• 한국소음진동공학회논문집
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• 제14권6호
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• pp.512-519
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• 2004

This paper described the free vibration characteristics of Optimized H Type (OHT) spacer grids (SG) supporting the PWR fuel rod. The vibration test and the finite element (FE) analysis are performed under the free boundary condition and the clamped at two points (or three points) in the bottom which is the same one as the experimental condition for the dummy rod continuously supported by spacer grids. A modal test is conducted by the impulse excitation method using an impulse hammer and an accelerometer, and the TDAS module of the I-DEAS software is used to acquire and analyze the sensor signals. The softwares related to the FE analysis are the I-DEAS for the geometrical shape modeling and meshing, and the ABAQUS for solving. The fundamental frequency of the OHT SG by experiment under a clamped condition at two points is 175.18 Hz, and shows a bending mode. We think there is no resonance between the fuel rod and the SG because the SG's frequency is higher than that of the fuel rod existing in the range from 30 to 120 Hz. The fundamental frequency of the SG under the free boundary condition is 349.2 Hz showing a bending mode, and the results between the test and the analysis have a good agreement with maximum 7 ％ in error It is also found that the FE analysis model of the OHT SGs to analyze an impact, a buckling and vibration et al. has been generated with reliability.

• 한국소음진동공학회논문집
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• 제18권7호
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• pp.725-731
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• 2008

This paper focused on the application of finite element model updating technique to evaluate the structural properties of the reinforced concrete specimen using the data collected from shaking table tests. The specimen was subjected to six El Centre (NS, 1942) ground motion histories with different peak ground acceleration (PGA) ranging from 0.06 g to 0.50 g. For model updating, flexural stiffness values of structural members (walls and slabs) were chosen as the updating parameters so that the converged results have direct physical interpretations. Initial values for finite element model were determined from the member dimensions and material properties. Frequency response functions (i.e. transfer functions), natural frequencies and mode shapes were obtained using the acceleration measurement at each floor and given ground acceleration history. The weighting factors were used to account for the relative confidence in different types of Inputs for updating (j.e. transfer function and natural frequencies) The constraints based on upper/lower bound of parameters and sensitivity-based constraints were implemented to the updating procedure in this study using standard bounded variable least-squares(BVLS) method. The veracity of the updated finite element model was investigated by comparing the predicted and measured responses. The results indicated that the updated model replicates the dynamic behavior of the specimens reasonably well. At each stage of shaking, severity of damage that results from cracking of the reinforced concrete member was quantified from the updated parameters (i.e. flexural stiffness values).

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2002년도 춘계학술대회논문집
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• pp.694-699
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• 2002

As the demand for slim laptops requires ion'-height optical disc drives, vibration problems of optical disc drives are of great concern. Additionally, with the decrease of a track width and a depth of focus in high density drives, studies on vibration resonance between mechanical parts become more important. From the vibration point of view, the performance of optical disc drives is closely related with the relative displacement between a disc and an objective lens which is controlled by servo mechanism. In other words, to read and write data properly, the relative displacement between an optical disc and an objective lens should be within a certain limit. The relative displacement is dependent on not only an anti-vibration mechanism design but also servo control capability. Good servo controls can make compensation for poor mechanisms, and vice versa. In a usual development process, robustness of the anti-vibration mechanism is always verified with the servo control of an objective lens. Engineers partially modify servo gain margin in case of a data reading error. This modification cannot correct the data reading error occasionally and the mechanism should be redesigned more robustly. Therefore it is necessary to verify a mechanism with respect to the possible servo gain plot. In this study we propose the experimental verification method far anti-vibration mechanism with respect to the existing servo gain plot. This method verifies axial vibration characteristics of optical disc drives on the basis of transmissibility. Using this method, we verified our mechanism and modified the mechanism for better anti-vibration characteristics.

