외부 흐름과 준설된 다열 함몰지형에 의한 파랑의 반사

조용식,이광준,이준환 한국수자원학회 2020 한국수자원학회논문집 Vol.53 No.10

Understanding the wave characteristics near the outlet of coastal power plants for cooling water in the vicinity of the dredged areas is critically important for the construction and operation of the plants. By Employing the eigenfunction expansion method, in this study, we analyzed the reflection of monochromatic water waves over (1) shear currents near the outlet and (2) multi-arrayed trenches representing dredged areas. We firstly optimized the number of grids expressing shear currents and the number of evanescent modes based on a convergence test. We then analyzed the sensitivity of the reflection coefficients depending on (1) magnitude of shear currents, (2) width of shear currents, (3) a distance between adjacent trenches, and (4) a number of trenches. The results showed that the reflection coefficient was more sensitive to the number of trenches and the distance between trenches than the velocity of shear currents and the width of shear currents. We also found that even the effect of shear currents is relatively small, the effect is not negligible in a relative water depth from shallow to near shallow water waves (0.010.70). 임해발전소의 냉각수 배출구 인근과 준설된 해역을 전파하는 파랑의 특성을 이해하는 것은 임해발전소 건설과 운영에 매우 중요하다. 본 연구에서는 (1) 배출구 주변 외부 흐름과 (2) 준설된 해저지형을 나타내는 함몰지형에 의한 파랑의 반사율을 고유함수전개법을 이용하여 해석하였다. 먼저, 외부흐름을 나타내기 위한 격자수와 소멸파수의 최적값을 수렴 테스트를 통해 산정하였다. 그리고 1)외부흐름의 속도, 2)외부흐름의 폭, 3)함몰지형간 거리, 4)함몰지형의 개수에 따른 반사율 변화 정도를 분석하였다. 분석결과, 함몰지형 수와 거리에 따른 반사율이 외부흐름의 속도와 폭에 따른 반사율보다 더 민감한 결과를 보였다. 또한, 외부흐름의 영향이 작을지라도 천해와 천해부근 상대수심 (0.01 0.70)에서는 외부흐름의 영향을 무시할 수 없다는 것을 확인하였다.

Numerical investigation of depth-varying currents on ship hydrodynamics in confined water

Terziev Momchil,Tezdogan Tahsin,Demirel Yigit Kemal,De Marco Muscat-Fenech Claire,Incecik Atilla 대한조선학회 2022 International Journal of Naval Architecture and Oc Vol.14 No.1

Vessels can operate in unpredictable environments depending on the geographical area and weather conditions. One example of conditions a vessel might not be assessed against is the presence of depthvarying currents, which are particularly relevant in confined waters where currents can be created due to tidal influences, or short fetches in inland waterways. The possible presence of depth-varying currents motivates a numerical assessment of the effects of sheared currents on the hydrodynamic performance of the KRISO Container Ship (KCS) in confined waters. The results highlight that exploiting currents, such as those generated by tides could be used to improve the energy efficiency of vessels considerably. These currents present significant possibilities for voyage optimisation based on geographical and meteorological conditions. The results specific for the KRISO container ship point to resistance reductions when the current assists ship motions, accompanied by considerable decreases in sinkage and trim. Conversely, when currents oppose ship motion, resistance, sinkage and trim can increase by a factor of 3 depending on the strength and shape of the depth-varying current. The results also show that a current with constant vorticity, a case frequently used in the literature to investigate the impact of sheared currents, creates the biggest increase and decrease for inhibiting and assisting currents, respectively.

전단 자극 시 심방근세포 간극접합 채널 활성화에 의한 P2 퓨린수용체-매개 비선택성 양이온 전류의 발생

손민정,김준철,브지바부 치디피,왕준,김경희,우선희 충남대학교 약학대학 의약품개발연구소 2016 藥學論文集 Vol.31 No.-

Atrial myocytes are subjected to shear stress under physiological and pathological conditions during cardiac cycle. We recently reported that gap junction hemichannels play a role in the generation of Ca2+ wave in atrial cells under shear stress. In the present study, we examined whether ionic current is generated by the activation of gap junction hemichannels in rat atrial myocytes under shear stress using whole-cell patch clamp method combined with a pressurized microflow system. Shear stress of ~16 dyne/cm2 (1-s long) produced a slow inward current (ISS) at –70 mV in symmetrical CsCl-rich solutions.Removal of external Ca2+ to enhance hemichannel opening increased this shear-activated current by approximately 140%. In addition, the ISS was almost completely inhibited by the hemichannel blockers carbenoxolone (50 μM) or La3+ (2 mM). We next tested whether P2 purinoceptors activated by ATP released via hemichannels contribute to ISS cells using P2-purinoceptor antagonist suramin. Pre-treatment of suramin (10 μM) suppressed ISS to ~28% of control. When the delayed rectifying K+ channels, that have slight permeability to Cs+, were blocked using 4-aminopyridine (200 μM), ISS was not altered. Our data suggest that shear stress may activate gap-junction hemichannels, resulting in ATP release with subsequent P2 purinoceptor-mediated nonselective cation current in atrial myocytes.

