• The KIPS Transactions:PartB
• /
• v.17B no.1
• /
• pp.69-78
• /
• 2010

Spectral modeling synthesis (SMS) has been used as a powerful tool for musical sound modeling. This technique considers a sound as a combination of a deterministic plus a stochastic component. The deterministic component is represented by the series of sinusoids that are described by amplitude, frequency, and phase functions and the stochastic component is represented by a series of magnitude spectrum envelopes that functions as a time varying filter excited by white noise. These representations make it possible for a synthesized sound to attain all the perceptual characteristics of the original sound. However, sometimes considerable phase variations occur in the deterministic component by using the conventional SMS for the complex sound such as whale sounds when the partial frequencies in successive frames differ. This is because it utilizes the calculated phase to synthesize deterministic component of the sound. As a result, it does not provide a good spectrum matching between original and synthesized spectrum in higher frequency region. To overcome this problem, we propose a modified SMS that provides good spectrum matching of original and synthesized sound by calculating complex residual spectrum in frequency domain and utilizing original phase information to synthesize the deterministic component of the sound. Analysis and simulation results for synthesizing whale sounds suggest that the proposed method is comparable to the conventional SMS in both time and frequency domain. However, the proposed method outperforms the SMS in better spectrum matching.

• Journal of Ocean Engineering and Technology
• /
• v.25 no.2
• /
• pp.7-14
• /
• 2011

Numerical simulations were performed for the evaluation of wave and current loads on a fixed cylindrical substructure model for an ocean wind turbine using the ANSYS-CFX package. The numerical wave tank was actualized by specifying the velocity at the inlet and applying momentum loss as a wave damper at the end of the wave tank. The Volume-Of-Fluid (VOF) scheme was adopted to capture the air-water interface. An accuracy validation of the numerical wave tank with a truncated vertical circular cylinder was accomplished by comparing the CFD results with Morison's formula, experimental results, and potential flow solutions using the higher-order boundary element method (HOBEM). A parametric study was carried out by alternately varying the length and amplitude of the wave. As a meaningful engineering application, in the present study, three kinds of conditions were considered, i.e., cases with current, waves, and a combination of current and progressive waves, passing through a cylindrical substructure model. It was found that the CFD results showed reasonable agreement with the results of the HOBEM and Morison's formula when only progressive waves were considered. However, when a current was included, CFD gave a smaller load than Morison's formula.

• Transactions of the Korean Society for Noise and Vibration Engineering
• /
• v.18 no.1
• /
• pp.20-25
• /
• 2008

Acoustic holography exhibits the spatial distribution of sound pressure in time or frequency domain. The obtained picture often contains far more than what we need in practice. For example. when we need to know only the locations and overall propagation pattern of sound sources. a method to show only what we need has to be introduced. One way of obtaining the necessary information is to use envelope in space. The spatial envelope is a spatially slowly-varying amplitude of acoustic waves which contains the information of sources' location. A spatial modulation method has been theoretically developed to get a spatial envelope. By applying the spatial envelope. not only the necessary information is obtained but also computation time is reduced during the process of holography. The spatial envelope is verified as an effective visualization scheme in time domain by being applied to complicated sound fields.

• Korean Journal of Fisheries and Aquatic Sciences
• /
• v.14 no.4
• /
• pp.265-268
• /
• 1981

The direction and spectra of underwater sound wave were a remarkable contrast to the sound wave in the air because of the difference of transmissive medium. The linear hydrophone array of passive system has so far been applied to find out the direction and spectra of underwater sound wave from the sources for many purposes. The conventional methods are generally classified into two systems such as, the system which varying frequency responses, other parameters and pattern of signal like an adaptive array controlled by internal feedback, and another system which obtaining maximum of S/N ratio by giving a appropriate delay and a weighting coefficient in the output of each hydrophone. The array device of passive system can easily change the amplitude and the phase of signal by separately controlled hydrophone. And here we introduce a method that the spectral analyzing and the direction finding can be simultaneously carried out using a linear array of hydrophones. By making a circular convolution of output of signal from each hydrophone with appropriate rectangular weighting coefficient on the array, a sharp response of single lobe directivity and the spectral analyzing by time averaging were simultaneously obtained. In tile computer simulation of the array system with the length of 250cm and the interhydrophone distance of l0cm the power levels of sound signals received from given array direction were 16dB higher than those from the other directions when processing with rectangular weightings, and 8dB higher when processing with rectangular sound signals and rectangular weightings.

