• Proceedings of the Korea Water Resources Association Conference
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• 2021.06a
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• pp.98-98
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• 2021

동역학파 기반 순간단위도 (Dynamic wave-based Instantaneous Unit Hydrograph)를 이용하여 유역에서의 강우에 의한 유출을 예측하는 기법을 개발하였으며, 국내 실제 자연 유역에 적용하여 기법의 타당성과 적용성을 검증하였다. 본 연구에서 제시한 '동역학파 기반 순간단위도 방법'은 물리기반 수치모형인 동역학파 강우유출모형과 개념적 순간단위도 방법을 결합하여 사용함으로써 물리적으로 정확하면서도 빠르고 안정적으로 강우-유출을 예측하는 것을 목적으로 한다. 유역의 순간단위도는 유역의 지형, 조도계수와 동역학파 강우유출모형인 tRIBS-OFM을 이용하여 계산된 S-수문곡선을 수치적으로 미분함으로써 유도되며, 유도된 순간단위도는 강우강도에 따라 변화하므로 회선적분을 통한 유출수문곡선 예측 시 강우-유출 관계의 비선형성을 고려할 수 있다. 본 연구에서 유도된 순간단위도의 첨두 값과 첨두 발생시간은 강우강도 값과 각각 양과 음의 상관관계를 가졌으며 강우강도 값과 멱 함수 (power function)의 관계를 가졌다. 이는 Paik and Kumar (2004) 등 기존 연구들에서 밝힌 순간단위도의 특성과 일치하였으며, 본 연구에서는 더 나아가 멱함수의 지수를 산정한 후 임의의 강우강도 값에 대응하는 순간단위도를 멱함수 관계를 이용하여 보간할 수 있는 방법을 제시하였다. 실제 유역에 대한 적용은 강원도 인제군에 위치한 내린천 유역을 대상으로 수행하였다. 유역을 여러 개의 소유역으로 분할하여 강우의 공간적 분포를 고려하였으며, 각 소유역에서의 유출량을 동역학파 기반 순간단위도를 이용해 계산한 뒤 물리기반의 하도추적모형을 이용하여 전체 유역에서의 유출수문곡선을 예측했다. 예측된 유출수문곡선을 관측 유출 자료와 비교해본 결과 NSE (Nash-Sutcliffe model efficiency coefficient)가 0.6 이상으로 측정되어 적절히 유출을 예측한 것으로 판단되었다.

• Advances in concrete construction
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• v.14 no.3
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• pp.153-167
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• 2022

The interaction between blast load and structures, as well as the interaction among structural members may well affect the structural response and damages. Therefore, it is necessary to analyse more realistic reinforced concrete structures in order to gain an extensive knowledge on the possible structural response under blast load effect. Among all the civilian structures, columns are considered to be the most vulnerable to terrorist threat and hence detailed investigation in the dynamic response of these structures is essential. Therefore, current research examines the effect of blast loads on the reinforced concrete columns via development of Pressure- Impulse (P-I) diagrams. In the finite element analysis, the level of damage on each of the aforementioned RC column will be assessed and the response of the RC columns when subjected to explosive loads will also be identified. Numerical models carried out using LS-DYNA were compared with experimental results. It was shown that the model yields a reliable prediction of damage on all RC columns. Validation study is conducted based on the experimental test to investigate the accuracy of finite element models to represent the behaviour of the models. The blast load application in the current research is determined based on the Lagrangian approach. To develop the designated P-I curves, damage assessment criteria are used based on the residual capacity of column. Intensive investigations are implemented to assess the effect of column dimension, concrete and steel properties and reinforcement ratio on the P-I diagram of RC columns. The produced P-I models can be applied by designers to predict the damage of new columns and to assess existing columns subjected to different blast load conditions.

