• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 1993.04a
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• pp.52-56
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• 1993

An efficient method is presented for determining transient responses of locally nonlinear structures using substructure eigenproperties and Lagrange multiplier technique. The method is based upon the mode synthesis formulation procedure, but does not construct the equations of motion of the combined whole structure compared with the conventional methods. For modal bases of each linear substructure, either fixed or free interface modes can be employed. The transient analysis is based upon the recurrence discrete-time state equations and offers the simplicity of the Euler integration method without requiring small time increment and iterative solution procedure. Numerical examples reveal that the method is very accurate and efficient in calculating transient responses compared with the direct numerical integration method.

• Transactions of the Korean Society of Mechanical Engineers
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• v.17 no.10
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• pp.2457-2466
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• 1993

A simple method is presented for determining transient responses of locally nonlinear structures using substructure eigenproperties and Lagrange multiplier technique. Although the method is based upon the mode synthesis formulation procedure, the equations of the combined whole structure are not constructed compared with the conventional methods. Lagrange multi-pliers are used to enforce the conditions of geometric compatibility between the substructure interfaces and they are treated as external forces on each substructure itself. Substructure eigenvalue problem is defined with the substructure interface free of fixed. The transient analysis is based upon the recurrence discrete-time state equations and offers the simplicity of the Euler integration method without requiring small time increment and iterative solution procedure. Numerical examples reveal that the method is very accurated and efficient in calculating transient responses compared with the direct numerical integration method.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2006.11a
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• pp.848-854
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• 2006

In this study, a computational analysis system has been developed in order to investigate flow-induced vibration(FIV) phenomenon for general stator-rotor cascade configurations. Relative movement of the rotor with respect to stator is reflected by modeling independent two computational domains. Fluid domains are modeled using the unstructured grid system with dynamic moving and local deforming methods. Unsteady, Reynolds-averaged Navier-Stokes equations with one equation Spalart-Allmaras and two-equation SST $k-\omega$ turbulence models are solved for unsteady flow problems. A fully implicit time marching scheme based on the Newmark direct integration method is used flow computing the coupled governing equations of the fluid-structure interaction problem. Detailed FIV responses for different flow conditions are presented with respect to time and vibration characteristics are also physically investigated in the time domain.

• 한국전산유체공학회:학술대회논문집
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• 2000.05a
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• pp.66-72
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• 2000

Aerodynamic sensitivity analysis is performed for the Navier-Stokes equations coupled with two-equation turbulence models using a discrete adjoint method and a direct differentiation method respectively. Like the mean flow equations, the turbulence model equations are also hand-differentiated to accurately calculate the sensitivity derivatives of flow quantities with respect to design variables in turbulent viscous flows. Both the direct differentiation code and the adjoint variable code adopt the same time integration scheme with the flow solver to efficiently solve the differentiated equations. The sensitivity codes are then compared with the flow solver in terms of solution accuracy, computing time and computer memory requirements. The sensitivity derivatives obtained from the sensitivity codes with different turbulence models are compared with each other. Using two-equation turbulence models, it is observed that a usual assumption of constant turbulent eddy viscosity in adjoint methods may lead to seriously inaccurate results in highly turbulent flows.

• Structural Engineering and Mechanics
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• v.38 no.2
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• pp.211-229
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• 2011

In this paper, we present a new explicit procedure using periodic cubic B-spline interpolation polynomials to solve linear and nonlinear dynamic equation of motion governing single degree of freedom (SDOF) systems. In the proposed approach, a straightforward formulation was derived from the approximation of displacement with B-spline basis in a fluent manner. In this way, there is no need to use a special pre-starting procedure to commence solving the problem. Actually, this method lies in the case of conditionally stable methods. A simple step-by-step algorithm is implemented and presented to calculate dynamic response of SDOF systems. The validity and effectiveness of the proposed method is demonstrated with four examples. The results were compared with those from the numerical methods such as Duhamel integration, Linear Acceleration and also Exact method. The comparison shows that the proposed method is a fast and simple procedure with trivial computational effort and acceptable accuracy exactly like the Linear Acceleration method. But its power point is that its time consumption is notably less than the Linear Acceleration method especially in the nonlinear analysis.

• Proceedings of the KSPS conference
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• 2002.11a
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• pp.205-208
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• 2002

Bimodal speech recognition based on lip reading has been studied as a representative method of speech recognition under noisy environments. There are three integration methods of speech and lip modalities as like direct identification, separate identification and dominant recording. In this paper we evaluate the robustness of lip reading methods under the assumption that lip parameters are estimated with errors. We show that the dominant recording approach is more robust than other methods with lip reading experiments. Also, a measure of lip parameter degradation is proposed. This measure can be used in the determination of weighting values of video information.

