• 대한조선학회논문집
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• 제47권4호
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• pp.553-564
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• 2010

This paper studies on the rudder shapes for the suppression of the cavitation around a horn-type rudder. To improve the problems due to cavitation, there have been several studies. However, these some studies are recognized as incomplete ways to suppress the rudder cavitation. In this study, the section shapes to suppress the cavitation phenomena are determined by moving the location of maximum thickness for reducing the curvature variation and changing the radius of leading edge. Also, in the pintle part, the curvature radius of the inlet outlet edge of rudder plate is changed. During the design of rudder shape, two-dimensional numerical simulations are firstly performed because those offer some advantages with that cavitation phenomena becomes predictable for a short time, and then the three-dimensional numerical simulations are performed to confirm the determination. The time mean distribution of the propeller slipstream is imposed on the inlet boundary condition. As some results, this paper shows the effects reducing the range of the occurrence of cavitation, and suggests the references on the design of a horn-type rudder for the suppression of cavitation phenomena.

• 대한조선학회논문집
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• 제57권2호
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• pp.114-123
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• 2020

A high-order potential-based panel method based on Green's theorem, with piecewise-linear dipole strength on triangular panels, is formulated for the analysis of potential flow around a three-dimensional wing. Previous low-order panel methods adopt square panels with piecewise-constant dipole strength, which results in inherent errors. Square panels can not represent a high curvature lifting body, such as propellers, since the four vertices of the square panel do not locate at the same flat plane. Moreover the piecewise-constant dipole strength induces inevitable errors due to the steps in dipole strength between adjacent panels. In this paper a high-order panel method is formulated to improve accuracy by adopting a piecewise linear dipole strength on triangular panels. Firstly, the square panels are replaced by triangular panels in order to increase the geometric accuracy in representing the shape of the object with large curvature. Next, the step difference of the dipole strength between adjacent panels is removed by adopting piecewise-linear dipole strength on the triangular panels. The calculated results by the present method is compared with analytical ones for simple non-lifting geometries, such as ellipsoid. The results for an elliptic wing with zero thickness at finite angle of attack are compared with Jordan's results. The comparison shows reasonable agrements for the both lifting and non-lifting bodies.

• 한국음향학회지
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• 제19권3호
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• pp.20-25
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• 2000

본 논문에서는 3차원 물체 인식을 위한 표면 분류 및 임계치 선정 방법에 대해 제안 하고자 한다. 3차원 영상 처리는 크게 거리 영상의 획득과 특징 추출 그리고 정합 과정으로 이루어진다. 본 논문에서는 전체 3차원 영상 처리 시스템중 거리 영상을 입력으로 했을 시 형상 특징을 추출하는 방법에 대해 제안하고자 한다. 이를 위해 첫째, 거리 영상의 깊이 변화 부호 값의 분포 특성에 따라 표면을 분류하는 방법을 제안하고자 한다. 또한 평균 곡률과 가우스 곡률을 이용하여 표면을 분류했던 기존 방법을 토대로 그의 문제점이었던 실제 거리 영상에서의 임계치 선정 방법에 대하여 제안하고자 한다. 끝으로 제안한 방법의 유용성을 실험에 의해 입증하고자 한다.

• Journal of Welding and Joining
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• 제28권2호
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• pp.39-46
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• 2010

IIn this study, used is the equivalent loading method based on the inherent strain to predict the welding deformation of panel members. Equivalent loads are computed from the inherent strain distribution around weld line, and then applied for the linear finite element analysis. Thermal deformation of panel members can be, of course, carried out through the rigorous thermal elasto-plastic analysis procedure but it is not practical in applying to predicting the welding deformation of large structures such as blocks found in a ship structure from view of computing time. The present equivalent load approach has been applied to flat plate model to verify the present approach, and to several curved plate models having the curvature in the welding direction to investigate the effect of the longitudinal curvature upon the weld-induced deformation. The results are compared with those by thermal elasto-plastic analysis. As far as the present results are concerned, it can be said that the present approach shows good agreement with the results by welding experiment and the rigorous thermal elasto-plastic analysis. The present approach has been also applied to predict the welding deformation of panel block as for application illustration to practical model.

• 한국해양공학회지
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• 제16권2호
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• pp.38-43
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• 2002

Die-less forming is a cold forming process which is to bend thick flat plates into compound curved plates using two asymmetric rollers. This forming method has several advantages compared with line heating which is widely used to fabricate compound curved pieces in shipyards. The die-less forming, however, has scarcely been studied. Even the deformation mechanism in this forming process has not been understood clearly. So, in this paper, the deformation characteristics of die-less forming is investigated analytically and numerically. for the analytic investigation, slab method based on equilibrium equation is applied. And the mechanism of curvature generation is derived for the asymmetry in roller applied. And three dimensional numerical analyses are performed with realistic modeling of interactions between the rollers and work-piece using finite element program, ABAQUS. It is shown that curvature generation is mainly due to the difference of normal positive strain distribution between the top and bottom surface of the work-piece. And a convex-type curved plate is formed if the center region of the work-piece is rolled with asymmetric rollers of which the lower is larger than the upper in diameter.

