Finite Element Based Method for Investigation of Exterior Acoustics
Typ
Examensarbete för masterexamen
Program
Applied mechanics (MPAME), MSc
Publicerad
2020
Författare
Eriksson, Olivia
Ansin, Caroline
Modellbyggare
Tidskriftstitel
ISSN
Volymtitel
Utgivare
Sammanfattning
A challenge with renewable energy is that the power source is time varying. To be able to
supply renewable power at all hours, the company Azelio is developing a Thermal Energy
Storing (TES) system. During the development, multiple design changes are made at a
rapid pace. Therefore, it is important to utilize numerical tools to save time and money.
Azelio’s TES system is Stirling engine based. The free mass loads in the engine causes
vibrations, which make sound propagate from the system. The sound level is mostly not
an issue since the system will be located in uninhabited areas, but it can be of importance
if the system would be serviced during operation. That is why a numerical method for
determining the exterior sound level would be of interest. The purpose is, thereby, to
develop a generic method that can be used to predict exterior sound. The method will
be developed for the current TES system, but should be possible to use when evaluating
new designs.
A numerical method for predicting the exterior far field sound level located in a free field
was developed using the finite element method in Ansys Mechanical APDL. The exterior
acoustics problem was solved using a one-way coupling from structure to fluid. The
structural vibrations were computed through mode-superposition in a harmonic analysis,
in which the system was assumed to be linear and time-invariant. The vibrations were
then used to generate waves in a fluid full harmonic analysis. To validate the numerical
model of the system, an experimental modal analysis was performed on the current TES
system, but no measurements during operation were made.
Due to the complexity of the system and time restriction, the results from the experiment
lacked in correlation with the results from the finite element analysis. However, this does
not say anything about the developed sound predicting method. One conclusion that can
be drawn is that it is difficult to model and do experiments on a complex system.
The developed method is generic and can be applied to any vibrating system. It can be
used to compute the sound pressure level in a plane or a point, at various engine speeds.
The sound level in a point can be compared to measurements, while the plane contour plot
can be used in the development process to identify parts that radiate a lot of sound. The
method was developed for a complex system and should be tested on a simpler system.
To validate the method, various tests should be performed.
Beskrivning
Ämne/nyckelord
Finite Element Method (FEM) , Modal Analysis , Harmonic Analysis , Superposition , Experimental Modal Analysis (EMA) , Exterior Acoustics , One-Way Coupling , Far Field , Stirling Engine