• 대한기계학회논문집A
• /
• 제24권5호
• /
• pp.1075-1083
• /
• 2000

The prediction of the inelastic behavior of the structure is an essential part of reliability assessment procedure, because most of the failures are induced by the inelastic deformation, such as creep and plastic deformation. During decades, there has been much progress in understanding of the inelastic behavior of the materials and a lot of inelastic constitutive equations have been developed. These equations consist of the definition of inelastic strain and the evolution of the state variables introduced to quantify the irreversible processes occurred in the material. With respect to the definition of the inelastic strain, the inelastic constitutive models can be categorized into elastoplastic model, unified viscoplastic model and separated viscoplastic model and the different integration methods have been applied to each category. In the present investigation, the generalized integration method applicable for various types of constitutive equations is developed and implemented into ABAQUS by means of UMAT subroutine. The solution of the non-linear system of algebraic equations arising from time discretization with the generalized midpoint rule is determined using line-search technique in combination with Newton method. The strategy to control the time increment for the improvement of the accuracy of the numerical integration is proposed. Several numerical examples are considered to demonstrate the efficiency and applicability of the present method. The prediction of the inelastic behavior of the structure is an essential part of reliability assessment procedure, because most of the failures are induced by the inelastic deformation, such as creep and plastic deformation. During decades, there has been much progress in understanding of the inelastic behavior of the materials and a lot of inelastic constitutive equations have been developed. These equations consist of the definition of inelastic strain and the evolution of the state variables introduced to quantify the irreversible processes occurred in the material. With respect to the definition of the inelastic strain, the inelastic constitutive models can be categorized into elastoplastic model, unified viscoplastic model and separated viscoplastic model and the different integration methods have been applied to each category. In the present investigation, the generalized integration method applicable for various types of constitutive equations is developed and implemented into ABAQUS by means of UMAT subroutine. The solution of the non-linear system of algebraic equations arising from time discretization with the generalized midpoint rule is determined using line-search technique in combination with Newton method. The strategy to control the time increment for the improvement of the accuracy of the numerical integration is proposed. Several numerical examples are considered to demonstrate the efficiency and applicability of the present method.

• 대한임상전기생리학회지
• /
• 제3권1호
• /
• pp.49-59
• /
• 2005

This study assigns each 8 of 24 normal persons to control group(Group I), strength increase group(Group II) and endurance increase group(Group III) to analyze differences in changes of strength and endurance with surface electromyography and kinetics according to application modes of neuromuscular electrical stimulation(NMES). Group I had not any treatment, group II performed 15 repeated contraction with 60% intensity of maximal voluntary isometric contraction(MVIC) by setting 10-sec on time and 50-sec off time and group III conducted 30 repeated contraction with 30% intensity of MVIC by setting 10-sec on time and 20-sec off time. For neuromuscular electrical stimulation, 2,500 Hz of Russian current, 35 pps of pulse rate and 200 of pulse width. Neuromuscular electrical stimulation was conducted by five times for total 4 weeks. Before and after experimentmotor unit action potential of vastus medialis, rectus femoris and vastus lateralis were measured with sEMG, median frequency(MDF) was analyzed, and thus the following results were obtained. There was significant difference in the period of measuring vastus medialis and rectus femoris in change of MDF and interaction among groups with analysis of surface electromyography before and after neuromuscular electrical stimulation(p<.001) and in particular, there was a remarkable change among groups according to the period of measurement. In conclusion, NMES influenced changes of strength and endurance according to its application modes and in particular, it was found that strength increment application had a significant influence on strength increment in applying short-time NMES.

