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

• Proceedings of the KOSOMBE Conference
• /
• v.1989 no.05
• /
• pp.55-59
• /
• 1989

A true three-dimensional cone-beam reconstruction (TTCR) algorithm for the complete sphere geometry is derived, which is applicable to the direct volume image reconstruction from 2-D cone-beam projections. The algorithm is based on the modified filtered backprojection technique which uses a set of 2-D space-invariant filters and is derived from the previously developed parallel-beam true three-dimensional reconstruction(TTR) algorithm. The proposed algorithm proved to be superior in spatial resolution compared with the parallel-beam TTR algorithm.

• Geophysics and Geophysical Exploration
• /
• v.5 no.2
• /
• pp.93-98
• /
• 2002

A three dimensional model for the orebody of an operating mine in Korea was constructed by using a program called '3-D Modeler'. The program allows the user to interactively construct a 3-D model of an orebody from its horizontal cross-sections. The 3-D Modeler is easily able to combine and display various spatial data for model construction. The result of modeling is strongly influenced by control points that correlate to the adjacent horizontal cross-sections. The control points are determined by comparing the geometrical shape of the adjacent cross-sections in conjunction with the geological features of the orebody. The resulting model can be evaluated in viewing the constructed object in three dimensional space or more closely evaluated by inspecting the cross-section. The model can iteratively be improved by modifying the shape of the cross-section and by using this new cross-section for the model building.

• Spatial Information Research
• /
• v.21 no.3
• /
• pp.55-69
• /
• 2013

In the modern society, as the city grows and constructive technology gradually develops, land usage has been sophisticated and three-dimensionalized. Consequently, issues such as property ownership and legal claim over ground and underground space have been triggered, which disclose the problems of using two-dimensional cadastral management system. Numerous researches on building three-dimensional cadastral are ongoing such as defining the right relationship of land space and providing the registration and management scheme so as to solve the imminent matter. It is the chief aim of this study to increase efficiency by analyzing the vocational practices through adding on necessary sections and properties for current registration to original research work. If three-dimensional cadastral management system is once constructed, highly qualified services for citizens will be available by providing accurate land related information swiftly, which can result in inevitable improvement of efficiency at work. Hence, this thesis will suggest the internationally suitable feature model development method in terms of standardization by probing into the factual profession to derive each attributes and properties that are related to three-dimensional cadastral and affix them to the classified item requisites of initial research studies.

• The Bulletin of The Korean Astronomical Society
• /
• v.42 no.2
• /
• pp.62.1-62.1
• /
• 2017

In space weather forecast, it is important to determine three-dimensional properties of CMEs. Using 29 limb CMEs, we examine which cone type is close to a CME three-dimensional structure. We find that most CMEs have near full ice-cream cone structure which is a symmetrical circular cone combined with a hemisphere. We develop a full ice-cream cone model based on a new methodology that the full ice-cream cone consists of many flat cones with different heights and angular widths. By applying this model to 12 SOHO/LASCO halo CMEs, we find that 3D parameters from our method are similar to those from other stereoscopic methods (i.e., a triangulation method and a Graduated Cylindrical Shell model). In addition, we derive CME mean density (${\bar{\rho}_{CME}}={\frac{M_{total}}{V_{cone}}}$) based on the full ice-cream cone structure. For several limb events, we determine CME mass by applying the Solarsoft procedure (e.g., cme_mass.pro) to SOHO/LASCO C3 images. CME volumes are estimated from the full ice-cream cone structure. For the first time, we derive average CME densities as a function of CME height for several CMEs, which are well fitted to power-law functions. We will compare densities (front and average) of geoeffective CMEs and their corresponding ICME ones.

• The Transactions of the Korea Information Processing Society
• /
• v.6 no.3
• /
• pp.821-831
• /
• 1999

Recognition of three-dimensional objects with convexities and concavities is a hard and challenging problem. This paper presents a feature extraction method out of three-dimensional objects for the purpose of classification. This new method not only provides invariance to scale, translation, and rotation $R^3$ but also distinguishes any three-dimensional model objects with concavities and convexities by measuring a relative similarity in the information space where a set of characteristics features of objects is mapped.

