Instructions for Muffler Analysis

Transcription

1 Instructions for Muffler Analysis Part 1: Create the BEM mesh using ANSYS Specify Element Type Preprocessor > Element Type > Add/Edit/Delete Add Shell Elastic 4 Node 181 Close Specify Geometry Preprocessor > Modeling > Create > Keypoints > In Active CS Point No. X Y Z / /

2 Create Lines between keypoints Preprocessor > Modeling > Create > Lines > Lines > Straight Lines Connect the points so you have the geometry shown in the plot below Create Arcs around duct opening Preprocessor > Modeling > Create > Lines > Arcs > By End Key Points Radius Click on the two end points and hit Okay Click on a point on the curvature side and hit Okay Enter the radius of.0348/2 and hit okay

3 Create all other needed points and lines on the inlet side Create Areas Preprocessor > Modeling > Create > Areas > By Lines Create rectangular areas on the boundary

4 Reflect the Areas Preprocessor > Modeling > Reflect > Areas > Pick All

5 Create connecting areas to complete muffler areas To Set the Mesh Size Preprocessor > Meshing > Size Ctrls > ManualSize > Global > Size Set the element edge length to 0.05 Set the Mesh Size and Mesh the Areas Preprocessor > Meshing > Size Ctrls > Manual Size > Lines > Picked Lines All Lines Element Edge Length (Use a length of.02 à Each element will have a size of.02 m) OK Preprocessor > Meshing > Mesh > Areas > Free Pick All OK Your mesh should look like that on the next page. The mesh at the end of each duct may look pretty poor. If so clear those mesh areas (Preprocessor > Meshing > Clear > Areas) and remesh the ends of the muffler using a mapped mesh.

6 Write out the mesh in an ASCII format that SYSNOISE can read Preprocessor > Archive Model > Write > (Select option db) In the middle box, type in duct.cdb for the filename (ignore the warnings) Save your model just in case File > Save as Jobname

7 Part 2: Virtual.Lab Direct BEM Analysis Startup Virtual.Lab Start > Acoustics > Acoustic Harmonic BEM Tools > Options Change length to m and mass to kg Tools > Edit the Model Type Definition (Select Direct BEM and Interior problem)

8 File > Import Mesh > Acoustic Mesh project.cdb Right click on Acoustic Mesh Preprocessing Set and Update Insert > Materials > New Materials > New Fluid Material

9 Insert > Properties > New Properties > New Acoustic Fluid Property Right click on Nodes and Elements > Generate Image > Acoustic Normal Vector Symbol

10 Insert > Mesh grouping > Auto update group > Feature angle Select muffler mesh from tree Click on Type Specific (see above picture) Select element at inlet Also, create an element group at the outlet.

11 Insert > Boundary Condition and Sources > Boundary Condition and Source Set Right click on Acoustic Boundary Conditions and Sources in the tree Double click on Faces from the tree

12 Double click Constant Values Insert > Properties > New Properties > Absorbent Panel Properties (select the outlet group for the application region)

13 Insert > Field Point Meshes > Point Set Field Point Meshes Add two points upstream of the muffler about 10 cm apart and one point downstream of the muffler. Right click on Point Set Field Point Mesh.1 and Set Mesh Part Type to Set as Field Point Mesh Insert > BEM Analysis Cases > Acoustic Response Analysis Case

14 Double click on Acoustic Response Solution Set.1 Right click on Acoustic Response Solution Set.1 and update. To See Contour Plots Right click on Acoustic Response Solution Set.1 and Generate Image

15 You can toggle between display types using the icon at the bottom of the screen. Select Right click on Nodes and Elements and then Hide/Show to improve the display. You should see plane wave behavior. Double click on Pressure (Nodal Values) to switch between frequencies.

16 To look at field point results Right click on Acoustic Response Solution Set.1 and New Function Display Add all three points and close Right click on plot and then Export all Data

17 This will write out the real part of the sound pressure for each point. Right click on the Y-axis and click imaginary Repeat the process shown above to output the imaginary part of the sound pressure for each point This data can be read into Matlab or Excel for processing.