• Journal of Power Electronics
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• 제16권3호
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• pp.1152-1162
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• 2016

The unequal impedances of the interconnecting cables between paralleled inverters in the island mode of microgrids cause inaccurate reactive power sharing when the traditional droop control is used. Many studies in the literature adopt low speed communications between the inverters and the central control unit to overcome this problem. However, the losses of this communication link can be very detrimental to the performance of the controller. This paper proposes an improved reactive power-sharing control method. It employs infrequent measurements of the voltage at the point of common coupling (PCC) to estimate the output impedance between the inverters and the PCC and then readjust the voltage droop controller gains accordingly. The controller then reverts to being a traditional droop controller using the newly calculated gains. This increases the immunity of the controller against any losses in the communication links between the central control unit and the inverters. The capability of the proposed control method has been demonstrated by simulation and experimental results using a laboratory scale microgrid.

• Coupled systems mechanics
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• 제9권2호
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• pp.125-145
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• 2020

In this paper, we present a 3D thermo-hydro-mechanical coupled discrete beam lattice model of structure built of the nonisothermal saturated poro-plastic medium subjected to mechanical loads and nonstationary heat transfer conditions. The proposed model is based on Voronoi cell representation of the domain with cohesive links represented as inelastic Timoshenko beam finite elements enhanced with additional kinematics in terms of embedded strong discontinuities in axial and both transverse directions. The enhanced Timoshenko beam finite element is capable of modeling crack formation in mode I, mode II and mode III. Mode I relates to crack opening, mode II relates to in-plane crack sliding, and mode III relates to the out-of-plane shear sliding. The pore fluid flow and heat flow in the proposed model are governed by Darcy's law and Fourier's law for heat conduction, respectively. The pore pressure field and temperature field are approximated with linear tetrahedral finite elements. By exploiting nodal point quadrature rule for numerical integration on tetrahedral finite elements and duality property between Voronoi diagram and Delaunay tetrahedralization, the numerical implementation of the coupling results with additional pore pressure and temperature degrees of freedom placed at each node of a Timoshenko beam finite element. The results of several numerical simulations are presented and discussed.

• 비교문화연구
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• 제26권
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• pp.43-71
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• 2012

In this article, we recognize the cross-cultural communication between Greece and Spain through El Greco's pictures. The Greeks of Crete kept to their culture and continued to look to the declining Byzantine Empire for spiritual and political guidance. For two centuries after the conquest, the strength of the Byzantine tradition had become the moral and spiritual sustenance of the conquered in Crete. The basic contribution of Cretan intellectuals or artists such as El Greco of the fifteenth and sixteenth centuries was the forging of connecting links between the Hellenism of the old Byzantine East and the rising, youthful Hellenism of the Renaissance West. In this way, Crete served as an important halfway point between East and West. The saint Mary Magdalene was symbol of Christian penitence, which represents the penitential life personified and became widespread during the Counter Reformation, when new emphasis was put on the value of prayer and repentance in the forgiveness of sin. In Spain, the Penitent Magdalene was popular and El Greco painted many versions, which at the first time, were reflected by Tiziano, on the contrary, at the time of Toledo, were recreated by his own style. Although El Greco was converted to Catholic in Spain, his faith in Greek Orthodox Church influenced on his original painting world. El Greco had never painted a picture whose subject treat with the emphasis of identification between Mary Magdalene and Mary, younger sister of Martha.

• 전력전자학회논문지
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• 제23권5호
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• pp.352-358
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• 2018

A split-capacitor (SC) dual-active-bridge (DAB) converter is proposed in this study. The DC-link capacitors of input and output are split in the proposed converter. The primary and secondary windings of transformer are connected to the midpoints of the DC-links. Hence, the SC DAB converter can inherently prevent transformer from saturation. Although the switch current stress of the proposed converter is twice that of the conventional DAB converter, the switch voltage stress is reduced by half. Therefore, the proposed converter can reduce switching loss and achieve high efficiency in a high switching frequency. Given the SC structure, the proposed converter can readily be connected to neutral-point-clamped- or half-bridge-type converters. The topology of the proposed converter is presented and the operating principle is analyzed in detail. A 3-kW hardware prototype was built and tested to verify the performance of the proposed converter.

• 한국컴퓨터정보학회논문지
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• 제21권1호
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• pp.65-72
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• 2016

Network virtualization is an emerging technology for solving the rigidity of the physical network infrastructure. The innovative technique virtualizes all resources in the network, including the network links and nodes, and provides a number of virtual networks on a single network infrastructure. In order to realize a virtual network, a thorough and complete monitoring of all resources in the network should be performed firstly. OpenFlow is an open source stack for network virtualization. However, it is impossible to apply OpenFlow to AP-based legacy wireless LAN environment because OpenFlow targets ethernet-based LAN environment. In this paper, we implement an adaptor-styled virtual switch for AP-based wireless LAN through customizing the Open vSwitch which is a virtual switch of OpenFlow. The evaluation test results show that the implemented OpenFlow stack operates successfully. The implemented OpenFlow stack can now be plugged immediately in existing AP-based wireless LAN environment and plays network resource monitoring. In the future, we can develop wireless LAN virtualization applications on the wireless OpenFlow stack.

