• Environmental Engineering Research
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• v.19 no.2
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• pp.175-184
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• 2014

Weirs are conventional structures that control water level and velocity in streams to facilitate water resource management. Despite many weirs built in streams, there is little information how weirs change hydrology regime and how that translates to sediment and phosphorus (P) responses. This study evaluated the influence of weirs on P retention and mobilization in an urban tributary of the Han River in Korea. Total P concentrations in sediments upstream of weirs were higher than the downstream site, mainly due to the increase of potentially available fractions (labile P and aluminum- and iron-bound P) (p < 0.05). Equilibrium phosphorus concentrations ($EPC_o$) were lower than soluble reactive phosphorus (SRP) concentrations of stream waters, but there was an increasing trend of sediment $EPC_o$ upstream of weirs compared to the downstream site (p < 0.001) indicating a greater potential for P release upstream of weirs. Sediment core incubation showed that SRP release rates upstream of weirs were higher than the downstream site under anoxic conditions of the water column (p < 0.01), but not under oxic conditions. SRP release rates under anoxic conditions were greater than that measured under oxic conditions. Un-neutral pH and increased temperature could also enhance SRP release rates upstream of weirs. We conclude that weirs can increase P retention within stream sediments and potentially promote significant P releases into waters, which in turn cause eutrophication.

• The Journal of Korean Physical Therapy
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• v.30 no.6
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• pp.224-228
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• 2018

Purpose: The most common cause of plantar ulceration is an excessive plantar pressure in patients with peripheral neuropathy. Foot orthosis and therapeutic footwear have been used to decrease the plantar pressure and prevent the plantar ulceration in in diabetes patients. We investigated whether protective sock with functional insoles reduce plantar pressure while walking in 17 diabetes patients. Methods: An in-shoe measurement device was used to measure the peak plantar pressure while walking. Peak plantar pressure data were collected while walking under two conditions: 1) wearing diabetic sock and 2) wearing the protective sock with functional insoles. Each subject walked 3 times in 10-m corridor under three conditions, and data were collected in 3 steps in the middle of corridor with in right and left feet, respectively. Pared t-test was used to compare the peak plantar pressures in three plantar areas under these two conditions. Results: The protective sock with functional insoles significantly reduced the peak plantar pressure on the lateral rearfoot, but significantly increased the peak plantar pressure on the middle forefoot, and medial midfoot (p<0.05). However, there were not significant in medial and lateral forefoot, lateral midfoot, and medial rearfoot between diabetic sock and the protective sock conditions (p>0.05). Conclusion: The protective sock with functional insoles reduced plantar pressures in the rearfoot and supported the medial longitudinal arch. However, it is necessary to change the position of metatarsal pad in the insole design of forefoot area to prevent diabetic foot ulceration.

• Journal of Power Electronics
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• v.19 no.1
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• pp.146-157
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• 2019

The inverter is an essential part of permanent magnet synchronous motor (PMSM) drive systems. The performance of an inverter is greatly influenced by its modulation strategy. Using a proper management of modulation strategies can guarantee high performance from a PMSM under various speed conditions. Switching between modulations is a pivotal technique that determines the performance of a PMSM. Most works on hybrid methods focus on two-level induction motors drive systems. In this paper, in order to improve the performance of PMSMs under various speed conditions, a hybrid method of a pulse width modulation (PWM) control scheme based on a neutral-point-clamped (NPC) three level topology was proposed. This hybrid PWM modulation comprised space vector PWM (SVPWM) and selective harmonic elimination PWM (SHEPWM). Under low speed conditions, the SVPWM is employed to cause the PMSM to start smoothly, and to obtain a rapid response from the control system. Under high speed conditions, the SHEPWM is employed to reduce the switching frequency and to eliminate particular current harmonics. Moreover, the harmonic characteristics of different modulations are analyzed to obtain a smooth transition between the SHEPWM and the SVPWM. Experimental and simulation results indicated the effectiveness of the proposed control method.

• Journal of Positioning, Navigation, and Timing
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• v.10 no.4
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• pp.263-269
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• 2021

The carrier-based differential global navigation satellite system (CD-GNSS) has been garnering significant attention as a promising technology for unmanned vehicles for its high accuracy. The CD-GNSS systems to be used for safety-critical applications should provide a certain level of integrity. The integrity of these systems must be analyzed under various conditions, including fault-free and satellite fault conditions. The systems should be able to detect the faults that can cause large biases on the user position errors and quantify the integrity risk by computing the protection level (PL) to protect the user against the faults that are left undetected. Prior work has derived and investigated the PL for the fault-free condition. In this study, the integrity of the CD-GNSS system under the fault condition is analyzed. The position errors caused by the satellite's fault are compared with the fault-free PL (PL_H0) to verify whether the integrity requirement can be met without computing the PLs for the fault conditions. The simulations are conducted by assuming the ephemeris fault, and the position errors are evaluated by changing the size of the ephemeris faults that missed detection. It was confirmed that the existing fault monitors do not guarantee that the position error under the fault condition does not exceed the PL_H0. Further, the impact of the faults on the position errors is discussed.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2020.06a
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• pp.155-156
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• 2020