• Proceedings of the Korea Water Resources Association Conference
• /
• 2018.05a
• /
• pp.148-148
• /
• 2018

Land subsidence caused by excessive groundwater pumping is a serious hydro-geological hazard. The spatial variability in land use, unbalanced groundwater extraction and aquifer characteristics are the key factors which make the problem more difficult to monitor using conventional methods. This study uses the European Space Agency (ESA) Sentinel satellites to investigate and monitor land subsidence varying with different land covers and groundwater use in the arid Quetta valley, Pakistan. The Persistent Scattering Differential Interferometry of Synthetic Aperture Radar (PS-DInSAR) method was used to develop 28 subsidence interferograms of the study area for the period between 16 Oct 2014 and 06 Oct 2016 using ESA's Sentinel-1 SAR data. The uncertainty of DInSAR result is first minimized by removing the dynamic effect caused by atmospheric factors and then filtered using the radar Amplitude Dispersion Index (ADI) to select only the stable pixels. Finally the subsidence maps were generated by spatially interpolating the land subsidence at the stable pixels, the comparison of DInSAR subsidence with GPS readings showed an R 2 of 0.94 and mean absolute error of $5.7{\pm}4.1mm$. The subsidence maps were also analysed for the effect of aquifer type and 4 land covers which were derived from Sentienl-2 multispectral images. The analysis show that during the two year period, the study area experienced highly non-linear land subsidence ranging from 10 to 280 mm. The subsidence at different land covers was significantly different from each other except between the urban and barren land. The barren land and seasonally cultivated area show minor to moderate subsidence while the orchard and urban area with high groundwater extraction rate showed excessive amount of land subsidence. Moreover, the land subsidence and groundwater drawdown was found to be linearly proportional to each other.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
• /
• v.15 no.6
• /
• pp.590-598
• /
• 2004

An active capacitance circuit which employs series feedback network for the implement of negative resistance and low noise operation is analyzed in depth and its application to low noise active RF BPF's is discussed. Whereas many authors reported a lot of circuits that embody negative resistance circuit most of them have concerns for the equivalent resistance and reactance value at the center frequency. In this case, it could be possible to face a problem that the negative resistance circuit becomes unstable, or have poor flatness in passband because of insufficient forecast for the negative resistance values as the frequency goes higher or lower. In this paper, we extracted the exact equivalent values of this circuit and analyzed the RF characteristics with the varying the values of active devices and feedback circuits and presented the method that the flatness of passband can be improved. We have designed a 4-pole active BPF, which has the bandwidth of 60 ㎒, 0.67 ㏈ insertion loss, 0.3 ㏈ ripple, and noise figure of 3.0 ㏈ at 1.99 ㎓ band.

• Journal of the Korean Geotechnical Society
• /
• v.32 no.12
• /
• pp.69-78
• /
• 2016

A suction bucket foundation has been considered to be a potential foundation type for offshore wind turbines. A suction bucket foundation is usually installed in soft soil, so the accumulated displacement of the foundation may occur under long-term cyclic loads. In this study, a series of 1-g model tests were performed to analyze the accumulated rotation of suction bucket foundations under long-term cyclic horizontal loads. The dry model ground was prepared to have two different soil densities by air-pluviation method. The model tests were performed varying the embedment depth of the suction bucket, the soil density, and the amplitude of cyclic load. A one-way horizontal cyclic load was applied over $10^4$ cycles. Test results showed that the accumulated rotation of the suction bucket foundation increased with the increase in the number of cycles and load magnitudes. Based on the model test results, a new equation was proposed to evaluate the accumulated rotation of the suction bucket foundations in dry sandy ground under long-term cyclic horizontal loads.

• Journal of the Korean GEO-environmental Society
• /
• v.16 no.7
• /
• pp.35-42
• /
• 2015

Grouting method has been widely used for the ground improvement and stabilization: mostly to block or control the ground water in the early years and to improve the ground, repair the structure in recent years, ever increasing its use. Despite many advantages so far, the existing grouting method also has some shortcomings including uncertain permeation of grouting with gravity type if the voids between the soil particles are narrow, and problems due to the relaxation of the neighboring ground when injected using injection pressure. As an alternative, a vibration injection method with constant amplitude and frequency has been developed in recent years, with the vibration grouting being reported to have a permeability increasing effect of grout material compared with the positive pressure injection type. Accordingly, the purpose of this study is to investigate the improvement effect of the vibration grouting that applies short-period vibration energy by varying vibration cycle, vibration time and ground conditions to evaluate the strength enhancing effect of grouting materials, expansion effect of grouting body, ground improvement effect of the grouting and the penetration characteristics of the rock joint. The findings of this study show the improved compressive strength of grout, expansion of grouting body and increased penetration rate, according to the vibration compared with non-vibration under the loose soil condition.