• Korean Journal of Metals and Materials
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• v.48 no.6
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• pp.477-488
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• 2010

Zr-based amorphous alloy matrix composites reinforced with stainless steel (STS) and tantalum continuous fibers were fabricated without pores or defects by a liquid pressing process, and their quasi-static and dynamic deformation behaviors were investigated by using a universal testing machine and a Split Hopkinson pressure bar, respectively. The quasi-static compressive test results indicated that the fiberreinforced composites showed amaximum strength of about 1050~1300 MPa, and its strength maintained over 700 MPa until reaching astrain of 40%. Under dynamic loading, the maximum stresses of the composites were considerably higher than those under quasi-static loading because of the strain-rate hardening effect, whereas the fracture strains were considerably lower than those under quasi-static loading because of the decreased resistance to fracture. The STS-fiber-reinforced composite showed a greater compressive strength and ductility under dynamic loading than the tantalum-fiber-reinforced composite because of the excellent resistance to fracture of STS fibers.

• The Transactions of the Korean Institute of Electrical Engineers A
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• v.52 no.6
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• pp.295-300
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• 2003

Voltage instability has been studied for some decade now. But, There is not generally accepted definition of voltage instability because of the complex phenomenon and the variety of ways in which it can manifest itself. Both IEEE and CIGRE have the respective definitions. The areas of voltage instability research are the analysis, simulation and countermeasure of voltage instability. It needs to model the components of the power system to simulate the voltage instability and voltage collapse. At the beginning, the static simulation was used. This method provides the voltage stability indices and it requires less CPU resource and gives much insight into the voltage and power problem. However, it is less accurate than the dynamic simulation peformed in the time domain simulation. So, when it appears difficult to secure the voltage stability margin in a static stability, it is necessary to perform the dynamic simulation. To perform time-domain simulation, we have to model the dynamic component of the power system like a generator and a load. The dynamic simulation provides the accurate result of the voltage instability. But, it is not able to provide the sensitivity information or the degree of stability and it is time consuming and it needs much CPU resource. In this Paper, we perform a dynamic simulation of voltage instability and voltage collapse using EMTP MODELS. The exponential load model is designed with MODEIS and this load model is connected with test power system. The result shows the process of voltage change in time domain when the voltage instability or voltage collapse occurs.

• Journal of Korean Association for Spatial Structures
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• v.10 no.1
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• pp.119-126
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• 2010

The some papers which deal with the dynamic instability for shell-like structures under the dynamic excitation have been published, but there are few papers which treat the essential phenomenon of the dynamic buckling using the phase plane for investigating occurrence of chaos. In nonlinear dynamic, examining the characteristics of attractor on the phase plane and investigating the dynamic buckling process are very important thing for understanding why unstable phenomena are sensitively originated by various initial conditions. In this study, the direct and indirect snapping of shallow EP shell considering geometrical nonlinearity are investigated by Galerkin method numerically. This finding out the characteristic of the dynamic instability through the phases curves and running response spectrum.

• The Journal of Asian Finance, Economics and Business
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• v.7 no.8
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• pp.485-494
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• 2020

The paper proposes a conceptual model which provides direction for researchers to empirically establish the connections between dynamic capabilities, innovation capabilities, entrepreneurial capabilities and financial and strategic performance. The author uses systematic literature review process to select the articles used in this study. First, the present paper review and discuss some major contributions to the theories of dynamic capabilities, innovation capabilities, entrepreneurial capabilities and their consequences. The author seeks to highlight different understandings of the concepts to clarify the distinctions between them. Second, the conceptual model and propositions for future studies were developed. The proposed model highlights the different measures of dynamic capabilities, innovation capabilities, entrepreneurial capabilities and their consequences. The model with its associated propositions was developed base on limitations and gaps observed from past studies. It is focused on empirically testing the direct impact of dynamic capabilities, innovation capabilities, and entrepreneurial capabilities on the performance of SMEs in Vietnam. Nevertheless, the proposed model can be applied to similar situations in different contexts and countries. Further empirical testing of proposed model would contribute to enriching existing knowledge of dynamic capabilities, innovation capabilities and entrepreneurial capabilities within SMEs and how these capabilities foster superior performance.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.23 no.6
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• pp.659-665
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• 2010

