• 제목/요약/키워드: gravity potential

검색결과 176건 처리시간 0.027초

Ni 첨가량에 따른 중력 주조 Mg-Ni 합금의 수소화 반응 특성의 변화 (Change of Hydriding Properties of Gravity Cast Mg-Ni Alloys with Ni Content)

  • 임창동;문용민;유봉선;나영상;배종수
    • 한국수소및신에너지학회논문집
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    • 제15권3호
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    • pp.250-256
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    • 2004
  • Magnesium and its alloys have the high potential as hydrogen storage materials because of their highest hydrogen storage capacity, low density and abundant resources. But poor kinetic properties of hydriding and dehydriding and high working temperature have limited their practical applications. In this study, the Mg-Ni binary alloys with different amount of Ni were produced by gravity casting and characterized in order to investigate the relationship between the microstructures and hydriding properties. The maximum hydrogen absorption capacity decreased, but the absorption kinetics increased with Ni content. The difference in the absorption kinetics was resulted from the differences in the sort and shape of primary solid phases and eutectic microstructure.

이온화세기, 제타전위, 입자크기에 따른 속도차 침전에서의 입자간 충돌특성에 관한 연구 (A Study of Collision Characteristics in differential sedimentation according to variation of Ionic Strength, Zeta Potential and Particle Size)

  • 한무영;독고석;박중현
    • 상하수도학회지
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    • 제12권1호
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    • pp.81-87
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    • 1998
  • The possibility of collision of two particles slowly settling one after another in water can be described using the collision efficiency factor in differential sedimentation (${\alpha}_{DS}$). ${\alpha}_{DS}$ was found to be a function of several parameters particle size, particle size ratio, Hamaker constant, density of liquid and particle, gravity acceleration. Previous researches were limited to the case when there is no electric repulsion assuming that the suspension is destabilized. In this paper, ${\alpha}_{DS}$ is calculated for the stabilized condition. The relative trajectory of two particles are calculated including hydrodynamics, attraction and repulsion forces. Ionic strength and surface potential significantly affect the collision possibility of two settling particles. Depending on the surface potential and ionic strength, ${\alpha}_{DS}$ value is divided into three regions; stable, unstable and transition zone. ${\alpha}_{DS}$ increases as the ionic strength increases, and as the surface charge decreases. This result can be used to model both destabilized and stabilized suspension incorporating the collision efficiency factors of the other coagulant mechanisms such as fluid shear and Browian motion.

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Potential Anomaly Separation and Archeological Site Localization Using Genetically Trained Multi-level Cellular Neural Networks

  • Bilgili, Erdem;Goknar, I. Cem;Albora, Ali Muhittin;Ucan, Osman Nuri
    • ETRI Journal
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    • 제27권3호
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    • pp.294-303
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    • 2005
  • In this paper, a supervised algorithm for the evaluation of geophysical sites using a multi-level cellular neural network (ML-CNN) is introduced, developed, and applied to real data. ML-CNN is a stochastic image processing technique based on template optimization using neighborhood relationships of the pixels. The separation/enhancement and border detection performance of the proposed method is evaluated by various interesting real applications. A genetic algorithm is used in the optimization of CNN templates. The first application is concerned with the separation of potential field data of the Dumluca chromite region, which is one of the rich reserves of Turkey; in this context, the classical approach to the gravity anomaly separation method is one of the main problems in geophysics. The other application is the border detection of archeological ruins of the Hittite Empire in Turkey. The Hittite civilization sites located at the Sivas-Altinyayla region of Turkey are among the most important archeological sites in history, one reason among others being that written documentation was first produced by this civilization.

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Secular Evolution of Nuclear Bulges through Sustained Star Formation

  • 김성수;;전명원
    • 천문학회보
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    • 제35권1호
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    • pp.72.1-72.1
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    • 2010
  • Gas materials in the inner Galactic disk continuously migrate toward the Galactic center (GC) due to interactions with the bar potential, magnetic fields, stars, and other gaseous materials. In case of the Milky Way, those in forms of molecules appear to accumulate around 200 pc from the center (the central molecular zone, CMZ) to form stars there and further inside. The bar potential in the GC is thought to be responsible for such acculmulation of molecules and subsequent star formation, which is believed to have been continous throughout the lifetime of the Galaxy. We present 3-D hydrodynamic simulations of the CMZ that consider self-gravity, radiative cooling, and supernova feedback, and discuss the efficiency and role of the star formation in that region. We find that the gas accumulated in the CMZ by a bar potential of the inner bulge effectively turns into stars, supporting the idea that the stellar cusp inside the central 200 pc is a result of the sustained star formation in the CMZ. The obtained star formation rate in the CMZ, 0.03-0.1 Msun, is consistent with the recent estimate based on the mid-infrared observations by Yusef-Zadeh et al. We discuss the secular evolution of nuclear bulges in general, based on our results.

