مجله انجمن مهندسی صوتیات ایران
سال سوم شماره 2 (پاییز و زمستان 1394)

The need to understand how to implement the structural quieting into the design processes has led the engineers to pay more attention to noise generation and transmission from the vibrating structures. In this study, utilizing the finite element software ABAQUS, the acoustical and vibrational response of stiffened steel plate opening wall in a RC room subject to blast has been investigated. Moreover, frequency analysis has been performed on each of the stiffener arrangements, in order to obtain the transmission loss of the generated noise in frequency domain under the effect of a diffused field of a white noise. The three stiffener arrangements of diagonal, cross, and parallel have been used in the analysis. The results indicate that the stiffener arrangements has marginal effect on the vibrational response of the system, whereas its influence on the acoustical response of the system is substantially high. For instance, the cross and diagonal stiffeners showed, in a descending order, the best performance in the noise transmission loss of the system.
Investigating the Acoustical and Vibrational Response of Stiffened Steel Plate Opening Wall in a RC Room Subject to Blast
Saeed Reza Massah , Hamid Zohrevand, Abbas Ghadami
Abstract: (441 Views)
The need to understand how to implement the structural quieting into the design processes has led the engineers to pay more attention to noise generation and transmission from the vibrating structures. In this study, utilizing the finite element software ABAQUS, the acoustical and vibrational response of stiffened steel plate opening wall in a RC room subject to blast has been investigated. Moreover, frequency analysis has been performed on each of the stiffener arrangements, in order to obtain the transmission loss of the generated noise in frequency domain under the effect of a diffused field of a white noise. The three stiffener arrangements of diagonal, cross, and parallel have been used in the analysis. The results indicate that the stiffener arrangements has marginal effect on the vibrational response of the system, whereas its influence on the acoustical response of the system is substantially high. For instance, the cross and diagonal stiffeners showed, in a descending order, the best performance in the noise transmission loss of the system.
Investigating the Acoustical and Vibrational Response of Stiffened Steel Plate Opening Wall in a RC Room Subject to Blast
Saeed Reza Massah , Hamid Zohrevand, Abbas Ghadami
Abstract: (441 Views)
The need to understand how to implement the structural quieting into the design processes has led the engineers to pay more attention to noise generation and transmission from the vibrating structures. In this study, utilizing the finite element software ABAQUS, the acoustical and vibrational response of stiffened steel plate opening wall in a RC room subject to blast has been investigated. Moreover, frequency analysis has been performed on each of the stiffener arrangements, in order to obtain the transmission loss of the generated noise in frequency domain under the effect of a diffused field of a white noise. The three stiffener arrangements of diagonal, cross, and parallel have been used in the analysis. The results indicate that the stiffener arrangements has marginal effect on the vibrational response of the system, whereas its influence on the acoustical response of the system is substantially high. For instance, the cross and diagonal stiffeners showed, in a descending order, the best performance in the noise transmission loss of the system.

In this study, we used 5 types of combination of MAGIC-f polymer gel and tissue mimicking phantom to extract the optimal structure of gel dosimetry to increase sensitivity and reduce gel manufacturing costs. 5 types of new structure gels were irradiated by a dose of 36 Gy using a gamma ray (cobalt-60) source. Irradiated gels again, were refrigerated at 5 ºC for about 24 hours before reading. The parameters: ultrasonic speed of sound, attenuation coefficient and quality index of 5 types of new structure gels were measured at 24 hours after exposure and at 25 ºC with Sonost 2000 ultrasound system, variation of sensitivity of dose-response curve for ultrasound parameters of 5 new structure polymer gels were evaluated.
The measurement results showed the D type of the new gel structures had the greatest change (34.6 m/s) in the speed of sound parameter. The change in A, B, C and E structures was measured to be 0, 20, 1 and 31.5 m/s respectively. Also, the obtained attenuation coefficient parameters for A, B, C, D and E structures were 0.2, 0.4, 0.2, 0.7 and 0.5 db/MHz respectively. Quality index parameter extracted for A, B, C, D and E structures, 0.4, 4.7, 0, 10 and 7.6 respectively.
The D type structure had the greatest sensitivity among the 5 types of the new structure of the gels in this study. Also increasing the amount of gelatin in gel structure, increases the sensitivity. The ultrasound parameters had no significant changes for structures not containing ascorbic acid, copper sulfate and metacrylic acid.

Postural stress is one of the major complaints of women machinery works at gas supply parts manufacturers which have noise levels equal or above 85 dB in some of their workstations. Postural stress is caused by workplace ergonomic risk factors: High work – speed, repetitive work, poor body posture, excessive force and inadequate break time. Knowledge of the effect of the noise on the strain index is the subject of this investigation. The sample size was decided to be 50 persons, two groups were selected as targets. One group exposed to high level of noise, and the other group subjected to low noise level. The administrative employees were treated as control group. Nordic questionnaire was used to collect informations. Posture was assessed by observing each task and SI checklist was filled out of effort variable was measured by person’s heat rate during her work and sport tester machine was used to this aim. Borg scale and then SI were calculated. Noise was measured by sound level meter and noise dosimeter in accordance with noise type. Data Analyzing was performed by man-whitney, Kruskal –Wallis, one – way ANOVA and spearman correlation in SPSS (ver.16) software. The results showed statistically significant relation between work experience and neck pain, shoulders pain and wrist/ hand pain. They also revealed that there is difference between strain indices two groups but it is not statistically significant. Strain index can be increased by noise levels above 85 dB but this is not of statistical consequence.

