• 상하수도학회지
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• 제22권3호
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• pp.307-314
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• 2008

In this study, the effects of applied voltage, solution pH and coexistence of other ions such as sulfate ion (${SO_4}^{2-}$) and chloride ion ($Cl^-$) were investigated on the removal of nitrate-nitrogen ($NO_3{^-}-N$) from ground water by electrodialysis. The examined operating conditions were evaluated for optimizing the removal efficiency of $NO_3{^-}-N$. Real ground water samples taken from a rural area of Yongin city and artificial ones with components similar to the real ground water were tested for the study, which contained $NO_3{^-}-N$ concentration of 17mg/L that exceeds current drinking water quality standard of 10 mg/L. The increase in the removal rate of $NO_3{^-}-N$ was observed as the applied voltage increased from 5V to 30V, while no significant increase in the removal rate appeared at the applied voltage beyond 20V during a given operating time. The removal rate appeared to get lower at both acidic and basic condition, compared to neutral pH. Coexistence of of ${SO_4}^{2-}$and $Cl^-$ demanded much longer operating time to achieve a given removal rate or to meet a certain level of treated water concentration. When nitrate ion was combined with ${SO_4}^{2-}$and $Cl^-$, the removal rate was reduced by 4.29% and 10.83%, respectively.

• 한국생산제조학회지
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• 제6권3호
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• pp.17-25
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• 1997

This paper aims to clarify the effects of grinding conditions on the grinding force, ground surface and chipping size of workpiece in surface grinding of various ferrites with the resin bond diamond wheel. The main conclusions obtained were as follows: In a constant peripheral wheel speed, the specific grinding energy is fitted by straight lines with grinding depth coefficient($\delta$) in a logarithmic graph. The effect of both depth of cut and workpiece speed on grinding energy becomes larger in the order of Mn-Zn, Cu-Ni-Zn and Sr. When using the diamond grain of the lower toughness, the roughness of the ground surface becomes lower. The ground surfaces show that the fracture process during grinding becomes more brittle in the order of Sr, Mn-Zn and Cu-Ni-Zn. The chipping size at the corner of workpiece in grinding increases with the the increases of the depth of cut and workpiece speed, and the decrease of peripheral wheel speed. The effect of both depth of cut and workpiece speed on chipping size becomes more larger in the order of Sr, Mn-Zn and Cu-Ni-Zn.

• 대한물리의학회지
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• 제6권2호
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• pp.145-151
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• 2011

Purpose: The study was designed to investigate the effects of landing heights on muscle activities and ground reaction force during drop landing. Methods: Sixteen healthy adults were recruited along with their written informed consent. They performed a drop-landing task at the height of 20, 40, and 60cm. They completed three trials in each condition and biomechanical changes were measured. The data collected by each way of landing task and analyzed by One-way ANOVA. Ground reaction forces were measured by force flate, muscle activities measured by MP150 system. Results: There were significant differences in ground reaction forces, and significant increases in muscle activities of tibialis anterior, medial gastrocnemius and biceps femoris with landing heights. Conclusion: These findings revealed that heights of landing increases risk factors of body damage because of biomechanical mechanism and future studies should focus on prevention from damage of external conditions.

• International Journal of Aeronautical and Space Sciences
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• 제17권2호
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• pp.139-148
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• 2016

The passive control methods such as horizontal and vertical fences on the lower surface of the bluff body were applied to suppress the vortex shedding and enhance the aerodynamic stability of flow. For investigating the effects of the passive control methods, wind tunnel experiments on the unsteady flow field around a bluff body near a moving ground were performed. The boundary layer and velocity profiles were measured by the Hot Wire Anemometer (HWA) system and the vortex shedding patterns and flow structures in a wake region were visualized via the Particle Image Velocimetry (PIV) system. Also, it is a measuring on moving ground condition that the experimental values of the critical gap distances, Strouhal numbers and aerodynamic force FFT analyses. Through the experiments, we found that the momentum supply due to moving ground caused the vortex shedding at the lower critical gap distance rather than that of fixed ground. The horizontal and vertical fences increase the critical gap distance and it can suppress the vortex shedding. Consequently, the stability characteristics of the bluff body near a moving ground could be effectively enhanced by the simple passive control such as the vertical fences.

• 수산해양기술연구
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• 제16권1호
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• pp.23-26
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• 1980

The pure polypropylen rope has been used for the head rope, and the lead cored polypropylen rope for the ground rope in the anchovy boat seine. These ropes revealed the disadvantage that deforms the net shape due to their elongation. Te improve the disadvantage, authors developed the rope of new construction which is cored by wires and wrapped by polypropylene fibers, 20mm in diameter for the head rope and 40tnm for the ground rope. To compare the physical properties of the improved rope with the conventional ones, some factors are valued and the following results are found. 1. The improved ropes rev~al some disadvantages, such as the head rope is heavier, the ground rope lighter, and both of them are stiffer than the conventional ones, contrary to the required condition of ropes) However no special difficulties are found in practical use. 2. The improved ropes display much advantages, such as elongation is 30 percent less, breaking strength is 35 precent greater, and elastic recovery is 10 percent greater than the conventional ones. Thus, it is considered that the improved ropes are more suitable for the head rope and the ground rope of the anchouy boat seine net than the conventional ones.

• 한국지열·수열에너지학회논문집
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• 제10권1호
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• pp.14-19
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• 2014

This paper presents a preliminary experimental and computational study on the evaluation of thermal performance and initial cost of U, W and coil type ground heat exchangers (GHEs). Heat exchange rate of the individual GHE was evaluated from the thermal resperformance test (TPT) results, and the construction cost was also calculated. For more information, GLD (ground loop design) simulations of various piping size are carried out. From simulation results, the optimized GHE was suggested based on the thermal performance and construction cost as well. Besides, the required borehole length of U and W type GHEs was calculated considering a real construction condition using GLD program.

