• 한국공간구조학회논문집
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• 제18권3호
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• pp.75-82
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• 2018

Large space structures exhibit different natural vibration characteristics depending on the aspect ratio of structures such as half-open angle. In addition, since the actual large space structure is mostly supported by the lower structure, it is expected that the natural vibration characteristics of the upper structure and the entire structure will vary depending on the lower structure. Therefore, in this study, the natural vibration characteristics of the dome structure are analyzed according to the natural frequency ratio by controlling the stiffness of the substructure. As the natural frequency of the substructure increases, the natural frequency of the whole structure increases similarly to the natural frequency of the upper structure. Vertical vibration modes dominate at $30^{\circ}$ and $45^{\circ}$, and horizontal vibration modes dominate at $60^{\circ}$ and $90^{\circ}$.

• 한국원자력학회:학술대회논문집
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• 한국원자력학회 1997년도 춘계학술발표회논문집(2)
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• pp.503-508
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• 1997

The effect of rotary inertia of concentrated masses on the natural vibration of the simply supported-simply supported fluid conveying pipe has been studied. For the analysis Galerkin's method is used fer transformation of the governing equation to the eigenvalue problem and the natural frequencies and mode shapes for the system have been found. Introduction of rotary inertia results in lots of change on the natural frequencies and mode shapes and its effect is highly noticed at the higher natural frequencies and mode shapes. Consideration of rotary inertia results in much decrease on the natural frequencies and its neglect could lead to erroneous results.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2002년도 추계학술대회논문초록집
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• pp.353.1-353
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• 2002

Impulse response of a slightly asymmetric cylindrical shell is derived. Receptance method is applied to obtain the vibration mode and natural frequency of the slightly asymmetric cylindrical shell. Impulse response model is used to identify the vibration beat characteristics of King Song-Dok Bell. The theretical mode is compared and verified by the measured mode of King Song-Dok Bell. (omitted)

• 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.

• 한국공작기계학회:학술대회논문집
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• 한국공작기계학회 1997년도 추계학술대회 논문집
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• pp.114-119
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• 1997

Natural vibration of the rotor system having multi-step cross-sections is analyzed. The rotary inertia and the shear deformation are considered. Torque is also included in order to simulate the power transmission system. The complex displacement and the variable separation are introduced. The exact solutions in uniform cross-section segment and the boundary conditions are used. Natural frequencies and mode shapes are obtained, especially the mode shapes are countinuous.

• 한국소음진동공학회논문집
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• 제22권4호
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• pp.358-364
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• 2012

This work dealt with dynamic characteristics of spur gear and helical gear system to understand the gear vibration and noise. To find out dynamic characteristics in the gear system, a finite element model and an analytic model for the gear system were used. Using the models, the natural frequency and mode-shape characteristics of spur gears and helical gears were calculated. Two models show that natural frequencies of helical gears were lower than those of spur gears. Mode-shape characteristics of gear pairs by analytical model and some issues of finite element modeling were also discussed. Impact test was used to validate the finite element model.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2002년도 춘계학술대회논문집
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• pp.423-428
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• 2002

A numerical method is presented to obtain natural frequencies and mode shapes of tapered beams with static deflections due to self-weight. The differential equation governing the free vibrations of beam taken into account the static deflection due to self-weight is derived and solved numerically. The hinged-hinged, clamped-clamped and clamped-hinged and clamped-free end constraints are applied in the numerical examples. As the numerical results, the lowest three natural frequencies versus distributed slenderness ratio and section ratio are reported in figures. And for the comparison purpose, the typical mode shapes with the effects of static deflection are presented in figures.

• 대한기계학회논문집A
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• 제20권9호
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• pp.2875-2886
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• 1996

This work present the experimental resutls for the free vibration of unstiffened, stiffened cylindrical shell filled with air, half water and full water. The natural frequencies and mode shapes of unstiffened, stiffened cylindrical shell are obtained experimentally also. The natural frequencies of stiffened cylindrical shell were generally highter than those of unstiffened cylindrical shell and natural requencies were decreased as cylindrical shell was filled with water. The effect of circumferential stiffener in the first mode was shown that natural frequency more increased 25% at air environment, 29% at half water environment and 37% at full water than those of unstiffened cylindrical shell, respectively. Also, the natural frequencies were decreased according to the added mass effect of fluid in the shell of unstiffened and stiffened cylindrical shell. The six mode shape results of all cases are simular and given. The natural frequencies are determined for a wide range of parameters : e.g. unstiffened shell, and filled with air, half and full water. The effects of varying the parameters on the free vibration frequencies and mode shapes are discussed.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2013년도 춘계학술대회 논문집
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• pp.816-821
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• 2013

This case study presents a practical method to reduce resonant vibration of generator-motor set. The generator is driven at 1800rpm by induction integral motor. The vibration is below alarm limits, but the dominant frequency of vibration is sub-synchronous and close to that of bearing fault signal in spite of new bearings. To find an mechanism of abnormal vibration, ODS and Modal analysis is carried out. The measured modal characteristics were compared with those of FE Analysis. The ODS mode at rated speed is consistent with system natural frequency mode that is excited by bearings. To reduce vibration level, the isolation mount at system base is changed with new rubber mount for lower natural frequency.

• Steel and Composite Structures
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• 제30권6호
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• pp.577-589
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• 2019

In this study, on-site testing was carried out to investigate the vibration performance of a composite steel-bar truss slab with steel girder system. Ambient vibration was performed to capture the primary vibration parameters (natural frequencies, damping ratios, and mode shapes). The composite floor possesses low frequency (< 10 Hz) and damping (< 2%). Based on experimental, theoretical, and numerical analyses on natural frequencies and mode shapes, the boundary condition of SCSC (i.e., two opposite edges simply-supported and the other two edges clamped) is deemed more reasonable for the composite floor. Walking excitations by one person (single excitation), two persons (dual excitation), and three persons (triple excitation) were considered to evaluate the vibration serviceability of the composite floor. The measured acceleration results show a satisfactory vibration perceptibility. For design convenience and safety, a crest factor ${\beta}_{rp}$ describing the ratio of peak acceleration to root-mean-square acceleration induced from the walking excitations is proposed. The comparisons of the modal parameters determined by ambient vibration and walking tests reveal the interaction effect between the human excitation and the composite floor.