• Title/Summary/Keyword: Averaged Sound Pressure Level

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Floor Impact Sound Pressure Level Characteristics by the Change of Reverberation Time in Mock-up Test Rooms (수음실 잔향시간 변화에 따른 중량 충격음 레벨 특성 - 실험실 환경을 중심으로 -)

  • Jeong, Jeong Ho;Lee, Byung Kwon;Yeon, Jun Oh;Jeon, Jin Yong
    • Transactions of the Korean Society for Noise and Vibration Engineering
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    • v.24 no.4
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    • pp.339-347
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    • 2014
  • Floor impact sound in high-rise apartment building became one of social problems. A lot of civil complaints on floor impact sound occur continuously and the number of disputes between neighbors in small and aged apartment buildings is increasing. Interests on heavy-weight impact sound pressure level measurement and evaluation method is increased. Previous study reported that heavy-weight impact sound level was changed by the sound field condition of receiving reverberation chamber. In this study, heavy-weight impact sound pressure level change by the receiving sound field condition was measured in standard test facility and mock-up test room. These two experimental conditions were designed to simulate averaged living room of common apartment units. By the change of sound absorption power in receiving room, heavy-weight impact sound pressure level in most of frequency bands were changed in standard test facility and mock-up room. Normalized maximum sound pressure level regulated in ISO 16032 showed wider range of heavy/soft impact sound pressure level. Heavy/soft impact sound pressure level change was became smaller by the application of standardized maximum sound pressure level and ISO/CD 10140-3 Amd 2 method. In the case of standardized maximum sound pressure level, absolute sound pressure level changed. From these results, receiving sound field correction method regulated in ISO/CD 10140-3 Amd 2 is needed for the precision measurement and evaluation of heavy-weight impact sound.

Study on Low Frequency Swishing Sound Field by a Singularity in Circular Motion with Large Radius (큰 반경의 원운동을 하는 점 음원에 의한 저주파수 스위싱 음장 분석)

  • Lee, Gwang-Se;Cheong, Cheolung
    • Transactions of the Korean Society for Noise and Vibration Engineering
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    • v.24 no.7
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    • pp.569-574
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    • 2014
  • In order to investigate low frequency swishing noise of wind turbines, acoustic source model using a singularity in circular motion is introduced to derive analytic solution of Lowson acoustic analogy in time domain. Results in time and frequency domains computed by the solution show apparent modulation of amplitude and frequency. The solution indicates that time histories of acoustic pressure at receiver points varied significantly according to receiver's directional location, even when the retarded time distributions are similar. However, the corresponding time-averaged spectra of sound pressure at the receiver locations where the retarded time distributions are almost same are not significantly different. It can be inferred from these results that the time-averaged sound pressure spectra which cannot take into account the detailed difference in the time-variation of wind turbine noise may not represent the sound quality of wind turbines due to its swishing. Finally, as an introduction of procedure to quantify low frequency swishing noise level, relative variation of overall sound pressure level is obtained using tonal low frequency noise model.

The Development and Application of Sound Quality Index for the Improving Sound Quality to Road Vehicle Power Window System (차량 윈도우 리프트 음질 향상을 위한 음질 지수 제작 및 개선에의 응용)

  • Kim, Seong-Hyeon;Park, Dong-Chul;Jo, Hyeon-Ho;Seong, Won-Chan;Kang, Yeon-June
    • Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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    • 2013.10a
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    • pp.525-530
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    • 2013
  • With the increasing the importance of emotional quality of vehicle, the sound quality of systems with electric motor components has become increasingly important. Electric motors are used for windows, seats, sun roof, mirrors, steering columns, windshield wiper, climate control blowers, etc. In this paper, a study was conducted to identify sound quality factors that contribute to customer's satisfaction and preference of the window lift system. Jury test for subjective evaluation was carried out and sound quality index was developed. Averaged sound pressure level and sharpness were significant factors when glass moves down. Also, maximum loudness at stop section and averaged loudness were significant factor when glass moves up. Noise source identification was carried out for the reduced the loudness and sharpness during glass transferred section and impulsive noise at stop section, Using the source identification result, several improvement points were applied. And finally, the degree of sound quality improvement was judged using sound quality index.

