• 한국음향학회지
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• 제42권3호
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• pp.250-261
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• 2023

본 연구에서는 펌프젯 추진기를 대상으로 공동, 비공동 조건에서의 유동 소음원을 규명하기 위하여 추진기의 각 구성품인 덕트와 스테이터, 로터에 의한 소음 기여도를 평가하였으며, 공동과 비공동 조건에서의 소음 수준을 비교하였다. 대형 캐비테이션 터널 내 Suboff 잠수함 선형과 펌프젯 추진기를 대상으로 균일혼상류 가정의 비정상 비압축성 Reynolds averaged Navier-Stokes(RANS) 방정식을 적용하였으며, 이상 유동을 모사하기 위해 Volume of Fluid(VOF) 기법과 Schnerr-Sauer 공동 모델을 적용하였다. 유동해석 결과를 기반으로 수중방사소음을 예측하기 위해 Ffowcs Williams and Hawkings(FW-H) 방정식 기반의 음향상사법을 적용하였으며, 덕트와 스테이터, 로터로 구성된 3개의 비투과성 적분면과 추진기를 감싸는 형태의 2가지 투과성 적분면을 선정하여 소음 기여도를 평가하였다. 소음 예측결과로부터 스테이터는 전체 소음에 대한 직접적인 기여도는 낮으나 덕트와 로터에서의 유동 박리에 의한 소음원 형성에는 영향을 미치는 것을 확인하였으며, 유동이 박리되는 연직상방과 우측방향으로 소음이 크게 방사되었다. 또한 로터에서는 날개의 흡입면과 압력면 간의 압력 섭동에 의해 추진방향으로 소음이 크게 방사되었으며, 투과성적분면을 통해 체적 소음원인 공동의 효과를 반영할 수 있음을 확인하였다.

• Wind and Structures
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• 제18권2호
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• pp.155-180
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• 2014

The safety of road vehicles on the ground in crosswind has been investigated for many years. One of the most important fundamentals in the safety analysis is aerodynamic characteristics of a vehicle in crosswind. The most common way to study the aerodynamic characteristics of a vehicle in crosswind is wind tunnel tests to measure the aerodynamic coefficients and/or pressure coefficients of the vehicle. Due to the complexity of wind tunnel test equipment and procedure, the features of flow field around the vehicle are seldom explored in a wind tunnel, particularly for the vehicle moving on the ground. As a complementary to wind tunnel tests, the numerical method using computational fluid dynamics (CFD) can be employed as an effective tool to explore the aerodynamic characteristics of as well as flow features around the vehicle. This study explores crosswind effects on a high-sided lorry on the ground with and without movement through CFD simulations together with wind tunnel tests. Firstly, the aerodynamic forces on a stationary lorry model are measured in a wind tunnel, and the results are compared with the previous measurement results. The CFD with unsteady RANS method is then employed to simulate wind flow around and wind pressures on the stationary lorry. The numerical aerodynamic forces are compared with the wind tunnel test results. Furthermore, the same CFD method is extended to investigate the moving vehicle on the ground in crosswind. The results show that the CFD results match with wind tunnel test results and the current way using aerodynamic coefficients from a stationary vehicle in crosswind is acceptable. The CFD simulation can provide more insights on flow field and pressure distribution which are difficult to be obtained by wind tunnel tests.

• 대한기계학회논문집B
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• 제41권6호
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• pp.373-380
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• 2017

본 연구에서는 레이놀즈 평균 나비어-스톡스(Reynolds-averaged Navier-Stokes, RANS) 방정식을 적용하여 스러스터(thruster) 상호작용에 대한 점성 유동 CFD 해석을 수행하였다. 수치해석은 상용 프로그램인 STAR-CCM+를 이용하였으며, 프로펠러와 No.19a 덕트로 스러스터 모델을 구성하였다. 프로펠러의 회전에 의한 동적인 움직임의 해석을 위해 슬라이딩 격자(sliding mesh)기법을 사용하였으며, 격자구성은 다중영역으로 구분하여 육면체 격자(hexahedral element)로 구성하였고, 계산 시간의 경제성을 고려하여 비등각(non-conformal) 격자를 이용하였다. 스러스터 배치를 그대로 유지한 상태에서 상류방향 스러스터의 방위각(azimuth angle)과 축 기울기에 따라 스러스터 상호작용이 크게 변화하였다. 이러한 결과를 통해 축 기울기와 방위각이 추진성능에 중요한 영향을 미치는 것을 확인하였다.

• International Journal of Naval Architecture and Ocean Engineering
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• 제11권2호
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• pp.875-882
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• 2019

The effects of Triangle Groove Strips (TGS) on Vortex-induced Vibration (VIV) suppression of marine riser are numerically investigated using Computational Fluid Dynamics (CFD) method. The range of Reynolds number in simulations is 4.0 × 10⁴ < Re < 1.2 × 10⁵. The two-dimensional unsteady Reynolds-Averaged Navier-Stokes (RANS) equations and Shear Stress Transport (SST) k-ω turbulence model are used to calculate the flow around marine riser. The Newmark-β method is employed for evaluating the structure dynamics of marine riser. The effect of the height ratio (ε) of TGS on VIV suppression is evaluated. The amplitude responses, frequency responses, vortex patterns and the flow around the structures are discussed in detail. With the increase of the height ratio of TGS, the suppression effect of TGS on VIV suppression is improved firstly and then weakened. When ε=0.04, the suppression effect of TGS is the best. Compared with the VIV responses of smooth marine riser, the amplitude ratio is reduced by 38.9%, the peak of the lift coefficient is reduced by 69% and the peak of the drag coefficient is reduced by 40% when Re=6.0 × 10⁴. With the increase of Reynolds number, the suppression effect of TGS on VIV suppression is improved firstly and then weakened. When the Reynolds number is 7.0 × 10⁴, the amplitude ratio can be reduced by 40.1%. As to the large-amplitude vibration cases, the TGS show nice suppression effect on VIV.

• 대한조선학회논문집
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• 제48권2호
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• pp.147-157
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• 2011

A RANS(Reynolds averaged Navier-Stokes) based numerical method is developed for the evaluation of ship resistance and self-propulsion performances. In the usability aspect of CFD for the hull form design, the field grid around practical hull forms is generated by solving a grid Poisson equation based on the hull surface grid generated from station offsets and centerline profile. A body force technique is introduced to model the effects of the propeller in which the propeller loads are obtained from potential flow analysis using an unsteady lifting surface method. The free surface is captured by using a two-phase level-set method and the realizable $k-{\varepsilon}$ model is used for turbulence closure. The hull attitude in vertical plane, i.e., trim and sinkage, is calculated by using a quasi-steady method and then considered in the computation by translating and rotating the grid system according to the values. For the validation of the proposed method, the numerical results of resistance tests for KCS, KLNG, and KVLCC1 and of self-propulsion test for KCS are compared with experimental data.

• 한국군사과학기술학회지
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• 제22권4호
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• pp.517-526
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• 2019

In the present study, unsteady flows around a projectile ejected from an aircraft platform have been numerically investigated by using a three dimensional compressible RANS flow solver based 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. Initial behavior of the projectile for varying conditions, such as roll and pitch-yaw command on the control surface of the projectile, flight Mach number, and platform pitch angle, was investigated. The ejection stability of the projectile was degraded as Mach number increases. In the transonic condition, the initial behavior of the projectile was found to be unstable as increase of platform pitch angle. By applying the command to control surfaces of the projectile, initial stability was highly enhanced. It was concluded that the proposed simulation data are useful for estimating the ejection behavior of a projectile in design phase.