배관 시스템의 실험-해석간 응답 비교에 관한 연구

라치웅(Chiwoong Ra),이은호(Eun-ho Lee),임진우(Jinwoo Im),박노철(No-cheol Park) 대한기계학회 2021 대한기계학회 춘추학술대회 Vol.2021 No.11

배관계 시간이력 다지점 가진 해석의 입력 방법에 관한 연구

라치웅(Chi Woong Ra),이은호(Eun-Ho Lee),이창균(Chang Kyun Lee),임진우(JinWoo Im),박노철(No-Cheol Park) 한국소음진동공학회 2021 한국소음진동공학회 논문집 Vol.31 No.5

The finite element analysis (FEA) of the nuclear power plant (NPP) system is generally excited by a single representative acceleration data as the supporting points have similar elevations. However, NPP pipes have multiple supporting points so that the multi-support excitation methodology which applies excitation on each support is generally considered to obtain the exact seismic responses. In this research, we study input methods for conducting multi-support excitations in FEA, and all the methods are constructed under time history analysis considered more precise than floor response spectrum analysis. Three types of input methods, namely large mass method, mode superposition transient, and displacement input transient analysis, were considered in this research. As a result, we conclude that all the methods generate similar motion parameters to the reference acceleration data on each supporting point. In addition, it is considered whether there is an appropriate input method to simulate another type of supports by changing the boundary condition on the support area.

인공지진파를 활용한 시간이력 입력 생성에 따른 기기 내진 응답에 관한 연구

라치웅(Chi Woong Ra),노현규(Hyungyu Roh),김정현(Jeonghyun Kim),박노철(No-cheol Park) 한국소음진동공학회 2024 한국소음진동공학회 논문집 Vol.34 No.2

In this study, our objective was to examine a time-history analysis method for simultaneously extracting the dynamic and static seismic responses of nuclear power plant (NPP) equipment. A finite element model of the reactor containment building (RCB) was constructed based on previous research to establish reference structural analysis responses. Additionally, we studied an alternative approach to the methodology presented in the previous regulatory guide, with a focus on time-historical input analysis. To generate a time-history seismic input, we specifically concentrated on creating time histories based on the spectrum-shaped inputs commonly used in the industry. To achieve this, we assessed the compliance of a self-developed MATLAB algorithm for artificial seismic wave generation with regulatory requirements. Subsequently, a seismic analysis was conducted in the time domain using uniform support motion and independent support motion. Furthermore, we proposed a method for generating inputs that reflected these features, and compared and evaluated it against other methods for generating structural analysis responses.

동특성 기반 유체-구조 연성의 부가 질량 효과 분석을 위한 변수 선정에 관한 연구

김정현,라치웅,노현규,박노철 한국소음진동공학회 2024 한국소음진동공학회 논문집 Vol.34 No.1

본 연구에서는 유체가 포함된 압력용기의 유체-구조 상호작용과 관련된 지배 방정식에 대해 파악하고, 유한요소해석을 통해 지정한 파라미터를 기반으로 동특성의 변화에 대한 경향성을 분석하고자 한다. 이를 위해 주파수 도메인에서의 활용도가 큰 Acoustic 요소를 통해 유체를 모델을 구축하였으며, 선정 파라미터를 기반으로 모드 분석을 통해 동특성 변화를 고찰하고자 한다. 이때 변수는 구조 대비 유체의 두께, 구조물의 밀도 및 강성을 변수를 선정하였다. 해당 변수는 동축 실린더의 형상 변화나 활용도가 높은 재료 물성을 상하한으로 선정하였다. 결론적으로 구조 대비 유체의 두께비가 작을수록 고유진동수 감소 효과가 두드러지며, 또한 압력용기의 영률 변화는 동특성 변화에 기여하지 않는 것으로 확인된다. In this research, we derive equations related to the fluid-structure interaction of pressure vessels containing fluids from previous research. Moreover, we analyze the changes in the dynamic characteristics based on parameters specified through the dimensions and material properties of the pressure vessel. A fluid is composed of acoustic elements that are adaptable in the frequency domain, and changes in the dynamic characteristics are examined through mode analysis based on the selected parameters. Specifically, the variables selected include the thickness of the fluid compared to the structure, the density, and the stiffness of the pressure vessel. These are selected as the upper and lower limits of the various arrangements of each cylinder and the variation of the material property’s value. In conclusion, the smaller the ratio of the thickness of the fluid to the structure, the more noticeable the natural frequency reduction effect (or added mass effect), and it is also confirmed that the change in Young's modulus of the pressure vessel does not contribute to the change in the dynamic characteristics in terms of reducing natural frequencies.

