• Nuclear Engineering and Technology
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• 제55권6호
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• pp.2230-2245
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• 2023

KANT (KAIST Advanced Nuclear Tachygraphy) is a PWR core simulator recently developed at Korea Advance Institute of Science and Technology, which solves three-dimensional steady-state and transient multigroup neutron diffusion equations under Cartesian geometries alongside the incorporation of thermal-hydraulics feedback effect for multi-physics calculation. It utilizes the standard Nodal Expansion Method (NEM) accelerated with various Coarse Mesh Finite Difference (CMFD) methods for neutronics calculation. For thermal-hydraulics (TH) calculation, a single-phase flow model and a one-dimensional cylindrical fuel rod heat conduction model are employed. The time-dependent neutronics and TH calculations are numerically solved through an implicit Euler scheme, where a detailed coupling strategy is presented in this paper alongside a description of nodal equivalence, macroscopic depletion, and pin power reconstruction. For validation of the steady, transient, and depletion calculation with pin power reconstruction capacity of KANT, solutions for various benchmark problems are presented. The IAEA 3-D PWR and 4-group KOEBERG problems were considered for the steady-state reactor benchmark problem. For transient calculations, LMW (Lagenbuch, Maurer and Werner) LWR and NEACRP 3-D PWR benchmarks were solved, where the latter problem includes thermal-hydraulics feedback. For macroscopic depletion with pin power reconstruction, a small PWR problem modified with KAIST benchmark model was solved. For validation of the multi-physics analysis capability of KANT concerning large-sized PWRs, the BEAVRS Cycle1 benchmark has been considered. It was found that KANT solutions are accurate and consistent compared to other published works.

• 한국콘텐츠학회논문지
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• 제8권10호
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• pp.37-44
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• 2008

논문은 암호문 송신 중 전송 오류에 의한 암복호화의 문제에 대한 해결책을 제시 한다. 블록 암호 알고리즘은 산사태(avalanche) 효과로 인해 단일 비트 오류에 대해서도 많은 비트에 오류를 발생시킨다. 이를 해결하기 위해 재배열 과정과 간단한 오류 정정 코드를 이용해서 산사태(avalanche) 효과에 강인한 방안을 제안한다. 재배열 과정은 간단한 오류 정정 코드를 사용하기 위한 것이다. 재배열 과정은 한 프레임 내에서 전송의 기본 단위인 n-비트 블록 내에 1비트의 단일 오류만이 존재 할 수 있도록 오류를 여러 단위에 분산시키는 역할을 하게 된다. 즉, n-비트 내에서 단일 오류만이 존재하게 되어 단일 오류 정정 코드로 쉽게 복원이 가능하게 된다. 이 방식은 보다 큰 데이터 단위에 확장하여 사용 될 수 있다.

• 한국전산유체공학회지
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• 제4권1호
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• pp.53-61
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• 1999

Two-dimensional, unsteady, incompressible and compressible Navier-Stokes codes are developed for the computation of the viscous turbulent flow over high-lift airfoils. The compressible code involves a conventional upwind-differenced scheme for the convective terms and LU-SGS scheme for temporal integration. The incompressible code with pseudo-compressibility method also adopts the same schemes as the compressible code. Three two-equation turbulence models are evaluated by computing the flow over single and multi-element airfoils. The compressible and incompressible codes are validated by predicting the flow around the RAE 2822 transonic airfoil and the NACA 4412 airfoil, respectively. In addition, both the incompressible and compressible code are used to compute the flow over the NLR 7301 airfoil with flap to study the compressible effect near the high-loaded leading edge. The grid systems are efficiently generated using Chimera overlapping grid scheme. Overall, the κ-ω SST model shows closer agreement with experiment results, especially in the prediction of adverse pressure gradient region on the suction surfaces of high-lift airfoils.

• Steel and Composite Structures
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• 제38권5호
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• pp.477-496
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• 2021

