• Journal of the Korean Society for Precision Engineering
• /
• v.18 no.12
• /
• pp.54-59
• /
• 2001

The stability of a thin plate structure is very crucial problem which results buckling. Because the buckling strength of thin plates is lower than the yield strength of the material, reinforcement plate must be used to increase the buckling strength. And, in this case, spot welding is commonly used, however, the spot welded joints are practically designed by experimental decisions, so it is Inefficient and has the risks of buckling demolition. In this study, two parameters, such as the area ratio and the distance ratio of spot welding which have influence on the buckling strength, should be chosen. Under compressive and shearing load, the effect of two parameters on the critical stress is discussed.

• International Journal of Computer Science & Network Security
• /
• v.21 no.12
• /
• pp.157-164
• /
• 2021

The aim of this study is to provide empirical evaluation of the accuracy of data-model fit using growing levels of invariance models. Overall model accuracy of factor solutions was evaluated by the examination of the order for testing three levels of measurement invariance (MIV) starting with configural invariance (model 0). Model testing was evaluated by the Chi-square difference test (∆𝛘²) between two groups, and root mean square error of approximation (RMSEA), comparative fit index (CFI), and Tucker-Lewis index (TLI) were used to evaluate the all-model fits. Factorial invariance result revealed that stability of the models was varying over increasing levels of measurement as a function of variable-to-factor ratio (VTF), subject-to-variable ratio (STV), and their interactions. There were invariant factor loadings and invariant intercepts among the groups indicating that measurement invariance was achieved. For VTF ratio (3:1, 6:1, and 9:1), the models started to show accuracy over levels of measurement when STV ratio was 6:1. Yet, the frequency of stability models over 1000 replications increased (from 69% to 89%) as STV ratio increased. The models showed more accuracy at or above 39:1 STV.

• Journal of the Korean Applied Science and Technology
• /
• v.4 no.2
• /
• pp.7-13
• /
• 1987

A preliminary investigation was performed to evaluate the possibility of partially replacing palm oil and beef tallow by rapeseed oil for frying oils of instant Ramyon manufacturing. The AOM stability of rapeseed oil was inferior than of palm oil, but was comparable to that of beef tallow. When rapeseed oil was blended with palm oil or beef tallow, the AOM stability of the blended oil was improved. As far as AOM stability is concerned, best results were obtained with a blending ratio of 3 part of rapeseed oil to 7 part of palm oil and a ratio of 4 part of rapeseed oil to 6 part of beef tallow. These blended rapesee oils was retarded the formation of conjugated dienes and polymers during heating. The antioxidative effects on the stabilities of AOM and thermal in blended rapeseed oils showed that TBHQ was superior to tocopherols and a mixture of BHA and BHT was inferior.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2007.05a
• /
• pp.1185-1190
• /
• 2007

In this paper the vibration system is consisted of a rotating cantilever pipe conveying fluid. The equation of motion is derived by using the Lagrange's equation. Also, the equation of motion is derived applying a modeling method that employs hybrid deformation variables. Generally, the system of pipe conveying fluid becomes unstable by flutter. So, we studied about the influences of the rotating angular velocity, mass ratio and the velocity of fluid flow on the stability of a cantilever pipe by the numerical method. The influences of mass ratio, the velocity of fluid, the angular velocity of a cantilever pipe and the coupling of these factors on the stability of a cantilever pipe are analytically clarified. The critical fluid velocity$(u_{cr})$ is proportional to the angular velocity of the cantilever pipe. In this paper Flutter(instability) always occur in the second mode of the system.

• Transactions of the Korean Society of Automotive Engineers
• /
• v.15 no.3
• /
• pp.91-98
• /
• 2007

This paper presents the induced mathematical modeling equations for evaluating the operation stability with automatic transmission of heavy duty vehicle. This theoretical approach indicates that linearized governing equations of system can be converted into eigen-value problems. if the eigen-value has positive number, we can predict the engine operating point locates an unstable operating region. To be a stable state, the unstable operating point diverges toward a stable point which is able to maintain uniform velocity. Based on the previous theoretical analysis, we carry out dynamic simulation to show the behavior of engine operating point and torque converter in transient state. As a result of the dynamic simulation, the suggested theoretical method is found to be reasonable for evaluating the operation stability of a torque converter. In addition, the numerical results explain the engine stops and fluctuating phenomenon in reality.

