• Title/Summary/Keyword: Boundary shape

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Defect Shape Recovering by Parameter Estimation Arising in Eddy Current Testing

  • Kojima, Fumio
    • Journal of the Korean Society for Nondestructive Testing
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    • v.23 no.6
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    • pp.622-634
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    • 2003
  • This paper is concerned with a computational method for recovering a crack shape of steam generator tubes of nuclear plants. Problems on the shape identification are discussed arising in the characterization of a structural defect in a conductor using data of eddy current inspection. A surface defect on the generator tube ran be detected as a probe impedance trajectory by scanning a pancake type coil. First, a mathematical model of the inspection process is derived from the Maxwell's equation. Second, the input and output relation is given by the approximate model by virtue of the hybrid use of the finite element and boundary element method. In that model, the crack shape is characterized by the unknown coefficients of the B-spline function which approximates the crack shape geometry. Finally, a parameter estimation technique is proposed for recovering the crack shape using data from the probe coil. The computational experiments were successfully tested with the laboratory data.

Level Set Based Shape Optimization of Linear Structures Using Topological Derivatives (Topological Derivative를 이용한 선형 구조물의 레벨셋 기반 형상 최적 설계)

  • Ha Seung-Hyun;Kim Min-Geun;Cho Seon-Ho
    • Proceedings of the Computational Structural Engineering Institute Conference
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    • 2006.04a
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    • pp.299-306
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    • 2006
  • Using a level set method and topological derivatives, a topological shape optimization method that is independent of an initial design is developed for linearly elastic structures. In the level set method, the initial domain is kept fixed and its boundary is represented by an implicit moving boundary embedded in the level set function, which facilitates to handle complicated topological shape changes. The 'Hamilton-Jacobi (H-J)' equation and computationally robust numerical technique of 'up-wind scheme' lead the initial implicit boundary to an optimal one according to the normal velocity field while minimizing the objective function of compliance and satisfying the constraint of allowable volume. Based on the asymptotic regularization concept, the topological derivative is considered as the limit of shape derivative as the radius of hole approaches to zero. The required velocity field to update the H -J equation is determined from the descent direction of Lagrangian derived from optimality conditions. It turns out that the initial holes is not required to get the optimal result since the developed method can create holes whenever and wherever necessary using indicators obtained from the topological derivatives. It is demonstrated that the proper choice of control parameters for nucleation is crucial for efficient optimization process.

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Lip Shape Model and Lip Localization using Shape Clustering (형태 군집화를 이용한 입술 형태 모델과 입술 추출)

  • 장경식
    • Journal of Korea Multimedia Society
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    • v.6 no.6
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    • pp.1000-1007
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    • 2003
  • In this paper, we propose an efficient method for locating lip. The lip shape is represented as a set of points based on Point Distribution Model. We use the Isodata clustering algorithm to find clusters for all training data. For each cluster, a lip shape model is calculated using principle component analysis. For all training data, a lip boundary model is calculated based on the pixel values around the lip boundary. To decide whether a recognition result is correct, we use a cost function based on the lip boundary model. Because of using different models according to the lip shapes, our method can localize correctly the flu far from the mean shape. The experiments have been performed for many images, and show correct recognition rate of 92%.

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Quality Evaluation of the High-purity Limestones for Lime Manufacturing Based on the Measurements of Shape Factor and Grain Boundary Frequency (형상계수 및 경계빈도수 측정에 의거한 생석회 제조용 고품위석회석의 품질 평가)

  • Noh, Jin-Hwan;Lee, Hyun-Chul
    • Journal of the Mineralogical Society of Korea
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    • v.22 no.4
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    • pp.371-383
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    • 2009
  • Crystallinity and textural relations, which are crucial in terms of the quality concept of high-purity limestone, have not been effectively applicable to the limestone evaluation as crude ore due to the difficulties in precise measurements. To overcome the above, as a new method of ore characterization, a measurement of shape factor and grain boundary frequency utilizing the image analysing system was adopted in this study. Some domestic limestones used for lime manufacturing were investigated by such a quality evaluation method, and its results are discussed and correlated each other samples. As the result, even though calcite contents of crude ore, i.e., limestone grade and its crystal size are similar, quality of manufactured lime is remarkably different depending on the degree of shape factor and grain boundary frequency. In other words, as the more irregular in crystal shape and the higher the grain boundary frequency, the manufactured quick lime became more superior in all terms of lime quality such as rate of calcination, porosity, reactivity, sintering and decrepitation effect. However, because the quick lime become easily overheated in case of relatively higher degree in shape factor and grain boundary effect, a technology minimizing heating time is necessary for the manufacturing of high quality lime. In limestone industry, such a ore characterization method will be much more reasonable than the conventional method by measurement of mean size, because the method may collectively comprise crystal shape and other textural factors which can not be numerically evaluated in the past.

On the Hydrodynamic Forces Acting on a Partially Submerged Bag

  • Lee, Gyeong-Joong
    • Selected Papers of The Society of Naval Architects of Korea
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    • v.2 no.1
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    • pp.140-155
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    • 1994
  • The hydrodynamic problem is treated here when a pressurized bag is submerged partially in the water and the end points of it oscillate. SES(Surface Effect Ship) has a bag filled with pressurized air at the stern in order to prevent the air leakage, and the pitch motion of SES is largely affected by the hydrodynamic force of the bag. The shape of a bag can be determined with the pressure difference between inside and outside. Once the hydrodynamic pressure is given, the shape of a bag can be obtained, however in order to calculate the hydrodynamic pressure we should know the shape change of the bag, and vice versa. Therefore the type of boundary condition on the surface of a bag is a moving boundary like a free surface boundary. The present paper describes the formulation of this problem and treats a linearized problem. The computations of the radiation problem for an oscillating bag are shown in comparison with the case that the bag is treated as a rigid body. The hydrodynamic forces are calculated for various values of the pressure inside the bag and the submerged depth.