• Structural Engineering and Mechanics
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• 제44권6호
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• pp.815-837
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• 2012

A plated beam is strengthened by bonding a thin plate to the tension face; it often fails because of premature debonding of the thin plate from the original beam in a brittle manner. A sound understanding of the mechanism of such debonding failure is very important for the effective use of this strengthening technique. This paper presents an improved analytical solution for interfacial stresses that incorporates multiple loading conditions simultaneously, including prestress, mechanical and thermal loads, and the effects of adherend shear deformations and curvature mismatches between the beam and the plate. Simply supported beams bonded with a thin prestressing plate and subjected to both mechanical and thermal loading were considered in the present work. The effects of the curvature mismatch and adherend shear deformations of the beam and plate were investigated and compared. The main mechanisms affecting the distribution of interfacial stresses were analyzed. Both the normal and shear stresses were found to be significantly influenced by the coupled effects of the elastic moduli with the ratios $E_a/E_b$ and $E_a/E_p$.

• Geomechanics and Engineering
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• 제32권2호
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• pp.179-191
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• 2023

To study the influences of tunneling on the earth pressure and ground settlement when the tunnel passes through the adjacent underground retaining structure, 30 two-dimensional model tests were carried out taking into account the ratios of tunnel excavation depth (H) to lateral width (w), excavation width (B), and excavation distance using a custom-made test device and an analogical soil. Tunnel crossing adjacent existing retaining structure (TCE) and tunnel crossing adjacent newly-built retaining structure (TCN) were simulated and the earth pressure variations and ground settlement distribution during excavation were analyzed. For TCE condition, the earth pressure increments, maximum ground settlement and the curvature of the ground settlement curve are negatively related to H/B, but positively related to H/s and H/w. For TCN condition, most trends are consistent with TCE except that the earth pressure increments and the curvature of ground settlement curve are negatively related to H/w. The maximum ground settlement is larger than that observed in tunnel crossing the existing underground structure. This study provides an assessment basis for the design and construction under confined space conditions.

• 천문학회보
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• 제40권1호
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• pp.66.3-67
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• 2015

Without scrutinizing reflection, the plasma comprising a coronal loop is usually regarded to reside within a flux rope. This picture seems to have been adopted from laboratory plasma pinches, in which a plasma of high density and pressure is confined in the vicinity of the flux rope axis by magnetic tension and magnetic pressure of the concave inward magnetic field. Such a configuration, in which the plasma pressure gradient and the field line curvature vector are almost parallel, however, is known to be vulnerable to ballooning instabilities (to which belong interchange instabilities as a subset). In coronal loops, however, ideal MHD (magnetohydrodynamic) ballooning instabilities are impeded by a very small field line curvature and the line-tying condition. We, therefore, focus on non-ideal (resistive) effects in this study. The footpoints of coronal loops are constantly under random motions of convective scales, which twist individual loop strands quite randomly. The loop strands with the axial current of the same direction tend to coalesce by magnetic reconnection. In this reconnection process, the plasma in the loop system is redistributed in such a way that a smaller potential energy of the system is attained. We have performed numerical MHD simulations to investigate the plasma redistribution in coalescence of many small flux ropes. Our results clearly show that the redistributed plasma is more accumulated between flux ropes rather than near the magnetic axes of flux ropes. The Joule heating, however, creates a different temperature distribution than the density distribution. Our study may give a hint of which part of magnetic field we are looking to in an observation.

• 한국강구조학회 논문집
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• 제14권6호
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• pp.711-720
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• 2002

본 연구에서는 곡선교에서 주행차량에 의한 동적 응답을 보다 정밀하게 구현할 수 있는 3차원 해석 모형을 개발하였다. 원심력에 의한 차량의 롤링운동에 따른 차량의 쏠림현상을 구현하여 곡선교의 대표적인 응답특성인 편경사와 곡률반경에 따른 동적응답과 받침의 변화에 따른 동적 응답 특성을 규명하였으며, 2가지 지점조건에 대하여 주행차량에 의한 곡선교의 동적 특성을 비교 분석하였다. 또한 이와 함께 곡선교에서 어떤 파라미터가 하중 분배에 가장 효율적인가를 비교 분석하였다. 동적해석결과 받침이 외측에 배치된 경우가 중앙에 배치된 경우보다 더 유리하게 분석되었으며, 여러 가지 조건에 따라 하중분배 특성이 다르게 나타남을 알 수 있었다.

• 한국지구과학회지
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• 제34권7호
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• pp.605-614
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• 2013

대부분의 급경사지의 붕괴는 지형적으로 불안정한 지역에서 발생한다. 백두산은 전형적인 산악 지역으로 잠재적 폭발 가능성을 지닌 활화산으로 알려져 있다. 본 연구에서는 백두산지역의 수치고도모형을 이용하여 지형요소와 선구조선 분석을 통해 재해 위험도를 작성하였다. 취약도 분석에 사용되는 요소는 지형으로부터 산정된 방위도, 경사도, 상부사면기여면적, 접선구배곡률, 윤곽구배 곡률, 습윤지수의 분포를 이용하였다. 더불어 선구조의 선밀도도를 작성하여 재해 위험도를 평가하는데 이용하였다. 지형요소를 이용한 백두산지역의 재해위험도 분석 결과 남쪽 내지 남서부 지역의 재해 위험도가 4-5등급으로 높게 나타나고 있다.