• Steel and Composite Structures
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• 제14권1호
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• pp.57-71
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• 2013

The prediction of the low cycle fatigue (LCF) life of beam-column connections requires an LCF model that is developed using specific geometric information. The beam-column connection has several geometric variables, and changes in these variables must be taken into account to ensure sufficient robustness of the design. Previous research has verified that the finite element model (FEM) can be used to simulate LCF behavior at the end plate moment connection (EPMC). Three critical parameters, i.e., end plate thickness, beam flange thickness, and bolt distance, have been selected for this study to determine the geometric effects on LCF behavior. Seven FEMs for different geometries have been developed using these three critical parameters. The finite element analysis results have led to the development of a modified LCF model for the critical parameter groups.

• 한국생산제조학회지
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• 제5권2호
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• pp.29-37
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• 1996

High speed engines with high power are increasingly on demands and almost engines employ crankshafts Such problems as bending and torsional vibrations become the point at issue in crankshaft analysis and design. In this study to overcome the diffiiculty with the large amount of computation in finite element vibration analysis of a crankshaft, a reduction method based on influence coefficient and lumped parameter is presented. which reduces the computation amount effectively and can be used in vibrational analysis and design of any types of crankshafts Crank journal and pinparts are meodelled as elements with 6degrees of freedom per node. Crank web part is modelled using equivalent mass and stiffness matices . based up on lumped parameter and influence coefficient respectively to reduce total degrees of freedom considerablely. To confirm the scheme of the study the results are compared with the known data and they are coincident. Also a simple crankshaft is designed and manufactured for experiments. The calculated results using reduction method and the experimental results agree well The scheme of this study can be utilized in evaluation results agree well. The calculated result are compared with the known data and they are coincident. Also a simple crankshaft is designed and manufactured for experiments. The calculated results using reduction method and the experimental results agree well. The scheme of this study can be utilized in evaluation and development of high speed engine.

• Geomechanics and Engineering
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• 제34권1호
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• pp.69-86
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• 2023

To overcome the dilemma of the [BQ] method's inability to predict mountain tunnel support loads, this study is based on the Hoek-Brown criterion and previous results to obtain the connection equations from GSI scores to each parameter of the Hoek-Brown criterion and the link between the [BQ] scores and the GSI system. The equations were embedded in the Hoek-Brown criterion of FLAC6.0 software to obtain tunnel construction forecasts without destroying the in-situ stratigraphy. The feasibility of the secondary development of the Hoek-Brown criterion was verified through comparative analysis with field engineering measurements. If GSI > 45 with a confining pressure of less than 10 MPa, GSI has little effect on the critical softening factor while we should pay attention to the parameter of confining pressure when GSI < 45. The design values for each parameter are closer to the FLAC3D simulation results and the secondary development of the Hoek-Brown criterion meets the design objectives. If the Class V surrounding rock is thinned with shotcrete or the secondary lining is installed earlier, the secondary lining may act as the main load-bearing structure. The study may provide ideas for rapid prediction of mountainous tunnels in China.

• 한국농공학회논문집
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• 제63권4호
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• pp.87-96
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• 2021

Determining design rainfall is the first step to plan an agricultural drainage facility. The objective of this study is to evaluate whether the current method for parameter estimation is reasonable for computing the design rainfall. The current Gumbel-Kendall (G-K) method was compared with two other methods which are Gumbel-Chow (G-C) method and Probability weighted moment (PWM). Hourly rainfall data were acquired from the 60 ASOS (Automated Synoptic Observing System) stations across the nation. For the goodness-of-fit test, this study used chi-squared (𝛘²) and Kolmogorov-Smirnov (K-S) test. When using G-K method, 𝛘² statistics of 18 stations exceeded the critical value (𝑥²_a=0.05,df=4=9.4877) and 10, 3 stations for G-C method, PWM method respectively. For K-S test, none of the stations exceeded the critical value (D^a=0.05_n=0.19838). However, G-K method showed the worst performances in both tests compared to other methods. Subsequently, this study computed design rainfall of 48-hour duration in 60 ASOS stations. G-K method showed 5.6 and 6.4% higher average design rainfall and 15.2 and 24.6% higher variance compared to G-C and PWM methods. In short, G-K showed the worst performance in goodness-of-fit tests and showed higher design rainfall with the least robustness. Likewise, considering the basic assumptions of the design rainfall estimation, G-K is not an appropriate method for the practical use. This study can be referenced and helpful when revising the agricultural drainage standards.

