• Proceedings of the Korean Society of Precision Engineering Conference
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• 1995.10a
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• pp.1000-1004
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• 1995

In the case of the external cylindrical grinding machine, the grinding mechanism can cause a wheel to vibrate due to a wheel cutter. This phenomena will bring about the unsymmetric wear up to high frequency without any relation of rotational speed. So far, when the grinding spindle is analyzed, it is assumed that a wheel is considered as lumped mass at the endof a beam. Nowadays, there is a tendency to use the wheel with a lsrge diameter or CBN wheel to achieve the high speed and accuracy grinding performance. Therefore, this kind of assumption is no longer valid. At the analysis of the grinding spindle, the parameter which dapends on the dynamic characteristics is a combination force between each part. For example, there is the tightness torque of a bolt and taper element in the grindle. In addition, the material property of the wheel can contribute the dynamic characteristics. This paper shows the mode participation of the shell mode of the wheel in the grindle and the dynamic characteristics according to the parameters which are the configuration of the flange and tightness torque of a bolt and taper. Modal parameter of the wheel, flange and the spindle can be extracted through frequency response function obtained by modal test. After that, by changing the tightness torque and kinds of wheel, we could accomplish the test in the whole combined grinding spindle. To perform modal analysis of vibration characteristics in the grinding spindle, we could develop the model of finite element method.

• International Journal of Ocean System Engineering
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• v.1 no.1
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• pp.1-8
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• 2011

Ocean structures and vehicles are exposed to severe ocean environment conditions such as waves, winds and currents. When such ocean structures and vehicles are designed, an accurate structure analysis is required to keep the system safely. Hydro-elastic analysis is one of key issues to design such structures and vehicles. In many previous investigations, numerical analyses for hydro-elastic problem have been used. In this study, an experimental analysis is carried out and the circular cylindrical shell is considered. Dynamical characteristics for a circular cylindrical shell are identified by experimental vibration analysis in air and water. The natural frequencies and mode shapes are compared in air and water to obtain hydro-elastic effects. Some interesting results are found in the variation of natural frequencies and damping ratios of the circular cylindrical shell for different water contact depths.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.29 no.2
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• pp.132-151
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• 1993

The proposed method in this paper. termed the substructural reanalysis technique, utilizes the computational merits of the component mode synthesis technique and of reanalysis technique for the design sensitivities of the dynamic characteristics of substructurally combined structure. It is shown that the dynamic characteristics of the entire structure can be obtained by synthesizing the substructural eigensolution and the characteristics of the eigensolution for the design variables of the modifiable substructure. In this paper , the characteristics of the eigenvalue problems obtained by this proposed method are compared to exact eigensolution in terms of accuracy and computational efficiency. and the advantage of this proposed method as compared to the direct application of the whole structure and experimental results is demonstrated through examples of numerical calculation for the dynamic characteristics (natural frequencies and mode shapes) of a flexible vibration of thin cylinderical shell with branch shell under 2-end fixed positions, boundary condition. Thin cylinderical shell of overall length 1280mm, external diameter 360mm, thickness 3mm with branch shell is made of mild steel. The load condition for dynamic response in this paper is impulsive load of which magnitude is 10kgf, which have short duration of 0.1 sec. and time interval applied to calculate. $\Delta$T is 1.0$\times$10 super(-4) seconds.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2001.05a
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• pp.668-674
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• 2001

An experimental study was performed for two types of co-axial cylindrical shell structures in order to establish the relationship between in-air dynamic characteristics and in-water ones and to observe hydrodynamic mass effects on their mode shapes when submerged. The outer cylinders are prepared with two kinds to get more insights on the fluid-structure interaction phenomena: one is flexible, which means that the outer cylinder has almost same stiffness as the inner one, and the other is a rigid one whose stiffness is more than ten times of the inner one's(it might be regarded as the scaled-down model of the reactor internals). The finite element. analyses were also implemented to support the experimental results. The results show that the natural frequencies of a co-axial cylindrical shell structure in water are remarkably lower than those in air due to the fluid mass effects. In case of the flexible-to-flexible cylinders, there exist in-phase and out-of-phase mode shapes and they are affected by the annular gap between the. co-axial cylinders. For the in-phase mode the in-water natural frequency decreases exponentially as the gap increases, while it slightly increases in case of the out-of-phase mode due to the squeezing effect of the gap fluid. In the flexible-to-rigid case, the normalized natural frequency(in-water frequency/in-air one) of the inner cylinder(core barrel model) ranges between in-phase and out-of-phase mode frequencies of the flexible-to-flexible co-axial cylindrical structure having identical dimensions. Also the normalized natural frequency of the inner cylinder of the flexible-to-rigid one moves from near of the in-phase mode frequency into the out-of-phase mode value of the flexible-to-flexible case as circumferential mode number(n) increases.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2000.06a
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• pp.831-836
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• 2000