• 한국축산식품학회:학술대회논문집
• /
• 한국축산식품학회 2005년도 정기총회 및 제35차 춘계 학술 발표대회
• /
• pp.290-296
• /
• 2005

This study was carried out to develop the efficient freeze concentration process of milk through controlling the recrystallisation phenomena of ice. Freeze-concentration was progressed with multi-stage freeze concentrator and there was artificial temperature control to induce recrystallisation phenomena. In each stage of freeze concentration process, the regular recrystallisation time was fixed as 1, 2, 4 and 8 hr to compare the solute increment, yield, brix and ice-crystal size among experimental conditions. Higher concentration as total solids was observed due to the elapse of recrystallisation time, and the maximum total solids in final products: 32.67% was obtained at the ripening time of 8 hr in two-stage process. This result was excessively high concentration comparing to the existing researches and presented the possibilities of milk freeze concentration in the dairy industry, The results of brix and ice-crystal size showed the direct correlation with the recrystallisation time that meant the increased processing time showed the increment of brix and ice-crystal size. Obtained results were numerically modelled to predict the progress of concentration in the industrial process and all of them had fairly high R2 of determination. Therefore, we regarded that these numerical models could be utilized for the development of efficient technology in industrial freeze concentration process.

• Structural Engineering and Mechanics
• /
• 제1권1호
• /
• pp.119-135
• /
• 1993

The paper presents a generalized optimal active control algorithm for earthquake-resistant structures. The study included the weighting matrix configuration, stability, and time-delays for achieving control effectiveness and optimum solution. The sensitivity of various time-delays in the optimal solution is investigated for which the stability regions are determined. A simplified method for reducing the influence of time-delay on dynamic response is proposed. Numerical examples illustrate that the proposed optimal control algorithm is advantageous over others currently in vogue. Its feedback control law is independent of the time increment, and its weighting matrix can be flexibly selected and adjusted at any time during the operation of the control system. The examples also show that the weighting matrix based on pole placement approach is superior to other weighting matrix configurations for its self-adjustable control effectiveness. Using the time-delay correction method can significantly reduce the influence of time-delays on both structural response and required control force.

• Applied Biological Chemistry
• /
• 제25권4호
• /
• pp.232-238
• /
• 1982

농가포장(農家圃場)(13개소(個所))에서 중질소비시험결과(重窒素肥試驗結果) 80%의 포장(圃場)에서 이용율(利用率)은 감법(減法)의 경우가 표식법(標識法)의 경우보다 높았으며 비료질소(肥料窒素)에 의(依)한 토양질소흡수(土壤窒素吸收)가 조장(助長)된 것을 나타낸다. 이 두 방법(方法)의 값은 포장간(圃場間)에에 류사(類似)한 경향(傾向)을 보였다. 황피뇨소(黃皮尿素)와 국지시용(局地施用)은 시비효율(施肥效率)(시비질소(施肥窒素) 당증수량(當增收量), Fe)을 분시(分施)의 15에서 23으로 증대(增大)시켰는데 이는 이용율(利用率)(Ef)을 29에서 50으로 증대시킨 때문이며 흡수시비질소효율(吸收施肥窒素效率)(Ef)은 50에서 46으로 감소하는 경향(傾向)을 보였다. 통일계(統一系)의 다수확능(多收穫能)은 흡수시비질소효율(吸收施肥窒素效率), 전이율(轉移率) 및 토양질소선호지수(土壤窒素選好指數)(시비질소흡수증가량(施肥窒素吸收增加量)에 대(對)한 토양질소흡수증가량(土壤窒素吸收增加量)의 비(比) PI)가 큰데 기인한 것 같다. 일련의 본(本) 연구(硏究)는 시비체계하(施肥體系下)의 수량(收量)은 이용율(利用率)과 흡수시비질소효율(吸收施肥窒素效率)의 적(積)인 시비효율(施肥效率)에 의존(依存)하며 비료(肥料)의 형태(形態)나 시비시기(施肥時期) 및 방법(方法) 등(方法) 시비관리(施肥管理)는 주(主)로 이용율(利用率)을 증대(增大)시키고 이용율(利用率)의 한계(限界)는 품종(品種) 특성(特性)에 주(主)로 기인(基因)하는 흡수시비질소효율(吸收施肥窒素效率)에 의(依)하여 조정(調整)됨을 보였다.

