입자법을 이용한 멤브레인 타입 슬로싱 시뮬레이션

김경성 한국융합학회 2019 한국융합학회논문지 Vol.10 No.10

In the field of fluid dynamics, the sloshing effects are most common and significant problem. It is usually appeared in the tank filled with fluid which is on the main structure, thus, sloshing effects and its impact load may affect to entire system. For the sloshing effects analysis, impact loads due to tank motion is generally investigated theocratically, experimentally and numerically. The difficulty of sloshing phenomenon is non-linearity induced by large deformation at the free-surface. In this regard, it is well known issue that the repeatability on the sloshing problems is very low. In this study, moving particle semi-implicit method was employed to simulate sloshing problem and then the results were compared with corresponding experiments captured by high accuracy high speed camera. The results from numerical simulation was compared to experimental results. 슬로싱 현상은 현상의 특성인 격렬한 자유표면을 가지는 유동 문제뿐만 아니라, 슬로싱이 발생하는 유체 탱크가 부유체 혹은 어떠한 물체에 탑재되어 전체 시스템에 영향을 줄 수 있다는 것이 가장 큰 논의점이다. 이러한 이유로 일반적인 슬로싱에 대한 해석은 탱크의 움직임에 의한 내부 유동의 발생, 그리고 그로 인해 야기되는 충격하중의 해석이 주를 이룬다. 이러한 슬로싱 현상은 비선형성이 강하며 자유표면에서의 대-변형이 발생한다. 매우 높은 비선형성으로 인해 실험에서는 재현성이 낮고, 수치 시뮬레이션에서는 정확도가 낮다는 것이 지속적으로 문제시 되어 왔다. 본 연구에서는 높은 정확도를 가지는 카메라 비전 기술을 이용한 실험과 입자법을 이용한 시뮬레이션을 비교하였다. 탱크의 주요 제원을 통해 구해진 고유 주기와 그 주변 주기를 가지는 운동에서의 슬로싱 현상을 수치적으로 시뮬레이션 하였으며, 비교를 통해 탱크 내 슬로싱 하중을 분석하였다.

다모드 고유 진동수를 고려한 슬로싱 억제용 용기 속도의 설계

심태권(Taegwon Sim),김동주(Dongjoo Kim) 대한기계학회 2017 大韓機械學會論文集B Vol.41 No.5

액체가 부분적으로 채워져 있는 용기를 고속으로 이송시키면 슬로싱이 발생하므로 신속한 이송 및 조정 안정성을 위해 슬로싱을 억제할 필요가 있다. 본 연구에서는 사각용기를 수평방향으로 이송시킬 때 삼각형 속도 프로파일의 가속도 크기와 가감속 시간이 슬로싱에 미치는 영향을 수치해석적으로 연구하였다. 선행연구에서는 슬로싱의 1차 모드만을 고려하여 용기의 가감속 시간이 1차 고유 주기와 일치할 때 슬로싱이 상당히 억제됨을 보고한 바 있다. 반면 본 연구에서는 CFD 해석을 통해 슬로싱이 최소가 되는 가감속 시간을 찾고, 1차 모드 이외에 고차 모드를 함께 고려하여 이를 설명하였다. 또한, 질량과 스프링에 기반한 등가 모델을 이용한 해석을 수행하고 CFD 결과와 비교함으로써, 등가 모델의 정확성을 평가하였다. Suppression of sloshing is essential to achieve fast transportation and stable maneuvering of tanks partially filled with liquid. In this study, numerical simulations are performed to investigate the effects of the acceleration magnitude and the acceleration duration of triangular velocity profiles on sloshing when a rectangular tank moves horizontally. We previously reported, based on only the first natural mode, that sloshing is significantly suppressed when the acceleration duration equals the first natural period of sloshing. On the other hand, the present CFD simulations find the best acceleration duration for minimum sloshing and explains the results considering higher modes as well as the first mode. We also perform the analysis using an equivalent model based on masses and springs, and evaluate its accuracy by comparing it with the CFD simulation results.

