• Journal of Advanced Research in Ocean Engineering
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• 제2권2호
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• pp.48-60
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• 2016

Accurate simulation of free-surface wave flows around a ship is very important for better hull-form design. In this paper, a computational fluid dynamics (CFD) code which is based on the open source libraries, OpenFOAM, was developed to predict the wave patterns around a ship. Additional anti-diffusion source term for minimizing a numerical diffusion, which was caused by convection differencing scheme, was considered in the volume-fraction transport equation. The influence of the anti-diffusion source term was tested by applying it to free-surface wave flow around the Wigley and KCS model ships. In results, the wave patterns and hull wave profiles of the Wigley and KCS model ships for various anti-diffusion coefficients showed quite close patterns. While, the band width of the water volume-fraction values between 0.1 to 0.9 at the Wigley and KCS model hull surfaces was narrowed by considering the anti-diffusion term. From the results, anti-diffusion source term decreased free-surface smearing.

• Ocean Systems Engineering
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• 제6권4호
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• pp.363-375
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• 2016

Large numbers of submarine pipelines are laid as the world now is attaching great importance to offshore oil exploitation. Free spanning of submarine pipelines may be caused by seabed unevenness, change of topology, artificial supports, etc. By combining Iwan's wake oscillator model with the differential equation which describes the vibration behavior of free-span submarine pipelines, the pipe-fluid coupling equation is developed and solved in order to study the effect of both internal and external fluid on the vibration behavior of free-span submarine pipelines. Through generalized integral transform technique (GITT), the governing equation describing the transverse displacement is transformed into a system of second-order ordinary differential equations (ODEs) in temporal variable, eliminating the spatial variable. The MATHEMATICA built-in function NDSolve is then used to numerically solve the transformed ODE system. The good convergence of the eigenfunction expansions proved that this method is applicable for predicting the dynamic response of free-span pipelines subjected to both internal flow and external current.

• 한국소음진동공학회논문집
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• 제16권1호
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• pp.12-18
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• 2006

This research investigates the electromechanical characteristics of a spindle motor in a free-falling mobile hard disk drive before unexpected shock. Electromechanical simulation includes a time-stepping finite element analysis of the magnetic field in a speed controlled brushless DC motor and dynamic analysis of the stationary and rotating part linked by the fluid dynamic bearing under the free-falling condition. Analysis results show that the dynamic characteristics of the rotating spindle system during free-falling state have an effect on the relative motion between the stationary and rotating part of HDD. It results from the variation of reaction force in the bearing area due to the gravity force exerted on the rotating part of HDD, and the free-falling condition can be detected by observing the signal of the spindle motor and disk-head interface without using an accelerometer.

• 한국가시화정보학회:학술대회논문집
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• 한국가시화정보학회 2002년도 추계학술대회 논문집
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• pp.67-72
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• 2002

Today, the research to examine a fact that interaction between the air and the fluid free surface affects the steady state flow and air. We proved the interaction between vortex pairs and free surface on each condition that is created by the end of delta wings. another purpose of this study is to investigate the effect of surface active material which can change the surface tension and we must consider when we refer to turbulent flow on surface tension. therefore, this research examined the growth process of vortex pairs on condition of clean, contaminated free surface and wall after we made vortex pairs through counter rotating flaps. The results of this study suggest that vortex pairs in clean free surface rise safely but the vortex pairs in contaminated free surface and rigid, no slip is made secondary vortex or rebounding. However the secondary vortex in rigid, no slip is stronger than before, and we can find the vortex shape which roll up more completely. However, these will disappear by the effect of wall.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2005년도 추계학술대회논문집
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• pp.324-329
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• 2005

This research investigates the electromechanical characteristics of a spindle motor in a free-falling mobile hard disk drive before unexpected shock. Electromechanical simulation includes a time-stepping finite element analysis of the magnetic field in a speed controlled brushless DC motor and dynamic analysis of the stationary and rotating part linked by fluid dynamic bearing under the free-failing condition. Analysis results show that the dynamic characteristics of the rotating spindle system during free-falling state have an effect on the relative motion between the stationary and rotating part of HDD. It results from the variation of reaction force in the bearing area due to the gravely force exerted on the rotating part of HDD, and the free-failing condition can be detected by observing the signal of the spindle motor and disk-head interface without using the accelerometer.

• International Journal of Naval Architecture and Ocean Engineering
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• 제13권1호
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• pp.1-11
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• 2021

Performance of a NACA 63₄-021 hydrofoil in motion under and in close proximity of a free surface for a large range of angles of attack is studied. Lift and drag coefficients of the hydrofoil at different submergence depths are investigated both numerically and experimentally, for 0° ≤ AoA ≤ 30° at a Reynolds number of 10⁵. The results of the numerical study are in good agreement with the experimental results. The agreement confirms the new finding that for a submerged hydrofoil operating at high angles of attack close to a free surface, the interaction between the hydrofoil-motion induced waves on the free surface and the hydrofoil results in mitigation of the flow separation characteristics on the suction side of the foil and delay in stall, and improvement in hydrofoil performance. In comparing with a baseline case, results suggest a 55% increase in maximum lift coefficient and 90% average improvement in performance for, based on the lift-to-drag ratio, but it is also observed significant decrease of lift-to-drag ratio at lower angles of attack. Flow details obtained from combined finite volume and volume of fluid numerical methods provide insight into the underlying enhancement mechanism, involving interaction between the hydrofoil and the free surface.

