• Journal of Aerospace System Engineering
• /
• v.7 no.3
• /
• pp.20-25
• /
• 2013

In case of cube satellite, it is difficult to realize the same performance as commercial satellite due to its highly restricted unit accommodation space. To maximize the performance of the cube satellite, design concept considering the multi-function of satellite is required. In this paper, mechanism design of cube satellite which is applicable for the holding and release of multi-deployable structures has been proposed and investigated. In addition, a switch mechanism design for the autonomous system operation just after the cube satellite separation from P-POD has also been proposed. The effectiveness of the mechanism design for holding and release of multi-deployable structures has been demonstrated by EM test of the holding and release mechanism.

• Journal of KIISE:Databases
• /
• v.30 no.5
• /
• pp.451-463
• /
• 2003

Recently, there have been various research efforts to develop strategies for accelerating OLAP operations on huge amounts of spatio-temporal data. Most of the work is based on multi-tree structures which consist of a single R-tree variant for spatial dimension and numerous B-trees for temporal dimension. The multi~tree based frameworks, however, are hardly applicable to spatio-temporal OLAP in practice, due mainly to high management cost and low query efficiency. To overcome the limitations of such multi-tree based frameworks, we propose a new approach called Hilbert Cube(H-Cube), which employs fractals in order to impose a total-order on cells. In addition, the H-Cube takes advantage of the traditional Prefix-sum approach to improve Query efficiency significantly. The H-Cube partitions an embedding space into a set of cells which are clustered on disk by Hilbert ordering, and then composes a cube by arranging the grid cells in a chronological order. The H-Cube refines cells adaptively to handle regional data skew, which may change its locations over time. The H-Cube is an adaptive, total-ordered and prefix-summed cube for spatio-temporal data warehouses. Our approach focuses on indexing dynamic point objects in static spatial dimensions. Through the extensive performance studies, we observed that The H-Cube consumed at most 20% of the space required by multi-tree based frameworks, and achieved higher query performance compared with multi-tree structures.

• Journal of computational fluids engineering
• /
• v.16 no.1
• /
• pp.83-89
• /
• 2011

Laminar flow over a cube near a plane wall is numerically investigated in order to understand the effects of the cube-wall gap on the flow characteristics as well as the drag and lift coefficients. The main focus is placed on the three-dimensional vortical structures and its relation to the lift force applied on the cube. Numerical simulations are performed for the Reynolds numbers between 100 and 300, covering several different flow regimes. Without a wall nearby, the flow at Re=100 is planar symmetric with no vortical structure in the wake. However, when the wall is located close to the cube, a pair of streamwise vortices is induced behind the cube. At Re=250, the wall strengthens the existing streamwise vortices and elongates them in the streamwise direction. As a result, the lift coefficients at Re=100 and 250 increase as the cube-wall gap decreases. On the other hand, without a wall, vortex shedding takes place at Re=300 in the form of a hairpin vortex whose strength changes in time. The head of hairpin vortex or loop vortex, which is closely related to the lift force, seems to disappear due to the nearby wall. Therefore, unlike at Re=100 and 250, the lift coefficient tends to decrease more or less as the cube approaches the wall.

• Journal of computational fluids engineering
• /
• v.13 no.1
• /
• pp.57-62
• /
• 2008

Laminar flows over a cube and a cuboid (cube extended in the streamwise direction) are numerically investigated for the Reynolds numbers between 50 and 350. First, vortical structures behind a cube and lift characteristics are scrutinized in order to understand the variation in vortex shedding characteristics with respect to the Reynolds number. As the Reynolds number increases, the flow over a cube experiences the steady planar-symmetric, unsteady planar-symmetric, and unsteady asymmetric flows. Similar to the sphere wake, the planar-symmetric flow over a cube can be divided into two different regimes: single-frequency regime and multiple-frequency regime. The former has a single frequency due to regular shedding of vortices with the same strength in time, while the latter has multiple frequency components due to temporal variation in the strength of shed vortices. Second, the effect of the length-to-height ratio of the cuboid on the flow characteristics is investigated for the Reynolds number of 270, at which planar-symmetric vortex shedding takes place behind a cube. With the ratio smaller than one, the flow over the cuboid becomes unsteady asymmetric flow, whereas it becomes steady flow for the ratios greater than one. With increasing the ratio, the drag coefficient first decreases and then increases. This feature is related to the flow reattachment on the side faces of the cuboid.

