• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.49 no.8
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• pp.609-615
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• 2021

Three-dimensional numerical study was carried out to evaluate the aerodynamic characteristics of the supersonic grid fins installed on SpaceX Falcon 9. The present three-dimensional flow results were compared to the results by the concept of the unit grid fin previously introduced for more efficient and simpler flow calculations, and the validity of the approach of the unit grid fin were evaluated. The aerodynamic characteristics in supersonic flights Mach 2.8 of SpaceX Falcon 9 with various angle of attacks were also obtained.

• Journal of Korean Society for Geospatial Information Science
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• v.18 no.2
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• pp.3-12
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• 2010

In previous studies, the digital measurement systems and analysis algorithms were developed by using the related techniques, such as the aerial photograph detection and high resolution satellite image process. However, these studies were limited in 2-dimensional geo-processing. Therefore, it is necessary to apply the 3-dimensional spatial information and coordinate system for higher accuracy in recognizing and locating of geo-features. The objective of this study was to develop a stochastic algorithm for the optimal sensor placement using the 3-dimensional spatial analysis method. The 3-dimensional information of the LiDAR was applied in the sensor field algorithm based on 2- and/or 3-dimensional gridded points. This study was conducted with three case studies using the optimal sensor placement algorithms; the first case was based on 2-dimensional space without obstacles(2D-non obstacles), the second case was based on 2-dimensional space with obstacles(2D-obstacles), and lastly, the third case was based on 3-dimensional space with obstacles(3D-obstacles). Finally, this study suggested the methodology for the optimal sensor placement - especially, for ground-settled sensors - using the LiDAR data, and it showed the possibility of algorithm application in the information collection using sensors.

• Journal of the Korean Society for Precision Engineering
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• v.16 no.11
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• pp.197-203
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• 1999

Increasing demands on precision machining have necessitated the tool to move not only position error as small as possible, but also with smoothly varying feedrates. Because of the lack of accurate and efficient algorithms for generation of 3-dimensional lines and circles, a full accomlishment for available machine tool resolution is generally unavailable. In this paper, a reference-pulse type 3-axis PC_NC milling system is developed for the precision machining of complex shapes in 3-dimensional space. Three AC servomotors are used as the actuator instead of the hand wheel to operate a 3-axis milling machine under the same mechanical structure. A PC is used to handle the control signal calculation for various types of motion command. To achieve the synchronous 3-axis motion, a real-time reference-pulse 3-dimensional linear and circular interpolator based on the intersection criteria is developed in software. The performance test via computer simulation and actual machining have shown that the PC-NC milling system is useful for the machining of arbitrary lines and circles in 3-dimensional space.

• Communications of the Korean Mathematical Society
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• v.18 no.1
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• pp.95-104
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• 2003

The deformation spaces of the six orientable 3-dimensional flat Riemannian manifolds are studies. It is proved that the Teichmuller spaces are homeomorphic to the Euclidean spaces. To state more precisely, let $\Phi$ denote the holonomy group of the manifold. Then the Teichmuller space is homeomorphic to (1) ${\mathbb{R}}^6\;if\;\Phi$ is trivial, (2) ${\mathbb{R}}^4\;if\;\Phi$ is cyclic with order two, (3) ${\mathbb{R}}^2\;if\;\Phi$ is cyclic of order 3, 4 or 6, and (4) ${\mathbb{R}}^3\;if\;\Phi\;\cong\;{\mathbb{Z}_2}\;\times\;{\mathbb{Z}_2}$.

• Journal of the Ergonomics Society of Korea
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• v.13 no.1
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• pp.37-46
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• 1994

The accurate error size and discrimination region in the perception of depth amount from 3-dimensional images by the human visual system will be the basic data for the utilization and application of the binocular 3- eimensional image system. This paper is focused on studying the accuracy of the depth amount perceived from 3- dimensional images by the human visual system. From the performed experiment, the following results have been obtained: (1) The depth amount perceived from the binocular 3- dimensional images has been displayed by a proper scale of distance, and found to be imprecise and also have a large variance. (2) In utilizing the binocular 3-dimensional image system, it seems more appropriate to make the images viewed outward rather than inward from the screen in the regard of error and variance. (3) The binocular 3-dimensional image system can be effectively applied to displaying unreal space, for example, the layout of room in design, from the viewpoint of perception characteristics of depth amount.

