Sound Wave Guide for Acoustic Cell Noise Attenuation
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Solution Overview
Problem
Existing acoustic structures, such as aircraft engine nacelles, face challenges in attenuating a wide range of noise frequencies, particularly low-frequency noise, without increasing thickness or weight, as deeper cells are required for lower frequencies, which contradicts the goal of maintaining thin and lightweight designs.
Innovation Solution
Incorporating a sound wave guide within the acoustic cell that divides it into two chambers, effectively increasing the resonator length without increasing the cell depth or number of cells, using a perforated acoustic guide wall that directs sound waves through an inner and outer chamber, allowing for varied acoustic properties by adjusting the wave guide's size, location, and shape.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If deeper acoustic cells are used to absorb low-frequency noise, then noise attenuation capability is improved, but nacelle thickness and weight increase
Solution Approach 1:
The patent places a sound wave guide structure inside the existing acoustic cell, nesting an additional acoustic path within the original cell depth. This allows the effective acoustic resonator length to be extended without increasing the physical thickness of the nacelle, as the sound wave travels through the inner chamber of the wave guide which adds acoustic path length while remaining contained within the original cell boundaries
Solution Approach 2:
The patent introduces a new spatial dimension by adding the sound wave guide structure that creates an inner chamber extending the acoustic path in a direction that does not increase the overall nacelle thickness. The wave guide transforms the acoustic path from a simple depth-dependent linear path to a multi-dimensional path that可以利用 the lateral space within the cell to extend the effective resonator length
2Object-affected harmful factors
If deeper acoustic cells are used to absorb low-frequency noise, then noise attenuation capability is improved, but nacelle weight increases
Solution Approach 1:
The sound wave guide is nested within the existing acoustic cell structure, utilizing the available space without requiring additional external structure. This nesting approach allows the effective acoustic resonator length to be extended while avoiding the weight penalty of adding external depth to the nacelle
Solution Approach 2:
The patent changes the acoustic parameters by extending the effective resonator length through the sound wave guide structure, which modifies the acoustic impedance and resonance characteristics to improve low-frequency attenuation without changing the physical dimensions or material quantity that would increase weight
3Object-affected harmful factors
If the number of acoustic cells is increased to improve noise attenuation, then noise attenuation capability is improved, but device complexity and weight increase
Solution Approach 1:
The patent segments the acoustic cell into two distinct chambers: an outer chamber and an inner chamber created by the sound wave guide. This segmentation allows each chamber to contribute to noise attenuation independently, with the inner chamber providing extended low-frequency absorption path while the outer chamber maintains the original acoustic function, thereby improving overall attenuation capability within the same physical footprint
Solution Approach 2:
The sound wave guide structure serves multiple functions: it divides the cell into two chambers for enhanced attenuation, provides an extended acoustic path for low-frequency noise, and maintains the structural integrity of the original cell. This multi-functionality allows improved noise attenuation without requiring additional separate components that would increase complexity
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach enables effective low-frequency noise attenuation in thinner, lighter acoustic structures, maintaining the design goals of reduced size and weight while enhancing noise suppression capabilities across a broader frequency range.
Implementation Method 1
a sound wave guide is located in the acoustic resonator. The sound wave guide includes an acoustic guide wall having interior and exterior surfaces... The wave guide inlet is located closer to the first edge of the honeycomb than the wave guide outlet... The inner and outer sound chambers, which are connected at the wave guide outlet, provide an effective acoustic chamber that is much longer than the thickness of the honeycomb
Implementation Method 2
acoustic materials are added to the honeycomb structure so that the honeycomb cells are acoustically closed at the end located away from the engine and covered with a porous covering at the end located closest to the engine. The closing of the honeycomb cells with acoustic material in this manner creates an acoustic resonator that provides attenuation, dampening or suppression of the noise
Implementation Method 3
acoustic resonators that contain relatively thin acoustic materials or grids that have millions of holes that create acoustic impedance to the sound energy generated by the engine
Data Source
Figure 1
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AI summary
The bandwidth or acoustical range of an acoustic structure is increased by locating a sound wave guide (30) within the acoustic cell (22). The wave guide divides the cell into two acoustical chambers (42,44). The two chambers provide an effective increase in resonator length of the cell.