• Journal of Power Electronics
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• 제11권2호
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• pp.120-131
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• 2011

This paper proposes two control strategies for the bidirectional Z-source inverters (BZSI) supplied by batteries for electric vehicle applications. The first control strategy utilizes the indirect field-oriented control (IFOC) method to control the induction motor speed. The proposed speed control strategy is able to control the motor speed from zero to the rated speed with the rated load torque in both motoring and regenerative braking modes. The IFOC is based on PWM voltage modulation with voltage decoupling compensation to insert the shoot-through state into the switching signals using the simple boost shoot-through control method. The parameters of the four PI controllers in the IFOC technique are designed based on the required dynamic specifications. The second control strategy uses a proportional plus resonance (PR) controller in the synchronous reference frame to control the AC current for connecting the BZSI to the grid during the battery charging/discharging mode. In both control strategies, a dual loop controller is proposed to control the capacitor voltage of the BZSI. This controller is designed based on a small signal model of the BZSI using a bode diagram. MATLAB simulations and experimental results verify the validity of the proposed control strategies during motoring, regenerative braking and grid connection operations.

• 정보보호학회지
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• 제4권1호
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• pp.44-52
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• 1994

정보화 사회에서는 가계, 기업, 정보 등의 정보 활동의 주체들이 가진 정보자산은 데이타 베이스(이하DB)와 소프트웨어(S/W)로 대변할 수 있으며, 이중 DB는 정보화 사회의 기반시설의 하나라고 볼 수 있다. 특별히 통계DB는 각 주체들에게는 필수적인 정보를 갖고 있다. 금융자산의 정보, 국방에 관련된 병력, 장비, 군수물자등의 정보, 회계정보 뿐 아니라 인구센서스, 경제계획수립 등등의 다양한 분야에 이 통계 DB는 사용되고 있다. 이러한 통계DB는 기존의DB에서의 데이타의 저장, 관리, 추출 기능외에 통계적인 데이타의 분석기능이 요구되고 있다. 통계 처리를 위한 데이타베이스관리 시스템(DBMS, database management system)은 주로 기존의 DBMS 에 통계처리를 위한 기능을 추가하거나 통계를 위한 DB를 따로 구축하는 방법을 사용하고 있다. 따라서 일반적인 DB 보호 기술과 더불어 통계 의 환경을 이해하는 보호 기술이 요구되고 있다. 일반적으로 DB 를 보호하는 방법으로는 물리적인 보안(physical security)과 운영체계 보안(operating system security) 이 있으며, 이들과 함께 데이타 암호화(data encryption)의 방법을 사용하고 있다. DB 의 보안 방법에 관한 연구 중 George I. Davida 등에 의한 방법은 중국인의 나머지 정리(chinese remainder thorem)를 사용하는 암호화 알고리즘을 이용하여 레코드(record) 단위의 암호화를 하며, Khamis A. Omar등에 의한 방법은 읽기, 쓰기, 갱신의 3단계의 사용자 등급을 부여하여 DB 접근의 제약을 가하는 기능을 갖고 있다. 본고에서는 특히 그 중요성이 더해가고 있는 통계 의 일반적인 개념을 살펴보며, 특성 지향형 질의 모델(characteristic-specified query model)의 보호기술을 살펴본다. 특별히 본고는 통계 DB의 보호에 대한 일반적인 조사 연구로서 잘 알려진 사실들을 많은 참고 문헌과 더불어 소개하는 내용으로 통계 DB의 보호에 관한 새로운 연구 결과는 아니다.

• Natural Product Sciences
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• 제11권4호
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• pp.199-206
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• 2005

Investigation of M. peregrina aerial parts revealed the isolation and identification of 4-flavonoidal compounds, quercetin, quercetin-3-0-rutinoside (rutin), chrysoeriol-7-0-rhamnoside 6,8,3',5'-tetramethoxy apigenin. The compounds were identified by TLC, PC, MS, and $H^1-NMR$. The fatty acids and unsaponifiable matter were studied. The $LD_{50}$ for M. peregrina was 113.4 mg/100g b.wt. Repeated intraperitoneal injection of 1/20 and 1/10 $LD_{50}$ (5.67 mg and 11.34 mg/100g b.wt.) of defatted alcoholic of M. peregrina for 30 days induced significant decrease in serum glucose, liver enzymes and lipid components. M. peregrina administered i.p., 30min prior to carrageenan at the above doses significantly inhibited the rat paw oedema response, In acute pain models, namely, the acetic acid-induced writing and hot-plate assay, M. peregrina exhibited marked analgesic properties. In addition, M. peregrina administered at time of indomethacin injection inhibited the development of gastric lesions in rats.

