• Steel and Composite Structures
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• 제8권1호
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• pp.53-83
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• 2008

A rational and efficient seismic design methodology for irregular space steel frames using advanced methods of analysis in the framework of Eurocodes 8 and 3 is presented. This design methodology employs an advanced static or dynamic finite element method of analysis that takes into account geometrical and material non-linearities and member and frame imperfections. The inelastic static analysis (pushover) is employed with multimodal load along the height of the building combining the first few modes. The inelastic dynamic method in the time domain is employed with accelerograms taken from real earthquakes scaled so as to be compatible with the elastic design spectrum of Eurocode 8. The design procedure starts with assumed member sections, continues with the checking of the damage and ultimate limit states requirements, the serviceability requirements and ends with the adjustment of member sizes. Thus it can sufficiently capture the limit states of displacements, rotations, strength, stability and damage of the structure and its individual members so that separate member capacity checks through the interaction equations of Eurocode 3 or the usage of the conservative and crude q-factor suggested in Eurocode 8 are not required. Two numerical examples dealing with the seismic design of irregular space steel moment resisting frames are presented to illustrate the proposed method and demonstrate its advantages. The first considers a seven storey geometrically regular frame with in-plan eccentricities, while the second a six storey frame with a setback.

• Journal of Power Electronics
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• 제17권3호
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• pp.756-765
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• 2017

The control of the power conversion system (PCS) in a battery energy storage system has a challenge due to the existence of grid impedance. This paper studies an impedance model of an LCL-based PCS in the d-q domain. The feature of a PCS connected to a weak grid is unveiled by use of an impedance model and a generalized Nyquist criterion. It is shown that the interaction between grid impedance and the PCS destabilizes the cascaded system in certain cases. Therefore, this paper proposes a novel control method that adopts virtual resistors to overcome this issue. The improvement in the control loop leads the PCS to a more stable condition than the conventional method. Impedance measurement is implemented to verify the correctness of the theoretical analysis. Experimental results obtained from a down-scaled prototype indicate that the proposed control method can improve the performance of the PCS under a weak grid.

• 한국광학회지
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• 제19권1호
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• pp.60-67
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• 2008

전광 그레이코드(gray code) 이진코드(binary code) 변환기를 상용화 전산모사 프로그램(VPI)을 이용하여 처음으로 구현하였다. 전자회로 디자인 방법을 상호 이득변조를 이용한 전광 논리회로에 적합하도록 변형하여, 이상적이지 않은 전광 논리게이트에 의한 신호 왜곡이 최소화 되도록 하였다. 2.5 Gbps의 20 dB 소광비를 가지는 입력 신호에 대해, 신호재생기 없이 가장 많이 왜곡된 출력 신호에 (최하위 비트-LSB) 대해 약 4 이상의 Q값을 얻을 수 있었다. 또한 그레이 코드 이진코드 변환기를 디자인하면서, 이단 단순화 방법을 (two-level simplification method) 변형하여, 그레이코드 이진코드 변환기뿐 아니라 일반적인 전광 회로에 적용할 할 수 있는 일반적 방법을(일단 단순화 방법: one-level simplification method) 얻을 수 있었다.

• The Korean Journal of Pain
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• 제30권4호
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• pp.250-257
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• 2017

Vitamin D is a cofactor responsible for autoimmune disorders. There is no agreement in the studies investigating the association between vitamin D and fibromyalgia. This study aims to combine the conflicting results of the primary studies which compared these patients with control groups regarding the serum concentration of vitamin D. This meta-analysis has been designed based on PRISMA guidelines. Relevant keywords were searched in PubMed, Science direct, Scopus, Cochrane, and Google scholar and primary studies were selected. After screening the eligible studies according to inclusion/exclusion criteria, we investigated the risk of bias in the selected studies and also the heterogeneity between the primary results using Cochrane (Q) and I-squared ($I^2$) indices. The primary results were combined using inverse variance method and Cohen statistics as well as a random effects model. Publication bias was assessed using Egger test. Sensitivity analysis was applied to investigate the influence of each primary study on the final result of the meta-analysis. Suspected factors in the heterogeneity were assessed using meta-regression models. We entered 12 eligible studies in the meta-analysis including 851 cases compared with 862 controls. The standardized mean difference of Vitamin D between the two groups was -0.56 (95% confidence interval: -1.05, -0.08). Our meta-analysis showed that vitamin D serum levels of patients with fibromyalgia was significantly lower than that of control group.

