• Transactions of the Korean Society of Mechanical Engineers B
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• v.21 no.7
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• pp.911-918
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• 1997

The turbulent viscous wake flows behind a single airfoil, two-dimensional stationary blade row and three-dimensional rotating blade row were calculated, and the numerical results were compared with experimental ones. The numerical technique was based on the SIMPLE algorithm using three turbulent closure models, standard k-.epsilon. model(WFM), low Reynolds number k-.epsilon. model(LRN) and Reynolds stress model (RSM). In the case of a single airfoil, WFM, LRN and RSM presented fairly good velocity distributions in the wake compared with experimental data. In the case of the stationary blade row, LRN and RSM presented better results than WFM for wake velocity distribution, and especially LRN showed best results among these three turbulent models. In the case of the rotating blade row, WFM and LRN showed fairly good agreement with experimental data of the three-dimensional velocity component distributions in the range from hub to mid span region. LRN was also superior to WFM in accuracy of prediction for the wake velocity distribution as same with the cases of a airfoil and the stationary blade row.

• 한국전산유체공학회:학술대회논문집
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• 2005.10a
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• pp.287-292
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• 2005

The flowfields generated by gaseous slot injection into a supersonic flow at a Mach number of 3.75 and a Reynolds number of $2.07{\times}10^7$ are simulated numerically. Fine-scale turbulence effects are represented by a two-equation(k-w SST model) closure model which includes $y^+$ effects on the turbulence model. Grid convergence index(GCI) is also considered to provide a measure of uncertainty of the grid convergence. Comparison is made with experimental data and other turbulence model in term of surface static pressure distributions, the length of the upstream separation region, and the penetration height. Results indicate that the k-w SST model correctly predicts mean surface pressure distribution and upstream separation length. However, it is also observed that the numerical simulation over predicts the pressure spike and penetration height compared with experimental data. All these results are taken within $1\%$ error band of grid convergence.

• Computers and Concrete
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• v.15 no.5
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• pp.735-758
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• 2015

This work deals with unilateral effect of quasi-brittle materials, such as concrete. For this propose, a two-dimensional meso-scale model is presented. The material is considered as a three-phase material consisting of interface zone, matrix and inclusions - each constituent modeled by an appropriate constitutive model. The Representative Volume Element (RVE) consists of inclusions idealized as circular shapes randomly placed into the specimen. The interface zone is modeled by means of cohesive contact finite elements developed here in order to capture the effects of phase debonding and interface crack closure/opening. As an initial approximation, the inclusion is modeled as linear elastic as well as the matrix. Our main goal here is to show a computational homogenization-based approach as an alternative to complex macroscopic constitutive models for the mechanical behavior of the quasi-brittle materials using a finite element procedure within a purely kinematical multi-scale framework. A set of numerical examples, involving the microcracking processes, is provided. It illustrates the performance of the proposed model. In summary, the proposed homogenization-based model is found to be a suitable tool for the identification of macroscopic mechanical behavior of quasi-brittle materials dealing with unilateral effect.

• Journal of computational fluids engineering
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• v.17 no.1
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• pp.94-100
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• 2012

In this paper, the cavitating flows around a hydrofoil have been numerically investigated by using a 2-d multi-phase RANS flow solver based on pseudo-compressibility and a homogeneous mixture model on unstructured meshes. For this purpose, a vertex-centered finite-volume method was utilized in conjunction with 2nd-order Roe's FDS to discretize the inviscid fluxes. The viscous fluxes were computed based on central differencing. The Spalart-Allmaras one equation model was employed for the closure of turbulence. A dual-time stepping method and the Gauss-Seidel iteration were used for unsteady time integration. The phase change rate between the liquid and vapor phases was determined by Merkle's cavitation model based on the difference between local and vapor pressure. Steady state calculations were made for the modified NACA66 hydrofoil at several flow conditions. Good agreements were obtained between the present results and the experiment for the pressure coefficient on a hydrofoil surface. Additional calculation was made for cloud cavitation around the hydrofoil. The observation of the vapor structure, such as cavity size and shape, was made, and the flow characteristics around the cavity were analyzed. Good agreements were obtained between the present results and the experiment for the frequency and the Strouhal number of cavity oscillation.

• International Journal of Concrete Structures and Materials
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• v.18 no.3E
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• pp.213-219
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• 2006

Modified singular fracture process zone(S-FPZ) model is proposed in this paper to determine a fracture criterion for continuous crack propagation in concrete. The investigated fracture properties of the proposed fracture model are strain energy release rate at a micro-crack tip and the relationship between crack closure stress(CCS) and crack opening displacement(COD) in the FPZ. The proposed model can simulate the actual fracture energy of experimental results fairly well. The results of the experimental data analysis show that specimen geometry and loading condition did not affect the CCS-COD relation. However, the strain energy release rate is a function of not only specimen geometry but also crack extension. The strain energy release rate remained constantly at the minimum value up to the crack extension of 25 mm, and then it increased linearly to the maximum value. The maximum fracture criterion occurred at the peak load for specimens of large size. The fracture criterion remained at the maximum value after the peak load. The variation of the fracture criterion is caused by micro-cracking and micro-crack localization. The fracture criterion of strain energy release rate can simply be the size effect of concrete fracture, and it can be used to quantify the micro-cracking and micro-crack localizing behavior of concrete.

