• 대한기계학회:학술대회논문집
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• 대한기계학회 2004년도 추계학술대회
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• pp.492-497
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• 2004

Three methods for design sensitivity such as numerical differentiation, analytical method and semi-analytical method have been developed for the last three decades. Although analytical design sensitivity analysis is exact, it is hard to implement for practical design problems. Therefore, numerical method such as finite difference method is widely used to simply obtain the design sensitivity in most cases. The numerical differentiation is sufficiently accurate and reliable for most linear problems. However, it turns out that the numerical differentiation is inefficient and inaccurate because its computational cost depends on the number of design variables and large numerical errors can be included especially in nonlinear design sensitivity analysis. Thus semi-analytical method is more suitable for complicated design problems. Moreover semi-analytical method is easy to be performed in design procedure, which can be coupled with an analysis solver such as commercial finite element package. In this paper, implementation procedure for the semi-analytical design sensitivity analysis outside of the commercial finite element package is studied and computational technique is proposed, which evaluates the pseudo-load for design sensitivity analysis easily by using the design variation of corresponding internal nodal forces. Errors in semi-analytical design sensitivity analysis are examined and numerical examples are illustrated to confirm the reduction of numerical error considerably.

• 동력기계공학회지
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• 제15권6호
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• pp.27-34
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• 2011

The increasing capabilities of the computers enable us to utilize various numerical schemes for the time-domain simulations concerned with 3-dimensional free-surface wave problems. There are still difficulties to solve such kind of problems, however. That's because long time simulations with large computational domain are needed in time-domain analysis. So, we need faster and more efficient numerical schemes to get the solutions practically for these problems. In this paper, a high-order spectral/boundary-element method is used for the numerical investigation of physics involved in wave-body interaction. This method is one of the most efficient numerical methods by which the nonlinear gravity waves can be simulated and hydrodynamic forces also can be calculated in time-domain. To get the robust study in these topics, various numerical tests are performed and compared with others' works.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2000년도 춘계학술대회논문집B
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• pp.154-161
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• 2000

As a mass flow controller is widely used in many manufacturing processes for controlling a mass flow rate of gas with accuracy of 1%, several investigators have tried to describe the heat transfer phenomena in a sensor tube of an MFC. They suggested a few analytic solutions and numerical models based on simple assumptions, which are physically unrealistic. In the present work, the heat transfer phenomena in the sensor tube of the MFC are studied by using both experimental and numerical methods. The numerical model is introduced to estimate the temperature profile in the sensor tube as well as in the gas stream. In the numerical model, the conjugate heat transfer problem comprising the tube wall and the gas stream is analyzed to fully understand the heat transfer interaction between the sensor tube and the fluid stream using a single domain approach. This numerical model is further verified by experimental investigation. In order to describe the transport of heat energy in both the flow region and the sensor tube, the Nusselt number at the interface between the tube wall and the gas stream as well as heatlines is presented from the numerical solution.

• 한국수학사학회지
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• 제21권4호
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• pp.153-168
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• 2008

이 연구는 수학교육에서 문제해결의 중요성에 근거하여 초등 수학 우수아들의 문제 푸는 방법에 대해 조사하였다. 조선시대 수학책인 <산학입문>에서 발췌하여 수정한 문제인 노몬의 넓이 구하는 문제가 주어질 때 84명의 초등 수학 우수아의 반응 및 풀이 과정을 분석하여 분류하였다. 이 중 정답을 얻은 학생들(73.8%)이 사용한 접근 방법은 크게 수치적 접근과 재구성 접근의 두 가지로 나뉜다. 두 접근은 다시 각각 세 가지, 여섯 가지 방법으로 세분할 수 있어 각각의 특징을 학생 사례와 함께 고찰하였다. 그 중 동양 수학사에서 이용된 방법을 포함하여 도형의 재구성을 통한 방법은 특히 주목할 만하다 전체 정답자의 절반에 가까운 수가 수치적 접근을 이용하였음에도 불구하고 동일 문제에 대한 다양한 풀이를 관찰할 수 있었고, 그 분석을 통해 학생들의 사고 특징을 파악할 수 있었다.

