• Journal of the Korean Society of Manufacturing Process Engineers
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• v.15 no.4
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• pp.40-45
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• 2016

Interrupted cutting has different cutting characteristics compared with continuous cutting. In interrupted cutting, the workpiece has a groove that regularly impacts the cutting tool and workpiece. Therefore, tool damage occurs rapidly, and this increases the cutting force and surface roughness. In this study, we performed interrupted cutting of carbon steel for machine structure (SM45C) using a coated carbide tool (TT7100). To predict the cutting force, we analyzed the experimental results with a regression analysis. The results were as follows: We confirmed that the factors affecting the principal force and radial force were cutting speed, depth of cut, and feed rate. From the multi-regression analysis, we deduced regression equations, and their coefficients of determination were 89.6, 89.27, and 28.27 for the principal, radial, and feed forces, respectively. This means that the regression equations were significant for the principal and radial forces but not for the feed force.

• Journal of Korea Water Resources Association
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• v.33 no.1
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• pp.39-50
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• 2000

Generally speaking, a hydrodynamic model needs a friction coefficient (Manning coefficient or Chezy coefficient) and eddy viscosity. For numerical solution the coefficients are usually determined by recursive calculations. The eddy viscosity in numerical model plays physical diffusion in flow and also acts as numerical viscosity. Hence its value has influence on the stability of numerical solution and for these reasons a consistent evaluation procedure is needed. By using records of stage and discharge in the downstream reach of the Han river, I-D models (HEC-2 and NETWORK) and 2-D model (SMS), estimated values of Manning coefficient and an empirical equation for eddy viscosity are presented. The computed results are verified through the recorded flow elevation data.n data.

• Water for future
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• v.27 no.2
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• pp.85-96
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• 1994

Numerical instability of Preissmann scheme is studied for unsteady flow analysis in a natural river. The solution strategies to overcome the instability problems are presented in this paper. The main causes of numerical instability of Preissmann scheme are transition flow, abrupt change in cross section, in-appropriate roughness coefficients, time step and distance step, rapidly rising hydrograph, dry bed and so on. Transition flow model is proposed for the analysis of the transition flow which changes from subcritical to supercritical or conversely. The subcritical and supercritical reaches are groped in the channel, then appropriate boundary conditions are introduced for each reach. The transition flow analysis produces stable solutions in calculating through the various transition conditions. Verification with an actual river system is necessary in the future.

• Journal of the Society of Naval Architects of Korea
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• v.48 no.4
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• pp.363-367
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• 2011

In this paper, friction coefficients between ices and model ship were studied in order to predict the resistance of ice. The friction coefficient is a dimensionless scalar value which describes the ratio of the force of friction between two bodies and the force pressing them together. The coefficient of friction depends on the materials, roughness on surface, lubrication, etc. We tested and analyzed the friction coefficient for the development of the test methodology. The friction coefficient for ice model test is very dominant to predict the ship performance, so every ice tank uses their own painting technique. In this study, the friction coefficient with changing the moving speed of ice was studies by using a flat plates which were made by the MOERI's paining technique and the basic research for the developing the paining methodology in the MOERI ice model basin was carried out.

• Journal of Korea Water Resources Association
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• v.33 no.4
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• pp.483-493
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• 2000

Two dimensional finite element model, RMA, is used to simulate flood inundation phenomena from main channel to floodplain. The marsh porosity method allows finite elements to simulate gradual transition between wet and dry states. The model is applied to prismatic trapezoidal channel to test the applicability of wetting and drying. The floodwave in a river which meanders through a floodplain is also analyzed. The short-circuiting effects, in which the flow leave the meandering main channel and takes a more direct route on the floodplain, are analyzed with various sinuosity factor and roughness coefficients. Finally, the model is applied to the midstream of the Keum River. Wet/dry calculation can simulate the various discharge condition with the same finite element networks.

• Proceedings of the Korea Water Resources Association Conference
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• 2007.05a
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• pp.780-784
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• 2007

본 연구는 수치모형을 이용하여 다양한 규모의 자연하천에서 조도계수를 산정하고 조도계수가 홍수위에 미치는 민감도를 분석하기 위함이다. 이를 위하여 한국건설기술연구원에서 개발된 SNS 1차원 모형을 사용하였으며, 한강 팔당댐${\sim}$전류구간, 금강 대청댐${\sim}$공주구간, 달천 괴산댐${\sim}$쌍천합류점 구간에 적용하였다. 본 연구에서 얻은 결론을 요약하면 다음과 같다: (1) 자연하천의 조도계수는 유량이 증가함에 따라 감소하며 어느 한계유량 이상에서 일정한 조도계수로 수렴된다. (2) 하천정비기본계획에 수록된 조도계수는 대하천의 경우 본 연구에서 산정된 계획홍수량 구간의 조도계수와 큰 차이를 보이지 않는다. 그러나 실제 홍수사상의 한강 적용 결과 일부 구간에서 최대 87.3cm의 수위차가 발생하였다. (3) 달천 지방1급구간의 경우 하천정비기본계획에 수록된 조도계수와 본 연구에서 산정한 조도계수는 상대적으로 큰 차이를 나타내고 있으며 전 구간에서 최대 97.5cm의 수위차가 발생하였다. (4) 따라서 다양한 규모의 하천에서 실측수위를 이용한 객관적이고 정량적인 조도계수 산정에 관한 연구가 필요한 것으로 판단된다.

