• Transactions of the Korean Society for Noise and Vibration Engineering
• /
• v.13 no.5
• /
• pp.400-408
• /
• 2003

This paper investigates the vibration characteristics of steam generator (SG) U-tubes with defect. The operating SG shell-side flow field conditions for determining the fluidelastic instability parameters such as added mass are obtained from three-dimensional SG flow calculation. Modal analyses are performed for the U-tubes either with axial or circumferential flaw with different sizes. Special emphases are on the effects of flaw orientation and size on the modal and instability characteristics of tubes, which are expressed in terms of the natural frequency, corresponding mode shape and stability ratio. Also, addressed is the effect of the internal pressure on the vibration characteristics of the tube.

• Journal of KSNVE
• /
• v.8 no.6
• /
• pp.1130-1136
• /
• 1998

A modelling method for the vibration analysis of rotating cantilever plates with a concentrated mass is presented. The equations of motion for the rotating plates with a concentrated mass located in an arbitrary position are derived and transformed into a dimensionless form. For the mathematical modelling of the concentrated mass. a mass density Dirac delta function is used. The effects of concentrated mass and its location. angular speed. plate aspect ratio. and hub radius of the rotating plate on the natural frequencies are studied. Particularly. mode shape variations due to some parameter variations are investigated.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.20 no.7
• /
• pp.2174-2181
• /
• 1996

Equations of chordwise and flapwise bending motions of pretwisted rotatin cantilever beams are derived. The two motions are coupled to each other due to the pretwist angle of the beam cross section. As the angular speed, hub radius ratio, and pretwist angle vary, the vibration characteristics of the beam change. It is found that engenvalue loci veering phenomena and associated mode shape variations occur between two vibration modes due to the pretwist angle. The effect of the pretwist angle on the critical angular speed is also investigated.

• Proceedings of the KSME Conference
• /
• 2001.11a
• /
• pp.495-500
• /
• 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.

• Journal of Mechanical Science and Technology
• /
• v.16 no.3
• /
• pp.320-326
• /
• 2002

A modeling method for the vibration analysis of rotating composite cantilever plates is presented in this paper. The coupling effects between inplane motions and the bending motion are considered and explicit mass and stiffness matrices are derived for the modal analysis. Numerical results are obtained and some of them are compared to those of a commercial program to confirm the accuracy of the present method. Numerical results show that the coupling effects become important only when laminates are stacked up unsymmetrically. Incidentally, natural frequencies loci veering, loci crossing, and associated mode shape variations are observed.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2002.11a
• /
• pp.390.1-390
• /
• 2002

In this study, we investigate the plugging effect on the CE type steam generator tube. The natural frequency and mode shape will be changed due to decrease of the effective mass distribution along the tube. We compared the variation of stability ratio for plugged tube with that fur unplugged one. The natural frequency increased because of removing the cooling water inside the steam generator tube, but the stability ratio decreased inversely because of changing the vibrational mode shape. We also investigated the turbulent excitation effect.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2001.11b
• /
• pp.1394-1399
• /
• 2001

The purpose of this paper is that investigates the dynamic behavior characteristic of W.T.S(Wind Turbine System) and carries out the evaluation analysis during operating W.T.S. To investigate the dynamic behavior characteristic of W.T.S. the experiments to measure vibration of the blade from the attached accelerometer on the flap and edge section of the blade that is one of the most important elements of dynamic characteristic of W.T.S are performed. Natural frequency and mode shape are calculated with commercial program (STAR MODAL) using the measured vibration acceleration that receives the signal with F.F.T Analyzer from the accelerometer. For validation of these experiments. the finite element analysis is performed with commercial F.E.M Program (ANSYS) on the basis of the natural frequency and mode shape. The results indicate that experimental values have good agreements with the finite element analysis.

• Transactions of the Korean Society of Mechanical Engineers
• /
• v.18 no.8
• /
• pp.1899-1909
• /
• 1994

This work presents the experimental and FEM results for the free vibration of cantilevered, symmetrically and antisymmetrically laminated composite rectangular plates. The natural frequencies, mode shapes and contour plots of a number of CFRP, GFRP, DFRP-Aluminum, GFRP-Aluminum and DFRP-GFRP hybrid composite plates are experimentally obtained. Determination of Young's modulus and test procedures are described. The natural frequencies are determined for a wide range of parameters : e.g. , composite material constants, fiber angles and stacking sequences. Natural frequency and nondimensional frequency parameter results are compared with the finite element analysis and existing literatures. Agreement between experimental and calculated frequencies is excellent. The effects of varing the parameters upon the free vibration frequencies and mode shapes are discussed.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2007.11a
• /
• pp.1455-1458
• /
• 2007

Vibration characteristics of concrete slabs were investigated using a 1:10 scale model and finite element method. A 1:10 scale model of a test building with 150 and 200mm slab thicknesses was made of acrylic materials. Modal test was conducted to investigate mode shape and modal frequencies. Results show that the mode shapes of two slabs with different thickness are similar each other, whereas natural frequency is different. Through modal analysis using FEM, it was revealed that both mode shapes and natural frequencies calculated from the FEM model are similar to those of the scale model measurement. It was also found that natural frequencies increased with increment of the slab thickness.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2008.11a
• /
• pp.49-53
• /
• 2008

This study deals a way to reduce the transformer noises. The first step is to identify the source of the transformer noises. The second step is obtaining the vibration characteristics of transformer; its natural frequencies and mode shapes. Based on these information, an method to reduce the vibration of transformer can be found. The cause of transformer noises is mainly due to the magnetostrictive vibration of a core which is made of ferromagnetic substances. It is well known that the magnetostrictive vibration of a core is unavoidable, and a way to reduce the transformer noise by structural design is needed. It requires understanding the vibration characteristics. The natural frequencies and the mode shapes of transformer are analyzed by performing the modal testing.