Circular duct analysis in ansys workbench
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1. The document describes conducting acoustic analyses in ANSYS to analyze circular ducts with different boundary conditions and excitations. 2. It examines natural frequencies of ducts with rigid walls, pressure distributions in ducts with harmonic excitations, and impedance of a duct radiating into free space. 3. The analyses are performed with acoustic elements like FLUID30 in ANSYS and examine properties like natural frequencies, pressure and velocity distributions, and mechanical impedance of a piston-duct system.
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Particle velocity along a Piston-Rigid Duct
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Mic Position along Duct [m]
Mic Position along Duct [m]
Mic Position along Duct [m]
Soundpressurelevel[dB]ParticleVelocity[m/s]
ImaginaryPressure[Pa]](https://image.slidesharecdn.com/circularductanalysisinansysworkbench-160820175738/85/Circular-duct-analysis-in-ansys-workbench-11-320.jpg)
![Imaginary part of mechanical impedance of piston attached to a Duct
Frequency [Hz]
Imaginaryimpedance[Ns/m]](https://image.slidesharecdn.com/circularductanalysisinansysworkbench-160820175738/85/Circular-duct-analysis-in-ansys-workbench-22-320.jpg)
![Mechanical power of piston Attached to the Duct
Frequency [Hz]
Power[Watts]](https://image.slidesharecdn.com/circularductanalysisinansysworkbench-160820175738/85/Circular-duct-analysis-in-ansys-workbench-23-320.jpg)
![Real part of mechanical impedance of piston attached to a Duct
Frequency [Hz]
Realimpedance[Ns/m]](https://image.slidesharecdn.com/circularductanalysisinansysworkbench-160820175738/85/Circular-duct-analysis-in-ansys-workbench-24-320.jpg)
Circular duct analysis in ansys workbench
- 1. Circular Duct analysis in ANSYS workbench
- 2. Objective 1. Calculate the natural frequencies of a 3D duct with rigid walls with various end conditions. 2. Sound pressure distribution along the duct for a harmonic volume velocity excitation at one end of a duct with finite length. 3. Pressure distribution along an infinitely long duct. 4. Pressure distribution along a duct with a finite length that has a frequency varying impedance at one end of the duct radiating into free space. 𝑢1 𝑢2 z x y L a
- 3. Element types available for Acoustic Analyses in ANSYS based on pressure formulation Name 2D/3D Nodes Description FLUID29 2D 4 Planar element FLUID129 2D 2 Line element for simulating an infinite boundary FLUID30 3D 8 Brick element FLUID130 3D 4,8 Planer element for simulating an infinite boundary FLUID220 3D 20 Brick element FLUID221 3D 10 Tetrahedral element
- 4. Natural frequencies Description parameter Value Diameter 2a 0.1m Length L 3m Speed of sound 𝑐0 343m/s Density ρ0 1.21 kg/m3 Velocity of piston 𝑢2 0.0 Velocity at rigid end 𝑢1 0.0 configuration schematic Mode index n= Natural frequencies Mode shape Rigid-rigid 0,1,2 n𝑐0/2L Cos(nπx/L) Open-rigid 1,3,5 n𝑐0/4L Cos(nπx/2L) Open-open 1,2,3 n𝑐0/2L sin(nπx/L)
- 5. • FLUID 30 acoustic element is used
- 6. Element per wavelength Element size Esize=λ/epw =𝑐0/f/epw
- 8. Natural frequency of open-rigid
- 9. Natural frequency of open-open Duct
- 10. Pressure and velocity distribution along the duct Description parameter Value Diameter 2a 0.1m Length L 3m Speed of sound 𝑐0 343m/s Density ρ0 1.21 kg/m3 Velocity of piston 𝑢2 1.0 m/s Velocity at rigid end 𝑢1 0.0 Excitation frequency f 200Hz Parameters used in the analysis of a circular duct with forced excitation at one end
- 11. -1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1 Particle velocity along a Piston-Rigid Duct 1 2 3 100 110 120 130 140 150 -500 -400 -300 -200 -100 0 100 200 300 400 500 Mic Position along Duct [m] Mic Position along Duct [m] Mic Position along Duct [m] Soundpressurelevel[dB]ParticleVelocity[m/s] ImaginaryPressure[Pa]
- 13. Semi-infinite duct • Applied an absorbing boundary to the outlet of the duct to simulate a semi-infinite duct • The upstream inlet end provides an acoustic excitation as a surface velocity of 1 m/s. • Outlet end has a radiation boundary applied which is one method of specifying an absorbing boundary.
- 14. SPL of semi-infinite duct= 20log10 ρ0∗𝑐0∗𝑢 20𝑒−6∗ 2 =143.3 dB
- 15. Radiation from an Open-ended Duct Piston velocity Free-field FLUID 130 element Transition region for the acoustic finite elements
- 18. Commands which will couple all the nodes associated with inlet axis which will create a rigid piston face and motion in the other direction will be zero
- 22. Imaginary part of mechanical impedance of piston attached to a Duct Frequency [Hz] Imaginaryimpedance[Ns/m]
- 23. Mechanical power of piston Attached to the Duct Frequency [Hz] Power[Watts]
- 24. Real part of mechanical impedance of piston attached to a Duct Frequency [Hz] Realimpedance[Ns/m]