액체 용기의 속도 프로파일이 슬로싱에 미치는 영향 해석

김동주(Dongjoo Kim) 대한기계학회 2016 大韓機械學會論文集B Vol.40 No.5

액체가 부분적으로 채워져 있는 용기에서 발생하는 슬로싱 현상을 이해하고 이를 효과적으로 제어하는 것은 매우 중요하다. 선행 연구들이 대부분 사인파형(sinusoidal) 가진에 의한 슬로싱 및 공진 현상에 관심을 가진 반면, 본 연구에서는 산업 현장에서 액체 용기를 빠르게 이송시킬 때 발생하는 슬로싱을 이해하고 억제하고자 하였다. 즉, 사각 용기를 수평방향으로 빠르게 이송시킬 때 발생하는 2상 유동을 수치해석으로 구한 후, 용기의 속도 프로파일(특히 가속 및 감속 시간)이 슬로싱에 미치는 영향을 분석하였다. 그 결과 용기의 가감속 시간이 1차 모드 고유주기의 정수배가 될 때 슬로싱이 상당히 억제되는 것을 관찰하였고, 이는 슬로싱 억제 방안으로 활용될 수 있을 것으로 기대된다. It is very important to understand and control the sloshing in a liquid container that is partially filled with liquid. Previous studies focused primarily on the sloshing and resonance caused by sinusoidal excitations, while the present study focuses on understanding and suppressing sloshing in a container that moves rapidly from a given point to another in industrial applications. To achieve this, we first numerically predict the two-phase flow induced by the horizontal movement of a rectangular container. Then we analyze the effects of container-velocity profile (in particular acceleration/deceleration duration) on sloshing. Results show that sloshing is significantly suppressed when the acceleration/deceleration duration is a multiple of the 1st-mode natural period of sloshing.

유체-구조 연성해석 기법을 이용한 LNG 화물창 강도평가

박준형(Jun-Hyeong Park),남재형(Jae-Hyung Nam),김성훈(Seong-Hoon Kim),오병택(Byung-Taek Oh),양영철(Young-Chul Yang),전인기(In-Ki Jun) 대한기계학회 2018 대한기계학회 논문집. Transactions of the KSME. C, 산업기술과 혁신 Vol.6 No.1

이 연구의 목적은 슬로싱 현상에 의한 CCS 강도평가를 위해 FSI 수치방법을 사용하여 계산된 슬로싱 압력의 유효성을 검증하는 것이다. FSI 슬로싱 해석을 위해, 상용소프트웨어인 STAR-CCM+과 ABAQUS를 사용하였으며, 1-way FSI와 2-way FSI 해석방법에 따른 슬로싱 압력을 비교하였다. 그 다음 슬로싱 압력에 의한 CCS 시스템의 구조안전성 결과를 평가하였다. The purpose of this study is to evaluate the validity of the sloshing pressure calculated by the FSI numerical method for the structurul strength assessment of CCS system on sloshing-phenomenon. For FSI sloshing analysis, we used both Star-CCM+ and Abqus in commercial software and compare sloshing pressure according to 1-way and 2-way FSI analysis methods. Then we evaluated the structural safety of CCS system by sloshing pressure.

사각탱크 내부에 슬로싱이 발생 시 생기는 공기 거동에 관한 수치해석적 연구

고종욱(Jong Wook Go),김태순(Tae Soon Kim),고성호(Sung Ho Ko) 대한기계학회 2014 대한기계학회 춘추학술대회 Vol.2014 No.11

Excitation forces induce fluid sloshing that finally leads to internal structural damage and fluid impact noise. Therefore, to minimizing sloshing effect, many researchers have been studying about it. However, most of researchers are not interested in air behavior on a free surface. If there are baffles which block the air in a tank, sloshing decrease but a tank is pressurized by air. The purpose of this paper is to examine air behavior over sloshing in a rectangular tank. We performed a numerical study using CFX, and k-ε model was used for it. To excite sloshing in the tank, we used a function about Asin(2πft) where A is amplitude, f is frequency and t is time. To verify the reliability of the results of analysis, the result is compared with the experimental results of the previous study. Also we analyzed air behavior and sloshing in a tank with baffles.

슬로싱의 영향이 포함된 사각형 부유체의 1자유도 및 2자유도 운동에 대한 실험적 연구

김윤호(YunHo Kim),성홍근(Hong G. Sung),조석규(SeokKyu Cho),정희운(HuiUn Jeong),최항순(Hang S. Choi) 한국해양환경·에너지학회 2012 한국해양환경·에너지학회 학술대회논문집 Vol.2012 No.5

This study is constructed to investigate the sloshing effect on the motions of a two-dimensional rectangular floater experimentally. There are two main categories. First, only roll motion is permitted and the other motions are firmly resticted. Secon,d sway and roll motions are are just allowed simultaneously with heave motion prevented. Sway motion is occurred along the flurre"s upper rail, while roll motion is performed at the center bearing of the model. Experiments are performed in the 2D flume at Seoul Nat"l University. The filling ratios are changed from empty to 50% and for the second experimental case, the ballast conditions are varied to quantify the rail friction effect. All tests are carried out under regular wave conditions. The motions measured by a non-contact camera, which can trace two different marks on the model accurately. The steady-state sway and roll motions are filtered out by post-processing. The spring system is installed to prevent the model drift off. For the first case, it is found that as the filling ratio is increased, the roll natural frequency becomes lower. And the sloshing effect is doserved at the vicinity of roll natural frequency and sloshing natural one, but the amount is not that much significant as the sway motion. For the second case, sway motion is dominant and roll motion is almost diminished except for cases near the sloshing natural frequency. Between 4.0~7.0rad/s, which is the interval between roll natural frequency and sloshing natural one, it is found that coupling of two motions leads the roll motion"s phese shift and finally internal fluid tank acts as ART(Anti-Rolling Tank) precisely.

