• Tunnel and Underground Space
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• v.18 no.6
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• pp.418-426
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• 2008

A surface blasting method with a single tree face is currently used in Pasir Coal Mine in Indonesia. The single free face is usually the ground surface. This kind of blasting method is easy to use but inevitably causes enormous ground vibrations, which, in turn, can affect the stability of the slopes comprising the various boundaries of the open pit mine. In this regard, we decided to make a specific blasting guideline for the control of found vibrations to ensure the safety of the pit slopes and waste dumps of the mine. Firstly, we derived a prediction equation for the ground vibration levels that could be occurred during blasting in the pits. Then, we set the allowable levels of ground vibrations for the pit slopes and waste dumps as peak particle velocities of 120mm/s and 60mm/s, respectively. From the prediction equation and allowable levels, safe scaled distances were established for field use. The blast design equations for the pit slopes and waste dumps were $D_s{\geq}5\;and\;D_S{\geq}10$ respectively. We also provide several standard blasting patterns for the hole depths of $3.3{sim}8.8m$.

• Journal of the Society of Naval Architects of Korea
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• v.28 no.1
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• pp.60-68
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• 1991

The updated Lagrangian Finite Element Method is introduced to analyse rigid body-fluid impact problem which is characterized by incompressible Navier-Stokes equations and impact-contact conditions between free surface and rigid body. For the convenience of numerical computation, velocity fields are splinted into vicous and pressure parts, and then the governing equations and boundary conditions are decomposed in accordance with the decomposition. However, Viscous stresses acting an the solid boundaries are neglected on the assumption that very small velocity gradients may occur during extremely small time interval of the impact. Four coded quadrilateral elements are used to discretize the space domain and the fully explicit time-marching algorithm is employed with a reasonably small time step. At the beginning of each time step, contact velocity of the rigid body is computed from the momentum balance between the body and the fluid. The velocity field is then computed to satisfy the discretized equations of motions and incompressibility and contact constraints as well as an exact free surface boundary condition. At the end of each time step, the fluid domain is updated from the velocity field. In the present time stepping numerical analysis, behaviour of the free surface near the body can be observed without any difficulty which is very important in the water impact problem. The applicability of the algorithm is illustrated by a wedge type falling body problem. The numerical solutions for time-varying pressure distributions and impact loadings acting ion the surface are obtained.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.30 no.4
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• pp.329-334
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• 2017

The structures, which are made up with the huge number of degrees-of-freedom and the assembly of substructures, have a great complexity. In order to increase the computational efficiency, the analysis models have to be simplified. Many substructuring techniques have been developed to simplify large-scale engineering problems. The techniques are very powerful for solving nonlinear problems which require many iterative calculations. In this paper, a modal derivatives-based model order reduction method, which is able to capture the stretching-bending coupling behavior in geometrically nonlinear systems, is adopted and investigated for its performance evaluation. The quadratic terms in nonlinear beam theory, such as Green-Lagrange strains, can be explained by the modal derivatives. They can be obtained by taking the modal directional derivatives of eigenmodes and form the second order terms of modal reduction basis. The method proposed is then applied to a co-rotational finite element formulation that is well-suited for geometrically nonlinear problems. Numerical results reveal that the end-shortening effect is very important, in which a conventional modal reduction method does not work unless the full model is used. It is demonstrated that the modal derivative approach yields the best compromised result and is very promising for substructuring large-scale geometrically nonlinear problems.

• Proceedings of the Korean Vacuum Society Conference
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• 2015.08a
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• pp.238.1-238.1
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• 2015

