• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2004년도 춘계학술대회논문집
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• pp.852-855
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• 2004

This experimental study describes the propagation characteristics of the impulse noise emitted from the exit of a straight pipe attached to the open end of a simple shock tube. The sound pressure level and directivity of the impulse noise propagating from the exit of pipe with several different diameters are measured in the far sound fold for the range of the incident shock wave Mach number between 1.07 and 1.26. The experimental results showed that the peak values of impulse noises had a strong dependance on the exit diameter of a pipe and the shock wave Mach number. The impulse noise had the directivity propagating toward to the pipe axis and the characteristics of inverse square law of propagation distance. Moreover, it was shown that the one-third octave band SPL of impulse noise was almost constant regardless of the frequency band.

• 대한기계학회논문집
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• 제18권2호
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• pp.251-259
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• 1994

Nearfield acoustic holography is known as a powerful tool to study sound radiation from a structure. In this work, the so called backward propagation of sound pressure field is studied to obtain the structure velocity distribution. The results, which were obtained using FFT algorithms, are presented for a finite plate excited at the frequencies above and below coincidence. These results illustrate the effect of stand-off distance and noise. An optimum cutoff frequency in wavenumber domain was suggested to reduce the effects of evanescent wave in the backward propagation. The experimental results were also included for a plate to demonstrate the effectiveness of the suggested cutoff frequency. The optimum cutoff frequency to exclude the unwanted noise in the process of reconstruction of the velocity field gives the good results in both simulations and experiments.

• 유체기계공업학회:학술대회논문집
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• 유체기계공업학회 1998년도 강연회 및 연구개발 발표회 논문집
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• pp.11-28
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• 1998

Crack initiation and propagation of blades is a serious matter in turbomachinery. Outages are common due to these problems that occur during the service of the machine resulting in a huge loss of revenue. Once in a while, the problems become serious and cause major shutdowns which can in some cases result in the loss of the whole machine in a catastrophic manner. In this presentation, we will discuss the crack initiation studies of a hydraulic machine runner blade by local stress strain approach and crack propagation at the root of a low pressure stage steam turbine blade by means of stress intensity factor approach. In both the cases, we will show how the present day technologies can predict actual field observations.

• 오토저널
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• 제4권2호
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• pp.69-78
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• 1982

The purpose of this study is to investigate the flame propagation phenomenon in the combustion chamber of spark-ignition gasoline engine for the idling condition. by means of four ion probes located through the cylinder head, the time intervals for the flame to arrive at the respective probes are read on th visicorder char. As results, the flame is considered to initiate after some ignition delay and to propagate through the central space of combustion chamber with rather constant speed on the order of 25m/sec, and thereafter to be slowed down approaching the wall. Additionally, the retardation of flame in the wall boundary layer could be inferred. The maximum pressure is developed when the flame nearly touches the wall diagonal to the spark plug. And some features of flame propagation are elucidate.

• International Journal of Naval Architecture and Ocean Engineering
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• 제4권4호
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• pp.374-385
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• 2012

The indoor noise of a ship is usually determined using the A-weighted sound pressure level. However, in order to better understand this phenomenon, evaluation parameters that more accurately reflect the human sense of hearing are required. To find the level of the satisfaction index of the noise inside a naval vessel such as "Loudness" and "Annoyance", psycho-acoustic evaluation of various sound recordings from the naval vessel was performed in a laboratory. The objective of this paper is to develop a single index of "Loudness" and "Annoyance" for noise inside a naval vessel according to a psycho-acoustic evaluation by using psychological responses such as Noise Rating (NR), Noise Criterion (NC), Room Criterion (RC), Preferred Speech Interference Level (PSIL) and loudness level. Additionally, in order to determine a single index of satisfaction for noise such as "Loudness" and "Annoyance", with respect to a human's sense of hearing, a back-propagation neural network is applied.