• Structural Engineering and Mechanics
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• 제75권6호
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• pp.785-797
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• 2020

As the growth of world trade has surged rapidly over the past years, the number is expected to continue growing over the coming years. Although the transportation costs can be reduced by using larger vessels, however, new berthing structures have to be constructed in order to cater for the larger vessels. This leads to a need for researching on designing a better berthing structure. For optimization of berthing structure design, we need to provide a better estimation of berthing energy than the previous methods in the existing guidelines. In this study, several berthing parameters were collected from previous works and researches. Moreover, the scenarios were selected efficiently by using a sampling technique. First, the berthing energy was calculated by executing 150 numerical simulations. Then, the numerical simulation results were compared with the results calculated by existing methods quantitatively to investigate the sensitivity of the berthing parameters and the accuracy of existing methods. The numerical method results have shown some deviation with respect to the existing method results in which the degree of deviation varies with the methods and the tendency of differences is dependent on certain berthing parameters. Then, one of the existing methods which has shown a small deviation was selected as a representative method and applied with several safety factors to obtain a suitable safety factor for the design.

• Journal of the Korean Society for Industrial and Applied Mathematics
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• 제26권4호
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• pp.185-223
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• 2022

The classical equation of Jonathan Homer Lane and Robert Emden, a nonlinear second-order ordinary differential equation, models the isothermal spherical clouded gases under the influence of the mutual attractive interaction between the gases' molecules. In this paper, the Adomian decomposition method (ADM) is presented to obtain highly accurate and reliable analytical solutions of a class of generalised Lane-Emden equations with strong nonlinearities. The nonlinear term f(y(x)) of the proposed problem is given by the integer powers of a continuous real-valued function h(y(x)), that is, f(y(x)) = h^m(y(x)), for integer m ≥ 0, real x > 0. In the end, numerical comparisons are presented between the analytical results obtained using the ADM and numerical solutions using the eighth-order nested second derivative two-step Runge-Kutta method (NSDTSRKM) to illustrate the reliability, accuracy, effectiveness and convenience of the proposed methods. The special cases h(y) = sin y(x), cos y(x); h(y) = sinh y(x), cosh y(x) are considered explicitly using both methods. Interestingly, in each of these methods, a unified result is presented for an integer power of any continuous real-valued function - compared with the case by case computations for the nonlinear functions f(y). The results presented in this paper are a generalisation of several published results. Several examples are given to illustrate the proposed methods. Tables of expansion coefficients of the series solutions of some special Lane-Emden type equations are presented. Comparisons of the two results indicate that both methods are reliably and accurately efficient in solving a class of singular strongly nonlinear ordinary differential equations.

• 한국산학기술학회논문지
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• 제19권3호
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• pp.8-13
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• 2018

외부 충격에 대한 연료탱크의 구조 건전성을 확인하기 위해서는 연료탱크 내부 연료의 거동과 그에 따른 영향성을 파악할 수 있는 유체-구조 연성해석을 수행해야 한다. 과거에는 유체-구조 연성해석을 수행하기 위해서는 상당한 전산자원과 과도한 계산시간이 필요하여 수치해석 결과를 도출하기까지 많은 제약이 있었다. 하지만, 최근 컴퓨터 성능이 획기적으로 향상되어 유체-구조 연성해석 등의 복잡한 수치해석이 가능하게 되었다. 유체-구조 연성해석을 위해 주로 사용되는 방법은 ALE(Arbitrary Lagrangian and Eulerian)와 입자법(Smoothed Particle Hydrodynamic)이 있다. 두 방법에는 상호 장단점이 있기 때문에 수치해석의 목적에 따라 적합한 방법을 적용하는 것이 필요하다. 본 연구에서는 ALE을 적용하여 연료탱크 충돌충격 시험 수치모사를 수행하였다. 수치해석 목적은 충돌충격하중에 의해 컨테이너 내부에 장착된 연료탱크의 파손 가능성을 확인하는 것인데, 수치해석의 결과로 연료탱크 내부의 유체 거동을 파악하고, 충격하중에 의해 연료탱크와 컨테이너 구조물에서 발생하는 응력을 계산하여 연료탱크 파손 여부에 따른 내부 유체의 누설 가능성을 제고하였다.

