• Journal of IKEEE
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• v.23 no.3
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• pp.954-961
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• 2019

This paper suggests an advanced 8T SRAM which can operate properly in subthreshold voltage regime. The memory cell consists of symmetric 8 transistors, in which the latch storing data is controlled by a column-wise assistline. During the read, the data storage nodes are temporarily decoupled from the read path, thus eliminating the read disturbance. Additionally, the cell keeps the noise-vulnerable 'low' node close to the ground, thereby improving the dummy-read stability. In the write, the boosted wordline facilitates to change the contents of the memory bit. At 0.4 V supply, the advanced 8T cell achieves 65% higher dummy-read stability and 3.7 times better write-ability compared to the commercialized 8T cell. The proposed cell and circuit techniques have been verified in a 16-kbit SRAM array designed with an industrial 180-nm low-power CMOS process.

• Journal of the Korea institute for structural maintenance and inspection
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• v.26 no.1
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• pp.39-48
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• 2022

In earthquake situations, broadcasting and communication services are directly linked to rapid on-site rescue and effective restoration works. Recently, a variety of base isolation devices are widely introduced on building floors to avoid critical seismic damages of telecommunication facilities. However, in buildings with long fundamental periods, those devices may have undesirable amplification of seismic responses due to resonance effect between the building floors and base isolation devices. This study performs the seismic safety evaluation of two types of base isolation devices deployed for telecommunication facilities in mid- and high-rise buildings through numerical and experimental approaches. It is found that mid- and high-rise buildings can have low-frequency dynamic responses at the top floor when being subjected to design basis earthquake loading. Furthermore, bi-directional shake table testing demonstrated that the selected base isolation devices can exhibit unstable dynamic behaviors under such low-frequency excitations of the floor.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.20 no.5
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• pp.627-635
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• 2019

A programmable drone is a drone developed not only to experience the basic principles of flight but also to control drones through Arduino-based programming. Due to the nature of the training drones, the main users are students who are inexperienced in controlling the drones, which often cause frequent collisions with external objects, resulting in high damage to the drones' frame. In this study, the structural stability of the drone was evaluated by means of a structural dynamics based collision simulation for educational drone frame. Collision simulations were performed on three cases according to the impact angle of $0^{\circ}$, $+15^{\circ}$ and $-15^{\circ}$, using an analytical model with approximately 240,000 tetrahedron elements. Using ANSYS LS-DYNA, which provides excellent functions for the simulation of the dynamic behavior of three-dimensional structures, the stress distribution and strain generated on the drone upper, the drone lower, and the ring assembly were analyzed when the drones collided against the wall at a rate of 4 m/s. Safety factors resulting from the equivalent stress and the yield strain were calculated in the range of 0.72 to 2.64 and 1.72 to 26.67, respectively. To ensure structural stability for areas where stress exceeds yield strain and ultimate strain according to material properties, the design reinforcement is presented.

• 한국방재학회:학술대회논문집
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• 2011.02a
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• pp.159-159
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• 2011

수자원 공급의 시 공간적 편차가 큰 우리나라에서는 수자원을 이용하기 위해서 다수의 댐을 건설하고 있다. 특히, 생활수준의 향상으로 용수 수요가 급증하였기 때문에 용수가 부족한 곳에는 광역상수도 사업 등을 통하여 용수를 공급하고 있다. 댐에서 용수가 공급되기까지의 과정은 일종의 관수로 흐름으로 생각할 수 있다. 관수로 내를 흐르는 유체가 갑자기 정지하게 되면, 유체 운동 에너지의 변화가 유발되고, 그로 인해 관내에 급격한 압력의 상승이 일어나게 된다. 반대로 정지하고 있던 유체가 빠른 속도로 흐르게 되면 압력 감소가 급격하게 발생한다. 이와 같이 유체 운동 상태의 급변에 의한 압력변화와 그에 따른 압력파가 음속의 속도로 상 하류로 전파되는 현상을 수격작용(waterhammer)이라 한다. 통상적으로 수격작용은 밸브 개폐 정도가 갑자기 바뀔 때, 펌프의 급격한 기동이나 정지 시, 터빈 내 전력소요가 갑자기 바뀔 때, 댐 수위의 갑작스런 변화, 펌프 임펠러의 진동, 물 수요의 급격한 변화 등에 의해 발생하며, 수격작용은 유체의 질량과 운동량 때문에 관 벽에 큰 힘을 가하게 되어 정상적인 동수압 보다 몇 배나 큰 압력을 발생시킴으로 관 자체는 물론 펌프, 밸브, 터빈 등 관 시설물을 파손시키거나 진동, 소음 등을 야기시킴으로 대규모 건물, 공장, 발전소 등을 설계할 경우 그에 대한 적절한 대책을 강구하여야 한다. 특히 댐에 연결된 저수지 또는 조정지로부터의 도수로가 압력수로이며 그 길이가 상당히 크면 수차가 급정지했을 경우 수격작용에 의해서 압력터널 내에 과도한 압력상승이 일어난다. 이 압력상승을 방지함과 함께 발전소 부하의 증감에 따라서 수량을 공급하거나, 흡수할 목적으로 압력도수로와 수압관과의 접합부에 자유수면이 있는 수조를 설치한다. 이것을 조압수조(surge tank)라 한다(최영박, 1979). 조압수조에서 부하의 급속한 차단에 의해서 수차로 유입될 수량이 차단되면 도수로 내로 흘러 들어온 물은 관성 때문에 수조 내의 수위를 상승시키고, 수조 수위가 어느 정도 이상으로 되어 저수지 수위 보다 상승하면 수조로의 유입이 정지하고 반대로 수조에서 저수지로 역류하여 수조수위는 하강한다. 즉, 조압수조는 도수로 내에 발생한 과도한 압력을 수조 내 수면의 승강운동을 이용하여 감소시키고 원래의 안정적인 수위로 회복시킨다. 본 연구에서는 수격작용에 대한 댐 안정성을 확보하는 수단 중의 하나인 조압수조에 대해 살펴보았다. 연구대상으로 용담댐을 선정하였다. 용담댐에 대한 기존의 검토결과 수직 갱의 지름이 5m 이상이면 조압수조의 동적안정조건을 만족 시키는 것으로 조사되었다. 댐의 설계홍수위인 EL. 265.5m를 기준으로 조압수조의 안정성을 감소시키지 않는 범위 내에서 조압수조 내 격벽 설치 유 무에 따른 수조의 최적 크기를 산정하였다. 산정결과를 분석한 결과 동일 조건에서 격벽을 설치한 경우가 격벽을 설치하지 않은 경우에 비해서 조압수조의 면적이 약 21% 감소하는 것으로 나타났다.