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Numerical Investigation of Motion Response of the Tanker at Varying Vertical Center of Gravities

  • Van Thuan Mai;Thi Loan Mai;Hyeon Kyu Yoon
    • 한국해양공학회지
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    • 제38권1호
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    • pp.1-9
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    • 2024
  • The vertical center of gravity (VCG) has a significant impact on the roll motion response of a surface ship, particularly oil tankers based on the oil level in the tanker after discharging oil at several stations or positional changes, such as changes in the superstructure and deck structure. This study examined the motion response of the Korea very large crude carrier 2 (KVLCC2) at various VCGs, especially roll motion when the VCG changed. The potential theory in the Ansys AQWA program was used as a numerical simulation method to calculate the motion response. On the other hand, the calculations obtained through potential theory overestimated the roll amplitudes during resonance and lacked precision. Therefore, roll damping is a necessary parameter that accounts for the viscosity effect by performing an experimental roll decay. The roll decay test estimated the roll damping coefficients for various VCGs using Froude's method. The motion response of the ship in regular waves was evaluated for various VCGs using the estimated roll-damping coefficients. In addition, the reliability of the numerical simulation in motion response was verified with those of the experiment method reported elsewhere. The simulation results showed that the responses of the surge, sway, heave, pitch, and yaw motion were not affected by changing the VCG, but the natural frequency and magnitude of the peak value of the roll motion response varied with the VCG.

달 동굴의 잠재적 주거환경에 관한 연구 (A Study of the Potential Shelters in the Lunar Lava Tubes)

  • 오종우
    • 한국위성정보통신학회논문지
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    • 제12권3호
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    • pp.41-49
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    • 2017
  • 본 연구에서는 달의 동굴에 대한 거주환경에 잠재적 요건이 될 수 있는 지질과 지형, 내부탐사, 안정성, 통신, 거주요건 등의 5분야에 대한 분석을 시도 하였다. 달 동굴관련 정성적 정량적인 자료 분석에서 다음과 같은 결과를 도출하였다. 달 동굴의 지질과 지형환경에서는 지구의 용암동굴의 규모와 형상에서 큰 차이를 확인하였다. 달의 지질은 내인적인 분화나 지진 보다 외인적인 환경인 운석의 낙하와 방사선의 공격 및 급격한 온도차에 의한 영향이 크다. 달 동굴의 지형과 내부형상은 중력의 차로 인한 대규모의 위험한 동굴지형으로 함몰구(skylight)와 사행 열구(sinuous rilles)에 대한 접근과 내부 지형형상 취득에 기술적인 한계가 있었다. 달 동굴의 안정성 분석에서는 대형의 동굴에 대한 지질과 지형적인 위험성에 두었다. 함몰에 대한 저 위험도 빈도, 저 중력, 동굴의 대규모와 두께 등의 안정성 인자 등으로 지구보다 상대적인 안정성이 확인되었다. 달 동굴내외의 통신환경은 동굴내부에서의 무선통신 운영의 경우 태양열 충전식에만 한계가 있을 것이나 전력의 무선전송기술로 이를 극복할 수 있을 것이다. 따라서 본 연구를 통하여 달 동굴에 대한 거주 가능성에 대한 학설과 기술의 대비 중에서 학술적이고 기술적인 차별성이 다양하게 확인되었다. 특히 무중력, 우주방사선의 피폭과 먼지 등의 외인적인 한계와 거칠고 급경사인 함몰구 등의 접근기술에 대한 통신과 토목 및 GIS기술 등에 대한 내인적인 한계의 극복의 필요성으로 이에 대한 향후의 연구개발에 기대감이 증폭되었다.

인공위성 해면고도계 중력자료를 이용한 황해 군산분지의 밀도 불연속면에 대한 연구 (Study on Density Discontinuous Layers of the Kunsan Basin in the Yellow Sea Using Satellite Altimetry Gravity Data)

  • 김경오;오재호
    • 자원환경지질
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    • 제40권6호
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    • pp.751-759
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    • 2007
  • 황해 군산분지의 지하 지질구조를 파악하기 위하여 인공위성 해면고도계 중력자료를 이용하여 파워 스펙트럼 분석(power spectrum analysis) 방법으로 밀도 불연속면의 평균 깊이를 계산하였다. 계산 결과에 의하면 군산분지를 포함한 본 연구지역에서는 각각 -1.1km, -3.4km, -9.1km 그리고 -31.0km의 평균 깊이를 가지는 밀도 불연속면이 검출되었다. -1.1km 평균 깊이의 밀도 불연속면은 본 연구지역의의 탄성파 단면에서 관찰되는 왕복 주시 1초 부근에서 나타나는 광역 부정합면으로 해석되었고, -3.4km 평균 깊이의 밀도 불연속면 또한 탄성파 단면에서 인지되는 음향기반암 상부면과 일치하는 것으로 해석되었다. -9.1km 평균 깊이의 밀도 불연속면은 본 연구지역의 시추공 자료, 탄성파 단면, 광역 지질 등을 고려하여 화성기원 기반암의 상부면으로 해석하였다. 이는 본 연구지역의 음향 기반암층은 기존의 연구에서 고려 대상이 되지 않았던 퇴적암으로 이루어져 있음을 의미한다. -31.0km의 평균 깊이를 가지는 밀도 불연속면은 일반적인 대륙지각의 평균 두께와 유사한 값을 보이므로 모호면으로 해석하였다. 화성기원 기반암 상부면으로 해석된 -9.1km 평균 깊이의 밀도 불연속면의 검출은 군산분지의 석유 가스 부존 가능성에 관한 연구에 있어 기존의 연구보다 심부층(음향 기반암층)에 대한 연구가 필요함을 시사하였다.

