Effect and importance of static-load on airflow resistivity determination and its consequences on dynamic stiffness

Airflow resistivity is a physical parameter which characterizes porous and fibrous sound absorbent materials. It is well-known that such property allows the evaluation of the acoustic behaviour of sound absorbent materials in various fields of application, including automotive noise mitigation, architectural acoustics and building acoustics. In structure-borne sound insulation, airflow resistivity is essential for the evaluation of the dynamic stiffness of porous and fibrous resilient insulating materials used as underlay in floating floors.However, an inconsistency between the dynamic stiffness and the airflow resistivity test conditions can be recognized. In order to evaluate dynamic stiffness of a resilient material, a static load of about 2 kPa is applied, while in airflow resistivity determination this condition is not explicitly required. As a result, the density of analyzed material, in dynamic stiffness and airflow measurements, is different. Since these two quantities are correlated, it is necessary to measure materials under the same conditions of applied static load.In this work the effects of static load (or density after compression) in airflow resistivity determination of various porous and fibrous resilient materials are investigated, and the consequent influence on dynamic stiffness is discussed. A simply empirical relation between density and airflow resistivity is also put forth.The main focus of this paper is to propose an harmonization among requirements of the Standards in order to prevent significant errors in dynamic stiffness determination and incorrect evaluations of the acoustic behaviour.     

The effect of head position on glottic closure in patients with unilateral vocal fold paralysis

The present study was designed to assess the effect of head position on glottic closure as reflected in airflow rates (open quotient and maximum flow declination rate), in patients with unilateral vocal fold paralysis. Ten patients, 2 males and 8 females ranging in age from 40 to 75, with a mean age of 57.3, served as subjects. Airflow measures were taken during sustained phonation of two vowels (/i/ and /a/) in 3 head positions (center, right, left). Vowels /i/ and /a/ were produced at subject's comfortable pitch and loudness, with random ordering of both vowel order and head orientation. Subjects were trained to focus eye gaze on right and left markers (70-degree angle) and a central marker at eye level directly in front of the subject. Theoretically, if turning the head during phonation alters the laryngeal anatomic relationship by bringing the vocal folds in closer proximity to one another, then airflow rate should lessen. Our results indicate that head position does not improve glottic closure in these patients, which is in contrast to previously published research.(1) Our results question the utility and underlying theoretical construct for the use of head turning as a therapeutic technique for improvement of voice in patients with unilateral vocal fold paralysis.     

Functional assessment of patients with spasmodic dysphonia

Assessment of function in patients with spasmodic dysphonia is necessary to confirm diagnosis, plan therapy, predict response, and assess effectiveness of treatment. This task is difficult because symptom severity fluctuates, the test environment is artificial, and the objective parameters used to measure vocal function may not adequately reflect the handicap experienced by the patient. Available methods for assessing these patients are reviewed and the utility of each considered, particularly in managing patients with botulinum toxin therapy. Assessment should include a battery of tests, including subjective perceptual ratings and direct physical measurements.     

Crosslinking of an unsaturated polyester resin in the mould: Modelling and heat transfer studies

The crosslinking of unsaturated polyester was studied by using an experiment and a mathematical model of the process. Temperature–time profiles were recorded in the centre of the sample inside the mould at the outer wall of the cylindrical copper mould, and in the bulk of the heated air bath. A numerical model was constructed by taking into account the heat transferred by convection from the air to the mould surface and the heat transferred by conduction through the resin, as well as the heat generated by the crosslinking reaction. The convection heat transfer coefficient was determined in independent experiments with the empty copper mould. Introduction of the carbon base filler reduced the amount of heat generated in the composite due to the less reactive component in the composite. As a result, it lowered the temperature of the resin. By recording the temperature-time and the degree of crosslinking time profiles developed within the sample extensive knowledge of the process can be obtained. The effects of the convection heat transfer on the rate of mould heating, and the conduction heat transfer through the mould as well as the internal heat generated by the crosslinking reaction are visibly shown, despite a complexity of the process.     