• Proceedings of the Korea Water Resources Association Conference
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• 2008.05a
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• pp.953-957
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• 2008

일반적으로 하천은 오랫동안 장기간의 변화를 겪으며 안정되어 있다. 산사태나 홍수 등 자연적인 변화뿐 아니라 댐이나 교량 등 인위적인 변화에 따라 흐름이나 유사량이 변하게 되며 이런 동적변형상태를 복원하는 과정에서 침식과 퇴적이 반복적으로 이루어져 대규모 하상변동이 이루어지게 된다. 이러한 하천에서 발생하는 대규모의 하상변동에는 일반적으로 1차원 해석이 적용된다. 하천의 일정 하도구간을 고려할 경우 구간의 상류단면으로부터 유입하는 유입토사량과 하류단면에서 유출되는 유출토사량과의 비에 따라 그 구간에는 하상상승(aggradation)및 하상저하(degradation)가 발생하게 되고 이것이 거시적 측면에서 하상변동이라 할 수 있다. 이러한 장기하상변동은 경우에 따라서 이수용도의 수문 혹은 취수구가 노출되거나, 교량의 교각에 국부세굴이 발생되어 붕괴위험이 생기는 등 심각한 문제가 발생할 수가 있다. 본 연구에서는 하상변동 예측 모형 중 신뢰성 및 적용성이 우수한 것으로 인식되고 있는 HEC-6 모형을 형산강수계에 적용하여 4가지 협착부 개선방안에 따른 장기하상변동에의 영향을 검토하고자 하였다. 하천기본계획상의 횡단면도와 유사량 실측값을 이용하여 유사모의 결과를 검증하고 2020년까지의 모형의 계산 값을 이용하여 4가지 대안에 따른 모의 결과와 원안의 결과와 비교 및 분석하였다. 모의한 결과 형산강의 하상변동치가 크지 않은 것은 형산강의 하상이 어느 정도 안정되어 있어 장기적인 하상변동이 크지 않기 때문이다. 따라서 협착부 개선에 따른 대안 1, 2, 3, 4의 하상이 크게 변하지 않음을 보였다. 지형 변화에 따른 장기하상변동에의 영향이 크지 않은 것을 확인할 수 있다.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.28 no.9B
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• pp.823-833
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• 2003

To satisfy the requirements of the real-time Internet services, queue management and scheduling schemes should be enhanced to accommodate the delay and jitter characteristic of them. Although the existing queue management schemes can address the congestion problems of TCP flows, they have some problems in supporting real-time services. That is, they show performance degradation when burst traffics are continuously going into the system after the queue is occupied at a predefined threshold level. In addition, under the congestion state, they show large jitter, which is not a desirable phenomenon for real-time transmissions. To resolve these problems, we propose a SDRED (State Dependent Random Early Detection) and dynamic scheduling scheme that can improve delay and jitter performances by adjusting RED parameters such as ma $x_{th}$ and $w_{q}$ according to the queue status. The SDRED is designed to adapt to the current traffic situation by adjusting the max,$_{th}$ and $w_{q}$ to four different levels. From the simulation results, we show that the SDRED decreases packet delays in a queue and has more stable jitter characteristics than the existing RED, BLUE, ARED and DSRED schemes.mes.mes.

