• Structural Engineering and Mechanics
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• 제88권5호
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• pp.439-449
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• 2023

Non-linear vibration characteristics of functionally graded CNT-reinforced composite (FG-CNTRC) cylindrical shell panel on elastic foundation have not been sufficiently examined. In this situation, this study aims at the profound numerical investigation of the non-linear vibration response of FG-CNTRC cylindrical panels on Winkler-Pasternak foundation by introducing an accurate and effective 2-D meshfree-based non-linear numerical method. The large-amplitude free vibration problem is formulated according to the first-order shear deformation theory (FSDT) with the von Karman non-linearity, and it is approximated by Laplace interpolation functions in 2-D natural element method (NEM) and a non-linear partial derivative operator H_NL. The complex and painstaking numerical derivation on the curved surface and the crucial shear locking are overcome by adopting the geometry transformation and the MITC3+ shell elements. The derived nonlinear modal equations are iteratively solved by introducing a three-step iterative solving technique which is combined with Lanczos transformation and Jacobi iteration. The developed non-linear numerical method is estimated through the benchmark test, and the effects of foundation stiffness, CNT volume fraction and functionally graded pattern, panel dimensions and boundary condition on the non-linear vibration of FG-CNTRC cylindrical panels on elastic foundation are parametrically investigated.

• 한국해양공학회지
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• 제22권6호
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• pp.75-82
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• 2008

Flame bending has been extensively used in the shipbuilding industry for hull plate forming In flame bending it is difficult to obtain the desired shape because the residual deformation dependson the complex temperature distribution and the thermal plastic strain. Mechanical bending such as reconfigurable press forming multi-point press forming or die-less forming has been found to improve the automation of hull plateforming because it can more accurately control the desired shape than line heating. Multi-point forming is a process in which external forces are used to form metal work-pieces. Therefore it can be a flexible and efficient forming technique. This paper presents an optimal approach to determining the press-stroke for multi-point press forming of curved shapes. An integrated configuration of Finite element analysis (FEA) and spring-back compensation algorithm is developed to calculate the strokes of the multi-point press. Not only spring-back is modeled by elastic plastic shell elements but also an iterative algorithm to compensate the spring-back is applied to adjust the amount of pressing stroke. An iterative displacement adjustment (IDA) method is applied by integration of the FEA procedure and the spring-back compensation work. Shape deviation between the desired surface and deform￡d plate is minimized by the IDA algorithm.

• 한국음향학회지
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• 제42권4호
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• pp.305-312
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• 2023

기포 크기 분포를 음파 감쇄 손실을 이용하여 역산하기 위해 Physics-Informed Neural Network(PINN)을 사용하였다. 역산에 사용되는 선형시스템을 풀기 위해 이미지 처리 분야에서 선형시스템 문제를 해결한 Adaptive Learned Iterative Shrinkage Thresholding Algorithm(Ada-LISTA)를 PINN의 신경망 구조로 이용하였다. 더 나아가, PINN의 손실함수에 선형시스템 기반의 정규항을 포함함으로써 PINN의 해가 기포 물리 법칙을 만족하여 더 높은 일반화 성능을 가지도록 하였다. 그리고 기포 추정값의 불확실성을 계산하기 위해 딥앙상블 기법을 이용하였다. 서로 다른 초기값을 갖는 20개의 Ada-LISTA는 같은 훈련데이터를 이용하여 학습되었다. 이 후 테스트시 훈련데이터와 다른 경향의 감쇄 손실을 입력으로 사용하여 기포 크기 분포를 추정하였고, 추정값과 이에 대한 불확실성을 20개 추정값의 평균과 분산으로 각각 구하였다. 그 결과 딥앙상블이 적용된 Ada-LISTA는 기존 볼록 최적화 기법인 CVX보다 기포 크기 분포를 역산하는데 더 우수한 성능을 보였다.

