• 한국지진공학회:학술대회논문집
• /
• 한국지진공학회 1999년도 춘계 학술발표회 논문집 Proceedings of EESK Conference-Spring
• /
• pp.35-40
• /
• 1999

In order to know the characteristics of attenuation of coda wave in the Kyungsang Sedimentary Basin quality factor for coda wave or coda Q is estimated from the earthquake data recorded in the KIGAM microearthquake network. The single scattering model for coda wave generation is adopted in estimating coda Q. Coda Q appears to be largely dependent on the normalized time(a) which is the ratio of elapsed time to S-wave travel time. In the present study coda Q(Qc) is estimated in the range of a=1.5-3.Q and expressed in terms of frequency(f). The deduced function in the range of 1 to 25 Hz is Qc=36.8283 f1.15095 to represent the strong dependence of coda Q on frequency. It is found that the difference of Qc between U-D N-S and E-W components is negligible, This face supports the back-scattering theory that coda were originates from scattered waves by randomly distributed heterogeneities in the crust. On the other hand it is observed that the coda Q increases with depth.

• 대한조선학회논문집
• /
• 제42권3호
• /
• pp.212-219
• /
• 2005

Real sea waves in a towing wave basin have been generated using random periodic motion of the segmented wave makers and the wave reflections of sidewalls. Theoretically, the real sea waves can be described by the superposition of many random oblique waves. This paper introduces numerical real sea wave generation in a rectangular wave basin using spectral method that uses a superposition of orthogonal functions which have to satisfy the Laplace equation. Oblique regular waves, long crested irregular waves and real sea waves were simulated and met the requirement of sidewall wave reflection and wave absorption. MLM (Maximum Likelihood Method) and Spatial Fourier Transform were used in order to obtain propagated wave direction characteristics. The estimated results proved the usefulness of the method and the performances showed reasonable directional patterns comparing with generating patterns.

• 한국물환경학회지
• /
• 제31권4호
• /
• pp.367-376
• /
• 2015

The momentum and kinetic turbulent energy carried by the wind to a stratified lake lead to basin-scale motions, which provide a major driving force for vertical and horizontal mixing. A three-dimensional (3D) hydrodynamic model was applied to Lake Tahoe, located between California and Nevada, USA, to simulate the dominant basin-scale internal waves in the deep lake. The results demonstrated that the model well represents the temporal and vertical variations of water temperature that allows the internal waves to be energized correctly at the basin scale. Both the model and thermistor chain (TC) data identified the presence of Kelvin modes and Poincare mode internal waves. The lake was weakly stratified during the study period, and produced large amplitude (up to 60 m) of internal oscillations after several wind events and partial upwelling near the southwestern lake. The partial upwelling and followed coastal jets could be an important feature of basin-scale internal waves because they can cause re-suspension and horizontal transport of fine particles from nearshore to offshore. The internal wave dynamics can be also associated with the distributions of water quality variables such as dissolved oxygen and nutrients in the lake. Thus, the basin-scale internal waves and horizontal circulation processes need to be accurately modeled for the correct simulation of the dissolved and particulate contaminants, and biogeochemical processes in the lake.

• 한국해양공학회지
• /
• 제37권1호
• /
• pp.1-7
• /
• 2023

The motion of small fishing vessels is significantly affected by small waves, leading to accidents, such as capsizing or sinking. This paper presents the results of two types of basin tests. The first test analyzed the characteristics of roll and pitch motions among regular waves with the same wave steepness using the drifting state of three (3G/T, 7G/T, 10G/T) small fishing vessels. The second test analyzed the motion characteristics of the 7G/T fishing vessel under different wave steepness. The first test showed that heave and roll motions are significant in the beam sea, while pitch motion is significant in the bow and stern seas. The second test shows that wave steepness has a linear relationship with roll and pitch motions in the bow and stern seas.

• 한국항해항만학회:학술대회논문집
• /
• 한국항해항만학회 2006년도 추계학술대회 논문집(제1권)
• /
• pp.205-210
• /
• 2006

해양구조물 설계시 급격한 파랑에 의한 충격력은 구조물 안전을 위한 중요한 설계인자이다. 이러한 충격력은 과도한 하중이 극히 짧은 시간 사이에 발생하는 현상으로 실험적 또는 수치해석적으로 해석하기 매우 어려운 문제이다. 본 연구에서는 급격한 파랑에 의한 충격력을 해석하기 위하여 수치파수조를 이용하여 N.S. 방정식에 기반한 수치해석을 수행하였다. 임의파를 선형중첩에 기반하여 조파기를 작동시켜 재현하였고 다블록격자하에서 수직실린더에 작용하는 충격력을 수치해석하였다. 한편 자유표면은 V.O.F. 및 local height function을 이용하여 추적하였다. 수치해석 검증을 위하여 수치해석 및 실험 결과와 비교를 수행하였는데 비교적 만족할 수 있는 결과를 확인하였으나 해양구조물 설계시 유용한 결과를 얻기 위해서는 쇄파와 같은 극한파 재현과 극한파에 의한 충격력에 대한 많은 연구가 지속되어야 함을 알 수 있었다.

