26-Dec-12
Pipes, Resonators, and Filters
26-Dec-12
NTU 522 M3970
1
Resonance in pipes
The fluid in a pipe of cross-sectional area S and length L is driven by a piston at x=0 and that the pipe is terminated at x=L in a mechanical impedance ZmL. If the pist
18-Dec-12
Cavities and Waveguides
18-Dec-12
NTU 522 M3970
1
Rectangular cavities
A rectangular cavity of dimension X, Y, Z, and its walls are perfectly rigid so that the normal component of the particle velocity vanishes. Governing equation
2 p =
1 2 p c
2012/12/9
Reflection and Transmission
9-Dec-12
NTU 522 M3970
1
Changes in media
A plane harmonic wave propagates in x-direction
pe j t = Pe j ( t -k1x )
Pi : the complex pressure amplitude of the incident wave
Pr : the complex pressure amplitude of the re
2012/12/12
Radiation and Reception
12-Dec-12
NTU 522 M3970
1
Acoustic reciprocity and monopoles
V: space that does not itself contain any sources but bounds them. S: surface of this volume 1 , 2 : velocity potential Applying divergence theorem
( - ) ndS
Sources of Sound
2012/10/24
NTU 522U5330
1
Sources of sound
Category 1 sources Sources that actively displace fluid in an unsteady manner. It is the rate of change of the rate of fluid volume displacement (i.e., the volume acceleration) that determines th
Spherical and Cylindrical Waves
2012/10/21
NTU 522U5330
1
Specific acoustic impedance
The specific acoustic impedance is
p (unit: rayl) u 1 SI rayl 1Pa S / m z
For plane harmonic waves in free space this ratio is z 0 c and the choice of sign depends on th
Sound Energy and Intensity
2012/10/17
NTU 522U5330
1
Sound Energy density
The energy transported by acoustic waves is of two forms: (1) The kinetic energy of the moving elements (2) the potential energy of the compressed fluid. Consider a small fluid elem
Sound in Fluids
2012/10/2
NTU 522U5330
1
Continuum model of fluid
Fluids connot resist steady applied shear forces. Solid react to steady shear forces by undergoing shear distorsion so that a state of static equilibrium is attained. In common with solids
One-Dimensional Wave Motion
2012/9/12
NTU 522U5330
1
Transverse waves on a string
df y = (T sin ) x + dx - (T sin ) x
(T sin ) df y = (T sin ) x + dx + - (T sin ) x x (T sin ) dx = x
If is small, then
df y =
y T dx x x
If is very large compared to its
2012/9/10
INTRODUCTION
2012/9/10
NTU 522U5330
1
What is Sound?
ARISTOTLE (384-322 BCE): "The sound emerges when a body moves the air, not by pressing into air a certain form, as some might think, but by putting this air into motion in an appropriate way,