• Journal of Mechanical Science and Technology
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• v.19 no.6
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• pp.1366-1377
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• 2005

Experimental study was carried out in an atmospheric pressure, laboratory-scale dump combustor showing features of combustion instabilities. Flame structure and heat release rates were obtained from OH emission spectroscopy. Qualitative comparisons were made between line-integrated OH chemiluminescence image and Abel-transformed one. Local Rayleigh index distributions were also examined. Mean temperature, normalized standard deviation and temperature fluctuations were measured by coherent anti-Stokes Raman spectroscopy (CARS). To see the periodic behavior of oscillating flames, phase-resolved measurements were performed with respect to the pressure wave in the combustor. Results on system damping and driving characteristics were provided as a function of equivalence ratio. It also could be observed that phase resolved temperatures have been changed in a well-defined manner, while its difference between maximum and minimum reached up to 280K. These results would be expected to play an important role in better understanding of driving mechanisms and thermo-acoustic interactions.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2000.11a
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• pp.495-499
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• 2000

The booming noise of a vehicle is usually caused by the vibration of the vehicle's body transmitted from the engine through the mounting system. Thus the engine mounting system must be cautiously designed to reduce the noise. Vector synthesis analysis is performed to predict the booming noise when the characteristic of the engine mounting system is changed., i.e., when magnitudes and phases of vibratory forces after the mounts are altered. To effectively use the method, the concept of 'effectiveness' is introduced to identify the contributions of each vibration sources and transmission paths to interior noise. When the magnitudes and phases of the forces due to the engine vibration are changed, the synthesized interior booming noise level is predicted by the vector synthesis diagram. Thus, the optimum characteristics of the forces are obtained through the simulations of the vector synthesis analysis. It is shown that the vector synthesis method can be used to obtain the optimum design characteristic of the mounting system to control the interior booming noise of a vehicle.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2000.11a
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• pp.384-388
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• 2000

One-port acoustic characteristics of an in-duct source can be measured by the multi-load method using an overdetermined set of open pipes with different lengths as applied loads. The input data. viz. load pressure and load impedance, are usually contaminated by measurement error in the actual measurements, which result in errors in the calculated source parameters. In this paper, the effects of the errors in the input data on the results have been studied numerically, varying the number of loads and their impedances in order to determine what combination of the loads will yield the best result. An error analysis is applied to each case of possible loads, which consist of open pipes. It is noted that, frequently, only a set of open pipes is used when applying the multi-load method to the intake or exhaust sides of internal combustion engines. A set of pipe lengths which cause the calculated results to be least sensitive to the input data error can be found when using open pipe loads. The present work is intended to produce guidelines for preparing an appropriate load set in order to obtain accurate source properties of fluid machines.

• Geomechanics and Engineering
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• v.18 no.5
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• pp.481-492
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• 2019

Due to the underground openings, the tangentially concentrated stress of the tunnel remains larger at excavation boundary and decreases toward the interior of the surrounding rock with a certain gradient. In order to study the effect of different gradient stress on rockburst, the true-triaxial gradient and hydraulic-pneumatic combined test apparatus were carried out to simulate the rockburst processes. Under the different gradient stress conditions, the rock-like specimen (gypsum) was tested independently through three principal stress directions loading--fast unloading of single surface--top gradient and hydraulic-pneumatic combined loading, which systematically analyzed the macro-mesoscopic damage phenomena, force characteristics and acoustic emission (AE) signals of the specimen during rockburst. The experimental results indicated that the rockburst test under the gradient and hydraulic-pneumatic combined loading conditions could perfectly reflect the rockburst processes and their stress characteristics; Relatively high stress loading could cause specimen failure, but could not determine its mode. The rockburst under the action of gradient stress suggested that the failure mode of specimen mainly depended on the stress gradient. When the stress gradient was lower, progressive and static spalling failure occured and the rockburst grades were relatively slight. On the other hand, shear fractures occurred in rockbursts accounted for increasingly large proportion as the stress gradient increased and the rockburst occurred more intensely and suddenly, the progressive failure process became unconspicuous, and the rockburst grades were moderate or even stronger.

