• Journal of the Korean Wood Science and Technology
• /
• v.25 no.2
• /
• pp.61-66
• /
• 1997

Paulownia wood has been used as sound board for Korean traditional musical instruments such as Keomungo(Korean lute), Kayagum(twelve-stringed Korean harp) and Changgu(hour-glass shaped drum), etc. The acoustic properties of wood affected not only by dimensions but also by density and stiffness of wood. Due to inhomogeneity and hygroscopicity of wood. the acoustic properties of wood are inconsistent. To clarify the effect of moisture content and air dry density on acoustic properties, longitudinal vibration experiment was accomplished in 3 moisture content levels of 9.6, 11.1 and 12.5% and in 3 air dry density levels of 0.22, 0.25 and 0.28g/$cm^3$. The results were as follows: As the moisture content increased, the fundamental frequency. specific dynamic Young's modulus and sound velocity decreased, but the internal friction increased so that loss of energy increased. The values in damping of sound radiation were rapidly decreased at 12.5%. It meant that the damping of internal friction was larger than damping of sound radiation at high moisture content. As the air dry density increased, the fundamental frequency, specific dynamic Young's modulus and sound velocity increased, but the internal friction and damping of sound radiation decreased so that loss of energy decreased. And acoustic converting efficiency was hardly influenced by increasing air drying density.

• Proceedings of the Earthquake Engineering Society of Korea Conference
• /
• 2005.03a
• /
• pp.228-235
• /
• 2005

The floor impact sound insulations are installed frequently for reducing the floor impact sound into the floor slab of the residential buildings in recent years. Therefore the analytical FE model considering the insulations is needed for the sound and vibration analysis of the floor and it is necessary to use a refined finite element model for considering the large number of modes involving in the dynamic responses. So it is very difficult to use FE model because of the tiresome task for constructing the FE model, taking a lot of times for analysis and the impossibility of using the proportional damping. The efficient analysis and modeling method are proposed to the dynamic analysis for the floor with floor impact sound insulations in this study. The floor slabs and finished layers are modeled individually and the spring elements that mean floor impact sound insulations use to connect two parts. The dynamic analysis by the $Newmark-{\beta}$ method is performed to solve the non-proportional damping problem due to the damping coefficient of insulations .

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 1991.04a
• /
• pp.41-45
• /
• 1991

구조 진동에 의해 발생하는 Relative Sound Power를 계산하는 문제가 최근 에 중요시되고 있다. 이 논문에서는 조화적인 집중하중에 대한 무한 탄성보 에서 방출하는 Relative Sound Power를 연구한다. Sound Power는 수치적으 로 적분되고 몇가지 인자들의 함수로써 적분인자를 표시하였다. Keitie와 Peng[2]는 진동하는 보로부터의 방출하는 Relative Sound Power에 대한 하 중 길이의 효과, 그리고 water 하중을 받는 보에서 방출하는 Acoustic radiation에 대한 Source 운동과 기초 강성의 효과를 연구하였다. 보의 진동 응답에서 light fluid loading과 heavy fluid loading에 의한 양쪽의 반응을 고 려한다. 보에는 기초 강성과 Damping 그리고 장력이 작용한다. water 하중 과 air 하중을 받는 보에서 Damping의 변화에 대한 보로부터 방출하는 relative sound power의 크기를 결정하였다. 일반적으로 인장력보다 압축력 이 작용할 때 relative sound power level이 크다는 것을 알고 있다. 실제로 인장력이나 압축력이 보에 작용할 때 relative sound power에 얼마나 영향을 미치는가를 계산하였다. 그리고 진동계로부터 방출하는 sound fluid loading 과 기초 강성에 기인한 복잡한 효과를 해석하였다. 이 논문의 목적은 강성계 수와 wavenumber 비, 그리고 fluid loading에 대한 sound power의 응답에 대하여 설명하고자 한다.

• Transactions of the Korean Society of Automotive Engineers
• /
• v.6 no.2
• /
• pp.92-99
• /
• 1998

The sound insulation capacity of honeycomb sandwich plates which have relatively higher strength ratios to weight is poorer than those of uniform and another sandwich plates. Therefore, improvement of the sound insulation capacity of the honeycomb sandwich plate which has a meritof lightness is required to use it in automobile and rapid rail road industries. In this study, to improving the sound insulation capacity of the honeycomb sandwich plate, the sound transmission loss of the structure is experimentally investigated by adding a viscoelastic damping layer, The effective add position and thickness of the layer were investigated from the viewpoints of both sound transmission loss and improved sound transmission loss over the frequency range from 800Hz to 10kHz.