2차원 탄소나노재료인 그래핀은 본연의 우수한 물성으로 인하여 전자소자, 에너지 저장매체, 유연성 전도막 등 다양한 분야로의 응용가능성이 제기되었다. 그러나 실제적인 응용을 위해서는 그래핀의 구조적인 결함을 최소화하며, 특성을 자유로이 제어하거나 향상시키는 공정의 개발이 필요하다. 일반적으로 화학적 도핑은 그래핀의 전기적 특성을 제어하는 효율적인 방법으로 알려져 있다. 화학적 도핑의 방법으로는 그래핀을 특정 가스 분위기에서 고온 열처리하거나 활성종들이 존재하는 플라즈마에 노출시킴으로써, 그래핀을 구성하는 탄소원자를 이종원자로 치환하거나 표면에 흡착시켜 기능화 된 그래핀을 얻는 방법 등이 제시되었다. 특히 플라즈마를 이용한 도핑방법은 저온에서 단시간의 처리로 효율적인 도핑이 가능하고, 인가전력, 처리시간 등의 플라즈마 변수를 변경하여 도핑정도를 수월하게 제어할 수 있다는 장점을 가지고 있다. 그러나 플라즈마 내에 존재하는 극성을 띄는 다양한 활성종들로 인하여 그래핀에 구조적인 결함을 형성하여 오히려 특성이 저하될 수 있어 이를 고려한 플라즈마 공정조건의 설정이 필수적이다. 따라서 본 연구에서는 플라즈마에 노출된 그래핀의 Raman 특성을 고찰함으로써 화학적 도핑과 구조적인 결함의 경계를 확립하고 구조결함의 형성을 최소화한 효율적인 도핑조건을 도출하였다. 고품질 그래핀은 물리적 박리법을 이용하여 300 nm 두께의 실리콘 산화막이 존재하는 실리콘 웨이퍼 위에 제작하였으며, 평행 평판형 직류 플라즈마 장치를 이용하여 전극의 위치, 인가전력, 처리시간을 변수로 암모니아(NH3) 플라즈마를 방전하여 그래핀의 Raman 특성변화를 관찰하였다. 그래핀의 구조적 결함 및 도핑은 라만 스펙트럼의 D, G, D', 2D밴드의 강도비와 G밴드의 위치와 반치폭(Full width at half maximum; FWHM)의 변화를 통해 확인하였다. 그 결과, 인가전력과 처리시간이 증가함에 따라 그래핀의 도핑레벨이 증가되고, 이후에는 도핑효과가 없어지고 결함의 정도가 상승하는 천이구역이 존재하며, 이를 넘어서는 너무 높은 인가적력의 처리는 그래핀에 결함을 형성하여 구조적인 붕괴를 야기함을 확인하였다.

• Journal of the Korean Society of Marine Environment & Safety
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• v.17 no.2
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• pp.167-172
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• 2011

In physical engineering, the turbulent flow on the surface roughness is very important. With the welding, design and paint, the hull surface roughness at each stage in the various aspects are important factors to be considered. In this study, the hull surface roughness geometry that was generalized to the PIV was applied to the tank test. The roughness of the surface changed the distance of the interval. Experimental velocity is Re = $1.1{\times}10^4$, Re = $2.0{\times}10^4$ and Re = $2.9{\times}10^4$. The turbulent intensity at the time-average were examined The roughness coefficient occurred with increasing turbulence intensities was stronger. The turbulence intensity away from the roughness in the shape was zero. The variation of turbulence intensity at the experimental flow conditions change was not affected.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.30 no.1
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• pp.29-38
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• 2018

In order to evaluate the performance of the floating wave power, which is an axisymmetric oscillating water column type, linearized free surface boundary condition considering the influence of PTO (power takeoff) was derived and a finite element numerical model was established. Numerical experiments were carried out by varying cylinder length, skirt length, and depth of water, which are design parameters that can change the resonance of water column in cylinder and heave resonance of the float, which is considered to affect the power generation efficiency. Finally, the basic data necessary for the optimum design of the power generation system were obtained. As a result, the efficiency of the power generation system is dominated by the heave motion resonance of the float rather than the water column resonance in the cylinder, and the resonance condition for the heave motion can be changed efficiently by attaching the skirt to the outside of the buoy.

• Proceedings of the Korea Water Resources Association Conference
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• 2020.06a
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• pp.391-391
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• 2020

