Instytut Podstawowych Problemów Techniki

Streszczenie:

The development of acoustic materials with broad spectrum efficiency remains a critical challenge, particularly for achieving effective low-frequency absorption. This study presents a composite sound absorber that combines a dense, conventional felt matrix with additively manufactured 3D printed inclusions designed to enhance low-frequency attenuation. These inclusions, fabricated using cost-effective Fused Filament Fabrication (FFF) technology, feature labyrinthine geometries with high tortuosity, designed to achieve subwavelength resonances. The combination of these elements results in a thin, lightweight, and scalable solution for sound attenuation. The design procedure developed for such composites is based on complex but fully analytical modelling. The composite material exhibits exceptional performance, achieving high levels of absorption at the designed low frequency due to inclusions, while maintaining efficient broadband characteristics of the matrix. The analytical predictions are confirmed experimentally by impedance tube measurements. By leveraging the advantages of additive manufacturing and conventional materials, this work paves the way for economically viable, tailored acoustic solutions.

Słowa kluczowe:

Acoustic composites, Conventional porous matrix, 3D printed labyrinthine inclusions, Multiscale modelling, Sound absorption

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Streszczenie:

This study explores numerically and experimentally innovative control strategies for self-adaptive shock absorbers designed to operate under varying impact conditions. The control problem is addressed with a fundamental constraint – a limited prior knowledge of excitation parameters. To tackle this challenge, state-dependent control methods with progressively enhanced adaptive capabilities are proposed and evaluated numerically. A dedicated experimental setup featuring a pneumatic adaptive shock absorber is developed to ensure validation of the proposed methods and facilitate their comparison. The system incorporates a fast-operating piezoelectric valve with a strain gauge for proportional opening control and enables optimal real-time response to unknown dynamic excitations. The conducted laboratory drop test results confirm the feasibility of the proposed control methods.

Słowa kluczowe:

Adaptive Impact Absorption, Self-Adaptive System, Pneumatic Shock Absorber

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Streszczenie:

The work presents a comprehensive approach to the design and modelling of acoustic materials based on labyrinth structures filled with fibres. It has recently been shown that exceptionally favourable acoustic properties can be obtained in labyrinthine materials due to their extreme tortuosity. Such materials, typically produced by methods such as 3D printing, exhibit high sound absorption values at lower frequencies. The next step in the development of this type of acoustic treatment (explored here) involves introducing fibres into labyrinthine channels. Such acoustic composite designs can have a beneficial effect of shifting the absorption peak to even lower frequencies and also widening its efficiency range. Two samples of slotted labyrinth materials, designed using analytical acoustic modelling, were 3D printed, and their slits were filled with selected fibrous materials, such as biofibres, cotton wool, acrylic yarn, etc. They were tested in an impedance tube to confirm the predicted improvement, but also to show a dramatic change in sound absorption.

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Słowa kluczowe:

Air-drop Capsule, Impact Mitigation, Adaptable Airbag, Discharge Valve

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