• Wind and Structures
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• 제2권1호
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• pp.25-40
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• 1999

In this paper, artificial neural networks, a new kind of intelligent method, are employed to model and predict amplitude dependent damping in buildings based on our full-scale measurements of buildings. The modelling method and procedure using neural networks to model the damping are studied. Comparative analysis of different neural network models of damping, which includes multi-layer perception network (MLP), recurrent neural network, and general regression neural network (GRNN), is performed and discussed in detail. The performances of the models are evaluated and discussed by tests and predictions including self-test, "one-lag" prediction and "multi-lag" prediction of the damping values at high amplitude levels. The established models of damping are used to predict the damping in the following three ways : (1) the model is established by part of the data measured from one building and is used to predict the another part of damping values which are always difficult to obtain from field measurements : the values at the high amplitude level. (2) The model is established by the damping data measured from one building and is used to predict the variation curve of damping for another building. And (3) the model is established by the data measured from more than one buildings and is used to predict the variation curve of damping for another building. The prediction results are discussed.

• 한국전자파학회논문지
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• 제15권11호
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• pp.1043-1050
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• 2004

본 연구에서는 위상 잡음이 OFDM통신 시스템 성능에 미치는 영향에 대해 연구하였다. OFDM통신 시스템의 정확한 분석을 위해 위상 잡음의 2차항을 고려한 비선형 근사 방법을 이용하여 위상 잡음으로 인해 나타나는 현상들을 보다 정확하게 분석하고 정량화 하였다. 분석결과 QPSK-OFDM통신 시스템에서 PLL주파수 합성기의 루프 대역을 5.0 kHz, 1.0 Hlz와 0.5 KHz로 각각 설정했을 때 위상 잡음으로 인해 발생하는 성능 저하 수치를 위상 잡음이 없는 이상적인 경우 AWGN 환경에서의 BER성능과 비교해 보면 BER=$10^{-4}$를 만족하기 위해 약0.6 dB, 1.0 dB와 1.7 dB 정도의 SNR손실이 발생한다. 16QAM 변조방식을 사용한 경우에는 루프 대역이 각각 5 kHz, 1.0 kHz, 그리고 0.5 kHz일 때에 약 1.9dB, 3.2dB, 그리고 6.7dB의 SNR 손실이 발생하게 된다. 기존 선형 근사화 기법과 본 연구에서 QPSK 변조방식을 사용하였을 경우 분산의 크기가 0.02까지는 두 곡선이 거의 비슷한 성능을 보이지만, 0.02 이상 분산 간이 더 커지게 되면 기존 연구와 본 연구 사이에 차이가 발생하게 된다. 또한 해석적 방법에 의한 BER성능 분석결과와 QPSK와 16QAM 변조를 사용하는 OFDM통신 시스템의 시뮬레이션 결과가 동일함을 보인다. 아울러 QPSK-OFDM 통신 시스템 에서 위상 잡음 분산이 0.03 이상이 되면 에러 floor가 생겨서 BER 성능이 악화된다.