• 한국해양공학회지
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• 제23권1호
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• pp.135-139
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• 2009

In the line heating for the plate forming of a ship's hull, an in line assessment of completion is necessary for an automated production system. In the current curved plate forming process, a fabricated plate is compared to a template that is made in the mold loft and is used for the determination of the heating line for the next step. In this paper, a new method is presented for the in line assessment of completion for curved plate forming. This method uses a 3-D scanner. For the registration of the scanned data for a surface and the target surface, the ICP (Iterative Closest Points) method was adopted. A computer program was developed to carry out the registration, check for similarities, visualize the surface, and control the results. This program was applied to a sample curved plate forming process.

• International Journal of Naval Architecture and Ocean Engineering
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• 제4권4호
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• pp.353-361
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• 2012

All current shipyards are using the customized CAD/CAM programs in order to improve the design quality and increase the design efficiency. Even though the data structures for ship design and construction are almost completed, the implementation related to the ship design processes are still in progress so that it has been the main causes of the bottleneck and delay during the middle of design process. In this study, we thought that the hole-plan system would be a good example which is remained to be improved. The people of outfitting division who don't have direct authority to edit the structural panels, should request the hull design division to install the holes for the outfitting equipment. For acceptance, they should calculate the hole position, determine the hole type, and find the intersected contour of panel. After consideration of the hull people, the requested holes are manually installed on the hull structure. As the above, many processes are needed such as communication and discussion between the divisions, drawings for hole-plan, and the consideration for the structural or production compatibility. However this iterative process takes a lot of working time and requires mental pressure to the related people and cross-division conflict. This paper will handle the hole-plan system in detail to automate the series of process and minimize the human efforts and time-consumption.

• 전자공학회논문지SC
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• 제41권6호
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• pp.27-35
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• 2004

유한 필드, 즉 Galois 필드는 에러 정정 코드, 디지털 신호처리, 암호법(cryptography)와 같은 광범위한 응용 분야에 사용되고 있다. 이 응용들은 종종 GF(2/sup m/)에서 지수제곱 연산을 필요로 한다. 기존에 제안되었던 방법들은 지수제곱 연산을 반복, 순환적인 곱셈으로 구현하여 계산시간이 많이 걸리거나, 또는 구현 시 하드웨어 구조가 복잡하여 하드웨어 비용이 큰 경우가 많았다. 본 논문에서는 지수제곱 연산을 하는 효과적인 방법을 제안하고 이를 VHDL로 구현하였다. 이 회로는 지수의 각 비트에 해당하는 곱셈 항들을 계산하고 이 들을 곱함으로써 지수제곱 연산을 계산한다. 과거에는 이 알고리즘이 원시 다항식의 근의 지수제곱 연산을 계산하는 데 사용되는 것으로 국한되어 있었으나, 본 논문에서는 이 알고리즘을 GF(2/sup m/)의 임의의 원소의 지수제곱 연산으로 확장하였다.

• Computers and Concrete
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• 제23권3호
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• pp.161-170
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• 2019

This paper aims at presenting a numerical method for estimating the elastic modulus of recycled concrete with crushed aggregates. In the method, polygonal aggregates following a given sieve curve are generated, and placed into a square simulation element with the aid of the periodic boundary condition and the overlap criterion of two polygonal aggregates. The mesostructure of recycled concrete is reconstructed by embedding an old interfacial transition zone (ITZ) layer inside each recycled aggregate and by coating all the aggregates with a new ITZ layer. The square simulation element is discretized into a regular grid and a representative point is selected from each sub-element. The iterative method is combined with the fast Fourier transform to evaluate the elastic modulus of recycled concrete. After the validity of the numerical method is verified with experimental results, a sensitivity analysis is conducted to evaluate the effects of key factors on the elastic modulus of recycled concrete. Numerical results show that the elastic modulus of recycled concrete increases with the increase of the total aggregate content and the elastic moduli of old and new ITZ but decreases with increasing the replacement ratio of recycled aggregate and the thicknesses of old and new ITZ. It is also shown that, for a replacement ratio of recycled aggregate smaller than 0.3, the elastic modulus of recycled concrete is reduced by no more than 10%.

