• Wind and Structures
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• v.30 no.5
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• pp.525-532
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• 2020

This work numerically investigates the effects of Reynolds number Re_D (= 100 - 150), cross-sectional aspect ratio AR = ( 0.25 -1.0), and attack angle α (= 0° - 90°) on the forces, Strouhal number, and wake of an elliptical cylinder, where Re_D is based on the freestream velocity and cylinder cross-section height normal to the freestream flow, AR is the ratio of the minor axis to the major axis of the elliptical cylinder, and α is the angle between the cylinder major axis and the incoming flow. At Re_D = 100, two distinct wake structures are identified, namely 'Steady wake' (pattern I) and 'Karman wake followed by a steady wake (pattern II)' when AR and α are varied in the ranges specified. When Re_D is increased to 150, an additional wake pattern, 'Karman wake followed by secondary wake (pattern III)' materializes. Pattern I is characterized by two steady bubbles forming behind the cylinder. Pattern II features Karman vortex street immediately behind the cylinder, with the vortex street transmuting to two steady shear layers downstream. Inflection angle α_i = 32°, 37.5° and 45° are identified for AR = 0.25, 0.5 and 0.75, respectively, where the wake asymmetry is the greatest. The α_i effectively distinguishes the dependence on α and AR of force and vortex shedding frequency at either Re_D. In Pattern III, the Karman street forming behind the cylinder is modified to a secondary vortex street. At a given AR and α, Re_D = 150 renders higher fluctuating lift and Strouhal number than Re_D = 100.

• Transactions of the Korean Society of Automotive Engineers
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• v.16 no.3
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• pp.38-43
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• 2008

The hydroforming technology has been spreaded dramatically in automotive industry last 10 years. Itmay cause many advantages to automotive applications in terms of better structural integrity of the parts, lower cost from fewer part count, material saving, weight reduction, lower springback, improved strength and durability and design flexibility. In this study, the whole process of rear sub-frame parts development by tube hydroforming using steel material having tensile strength of 440MPa grade is presented. At the part design stage, it requires feasibility study and process design aided by CAE (Computer Aided Design) to confirm hydroformability in details. Effects of parameters such as internal pressure, axial feeding and geometry shape in automotive rear sub-frame by hydroforming process were carefully investigated. Overall possibility of hydroformable sub-frame parts could be examined by cross sectional analyses. Moreover, it is essential to ensure the formability of tube material on every forming step such as pre-bending, preforming and hydroforming. In addition, all the components of prototyping tool are designed and interference with press is examined from the point of geometry and thinning.

• Journal of the Korean Applied Science and Technology
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• v.37 no.2
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• pp.340-353
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• 2020

The purpose of this study is to introduce surfing which is not a familiar leisure activity in Korea and provide understanding of surfing participants through the cross-sectional analysis on the process of forming recreational specialization from introductory levels with enthusiastic surfing participants. This study employs a qualitative approach to analyze each participant's experience on recreation specialization in detail, and in particular uses ethnographic research methods to derive participants' meaning of life and daily routines and cultural behavioral patterns changed through surfing. First, through the analysis of in-depth interview data, total 531 conceptual words were identified and the first categorization was established. Second, surfing participants mentioned that they had high expectations of surfing even before they first encountered it. Third, surfing participants noted that they experienced leisure constraints and made efforts to resolve this issue before reaching the recreation specialization process. Fourth, surfing participants were found to go through a recreation specialization process. Fifth, surfing participants were found to undergo life changes. They worked hard in their everyday life through physical training, improvement of surfing skills, and analysis of their own videos to be better at surfing.

• Journal of the Korea Institute of Building Construction
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• v.14 no.1
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• pp.1-10
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• 2014

The SC structure can have relatively liberal sectional surfaces, and allows modularization for pre-forming in factories and structural stability. It can be used for the shear walls in the core of general buildings or the structural members for parking buildings. In the future, it could be applied to moving large bus terminals, and widely used for general industrial structures as it can expedite the process compared to other methods. This study examined the applicability of SC structures to the retaining walls of a parking building and reviewed its economic value by comparing its construction term, quality control benefits, and cost compared to RC structures. It was found that SC structures are about 1.6-1.7 times more expensive than RC structures in terms of the cost of fabrication and installation. However, the construction term can be reduced by 27% to save indirect costs for constructors, as well as the cost of removing molds and material loss required when installing RC structures.

• Transactions of Materials Processing
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• v.11 no.1
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• pp.45-53
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• 2002

The forming process of metal matrix composites by die casting and squeeze casting process are limited in size and dimension In term of final parts. The melt strirring method have the problems that the homogeneous distribution of the reinforcements is difficult due to the low weldability and the density difference between the molten metal and the reinforcement. The thixoforming process for metal matrix composites has numerous advantages compacted to die casting, squeeze casting and compocasting. However, for the thixofoming process, the billet with the desired volume fraction must be heated to obtain a uniform temperature distribution over the entire cross-sectional areas. To obtain the reheating conditions of composites, the particulate reinforced metal matrix composites for thixoforming were fabricated by combined stirring process which is simultaneously performed with electro-magnetic stirring and mechanical stirring process. The matrix alloy and reinforcement are used to aluminum alloy(A357) and SiCp with diameter 14, $25{\mu}m$, respectively. The microstructure characteristics were investigated by changing the volume fraction and reinforcement size. The heating conditions to obtain the uniform temperature distribution in cross section area of fabricated metal matrix composites billet are proposed with heating time, the heating temperature and the holding time.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.32 no.3
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• pp.240-249
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• 2008

