• 해양환경안전학회지
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• 제21권6호
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• pp.784-789
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• 2015

본 연구는 소형 고속정의 운항한계를 검토하기 위하여 수행되었다. 일반적으로 내항성능의 검토는 선형의 결정 단계 전에 이루어지지만 본 연구는 선박의 건조가 완료된 후에 이루어졌다. 검토 결과, 종동요, 수직 및 수평가속도, 슬래밍의 운동성능은 특정한 조우각을 제외하고는 만족하였으나 갑판침수의 경우에는 해석을 수행한 모든 조건에서 만족하지 않았다. 이것은 대상선박의 크기가 소형이기 때문에 선박의 속도나 파도와의 조우각보다는 해상상태가 설정한 내항성능 기준의 만족 여부에 더 큰 영향을 미쳤기 때문으로 보인다.

• 한국통신학회논문지
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• 제38B권7호
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• pp.519-525
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• 2013

응용 레벨 트래픽 분류는 안정적인 네트워크 운영과 자원 관리를 위해서 필수적으로 요구된다. 트래픽분류에 있어서 페이로드 시그니쳐 기반 응용 레벨 트래픽 분류 방법은 고속 링크의 트래픽을 실시간으로 처리하는 과정에서 헤더 정보 및 통계 정보 이용 방법론에 비해 상대적으로 높은 부하를 발생시키며 처리 속도가 느린 단점을 갖는다. 본 논문에서는 페이로드 시그니쳐 기반 트래픽 분류 시스템의 처리 속도를 향상 위하여 응용 트래픽의 지역성을 이용한 서버 IP, Port캐쉬 기반 트래픽 분석 시스템을 제안한다. 제안하는 방법을 학내 망의 실제 트래픽에 적용하여 최대 10배 이상의 처리 속도 향상과 10% 이상의 플로우 분석률을 향상 시킬 수 있었다.

• 한국정밀공학회지
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• 제18권12호
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• pp.124-129
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• 2001

Recently, life cycle and lead-time of products have been shortened with the demand of customers. Therefore, it is important to reduce time and cost at the step of manufacturing trial molds. High speed machining can be applied for this kind of purpose with a lot of practical advantages. In our research, several fundamental experiments are carried out to obtain machining parameters such as cutting force, machining time and surface characteristics for tool paths that are appropriate to high-speed machining. Moreover, a trial mold for an automatic transmission knob is fabricated with aluminum-7075 material. Using automatic set-up equipments, an ABS rapid prototype of a trial product of an AT knob is also manufactured with a filling process.

• 국제물리치료학회지
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• 제12권2호
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• pp.2359-2364
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• 2021

Background: Patients with stroke have limited ankle range of motion (ROM) due to soft tissue abnormalities around the ankle and thus experience functional impairment. Increased muscle tension and reduced ankle ROM impair gait and hinder the activities of daily living. Joint mobilization and stretching are effective interventions that improve gait performance by enhancing the ankle ROM. Objectives: To investigate the effects of ankle joint mobilization and calf muscle stretching on gait speed and gait performance in patients with stroke. Design: This was a randomized controlled trial. Methods: Twenty patients with stroke patients were randomized into two groups. The joint mobilization group (JMG) underwent anteroposterior mobilization of the talocrural joint and the joint mobilization stretching group (JMSG) underwent calf muscle stretching in addition to joint mobilization. Gait speed and gait parameters were measured using the 10-meter walk test and the GAITRite. Results: Both the JMG and JMSG groups showed significant improvements in gait speed, affected-side step length, and cadence after the intervention (P<.05). Conclusion: Joint mobilization and stretching were effective interventions for improving gait performance by enhancing ankle function in patients with stroke.

• 한국컴퓨터정보학회논문지
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• 제28권2호
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• pp.209-216
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• 2023

본 논문에서는 조선소 페인트 분사작업에서 분사 거리와 속도의 변화에 따라 페인트 두께를 추정할 수 있는 모델을 개발하고자 한다. 이를 위해 도장로봇을 이용하여 다섯가지 서로 다른 분사 거리와 속도값에 대한 실험 데이터를 취득하였다. 또한 노즐의 훼손 등으로 인해 노이즈가 발생하는데 이를 처리하기 위해 적절한 전처리과정을 적용하였다. 제안하는 방법은 주어진 데이터로부터 분사 거리와 속도에 대한 페인트 두께 추정 함수를 새로운 분사 거리와 속도에 대한 페인트 두께 추정 함수로 변형하는 계산을 한다. 인공신경망기반 예측 모델과 비교한 결과 제안하는 방법이 더욱 안정적이고 정확하게 예측할 수 있음을 확인할 수 있었다.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2009년 추계학술대회논문집
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• pp.1-1
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• 2009

In this presentation, I talk about various fluid simulation methods that have been developed for computer graphics special effects since 1996. They are all based on CFD but sacrifice physical reality for visual plausability and time. But as the speed of computer increases rapidly and the capability of GPU (graphics processing unit) improves, methods for more physical realism have been tried. In this talk, I will focus on four aspects of fluid simulation methods for computer graphics: (1) particle level-set methods, (2) particle-based simulation, (3) methods for exact satisfaction of incompressibility constraint, and (4) GPU-based simulation. (1) Particle level-set methods evolve the surface of fluid by means of the zero-level set and a band of massless marker particles on both sides of it. The evolution of the zero-level set captures the surface in an approximate manner and the evolution of marker particles captures the fine details of the surface, and the zero-level set is modified based on the particle positions in each step of evolution. (2) Recently the particle-based Lagrangian approach to fluid simulation gains some popularity, because it automatically respects mass conservation and the difficulty of tracking the surface geometry has been somewhat addressed. (3) Until recently fluid simulation algorithm was dominated by approximate fractional step methods. They split the Navier-Stoke equation into two, so that the first one solves the equation without considering the incompressibility constraint and the second finds the pressure which satisfies the constraint. In this approach, the first step introduces error inevitably, producing numerical diffusion in solution. But recently exact fractional step methods without error have been developed by fluid mechanics scholars), and another method was introduced which satisfies the incompressibility constraint by formulating fluid in terms of vorticity field rather than velocity field (by computer graphics scholars). (4) Finally, I want to mention GPU implementation of fluid simulation, which takes advantage of the fact that discrete fluid equations can be solved in parallel.

