• 한국군사과학기술학회지
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• 제20권3호
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• pp.405-412
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• 2017

In the present study, two phase flows around a projectile vertically launched from an underwater platform have been numerically investigated by using a three dimensional multi-phase RANS flow solver based on pseudo-compressibility and a homogeneous mixture model on unstructured meshes. The relative motion between the platform and projectile was described by six degrees of freedom(6DOF) equations of motion with Euler angles and a chimera technique. The propulsive power of the projectile was modeled as the fluid force acting on the lower surface of the body by the compressed air emitted from the platform. Qualitative analysis was conducted for the time history of vapor volume fraction distributions. Uncorking pressure around the projectile and platform was analyzed to predict impact force acting on the surfaces. The results of 6DOF analysis presented similar tendency with the surficial pressure distributions.

• 한국정밀공학회지
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• 제28권9호
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• pp.1018-1024
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• 2011

Liquid sloshing occurs when a partially filled liquid tank is subjected to undesirable external forces or acceleration/deceleration for positioning control. Installation of baffles is still the most popular way to suppress the sloshing, but recent successes of input shaping in reducing structural vibrations may give a possible alternative. We aim at investigating the applicability of input shaping to sloshing suppression by numerically solving fluid motions in a rectangular tank. The tank is partially filled with water and it is suddenly put into a sequence of horizontal motions of acceleration and constant speed. The flow is assumed to be two-dimensional, incompressible, and in viscid, and a VOF two-phase model is used to capture the free surface. Results show that the sloshing can be successfully suppressed by shaping the input, i.e., the velocity or acceleration profile of tank. Three different input shapers (ZII, ZVD, and two-mode convolved ZV shapers) are tested and compared in this study Among them, the convolved ZV shaper shows a best performance to eliminate the sloshing almost completely.

• 대한기계학회논문집B
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• 제27권12호
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• pp.1716-1723
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• 2003

A stereoscopic PIV(Particle Image Velocimetry) technique was employed to measure the 3 dimensional flow structure of turbulent wake behind a marine propeller with 5 blades. The out-of-plane velocity component was determined using two CCD cameras with the angular displacement configuration. Four hundred instantaneous velocity fields were measured for each of four different blade phases and ensemble averaged to investigate the spatial evolution of the propeller wake in the near-wake region from the trailing edge to one propeller diameter(D) downstream. The phase-averaged velocity fields show the potential wake and the viscous wake developed along the blade surfaces. Tip vortices were generated periodically and the slipstream contraction occurs in the near-wake region. The out-of-plane velocity component and strain rate have large values at the locations of tip and trailing vortices. As the flow goes downstream, the turbulence intensity, the strength of tip vortices and the magnitude of out-of-plane velocity component at trailing vortices are decreased due to viscous dissipation, turbulence diffusion and blade-to-blade interaction.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2003년도 추계학술대회
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• pp.472-477
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• 2003

This study was performed to investigate the behavior of vapor phase of fuel mixtures with different piston cavity diameters in a optically accessible engine. The images of vapor phases were measured in the motoring engine using exciplex fluorescence method. The conventional engine was modified as GDI engine with swirl flow. Fuel was injected into atmospheric nitrogen to prevent quenching phenomenon by oxygen. Injection pressure is 5.1MPa. Two dimensional spray fluorescence image of vapor phases was acquired to analyze spray behavior and fuel distribution inside of cylinder. Three injection timings were set at BTDC $180^{\circ}$, $60^{\circ}$and $60^{\circ}$. With a fuel injection timing of BTDC $60^{\circ}$, fuel-rich mixture was concentrated in near the cavity center. With a fuel injection timing of BTDC $60^{\circ}$, fuel-rich mixture level in the center region was highest in the S-type during the late compression stroke. With a fuel injection timing of BTDC $180^{\circ}$, fuel was not affected in a piston cavity and generally distributed as homogeneous mixture.

• International Journal of Ocean System Engineering
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• 제1권3호
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• pp.136-143
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• 2011

In this paper, three-dimensional free-surface flows are simulated by using two different numerical methods, the constrained interpolation profile (CIP)-based and finite volume (FV)-based methods. In the CIP-based method, the governing equations are solved on stationary staggered Cartesian grids by a finite difference method, and an immersed boundary technique is applied to deal with wave-body interactions. In the FV-based method, the governing equations are solved by applying collocated finite volume discretization, and body-fitted meshes are used. A free-surface boundary is considered as the interface of the multi-phase flow with air and water, and a volumeof-fluid (VOF) approach is applied to trace the free surface. Among many variations of the VOF-type method, the tangent of hyperbola for interface capturing (THINC) and the compressive interface capturing scheme for arbitrary meshes (CICSAM) techniques are used in the CIP-based method and FV-based method, respectively. Numerical simulations have been carried out for dam-breaking and wave-body interaction problems. The computational results of the two methods are compared with experimental data and their differences are observed.