• Journal of the Society of Naval Architects of Korea
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• v.48 no.2
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• pp.141-146
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• 2011

This study numerically carried out the propeller open water test(POW) by solving Navier-Stokes equations governing the three-dimensional unsteady incompressible viscous flow with the turbulence closure model of the ${\kappa}-{\omega}$ SST model. Numerical simulations are performed at various range of advance ratios. Corresponding to Reynolds numbers of $5.89{\times}105{\sim}6.47{\times}105$ based on free stream velocity and the chord length at 0.7 propeller radius. The present results give a good agreement with those of the experiment. The propeller induced vortical structures have been analyzed by visualizing the resultant vorticity. As the advance ratio increases, the magnitude and length of the resultant vorticity decrease significantly. As the main focus of present study, the numerical model to present the ($r-{\theta}$) plane-averaged resultant vorticity along the streamwise direction for various advance ratios has been suggested.

• Journal of Biomedical Engineering Research
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• v.17 no.1
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• pp.43-48
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• 1996

We investigated the energistics of the physiological heart model by comparing predictive indexes of the myocardial oxygen consumption (MOC), such as tension-time index (R), tension-time or force-time inteual (FTI), rate-pressure product (RPP), pressure-work index, and systolic pressure-volume area (PVA) when using the electro-hydraulic left ventricular device (LVAD). We developed the model of LVAD incorporated the closed-loop cardiovascular system with a baroreceptor which can control heart rate and time-varying elastance of left and right ventricles. On considering the benefit of the LVAD, the effects of various operation modes, especially timing of assistance, were evaluated using this coupled computer model. Overall results of the computer simulation shows that our LVAD can unload the ischemic (less contractile) heart by decreasing the MU and increasing coronary flow. Because the pump ejection at the end diastolic phase of the natural heart may increase the afterload of the left ventricle, the control scheme of our LVAD must prohibit ejecting at this time. Since the increment of coronary flow is proportional to the peak aortic pressure after ventricle contraction, the LVAD must eject immediately following the closure of the aortic valve to increase oxygen availability.

• Transactions of the Korean Society of Mechanical Engineers
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• v.13 no.5
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• pp.962-978
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• 1989

A new model of the combustion rates of soot particle in turbulent flames has been suggested. This model applies the combustion rate of soot particles in laminar flames and uses local time-averaged quantities in order to consider the effect of the chemical reaction on the soot combustion in turbulent flames. The proposed rate equation has been tested for two propane-air turbulent round-jet diffusion flames and gives better predictions for the soot concentration field of two flames than the model previously used, especially in low temperature regions. A modified Monte carlo Method for analyzing radiative heat transfer of a flame also has been suggested and tested, which reveals good results.

• Journal of The Geomorphological Association of Korea
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• v.24 no.2
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• pp.91-101
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• 2017

Quantitative forecasting methods based on spatial data and geographic information system have been used in predicting the landslide location. This study compared the simulated results of logistic, Bayesian, and maximum entropy models to understand the uncertainties of each model and identify the main factors that influence landslide. The study area is Boeun gun where 388 landslides occurred in the year of 1998. The verification results showed that the AUC of the three models was 0.84. However, the landslide susceptibility distribution of Maxent model was different from those of the other two models. With the same landslide occurrence data, the result of high susceptible area in Maxent model is smaller than Logistic or Bayesian. Maxent model, however, proved to be more efficient in predicting landslide than the other two models. In Maxent's simulations, the responsible factors for landslide susceptibility are timber age class, land cover, timber diameter, crown closure, and soil drainage. The results suggest that it is necessary to consider the possibility of overestimation when using Logistic or Bayesian model, and forest management around the study area can be an effective way to minimize landslide possibility.

• Journal of Radiation Industry
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• v.17 no.2
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• pp.209-217
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• 2023

The biosphere has important function in the safety assessment of a radioactive waste disposal facility. A biosphere model in the safety assessment needs various input data that contain significantly inherent uncertainties. This paper reviews the effects of the input data on the radiological impact assessment from main radionuclides such as ¹⁴C and ⁹⁹Tc in the biosphere model. In addition, it is confirmed that the safety criteria is met, when the conservative input data for the intake rate, soil to plant concentration ratio, and distribution coefficients of the radionuclides are applied and probabilistic analysis are conducted in the biosphere model. Nevertheless, it is required to generate site-specific input data for the confidence building and reduce excessive conservatism in the biosphere model.