• Journal of The Korean Society of Integrative Medicine
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• v.9 no.4
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• pp.201-210
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• 2021

Purpose : There is a lack of research on this field in the Republic of Korea, especially those that have seen the effect of interaction between transcranial direct current stimulation and computerized cognitive rehabilitation therapy. This study divided 30 dementia patients into a treatment group, which received transcranial direct current stimulation and computerized cognitive rehabilitation, and a control group, which received pseudo-transcranial direct current stimulation and pseudo-computerized cognitive rehabilitation. This study evaluated the effects of these treatments on the visual perception, cognition functions, and daily activities of dementia patients. Methods : Fifteen subjects were allocated to the treatment group and the other 15 subjects were allocated to the control group. Treatments were given at intervals of five sessions per week (30 minutes per session) for six weeks (30 times in total). This study used the Neurobehavioral Cognitive Status Examination (NCSE) to examine cognitive functions, MVPT to evaluate visual perception, and FIM to test daily living activities before and after applying the treatments. Results : The results of this study showed that cognitive functions, visual perception, and daily living activities significantly (p<.05) improved after the intervention in the treatment group and the control group. The changes in cognitive functions, visual perception, and daily living activities due to the treatments were significantly different between the groups (p<.05). Conclusion : The results indicated that transcranial direct current stimulation and computerized cognitive rehabilitation therapy improved visual perception and daily living activities by increasing cognitive functions. Consequently, it was found that the simultaneous application of transcranial direct current stimulation in conjunction with a computerized cognitive rehabilitation program was an intervention method that could positively affect the visual perception, cognitive function, and daily living activities of dementia patients. Based on the results of this study, the study of arbitration protocols for demential will have to be more active.

• Journal of The Korean Society of Integrative Medicine
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• v.9 no.3
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• pp.155-164
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• 2021

Purpose : The purpose of this study is to investigate the effects of transcranial direct current stimulation and virtual reality program application on cognition and depression of patients with mild cognitive impairment, and to find an intervention method that can enhance active participation of patients with mild cognitive impairment. Methods : In this study, 50 mild cognitive impairment patients were divided into a treatment group (25 patients) and a control group (25 patients). The treatment group was applied with a transcranial direct current stimulation and a virtual reality program, while the control group received a placebo transcranial direct current stimulation and a virtual reality program. Both groups received five 50-minute sessions per week (one session per day) for six weeks (total of 30 sessions). NCSE was used to evaluate the cognitive functions of the patients before and after treatment intervention. Moreover, K-BDI was conducted to examine the depression of the patients. Results : As a result of the transcranial direct current stimulation and a virtual reality program intervention, the cognitive function of both treatment and control group significantly (p<.05) improved, and the depression of both treatment and control group significantly (p<.05) decreased. Moreover, the changes in cognitive functions and depression were significant between the two groups¸ treatment and control group (p<.05). Conclusion : The results of the study showed that the application of the transcranial direct current stimulation and virtual reality program significantly improved the cognitive function of mild cognitive impairment patients and decreased the depression of them. Therefore, it could be concluded that the transcranial direct current stimulation and virtual reality program was an intervention method which positively affects the cognitive function and depression of mild cognitive impairment patients.

• Journal of computational fluids engineering
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• v.13 no.4
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• pp.114-125
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• 2008

Current state and perspective of DNS of turbulence and turbulent combustion are discussed with feature trend of the fastest supercomputer in the world. Based on the perspective of DNS of turbulent combustion, possibility of perfect simulations of IC engine is shown. In 2020, the perfect simulation will be realized with 30 billion grid points by 1EXAFlops supercomputer, which requires 4 months CPU time. The CPU time will be reduced to about 4 days if several developments were achieved in the current fundamental researches. To shorten CPU time required for DNS of turbulent combustion, two numerical methods are introduced to full-explicit full-compressible DNS code. One is compact finite difference filter to reduce spatial resolution requirements and numerical oscillations in small scales, and another is well-known point-implicit scheme to avoid quite small time integration of the order of nanosecond for fully explicit DNS. Availability and accuracy of these numerical methods have been confirmed carefully for auto-ignition, planar laminar flame and turbulent premixed flames. To realize DNS of IC engine with realistic kinetic mechanism, several DNS of elemental combustion process in IC engines has been conducted.

• 한국전산유체공학회:학술대회논문집
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• 2008.03a
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• pp.359-366
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• 2008

Current state and perspective of DNS of turbulence and turbulent combustion are discussed with feature trend of the fastest supercomputer in the world. Based on the perspective of DNS of turbulent combustion, possibility of perfect simulations of IC engine is shown. In 2020, the perfect simulation will be realized with 30 billion grid points by 1EXAFlops supercomputer, which requires 4 months CPU time. The CPU time will be reduced to about 4 days if several developments were achieved in the current fundamental researches. To shorten CPU time required for DNS of turbulent combustion, two numerical methods are introduced to full-explicit full-compressible DNS code. One is compact finite difference filter to reduce spatial resolution requirements and numerical oscillations in small scales, and another is well-known point-implicit scheme to avoid quite small time integration of the order of nanosecond for fully explicit DNS. Availability and accuracy of these numerical methods have been confirmed carefully for auto-ignition, planar laminar flame and turbulent premixed flames. To realize DNS of IC engine with realistic kinetic mechanism, several DNS of elemental combustion process in IC engines has been conducted.