• Journal of the Korean Society of Propulsion Engineers
• /
• v.19 no.4
• /
• pp.15-23
• /
• 2015

This study predicts the basic characteristics of combustion instabilities in a gas turbine lean premixed combustor using ASCI3D code which is a FEM(Finite Element Method)-based Helmholtz solver. The prediction results show the good agreement with the measured data in modeling the overall combustion instability features, however, the code is found to overpredict the unstable conditions. As one of the efforts to improve the model accuracy, the effects of acoustic boundary conditions on the instability growth rate are analyzed. As a result, it is shown that the acoustic reflection coefficient has a great impact on the instability and the prediction accuracy can be enhanced by defining the precise acoustic conditions.

• Transactions of the Korean Society for Noise and Vibration Engineering
• /
• v.26 no.3
• /
• pp.331-339
• /
• 2016

To improve the acoustic performance of sound absorbing materials, the thickness of the material should be increased or the sound absorbing material having an irregular surface shape should be used. In this study, the acoustic characteristics and methods to improve the acoustic performance of a sound absorbing system equipped with double layered polyester sound absorbing materials were investigated. The numerical model was set up and the results obtained from the model were compared with the actual measurement data. And, strategies to improve the acoustic performance of sound absorbing systems with double layered sound absorbing materials made of polyester with different configuration were shown. So, this study is expected to be usefully used at sites that require high acoustic absorption performance with minimal installation thickness to reduce sounds reflection in narrow spaces such as interior of subway tunnels or in noise barriers installed adjacent to rails.

• Journal of the Korean Society for Nondestructive Testing
• /
• v.34 no.2
• /
• pp.119-127
• /
• 2014

An epoxy coating applied to the concrete surface of a containment building deteriorates in hazardous environments such as those containing radiation, heat, and moisture. Unlike metals, the epoxy coating on a concrete liner absorbs and discharges moisture during the degradations process, so it has a different density and volume during service. In this study, acoustic impedance was adopted for characterizing the degradation of a glass-reinforced epoxy coating using the acoustic reflection coefficient (reflectance) on a rough epoxy coating. For estimating the acoustic reflectance on a wavy epoxy coating surface, a probabilistic model was developed to represent the multiple irregular reflections of the acoustic wave from the wavy surface on the basis of the simulated annealing technique. A number of epoxy-coated concrete specimens were prepared and exposed to accelerated aging conditions to induce an artificial aging degradation in them. The acoustic impedance of the degraded epoxy coating was estimated successfully by minimizing the error between a waveform calculated from the mathematical model and a waveform measured from the surface of the rough coating.

• Journal of the Korean Society for Nondestructive Testing
• /
• v.33 no.1
• /
• pp.54-62
• /
• 2013

In this study, a wireless and non-power SAW (surface acoustic wave) temperature sensor was developed. The single inter-digital transducer (IDT) of SAW temperature sensor of which resonance frequency is 434 MHz was fabricated on $128^{\circ}$ rot-X $LiNbO_3$ piezoelectric substrate by semiconductor processing technology. To find optimal acoustic reflector for SAW temperature sensor, various kinds of acoustic reflectors were fabricated and their reflection characteristics were analyzed. The IDT type acoustic reflector showed better reflection characteristic than other reflectors. The wireless temperature sensing system consisting of SAW temperature sensor with dipole antenna and a microprocessor based control circuit with dipole antenna for transmitting signal to activate the SAW temperature sensor and receiving the signal from SAW temperature sensor was developed. The result with wireless SAW temperature sensing system showed that the frequency of SAW temperature sensor was linearly decreased with the increase of temperature in the range of 40 to $80^{\circ}C$ and the developed wireless SAW temperature sensing system showed the excellent performance with the coefficient of determination of 0.99.

