• Journal of the Korean Society of Combustion
• /
• v.23 no.1
• /
• pp.13-20
• /
• 2018

Transverse acoustic mode in annular combustion chambers affects air-fuel mixing characteristics in the nozzle and can result in heat release fluctuations in the combustor. In addition, the acoustic mode coupling between the nozzle and the combustion chamber is one of the key parameters determining combustion instability phenomenon in the annular combustor. In this study, acoustic coupling between the nozzle and annular combustor was numerically analyzed using 3D-based in house FEM code. As a result, it was found that the acoustic mode inside the combustion chamber at anti-node locations of the transverse mode was strongly influenced by the nozzle inlet boundary conditions.

• Transactions of the Korean Society of Automotive Engineers
• /
• v.10 no.5
• /
• pp.160-167
• /
• 2002

The transient thermoelastic analysis of automotive disk brakes with frictional contact is performed by using the finite element method. To analyze the thermoelastic behaviors occurring in disk brakes, the coupled heat conduction and elastic equations are solved. The fully implicit transient scheme is used to improve the computation accuracy at every time step. The numerical results of the thermoelastic behaviors are obtained during the repeated braking condition. The computational results show that the thermoelastic instability(TEI) phenomenon(the growth of non-uniformities in contact pressure) occurs in disk brakes. Also, the effect of material properties on the thermoelastic behaviors is investigated to facilitate the conceptual design of the brake system.

• Transactions of the Korean Society of Mechanical Engineers
• /
• v.18 no.9
• /
• pp.2284-2296
• /
• 1994

Force control of robotic mechanisms continues to be a challenging area. Previous implementation have seldom produced satisfactory results, and researchers in the past have experienced significant instability problems associated with their force controllers. In this study, a new stability factor in force control will be pointed out. When a manipulator is constrained to an environment(force-controlled), geometric instability due to the relationship between the manipulator configuration and the force-controlled direction is shown to be a significant factor in overall system stability. This exploratory study points out a rather intuitive, geometrically based stability factor in terms of an effective system stiffness and analyzes the phenomenon both analytically and graphically. Also, a stiffness control algorithm using the kinematic redundancy of a kinematically redundant manipulator is proposed to improve the overall stability in force control.

• 한국전산유체공학회:학술대회논문집
• /
• 1999.11a
• /
• pp.48-58
• /
• 1999

The Characteristic Flux Difference Splitting (CFDS) scheme designed to adapt the characteristic boundary conditions at the wall and inflow/outflow boundary planes satisfies Roe's property U, although the CFDS Jacobian matrix is decomposed by a product of elaborate transformation matrices and explicit eigenvalue matrix. When the CFDS algorithm, thus a variant of Roe's scheme, is applied straightforwardly to hypersonic flows over a blunt body, the strong bow shock gradually breaks down near the stagnation point. This numerical instability is widely observed by many researchers employing flux-difference method, known in the literature as the carbuncle phenomenon. Many remedies have been proposed and resulted in partial cures. When the idea of Sanders et al. which identifies the minimum eigenvalues near the discontinuity present is applied to CFDS method, it is shown that the instability problem can be controlled successfully. A few flux splitting methods have also been tested and results are compared against the Nakamori's Mach 8 blunt body flow.

• Journal of the Korean Society for Precision Engineering
• /
• v.13 no.8
• /
• pp.96-101
• /
• 1996

Glass fiber reinforced polymeric composites hold considerable promise for increased use in low cost high volume applications because of the potential for processing by solid phase forming. Unfortunately, because of the wide variety of such materials, inherent bariability in properties, and complex temperature and strain rate dependence, large strain behavior of these materials has not been well characterized. Of particular importance is failure during processing due to localized necking instability, and it is this phenomenon that is primary focus of this study. The strain rate and temperature dependence is used to predict limiting tensile strains, based on Mackinack imperfection theory. Excellent correlation was obtained between theory and experiment, and the results are summarized in the limit strains as a function of temperature and stain rate.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 1997.04a
• /
• pp.621-626
• /
• 1997