The main objective of this paper is to study vibration of sandwich open cylindrical panel with damaged core and FG face sheets based on three-dimensional theory of elasticity. The structures are made of a damaged isotropic core and two external face sheets. These skins are strengthened at the nanoscale level by randomly oriented Carbon nanotubes (CNTs) and are reinforced at the microscale stage by oriented straight fibers. These reinforcing phases are included in a polymer matrix and a three-phase approach based on the Eshelby-Mori-Tanaka scheme and on the Halpin-Tsai approach, which is developed to compute the overall mechanical properties of the composite material. Three complicated equations of motion for the panel under consideration are semi-analytically solved by using 2-D differential quadrature method. Several parametric analyses are carried out to investigate the mechanical behavior of these multi-layered structures depending on the damage features, through-the-thickness distribution and boundary conditions. It is seen that for the large amount of power-law index "P", increasing this parameter does not have significant effect on the non-dimensional natural frequency parameters of the FG sandwich curved panel. Results indicate that by increasing the value of isotropic damage parameter "D" up to the unity (fully damaged core) the frequency would tend to become zero. One can dictate the fiber variation profile through the radial direction of the sandwich panel via the amount of "P", "b" and "c" parameters. It should be noticed that with increase of volume fraction of fibers, the frequency parameter of the panels does not increase necessarily, so by considering suitable amounts of power-law index "P" and the parameters "b" and "c", one can get dynamic characteristics similar or better than the isotropic limit case for laminated FG curved panels.

• Steel and Composite Structures
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• 제48권1호
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• pp.1-17
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• 2023

The main goal of this paper is to study vibration of damaged core laminated sectorial plates with Functionally graded (FG) face sheets based on three-dimensional theory of elasticity. The structures are made of a damaged isotropic core and two external face sheets. These skins are strengthened at the nanoscale level by randomly oriented Carbon nanotubes (CNTs) and are reinforced at the microscale stage by oriented straight fibers. These reinforcing phases are included in a polymer matrix and a three-phase approach based on the Eshelby-Mori-Tanaka scheme and on the Halpin-Tsai approach, which is developed to compute the overall mechanical properties of the composite material. Three complicated equations of motion for the sectorial plates under consideration are semi-analytically solved by using 2-D differential quadrature method. Using the 2-D differential quadrature method in the r- and z-directions, allows one to deal with sandwich annular sector plate with arbitrary thickness distribution of material properties and also to implement the effects of different boundary conditions of the structure efficiently and in an exact manner. The fast rate of convergence and accuracy of the method are investigated through the different solved examples. The sandwich annular sector plate is assumed to be simply supported in the radial edges while any arbitrary boundary conditions are applied to the other two circular edges including simply supported, clamped and free. Several parametric analyses are carried out to investigate the mechanical behavior of these multi-layered structures depending on the damage features, through-the-thickness distribution and boundary conditions.

• 대한기계학회논문집B
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• 제27권10호
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• pp.1457-1463
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• 2003

In this paper, the response surface method using three-dimensional Navier-Stokes analysis to optimize the shape of a multi-blade centrifugal fan, is described. For numerical analysis, Reynolds-averaged Navier-Stokes equations with standard k - c turbulence model are transformed into non-orthogonal curvilinear coordinate system, and are discretized with finite volume approximations. Due to the large number of blades in this centrifugal fan, the flow inside of the fan is regarded as steady flow by introducing the impeller force models for economic calculations. Linear Upwind Differencing Scheme(LUDS) is used to approximate the convection terms in the governing equations. SIMPLEC algorithm is used as a velocity-pressure correction procedure. Design variables, location of cur off, radius of cut off, expansion angle of scroll and width of impeller were selected to optimize the shapes of scroll and blades. Data points for response evaluations were selected by D-optimal design, and linear programming method was used for the optimization on the response surface. As a main result of the optimization, the efficiency was successfully improved. It was found that the optimization process provides reliable design of this kind of fans with reasonable computing time.

• 소음진동
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• 제8권4호
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• pp.632-642
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• 1998

A method based on finite element discretization is developed for optimizing the polarization profile of PVDF film to create the modal transducer for specific modes. Using this concept, one can design the modal transducer in two-dimensional structure having arbitrary geometry and boundary conditions. As a practical means for implementing this polarization profile without repoling the PVDF film the polarization profile is approximated by optimizing electrode patterns, lamination angles, and poling directions of the multi-layered PVDF transducer. This corresponds to the approximation of a continuous function using discrete values. The electrode pattern of each PVDF layer is optimized by deciding the electrode of each finite element to be used or not. Genetic algorithm, suitable for discrete problems, is used as an optimization scheme. For the optimization of each layers lamination angle, the continuous lamination angle is encoded into discrete value using binary 5 bit string. For the experimental demonstration, a modal sensor for first and second modes of cantilevered composite plate is designed using two layers of PVDF films. The actuator is designed based on the criterion of minimizing the system energy in the control modes under a given initial condition. Experimental results show that the signals from residual modes are successfully reduced using the optimized multi-layered PVDF sensor. Using discrete LQG control law, the modal peaks of first and second modes are reduced in the amount of 12 dB and 4 dB, resepctively.

