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In this contribution a method for the prediction of the radiated sound out of the velocity field of a vibrating ceiling is presented. The numerical method was validated via measurements on a real structure using a pp-probe. It is based on Integral Transform techniques and can be applied in the postprocessing of a FEM simulation
(harmonic analysis) [1]. The method was verified by measurements on the real structure and can be used for parametrical studies.
Rounding off the Parts 1 and 2 of this publication nomograms, based on dimensionless parameters, can be developed to predict the sound radiation of light weight slabs. Hereby different sets of geometry as well as different configurations of ceilings can be studied in order to describe the acoustical and dynamical behaviour of wooden ceilings.
This paper investigates the prediction of low-frequency impact sound insulation for a solid timber floor formed from dowel-connected joists with Swiss hardwood.
A finite element model was developed for the dynamic response of the floor as it is neither homogeneous nor isotropic and has complex connections.
With point force excitation, a FEM model for the dynamic response of the floor was validated using experimental modal analysis in the laboratory.
Two different FEM models were developed, one using spring connectors and the other using join connectors. Good agreement between FEM and measurements in terms of the Modal Assurance Criterion (MAC) and eigenfrequencies was achieved for the first 14 modes with the spring connector model and for the first 7 modes with the join connector model.
However, for the vibroacoustic analysis it was necessary to use the join connector model due to the computational instabilities of the spring model above 100 Hz when it was coupled to the acoustic medium.
With mechanical excitation the radiated sound power from the underside of the timber floor was measured with sound intensity in order to calculate the radiation efficiency. Comparison of measurements and FEM showed reasonable agreement between 20Hz and 200Hz
In order to set up guidelines for the design of light-weighted ceilings for timber constructions to be used by engineers in practice, investigations based on both measurements and numerical models have been carried out [1, 2, 3].
The setup and the calibration of the numerical model of the structure are outlined briefly.
A semi-analytical approach for the prediction of radiated sound is presented, which is based on Integral Transform Methods. The method can be applied in the post processing of a Finite Element computation.
Thus as a first step the structure, consisting of a timber slab, a floating floor and a suspended ceiling, is built up in a Finite Element model, where the material properties of wood and the characteristics of the system are considered.
The model is parameterized in order to enable computations with varying geometry and material parameters and calibrated with the help of measurements using model updating techniques.
The velocity pattern resulting out of the FEM computation is transformed from the spatial into the wavenumber domain and from the time into the frequency domain using Fourier Transform Methods. Applying this velocity pattern as a boundary condition to the Helmholtz Equation, which results out of the Fourier Transform of the wave equation, the wavenumbers, which fulfil the radiation condition, can be selected and the pressure field in the adjacent acoustic fluid can be computed.
Due to the properties of the Fourier-Transform the radiated sound power can be calculated efficiently in the transformed domain out of pressure and velocity.
In a second part of the contribution the model for the air cushion in the suspended ceiling is discussed, where a FSI-model for the acoustic fluid and the structure is compared against engineering approaches using simplifications concerning mass distribution and transfer impedances between the individual nodes at the interface
Numerical models for the prediction of vibroacoustical characteristics of light-weighted ceilings
(2013)
In order to set up guidelines for the design of light-weighted ceilings for timber constructions to be used by engineers in practice, investigations based on both measurements and numerical models have been carried out within the cooperative research project “VibWood”.
In this contribution the setup and the calibration of the numerical model of the structure as well as the prediction of radiated sound are discussed, where a special focus is set on a dimensionless description in order to deduce information for a wide range of system’s specifications.
The structure, consisting of a timber slab, a floating floor and a suspended ceiling, is built up in a Finite Element model, where the material properties of wood and the characteristics of the system (e.g.support conditions, contact phenomena dynamic properties of individual parts) are considered.
The model is parameterized in order to enable computations with varying geometry and material parameters.
After calibrating the FE-model with the help of measurements using model updating techniques dimensionless parameters are defined based on the Buckingham-π- Theorem and computations are carried out in order to specify guidelines for various systems. The radiation of sound is computed in a post processing using Integral Transform Methods.
Within the scope of the recently finished cooperate research project "VibWood" at Technical University of Munich and Rosenheim University of Applied Sciences, fully parametrized numerical models for lightweight wooden floor constructions have been developed and calibrated by experimental modal analyses.
Based on a vast parametric study including floating floors and suspended ceilings a database of narrowband sound power levels in the frequency range up to 125 Hz for a wide range of floor dimensions has been set up.
A procedure will be presented on how to process the numerical data and derive single number values that allow a comparison to the standardized rating of impact sound insulation according to DIN EN ISO 717-2.
The derived data is implemented into a graphical user interface (GUI). This GUI is available for free. The database is open for additional geometries and will be enhanced by different constructions in the near future.