• Journal of the Korea Institute of Military Science and Technology
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• v.13 no.5
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• pp.725-733
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• 2010

A simulator is proposed in this paper for predicting the RF signal level after propagating over sea and land surfaces. Various sea and land types and transmit/receive antenna patterns, as well as the locus of the transmit antenna, are considered for this simulator. At first, microwave reflection characteristics of various sea surfaces have been computed, based on an empirical formula which is developed in this study for the relation between the sea surface roughness and wind speed. Then, microwave reflections from land surfaces such as forests, agricultural areas, and bare surfaces, are computed using the first-order vector radiative transfer theory. Finally, the signal paths over sea and land surfaces are found using the ray tracing technique and the digital elevation model, and the signal level received by a receiving antenna is computed by the using the reflection coefficients of sea and land surfaces and the signal paths.

• Korean Journal of Applied Biomechanics
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• v.18 no.3
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• pp.1-10
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• 2008

One of the major factors affecting maneuverability of an athlete is frictional force caused at an outsole of his shoe. The magnitude of the frictional force is closely related to pattern and hardness of outsole and roughness of ground or floor. This study then focuses on the effect of outsole pattern of sports shoes on the frictional force. After surveying outsole patterns of sports shoes in markets, we select 4 types of outsole patterns, such as straight, W, O, and wave as primary outsole patterns of sports shoe and we also select depth, pitch and slope as design parameters of each pattern. Corresponding to those patterns and design parameters, various outsole specimen are prepared for frictional experiments. After performing frictional tests with those specimen, coefficients of friction(COF) are collected and analyzed with a statistical tool to draw useful conclusion.

• Proceedings of the Korea Water Resources Association Conference
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• 2012.05a
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• pp.576-580
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• 2012

하도내 수리구조물 건설과 준설로 인해 발생되는 급격한 수리특성의 변화와 편수위로 야기될 수 있는 제방의 파괴 및 침식을 검토하기 위해서는 다차원 모형의 검토가 필요하다. 본 연구에서는 HEC-RAS로 산정한 조도계수를 다차원 모형에 적용하여 수리거동을 분석하였다. 낙동강 수계에 대해 2003년, 2004년, 2006년 그리고 2007년 태풍 사상에 대해 적용하였으며 HEC-RAS 모형의 조도계수를 0.01부터 0.04까지 0.001씩 증가하여 HEC-RAS 모형에 적용하였고 부정류 흐름모의를 수행하여 RMSE와 NRMSE를 이용해 관측 값과 비교하였다. 공간단위 다차원 모형은 격자크기, 만곡도, 난류 등으로 인한 손실이 추가적으로 반영되기 때문에 선단위 1차원 모형에서 산정된 조도계수를 적용할 경우 실측 관측 수위보다 큰 값이 산정되었다. 따라서, 1차원 수치모형에 의해 산정된 조도계수를 다차원 모형에 그대로 적용할 경우 과대한 수위를 산정할 수 있기 때문에 모형 차원에 따른 별도의 보정을 수행하여 얻어진 조도계수를 적용해야 할 것으로 판단된다.

• Proceedings of the Korea Water Resources Association Conference
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• 2011.05a
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• pp.327-327
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• 2011

본 연구에서는 영국 환경청의 지원 하에 HR Wallingford에서 2003년에 개발한 Conveyance Estimation System(CES)을 이용하여 하천 조도계수를 산정해보고자 하였다. CES프로그램은 하천지형 정보인 단면 형상, 하상경사, 하상재료, 식생 상태 등의 정보를 바탕으로 임의 단면내 각 저항요인에 따라 프로그램에서 제시하고 있는 조도계수를 적용함으로써 수위변화에 따른 단면적, 유량, 통수능, 동수반경 등의 계산 결과를 제공한다. 이러한 계산 결과들을 Manning식에 대입함으로 써 유량 변화에 따른 조도계수를 산정할 수 있다. 섬진강 곡성 지점에 CES프로그램을 적용하여 계산된 조도계수를 실측 조도계수, 하천정비기본 계획에 제시된 조도계수와 비교하였다. 산정된 조도계수는 모두 유량 증가에 따라 감소하는 경향을 보이며, 약 $1,000m^3/s$이상의 고유량에서 실측자료를 이용하여 산정된 조도계수와 유사한 값에서 수렴하는 결과를 나타내고 있다. 섬진강 곡성지점 외에 추가 지점을 분석한 결과에서도 실측 조도계수와 CES를 이용한 조도계수가 큰 차이를 보이지 않았다. 따라서 CES프로그램을 이용하면 하천의 지형 정보만을 가지고도 조도계수, 수위-유량 관계식 등의 추정이 가능하기 때문에 실무적으로 유용하게 사용될 것이다.