• International Journal of Precision Engineering and Manufacturing
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• 제8권2호
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• pp.59-63
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• 2007

We propose a controller design analysis for a cross-coupling control system, which is essential for achieving high contouring accuracy in multi-axis CNC systems. The proposed analysis combines three axial controllers for each individual feed drive system together with a cross-coupling controller at the beginning of the design stage in an integrated manner. These two types of controllers used to be separately designed and analyzed since they have different control objectives. The proposed scheme is based on a mathematical formulation of a three-dimensional contour error model and includes a stability analysis for the overall control system and a performance analysis in terms of contouring and tracking accuracy at steady state. A computer simulation was used to demonstrate the validity of the proposed methodology. The performance variation was investigated under different operating conditions and controller gains, and a design range was elicited that met the given performance specifications. The results provide basic guidelines in systematic and comprehensive controller designs for multi-axis CNC systems. A cross-coupling control system was also implemented on a PC-based three-axis CNC testbed, and the experimental results confirmed the usefulness of the proposed control system in terms of contouring accuracy.

• 정보처리학회논문지D
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• 제12D권2호
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• pp.233-246
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• 2005

멀티미디어 데이터를 위한 내용기반 검색 서비스의 속도를 증진하기 위해 다차원 색인 기법에 대한 연구가 활발하게 진행되고 있다. 다차원 색인 기법의 하나인 M-트리는 노드의 중심점과 객체간의 상대적 거리를 이용하여 색인을 구성하고, 검색 공간에 포함되는 객체를 액세스하는 기법으로서 노드들은 페이지 단위로 구성되며 하위 엔트리들을 포함할 수 있는 반경, 즉 유사도 거리에 의해 노드의 영역이 표현되어진다. 그러나 이와 같은 노드의 영역 표현에 있어서 노드 색인 공간의 중첩으로 인해 질의 시 검색해야 하는 노드수가 증가하고 이는 거리계산과 디스크 입출력의 횟수를 증가시킨다. 본 논문에서는 M-트리에서 문제가 되고 있는 노드 색인 공간 중첩을 최소화하는 노드 분할 정책을 제안한다. M-트리의 기존 분할 정책들과는 다르게 노드의 가상 중심점을 계산하여 라우팅 객체로 이용하여 노드 색인 공간의 중첩을 최소화하고 노드 안의 엔트리 재분배를 통해 노드의 색인 공간의 크기를 작게 유지하며 밀도 높은 노드를 구성하도록 한다. 실험으로부터 제안된 노드 분한 알고리즘이 라우팅 노드의 색인 공간의 반경을 작게 유지하며 결과적으로는 사용자 질의에 대해 개선된 응답 시간을 제공하는 것으로 판명되었다.

• 한국통신학회논문지
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• 제29권3B호
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• pp.339-348
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• 2004

패킷 분류근 인터넷 망에서 QoS(Quality of Service)보장, VPN(Virtual Private Network)등과 같은 사용자들의 다양한 서비스를 수용하기 위한 중요한 요소이다. 패킷 헤더는 기본적으로 IP(Internet Protocol) 패킷 헤더 내의 목적지 주소뿐만 아니라 발신지 주소, 프로토콜, TCP(Transmission Control Protocol)포트 번호 등 여러 필드들을 조합하여 룰 테이블로부터 best matching 룰을 찾는 것이다. 본 논문에서는 멀티 비트 트라이 구조의 트리 비트맵을 이용하여 하드웨어적인 룰 검색이 가능한 패킷 분류 기법을 제안한다. 검색 대상 필드 및 패킷 분류 룰을 구성하는 프레픽스를 비교 단위가 되는 일정한 비트 크기의 멀티 비트로 나누고, 이와 같이 구분된 멀티 비트 단위로 트리 비트맵 기반의 룰 검색 기능을 수행한다. 제안한 기법은 프레픽스의 일정한 상위 비트들에 대해서는 인덱싱 키로 사용하여 룰 검색을 위한 메모리 액세스 횟수를 줄이도록 하였다. 또한 룰 검색시 성능 저하를 초래하는 백트랙킹이 발생하지 않도록 하기 위하여 룰 테이블 구축시 마커 프레픽스에 대한 처리 기법을 제안하였다 그리고 본 논문에서는 IPMA(Internet Performance Measurement Analysis) 프로젝트에서 제공하는 라우팅 테이블의 프레픽스들을 이용하여 2차원 즉, 목적지 주소와 발신지 주소의 2필드로 구성되는 랜덤 룰 셋을 생성하고 제안한 기법에 대한 메모리 소요량 및 성능 비교를 하였다.