• International Journal of Fluid Machinery and Systems
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• 제2권3호
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• pp.197-205
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• 2009

Since large-scale commercial wind turbine generator systems such as MW-class wind turbines are becoming widely operated, the vibration and distortion of the blade are becoming larger and larger. Therefore the soft structure design instead of the solid-design is one of the important concepts to reduce the structural load and the cost of the wind turbine rotors. The objectives of the study are development of the fluid-structure coupled analysis code and evaluation of soft rotor-blade design to reduce the unsteady structural blade load. In this paper, fluid-structure coupled analysis for the HAWT rotor blade is performed by free wake panel method coupled with hinge-spring blade model for the flapwise blade motion. In the model, the continuous deflection of the rotor blade is represented by flapping angle of the hinge with one degree of freedom. The calculation results are evaluated by comparison with the database of the NREL unsteady aerodynamic experiment. In the analysis the unsteady flapwise moments in yawed inflow conditions are compared for the blades with different flapwise eigen frequencies.

• Structural Engineering and Mechanics
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• 제81권4호
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• pp.523-527
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• 2022

The objective of this study is to simulate the flow in pipes with various boundary conditions. Free-pressure fluid model, is used in the pipe based on Navier-Stokes equation. The models are solved by using the numerical method. A problem called "stability of pipes" is used in order to compare frequency and critical fluid velocity. When the initial conditions of problem satisfied the instability conditions, the free-pressure model could accurately predict discontinuities in the solution field. Employing nonlinear strains-displacements, stress-strain energy method the governing equations were derived using Hamilton's principal. Differential quadrature method (DQM) is used for obtaining the frequency and critical fluid velocity. The results of this paper are analyzed by hyperbolic numerical method. Results show that the level of numerical diffusion in the solution field and the range of well-posedness are two important criteria for selecting the two-fluid models. The solutions for predicting the flow variables is approximately equal to the two-pressure model 2. Therefore, the predicted pressure changes profile in the two-pressure model is more consistent with actual physics. Therefore, in numerical modeling of gas-liquid two-phase flows in the vertical pipe, the present model can be applied.

• 전산구조공학
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• 제10권4호
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• pp.291-302
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• 1997

이 논문은 압축성 유체로 채워진 원통형 탱크의 고유진동 특성을 파악하기 위한 해석적 방법을 제시하고 있다. 탱크의 동적거동은 유한 Fourier 급수전개 방법으로 전개하였으며, 압축성 유체는 선형 포텐셜 이론으로 전개하였다. 해석방법의 타당성을 검증하기 위하여 물로 채워진 양단고정의 경계조건을 갖는 원통형 탱크의 고유진동수를 해석적 방법으로 구한 다음, 상용 유한요소해석 프로그램인 ANSYS 5.2를 이용하여 검증하였다. 그 결과, 유한요소해석결과와 이론적인 방법으로 구한 이론해가 잘 일치하고 있음을 확인하였다. 또한 유체의 밀도와 압축성이 탱크의 고유진동수에 미치는 영향을 정규화된 무차원 고유진동수를 통해서 평가하였다. 유체의 밀도는 탱크의 모든 진동 모드의 고유진동수에 영향을 주지만, 유체 압축성의 영향은 저차 원주방향 모드의 진동수에서 더 크게 나타나고 있음을 확인할 수 있었다.

• Asian-Australasian Journal of Animal Sciences
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• 제31권8호
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• pp.1169-1175
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• 2018

Objective: The present study was conducted to investigate the impacts of active and passive immunization against synthetic inhibin and steroid-free bovine follicular fluid, respectively, on reproductive fecundity out of breeding season in Iraqi Awassi ewes. Methods: Follicular fluid was aspired from mature bovine follicles, treated with activated charcoal, and used for immunization of male rabbits for obtaining steroid free bovine follicular fluid (SFBFF) antiserum. Forty non-pregnant Awassi ewes were allocated into 4 groups (n = 10 each). At day 38 of experiment, ewes were treated with intra-vaginal MPA sponge (60 mg for 12 days). At days 0, 28, and 50, ewes were treated with 4, 2, and 2 mL of normal saline (control; C-ve), 400, 200, and $200{\mu}g$ of ovalbumin (C+ve), 400, 200 and $200{\mu}g$ of inhibin (SI group), respectively, and 4 mL of normal saline at day 0, and 4 and 2 mL of SFBFF antiserum at days 28 and 50, respectively, (AI group). After mating with Awassi rams, pregnancy and embryo number were diagnosed, at day 38 of pregnancy, using ultrasonography. Blood samples were collected at days 30, 60, 90, and 120 of pregnancy, for assessment of estradiol-$17{\beta}$ (E2) and progesterone (P4) levels. After parturition, numbers of delivered lambs were recorded. Results: The results revealed significant increase of P4 and significant decrease of E2 levels in SI and AI pregnant ewes than controls at days 30, 60, 90, and 120. Newborn number increased significantly in SI and AI treated than control ewes. Conclusion: Active or passive immunization against endogenous inhibin could augment reproductive fecundity out of breeding season in Iraqi Awassi ewes.