• Tunnel and Underground Space
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• v.19 no.3
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• pp.167-173
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• 2009

Underground storage cavern is known as the most complicated underground project because of the complexity of construction schedule, tunnel size, and geological problems. In order to optimize the construction schedule of underground storage cavern, two up-to-date technologies were applied. The first technology was 3 dimensional visualization of complicated underground structures, and the second was 4 dimensional simulation considering construction resources, geological conditions and construction schedule. This application case shows that we can achieve optimized construction schedule in the ways to optimize the number of work teams, fleets, the sequence of tunnel excavation, the commencement time of excavation and the hauling route of materials and excavated rocks. 3 dimensional modeling can help designer being able to understand the status of complicated underground structures and to investigate the geological data in the exact 3 dimensional space. Moreover, using 4 dimensional simulation, designer is able to determine the bottle neck point which appear during hauling of excavated rocks and to investigate the daily fluctuation in cost.

• Korean Institute of Interior Design Journal
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• v.22 no.3
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• pp.33-42
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• 2013

The purpose of this study was to analyze the design trend of the vertical garden design in the indoor space through the examples of green wall in the lobby space. For the analysis, this study looks into the 'Guide for the Building Greening System' to understand the technical consideration for the green wall. After that, the key design elements was drawn from existing green walls through the literature review and field survey and field-survey. The study picked six green walls which was completed after 2000 in the lobby space in Seoul. The major findings of this study were as follows: First, the design factors mainly depend on the plant selection, which leads to the outlook and texture of the vertical walls. The texture is expressed by the two-dimensional or three-dimensional planting methods which is related to the selection of plant species. Second, the vertical walls in the lobby area should be planned for the function of space which could be transition, human traffic, mood and attraction. Third, the vertical wall should be integrated with the surroundings in order to reinforces the dynamic or static space experience.

• Journal of the Korean Mathematical Society
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• v.59 no.4
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• pp.651-684
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• 2022

Let G be an arbitrary, connected, simply connected and unimodular Lie group of dimension 3. On the space 𝔐(G) of left-invariant Lorentzian metrics on G, there exists a natural action of the group Aut(G) of automorphisms of G, so it yields an equivalence relation ≃ on 𝔐(G), in the following way: h₁ ≃ h₂ ⇔ h₂ = 𝜙^*(h₁) for some 𝜙 ∈ Aut(G). In this paper a procedure to compute the orbit space Aut(G)/𝔐(G) (so called moduli space of 𝔐(G)) is given.

• Spatial Information Research
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• v.13 no.2 s.33
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• pp.119-128
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• 2005

Most spatial data handled in GIS is two-dimensional. These two-dimensional data is established by selecting 2D aspects form 3D, or by projecting 3D onto 2D space. During this conversion, without user's intention, data are abstracted and omitted. This unwanted data loss causes disadvantages such as restrictingof the range of data application and describing inaccurate real world. Recently, three dimensional data is getting wide interests and demands. One of the examplesis Database Management System which can store and manage three dimensional spatial data. However, this DBMS does not support spatial query which is the essence of the database management system. So, various studies are needed in this field. This research designs spatial relationship that is defined in space database standard using the three-dimension space model. The spatial data model, which is used in this research, is the one defined in OGC for GMS3, and designing tool is DE-9IM based on Point-Set Topology blow as the best method for topological operation.

• Tunnel and Underground Space
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• v.14 no.6 s.53
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• pp.423-428
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• 2004

The stability of tunnels is usually analyzed as plain strain condition and rock bolts are assumed as 2 dimensional equivalent continuum structures. In this study, 2 and 3 dimensional numerical analyses were conducted to verify the validity of 2 dimensional analysis of rock bolts. Since the results of 2 dimensional analysis showed more than $10\%$ differences in poor rocks, it seems that 3 dimensional analysis is required in poor rocks.