• 한국터널지하공간학회 논문집
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• 제6권2호
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• pp.129-139
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• 2004

터널의 환기설계에 관련하여 종류식과 횡류식의 환기용량의 산정을 위해서 필요한 제반 가정들을 검토하였고, 종류식 설계에서의 최종 값인 임계유속 산정을 위한 몇 가지의 공식을 분석하였다. 이를 토대로 특정 공식을 개선하기 위한 방안을 실험결과를 토대로 제시하였다. 횡류식 설계에서 국제적으로 사용되고 있는 용량산정에 관한 지침은 화재공학적 의미가 전혀 없으며 관행적으로 적용되어 온 것임을 알 수 있었다. 뿐만 아니라 기존의 횡류식 환기설계에는 설계개념조차 명확하지 않음을 입증하였다. 즉 횡류식 시스템에서는 종류식에서의 "연기의 역류 방지를 위한 최소 유속의 유지"라는 개념조차 없이 환기용량이 결정되어 왔으며, 이것은 터널의 화재환기가 오염물질의 환기로부터 시작되어 정확한 화재공학적 분석이 결여되었기 때문이다. 이러한 문제를 해결하기 위한 시도로 횡류식 환기의 설계개념으로서 연기전파거리와 연기축적을 제안하였다. 축소모델 터널을 이용하여 연기전파거리에 관한 실험결과를 제시하였고, 이를 이용하여 기존의 관행대로 설계된 유럽의 터널들에 적용하였을 때 안전성에 문제가 있음을 보였다.

• Nuclear Engineering and Technology
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• 제54권11호
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• pp.4181-4194
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• 2022

Main steam safety valves are commonly used in nuclear power plants to provide final protections from overpressure events. Blowdown and dynamic stability are two critical characteristics of safety valves. However, due to the parameter sensitivity and multi-parameter features of safety valves, using traditional method to design and/or optimize them is generally difficult and/or inefficient. To overcome these problems, a surrogate model-based valve design optimization is carried out in this study, of particular interest are methods of valve surrogate modeling, valve parameters global sensitivity analysis and valve performance optimization. To construct the surrogate model, Design of Experiments (DoE) and Computational Fluid Dynamics (CFD) simulations of the safety valve were performed successively, thereby an ensemble surrogate model (E-AHF) was built for valve blowdown and stability predictions. With the developed E-AHF model, global sensitivity analysis (GSA) on the valve parameters was performed, thereby five primary parameters that affect valve performance were identified. Finally, the k-sigma method is used to conduct the robust optimization on the valve. After optimization, the valve remains stable, the minimum blowdown of the safety valve is reduced greatly from 13.30% to 2.70%, and the corresponding variance is reduced from 1.04 to 0.65 as well, confirming the feasibility and effectiveness of the optimization method proposed in this paper.

• Structural Engineering and Mechanics
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• 제50권1호
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• pp.19-36
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• 2014

This paper focuses on a model order reduction (MOR) for large-scale rotordynamic systems by using finite element discretization. Typical rotor-bearing systems consist of a rotor, built-on parts, and a support system. These systems require careful consideration in their dynamic analysis modeling because they include unsymmetrical stiffness, localized nonproportional damping, and frequency-dependent gyroscopic effects. Because of this complex geometry, the finite element model under consideration may have a very large number of degrees of freedom. Thus, the repeated dynamic analyses used to investigate the critical speeds, stability, and unbalanced response are computationally very expensive to complete within a practical design cycle. In this study, we demonstrate that a Krylov subspace-based MOR via moment matching significantly speeds up the rotordynamic analyses needed to check the whirling frequencies and critical speeds of large rotor systems. This approach is very efficient, because it is possible to repeat the dynamic simulation with the help of a reduced system by changing the operating rotational speed, which can be preserved as a parameter in the process of model reduction. Two examples of rotordynamic systems show that the suggested MOR provides a significant reduction in computational cost for a Campbell diagram analysis, while maintaining accuracy comparable to that of the original systems.

