• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.20 no.10
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• pp.931-939
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• 2010

A dash panel plays an important role to protect noise as well as heat. Meanwhile, it is also the most important path that transfers energy to the interior cavity, so that some of noises are transferred via air and its structural vibration becomes a major issue. From the viewpoint of NVH performance, simplified structures analogues to the dash wall are dealt with. Stiffeners, damping sheets and sound packages attached to a flat panel are taken into account as design variables. Structural radiation characteristics(thus, structure borne) such as radiation efficiency and radiation power are mainly discussed. For the case when an excitation is applied on a frame that surrounds the panel, it is shown that the radiation efficiency increases by attaching a stiffener to the panel, which is similarly found from the case when a panel is directly excited. It seems more effective to attach damping sheets along the boundary area of the panel rather than its middle area. The radiation efficiency of sound packages may make a dominant contribution to transmission loss as well as sound radiation. Experimental work was carried out to verify the results based on the simulation study.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2007.11a
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• pp.1366-1370
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• 2007

Predicting the noise radiated from vibrating structures is important in the automotive, aerospace, construction equipment, and defense industries. In this paper, a numerical implementation of the boundary element method in solving the Helmholtz integral equation for radiated noise prediction is presented. To predict the noise emitted by vibrating structure, the developed code can use the results from a structure analysis performed by a multi-purpose structural finite element code like ANSYS and directly measured data by non-contact vibration sensor like Laser Doppler Vibrometer. To verify the accuracy of developed code, two kinds of verification are perfomed. Firstly, the computer code used the harmonic analysis results of ANSYS in simple model and try to match with SYSNOISE. After matching with simulation results, the code compared with the result from SYSNOISE which used the velocity data from the LDV measurement with different number of points. The performance of the developed code for vibro-acoustic noise prediction is presented using the experimental results of the non-contact sensor

• Journal of the korean Society of Automotive Engineers
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• v.8 no.4
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• pp.43-55
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• 1986

In the studies of noise reduction, it is important to know the generation mechanism of noise in order to identify the noise source. The relation between the structural vibration and the radiated sound is very complex and so this paper deals with a simplified radiation model that was originally developed as a verification tool for the acoustic intensity measurement procedure. As the first step for the identification of the noise source, this study deals with the noise evaluation by measuring sound pressure. On the next step, the acoustic radiational pattern is determined by the acoustic intensity method and this paper established that the acoustic intensity method is effective on the detection of noise. In the study, furthermore, the method could be used to predict the change in the sound radiational characteristics with the attachment of absorber and could be used in determining the attachment position.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.19 no.2
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• pp.184-191
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• 2009

This study examined small-size specimen's effectiveness that is used to evaluate floor impact sound performance. Floor impact sound level of small-size specimen is higher than full-size. This is due to excessive impact power of Bang machine. Impact hammer that has small impact power relatively can solve this problem. But, according to the size of specimen, mode shape and frequency that influence to structural borne sound is changed. Slab mode of full-size specimen was changed to frequency design of resilient materials. But in case of small-size specimen, there is no change of vibration mode by resilient materials change, Vibration mode of small-size specimen is the same. Therefore, it is not proper that use small-size specimen in floor impact sound estimation.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2001.11a
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• pp.179-184
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• 2001

대부분의 제품 생산 시에는 시제품을 제작하여 이에 대한 성능 심사를 통해 미비한 부분을 보완하기 위한 재설계 작업과정을 필요로 한다. 설계 작업에 가장 중요한 부분인 특정 설계 변수에 대한 민감도의 파악은 설계 작업의 핵심적인 역할을 하고 있다. 대개의 경우 진동설계를 위한 설계변수로 구조물의 단위면적, 길이, 재료의 성질과 같은 물리적인 변수를 많이 활용하고 있으며 이러한 변수들에 대한 민감도 해석 기법들은 이미 많은 연구를 통해 실용화되고 있다. 그러나 이러한 변수만으로는 주어진 조건을 만족하도록 설계하기가 어려운 경우가 있다. 이런 경우는 부가구조물을 첨가하여 저진동 설계조건을 만족하는 구조물을 제작하는 것이 보편적이다. 한편, 구조물의 최적화 과정에서 고유진동수를 고려해야 하는 경우가 많다. 저주파 영역의 문제에서는 첫번째 고유진동수가 구조물의 진동량에 관계되는 중요한 요인이 되고, 또한 공진에 의한 문제가 발생했을 경우에는 고유진동수를 옮겨서 공진을 회피할 수 있기 때문이다. 본 연구에서는 에어컨 실외기의 진동을 저감하고 그로 인한 구조기인 소음을 저감하기 위하여 음압 레벨을 바탕으로 정한 관심 주파수 영역에 고유진동수가 존재하지 않도록 부가구조물을 최적화하였다. 최적화에 필요한 민감도는 신뢰성 있는 유한요소 모델을 구성하는 것이 쉽지 않으므로 실험으로 구한 주파수 응답함수를 이용하였다.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.37 no.5
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• pp.673-678
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• 2013

