• 한국자동차공학회논문집
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• 제10권3호
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• pp.192-200
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• 2002

Semi-active suspension systems are greatly expected to be in the mainstream of future controlled suspensions for passenger cars. In this study, a continuous variable damper for a passenger car suspension is developed, which is controlled actively and exhibits high performance with light weight, low cost, and low energy consumption. To get fast response of the damper, reverse damping mechanism is adapted, and to get small pressure change rate after blow-off, a pilot controlled proportional valve is designed and analyzed. The reverse continuous variable damper is designed as a HS-SH damper that offers good body control with reduced transferred input force from tire, compared with any other type of suspension system. The damper structure is designed, so that rebound and compression damping force can be tuned independently, of which variable valve is placed externally. The rate of pressure change with respect to the flow rate after blow-off becomes smooth when the fixed orifice size increases, which means that the blow-off slope is controllable using the fixed orifice size. The damping force variance is wide and continuous, and is controlled by the spool opening, of which scheme is usually adapted in proportional valves. The reverse continuous variable damper developed in this study is expected to be utilized in the semi-active suspension systems in passenger cars after its performance and simplicity of the design is confirmed through real car test.

• Journal of Ecology and Environment
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• 제40권1호
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• pp.12-19
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• 2016

Background: Direct impact of inorganic carbon (i.e., carbon dioxide ($CO_2$)) on the periphyton community is important to understand how and to what extent atmospheric conditions can affect the structure and dynamics of these communities in lotic systems. We investigated the influence of elevated $CO_2$ concentration on the periphyton community in the artificially constructed channels during the winter period. The channels made of acrylic paneling were continuously supplied with surface water discharged from a small reservoir, which was supported with ground water, at a flow rate of 5 L/min, and water temperature ranging $4-5^{\circ}C$. The effects of elevated $CO_2$ concentrations (790 ppm) were evaluated in comparison with the control (395 ppm $CO_2$) by analyzing pH, water carbon content and nutrients in water, periphyton composition and biomass, chlorophyll-a, ash-free dry-matter at 2-day intervals for 10 days. Results: After the addition of $CO_2$, significant decreases of pH, $NH_3-N$, and $PO_4-P$ (p < 0.05) and increases of chlorophyll-a, ash-free dry-matter, and the cell density of periphyton (p < 0.01) were observed, whereas the species composition of periphyton and water carbon content did not change. Conclusions: These results suggest that elevated $CO_2$ in flowing water system with low temperature could facilitate the growth of periphyton resulting in biomass increase, which could further influence water quality and the consumers throughout the food web.

• 정보보호학회논문지
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• 제30권4호
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• pp.605-616
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• 2020

난독화 기술은 프로그램의 기능성은 그대로 유지하면서 자료구조, 제어흐름 등 내부 로직을 변형함으로써 프로그램의 분석을 지연시키는 기술이다. 그러나 이러한 난독화 기술을 악성코드에 적용함으로써 안티바이러스 소프트웨어의 악성코드 탐지율을 저하시키는 사례가 빈번하게 발생하고 있다. 소프트웨어 지적재산권을 보호하기 위하여 적용되는 난독화 기술이 역으로 악성코드에 적용됨으로써 악성코드 탐지율을 저해할 뿐만 아니라 이의 분석을 어렵게 하여 악성코드의 기능성 파악에도 어려움을 주게 되므로 난독화가 적용된 코드를 원본에 가깝게 복원할 수 있는 역난독화 기술의 연구 또한 꾸준히 지속 되어야 한다. 본 논문에서는 상용 난독화 도구 중 대중적으로 널리 알려져 있는 도구인 VMProtect 3.4.0에서 제공하는 세부 난독화 기술 중 Pack the Output File, Import Protection의 옵션이 적용되어 난독화 된 코드의 특징을 분석하고 이의 역난독화 알고리즘을 제시하고자 한다.

