Acoustic and Vibration Response Analysis of Heavy-Duty Gearbox
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The most complex approach is based on the multibody simulation (MBS), which
is solved in time domain. To get results with high level of accuracy needs to incorporate the modal and harmonic analysis including validation of them by technical
experiment [8]. In the presented paper the modal and harmonic analysis is described
including the acoustics part.
2.1 Modal Analysis
The gearbox housing from the single stage gearbox for application in train is used.
The dimensions of gearbox are in max approx. length 980 mm, width 770 mm,
depth 180 mm. First the modal analysis by using FEM was performed in software
Ansys Workbench. The CAD data and material properties based on the material list
were used. The free boundary conditions were applied on the model. The model of
bolts was simplified and the pretension corresponding to the tightening moment was
applied at first step. Afterward, the modal analysis was performed in frequency range
up to 3 kHz.
Subsequently the experiment was performed also with the free boundary conditions. This was simulated by hang up the gearbox housing on the flexible rope. The
excitation was performed by using modal hammer and the response was measured by
triaxial accelerometer. The accelerometer was placed in the exterior part of housing
into locations, which were determined based on the results from numerical simulation. For each side the location was changed. The excitation force was applied into
other location based on the grid, which was 60–70 mm, see Fig. 1. The force and
response were recorded by using analyzer from Brüel & Kjaer company, where four
channels were occupied (impact hammer and three for ACC sensor). The geometry
model was simplified to create structure for visualization in software to determine
the corresponded eigen shape.
2.2 Harmonic Analysis
For the purpose to get accurate excitation force the experiment of structure harmonic
analysis was performed first. The measurement was performed in a fully anechoic
chamber, because the measurement of acoustic response by microphones. The
housing was hung by rope similar to the modal harmonic. The excitation of structure
was performed by modal vibration exciter, which was connected to the support. The
thin rod with low stiffness in radial direction was screwed on the output of exciter,
see Fig. 2. The modal exciter was encapsulated to minimize noise, which is not
connected to the gearbox housing. The force sensor was placed on second end of rod
and screwed into one hole of housing close to the bearing location. The harmonic
signal of the specified amplitude and frequency was transmitted to the structure.
445
The most complex approach is based on the multibody simulation (MBS), which
is solved in time domain. To get results with high level of accuracy needs to incorporate the modal and harmonic analysis including validation of them by technical
experiment [8]. In the presented paper the modal and harmonic analysis is described
including the acoustics part.
2.1 Modal Analysis
The gearbox housing from the single stage gearbox for application in train is used.
The dimensions of gearbox are in max approx. length 980 mm, width 770 mm,
depth 180 mm. First the modal analysis by using FEM was performed in software
Ansys Workbench. The CAD data and material properties based on the material list
were used. The free boundary conditions were applied on the model. The model of
bolts was simplified and the pretension corresponding to the tightening moment was
applied at first step. Afterward, the modal analysis was performed in frequency range
up to 3 kHz.
Subsequently the experiment was performed also with the free boundary conditions. This was simulated by hang up the gearbox housing on the flexible rope. The
excitation was performed by using modal hammer and the response was measured by
triaxial accelerometer. The accelerometer was placed in the exterior part of housing
into locations, which were determined based on the results from numerical simulation. For each side the location was changed. The excitation force was applied into
other location based on the grid, which was 60–70 mm, see Fig. 1. The force and
response were recorded by using analyzer from Brüel & Kjaer company, where four
channels were occupied (impact hammer and three for ACC sensor). The geometry
model was simplified to create structure for visualization in software to determine
the corresponded eigen shape.
2.2 Harmonic Analysis
For the purpose to get accurate excitation force the experiment of structure harmonic
analysis was performed first. The measurement was performed in a fully anechoic
chamber, because the measurement of acoustic response by microphones. The
housing was hung by rope similar to the modal harmonic. The excitation of structure
was performed by modal vibration exciter, which was connected to the support. The
thin rod with low stiffness in radial direction was screwed on the output of exciter,
see Fig. 2. The modal exciter was encapsulated to minimize noise, which is not
connected to the gearbox housing. The force sensor was placed on second end of rod
and screwed into one hole of housing close to the bearing location. The harmonic
signal of the specified amplitude and frequency was transmitted to the structure.