• 설비공학논문집
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• 제28권3호
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• pp.103-109
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• 2016

The purpose of this study is to perform comparative economic evaluation for the systems of ground source heat pump (GSHP) and district heating and cooling (DHC) by focusing on the analysis of operation case of GSHP. The adapted research object is a public office building located in Seoul. The capacity of ground source pump is about 3,900 kW. Ground heat exchanger is closed loop type. The analysis period for life cycle cost is 30 years. Economic evaluation is assessed from the viewpoints of the following four parts: initial cost, energy cost, maintenance and replacement cost, and environment cost. The total life cycle cost of GSHP is approximately 8,447 million won. The cost of the DHC System is approximately 3,793 million won. The cost of the DHC is approximately 46% lower than GSHP system under the condition of current rate for GSHP and DHC.

• 한국철도학회:학술대회논문집
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• 한국철도학회 2008년도 추계학술대회 논문집
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• pp.169-178
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• 2008

In this paper, it is shown that Carson's equation can still be applied for the calculation of the series reactance of transmission lines with no ground return current as well as the one with ground return. It is proved in the following method. First two voltage drop equations for three-phase three wire transmission line are derived, one without considering ground return and the other using Carson's equation. The impedance matrix of the two equations are different from each other. But if we put the condition of zero ground current, $I_a+I_b+I_c=0$, those two equations becomes the identical equations. Therefore even a transmission line is not grounded, its line parameters can still be obtained using the Carson's equation. It has been confused whether or not Carson's equation can be used for an ungrounded system. It is because where ever Carson's equation is shown in the book, it also says that the system has ground return current paths as a premise. It is also verified with EMTP studies on the test circuit.

• Geomechanics and Engineering
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• 제29권3호
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• pp.229-236
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• 2022

In this study, a model experiment and field experiment was conducted to introduce the optimal tensile force when constructing a non-open cut tunnel according to the ground conditions of sandy soil. CMR (Concrete Modular Roof) method is economical because of the high precision and excellent durability, and corrosion resistance, and the inserted parts can be used as the main structure of a tunnel. In addition the CMR method has a stable advantage in interconnection because the concrete beam is press-fitted compared to the NTR (New Tubular Roof) method, and the need for quality control can be minimized. The ground conditions were corrected by adjusting the relative density of sandy soil during the construction of non-open cut tunnels, and after introducing various tensile forces, the surface settlement according to excavation was measured, and the optimal tensile force was derived. As a result of the experiment, the amount of settlement according to the relative density was found to be minor. Furthermore, analysis of each tensile force based on loose ground conditions resulted in an average decrease of approximately 22% in maximum settlement when the force was increased by 0.8 kN per segment. Considering these results, it is indicated that more than 2.0 kN tensile force per segment is recommended for settlement of the upper ground.

• 한국축산시설환경학회지
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• 제17권2호
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• pp.61-70
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• 2011

본 연구는 한우사육 305 농가에 대하여 우사바닥상태, 습기제거방법, 급이시설, 방역실태 등과 같은 사육환경을 조사 분석하여 환경개선을 통한 효율적인 농장관리 프로그램에 필요한 지표를 설정하고자 실시하였다. 그 결과를 요약하면 다음과 같다. 첫째는, 한우농가의 우사바닥 상태는 "보통이다" 으로 관리하는 경우가 가장 많았으며(46.4%), 건조한 편 (35.5%)도 많이 있어 비교적 잘 관리되고 있으나, 질척거리는 수준(18.1%)도 많이 있는 것으로 보아 아직도 바닥관리에 톱밥이나 송풍홴을 설치하여 습기를 제거해야 할 것으로 생각된다. 둘째는, 우사바닥 습기제거는 "송풍홴" 을 이용 (36.4%)하는 경우가 가장 많은 것으로 나타나 시설구입이나 에너지 비용을 절감할 수 있는 자연빛이나 통풍을 이용하도록 권장해야 한다. 셋째는, 축사 내 냄새 악취는 "깔짚교체"로(33.7%) 제거하는 경우가 가장 많았으나, 자연송풍 등을 효율적으로 이용하여 환기를 시켜야 할 것으로 생각된다. 넷째는, 여름철 축사내 "송풍홴 설치" 않은 농가 (37.7%)가 비교적 많았는데, 체온조절이나 습기제거용으로 적절히 설치되어야 할 것으로 판단된다. 다섯째는, 사료급이시설은 "수동식" (88.2%)이 가장 많은 것으로 조사되었는데, 자동화시스템으로 전업화 농장 경영관리가 이루어져야 할 것이다. 여섯째는, 농가의 사양관리기술수준은 5점 만점 중 "2.80점" 으로 중등수준으로 평가되고 있어서 경쟁력을 갖춘 기술 습득이 요구된다. 일곱째로, 농장의 방역시설 중 "분무기" 사용 (80.8%) 농가가 가장 많았으나 소독장비가 없는 농가도 3.0%나 되었다. 그리고 "1주 1회" 방역실시 (40.0%) 농가가 가장 많았으나, 방역을 전혀 실시 않는 농가도 5.2%나 되는 것으로 조사되어 방역의 중요성 인식과 최적 방역 프로그램 개발이 더욱 요구된다. 따라서 아직도 열악한 환경에서 사육하는 우리나라 한우농가는 악취, 우사바닥, 송풍, 온도, 방역시스템 등과 같은 사육환경 관리시스템이 효율적으로 구축되어야 할 것으로 생각된다.