• 대한기계학회:학술대회논문집
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• 대한기계학회 2008년도 추계학술대회A
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• pp.418-423
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• 2008

Among various sensitivity evaluation techniques, semi-analytical method is quite popular since this method is more advantageous than analytical method and global finite difference method. However, SAM reveals severe inaccuracy problem when relatively large rigid body motions are identified for individual elements. Such errors result from the numerical differentiation of the pseudo load vector calculated by the finite difference scheme. In the present study, the adjoint variable method combined with complex variable is proposed to obtain the shape and size sensitivity for structural optimization. The complex variable can present accurate results regardless of the perturbation size as well as easy to be implemented. Through a few numerical examples of the static problem for the structural sensitivity, the efficiency and reliability of the adjoint variable method combined with complex variable is demonstrated.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 1998년도 춘계학술대회논문집
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• pp.214-219
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• 1998

Analytic and experimental methods have been used for the characterization of flow behavior of semi-solid Al2024 alloy. Backward extrusion experimnet was chosen to avoid the crack on the unconstrained surface. The material constants for the flow stress by the upper bound technique that agreed with experimental results were determined. The various material constants obtained for al temperature range above the solidus temperature have been fitted and represented in the function of temperature and solid fraction. The obtained result has good agreement only in the high solid fraction.

• 전기의세계
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• 제30권7호
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• pp.448-453
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• 1981

To solve alternating magnetic field problems, the program TDEDDY is developed with the use of the finite element method. Triangular finite elements of the first order are employed for the discretization of the field region. This program is constructed through an interactive system to check errors immediately when every routine is executed, and several subprograms are employed for the graphic representation of computed results. As an example, it is applied to a model of semi-infinite slab excited by an alternating current source. Results by the program TDEDDY show the satisfactory accuracy in comparision with those of analytic calculations.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2009년도 제7회 압연 심포지엄
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• pp.97-102
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• 2009

In hot strip rolling, sound prediction of the temperature of the strip is vital for achieving the desired finishing mill draft temperature (FDT). In this paper, a precision on-line model for the prediction of temperature distributions along the thickness of the strip in the finishing mill is presented. The model consists of an analytic model for the prediction of temperature distributions in the inter-stand zone, and a semi-analytic model for the prediction of temperature distributions in the bite zone in which thermal boundary conditions as well as heat generation due to deformation are predicted by finite element-based, approximate models. The prediction accuracy of the proposed model is examined through comparison with predictions from a finite element process model.

• 대한조선학회논문집
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• 제54권3호
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• pp.227-241
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• 2017

In this study, a Volterra system for the variations of metacentric height (GM) in waves is employed to simulate the parametric roll phenomena of ships in head sea condition. Using the present Volterra system, the transfer function of each harmonic component in the GM variation is computed for different ship models, including mathematical models and a real containership, and the results are validated through the comparison with the values obtained using the direct calculations based on a weakly nonlinear time-domain method. Then, a semi-analytic approach employing a 1-degree of freedom equation for roll motion is developed to simulate the parametric roll motions in irregular waves. In the derived approach, the nonlinear and time-varying restoring forces in the waves are approximated using the Volterra system. Through simulations of the parametric roll for different sea states, the effects of the 1st and 2nd-order harmonic components of the variations in the occurrence and amplitude of the parametric roll motions are investigated. Because of the strong nonlinearities in the phenomena, a stochastic analysis is conducted to examine the statistical properties of the roll motions in consideration of the sensitivities and uncertainties in the computations.

• Structural Engineering and Mechanics
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• 제88권2호
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• pp.189-200
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• 2023

Silicate glass is usually a brittle and plate-like material, and it is difficult to measure the elastic modulus by the traditional method. This paper develops a test method for the glass elastic modulus based on the fundamental frequency of the cantilever beam with an elastic support and a free end. The method installs the beam-type specimen on a semi-rigid support to form an elastic support-free end beam. The analytic solution of the stiffness coefficients of the elastic support is developed by the fundamental frequency of the two specimens with known elastic modulus. Then, the glass elastic modulus is measured by the fundamental frequency of the specimens. The method significantly improves the measurement accuracy and is suitable for the elastic modulus with the beam-type specimen whether the glass is homogeneous or not. Several tests on the elastic modulus measurement are conducted to demonstrate the reliability and validity of the test method.

• Geomechanics and Engineering
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• 제29권2호
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• pp.171-182
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• 2022

Reusing the used pile has not yet been implemented due to the unpredictability of the bearing capacity evolution. This paper presents an analytic approach to estimate the sides shear setup after the dissipation of pore pressure. Long-term evolution of adjacent soil is simulated by viscoelastic-plastic constitutive model. Then, an innovative concept of quasi-overconsolidation is proposed to estimate the strength changes of surrounding soil. Total stress method (α method) is employed to evaluate the long term bearing capacity. Measured data of test piles in Louisiana and semi-logarithmic time function are cited to validate the effectiveness of the presented method. Comparisons illustrate that the presented approach gives a reasonably prediction of the side shear setup. Both the presented method and experiment show the shaft resistance increase by 30%-50%, and this highlight the potential benefit of piles reutilization.

• 한국대기환경학회지
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• 제14권4호
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• pp.303-312
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• 1998

To obtain the solution to the time-dependent particle size distribution of an aerosol undergoing gravitational coagulation, the moment method was used which converts the non linear integro-differential equation to a set of ordinary differential equations. A semi-numerical solution was obtained using this method. Subsequently, an analytic solution was given by approximating the collision kernel into a form suitable for the analysis. The results show that during gravitational coagulation, the geometric standard deviation increases and the geometric mean radius decreases as time increases.

• 한국전산구조공학회논문집
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• 제14권2호
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• pp.135-141
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• 2001

차량 충돌시 자동차의 시트는 승객 및 운전자를 보호해야 한다. 따라서 자동차시트는 충분한 강도를 가져야 하며 이것은 여러 가지 법규에 의해서 제재되고 있다. 물리적 실험 결과가 법규에 정한 규정치를 만족시키기 위해 과대설계 될 수 있다. 그러나 이것은 연비를 줄이기 위한 경량화의 만족이라는 설계요구에 상충한다. 본 논문에서는 헤드레스트 강도시험을 시뮬레이션하고 과대 설계되어 있다고 판단되는 어퍼암을 최적화 모델로 최적설계를 수행하였다. 순차 이차 계획법인 PLBA 알고리즘과 민감도 해석을 위하여 직접근사해석법을 사용하였다.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2011년 춘계학술대회논문집
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• pp.278-285
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• 2011

In the present study, the numerical prediction of the oil amount leaked from the hole of a damaged tank is investigated using the improved MPS (Moving Particle Semi-implicit) method, which was originally proposed by Koshizuka and Oka (1996) for incompressible flow. The governing equations, which consist of the continuity and Navier-Stokes equations, are solved by Lagrangian moving particles, and all terms expressed by differential operators should be replaced by the particle interaction models based on a Kernel function. The simulation results are validated though the comparison with the analytic solution based on Torricelli's equilibrium relation. Furthermore, a series of numerical simulations under the various conditions are performed in order to estimate more accurately the initial amount of leaked oil.