Magnetic-field-dependent Shear Modulus of a Magnetorheological Elastomer Based on Natural Rubber

양인형,윤지현,정재은,정운창,김진수,정경호,오재응 한국물리학회 2013 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.62 No.2

A magnetorheological elastomer (MRE) is a smart material that has a reversible and variable modulus in a magnetic field. Natural rubber, which has better physical properties than silicone matrices, was used as a matrix in the fabrication of the MREs used in this study. Carbonyl iron powder (CIP), which has a rapid magnetic reaction, was selected as a magnetic material to generate the magnetic-field-dependent modulus in the MREs. The MRE specimens were cured in an anisotropic mold, which could be used to induce a uniaxial magnetic field via permanent magnets, to control the orientation of the CIP, and the shear modulus of the MREs was evaluated under a magnetic field induced by using a magnetic flux generator (MFG). Because the use of a conventional evaluation system to determine the magnetic-field-dependent shear modulus of the MREs was difficult, an evaluation system based on single degree-of-freedom vibration and electromagnetics that included an MFG, which is a device that generates a magnetic field via a variable induced current, was designed. An electromagnetic finite element method (FEM) analysis and design of experiments (DoE) techniques were employed to optimize the magnetic flux density generated by the MFG. The optimized system was verified over the range to determine the magnetic flux density generated by the MFG in order to use a magnetic circuit analysis to identify the existence of magnetic saturation. A variation in the shear modulus was observed with increasing CIP volume fraction and induced current. The experimental results revealed that the maximum variation in the shear modulus was 76.3% for 40 vol% CIP at an induced current of 4 A. With these results, the appropriate CIP volume fraction, induced current, and design procedure of the MFG can be proposed as guidelines for applications of MREs based on natural rubber.

정현형 지형과 다양한 외부흐름에 의한 반사

이준환,서규학,조용식 한국방재학회 2013 한국방재학회논문집 Vol.13 No.3

The resonant reflection caused by sinusoidally varying submerged structure and wave could protect coastal facilities from wave attack by reducing wave energy. Water waves deform by not only bottom topography but also interaction with shear currents. In this study, a resonant reflection by a sinusoidally varying topography with various shear currents is investigated. The water depth and the slope of shear currents are represented by a finite number of tiny steps. The proper numbers of steps are proposed and the effects of evanescent modes are shown. 정현형 수중구조물과 파랑의 공명을 이용하여 파랑의 에너지를 감소시킴으로써 파랑으로부터 해안 시설물을 보존할 수 있다. 파랑은 해저지형뿐만 아니라 외부흐름과의 상호작용에 의하여 변형한다. 본 연구에서는 정현형 지형과 다양한 외부흐름에 의한 공명을 해석하였다. 수심과 외부흐름의 경사를 작은 구간의 계단형으로 단순화하였다. 계산에 필요한 적절한 구간의 수를 제안했으며, 소멸파 성분 고려 여부에 따른 차이를 보였다.

연안표사 산정에 사용되는 평균 연안유속공식의 평가

이호진 ( Ho-jin Lee ) 한국환경기술학회 2004 한국환경기술학회지 Vol.5 No.3

연안 표사는 해안구조물과 관련하여 해안선 변형에 영향을 미치는 주요 인자로 작용하므로, 연안 표사의 추정은 해안공학자에게 있어서 가장 중요한 연구 주제가 되어 왔다. 해안부근으로 접근하는 파랑은 운동량도 함께 운반하고, 해안선에 평행한 운동량 성분은 연안류를 발생시킨다. 이와 같은 흐름은 해안선을 따라서 표사가 운반되는데 매우 중요한 역할을 한다. 본 연구에서는 대표적인 6개의 평균연안유속식을 사용하여, 연안표사량을 계산하였다. 평균연안유속에 의해서 계산된 연안표사량을 실측치와 비교함으로써 연안표사량 산정에 사용되는 평균연안유속공식의 특징을 분석하였다. 평균연안유속에 의해 계산된 연안표사량을 실측치와 비교한 결과 Inman-Quinn 공식과 Harrison 공식에 의한 결과를 제외하고는 실측치와 좋은 일치를 보이고 있다. Longshore sediment transport is an important factor in shore line change in response to the presence of coastal structure. Thus prediction of longshore sediment transport is central to most coastal engineering studies and because of its practical engineering importance, it is treated and described by many researchers. The waves approaching the shore carry momentum with them. The component of momentum parallel to the coast causes a longshore current. This current is of great importance in the transport of sediment along the coast. In this study, Representative 6 mean longshore current formulas are used for calculating longshore sediment transport rate. The results computed by mean longshore currents are compared with the measurements and the characteristics of mean longshore current formulas are analyze. The results computed by mean longshore currents are compared with the measurements and they show a good agreement except Inman-Quinn and Harrison formulas.