본 연구의 목적은 2006년 6월 ~ 10월에 발생한 메콩강 하류 지역의 홍수를 모의하는 것이다. 강우자료는 위성강우 자료인 미국 NOAA의 CMORPH를 적용하였으며, 홍수유출 해석은 GRM 모델을 적용하였다. Tonlesap 호수를 포함하는 메콩강 하류 지역의 침수분석은 G2D 모델을 적용하였다. 위성강우 자료는 NOAA의 3시간 간격의 CMORPH 위성강우자료를 일일강우량 자료로 변환하고, 일본의 Research Institute for Humanity and Nature (RIHN)과 Meteorological Research Institute of the Japan Meteorological Agency (MRI/JMA)의 APHRODITE 프로젝트에 의해 구축된 APHRODITE 강우량 자료를 이용하여 보정한 후 홍수모의에 적용하였다. DEM 자료는 HydroSHED 15s자료를 이용하였고, 토양도는 UN FAO의 HWSD, 그리고 토양도는 Global map landcover ver3.0을 이용하였다. GRM 모델과 G2D 모델은 Github(https://github.com/floodmodel)에 공개되어 있으며, 이를 이용하였다. 유출 모델은 메콩강 전체 유역을 대상으로 2682.815m의 공간해상도로 구축하였다. 보정한 강우를 이용하여 유출모의 한 결과 첨두유량은 23,796.8 ㎥/sec로 계산되었다. Kratie 지점의 유출량과 Tonlesap 호수로 집수되는 유량을 상류단 경계조건으로 이용하여 약 150일 동안의 침수모의를 하였다. 450 m 공간해상도로 침수모의 도매인을 구축하였으며, 조도계수는 0.045를 사용하였고, 하류단은 자유수면 유출조건을 적용하였다. 침수분석 결과 메콩강 본류를 흐르는 유량이 Tonlesap 호수로 유입되어 호수의 수위가 상승하였다. Tonlesap 호수의 최대침수심은 약 11 m를 나타내었으며, 호수로 유입된 유량은 모의기간 중에 호수에 저류되어 있었다. 메콩강 본류의 Kratie 지점으로 유입되는 유량이 첨두값을 지난 후에도 모의 기간이 길어질수록 메콩강 하류 델타지역과 그 주변의 평지로 침수범위가 확대 되었다. 모의 종료시에는 메콩강 하류가 광범위하게 침수되면서 최대 침수면적을 나타내었다. 본 연구에서 메콩강을 범람한 홍수는 메콩강 하류의 서쪽 해안으로 먼저 유출이 되었다. 이는 침수모의에 적용된 DEM 자료가 북동쪽에서 서남쪽 방향으로 빗살무늬 형태의 고도분포를 가지기 때문인 것으로 판단되며, 대상 지역의 DEM 정확성 평가와 함께 추가적인 연구가 필요하다.

• Journal of the Korea institute for structural maintenance and inspection
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• v.20 no.5
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• pp.93-101
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• 2016

In this study, the governing equations of motion for multi-cracked nonuniform nanobeam based on nonlocal elasticity theory and embedded in an elastic medium were derived. DTM(differential transformation method) was applied to vibration analysis of multi-cracked nonuniform nanobeam based on nonlocal elasticity theory and embedded in an elastic medium. The non-dimensional natural frequencies of this nanobeam were obtained for eoe, crack stiffness and elastic medium stiffness with various boundary conditions. The results obtained by this method was compared with previous works and showed the close agreement between two methods. The important conclusions obtained by this study are as follows : 1. As the length of nanobeam is shorter, the effect of scale coefficient is greater. 2. The locations of crack change non-dimensional natural frequency, In the case of fixed-fixed ends, the non-dimensional natural frequency is the biggest in the first crack location of 0.6L of nanobeam length, and the smallest in both ends. In the case of fixed-free ends, the closer the location of first crack go tho the free end, the bigger the non-dimensional natural frequency. 3. As the stiffness of crack is greater, the non-dimensional natural frequency is smaller, And the effect of crack stiffness is similar on both fixed-free ends and fixed-fixed ends. 4. The bigger the stiffness of elastic medium, the greater the non - dimensional natural frequency.

• Journal of Navigation and Port Research
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• v.30 no.10 s.116
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• pp.869-875
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• 2006

This paper presents the method for developing an optimum hull form with minimum wave resistance using SQP(sequential quadratic programming) as an optimization technique. The wave resistance is evaluated by a Rankine source panel method with non-linear free surface conditions and the ITTC 1957 friction line is used to predict the frictional resistance coefficient. The geometry of the hull surface is represented and modified using NURBS(Non-Uniform Rational B-Spline) surface patches. To verity the validity of the developed program the numerical calculations for Wigley hull and Series 60( $C_B=0.6$) hull have been performed and the results obtained by the numerical calculations have been compared with the original hulls.

• Journal of Navigation and Port Research
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• v.37 no.1
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• pp.1-7
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• 2013

In this paper the developed prediction technique of wave-making resistance performance for a ship attached with a vertical blade had been verified. Numerical analysis program as a prediction technique had been developed using the Rankine source panel method and the vortex lattice method(VLM). The nonlinearity of the free surface conditions was fully taken into account using the iterative method and the trim and the sinkage of the ship were also considered in the numerical analysis program. Panel cutting method was applied to get hull surface panels. Numerical computations were carried out for a 4000TEU container carrier and the vertical blade was attached 6 different locations astern. To investigate the validity of the numerical analysis program the commercial viscous flow field analysis program FLUENT was used to obtain the viscous flow field around the ship and the model test was performed. The model test results were compared with the numerical analysis results.