• Journal of the Korea institute for structural maintenance and inspection
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• v.28 no.2
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• pp.9-16
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• 2024

In this paper, we aimed to convert the fire curve in volume units to a fire curve per unit area for application in the Fire Dynamic Simulator (FDS) surface heat release rate method. The fire curve was expressed dimensionlessly considering the total combustion characteristic time, and improvements were made to represent the appropriate ratios for the growth , steady, and decay phases concerning the fire intensity. Additionally, a correction function for combustion characteristic time varying with mass increase was derived. Also to control the growth time values according to the increase in mass, a function to correct the growth phase ratio was derived. Consequently, utilizing existing data, a formula was established to determine the reference mass for combustion materials and predict the fire curve based on mass increase.

• Applied Chemistry for Engineering
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• v.4 no.4
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• pp.753-759
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• 1993

The research and motor octane numbers (RON & MON, respectively) of a gasoline are dynamic measures of its quality of performance as a fuel. ASTM standard engine test methods (RON:ASTM D-2699, MON:ASTM D-2700) have been used for determining the octane numbers (RON,MON)of gasolines. But these methods have been widely criticized because their repeatability and reproducibility of the test method are very poor. In addition to these objections, the cost and operation time involved in measuring by the standard method led to searches for "non -engine" methods (Gas Chromatographic method, Nuclear Magnetic Resonance Spectroscopic method). In this study, we determined the carbon type structural compositions of the gasolines by $^{13}C-NMR$ spectroscopy and predicted the octane number (RON & MON) with good accuracy. we presented an assessment of the effects of molecular structural composition on octane numbers.

• Transactions of Materials Processing
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• v.25 no.1
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• pp.36-42
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• 2016

Fiber metal laminates (FMLs) are well known for improved fatigue strength, better impact resistance, superior damage tolerance and slow crack growth rate compared to traditional metallic materials. However, defects and loss of strength of a composite material can occur due to the vertical load from the punch during the joining with a dissimilar material using a conventional clinching method. In the current study, tapered-hole clinching was an alternative process used to join Al 5052 and FMLs. The tapered hole was formed in the FML before the joining. For the better understanding of static and dynamic characteristics, a clinched joining followed by a tensile-shear test was numerically simulated using the finite element analysis. The design parameters were also evaluated for the geometry of the tapered hole by the Taguchi method in order to improve and compare the lateral joining strength of the clinched joint. The influence of the neck thickness and the undercut were evaluated and the contribution of each design parameter was determined. Then, actual experiments for the joining and tensile-shear test were conducted to verify the results of the numerical simulations. In conclusion, the appropriate combination of the design parameters can improve the joining strength and the cross-sections of the tapered-hole clinched joint formed in the actual experiments were in good agreement with the results of the numerical simulations.

• Journal of the Society of Naval Architects of Korea
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• v.36 no.4
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• pp.21-27
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• 1999

A low order panel method based on the perturbation potential is applied for prediction of performance of blown-flap rudders. In order to improve the solution behavior at the large angle of attacks, the geometry of the trailing wake sheet is computed by aligning freely with the local flow. The effect of the wake sheet roll-up is also included with use of a high order panel method. The flow in the gap between the main component and the flap of the rudder is modeled as Couette flow. The effects of the gap and the flow jet are included in application of a kinematic and a dynamic boundary condition on the inlet and the outlet of the gap as well as on the flap and the wake. The results with the present method are compared with existing experimental data. The method is shown to be capable of determining accurately the flow characteristics even for large flap angles.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.66 no.2
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• pp.261-284
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• 2017

This paper describes the results of a low-frequency oscillation analysis using data measured in PMU installed in the KEPCO system, and the comparison with eigenvalues computed from the linear model. The dominant oscillation modes are estimated by applying various algorithms. The algorithms are: the extended Prony method; multiple time interval parameter estimation method; subspace system identification method; and spectral analysis. From the measurement data, modes of frequency 0.68[Hz] and 0.92[Hz] were estimated, and modes of frequency 0.63[Hz] and 0.80[Hz] were computed from the eigenvalue calculation. There was a difference between the mode estimated from measurement data and that from the linear model. This is possibly because of an error in the dynamic data of the KEPCO system used in eigenvalue calculation. Because wide area modes exist in the KEPCO system, these modes should be monitored continuously for the reliable operation of the system. In order to prevent total blackouts caused by wide area oscillation, moreover, contingency analysis should be performed in relation to this mode and appropriate measures should be established.