백서 심방 근세포에서 전단자극에 의한 P2X 퓨린수용체의 활성화

손민정(Min-Jeong Son),김준철(Joon-Chul Kim),왕 준(Jun Wang),김경희(Kyeong-Hee),우선희(Sun-Hee Woo) 대한약학회 2016 약학회지 Vol.60 No.5

Atrial myocytes are subjected to shear stress under physiological and pathological conditions during cardiac cycle. It has been recently suggested that ATP release of atrial cells induces longitudinal Ca 2+ wave via activation of P2Y 1 purinergic signaling in rat atrial myocytes under shear stress. In the present study, we examined whether P2X purinoceptor, a non-selective cation channel, is activated in these cells using a whole-cell patch clamp combined with a pressurized microflow system. Shear stress of ~16 dyne/cm 2 (1-s long) produced a slow inward current(I SS ) at −70 mV in symmetrical CsClrich solutions. Removal of external Ca 2+ significantly enhanced the I SS by approximately 140%. Pre-treatment of suramin(10 µM), the general P2-purinoceptor antagonist, suppressed the I SS by ~70%. In addition, the I SS was inhibited by ~50% by pre-exposure to P2X purinoceptor inhibitor, iso-PPADS(100 µM). Inhibition of transient receptor potential melastatin 4, the Ca 2+ -activated non-selective cation channel, using 9-phenanthrol(30 µM) decreased I SS by ~30%. When the delayed rectifying K + channels, that have slight permeability to Cs + , were blocked using 4-aminopyridine(200 µM), I SS was not altered. Our data suggest that shear stress activates P2X purinoceptors in atrial myocytes, thereby partly contributing to shear-activated slow cation influx at resting membrane potential.

Fatigue Analysis for a Multi-lap Spot Welded Joint of High Strength Steel Using Quasi Static Tensile-shear Test

S. R. SIN,양성모,유효선,김채원,강희용 한국자동차공학회 2008 International journal of automotive technology Vol.9 No.1

The welding quality of spot weldment is an important factor that significantly affects the strength, stiffness, safety, and other performance characteristics of vehicles. Therefore, quality control and fatigue life evaluation of spot weldment are necessary processes. This paper presents a method for determining the fatigue life of multi-lap spot weldment of a high strength steel sheet. In this method, the fatigue life is estimated using the lethargy coefficient, which is the total defect coefficient according to rupture stress and time obtained by the quasi static tensile-shear test. The DC potential drop method was used to check initiation and propagation of cracks in addition to the test. Also, in this study, we modified the lethargy coefficient by using the welding current. Furthermore, we define a specific lapping constant, which is a characteristic constant of 2 or 3 lap weldments. The fatigue life obtained by the fatigue estimate equation, which contains a specific lapping constant was compared and verified with an experimental value. Finally we analyzed the relation of lap number, welding current and fatigue life. This method can save processing time and cost for predicting the life cycle of a structure.

자동차용 박판 점 용접부의 용접성 평가

나의균(Eui-guyen Na),고승기(Seung-Kee Koh),백태현(Tae-Hyun Baek),오석형(Suck-Hyung Oh),오원철(Won-Cherl Oh) 대한기계학회 2001 대한기계학회 춘추학술대회 Vol.2001 No.9

The purpose of this study is to evaluate the strength at spot welded region for the automotive thin plates and to find out the fracture region by a finite element method. spot welding against the thin plate of 0.8㎜, 1.0㎜, 1.2㎜ and 1.6㎜ was conducted under various welding currents. The weldability of spot welded region was dependent upon the thickness and welding current, Nugget diameter of the spot welded region was proportional to the applied current. Generally, Maximum load at spot welded region increased with the welding current. However, too high current was inappropriate in acquiring the better weldability because of the sputtering effect. It was verified through FEM analysis that fracture was initiated at boundary region between nugget and parent.

Sheared current를 고려한 스파플랫폼의 VIM 시뮬레이션

옥대경(Dae-Kyung Ock),박종천(Jong-Chun Park),정세민(Se-Min Jeong),박영찬(Young-Chan Park) 한국해양환경·에너지학회 2017 한국해양환경공학회 학술대회논문집 Vol.2017 No.10