• Transactions of the Korean Society of Automotive Engineers
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• v.20 no.3
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• pp.119-125
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• 2012

Caliper intergrated Electric Parking Brake (EPB) is an automatic parking brake system, attached to rear caliper. Because EPB uses luxury vehicles recently, the drivers of vehicles are sensitive to the EPB noise. EPB is operated by the motor and gear, so noise is generated by motor and gear. In order to reduce noise, One of EPB manufacturers uses helical gear and changes the shape of EPB housing. But these methods are not optimized for reduction of interior noise. There are many noise transfer paths into vehicle interior and it is difficult to identify the noise sources. Therefore, in this study, we performed contribution analysis and modal testing in the vehicle system. It is possible to distinguish between air-borne noise and structure-borne noise in the vehicle interior noise by comparing interior noise peak with resonance mode map.

• International Journal of Naval Architecture and Ocean Engineering
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• v.8 no.2
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• pp.127-136
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• 2016

Springing is the resonance phenomenon of a ship hull girder with incoming waves having the same natural frequency of the ship. In this study, a simple and reliable calculation method was developed based on quadratic strip theory using the Timoshenko beam approach as an elastic hull girder. Second-order hydrodynamic forces and Froude-Krylov forces were applied as the external force. To improve the accuracy of the strip method, the variation in the added mass along the ship hull longitudinal direction, so called tip-effect, was considered. The J-factor was also employed to compensate for the effect of three-dimensional fluid motion on the two-node vibration of the ship. Using the developed method, the first- and second-order vertical bending moments of the Flokstra ship were compared. A comparative study was also carried out for a uniform barge ship and a 10,000 TEU container ship with the respective methods including the J-factor and tip-effect.

• Transactions of the Korean Society of Mechanical Engineers
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• v.16 no.9
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• pp.1711-1721
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• 1992

A nonlinear dissipative dynamical system can often have multiple attractors. In this case, it is important to study the global behavior of the system by determining the global domain of attraction of each attractor. In this paper we study the global behavior of a forced beam with two mode interaction. The governing equation of motion is reduced to two second-order nonlinear nonautonomous ordinary differential equations. When .omega. /=3.omega.$_{1}$ and .ohm.=.omega $_{1}$, the system can have two asymptotically stable steady-state periodic solutions, where .omega./ sub 1/, .omega.$_{2}$ and .ohm. denote natural frequencies of the first and second modes and the excitation frequency, respectively. Both solutions have the same period as the excitation period. Therefore each of them shows up as a period-1 solution in Poincare map. We show how interpolated mapping method can be used to determine the two four-dimensional domains of attraction of the two solutions in a very effective way. The results are compared with the ones obtained by direct numerical integration.

• The Transactions of the Korean Institute of Electrical Engineers B
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• v.49 no.5
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• pp.305-312
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• 2000

This study deals with the dynamic response of a rotor in Switched Reluctance Motor(SRM) caused by the unbalance force such as the unbalanced mass and electromagnetic force. The method to analyze the mechanical response of the rotor supported on the bearing is based on an extension of the 3-dimensional Transfer Matrix Method(TMM) coupled with the electromagnetic force calculated by Maxwell stress tensor. The displacement of the rotor as a function of frequency according to the position of the unbalanced mass is evaluated from the frequency response function (FRF). The rotor behaviour with the electromagnetic force is compared with that without the electromagnetic force. In addition, the resonance speeds and the vibration modes are analyzed and demonstrated in this paper. These results are useful in designing the mechanical rotor and in balancing properly the rotor to reduce vibration and noise.

• Korean Journal of Materials Research
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• v.31 no.1
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• pp.43-53
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• 2021

Dynamic behavior of piezoelectric ZnO nanowires is investigated using finite element analyses (FEA) on FE models constructed based on previous experimental observations in which nanowires having aspect ratios of 1:2. 1:31, and 1:57 are obtained during a hydrothermal process. Modal analyses predict that nanowires will vibrate in lateral bending, uniaxial elongation/contraction, and twisting (torsion), respectively, for the three ratios. The natural frequency for each vibration mode varies depending on the aspect ratio, while the frequencies are in a range of 7.233 MHz to 3.393 GHz. Subsequent transient response analysis predicts that the nanowires will behave quasi-statically within the load frequency range below 10 MHz, implying that the ZnO nanowires have application potentials as structural members of electromechanical systems including nano piezoelectric generators and piezoelectric dynamic strain sensors. When an electric pulse signal is simulated, it is predicted that the nanowires will deform in accordance with the electric signal. Once the electric signal is removed, the nanowires exhibit a specific resonance-like vibration, with the frequency synchronized to the signal frequency. These predictions indicate that the nanowires have additional application potential as piezoelectric actuators and resonators.

