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State University of Nuevo Leon, MexicoMechanical & Electrical Engineering School

SIMULATION OF THE SIMULATION OF THE ACOUSTIC WAVE ACOUSTIC WAVE

BEHAVIOR OF DUCTS BEHAVIOR OF DUCTS AND PLENUMS USINGAND PLENUMS USING

ANSYSANSYS

JOSE DE JESUS VILLALOBOS LUNAPEDRO LOPEZ CRUZCARLOS A. LARA OCHOAFERNANDO J. ELIZONDO G.

ACOUSTICS LABORATORYACOUSTICS LABORATORY

I. BACKGROUNDI. BACKGROUND

The ducts and plenum systems used in air The ducts and plenum systems used in air conditioned systems have been analyzed as a conditioned systems have been analyzed as a transfer function, output vs. input.transfer function, output vs. input.

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This concept is very useful for practical This concept is very useful for practical purposes, but, for didactic purposes, it purposes, but, for didactic purposes, it doesn't have the understanding of the doesn't have the understanding of the acoustical phenomena inside these systems.acoustical phenomena inside these systems.

I. BACKGROUNDI. BACKGROUND

II. OBJECTIVEII. OBJECTIVE

To present the necessary aspects to the FEM simulation of duct and plenum systems withANSYS.Discus the necessary parameters in order to obtain the accurate results. To show the propagation, reflection and absorption phenomena inside the systems.

III. SIMULATION OF THE ACOUSTIC III. SIMULATION OF THE ACOUSTIC BEHAVIOR BY FEM USINGBEHAVIOR BY FEM USING ANSYSANSYS

Ducts

Plenums

Finite Element Software used: ANSYS

GENERAL CONSIDERATIONS FOR THE GENERAL CONSIDERATIONS FOR THE SIMULATION OF BOTH SYSTEMS:SIMULATION OF BOTH SYSTEMS:

IV. ANALYSIS SEQUENCEIV. ANALYSIS SEQUENCE

A.A. PREPROCESSINGPREPROCESSING1.1. Analysis Type: Analysis Type: ANSYS ANSYS FLUIDFLUID2.2. Element TypeElement Type3.3. Real ConstantsReal Constants4.4. Material Properties (Air and Absorption Material).Material Properties (Air and Absorption Material).5.5. FE ModelFE Model6.6. Define AttributesDefine Attributes7.7. FE FE DiscratitationsDiscratitations (Meshing the Model)(Meshing the Model)

B.B. SOLUTION SOLUTION 1.1. Analysis Type (Harmonic)Analysis Type (Harmonic)2.2. Solution OptionsSolution Options3.3. Boundary Conditions Applications Boundary Conditions Applications

(Loads, Constraints)(Loads, Constraints)4.4. Analysis Frequency RangeAnalysis Frequency Range5.5. SolutionSolution

C.C. POSTPOST--PROCESSINGPROCESSING1.1. Check Results and Visualizations.Check Results and Visualizations.

IV. A.IV. A.-- PREPROCESSINGPREPROCESSINGIV. ANALYSIS SEQUENCEIV. ANALYSIS SEQUENCE

Type 1, Reference Pressure = 20 µPaType 2, Reference Pressure = 20 µPa

3. REAL 3. REAL CONSTANTSCONSTANTS

4. MATERIAL 4. MATERIAL PROPERTIESPROPERTIES

Type 1, FLUID30, Structure AbsentType 2, FLUID30, Structure Present

2. ELEMENT 2. ELEMENT TYPETYPE

ANSYS FLUID1. ANALYSIS 1. ANALYSIS TYPETYPE




MATERIAL NUMBER 1 (AIR)Density= 1.21 kg/m3

Sonic Velocity = 344 m/seg








MATERIAL NUMBER 1 (AIR)Density= 1.21 kg/m3

Sonic Velocity = 344 m/segMATERIAL NUMBER 2 (ACOUSTIC MATERIAL)Density=28 kg/m3

Absortion Coeficient = SPECIFIC MATERIAL PROPERTIESSonic Velocity = 344 m/seg





Absorption Coefficient vs. Frequency for Acoustics Commercial Material(FONAC)

Acoustic Absorption Curve

0

0.1

0.2

0.3

0.4

0.5

0.6

125 Hz 250 Hz 500 Hz 1000 y 2000 Hz 4000 y 8000 Hz

Frequency (Hz)

Acou

stic

Abs

orpt

ion

Coe

ficie

nt (s

abin

e/m

2)


5. FINITE ELEMENT MODEL5. FINITE ELEMENT MODEL

ANSYS TOOLSCREATE>VOLUMES>...

EXTERNAL MODELING SOFTWARESOLID WORKSMECHANICAL DESKTOPACADOTHERS.


IV. A.IV. A.-- PREPROCESSINGPREPROCESSING


Volume = 2 (EXTERNAL)Material Number : 2 (ABSORPTION MATERIAL)Real Constant Set Number: 1Element Type Number: 1 (FLUID30)

Volume = 1 (INTERIOR)Material Number : 1 (AIR)Real Constant Set Number: 1Element Type Number: 1 (FLUID30)

6. DEFINE ATTRIBUTES6. DEFINE ATTRIBUTES





6. DEFINE ATTRIBUTES6. DEFINE ATTRIBUTES

7. MODEL MESHING7. MODEL MESHING

DUCT MESHINGMESH TOOL...

Using smart sizeUsing Mesh VolumesShape, Tet or HexMesher Free

Command “Meshing”

A MESHING EXAMPLE:



5. FINITE ELEMENT MODEL5. FINITE ELEMENT MODEL

ANSYS TOOLSCREATE>VOLUMES>...

