• Title/Summary/Keyword: Free-form Surface

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Variable Free Surface Panel Method for Potential Flow Analysis around a Ship (가변 자유수면 패널법을 이용한 선체 주위 포텐셜 유동 해석)

  • Choi, Hee-Jong;Kim, Jin;Van, Suak-Ho;Park, Il-Ryong;Kim, Kwang-Soo
    • Journal of the Society of Naval Architects of Korea
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    • v.45 no.1
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    • pp.54-62
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    • 2008
  • A new solution method was developed to solve the free surface flow around a hull and named as 'Variable Free Surface Panel Method'. In the method the non-linearity of the free surface boundary conditions was fully taken into account and the raised panel method was employed to effectively solve the problem. The transom stern flow was also considered and the panel on the hull was generated using the panel cutting method. Numerical calculations were performed for KCS(KRISO Container Ship) hull form and compared with the experimental data to confirm the validity of the method. The comparison with the conventional free surface panel method was also accomplished. It is confirmed that new method gives more reliable results than the conventional method.

An Exper imenta1 Study for Bow Hull Form Development of Catamaran Type Sweeping Vessel (쌍동형 부유쓰레기 청소선의 선수선형 개량을 위한 실험적 연구)

  • 정우철;박찬원;홍기섭;유호근
    • Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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    • 2001.05a
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    • pp.53-59
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    • 2001
  • In this Paper, the resistance performances of twin hull forms, which are simplified as two-dimensional wedge shape, are experimentally investigated in low and middle speed ranges to find out the effect of distance between two hulls and fore-body shape for the future hull form development of catamaran type sweeping vessel. The model tests are performed for seven different cases for three models in the circulating water channel(CWC) of Inha Technical College. The free surface flows are observed together to investigate the relation between resistance performance and free surface characteristics. A conceptual design for the modification of bow hull form is presented and the efficiency is discussed.

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Hydrodynamic Forces produced by the Swaying Oscillation of Cylinders with Chine Sections on the Free Surface. (배골형단면(背骨型斷面) 주상체(柱狀體)의 좌우동요(左右動搖)에 있어서의 동유체역학적(動流體力學的) 힘에 관하여)

  • J.H.,Hwang;Y.S.,Yang
    • Bulletin of the Society of Naval Architects of Korea
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    • v.11 no.1
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    • pp.1-8
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    • 1974
  • Hydrodynamic forces and moments produced by the swaying oscillation on the free surface were exactly calculated by Ursell-Tasai method for the cylinders with Kim's chine form sections and the sway responses of the cylinders of those chine form sections among the regular beam sea were also calculated. The results of the computation were compared with those of Lewis form sections. It is concluded that the effects of the section form on the added mass, and damping are small, if the section forms had same beam-draft ratio and sectional area coefficient in the case of sway motion. It is also known that the above little effects of section shapes on the basic hydrodynamic forces do not effect on the sway motion responses of cylinderical bodies among the regular beam sea. The sway motion responses of cylinderical bodies are varied linearly with the wave numbers.

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Accuracy Improvement and Systematic Bias Analysis of Scanning White Light Interferometry for Free-form Surfaces Measurements (자유 곡면 형상 측정을 위한 백색광 주사 간섭계의 정확도 향상 및 시스템 오차 분석)

  • Ghim, Young-Sik;Davies, Angela;Rhee, Hyug-Gyo
    • Journal of the Korean Society for Precision Engineering
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    • v.31 no.7
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    • pp.605-613
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    • 2014
  • Scanning white-light interferometry is an important measurement option for many surfaces. However, serious profile measurement errors can be present when measuring free-form surfaces being highly curved or tilted. When the object surface slope is not zero, the object and reference rays are no longer common path and optical aberrations impact the measurement. Aberrations mainly occur at the beam splitter in the interference objective and from misalignment in the optical system. Both effects distort the white-light interference signal when the surface slope is not zero. In this paper, we describe a modified version of white-light interferometry for eliminating these measurement errors and improving the accuracy of white-light interferometry. Moreover, we report systematic errors that are caused by optical aberrations when the object is not flat, and compare our proposed method with the conventional processing algorithm using the random ball test.

Sensitive Determination of Natural and Synthetic Steroidal Hormones of a Free and Conjugated Form in Surface Water by Gas Chromatography-Mass Spectrometry

  • Shin, Ho-Sang;Oh, Jin-Aa;Shin, Sun-Kyoung
    • Bulletin of the Korean Chemical Society
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    • v.32 no.3
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    • pp.809-814
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    • 2011
  • A method based on the TMS derivatives and acidic hydrolysis was developed for the simultaneous determination of free and conjugated steroidal hormones in surface water. A silylation of five natural and two synthetic steroidal hormones was achieved with N-methyl-N-(trimethylsilyl) trifluoroacetamide/$NH_4I$ (1000:3) under catalysis of dithioerythritol for 60 min at $80^{\circ}C$. TMS derivatives of the steroid hormones containing multifunctional groups offer a single derivative product under this condition. The accuracy of the analytes was in the range of 87 to 110% at a concentration of 20 and 50 ng/L with relative standard deviations of less than 10%. The method detection limit was in the range of 0.01 to 0.02 ng/L for surface water. Natural steroidal hormones were detected in a concentration range of 0 to 1.03 ng/L in free form and 0 to 14.6 ng/L in conjugated form, respectively. We found that most of the natural hormonal steroids exist in conjugate forms (43 to 100%) in river water.

