• The Transactions of the Korean Institute of Electrical Engineers
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• v.43 no.5
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• pp.693-702
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• 1994

This paper deals with direct voltage stability analysis using a power system energy function. The structure preserved energy function is proposed as an energy function for voltage stability analysis. With the use of the proposed energy function voltage collapse conditions are derived, which yields the exactly same results with the Jacobian matrix approach. The voltage collapse phenomenon is analyzed by several methods, which shows that all of the methods produce the same voltage condition. This study also investigates the voltage collapse dynamics by using the proposed energy function. As a result, it has been found that the voltage collapse can be classified into two categories: static and dynamic instablilties which have quite different behaviors. In addition a new method is presented to calculate the power capacity limit of transmission lines with respect to voltage stability. The proposed method is tested for a 2-bus sample system, which shows the characteristics of voltage collapse phenomenon via the energy function.

• Journal of the Korean Geotechnical Society
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• v.16 no.4
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• pp.51-61
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• 2000

This paper reviews fundamentals of a pseudo-static seismic design/analysis method for soil-reinforced segmental retaining walls. A comparative study on NCMA and FHWA seismic design guidelines, which are one of the most well known design guidelines for mechanically stabilized earth walls, was also performed. The results demonstrate that there exist significant discrepancies in the results of external stability analysis despite the same calculation model used in the two guidelines, due primarily to different seismic coefficient selection criteria. It is also demonstrated that the internal stability calculation model for NCMA guideline tends to yield larger seismic reinforcement force in the shallower reinforcement layers, resulting in an increased number of reinforcement layers at the top of reinforced wall and increased reinforcement lengths to ensure adequate anchorage capacity. The internal stability calculation model adopted by FHWA guideline, however, leads to redistribution of dynamic force to the lower reinforcement layers and thus results n an opposite trend of NCMA guideline. Findings from this study clearly demonstrate a need for more in-depth studies to develop a generally acceptable design/analysis method.

• Journal of Korean Society of Steel Construction
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• v.17 no.5 s.78
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• pp.537-547
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• 2005

MABB(Editor's note: Please spell out "MABB" upon first mention)is a new structural type of arch that connects arch ribs and stiffened girders with two internal arches. In this study, the static and dynamic behavior of MABB were analyzed in comparison with those of conventional arches for the investigation of the structural effect of MABB on moving loads. For the purpose of surveying the effect of internal arches on the dynamic behavior of structure, natural frequency and natural vibration mode were investigated and the static and dynamic behavior were analyzed by the method of idealizing train loads as traveling loads consisting of a group of concentrated loads. From the results, the following conclusions were known. First, it is concluded that with MABB, decreasing the section of stiffened girders is possible as compared with conventional arches because the increase of stiffness by internal arches is larger than that of the mass of internal arches. Second, MABB has the advantage of assurance of stability of dynamic behavior because the dynamic behavior of MABB on moving loads is usually investigated in a more stable way than that of conventional arches.

• Journal of the Korea institute for structural maintenance and inspection
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• v.12 no.3
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• pp.155-166
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• 2008

Research dam is consisted of concrete gravity dam that right bank department is built to concrete material, left bank department is composition dam that is consisted of rockfill dam that consist of rockfill material In domestic case, composition dam form of storage of water facilities of about 17,000 does not exist hardly in dam of irrigation water industry drinking water purpose that manage local government or other institution, Even if exist, is real condition that there is total nonexistence administrator fare of facilities, Choose unique dam of domestic multipurpose dam and analyzed conduct special quality of con'c gravity dam and rockfill dam joint part To analyze dynamic conduct special quality of composition dam by analytic method in this research, Do modelling via axis of dam and achieved static(Psuedo-static, modify Psuedo-static) and dynamic analysis, When achieving earthquake response analysis, analyzed seismic response analysis between concrete part and rockfill's part.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.16 no.6
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• pp.4115-4120
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• 2015

To ensure the transient stability of power system connected to a wind farm, wind power plant must be able to supply reactive power at the point of the common coupling(PCC). The reactive power capability of each individual wind turbine may not sufficient to maintain stability. Also, there are large reactive power losses in connection cables between wind farm and PCC. The static synchronous compensator(STATCOM) is considered for transient stability enhancement, because it provides many advantages such as the fast response time and superior reactive power support capability. In this paper, the effectiveness of a STATCOM in enhancing transient stability of power system connected to a wind farm is presented. The results of dynamic simulations show that STATCOM installed at the PCC can enhance transient stability.

