• 대한전기학회:학술대회논문집
• /
• 대한전기학회 2006년도 제37회 하계학술대회 논문집 A
• /
• pp.525-526
• /
• 2006

Recently, much research has been done and many improvements have been developed for islanding protection of distributed generation(DG). Anti-islanding protection for DG must be act very quickly to prevent equipment damage at the time of disconnection and for the safety of maintenance and repair personnel. DG-based detection methods have included both passive and active types, and now research has shifted towards new anti-islanding detection methods that make up for the defects of the previous types. Because differences occur between the utility grid and the DG when connecting and disconnecting depending on the phase difference, voltage, current, relative capacity of electric power, and system operation characteristics, voltage phase angle is an important consideration. In this paper, we simulated islanded operation characteristics comparing phase difference of DG and the connected utility grid, and analyzed various parameters (real power, reactive power, RMS voltage, RMS current, power factor angle, and frequency) by varying the DG's voltage phase angle. Using this information, we propose a suitable DG voltage phase angle for enhanced passive islanding detection techniques.

• Journal of Welding and Joining
• /
• 제17권6호
• /
• pp.84-89
• /
• 1999

Most of ferrous b.c.c weld materials may experience martensitic transformation during rapid cooling after welding. It is well known that volume expansion due to the phase transformation could influence on the relaxation of welding residual stress. To apply this effect practically, it is a prerequisite to establish a numerical model which is able to estimate the effect of phase transformation on residual stress relaxation quantitatively. For this purpose, the analysis is carried out in two regions. i.e., heating and cooling, because the variation of material properties following a phase transformation in cooling is different in comparison with the case in heating, even at the same temperature. The variation of material properties following phase transformation is considered by the adjustment of specific heat and thermal expansion coefficient, and the distribution of residual stress in analysis is compared with that of experiment by previous study. consequently, in this study, simplified numerical procedures considering phase transformation, which based on a commercial finite element package was established through comparing with the experimental data of residual stress distribution by other researcher. To consider the phase transformation effect on residual stress relaxation, the transition of mechanical and thermal property such as thermal expansion coefficient and specific heat capacity was found by try and error method in this analysis.

• Animal Bioscience
• /
• 제35권10호
• /
• pp.1592-1605
• /
• 2022

Objective: The objective of this study was to select an effective in vitro digestion-fermentation model to estimate the effect of decreasing dietary crude protein (CP) on odor emission during pig production and to suggest potential prediction markers through in vitro and in vivo experiments. Methods: In the in vitro experiment, three diet formulations with different CP contents (170 g/kg, 150 g/kg, and 130 g/kg) but containing the same standardized ileal digestible essential amino acids (SID-EAA) were assessed. Each diet was evaluated by two different in vitro gastric-intestinal phase digestion methods (flask and dialysis), combined with fresh pig feces-ferment inoculation. Eighteen growing barrows (31.9±1.6 kg) were divided into three groups: control diet (180 g CP/kg, without SID-EAA adjustment), 170 g CP/kg diet, and 150 g CP/kg diet for 4 weeks. Results: The in vitro digestion results indicated that in vitro digestibility was affected by the gastric-intestinal phase digestion method and dietary CP level. According to the gas kinetic and digestibility results, the dialysis method showed greater distinguishability for dietary CP level adjustment. Nitrogen-related odor compounds (NH₃-N, indole, p-cresol, and skatole) were highly correlated with urease and protease activity. The feeding study indicated that both EAA-adjusted diets resulted in a lower odor emission especially in p-cresol and skatole. Both protease and urease activity in feces were also closely related to odor emissions from nitrogen metabolism compounds. Conclusion: Dialysis digestion in the gastric-intestinal phase followed by fresh fecal inoculation fermentation is suitable for in vitro diet evaluation. The enzyme activity in the fermentation and the fecal samples might provide a simple and effective estimation tool for nitrogen-related odor emission prediction in both in vitro and in vivo experiments.

• Journal of Hospice and Palliative Care
• /
• 제10권3호
• /
• pp.120-127
• /
• 2007

Bereavement is the state of loss resulting from death. Grief is the emotional response associated with loss, intense and acute sorrow resulting from loss. Complicated grief represent a pathological outcome involving social, physical, emotional, cognitive, spiritual morbidity. The common psychiatric disorders associated complicated grief or abnormal grief responses include clinical depression, anxiety disorders, alcohol abuse or other substance abuse, and dependence, psychotic disorders, and post-traumatic stress disorder (PTSD). Grief tasks involve a series of stage or phases following an important loss that gradually permit adjustment and recovery. Three phases of grief involve phase 1 (walking the edges), phase 2 (entering the depths), and phase 3 (reconnecting the world). For intervention to be effective they need to be individually tailored to abnormal grief reaction or unresolved grief reaction. Clear understandings of complicated grief, abnormal responses, factors increasing risk after bereavement will often enable us to prevent psychiatric disorders in bereaved patients.