The finite element method(FEM) is proven to be an effective approximate method of structural analysis if proper element types and meshes are chosen, and recently, the method is often applied to solve complex dynamic and nonlinear problems. A properly chosen element type and mesh yields reliable results for dynamic finite element structural analysis. However, dynamic behavior of a structure may include unpredictably large strains in some parts of the structure, and using the initial mesh throughout the duration of a dynamic analysis may include some elements to go through strains beyond the elements' reliable limits. Thus, the finite element mesh for a dynamic analysis must be dynamically adaptive, and considering the rapid process of analysis in real time, the dynamically adaptive finite element mesh generating schemes must be computationally efficient. In this paper, a computationally efficient dynamically adaptive finite element mesh generation scheme for dynamic analyses of structures is described. The concept of representative strain value is used for error estimates and the refinements of meshes use combinations of the h-method(node movement) and the r-method(element division). The shape coefficient for element mesh is used to correct overly distorted elements. The validity of the scheme is shown through a cantilever beam example under a concentrated load with varying values. The example shows reasonable accuracy and efficient computing time. Furthermore, the study shows the potential for the scheme's effective use in complex structural dynamic problems such as those under seismic or erratic wind loads.

• Journal of Power Electronics
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• v.18 no.1
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• pp.34-44
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• 2018

This paper presents a pulse-width adjustment (PWA) strategy for a novel bidirectional DC-DC boost converter to improve the performance of the dynamic inductor current response. This novel converter consists of three main components: a full-bridge converter (FBC), a high-frequency isolated transformer with large leakage inductance, and a three-level voltage-doubler rectifier (VDR). A number of scholars have analyzed the principles, such as the soft-switching performance and high-efficiency characteristic, of this converter based on pulse-width modulation plus phase-shift (PPS) control. It turns out that this converter is suitable for energy storage applications and exhibits good performance. However, the dynamic inductor current response processes of control variable adjustment is not analyzed in this converter. In fact, dc component may occur in the inductor current during its dynamic response process, which can influence the stability and reliability of the converter system. The dynamic responses under different operating modes of a conventional feedforward control are discussed in this paper. And a PWA strategy is proposed to enhance the dynamic inductor current response performance of the converter. This paper gives a detailed design and implementation of the PWA strategy. The proposed strategy is verified through a series of simulation and experimental results.

• Proceedings of the Membrane Society of Korea Conference
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• 2001.05a
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• pp.120-123
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• 2001

• Journal of Welding and Joining
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• v.20 no.4
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• pp.459-466
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• 2002

• 제어로봇시스템학회:학술대회논문집
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• 1991.10b
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• pp.1705-1711
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• 1991

On-line fault detection and diagnosis has an increasing interest in a chemical process industry, especially for a process control and automation. The chemical process needs an intelligent operation-aided workstation which can do such tasks as process monitoring, fault detection, fault diagnosis and action guidance in semiautomatic mode. These tasks can increase the performance of a process operation and give merits in economics, safety and reliability. Aiming these tasks, series of researches have been done in our lab. Main results from these researches are building appropriate knowledge representation models and a diagnosis mechanism for fault detection and diagnosis in a chemical process. The knowledge representation schemes developed in our previous research, the symptom tree model and the fault-consequence digraph, showed the effectiveness and the usefulness in a real-time application, of the process diagnosis, especially in large and complex plants. However in our previous approach, the diagnosis speed is its demerit in spite of its merits of high resolution, mainly due to using two knowledge models complementarily. In our current study, new knowledge representation scheme is developed which integrates the previous two knowledge models, the symptom tree and the fault-consequence digraph, into one. This new model is constructed using a material balance, energy balance, momentum balance and equipment constraints. Controller related constraints are included in this new model, which possesses merits of the two previous models. This new integrated model will be tested and verified by the real-time application in a BTX process or a crude unit process. The reliability and flexibility will be greatly enhanced compared to the previous model in spite of the low diagnosis speed. Nexpert Object for the expert system shell and SUN4 workstation for the hardware platform are used. TCP/IP for a communication protocol and interfacing to a dynamic simulator, SPEEDUP, for a dynamic data generation are being studied.

• 한국생물공학회:학술대회논문집
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• 2003.10a
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• pp.477-477
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• 2003