− 5 load-bearing beams (72 x 23 mm2 cross-section / cc 295 mm)

− OSB-floor surface (9 mm thick)

• Full interaction / 105k dofs / Linear behaviour / Damping 5%

• Loading case:

• Comparison

− RMS:

− NRFD:


Time domain analysis (I)

• Implicit dynamic procedure

− Hilber-Hughes-Taylor time integration operator employed

» Automatic or fixed time integration

» Unconditionally stable for linear systems

• Influence of time step

− Automatic time step does not resolve the 5 hammer hits

Reference model: 0.00001 s. step / 5 hammers / 0.5 s. analysis time


Time domain analysis (II)

• Influence of analysis time

− Steady-state reached after 1 s for f >16 Hz

» Better accuracy if t > 2 s

» Should be verified for each specific floor/case cumbersome

Reference model: 0.00025 s. step / 5 hammers / 0.5 s. analysis time


Time domain analysis (II)

• Influence of number of hammers

− Necessary to model 5 hammers (and several positions)

− Good average of the vibration pattern

Reference model: 0.00025 s. step / 5 hammers / 1 s. analysis time


Overview

Equivalent?


Frequency domain analysis

• Drawback (at this stage): frequency content of the load

− Convergence analysis (frequency span)

• Different frequency steps

− Calculation times further reduced

» Vibration modes must be caught


Calculation time comparison

• Marked reduction of calculation times

NOTE: The simulations were performed on a computer equipped with 2 Xeon E5-2650v2

(2.0 Ghz, 8-core) CPU, and a RAM memory of 64 GB


Concluding remarks

Modelling guidelines

• Both approaches ultimately yield identical results

• Frequency approach:

» Inclusion of more frequencies of the spectrum

» Method applicable to other excitation sources

» Steady-state regime (no need to check the time to reach it)

» No numerical damping

» Much faster

Further work

• Model improvements

» Floor/hammer interaction

• Validation measurements


Thank you for your attention! [email protected]

Modelling of the tapping machine for finite element ...

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