• 한국정밀공학회지
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• 제12권6호
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• pp.137-144
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• 1995

The purpose of this study is to obtain a foundation data for chassis design and road noise reduction of automobiles. Using the combination of the automobile, radial tires and instrumentation equipment, experimental investigation was carried out to examine the characteris- tics of the structural vibration of tire as the key to obtaining the effective parameters for reducing road noise. From the results of this studies it has been confirmed that the specific ranges of natural frequency of tire exciting the suspension and chassis system. And the tire, axle and chassis natural frequency of automobile govern the road noise. Results show that material properties of tire and experimental condition are major parameter for shifting of tire natural frequency. These results would be utilized as basic materials for the design of chassis design with papametric study, which enables a designer of an automobile to foresee the influence of the various design factors or operating conditions.

• 한국해안해양공학회지
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• 제17권3호
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• pp.138-148
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• 2005

부유체 및 부유식 교량과 같은 부유식 구조물이 파랑하중에 대하여 나타내는 동적거동을 주파수영역에서 구하는 연구를 수행하였다. 먼저, 부분적으로 유체에 잠겨 파랑하중의 작용을 받는 부유체에 대하여, 이의 강체운동과 관련된 동유체력계수인 부가질량, 감쇠 및 파강제력를 선형포텐셜이론과 경계요소법을 이용하여 주파수 영역에서 산정한다 다음으로,부유식 교량과 같이 앞에서 구한 부유체로 지지되며 유한요소를 이용하여 모델링 되는 부유식 구조물에 대하여, o)의 동적거동에 관한 운동방정식을 수립한다. 동유체력계수들이 주파수 의존적 성질을 가지므로 해석은 주파수영역에서 수행한다. 적용 예제로서 반구와 같은 부유체를 이용하여 해석결과를 문헌과 비교 검증한 후,부유식 교량을 지지하는 폰툰형 부유체에 대한 동유체력계수들을 구하고, 이를 이용하여 설계 파랑하중을 받는 부유식 교량의 동적 거동해석을 수행한다. 해석 예제를 주파수영역에서 해석한 결과 입사파스펙트림의 피크 주파수와 교량의 고유진동수가 가까워 응답이 증폭될 소지가 있었으나 주파수 의존적인 파강제력의 피크가 벗어난 영향으로 응답이 증폭되지 않음을 알 수 있다.

• 한국자기학회지
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• 제21권4호
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• pp.121-126
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• 2011

자유층과 고정 기준층으로 이루어진 자기 터널 접합의 스핀 동역학을 강자성 공명 시늉내기로 연구 하였다. 먼저 교환 바이어스 인위적 준강자성 기준층을 포함한 자기 터널 접합에서 DC 자기장에 대한 각 층의 자화 방향을 확인하고 터널 자기저항을 계산하였다. 자기 터널 접합에서 스핀의 들뜸 모드들을 확인하기 위해 DC와 RF 자기장을 함께 인가하여 강자성 공명 주파수 스펙트라를 관찰 하였다. 각 층 별로 들뜸 모드들을 확인하여 자유층과 기준층의 자화 방향의 차이로 계산된 터널 자기저항의 들뜸 모드들을 분석 하였다. 전체적으로 스핀의 들뜸 모드는 자유층이나 기준층의 자화 방향에 관련해서 DC 자기장의 음, 양의 방향에 따라 상이하게 나타났다. 음의 방향 자기장에 대해서 자유층과 기준층의 강자성 공명 주파수 스펙트라는 수정된 Kittel 방정식으로 잘 설명되지만 양의 방향 자기장에 대해서는 예측하기 어려운 들뜸 모드들로 인해 분석적 해답을 찾기 어려웠다. 자기터널 접합의 강자성 층들은 서로 상호 작용을 하기 때문에 이에 대한 스핀 동역학 연구는 자유층 뿐만 아니라 기준층, 고정층과도 밀접하게 연관되어 있다.