• Journal of the Korea Institute of Military Science and Technology
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• v.24 no.1
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• pp.22-30
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• 2021

The ship wake generated by rotation of the propeller yields changes of characteristics of sound wave such as attenuation and scattering. To develope a battle field environment simulator for military purposes, it is very important to understand acoustical properties of ship wake. Existing research results have limitations in direct application because they performed under simple conditions or model ships were applied. In this study, we developed a ship wake generation model based on the ship's geometric wake distribution theory. The model can provide spatial distribution and void fraction with various marine environments as well as ship size. Through the developed model, geometric distribution features of ship wake according to the ship's maneuvering conditions were successfully simulated. In addition, changes of the bubble void fraction with time at any location within the battle field environment were identified. Therefore, the developed model is expected to be used in the development of a simulator to measure the acoustic characteristics of the ship wake.

• Geomechanics and Engineering
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• v.24 no.1
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• pp.81-89
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• 2021

Uniaxial compression tests were conducted on sandstone-CGFB composite samples with different interface angles, and their strength, acoustic emission (AE), and failure characteristics were investigated. Three macro-failure patterns were identified: the splitting failure accompanied by local spalling failure in CGFB (Type-I), the mixed failure with small sliding failure along with the interface and Type-I failure (Type-II), and the sliding failure along with the interface (Type-III). With an increase of interface angle β measured horizontally, the macro-failure pattern changed from Type-I to Type-II, and then to Type-III, and the uniaxial compressive strength and elastic modulus generally decreased. Due to the small sliding failure along with the interface in the composite sample with β of 45°, AE events underwent fluctuations in peak values at the later post-peak failure stage. The composite samples with β of 60° occurred Type-III failure before the completion of initial compaction stage, and the post-peak stress-time curve initially exhibited a slow decrease, followed by a steep linear drop with peaks in AE events.

• The Journal of the Acoustical Society of Korea
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• v.27 no.4
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• pp.183-190
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• 2008

In this paper, radiation characteristics of the beating sound are analytically investigated on a slightly asymmetric cylindrical shell. The cylindrical shell isan efficient model to consider the beat characteristics of Korean bells. Slight asymmetry in Korean bells makes mode pair which has close frequency components and the interaction of each mode pair produces beating sound. Based on the analytical model, the radiated sound field is determined. Using the sound beat map, the beating sound vs. direction and distance is investigated. Finally, results of the theoretical method are compared with those of the boundary element method to verify the validity.

• The Journal of the Acoustical Society of Korea
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• v.24 no.4E
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• pp.128-131
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• 2005

A new algorithm for speech signal segmentation is proposed. This algorithm is based on finding successive similar frames belonging to a segment and represents it by an average spectrum. The speech signal is a slowly time varying signal in the sense that, when examined over a sufficiently short period of time (between 10 and 100 ms), its characteristics are fairly stationary. Generally this approach is based on finding these fairly stationary periods. Advantages of the. algorithm are accurate border decision of segments and simple computation. The automatic segmentations using frame averaging show as much as $82.20\%$ coincided with manually verified segmentation of CMU ARCTIC corpus within time range 16 ms. More than $90\%$ segment boundaries are coincided within a range of 32 ms. Also it can be combined with many types of automatic segmentations (HMM based, acoustic cues or feature based etc.).

• The Journal of the Acoustical Society of Korea
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• v.17 no.2E
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• pp.10-15
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• 1998

Application of the Filtered-X LMS adaptive filter to active noise cancellation requires to estimate the transfer characteristics between the output and the error signal of the adaptive canceler. In this paper, we derive an adaptive cancellation algorithm and analyze is convergence behavior when the acoustic noise is assumed to consist of multiple sinusoids. The results of the convergence analysis of the Filtered-X LMS algorithm indicate that the effects of parameter estimation inaccuracy on the convergence behavior of the algorithm are characterize by two distinct components : Phase estimation error and estimated magnitude. In particular, the convergence of the Filtered-X LMS algorithm is show to be strongly affected by the accuracy of the phase response estimate. Simulation results of the algorithm are presented which support the theoretical convergence analysis.

• Proceedings of the KOSOMBE Conference
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• v.1991 no.05
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• pp.98-100
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• 1991

A sensitive surface acoustic wave (SAW) sensor for the detection of odorants has been constructed by depositing different phospholipids and fatty acids on the surface of the SAW device wi th the Langmuir-Blodgett technique. The characteristics of SAW device operating at 310 MHz deposited with phosphatidylcholine were analyzed. Amyl acetate, acetoin, menthone and other organic gases showed different affinities. The identification of odorants depending on the species of lipid used for coating is discussed in terms of the similarity of the normalized resonant frequency shift pattern. Using a number of different lipid-coated SAW devices, odorants could be identified by a neural-network pattern recognition with back-propagation algorithm.