• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.21 no.7
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• pp.650-656
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• 2011

The noise inside a naval vessel is very important in considering the need for hearing protection, improving the working environment and maintaining good communications for crews living on board a naval vessel. The indoor noise of a ship usually is specified by the A-weighted sound pressure level, but other evaluating parameters are required to reflect human senses more effectively. This paper uses additional noise indices related to room acoustics, such as NR(noise rating), NC(noise criterion), RC(room criterion), PSIL(preferred speech interference level) and loudness level to evaluate the noise inside cabins on a naval vessel. Using these psychological noise indices, allowable limit of noise level in cabins is suggested through psycho-acoustic evaluation for the noise in cabins.

• Journal of the Korean Society for Precision Engineering
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• v.18 no.12
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• pp.145-151
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• 2001

The dimensional accuracy of the cold forged part is depended on the elastic characteristics of the die. To increase the stiffness of the prestressed die, the first stress ring of the tungsten carbide alloy (WC) is considered. For the design, Lame's equation is used. Diameter ratios and interferences have been determinated by maximum inner pressure without yielding of materials. The design of the prestressed die has been compared with the conventional one. For the comparison, the FE-analysis using ANSYS has been performed. The results indicate that the prestressed die with the high stiffness can be obtained by the using the high stiffness material as the first stress ring.

• Journal of the Korean Society for Precision Engineering
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• v.16 no.3 s.96
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• pp.136-144
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• 1999

This paper presents an in-process measurement system for shaft radius measurement during grinding process. This system does not require to stop the grinding process, which can enhance productivity and quality. In order to measure the radius, the system employs an eddy current sensor that can measure without any contact with the shaft. This type of sensor is very appropriate because it is insensitive to interference such as cutting fluid, coolant, contact pressure, and wear. For data analysis, the measurement system is modeled as a linearized discrete form where the states with noise are estimated by an extended Kalman filter. This system has been validated through simulations and experiments.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2001.11b
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• pp.1329-1334
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• 2001

This paper deals with the application of a sound-ray method to the analysis of the sound field in an ultrasonic cleaner. In order to include the wave interference phenomenon, the method has been modified to consider the phase of sound rays, The improved algorithm has been implemented by developing a Visual C＋＋ program, The algorithm has been verified by comparing the analysis results of BEM reported earlier. It has been shown that the algorithm can be used to calculate ultrasonic fields in a cleaning- container with an object to be cleaned.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 1997.10a
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• pp.237-243
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• 1997

Most outdoor sounds go from sources relatively near the ground to receivers near the ground. When either source or receiver are near the ground, interference can occur between the direct sound and that reflected at the ground which travels a slightly longer path. The sound pressure at the receiver is very different depending on the state of ground surface i.e. ground impedance. Ground impedances could be characterized by the value of a single parameter, namely the flow resistivity of the ground surface. This study suggests the measurement method of the flow resistivity using two microphones and predicts the flow resistivities of various ground surfaces.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2000.11a
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• pp.726-730
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• 2000

In this article, the scattering effect around a microphone is studied by using boundary element method, because it is hard to find the scattering experimentally. The scattering problem is defined by impinging an obstacle, i.e. a solid cylinder, with an incident plane wave. From this analysis, the scattering is numerically calculated by varying the microphone shape, the incident angle and the distance between microphones. It is found that the scattering effect of a microphone increases as the frequency increases and is not considerable in the low frequency region. However, it is noted that there might be the pressure distortion above 4 kHz due to the scattering in microphone measurement.