Unlike new construction projects, road paving maintenance work shows large productivity discrepancies depending on the conditions of the worksite. The current construction cost calculation scheme, however, only provides daily construction volume categorized by work scope and scale: There are no detailed standards that can be implemented on various types of worksites. To develop standards that enable the calculation of appropriate construction costs by taking into account worksite conditions, the current study conducted on-site surveys and interviews. The on-site research and analysis revealed that location, construction width, the day's worksite lot, work scope, and construction objectives were found to cause differences in construction volume. In addition to the existing work scope and work scape variables, the current study added weight constants reflecting the daily work volume based on movement conditions at site and the size of the worksite lot. In this process, the current study found that even one type of construction project can have fifteen different levels of daily construction volume. Such detailed classification was deemed to enable the proper calculation of construction costs based on worksite conditions.

• Nuclear Engineering and Technology
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• v.55 no.12
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• pp.4607-4616
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• 2023

We implement machine learning regression models to predict peak pressures of primary and secondary systems, a major safety concern in Loss Of Condenser Vacuum (LOCV) accident. We selected the Multi-dimensional Analysis of Reactor Safety-KINS standard (MARS-KS) code to analyze the LOCV accident, and the reference plant is the Korean Optimized Power Reactor 1000MWe (OPR1000). eXtreme Gradient Boosting (XGBoost) is selected as a machine learning tool. The MARS-KS code is used to generate LOCV accident data and the data is applied to train the machine learning model. Hyperparameter optimization is performed using a simulated annealing. The randomly generated combination of initial conditions within the operating range is put into the input of the XGBoost model to predict the peak pressure. These initial conditions that cause peak pressure with MARS-KS generate the results. After such a process, the error between the predicted value and the code output is calculated. Uncertainty about the machine learning model is also calculated to verify the model accuracy. The machine learning model presented in this paper successfully identifies a combination of initial conditions that produce a more conservative peak pressure than the values calculated with existing methodologies.

• Journal of the Korea Institute of Building Construction
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• v.23 no.4
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• pp.417-428
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• 2023

The demolition of domestic infrastructures mirrors other significant construction initiatives in presenting a markedly high accident rate. A comprehensive investigation into the origins of such accidents is crucial for the prevention of future incidents. Upon detailed inspection, the causes of demolition construction accidents are multifarious, encompassing unsafe worker behavior, hazardous conditions, psychological and physical states, and site management deficiencies. While statistics relating to demolition construction accidents are consistently collated and reported, there exists an exigent need for a more foundational cause categorization system based on accident type. Drawing from Heinrich's Domino Theory, this study classifies the origins of accidents(unsafe behavior, unsafe conditions) and human errors(human factors) as per the type of accidents experienced during demolition construction. In this study, a three-step model of QFD-FMEA(Quality Function Deployment - Failure Mode Effect Analysis) is employed to systematically categorize accident causes according to the types of accidents that occur during demolition construction. The QFD-FMEA method offers a technique for cause classification at each stage of the demolition process, including direct causes(unsafe behavior, unsafe environment), and human errors(human factors) through a tri-stage process. The results of this accident cause classification can serve as safety knowledge and reference checklists for accident prevention efforts.

• Proceedings of the Korea Concrete Institute Conference
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• 1999.10a
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• pp.363-366
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• 1999

This paper describes the behavior of prestressed concrete storage tanks under cryogenic temperatures by thermal stress analysis. In concrete tanks to store up LNG, a thermal shock can occur over a global area resulting from the sudden filling of the outer tank with cryogenic storage contents. Analysis results show that internal surface of concrete tank is cooled down rapidly. Tank is subjected mostly to thermal constraint moment due to temperature gradient across its section. Constraint moment may cause tensile stresses beyond tensile strength in the wall. Problems related with concrete cracking due to temperature gradient have been considered.

• Water for future
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• v.8 no.2
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• pp.56-60
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• 1975

Traditional descriptions of water movement in soils and of calculations of infiltration rates neglect the air movement and its compressibility. The movement of two fluids in the bounded layered porous medium is treated analytically and computer simulations are conducted for given boundary conditions and initial saturation profiles. The movement of a given saturation across the interface between the different soil layers is theoretically developed by considering the conservation of mass. It is shown that the existence of the interface affects the infiltration rate when the average total velocity is greater than zero. The transition from one layer to another layer cause a change in the capillary drive and consequently influences the infiltration rate.

• Journal of the Korean Society for Railway
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• v.3 no.4
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• pp.213-218
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• 2000

Waste landfill is so loose that it may cause the insufficient bearing capacity and the differential settlement. And so, characteristics and conditions of the ground should be considered in applications of ground improvement in waste landfill. In this paper, analysis of field tests as the static loading test and the bearing capacity test were performed. In result, PG(Pack Grouting) pile method is proved effective and economic, because it could bring about the increase of end bearing capacity, the prevention of differential settlement and increase of density by expansion of pile.