• Title/Summary/Keyword: 에너지적분

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Numerical simulation of dense interflow using the k-ε turbulence model (k-ε 난류모형을 이용한 중층 밀도류의 수치모의)

  • Choi, Seongwook;Choi, Sung-Uk
    • Journal of Korea Water Resources Association
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    • v.50 no.9
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    • pp.637-646
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    • 2017
  • This study presents a numerical model for simulating dense interflows. The governing equations are provided and the finite difference method is used with the $k-{\varepsilon}$ turbulence model. The model is used to simulate a dense interflow established in a deep ambient water, resulting velocity and excess density profiles. It is observed that velocity decreases in the longitudinal direction due to water entrainment in the vicinity of the outlet and rarely changes for increased Richardson number. Similarity collapses of velocity and excess density are obtained, but those of turbulent kinetic energy and dissipation rate are not. A shape factor for the dense interflow is obtained from the simulated profiles. The value of this shape factor can be used in the layer-averaged modeling of dense interflows. In addition, a buoyancy-related parameter ($c_{3{\varepsilon}}$) for the $k-{\varepsilon}$ model and the volume expansion coefficient (${\beta}_0$) are obtained from the simulated results.

A Four-node General Shell Element with Drilling DOFs (면내회전자유도를 갖는 4절점 곡면 쉘요소)

  • Chung, Keun-Young;Kim, Jae-Min;Lee, Eun-Haeng
    • Journal of the Earthquake Engineering Society of Korea
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    • v.16 no.4
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    • pp.37-52
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    • 2012
  • In this study, a new 4-node general shell element with 6 DOFs per node is presented. Drilling rotational degrees of freedom are introduced by the variational principle with an independent rotation field. In formulation of the element, substitute transverse shear strain fields are used to avoid shear locking, while four nonconforming modes are applied in the in-plane displacement fields as a remedy for membrane locking. In addition, a direct modification method for nonconforming modes is employed in the numerical implementation of nonconforming modes to represent constant strain states. A 9-points integration rule is adopted for volume integration in the computation of the element stiffness matrix. With the combined use of these techniques, the developed shell element has no spurious zero energy modes, and can represent a constant strain state. Several numerical tests are carried out to evaluate the performance of the new element developed. The test results show that the behavior of the elements is satisfactory.

Analysis of Ranging Performance According to Analog Front End Characteristics in a Noncoherent UWB System (Noncoherent UWB 시스템에서 Analog Front End 특성에 따른 레인징 성능 분석)

  • Kim, Jae-Woon;Park, Young-Jin;Lee, Soon-Woo;Shin, Yo-An
    • The Journal of Korean Institute of Communications and Information Sciences
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    • v.35 no.1C
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    • pp.77-86
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    • 2010
  • In this paper, we present a noncoherent IR-UWB (Impulse Radio-Ultra Wide Band) ranging system with an AFE (Analog Front End) composed of a simple integrator and an 1-bit ADC (Analog-to-Digital Converter), and define AFE characteristics affecting the ranging performance. This system is realistic and easy to implement, since the integrator simply accumulates signal energies and the simple 1-bit ADC is applied instead of the multi-bit ADCs for coherent IR-UWB systems. On the other hand, its ranging accuracy is largely affected channel environments such as noise, multipath fading and so on, since the noncoherent receiver simply squares and integrates the received signals. However, despite these practical importances, there are few conventional researches on the performance analysis according to AFE characteristics in IR-UWB ranging systems. To this end, we analyze in this paper ranging performance according to AFE characteristics for the noncoherent IR-UWB ranging system in various wireless channel environments, and through these results we also present system parameters to be considered in UWB hardware designs.

Loads of a Rigid Link Connecting a Container Ship and a Catamaran Type Container Offloading Vessel in Waves (파랑중 컨테이너선과 하역선의 연결장치에 작용하는 하중계산)

  • Hong, Do-Chun;Kim, Yong-Yook;Han, Soon-Hung
    • Journal of the Korean Society for Marine Environment & Energy
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    • v.13 no.2
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    • pp.83-90
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    • 2010
  • The hydrodynamic interaction of two floating bodies in waves freely floating or connected by a rigid link is studied by using a boundary element method in the frequency-domain. The exact two-body hydrodynamic coefficients of added mass, wave damping and exciting force are calculated from the radiation-diffraction potential solution of the improved Green integral equation associated with the free surface Green function. The irregular frequencies in the conventional Green integral equation make it difficult to predict the physical resonance of the fluid in the gap between two bodies floating side by side. However, the improved Green integral equation employed in this study is free of irregular frequencies and always yields the exact solution of the multi-body radiation-diffraction potential boundary value problem. The 6 degree-of-freedom motions of two bodies freely floating side by side or connected parallel by a rigid link have been calculated for the incident wave frequencies ranging from 0.1 to 5 radians per second in head, left and right bow quartering seas. The 6-component load of the rigid link have also been presented.

Enhanced Flame Resistant Properties of Aluminum Hydroxide Addition on Electrospun Polyurethane Nanofibers (전기방사법에 의해 제조된 폴리우레탄 나노섬유의 수산화알루미늄 내첨에 의한 내염화 특성 향상)

  • Kim, Hyeong Gi
    • Fire Science and Engineering
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    • v.30 no.6
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    • pp.9-13
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    • 2016
  • Anti-oxidation and flame resistant polyurethane nanofibers were prepared by electrospinning and aluminum hydroxide addition. Electrospinning was carried out under the following procedure conditions; applied voltage, 20 kV; polymer solution feeding rate, 1.2 ml/h; collector rolling speed, 120 rpm; and tip to collector distance, 15 cm. Aluminum hydroxide was added to the prepared polymer solution for electrospinning to enhance the oxidation and flame resistant properties. The thermal properties were investigated by thermogravimetric analysis to determine the polymer decomposition temperature, integral procedure decomposition temperature, final decomposition temperature, and remaining amount after thermal decomposition. The activated energy for polymer degradation was also investigated using the Horowitz-Metzger equation. The activation energy increased to more than 50%. The thermal properties of the polyurethane nanofibers were improved by a hydration reaction during the thermal decomposition of aluminum hydroxide around $300{\sim}500^{\circ}C$.

