Some new methods of damping impact-induced vibrations in badminton racquets

Some new methods of damping impact-induced vibrations in badminton racquet

Damping of flexural vibrations in rectangular plates using the acoustic black hole effect

The reduction of flexural vibration in plate structures has been investigated using the recently reported acoustic black hole effect for flexural wave reflection in plates with the local thickness varying according to h(x) = epsilon x(m) and m >= 2. Since sharp edges of such plates (wedges) are always truncated before x=0, the real reflection coefficients are relatively high, therefore the application of a small amount of damping is required to achieve large reductions in vibration amplitude. This paper presents a numerical model of a plate incorporating an acoustic black hole wedge, with predictions for vibration amplitudes. These are compared to equivalent experimental measurements for a range of applied damping layers. It is concluded that the above-mentioned power-law wedges can be used as effective vibration dampers in plate structures over a wide frequency range of interest. (C) 2010 Elsevier Ltd. All rights reserved

Experimental study on damping of flexural waves in rectangular plates by means of one-dimensional acoustic 'Black Holes'

In this paper we present some recent experimental results on new lightweight and broad-band damping treatment for rectangular plates based on the so-called acoustic ‘black hole’ effect [1-5], which represents one of the most efficient ways of creating graded impedance interfaces [6] to reduce edge reflections of flexural waves. These acoustic black holes, or vibration 'traps', use elastic wedges of variable thickness defined by a power-law relationship h(x) = ε·xm (with m ≥ 2) to reduce edge reflections. In the ideal case of no edge truncations, bending wave velocities decrease to zero in such a way that the waves never reach the end and hence do not reflect back. They thus represent one-dimensional acoustic ‘black holes’ for flexural waves. It was predicted [2,3] that very low values of reflection coefficient can be achieved even in the presence of truncations and imperfections when a narrow layer of absorbing material is attached to its surface in order to dissipate the remaining energy (note that direct application of thin layers of absorbing materials to the surfaces of rectangular plates has a negligible influence on damping, which has also been demonstrated during the tests). (Continues...

Damping of flexural vibrations in tapered rods of power-law profile: experimental studies

Damping of flexural vibrations in tapered rods of power-law profile: experimental studie

A polypropylene mesh modified with poly-ε-caprolactone nanofibers in hernia repair: large animal experiment

Barbora East,1,2 Martin Plencner,3,4 Martin Kralovic,1,3,5 Michala Rampichova,3 Vera Sovkova,1,3,5 Karolina Vocetkova,1,3,5 Martin Otahal,6,7 Zbynek Tonar,8,9 Yaroslav Kolinko,8,9 Evzen Amler,1,3,5 Jiri Hoch1,10 1Second Medical Faculty, Charles University in Prague, Prague, Czech Republic; 2Third Department of Surgery, Motol Faculty Hospital, First Medical Faculty, Charles University in Prague, Prague, Czech Republic; 3Institute of Experimental Medicine, The Czech Academy of Sciences, Prague, Czech Republic; 4The Czech Academy of Sciences, Institute of Physiology, Prague, Czech Republic; 5University Centre of Energy Efficient Buildings, Czech Technical University in Prague, Bustehrad, Czech Republic; 6Department of Anatomy and Biomechanics, Faculty of Physical Education, Charles University in Prague, Prague, Czech Republic; 7Department of Natural Sciences, Faculty of Biomedical Engineering, Czech Technical University in Prague, Kladno, Czech Republic; 8Department of Histology and Embryology, 9Biomedical Centre, Faculty of Medicine in Pilsen, Charles University in Prague, Pilsen, Czech Republic; 10Surgery Department, Motol Faculty Hospital, Second Medical Faculty, Charles University in Prague, Prague, Czech Republic Purpose: Incisional hernia repair is an unsuccessful field of surgery, with long-term recurrence rates reaching up to 50% regardless of technique or mesh material used. Various implants and their positioning within the abdominal wall pose numerous long-term complications that are difficult to treat due to their permanent nature and the chronic foreign body reaction they trigger. Materials mimicking the 3D structure of the extracellular matrix promote cell adhesion, proliferation, migration, and differentiation. Some electrospun nanofibrous scaffolds provide a topography of a natural extracellular matrix and are cost effective to manufacture.Materials and methods: A composite scaffold that was assembled out of a standard polypropylene hernia mesh and poly-ε-caprolactone (PCL) nanofibers was tested in a large animal model (minipig), and the final scar tissue was subjected to histological and biomechanical testing to verify our in vitro results published previously.Results: We have demonstrated that a layer of PCL nanofibers leads to tissue overgrowth and the formation of a thick fibrous plate around the implant. Collagen maturation is accelerated, and the final scar is more flexible and elastic than under a standard polypropylene mesh with less pronounced shrinkage observed. However, the samples with the composite scaffold were less resistant to distracting forces than when a standard mesh was used. We believe that the adverse effects could be caused due to the material assembly, as they do not comply with our previous results.Conclusion: We believe that PCL nanofibers on their own can cause enough fibroplasia to be used as a separate material without the polypropylene base, thus avoiding potential adverse effects caused by any added substances. Keywords: nanofibers, hernia, mesh, PCL, minipig, biomechanical, large anima

Acoustic Black Holes for Flexural Waves: A Smart Approach to Vibration Damping

Presented at the X International Conference on Structural Dynamics, EURODYN 2017. This is an Open Access Article. It is published by Elsevier under the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 Unported Licence (CC BY-NC-ND). Full details of this licence are available at: http://creativecommons.org/licenses/by-nc-nd/4.0/The present paper provides a brief review of the theoretical and experimental investigations of 'acoustic black holes' for flexural waves in plate-like structures. Such acoustic black holes are relatively new physical objects that can absorb almost 100% of the incident wave energy. This makes them attractive for vibration damping in plate-like structures. The main principle of the acoustic black holes is based on a linear or higher order decrease in velocity of the incident flexural wave with propagation distance to almost zero. The decrease in velocity should be accompanied by efficient energy absorption in the area of very low velocity via insertion of small pieces of absorbing materials. This principle can be applied to achieve efficient damping of flexural waves and vibrations in plate-like structures using both one-dimensional acoustic black holes (power-law-profiled wedges) and two-dimensional acoustic black holes (power-law-profiled cylindrical indentations). The key advantage of using acoustic black holes for damping structural vibrations is that it requires very small amounts of added damping materials, in comparison with traditional methods, which is especially important for vibration damping in light-weight structures

Poly-ϵ-caprolactone and polyvinyl alcohol electrospun wound dressings: Adhesion properties and wound management of skin defects in rabbits

Aim: This study evaluates the effect of electrospun dressings in critical sized full-thickness skin defects in rabbits. Materials & methods: Electrospun poly-ϵ-caprolactone (PCL) and polyvinyl alcohol (PVA) nanofibers were tested in vitro and in vivo. Results: The PCL scaffold supported the proliferation of mesenchymal stem cells, fibroblasts and keratinocytes. The PVA scaffold showed significant swelling, high elongation capacity, limited protein adsorption and stimulation of cells. Nanofibrous dressings improved wound healing compared with the control group in vivo. A change of the PCL dressing every 7 days resulted in a decreased epithelial thickness and type I collagen level in the adhesive group, indicating peeling off of the newly formed tissue. In the PVA dressings, the exchange did not affect healing. Conclusion: The results demonstrate the importance of proper dressing exchange