• Proceedings of the Earthquake Engineering Society of Korea Conference
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• 2001.04a
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• pp.387-393
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• 2001

Installing vibration control devices in the structure rises as a solution instead of increasing structural strength considering construction cost. Especially, viscoelastic dampers show excellent vibration control performance at low cost and are easy to install in existing structures compared with other control devices. Therefore, cost-effectiveness of structure with viscoelastic dampers needs to be evaluated. Previous cost-effectiveness evaluation method for the seismically isolated structure(Koh et al., 1999;2000)is applied on the building structure with viscoelastic dampers, which combines optimal design and cost-effectiveness evaluation for seismically isolated structures based on minimum life-cycle cost concept. Input ground motion is modeled in the form of spectral density function to take into account acceleration and site coefficients. Damping of the viscoelastic damper is considered by modal strain energy method. Stiffness of shear building and shear area of viscoelastic damper are adopted as design variables for optimization. For the estimation of failure probability, transfer function of the structure with viscoelastic damper for spectral analysis is derived from the equation of motion. Results reveal that cost-effectiveness of the structure with viscoelastic dampers is relatively high in how seismic region and stiff soil condition.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.19 no.2 s.72
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• pp.213-219
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• 2006

Topology optimization problem requires numerous repeated evaluations of objective function and design sensitivity for elements within design domain with various density distributions. The recently proposed two-level condensation scheme(TLCS) is very promising for the construction of reduced system and for an accurate and efficient analysis concerned about eigenvalue and dynamic problems. We used the two-level dynamic condensation scheme for the analysis and sensitivity computation part in the structural topology optimization problem. The results of the topology optimization for the reduced system show the TLCS provides high accuracy and computation efficiency compared to the full scale system within engineering accuracy.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.21 no.8
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• pp.714-719
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• 2011

This paper presents vibration characteristics of magnetorheological(MR) elastomer, whose elastic modulus are controllable by applied magnetic field. By using this property, the material can be applied to vibration absorber, so that the stiffness of the absorber can be changed and actively controlled according to the magnetic flux density. However, the various performances of MR elastomer depends on different polarized direction of particles by applied magnetic field and dimension during the manufacturing process. In this paper, in order to obtain the optimal characteristics of MR elastomer, MR elastomers with different types and dimensions are prepared for a series tests. Using this test setup, extent of natural frequency shifted against magnetic field at various excitation frequencies can be measured. Specimens are prepared with 3 types, as cylinder samples exposed to magnetic field vertically, horizontally and unexposed during cure, respectively. Also, a set of design variables are considered to produce MR elastomers. Through the modal tests of mass structure with MR elastomer, the optimal design as well as the polarization direction of MR elastomer is obtained among the various dimensions and 3 directional types of MR elastomers.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1997.10a
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• pp.568-571
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• 1997

The overall aim of this paper is to determine coupling loss factor using loss factor and structural loss factor. For this purpose, two kinds of loss factor were adopted. One is loss factor of each sub structure, another is structural loss factor based on the complex welded or assembled structure. Using these two parameters, it is possible to derive the coupling loss factor which represent characteristic condition of SEA theory. Coupling loss factor of conjunction in complex structure was expressed as power balance equation. The derived equation for a coupling loss factor has been simplified on the assumption of one directional power flow between two sub structures. Using these conditions, it is possible to find the coupling loss factor equation. The comparison between theory of power transmission on conjunction and above equation, show a good agreement in simple beam structure. To check the effectiveness of above equation, it was adopted rotary compressor. Rotary compressor has three main conjunctions between shell and internal vibration part. This equation was applied to find out the optimum welding point with respect to reduce the noise propagation. It shows the effective tool to evaluate the coupling loss factor in complex structure.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.14 no.5
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• pp.370-376
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• 2004

The overall aim of this paper is to determine coupling loss factor of welding point between shell and cylinder using loss factor and structural loss factor. For this purpose, two kinds of loss factor were adopted. One is loss factor of each sub structure, another is structural loss factor based on the complex welded or assembled structure. Using these two parameters, it ispossible to derive the coupling loss factor which represent characteristic condition of SEA theory. Coupling loss factor of conjunction in complex structure was expressed as power balance equation. The derived equation for a coupling loss factor has been simplified on the assumption of one way (uni-directional) power flow between multi-sub structures. Using these conditions, it is possible to find the equation of coupling loss factor expressed as above two loss factors. To check the effectiveness of above equation, this paper used two-stage application. The first approach was application between simple cylinder and shell. The next was adopted rotary compressor. Rotary compressor has three main conjunctions between shell and internal vibration part. This equation was applied to find out the optimum welding point with respect to reduce the noise propagation. It shows the effective tool to evaluate the coupling loss factor in complex structure

