• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 1994.10a
• /
• pp.288-294
• /
• 1994

A study of prediction and qualification techniques for structure borne booming noise is presented in this paper. Result from acoustic normal mode finite element analysis of a 1/2 size vehicle cavity sample model is compared to the that from an experiment. Coupled structural-acoustic analysis is performed on a 1/4 size vehicle cavity sample model surrounded by 2 mm thick normal steel plates. Interior noise levels around passensger's ear position are predicted and reduced by structural modification based on panel participation factor analysis about the sample cavity model. Futhermore, optimization technique in application of anti-vibration pad is studied.

• The Bulletin of The Korean Astronomical Society
• /
• v.39 no.1
• /
• pp.37.2-37.2
• /
• 2014

Gas in disk galaxies interacts nonlinearly with a underlying stellar spiral potential to form galactic spiral shocks. Numerical simulations typically show that these shocks are unstable to the wiggle instability, forming non-axisymmetric structures with high vorticity. While previous studies suggested that the wiggle instability may arise from the Kelvin-Helmholtz instability or orbit crowding of gas elements near the shock, its physical nature remains uncertain. It was even argued that the wiggle instability is of numerical origin, caused by the inability of a numerical code to resolve a shock that is inclined to numerical grids. In this work, we perform a normal-mode linear stability analysis of galactic spiral shocks as a boundary-value problem. We find that the wiggle instability originates physically from the potential vorticity generation at a distorted shock front. As the gas follows galaxy rotation, it periodically passes through multiple shocks, successively increasing its potential vorticity. This sets up a normal-mode that grows exponentially, with a growth rate comparable to the orbital angular frequency. We show that the results of our linear stability analysis are in good agreement with the those of local hydrodynamic simulations of the wiggle instability.

• The Transactions of the Korean Institute of Power Electronics
• /
• v.18 no.5
• /
• pp.448-457
• /
• 2013

This paper proposes a control method under stand-alone operating mode for distributed-module type photovoltaic power conditioners. In conventional schemes, there are some problems of a controller saturation in the DC-link (or load) voltage controller when overly-heavy load, light load, and the generated PV power reduction occurs, as well as when a transition occurs from an overly-loaded to normal conditions. To overcome these problems, the proposed controller method switches the main control target from DC-link voltage to the maximum power point, which is closer to the stable operating point when it returns to normal operating conditions. For the analysis, a state-plane trajectory was given and the circuit analysis by PSIM simulation was done. For the verification, a prototype hardware with 110[W] and 50[W] dual photovoltaic modules has been implemented. From the results, it can be seen that PV power tracking is successfully done with the proposed method even under a stand-alone operation mode.

• Aerospace Engineering and Technology
• /
• v.6 no.1
• /
• pp.35-44
• /
• 2007

In this study was made the flutter analysis for the export model of Firefly(Bandi-ho), the small canard aircraft. Stiffness model based on internal load generation finite element model was generated. Mass model based on the weight DB for weight control was generated. Aerodynamic model based on Doublet Lattice Method was generated. Preliminary flutter analysis was made. Based on it, major vibration modes are identified and experimentally obtained via the ground vibration test. The obtained normal mode frequencies were used to correlate the finite element model. Flutter analysis was made again and major flutter mechanisms were summarized. The most important flutter root was identified as a coupled root between rigid body roll mode and anti-symmetric wing pitching mode.

• Journal of the Korea institute for structural maintenance and inspection
• /
• v.5 no.1
• /
• pp.237-246
• /
• 2001

This study is to measure the creep coefficient by 3 days, 7 days and 28 days in the age when loading for the quality assessment of $350kgf/cm^2$ in the high-strength concrete. And it is to analyze the behavior of creep coefficient by applying the experimental data though the compressive strength test, the elastic modulus test and the dry shrinkage test to the ACI-209, AASHTO-94 and CEB/FIP-90, the prediction mode, and the basis of concrete structural design. Also it is to analyze the behavior of short-term creep coefficient during 91 days in the age when loading through the experiment by using the regression analysis, the statistical theory. As applying it to the long-term behavior during 365 days and comparing with the creep prediction mode and examining it, the result from the analysis of the quality of the concrete is as follows. As the result of comparison and analysis about the ACI-209, AASHTO-94 and CEB/FIP-90, the prediction mode, and the basis of concrete structural design, the normal Portland cement class 1 shows the approximate value with the prediction of GEE/PIP-90 and the basis of concrete structural design, but in case of the prediction of ACI-209 and AASHTO-94, there would be worry of underestimation in the application.