• 한국소음진동공학회논문집
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• 제12권11호
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• pp.833-839
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• 2002

As the demand for slim laptops requires low-height optical disc drives, vibration problems of optical disc drives are of great concern. Additionally, with the decrease of a track width and a depth of focus in high density drives, studies on vibration resonance between mechanical parts become more important. From the vibration point of view, the performance of optical disc drives is closely related with the relative displacement between a disc and an objective lens which is controlled by servo mechanism. In other words, to read and write data properly, the relative displacement between an optical disc and an objective lens should be within a certain limit. The relative displacement is dependent on not only an anti-vibration mechanism design but also servo control capability. Good servo controls can make compensation for poor mechanisms, and vice versa. In a usual development process, robustness of the anti-vibration mechanism is always verified with the servo control of an objective lens. Engineers partially modify servo gain margin in case of a data reading error. This modification cannot correct the data reading error occasionally and the mechanism should be redesigned more robustly. Therefore it is necessary to verify a mechanism with respect to the possible servo gain plot. In this study we propose the experimental verification method for anti-vibration mechanism with respect to the existing servo gain plot. Thismethod verifies axial vibration characteristics of optical disc drives on the basis of transmissibility. Using this method, we verified our mechanism and modified the mechanism for better anti-vibration characteristics.

• 한국산학기술학회논문지
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• 제21권6호
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• pp.218-226
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• 2020

해상풍력터빈 하부구조물은 중요한 기능의 수행, 접근성의 제약 등으로 인하여 건전성 모니터링을 통한 효과적 유지관리가 필요하다. 본 연구에서는 해상풍력터빈 트라이포드 하부구조물의 건전성 모니터링을 위한 기저모델개선 및 결함추정 기법을 실험적으로 연구한다. 우선 하부구조물 건전성 모니터링을 위한 절차를 제안한 후 이 과정을 트라이포드 하부구조물 축소모형에 대하여 적용한다. 즉, 축소모형에 대한 초기 기저모델을 수치적으로 수립한 후 모드특성을 추정하고, 건전상태 진동실험 결과로부터 구한 고유주파수와 모드형상을 기준으로 기저모델을 개선하는데, 이때 구조물의 경계조건을 고려하고 신경망기법을 이용한다. 이후, 개선된 기저모델을 이용하여 신경망의 훈련패턴을 생성하고, 손상상태 진동실험 결과로부터 구한 모드특성을 훈련된 신경망에 입력함으로써 결함을 추정한다. 유효고정부 모델을 이용하여, 건전상태에서 측정된 모드특성에 맞추어 합리적으로 기저모델을 수립할 수 있었다. 또한, 축소모형에 대한 손상실험을 수행하였는데, 4가지 손상경우에 대하여 손상을 추정한 결과, 합리적으로 손상위치를 추정할 수 있었으며, 실제 손상정도가 심해질수록 손상정도 추정치도 증가하였다. 그러나 손상정도가 상대적으로 미소한 경우, 해당 손상위치가 판정은 되지만 다른 위치와 비교하여 확실한 손상위치의 식별이 어려웠다. 향후, 이러한 미소손상 추정 및 손상정도 추정치의 강성감소에 대한 정량화 등에 대한 후속연구가 수반된다면, 해상풍력터빈 트라이포드 하부구조물의 건전성 모니터링에 제안 기법을 효과적으로 활용할 수 있을 것으로 판단된다.

• 한국전자파학회논문지
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• 제12권1호
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• pp.18-26
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• 2001

본 논문에서는 압전체를 전기기계 압전파동방정식과 경계조건을 이용하여 고유치 제로 정식화하고, 3차원 유한요소법을 적용하여 초고주파 대역에서 동작하는 압전박막공진기의 공진모드 및 공진특성을 공진기의 입력 임피던스를 통하여 해석하였다. 이를 통하여 1차원 해석에서는 불가능하였던 공진기의 전극형상과 상, 하부 전극의 비대칭 구조에 따른 공진특성과 스퓨리어스특성을 추출하였다. 본 논문에서 제안한 방법으로 계산된 공진주파수를 Mason 등기모델 해석결과 및 실제 제작한 ZnO 압전박막공진기의 공진 특성과 비교한 결과 정확하게 일치함을 확인하였다. 또한 두께진동모드로 동작하기 위한 최적의 길이와 두께의 비가 20 : 1이고 최소한의 길이와 두께의 비가 5:1 이상임을 알 수 있었다.

