• 인터넷정보학회논문지
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• 제7권1호
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• pp.39-47
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• 2006

MD4를 기반으로 하는 MDx계열 해쉬 함수는 입력 워드의 치환, 순환 시프트 변수의 연쇄, 비선형 함수 등을 이용하여 구성된다. 그러나, 그 구성 방법에 대한 이론적, 실험적 배경은 알려져 있지 않고, 평가를 위한 일반적인 모델도 알려져 있지 않다. 본 논문에서는 해쉬 함수의 설계와 평가를 위하여 해쉬 함수를 일반화하기 위한 근사 모델을 제안하고, MD5에 근사모델을 적용하여 입력 차분의 확산을 고찰하였다. 그 결과, MD5의 약점이 완전 확산을 제공하지 않는데 있다는 것을 확인하였다. 제안된 근사 모델에서 완전 확산을 제공하기 위하여 해쉬 함수 내에 여러 가지 연쇄 패턴을 이용하는 다중 연쇄 패턴을 제안하고, 여분의 계산과 메모리 없이 완전 확산을 제공함을 MD5를 이용한 실험을 통하여 보이고, 그 차분 특성이 갖는 확률이 MD5보다 작음을 증명하였다.

• Biotechnology and Bioprocess Engineering:BBE
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• 제5권1호
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• pp.65-70
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• 2000

An approximated analytical solution of mathematical model for the three phase fluidized bed bioreactor (TFBBR) was proposed using the linearization technique to describe oxygen utilization rate in wastewater treatment. The validation of the model was done in comparison with the experimental results. Satisfactory agreement was obtained in the comparison of approximated analytical solution and numerical solution in the oxygen concentration profile of a TFBBR. The approximated solutions for three modes of the liquid phase flow were compared. The proposed model was able to predict the biomass concentration, dissolved oxygen concentration the height of efficient column, and the removal efficiency.

• 전자공학회논문지A
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• 제32A권1호
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• pp.45-52
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• 1995

A new Kirchhoff approximation(KA) method was proposed for microwave scttering from randomly rough surfaces. Using the spectral representation of delta function and its sifting theorem, a new KA was formulated directly without any further approximation, and this formulated was used to compute exact backscttering coefficients. The validity of the KA was verified by a numerical method, and this new KA technique was used to evaluate the existing approximated KkA methods; i.t., the zeroth-order and the first-order approximated physical optics(PO) models. It was shown that the first-order approximated PO model has small error than the zeroth-order approximated PO model at low incidence angles and the opposite happens at higher incidence angles. This new KA model can be used to compute exact scattering coefficients in the validity regions of KA and to evaluate other theoretical and numerical models for scattering from randomly rough surfaces.

• 한국소음진동공학회논문집
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• 제22권8호
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• pp.748-755
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• 2012

Friction causes self-excited vibration, stick-slip vibration and any other friction-induced phenomena. That kinds of vibrations cause chatter and squeal. In order to predict such vibrations accurately, employing an accurate friction model is very important because a dynamic behavior of a system with friction is dominantly governed by a friction model. A Coulomb friction model is the most widely known model. Coulomb friction model is useful model to obtain analytical solutions of the system with friction and the model gives relatively good simulation result. However, defining a friction force at a stick state in simulation is hard because of the characteristic itself and a Coulomb friction model is discontinuous function between a static and a dynamic friction coefficient. Therefore, applying the Coulomb friction model to a simulation is not appropriate. In order to resolve these problems, an approximated Coulomb friction model was developed using simple and continuous function. However, an approximated Coulomb friction model cannot realize stick. Therefore, an approximated Coulomb friction model cannot describe friction phenomena accurately. In order to analyze a friction phenomenon accurately, a friction model for a simulation was proposed in this paper. A proposed friction model realizes stick and gives reasonably good results compared to results obtained by the simulation employing an approximated Coulomb friction model. Accuracy of a proposed friction model was verified by comparing experimental results.

• 전자공학회논문지A
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• 제31A권4호
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• pp.77-83
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• 1994

In this paper we numerically approximated the field-effect mobility of a-Si:H TFT. Field-effect mobility, based on the charge-trapping model and new effective capacitance model in our study, used Chebyshev approximation was approximated as the function of gate potential(gate-to-channel voltage). Even though various external factors are changed, this formula can be applied by choosing the characteristic coefficients without any change of the approximation formula corresponding to each operation region. Using new approximated field-effect mobility formula, the dependences of field-effect mobility on materials and thickness of gate insulator, thickness of a-Si bulk, and operation temperature in inverted staggered-electrode a-Si:H TFT were estimated. By this was the usefulness of new approximated mobility formula proved.

