Vibration Damping Apparatus for Aircraft Stringers
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Solution Overview
Problem
Existing reinforced skin structures, such as those in aircraft, face challenges in reducing mid-frequency noise and vibrations between 200-600 Hz due to resonant frequencies of support members, which are not effectively addressed by current damping methods that either add weight or compromise corrosion inspection and structural efficiency.
Innovation Solution
A vibration damping apparatus comprising a stiffening member with elongated members and a truss member, along with an energy dissipation member, is attached to the stringers to adjust bending and torsional modes, using viscoelastic materials to dissipate vibrational energy, thereby reducing noise and vibrations while allowing for corrosion inspection through triangular apertures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If lead blankets are attached to stringers and skin to absorb vibrations, then noise and vibration are reduced, but weight increases substantially causing inefficient operation
Solution Approach 1:
The vibration damping apparatus is segmented into multiple functional components: stiffening members (including hat-section and ladder-section stiffeners), damping members (constrained layer dampers), and energy dissipation members. This segmentation allows each component to perform its specific function efficiently while minimizing overall weight compared to solid lead blankets.
Solution Approach 2:
The apparatus uses composite material structures, particularly in the damping members which employ constrained layer damper technology with multiple layers (damping layer, constraining layers, and adhesive layers). This composite structure provides superior vibration damping per unit weight compared to homogeneous lead blankets.
2Object-affected harmful factors
If full-hat dampers are applied continuously to cover the entire hat-section of stringers, then vibration constraint is maximized, but corrosion inspection becomes impossible and weight increases
Solution Approach 1:
The damping members are applied in a segmented or discontinuous pattern along the stringers rather than as continuous solid coverage. This segmentation maintains vibration damping effectiveness while creating gaps that allow visual access for corrosion inspection of the underlying stringer structure.
Solution Approach 2:
The damping members are strategically positioned at specific locations where vibration damping is most needed (such as at vibration nodes or antinodes), rather than providing uniform continuous coverage. This local quality approach maintains effectiveness while enabling inspection access in critical areas.
3Weight of moving object
If ladder-shaped stiffeners with rectangular cutouts are used, then weight is reduced and corrosion inspection is enabled, but torsional twisting stiffness becomes inadequate
Solution Approach 1:
The stiffening members employ asymmetric geometric configurations (such as hat-section stiffeners with specific flange orientations and ladder-section stiffeners with optimized rung placements) that provide superior torsional stiffness compared to symmetric rectangular cutout designs. The asymmetric geometry is optimized to resist the specific loading conditions and vibration modes of the aircraft structure.
Solution Approach 2:
The combination of stiffening members and damping members creates a composite structural system where the stiffeners provide structural integrity and torsional stiffness, while the damping members add vibration damping capabilities. This composite approach achieves both weight reduction and maintained strength.
4Object-affected harmful factors
If skin fundamental frequency is made higher than stringer fundamental frequency, then low to mid frequency noise is reduced, but coupled mode becomes a strong radiator of sound
Solution Approach 1:
The apparatus specifically targets and dampens the coupled vibration modes between skin and stringers that occur in the problematic frequency range. The damping members are positioned and configured to maximize energy dissipation in these coupled modes, converting the harmful vibrational energy into heat and preventing its radiation as sound.
Solution Approach 2:
The design modifies the dynamic parameters of the stringers and skin structure through the addition of stiffening and damping members, changing the natural frequencies and mode shapes of the structure. This parameter change shifts the problematic coupled modes away from the critical frequency range or reduces their amplitude through targeted damping.
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
The solution effectively reduces cabin noise by up to 2 dB(A) in mid-frequency ranges, decreases weight, and enhances operational efficiency by dissipating vibrational energy as heat, while maintaining structural integrity and enabling visual inspection.
Implementation Method 1
The energy dissipation member is configured to dissipate vibrational energy of the stringer and comprises a viscoelastic material member
Implementation Method 2
The stiffening member is configured to adjust at least one of a bending mode and a torsional twisting mode of the stringer
Implementation Method 3
Methods and apparatus for reducing noise in reinforced skin structures... the energy dissipation member is configured to dissipate vibrational energy of the stringer
Data Source
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AI summary
Assemblies, methods, and an apparatus for damping vibrational energy induced to a reinforced skin structure (100) are disclosed. The reinforced skin structure includes an outer wall (102) and at least one stringer (104) coupled to the outer wall. The method includes providing a damping apparatus that includes a stiffening member (200) configured to adjust at least one of a bending mode and a torsional twisting mode of the stringer and an energy dissipation member (300) configured to dissipate vibrational energy of the stringer. The stiffening member includes at least two elongated members (202) that are spaced a distance apart and at least one truss member (204) that extends obliquely between the at least two elongated members. The damping apparatus is attached to the at least one stringer. The damping apparatus may be configured to dampen vibration in the range of between about 200-600 Hz.