• Journal of Mechanical Science and Technology
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• v.17 no.5
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• pp.679-690
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• 2003

As the rate of increase in areal density of the HDD has accelerated, dynamic characteristics of the HDD actuator need to be improved with respect to the performance of the tracking servo and shock transmission. Therefore, it is important to analyze the vibration characteristic of the HDD actuator that consists of the VCM part, E-block and pivot bearing. In this paper, vibration modes of the HDD actuator are investigated the using finite element and experimental modal analyses methods. To develop a detailed finite element model, finite element models of each components of the actuator assembly are constructed and tuned to the results of the EMA. The VCM coil is modeled as an equivalent finite element model that has an orthotropic material property using auto-model updating program. Auto-model updating program with improved sensitivity based iterative method is applied to build a detailed finite element model using the result of the EMA. A detailed finite element model of the HDD actuator is then constructed and analyzed.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2011.04a
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• pp.752-757
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• 2011

This paper presents vibration characteristics of magnetorheological (MR) elastomer, whose elastic modulus are controllable by an applied magnetic field. By using this property, the material can be applied to vibration absorber, so that the stiffness of the absorber can be changed and actively controlled according to the magnetic flux density. However, the various performances of MR elastomer depends on different magnetically polarization direction and dimension during the manufacturing process. In this paper, in order to obtain the optimal characteristics of MR elastomer, MR elastomers with different types and dimensions are prepared for a series tests. Using this test setup, extent of natural frequency shifted against magnetic field at various excitation frequencies can be measured. Specimens prepared with 3 types which are exposed to magnetic field vertically, horizontally and unexposed during cure. Also, a set of design variables are considered to produce MR elastomers. Through the modal tests of mass structure with MR elastomer, the optimal design as well as the polarization direction of MR elastomer is obtained among the various dimensions and 3 directional types of MR elastomers.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.24 no.5
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• pp.390-398
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• 2014

Heavy-weight floor impact noise is directly related to the impact source and floor vibration property. Dynamic properties of the standard floating floor that is used in Korea was investigated using accelerance, acceleration energy spectral density(ESD), and structural modal test. In the standard floating floor, natural frequency was decreased by the finishing mortar mass and the damping ratio was increased. Bang-machine force spectrum acting on the concrete slab can be calculated using inverse system analysis. Impact force acting on concrete slab is changed by interaction of finishing mortar and resilient material. The amplitude of the bang-machine force spectrum was amplified in low frequency range(below 100 Hz), and over 100 Hz was decreased. Changed force spectrum influence to the response of structure vibration, so the heavy-weight floor impact noise level was changed.

• Journal of Theoretical and Applied Mechanics
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• v.2 no.1
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• pp.1-14
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• 1996

In this paper, breaking waves are generated in a 2-D wave tank and simulated by using a higher-order boundary element method. A piston-type wavemaker is operated by signals composed of elementary waves. The phase of elementary waves is determined by the linear theory such that they are focused to a prescribed position. Calculated plunging waves coincide well with experiment. A steel box with different plate thicknesses is installed at a predetermined position in the tank. Measured impulsive pressures due to breaking waves are found to be 0.8-1.2$\rho$C2, where $\rho$ corresponds to water density and C to wave celerity. The transverse displacement of the plate is described in terms of modal eigenfunctions. The natural frequencies measured by impact tests in air for thin plate coincide with the computational and theoretical values. The radiationpotential due to plate vibration is derived and the radiation force is expressed in terms of hydroelastic added mass and damping forces. Comparison of natural frequencies of plate in water proves that hydroelastic added mass and damping are properly considered. The measured strain due to regular waves supports the calculated one, but there are apparent discrepancies between theory and experiment in the impulsive case.

• Wind and Structures
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• v.7 no.2
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• pp.107-130
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• 2004

This paper presents a time-domain approach for analyzing nonlinear random vibrations of long-span suspended cables under transversal wind. A consistent continuous model of the cable, fully accounting for geometrical nonlinearities inherent in cable behavior, is adopted. The effects of spatial correlation are properly included by modeling wind velocity fluctuation as a random function of time and of a single spatial variable ranging over cable span, namely as a one-variate bi-dimensional (1V-2D) random field. Within the context of a Galerkin's discretization of the equations governing cable motion, a very efficient Monte Carlo-based technique for second-order analysis of the response is proposed. This procedure starts by generating sample functions of the generalized aerodynamic loads by using the spectral decomposition of the cross-power spectral density function of wind turbulence field. Relying on the physical meaning of both the spectral properties of wind velocity fluctuation and the mode shapes of the vibrating cable, the computational efficiency is greatly enhanced by applying a truncation procedure according to which just the first few significant loading and structural modal contributions are retained.