• Journal of KIISE:Databases
• /
• v.31 no.3
• /
• pp.331-339
• /
• 2004

XML has got to be a new standard for data representation and exchanging by its many good points, and the core part of many new researches and emerging technologies. However, the self-describing characteristic, which is one of XML's good points, caused the spreading of XML documents with different structures, and so the need of the research for the effective XML-document search has been proposed. This paper is for the analysis of the problem in BitCube, which is a bitmap indexing that shows high performance grounded on its fast retrieval. In addition, to resolve the problem of BitCube, we did design and implement xPlaneb(XML Plane Web) which it a new 3-dimensional bitmap indexing made of linked lists. We propose an effective information retrieval technique by replacing BitCube operations with new ones and reconstructing 3-dimensional array index of BitCube with effective nodes. Performance evaluation shows that the proposed technique is better than BitCube, as the amount of document increases, in terms of memory consumptions and operation speed.

• Journal of the Korea Society of Computer and Information
• /
• v.12 no.4
• /
• pp.179-189
• /
• 2007

Every purchase a customer makes builds patterns about how products are purchased together. The process of finding these patterns, called market basket analysis, is composed of two steps in the Microsoft Association Algorithm. The first step is to find frequent item-sets. The second step which requires much less time than the first step does is to generate association rules based on frequent item-sets. Even though the first step, finding frequent item-sets, is the core part of market basket analysis, when applied to Online Analytical Processing(OLAP) cubes it always raises several points such as longitudinal analysis becomes impossible and many unpractical transactions are built up. In this paper, a new OLAP cube structures designing method which makes longitudinal analysis be possible and also makes only real customers' purchase patterns be identified is proposed for market basket analysis.

• Wind and Structures
• /
• v.5 no.2_3_4
• /
• pp.165-176
• /
• 2002

Results of measurements of surface pressure and of velocity field made on a full-scale 6 m cube in natural wind are reported. Comparisons are made with results from boundary-layer wind-tunnel studies reported in the literature. Two flow angles are reported; flow normal to a face of the cube (the $0^{\circ}$ case) and flow at $45^{\circ}$. In most comparisons, the spread of wind-tunnel results of pressure measurements spans the full-scale measurements. The exception to this is for the $0^{\circ}$ case where the roof and side-wall pressures at full-scale are more negative, and as a result of this the leeward wall pressures are also lower. The cause of this difference is postulated to be a Reynolds Number scale effect that affects flow reattachment. Measurements of velocity in the vicinity of the cube have been used to define the mean reattachment point on the roof centre line for the $0^{\circ}$ case, and the ground level reattachment point behind the cube for both $0^{\circ}$ and $45^{\circ}$ flow. Comparisons are reported with another full-scale experiment and also with wind-tunnel experiments that indicate a possible dependency on turbulence levels in the approach flow.

• Journal of the Korean Society for Aeronautical & Space Sciences
• /
• v.41 no.9
• /
• pp.720-725
• /
• 2013

Nylon wire cutting method by nichrome wire is generally applicable for cube satellite applications due to its advantages of simplicity. However, the system complexity is not avoidable to apply it on the cube satellite with multi-deployable structures. A lower constraint force of the mechanism is also one of the disadvantages of the mechanism. In this study, we proposed a preliminary structure design of cube satellite with the separation mechanism which is applicable for holding and release of the multi-deployable structures. The effectiveness of the mechanism design was verified through function test of EM mechanism. The structure analysis results showed that the structure design proposed in this study is feasible.

• Wind and Structures
• /
• v.37 no.1
• /
• pp.25-38
• /
• 2023

Due to the complexity and difficulty in meeting the multiphase flow complexity, similarity, and multiscale characteristics, the mechanism of snow drift is so complicated that the snow deposition prediction is still inaccurate and needs to be far improved. Meanwhile, the validation of prediction methods is also limited due to a lack of field-measured data about snow deposition. To this end, a field measurement activity about snow deposition around a cube with time was carried out, and the snow accumulation process was measured under blowing snow conditions in northwest China. The maximum snow depth, snow profile, and variation in snow depth around the cube were discussed and analyzed. The measured results indicated three stages of snow accumulation around the cube. First, snow is deposited in windward, lateral and leeward regions, and then the snow depth in windward and lateral regions increases. Secondly, when the snow in the windward region reaches its maximum, the downwash flow erodes the snow against the front wall. Meanwhile, snow range and depth in lateral regions have a significant increase. Thirdly, a narrow road in the leeward region is formed with the increase in snow range and depth, which results in higher wind speed and reforming snow deposition there. The field measurement study in this paper not only furthers understanding of the snow accumulation process instead of final deposition under complex conditions but also provides an important benchmark for validating prediction methods.

• Korean Journal of Optics and Photonics
• /
• v.26 no.1
• /
• pp.17-22
• /
• 2015

The applications for retro-reflectors, with their unique reflection characteristics, have been expanding, to include venetian blind slats, displays, traffic safety mark, etc. We propose expandable structures of inclined corner cube retro-reflectors and analyze their corresponding reflection characteristics. Various traffic safety structures with retro-reflectors may be designed more quantitatively using the chart of characteristics we have presented.