• Fire Science and Engineering
• /
• v.16 no.1
• /
• pp.39-44
• /
• 2002

In this paper, we analysed the flame patterns and the electrical characteristics of the electric outlet which was fired at standby mode. The carbonized patterns indicated that the flame had spread about 50 cm to 70 cm. After the combustibles on wall started to burn, the temperature went up to about $300^{\circ}c$ in 150 sec. The flame formed ceiling jet and spread quickly. The tracking was generated at the shortest distance between two electrodes and the resistance was about 100$\Omega$ to 300$\Omega$ As the result of analysis using metallurgical microscope, the normal part of a blade holder showed amorphous structure, but the melted part of a blade holder damaged by tracking showed dendrite structure and void evenly. When the blade holder of damaged outlet was analyzed by SEM and EDX, we found that the structure and components of the normal part were different from those of melted part.

• International Journal of Precision Engineering and Manufacturing
• /
• v.2 no.4
• /
• pp.30-39
• /
• 2001

This paper investigates vibrational motion of a flexible beam fixed on a moving cart and carrying a moving mass. The equations of motion of the beam-mass-cart system are analysed through the unconstrained modal analysis. The exact normal mode solution used in modal analysis correspond to the eigenfrequencies for each position of the moving mass and to the ratios of the weight of the beam-mass-car system. Time solutions of normal modes are also transformed properly according to the position of the moving mass. Numerical simulations are carried out to obtain open-loop responses of the system in tracking pre-designed paths of the moving mass. The simulation results show that the model predicts the dynamic behavior of the beam-mass-cart system well. Experiments are carried out to show the validity of the proposed analytical method.

• Journal of Mechanical Science and Technology
• /
• v.14 no.9
• /
• pp.968-977
• /
• 2000

The motion of an aircraft landing gear over a rough runway can be modeled by a nonclassically damped system subject to nonstationary random excitations. In this paper, the approximate analysis methods based on either the real or complex normal modes for the computation of nonstationary response covariances are proposed. It has been found by simulation involving a realistic example that, for the nonclassically damped random vibrational systems, the approximate solution method based on the complex normal mode is superior to other approaches with respect to the accuracy and computation time.

• Bulletin of the Korean Chemical Society
• /
• v.6 no.1
• /
• pp.29-32
• /
• 1985

Normal modes of crystalline orthorhombic sulfur belonging to the space group $D_{2h}$-Fddd, have been evaluated by taking the lowest temperature phase in the solid. Normal modes are obtained by the valence force field with modified force constants and a quantitative description of the mode is adjusted by the potential energy distribution. Since the full crystal system of orthorhombic sulfur is so large, we intended to calculate the normal modes simply by constructing the imaginary box made by the infinite mass boundary. And the Raman experiment is done by using the more powerful Ar-Kr gas laser with lowering the temperature to ${\sim}10^{\circ}K$.

• Journal of the Korean Society of Manufacturing Process Engineers
• /
• v.12 no.5
• /
• pp.67-75
• /
• 2013

This study is flow analysis on the smoke collector in smoking room. The smoke collector for improving impure air at smoking area is analyzed and the inner flow filed in smoke collector is confirmed on the study result. The velocity with pressure distribution according to suction flow rate at filter entrance is also compared. Pressure characteristic and pressure resistance coefficient are analyzed according to flow analysis result for each other filter. The pressure drop of about 15 Pa occurs at the normal driving mode to strainer inlet from HEPA filter outlet. On the other hand, the pressure drop about 44% increases at turbo mode.