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Elasto-Plastic Contact Analysis for a Rigid Surface with an Arbitrary Shape in SPH (SPH에서 임의 형상의 강체면에 대한 탄소성 접촉 해석)

  • Seo, Song-Won;Lee, Jae-Hoon;Min, Oak-Key
    • Proceedings of the KSME Conference
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    • 2004.04a
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    • pp.450-455
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    • 2004
  • There is few research about contact problem for a rigid surface with an arbitrary shape in SPH. The variational equation based on the virtual work principle is derived and its solution is obtained by the penalty method. It is proposed a new method that can determine the parameters for a penetration and a penetration rate used in the penalty method. The reproducing condition is adopted to correct the deficiency of kernel on the boundary. In order to calculate a penetration of particles, after checking boundary particles for deformable body boundary normal vectors were determined on the rigid surface. Numerical simulations for models which have rigid surface with an arbitrary shape were conducted to validate the proposed method in 2D. The results of those analysis represent that the contact algorithm proposed in this study works properly.

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SPH Algorithm for an Elasto-Plastic Contact Analysis on a Rigid Surface with an Arbitrary Shape (임의 형상의 강체면 탄소성 접촉 해석을 위한 SPH 알고리듬)

  • Lee Jaehoon;Min Oakkey;Seo Songwon
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.29 no.1 s.232
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    • pp.30-37
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    • 2005
  • There is few research about contact problem for a rigid surface with an arbitrary shape in SPH. The variational equation based on the virtual work principle is derived and its solution is obtained by the penalty method. It is proposed a new method that can determine the parameters for a penetration and a penetration rate used in the penalty method. The reproducing condition is adopted to correct the deficiency of kernel on the boundary. In order to calculate a penetration of particles, after checking boundary particles for deformable body, boundary normal vectors were determined on the rigid surface. Numerical simulations for models which have rigid surface with an arbitrary shape were conducted to validate the proposed method in 2D Cartesian and cylindrical coordinate. The results of those analysis represent that the contact algorithm proposed in this study works properly.

Numerical simulation of coextrusion process of viscoelastic fluids using the open boundary condition method

  • Park, Seung-Joon;Ahn, Kyung-Hyun;Lee, Seung-Jong
    • Korea-Australia Rheology Journal
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    • v.13 no.1
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    • pp.37-45
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    • 2001
  • Numerical simulation of coextrusion process of viscoelastic fluids within a die has been carried out. In the coextrusion process velocity profile at the outflow boundary is not known a priori, which makes it difficult to impose the proper boundary condition at the outflow boundary. This difficulty has been avoided by using the open boundary condition (OBC) method. In this study, elastic viscous stress splitting (EVSS) formulation with streamline upwind (SU) method has been used in the finite element method. In order to test the validity of the OBC method, comparison between the results of fully developed condition at the outlet and those of OBC has been made for a Newtonian fluid. In the case of upper convected Maxwell (UCM) fluid, the effect of outflow boundary condition on the interface position has been investigated by using two meshes having different downstream lengths. In both cases, the results with the OBC method showed reasonable interface shape. In particular, for the UCM fluid the interface shape calculated with OBC was independent of the downstream length, while the results with the zero traction condition showed oscillation of interface position close to the outlet. Viscosity difference was found to be more important than elasticity difference in determining the final interface position. However, the overshoot of interface position near the con-fluent point increased with elasticity.

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Optimum design of blank shape for press forming (최적 프레스가공을 위한 블랭크형상 설계)

  • Kim, Yeong-Seok;Park, Gi-Cheol
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.21 no.7
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    • pp.1141-1148
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    • 1997
  • In the stamping industry the blank shape to be stamped into a designed shape has been conventionally determined from the try out process by the press engineers. The work needs a lot of time and thus leads a loss of productivity. In this study boundary element method for 2-dimensional potential problem was used to design optimum blank shapes for irregular press forming. Here we assumed that the blank is controlled by blank holder only and material flow at blank holder was under potential flow. The developed PC code for designing the optimum blank shape shows that the blank shapes for optimal drawing can be calculated within a few minute in pentium PC and the calculated shapes agree well with the experiments. However the application of this method is constrained only to the pressed product with flat bottom.

Prediction of Nuggest Shape by Finite Element Modeling in Arc-spot Welding (유한요소 모델링을 이용한 아크 스폿 용접의 너깃 형상 예측)

  • 황종근;장경복;김기순;강성수
    • Journal of Welding and Joining
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    • v.17 no.2
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    • pp.84-90
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    • 1999
  • The shape of weld nuggest in arc spot welding of 304 stainless steel was found by searching thermal history of a weld joint through a three-dimensional finite element model. The problem consists of one in which the finite element mesh is growing continuously in time in order to accomodate metal transfer in arc spot welding using element rebirth technique. The analysis was performed on the basis of experimental results. The finite element program MARC, along with a few user subroutines, was employed to obtain the numerical results. Temperature-dependent thermal properties, stir effect in weld pool, effect of phase transformation, and the convective and radiative boundary conditions are included in the model. Numerically predicted shape of weld nuggest is compared with the experimentally observed shape.

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