Creep groan noise occurs at low frequencies immediately after releasing brake pressure or when a car stops. This noise can be used to predict problems in not only the brake system but also the vehicle system. Because of its complexity, it is difficult to determine its characteristics. Therefore, most improvements are conducted by changing the brake pad, and it still remains difficult to conduct a test using a vehicle. In this study, the characteristics of creep groan noise and the effects from a vehicle system are investigated by using vehicles and an NVH chassis-dynamometer through various tests. A new evaluation method for creep groan noise by using a vehicle is proposed, and the possibility of reduction schemes from the viewpoint of the vehicle system is confirmed from the results mentioned above.

• Journal of the Society of Disaster Information
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• v.10 no.2
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• pp.274-281
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• 2014

Since the vibration induced by a train is transferred directly to a station via a roadbed structure, the elevated station is particularly vulnerable to noise and vibration. To establish more appropriate measures to reduce vibration, the structural behavior and damping characteristics depending on the structural type and the composition of a elevated station should be identified, because the noise inside the station is mainly structure borne noise by the vibration of a station structure. In this paper, the vibration characteristic changes depending on mechanical connection types between an elevated station and a connected bridge are analyzed. The finite element model for Daecheon Station is constructed for the purpose of this study, and the analysis is performed using ABAQUS. The analyses are conducted for with and without bridge connections, and for the bridge connections, ramen and bearing types are considered in the analysis.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.36 no.7
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• pp.789-796
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• 2012

Radiated noise analysis from a ship structure is a challenging topic owing to difficulties in the accurate calculation of the fluid-structure interaction as well as owing to a massive degree of freedom of the problem. To reduce the severity of the problem, a new fluid-structure interaction formulation is proposed in this paper. The complex frequency-dependent added mass and damping matrices are calculated using the high-order Burton-Miller boundary integral equation formulation to obtain accurate values over all frequency bands. The calculated fluid-structure interaction effects are added to the structural matrices calculated by commercial finite element software, MSC/NASTRAN. Then, the impedance and underwater radiation noise due to an excitation of structure are calculated. The present formulation is applied to a ship to calculate the underwater radiated noise.

• Journal of the Korea institute for structural maintenance and inspection
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• v.20 no.4
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• pp.94-103
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• 2016

For elevated railway station on which track is connected with superstructure of station, structural vibration level and structure-borne-noise level has exceeded the reference level due to structural characteristics which transmits vibration directly. Therefore, existing elevated railway station is in need of economical and effective vibration reduction method which enable train service without interruption. In this study, structural vibration non-transmissible system which is applied to vibroisolating material for column member is developed to reduce vibration. That system is cut covering material of the column section using water-jet method and is installed with vibroisolating material on cut section. To verify vibration reduction effect and structural performance for structural vibration non-transmissible system, impact hammer test and cyclic lateral load test are performed for 1/4 scale test specimens. It is observed that natural period which means vibration response characteristics is shifted, and damping ratio is increased about 15~30% which means that system is effective to reduce structural vibration through vibration test. Also load-displacement relation and stiffness change rate of the columns are examined, and it is shown that ductility and energy dissipation capacity is increased. From test results, it is found that vibration non-transmissible system which is applied to column member enable to maintains structural function.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.18 no.3
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• pp.694-702
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• 2017

In the case of an elevated railway station, structure borne noise and vibration due to structural limitations allow the load and vibration from railway vehicles to be directly transmitted to the station structure, resulting in an increase in the number of civil complaints from customers and staff of the station. The floating slab track system, which is well known as one of the solutions for reducing the noise and vibration from elevated railway stations, usually contains rubber mounts or rubber pads under the railway slab which act as a damper. These types of device have the disadvantage that is difficult to predetermine the exact stiffness and damping ratio under the nonlinear loads resulting from train services. In this study, an isolator with a friction type of wedge is introduced, which can be applied to floating slab track systems and to be designed with precisely the required stiffness. Furthermore, a comparative analysis of the stiffness between the designed and experimental values is carried out, while the damping ratio, which is closely related to the friction wedge blocks, is deduced according to the train load condition. The performance tests of the isolator were conducted in accordance with the DIN 45673-7 standard which includes both static and dynamic load tests. The load conditions for the performance tests are designed to conform to the DIN standard related to the weight of the train and rail track, in order to perform vertical and horizontal load tests, so as to ensure the secure structural safety of the railway. Also, by checking the change aspect of the friction coefficients of the friction elements according to the loading rate, the vibration reduction performance of the friction type isolator with variable loading rate conditions is examined.