• International Journal of Aeronautical and Space Sciences
• /
• v.2 no.1
• /
• pp.28-43
• /
• 2001

Developed in these two series of paper is a complex dynamic model representing the motion of aircraft on the ground and a computer program for numerical simulation. The first part of paper presents the theoretical derivation of equations of motion of the landing gear system based on the physical principle. Developed model is 'structured' in the sense that the undercarriage system is regarded as an assembly of strut, tire, and wheel, where each component is modeled by a separate module. These modules are linked with two external modules-the aircraft and the runway characteristics-to carry out dynamic analysis and numerical simulation of the aircraft motion on the ground. Three sets of coordinate system associated with strut, wheel/tire and runway are defined, and external loads to each component and response characteristics are examined. Lagrangian formulation is used to derive the undercarriage equations of motion relative to the moving aircraft, and the resultant forces and moments from the undercarriage are transformed to aircraft body axes.

• International Journal of Fluid Machinery and Systems
• /
• v.8 no.4
• /
• pp.240-253
• /
• 2015

The objective of this paper is to evaluate the applicability of mass transfer cavitation models and determine appropriate numerical parameters for cavitating flow simulations. CFD simulations were performed for a NACA66 hydrofoil at cavitation numbers of 1.49 and 1.00, corresponding to steady sheet and unsteady sheet/cloud cavitating regimes using the Kubota and Merkle cavitation models. The Merkle model was implemented into CFX by User Fortran code. The Merkle cavitation model is found to give some improvements for cavitating flow simulation results for these cases. Turbulence modeling is also found to have an important contribution to the prediction quality of the simulations. The relationship between the turbulence viscosity modification, in order to take into account the local compressibility at the vapor/liquid interfaces, and the predicted numerical results is clarified. The limitations of current cavitating flow simulation techniques are discussed throughout the paper.

• Proceedings of the Korea Water Resources Association Conference
• /
• 2007.05a
• /
• pp.1287-1292
• /
• 2007

Recently, the frequency of unexpecting heavy rains has been increased due to abnormal climate and extreme rainfall. There was a limit to analyze 1D or 2D stream flow that was applied simple momentum equation and fixed energy conservation. Therefore, hydrodynamics flow analysis in rivers has been needed 3D numerical analysis for correct stream flow interpretation. In this study, CFD model on FLOW-3D was applied to stream flow analysis, which solves three dimenson RANS(Reynolds Averaged Navier-Stokes Equation) control equation to find out physical behavior and the effect of hydraulic structures. Numerical simulation accomplished those results was compared by using turbulence models such as ${\kappa}-{\varepsilon}$, RNG ${\kappa}-{\varepsilon}$ and LES. Those numerical analysis results have been illustrated by the turbulence energy effects, velocity of flow distributions, water level pressure distributions and eddy flows around the piers at Jangwall bridge in urbarn stream.

• Structural Engineering and Mechanics
• /
• v.15 no.4
• /
• pp.477-493
• /
• 2003

Masonry is not a simple material, the influence of mortar joints as a plane of weakness is a significant feature and this makes the numerical modelling of masonry very difficult especially when dynamic (seismic) analysis is involved. In order to develop a simple numerical model for masonry under earthquake load, an analytical model based on Distinct Element Method (DEM) is being developed. At the first stage, the model is applied to simulate the in-plane shear behaviour of an unreinforced masonry wall with and without opening where the testing results are available for comparison. In DEM, a solid is represented as an assembly of discrete blocks. Joints are modelled as interface between distinct bodies. It is a dynamic process and specially designed to model the behaviour of discontinuities. The numerical solutions obtained from the distinct element analysis are validated by comparing the results with those obtained from existing experiments and finite element modelling.

• Proceedings of the KSR Conference
• /
• 2009.05b
• /
• pp.491-495
• /
• 2009

This study aims to develope a numerical model of the huge obstacle defined in the Korean Rollingstock Safety Regulations. The shape and mechanical properties to be satisfied in the numerical model were based on the Regulations. Through a troublesome trial and error simulations, we developed the numerical model of the huge obstacle to satisfy physical properties of the specified guideline in the regulations. By applying the developed numerical obstacle, we carried out a crash simulation to evaluate vehicle crashworthiness.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.31 no.8
• /
• pp.653-662
• /
• 2007