• 한국지반공학회논문집
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• 제21권5호
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• pp.33-43
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• 2005

본 연구는 단부의 경계조건에 따른 매설관의 동적응답을 규명하기 위해 축방향 및 축직각방향에 대해서 자유진동과 강제진동 해석을 수행하였다. 각 경계조건에서의 모드형상을 결정한 후 고유진동수를 구하고, 이들을 이용하여 강제 진동시 발생하는 매설관의 축방향에 대해 변위, 변형률 산정식과 축직각방향에 대한 변위, 휨변형률 산정식을 유도하였다. 또한 가능한 모든 단부 경계조건의 매설관에 대해 최대응력이 발생하는 위치와 크기를 산정하였으며, 매설관의 동적거동에 영향을 가장 많이 발생시킬 수 있는 공진현상을 나타내는 모드수를 예측할 수 있는 식을 제안하였고 관 단부 경계조건이 매설관의 동적응답에 미치는 영향에 대한 규명과 관의 동적응답에 영향을 주는 매개변수들의 영향에 대해 규명하였다.

• 한국소음진동공학회논문집
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• 제18권9호
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• pp.961-971
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• 2008

In the design of a rotor shaft, care should be taken to minimize vibration by taking into account the sources of vibration. In addition, the intensity critical speed, stability, and other related aspects of the system must be considered. especially when it is operated at a critical speed, it is important to address issues related to vibration, as an increase in the whirling response of the rotor shaft can cause damage to the shaft, destruction of the rotor parts, and detrimental abrasions on the bearings. In this thesis, the vibration characteristics of a rotor shaft are investigated through the use of the finite element method. Variations of the diameters and lengths were used to determine the effect of a rotor shaft using Beam No.188(3D linear strain beam) in ANSYS version 11.0 as a universal interpretation program for finite elements. Special care was taken to prevent excessive vibration, which can result from resonance at the initial stage, in the formulation of a dynamic design for a rotor shaft through calculations while changing the diameters and the lengths of the shaft. Moreover, the dynamic characteristics of the critical speed, total mass, D/L(diameter to length) ratio, and natural frequency were verified. Furthermore, the rotor shaft applied by bearing element was calculated and compared by using Combi No. 214(2-D spring-damper bearing).

• 한국자동차공학회논문집
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• 제18권6호
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• pp.130-137
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• 2010

Due to test facility and specialty, it is physically difficult to conduct the modal tests of large-sized structures such as truck, bus and airplane. So, in case of a large-sized truck, the mode analysis on a full vehicle model comprised of reliable cabin, frame, and deck has been generally performed. However, the reliability of overall vibrational characteristics of the analytic model has not been fairly guaranteed by the testified models of each subsystem owing to the existence of cab suspension and the nonlinear mounting between a chassis frame and a special deck system. In this paper, a method to find out the modal characteristics of a large-sized military truck is presented. New modal test equipment is developed to set the boundary conditions of three military truck variants as close as a free-free condition. And the mode analysis method using coupled structure and dynamic models is established to consider the above-mentioned dynamic non-linearities of the vehicle itself. The usefulness of the suggested method is verified by comparing with the modal test results. Finally, the modal parameters of the final variant are extracted using the proved analytic method.

• 한국전산구조공학회논문집
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• 제30권1호
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• pp.39-46
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• 2017

본 논문에서는 반응표면법과 다목적최적화 기법을 이용한 유한요소모델개선기법의 절차를 제안하고 이를 저층의 철근콘크리트건물의 모델개선에 적용하였다. 대상건물은 전단벽 신설 및 댐퍼부착을 위한 부재의 강재보강을 통해 내진보강이 이루어진 건물로서 보강전후에 소형 가진기를 이용한 진동실험을 실시하여 동특성을 구하였다. 대상건물의 개선에 사용된 변수는 기존콘크리트, 신규타설된 콘크리트, 조적의 탄성계수, 신축줄눈부의 스프링계수, 강재보강된 부재의 유효강성비이다. 보강전후 건물의 초기모델을 구축한 후 중심합성법에 따라 개선변수의 값을 변화시키면서 얻은 해석결과를 통해 고유진동수의 오차와 모드형상의 오차를 나타내는 2개의 반응함수를 구하고, 이를 다목적최적화의 목적함수로 사용하였다.