Sensitivity of SNF transport cask response to uncertainty in properties of wood inside the impact limiter under drop accident conditions

이은호,라치웅,노현규,이상정,박노철 한국원자력학회 2022 Nuclear Engineering and Technology Vol.54 No.10

It is essential to ensure the safety of spent nuclear fuel (SNF) transport cask in drop situation that is included in transport accident scenarios. The safety of the drop situation is affected by the impact absorption performance of impact limiters. Therefore, when designing an impact limiter, the uncertainty in the material properties that affect the impact absorption performance must be considered. In this study, the material properties of the wood inside the impact limiter were selected as the variables for a parametric study. The sensitivity analysis of the drop response of the SNF transport cask with impact limiter was performed. The minimum wood strength required to prevent a direct collision between the cask and floor was derived from the analysis results. In addition, the plastic strain response was analyzed and strain-based evaluation was performed. Based on this result, the critical values of wood properties that change the impact dynamic characteristics were investigated. Finally, the optimal material properties of wood were obtained to secure the structural safety of the SNF transport cask. The results of this study can contribute to the development of SNF transport cask, thereby ensuring safety in transport accident conditions

대형 레이더의 수송 진동 해석을 위한 주요 모드 결정 방법론

이은호,임선빈,라치웅,김흥태,이종학,강석원,박노철 한국소음진동공학회 2022 한국소음진동공학회 논문집 Vol.32 No.4

Securing the durability of transport vibration for large radars is essential. Transport vibration evaluation is performed via random vibration analysis. The response of random vibrations is determined by the covariance matrix, which is the correlation between the input power spectral density and dynamic characteristics of the radar. Therefore, in this study, the eigen-modes that have a dominant influence on the response are selected by normalizing the covariance matrix. Further, selective mode superposition ensures the accuracy of random vibration analysis. In addition, based on the analysis results, transport vibration durability evaluation for a large radar is performed.

건식저장용기의 연속 충돌 경사낙하 유한요소해석

임진우(Jinwoo Im),이은호(Eun-Ho Lee),라치웅(Chi Woong Ra),박노철(No-Cheol Park) 한국소음진동공학회 2022 한국소음진동공학회 논문집 Vol.32 No.1

As dry storage casks are used to store nuclear fuel, it is necessary to verify their stability against a drop accident that may occur during transport. In this study, a finite element analysis was conducted for the 9-m oblique drop prescribed by the International Atomic Energy Agency (IAEA). There are two types of oblique drops: corner drop and slap down drop. This research studied the bottom slab down drop, with the angle being changed at intervals of 5 degrees for an oblique angle ranging from 0 to 30 degrees. The bottom slap down drop confirmed that the impact response was highest during the second impact than during the first impact. The largest impact response occurred at an oblique angle of 15 degrees, confirmed using the secondary impact velocity and floor reaction force. We also verified the stress results of the internal structures—the canister and disc. The maximum stresses of the canister and disc occurred at 15 degrees and appeared in the region where additional collisions between internal structures occur, showing the same tendency as the secondary impact velocity and floor reaction force.