• The Transactions of the Korean Institute of Electrical Engineers A
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• v.50 no.1
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• pp.6-12
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• 2001

This paper deals with the development of dynamic equivalents of the Korea Electric Corporation (KEPCO) systems. The weak coupling method is chosen for the most suitable coherency identification to represent the characteristics of the KEPCO system by the dynamic characteristic comparison of several coherency identification methods. Also, this paper shows the detail aggregation of generator groups makes a better representation of the dynamic and static characteristics of the original system than the classical aggregation. The simulation results of the developed KEPCO equivalent system are presented in comparison with the original system to illustrate the validity of the equivalent system are presented in comparison with the original system to illustrate the validity of the equivalent system.

• Journal of the Korean Society for Railway
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• v.10 no.6
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• pp.701-708
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• 2007

A tilting train, which was developed to run the curve section without reducing the speed and compromising the riding quality, can improve the speed so as to reduce the travel time, compared to the existing trains. Then the force generated by the train operation to the track is in proportion to train operation speed, which means the track shall bear the increased force as much as the increase in train operation speed. Particularly, wheel load and lateral wheel load generated by train operation and distributed to the rail tend to cause the track to suffer the strain and furthermore the severe disaster such as derailment. To deal with such problem and ensure the train will run safety and stably, the tolerance in wheel load change, lateral wheel load and derailment coefficient was determined for quantitative evaluation of the train operation stability. In this study, derailment coefficient of inner and outer rail at existing curve section of tilting train was determined to evaluate the curve radius, possibility of acceleration and the need of rail improvement, which was then compared with the existing traditional train and high speed train. Conducting the quantitative evaluation of dynamic wheel load and lateral wheel load of each train, which was based on field survey, derailment coefficient and static & dynamic wheel load change, which serve the evaluation criteria of train operation stability, were determined for comparison with the standards, thereby analyzing the stability of the tilting train.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.14 no.5
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• pp.402-409
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• 2004

Numerical analysis of static and dynamic wind effects on civil engineering structures was performed. Long-span suspension bridges are flexible structures that are highly sensitive to the action of the wind. Aerodynamic effect often becomes a governing factor in the design process of bridges and aeroelastic stability boundary becomes a prime criterion which should be confirmed during the structural design stage of bridges because the long-span suspension bridges are prone to the aerodynamic instabilities caused by wind. If the wind velocity exceeds the critical velocity that the bridge can withstand, then the bridge fails due to the phenomenon of flutter. Buffeting caused by turbulence results in structural fatigue, which could lead to the failure of a bridge. Navier-Stokes equations are used for the aeroelastic analysis of bridge girder section. The aeroelastic simulation is carried out to study the aeroelastic stability of bridges using both Computational Fluid Dynamic (CFD) and Computational Structural Dynamic (CSD) schemes.

• The Journal of Korean Physical Therapy
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• v.17 no.3
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• pp.351-367
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• 2005

The purpose of this study was to identity effects of virtual reality(VR) program related to standing postural control on balance, gait and brain activation patterns in chronic hemiplegic stroke patients. Subjects were assigned randomly to either VR group (n=12) or the control group (n=12) when the study began. Both groups received conventional physical therapy for 2 to 3 times per week. In addition to conventional physical therapies, VR group trained 3 types of virtual reality programs using IREX for standing postural control during 4 weeks (4 times/week, 30 minutes/time). Subjects were assessed for static and dynamic balance parameters using BPM, functional balance using Berg Balance Scale related to movement of paretic lower limb before and after 4 weeks of virtual reality training. The results of this study were as follows. 1. Following VR training, VR group demonstrated the marked improvement on dynamic mean balance, anteroposterior limits of stability (AP angle) and mediolateral limits of stability (ML angle). 2. Following VR training, both groups scored higher on Berg Balance Scale. However, a comparison of mean change revealed differences between groups. In conclusion, these data suggest that the postural control training using VR programs improve dynamic and functional balance performance in chronic hemiplegic stroke patients.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.11 no.8
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• pp.314-321
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• 2001

Static and oscillatory loss of stability of composite pipes conveying fluid is Investigated. The theory of than walled beams is applied and transverse shear. rotary inertia, primary and secondary warping effects are incorporated. The governing equations and the associated boundary conditions are derived through Hamilton's variational principle. The governing equations and the associated boundary conditions are transformed to an eigenvlaue problem which provides the Information about the dynamic characteristics of the system. Numerical analysis is performed by using extended Gelerkin method. Variation of critical velocity of fluid with fiber angles and mass patios of fluid to pipe Including fluid is investigated.