• 응용통계연구
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• 제29권5호
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• pp.887-896
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• 2016

대표적인 강우생성 모형인 Neyman-Scott 구형펄스모형은 점과정(point process)을 이용하여 강우를 생성하는 모형으로 강우의 발생, 강우세포의 강우강도 그리고 지속시간의 분포로 표현된다. 특히 이 모형은 구형펄스모형(rectangular pulse model)에서 포함하지 않았던 강우사상의 군집특성을 반영하였다는 장점을 가지고 있다. NSRPM의 매개변수를 추정하는데 있어 moment를 이용한 여러가지 최적화 기법들이 연구되어 왔는데, 이러한 방법들은 목적함수를 추가하거나 조정하기 위해서는 복잡한 수식을 다시 계산하여야 하는 단점이 있으며, 전체적인 강우의 특성을 반영하기 어렵고 스케일에 따른 추정값의 변동도 크게 나타난다. 또한 moment를 이용한 추정값은 추정오차를 구할 수 없기 때문에 신뢰구간을 구할 수 없다는 단점이 있다. 이에 본 연구에서는 누적강수량에 대한 근사적인 우도함수(approximated likelihood function)를 소개하고 이를 통해 NSRPM의 매개변수를 추정하고자 한다. 또한 분석에 사용되는 누적강수량의 시간 스케일에 따른 추정치의 변동성도 함께 알아보고자 한다.

• Nuclear Engineering and Technology
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• 제43권5호
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• pp.447-458
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• 2011

This paper proposes an approximated contact force model to identify the nonlinear behavior of a fuel rod with gap supports; also, the numerical prediction of interfacial forces in the mechanical contact of fuel rods with gap supports is studied. The Newmark integration method requires the current status of the contact force, but the contact force is not given a priori. Taylor's expansion can be used to predict the unknown contact force; therefore, it should be guaranteed that the first derivative of the contact force is continuous. This work proposes a continuous and differentiable contact force model with the ability to estimate the current state of the contact force. An approximated convex and differentiable potential function for the contact force is described, and a variational formulation is also provided. A numerical example that considers the particularly stiff supports has been studied, and a fuel rod with hardening supports was also examined for a realistic simulation. An approximated proper solution can be obtained using the results, and abrupt changes from the contacting state to non-contacting state, or vice versa, can be relieved. It can also be seen that not only the external force but also the developed contact force affects the response.

• 전기학회논문지
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• 제56권9호
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• pp.1589-1595
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• 2007

This paper suggests the advanced reliability assessment tool for railway signaling Hot-Standby sparing system. Existing reliability assessment for Hot-Standby sparing system controller is done by using single module mean failure rate based on approximated Hot standby sparing system function. Although approximated Hot standby sparing system function can be applied to various Hot standby sparing system, however, it is not able to reflect the exact system structure. In this paper, we suggest the advanced reliability function by identifying changeover-related failure factors and common failure mode which is not considered in existing approximated Hot standby sparing system reliability function via developing Hot standby sparing system model for railway signaling and applying FMECA to this model. Also. we compare reliability assessment results for model system to reliability assessment for existing system.

• Journal of the Korean Data and Information Science Society
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• 제27권5호
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• pp.1119-1131
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• 2016

Neyman-Scott 구형펄스모형 (Neyman-Scott rectangular pulses model; NSRPM)은 강우의 발생, 강우세포의 강우강도 그리고 지속시간으로 표현되는 점과정에 기초한 강우생성 모형으로, 기존의 구형펄스모형 (rectangular pulse model)과 비교해서 강우사상의 군집특성을 잘 반영하기 때문에 여러 연구에서 많이 사용되는 모형이다. 하지만 NSRPM의 매개변수를 추정하는데 있어서 모멘트를 이용한 여러가지 최적화 기법들은 그 계산이 복잡하고 또한 목적함수의 구성에 따라 추정값의 변동도 크게 나타난다. 이를 보완하기 위해서, 최근 누적강수량에 대한 근사적인 우도함수 (approximated likelihood function)와 이를 통해 NSRPM의 매개변수를 추정하는 방법이 소개되었다. 본 논문에선 이 근사적 우도함수를 바탕으로 계층적 베이지안 모형을 이용하여 NSRPM에 공간구조를 표현하고 이를 통해 강우생성 모형의 공간적 특성을 알아보고자 한다.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1989년도 하계종합학술대회 논문집
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• pp.101-105
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• 1989

The iterative learning controller makes the system output follow the desired output over a finite time interval through iterating trials. In this paper, first we discuss that the design problem of learning controller is originally the design problem of the inverse model. Then we show that the tracking error which is the difference between the desired output and the system output is reduced monotonically by properly modeled inverse system if the magnitude of the learning operator being introduced is bounded within the unit circle in complex domain. Also it would be shown that the conventional learning control method is a kind of extremely simplified inverse model learning control method of the objective controlled system. Hence this control method can be considered as a generalization of the conventional learning control method. The more a designer model the objective controlled system precisely, the better the performance of the approximated inverse model learning controller would be. Finally we compare the performance of the conventional learning control method with that of the approximated inverse model learning control method by computer simulation.