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Simulating three dimensional wave run-up over breakwaters covered by antifer units

  • Najafi-Jilani, A.;Niri, M. Zakiri;Naderi, Nader
    • International Journal of Naval Architecture and Ocean Engineering
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    • v.6 no.2
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    • pp.297-306
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    • 2014
  • The paper presents the numerical analysis of wave run-up over rubble-mound breakwaters covered by antifer units using a technique integrating Computer-Aided Design (CAD) and Computational Fluid Dynamics (CFD) software. Direct application of Navier-Stokes equations within armour blocks, is used to provide a more reliable approach to simulate wave run-up over breakwaters. A well-tested Reynolds-averaged Navier-Stokes (RANS) Volume of Fluid (VOF) code (Flow-3D) was adopted for CFD computations. The computed results were compared with experimental data to check the validity of the model. Numerical results showed that the direct three dimensional (3D) simulation method can deliver accurate results for wave run-up over rubble mound breakwaters. The results showed that the placement pattern of antifer units had a great impact on values of wave run-up so that by changing the placement pattern from regular to double pyramid can reduce the wave run-up by approximately 30%. Analysis was done to investigate the influences of surface roughness, energy dissipation in the pores of the armour layer and reduced wave run-up due to inflow into the armour and stone layer.

Development of Multi-Material DLP 3D Printer (다중재료 DLP 3차원 프린터의 개발)

  • Park, Se-Won;Jung, Min-Woo;Son, Yong-Un;Kang, Tae-Young;Lee, Chibum
    • Journal of the Korean Society of Manufacturing Technology Engineers
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    • v.26 no.1
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    • pp.100-107
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    • 2017
  • 3D printing is a technology that converts a computer-generated 3D model into a real object with additive manufacturing technology. A majority of 3D printing technologies uses one material, and this is considered a limitation. In this study, we developed a multi-material 3D printer by adopting dual resin vat and cleaning system with DLP (Digital Light Processing) 3D printing technology. The developed multi-material DLP 3D printer is composed of a manufacturing system, cleaning system, transporting system, and automatic resin recharging system. Various 3D structures were 3D printed with two materials, thus demonstrating the potential. Printing performance of the multi-material DLP 3D printer was studied by performing a comparative surface roughness test and tension test on specimens composed of one material as well as those composed of two materials.

Investigation into effect of cutting angle on the thermal characteristics in the linear heat cutting of EPS foam (EPS foam의 선형 열선 절단시 절단 경사각의 영향에 관한 연구)

  • 안동규;이상호;양동열;윤석환
    • Proceedings of the Korean Society of Precision Engineering Conference
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    • 2002.05a
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    • pp.947-951
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    • 2002
  • During the hotwire cutting of EPS foam sheet, the dimensional accuracy and part quality of the cut par are highly dependent upon the thermal field in the EPS. The thermal field is determined by operating parameters such as heat input, cutting speed and cutting angle. The objective of this study is to investigate into the influence of cutting angle on the kerfwidth and part quality of the cut part in hotwire cutting of EPS foam using the experiments and the numerical analysis in the case of a single sloped cutting. In order to estimate an accurate temperature field, the transient thermal analysis using a moving coordinate system and the sloped heat flux model is carried out. From the results of the experiments and the analysis, it has been found that the effect of cutting angle on the kerfwidth and the melted area at the edge are 0.1 mm and 0.11 mm2 respectively. The results of the experiments show that the surface roughness is not appreciably influenced by the cutting angle.

