• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2014.10a
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• pp.285-287
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• 2014

Equations of motion for the vibration analysis of rotating pre-twisted beams with functionally graded material properties are derived in this paper. Based on Timoshenko beam theory, the effects of shear and rotary inertia are considered. The pre-twisted beam has a rectangular cross-section and is mounted on a rotating rigid hub with a setting angle. Functionally graded material (FGM) properties are considered along the height direction of the beam. The equations of stretching and bending motion are derived by Kane's method employing hybrid deformation variables. To validate the derived equations, natural frequencies of a rotating FGM pre-twisted beam are compared to those obtained by a commercial software ANSYS. The effects of the pre-twisted angle, slenderness ratio, hub radius, volume fraction exponent, and angular speed on the modal characteristics of the system are investigated with the proposed model.

• 한국정보디스플레이학회:학술대회논문집
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• 2004.08a
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• pp.1155-1158
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• 2004

Various inorganic alignment layers of nematic liquid crystal (NLC) molecules were investigated. Ar ion beam (IB) irradiation was utilized for alignment method and homogenous and homeotropic orientations with tilt angle were obtained on the suitable inorganic thin films. Proper doping materials were added to diamond-like carbon (DLC) films. In the case of homogeneous alignment, nitrogen doping affected the increase of pretilt angle, while the fluorine bonding in the DLC films was induced the tilted homeotropic alignment cause its extreme hydrophobic property. These results showed that ion beam irradiation method could be applied to the various alignment mode of NLC such as IPS, TN and MVA.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2007.11a
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• pp.370-370
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• 2007

The liquid crystal (LC) aligning capabilities treated on the Organic overcoat thin film surfaces by ion beam irradiation and rubbing method was successfully studied for the first time. The Organic overcoat layer was coated by spin-coating. In order to characterize the LC alignment, the microscope, pretilt angle, thermal stress, and atomic force microscopy (AFM) image was used. The good LC aligning capabilities treated on the Organic overcoat thin film surfaces with ion beam exposure of $45^{\circ}$ above ion beam energy density of 1200 eV can be achieved. But, the alignment of defect of NLC on the Organicovercoat surface at low energy density of 600 eV was measured. The pretilt angle of NLC on the Organic overcoat thin film surface with ion beam exposure of $45^{\circ}$ for 1 min at energy density of 1800eV was measured about 1.13 degree. But, low pretilt angles of NLC on the Organic overcoat thin film surface with ion beam exposure at energy density of 600, 1200, 2400, and 3000 eV was measured. Also, the pretilt angle of NLC on the rubbed Organic overcoat thin film surfaces was measured about 0.04 degrees. Finally, the good thermal stability of LC alignment on the Organic overcoat thin film surface with ion beam exposure of $45^{\circ}$ for 1 min can be measured.

• Journal of Advanced Marine Engineering and Technology
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• v.26 no.4
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• pp.464-471
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• 2002

Porosity formation in partial penetration welds by high power lasers is a serious problem in industry. There are two main causes that induce porosity formation. One form of porosity is due to gases (e.g. hydrogen, oxygen) dissolving into the weld pool because of the high temperature and then the rapid solidification traps gases as a bubble in the weld metal. The second problem is voids formed by the keyhole collapsing due to unstable keyhole fluid dynamics. The voids that form at the bottom of the keyhole are relatively large and irregular in shape compared to the gas bubbles; this void formation is the primary concern in this paper. The reduction of voids formed by keyhole collapse is achieved by improving the stability of keyhole. Two methods to improve keyhole stability are discussed in this paper: pulse modulation and beam incident angle. Pulse modulation of the laser beam was performed between 100 Hz and 500 Hz to find out the optimum frequency for the keyhole dynamics. The incident beam angle changed the impact angle of the laser beam to the work surface in a range of 0 to 25 degrees. Glycerin in a semi-solidified state is used as a medium for performing the welding because its transparency allows of visualization of the keyhole.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2005.11a
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• pp.311-312
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• 2005

