Changhwan Jang

Simulation of Seasonal Bathymetric Change at Haeundae Beach with Two Representative Wave Settings

ABSTRACT Kim, H.; Jin, J.Y.; Jang, C.; Yoo, H.J., and Hwang, D.H., 2014. Simulation of seasonal bathymetric change at Haeundae Beach with two representative wave settings. Long-term shoreline position of Haeundae Beach has been quite stable notwithstanding seasonal oscillatory movement. Bathymetry around Haeundae Beach was surveyed on 7 August 2007 and 12 November 2007 by using an echo-sounder, while wave, tide, and tidal current were measured between the two survey days, so that bathymetric change at Haeundae Beach was obtained from the two surveys. According to the surveys the east part of the beach was eroded, and the west part of the beach was accreted. Measured waves from SSE, SE, ESE, E during the period were stronger than measured waves from S, SSW, SW, WSW. A numerical model system CST3D was adopted to reproduce the bathymetric change at Haeundae Beach during the period. Two representative wave settings are chosen for the period as a minimum number to represent the time-series of wave record, based on equivalent sediment flux concept contained in the CERC formula. Wave field, wave-induced force field, wave-induced current field, sediment transport field, and bathymetric change are computed from individual modules, SWAN, WIF, FLOW, SED in CST3D, respectively. Computed bathymetric change agrees reasonably well with measured one. It is believed that selection of two representative wave settings is useful for simulation of seasonal bathymetric change for fairly straight morphology like Haeundae. CST3D is thought to effectively describe overall seasonal sediment transport pattern and consequent bathymetric change at Haeundae Beach.

A Practical Algorithm to Simulate Erosion of On-Shore Zone

Abstract An algorithm to allow shoreline movement during numerical experiment on sediment transport, deposition or resuspension for general coastal morphology is proposed here. The bed slope near shoreline, i.e. mean sea level, is influenced by bed material, tidal current, waves, and wave-induced current, but has been reported to remain within a stable range. Its annual variation is not large, either. The algorithm is adjusting the bathymetry, if the largest bed slope within shoreline band exceeds a given bed slope due to continuous erosion at zones below the shoreline. This algorithm automatically describes retreat of shoreline caused by erosion, when used within a numerical system. The algorithm was tested to a situation which includes a continuous dredging at a point, and showed satisfactory development of concentric circle contours. Next, the algorithm was tested to another situation which includes sinking of eroded part of bed plate, and produced satisfactory results, too. Finally, the algorithm was tested to a movable-bed laboratory experimental conditions. The shoreline movement behind detached breakwater was reasonably reproduced with this algorithm.

Modeling Three-dimensional Free Surface Flow around Thin Wall Incorporation Hydrodynamic Pressure on δ-coordinate

DepartmentofCivilEngineering,kookminuniversity*DepartmentofCoastalOceanographyandEngineering,GeosystemResearchCorporation**CoastDisasterResearchCenter,KoreaInstituteofOceanScienceTechnology***CivilEngineeringandEnvironmentExaminationDivision,KoreanIntellectualPropertyOffice요 약물에잠긴얇은벽은잠제사각형블록의극단적인경우라고할수있으며, 하천이나해안지역에서다양한목적으로사용될수있다. 잠제구조물의얇은벽주위흐름과압력을계산하기위하여동수압이포함된-격자체계의3차원수치모델을수행하였고, 그주변의유속흐름을파악하였다. -격자체계는완경사하상에유동시뮬레이션을적용할수있는강력한장점을가지고있다. 반면에-격자체계는하상에날카로운구조물등에대한해석에는한계를갖고있다. 동압력계산은직교격자시스템에서만유효하다. CST3D시스템내에SOLA 기법을-격자체계에맞게수정하여채택하였다. 모델은2차원수조에서의1차원전자자기식유속계를통한관측자료를통하여검증하였고, 정수압가정의-격자체계수치모형과의비교를통하여정량적인비교·검토를수행하였다. 전체적으로계산된수평유속과측정된수평유속이유사한것으로나타났다. 수리모형실험을통한관측자료의결과를수치모형이10% 이내로정확하게모의하였고, 관측자료와대조하였을시와도의분포를유사하게재현하였다. 수정SOLA 방식을채택하여동수압이고려되었고, -격자체계에적용한본연구는실제관측자료를잘재현하였으며, 하구, 하천등의구조물주변에서의유속분포를검증할시매우유용한것으로판단된다.핵심용어:CST3D, 시그마격자체계수치모형, 동수압고려수치모형AbstractSubmerged thin walls are extreme case of submerged rectangular blocks, and could be used for many purposes in rivers orcoastal zones, e.g. to tsunami. To understand flow characteristics including flow and pressure fields around a specificsubmerged thin wall a numerical model was applied which includes computation of hydrodynamic pressure on -coordinate.-coordinate has strong merits for simulation of subcritical flow over mild-sloped beds. On the other hand -coordinate isquite poor to treat sharp structures on the bed. There have been a few trials to incorporate dynamic pressure in -coordinate by some researchers. One of the previous approaches includes process of sloving the Poisson equation. However,the above method includes many high-order terms, and requires long cpu for simulation. Another method SOLA wasdeveloped by Hirt et al. for computation of dynamic pressure, but it was valid for straight grid system only. PreviousSOLA was modified for -coordinate for the present purpose and was adopted in a model system, CST3D. Computed flowfield shows reasonable behaviour including vorticity is much stronger than the upstream and downstream of the structure.The model was verified to laboratory experiments at a 2DV flume. Time-average flow vectors were measured by usingone-dimensional electro-magnetic velocimeter. Computed flow field agrees well with the measured flow field within 10 %error from the speed point of view at 5 profiles. It is thought that the modified SOLA scheme is useful for

Application of Inclusive Environmental Impact Assessment for Newly-Proposed Airport in Korea

The need and importance of developing and utilizing the oceans, not only as sources of renewable energy and mineral resources, but also as countermeasures to global warming such as for CCS (carb on capture and storage), have continued to increase, especially in countries with limited land areas and resources. Therefore, it is necessary to assess the sustainability of an ocean utilization technology or system not only from an economic point of view but also from an ecological one. For this purpose, it might be effective to develop a comprehensive evaluation method and/or index, by which the assessment of and decisions about a technology and system can be made more objectively. It would also be useful to have an environmental simulation model, which was developed and reported in a previous research. The aim of this study was to modify a reasonable and quantitative index, with which a comprehensive evaluation system can be established, to assess environmental su stainability and risk.