• International Journal of Aeronautical and Space Sciences
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• v.10 no.2
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• pp.23-33
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• 2009

The inherent aeromechanical complexity of a rotor system necessitated the comprehensive analysis code for helicopter rotor system. In the present study, an aerodynamic analysis module has been developed as a part of rotorcraft comprehensive program. Aerodynamic analysis module is largely classified into airload calculation routine and inflow analysis routine. For airload calculation, quasi-steady analysis model is employed based on the blade element method with the correction of unsteady aerodynamic effects. In order to take unsteady effects - body motion effects and dynamic stall - into account, aerodynamic coefficients are corrected by considering Leishman-Beddoes's unsteady model. Various inflow models and vortex wake models are implemented in the aerodynamic module to consider wake induced inflow. Specifically, linear inflow, dynamic inflow, prescribed wake and free wake model are integrated into the present module. The aerodynamic characteristics of each method are compared and validated against available experimental data such as Elliot's induced inflow distribution and sectional normal force coefficients of AH-1G. In order to validate unsteady aerodynamic model, 2-D unsteady model for NACA0012 airfoil is validated against aerodynamic coefficients of McAlister's experimental data.

• Journal of the Korean Society of Combustion
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• v.5 no.2
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• pp.19-27
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• 2000

A turbulent combustion model, based on edge flame dynamics, is discussed in order to predict global extinction of turbulent flames. The model is applicable to the broken flamelet regime of turbulent combustion, in which global extinction of turbulent flame is achieved by gradual expansion of flame holes. The edge flame dynamics is the key mechanism to describe the flame hole expansion or contraction. For flames with Lewis numbers near unity, there is a $Damk{\ddot{o}}hler$ number, namely the crossover $Damk{\ddot{o}}hler$ number, at which edge flame changes its direction of propagation. The parametric region between the quasi-steady extinction condition and the edge-flame crossover condition is a metastable region, in that flames without edge can stay in their burning states while flames with edge have to retract to expand quenching holes. Using the above properties of edge flame, Hartley and Dold proposed a Lagrangian hole dynamics, which allows us to simulate transient variation of quenching holes. In their model, each stoichiometric surface is subjected to a random sequence of scalar dissipation rate compatible to the equilibrium turbulence. Then, each stoichiometric surface will evolve, according to the combustion map, dependent on the scalar dissipation rate and existence of flame edge, If all the burning surfaces are annihilated, the event can be declared as a global extinction. The consequence obtained from the above model also can be used as a subgrid model to determine local extinction occurring in a calculation grid.

• Wind and Structures
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• v.18 no.1
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• pp.1-20
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• 2014

Modern design of long suspension bridges must satisfy at the same time spanning very long distances and limiting their response against several external loads, even if of high intensity. Structural Control, with the solutions it provides, can offer a reliable contribution to limit internal forces and deformations in structural elements when extreme events occur. This positive aspect is very interesting when the dimensions of the structure are large. Herein, an updated numerical model of an existing suspension bridge is developed in a commercial finite element work frame, starting from original data. This model is used to reevaluate an optimization procedure for a passive control strategy, already proven effective with a simplified model of the buffeting wind forces. Such optimization procedure, previously implemented with a quasi-steady model of the buffeting excitation, is here reevaluated adopting a more refined version of the wind-structure interaction forces in which wind actions are applied on the towers and the cables considering drag forces only. For the deck a more refined formulation, based on the use of indicial functions, is adopted to reflect coupling with the bridge orientation and motion. It is shown that there is no variation of the previously identified optimal passive configuration.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.24 no.9
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• pp.1166-1174
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• 2000

This work presents a two-dimensional quasi-steady state model to study the fluid flow and heat transfer in high-power density welding process of thin AISI-304 stainless steel plates. The enthalpy method and the finite volume method were used for a numerical analysis of the mushy region phase change as well as the heat flow at the weld pool and the heat-affected zone. The results show that the mushy region distributed around the weld pool becomes wider downstream and the surface heat losses by convection and radiation can be significant factors in welding process especially when a welding speed is relatively low.

• 한국전산유체공학회:학술대회논문집
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• 2001.05a
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• pp.203-208
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• 2001

Any circumferential variations of the impeller exit flow conditions influences on the volute inlet flow conditions. All these interactions are strongly coupled phd affect consequently the performance of centrifugal pumps. In this paper, a commercial CFD code, which solves three-dimensional quasi-steady Wavier-Stokes equations with an impeller/volute interaction, is used for the prediction of a centrifugal pump performance. The simplified model of an impeller/volute interaction requires affordable computing time and provides relevant results. As a result, detailed flow structures such as pressure rise, recovery and loss mechanism on the centrifugal pumps are obtained. Especially, hydraulic performances are compared between the case of impeller only and the case of impeller with volute configuration. In addition, pump performance at off-design operation are observed and discussed.

