• Bulletin of the Korean Chemical Society
• /
• v.30 no.12
• /
• pp.3061-3065
• /
• 2009

A series of mono- and 1,1'-bis(heteroaryl)-substituted ferrocenes were prepared by employing Frielander reaction of acetyl- and 1,1'-diacetylferrocene with a series of o-aminoaldehydes. Reactions of 1,1'-diacetylferrocene with two equivalents of 1-aminonaphthalene-2-carbaldehyde and 8-aminoquinoline-7-carbaldehyde afforded a mixture of mono- and 1,1'-bis(heteroaryl)-substituted ferrocenes in a ratio of 1 : 3.1 - 3.8, while the reaction with 4-aminoacridine-3-carbaldehyde did not provide any characterizable product presumably due to the redox instability of the product induced by low reduction potential of benzo[b]-1,10-phenanthroline. Structural and optical properties of the compounds prepared were described.

• Structural Engineering and Mechanics
• /
• v.33 no.6
• /
• pp.709-724
• /
• 2009

In this paper a free-free uniform beam with damping effects subjected to follower and transversal forces at its end is considered as a model for a space structure. The effect of damping on the stability of the system is first investigated and the effects of the follower and transversal forces on the vibration of the beam are shown next. Proportional damping model is used in this work, hence, the effects of both internal (material) and external (viscous fluid) damping on the system are noted. In order to derive the frequency of the system, the Ritz method has been used. The mode shapes of the system must therefore be extracted. The Newmark method is utilized in the study of the system vibration. The results show that an increase in the follower and transversal forces leads to an increase of the vibrational motion of the beam which is not desirable.

• Journal of Applied Reliability
• /
• v.10 no.2
• /
• pp.137-148
• /
• 2010

This study deals with the accelerated life test of high power phosphor converted white Light Emitting Diodes (High power LEDs). Samples were aged at $110^{\circ}C$/85% RH and $130^{\circ}C$/85% RH up to 900 hours under non-biased condition. The stress induced a luminous flux decay on LEDs in all the conditions. Aged devices exhibited modification of package silicon color from white to yellowish brown. The instability of the package contributes to the overall degradation of optical lens and structural degradations such as generating bubbles. The degradation mechanisms of lumen decay and reduction of spectrum intensity were ascribed to hygro-mechanical stress which results in package instabilities.

• Journal of the Korean Society of Marine Environment & Safety
• /
• v.2 no.1
• /
• pp.77-82
• /
• 1996

Subsea pipelines are exposed to several potential risks of damage due to wave, soil instability and other hazards. Structural failure of the steel pipelines will result in serious consequences such as release of transported hydrocarbons, pollution to the ocean environment and heavy costs due to repair. This paper examines the safety of subsea pipelines with free span which is one of high potential damages. The variation of an allowable length of static free span is examined for different boundary conditions and is given in a curve which is useful for the dsign of the subsea pipeline with a free span.

• International Journal of Safety
• /
• v.10 no.1
• /
• pp.1-4
• /
• 2011

The fuel cell is one of the green energy receiving a lot of attention. Among the fuel cells, it is generally referred to SOFC(solid oxide fuel cell) which is made up composites of a solid. SOFC has excellent merits in the side of environment and energy. However because of the high operating temperature, it has economic loss by the using of expensive materials and problems of structural instability by thermal stresses. Therefore, this study aims to the effect of analysis by the FEMLAB. The results have deformations and the maximum stresses from the variation of the thickness of vulnerability spots. The deformation shows expansion as 0.82% and the stress ${\sigma}_{xx}$ is 392MPa in electrolyte and -56.31MPa in anode. When increasing or decreasing the thickness to 50% of the reference thickness about the electrolyte which is vulnerable spots.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 1993.10a
• /
• pp.5-18
• /
• 1993

This paper reports the recent trends in active vibration control in Japan, especially, based on papers selected in the Proceedings of First International Conference on Motion and Vibration Control (1st MOVIC) held at Yokohama, Japan on Sept.7-11, 1992. Firstly, it classifiers vibration control methods and vibration controllers, especially active dynamic absorbers which are widely used in mechanical and civil engineering. Secondly, it covers basic problems in the control of vibration of flexible structures such as formulating a reduced-order model required for designing vibration controller, proper arranging of sensors and actuators, and preventing of spillover instability. Finally, the practical use of control theories such as LQ control theory, $H^{\infty}$ control theory, neural network theory, and other topics are discussed..

• Transactions of the Korean Society for Noise and Vibration Engineering
• /
• v.12 no.11
• /
• pp.873-881
• /
• 2002

The fluid induced vibration (FIV) phenomena of an equivalent airfoil system of MAV have been investigated in low Reynolds number flow region. Unsteady flows with viscosity are computed using two-dimensional incompressible Navier-Stokes equations. The present fluid/structure interaction analysis is based on one of the most accurate computational approach with computational fluid dynamics (CFD) and computational structural dynamics (CSD) techniques. The highly nonlinear fluid/structure interaction phenomena due to severe flow separations have been analyzed for the low Reynolds region that has a dominancy of flow viscosity. The effects of Reynolds number and initial angle of attack on the fluid/structure coupled vibration instability are shown and the qualitative trend of FIV phenomenon is investigated.

• Structural Engineering and Mechanics
• /
• v.71 no.3
• /
• pp.223-232
• /
• 2019

Since the actuators with small- scale structures may be exposed to external reciprocal actions lead to create undesirable loads causing instability, the buckling behaviors of them are interested to make reliable or accurate actions. Therefore, the purpose of this paper is to analyze plastic buckling behavior of the micro beam structures by adopting a Conventional Mechanism-based Strain Gradient plasticity (CMSG) theory. The effect of length scale on critical force is considered for three types of boundary conditions, i.e. the simply supported, cantilever and clamped - simply supported micro beams. For each case, the stability equations of the buckling are calculated to obtain related critical forces. The constitutive equation involves work hardening phenomenon through defining an index of multiple plastic hardening exponent. In addition, the Euler-Bernoulli hypothesis is used for kinematic of deflection. Corresponding to each length scale and index of the plastic work hardening, the critical forces are determined to compare them together.

• International Journal of Internet, Broadcasting and Communication
• /
• v.11 no.2
• /
• pp.11-18
• /
• 2019

One of the key objectives of control systems is to maintain a system in a specific stable state. To achieve this goal, a variety of control techniques can be used and it is often uses a feedback control method. As known this kind of control methods requires mathematical model of the system. This article presents seesaw unstable system with two propellers which are controlled without use of a mathematical model instead. The goal was to control it using training data. For system control we use a logistic regression technique which is one of machine learning method. We tested our controller on the real model created in our laboratory and the experimental results show that instability of the seesaw system can be fixed at a given angle using the decision boundary estimated from the classification method. The results show that this control method for structural equilibrium can be used with relatively more accuracy of the decision boundary.

• Journal of the Korean Society of Safety
• /
• v.37 no.4
• /
• pp.51-57
• /
• 2022

In recent years, the government's urban housing expansion policy has resulted in increased construction and remodeling work of residential houses and apartments, causing more industrial accidents at elevator installation sites. Typically, accidents occur during the installation and dismantling of work scaffolds inside the hoistways or using non-standardized work scaffolds due to their structural instability. In view of this, the present study deals with the development of a standardized elevator system scaffolding that can be safely installed outside the hoistway, securing the work platform inside the hoistway. An improved version of the scaffolding system eliminates the need to enter the hoistway for the scaffolding installation, thereby preventing accidents.