3차원 비선형 조파문제 해석을 위한 수치해법 연구 (A Study of Numerical Method for Analysis of the 3-Dimensional Nonlinear Wave-Making Problems)

  • 하영록;안남현
    • 동력기계공학회지
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    • 제16권5호
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    • pp.40-46
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    • 2012
  • 본 연구에서는 자유표면 유동문제를 효율적으로 계산하기 위한 방법으로서, 수치 파수조를 구현하여 잠수체에 의한 조파현상을 시간영역에서 다룰 수 있는 수치해법에 대하여 소개하였다. 그리고 이를 이용하여 수행된 연구내용들을 검토하고 양력물체의 경우를 포함하기 위하여 개선된 수학적 정식화 및 수치해법의 개요를 다루었다. 임의의 운동을 하는 양력물체에 의한 조파현상을 전산기로 구현하는 수치 파수조는 과중한 계산시간이 문제가 되는데, 이는 수치 Kutta 조건의 구현과 양력표면 후방의 wake 영역을 계산에서 고려해야 하기 때문이다. 따라서 한층 더 수치계산의 효율성이 중요하다고 판단되므로, 본 연구에서 소개된 3차원 고차 스펙트럴/경계요소법(High-Order Spectral/Boundary Element Method)은 자유표면 요소수를 N이라 할 때 그 계산량이 NlogN에 비례(N이 클 때는 거의 선형적으로 비례)하여 증가하므로 기존의 방법들 보다 매우 효율적인 수치해법이라 할 수 있다. 향후, 본 연구의 타당성 검증을 위한 수치코드의 개선과 여러 가지 수치계산결과 비교 등의 노력이 더 필요하다고 생각된다.

Effect of Earthquake characteristics on seismic progressive collapse potential in steel moment resisting frame

  • Tavakoli, Hamid R.;Hasani, Amir H.
    • Earthquakes and Structures
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    • 제12권5호
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    • pp.529-541
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    • 2017
  • According to the definition, progressive collapse could occur due to the initial partial failure of the structural members which by spreading to the adjacent members, could result in partial or overall collapse of the structure. Up to now, most researchers have investigated the progressive collapse due to explosion, fire or impact loads. But new research has shown that the seismic load could also be a factor for initiation of the progressive collapse. In this research, the progressive collapse capacity for the 5 and 15-story steel special moment resisting frames using push-down nonlinear static analysis, and nonlinear dynamic analysis under the gravity loads specified in the GSA Guidelines, were studied. After identifying the critical members, in order to investigate the seismic progressive collapse, the 5-story steel special moment resisting frame was analyzed by the nonlinear time history analysis under the effect of earthquakes with different characteristics. In order to account for the initial damage, one of the critical columns was weakened at the initiation of the earthquake or its Peak Ground Acceleration (PGA). The results of progressive collapse analyses showed that the potential of progressive collapse is considerably dependent upon location of the removed column and the number of stories, also the results of seismic progressive collapse showed that the dynamic response of column removal under the seismic load is completely dependent on earthquake characteristics like Arias intensity, PGA and earthquake frequency contents.

대단면터널 특성을 고려한 지보설계 개선방안 연구 (Large-span Tunnel Support Design supplemented by Analytical Methods)

  • 정재호;이희석;허종석;윤상길
    • 한국지반공학회:학술대회논문집
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    • 한국지반공학회 2006년도 춘계 학술발표회 논문집
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    • pp.949-959
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    • 2006
  • Despite of the popularity of using empirical methods for support design, empirical rules suffer from the inherent problem of providing no indication of the safety degree of the design. For the support design of large span tunnel, it was considered that the empirical design guidelines should be augmented by more explicit design methods. This paper presents an overview of the analytical support design methodology that is used to refine initial empirical recommendations. The initial support design supplemented by analytical methods is validated by probabilistic and deterministic approach applied to stress-induced and structurally controlled gravity-driven instability problem each. As a result, the extent of the potential failure zone is sorted out and numerical parametric studies were performed to gain insight into the overall behavior of tunnel in the potential failure zone. Concequently, it was decided that additional conservation techniques have to be planed as a reserved support pattern.

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