• Journal of the Society of Naval Architects of Korea
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• v.49 no.2
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• pp.196-202
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• 2012

In this study, numerical analysis of viscous flows is carried out based on the unstructured grid. There exist some difficulties in expressing and computing numerical derivatives on the unstructured grid due to lack of the structured characteristics. The general computer algorithms are developed to perform numerical derivatives easily and extended to be applicable to various geometries composed of hybrid meshes. And the optimal method of strongly implicit procedure is newly contrived to accelerate the rate of convergence in solving the pressure Poisson equation. To verify numerical schemes, the driven cavity problems of 2 and 3 dimension are simulated. The numerical results are compared with others and our numerical schemes are shown to be valid.

• 한국전산유체공학회:학술대회논문집
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• 2005.04a
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• pp.153-158
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• 2005

Numerical simulations of two-dimensional steady incompressible lid-driven flow in a square cavity are presented to verify the validity of a new solution code(PowerCFD) with unstructured grids. The code uses the non-staggered(collocated) grid approach which is very popular for incompressible flow analysis because of its numerical efficiency on the curvilinear or unstructured grids. Solutions are obtained for configurations with a Reynolds number as high as 10,000 with both rectangular and hybrid types of unstructured grid mesh. Interesting features of the flow are presented in detail and comparisons are made with benchmark solutions found in the literature. It is found that the code is capable of producing accurately the nature of the lid-driven cavity flow at high Reynolds numbers.

• Journal of computational fluids engineering
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• v.11 no.1 s.32
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• pp.36-42
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• 2006

The existing numerical approximations of convection flux, especially the spatial higher-order difference schemes, in unstructured cell-centered finite volume methods are examined in detail with each other and evaluated with respect to the accuracy through their application to a 2-D benchmark problem. Six higher-order schemes are examined, which include two second-order upwind schemes, two central difference schemes and two hybrid schemes. It is found that the 2nd-order upwind scheme by Mathur and Murthy(1997) and the central difference scheme by Demirdzic and Muzaferija(1995) have more accurate prediction performance than the other higher-order schemes used in unstructured cell-centered finite volume methods.

• Transactions of the Korean Society of Mechanical Engineers
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• v.19 no.11
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• pp.3031-3040
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• 1995

Two-dimensional incompressible Navier-Stokes equations have been solved by the node-centered finite volume method with the unstructured triangular meshes. The pressure-velocity coupling is handled by the artificial compressibility algorithm due to its computational efficiency associated with the hyperbolic nature of the resulting equations. The convective fluxes are obtained by the Roe's flux difference splitting scheme using edge-based connectivities and higher-order differences are achieved by a reconstruction procedure. The time integration is based on an explicit four-stage Runge-Kutta scheme. Numerical procedures with local time stepping and implicit residual smoothing have been implemented to accelerate the convergence for the steady-state solutions. Comparisons with experimental data and other numerical results have proven accuracy and efficiency of the present unstructured approach.

• Journal of Korea Multimedia Society
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• v.21 no.2
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• pp.211-223
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• 2018

To understand the meaning of data is a common goal of research on unstructured data. Among these unstructured data, there are difficulties in analyzing the meaning of unstructured data related to corpus and sentences. In the existing researches, the researchers used LSA to select sentences with the most similar meaning to specific words of the sentences. However, it is problematic to examine many sentences continuously. In order to solve unstructured data classification problem, several search sites are available to classify the frequency of words and to serve to users. In this paper, we propose a method of classifying documents by using the frequency of similar words, and the frequency of non-relevant words to be applied as weights, and storing them in terms of a multi-pattern storage. We use Tensorflow's Softmax to the nearby sentences for machine learning, and utilize it for unstructured data analysis and the inference of traffic information.

• 한국전산유체공학회:학술대회논문집
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• 2011.05a
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• pp.483-487
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• 2011

In the present study, a CFD program based on a finite volume method was developed by using an unstructured polyhedral grid system for the accurate simulation with the complex geometry of computational domain. To simulate the transient flow induced by the moving solid object, the program used a fractional step method and a ALE (Algebric Lagrangian-Eulerian) method. The grid deformation for the moving of solid object were performed with a spring analogy based on the center coordinate of each computational grid. To verify the present program with these methodologies, the numerical results of the flow around the fixed and oscillating circular cylinder were compared with the previous numerical results.