• 한국전자통신학회논문지
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• 제8권12호
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• pp.1865-1874
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• 2013

본 논문은 IPMSM(Interior Permanent Magnet Synchronous Motor)의 센서리스 운전을 위해 엔센티드 칼만필터를 기반으로 하는 속도와 위치 추정기의 설계방법을 제안한다. 제안된 방법은 회전축에 동기하여 설계된 관측기에 비해, 간단한 전류계측이 가능하고 관측기의 비선형 항이 포함되도록 상태 추정기를 설계하였다. 제어기는 비선형 백스텝핑 제어기법으로 구성하고, 추정된 속도와 위치정보로 속도와 전류제어를 수행하였다. 설계된 추정기의 성능은 시뮬레이션을 통해 dq축에 동기하여 설계된 추정기의 성능과 비교 검증하였다.

• 한국전산유체공학회지
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• 제20권4호
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• pp.1-6
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• 2015

Centrifugal pumps consume considerable amount of energy in various industrial applications. Therefore, improvement of the efficiency of these machines has become a major challenge. Cavitation is a phenomenon which decreases the pump efficiency and even causes structural demage. Hence, the goal of this paper is to investigate the cavitation problem in the single-stage and double-stage centrifugal pumps. The Volume of Fraction (VOF) method has been used for the numerical simulations together with Rayliegh-Plesset model for the gas-liquid two-phase flow inside the pump. In order to capture the turbulent phenomena, the standard k-${\varepsilon}$ turbulence model has been adopted, and the simulations have been done as unsteady cases. In addition, the motion of the rotating parts has been simulated using Multi Reference Frame(MRF) method. The results are presented and compared in terms of hydraulic head and NPSH for both the single-stage and double-stage pumps. The H-Q curves show the effects of cavitation on decreasing the pumps performances.

• 기술사
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• 제14권3호
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• pp.9-21
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• 1981

The rationalization for Tunnel Drifting is based on the high productivity which is achievable due to Continuous work with a Jumbo Drill, resulting in a much higher efficiency them the Conventional method of blasting, mucking and supporting services. Large projects of over 4,000m Tunnel Drifting are condidated to justify the use of a Jumbo Drill with a combination of superior explosives, machinery and techniques. During a Tunnel Drifting test, Gulita, Nabit and slurry made by Nitro Nobel were employed with following results. 1, Conditions: a. Granite Rock with Two free face b. Burden (W), 2m c. Diameter of hole, 42mm d. Depth of hole 3.5m e. Hole pitch 0.6m f. Charged Explosive per hole Gelatin Dynamite 4 pieces (112.5${\times}$4ea)+Guuita 5 pieces(110g${\times}$5ea) g. Simal-taneous Detonation h. After the blasting resultant rock size was Less 40% of the 0.3m Lumps. 2. Calculation results W=q/Wn=100cm‥‥‥Burden in simultaneous blasting 0.865kg(7.7ea)/hole ‥‥‥Amount of charge but hole pitch is 1.5W-2W The estimated cost of using a Jumbo Drill for the Construction of a 3,000,000 bbL sub-surface oil storage would be as follows: This calculation is based on the Jumbo Drill advancing 3.6m per blasting cycle. Unit cost/bbL Excavation $3.13 The attached sheet shows ideal Drilling pattern with Burn Cut & Smooth blasting method. In conclusion, it is my opinion that this method will assure safety and save cost and improve our technical know-how.

• 상하수도학회지
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• 제25권2호
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• pp.193-199
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• 2011

A method to improve internal corrosion control efficiency by adding lime and carbon dioxide, which, in turn increases the Langelier Index (LI) for filtered water at a conventional drinking water treatment plant (WTP) was investigated. The SJ WTP (Q=100,000 $m^{3}$/d) has been operating an internal corrosion control system since 2006. The system has achieved stable operation through technical development and trial and error over a period of several years. As a result of the operation, the LI of treated water has increased up to 29% by adjusting pH of filtered water to 7.8 with the addition of lime and carbon dioxide. Coupon tests in the distribution system indicated that the corrosion rate has been delayed by 24% when the internal corrosion method was implemented. The increase of LI by lime and carbon dioxide has been proven to be a practical method for controlling corrosion.