• 한국지진공학회:학술대회논문집
• /
• 한국지진공학회 2006년도 학술발표회 논문집
• /
• pp.64-69
• /
• 2006

At starting point, 1D velocity models were inverted by using 430 events with P-wave 5147, S-wave 3729 from KIGAM, KMA, KEPRI, and KINS's seismic networks. A minimum 1D model shows that P-wave velocities are around $6.0{\pm}0.5\;km/s$ slowly increasing with depth between surface and 15 km. The velocities are about $6.4{\pm}0.2\;km/s$ below 15km to 35km. The earthquake data number for 3D tomography was 630 adding to previous 430 events with limitation of more than 6 station detection and relocation stability of location. The checkerboard test shows that only upper curst part from surface to 17 km have reliable resolution. The results of upper crust part present that the boundary of Gyeong-sang basin and Youngnam massif is mach well velocity variation pattern. The western part of the basin is shown as lower velocity and south-eastern part as higher. This is because that sedimentary rocks are widely located around western part of the basin and volcanic origin rocks are distributed around south-eastern part.

• Geomechanics and Engineering
• /
• 제13권1호
• /
• pp.99-117
• /
• 2017

Rock physics modeling of sandstone reservoir from gas fields of Krishna-Godavari basin represents the link between reservoir parameters and seismic properties. The rock physics diagnostic models such as contact cement, constant cement and friable sand are chosen to characterize reservoir sands of two wells in this basin. Cementation is affected by the grain sorting and cement coating on the surface of the grain. The models show that the reservoir sands in two wells under examination have varying cementation from 2 to more than 6%. Distinct and separate velocity-porosity and elastic moduli-porosity trends are observed for reservoir zones of two wells. A methodology is adopted for generation of Rock Physics Template (RPT) based on fluid replacement modeling for Raghavapuram Shale and Gollapalli Sandstones of Early Cretaceous. The ratio of P-wave velocity to S-wave velocity (Vp/Vs) and P-impedance template, generated for this above formations is able to detect shale, brine sand and gas sand with varying water saturation and porosity from wells in the Endamuru and Suryaraopeta gas fields having same shallow marine depositional characters. This RPT predicted detection of water and gas sands are matched well with conventional neutron-density cross plot analysis.

• International Journal of Naval Architecture and Ocean Engineering
• /
• 제2권1호
• /
• pp.34-38
• /
• 2010

Field investigations have been carried out in two 60-day stages on the surf beat low frequency waves in Anzali port, one of the main commercial ports in Iran, located in southwest coast of the Caspian Sea. The characteristics of significant water waves were measured at three metering stations in the sea, one at the entrance of the port and three in the basin. The measured data were inspected to investigate the surf beat negative effects on the tranquility of the port. Using field measurements and complementary numerical modeling, the response of the basin to the infra-gravity long waves was inspected for a range of wave frequencies. It was concluded that the water surface fluctuations in the port is strongly related to the incident wave period. The long waves with periods of about 45s were recognized as the worst cases for water surfaceperturbation in the port. For wave periods higher than the mentioned range, the order of fluctuation was generally low.

• IUGG한국위원회:학술대회논문집
• /
• IUGG한국위원회 2003년도 정기총회 및 학술발표회
• /
• pp.18-18
• /
• 2003

Three-dimensional finite-difference simulation of earthquake ground motion is performed using a locally variable time-step (LVTS) scheme matching with discontinuous grids. Discontinuous grids in three directions and extension of the discontinuous grids' boundary to the free-surface in the LVTS scheme minimize the cost of both the computational memory and the CPU time for models like the localized sedimentary basin. A simplified model of sedimentary basin is dealt to show the feasibility and efficiency of the LVTS scheme. The basin parameters are examined to understand the main characteristics on ground-motion response in the basin. The results show that the seismic energy is concentrated on a marginal area of the basin far from the source. This focusing effect is mainly due to the constructive interference of the direct S-wave with the basin-edge induced surface waves. The ground-motion amplification over the deepest part of the basin is relatively lower than that above the shallow basin edge. Therefore the ground-motion amplification may be more related to the source azimuth or the direction of the incident waves into the basin rather than the depth of it.

• 한국해양공학회:학술대회논문집
• /
• 한국해양공학회 2004년도 학술대회지
• /
• pp.96-101
• /
• 2004

When the wind blows hard, most waves are breaking in sea. Breaking waves occur, exceeding limitation of wave steepness(wave height/wave length=l/7). Because a wave of single angular frequency couldn't generate the breaking phenomena at two dimensional ocean engineering basin, the breaking wave can be generated by the superposition of waves with various angular frequencies. We research how are the particle kinematics in the breaking wave and the magnitude of the breaking wave exciting force. We compare the force in a regular wave which has same specifications(wave height, period and length) as the breaking wave. Also the experimental results of wave exciting force and particle velocity are investigated by comparison on the analytic results using the potential theory.