Transmission loss and noise reduction of reactive mufflers are determined by linear acoustic theory and unsteady flow field study, respectively. The effects of extending the inlet tube of the muffler, adding holes to the extension, and the number of holes on both transmission loss and noise reduction are investigated. In noise reduction analysis, the Navier-Stokes equations and k-ε model are us...

diesel exhaust particles are a complex mixture of thousands of gases and fine substances that contain more than 40 different environmental contaminants. being exposed to these exhaust particles (called soot) can cause lung damage and respiratory problems. diesel particulate filters are used in many countries for mobile sources as a legal obligation to decrease harmful effect of these fine parti...

This paper reports the results of an experimental study on non-native production of English vowels. Two groups of Persian EFL learners varying in language proficiency were tested on their ability to produce the nine plain vowels of American English. Vowel production accuracy was assessed by means of acoustic measurements. Ladefoged and Maddison’s (1996) F1 F2 measurements for American English v...

Negative surges are caused by a sudden change in flow resulting from a decrease in water depth. New experiments were conducted in a horizontal channel (L = 12 m, W = 0.5 m) to record the unsteady water depth and turbulence in negative surges. The data were collected using video imagery, acoustic displacement meters and acoustic Doppler velocimetry (ADV). The experimental setup was designed to r...

This paper aims to explore some acoustic properties (i.e. duration and pitch amplitude of speech) associated with three different emotions: anger, sadness and joy against neutrality as a reference point, all being intentionally expressed by six Persian speakers. The primary purpose of this study is to find out if there is any correspondence between the given emotions and prosody patterning in P...

A theoretical study analyzing three-dimensional combustion acoustic instabilities in a liquid propellant rocket engine combustor has been conducted. A linear theory based on Crocco’s pressure sensitive time lag model is used. To apply this theory the combustor is divided into two main components, including the combustion chamber and the converging part of the nozzle. The assumption of concentra...

this paper aims to explore some acoustic properties (i.e. duration and pitch amplitude of speech) associated with three different emotions: anger, sadness and joy against neutrality as a reference point, all being intentionally expressed by six persian speakers. the primary purpose of this study is to find out if there is any correspondence between the given emotions and prosody patterning in p...

acoustic experimental data of irib (islamic republic of iran broadcasting) server room was taken to measure the acoustic noise characteristics of frequency and sound pressure level (spl). the purposes of this paper are measuring the noise pollution and its evaluation through the regulations. the measurements were taken in two stages. the first one was taken at 10 points by sound investigator 22...