• 경영과학
• /
• 제24권2호
• /
• pp.43-56
• /
• 2007

VRP(Vehicle Routing Problem) is studied in this paper, where two different kinds of missions are to be completed. The objective is to minimize the total vehicle operating distance. A mixed integer programming formulation and a heuristic algorithm for a practical use are suggested. A heuristic algorithm consists of three phases such as clustering, constructing routes, and adjustment. In the first phase, customers are clustered so that the supply nodes are grouped with demand nodes to be served by the same vehicle. Vehicle routes are generated within the cluster in the second phase. Clusters and routes are adjusted in the third phase using the UF (unfitness) rule designed to determine the customers and the routes to be moved properly. It is shown that the suggested heuristic algorithm yields good performances within a relatively short computational time through computational experiment.

• 전기학회논문지P
• /
• 제50권3호
• /
• pp.101-108
• /
• 2001

Frequency is an important operating parameter of a power system. Electric power systems sustain transient frequency swings whenever the balance between generation and load does not no longer hold. To cope with this constraints, it requires an accurate and high speedy frequency deviation estimation technique and suitable adjustment to obtain the Power system energy balance. This paper describes a digital signal processing technique for measuring the operating frequency of a power system. The fundamental frequency component of 3-phase signal is first extracted by using an algorithm based on FIR filter. The rate change of the phase angle is used for estimation. To confirm the validity of the proposed algorithm, the simulation studies carried out on a typical 154KV double T/L system by using EMTP software. Some test results are presented in the paper.

• 전기의세계
• /
• 제17권4호
• /
• pp.7-12
• /
• 1968

In recent years the development of the SCR has made possible the control of the power system. It is one example that the speed control of the induction motor can be done by changing the frequency with the S.C.R. This paper is devoted primarily to a study of the running characteristics of the single phase induction motor through the experimental and theoretical methods when the speed of the motor is controlled by varying the conduction period in current with S.C.R. under the constant frequency. We conclude from the experiments that the adjustment of the phase angle in current is equivalent to the change of the supply voltage to the motor. Therefore, the speed control of the motor such as a fan duty motor is possibly by this methods.

• 대한기계학회논문집
• /
• 제16권5호
• /
• pp.933-942
• /
• 1992

본 연구에서는 이상류 동축 노즐의 미립화 기구를 규명하기 위한 기초단계로 20˚의 증류수를 사용하여 이상류 동축노즐의 평균액적 직경에 미치는 공급유량의 영 향을 직접사진 촬영법을 사용하여 규명하고자 한다.

• 한국정밀공학회지
• /
• 제17권11호
• /
• pp.151-157
• /
• 2000

The MRAC theory has proved to be one of the most popular algorithms in the field of adaptive control, particularly for practical application to devices such as an hydraulic servosystem of which parameters are unknown or varying during operation. For small sampling period, the discrete time system becomes a nonminimal phase system. The $\delta$-MRAC was introduced to obtain the control performance of nonminimal phase system, because the z-MRAC can not control the plant for small sampling period. In this paper, $\delta$-MRAC is applied to the control of an hydraulic servosystem which is composed of servovalve, hydraulic cylinder and inertia load.

• 한국측량학회지
• /
• 제14권2호
• /
• pp.181-188
• /
• 1996

측지학적인 절대측위 방법들은 아직 관측상의 많은 문제점과 어려움을 내포하고 있으며, 국내에서도 정확한 절대측위 성과의 필요성 때문에 GPS를 이용한 절대위치결정에 관한 연구가 일부기관에서 수행되고 있다. 본 연구에서는 2주파 GPS 반송파 맥놀이 위상(carrier bast phase)자료에 의한 절대위치 결정의 기본 이론을 정립하고 각종오차 보정량을 산출하며, 정밀궤도력과 정밀시계상태를 이용해 독립적인 절대위치를 결정하여 이에 대한 정확도를 분석하고자 한다. 또한 독립적인 절대좌표를 상대측위에 의한 상대좌표와 비교함으로써 국내에서도 GPS를 이용한 측지학적인 절대위치 결정의 가능성을 제시하고자 한다.