Dual-Mode Tuned Vibration Absorber for Blade-Pass Harmonics
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Solution Overview
Problem
Existing tuned vibration absorbers are designed to attenuate vibrations at a single frequency, which is insufficient for propeller-driven aircraft that produce noise and vibration at multiple frequencies, such as the blade pass frequency and its harmonics, necessitating a solution that can effectively reduce vibrations at multiple frequencies.
Innovation Solution
A dual-frequency vibration-reduction apparatus comprising a beam with uneven mass distributions at its ends, capable of vibrating in both bending and torsional modes, is designed to attenuate primary and secondary frequency vibrations by mechanically coupling the beam to a structure, allowing for adjustment of mass positions and amounts to target specific frequency ranges.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a single-frequency tuned vibration absorber is used, then the device complexity is low, but the adaptability to attenuate vibrations at multiple frequencies is insufficient
Solution Approach 1:
The beam structure is designed to perform multiple vibration attenuation functions simultaneously by supporting both bending mode and torsional mode vibrations. The same beam structure attenuates vibrations at two different frequency ranges (primary blade pass frequency and secondary harmonic frequencies) through its dual-mode capability, eliminating the need for separate single-frequency absorbers for each frequency range.
Solution Approach 2:
The patent combines two separate vibration attenuation functions (bending mode for primary frequency and torsional mode for secondary frequency) into a single integrated beam structure. The beam simultaneously provides both bending stiffness and torsional stiffness, merging what would traditionally require two separate devices into one unified apparatus.
2Reliability
If masses are added to the beam to tune vibration frequencies, then the attenuation effectiveness at target frequencies improves, but the weight of the apparatus increases
Solution Approach 1:
Masses are strategically positioned at specific locations along the beam (e.g., at the ends or at specific distances from the support) to optimize their effect on both bending and torsional modes. The uneven mass distribution along the transverse axis of the beam creates the necessary torsional moment while minimizing the total mass required, achieving effective frequency tuning with reduced weight.
Solution Approach 2:
The beam is designed with asymmetric mass distribution where masses are placed unevenly along the transverse axis rather than symmetrically. This asymmetric configuration generates the torsional moment arm needed for torsional mode vibration while using less total mass compared to symmetric configurations, thereby reducing overall apparatus weight while maintaining attenuation effectiveness.
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 apparatus effectively reduces vibrations at both the blade pass frequency and its harmonic frequencies, providing a broad frequency range attenuation, thus mitigating noise and vibration in propeller-driven aircraft during various flight phases and regimes.
Implementation Method 1
The first mass and the second mass are adapted to provide a bending mode of the beam for attenuating the primary frequency vibration of the structure
Implementation Method 2
The uneven mass distributions of the first mass and the second mass are adapted to excite a torsional mode of the beam, based on the bending mode. The torsional mode is adapted for attenuating the secondary frequency vibration of the structure
Implementation Method 3
a dual-frequency vibration-reduction apparatus includes a beam having a longitudinal axis and a transverse axis perpendicular to the longitudinal axis... such that the dual-frequency vibration-reduction apparatus vibrates bi-modally at a first frequency and a second frequency for reducing vibrations of the structure
Data Source
AI summary
A dual-frequency vibration-reduction apparatus includes a beam having a longitudinal axis and a transverse axis perpendicular to the longitudinal axis. An attachment mechanism mechanically couples a portion of the beam to a structure. One or more masses are attached to the beam such that the apparatus vibrates bi-modally at a primary frequency and a secondary frequency for reducing vibrations of the structure at the primary frequency and the secondary frequency. A first mode may be a bending mode of the apparatus, while a second mode is a torsion mode. The vibration reduction apparatus may be tuned such that the primary frequency substantially matches a blade-pass frequency of a propeller-driven aircraft and the secondary frequency substantially matches a harmonic of the blade-pass frequency. The vibration reduction apparatus includes a mounting mechanism for mounting to any structure requiring low-frequency vibration attenuation.