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Head-Disk Interface : Migration from Contact-Start-Stop to Load/Unload

  • Suk, Mike
    • Journal of KSNVE
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    • v.9 no.4
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    • pp.643-651
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    • 1999
  • A brief description of the current technology (contact-start-stop) employed in most of today's hard disk drive is presented. The dynamics and head/disk interactions during a start/stop process are very complicated and no one has been able to accurately model the interactions. Thus, the head/disk interface that meets the start/stop durability and stiction requirements are always developed statistically. In arriving at a solution. many sets of statistical tests are run by varying several parameters. such as, the carbon overcoat thickness. lubricant thickness. disk surface roughness, etc. Consequently, the cost associated III developing an interface could be significant since the outcome is difficult to predict. An alternative method known as Load/Unload technology alters the problem set. such that. the start/stop performance can be designed in a predictable manner. Although this techno¬logy offers superior performance and significantly reduces statistical testing time, it also has some potential problems. However. contrary to the CSS technology. most of the problems can be solved by design and not by trial and error. One critical problem is that of head/disk contacts during the loading and unloading processes. These contact can cause disk and slider damage because the contacts are likely to occur at high disk speeds resulting in large friction forces. Use of glass substrate disks also may present problems if not managed correctly. Due to the low thermal conductivity of glass substrates. any head/disk contacts may result in erasure due to frictional heating of the head/disk interface. In spite of these and other potential problems. the advantage with L/UL system is that these events can be understood. analyzed. and solved in a deterministic manner.

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An Analysis of Wind Force Coefficient Distributions for Optimum Design of Single-Span Arched Greenhouse (아치형 단동온실의 최적설계를 위한 풍력계수분포도의 분석)

  • 이석건;이현우;권무남
    • Journal of Bio-Environment Control
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    • v.4 no.1
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    • pp.1-8
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    • 1995
  • One of the most destructive forces around greenhouses is wind. Wind loads can be obtained by multiplying velocity pressure by dimensionless wind force coefficient. Generally, wind force coefficients can be determined by wind tunnel experiments. The wind force coefficient distribution on a single - span arched greenhouse was estimated using experimental data and compared with reported values from various countries. The results obtained are as follows : 1. The coefficients obtained from this study agree with the values proposed by G. L. Nelson except about 0.5 of difference in the middle region of roof section. This discrepancy is mainly attributed to the dissimilarity of experimental conditions (or wind tunnel test such as Reynolds number, type of terrain, surface roughness of model, location of the lapping and measuring methods. 2. Considering that the wind force coefficients are varied along the height of a wall at wind direction perpendicular to wall, structural analysis using subdivided wind force coefficient distribution is more resonable for wall. 3. It is recommendable that wind force coefficient distribution on a roof should take more subdivision than the existing four equal divisions for more accurate structural design. 4. Structural design using wind forces close to real values is more advantageous in safety and expense.

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A Study on the Tolerance Modeler for Feature-based CAPP (특징형상에 기반한 자동공정설계용 공차 모델러 연구)

  • Kim, Jae-Gwan;No, Hyeong-Min;Lee, Su-Hong
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.26 no.1
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    • pp.48-54
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    • 2002
  • A part definition must not only provide shape information of a nominal part but also contain non-shape information such as tolerances, surface roughness and material specifications. Although machining features are useful for suitable shape information fur process reasoning in CAPP, they need to be integrated with tolerance information for effective process planning. We develop a tolerance modeler that efficiently integrates the machining features with the tolerance information fur feature-based CAPP. It is based on the association of machining features, tolerance features, and tolerances. The tolerance features in this study, where tolerances are assigned, are classified into two types; one type is a face that is a topological entity on a solid model and the other type is a functional geometry that is not referenced to topological entities. The (unctional geometry is represented by using machining features. All the data fur representing the tolerance information are stored completely and unambiguously in an independent tolerance data structure. The developed tolerance modeler is implemented as a module of a comprehensive feature-based CAPP system.

Optimal design of slider for stable flying characteristic using 4×l near-field probe array

  • Jung Min-su;Hong Eo-Jin;Park Kyoung-Su;Park No-Cheol;Yang Hyun-Seok;Park Young-Pil;Lee Sung-Q;Park Kang-Ho
    • 정보저장시스템학회:학술대회논문집
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    • 2005.10a
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    • pp.171-176
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    • 2005
  • In the information storage development, the trend of the storage device is to increase the recording density. Among such an effort, near-field probe recording is spotlighted as a method of high increasing recording density. For the successfully embodiment of storage device, the actuating mechanism of near-field probe is essentially designed. In this paper, we suggest the slider similar with conventional HDDs and design the slider using near- field probe for the purpose of applying the slider in order to control gap between probe and media. The most important object of slider design is to guarantee the flying ability and stability. For achievement of these design objects, we perform two step of optimal design process. The media is mod! eled as random displacement, which is only considered roughness of disk surface. The design slider is analyzed with dynamic state in assumed media. At this process, the optimal model is confirmed to stable flying stability.