This paper presents an electromagnetic design method for magneto-rheological (MR) valves. Since the apparent viscosity of MR fluids is adjusted by applying magnetic fields, the MR valves can control high-level fluid power without any mechanical moving parts. In order to improve the performances of the MR valve, it is important that the magnetic field is effectively supplied to the MR fluid. For the purpose, the magnetic circuit composed with the yoke for forming magnetic flux path, the electromagnetic coil and the MR fluid should be well designed. In order to improve the static characteristic of the MR valve, the length of the magnetic flux path is decreased by removing the unnecessary bulk of the yoke. Also, in order to improve its dynamic and hysteretic characteristics, the magnetic reluctance of the magnetic circuit should be increased by minimizing the cross-sectional area of the yoke through which the magnetic flux passes. After two MR valves, one is a conventional type valve and the other is the proposed one, are designed and fabricated, their performances are evaluated experimentally.

• Journal of Korea Technical Association of The Pulp and Paper Industry
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• v.30 no.1
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• pp.7-17
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• 1998

With the advent of CLSM in the end of 1980s, it has been applied to the field of pulp and paper science in various ways. This study showed the potentials of CLSM In analyzing a change of pulp fiber and paper properties before and after mechanical treatment. In particular, a quantification of internal fibrillation has been done using cross-sectional images of fibers and image analysis technique, then evaluated the effects of fiber wall delamination on fiber and paper properties. It showed that the delaminated fibers were closely associated to development of the interfiber bonding in a fiber network. The CLSM made it possible to investigate a density profile along the sheet thickness, which was created by some papermaking processes like pressing, drying and calendering. Through the attempt to observe the forming procedure of a fiber network during handsheet making, the CLSM images showed that the pressing stage was considered greatly to contribute to generation of interfiber bonding with removing a free water and partly a bound water between fibers. In addition, the CLSM could be used to illustrate not only a surface profile of paper showing the extent of smoothness or roughness, but also a density profile in a B-direction of the network. Finally it became evident that the CLSM could be used as an excellent tool to predict development in fiber and paper properties before and after mechanical treatment during papermaking processes.

• Transactions of Materials Processing
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• v.26 no.1
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• pp.28-34
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• 2017

Multi-pass shape rolling is performed to produce long products of arbitrary cross-sectional shapes. In the past, the multi-pass shape rolling process has been designed by the trial and error method or the experience of experts based on the empirical approach. Particularly, the design of roll caliber in shape rolling is important to improve product quality and dimensional accuracy. In this paper, the caliber design and pass schedule of multi-pass shape rolling were proposed for manufacturing piston ring wire. In order to design roll caliber, major shape parameter and dimension was determined by analysis of various caliber design. FE-simulation was conducted to verify effectiveness of proposed process design. At first, forming simulation was performed to predict shape of the product. Then, fracture of the wire was evaluated by critical damage value using normalized Cockcroft-Latham criteria. The experiment was carried out and the results are within the allowable tolerance.

• Steel and Composite Structures
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• v.25 no.5
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• pp.625-638
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• 2017

This paper presents a novel approach that describes the first-order (linear elastic) partial interaction analysis of members formed by multi-components based on the Generalised Beam Theory (GBT). The novelty relies on its ability to accurately model the partial interaction between the different components forming the cross-section in both longitudinal and transverse directions as well as to consider the cross-sectional deformability. The GBT deformations modes, that consist of the conventional, extensional and shear modes, are determined from the dynamic analyses of the cross-section represented by a planar frame. The partial interaction is specified at each connection interface between two adjacent elements by means of a shear deformable spring distributed along the length of the member. The ease of use of the model is outlined by an application performed on a multi-component member subjected to an eccentric load. The values calculated with an ABAQUS finite element model are used to validate the proposed method. The results of the numerical applications outline the influence of specifying different rigidities for the interface shear connection and in using different order of polynomials for the shape functions specified in the finite element cross-section analysis.

• KIEAE Journal
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• v.13 no.1
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• pp.9-15
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• 2013

This study aims to analyze, by forming an experimental area of artificial soil green area that is of equal scale and analyzing the characteristics of runoff water in accordance with the cross-section configuration, applied the benefits in an actual multi-housing case study complex. In examining the measurement test results of the runoff water infiltration amount and surface runoff amount of a low-profile type green area(Dish type) and a general type green area(Mound type), Dish type was seen to have 1.5-times higher runoff water infiltration amount than Mound type during heavy rainfalls and showed about a 50% reduction with respect to the surface runoff amount. In other words, artificial soil green area offers the benefit of reduction of surface runoff amount and suggests, in actuality even with a change to the cross-sectional configuration of artificial soil green area alone at the time of construction of multi-housings, the possibility of benefits and reduction of costs spent on existing rainwater management facilities.