• Journal of Electrical Engineering and Technology
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• 제12권4호
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• pp.1484-1494
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• 2017

We present a two-stage inverter with high step-up conversion ratio engaging modified finite-set Model Predictive Control (MPC) for utility-integrated photovoltaic (PV) applications. The anticipated arrangement is fit for low power PV uses, the calculated efficiency at 150 W input power and 19 times boosting ratio was around 94%. The suggested high-gain dc-dc converter based on Cockcroft-Walton multiplier constitutes the first-stage of the offered structure, due to its high step-up ability. It can boost the input voltage up to 20 times. The 3S current-source inverter constitutes the second-stage. The 3S current-source inverter hires three semiconductor switches, in which one is functioning at high-frequency and the others are operating at fundamental-frequency. The high-switching pulses are varied in the procedure of unidirectional sine-wave to engender a current coordinated with the utility-voltage. The unidirectional current is shaped into alternating current by the synchronized push-pull configuration. The MPC process are intended to control the scheme and achieve the subsequent tasks, take out the Maximum Power (MP) from the PV, step-up the PV voltage, and introduces low current with low Total Harmonic Distortion (THD) and with unity power factor with the grid voltage.

• Wind and Structures
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• 제23권4호
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• pp.301-311
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• 2016

The numerous benefits of Savonius turbine such as simple in structure, has appropriate self-start ability, relatively low operating velocity, water acceptance from any direction and low environmental impact have generated interests among researchers. However, it suffers from a lower efficiency compared to other types of water turbine. To improve its performance, parameters such flow pattern, pressure and velocity in different conditions must be analyzed. For this purpose, a detailed description on the flow field of various types of Savonius rotors is required. This article presents a numerical study on a nonlinear two-dimensional flow over a classic Savonius type rotor and a Benesh type rotor. In this experiment, sliding mesh was used for solving the motion of the bucket. The unsteady Reynolds averaged Navier-Stokes equations were solved for velocity and pressure coupling by using the SIMPLE (Semi-Implicit Method for Pressure linked Equations) algorithm. Other than that, the turbulence model using $k-{\varepsilon}$ standard obtained good results. This simulation demonstrated the method of the flow field characteristics, the behavior of velocity vectors and pressure distribution contours in and around the areas of the bucket.

• Biotechnology and Bioprocess Engineering:BBE
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• 제11권3호
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• pp.223-229
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• 2006

In this study, we have conducted kinetics and modelling studies of Centella asiatica cell growth and substrate uptake, in an attempt to evaluate cell growth for a better understanding and control of the process. In our bioreactor cultivation experiment, we observed a growth rate of 0.18/day, a value only 20% higher than was seen in the shake flask cultivation trial. However, the observed maximum cell dry weight in the shake flask, 10.5g/L, was 14% higher than was achieved in the bioreactor. Ninety seven percentage confidence was achieved via the fitting of three unstructured growth models; the Monod, Logistic, and Gompertz equations, to the cell growth data. The Monod equation adequately described cell growth in both cultures. The specific growth rate, however, was not effectively predicted with the Logistic and Gompertz equations, which resulted in deviations of up to 73 and 393%, respectively. These deviations in the Logistic and Gompertz models may be attributable to the fact that these models were developed for substrate-independent growth and fungi growth, respectively.