• Journal of computational fluids engineering
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• v.12 no.4
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• pp.44-53
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• 2007

A three-dimensional (3D) unstructured hydrodynamic solver for transient two-phase flows has been developed for a 3D component of a nuclear system code and a component-scale analysis tool. A two-fluid three-field model is used for the two-phase flows. The three fields represent a continuous liquid, an entrained liquid, and a vapour field. An unstructured grid is adopted for realistic simulations of the flows in a complicated geometry. The semi-implicit ICE (Implicit Continuous-fluid Eulerian) numerical scheme has been applied to the unstructured non-staggered grid. This paper presents the numerical method and the preliminary results of the calculations. The results show that the modified numerical scheme is robust and predicts the phase change and the flow transitions due to boiling and flashing very well.

• Journal of Korean Academy of Nursing
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• v.7 no.1
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• pp.88-98
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• 1977

This study was designed to identify a more effective method of nursing interview in gathering informations by comparing the two, the structured and unstructured methods. May through October, 1976, 40patients on psychiatric wards of Korea University Hospital and National Mental Hospital, Seoul, were sampled and interviewed on their admission/within one week of admission. Both methods were used simultaneously by different interviewers ; 48 hour interval were kept between the two approaches of interview. Contents of informations gathered were grouped according to the criteria developed by the researcher, frequency, percentile score and the means were scored, and the two methods were compared; the amount of information gathered, number of questions used, time spent and the general response towards the methodologies. Results of the study are summarized as follows ; 1. 1. 5 times as many informations were gathered through the structured interview. (1366 ; 849) 2. 68.32% of informations gathered through the unstructured interview and 42.46% of the structured interview revealed to be overlapping; through structured interview, more unique informations (57.54%) were gathered. 3. The average of 33.25 minutes were consumed for the structured interview while 95, 50 minutes for the unstructured. Much higher time consumption is revealed in the unstructured. 4. Majority of patients showed positive response towards both approaches of interview (90% each), however, interviewers responded to experience of certain degree of tension (stress) in the unstructured method (35%) 5. The average of 0.88 question were used to gather one information in the structured while 1.87questions for the unstructctured were used. 6. The average of 0.97 minutes were consumed to gather one information in the structured while 4.50minutes for the unstructured. 7. The average of 1.11 minutes were consumed for one question for the structured while 2.41 minutes for the unstructured. The results of the study revealed that the structured interview were more effective in gathering informations; a larger quantity of informations were gathered in shorter time. Recommendations for further in investigations are as follows ; 1. Comparative analysis of informations gathered through the two methods by experienced professional nurse- interviewers is recommended. 2. Comparative analysis of the quality of informations is recommended. 3. Comparative analysis of the interviewing process (interactions) in relation to the characteristics of patients'health problems is recommended.

• The KSFM Journal of Fluid Machinery
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• v.8 no.3 s.30
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• pp.7-15
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• 2005

A Navier-Stokes code has been developed to simulate the flow through a cross flow fan. It is based on an unstructured finite volume method and uses moving grid technique to model the rotation of the fan. A low Reynolds number turbulence model is used to calculate eddy viscosity. The basic algorithm is SIMPLE. Numerical simulations over a wide range of flow rate aye carried out to validate the code. Comparison of all numerical solutions with experimental data confirms the validity of the present code. Present numerical solutions show a noticeable improvement over a previous numerical method which is based on a model of body force to simulate the rotation of the impeller.

• Journal of Institute of Control, Robotics and Systems
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• v.18 no.12
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• pp.1115-1121
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• 2012

This paper proposes a method to extract accurate plane of an object in unstructured environment for a humanoid robot by using a laser scanner. By panning and tilting 2D laser scanner installed on the head of a humanoid robot, 3D depth map of unstructured environment is generated. After generating the 3D depth map around a robot, the proposed plane extraction method is applied to the 3D depth map. By using the hierarchical clustering method, points on the same plane are extracted from the point cloud in the 3D depth map. After segmenting the plane from the point cloud, dimensions of the planes are calculated. The accuracy of the extracted plane is evaluated with experimental results, which show the effectiveness of the proposed method to extract planes around a humanoid robot in unstructured environment.