EXTERNAL MODELING SOFTWARESOLID WORKSMECHANICAL DESKTOPACADOTHERS.



7. MODEL MESHING7. MODEL MESHING

DUCT MESHINGMESH TOOL...

Using smart sizeUsing Mesh VolumesShape, Tet or HexMesher Free

Command “Meshing”

A MESHING EXAMPLE:



1. Analysis Type2. Solution Options3. Boundary Conditions

Applications (Loads)4. Analysis Time Range5. Solution

IV. B.IV. B.-- SOLUTIONSOLUTION


1. ANALYSIS TYPE: HARMONIC1. ANALYSIS TYPE: HARMONIC

2. SOLUTION OPTIONS: 2. SOLUTION OPTIONS: FromFrom 1 1 oror FastFast (More (More AccurateAccurate) ) toto 4 (4 (SpecificSpecific ProposalsProposals).).



3. BOUNDARY CONDITIONS FOR BOTH, 3. BOUNDARY CONDITIONS FOR BOTH, DUCTS AND PLENUM SYSTEMS.DUCTS AND PLENUM SYSTEMS.

INLETINLETInteraction between fluid Interaction between fluid and structure.and structure.

Sound pressure =1 PaSound pressure =1 Pa

LOADS>APPLY>LOADS>APPLY>Fluid Structure Interface Fluid Structure Interface ((FSIFSI))

Pressure> On Nodes> Pressure> On Nodes> Value= 1 PaValue= 1 Pa






INLETINLETInteraction between fluid Interaction between fluid and structure.and structure.

Sound pressure =1 PaSound pressure =1 Pa

Pressure = 1 Pa

OUTLETOUTLETNo interaction between fluid and structure.

Sound pressure = No declared

Impedance = 0(simulating an infinite medium of propagation)

LOADS>APPLY>

Impedance = 0




OUTLETOUTLETNo interaction between fluid and structure.

Sound pressure = No declared

Impedance = 0(simulating an infinite medium of propagation)




Material Properties Sequence:Preprocessor>Material Properties>Isotropic Material Properties>Material Number>Write 2




AbsorptionAbsorption AcousticsAcoustics MaterialMaterial

Material Material NumberNumber 2 2 isisthethe ExternalExternal VolumeVolume

4. ANALYSIS FREQUENCY RANGE.4. ANALYSIS FREQUENCY RANGE.

Ducts and PlenumsDucts and PlenumsStandard Frequency Range in Octave Bands starting at 125, 250, 500, 1000, 2000



The wave frequency is defined as a boundary condition in the application of an harmonic pressure.

For each interesting frequency it´s necessary to do an individual analysis and . . .

The Absorption Coeficient of the Acoustics Material is different at each frequency…



IV.C.1. CHECK RESULTS AND VISUALITATIONS FOR DUCTSDUCTS AND PLENUMS.

PROPAGATIONPRESSUREDIFFERENT FREQUENCY ANALYSISATTENUATION VS FREQUENCY

IV. C.IV. C.-- POST POST -- PREPROCESSINGPREPROCESSING


PROPAGATIONPROPAGATION

PRESSUREPRESSURE

125 Hz

250 Hz

ANALYSIS AT DIFFERENT FREQUENCIESANALYSIS AT DIFFERENT FREQUENCIES

500 Hz

1000 Hz


2000 Hz

ATTENUATION VS FREQUENCYATTENUATION VS FREQUENCY

Outlet atenuation at each characteristic frequencyAcoustic Absorption Material

0.22 0.17

4.34

6.79

9.04

11.97

1.41

0.00

2.00

4.00

6.00

8.00

10.00

12.00

14.00

63 Hz 125 Hz 250 Hz 500 Hz 1000 Hz 2000 Hz 4000 Hz

Frequency (Hz)

Aten

uaci

on (

dB/ f

t )

IV.C.1. CHECK RESULTS AND VISUALITATIONS FOR DUCTS AND PLENUMSPLENUMS.

PROPAGATIONPRESSUREDIFFERENT FREQUENCY ANALYSISATTENUATION VS FREQUENCY

IV. C.IV. C.-- POST POST -- PREPROCESSINGPREPROCESSING


PROPAGATION PROPAGATION

125 Hz 500 Hz


1000 Hz500 Hz


2000 Hz


ATTENUATION VS FREQUENCYATTENUATION VS FREQUENCYATTENUATION VS FREQUENCY

8.84

0.21 0.00

28.04

16.12

4.87

1.00

28.04

0.00

0.210.002.004.006.008.00

10.0012.0014.0016.0018.0020.0022.0024.0026.0028.0030.00

125 250 500 1000 2000

FREQUENCY Hz

dB a

t the

ple

num

oul

et Plenum Absorption Curve with Acoustic

Material

Plenum Absorption Curve without Acoustic

Material

V. FINAL COMMENTSV. FINAL COMMENTS

V. FINAL COMMENTSV. FINAL COMMENTS

With Simulations:

It´s easier to understand the behavior on acoustic waves into duct and plenum systems.

We can see the propagation of a wave.The frontwave going along the duct.The effect of the absorbing material by frequency.

The graphical results give us the chance to see the propagation, reflection, amplification and attenuation phenomenon into the plenum.

The graphical results help “Beginners” in the acoustical studies to understand in a integral way the phenomenon and propose modeling improves...

With the simulation of ducts and plenums is possible to prove designs with different geometries and materials looking for an economy.

When we are investigating, we begin to understand, but more interesting questions surges...

And our goal is try to respond that interesting questions improving the previous models...

Thank you!E-mails:[email protected]@[email protected]@ccr.dsi.uanl.mx

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