Due to the difficulty raised from the coupling of cavitation modeling with turbulent flow, numerical simulation for two phase flow remains one of the challenging issues in the society. This research focuses on the development of numerical code to deal with incompressible two phase flow around 2D hydrofoil by combing the cavitation model suggested by Kunz et al. with $k-{\varepsilon}$ turbulent model. The simulation results are compared to experimental data to verify the validity of the developed code. Also, the comparison of the calculation results is made with LES results to evaluate the capability of $k-{\varepsilon}$ turbulence model. The calculation results show very good agreement with experimental observations even though this code can not grasp the small scaled bubbles in the calculation wheres LES can hold the real physics. This code will be extended to 3D compressible two phase flow for the study on the fluid dynamics in the inducers and impellers.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.32 no.7
• /
• pp.504-512
• /
• 2008

The characteristics of nonpremixed oxy-fuel flame in a multi-jet burner were experimentally and numerically investigated. The overall flow rate of fuel and oxygen was fixed, and the oxygen feeding ratio (OFR) was varied by 0.25, 0.5, and 0.75. The results of numerical simulation were compared with the measured results which are temperature profile and direct flame observation. The probability density function (PDF) model was applied accounting to the description between turbulence and chemistry, and standard ${\kappa}-{\varepsilon}$ model was used for turbulent flow field. Equilibrium assumption is very reasonable due to fast chemistry of the oxy-fuel combustion. Thus, the equilibrium calculation based on Gibbs free energy minimization was guaranteed to generate the solution of the oxy-fuel combustion. The result was obtained by numerical simulation. The predicted radial temperature profiles were in good agreement with the measured results. The flame length was shorten and was intensified with the decrease of OFR because the mixture of fuel and oxidizer are fast mixed and burnt. The maximum temperature became lower as the OFR increased, as a consequence of large flame surface area.

• 한국방재학회:학술대회논문집
• /
• 2011.02a
• /
• pp.198-198
• /
• 2011

The numerical simulation of dam break problem suffers from several challenges in terms of accuracy, stability, and versatility of the simulation algorithm since the water flow is generally discontinuous and presents abrupt variations. Thus, to obtain stable and accurate solutions, flow models for this purpose require numerical schemes provided with shock-capturing properties, and with the ability to work with flexible two-dimensional meshes. In this context, SU/PG method(Hughes and Brooks, 1979) is excellent candidate for the solution of the dam break problem. The weak formulation of the equations and the discontinuous polynomial basis lead to an accurate representation of bore waves(shocks). Furthermore, the discretization of the domain in finite elements is extremely effective in modeling complex geometries. In this study, a finite element model based on the SU/PG scheme is developed to solve shallow water equations and the model is applied to dam break problem. It is found that the present model accurately captures the bore wave that propagates downstream while spreading laterally and the depression wave that moves upstream. Furthermore, the propagation and formation of water surface profile compared favorably with those obtained by the previously published results.

• Journal of Mechanical Science and Technology
• /
• v.15 no.12
• /
• pp.1768-1774
• /
• 2001

Drifting Cups on a Meandering Stream (Kyokusui-no-En) is a Poetry Party that had its origin In ancient China, and was introduced to Japan passing through Korea. The flow of the meandering stream was made clear using the flow visualization techniques, surface floating method, PTV and the numerical simulation. At the same time, the motions of floating cup, the floating speed, relating speed and the trajectory of the cup were also analysed by using an originally developed image processing technique. Based on these researches, the model channel was considered. To make this party interesting the channel must has the characteristic that the drifting cups take the random pass and stagnant at the unexpected place. This model channel is satisfied with these conditions and the fluid mechanics consideration is performed on the both points of the experimental visualization and numerical simulation.

• Geomechanics and Engineering
• /
• v.30 no.3
• /
• pp.313-324
• /
• 2022

With the development of the economy, people's utilization of underground space are also improved, and a large number of cities have begun to build subways to relieve traffic pressure. The choice of subway station construction method is crucial. If an inappropriate construction method is selected, it will not only waste costs but also cause excessive deformation that may also threaten construction safety. In this paper, a subway station construction scheme selects model based on the AHP-fuzzy comprehensive evaluation. The rationality of the model is verified using numerical simulation and monitoring measurement data. Firstly, considering the economy and safety, a comprehensive evaluation system is established by selecting several indicators. Then, the analytic hierarchy process is used to determine the weight of the evaluation index, and the dimensionless membership in the fuzzy comprehensive evaluation method is used to evaluate the advantages and disadvantages of the construction method. Finally, the method is applied to Liaoyang east road station of Qingdao metro Line 2, and the results are verified by numerical simulation and monitoring measurement data. The results show that the model is scientific, practical and applicable.