Combustion instability is a common phenomenon in a ducted flame burner and is known as accompanying low frequency oscillation. This is due to the interaction between unsteady heat release rate and sound pressure field, that is, thermoacoustic feedback. In Rayleigh criterion, combustion instability is triggered when the heat additions is in phase with acoustic oscillation. A Rijke type burner with a pre-mixed flame is built for investigating the effect of Reynolds number and equivalence ratio on thermoacoustic oscillation. In addition, the effect of wall temperature is presented. The results suggest that the frequency of max. oscillation is dependent on Reynolds number and equivalence ratio whereas its magnitude is not a strong function of these two parameters. On the other hand, the wall temperature distribution has much strong effects on the oscillation, even creates different mode of acoustic resonance.

• Proceedings of the Computational Structural Engineering Institute Conference
• /
• 2001.10a
• /
• pp.167-174
• /
• 2001

A shape resistant shell structure is an extremely efficient mechanical creation because it transmits forces mainly by in-plane forces, but at a certain load level it changes from a stable condition to an unstable condition or vise versa. The instability phenomenon of Geiger-type cable dome structure is generated due to the in-plane twisting near critical load level. Therefore the effect of bracing reinforcement is investigated for the Geiger-type model reinforced by bracing. The effect of initial imperfection is also studied since the structural instability behavior characteristic of shell-like structure is significantly sensitive according to the initial condition.

• The Transactions of the Korean Institute of Electrical Engineers B
• /
• v.53 no.6
• /
• pp.402-408
• /
• 2004

This paper proposes the novel V/f control method to improve the stability of a V/f controlled induction motor drive system. The conventional V/f control method used in the proposed V/f control method is a vector-based method that is slightly different from the existing conventional V/f control method. The proposed control method uses a dynamic current compensator to improve the stability of a V/f controlled induction motor drive system. This proposed method is easy to implement and completely eliminates the motor oscillation phenomenon causing the instability of a V/f controlled induction motor drive system, especially when the system is driven near the resonant frequency in steady-state with light load. Additionally, this paper analyzes theoretically the instability of a V/f controlled induction motor drive system and shows the validity of the Proposed V/f control method through simulation and experimental results.

• The Journal of Internal Korean Medicine
• /
• v.45 no.2
• /
• pp.219-233
• /
• 2024

A 69-year-old female diagnosed with idiopathic Parkinson's disease and treated with anti-Parkinsonian medications, including levodopa, for 7 years presented with complaints of wearing-off phenomenon and delayed onset of medication efficacy, resulting in postural instability and feeling of severe exhaustion. The patient underwent a 50-day course of treatment with Bonoesikpungjigyeong-tang formula. The effects of the treatment were evaluated by recording the average time to onset of medication efficacy, the average time to medication wearing-off, and discomfort due to wearing-off phenomenon. Postural instability was assessed using the Numeric Rating Scale (NRS). The patient's overall quality of life was assessed using the EQ-5D-3L. After 50 days of treatment, the average time to onset of medication efficacy decreased, and the average time to medication wearing-off increased. Discomfort due to wearing-off phenomenon and postural instability decreased. This case suggests that Bonoesikpungjigyeong-tang might be an alternative for improving discomfort caused by long-term levodopa intake.

• Journal of Mechanical Science and Technology
• /
• v.15 no.5
• /
• pp.569-579
• /
• 2001

This study investigates the effects of operating conditions on the chattering of an automotive disk brake by experimental and computational methods. Design factors, which cause chattering in automobiles, have attracted great attentions for long time; but they are not well understood yet. For this study, we construct a brake dynamometer for measuring the disk surface temperature during chattering, and propose an efficient hybrid algorithm (combining FFT-FEA and traditional FEA program) for analyzing the thermo-elastic behavior of three-dimensional brake system. We successfully measure the judder in a brake system via the dynamometer and efficiently simulate the contact pressure variation by the hybrid algorithm. The three-dimensional simulation of thermo-mechanical interactions on the automotive brake, showing the transient thermo-elastic instability phenomenon, is presented for the first time in this academic community. We also find from the experimental study that the disk bulk temperature strongly influences the brake chattering in the automotive disk brakes.