• 한국전자파학회논문지
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• 제14권1호
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• pp.8-13
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• 2003

본 논문에서는 이동통신 품질 보호를 위한 주파수 1 GHz CISPR 허용기준 설정의 적정성을 조사하였으며, 주파수 1 GHz 이상의 장해파 측정에 있어 최대값 추출의 정확성을 높이기 위해 사전 시험에 이용될 수 있는 피시험체의 최적 회전 스텝 분해능에 대해 조사하였다. 마이크로 프로세스의 클럭속도 500 MHz 및 1.7 GHz인 퍼스널 컴퓨터를 피시험체로 측정한 결과, 클럭속도 500 MHz의 경우, 미국 표준과학연구원 Koepke 방식에 의해 추출된 최적 스텝 분해능은 40 개이었으며, 클럭속도 1.7 GHz 퍼스널 컴퓨터의 경우 스텝 분해능은 36개로 평가되었다. 완전 스캔(fully scan) 방식의 측정이 요구되는 기가헤르쯔 측정에서 회전 스텝 분해능에 대한 예측은 측정의 정확성뿐만 아니라 측정 시간을 상당히 단축시켜 줄 것이다.

• KEPCO Journal on Electric Power and Energy
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• 제3권1호
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• pp.29-34
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• 2017

Leaching kinetics for extracting yttrium from the coal fly ash was investigated in the presence of sulfuric acid during extraction. The leaching kinetics of yttrium were conducted at reactant densities of 5~1,000 g coal fly ash per L of $1.0{\sim}10.0N\;H_2SO_4$, agitation speed of 250 rpm and temperature ranging from 30 to $90^{\circ}C$. As a result, the leaching kinetic model was determined in a two-step model based on the shrinking core model with spherical particles. The first step was proceeded by chemical reaction at ash surface, and the second step was proceeded by ash layer diffusion because the leaching conversion of yttrium by the first chemical reaction increases with increased the time irrelevant to the temperature whereas it increases with increased the leaching temperature. The activation energy of the first chemical leaching step was determined to be $1.163kJmol^{-1}$. After the first chemical reaction, the activation energy of ash layer diffusion leaching was derived to be $41.540kJmol^{-1}$. The optimum conditions for leaching the yttrium metal of 60 % were found to be the slurry density of 250 g fly ash per L of $H_2SO_4$, solvent concentration of $2.0N\;H_2SO_4$, second step leaching of temperatures of $30^{\circ}C$ for 3 hours and then $90^{\circ}C$ for 3 hours at agitation rate of 250 rpm.

• 한국정밀공학회지
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• 제21권4호
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• pp.39-47
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• 2004

In mold machining, there are many concave machining regions where chatter and tool deflection occur since MRR(material removal rate) increases as curvature increases even though cutting speed and depth of cut are constant. Boolean operation between stock and tool model is widely used to compute MRR in NC milling simulation. In finish cutting, the side step is reduced to about 0.3mm and tool path length is sometimes over loom, so Boolean operation takes long computation time and includes much error if the resolution of stock and tool model is larger than the side step. In this paper, curvature of CL (cutter location) surface and side step of tool path is used to compute the feedrate for constant MRR machining. The data structure of CL surface is Z-map generated from NC tool path. The algorithm to get local curvature from discrete data was developed and applied to compute local curvature of CL surface. The side step of tool path was computed by point density map which includes cutter location point density at each grid element. The feedrate computed from curvature and side step is inserted to new tool path to regulate MRR. The resultants were applied to feedrate optimization system which generates new tool path with feedrate from NC codes for finish cutting. The system was applied to the machining of speaker and cellular phone mold. The finishing time was reduced to 12.6%, tool wear was reduced from 2mm to 1.1mm and chatter marks and over cut on corner were reduced, compared to the machining by constant feedrate. The machining time was shorter to 17% and surface quality and tool was also better than the conventional federate regulation using curvature of the tool path.

• 인터넷정보학회논문지
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• 제21권2호
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• pp.49-55
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• 2020

랜덤 심볼열을 기반으로 한 정보이론적 학습법 (ITL)은 특정 확률분포를 갖도록 랜덤하게 발생시킨 심볼열을 타겟 데이터로 활용하고, 입력 데이터 사이의 확률분포 거리 최소화를 비용함수로 하여 설계된다. 이 방식의 단점으로, 고정상수를 알고리듬 갱신의 스텝사이즈로 사용하므로 입력 전력의 통계적 추이를 활용할 수 없다. 정보포텐셜 출력(information potential output, IPO)와 연관된 기울기에서는 정보포텐셜 입력(information potential input, IPI)이, 정보포텐셜 오차(information potential error, IPE)와 관련된 기울기에서는 입력자체가 입력으로 작용함을 이 연구에서 밝혀내고, 입력의 전력 추이를 따로 계산하여 스텝사이즈 (step size)를 정규화하도록 제안하였다. 제안된 알고리듬은 충격성잡음과 다중경로 페이딩 환경의 통신시스템 실험에서 기존 방식보다 약 4dB 정도 더 낮은 정상상태 오차 전력, 약 2배 이상 빠른 수렴속도를 나타냈다.