Effects of Volume and Neck Length of Helmholtz Resonator on Thermo-acoustic Instability

The acoustic performance of a typical Helmholtz resonator is important for optimizing sound absorption coefficient. The acoustic impedance of the Helmholtz resonator varies with different geometric features. As such, various studies have been conducted to investigate some parametric effects like neck length, extended neck, orifice size, cavity size and glazing flow speed. In this study, we explore, numerically, the effect of cavity shape and geometric aspect ratios among other features. We determined the optimum geometric shapes, dimension and flow condition for better sound absorption of the Helmholtz resonator.

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Hip geometry in hip fracture patients in Greenland occurring over a 7.7-year period

Journal of Orthopaedic Surgery and Research ◽

10.1186/s13018-021-02482-7 ◽

2021 ◽

Vol 16 (1) ◽

Author(s):

Inuuteq Fleischer ◽

Mogens Laursen ◽

Stig Andersen

Keyword(s):

Hip Fracture ◽

Femoral Neck ◽

Fracture Risk ◽

Cortical Thickness ◽

Geometric Analysis ◽

Osteoporotic Fractures ◽

Premature Death ◽

Neck Length ◽

Hip Geometry ◽

Lesser Trochanter

Abstract Background Hip geometry influences hip fracture risk. Hip fractures are common, and they are associated with pain, disability, premature death and marked costs on society. Osteoporotic fractures are frequent in Arctic populations and increase with advancing age in this society with a steep rise in life expectancy. Greenland Inuit is a distinct ethnic group, and data on hip geometry is missing. We thus aimed to describe hip geometry in 7.7 years of consecutive hip fracture patients in Greenland. Methods We evaluated collodiaphysial angle, femoral neck length, the outer and inner diameter of the femur at 2 and 5 centimetres below the centre of the lesser trochanter and the cortical thickness from pelvic and hip radiographs in all patients operated in Greenland over 7.7 years. We included all 84 patients with one non-fractured hip visible for geometric analysis. Analyses were conducted in duplicate. Results We found a collodiaphysial angle of 134.8/132.6o in men/women (p = 0.06) and a femoral neck length of 38.0/33.9 mm in men/women (p = 0.001). Cortical thickness was affected by sex in the adjusted analysis (p < 0.001). Cortical thickness index at 5 cm below the centre of the lesser trochanter decreased with age (p = 0.026) and may be influenced by height (2 cm below the centre of the lesser trochanter, p = 0.053). Conclusion Our findings differed from European data and suggest a delicate balance in hip geometry in Arctic populations. Ethnic peculiarities influence the structure of the hip and may influence fracture risk. A focus on hip geometry and risk factors for osteoporotic fractures in Arctic populations is warranted.

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Broadband acoustic focusing via binary rectangular cavity/Helmholtz resonator metasurface

Journal of Applied Physics ◽

10.1063/5.0049407 ◽

2021 ◽

Vol 129 (15) ◽

pp. 155307

Author(s):

Shuai Tang ◽

Bin Ren ◽

Yuxin Feng ◽

Jie Song ◽

Yongyuan Jiang

Keyword(s):

Helmholtz Resonator ◽

Rectangular Cavity ◽

Acoustic Focusing

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Computing the Sound of the Sea in a Seashell

Foundations of Computational Mathematics ◽

10.1007/s10208-021-09509-9 ◽

2021 ◽

Author(s):

Jonathan Ben-Artzi ◽

Marco Marletta ◽

Frank Rösler

Keyword(s):

Characteristic Function ◽

Helmholtz Resonator ◽

Positive Answer ◽

Approximation Procedure ◽

Universal Algorithm

AbstractThe question of whether there exists an approximation procedure to compute the resonances of any Helmholtz resonator, regardless of its particular shape, is addressed. A positive answer is given, and it is shown that all that one has to assume is that the resonator chamber is bounded and that its boundary is $${{\mathcal {C}}}^2$$ C 2 . The proof is constructive, providing a universal algorithm which only needs to access the values of the characteristic function of the chamber at any requested point.

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