• 한국환경복원기술학회지
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• 제4권2호
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• pp.62-73
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• 2001

The riparian environments of urban streams in Korea have been disturbed through the channelization for flood control and artificial land use as well as water pollution and flow decrease due to industrialization and urbanization. The flora and vegetation structure were investigated and an implication of stream restoration was discussed for the conservation of biodiversity in the riparian area of the Seunggi stream in Incheon. Naturalized plants and ruderal plants were widely distributed in the riparian area which was disturbed from cultivating, trampling, dumping etc. Submerged and floating hydrophytes were not found in the stream due to channelization and water pollution. Some halophytes were remained in downstream and reservoir after reclamation and embankment. The communities of Humulus japonicus, Panicum dichotomiflorum, Digitaria sanguinalis, Artemisia montana, Amaranthus retroflexus, and Aster pilosus were distributed in the disturbed area of bank slope and floodplain in the stream. As a natural potential vegetation, Phragmites australis in the wet meadow, Typha latifolia, Typha angustifolia, Oenanthe javanica, Persicaria thunbergii, and Penthorum chinense in the marsh, and Salix babylonica and Salix matsudana for. tortuosa in the woodland appeared in the floodplain. The topography in the stream played an important role on the distribution of riparian vegetation in the Seunggi stream. Appropriate methods for conservation and restoration of the riparian ecosystems must be planned on the basis of the actual vegetation in the disturbed urban stream.

• 한국자동차공학회논문집
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• 제20권4호
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• pp.25-32
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• 2012

Cold start driving cycles exhibit an increases in friction losses due to the low temperatures of metal components and media compared to the normal operating engine conditions. These friction losses are adversely affected to fuel economy. Therefore, in recent years, various techniques for the improvement of fuel economy at cold start driving cycles have been introduced. The main techniques are the upward control of coolant temperature and the fast warm-up techniques. In particular, the fast warm-up techniques are implemented with the coolant flow-controlled water pump and the WHRS (waste heat recovery system). This paper deals with an effect of fast ATF (automatic transmission fluid) warm-up on fuel economy using a recovery system of EGR gas waste heat in a diesel engine. On a conventional diesel engine, two ATF coolers have been connected in series, i.e., an air-cooled ATF cooler is placed in front of the condenser of air conditioning system and a water-cooled one is embedded into the radiator header. However, the new system consists of only a water-cooled heat exchanger that has been changed into the integrated structure with an EGR cooler to have the engine coolant directly from the EGR cooler. The ATF cooler becomes the ATF warmer and cooler, i.e., it plays a role of an ATF warmer if the temperature of ATF is lower than that of coolant, and plays a role of an ATF cooler otherwise. Chassis dynamometer experiments demonstrated the fuel economy improvement of over 2.5% with rapid increase in the ATF temperature.

• Geomechanics and Engineering
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• 제11권3호
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• pp.345-359
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• 2016

In order to investigate the influence of the interfacial angel on failure characteristics and mechanism of combined coal-rock mass, 35 uniaxial/biaxial compressive simulation tests with 5 different interfacial angels of combined coal-rock samples were conducted by PFC2D software. The following conclusions are drawn: (1) The compressive strength and cohesion decrease with the increase of interfacial angle, which is defined as the angle between structure plane and the exterior normal of maximum principal plane, while the changes of elastic modulus and internal friction angle are not obvious; (2) The impact energy index $K_E$ decreases with the increase of interfacial angle, and the slip failure of the interface can be predicted based on whether the number of acoustic emission (AE) hits has multiple peaks or not; (3) There are four typical failure patterns for combined coal-rock samples including I (V-shaped shear failure of coal), II (single-fracture shear failure of coal), III (shear failure of rock and coal), and IV (slip rupture of interface); and (4) A positive correlation between interfacial angle and interface effect is shown obviously, and the interfacial angle can be divided into weak-influencing scope ($0-15^{\circ}$), moderate-influencing scope ($15-45^{\circ}$), and strong-influencing scope (> $45^{\circ}$), respectively. However, the confining pressure has a certain constraint effect on the interface effect.