• International Journal of Naval Architecture and Ocean Engineering
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• v.13 no.1
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• pp.526-544
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• 2021

Based on the potential flow theory, a fully nonlinear numerical procedure is developed with boundary element method to analyze the interaction between a fixed semi-submersible platform and incident waves in open water. The incident wave is separated from the scattered wave under fully nonlinear boundary conditions. The mixed Euler-Lagrangian method is used to capture the position of the disturbed wave surface in local coordinate systems. The wave forces exerted on an inverted conical frustum are used to ensure the accuracy of the present method and good agreements with published results are obtained. The hydrodynamic characteristics of the semi-submersible platform interacting with regular waves are analyzed. Pressure distribution with time and space, tension and compression of the platform under wave action are investigated. 3D behaviors of wave run-ups are predicted. Strong nonlinear phenomena such as wave upwelling and wave interference are observed and analyzed.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.37 no.8
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• pp.1029-1033
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• 2013

Elliptical gear is used as a rotor of oval flowmeter. The elliptical gear can assist water flow-rate measurement by the space of the elliptical shape. Presently, elliptical gears have been processed using hob tool imported from Japan. But if it were not for the technical cooperation with Japan company, the Elliptical gears can't be processed. The purpose of this study is developing a domestic technology for elliptical gears and overcoming the dependence of foreign technical skills. It will bring the import substitution effect. In case of pressure angle $20^{\circ}$, the elliptical gears have an interference of tooth. The increase of pressure angle makes the root of a tooth thick and the top of tooth thin. By results of this study, tooth of elliptical gear was designed and verified through the 2D and 3D simulation.

• 한국신재생에너지학회:학술대회논문집
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• 2009.06a
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• pp.711-711
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• 2009

Global warming has been widely recognized as a serious problem threatening the future of human beings. It is caused by the buildup in the atmosphere of greenhouse gases, such as carbon dioxide, methane, hydrofluorocarbons (HFCs), and sulfur hexafluoride (SF6). Particularly, SF6 has extremely high global warming potential compare to those of other global warming gases. One option for mitigating this greenhouse gas is the development of an effective process for capturing and separating these gases from anthropogenic sources. In general, gas hydrates can be formed under high pressure and low temperature. However, SF6 gas is known to form hydrate under relatively milder conditions. Therefore, technological and economical effects could be expected for the separation of SF6 gas from waste gas mixtures. In this study, we carried out morphological study for the SF6 hydrate crystals to understand its formation and growth mechanisms. The observations were made in high-pressure optical cell charged with liquid water and SF6 gas at constant pressure and temperature. Initially SF6 hydrate formed at the surface between gas and liquid regions, and then subsequent dendrite crystals grew at the wall above the gas/water interface. The visual observations of crystal nucleation, migration, growth and interference were reported. The detailed growth characteristics of SF6 hydrate crystals were discussed in this study.

• Journal of Advanced Marine Engineering and Technology
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• v.32 no.1
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• pp.82-93
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• 2008

The flowfield behind two cylinders and flow-induced noise generated from the cylinders in various arrangement are numerically investigated based on the finite difference lattice Boltzmann model with 21 velocity bits. which is introduced a flexible specific heat ${\gamma}$ to simulate diatomic gases like air. In an isolated cylinder with two type of mesh. some flow parameters such as Strouhal number $S_t$ and acoustic pressure ${\Delta}p$ simulated from the solution are given and quantitatively compared with those provided the previous works. The effects of the center-to-center pitch ratio $L_{cc}/d=2.0$ in staggered circular cylinders as shown in Fig. 1 and angles of incidence ${\alpha}=30^{\circ}(T_{cc}/d=0.5)$, $45^{\circ}(T_{cc}/d =0.707)$ and $60^{\circ}\;(T_{cc}/d=0.866)$, respectively, are studied. Our analysis focuses on the small-scale instabilities of vortex shedding, which occurs in staggered arrangement. With the results of drag $C_d$ and lift $C_l$ coefficients and vorticity contours. the mechanisms of the interference phenomenon and its interaction with the two-dimensional vortical structures are present in the flowfields under $Re\;{\le}\;200$. The results show that we successively capture very small pressure fluctuations, with the same frequency of vortex shedding, much smaller than the whole pressure fluctuation around pairs of circular cylinders. The upstream cylinder behaves like an isolated single cylinder, while the downstream one experiences wake-induced flutter. It is expected that, therefore, the relative position of the downstream cylinder has significant effects on the flow-induce noise, hydrodynamic force and vortex shedding characteristics of the cylinders.