• Structural Engineering and Mechanics
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• 제50권5호
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• pp.697-708
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• 2014

The intentional buckling design of micro-films has various potential applications in engineering. The buckling amplitude and critical strain of micro-films are the crucial parameters for the buckling design. In the reported studies, the film parameters were regarded as deterministic. However, the geometrical and physical parameters uncertainty of micro-films due to manufacturing becomes prominent and needs to be considered. In the present paper, the probabilistic nonlinear buckling analysis of micro-films with uncertain parameters is proposed for design accuracy and reliability. The nonlinear differential equation and its asymptotic solution for the buckling micro-film with nominal parameters are firstly established. The mean values, standard deviations and variation coefficients of the buckling amplitude and critical strain are calculated by using the probability densities of uncertain parameters such as the film span length, thickness, elastic modulus and compressive force, to reveal the effects of the film parameter uncertainty on the buckling deformation. The results obtained illustrate the probabilistic relation between buckling deformation and uncertain parameters, and are useful for accurate and reliable buckling design in terms of probability.

• 항공우주기술
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• 제6권1호
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• pp.201-208
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• 2007

75톤급 액체 로켓 엔진용 터보펌프의 연료펌프 및 터빈에 대한 회전체 동역학 설계가 이루어졌다. 후방 베어링으로부터 터빈까지의 거리를 베어링 하중 설계에 대한 설계 변수로 고려하였고, 터빈의 질량 및 전방 베어링과 후방 베어링의 강성을 변화시키면서 회전속도에 따른 비동기 고유진동수 해석을 수행하여 연료펌프/터빈의 임계속도를 고찰하였다. 터빈의 큰 관성으로 인하여 전방 베어링의 강성이 임계속도에 미치는 영향은 무시할만 한 것으로 나타났다. 후방 베어링의 강성이 $2{\times}10^{8}N/m$ 이상일 경우, 장축의 후방 베어링 간 축길이 및 20 kg이하의 터빈 질량에서 연료펌프/터빈 회전체의 임계속도는 설계속도 11,000 rpm 대비 70% 이상에 있음이 확인되었다.

• 한국산학기술학회논문지
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• 제18권10호
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• pp.81-87
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• 2017

본 연구는 고속열차 시운전 시험과 이에 따른 주행동특성 고찰 및 개선에 관한 것이다. 고속열차 시운전 시험을 통한 선행 연구에서 도출한 요댐퍼 설치 방법에 따른 후미 진동 개선 방안을 실제 고속철도 차량의 시운전시에 적용하여 후미 진동 저감 효과가 있음을 확인하였다. 또한 전체 차량에 대한 진동저감 방안을 동역학 해석 소프트웨어를 사용하여 수치 해석적 방법으로 도출하였으며, 그 효과를 시운전 시험을 통하여 확인하였다. 개선된 설계안은 실제 2층 고속열차 객차에 적용되어 주행동특성 문제없이 시운전을 진행하였다. 차세대 고속열차 임계속도에 영향을 미치는 현가장치 파라미터들에 대한 민감도 분석을 수행하였으며, 임계속도에 크게 영향을 미치는 4개의 설계변수를 도출하였는데, 이는 1차 탄성조인트 열차진행 방향 강성, 2차 요댐퍼 시리즈 강성, 2차 횡댐퍼 댐핑계수, 차간 댐퍼 댐핑계수 순이었다. 이 설계변수에 대한 최적화를 통하여 임계속도를 23.3% 향상시키는 현가장치 파라미터를 제시하였으며, 이는 차세대 고속열차 상용화 모델의 설계에 이용될 수 있다.