• Geophysics and Geophysical Exploration
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• v.12 no.1
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• pp.8-16
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• 2009

The holistic inversion approach for frequency domain airborne electromagnetic data has previously been employed to simultaneously calibrate, process and invert raw frequency-domain data where prior information was available. Analternative formulation has been developed, which is suitable in the case where explicit prior information is not available. It incorporates: a multi-layer vertically-smooth conductivity model; a simplified bias parameterisation; horizontal smoothing with respect to elevation; and cluster computer parallelisation. Without using any prior data, an inversion of 8.0 million data for 3.4 million parameters yields results that are consistent with independently derived calibration parameters, downhole logs and groundwater elevation data. We conclude that the success of the holistic inversion method is not dependent on a sophisticated conceptual model or the direct inclusion of survey-area specific prior information. In addition, acquisition costs could potentially be reduced by employing the holistic approach which largely eliminates the need for high altitude zero-level measurements.

• Magazine of the Korean Society of Agricultural Engineers
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• v.29 no.2
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• pp.53-63
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• 1987

Due to their wide range of application, deterministic comprehensive hydrologic models using digital computers have been developed in all countries of the world and researches are being undertaken for their appropriate applications. The aim of this study has been to demonstrate the practical implementation of a physically based distributed hydrologic model, the USDAHL-74 model and to investigate its ability to simulate the long term estimate of water balance quantities in a Korean mountainous watershed. Application of the model to Dochuk watershed indicates the following results. 1.Since the USDAHL-74 model includes all the major components of the hydrologic cycle in agricultural watersheds, thus is comprehnsive, the model seems to have a wide range of application from the fact that simulation results obtained are not only runoff volumes m various time units but their spatial variation as well as even soil moisture within the watershed. 2.An approximate calibration to determine the parameter values in the model using various data obtained from D0chuk shed shows that the simulation error of yearly runoff volume is only 0.6 % and a correlation coefficient between observed daily runoff volume and simulated one is 0.91 in all calibrated period.3.As a verification test of the model, runoff volumes are simulated using 1986 year data without changing the parameter values determined by 1985 year data. The tests show that the USDAHL-74 model is a flexible tool and that realistic production to simulate the long term estimate of runoff in Korean mountainous watershed could be obtained using only a short period of calibration.4. Despite of the encouraging results, there still remain minor problems concerning the practical application of the model to improve the result of simulations. Some of these are the small descrepancies between observed and simulated daily runoff volume appeared in the vicinity of peaks and the recession of1 the daily hydrographs and the model performance for the frozen ground and melting process in the model. 5. Alough the use of parameter with physical significance and the ability to improve calibrations on the basis of physical reasoning represents advantages in the simulation for ungaged watersheds, further researches are needed to use the USDAHL-74 mode to simulate runoff in ungaged watersheds.

• Journal of the Korean Geosynthetics Society
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• v.13 no.2
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• pp.11-20
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• 2014

To create a large-scale complex, it is often the case to perform ground improvement by using vertical drain method after the reclamation of coastal soft ground, for construction period shortening and stable site renovation. During this process, the pore water migrates to the horizontal drainage layer of the ground surface through the vertical drain installed in the soft ground and discharged out to the open. In the past sand was used as the material for the horizontal drainage layer in numerous cases, however recently, due to material shortage and high pricing, the use of crushed stones has increased. To prevent mixing of the materials between the horizontal drainage layer and the upper landfill, geosynthetics (PPMat) are installed. However, the use of geosynthetics results in high additional cost for material purchase and installation, therefore it is necessary to examine the validity of the installation itself. In this study, to verify the necessity, model tests were performed. Results from the model tests indicate that the drainage ability of the horizontal drainage layer is barely affected by the application of geosynthetics.

• Journal of the Korean Society of Propulsion Engineers
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• v.24 no.1
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• pp.1-8
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• 2020

In this study, a configuration design of a CH₄/LOx small rocket engine was made and test system was established for the performance evaluation. A coaxial swirl injector was chosen because of its remarkable atomization performance and low combustion instability. Three aspect ratios for the combustion chamber configuration, i.e., 1.5, 1.8, and 2.1 were also set for the comparison of the combustion efficiency. The reliability of the thrust measurement rig was enhanced by pre-and post-calibration process. From the preliminary ground hot-firing test, the measured thrust and specific impulse values were 89.2 N and 181.8 s, respectively, which were 21.6% lower than the ideal values. In addition, the efficiency of characteristic velocity was measured as 84.2%.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.10 no.9
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• pp.2261-2266
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• 2009

A novel adaptive phase calibration method is proposed for nonlinear amplifiers. Based on the adaptive process of simple phase vector calculations, the AM/PM distortion can be significantly reduced for various input power. The performance of the proposed method is evaluated for up to 80 % improvements in AM/PM distortions, compared with the distortion of a conventional amplifier. Moreover, by means of an additional envelope-compensation technique, the improvement of the adjacent channel power ratio (ACPR) is presented.