Surface Creation using B-Spline Surface Method (B-Spline 곡면기법을 이용한 곡면형상 도출)

  • Soo-Young Kim;Il-Guk Woo
    • Journal of the Society of Naval Architects of Korea
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    • v.29 no.3
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    • pp.1-14
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    • 1992
  • Using form parameters representing geometric characteristics of the form, this paper attempts the generation of 3-D free surface given in terms of B-spline surface equation. This is achieved by coupling the form parameter decision, Coons surface of the form parameters, and B-spline. To check the validing of the present method, a analogous surface to the bulbous bow was generated.

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NUMERICAL DIFFUSION DECREASE OF FREE-SURFACE FLOW ANALYSIS USING SOURCE TERM IN VOLUME FRACTION TRANSPORT EQUATION (볼륨비 이송방정식의 소스항을 이용한 자유수면 유동 해석의 해 확산 감소)

  • Park, Sunho;Rhee, Shin Hyung
    • Journal of computational fluids engineering
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    • v.19 no.1
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    • pp.15-20
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    • 2014
  • Accurate simulation of free-surface wave flows around a ship is very important for better hull-form design. In this paper, a computational fluid dynamics (CFD) code, termed SNUFOAM, which is based on the open source libraries, OpenFOAM, was developed to predict the wave patterns around a ship. Additional anti-diffusion source term for minimizing a numerical diffusion, which was caused by convection differencing scheme, was considered in the volume-fraction transport equation. The influence of the anti-diffusion source term was tested by applying it to free-surface wave flow around the Wigley model ship. In results, the band width of the volume fraction contours between 0.1 to 0.9 at the hull surface was narrowed by considering the anti-diffusion term.

Machining of Anode and Cavity applying Ultraprecision Machining Characteristics of OXFC (무산소동의 초정밀 절삭 특성을 이용한 아노드 및 캐비티의 가공)

  • 원종호;김주환;박순섭;김건희;김상석
    • Proceedings of the Korean Society of Precision Engineering Conference
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    • 2002.05a
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    • pp.922-925
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    • 2002
  • Klystron which is micro wave amplifier tube are mainly used in fields of science such as accelerator, nuclear fusion, broadcasting, communication fields, and defense industry fields, tract. The quality of Klystron anode and cavity are determined by form accuracy and roughness of the worked surface. Therefore anode and cavity are restricted the from accuracy strictly and the surface roughness be under Rmax 0.03S. As a work material of anode and cavity, the oxygen-free copper, that is used for optical pares of aerospace and laser mirror is selected. An outside diameter of material is $\Phi$100 mm and an inside diameter is $\Phi$30~33 mm. In this study, to find the optimum ultra precision cuffing condition of oxygen-free copper with diamond turning machine, the surface roughness is examined for various diamond toot nose radius, main spindle speed, fred rate and depth of cut. As a result of experiment, we could machined the anode and cavity with a surface roughness within Ra 3.2 nm, a form accuracy within 0.01 $\mu\textrm{m}$.

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A Study on the Visualization of Ship Hull using Computer Graphics Techniques (컴퓨터 그래픽스 기법을 이용한 선체곡면 가시화 연구)

  • H. Shin;K.W. Park
    • Journal of the Society of Naval Architects of Korea
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    • v.29 no.3
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    • pp.15-20
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    • 1992
  • This paper outlines the methods of visualizing 3-dimensional free form surfaces employing the Painter's algorithm, especially for the ship hull forms which are defined as open uniform Bi-cubic B-spline surfaces. The computer graphic codes are developed for the transparent wire-frame, the hidden surface removal and the shading visualization techniques, The codes are applied to the ship hull 3-dimensional surface visualization and the color graphic figures are displayed. Also Gaussian curvature is displayed on the color plots of the isoparametric net of the ship hull surface.

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A Development of Pre and Post Processor for Design of Surface System of Free Form Building (비정형 건축물의 외피시스템 설계를 위한 전·후처리 모듈 개발)

  • Park, Se-Hee;Jung, Sung-Jin;Lee, Jae-Sung
    • Journal of the Korea Academia-Industrial cooperation Society
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    • v.19 no.9
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    • pp.333-340
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    • 2018
  • Recently, free-form buildings have been designed with complex shapes due to digitization of the construction industry. Exterior and interior components of free-form buildings have free cross sections and curved shapes. Therefore, structural members with curvature are frequently seen. In the modeling and stability evaluation of these structures, commercial programs using classical finite element analysis are not able to perform rapid shape modeling, resulting in a decrease in productivity. Therefore, in this study, pre- and post-processing modules were developed using a prior study to rapidly model the surface of a free-form building and to automatically generate frame structures that make up the cladding. The developed modules use a subdivision algorithm with spline curves. This algorithm is used to automatically generate analytical elements from the configuration information of NURBS curves. In addition, the deformation after analysis can be viewed more realistically. The modules can quickly construct complex curved surfaces. An analysis model of the frame structure was also automatically generated. Therefore, the modules could contribute to the productivity improvement of free-form building design.