• Journal of Korean Society of Forest Science
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• v.112 no.1
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• pp.83-92
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• 2023

This study was established to investigate the site environment of mixed forests in Korea and to estimate the growth and yield of stands using national forest resources inventory data. The growth of mixed forests was derived by applying the Chapman-Richards model with diameter at breast height (DBH), height, and cross-sectional area at breast height (BA), and the yield of mixed forests was derived by applying stepwise regression analysis with factors such as cross-sectional area at breast height, site index (SI), age, and standing tree density per ha. Mixed forests were found to be growing in various locations. By climate zone, more than half of them were distributed in the temperate central region. By altitude, about 62% were distributed at 101-400 m. The fitness indexes (FI) for the growth model of mixed forests, which is the independent variable of stand age, were 0.32 for the DBH estimation, 0.22 for the height estimation, and 0.18 for the basal area at breast height estimation, which were somewhat low. However, considering the graph and residual between the estimated and measured values of the estimation equation, the use of this estimation model is not expected to cause any particular problems. The yield prediction model of mixed forests was derived as follows: Stand volume =-162.6859+6.3434 ∙ BA+9.9214 ∙ SI+0.7271 ∙ Age, which is a step- by-step input of basal area at breast height (BA), site index (SI), and age among several growth factors, and the determination coefficient (R²) of the equation was about 96%. Using our optimal growth and yield prediction model, a makeshift stand yield table was created. This table of mixed forests was also used to derive the rotation of the highest production in volume.

• Journal of the Society of Naval Architects of Korea
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• v.46 no.6
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• pp.611-621
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• 2009

This paper first reviews the physical meanings and the expressions of two representative strain rate models: CSM (Cowper-Symonds Model) and JCM (Johnson-Cook Model). Since it is known that the CSM and the JCM are suitable for low-intermediate and intermediate-high rate ranges, many studies regarding marine accidents such as ship collision/grounding and explosion in FPSO have employed the CSM. A formula to predict the material constant of the CSM is introduced from literature survey. Numerical simulations with two different material constitutive equations, classical metal plasticity model based on von Mises yield function and micromechanical porous plasticity model based on Gurson yield function, have been carried out for the stiffened plates under impact loading. Simulation results coincide with experimental results better when using the porous plasticity model.

• Journal of Korean Society of Forest Science
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• v.98 no.6
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• pp.646-651
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• 2009

In this study, it was intended to prepare a stem volume table (with or without bark) and a stand yield table for Juglans mandshurica, plantations in Chungju, located in Chungcheongbuk-do, Korea. For the calculation of stem volume, we applied Kozak's growth model, which showed the best fitness index (97%). With this model, it was able to prepare the first yield table for Juglans mandshurica in Korea. Site index model, an indicator of forest productivity, was derived by using the Chapman-Richard model, in which the basic stand age was set to 30 years. The resulted site index ranged between 16 and 22. Based on the yield table of Juglans mandshurica resulted from this study, the volume for a 70-year-old stand with a midium site index class was estimated to be $238m^3/ha$, which is $100m^3/ha$ higher than the volume estimated from the yield table of Quercus acutissima. The yield table of oak trees has been used in the estimation of most broadleaf stands in Korea. However, the result of this study indicated that it is necessary to generate a stand yield table for each broadleaf species. The annual $CO_2$ removals of 30-year-old Juglans mandshurica plantations in the ChungJu region was estimated to be $5.84tCO_2/ha$. The stem volume and stand yield table of Juglans mandshurica plantation resulted from this study would provide a good information in decision making for forest management in ChungJu region.

• Steel and Composite Structures
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• v.38 no.2
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• pp.151-164
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• 2021

During the pipe forming process, a steel plate undergoes inelastic behavior multiple times under a load condition repeating tension and compression in the circumferential direction. It derives local reduction or increase of yield strength within the thickness of steel pipes by the plastic hardening and Bauschinger effect. In this study, a combined hardening model is proposed to effectively predict variations of yield strength in the circumferential direction of API-X65 and X70 steel pipes with relatively low t/D ratio during the forming process, which is expected to experience accumulated plastic strain of 2~3%, the typical Lüder band range in a low-carbon steel. Cyclic tensile tests of API-X65 and X70 steels were performed, and the parameters of the proposed model for the steels were calibrated using the test results. Bending-flattening tests to simulate repeated tension and compression during pipe forming were followed for API-X65 and X70 steels, and the results were compared with those by the proposed model and Zou et al. (2016), in order to verify the process of material model calibration based on tension-compression cyclic test, and the accuracy of the proposed model. Finally, parametric analysis for the yield strength of the steel plate in the circumferential direction of UOE pipe was conducted to investigate the effects of t/D and expansion ratios after O-forming on the yield strength. The results confirmed that the model by Zou et al. (2016) underestimated the yield strength of steel pipe with relatively low t/D ratio, and the parametric analysis showed that the t/D and expansion ratio have a significant impact on the strength of steel pipe.

• Korean Journal of Remote Sensing
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• v.33 no.5_2
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• pp.631-640
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• 2017

The estimation of rice yield affects the income of farmers as well as the fields related to agriculture. Moreover, it has an important effect on the government's policy making including the control of supply demand and the price estimation. Thus, it is necessary to build the crop yield estimation model and from the past, many studies utilizing empirical statistical models or artificial neural network algorithms have been conducted through climatic and satellite data. Presently, scientists have achieved successful results with deep learning algorithms in the field of pattern recognition, computer vision, speech recognition, etc. Among deep learning algorithms, the SSAE (Stacked Sparse AutoEncoder) algorithm has been confirmed to be applicable in the field of forecasting through time series data and in this study, SSAE was utilized to estimate the rice yield in South Korea. The climatic and satellite data were used as the input variables and different types of input data were constructed according to the period of rice growth in South Korea. As a result, the combination of the satellite data from May to September and the climatic data using the 16 day average value showed the best performance with showing average annual %RMSE (percent Root Mean Square Error) and region %RMSE of 7.43% and 7.16% that the applicability of the SSAE algorithm could be proved in the field of rice yield estimation.