• Journal of the Society of Naval Architects of Korea
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• v.30 no.1
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• pp.125-133
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• 1993

Most studies on the vibration analysis of a beam-column with ends elastically restrained and various intermediate constraints have been based on the Euler beam theory, which is inadequate for beam-columns of low slenderness ratios. In this paper, analytical methods for vibration and dynamic sensitivity of a Timoshenko beam-column with ends elastically restrained and various intermediate constraints are presented. Firstly, an exact solution method is shown. Since the exact method requires considerable computational effort, a Rayleigh-Ritz analysis is also investigated. In the latter two kinds of trial functions are examined for comparisions : eigenfunctions of the base system(the system without intermediate constraints) and polynomials having properties corresponding to the eigenfunctions of the base system. The results of some numerical Investigations show that the Rayleigh-Ritz analysis using the characteristic polynomials is competitive with the exact solutions in accuracy, and that it is much more efficient in computations than using the eigenfunctions of the base system, especially in the dynamic sensitivity analysis. In addition, the prediction of the changes of natural frequencies due to the changes of design variables based on the first order sensitivity is in good agreements with that by the ordinary reanalysis as long as the changes of design variables are moderate.

• Journal of the Korean Geotechnical Society
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• v.31 no.4
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• pp.57-66
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• 2015

Empirical seismic displacement equations based on the Newmark sliding block method are widely used to develop seismic landslide hazard map. Most proposed equations have been developed for embankments and landfills, and do not consider the dynamic response of sliding block. Therefore, they cannot be applied to Korean mountain slopes composed of thin, uniform soil-layer underlain by an inclined bedrock parallel to the slope. In this paper, a series of two-dimensional dynamic nonlinear finite difference analyses were performed to estimate the permanent seismic slope displacement. The seismic displacement of mountain slopes was calculated using the Newmark method and the equivalent acceleration time history. The calculated seismic displacements of the mountain slopes were compared to a widely used empirical displacement model. We show that the displacement prediction is significantly enhanced if the slope is modeled as a flexible sliding mass and the amplification characteristics are accounted for. Regression equation, which uses PGA, PGV, Arias intensity of the ground motion and the fundamental period of soil layer, is shown to provide a reliable estimate of the sliding displacement. Furthermore, the empirical equation is shown to reliably predict the hazard category.

• International Journal of Highway Engineering
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• v.4 no.4 s.14
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• pp.41-52
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• 2002

This study dealt with analysis of size effect of testing apparatus for Kim test which measures rut resistance characteristics of asphalt mixture under static loading. Two columns in different diameter with each column having different radios of round cut (Curvature) at the bottom were used for testing asphalt mixture. Deformation load ($P_{max}$) and deformation strength ($K_D$) were found to have relatively high correlation with rut depth and dynamic stability of asphalt concrete. Diameter of specimen was not a significant factor in this test. From the statistical correlation analysis with rutting properties, the radius of curvature and diameter of loading column were found to be important factor affecting the results of the test. Among the radios (r) of curvatures, r=0.5cm and 1.0cm showed much higher correlation than the column without curvature, and r=1.0cm being better between the two. The column with diameter of 4cm showed better correlation than diameter of 3cm. Therefore, the column of 4cm diameter with r=1.0cm was found to be the best among various apparatus sizes. Prediction models for rut depth and dynamic stability were developed for each aggregate mixture based on Kim test variables using SAS STEPWISE procedure. Therefore, if this test method is validated through further study, Kim test can be used for selecting asphalt mixture with the highest resistance against permanent deformation.