• Wind and Structures
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• v.8 no.6
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• pp.407-426
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• 2005

A hybrid RANS/LES approach, based on the Limited Numerical Scales concept, is applied to the numerical simulation of the flow around a square cylinder. The key feature of this approach is a blending between two eddy-viscosities, one given by the $k-{\varepsilon}$ RANS model and the other by the Smagorinsky LES closure. A mixed finite-element/finite-volume formulation is used for the numerical discretization on unstructured grids. The results obtained with the hybrid approach are compared with those given by RANS and LES simulations for three different grid resolutions; comparisons with experimental data and numerical results in the literature are also provided. It is shown that, if the grid resolution is adequate for LES, the hybrid model recovers the LES accuracy. For coarser grid resolutions, the blending criterion appears to be effective to improve the accuracy of the results with respect to both LES and RANS simulations.

• 한국연소학회:학술대회논문집
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• 2000.05a
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• pp.189-196
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• 2000

A numerical simulation was conducted to analyze the interaction of flame and vortices. The characteristic scales of flame and vortices were limited in the thin laminar flamelet regime. Within this regime, flame is assumed as discontinuity surface and its motion in flow field was described by G-equation instead of full governing equations. Additional approximations include distribution of line volume sources on flame surface to simulate effect of volume expansion. Contrast to previous calculations, current study employed vortex transport equation to evaluate attenuation and smearing of vortices. Two extreme conditions of frozen vortex and frozen flame were considered to validate the current method. Comparison with direct numerical simulation resulted in satisfactory quantitative agreement with higher computational efficiency which warrants the usefulness of the present model in more complex situation.

• Smart Structures and Systems
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• v.14 no.3
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• pp.285-305
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• 2014

This study employs a novel beam-type wavelet finite element model (WFEM) to fulfill an adaptive-scale damage detection strategy in which structural modeling scales are not only spatially varying but also dynamically changed according to actual needs. Dynamical equations of beam structures are derived in the context of WFEM by using the second-generation cubic Hermite multiwavelets as interpolation functions. Based on the concept of modal strain energy, damage in beam structures can be detected in a progressive manner: the suspected region is first identified using a low-scale structural model and the more accurate location and severity of the damage can be estimated using a multi-scale model with local refinement in the suspected region. Although this strategy can be implemented using traditional finite element methods, the multi-scale and localization properties of the WFEM considerably facilitate the adaptive change of modeling scales in a multi-stage process. The numerical examples in this study clearly demonstrate that the proposed damage detection strategy can progressively and efficiently locate and quantify damage with minimal computation effort and a limited number of sensors.

• Journal of the Korean Operations Research and Management Science Society
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• v.25 no.2
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• pp.67-76
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• 2000

We consider the determinant of the most economical target value through the sampling inspection by two consecutive machines. The machine sequence is fixed as products have to be processed by machine 1 first and then by machine 2 next, In this paper we assume that if quality of a unit is lower than inspection lower specification limited then the goods is not accepted, otherwise it is accepted. And we assume that the quality characteristics is larger-the-better characteristics and its distribution is the normal distribution whose standard deviation is known. This paper ends up with an numerical example by using the total expected profit function model that consider the scales profits inspection costs and material costs. And we analyze the variation of the total expected profit by changing coefficients of the functions.

• 한국전산유체공학회:학술대회논문집
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• 2009.04a
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• pp.19-19
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• 2009

Dynamic Stall is a flow phenomenon which occurs on the retreating side of helicopter rotor blades during forward flight. It also occurs on blades of stall regulated wind turbines under yawing conditions as well as during gust loads. Time scales occurring during this process are comparable on both helicopter and wind turbine blades. Dynamic Stall limits the speed of the helicopter and its manoeuvrability and limits the amount of power production of wind turbines. Extensive numerical as well as experimental investigations have been carried out recently to get detailed insight into the very complex flow structures of the Dynamic Stall process. Numerical codes have to be based on the full equations, i.e. the Navier-Stokes equations to cover the scope of the problems involved: Time dependent flow, unsteady flow separation, vortex development and shedding, compressibility effects, turbulence, transition and 3D-effects, etc. have to be taken into account. In addition to the numerical treatment of the Dynamic Stall problem suitable wind tunnel experiments are inevitable. Comparisons of experimental data with calculated results show us the state of the art and validity of the CFD-codes and the necessity to further improve calculation procedures. In the present paper the phenomenon of Dynamic Stall will be discussed first. This discussion is followed by comparisons of some recently obtained experimental and numerical results for an oscillating helicopter airfoil under Dynamic Stall conditions. From the knowledge base of the Dynamic Stall Problems, the next step can be envisaged: to control Dynamic Stall. The present discussion will address two different Dynamic Stall control methodologies: the Nose-Droop concept and the application of Leading Edge Vortex Generators (LEVoG's) as examples of active and passive control devices. It will be shown that experimental results are available but CFD-data are only of limited comparison. A lot of future work has to be done in CFD-code development to fill this gap. Here mainly 3D-effects as well as improvements of both turbulence and transition modelling are of major concern.

• The Bulletin of The Korean Astronomical Society
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• v.43 no.1
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• pp.62.1-62.1
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• 2018

Galaxies in the cluster environment interact with the intracluster medium (ICM), losing the interstellar medium (ISM) and alternating their evolution. Observational evidences of the extraplanar ISM stripped by the ICM's ram pressure are prevalent in HI imaging studies of cluster galaxies. However, current theoretical understanding of the ram pressure stripping (or ICM-ISM interaction in general) is still limited mainly due to the lack of numerical resolution at ISM scales in large-scale simulations. Especially, self-consistent modeling of the turbulent, multiphase ISM is critical to understand star formation in galaxies interacting with the ICM. To achieve this goal, we utilize the TIGRESS simulation suite, simulating a local patch of galactic disks with high resolution to resolve key physical processes in the ISM, including cooling/heating, self-gravity, MHD, star formation, and supernova feedback. We then expose the ISM disk to ICM flows and investigate the evolution of star formation rate and the properties of the ISM. By exploring ICM parameter space, we discuss an implication of the simple ram pressure stripping condition (so called the Gunn-Gott condition) to the realistic ISM.

• Advances in nano research
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• v.12 no.6
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• pp.567-581
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• 2022

The free and forced vibration in addition to electric energy harvesting of a piezoelectric disk resting on two-parameter foundation modeled by modified couple stress as well as Kirchhoff plate theory is probed. The governing equations and boundary conditions are obtained using Hamilton's principle. Then, the free and forced vibration are solved using numerical solutions, generalized differential quadrature method (GDQM) and Newmark-beta method. The forced vibration is resulted from a base excitation load. Also, the possible voltage which can be harvested from this system is obtained using generalized integral quadrature method. The validity of the formulation and solution procedure is confirmed using a compassion study. The impact of parameters such as length effect, inner to outer radius ratio, and foundations parameters on the free and forced vibration as well as energy harvesting is investigated in detail. This paper can be a basis for future studies in the area of piezoelectric harvesters in small scales.