해양플랜트에 병렬 계류된 LNG 운반선의 거동에 슬로싱이 미치는 영향

이승재(Seung Jae Lee) 한국해양공학회 2010 韓國海洋工學會誌 Vol.24 No.5

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 uxre calculated in the frequency domain using the 3D radiation/diffraction panel program based on potential theory. The calculated values wave 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 Jed 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 INGC 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.

판형 및 다공형 배플을 포함한 탱크 내 슬로싱에 대한 유동해석

이상혁(Sang Hyuk Lee),허남건(Nahmkeon Hur) 한국전산유체공학회 2009 한국전산유체공학회 학술대회논문집 Vol.2009 No.4

In the present study, a numerical analysis on the sloshing in a tank with the harmonic motion was investigated. A VOF method was used for two-phase flows inside the sloshing tank and a source term of the momentum equation was applied for the harmonic motion. This numerical method was verified by comparing its results with the available experimental data. The sloshing in a tank causes the instability of the fluid flows and the fluctuation of the impact pressure on the tank. By these phenomena of the tank sloshing, the sloshing problems such as the failure and the noise of system can be generated. For the reduction of these sloshing problems, the various baffles such as the horizontal/vertical plate baffles and the porous baffles inside the tank are installed. With the installations of these baffles, the characteristics of the liquid behavior in the sloshing tank, the impact pressure on the wall, the amplitude of the free surface near the wall and the sloshing noise were numerically analyzed.

슬로싱 유동에 대한 2유체 방법과 VOF 방법의 비교 연구

박수현(Soo-Hyeon Park),김병재(Byoung Jae Kim) 대한기계학회 2020 大韓機械學會論文集B Vol.44 No.12

슬로싱은 탱크 내부에 채워져 있는 유체가 회부의 가진에 의해 발생하는 유동현상이다. 슬로싱은 다양한 산업분야에서 발생하므로 많은 실험과 수치해석 연구가 수행되어 왔다. 기체-액체 2상유동은 1유체 방법 또는 2유체 방법으로 해석할 수 있다. 두 방법은 각각의 장단점이 있고 해석하고자 하는 유동의 특징에 따라 사용될 수 있다. 본 연구에서는 슬로싱에 대하여 두 방법의 성능을 비교한다. 1유체 방법으로는 VOF 방법을 채택하였다. 가진의 종류는 수평 선형요동과 수평축 회전요동을 선택하였다. 2유체 방법은 격자 크기와 시간 간격에 결과가 민감하게 반응하였다. 그러나 2유체 방법의 수렴된 결과는 VOF 방법의 수렴된 결과보다 좀 더 실험에 일치하는 결과를 보여주었다. Sloshing refers to the movement of liquid inside a tank that is in motion. A gas-liquid free surface in the sloshing flow can be predicted using either the one-fluid or two-fluid method. Both methods have their advantages and disadvantages. The present study presents comparisons of the accuracies of the two methods for prediction of sloshing flows. The VOF approach is used for the one-fluid method. Numerical simulations are performed for two types of oscillations: horizontal rectilinear and rotational oscillations. The two-fluid method shows apparent dependencies of time and grid size on the result. However, the converged result of the two-fluid method is slightly better than that of the VOF method.

액체로켓 연료 탱크 내부의 슬로싱이 연료 배출에 미치는 영향에 대한 수치적 분석

서권휘,김현지,김종암 한국전산유체공학회 2020 한국전산유체공학회지 Vol.25 No.2

The objective of this study is to investigate the effect of sloshing in the propellant tank on the discharge flow during re-ignition of the space vehicle. A parametric study was conducted considering phase interface, vapor ingestion phenomenon, and velocity/pressure fluctuations in the discharge pipe. The vapor ingestion, which can develop during the propellant discharge, occur easily with smaller thrust and lower boundary surface height. When dip occur at the face interface, sloshing had the effect of lowering the phase interface periodically, resulting in a shorter vapor ingestion time and less usable residual propellant. The velocity fluctuations in the discharge pipe cross section due to sloshing were expected to generate a pump head/torque performance and a lateral force on the pump shaft meaningfully. In addition, in the case of pressure fluctuations, sloshing did not directly affect pump performance because the scale of pressure fluctuations due to sloshing is small compared to the scale of one caused by pump operation.