• 한국해양공학회지
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• 제24권5호
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• pp.16-21
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• 2010

During the loading/offloading operation of a liquefied natural gas carrier (LNGC) that is moored in a side-by-side configuration with an offshore plant, sloshing that occurs due to the partially filled LNG tank and the interactive effect between the two floating bodies are important factors that affect safety and operability. Therefore, a time-domain software program, called CHARM3D, was developed to consider the interactions between sloshing and the motion of a floating body, as well as the interactions between multiple bodies using the potential-viscous hybrid method. For the simulation of a floating body in the time domain, hydrodynamic coefficients and wave forces were calculated in the frequency domain using the 3D radiation/diffraction panel program based on potential theory. The calculated values were used for the simulation of a floating body in the time domain by convolution integrals. The liquid sloshing in the inner tanks is solved by the 3D-FDM Navier-Stokes solver that includes the consideration of free-surface non-linearity through the SURF scheme. The computed sloshing forces and moments were fed into the time integration of the ship's motion, and the updated motion was, in turn, used as the excitation force for liquid sloshing, which is repeated for the ensuing time steps. For comparison, a sloshing motion coupled analysis program based on linear potential theory in the frequency domain was developed. The computer programs that were developed were applied to the side-by-side offloading operation between the offshore plant and the LNGC. The frequency-domain results reproduced the coupling effects qualitatively, but, in general, the peaks were over-predicted compared to experimental and time-domain results. The interactive effects between the sloshing liquid and the motion of the vessel can be intensified further in the case of multiple floating bodies.

• 대한기계학회논문집B
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• 제29권6호
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• pp.671-686
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• 2005

The transient nature and complex geometries of two-phase gas-liquid flows cause fundamental difficulties when measuring flow velocity using an electromagnetic flowmeter. Recently, a current-sensing flowmeter was introduced to obtain measurements with high temporal resolution (Ahn et al.). In this study, current-sensing flowmeter theory was applied to measure the fast velocity transients in slug flows. The velocity fields of axisymmetric gas-liquid slug flow in a vertical pipe were obtained using Volume-of-Fluid (VOF) method, and the virtual potential distributions for the electrodes of finite size were also computed using the finite volume method for simulating slug flow. The output signal prediction for slug flow was carried out from the velocity and virtual potential (or weight function) fields. The flowmeter was numerically calibrated to obtain the cross-sectional liquid mean velocity at an electrode plane from the predicted output signal. Two calibration parameters are proposed for this procedure: a flow pattern coefficient and a localization parameter. The flow pattern coefficient was defined by the ratio of the liquid resistance between the electrodes for two-phase flow with respect to that for single-phase flow, and the localization parameter was introduced to avoid errors in the flowmeter readings caused by liquid acceleration or deceleration around the electrodes. These parameters were also calculated from the computed velocity and virtual potential fields. The results can be used to obtain the liquid mean velocity from the slug flow signal measured by a current-sensing flowmeter.

• Advances in nano research
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• 제9권3호
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• pp.133-145
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• 2020

In this study, nonlinear vibrations and dynamic instabilities of a smart embedded micro shell conveying varied fluid flow and subjected to the combined electro-thermo-mechanical loadings are investigated. With the aim of designing new hydraulic sensors and actuators, the piezoelectric materials are employed for the body and the effects of applying electric field on the stability of the system as well as the induced voltage due to the dynamic behavior of the system are studied. The nonlocal piezoelasticity theory and the nonlinear cylindrical shell model in conjunction with the energy approach are utilized to mathematically modeling of the structure. The fluid flow is assumed to be isentropic, incompressible and fully develop, and for more generality of the problem both steady and time dependent flow regimes are considered. The mathematical modeling of fluid flow is also carried out based on a scalar potential function, time mean Navier-Stokes equations and the theory of slip boundary condition. Employing the modified Lagrange equations for open systems, the nonlinear coupled governing equations of motion are achieved and solved via the state space problem; forth order numerical integration and Bolotin's method. In the numerical results, a comprehensive discussion is made on the dynamical instabilities of the system (such as divergence, flutter and parametric resonance). We found that applying positive electric potential field will improve the stability of the system as an actuator or vibration amplitude controller in the micro electro mechanical systems.

• Computers and Concrete
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• 제22권2호
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• pp.221-225
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• 2018

In this paper, vibration analysis of concrete foundations resting on soil medium is studied. The soil medium is simulated by Winkler model considering spring element. The concrete foundation is modeled by thick plate elements based on classical plate theory (CPT). Utilizing energy method consists of potential energy, kinetic energy and external works in conjunction with Hamilton's principle, the motion equations are derived. Assuming the simply supported boundary condition for the concrete foundation, the Navier method is used for calculating the frequency of the structure. The effect of different parameters such as soil medium, mode numbers, length to width ratio and length to thickness ratio of the concrete foundation are shown on the frequency of the structure. At the first, the results are validated with other published works in order to show the accuracy of the obtained results. The results show that considering the soil medium, the frequency of the structure increases significantly.