• 한국해양공학회지
• /
• 제32권3호
• /
• pp.151-157
• /
• 2018

Offshore structures are exposed to low- and high-frequency responses due to environmental loads, and fatigue damage models are used to calculate the fatigue damage from these. In this study, we tried to optimize the main parameters used in fatigue damage calculation to derive a new fatigue damage model. A total of 162 bi-modal spectra using the elliptic equation were defined to describe the response of offshore structures. To calculate the fatigue damage from the spectra, time series were generated from the spectra using the inverse Fourier transform, and the rain-flow counting method was applied. The considered optimization variables were the size of the frequency increments, ratio of the time increment, and number of repetitions of the time series. In order to obtain optimized values, the fatigue damage was calculated using the parameter values proposed in previous work, and the fatigue damage was calculated by increasing or decreasing the proposed values. The results were compared, and the error rate was checked. Based on the test results, new values were found for the size of the frequency increment and number of time series iterations. As a validation, the fatigue damage of an actual tension spectrum found using the new proposed values and fatigue damage found using the previously proposed method were compared. In conclusion, we propose a new optimized calculation process that is faster and more accurate than the existed method.

• 한국지진공학회논문집
• /
• 제8권6호통권40호
• /
• pp.73-80
• /
• 2004

구조물의 손상 진단을 위해 측정 가속도 데이터를 사용한 비선형 시간영역 SI 알고리듬을 개발하였다. 구조물의 비선형 거동을 고려하기 위하여 측정 가속도 증분과 해석에 의한 가속도 증분의 차이로 출력오차를 정의하고, 구속 비선형 최적화 문제를 풀어 최적 구조변수를 구하였다. 개발된 알고리듬은 시간에 따라 변하는 강성도와 감쇠 변수를 추정하도록 하였다. 구조물의 비선형 거동에 의한 복원력은 추정된 시간에 따라 변하는 구조변수와 Newmark-$\beta$법으로 계산한 변위를 사용하여 복원하였으며, 복원 과정에서 비탄성 거동에 대한 어떤 모델도 사전에 설정하지 않았다. 개발한 알고리듬에서는 측정오차와 공간 및 상태에 대한 불완전 측정의 경우를 고려하였다. 개발한 알고리듬을 검증하기 위하여 3층 전단건물에 대한 수치 모의시험과 실내 모형실험을 통한 연구를 수행하였다.

• 한국경영과학회지
• /
• 제39권1호
• /
• pp.49-67
• /
• 2014

This paper proposes a real time pricing model for smart grid considering consumers' behavior, real time price elasticity, and exogenous price. Based on the proposed model, we found the weight of utility over cost is the most sensitive factor compared to other factors. Also, if the electricity price is set to be changed too sensitively to energy consumption, it is warned that real time pricing sometimes can cause increment of peak-time demand and volatility. Finally, real time pricing could be less efficient when the difference between the maximum and the minimum consumption level is small.

• 대한전기학회논문지:전력기술부문A
• /
• 제48권2호
• /
• pp.168-175
• /
• 1999

In this paper, a modified RBF(Radial Basis Function) network structure is suggested for the prediction of a time-series with non-linear, non-stationary characteristics. Coventional RBF network predicting time series by using past outputs sense the trajectory of the time series and react when there exists strong relation between input and hidden activation function's RBF center. But this response is highly sensitive to level and trend of time serieses. In order to overcome such dependencies, hidden activation functions are modified to react to the increments of input variable and multiplied by increment(or dectement) for prediction. When the suggested structure is applied to prediction of Macyey-Glass chaotic time series, Lorenz equation, and Rossler equation, improved performances are obtained.

• International Journal of Contents
• /
• 제5권2호
• /
• pp.16-19
• /
• 2009

In this paper, we concern about the distribution characteristics of surface temperature by the increment of time, diffusivity and heat flux on irradiating of a laser. The penetration depth corresponding to the induced constant heat flux or irradiated laser, is simulated by a computer algorithm. The distribution of temperature versus penetration depth for the variation of time and diffusivity is characterized at the constant heat flux and on irradiating of a laser. The temperature of constant heat flux at the fixed diffusivity or time, is decreased by the pattern of exponential function as the time t or diffusivity a is increased (a=10, 100, 1000). The temperature of constant heat flux is not changed but exponentially fixed with the increasing diffusivity and the fixed time. On the other hand, the temperature of laser at the fixed diffusivity or time is decreased linearly. Our results show that the characteristics of the simulated surface temperature in a semi-infinite solid are similar to the graphs on theoretical consideration.