• Journal of Korea Foundry Society
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• v.9 no.1
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• pp.39-48
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• 1989

A basic three dimensional thermal model has been developed to simulate the solidification sequence for gravity die casting process. The finite difference method was used to analyze the solidification process during all the casting cycles. The prediction of die temperature in the quasi-steady state was analyzed by the boundary element method. The influence of die cooling on the heat flow in the cast/mold system was also investigated. Predictions of the computer simulation on temperature profiles and location of shrinkage defects were in good agreement with those observed in experimental die castings. Models of computer simulation which is developed by this work can be useful for the design and process control of die casting.

• Journal of Mechanical Science and Technology
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• v.20 no.7
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• pp.929-940
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• 2006

Early detection and diagnosis of incipient induction machine faults increases machinery availability, reduces consequential damage, and improves operational efficiency. However, fault detection using analytical methods is not always possible because it requires perfect knowledge of a process model. This paper proposes a neural network based expert system for diagnosing problems with induction motors using vibration analysis. The short-time Fourier transform (STFT) is used to process the quasi-steady vibration signals, and the neural network is trained and tested using the vibration spectra. The efficiency of the developed neural network expert system is evaluated. The results show that a neural network expert system can be developed based on vibration measurements acquired on-line from the machine.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
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• 1998.03a
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• pp.154-160
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• 1998

This study describes a theoretical and experimental investigation of gas wave propagation in the pipe system. Most calculations of compressible flows in the pipe have been based on the method of characteristics. This technique has propensity to truncate waves and is difficult to apply to non-perfect gas. A method that describes the application of a two-step Lax-Wendroff acheme to solution of the unsteady one-dimentional flow in the pipe was developed. Theoretical calculations using both the method of characteristics and the two-step Lax-Wendroff method are presented including a realistic model for heat transfer and friction processes. In the present work, account is taken of the nonlinear behavior. For sections of parallel pipe, an one dimensional unsteady homentropic analysis is employed, and a numerical solution is obtained with the aid of a digital computer, using the method of characteristics and two-step Lax-Wendroff method. This analysis is then combined with boundary models, based on a quasi-steady flow approach, to give a complete treatment of the flow behavior in the pipe system.

• International Journal of Vascular Biomedical Engineering
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• v.4 no.2
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• pp.13-18
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• 2006

Direct injection of a fibrinolytic agent to the intra-arterial thrombosis may increase the effectiveness of thrombolysis by enhancing the permeation of thrombolytic agents into the blood clot. Permeation of fibrinolytic agents into a clot is influenced by the surface pressure, which is determined by the injection velocity of fibrinolytic agents. Computational fluid dynamic methods were used in order to predict clot lysis for different jet velocities and nozzle arrangements. Firstly, thrombolysis of a clot was mathematically modeled based on the pressure and lysis front velocity relationship. Direct injection of a thrombolytic agent increased the speed of thrombolysis significantly and the effectiveness was increased as the ejecting velocity increased. The nine nozzles model showed about 20% increase of the lysed volume, and the one and seventeen nozzles models did not show significant differences. Secondly, thrombolysis was modeled based on the enzyme transport and the fluid flow equations, and quasi steady numerical analysis was performed. Clot lysis efficiency was also increased as injection velocity increased.

• Proceedings of the Korea Water Resources Association Conference
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• 2011.05a
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• pp.36-36
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• 2011

일반적으로 저수지 퇴사는 연간 저수지의 유효용량의 0.5~1%을 감소시키고 홍수 시에는 홍수위를 상승시키는 등 저수지에 여러 가지 문제를 일으킨다. 따라서 댐 설계시 장기적으로 저수지 퇴사를 적절히 예측하고, 유지 관리 중에는 주기적인 퇴사 조사를 하여 퇴사의 진행 상황과 분포 등을 분석하여 필요시 댐 조작 방법의 개선이나 나아가 배사와 같은 적극적인 대책이 요구된다. 이에 본 연구는 저수지 배사작업의 지침을 제시하기 위하여 1차원 저수지 퇴 배사 모형을 제시하였다. 1차원 배사수치모의는 수위하강(drawdown)에 의한 배사를 고려하였으며, 준정류가정을 적용한 비연계 모형으로 구현하였다. 소류사량 산정을 위해서는 MPM 공식을 사용하였다. 모형의 적합성을 검증하기 위해 기존 선행 연구에서 수행한 수리실험의 제원 및 실험조건들을 적용하여 수치모의를 수행하였고, 수치모의 결과와 실험결과를 비교하였을 때, 본 연구에서 제시한 1차원 배사 수치모형의 적용성을 확인할 수 있었다.