• 한국소음진동공학회논문집
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• 제19권10호
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• pp.1028-1033
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• 2009

To detect faults and monitor thinning on a pipe, many people use ultra sonic sensors that are operated in high frequency range. Because there are many modes in high frequency range, it is difficult to find faults and monitor pipe thinning on a structure. If we deal with signals in a low frequency range which include only A0 wave and S0 wave, the information of monitoring and diagnosis can be easily obtained. In this paper, the technique for exciting low frequency range using ultra sonic sensors is proposed. The main idea of the proposed method comes from the beat phenomenon. The beat frequency is equal to the absolute value of the difference in frequency of the two waves. If the beat frequency is tuned by two ultra waves, we can excite A0 mode and S0 mode of structures. To verify the proposed method, we have performed a steel plate and pipe experiments. Experimental results show that two ultra sonic sensors can well excite low frequency range.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2002년도 춘계학술대회 논문집
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• pp.803-806
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• 2002

This paper estimated the stability of centrifuge as its rotating speed compared with the natural frequency of cylinder and screw by finite element analysis. It shows that the one of exciting causes is the tooth passing frequency of input and output parts by the periodic characteristics of transmission error due to an planetary gear having three stages. Also, it proposed the critical speed of cylinder and screw by the Campbell diagram.

• 한국기계가공학회지
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• 제9권2호
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• pp.20-25
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• 2010

A camera module is supported by a gimbal structure in collection equipment of image information. During flight, the gimbal system undergoes serious accelerations with wide frequencies. To get the correct images, the camera module must be stably vibrated under these conditions. If natural frequency unfortunately exists in a exciting frequency range, resonance occurs there. Hence, harmonic responses analysis is needed to know correct vibration characteristic of the gimbal system. Finite element analysis was performed to get an acceleration of the gimbal system by mode superposition after extracting mode shapes and natural frequencies. Considering damping ratio of 2%, the reponses of gimbal structure were calculated from excitations with a design frequency band. As results, a maximum acceleration transmissibility, which is the ratio of response to excitation, was obtained and it can be used to design the gimbal structure effectively.

• Structural Engineering and Mechanics
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• 제40권3호
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• pp.373-392
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• 2011

Periodic and quasi-periodic Timoshenko beams on Pasternak foundation are investigated using the differential quadrature method. Not only band gaps in the beams but also the dynamic response of them is analyzed. Numerical results show that vibration in periodic beams can be dramatically attenuated when the exciting frequency falls into band gaps. Different from the band structures of periodic beams without foundation, the so-called critical frequency was found because of the Pasternak foundation. Its physical meaning was explained in detail and a useful formula was given to calculate the critical frequency. Additionally, a comprehensive parameter study is conducted to highlight the influence of foundation modulus on the band gaps.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 추계학술대회논문집A
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• pp.495-500
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• 2001

Because of resonance between natural frequency of the second floor base for IPB(Isolated Phase Bus) duct supports in a power plant and operation frequency of the turbine, there was high amplitude vibration on IPB duct. To reduce vibration of IPB duct, Firstly it was set a FEM model to seek the mode shape for the concrete structure. Secondly, it was carried out dynamic analysis for the FEM model. Lastly, because the natural frequency of the concrete structure could not be changed, it was changed supports position for the IPB duct near to beams. It resulted in reducing vibration of IPB duct.

• 한국소음진동공학회논문집
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• 제16권5호
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• pp.521-528
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• 2006

The vibration fatigue is suitable case of fatigue problem that system is exposed to the random or other irregular sources. Even some kinds of effort using power spectral density (PSD) and statistical concept was presented to cope with the intangible force signal, it is still lack of providing a reasonable solution when its exciting frequency is near or beyond of first eigenvalue. In this paper, energy approach method is presented to calculate a vibration induced fatigue damage in frequency domain. Since the corresponding damage become much larger than nominal case when the vibration is coupled with a mode shape of given structure, the new technique compensate the characteristics of structure with a measured frequency response function (FRF) between forcing acceleration and responding stress.

• 한국철도학회:학술대회논문집
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• 한국철도학회 2005년도 추계학술대회 논문집
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• pp.211-216
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• 2005

Resonance of railroad bridge can be broken out when natural frequency of the bridge coincides with exciting frequency of moving forces. In order to avoid aforementioned unpleasant response of the structure, exact determination of dynamic structural properties is important to understand dynamic behavior of the structure under moving train loads. In the present paper, a 25 meters long full scale IPC girder and 15m Precom girder models were fabricated as a test specimen and modal testing was carried out to evaluate modal parameters including natural frequencies and modal damping ratios. In the modal testing, a digitally controlled vibration exciter as well as an impact hammer is applied to obtain frequency response functions more exactly and the modal parameters are evaluated varying with structural status.