등가점성감쇠법을 이용한 배관곡관요소 비선형 거동의 감쇠효과 분석

이창균(ChangKyun Lee),이은호(EunHo Lee),임진우(JinWoo Im),라치웅(ChiWoong La),박노철(No-Cheol Park) 대한기계학회 2021 대한기계학회 춘추학술대회 Vol.2021 No.4

설계 초과지진하중에 대한 변형률 기반 평가방법 도입에 대한 연구가 활발하게 이루어지는 가운데, 비선형거동 확인을 위해서 유한요소 해석방법을 주로 이용하고 있다. 이에 따라 소성이 발생하였을 때의 감쇠효과에 대한 분석방법이 필요하게 되었다. 기존 탄성 영역에서 수행되던 유한요소해석에서는 영구변형에 따른 에너지 소산효과가 존재하지 않기 때문에 시스템 구조 자체에서 발생하는 감쇠효과를 보수적으로 고려하는 방법을 차용하였다. 하지만 변형이 발생하는 비선형해석에서는 시스템 구조 자체의 감쇠율 뿐 아니라 영구변형, 즉 소성변형에 따른 에너지 소산율도 고려되기 때문에 적절한 감쇠율 적용에 대한 고찰이 필요하다. 본 연구에서는 유한요소해석 모델에서 등가점성감쇠법을 이용하여 비선형거동을 하는 배관요소의 감쇠효과를 분석하고, 이를 활용한 유한요소해석에서의 적용 방안에 대해서 연구해보았다. 등가점성감쇠법이란, 선형 시스템에 감쇠율을 적용하여 비선형 응답을 예측하기 위해 적용되던 방식으로, 대표적으로 Jenning 의 연구를 통해 단자유도계 시스템의 비선형 거동을 예측하는 방법으로 3 가지 관점이 제시되었다.⁽¹⁾ 또한 등가점성감쇠법은 DDBD(Direct Displacement-Based Design) 방법을 활용하여 실제 구조물의 비선형응답을 예측하는 방법론으로 정리된 바 있다.⁽²⁾ 고찰을 위해 유한요소해석법을 이용하여 곡관 시스템의 탄소성해석의 결과를 바탕으로 Effective Stiffness 와 Effective Natural Frequency 를 계산하는 방법을 제시하고, 이를 활용하여 등가점성감쇠율을 계산하였다. 해당 방법을 곡관 요소의 파손실험결과에 활용하여 등가점성감쇠율을 활용한 곡관의 비선형 거동 예측 가능성을 확인할 수 있을 것으로 기대된다. In the process of studying on introduction of strain-based evaluation methods for BDBE(Beyond Design Basis Earthquake) Conditions are actively conducted, finite element analysis methods are commonly used to confirm. Accordingly, it is necessary to analyze damping effect. In the existing evaluation, since energy dissipation effect due to plastic deformation does not exist, a method of conservatively considering the damping effect occurring in the system structure itself was adopted. However, in nonlinear domain, in which deformation occurs, not only damping rate of the system structure itself, but also energy dissipation due to plastic deformation are considered, so it is necessary to consider appropriate damping. In this study, the damping effect of nonlinear curved pipe element using the equivalent viscous damping method was analyzed by finite element analysis and studied the application of this method. Equivalent viscosity damping method is applied to predict the nonlinear response by applying a damping factor to a linear system, and representatively, through Jenning's research, three viewpoints were presented as a method of predicting the nonlinear behavior of SDOF system.⁽¹⁾ In addition, the equivalent viscous damping method summarized as a methodology for predicting the nonlinear response of actual structure using Direct Displacement-Based Design (DDBD) method.⁽²⁾ For consideration, a method of calculating Effective Stiffness and Effective Natural Frequency based on the results of the elasto-plastic analysis of a curved pipe system using finite element analysis was presented, and the equivalent viscous damping ratio was calculated using this method. It is expected that the feasibility of predicting the nonlinear behavior of the curved pipe using the equivalent viscous damping method can be confirmed by the failure test results.