• Structural Engineering and Mechanics
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• 제81권4호
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• pp.411-428
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• 2022

This paper presents the Campbell diagram analysis of the rotordynamic system using the full order model (FOM) and the reduced order model (ROM) techniques to determine the critical speeds, identify the stability and reduce the computational time. Due to the spin-speed-dependent matrices (e.g., centrifugal stiffening matrix), several model order reduction (MOR) techniques may be considered, such as the modal superposition (MS) method and the Krylov subspace-based MOR techniques (e.g., Ritz vector (RV), quasi-static Ritz vector (QSRV), multifrequency quasi-static Ritz vector (MQSRV), multifrequency/ multi-spin-speed quasi-static Ritz vector (MMQSRV) and the combined Ritz vector & modal superposition (RV+MS) methods). The proposed MMQSRV method in this study is extended from the MQSRV method by incorporating the rotational-speed-dependent stiffness matrices into the Krylov subspace during the MOR process. Thus, the objective of this note is to respond to the question of whether to use the MS method or the Krylov subspace-based MOR technique in establishing the Campbell diagram of the shaft-disc-blade assembly systems in three-dimensional (3D) finite element analysis (FEA). The Campbell diagrams produced by the FOM and various MOR methods are presented and discussed thoroughly by computing the norm of relative errors (ER). It is found that the RV and the MS methods are dominant at low and high rotating speeds, respectively. More precisely, as the spinning velocity becomes large, the calculated ER produced by the RV method is significantly increased; in contrast, the ER produced by the MS method is smaller and more consistent. From a computational point of view, the MORs have substantially reduced the time computing considerably compared to the FOM. Additionally, the verification of the 3D FE rotordynamic model is also provided and found to be in close agreement with the existing solutions.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2002년도 추계 학술대회논문집
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• pp.150-155
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• 2002

A commercial CFD code is applied to analyze the 3-D viscous flow field within vertical multi-stage centrifugal pump including impeller with 6 blades and guide vane with 11 blades and is performed by changing flow rate from 10 to $26m^3/h$ at the constant 3500rpm. The purpose of this 3-D numerical simulation is not only to confirm how much the effect of three kinds of blade inlet breadth (11mm, 11.5mm, 12mm) of impeller has influence on the performance of vertical multi-stage pump but also to make clear the cause about performance difference at the exit side of impeller and guide vane. The vertical multi-stage pump consisit of the impeller, guide, vane and cylinder. The grid of numerical analysis used to the vertical multi-stage pump is 18,000, 45,000, and 100000 cells in case of the impeller, guide vane, cylinder and total grid is 730,000 cells. The characteristics such as total pressure coefficient, total head, shaft horse power, power efficiency at the exit side of impeller and guide vane, discharge coefficient are represented according to flow rage changing.

• 한국수소및신에너지학회논문집
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• 제34권6호
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• pp.758-766
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• 2023

Multi-copter of unmanned aerial vehicle (UAV) was initially developed as strategic technology in the only military field, but it is developing into an industrial field with a wide range of applications in the civil sector based on the development and convergence of aviation technology and information and communication technology. Currently, the degree of utilization of multi-copter is increasing in various industries for the purpose of performing classic tactical missions, logistics transportation, farm management, internet supply, video filming, weather management, life-saving, etc, and active technology development responding to market demand. Existing commercial multi-copter mainly use an electric energy propulsion system consisting of an electric battery and a brushless direct current (BLDC) motor. It is the limitations for usage in the flying time (up to 20 minutes) and payload (less than 20 kg). this study aims to overcome these limitations and expand the commercialization of engine-powered multi-copter of UAV in various industries in the futures.

• 한국식품과학회지
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• 제31권1호
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• pp.138-146
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• 1999

한국산 밀 우리, 은파, 올그루, 그루, 탑동 5 품종과 호주산 연질 밀(ASW), 미국산 연질 밀(WW)과 경질 밀(DNS)로 국수를 제조한 후 조리특성, 기계적 및 관능적 조직감 특성을 비교 검토하였으며 밀가루의 이화학적 성질과의 연관성을 살펴보았다. 국수의 조리 손실율은 밀가루의 단백질 함량이 높을수록 낮고, 수분흡수율은 손상전분의 함량이 높을수록 컸다. 측정 방법을 달리한 기계적 특성에서는 견고성, 씹음성, 인장력 등이 경질 밀인 탑동밀과 DNS가 연질 밀보다는 높은 값을 보이고, 외국산 연질 밀인 ASW, WW가 한국산 밀들보다 낮은 값을 나타냈다. 관능적 특성과 기계적 특성과의 상관관계를 맺어본 결과 multi-blade compression shear test가 10% 압착시험이나 반복 압착시험 및 인장력 시험보다도 더 나은 관계를 보였으며, 표면굳기는 multi-blade compression shear test의 면적과 가장 나은 상관관계를 보였고(r=0.76) 내부굳기와 씹음성은 기울기와 잘 연관되었다. 국수의 관능적 특성과 밀가루의 물리화학적 특성과의 상관관계에서는 단백질의 함량이 국수의 조직감에 가장 큰 영향을 미쳤다. 아밀로즈의 함량은 국수의 유연성 및 미끄럼성과 양의 관계를, 표면굳기, 내부굳기, 씹음성과는 음의 관계를 보였다. 삶은 국수의 색도는 외국산 밀(WW, ASW)에 비해 한국산 밀의 국수가 더욱 더 어두운 색을 띄었다. 기호도 검사 결과, 한국산 연질밀인 그루밀이 수입밀인 WW 및 ASW보다 더 선호하는 것으로 나타났다.

