Analysis of Static Flow Resistivity of a Modified Impedance Tube

The static flow resistivity is a fundamental parameter for measuring and classifying the sound absorption behavior of various types of materials. Several methods have been developed for measuring the static flow resistivity acoustically. Most of these methods cannot be implemented directly in the standard tubes which are widely used for measurements of sound absorption coefficients and impedance as defined in ISO 10534.2. The accuracy of the proposed method and the tube is verified through finite element analysis and the feasibility to determine the static flow resistivity is validated through experiments. It is validated that the accuracy of the proposed method is highly dependent on the position of the acoustic center of the measurement microphones and the accuracy can be enhanced by increasing the back cavity depth and/or decreasing the measurement frequency.

T-Y TUBE MODEL OF HUMAN ASCENDINGAORTIC INPUT IMPEDANCE

This paper proposed a T- Y tube model to simulate foe input impedance of arterial system. It improves and extends the asymmetric T-tube model which was firstproposed by O' Rourke[1] and developed laier by Liu et al.[2]. Based on foe asymmetricT-tube model. a T-Y tube model was proposed by adding branching tubes whichrepresem the iliac arteries.All the tubes are considered to be uniform,viscoelasticlongitudinally tethered cylindrical tubes.The upper tube terminates with a windkesselmodel, while the terminal arterioles of the lowr tube are expressed as a resistance.After proper eraluation of the parameters.the impedance of the arterial system iscalculated under normal physiological and hypertensive condition.The model canpredict impedance in good agreement with the experimentally obtained data no matterin normal physiological condition or in pathological condition In comparison with theasymmeric T-tube model,T- Y tube model is closer to anatomy structure of the human arlerial system and at the sametime much simpler than the extremely complex multiplebranching tube model Therefore it will be a valuable model in studying the influencesof various parameters on aorta impedance and ventricular-vascular coupling.

Acoustic Properties of Micro-Perforated Panels Made from Oil Palm Empty Fruit Bunch Fiber Reinforced Polylactic Acid

This paper presents the development and performance of micro-perforated panels(MPP)from natural fiber reinforced composites.The MPP is made of Polylactic Acid(PLA)reinforced with Oil Palm Empty Fruit Bunch Fiber(OPEFBF).The investigation was made by varying the fiber density,air gap,and perforation ratio to observe the effect on the Sound Absorption Coefficient(SAC)through the experiment in an impedance tube.It is found that the peak level of SAC is not affected,but the peak frequency shifts to lower frequency when the fiber density is increased.This phenomenon might be due to the presence of porosity in the inner wall of the holes.Increasing or decreasing the air gap and perforation ratio shifts the peaks of acoustic absorption either way.

Light Electrospun Polyvinylpyrrolidone Blanket for Low Frequencies Sound Absorption

Light polymeric soundproofing materials （density = 63 kg/m3） of interest for the transportation industry were fabricated through electrospinning. Blankets of electrospun polyvinylpyrrolidone （average fiber diameter = （1.6 ± 0.5） or （2.8 ± 0.5） μm） were obtained by stacking disks of electrospun mats. The sound absorption coefficients were measured using the impedance tube instrument based on ASTM E1050 and ISO 10534-2. For a given set of disks （from a minimum of 6） the sound absorption coefficient changed with the frequency （in the range 200-1600 Hz） following a bell shape curve with a maximum （where the coefficient is greater than 0.9） that shifts to lower frequencies at higher piled disks number and greater fiber diameter. This work showed that electrospinning produced sound absorbers with reduced thickness （2-3 cm） and excellent sound-absorption properties in the low and medium frequency range.

Analysis on the influence factors of the acoustic absorption performance of porous fiber materials

Porous fiber materials are the most widely used acoustic absorption materials at present,and they have excellent acoustic absorption performance.This paper uses the finite element method to explore the factors affecting the acoustic absorption performance of porous fiber materials,including flow resistance,thickness of the porous fiber material,incidence angle,and back cavity thickness.Due to the complex acoustic absorption mechanism of porous fiber materials,an equivalent fluid model is used to simulate the acoustic absorption properties of the porous fiber materials.The correlation of acoustic absorption performance and the model of the back cavity was analyzed.An impedance tube test was implemented to verify the simulation results.