• Nuclear Engineering and Technology
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• v.44 no.7
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• pp.791-798
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• 2012

Since standardized fracture test specimens cannot be easily extracted from in-service components, several alternative fracture toughness test methods have been proposed to characterize the deformation and fracture resistance of materials. One of the more promising alternatives is the local approach employing the SP(Small Punch) testing technique. However, this process has several limitations such as a lack of anisotropic yield potential and tediousness in the damage parameter calibration process. The present paper investigates estimation of ductile fracture resistance(J-R) curve by FE(Finite Element) analyses using an anisotropic damage model and enhanced calibration procedure. In this context, specific tensile tests to quantify plastic strain ratios were carried out and SP test data were obtained from the previous research. Also, damage parameters constituting the Gurson-Tvergaard-Needleman model in conjunction with Hill's 48 yield criterion were calibrated for a typical nuclear reactor material through a genetic algorithm. Finally, the J-R curve of a standard compact tension specimen was predicted by further detailed FE analyses employing the calibrated damage parameters. It showed a lower fracture resistance of the specimen material than that based on the isotropic yield criterion. Therefore, a more realistic J-R curve of a reactor material can be obtained effectively from the proposed methodology by taking into account a reduced load-carrying capacity due to anisotropy.

• Journal of The Korean Society of Agricultural Engineers
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• v.54 no.1
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• pp.99-108
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• 2012

Soil erosion and sediment from agricultural farmland has caused various negative impacts on environment in recent years. The effect of rice straw mat on soil erosion has been investigated by many researchers these days. In this study, the SWAT model was applied to Hongcheon watershed to evaluate SWAT flow and sediment, and the effect of rice straw mat on sediment yield at watershed outlet was evaluated. The Nash-Sutcliffe model efficiency (NSE) and coefficient of determination ($R^2$) values for flow simulation (calibration period) were 0.66 and 0.67, and the NSE values for sediment was 0.90. The calibrated parameters were used to analyze the reduction of sediment yield in the farmland with rice straw mat. Average daily sediment yield without rice straw mat was 49.8 ton/day and sediment yield with rice straw mat was 25.5 ton/day, and the reduction rate was 38.7 %. Also, average daily sediment yield with/without rice straw mat were 97.5 ton/day and 190.7 ton/day during the rainy season (Jun. 2008 - Aug. 2009), with the reduction rate 46.3 %.

• The Korean Journal of Financial Management
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• v.25 no.2
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• pp.1-31
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• 2008

Before the financial crisis in 1997, Korean bond markets had been those of corporate bonds with relatively high market yield. During the period, most of major institutional investors tend to utilize passive strategies such as buying and holding. After the crisis, however, they could not help choosing active bond management strategies because of lowed yield level and intensified competition among the financial institutions. This study is forced on the yield curve, which is the reflection of all information on the bond investment environments. The study also make analysis on the major economic and securities market factors and its structural relationship with the shape of the curve such as level, curvature and slope. For these purposes, an empirical model based on the Nelson-Siegel Model is estimated with the data during $1999{\sim}2006$. Out-of-sample forecasting is also made to test the usefulness of the estimated model. In addition, the dependent variables which are the estimates of level and slope are estimated on the macro variables and securities market variables. VAR and SUR models are used for the estimation. Estimation results show that level and slope of the yield curve are influenced by the target call rate change, exchange rate change rate, inflation rate. These results provide practical implications for the active managements in the overall treasury bond markets.

• Nuclear Engineering and Technology
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• v.42 no.4
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• pp.450-459
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• 2010

The present paper investigates the collapse pressure of cylinders with intermediate thickness subjected to external pressure based on detailed elastic-plastic finite element (FE) analyses. The effect of the initial ovality of the tube on the collapse pressure was explicitly considered in the FE analyses. Based on the present FE results, the analytical yield locus, considering the interaction between the plastic collapse and local instability due to initial ovality, was also proposed. The collapse pressure values based on the proposed yield locus agree well with the present FE results; thus, the validity of the proposed yield locus for the thickness range of interest was verified. Moreover, the partial safety factor concept based on the structural reliability theory was also applied to the proposed collapse pressure estimation model, and, thus, the priority of importance of respective parameter constituting for the collapse of cylinders under external pressure was estimated in this study. From the application of the partial safety factor concept, the yield strength was concluded to be the most sensitive, and the initial ovality of tube was not so effective in the proposed collapse pressure estimation model. The present deterministic and probabilistic results are expected to be utilized in the design and maintenance of cylinders subjected to external pressure with initial ovality, such as the once-through type steam generator.

• Proceedings of the KSME Conference
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• 2003.04a
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• pp.310-315
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• 2003

This paper presents the effect of boundary condition of failure pressure model for buried pipelines on failure prediction by using a failure probability model. The first order Taylor series expansion of the limit state function is used in order to estimate the probability of failure associated with various corrosion defects for long exposure periods in years. A failure pressure model based on a failure function composed of failure pressure and operation pressure is adopted for the assessment of pipeline failure. The effects of random variables such as defect depth, pipe diameter, defect length, fluid pressure, corrosion rate, material yield stress, material ultimate tensile strength and pipe thickness on the failure probability of the buried pipelines are systematically studied by using a failure probability model for the corrosion pipeline.