• Korean Journal of Optics and Photonics
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• v.16 no.3
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• pp.266-274
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• 2005

We have designed photonic crystal based bandpass filters whose characteristics are suitable for WDM communication system. The filters consist of coupled point defect resonators in two-dimensional photonic crystal. The frequency response of coupled resonators has been analyzed by the coupling of modes in time, from which the design parameters for the coupled resonator filters have been extracted. For the appropriate choice of the design parameters, each resonator is treated as a lumped L-C resonance circuit, and from the analogy between the equivalent circuit and the standard L-C filter circuits, the design parameters are simply determined from the table for general filter circuit design. Based on the determined design parameters, a photonic crystal based filter has been designed and its performance has been calculated using the finite-difference time-domain method. The designed filter shows a pass band of 50GHz and 0.5 dB in-band ripple, which is suitable for typical WDM communication systems with 100GHz channel spacing.

• Advances in aircraft and spacecraft science
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• v.3 no.1
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• pp.15-28
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• 2016

Although the aircraft industry was the first to use fibre composites, now they are increasingly used in a range of structural applications such as flooring, decking, platforms and roofs. Interlayer delamination is a major failure mode which threatens the reliability of composite structures. Delamination can grow in size under increasing loads with time and hence leads to severe loss of structural integrity and stiffness reduction. Delamination reduces the natural frequency and as a consequence may result in resonance. Hence, the study of the effects of delamination on the free vibration behaviour of multilayer composite structures is imperative. The focus of this paper is to develop a 3D FE model and investigate the free vibration behaviour of fibre composite multilayer sandwich panels with interlayer delaminations. A series of parametric studies are conducted to assess the influence of various parameters of concern, using a commercially available finite element package. Additionally, selected points in the delaminated region are connected appropriately to simulate bolting as a remedial measure to fasten the delamination region in the aim of reducing the effects of delamination. First order shear deformation theory based plate elements have been used to model each sandwich layer. The findings suggest that the delamination size and the end fixity of the plate are the most important factors responsible for stiffness reduction due to delamination damage in composite laminates. It is also revealed that bolting the delaminated region can significantly reduce the natural frequency variation due to delamination thereby improving the dynamic performance.

• Journal of the Korea institute for structural maintenance and inspection
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• v.17 no.3
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• pp.20-27
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• 2013

Simple Iteration Method for calculating the natural frequency is presented in this paper. This method is simple but exact method of calculating natural frequencies corresponding to the modes of vibration of beams and tower structures with irregular cross sections and arbitrary boundary conditions. This method consists of determining the deflected mode shape of the member due to the inertia force under resonance condition. Finite difference method is used for this purpose. The influence of the $D_{22}$ stiffness on the natural frequency is rigorously investigated. In this paper, the influence of the loading sizes, different cross section on the natural frequency of vibration of some structural elements is presented. This method extends to two dimensional problems including advanced composite material structures.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.27 no.3
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• pp.156-161
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• 2014

We have investigated the optical properties of plamonic waveguide with tapered structure based on InP material for photonic integrated circuit(PIC). The proposed plasmonic waveguide is covered with the Ag thin film to generate the plasmonic wave on metallic interface. The optical characteristics of plasmonic waveguide were calculated using the three-dimensional finite-difference time-domain method. The plasmonic waveguide was fabricated with the lengths of 2 to $10{\mu}m$ and the widths of 400 to 700 nm, respectively. The plasmonic mode and optical loss were measured. The optimum plasmonic length is $10{\mu}m$ and widths are 600 and 700 nm in the fabricated waveguide. This plasmonic waveguide can be directly integrated with other conventional optical devices and can be essential building blocks of PIC.

• Atmosphere
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• v.23 no.2
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• pp.205-220
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• 2013

Upper ocean response to typhoon Ewiniar (0603) and its impact on the following typhoon Bilis (0604) are investigated using observational data and numerical experiments. Data used in this study are obtained from the Ieodo Ocean Research Station (IORS), ARGO, and satellite. Numerical simulations are conducted using 3-dimensional Princeton Ocean Model. Results show that when Ewiniar passes over the western North Pacific, unique oceanic responses are found at two places, One is in East China Sea near Taiwan and another is in the vicinity of IORS. The latter are characterized by a strong sea surface cooling (SSC), $6^{\circ}C$ and $11^{\circ}C$ in simulation and observation, under the condition of typhoon with a fast translation speed (8m $s^{-1}$) and lowering intensity (970 hPa). The record-breaking strong SSC is caused by the Yellow Sea Bottom Cold Water, which produces a strong vertical temperature gradient within a shallow depth of Yellow Sea. The former are also characterized by a strong SSC, $7.5^{\circ}C$ in simulation, with a additional cooling of $4.5^{\circ}C$ after a storm's passage mainly due to enhanced and maintained upwelling process by the resonance coupling of storm translation speed and the gravest mode internal wave phase speed. The numerical simulation reveals that the Ewiniar produced a unfavorable upper-ocean thermal condition, which eventually inhibited the intensification of the following typhoon Bilis. Statistics show that 9% of the typhoons in western North Pacific are influenced by cold wakes produced by a proceeding typhoon. These overall results demonstrate that upper ocean response to a typhoon even after the passage is also important factor to be considered for an accurate intensity prediction of a following typhoon with similar track.