• ETRI Journal
• /
• v.44 no.2
• /
• pp.286-299
• /
• 2022

Human activity recognition in real time is a challenging task. Recently, a plethora of studies has been proposed using deep learning architectures. The implementation of these architectures requires the high computing power of the machine and a massive database. However, handcrafted features-based machine learning models need less computing power and very accurate where features are effectively extracted. In this study, we propose a handcrafted model based on three-dimensional sequential skeleton data. The human body skeleton movement over a frame is computed through joint positions in a frame. The joints of these skeletal frames are projected into two-dimensional space, forming a "movement polygon." These polygons are further transformed into a one-dimensional space by computing amplitudes at different angles from the centroid of polygons. The feature vector is formed by the sampling of these amplitudes at different angles. The performance of the algorithm is evaluated using a support vector machine on four public datasets: MSR Action3D, Berkeley MHAD, TST Fall Detection, and NTU-RGB+D, and the highest accuracies achieved on these datasets are 94.13%, 93.34%, 95.7%, and 86.8%, respectively. These accuracies are compared with similar state-of-the-art and show superior performance.

• Korean Journal of Computational Design and Engineering
• /
• v.12 no.1
• /
• pp.39-49
• /
• 2007

Recently three-dimensional (3-D) die design and production process has been widely introduced into the tooling shops of automotive manufacturers to reduce time-to-production of brand-new automobiles. 3-D solid models created in CAD systems are used not only for various simulations for design verification, but also for NC tool path generation to machine dies and their Styrofoam patterns. However, a lot of time and cost will be required to build solid models for dies if designers use only the generalized modeling capabilities of commercial 3-D CAD systems. To solve this problem, it is necessary to customize 3-D CAD system for the specific die design and manufacturing process. This paper describes a dedicated 3-D CAD system based on Unigraphics for die design for automotive body panels. The system provides not only 3-D design capabilities, but also standard part libraries, to enhance design productivity. The design process modeling technology has been introduced to facilitate redesign of the die for the modified panel. By introducing this system, dies can be designed more rapidly in the 3-D space, and their solid data can be directly transferred to CAM tools for NC tool path generation and simulation tools for virtual manufacturing.

• Nuclear Engineering and Technology
• /
• v.45 no.5
• /
• pp.613-624
• /
• 2013

Multi-dimensional two-phase phenomena occur in many industrial applications, particularly in a nuclear reactor during steady operation or a transient period. Appropriate modeling of complicated behavior induced by a multi-dimensional flow is important for the reactor safety analysis results. SPACE, a safety analysis code for thermal hydraulic systems which is currently being developed, was designed to have the capacity of multi-dimensional two-phase thermo-dynamic phenomena induced in the various phases of a nuclear system. To validate the performance of SPACE, a two-dimensional two-phase flow test was performed with slab geometry of the test section having a scale of $1.43m{\times}1.43m{\times}0.11m$. The test section has three inlet and three outlet nozzles on the bottom and top gap walls, respectively, and two outlet nozzles installed directly on the surface of the slab. Various kinds of two-dimensional air/water flows were simulated by selecting combinations of the inlet and outlet nozzles. In this study, two-dimensional two-phase void fraction profiles were quantified by measuring the local gap impedance at 225 points. The flow conditions cover various flow regimes by controlling the flow rate at the inlet boundary. For each selected inlet and outlet nozzle combination, the water flow rate ranged from 2 to 20 kg/s, and the air flow rate ranged from 2.0 to 20 g/s, which corresponds to 0.4 to 4 m/s and 0.2 to 2.3 m/s of the superficial liquid and gas velocities based on the inlet port area, respectively.

• Journal of Korean Tunnelling and Underground Space Association
• /
• v.20 no.4
• /
• pp.717-729
• /
• 2018

Considering the stability of the ground in the process of excavation design is essential because there is a risk of basal heave due to the load of the surrounding ground during the vertical excavation. However, calculation of the factor of safety for basal heave should be performed with two-dimensional equation, and the equation cannot reflect three-dimensional shape of vertical excavation. In this study, an equation for factor of safety for the basal heave was proposed with considering the effect of three-dimensional shape. It is confirmed that the equation can more appropriately reflect the basal heave stability 3D circular vertical excavation than the existing equation. Using the equation proposed in this study, it is possible to derive an appropriate factor of safety according to the 3D excavation shape during the circular vertical shaft excavation.