By Uno Ingard
Written by way of a famous authority within the topic region, this booklet is a finished examine of the idea and functional software of noise aid to various fields. it can be used as a reference by way of scientists and engineers or in a senior-undergraduate or graduate-level direction. the 1st six chapters take care of the elemental mechanisms of sound absorption through which acoustic strength is switched over into warmth in viscous and thermal limitations in a legitimate box. the second one half covers duct attenuators with a dialogue of ways their functionality is defined and measured. the most a part of each one bankruptcy is deliberate to be descriptive, and includes numerical effects that are supposed to be of direct curiosity for layout paintings. Mathematical research is positioned on the finish of the chapters.
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Additional resources for Noise Reduction Analysis (Physics)
H : Eq. 94. 7: Eqs. ). The ordinate in the ﬁgure is the compressibility normalized with respect to the isentropic (free ﬁeld) value κ and the abscissa is a/dh , where dh is the thermal boundary layer thickness and a the half-width of the channel. 4 for air. 4 and the imaginary part is zero (no losses). For large values of a/dh (a/dh >> 1), on the other hand, the compressibility becomes isentropic, and again, there are no losses. 16. We shall take this condition to represent the transition from isothermal to isentropic conditions.
The result obtained for a plane boundary can be used also for a curved boundary, if the local radius of curvature is much larger than the thermal boundary layer thickness. 14 NOISE REDUCTION ANALYSIS Example: The Q-Value of a Cavity Resonator For a simple mass-spring oscillator with relatively small damping, the sharpness of its resonance is usually expressed as 1/(2π) times the ratio of the total energy of oscillation (twice the kinetic energy) and the power dissipated in one period. This relation is valid also for an acoustic cavity resonator.
K: Heat conduction coeff. Cp : Spec. heat, unit mass. 7: Eq. ) The reverse situation when a temperature ﬂuctuation far from the plate varies harmonically and the temperature ﬂuctuation at the plate is zero is analogous to the case of an oscillating ﬂuid above a stationary plate. The temperature ﬂuctuation goes to zero at the plate through the thermal boundary layer. The reason why the temperature ﬂuctuation at the solid boundary can be considered to be zero is that the thermal conduction (and heat capacity) of a solid is much greater than for air.