• International Journal of Naval Architecture and Ocean Engineering
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• 제12권1호
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• pp.680-690
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• 2020

In ocean environment, the sound speed gradient of seawater has an important influence on far field sound propagation. The FEM/BEM is used to decouple the vibroacoustic radiation of the spherical shell, and the Green function of the virtual source chain is adopted for decoupling. For far field radiated Sound Pressure Level (SPL), the Beam Displacement Ray normal Mode (BDRM) is employed. The vibration and near-/far-field radiated SPL of spherical shell is analyzed in shallow sea uniform layer, negative/positive gradient, negative thermocline environment, and deep-sea sound channel. Results show that the vibroacoustic radiation of spherical shell acted at 300Hz can be analogous to dipole. When the radiated field of the spherical shell is dominated by large-grazing-angle waves, it can be analogous to vertically distributed dipole, and the far field radiated SPL is lower; while similar to horizontally distributed dipole if dominated by small-grazing-angle waves, and the far field SPL is high.

• 대한기계학회논문집B
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• 제23권8호
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• pp.1040-1047
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• 1999

The characteristics of flame propagation in inert particle-laden $H_2$/Air premixed gas are numerically investigated on this study. The 2nd order TVD scheme is applied to numerical analysis of governing equations and multi-step chemical reaction model and detailed transport properties are sued to solve chemical reaction terms. Radiation heat transfer is computed by applying the finite volume method to a radiative transfer equation. The burning velocities against the mole fractions of hydrogen agree well with results performed by different workers. The inert particles play significant roles in the flame propagation on account of momentum and heat transfer between gas and particles. Gas temperature, pressure and flame propagation speed are decreased as the loading ratio of particle is increased. Also the products behind flame zone contain lots of water vapor whose absorption coefficient is much larger than that of unburned gas. Thus, the radiation effect of gas and particles must be considered simultaneously for the flame propagation in a mixture of $H_2$/Air and inert particles. As a result, it is founded that because the water vapor emits much radiation and this emitted radiation is released at boundaries as radiant heat loss as well as reabsorbed by gas and particles, flame propagation speed and flame structure are altered with radiation effect.

• 한국자동차공학회논문집
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• 제15권1호
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• pp.186-192
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• 2007

In general, pulsation damper is installed in fuel rail for conventional MPI engine to decrease undesirable noise in vehicle cabin room. However, pulsation damper is so expensive that there are prevailing studies to reduce fuel pressure pulsations with integrated damping effect. This paper is one of basic studies for development of fuel rail to abate pulsations with self-damping effect. Primarily, the pressure pulsation characteristics was investigated with aspect ratio of cross section, wall thickness, and materials of fuel rail. A high aspect ratio or thin wall was found to absorb the pressure pulsations effectively. But volume effects on the fuel pressure pulsation reductions were not especially significant than cross section effects because volume increment rate is larger than pressure pulsation reduction rate. The fuel rail made of aluminum is effective for reduction of pressure pulsation than that of low-carbon steel. Pressure change period increases on the basis of same lengths of supply line and fuel rail as the volume is enlarged and/or the thickness of wall is thinned.

• 한국자동차공학회논문집
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• 제11권1호
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• pp.179-184
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• 2003

It has been recognized that the compressibility of hydraulic fluid, which is characterized by the value of its bulk modulus, heavily affects on the system behavior and performance. In practice, the value of the oil bulk modulus varies by the operational and structural characteristics of the hydraulic system. This study presents the theoretical derivation of the effective bulk modulus and describes an experimental impulse technique that allows accurate measurement of oil effective bulk modulus with pressure variation in a hydraulic system. Experimental and analytical results show that the value of the effective bulk modulus varies a lot in low pressure region by the effect of entrained air, while the effective bulk modulus can be estimated just using the oil and container bulk modulus on the other high pressure region.

• Wind and Structures
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• 제30권3호
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• pp.289-298
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• 2020

Gusts generated by downburst have caused a great variety of structural damages in many regions around the world. It is of great significance to accurately evaluate the downburst-induced wind load on high-rise building for the wind resistance design. The main objective of this paper is to propose a computational modeling approach which can satisfactorily predict the mean and fluctuating wind pressure coefficients induced by downburst on high-rise building surfaces. In this study, using an impinging jet to simulate downburst-like wind, and simultaneous pressure measurements are obtained on a high-rise building model at different radial locations. The model test data are used as the database for developing back propagation neural network (BPNN) models. Comparisons between the BPNN prediction results and those from impinging jet test demonstrate that the BPNN-based method can satisfactorily and efficiently predict the downburst-induced wind pressure coefficients on single and overall surfaces of high-rise building at various radial locations.