• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2001년도 춘계학술대회논문집
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• pp.942-947
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• 2001

This paper provides a stability analysis of the transverse vibration of a spinning disk under the torque fluctuation from a permanent magnetic motor. An analytical model has been formulated for a flexible annular disk with its spinning velocity varying harmonically with the same frequency as the cogging torque. A perturbation method based on multiple time scales is applied to perform the stability analysis. Based on expressions for the amplitude and frequency of the parametric excitation, stability boundaries are determined in terms of a nominal spindle velocity, the least common multiple of poles and slots, the magnitude of torque fluctuation and the modal characteristics of. the disk. The stability diagrams predicted by perturbation have been verified numerically using the Floquet theory, which is in good agreement. In conclusion, the fluctuation in spinning velocity is found to affect the stability of the transverse vibration of a rotating disks. The results of this work can be applied to high precision spindle systems such as computer storage systems.

• 한국정밀공학회지
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• 제27권3호
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• pp.41-49
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• 2010

Two promising control candidates have been selected to test the sinusoidal reference tracking performance for a brush-type polishing machine having strong nonlinearities and disturbances. The controlled target system is an oscillating mechanism consisting of a common positioning stage of one degree-of-freedom with a screw and a ball nut driven by a servo motor those can be obtained commercially. Beside the strong nonlinearity such as stick-slip friction, the periodic contact of the polishing brush and the work piece adds an external disturbance. Selected control candidates are a Sliding Mode Control (SMC) and a variant of a feedback linearization control called Smooth Robust Nonlinear Control (SRNC). A SMC and SRNC are selected since they have good theoretical backgrounds, are suitable to be implemented in a digital environment and show good disturbance and modeling uncertainty rejection performance. It should be also noted that SRNC has a nobel approach in that it uses the position information to compensate the stickslip friction. For both controllers analytical and experimental studies have been conducted to show control design approaches and to compare the performance against the strong nonlinearity and the disturbances.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2003년도 추계학술대회
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• pp.1718-1723
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• 2003

This paper presents a computational method for deformation modes of a flexible body in multibody system from the experimental modal analysis and an efficient method for flexible multibody dynamic analysis by use of the modes. It is difficult to directly use experimental modal parameters in flexible multibody dynamic analysis. The major reasons are that there are many inconsistencies between experimental and analytical modal data and experimental noises are inherent in the experimental data. So two methods, such as, a method for ortho-normalization of experimental modes and the other one for mode expansion, are suggested to gain deformation modes of a flexible body from the experimental modal parameters. Using the virtual work principle, the equation of motion of a flexible body is derived. The effectiveness of the proposed method will be verified in the numerical example of cab vibration of a truck by comparing analysis and test results.

• 한국강구조학회 논문집
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• 제13권6호
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• pp.651-659
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• 2001

이 논문은 두 변수 탄성지반 위에 놓인 불연속 변단면 수평 곡선부재의 자유 진동에 관한 연구이다. 회전관성과 전단변형효과를 고려하여 두 변수 탄성지반 위에 놓인 변단면 수평 곡선부재의 자유진동을 지배하는 무차원 상미분방정식을 유도하였다. 변단면은 불연속 변단면으로 채택하였고, 회전-회전, 회전-고정 및 고정-고정의 단부조건을 갖는 원호형, 포물선형, 정현형, 타원형 곡선보의 고유진동수를 산출하였다. 수치해석의 결과로 무차원 고유진동수와 곡선부재의 변수들 사이의 관계를 표 및 그림에 나타내었으며 진동형의 예를 그림과 같이 나타내었다.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2011년도 추계학술대회 논문집
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• pp.124-129
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• 2011

An improved NDIF method is introduced to efficiently extract eigenvalues of two-dimensional, arbitrarily shaped acoustic cavities. The NDIF method, which was developed by the authors for the eigen-mode analysis of arbitrarily shaped acoustic cavities, membranes, and plates, has the feature that it yields highly accurate eigenvalues compared with other analytical methods or numerical methods (FEM and BEM). However, the NDIF method has the weak point that the system matrix of the NDIF method depends on the frequency parameter and, as a result, a final system equation doesn't take the form of an algebra eigenvalue problem. The system matrix of the improved NDIF method developed in the paper is independent of the frequency parameter and eigenvalues can be efficiently obtained by solving a typical algebraic eigenvalue problem. Finally, the validity and accuracy of the proposed method is verified in two case studies, which indicate that eigenvalues and mode shapes obtained by the proposed method are very accurate compared to the exact method, the NDIF method or FEM(ANSYS).

