• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.24 no.6
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• pp.429-436
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• 2014

Most mechanical systems are now operating consistently and getting faster due to the development of automation systems. Peoples' dependence on machines have increased as when problems occur within the mechanical system, personal injury and production loss may come as a result, as most of the mechanical system's malfunctions are caused by the failure of the rotational bearing. What we need now is a maintenance system that can warn us when it detects abnormal conditions before significant damage occurs to the bearing. In this study, we have developed an acoustic emissions sensor that can figure if the bearing works under the normal condition. With this acoustic emissions sensor, we can inspect the bearing for defects by using the Heterodyne technique, which converts the ultrasound signal into audio, as a signal conditioning process.

• Proceedings of the Korea Contents Association Conference
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• 2009.05a
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• pp.169-172
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• 2009

In this paper, we propose the method to improving touch recognition using edge mask on a touched object at vision-based touchscreen. Because vision-based touchscreen recognizes touch using threshold simply, noise occur in fist or wrist in case of touch directly with hand, correct touch recognition was difficult. However, in this paper, we execute morphology and extract surrounding mask in object that approximate to touchscreen, use change of contrast for the mask. When we touch screen to use these dynamic information, prevent noise. The goal of this paper is when hand was touched on screen it can recognize to touch.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 1995.10a
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• pp.62-67
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• 1995

A method for determining impulsive responses and acoustic radiation for submerged shells of finite length has been presented. The method is a modal-based method, and uses a surface variational principle to obtain data in the frequency domain. The fast Fourier transform technique is used to convert the data to the time domain. The surface pressure responses of a cylindrical shell with endcaps wer compared with those of an infinite shell. It was shown that the surface pressures coincide exactly before any significant reflections from the endcaps occur. Traces of different types of waves were identified from the dispersion relations of the infinite shell. The contributions of flexural and longitudinal waves and these due to the direct radiation from the driving force to the fluid pressure were demonstrated using near-field plots. The exchange of energy between the shell and fluid was examined for shells with and without bulkheads. It was shown that a significant amount of the energy which enters the fluid returns to the shell and most of the energy is dissipated in the shell. It was also shown that the shell with bulkheads radiate significantly more energy into the far-field than the empty shell.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.26 no.1
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• pp.13-19
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• 2016

The flow-excited Helmholtz resonance phenomenon was investigated numerically using Reynolds averaged Navier-Stokes approach. The fundamental cause of the Helmholtz resonance phenomenon is known as shedding of a single discrete vortex from orifice edge that travels during one period of the oscillation. In this study, serrated deflector, which is biomimetic design of the owl's feather, is used to split a single vortex into small vortices. Rectangular deflector and serrated deflector are compared with numerical results of pressure and streamline inside the cavity. Consequently, the serration breaks the shedding period of vortex core and eliminates the resonance. Also, it changes the flow pattern in according to the location of different serration height. By making inflows and outflows occur simultaneously in spanwise direction in the cavity, the period of Helmholtz resonance disappears. Comparing between rectangular deflector and serrated deflector, the serrated deflector can deal with the Helmholtz resonance more effectively.

• Wind and Structures
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• v.24 no.4
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• pp.351-365
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• 2017

The minimization method is widely used to predict the dynamic characteristics of a system. Generally, data recorded by experiment (for example displacement) tends to contain noise, and the error in the properties of the system is proportional to the noise level (NL). In addition, the accuracy of the results depends on various factors such as the signal character, filtering method or cut off frequency. In particular, coupled terms in multimode systems show larger differences compared to the true value when measured in an environment with a high NL. The iterative least square (ILS) method was proposed to reduce these errors that occur under a high NL, and has been verified in previous research. However, the ILS method might be sensitive to the signal processing, including the determination of cutoff frequency. This paper focused on improving the accuracy of the ILS method, and proposed the modified ILS (MILS) method, which differs from the ILS method by the addition of a new calculation process based on correlation coefficients for each degree of freedom. Comparing the results of these systems with those of a numerical simulation revealed that both ILS and the proposed MILS method provided good prediction of the dynamic properties of the system under investigation (in this case, the damping ratio and damped frequency). Moreover, the proposed MILS method provided even better prediction results for the coupling terms of stiffness and damping coefficient matrix.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.17 no.9
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• pp.826-834
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• 2007