• 대한기계학회논문집A
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• 제29권1호
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• pp.1-13
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• 2005

Kinematics of grasping and manipulation by a multi-fingered robotic hand where multi-fingertip surfaces are in contact with an object is solved. The surface of the object was represented by B-spline surfaces in order to model the objects of various shapes. The fingers were modeled by cylindrical links and a half ellipsoid fingertip. Geometric equations of contact locations have been solved for all possible contact combinations between the fingertip surface and the object. The simulation system calculated joint displacements and contact locations for a given trajectory of the object. Since there are no closed form solutions for contact or intersection between these surfaces, kinematics of grasping was solved by recursive numerical calculation. The initial estimate of the contact point was obtained by approximating the B-spline surface to a polyhedron. As for the simulation of manipulation, exact contact locations were updated by solving the contact equations according to the given contact states such as pure rolling, twist-rolling or slide-twist-rolling. Several simulation examples of grasping and manipulation are presented.

• The Journal of Asian Finance, Economics and Business
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• 제7권2호
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• pp.291-300
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• 2020

This paper studies the factors affecting university and industry collaboration in education in the hospitality industry in Ho Chi Minh City (Vietnam) from a company perspective. The authors use qualitative method and quantitative research to study the matters, specifically using scales and data collected for Cronbach alpha reliability testing, analysizing the discovery factor of EFA, CFA and verifying the regression models through AMOS software with SEM linear modeling. The study proposes four factors: (1) organization factors, (2) contextual factors, (3) process factors, and (4) cooperation perspective impacting on the benefits factors and university and industry collaboration in education. In addition, it is also found that benefits factors has a direct and positive impact on the collaboration in education. The results suggest that the process factor had the strongest positive, followed by the contextual factor. The findings revealed that the benefit factors were significantly related to collaboration in education, which affects university and industry hospitality alliances. This finding confirm that the cooperation perspective (QD) and contextual factors (HC) are critical in collaboration between university and industry. A new point of interest is also identified that the benefits of training links are quite dependent on the linking perspective from tourism businesses.

• 대한기계학회논문집
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• 제16권4호
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• pp.737-752
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• 1992

본 연구에서는 링크를 여러개의 2절점 6자유도의 보 요소로 이상화하고 링크 의 운동을 평면 운동으로 한정하며 링크의 지지부의 강성은 무한대이고 회전 대우 부 분의 간극은 없는 것으로 가정하여 링크의 탄성 변형에 관한 운동 반정식을 유도하였 다. 즉, 변위법에 기초한 정적 변위 해석에 관한 유한 요소법에서 관성력, 중력 그 리고 외력을 외부 부하로 간주하여 동적인 운동 방정식을 유도하였다. 여기에, 회전 대우의 베어링을 선형 스프링으로 이상화하여 유연성 링크의 일부분으로 고려함으로써 베어링의 탄성 변형이 유연성 링크의 동적 변형에 미치는 영향에 대하여 고찰하였다. 베어링의 탄성 변형이 고려된 유연성 링크에 관한 운동 방정식을 모우드 중첩법에 근 거를 둔 수치해법으로 그 해를 구하였다.

• 터널과지하공간
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• 제9권1호
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• pp.12-19
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• 1999

장약량, 측정거리 등과 같은 발파조건들이 지반진동에 미치는 영향을 조사하기 위하여 골프장 조성공사를 위한 지표발파와 고속도로 건설공사를 위한 터널발파에서 지반진동을 측정하였다. 지표발파에서 삼승근 환산거리방법으로 구한 입지상수 K와 n은 각각 74.1, 01.37로 나타났다. 측정거리가 멀어질수록 Khk n의 절대값은 증가하였다. 지표발파에서 주주파수 대역은 5~60 Hz 이었으며, 그 중에 80% 정도는 10~30 Hz의 범위에 분포하였다. 반면에 터널발파의 주주파수 대역은 25~98Hz로서 지표발파보다 크게나타났다.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제10권4호
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• pp.1630-1642
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• 2016

Inter-domain routing is the most critical function of the Internet. The routing system is a logical network relying on the physical infrastructure with geographical characteristics. Nature disasters or disruptive accidents such as earthquakes, cable cuts and power outages could cause regional failures which fail down geographically co-located network nodes and links, therefore, affect the resilience of inter-domain routing system. This paper presents a model for regional failures in inter-domain routing system called REFER for the first time. Based on REFER, the resilience of the inter-domain routing system could be evaluated on a finer level of the Internet, considering different routing policies of intra-domain and inter-domain routing systems. Under this model, we perform simulations on an empirical topology of the Internet with geographical characteristics to simulate a regional failure locating at a city with important IXP (Internet eXchange Point). Results indicate that the Internet is robust under a city-level regional failure. The reachability is almost the same after the failure, and the reroutings occur at the edge of the Internet, hardly affecting the core of inter-domain routing system.