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2013년도 춘계학술대회 논문집
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• pp.528-532
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• 2013

본 연구에서는, 해석적 모델로 불규칙하게 분포된 질량을 가진 열탄성 댐핑을 포함하는 마이크로빔 구조물을 연구하였다. 마이크로 스케일의 기계적 공명체(mechanical resonator)에 대한 열탄성 댐핑의 중요성은 높은 Q-factor를 설계하는데 고려된다. 본 연구에서의 빔 모델은 Euler-Bernoulli 빔 이론을 기조로 한다. 빔의 고유 진동수를 결정하기 위하여, 에너지 기법이 적용되었다. 또한, 열탄성 댐핑 효과는 열전도 방정식을 사용할으로써 고려되었고, Q-factor가 결정될 수 있었다. 운동방정식의 유도에는 체계적인 무차원화를 수행하였다. 임의의 집중된 질량을 포함하는 열탄성 댐핑을 가진 마이크로빔에 대해 모델의 결과값을 입증하였고 mode shape과 Q-factor를 제시하였다.

• 대한기계학회논문집
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• 제10권5호
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• pp.724-734
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• 1986

본 연구에서는 타이어의 동적설계의 기초자료를 제시하는데 그 목적이 있다. 해석적 방법으로는 복합막트로이드 유한요소를 이용하여 타이어의 고유진동수 및 진동 모우드를 구하였으며, 그 정확성을 입증하기 위하여 멀디찬널 F.F.T.분소기를 이용한 실험적 결과 및 G.R. Potts의 해석결과와 비교하였다.

• 한국강구조학회 논문집
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• 제14권4호
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• pp.519-527
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• 2002

쉘 구조물은 지붕 구조물, 굴뚝 구조물, 압력구조물, 선박구조물, 항공구조물 등에 널리 사용되는 구조물이다. 본 논문은 전단변형 효과를 고려한 비등방성 복합성층 원뿔형 쉘의 자유진동에 관하여 연구하였다. 복합재료는 2개 또는 이상의 재료들로 구성되어 구조적인 효율성을 증진시키도록 구성된 재료이다. 이러한 복합재료로 구성된 구조물의 거동은 매우 복잡하기 때문에 해석해를 구하기가 거의 불가능하다. 따라서 본 연구에서는 이러한 복합재료로 구성된 원뿔형 쉘의 자유진동을 해결하는데 유한차분법을 사용하였다. 중심각, 정점각 및 다른 기하학적 파라미터의 진동에 대한 효과를 연구하였고, 진동모드 형상을 예시함으로서 진동모드에 관한 물리적 및 공학적인 이해를 증진시키고자 하였다.

• 한국소음진동공학회논문집
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• 제15권5호
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• pp.604-611
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• 2005

The relationship between floor impact sound and vibration has been studied by field measurements, and the vibration modal characteristics have been analyzed. Vibration levels impacted by a standard heavy-weight impact source have been predicted according to the main design parameters using finite element method. Experimental results show that the dominant frequencies of the heavy impact sounds range below 100 Hz and that they are coincident with natural frequencies of the concrete slab. In addition, simple 2-dimensional finite element models are proposed to substitute 2 types of 3-dimensional models of complicated floor structural slabs those by The analytical result shows that the natural frequencies from first to fifth mode well correspond to those by experiments with an error of less than $12\%$, and acceleration peak value iscoincident with an error of less than $2\%$. Using the finite element model. vibration levels areestimated according to the design Parameters, slab thickness, compressive strength, and as a result, the thickness is revealed as effective to increase natural frequencies by $20\~30\%$ and to reduce the vibration level by 3$\~$4 dB per 30 mm of extra thickness.

• 한국소음진동공학회논문집
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• 제22권11호
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• pp.1144-1151
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• 2012

A damage in structure alters its dynamic characteristics. The change is characterized by changes in the modal parameter, i.e., modal frequencies, modal damping value and mode shape associated with each modal frequency. Changes also occur in some of the structural parameters; namely, the mass, damping, stiffness matrices of the structure. In this paper, evaluation of changes in stiffness matrix of a structure is presented as a method not only for identifying the presence of the damage but also locating the damage. It is shown that changed stiffness matrix can be accurately estimated a sensitivity coefficient matrix derived from modifying mode shapes, First, with 4 story shear structure models, the effect of presence of damage in a structure on its stiffness matrix is studied. By using these analytical model, the effectiveness of using change of stiffness matrix in detecting and locating damages is demonstrated. To validate the predicted changing stiffness and its location, the obtained results are compared to the reanalysis result which shows good agreement.