A Kinetic Study of Thermal-Oxidative Decomposition of Waste Polyurethane (폐폴리우레탄의 열적 산화분해에 대한 속도론적 연구)

  • Jun, Hyun Chul;Oh, Sea Cheon;Lee, Hae Pyeong;Kim, Hee Taik
    • Applied Chemistry for Engineering
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    • v.17 no.3
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    • pp.296-302
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    • 2006
  • The kinetics of the thermal-oxidative decomposition of waste polyurethane (PU) according to oxygen concentration has been studied using a non-isothermal thermogravimetric technique at several heating rates from 10 to $50^{\circ}C/min$. A kinetic model accounting for the effects of the oxygen concentration by the differential and integral method based on Arrhenius equation was proposed to describe the thermal-oxidative decomposition of waste PU. To obtain the information on the kinetic parameters such as activation energy, reaction order, and pre-exponential factor, the thermogravimetric analysis curves and its derivatives have been analyzed using the kinetic analysis method proposed in this work. From this work, it was found that reaction orders for oxygen concentration had a negative sign, and activation energy decreased as the oxygen concentration increased. It was also found that the kinetic parameters obtained from the integral method using the single heating rate experiments varied with heating rates. Therefore, it is thought that the differential method using the multiple heating rate experiments more effectively represents the thermal-oxidative decomposition of waste polyurethane.

Analysis on the Harbor Tranquility by Boundary Integral Equation Method (경계적분 방정식법에 의한 항내 청정도 해석)

  • 이철응;편종근;이길성
    • Journal of Korean Society of Coastal and Ocean Engineers
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    • v.3 no.4
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    • pp.223-234
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    • 1991
  • In this paper, the harbor tranquility problem is analysed by an improved boundary integral equation method. The effect of the diffracted wave transformation induced by the breakwater and structures located at a harbor mouth is considered. Partial reflection concept is also used to consider energy dissipation effects. The present model is verified by comparing the results of the model for rectangular and semi-circular harbors with the analytic solutions. they show a reasonable agreement. Also the wave height distribution of the HUPO harbor computed using the present model agree well to those from the previous hydraulic model tests. It also shows a good agreement with the results from the time-dependent mild slope equation model.

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Generalized Integral Hellmann-Feynam Theorem and Configuration Interaction in Crystal Field Theory (광의의 Integral Hellmann-Feynman Theorem과 결정장론에서의 배치간 작용의 효과)

  • Ho Jing Kim
    • Journal of the Korean Chemical Society
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    • v.20 no.3
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    • pp.198-205
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    • 1976
  • The integral Hellmann-Feynman Theorem of Parr is generalized to give a full significance to the off-diagonal form, and certain aspects of it are discussed. By use of the generalized form of the theorem, effects of configuration interaction to the crystal field theory are examined, taking perturbation energies of all order collectively into account. Thus, it is shown that there do not exist, especially when the field is strong, the radial integral which is common to all states characterized by ${\Gamma}$, S and m, and could be parametrized. If, however, one restricts the perturbing excited states only to those angularly undistorted and radially equally distorted, there results simple scaling of the crystal field parameter 10 Dq and Condon-Slater parameter $F^n$ defined within the framework of the classical crystal field theory.

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A Robustness of Hierarchic Element Formulated by Integrals of Legendre Polynomial (적분형 르장드르 함수에 의한 계층요소(階層要素)의 통용성(通用性))

  • Woo, Kwang Sung
    • KSCE Journal of Civil and Environmental Engineering Research
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    • v.12 no.1
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    • pp.43-50
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    • 1992
  • The purpose of this study is to ascertain the robustness of p-version model with hierarchic intergrals of Legendre shape functions in various applications including plane stress/strain, axisymmetric and shell problems. The most important symptoms of accuracy failure in modern finite elements are spurious mechanisms and a phenomenon known as locking which are exhibited for incompressible materials and irregular shapes which contain aspect ratios(R/t, a/b), tapered ratio(d/b), and skewness. The condition numbers and energy norms are used to estimate numerical errors, convergence characteristics and algorithmic efficiencies for verifying the aforementioned symptoms of accuracy failure. Numerical results from p-version models are compared with those from NASTRAN, SAP90, and Cheung's hybrid elements.

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A Study on the State feedback with Integral Control for a Variable Air Volume Unit (가변 풍량 유닛에 대한 적분기를 가진 상태 궤환 제어에 관한 연구)

  • 박세화
    • Journal of the Korea Academia-Industrial cooperation Society
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    • v.1 no.2
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    • pp.9-14
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    • 2000
  • State feedback with integral control for a variable air volume(VAV) unit which is recently taken notice of for the energy efficiency and saving in the building is studied to investigate the performance of the digital control methodology for the possible practical application. The digital controller which acquires the targat zone temperature and the air flow rate of the supplied air to the zone controls the opening of the damper in the VAV unit. Simulation results are performed for the conditions including reference changes and external thermal variations. In the simulation. simplified conditioned zone and the damper actuator modelling is considered. and relationships between controller gain Parameters and the system dynamics are investigated.

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