http://ir.lib.ruh.ac.lk/handle/iruor/7376 2026-07-18T13:31:06Z 2026-07-18T13:31:06Z Madushika, J.W.A. Lanarolle, W.D.G. http://ir.lib.ruh.ac.lk/handle/iruor/21487 2026-07-14T16:43:33Z 2022-01-01T00:00:00Z

A Review on Novel Approaches to Enhance Sound Absorbing Performance Using Textile Fibers Madushika, J.W.A.; Lanarolle, W.D.G. Fibreglass, foam, mineral fibres and their composites are the conventional materials used in applica tions that require absorption of sound. However, due to the health risks associated with the traditional materials, textile fibrous structures are becoming a valid alternative in spite of their comparatively lower sound absorption properties. The existing textile structures and textile structures specifically modified physically or chemically to enhance sound absorption properties have been experimented for better performance in sound-related properties. The fibres have been chemically modified using plasma treatments and alkali treatments, while microfibres, nanofibres, hollow fibres, bicomponent fibres, crimp fibres and aerogel-treated fibres are produced to modify the physical structures of fibres. The basic principle employed in these fibre modifications to enhance sound absorption is the increase of energy dissipation by increasing the fibre surface area, fibre roughness and tortuosity of the mater ial. This article critically reviews the techniques of modifying the fibrous structures to enhance sound absorption properties and their effectiveness. The sound absorption coefficient of natural fibres can be enhanced up to 0.9 in mid and high frequencies by alkali treatments, while the sound absorption coefficients of microfibres, hollow fibres, bicomponent fibres and nanofibres significantly higher than regular fibres.

2022-01-01T00:00:00Z Madushika, J.W.A. Wijerathne, J.K. Lanarolle, W.D.G. http://ir.lib.ruh.ac.lk/handle/iruor/21486 2026-07-14T16:40:05Z 2021-01-01T00:00:00Z

Mathematical Modeling and Simulation of Acoustic Properties of Knitted Fabrics Backed by an Air Cavity Madushika, J.W.A.; Wijerathne, J.K.; Lanarolle, W.D.G. Noise pollution has become a critical issue in the modern world of ever-increasing industries and machinery. Noise should be controlled due to the physical and psychological health effects associated with noise. Textiles as lightweight and cost-effective porous structures have received increasing interest for acoustic controlling applications. In-room acoustics, knitted fabrics represent a strong source of innovation due to drapability and aesthetic appearance. However, in general, the sound absorption performance of knitted fabrics is relatively low. Therefore, the primary goal of this work is to enhance sound absorption by introducing an air gap between the fabric and a solid wall. The diffuse incident sound absorption coefficient of knitted fabrics was mathematically modeled and simulated using basic equations of fluid dynamics where the fabric is acoustically described by its porosity, thickness, density and airflow resistivity. The air gap varied from 10 to 25 mm in 5 mm increments. Modeling predictions were compared with the experimental data obtained from the literature for sound absorption of knitted fabrics. The modeling predictions were in good agreement with the experimental data for different values of air gap thicknesses. The simulation results indicated that when the air layer thickness increases, the sound absorption coefficient of knitted fabrics increases significantly at low frequencies. The peak value of the sound absorption coefficient moves in the direction of a lower frequency. The sound absorption coefficient reached a maximum value of 0.45 at a resonance frequency equivalent to the quarter wavelength of the air layer thickness.

2021-01-01T00:00:00Z Madushika, J.W.A. Wijerathne, J.K. Lanarolle, W.D.G. http://ir.lib.ruh.ac.lk/handle/iruor/21485 2026-07-14T16:36:34Z 2023-01-01T00:00:00Z

Development of a small-scale reverberation chamber and validation of the diffuse field Madushika, J.W.A.; Wijerathne, J.K.; Lanarolle, W.D.G. Noise absorbers are in a growing demand in the automotive, aerospace and building construction industries. Testing acoustic properties of materials is mandatory for developing an efficient acoustic controlling product design. Two main methods available to measure acoustic properties of materials are impedance tube method and reverberation room method. Impedance tube method uses small test specimens (usually less than 10 cm in diameter) and measures only normal incidence sound absorption, whereas reverberation room method is a relatively expensive setup which usually requires a large space (100-200 m3 ) and allows large samples (10-12 m2 ). To overcome the drawbacks of the current test methods and to make a comparative analysis of the test samples, a small scale reverberation room was designed. A chamber with 2.06 m3 volume was constructed. All the inner surfaces including the door were lined with highly reflective ceramic tiles to obtain maximum reflectivity. The randomness of the incident angles was achieved by an asymmetric shaped room with an inclined roof to obtain all walls non parallel. A modal analysis was performed to validate the small scale reverberation chamber for acoustic measurements. The pressure variations inside the enclosure within resonance frequencies are too small. Even though the cut-off frequency of a purely rectangular chamber with the same volume is 270 Hz, the new design of the reverberation room allows taking measurements below 270 Hz.

2023-01-01T00:00:00Z Weerarathne, K.K.D.C.S. http://ir.lib.ruh.ac.lk/handle/iruor/21484 2026-07-14T16:33:20Z 2020-01-01T00:00:00Z

Prosthetic Heart Valves – "The Beat Goes On" Weerarathne, K.K.D.C.S.

2020-01-01T00:00:00Z