• Journal of Advanced Marine Engineering and Technology
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• v.28 no.3
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• pp.423-433
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• 2004

A large eddy simulation (LES) is performed for turbulent flow in a combustion device. The combustion device is simplified as a cylindrical chamber with sudden expansion. A flame holder is attached inside a cylindrical chamber in order to promote turbulent mixing and to accommodate flame stability. The turbulent sub-grid scale models are applied and validated. Emphasis is placed on the evaluation of turbulent model for the LES of complex geometry. The simulation code is constructed by using a general coordinate system based on the physical contravariant velocity components. The calculated Reynolds number is 5000 based on the bulk velocity and the diameter of inlet pipe. The predicted turbulent statistics are evaluated by comparing with the LDV measurement data. The Smagorinsky model coefficients are estimated and the utility of dynamic SGS models are confirmed in the LES of complex geometry.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2013.10a
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• pp.815-824
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• 2013

Pneumatic exciters can be good replacements of electrodynamic, piezoelectric and hydraulic exciters owing to simple structure and large exciting force. One problem to be solved is a slow response caused by compressibility of air. Desirable frequency response characteristics of exciter are constant magnitude and zero degree phase, because users want no time delay between input signal and output force. For this reason, frequency range of pneumatic exciters is limited about 0~1 Hz. Therefore, expansion of frequency range is an important issue when designing the pneumatic exciter. In this paper, the pneumatic exciter which has same structure with active pneumatic isolator is dealt with. The dynamic characteristics are presented, and its limitation of expanding frequency range is shown based on analytical studies. Then the pneumatic exciter with dual-chamber is suggested to overcome this problem. Based on simulation study, a design method is presented.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2007.11a
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• pp.1354-1359
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• 2007

This paper discusses the acoustic performance of simple expansion chamber using computational fluid dynamics(CFD). The CFD model consists of an axisymmetric grid with a single period sinusoid of acceptable amplitude and duration imposed at the inlet boundary condition. The time history of the static pressure is recorded at two points, one in the inlet pipe and one point in outlet pipe. The time history of the static pressure is converted to the frequency domain using Fourier Transform and the transmission loss (TL) of the muffler is obtained from the ratio of the static pressure at the inlet and outlet pipe. The transmission loss of CFD result is compared with that of the computational acoustic analysis using the boundary element method (BEM). There are some differences in two results due to the pressure drop according to the inlet and outlet pipe length. Therefore, the effects of the pressure drop to the transmission loss have to be considered.

• The Transactions of the Korean Institute of Electrical Engineers B
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• v.53 no.12
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• pp.725-731
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• 2004

In this study, the three type hybrid interrupters according to the arrangement of the thermal expansion chamber and the puffer cylinder(they are called 'serial type', 'parallel/exchanged type', and 'parallel/separated type' respectively in this work) were designed and manufactured. This paper presents the tested results of the thermal recovery characteristics on the interrupters using a simplified synthetic test facility. The 'serial type' hybrid interrupter which is to obtain more easily the pressure rise for the thermal recovery compared with the others has the best capability in the thermal recovery characteristics. In order to investigate the stress on the operating mechanism, the distortion of the stroke wave in on-load test was examined to the stroke curve in no-load test. The biggest distortion was occurred in the 'parallel/exchanged type' hybrid interrupter. Finally, the small interruption capability on the three type interrupters was estimated by a theoretical form and the 'parallel/separated type' hybrid interrupter has the advantage of the others in the view of structure.

• Journal of Advanced Marine Engineering and Technology
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• v.34 no.2
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• pp.275-281
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• 2010

In this paper, a geometric similarity law is introduced to the performance test of a large-sized silencer used in ship engine or plant system. A test of scale-down model enable to yield the cost and time saving in developing large-sized silencer considerably. Two types of silencer, resonator and expansion chamber, were analyzed by a theoretical method and an acoustical FEM(finite element method) in order to obtain geometric similarity variables. A method is proposed to estimate the transmission loss of prototype model using the test results of scale-down model. Two actual large-sized silencer, which consist of resonator and expansion chamber, were analysed by an acoustical FE analysis. Consequently, the proposed method predicts effectively the performance of prototype silencers using those of scale-down models.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.25 no.2
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• pp.116-123
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• 2015

This paper proposed a new formula for predicting acoustic power transmission loss of simple expansion chamber with two internal partitions. Seventeen cases of computational results were performed and the database was constructed for the TL according to the various positions of internal partitions. Using this database, firstly, the formula for the peak values of TL at certain frequencies was developed using the least square estimation. Secondly, the formula for the TL curve could be obtained automatically with the input data of the positions of two internal partitions. The formula of TL developed in this paper showed good agreement with computational results. This formula will be helpful for the positioning of internal partitions to improve TL at target frequencies.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.22 no.10
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• pp.994-1002
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• 2012

Acoustic power transmission loss(TL) is an important performance of the muffler system. TL will be affected by the velocity of the fluid in duct since acoustic pressure varies according to the fluid velocity. In this paper, two kinds of fluid model, potential flow and turbulent flow, for the fluid flowing in simple expansion chamber are considered. The effects of their two fluid models in acoustic TL are investigated for the straight and L-shaped simple expansion chamber. In higher frequency range, the characteristics of TL of the two fluid models show different results. The variation of TL according to the fluid velocity is shown more distinctly when turbulence model is used. Turbulent flow model should be used to obtain better estimation of acoustic TL in higher frequency range.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.14 no.11
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• pp.1083-1090
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• 2004

Two noise reduction systems are proposed in order to overcome the geometric restriction of the reactive muffler such as an expansion chamber. First, membrane is installed as a part of a duct wall and an air cavity is covered outside membrane. Second, membrane is installed inside a duct, which gives no volume change of the duct. Structural-acoustic coupling between membrane and fluid inside the cavity and duct causes rapid impedance mismatching and thereby reflected wave. Theoretical prediction is conducted by using modal expansion approach. The results are compared with the experimental results, which show better noise reduction performance than an expansion chamber.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2004.05a
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• pp.474-479
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• 2004

Two noise reduction systems are proposed in order to overcome the geometric restriction of the reactive muffler such as an expansion chamber. First, membrane is installed as a part of a duct wall and an air cavity is covered outside membrane. Second, membrane is installed inside a duct, which gives no volume change of the duct. Structural-acoustic coupling between membrane and fluid inside the cavity and duct causes rapid impedance mismatching and thereby reflected wave. Theoretical prediction is conducted by using modal expansion approach. The results are compared with the experimental results, which show better noise reduction performance than an expansion chamber.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.31 no.10
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• pp.1046-1052
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• 2007

Elastic-plastic structural analysis for regenerative cooling chamber of gas generator was performed. Uniaxial tension test was conducted for STS316L at room and high temperature conditions to get the material data necessary for the structural analysis of the chamber which was operated under thermal load and high internal pressure. Physical properties including thermal conductivity, specific heat and thermal expansion were also measured. The structural analysis for four different types of regenerative cooling chamber of gas generator revealed that increased cooling performance decreased the thermal load and strain of the cooling channel structure. The results propose that in order for the regenerative cooling gas generator chamber to have high structural stability with endurance to high mechanical and thermal loads, it is important for the chamber to be designed to have high cooling performance.