• Journal of Korean Society of Steel Construction
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• v.19 no.2
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• pp.147-160
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• 2007

In this paper, we described the aeroelastic full-bridge model tests that were conducted to investigate the effect of alternative temporary stabilizing measures for thecable-stayed bridge during construction to ensure aerodynamic stability in the event of a typhoon or similar disasters. The effect of alternative temporary stabilizing measures was investigated through various configurations on two cable-stayed bridges with a main span of 475 m and 230 m, respectively. To investigate the bridge's aerodynamic behaviour and dynamic wind force during construction, the deflections at the end of the cantilever, the accelerations atthe top of the pylon and the moments at the lower part of the pylon were measured. As the result, the system with two sets of vertical cables per cantilever seemed to be the overall most effective solution, but the system with single vertical cable may also work. The combined system using the caisson support and vertical cables and the system with two sets of inclined cables per cantilever on the same anchor block may also be a solution. The inclined cables from the caisson to the girder were effective for some early stages of erecting the deck.

• The KIPS Transactions:PartB
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• v.13B no.5 s.108
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• pp.561-568
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• 2006

WPS(Wearable Personal Station) for next generation PC can define as a core terminal of 'Ubiquitous Computing' that include information processing and network function and overcome spatial limitation in acquisition of new information. As a way to acquire significant dynamic gesture data of user from haptic devices, traditional gesture recognizer based on desktop-PC using wire communication module has several restrictions such as conditionality on space, complexity between transmission mediums(cable elements), limitation of motion and incommodiousness on use. Accordingly, in this paper, in order to overcome these problems, we implement hand gesture recognition system using fuzzy algorithm and neural network for Post PC(the embedded-ubiquitous environment using blue-tooth module and WPS). Also, we propose most efficient and reasonable hand gesture recognition interface for Post PC through evaluation and analysis of performance about each gesture recognition system. The proposed gesture recognition system consists of three modules: 1) gesture input module that processes motion of dynamic hand to input data 2) Relational Database Management System(hereafter, RDBMS) module to segment significant gestures from input data and 3) 2 each different recognition modulo: fuzzy max-min and neural network recognition module to recognize significant gesture of continuous / dynamic gestures. Experimental result shows the average recognition rate of 98.8% in fuzzy min-nin module and 96.7% in neural network recognition module about significantly dynamic gestures.

• Journal of Korea Port Economic Association
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• v.40 no.2
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• pp.157-173
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• 2024

This study analyzed the connectivity of the dry bulk carrier market before and after COVID-19 to examine the impact of COVID-19 on the global shipping market. Using the Quantile Time Frequency Connectedness methodology, we analyzed the dynamic connectedness of major dry bulk indices: the Capesize Index (BCI), Supramax Index (BSI), Panamax Index (BPI), and Handysize Index (BHSI). The results are as follows. First, the total spillover connectedness of the dry bulk carrier market increased during the entire period and in the short term after the outbreak of COVID-19, while it slightly decreased in the long term. Second, the roles among the indices changed according to market conditions, with COVID-19 causing the BPI to change from a net receiver to a net transmitter in the short term and the BSI in the long term, affecting net spillover connectedness. Third, it was observed that long-term connectivity tended to increase more than short-term connectedness under extreme conditions. Fourth, the phenomenon of strengthened connectedness under extreme market conditions was confirmed. These results provide important insights into understanding short-term market shocks and long-term stability trends, demonstrating that the connectedness among dry bulk carrier markets strengthens in global crisis situations such as COVID-19. This provides a basis for assessing the resilience and vulnerability of the shipping market and offers useful information for investors and policymakers in crisis management and investment strategy formulation.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.18 no.11
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• pp.794-801
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• 2017

When a radial wheel is placed so as to partially overlap a conductive plate and rotated, a lift force is generated on the wheel, a thrust force along the edge, and a lateral force which tends to reduce the overlap region. When several of these wheels are combined, it is possible to realize a system in which the stability of the remaining axes is ensured, except in the traveling direction. To validate the overall characteristics of the multi-wheel system, we propose a transfer system levitated magnetically using radial electrodynamic wheels. The proposed system is floated and propelled by four wheels and arranged in a structure that allows the thrusts generated by the front and rear wheels to offset each other. The dynamic stability of the wheel and the effect of the pole number on the three-axial forces are analyzed by the finite element method. At this time, the thrust and levitation force are strongly coupled, and the only factor affecting them is the wheel rotation speed. Therefore, in order to control these two forces independently, we make use of the fact that the ratio of the thrust to the levitation force is proportional to the velocity and is independent of the size of the gap. The in-plane and out-of-plane motion control of the system is achieved by this control method and compared with the simulation results. The experimental results show that the coupled degrees of freedom can be effectively controlled by the wheel speed alone.