In this study, the Rayleigh inextensional theory and extensional theory for thin shells was employed to predict the natural frequencies of the hemi-spherical shell with free and simply. supported boundary condition. The frequencies and mode shapes from theoretical calculation were compared with those of commercial finite element code, ANSYS. In order to validate the theory, modal test was also performed by impact test and FFT analysis. Modal test and FEM analysis of the free, simply supported and clamped boundary condition was also carried out.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2007.05a
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• pp.36-40
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• 2007

It uses a tank to store, purify and feed lube oil in power plants, which is made by steel plate. Several pumps to feed lube oil are installed on the top plate of the oil tank. In this case if pumps on the top plate are removed or added, the dynamic characteristics of the structure will be changed. In this paper, we present that we analyze in detail the similar case with a finite element model for tank & pump structure coupled with oil and that we set plan to change mode shapes on the top plate of the tank.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.12 no.2
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• pp.150-160
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• 2002

The free vibration characteristics of the triple cylindrical shells filled with fluid are investigated. The triple cylindrical shells are filled with compressible fluid. The boundary condition is clamped at both ends. Analytical method is developed to evaluate natural frequencies of triple cylindrical shells using Sanders' shell theory and courier series expansion by Stokes' transformation. Their results are compared with those of finite element method to verify the validation of the method developed. The modal characteristics of shells filled with fluid at region 1, 2 and 3 are evaluated.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2004.05a
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• pp.169-172
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• 2004

This paper proposes a new MR(magneto-rheological) brake utilizing composite modes of MR fluid. Its basic structure and design scheme are almost the same with the conventional MR brake, but for slots in a rotating disk or shell. The slots enable the proposed MR brake to use a new mode, so-called, ‘direct cutting chain mode’as well as shear mode, which results in increasing the braking force(almost 150% compared to the case without slots). Some experimental results show that the proposed MR brake provide the sufficient braking force to be adopted for small portable force feedback devices.

• Smart Structures and Systems
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• v.6 no.7
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• pp.767-792
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• 2010

In this paper, the optimal design of vibration control system for smart structures has been investigated semi-analytically via the optimization of geometric parameters like the placements and sizes of piezoelectric sensors and actuators (S/As) bonded on the structures. The criterion based on the maximization of energy dissipation was adopted for the optimization of the control system. Based on the sensing and actuating equations, the total energy stored in the system which is used as the objective function was analytically derived with design variables explicitly presented. Two cases of single and combined vibration modes were addressed for a simply supported beam and a simply supported cylindrical shell. For single vibration mode, the optimal distributions of the piezoelectric S/As could be obtained analytically. However, the Sequential Quadratic Programming (SQP) method has to be employed to solve those which violated the prescribed constraints and to solve the case of combined vibration modes. The results of three examples, which include a simply supported beam, a simply supported cylindrical shell and a simply supported plate, showed good agreement with those obtained by the Genetic Algorithm (GA) method. Moreover, in comparison with the GA method, the proposed method is more effective in obtaining better optimization results and is much more efficient in terms of computation time.

• Transactions of the Korean Society of Mechanical Engineers
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• v.10 no.6
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• pp.929-936
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• 1986

Free vibration characteristics of laminated orthotropic circular cylindrical shells with clamped free boundary condition are investigated. The solution is obtained through a direct solution procedure with axial mode displacements represented as simple Fourier series expressions. On the basis of the thin shell theories of Sanders, Love, Loo, Morley and Donnell, the 4*$ frequency determinant is derived and is expressed in a unified form. Various numerical examples determining the natural frequencies of circular cylindrical shells with isotropic material and also with layers of orthotropic elastic material arbitraily laminated either symmetrically or anti-symmetrically about the shell middle surface. The results obtained compared very well with some available experimental and numerical results.