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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)
J. Negreira / ICA 2016 / Buenos Aires, 6th September 2016
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
J. Negreira / ICA 2016 / Buenos Aires, 6th September 2016
Introduction (I)
• Multi-storey wooden buildings allowed in 1994
– Many advantages
– Main disadvantages
» Disturbing vibrations
» Variability
• Sound transmission
– Airborne
– Structure-borne
J. Negreira / ICA 2016 / Buenos Aires, 6th September 2016
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)
J. Negreira / ICA 2016 / Buenos Aires, 6th September 2016
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?
J. Negreira / ICA 2016 / Buenos Aires, 6th September 2016
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???
J. Negreira / ICA 2016 / Buenos Aires, 6th September 2016
Overview
Equivalent?
J. Negreira / ICA 2016 / Buenos Aires, 6th September 2016
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:
J. Negreira / ICA 2016 / Buenos Aires, 6th September 2016
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
J. Negreira / ICA 2016 / Buenos Aires, 6th September 2016
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
J. Negreira / ICA 2016 / Buenos Aires, 6th September 2016
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
J. Negreira / ICA 2016 / Buenos Aires, 6th September 2016
Overview
Equivalent?
J. Negreira / ICA 2016 / Buenos Aires, 6th September 2016
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
J. Negreira / ICA 2016 / Buenos Aires, 6th September 2016
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
J. Negreira / ICA 2016 / Buenos Aires, 6th September 2016
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
J. Negreira / ICA 2016 / Buenos Aires, 6th September 2016
Thank you for your attention! [email protected]