An experimental study on the effects of compression on the acoustic performance of porous fibrous materials

The current investigation experimentally studied the effects of compression on the acoustic performance of porous fibrous material. Two inch and four inch thick samples of fiberglass and three varying densities of mineral wool were tested using two different impedance tube sizes at compression rates of 1, 1.3 and 2. The absorption coefficient was measured using Chung and Blaser’s method. The flow resistivity was measured using Tao et al.’s method. Overall, the 4” samples resulted in steadier results than the 2” samples. Compression generally led to a decrease in absorption coefficient and an increase in flow resistivity. These effects were most evident in the lower frequency range. Although there were some experimental errors in sample preparation, sample variation, compression technique, testing order and other initial errors, the current study demonstrated that the effects of compression on insulation should be not be overlooked.

An experimental study on the effects of compression on the acoustic performance of porous fibrous materials

The current investigation experimentally studied the effects of compression on the acoustic performance of porous fibrous material. Two inch and four inch thick samples of fiberglass and three varying densities of mineral wool were tested using two different impedance tube sizes at compression rates of 1, 1.3 and 2. The absorption coefficient was measured using Chung and Blaser’s method. The flow resistivity was measured using Tao et al.’s method. Overall, the 4” samples resulted in steadier results than the 2” samples. Compression generally led to a decrease in absorption coefficient and an increase in flow resistivity. These effects were most evident in the lower frequency range. Although there were some experimental errors in sample preparation, sample variation, compression technique, testing order and other initial errors, the current study demonstrated that the effects of compression on insulation should be not be overlooked.

MEASUREMENT OF THERMOPHYSICAL PROPERTIES OF FLEXIBLE THERMAL INSULATION

The paper presents the results of measuring thermal conductivity and heat capacity of a flexible thermal insulation. Flexible thermal insulation is a highly porous fibrous material, a construction that includes felt, covered on all sides with fabric. The whole structure is stitched with a thread. The fibrous core, fabric and sewing thread are composed of silica fibers. Thermal conductivity was measured by the stationary method on flat samples. The heat capacity was determined using a NT-1000 calorimeter. The calculation of heat transfer was carried out for the conditions characteristic of those in effect when the spacecraft entered the orbit.

On the acoustic transparency of perforated metal plates facing a porous fibrous material

Thin impervious layers, cloths or perforated plates are usually utilized with fibrous absorbing materials in order to avoid small particles, coming from deterioration over time or from flow abrasive effect, becoming dislodged and polluting the environment. These protective facings are to be carefully considered and analyzed, since they can affect the acoustical behavior of the “backing” material. This study addresses this issue through an experimental survey and a theoretical analysis using the Transfer Matrix Method (TMM). Experiments have been performed in the frequency range 160–2,500 Hz, analyzing the different behaviors due to multiple combinations of percentage of open area and air gap between perforated facing and absorbing material. Experimental data have shown a marked effect of the percentage of perforation, at least up to a threshold value of 20%, whereas the air gap slightly affected the acoustic behavior of the covered absorbing material. The TMM was applied to the tested faced absorbing system, and experimental and theoretical results were compared, showing the good accuracy of the model. Several geometrical configurations were then modeled through TMM and the possibility of using this method in order to assess the acoustic transparency of perforated metal plates was assessed.

Biomechanical Evaluation of Neuro-occlusal Rehabilitation for Occlusal Imbalance Correction in Children with Facial Asymmetry

Contemporary eating habits may cause malformations in children jaw, that are difficult to evaluate and treat clinically. In this work, a computational methodology for the diagnosis and the treatment of this pathology is proposed. It combines porous-fibrous material models, medical devices and computational models of patients with facial asymmetries from the perspective of neuro-occlusal rehabilitation.

Evaluation of changes in thermodiffusion properties of mineral wool resulting from treatment with water and re-drying

The work presents the formulation of inverse problem that allows to estimate the basic parameters describing coupled thermodiffusion of moisture in porous fibrous material and construction of the measuring stand in order to obtain the necessary data to carry out calculations for this purpose. This approach was used to evaluate the changes in the thermodiffusion properties of stone wool samples for the indoor applications that were treated with water and re-dried. In the mathematical model, one introduced a simplification that coupling in the thermodiffusion process is unilateral and includes only the influence of heat transport on moisture transport.

Acoustic Performance Analysis of Bionic Coupling Multi-Layer Structure

The interest of this paper lies in the proposition of using bionic method to develop a new sound absorption structure. Inspired by the coupling absorption structure of the skin and feather of a typical silent flying bird – owl, a bionic coupling multi-layer structure model is developed, which is composed of a micro-silt plate, porous fibrous material and a flexible micro-perforated membrane backed with airspace. The impedance transfer method is applied to calculate the absorption coefficients and analyze the influences of different parameters of each layer on absorption coefficients of this model. Based on numerical simulations, the effectiveness of this proposed model is tested. The average absorption coefficient reaches 0.85 within the frequency range from 200 Hz to 2000 Hz. The significant improvement of absorption coefficients can be mainly due to the Helmholtz effects of the micro-silt plate and flexible micro-perforated membrane, and the combination with porous materials can lead to even better absorption performance in broadband.