• Journal of Advanced Marine Engineering and Technology
• /
• v.33 no.6
• /
• pp.965-974
• /
• 2009

The current study reviews the formula used to calculate the stability of an artificial reef in the breaking wave zone of coastal waters. A comparison was carried out between the existing formula and a new formula that takes into account the water particle velocity in the breaking wave zone. Water particle velocity was analyzed using the Fluent (CADMAS-SURF) software program. The new formula took into various factors, including the difference in the drag coefficient due to the direction of the current and the ratio of distance between two reefs. The drag coefficient of the artificial reef due to the direction of the current was 0.84 when the distance ratio was 0.5. When the artificial reef was placed at 45 degree angle to the current, the product of the drag coefficient and the project area were 40 to 46 % greater than when the reef was placed at 90 degree angle. Our results regarding the stability of an artificial reef indicate that the new formula provides the designers of artificial reefs with a more rational and economic design rationale rather than the existing formula.

• Transactions of the Korean Society for Noise and Vibration Engineering
• /
• v.18 no.1
• /
• pp.101-109
• /
• 2008

The stability of a rotating cantilever pipe conveying fluid with a crack and tip mass is investigated by the numerical method. That is, the effects of the rotating angular velocity, mass ratio, crack severity and tip mass on the critical flow velocity for flutter instability of system are studied. The equations of motion of rotating pipe are derived by using the Euler-Bernoulli beam theory and the extended Hamilton's principle. The crack section of pipe is represented by a local flexibility matrix connecting two undamaged pipe segments. Also, the crack is assumed to be in the first mode of fracture and always opened during the vibrations. When the tip mass and crack are constant, the critical flow velocity for flutter is proportional to the rotating angular velocity of pipe. In addition, the stability maps of the rotating pipe system as a rotating angular velocity and mass ratio ${\beta}$ are presented.

• Journal of the Korea institute for structural maintenance and inspection
• /
• v.14 no.3
• /
• pp.178-185
• /
• 2010

This paper presents the evaluation of foundation stability according to decrease of the foundation contact area on the ground. In order to carry out this research, the experimental and numerical studies are performed. In the experimental study, the carefully controled laboratory model tests are carried out with different foundation size and types. The model test results are analyzed and interpreted by analytical and numerical calculation in order to verify both results obtained from experimental and numerical studies. It is clearly found from the results that the foundation stability is considerably reduced when the foundation contact area ratio is less than 75%. This research may be very useful to develop the economical foundation type.

• Structural Engineering and Mechanics
• /
• v.90 no.4
• /
• pp.391-401
• /
• 2024

The present study focuses on the effect of extension-bending coupling on the elastic stability (buckling) of laminated composite plates. These plates will be loaded under uni-axial or bi-axial in-plane mechanical loads, especially in the orthotropic or anti-symmetric cross-angle cases. The main objective is to find a limit where we can approximate the elastic stability behavior of angularly crossed anti-symmetric plates by the simple behavior of specially orthotropic plates. The contribution of my present study is to predict the explicit effect of extension-flexion coupling on the elastic stability of this type of panel. Critically, a parametric study is carried out, involving the search for the critical buckling load as a function of deformation mode, aspect ratio, plate anisotropy ratio and finally the study of the effect of lamination angle and number of layers on the contribution of extension-flexure coupling in terms of plate buckling stability. We use first-order shear deformation theory (FSDT) with a correction factor of 5/6. Simply supported conditions along the four boundaries are adopted where we can develop closed-form analytical solutions obtained by a Navier development.

• Journal of the Korean Society for Precision Engineering
• /
• v.22 no.4
• /
• pp.27-36
• /
• 2005

Some studies have shown that unstable factors are inherent in WEDM process, causing the instability of the discharging pulse to reach about 40∼60％ in normal machining. Transient stability is an important subject in WEDM process since there is a close relationship between stability and machining performance, such as the characteristics of a machined surface, machining speed and problem of instability like wire rupture phenomenon. Among the many machining parameters affecting WEDM machining state, three specific parameters (Vr, Ip, off time ) are major controllable variables that can be applied in transient stability control. And, this research investigates the implementation and analysis of real-time micro control of the discharging stability of WEDM (Wire Electric Discharge Machining) process.