• 한국전산구조공학회논문집
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• 제29권2호
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• pp.123-130
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• 2016

선박 건조 시장의 요구를 맞추기 위하여 신속한 건조의 목표로 노력하고 있는 조선소가 선박 정도관리에 대한 요구가 갈수록 높아지고 있다. 선박 건조 공정에서 생산성의 향상과 생산 주기의 단축을 위하여 선박 부재의 정도평가를 전 주기에서 수행해야 하는 것은 중요하다. 선박의 품질을 높이기 위하여 조선소에서 블록의 정도제어를 수행하는 것은 선박의 건조 주기를 단축할 수 있을 뿐만 아니라 건조 비용도 줄일 수 있다. 선박 블록의 정도를 제어하는 중심은 선박 블록 통합 정도관리 시스템을 만들어야 한다. 이 시스템은 "Non-allowance Shipbuilding"의 목표로 정도관리의 총괄성, 블록 정도의 향상, 정도 관리 과정의 표준화 등이 이루어져야 한다. 일반적으로 정도관리를 수행하는 관리자가 광파측정기를 이용하여 선박 블록의 접합면에 있는 주요 포인트(vital point)를 측정하고 수집하지만 무거운 계측장비를 가지고 블록의 정도관리를 수행하는 것은 불편할 뿐만 아니라 시간도 오래 걸린다. 본 논문에서는 선박 블록의 정도관리 시간을 단축할 수 있는 포인트 클라우드 기반으로 3차원 레이저 스캐너를 이용한 선박 블록 탑재 전에 오차예측 방법을 제안하였다. 이 방법은 ICP(iterative closest point) 알고리즘으로 측정된 포인트 클라우드와 설계된 점들의 비교 작업을 수행한 다음에 허용범위 내의 오차를 만족하는 지를 판단한다.

• 한국해양공학회지
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• 제25권4호
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• pp.18-22
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• 2011

The Ranking source panel method was used to predict the flow phenomenon of a ship with a goose-neck type bulbous bow penetrating the free surface. The non-linearity of the free surface boundary condition was fully satisfied using an iterative calculation method, and the raised panel method was adopted to obtain a more stable solution at each iteration step. The panel cutting method was applied to generate a hull calculation grid at each iteration step, including the first step. At that time, the nose of the goose-neck type bulbous bow was divided by the free surface and the free surface panel was modified at each iteration step using the variable free surface panel method. Numerical calculations were performed to investigate the validity and efficiency of the applied numerical algorithm using the 3600 TEU container carrier. The computed wave resistance coefficients were compared with the experimentally achieved residual resistance coefficients.

• 대한조선학회논문집
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• 제48권6호
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• pp.528-538
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• 2011

As a forming method for curved hull plates more efficient than the flame bending, mechanical bending using multi point press forming and die-less forming is discussed in this paper. the mechanical forming is a flexible manufacturing system for automatically forming of hull parts. It is especially suited to varied curved parts. This paper discusses a multiple point pressing machine composed of a pair of reconfigurable punches in order to achieve the rapid forming of curved hull plates using division forming and presents how forming information is obtained from the given design surface. Although the mechanical forming can be efficient in the metal forming, spring back after pressing is a phenomenon which must be carefully considered when quantifying the process variables. If the spring back is not accurately controlled, the fabricated shell plate cannot meet assembly tolerance. This paper describes the principles to calculate the proper stroke of each punch at the divided areas. the strokes are determined by an iterative process of sequential pressing and spring back compensation from an unfolded flat shape to its given design surface. FEA(finite element analysis) is used to simulate the spring back of the plate and the IDA(iterative displacement adjustment) method adjusts the offset of pressing punches from the deformation results and the design surface. The shape deviations of two surfaces due to spring back are compensated by integrated system using FEA and IDA method. For the practical application, It is aimed to develop an integrated system that can automatically perform the compensation process and calculate strokes of punches of the double sides' reconfigurable multiple-press machine and some experimental results obtained with mechanical bending are presented.