Vibroacoustic Diagnostics …
419
3.1 Harmonic Response in Structural Domain
At the very beginning, the modal and harmonic analysis was interconnected in
the computational model. A modal superposition method could be used during the
solution process.
The finite element model was created by using the solid186 and solid187 elements.
Based on the sensitivity analysis, two elements were considered through the thickness
of the plate. The final discretized geometry model contained approx. 3200 elements
in the structural analysis.
The structure in the analyses was not bound by any constraints—free boundary
condition. The force load was applied—the force by which the structure was excited
was used from the laboratory testing. See position p. F in Fig. 1, where the force
transducer was placed in technical measurement and in parallel the location where
the force was applied in the numerical model. The damping parameter was also
applied from the modal experimental analysis. The damping ratio was included in
the computational model.
Evaluation of the normal acceleration in points based on a technical experiment
was given.
3.2 Harmonic Response in Acoustic Domain
The structure-acoustic analysis linking approach was chosen when creating the
acoustic model. Creating a 3D model—the rectangular plate model has been cut into
the sphere volume that formed the acoustic space. Furthermore, only the acoustic
space was used in whole analysis. Creation of FE mesh—in the model discretization,
the minimum element size L min [mm] was chosen in acoustic model according to (1)
from [5]:
L min = λ/5 = c/(5 ∗ f max ),
(1)
where λ [m] is wavelength,
c [m/s] is the speed of sound,
f max [Hz] is considered frequency maximum in analysis.
In the acoustic analysis, the fluid220 and the fluid221 elements were used, which
are a high order 3-D solid elements that exhibit quadratic pressure behavior. The
final discretized model contained approx. 93,500 elements in the acoustic analysis.
Boundary conditions—in Fig. 3 are shown the boundary conditions used in the
acoustic numerical model. On the left side of the picture, the import of surface normal
velocities from structural harmonic analysis is depicted. In the middle part of the
model, a specific envelope was applied. From this surface area, the acoustic features
outside of the FEM model were approximated. An important boundary condition of
the “Infinite elements” was applied to the outside surface of the acoustic space. In
419
3.1 Harmonic Response in Structural Domain
At the very beginning, the modal and harmonic analysis was interconnected in
the computational model. A modal superposition method could be used during the
solution process.
The finite element model was created by using the solid186 and solid187 elements.
Based on the sensitivity analysis, two elements were considered through the thickness
of the plate. The final discretized geometry model contained approx. 3200 elements
in the structural analysis.
The structure in the analyses was not bound by any constraints—free boundary
condition. The force load was applied—the force by which the structure was excited
was used from the laboratory testing. See position p. F in Fig. 1, where the force
transducer was placed in technical measurement and in parallel the location where
the force was applied in the numerical model. The damping parameter was also
applied from the modal experimental analysis. The damping ratio was included in
the computational model.
Evaluation of the normal acceleration in points based on a technical experiment
was given.
3.2 Harmonic Response in Acoustic Domain
The structure-acoustic analysis linking approach was chosen when creating the
acoustic model. Creating a 3D model—the rectangular plate model has been cut into
the sphere volume that formed the acoustic space. Furthermore, only the acoustic
space was used in whole analysis. Creation of FE mesh—in the model discretization,
the minimum element size L min [mm] was chosen in acoustic model according to (1)
from [5]:
L min = λ/5 = c/(5 ∗ f max ),
(1)
where λ [m] is wavelength,
c [m/s] is the speed of sound,
f max [Hz] is considered frequency maximum in analysis.
In the acoustic analysis, the fluid220 and the fluid221 elements were used, which
are a high order 3-D solid elements that exhibit quadratic pressure behavior. The
final discretized model contained approx. 93,500 elements in the acoustic analysis.
Boundary conditions—in Fig. 3 are shown the boundary conditions used in the
acoustic numerical model. On the left side of the picture, the import of surface normal
velocities from structural harmonic analysis is depicted. In the middle part of the
model, a specific envelope was applied. From this surface area, the acoustic features
outside of the FEM model were approximated. An important boundary condition of
the “Infinite elements” was applied to the outside surface of the acoustic space. In