• 지능정보연구
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• 제7권1호
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• pp.27-45
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• 2001

데이터마이닝에서 시계열 데이터로부터 순차패턴을 발견하는 연구는 사건이나 아이템이 주로 연구되어왔지만, 최근에는 설비의 상태를 알 수 있는 센서와 같은 수치 값의 형태를 가지는 분야에 관심을 가지게 되었다. 그러나 수치 형태의 데이터는 패턴을 만드는 동안 동일한 값을 가지는 경우가 거의 없기 때문에 기존의 사건이나 아이템 등으로 변환될 수 있는 패턴요소의 특징을 만드는 것이 가장 중요하다. 이러한 패턴요소를 발견하는 지금가지 방법은 이동 윈도우와 클러스터링을 사용하는 방법을 적용하였는데, 이러한 방법은 다양한 윈도우의 크기와 클러스터 값을 적용하여 반복적으로 작업을 하며, 찾아진 결과를 해석하는데도 많은 문제가 있다. 본 연구는 수치 값을 가진 데이터를 벡터의 형태로 만들어 패턴요소를 만드는 방법을 제시한다. 이렇게 만들어진 패턴요소는 전체 데이터를 사용하는 것 보다 이해되기 쉽고 보다 빠르게 순차패턴을 찾을 수 있다. 벡터로 변환된 패턴요소는 각도와 크기를 가지는데 우리는 이들 벡터들의 상호 연관성을 정의하고, 이들 연관성을 이용하여 순차패턴을 찾는 방법을 제시한다.

• Smart Structures and Systems
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• 제30권1호
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• pp.49-62
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• 2022

Experimental and discrete element methods were used to investigate the effects of triple joints lengths and triple joint angle on the failure behavior of rock mass under uniaxial compressive test. Concrete samples with dimension of 20 cm × 20 cm × 5 cm were prepared. Within the specimen, three imbedded joint were provided. The joint lengths were 2 cm, 4cm and 6 cm. In constant joint lengths, the angle between middle joint and other joints were 30°, 60°, 90°, 120° and 150°. Totally 15 different models were tested under compression test. The axial load rate on the model was 0.05 mm/min. Concurrent with experimental tests, the models containing triple joints, length and joint angle are similar to the experiments, were numerical by Particle flow code in two dimensions (PFC2D). Loading rate in numerical modelling was 0.05 mm/min. Tensile strength of material was 1 MPa. The results show that the failure behaviors of rock samples containing triple joints were governed by both of the angle and the length of the triple joints. The uniaxial compressive strengths (UCS) of the specimens were related to the fracture pattern and failure mechanism of the discontinuities. Furthermore, it was shown that the compressive behavior of discontinuities is related to the number of the induced tensile cracks which are increased by decreasing the joint length. Along with the damage failure of the samples, the acoustic emission (AE) activities are excited. There were only a few AE hits in the initial stage of loading, then AE hits rapidly grow before the applied stress reached its peak. In addition, every stress drop was accompanied by a large number of AE hits. Finally, the failure pattern and failure strength are similar in both methods i.e., the experimental testing and the numerical simulation methods.

• 한국국방경영분석학회지
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• 제23권2호
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• pp.45-71
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• 1997

There has been considerable research recently on uncertainty handling in the fields of artificial intelligence and knowledge-based system. Various numerical and non-numerical methods have been proposed for representing and propagating uncertainty in knowledge-based system. The Bayesian method, the Dempster-Shafer's Evidence Theory, the Certainty Factor model and the Fuzzy Set Theory are most frequently appeared in the knowledge-based system. Each of these four methods views uncertainty from a different perspective and propagates it differently. There is no single method which can handle uncertainty properly in all kinds of knowledge-based systems' domain. Therefore a knowledge-based system will work more effectively when the uncertainty handling method in the system fits to the system's environment. This paper proposed a framework for selecting proper uncertainty handling methods in knowledge-based system with respect to characteristics of problem domain and cognitive styles of experts. A schema with strategic/operational and unstructured/structured classification is employed to differenciate domain. And a schema with systematic/intuitive and preceptive/receptive classification is employed to differenciate experts' cognitive style. The characteristics of uncertainty handling methods are compared with characteristics of problem domains and cognitive styles respectively. Then a proper uncertainty handling method is proposed for each category.