• Proceedings of the Acoustical Society of Korea Conference
• /
• 1994.06a
• /
• pp.1021-1026
• /
• 1994

This paper proposes a filter structure suitable for speech synthesis applications. We first derive the lossy pole-zero model by employing the wave digital filter(WDF) adaptor formula, and by converting the fixed termination value - 1 into a loss factor $\mu$c$\in$(-1, 1). Then we discuss how to determine the reflection We employ the Durbin's method in estimating the numerator polynomial of the lossy pole-zero transfer function from the given speech sound, and then apply the step-down algorithm on the numerator to extract the reflection coefficients of the closed-termination tract. For determining the reflection coefficients of the other parts we employ a pre-calculated pole-estimator polynomial.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2013.10a
• /
• pp.445-446
• /
• 2013

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2007.11a
• /
• pp.148-152
• /
• 2007

In recent days, on account of the cultural development and the improvement of citizen's consciousness level, it is the real situation that the construction of small-scaled Multi-Purpose Hall where various cultural events could be performed, is on increasing. However, since the most of Multi-Purpose Hall had been designed and built up without any consideration on Acoustic Factor, many problems are on occurring thereat. Since those small-scaled Multi-Purpose Hall have been mostly used with the finishing material which contains a high degree of Acoustic Absorption indiscreetly, both diffusion and reflection of sound are not establishing properly, and because thereverberation of sound is very low, in case of musical performance by musical instrument, its sound hears too arid and stiff, there occurs some acoustic defect such as it becomes difficult for music appreciation with sufficient timbre, so that the capability improvement on the matter is urgently requiring situation. Therefore, this Study has tried to seize the satisfaction level about the small-scaled Multi-Purpose Hall after betterment of the acoustic performance by appraise the acoustic condition of the Hall, using Auralization Technique that can experience Virtual Acoustic Field regarding to the small-scaled Multi-Purpose Hall as its object. It is deemed that such research result could be practically used as the useful material which enables to bring a reduction effect of construction cost as well asenhancement of the acoustic performance through its presupposition?control on the acoustic problem when construction or renovation of other similar small-scaled Multi-Purpose Hall in the future.

• Transactions of the Korean Society for Noise and Vibration Engineering
• /
• v.24 no.5
• /
• pp.399-406
• /
• 2014

Underwater acoustic materials are installed in order to reduce reflection, transmission and radiation of an underwater structure. The acoustic performance of the materials should be evaluated in accurately-controlled environment in terms of temperature and static pressure. In this paper, two pulse tubes, which are equipped with temperature and pressure controllers, are designed and developed to evaluate echo reduction(ER) and transmission loss(TL) of underwater acoustic materials. The procedures of the evaluation are suggested and the validation is carried out by comparing theoretical values to experimental results for a simple stainless steel specimen and free surface. In result, it is validated that developed pulse tubes are able to measure ER and TL with 2 dB tolerance.

• Korean Journal of Fisheries and Aquatic Sciences
• /
• v.23 no.6
• /
• pp.451-456
• /
• 1990

Underwater acoustic navigation and position fixing systems have been extensively used not only in surface position fixing but also in underwater position fixing. Tn recently, application of these systems has been in the field of underwater inspection of offshore platforms, where it is vital to track the position of an unmanned submersible or diver carrying underwater cameras and nondestructive testing equipment. But these systems are included the fixing errors as results of a signal with additive noise, the attenuation of sound and the interference effects due to multipath reflection and forward scattering. In this paper to improve the position fixing by the supershort baseline acoustic position system, a method to apply the Kalman filter to the fix of the system is proposed and the digital simulation under noise condition is conducted. The optimal positions by the Kalman filter are compared with original positions, and it is confirmed that the results of the pro-posed method are evidently more accurate.

• Journal of information and communication convergence engineering
• /
• v.14 no.2
• /
• pp.78-83
• /
• 2016

In underwater acoustic communication, the transmitted signals are severely influenced by the reflections from both the sea surface and the sea bottom. As very large reflection signals from these boundaries cause an inter-symbol interference (ISI) effect, the communication quality worsens. A channel estimation-based equalizer is usually adopted to compensate for the reflected signals under the acoustic communication channel. In this study, a feed-forward equalizer (FFE) with the least mean squares (LMS) algorithm was applied to a quadrature phase-shift keying (QPSK) transmission system. Two different types of equalizers were adopted in the QPSK system, namely a real-coefficient equalizer and a complex-coefficient equalizer. The performance of the complex-coefficient equalizer was better than that of two real-coefficient equalizers. Therefore, a Hilbert transform was applied to the real-coefficient binary phase-shift keying (BPSK) system to obtain a complex-coefficient BPSK system. Consequently, we obtained better results than those of a real-coefficient equalizer.