A 7K60MC-S low speed diesel engine in a power plant has frequently experienced high vibration since the unit completed construction works. Up to date, no fundamental vibration solutions were reached. Hence, several vibration tests and analyses were conducted to identify the root cause of this high vibration and to suggest the optimal countermeasures for diesel engine. The 9.25 Hz and 25.4 Hz vibrations have been observed on main body during operation. The magnitude of engine upper structural vibration is generally similar in horizontal transverse direction. However, differences in the 'Fore' and 'After' vibration magnitude with the same vibration phase angle at 9.25 Hz occur due to the explosion pulsations of 7 cylinders and the Inertia momentum added by the SCR (selective catalytic reduction) duct system. It was analyzed that the excess structural vibration occurred when the natural frequency of engine body is affected by the exciting sources due to the explosion pressure and the discharge pulsation of the seven cylinders in resonance range.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2014.10a
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• pp.411-414
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• 2014

Numerical modeling was conducted to estimate the amount of dislocation that may occur across a frictionless fracture during an earthquake using commercial code FLAC3D (Fast Lagrangian Analysis of Continua in 3 Dimensions). The applied motion was calculated to represent a Richter 6.0 magnitude earthquake at distances of 2 km from the fracture. The velocity-time history was generated from Svensk $K{\ddot{a}}arnbr{\ddot{a}}anslehantering$ AB report. In the report, The velocity field resulting from an earthquake on a fault located in the near-field (2 km distance) was modelled using a finite difference program, WAVE. The stress-time history was substituted for velocity-time history to perform dynamic analysis using FLAC3D. During the earthquake, the maximum dislocation and change of shear stress were about 1 cm and 2MPa, respectively. Because the fracture is frictionless in this study, all dislocations relax to zero after the earthquake motions have ceased.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2014.10a
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• pp.862-867
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• 2014

When the vehicle is traveling, the deformation caused by friction continued with the ground is made to occur because the tire is the composite material of a viscoelastic. Part of the deformation energy is converted into heat energy as Hysteresis and temperature inside the tire rises. The generated heat is shed to the outside through the convection and evangelism. Increase in the internal temperature of the tire is difficult to ensure the safety of vehicle by damage to the tire during driving. Recently, Even when the tire is damaged, it is designed to be possible to driving in case of run-flat tires but the fact is that the development of the technology for the synergistic effect of heat release inside the tire by the side reinforcement is necessary. In this study, by using the Finite Element Method (FEM), applying the cooling fins to the tire sidewall, it is intended to check the temperature distribution along the shape of the cooling fins and the temperature reduction effect.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.19 no.12
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• pp.1252-1259
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• 2009

Due to the international competition and global pressure, the roll speed is increased. However, higher speeds increase the power density in the process as well as the plant's potential to react with vibrations. Under certain operating conditions, vibrations may occur, which again cause chattermarks, strip rupture or coil break fault. The appropriate condition monitoring is needed to improve product quality and availability. The aim of condition monitoring is to reduce maintenance costs, increase productivity and improve product quality. This paper proposes a condition monitoring tool designed for the classification of coil break fault. This method is used to cold rolling mill for faults monitoring based on vibration and motor current signals. The results show that the performance of classification has high accuracy based on experimental work.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.17 no.1 s.118
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• pp.55-64
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• 2007

In the built-up structure consisting of a stiff beam and a flexible plate, Grice showed that the plate behaves as an energy absorber in narrow frequency bands(called plate blocking effect). This paper deals with such beam-plate coupled structures, where the plate is an energy absorber and the excited beam is an energy path. It is found that such energy dissipation can occur in the relatively broad bands, if different stiffnesses are used in the rectangular plate. It was experimentally verified by Heckl that the energies in terms of one-third octave band averages transferred to the plate(or dissipated in the plate) increase for increased plate damping. This Paper, however, shows that the energy absorption suddenly reduces at the certain narrow frequency bands where the plate damping effect upon the coupled beam is maximum. Also, in order to minimize energy transfer through the beam in terms of one-third octave band averages, it is advantageous to increase the plate damping closer to the excitation point All these results are based on the wane method.