• Journal of Korean Dental Science
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• v.13 no.2
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• pp.43-51
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• 2020

Purpose: The practical examination portion of the National Dental Licensing Examination (NDLE) is slated to be administered in the latter half of 2021 in the form of a clinical performance examination that comprehensively evaluates the patient-dentist interaction using standardized patients (SPs). The SPs should be equipped with the basic qualities and capacity as evaluators for a fair and reliable administration of the test. Materials and Methods: In this study, we analyzed the existing training materials for SPs who participated in domestic and overseas practical tests for the development of training materials for SPs through seminars and surveys of 11 dentistry schools and colleges. Result: First, SPs should be selected according to the basic quality criteria and capacity, which they must possess, and the preliminary basic training about the details which they must have knowledge of and be provided through videorecorded cases before the implementation of the preliminary field training. Second, the roles of SPs and the calibration process of the evaluation result forms are needed when conducting the preliminary field training for SPs. After watching video-recorded scenario cases, the SPs participate in discussions about the watched videos before proceeding to calibration practices of evaluation result forms. Third, because the Type A questionnaire of the practical examination of the NDLE is dependent on the SPs' capacity and training, the fairness of the practical test is largely dependent on the SPs. Therefore, practicing the roles as evaluators and evaluation training should be provided using practical test items that can improve the reliability of the test and show a high level of reproducibility about the same case. Conclusion: The findings of this study will be utilized for the development of training materials for SPs, so they can participate in the administration of a fair and reliable practical examination of the NDLE.

• Geomechanics and Engineering
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• v.28 no.5
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• pp.521-529
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• 2022

This research work deals with the development of air pluviation method for preparing uniform sand specimens for conducting large scale laboratory testing. Simulating real field conditions and to get reliable results, air pluviation method is highly desirable. This paper presents a special technique called air pluviation or sand raining technique for achieving uniform relative density. The apparatus is accompanied by a hopper, shutters with different orifice sizes and numbers and set of sieves. Before using this apparatus, calibration curves are drawn for relative density against different height of fall (H) and shutter sizes. From these calibration curves, corresponding to the desired relative density of 60%, the shutter size of 13mm and height of fall of 457.2 mm, are selected and maintained throughout the pluviation process. The density obtained from the mobile pluviator is then verified using the Dynamic Cone Penetrometer (DCP) test where the soil is poured in the box using defined shutter size and fall height. The results obtained from the DCP test are averaged as 60±0.5 which was desirable. The mobile pluviator used in this research is also capable of obtaining relative densities up to 90%. The instrument is validated using experimental and numerical approach. In numerical study, Plaxis 3D software is used in which the soil mass is defined by 10-Node tetrahedral elements and 6-Node plate is used to simulate plate behavior in the validation phase. The results obtained from numerical approach were compared with that of experimental one which showed very close correlation.

• Proceedings of the Korea Water Resources Association Conference
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• 2021.06a
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• pp.207-207
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• 2021

The Vietnamese Mekong Delta(VMD) covers an area of 62,250 km² in the lowest basin of the Mekong Delta where more than half of the country's total rice production takes place. In 2016, an estimated 1.29 million tonnes of Vietnam's rice were lost to the country's biggest drought in 90 year and particularly in VMD, at least 221,000 hectares of rice paddies were hit by the drought and related saltwater intrusion from the South China Sea. In this study, 3D numerical simulations using Delft3D hydrodynamic models with calibration and validation process were performed to examine flow characteristics, climate change scenarios, water level changes, and salinity concentrations in the nine major estuaries and coastal zones of VMD during the 21^st century. The river flows and their interactions with ocean currents were modeled by Delft3D and since the water levels and saltwater intrusion in the area are sensitive to the climate conditions and upstream dam operations, the hydrodynamic models considered discharges from the dams and climate data provided by the Coupled Model Intercomparison Project Phase 6(CMIP6). The models were calibrated and verified using observational water levels, salinity distribution, and climate change data and scenarios. The results agreed well with the observed data during calibration and validation periods. The calibrated models will be used to make predictions about the future salinity intrusion events, focusing on the impacts of sea level rise due to global warming and weather elements.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.29 no.3C
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• pp.105-113
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• 2009

Pressuremeter test estimates deformational properties of soil from the relationship between applied pressure and the displacement of cavity wall, and the results reflect the in-situ stress condition and the structure of soil particles. This study suggests the overall process of test and analysis for the evaluation of nonlinear degradation characteristics of shear moduli, based on the reloading curve of pressuremeter test. The method estimates the maximum shear modulus, taking into account the difference between the stress states around the probe in reloading and that of the in-situ state, and then combines the degradation characteristics of shear moduli taken from reloading curve. This procedure derives the shear moduli in overall strain range. Pressuremeter tests were carried out in various ground conditions using large calibration chamber, together with various reference tests. Shear moduli taken from pressuremeter tests were compared with bender element test and resonant column test results.

• Journal of the Korean Society of Marine Environment & Safety
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• v.23 no.3
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• pp.258-265
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• 2017

This paper validates a system identification method using mathematical optimization using sea trial measurement data as a benchmark. A fast time simulation tool, SIMOPT, and a Rheinmetall Defence mathematical model have been adopted to conduct initial hydrodynamic coefficient estimation and simulate ship modelling. Calibration for the environmental effect of sea trial measurement and sensitivity analysis have been carried out to enable a simple and efficient optimization process. The optimization process consists of three steps, and each step controls different coefficients according to the corresponding manoeuvre. Optimization result of Step 1, an optimization for coefficient on x-axis, was similar compared to values applying an empirical regression formulae by Clarke and Norrbin, which is used for SIMOPT. Results of Steps 2 and 3, which are for linear coefficients and nonlinear coefficients, respectively, was differ from the calculation results of the method by Clarke and Norrbin. A comparison for ship trajectory of simulation results from the benchmark and optimization results indicated that the suggested stepwise optimization method enables a coefficient tuning in a mathematical way.