• Transactions of the Korean Society for Noise and Vibration Engineering
• /
• v.22 no.2
• /
• pp.115-122
• /
• 2012

Sound packages and damping materials have been widely applied on the floor to decrease the interior noise of a vehicle. Based on the previous researches on the low-noise vehicles, weight optimization through minimization of damping material usage is required while decreasing mid and high frequency range noise by application of sound packages. This paper describes the analysis process of robust design of vehicle body structure before applying damping materials and focuses on the analysis and test process of the location optimization at the stage of damping material application. A vibration experiment for the analysis of floor panel velocity with respect to the excitation of suspension attachment parts at the underfloor of a vehicle is performed. And through the improvement correlation between FEA and TEST, a design guide to optimize damping materials application in the early design stage is proposed. A research on vibration damping steel sheets and liquid acoustic spray on deadener(LASD) is performed to minimize manufacturing time and to minimize the space for pre-existing asphalt damping materials. As results of this study, panel stiffness is achieved through curved surface panel and bead optimization. And test baseline of optimum design is suggested through damping material optimization. And finally, through re-establishing the analysis process for vibration reduction of vehicle floors and lightweight design of damping materials, it is possible to design damping materials efficiently in the preceding stage of design.

• Transactions of the Korean Society for Noise and Vibration Engineering
• /
• v.16 no.10 s.115
• /
• pp.1036-1043
• /
• 2006

Damping materials for reducing heavy-weight floor impact noise in reinforced concrete structures were tested in apartment buildings. The effect of damping materials and an impact isolator were compared with an on-site experiment conducted in a high-rise apartment building. The loss factor of damping material analyzed more than 2 times than rubber to $1.5{\sim}2.3$, could know that Damping layer has excellent attenuation performance in side of vibration reduction. The results showed that the resonance frequency increased but vibration acceleration level decreased when the damping materials were used. The heavy-weight impact sound levels of the structure decreased substantially at 63 Hz, whereas the sound levels of the structure with the impact isolator increased.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2005.05a
• /
• pp.79-82
• /
• 2005

This study aims to propose fundamental data for development of noise reduction system that is applied to classification for light-weight impact sound. For this reason, eight types of damping materials were constructed in new construction field. Comparison and analysis among the reduction materials were carried out on the acoustical characteristics through test. In the end, the suitability as a damping material was evaluated by the analysis.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2003.11a
• /
• pp.333-337
• /
• 2003

The use of reactive shearing structural intensity to place small patches of constrained layer damping material in order to achieve the largest reduction in the radiated sound power of Air-conditioner outdoor unit is described. The normal surface velocity of each panel was measured using a laser doppler vibrometer. Experimental results indicated that patches of constrained layer damping material placed over areas of high reactive structural intensity reduced the radiated sound power significantly more than patches of the same area placed over areas of low reactive structural intensity

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 1997.04a
• /
• pp.443-446
• /
• 1997

This paper raises issues in testing the absorption coefficients of sound-absorptive samples in the standing wave tube according to the Korean standard of KS F 2814. The code does not consider any effect of air-damping during test. This limitation has been shown to yield much variation of sound absorption coefficients for recent sample tests whose coefficients are less than 10 %. An improved method of calculating the sound absorption coefficients is proposed in this work and its effectiveness in real test is also illustrated. Finally, the guide line for the modification of our national standard code KS F 2814 is suggested for the future.

• Journal of Industrial Technology
• /
• v.26 no.A
• /
• pp.81-88
• /
• 2006

The Chun-cheon Citizen's Bell was cast in memory of hosting the 2010 world leasure conference and a striking ceremony was held at the city hall on December 31, 2005. In this study, vibration and sound of the bell are measured and the property of the magnificent sound of the bell is scientifically investigated. Frequency components making the sound are identified and how the frequency components decrease with time is observed using waterfall plot(3-dimensional frequency spectrum). Beat characteristics of the hum(1st frequency) and the fundamental(2nd frequency)are examined by experiment. Directivity of the sound radiation of the bell is examined by measuring the vibration and sound in several directions. Duration of the vibration and the sound is estimated using damping ratio.