• Journal of the Korean Society for Marine Environment & Energy
• /
• v.5 no.1
• /
• pp.11-18
• /
• 2002

Directional breaking waves are generated by the component wave focusing both in direction and frequency based on constant wave steepness and constant wave amplitude spectrum models. The generated breaking waves are classified in the incipient, single and multi breaking waves. The characteristics of directional breaking waves are investigated in terms of surface profile parameters of wave crest steepness and asymmetry. The evolution of breaking wave characteristics is analyzed in a view of focusing efficiency. It shows that the front steepness and vertical asymmetry play an important role in breaking process, while the crest rear steepness and horizontal asymmetry are nearly constant during the process. The superposition of directional components greatly enhances the focusing efficiency and it suggests that characteristics of directional breaking waves may significantly different from uni-directional ones.

• Ocean and Polar Research
• /
• v.25 no.4
• /
• pp.437-446
• /
• 2003

Field measurements of directional waves were carried out during the summer of 2002 at two coastal sites in water of finite depth. A couple of general purpose instruments were used employing acoustic Doppler technology. The aim of the study was to investigate the spatial behavior of the directional movement of waves as they come ashore. In total,74 tests were carried out during which sea states of low to moderate intensity were recorded. A great number of these runs displayed bimodal characteristics of the spreading function at high frequencies. It was found that in general, the frequency-integrated directional width tends to broaden as the water shoals and when refraction effects are negligible. This is attributed to wave-wave interactions that become pronounced in shallow water. The same directional width showed, also, a tendency to increase with increasing peak frequency of the sea state spectrum. The behavior of the kurtosis of the spreading function was also examined. It was found that for higher frequencies this index tends to increase in wave spectra above a certain sea severity threshold.

• Proceedings of the Korea Institute of Convergence Signal Processing
• /
• 2000.08a
• /
• pp.309-312
• /
• 2000

In this work, a new algorithm for canceling MRI artifact due to translational motion in image plane is described. In the previous approach, the motions in the x direction and the y direction are estimated simultaneously. By analyzing their features, each x and y directional motion is canceled by different algorithms in two steps. First, it is noticed that the x directional motion corresponds to a shift of the x directional spectrum of the MRI signal. Next, the y directional motion is canceled by using a new constraint condition. This algorithm is shown to be effective by using a phantom image with simulated motion.

• Journal of Satellite, Information and Communications
• /
• v.11 no.4
• /
• pp.68-73
• /
• 2016

This paper describes the prototyping of CDMA bi - directional group search system using USRP and LTE. This paper describes the results of RF signal generation and transmission by implementing a spread spectrum signaling system, which is a new standard of COSPAS SARSAT, using a bi-directional search structure system using commercial LTE network and USRP.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.22 no.3
• /
• pp.401-409
• /
• 1997

In this paper, a pattern spectrum component function is introduced for an oriented shape analysis and its properties are discussed. It can represent directional information of shape more precisely than the conventional oriented pattern spectrum. An adaptive distance function between two pattern spectrum component functions is presented to recognize different shapes in noise. As a practical application, the pattern spectrum component function is applied to warning traffic sign recognitions utilizing the adaptive distance functions. Favorable results are obtained compared to the oriented pattern spectrum.

• Journal of the Institute of Electronics Engineers of Korea TC
• /
• v.40 no.1
• /
• pp.15-23
• /
• 2003

This paper proposes a fast direction of arrival (DOA) estimation algorithm that can rapidly estimate incidence angles of incoming signals using a pseudo covariance matrix. The conventional subspace DOA estimation methods such as MUSIC (multiple signal classification) algorithms need many sample signals to acquire covariance matrix of input signals. Thus, it is difficult to estimate the DOAs of signals because they cannot perform DOA estimation during receiving sample signals. Also if the D0As of signals are changing rapidly, conventional algorithms cannot estimate incidence angles of signals exactly. The proposed algorithm obtains bearing response and directional spectrum after acquiring pseudo covariance matrix of each snapshot. The incidence angles can be exactly estimated by using the bearing response and directional spectrum. The proposed DOA estimation algorithm uses only concurrent snapshot so as to obtain covariance matrix. Compared to conventional DOA estimation methods. The proposed algorithm has an advantage that can estimate DOA of signal rapidly.