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NUMERICAL ANALYSIS FOR TURBULENT FLOW AND AERO-ACOUSTIC OVER A THREE DIMENSIONAL CAVITY WITH LARGE ASPECT RATIO (3차원 고세장비 공동 주위의 난류유동 및 음향 특성에 관한 수치적 연구)

  • Mun, P.U.;Kim, J.S.
    • 한국전산유체공학회:학술대회논문집
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    • 2008.03a
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    • pp.297-301
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    • 2008
  • The flight vehicles have cavities such as wheel wells and bomb bays. The flow around a cavity is characterized as unsteady flow because of the formation and dissipation of vortices due to the interaction between the freestream shear layer and cavity internal flow, the generation of shock and expansion waves. Resonance phenomena can damage the structures around the cavity and negatively affect aerodynamic performance and stability. The flow field is observed to oscillate in the "shear layer mode" with low aspect ratio. In the present study, numerical analysis was performed for cavity flows by the unsteady compressible three dimensional Reynolds-Averaged Navier-Stokes (RANS) equations with Wilcox's $\kappa$-$\omega$ turbulence model. The flow field is observed to oscillate in the shear layer mode" with large aspect ratio. Based on the SPL(Sound Pressure Level) analysis of the pressure variation at the cavity trailing edge, the dominant frequency was analyzed and compared with the results of Rossiter's formul. The aero-acoustic wave analyzed with CPD(Correlation of Pressure Distribution).

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NUMERICAL ANALYSIS FOR TURBULENT FLOW AND AERO-ACOUSTIC OVER A THREE DIMENSIONAL CAVITY WITH LARGE ASPECT RATIO (3차원 고세장비 공동 주위의 난류유동 및 음향 특성에 관한 수치적 연구)

  • Mun, P.U.;Kim, J.S.
    • 한국전산유체공학회:학술대회논문집
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    • 2008.10a
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    • pp.297-301
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    • 2008
  • The flight vehicles have cavities such as wheel wells and bomb bays. The flow around a cavity is characterized as unsteady flow because of the formation and dissipation of vortices due to the interaction between the freestream shear layer and cavity internal flow, the generation of shock and expansion waves. Resonance phenomena can damage the structures around the cavity and negatively affect aerodynamic performance and stability. The flow field is observed to oscillate in the "shear layer mode" with low aspect ratio. In the present study, numerical analysis was performed for cavity flows by the unsteady compressible three dimensional Reynolds-Averaged Navier-Stokes (RANS) equations with Wilcox's ${\kappa}-{\varepsilon}$ turbulence model. The flow field is observed to oscillate in the "shear layer mode" with large aspect ratio. Based on the SPL(Sound Pressure Level) analysis of the pressure variation at the cavity trailing edge, the dominant frequency was analyzed and compared with the results of Rossiter's formul. The aero-acoustic wave analyzed with CPD(Correlation of Pressure Distribution).

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NUMERICAL ANALYSIS OF TWO- AND THREE-DIMENSIONAL SUBSONIC TURBULENT CAVITY FLOWS (2차원과 3차원 아음속 공동 유동 특성에 대한 수치적 연구)

  • Choi, Hong-Il;Kim, Jae-Soo
    • 한국전산유체공학회:학술대회논문집
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    • 2007.10a
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    • pp.187-193
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    • 2007
  • The flight vehicles have cavities such as wheel wells and bomb bays. The flow around a cavity is characterized as unsteady flow because of the formation and dissipation of vortices due to the interaction between the freestream shear layer and cavity internal flow, the generation of shock and expansion waves. Resonance phenomena can damage the structures around the cavity and negatively affect aerodynamic performance and stability. In the present study, numerical analysis was performed for cavity flows by the unsteady compressible three dimensional Reynolds-Averaged Navier-Stokes (RANS) equations with Wilcox's ${\kappa}\;-\;{\omega}$ turbulence model. The cavity has the aspect ratios of 2.5, 3.5 and 4.5 for two-dimensional case, same aspect ratios with the W/D ratio of 2 for three-dimensional case. The Mach and Reynolds numbers are 0.53 and 1,600,000 respectively. The flow field is observed to oscillate in the "shear layer mode" with a feedback mechanism. Based on the SPL(Sound Pressure Level) analysis of the pressure variation at the cavity trailing edge, the dominant frequency was analyzed and compared with the results of Rossiter's formula. The MPI(Message Passing Interface) parallelized code was used for calculations by PC-cluster.