• Computers and Concrete
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• 제12권2호
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• pp.131-149
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• 2013

Various types of reinforcement splicing methods have been developed and implemented in reinforced concrete construction projects for achieving the continuity of reinforcements. Due to the complicated reinforcement arrangements and the difficulties in securing bar spacing, the traditional lap splicing method, which has been widely used in reinforced concrete constructions, often shows low constructability and difficulties in quality control. Also, lap spliced regions are likely to be over-reinforced, which may not be desirable in seismic design. On the other hand, mechanical splicing methods can offer simple and clear arrangements of reinforcement. In order to utilize the couplers for the ribbed-deformed bars, however, additional screw processing at the ends of reinforcing bars is typically required, which often lead to performance degradations of reinforced concrete members due to the lack of workmanship in screw processing or in adjusting the length of reinforcing bars. On the contrary, the use of screw-ribbed reinforcements can easily solve these issues on the mechanical splicing methods, because it does not require the screw process on the bar. In this study, the mechanical coupler suitable for the screw-ribbed reinforcements has been developed, in which any gap between the reinforcements and sleeve device can be removed by grouting high-flow inorganic mortar. This study presents the uniaxial tension tests on the screw-ribbed reinforcement with the mechanical sleeve devices and the cyclic loading tests on RC columns with the developed coupler. The test results show that the mechanical sleeve connection developed in this study has an excellent splicing performance, and that it is applicable to reinforced concrete columns with a proper confinement by hoop reinforcement.

• Wind and Structures
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• 제25권1호
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• pp.79-100
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• 2017

The use of wind energy resources is developing rapidly in recent decades. There is an increasing number of wind farms in high wind-velocity areas such as the Pacific Rim regions. Wind turbine towers are vulnerable to tropical cyclones and tower failures have been reported in an increasing number in these regions. Existing post-disaster failure case studies were mostly performed through forensic investigations and there are few numerical studies that address the collapse mode simulation of wind turbine towers under strong wind loads. In this paper, the wind-induced failure analysis of a conventional 65 m hub high 1.5-MW wind turbine was carried out by means of nonlinear response time-history analyses in a detailed finite element model of the structure. The wind loading was generated based on the wind field parameters adapted from the cyclone boundary layer flow. The analysis results indicate that this particular tower fails due to the formation of a full-section plastic hinge at locations that are consistent with those reported from field investigations, which suggests the validity of the proposed numerical analysis in the assessment of the performance of wind-farms under cyclonic winds. Furthermore, the numerical simulation allows to distinguish different failure stages before the dynamic collapse occurs in the proposed wind turbine tower, opening the door to future research on the control of these intermediate collapse phases.

• 한국정보통신학회논문지
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• 제20권3호
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• pp.549-557
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• 2016

효과적인 시각화는 일반적으로 대용량의 디버깅 정보와 프로그램의 추상적 수행모델을 표현하는 것이 중요하다. 본 논문에서는 스레드들간의 논리적 병행성 관계를 나타내는 부분순서 수행그래프를 이용하여 내포병렬성과 임계구역을 가진 OpenMP 병렬 프로그램의 수행양상과 경합정보의 효과적 디버깅을 위해서 효과적으로 제공하는 추상적 시각화 도구를 제안한다. 본 도구는 수행중 추적선택 기법으로 시각화 정보를 위한 공간적 복잡성을 줄이고, 추적된 시각화 정보에 프로그램의 내포병렬성과 임계구역 동기화를 위한 그래프 추상화를 제공하여 시각적 복잡성을 해결한다. 그래프 추상화를 통한 스레드들간의 부분순서 관계와 경합탐지 정보는 프로그램의 제어흐름과 경합의 위치를 구조적으로 파악할 수 있게 하므로 프로그램 수행의 이해와 경합 탐지 및 수정에 효과적이다.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2009년도 제33회 추계학술대회논문집
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• pp.11-14
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• 2009

젤(gel) 추진제는 고체 및 액체 추진 시스템의 장점 중 높은 비추력, 저장성, 추력 제어, 비독성, 누설 방지와 같은 특성으로 고성능 추진 시스템에 활용되어 지능형 전략 미사일 또는 발사체의 부스터 및 여러 추진 시스템에 사용될 수 있다. 젤 모사 추진제는 물, Carbopol 941, NaOH 농축액을 혼합하여 제작되었으며, 물과 젤 모사 추진제를 충돌형 인젝터에서 분사시켜 분무 특성을 고찰하였다. 젤 모사 추진제의 충돌 분무에 의해 나타난 긴 액막(liquid sheet)은 강한 상호 분자력에 관련한 중합(polymeric)효과를 나타낸다. 물 분사와 비교했을 때 젤 모사 추진제의 미립화 억제와 난류 천이 지연에 관련된 높은 점도로 인하여 저조한 미립화 특성과 좁은 범위의 분무각을 나타내었다.