Numerical analysis of respiratory flow patterns within human upper airway

A computational fluid dynamics （CFD） approach is used to study the respiratory airflow dynamics within a human upper airway. The airway model which consists of the airway from nasal cavity, pharynx, larynx and trachea to triple bifurcation is built based on the CT images of a healthy volunteer and the Weibel model. The flow character- istics of the whole upper airway are quantitatively described at any time level of respiratory cycle. Simulation results of respiratory flow show good agreement with the clinical mea- sures, experimental and computational results in the litera- ture. The air mainly passes through the floor of the nasal cavity in the common, middle and inferior nasal meatus. The higher airway resistance and wall shear stresses are distrib- uted on the posterior nasal valve. Although the airways of pharynx, larynx and bronchi experience low shear stresses, it is notable that relatively high shear stresses are distrib- uted on the wall of epiglottis and bronchial bifurcations. Besides, two-dimensional fluid-structure interaction models of normal and abnormal airways are built to discuss the flow-induced deformation in various anatomy models. The result shows that the wall deformation in normal airway is relatively small.     

Laboratory measurement of the acoustical and airflow performance of interior natural-ventilation openings and silencers

This paper discusses laboratory measurements of the acoustical and airflow performance of interior natural-ventilation openings and silencers (‘ventilators’). The objective was to create and characterize a purpose-built test facility, and use it to measure the combined acoustical and airflow performance of a number of ventilators of interest, to understand and optimize it, and provide design guidelines to practitioners. The paper discusses the characterization of ventilator performance, and methods and theory for measuring it. The design and performance of a purpose-built, two-room laboratory facility are described. The facility was used to investigate the performance of a non-acoustical grille, an acoustical louver, slot ventilators, crosstalk silencers and a novel door-vent silencer. The results identify a number of best practices for successful ventilator design: non-acoustical grilles should be avoided; the addition of a glass-fiber absorptive liner to the surface adjacent to a slot ventilator increases acoustical performance by STC 3–6; acoustically-lined crosstalk silencers can be very effective – the straight configuration is best and performance increases with the length of the flow path; acoustical liners should be at least 50-mm thick. A prototype door-vent silencer showed very promising performance, but needs to be optimized.     

冷藏运输车内气体流场的数值模拟及分析

利用计算流体力学(ANSYS)软件,建立了冷藏运输模拟试验台的物理模型,对冷藏运输车内流场进行了数值模拟研究。主要研究内容包括:(1)不同送风速度对冷藏运输车内流场分布的影响;(2)不同时间内库内流场变化情况。冷藏运输模拟试验台采用前端送风,两侧回风口的送风方式。风机吹出的冷气能够在库体内形成大的回流,从而降低库体温度并且使库体内温度分布的均匀。不同送风速度影响车体内速度场的分布,而当送风速度较大时,库内的温度会在短期内均匀。但是过大的送风速度会风干冷藏车内的食品。     

Aerodynamic characteristics of laryngectomees breathing quietly and speaking with the electrolarynx

The primary purpose of this study was to investigate the aerodynamic characteristics of laryngectomees under two conditions: breathing quietly and speaking with electrolarynx. Twenty male adult subjects, 8 normal speakers, and 12 laryngectomees participated the experiment. Airflow, pressure, and speech data were obtained simultaneously. The acceptability of electrolarynx speech under different conditions was also evaluated by 20 listeners (14 men, 6 women). Results indicated a higher peak expiration airflow and pressure among the laryngectomees as compared with the normal during breathing. Three different breathing patterns appeared among the laryngectomees when speaking with the electrolarynx: holding breath, exhaling, and breathing. Four long-time electrolarynx users held breath during speaking. Seven of 12 laryngectomees kept exhaling, whereas only 1 could breathe during speech production. In addition, (1) the acceptability of electrolarynx speech was the highest when speaking breathlessly; (2) no significant difference was found in the acceptability between the patterns of exhaling and breathing smoothly; and (3) the acceptability decreased if breathing quickly during phonation with the electrolarynx. It also suggests that the laryngectomees who can breathe during speaking may be more appropriate to use the new electrolarynx controlling the pitch by expiration pressure.