• 한국해양학회지
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• 제29권1호
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• pp.50-63
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• 1994

두 가지의 서로 다른 난류 변수화를 삼차원적이고 시간의존적인 연안해역의 모델 실험으로 수행하였다. 난류 변수화 중의 하나는 일정한 와동복합화 한 것, C1이고 다 른 하나는 층화 의존적인 와동혼합화, C2이다. C2를 이용한 유체흐름은 강한 경압적 흐름이며 담수와 염수의 수직적인 혼합을 제한하고 있다. 하구언으로부터 방출되는 유 출류는 C2의 경우가 C1의 경우보다 훨씬 더 관성적이며 강한 플륨(plume) 전선을 형성 한다. C에서는 강한 유출류로 인하여 초림계적인 유체흐름의 상태, 즉 표층류의 유출 소도가 경압적 위상속도를 능가하는 상황이 하구언의 외해쪽에 존재할 수 있다. 담수 영역에서 의 유체의 조율과정은 C1의 경우와 C2의 경우가 상당이 바른 바, C에서 의 유체의 흐름은 강한 경압적인 특성을 보여준다.

• 설비공학논문집
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• 제23권12호
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• pp.843-851
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• 2011

A two-dimensional immiscible water meniscus deformation phenomena on a moving tip in a channel has been investigated by using lattice Boltzmann method involving two-phase model. We studied the behavior of a water meniscus between the tip and a solid surface. The contact angles of the tip and a solid surface considered are in the range from $10^{\circ}$ to $170^{\circ}$. The velocity of the tip used in the study are 0.01, 0.001, and 0.0001. The shapes of tip considered are rectangular and circular. The behavior of water confined between the tip and a solid surface depends on the contact angles of the tip and a solid surface, and the tip velocity. When the tip is moving, we can observe the various behaviors of shear deformation of a water meniscus. As time goes on, the behavior of a water meniscus can be classified into three different patterns which are separated from the tip or adhered to the tip or sticked to a solid surface according to the contact angles and the tip velocity.

• 한국전산유체공학회지
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• 제21권3호
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• pp.15-23
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• 2016

In the present study, two phase flows around a projectile vertically launched from an underwater platform have been numerically investigated by using a three dimensional multi-phase RANS flow solver based on pseudo-compressibility and a homogeneous mixture model on unstructured meshes. The relative motion between the platform and projectile was described by six degrees of freedom equations of motion with Euler angles and a chimera technique. The propulsive power of the projectile was modeled as the fluid force acting on the lower surface of the body by the compressed air emitted from the underwater platform. Various flow conditions were considered to analyze the fluid-dynamics motion parameters of the projectile. The water level of platform and the current speed around the projectile were the main parametric variables. The numerical calculations were conducted up to 0.75sec in physical time scale. The dynamics tendency of the projectile was almost identical with respect to the water level variation due to the constant buoyancy term. The moving speed of the projectile along the vertical axis inside the platform decreased when the current speed increased. This is because the inflow from outside of the platform impeded development of the compressed air emitted from the floor surface of the launch platform. As a result, the fluid force acting on the lower surface of the projectile decreased, and injection time of the projectile from the platform was delayed.

• 한국수소및신에너지학회논문집
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• 제21권1호
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• pp.1-11
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• 2010

Current distribution measurement technique based on a segmented bipolar plate (BP) has been widely adopted to visualize the distribution of current density in a polymer electrolyte membrane. However, a concern is raised how closely the current density of a segmented BP can approach that of a corresponding non-segmented membrane. Therefore, in this paper, the accuracy of the measurement technique is numerically evaluated by applying a three-dimensional, two-phase fuel cell model to a $100\;cm^2$ area fuel cell geometry in which segmented BPs and non-segmented membrane are combined together. The simulation results reveal that the errors between the current densities of the segmented BPs and non-segmented membrane indeed exist, predicting the maximum relative error of 33% near the U-turn regions of the flow-field. The numerical study further illustrates that the erroneous result originates from the BPs segmented non-symmetrically based on the flow channels that allows some currents bypassing flow channels to flow into its neighboring segment. Finally, this paper suggests the optimal way for bipolar plate segmentation that can minimize the deviation of current measured in a segmented BP from that of a corresponding membrane region.

• Wind and Structures
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• 제38권3호
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• pp.161-170
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• 2024

In recent years, there have been an increasing number of experimental studies showing the need to include robustness criteria in the design process to develop complex active control designs for practical implementation. The paper investigates the crosswind aerodynamic parameters after the blocking phase of a two-dimensional square cross-section structure by measuring the response in wind tunnel tests under light wind flow conditions. To improve the accuracy of the results, the interpolation of the experimental curves in the time domain and the analytical responses were numerically optimized to finalize the results. Due to this combined effect, the three aerodynamic parameters decrease with increasing wind speed and asymptotically affect the upper branch constants. This means that the aerodynamic parameters along the density distribution are minimal. Taylor series are utilized to describe the fuzzy nonlinear plant and derive the stability analysis using polynomial function for analyzing the aerodynamic parameters and numerical simulations. Due to it will yield intricate terms to ensure stability criterion, therefore we aim to avoid kinds issues by proposing a polynomial homogeneous framework and utilizing Euler's functions for homogeneous systems. Finally, we solve the problem of stabilization under the consideration by SOS (sum of squares) and assign its fuzzy controller based on the feasibility of demonstration of a nonlinear system as an example.