• Journal of Theoretical and Applied Mechanics
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• 제3권1호
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• pp.66-80
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• 2002

The bilinear formulation proposed earlier by Peters and Izadpanah to develop finite elements in time to solve undamped linear systems, Is extended (and found to be readily amenable) to develop time finite elements to obtain transient responses of both linear and nonlinear, and damped and undamped systems. The formulation Is used in the h-, p- and hp-versions. The resulting linear and nonlinear algebraic equations are differentiated to obtain the first- and second-order sensitivities of the transient response with respect to various system parameters. The present developments were tested on a series of linear and nonlinear examples and were found to yield, when compared with results obtained using other methods, excellent results for both the transient response and Its sensitivity to system parameters. Mostly. the results were obtained using the Legendre polynomials as basis functions, though. in some cases other orthogonal polynomials namely. the Hermite. the Chebyshev, and integrated Legendre polynomials were also employed (but to no great advantage). A key advantage of the time finite element method, and the one often overlooked in its past applications, is the ease In which the sensitivity of the transient response with respect to various system parameters can be obtained. The results of sensitivity analysis can be used for approximate schemes for efficient solution of design optimization problems. Also. the results can be applied to gradient-based parameter identification schemes.

• 대한전기학회논문지:전기기기및에너지변환시스템부문B
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• 제50권4호
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• pp.170-178
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• 2001

Deadbeat technique has been proposed as a digital controller for an UPS inverter to achieve the fast, response to a load variation and to conserve a very low THD under a nonlinear load condition. This scheme contains a fatal drawback, sensitivity against parameter variation and calculation time delay. This paper proposes a second order deadbeat controller, which fundamentally solves the calculation time delay problem and certainly guarantees the robustness of the parameter's variation. RLP(Repetitive Load Predictor) which predicts the load current ahead of two sampling time and FVR(Fundamental Voltage Regulator) which eliminates the fundamental errors of the output voltage are also proposed for the second order deadbeat controller to apply to UPS inverter systems. These are shown theoretically and practically through simulation and experiment.

• International Journal of Naval Architecture and Ocean Engineering
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• 제10권3호
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• pp.259-269
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• 2018

In this study, the second order bending moment induced by sea waves is calculated using the quadratic strip theory. The theory has the fluid forcing terms including the quadratic terms of the hydrodynamic forces and the Froude-Krylov forces. They are applied to a ship as the external forces in order to estimate the second order ship responses by fluid forces. The sensitivity of the second order bending moment is investigated by implementing the quadratic terms by varying the ship side angle for two example ships. As a result, it was found that the second order bending moment changes significantly by the variation of the ship side angle. It implies that increased flare angles at the bow and the stern of ships being enlarged would amplify their vertical bending moments considerably due to the quadratic terms and may make them vulnerable to the fatigue.

• Nuclear Engineering and Technology
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• 제49권1호
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• pp.29-42
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• 2017

The purpose of the present study is the presentation of the appropriate element and shape function in the solution of the neutron diffusion equation in two-dimensional (2D) geometries. To this end, the multigroup neutron diffusion equation is solved using the Galerkin finite element method in both rectangular and hexagonal reactor cores. The spatial discretization of the equation is performed using unstructured triangular and quadrilateral finite elements. Calculations are performed using both linear and quadratic approximations of shape function in the Galerkin finite element method, based on which results are compared. Using the power iteration method, the neutron flux distributions with the corresponding eigenvalue are obtained. The results are then validated against the valid results for IAEA-2D and BIBLIS-2D benchmark problems. To investigate the dependency of the results to the type and number of the elements, and shape function order, a sensitivity analysis of the calculations to the mentioned parameters is performed. It is shown that the triangular elements and second order of the shape function in each element give the best results in comparison to the other states.

• Nuclear Engineering and Technology
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• 제51권4호
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• pp.968-976
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• 2019

This paper presents a number of verification case studies for a recently developed sensitivity/uncertainty code package. The code package, ROMUSE (Reduced Order Modeling based Uncertainty/Sensitivity Estimator) is an effort to provide an analysis tool to be used in conjunction with reactor core simulators, in particular the Virtual Environment for Reactor Applications (VERA) core simulator. ROMUSE has been written in C++ and is currently capable of performing various types of parameter perturbations and associated sensitivity analysis, uncertainty quantification, surrogate model construction and subspace analysis. The current version 2.0 has the capability to interface with the Design Analysis Kit for Optimization and Terascale Applications (DAKOTA) code, which gives ROMUSE access to the various algorithms implemented within DAKOTA, most importantly model calibration. The verification study is performed via two basic problems and two reactor physics models. The first problem is used to verify the ROMUSE single physics gradient-based range finding algorithm capability using an abstract quadratic model. The second problem is the Brusselator problem, which is a coupled problem representative of multi-physics problems. This problem is used to test the capability of constructing surrogates via ROMUSE-DAKOTA. Finally, light water reactor pin cell and sodium-cooled fast reactor fuel assembly problems are simulated via SCALE 6.1 to test ROMUSE capability for uncertainty quantification and sensitivity analysis purposes.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1996년도 하계학술대회 논문집 B
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• pp.749-753
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• 1996