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The Development and Application of Sound Quality Index for the Improving Luxury Sound Quality of Road Vehicle Power Window System (차량 윈도우 리프트 음질 고급감 향상을 위한 음질 지수 제작 및 개선에의 응용)

  • Kim, Seonghyeon;Park, Dong Chul;Jo, Hyeonho;Sung, Weonchan;Kang, Yeon June
    • Transactions of the Korean Society for Noise and Vibration Engineering
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    • v.24 no.2
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    • pp.108-116
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    • 2014
  • With the increasing the importance of emotional quality of vehicle, the sound quality of systems with electric motor components has become increasingly important. Electric motors are used for windows, seats, sun roof, mirrors, steering columns, windshield wiper and climate control blowers, etc. In this paper, a study was conducted to identify sound quality factors that contribute to customer's satisfaction and preference of the window lift system. Jury test for subjective evaluation was carried out and sound quality index was developed. Averaged sound pressure level and sharpness were significant factors when glass moves down. Also, maximum loudness at stop section and averaged loudness were significant factor when glass moves up. Next, noise source identification was carried out using beam forming method during glass transferred section and impulsive noise at stop section. Several improvement methods were applied using the source identification result. And finally, the degree of sound quality improvement was judged using sound quality index.

A Study on Aerodynamic and Noise Characteristics of a Sirocco Fan for Residential Ventilation (주거환기용 시로코홴의 공력 및 소음 특성 연구)

  • Kim, Jin-Hyuk;Song, Woo-Seog;Lee, Seung-Bae;Kim, Kwang-Yong
    • The KSFM Journal of Fluid Machinery
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    • v.13 no.2
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    • pp.18-23
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    • 2010
  • This paper presents a procedure for the aerodynamic and aeroacoustic characteristics of a sirocco fan. For the aerodynamic and aeroacoustic analyses of the sirocco fan, three-dimensional steady and unsteady Reynolds-averaged Navier-Stokes equations are solved with a shear stress transport turbulence model for turbulence closure. The flow analyses were performed on a hexahedral grid using a finite-volume solver. The validation of the numerical results is performed by comparing with experimental data for the pressure, efficiency and power. The internal flow analyses of the sirocco fan are performed to understand the unstable flow phenomenon on the casing for the wall pressure and internal flow characteristics at each position. It was found that fluctuation of pressure and locally concentrated noise source are observed near the cut-off and expansion regions of the casing.

NUMERICAL ANALYSIS OF THREE-DIMENSIONAL SUBSONIC TURBULENT CAVITY FLOWS (3차원 아음속 난류 공동 유동에 대한 수치적 연구)

  • Choi, Hong-Il;Kim, Jae-Soo
    • Journal of computational fluids engineering
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    • v.13 no.1
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    • pp.35-40
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    • 2008
  • Generally flight vehicles have many cavities such as wheel wells, bomb bays and windows on their external surfaces and the flow around these cavities makes separation, vortex, shock and expansion waves, reattachment and other complex flow phenomenon. The flow around the cavity makes abnormal and three-dimensional noise and vibration even thought the aspect ratio (L/D) is small. The cavity giving large effects to the flow might make large noise, cause structural damage or breakage, harm the aerodynamic performance and stability, or damage the sensitive devices. In this study, numerical analysis was performed for cavity flows by the unsteady compressible three dimensional Reynolds-Averaged Navier-Stokes (RANS) equations with Wilcox's $\kappa-\omega$ turbulence model. The MPI(Message Passing Interface) parallelized code was used for calculations by PC-cluster. The cavity has the aspect ratios of 2.5, 3.5 and 4.5 with the W/D ratio of 2 for three-dimensional cavities. The Sound Pressure Level (SPL) analysis was done with FFT to check the dominant frequency of the cavity flow. The dominant frequencies were analyzed and compared with the results of Rossiter's formula and Ahuja& Mendoza's experimental datum.

A Study on the Reverberation Time Characteristics of Inside Space of Apartment Buildings (공동주택 내부 공간의 잔향시간 특성 조사 연구)

  • Jeong, Jeong Ho;Lee, Byung Kwon;Jeon, Jin Yong
    • Transactions of the Korean Society for Noise and Vibration Engineering
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    • v.25 no.4
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    • pp.291-298
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    • 2015
  • In this study, the reverberation time of apartment living room was measured and distribution of the reverberation time was analyzed. In addition, sound field characteristics of mock-up test room similar with living room and timber structured bedroom was investigated with addition of furniture and sound absorption material. Average reverberation time of unfurnished apartment unit was 1.11 s, and reverberation time in 630 Hz~2000 Hz bands were longer than 1.2 s. It was found that from the field measurement results, reverberation time characteristic of furnished apartment living room was uniform in most of frequency bands. Averaged reverberation time of furnished living room was 0.48 s and the reverberation time of bedroom was 0.44 s. Standardized sound pressure level correction values were calculated from the average reverberation time of furnished and unfurnished apartment units. The correction value of unfurnished living room was −3.4 dB and that of furnished living room was 0.2 dB. Measured reverberation time of furnished and unfurnished apartment units indicated that reference reverberation time; 0.5 s, in KS and ISO standards is reasonable also in Korean residential environment.