• Structural Engineering and Mechanics
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• 제50권2호
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• pp.201-214
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• 2014

Due to the confinement effects, Steel-Straps Tensioning Technique (SSTT) can significantly enhance the strength and ductility of high-strength concrete (HSC) members (Moghaddam et al. 2008). However, the enhancement especially in strength may result in slender member and more susceptible to instability (Jiang and Teng 2012a). This instability is particularly significant in HSC member as it inherent the brittle nature of the material (Galano et al. 2008). The current slenderness limit expression used in the design is mainly derived from the experiment and analysis results based on Normal strength concrete (NSC) column and therefore the direct application of these slenderness limit expressions to the HSC column is being questioned. Besides, a particular slenderness limit for the SSTT-confined HSC column which incorporated the pre-tensioned force and multilayers effects is not yet available. Hence, an analytical study was carried out in the view of developing a simple equation in order to determine the slenderness limit for HSC column confined with SSTT. Based on the analytical results, it was concluded that the existing slenderness limit expressions used in the design are appropriate for neither HSC columns nor SSTT-confined HSC columns. In this paper, a slenderness limit expression which has incorporated the SSTT-confinement effects is proposed. The proposed expression can also be applied to unconfined HSC columns.

• Structural Engineering and Mechanics
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• 제58권6호
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• pp.1087-1107
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• 2016

A method of damage detection based on the moving harmonic excitation and continuous wavelet transforms is presented. The applied excitation is used as a moving actuator and its frequency and speed parameters can be adjusted for an amplified response. The continuous wavelet transforms, CWT, is used for cracks detection based on the resulting amplified signal. It is demonstrated that this identification procedure is largely better than the classical ones based on eigenfrequencies or on the eigenmodes wavelet transformed. For vibration responses, free and forced vibration analyses of multi-cracked beams are investigated based on both analytical and numerical methodological approaches. Cracks are modeled through rotational springs whose compliances are evaluated using linear elastic fracture mechanics. Based on the obtained forced responses, multi-cracks positions are accurately identified and the CWT identification can be highly improved by adjusting the frequency and the speed excitation parameters.

• Steel and Composite Structures
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• 제17권3호
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• pp.271-285
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• 2014

This paper aims to examine the behavior of slender reinforced concrete columns confined with external glass fiber reinforced polymers (GFRP) sheets under eccentric loads. The experimental work conducted in this paper is an extension to previous work by the author concerning the behavior of eccentrically loaded short columns strengthened with GFRP wrapping. In this study, nine reinforced concrete columns divided into three groups were casted and tested. Three eccentricity ratios corresponding to e/t = 0, 0.10, and 0.50 in one direction of the column were tested in each group. The first group was the control one without confinement with slenderness ratio equal 20. The second group was the same as the first group but fully wrapped with one layer of GFRP laminates. The third group was also fully wrapped with one layer of GFRP laminates but having slenderness ratio equal 15. The experimental results of another two groups from the previous work were used in this study to investigate the difference between short and slender columns. The first was control one with slenderness ratio equal 10 and the second was fully wrapped and having the same slenderness ratio. All specimens were loaded until failure. The ultimate load, axial deformation, strain in steel bars, and failure mechanisms of each specimen were generated and analyzed. The results show that GFRP laminates confining system is less effective with slender columns compared with short one, but this solution is still applied and it can be efficiently utilized especially for slender columns with low eccentric ratio.

• Coupled systems mechanics
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• 제9권5호
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• pp.433-454
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• 2020

In-place analysis for offshore platforms is essentially required to make proper design for new structures and true assessment for existing structures. The structural integrity of platform components under the maximum and minimum operating loads of environmental conditions is required for risk assessment and inspection plan development. In-place analyses have been executed to check that the structural member with all appurtenances robustness and capability to support the applied loads in either storm condition or operating condition. A nonlinear finite element analysis is adopted for the platform structure above the seabed and the pile-soil interaction to estimate the in-place behavior of a typical fixed offshore platform. The analysis includes interpretation of dynamic design parameters based on the available site-specific data, together with foundation design recommendations for in-place loading conditions. The SACS software is utilized to calculate the natural frequencies of the model and to obtain the response of platform joints according to in-place analysis then the stresses at selected members, as well as their nodal displacements. The directions of environmental loads and water depth variations have important effects on the results of the in-place analysis behavior. The result shows that the in-place analysis is quite crucial for safe design and operation of offshore platform and assessment for existing offshore structures.