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Determination of optical constants and thickness of organic electroluminescence thin films using variable angle spectroscopic ellipsometry (가변입사각 분광타원 법을 이용한 유기 발광 박막의 광학상수 및 두께 결정)

  • 김상열;류장위;김동현;정혜인
    • Korean Journal of Optics and Photonics
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    • v.12 no.6
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    • pp.472-478
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    • 2001
  • We determined the optical constants and thickness of organic electroluminescence thin films using variable angle spectroscopic ellipsometry. Using the measured transmittance spectra and the spectroscopic ellipsomeoy data of the organic films on glass substrates in the optically transparent region, we determined the effective thickness and the refractive indices of organic thin films. Then by applying a numerical inversion method to variable angle spectro-ellipsometry data, we determined the complex refractive index at each wavelength including the optically absorbing region, as well as the thickness and surface micro-roughness of the organic thin films. The calculated transmittance spectra showed a tight agreement with the measured ones, confining the validity of the present model analysis.

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Development of an RF Signal Level Prediction Simulator for Radiowave Propagation in Natural Environments (비행체의 원격신호측정을 위한 전파환경을 고려한 RF 수신신호 예측 시뮬레이터 개발)

  • Hyun, Jong-Chul;Kim, Sang-Keun;Oh, Yi-Sok;Seo, Dong-Soo;Kim, Heung-Bum
    • Journal of the Korea Institute of Military Science and Technology
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    • v.13 no.5
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    • pp.725-733
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    • 2010
  • A simulator is proposed in this paper for predicting the RF signal level after propagating over sea and land surfaces. Various sea and land types and transmit/receive antenna patterns, as well as the locus of the transmit antenna, are considered for this simulator. At first, microwave reflection characteristics of various sea surfaces have been computed, based on an empirical formula which is developed in this study for the relation between the sea surface roughness and wind speed. Then, microwave reflections from land surfaces such as forests, agricultural areas, and bare surfaces, are computed using the first-order vector radiative transfer theory. Finally, the signal paths over sea and land surfaces are found using the ray tracing technique and the digital elevation model, and the signal level received by a receiving antenna is computed by the using the reflection coefficients of sea and land surfaces and the signal paths.

Investigation of the effects due to a permeable double skin façade on the overall aerodynamics of a high-rise building

  • Pomaranzi, Giulia;Pasqualotto, Giada;Zassso, Alberto
    • Wind and Structures
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    • v.35 no.3
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    • pp.213-227
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    • 2022
  • The design of a building is a complex process that encompasses different fields: one of the most relevant is nowadays the energetic one, which has led to the introduction of new typologies of building envelopes. Among them, the Permeable Double Skin Façades (PDSF) are capable to reduce the solar impact and so to improve the energetic performances of the building. However, the aerodynamic characterization of a building with a PDSF is still little investigated in the current literature. The present paper proposes an experimental study to highlight the modifications induced by the outer porous façade in the aerodynamics of a building. A dedicated wind tunnel study is conducted on a rigid model of a prismatic high-rise building, where different façade configurations are tested. Specifically, the single-layer façade is compared to two PDSFs, the former realized with perforated metal and the latter with expanded metal. Outcomes of the tests allow estimating the cladding loads for all the configurations, quantifying the shielding effects ascribable to the porous layers that are translated in a significant reduction of the design pressure that could be up to 50%. Moreover, the impact of the PDSFs on the vortex shedding is investigated, suggesting the capability of the façade to suppress the generation of synchronised vortices and so mitigate the structural response of the building.