• 한국공작기계학회:학술대회논문집
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• 한국공작기계학회 1998년도 추계학술대회 논문집
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• pp.158-163
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• 1998

In this paper, the cutting characteristics and cutting mechanism of polystyrene foam was experimentally investigated. It was found that polystyrene foam has different cutting characteristics and cutting mechanism comparing with that of normal metal materials. By using the experimental results, the optimal cutting tool was designed and examined for approving the cuttingability of polystyrene foam.

• 한국자동차공학회논문집
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• 제16권2호
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• pp.58-65
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• 2008

The finite element programs have been developed for structure, collision, flow, dynamics, heat transfer, acoustics, electromagnetism, MEMS (Micro Electro Mechanical Systems), and etc. These programs can be classified as either "package" program or "single purpose" program. Single purpose programs usually have convenient and powerful functions, but these programs have limited expandability to different fields of analysis. Therefore, the method to converter the analysis results of single purpose program to other programs is needed. In the research, multi-body data conversion methods of 1) finite element model and 2) solid model were created to convert fluid analysis result of CFD-ACE+ to ANSYS data structure. Automatic boundary condition algorithms were developed for blade, and finite element model was compared with solid model. It is expected that, by sealess data transfer, the Multi-body Data Conversion Program could reduce the development period of torque converters.

• 한국소음진동공학회논문집
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• 제24권5호
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• pp.363-373
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• 2014

In this study, computational multi-body dynamic analyses for the drivetrain system of a 5 MW class offshore wind turbine have been conducted using efficient equivalent modeling technique based on the design guideline of GL 2010. The present drivetrain system is originally modeled and its related system data is adopted from the NREL 5 MW wind turbine model. Efficient computational method for the drivetrain system dynamics is proposed based on an international guideline for the certification of wind turbine. Structural dynamic behaviors of drivetrain system with blade, hub, shaft, gearbox, supports, brake disk, coupling, and electric generator have been analyzed and the results for natural frequency and equivalent torsional stiffness of the drivetrain system are presented in detail. It is finally shown that the present multi-body dynamic analysis method gives good agreement with the previous results of the 5 MW class wind turbine system.

• 유체기계공업학회:학술대회논문집
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• 유체기계공업학회 2002년도 유체기계 연구개발 발표회 논문집
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• pp.111-115
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• 2002

The objective of this work is to develop improved slip factor model and correction method to predict flow through impeller in forward-curved centrifugal fan by investigating the validity of various slip factor models. Both steady and unsteady three-dimensional CFD analyses were performed with a commercial code tn validate the slip factor model and the correction method. The results show that the improved slip factor model presented in this paper could provide more accurate predictions for forward-curved centrifugal impeller than the other slip factor models since the presented model takes into account the effect of blade curvature. The comparison with CFD results also shows that the improved slip factor model coupled with the present correction method provides accurate predictions for mass-averaged absolute circumferential velocity at the exit of impeller near and above the flow rate of peaktotal pressure coefficient.

• International Journal of Fluid Machinery and Systems
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• 제8권3호
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• pp.209-219
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• 2015

A robust multi-fidelity optimization methodology has been developed, focusing on efficiently handling industrial runner design of hydraulic Francis turbines. The computational task is split between low- and high-fidelity phases in order to properly balance the CFD cost and required accuracy in different design stages. In the low-fidelity phase, a physics-based surrogate optimization loop manages a large number of iterative optimization evaluations. Two derivative-free optimization methods use an inviscid flow solver as a physics-based surrogate to obtain the main characteristics of a good design in a relatively fast iterative process. The case study of a runner design for a low-head Francis turbine indicates advantages of integrating two derivative-free optimization algorithms with different local- and global search capabilities.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2007년도 추계학술대회논문집
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• pp.875-879
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• 2007

The effects of the statistical properties of the Coulomb friction coefficients on the dynamic responses of a galloping quadruped robot are investigated in this paper. In general, the Coulomb friction coefficients are assumed to be deterministic for a controller design to achieve required motion characteristics. However, the friction coefficients between the ground and the robot legs are not constant in reality. Therefore, statistical characteristics of the friction coefficients need to be considered for a multi-body modeling of the robot galloping on the ground. The effects of the statistical properties on the dynamic responses of the quadruped robots are investigated.