By using 45$^{\circ}$ obliqued evaporation method with electron beam system, uniformly vertical liquid crystal (LC) alignment was achieved. And a high pretilt angles of about 2.5$^{\circ}$ were measured. Also, it was verified that there are no variations of pretilt angle as a function of $SiO_x$ thin film thickness 20nm and 50nm. A good LC alignment states were observed at annealing temperature of 250$^{\circ}C$. The high pretilt angle and the good thermal stability of LC alignment by 45$^{\circ}$ obliqued electron beam evaporation method on the $SiO_x$ thin film can be achieved.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.18 no.11
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• pp.1024-1027
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• 2005

By using $45^{\circ}$ obliqued evaporation method with electron beam system, uniformly vertical liquid crystal (LC) alignment was achieved. And a high pretilt angles of about $2.5^{\circ}$ were measured. Also, it was verified that there are no variations of pretilt angle as a function of $SiO_x$ thin film thickness 20 nm and 50 nm. A good LC alignment states were observed at annealing temperature of $250^{\circ}C$. Consequently, the high pretilt angle and the good thermal stability of LC alignment by $45^{\circ}$ obliqued electron beam evaporation method on the $SiO_x$ thin film can be achieved.

• Proceedings of the Korean Society of Marine Engineers Conference
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• 2006.06a
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• pp.201-204
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• 2006

In the side scan sonar method, use is made of the back-scattering, at low grazing angles of incidence to the seabed, of relatively high-frequency acoustic waves radiated in a fan-shaped beam from a transducer contained in a towed body. The fan beam is oriented so that the wider angle is in the vertical plane (scan range) and the narrower angle in the horizontal plane (beam width) with the axis of the beam normal to the ship track. The display of the returns is usually realized as a series of closely spaced intensity-modulated lines on a paper recorder or computer screen display. In this way a two-dimensional picture of the seabed is build up.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.22 no.5
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• pp.87-92
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• 2022

In this paper, a study was conducted on the design of an array element that can be applied to the AESA radar for seeker. An antenna for application to AESA radar should choose an optimal radiation element to be applied to an array antenna in order to secure electronical beam steering characteristics, and consider beam steering characteristics when designing. In particular, in order to satisfy the wide-angle beam steering characteristics, the wide-angle impedance matching technique should be used to minimize the scan blindness region that may occur during wide-angle steering. As such, securing the stability of system operation is becoming an important design consideration for AESA radar. In this paper, WAIM is applied to the end of the radiation element to improve the characteristics of the radiation element applied to the AESA radar antenna device, and the change in the performance of the active reflection coefficient, which is a stable operation index of the system, is reviewed. The final performance result verified the validity of the proposed method by mathematically synthesizing the simulation data.

• Journal of the Korean Institute of Telematics and Electronics D
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• v.35D no.2
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• pp.101-109
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• 1998

In this paper, we implemented holographic optical memory systm which can store and reconstruct many images using new input and angular multiplexing method. In the new input method, phase infomation of input image is inputed in the recording material instead of brightness information. To do so, we represented the images, which captured with CCD camera or displayed on the computer monitor, on the liquid crystal television(LCTV) which removed polarizer/analyzer. Therefore, we can generate uniform input beam intensity regardless of the total brightness of input image, and apply the scheduled recording method. Also we can increase the intensity of input beam so reduce the recording time of input image. And reconstructedimage is acquired by transforming phase information into brightness information of image with analyzer. The incident angle of reference beam is acquired by Fourier transform of the binary phase hologram(BPH) which designed with SA algorithm on the LCTV. The proposed optical memory system is stable because the incident angle of the reference beam is controlled easy and electronically. We demonstreated optical experiment which store and reconstruct various type images in BaTiO$_{3}$ using proposed holographic memory system.

• Journal of Industrial Technology
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• v.17
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• pp.305-312
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• 1997

Shear connections in steel structures should satisfy dual criteria of shear strength and rotational flexibility and ductility. The connection should be strong enough to transfer the shear reaction of the beam, and should have sufficient rotational flexibility and ductility to rotate easily and supply the end rotation demand of the beam. This paper is concerned with the behavior of double-angle shear connections where the parameters are numbers of high strength bolts, bolt pitch, the length of angle leg, and connection method. An experimental investigation of shear connection was conducted by testing 12 beam-to-column joint specimens. Based on experimental and analytical study, the failure modes are developed and proposed design formulas.