• Journal of Navigation and Port Research
• /
• v.33 no.9
• /
• pp.645-651
• /
• 2009

In this study, a series of laboratory experiments were carried out to investigate the weak reflection of regular and random water waves over a train of protruded permeable shore structures. A cylindrical slit type breakwater and the alternatives are employed and compared for reflecting and transmitting capabilities of incident waves including wave forces. A series of random waves were generated by using the Bretschneider-Mitsuyasu frequency and directional spectrum. Measured spectrum of irregular waves without breakwaters is verified by comparing with those of the input waves generated. Weak reflection is occurred at the breakwater center of the peak frequency. If the row of breakwaters is fixed at three layers and the relative height of breakwater is fixed at 0.6, around 45% of incident wave energy is reflected to offshore. It is also found that the transmission of directional random waves increases as the maximum frequency parameter increases. A very good agreement is observed. Reflection coefficients of permeable submerged breakwaters are less than those of impermeable breakwaters. The upside-down L shape is recommended for a small fishery harbor mooring in terms of reflecting capability and of practical application. The final design was applied to the wharf of a small beach of Seolly, near Namhae at the southeast coast of Korea.

• Journal of the Institute of Electronics Engineers of Korea SP
• /
• v.41 no.5
• /
• pp.53-62
• /
• 2004

In this study, an improved post-processing technique for correcting MRI artifact due to the unknown respiratory motion in the imaging plane is presented. Respiratory motion is modeled by a two-Dimensional linear expending-shrinking movement. Assuming that the body tissues are incompressible fluid like materials, the proton density per unit volume of the imaging object is kept constant. According to the introduced model, respiratory motion imposes phase error, non-uniform sampling and amplitude modulation distortions on the acquired MRI data. When the motion parameters are known or can be estimatead a reconstruction algorithm based on biliner superposition method was used to correct the MRI artifact. In the case of motion parameters are unknown, first, the spectrum shift method is applied to find the respiratory fluctuation function, x directional expansion coefficient and x directional expansion center. Next, y directional expansion coefficient and y directional expansion center are estimated by using the minimum energy method. Finally, the validity of this proposed method is shown to be effective by using the simulated motion images.

• Journal of the Society of Naval Architects of Korea
• /
• v.38 no.2
• /
• pp.1-9
• /
• 2001

Based on the linear potential theory with the side wall reflection. the directional spectrum waves are numerically simulated by a source distribution method and these together with long-crested irregular waves are also generated at the towing tank of Pusan National University by considering the transfer function of the wave maker obtained from the regular waves. In the numerical simulation, the characteristics of the directional spreading function are investigated by changing the breadth of the wave-maker unit. the width of the towing tank and the wave period. In the experimental generation, the statistical properties and the power spectrums of the long-crested irregular and directional waves are compared along the towing tank length. The directional spreading functions are also investigated at various positions in the tank.

• Proceedings of the Korea Water Resources Association Conference
• /
• 1991.07a
• /
• pp.220-220
• /
• 1991

불규칙 파랑장의 frequency spectrum 에 쇄파로 인한 영향을 도입할 수 있는 기법이 제시되었다. 제시된 기법을 심해에서 발달된 방향성불규칙 파랑장이 흐름이 존재하는 해역으로 전이해 갈때 흐름과의 상호작용, 굴절, 천수효과, 및 쇄파로 인해 겪게되는 변화양상을 예측하기위해 두가지 형태의 연안류 즉, shear current, upwelling current 가 존재하는 일정 경사면을 갖는 해역에 대해 각각 적용했다.