• 대한화학회지
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• 제20권5호
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• pp.340-350
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• 1976

글라스(glass) 전이온도 이하에서 고체 중합체들의 역학적 분광학의 여러 현상들을 이론적으로 기술하는 데 적용된 線形 반응 이론을 제안하였다. 시료에 의한 에너지 분산을 어떤 시간 相關函數들로 나타내었다. Liouville 연산자를 Kirkwood의 확산식 연산자로 대치하면, 여기에서 시간은 결과로부터 다리결합을 한 중합체들의 에너지 상실과 완화에 대한 Kirkwood의 결과가 나옴을 보였다. 완화시간을 계산하는 방법을 보이기 위하여 상관함수들을 계산하는 근사법을 고찰하였다. 여기에서 제안한 이론과 저온에서 매달린 (pendant) 시클로헥실기들을 가진 고체 중합체들의 역학적 에너지 완화 현상을 기술하는 데 사용된 한 모형 이론과의 관련성을 찾아 보기 위해, 이 근사법을 써서 二重우물 퍼텐셜 모형을 고찰하였다.

• 한국전문물리치료학회지
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• 제26권3호
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• pp.106-114
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• 2019

Background: It is difficult to assess whether community-dwelling frail older adults may remain pre-frail status or improve into a robust state without being directly checked by health care professionals. The health information perceived by older adults is considered to be one of best sources of potential concerns in older adult population. An online measurement system combined with item response theory (IRT) and computer adaptive testing (CAT) methods is likely to become a realistic approach to remotely monitor physical activity status of frail older adults. Objects: This article suggests an approach to provide a precise and efficient means of measuring physical activity levels of community-dwelling frail older adults. Methods: Article reviews were reviewed and summarized. Results: In comparison to the classical test theory (CTT), the IRT method is empirically aimed to focus on the psychometric properties of individual test items in lieu of the test as a whole. These properties allow creating a large item pool that can capture the broad range of physical activity levels. The CAT method administers test items by an algorithm that select items matched to the physical activity levels of the older adults. Conclusion: An online measurement system combined with these two methods would allow adequate physical activity measurement that may be useful to remotely monitor the activity level of community-dwelling frail older adults.

• 전기화학회지
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• 제17권2호
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• pp.119-123
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• 2014

Here I report on how Fourier Transform Electrochemical Impedance Spectroscopy (FTEIS) overcomes the potential-current linearity problem encountered in the impedance calculation process. FTEIS was first invented to solve the time-related drawback of the conventional impedance technique. The dramatic time reduction of FTEIS enabled the real-time impedance measurement but brought about the linearity problem at the same time. While the conventional method circumvents the problem using the steady-state made by a sufficiently long measurement time, FTEIS cannot because of its real-time function. However, according to the mathematical development reported in this article, the potential step used in FTEIS is proved to avoid the linearity problem. During the step period, the potential and the current are linearized by the electrochemical impedance. Also, Fourier transform of the differentiated potential and current is proved to give the same result of the original ones.

• Bulletin of the Korean Chemical Society
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• 제3권3호
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• pp.83-88
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• 1982

Viscosity and zeta-potential of 11.0 wt. % aqueous bentonite suspension containing various electrolytes and hydrogen-ion concentration were measured by using a Couette type automatic rotational viscometer and Zeta Meter, respectively. The effects of pH and elcctrolytes on the rheological properties of the suspension were investigated. A system, which has a large zeta-potcntial, has a small intrinsic relaxation time ${\beta}$ and a small intrinsic shear modulus $1/{\alpha}$ in the Ree-Eyring generalized viscosity equation, i.e., such a system has a small viscosity value, since ${\eta}={\beta}/{\alpha}$. In general, a stable suspension system has large zeta-potential. The stability condition of clay-water suspension can be estimated by viscometric method since stable suspension generally has small viscosity. The correlation between the stability, viscosity and zeta-potential has been explained by the Ree-Eyring theory of viscous flow.

• 한국기계연구소 소보
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• 통권14호
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• pp.135-144
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• 1985

A method is described to obtain the first order force and second order steady force on the fixed two dimensional submerged or semisubmerged cylinders at infinite depth of water due to regular waves. The first order diffraction wave velocity potential which describes the flow diffracted by a body is obtained numerically using source distribution method on the mean wetted surface. And a technique to remove the irregular frequency phenomena of the source distribution method is also applied. The second order steady force is calculates by means of direct integration of the pressures on the body as derived from the first order velocity potential and is also computed by means of reflection wave height derives from momentum conservation theory. The results are compared with those of published works, and show good agreement.

• JSTS:Journal of Semiconductor Technology and Science
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• 제13권5호
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• pp.530-537
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• 2013

An explicit surface potential calculation method of gate-all-around MOSFET (GAAMOSFET) devices which takes into account both interface trap charge and varying doping levels is presented. The results of the method are extensively verified by numerical simulation. Results from the model are used to find qualitative and quantitative effect of interface trap charge on subthreshold slope (SS) of GAAMOSFET devices. Further, design constraints of GAAMOSFET devices with emphasis on the effect of interface trap charge on device SS performance are investigated.