This paper presents a new method for first and second order eigen-sensitivity analysis of system matrix in augmented form. Eigen-sensitivity analysis provides invaluable informations in power system planning and operation. However, conventional eigen-sensitivity analysis methods, which need all the eigenvalues and eigenvectors, can not be applicable to large scale power systems due to large computer memory and computing time required. In the proposed method, all sensitivity computations for a mode are carried out using the augmented system matrix and its own eigenvalue and right & left eigenvectors. In other words sensitivity analysis for a mode does not need informations on the other eigenvalues and eigenvectors and sparsity technique can be fully utilized. Thus compuations can be done very efficiently with moderate computer memory and computing time even for large power systems. The proposed algorithm is tested for one machine infinite bus system.

• 대한전자공학회논문지
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• 제11권3호
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• pp.36-41
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• 1974

임의의 차수의 전진함수의 실현에 전류변환 GIC를 쓰는데 고 admittance변환함수 h(s)가 k/s 되게 하는 경우와 k/s가 되게 하늘 경우와 두가지에 대해서 실현방법을 제시하였다. h(s)=k/s의 방법이 수동회로망에 Capacitor를 표구하지 않은 이점이 있으나 필요한 GIC의 개수가 h(s)=k/s의 경우보다 많아진다. 제시된 두가지 방법으로 2차의 부원함수를 실현하였고 회로소자의 Q와 발진주파수에 대한 Sensitivity를 조사하여 h(s)=k/s 의 방식이 비교적으로 유리함을 밝혔다.

• Structural Engineering and Mechanics
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• 제32권1호
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• pp.167-178
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• 2009

Initial imperfections, such as initial deflection or remaining stress, cause deterioration of buckling strength of structures. The Koiter imperfection sensitivity law has been extended to describe the mechanism of reduction for structures. The extension is twofold: (1) a number of imperfections are considered, and (2) the second order (minor) imperfections are implemented, in addition to the first order (major) imperfections considered in the Koiter law. Yet, in reality, the variation of external loads is dominant over that of imperfection. In this research, probabilistic evaluation of buckling loads against external loads subjected to probabilistic variation is conducted by extending the concept of imperfection sensitivity. A truss arch subjected to dead and live loads is considered as a numerical example. The mechanism of probabilistic variation of buckling strength of this arch is described by the proposed method, and its reliability is evaluated.

• 한국철도학회:학술대회논문집
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• 한국철도학회 1999년도 추계학술대회 논문집
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• pp.566-573
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• 1999

This paper is the result of sensitivity analysis of derailment with respect to the selected suspension elements for the rail vehicle. Derailment phenominon has been explained by the derailment quotient. Thus, the sensitivity of derailment is suggested by a response surface model(RSM) which is a functional relationship between derailment quotient and characteristics of suspension elements. To summarize generation of RSM, we can introduce the procedure of sensitivity analysis as follows. First, to form a RSM, a experiment is performed by a dynamic analysis code, VAMPIRE according to a kind of the design of experiments(DOE). Second, RSM is constructed to a 1$\^$st/ order polynomial and then main effect fators are screened through the stepwise regression. Finally, we can see the sensitivity level through the RSM which only consists of the main effect factors and is expressed by the liner, interaction and quadratic effect terms.

• Structural Engineering and Mechanics
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• 제11권4호
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• pp.373-392
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• 2001

The main idea behind the paper is to present two alternative methods of homogenization of the heat conduction problem in composite materials, where the heat conductivity coefficients are assumed to be random variables. These two methods are the Monte-Carlo simulation (MCS) technique and the second order perturbation second probabilistic moment method, with its computational implementation known as the Stochastic Finite Element Method (SFEM). From the mathematical point of view, the deterministic homogenization method, being extended to probabilistic spaces, is based on the effective modules approach. Numerical results obtained in the paper allow to compare MCS against the SFEM and, on the other hand, to verify the sensitivity of effective heat conductivity probabilistic moments to the reinforcement ratio. These computational studies are provided in the range of up to fourth order probabilistic moments of effective conductivity coefficient and compared with probabilistic characteristics of the Voigt-Reuss bounds.