Low frequency underwater sound propagation is one of the most important topics of research in recent years. This can be attributed to the noise generated by underwater and surface vessels. To better understand the behavior of the underwater sound, different factors affecting sound must be investigated. In the current study, numerical analysis of the effects of regular geometry and three materials of seabed on sound propagation is conducted. To this end, parabolic equation governing the sound wave propagation is solved using implicit finite difference scheme. The obtained results indicate that transmission loss (TL) of the granite bottom with triangular and semicircular geometries is reduced by an increase in distance. However, TL gradually increases in the case of rectangular geometry. Values of transmission loss of the sandstone bottom are increased by an increase in the range for the mentioned geometries. However, average value of TL for the semicircular geometry is about 4 decibels less than the other two geometries. On the other hand, rigid, sandstone, and granite seabed have no significant influence on the graph of TL for the rectangular geometry at 30m depth.

In this research, the effect of ultrasound (US) on the activity and the kinetic parameters of enzymatic hydrolysis of starch by alpha-amylase were investigated. To this aim, alpha-amylase was exposed to ultrasonic irradiation for different time intervals and a constant frequency of 20 kHz, then its enzymatic activity was measured. According to the results, the maximum activity of amylase was recorded in the absence of US and increasing the irradiation time reduced the enzymatic activity. The relative activity of amylase under irradiation time intervals of 0, 10, 20 and 30 min were 100, 92.13, 34.62 and 7.47 percent, respectively. The optimum pH and temperature for amylase activity in both, the absence and presence of US were similar (T=50º C and pH=6). There was no considerable change in Km, while the results showed a decrease in the value of Vmax. In comparison with the corresponding value in the absence of US, the enzymatic hydrolysis increased when the enzyme and starch solutions were exposed to the US for 10 minutes. However, this value decreased when the solutions were exposed to US for 20 and 30 minutes. Furthermore, the effect of ultrasound on the structure of amylase were studied using viscometeric and florescence spectroscopy. These results indicated that, US have equivocal effect on enzyme activity. One effect was a destructive one on the structure of amylase and the other effect was increasing the collision frequency of substrate - enzyme, and consequently, an increase in hydrolysis.

The aim of this study was assessment of Distortion Product Otoacoustic Emissions (DPOAEs), in noise exposed guinea pigs. Ten guinea pigs in two control groups (without noise exposure) and a case group (that was exposed to a white noise with 95 dB SPL, 6h/d, 5d/wk for 2 consecutive weeks) were assessed in a Plexiglas cage. In order to stabilize permanent thresholds, DPOAEs before and two weeks after the last exposure were recorded by a DPOAEs analyzer. There is no significant difference in the control groups DPOAEs amplitude in the assessment frequencies, while in the noise exposed group a significant difference (with range 1.12- 6.24) was found between all the assessment frequencies, as the greatest and lowest decline was seen at 3937 and 562 frequencies (with 6.24 and 1.12 dB respectively). DPOAEs amplitude decline following noise exposure can indicate the noise adverse effects on outer hair cells function. Therefore hearing protection in noisy environments is necessary.

The use of ultrasound waves in the processes of marination is a new method to reduce time duration of marinating and improve the characteristics of meat. In this research¡ 2.5 ×2.5 ×2.5 cm cubic meat samples were treated by 20 kHz ultrasound waves for 30 minutes with intensities 5¡ 8¡ and 12 W/cm2. Then the meat samples were marinated by molar lactic acid for 8 and 12 hours. Acid absorption and pH parameter were measured and then cooking process in hot water bath took place at . Afterward¡ cooking loss¡ pH¡ color change and tenderness were analyzed. The results showed no significant differences in pH values between the ultrasound-treated meat and the control samples. The ultrasound treatment has significant effect on acid absorption. At intensity of 5 W/cm2, tenderness increases and color changes significantly with less cooking loss from others. By increasing marinating time duration¡ color¡ cooking loss¡ and tenderness features improve and it has no significant effects on the sensory evaluation.

This paper studies the performance of electro-acoustical modeling technique for mechanical noise reducers in low-frequency applications. To this end, firstly we introduce the electrical equivalents of fundamental acoustic elements and then, propose an equivalent circuit for the entire noise reduction system, which enables us to derive its overall frequency response. In order to validate the proposed modeling method, we implement the complete acoustical sensing system in real environment and compare its performance with simulated mathematical model. Empirical results confirm the proposed modeling technique for acoustical noise-reduction spectrum sensing applications.