• Transactions of the Korean Society of Mechanical Engineers A
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• v.21 no.6
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• pp.981-987
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• 1997

Modern helicopter rotor blades with non-homogeneous cross section composed of anisotropic material rquire highly sophisticated structural analysis. Variation in cross section geometry makes this task of analysis more complicated. Since rotor blades generally are much longer than their lateral dimensions, one-dimensional models seem feasible, at least from a computational point of view. Therefore determination of the principal coordinate system is very important to remove the structural coupling for one-dimensional beam modelling. In this study, shear center, and principal direction. The method will be verified by comparing the results with confirmed experimental results.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.21 no.6
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• pp.896-906
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• 1997

The effect of duplicate flexible disks on the vibrational modes of a flexible rotor system is investigated by using an anlytical method based on the assumed modes method. The rotor model to be analyzed consists of duplicate disks on a flexible shaft. In modeling the system, centrifugal stiffening and disk flexibility effects are taken into account. To demonstrate the effectiveness of the method, a hard disk drive spindle system commonly used in personal computers and a simple flexible rotor system with two disks are selected as examples. In particular, the dynamic coupling between the vibrational modes of the shaft and the duplicate disks is investigated with the shaft rotational speed varied.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.10 no.6
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• pp.140-145
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• 2011

An anisotropic beam model is proposed by employing an asymptotic expansion method for thermo-mechanical multiphysics environment. An asymptotic method based on virtual work is introduced first, and then the variables of mechanical displacement and temperature rise are asymptotically expanded by taking advantage of geometrical slenderness of elastic bodies. Subsequently substituting these expansions into the virtual work principle allows us to asymptotically expand the virtual work. This will yield a set of recursive virtual works from which two-dimensional microscopic and one-dimensional macroscopic equations are systematically derived at each order. In this way, homogenized stiffnesses and thermomechanical coupling coefficients are derived. To demonstrate the validity and efficiency of the proposed approach, composite beams are taken as a test-bed example. The results obtained herein are compared to those of three-dimensional finite element analysis.

• Bulletin of the Society of Naval Architects of Korea
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• v.23 no.3
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• pp.1-9
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• 1986

Herein the dynamic response of an axisymmetric buoy to regular wave is studied within linear potential theory. The buoy has a particular geometry so that it should experience minimum wave-exiting force on the vertical direction at a precribed wave number in water of finite depth. Invoking the Green's theorem a velocity potential is generated by distributing pulsating sources and doublets on the immersed surface of the buoy at its mean position. Hydrodynamic forces and moments are obtained approximately by summation of the products of linear pressure and directional mesh area over the immersed surface. Model tests are carried out to measure the wave-exciting forces, hydrodynamic forces and motion responses. The experimental results in general agree fairly well with the numerical ones. From the analytical and experimental works it is found that the pitching motion and its coupling effect affect significantly the motion characteristics of the freely-floating axisymmetric buoy in regular waves.

• Journal of Magnetics
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• v.3 no.3
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• pp.89-91
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• 1998

The magnetisation behaviour of polycrystalline permalloy/copper multilayers with mixed antiferromagnetic/ferromagnetic coupling was investigated as function of temperature. The results are discussed in a framework of a realistic model of anitferromagnetically coupled layers connected by ferromagnetic pinholes. A microstructure of pinholes (their density and dimensions) was varied either by a proper annealing treatment or by choosing samples with various Cu spacer thicknesses. It was demonstrated that the temperature changes of the net magnetic moment measured in a magnetic field smaller than the saturation field was strongly affected by the composition of the pinholes, their density, cross-sectional area and their lengths.

• Journal of Magnetics
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• v.10 no.1
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• pp.36-39
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• 2005

We report element-resolved and interface-sensitive magnetization reversals investigated from an oppositely exchange-biased NiFe/FeMn/Co structure by employing soft x-ray resonant Kerr rotation measurements. We have found not only switchable uncompensated antiferromagnetic regions with its sizable thicknesses at both interfaces of the FeMn layer but also their strong coupling to the individual ferromagnetic layers. These experimental results provide a better insight into experimentally observed reductions in exchange-bias field on the basis of an interface-proximity model proposed in this work.

• Proceedings of the IEEK Conference
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• 2000.07b
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• pp.1005-1008
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• 2000

This paper presents a simple method to estimate short-circuit power dissipation and propagation delay for static CMOS logic circuits. Short-circuit current expression is derived by accurately interpolating peak points of actual current curves which is influenced by the gate-to-drain coupling capacitance. The macro model and its expressions estimating the delay of CMOS circuits, which is based on the current modeling expression, are also proposed after investigating the voltage waveforms at transistor output modes. It is shown through simulations that the proposed technique yields better accuracy than previous methods when signal transition time and/or load capacitance decreases, which is a characteristic of the present technological evolution.

• Journal of the Korean Institute of Telematics and Electronics S
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• v.35S no.5
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• pp.35-41
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• 1998

This paper presents a decoupling controller of the missile seeker scan loop with a spin-stabilized platform. A precise seeker motion with respect to the scan command is essential for the higher acquisition probability of the target. As the seeker scan loop is a deeply cross-coupled two input two output system, an accurate pointing or scanning for each axis to the target is very difficult, even though provided with the help of a high performance controller. When a decoupling control is applied to the seeker scan loop, the cross-coupling between two axes can be reduced to a remarkable amount. As a low order of controller is required for the real time operation, a PI controller with decoupling filter is suggested and compared with other controllers. A linearized dynamic model of seeker scan loop is used and validated through the comparison of experimental results of step responses.

• Journal of Ship and Ocean Technology
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• v.7 no.3
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• pp.13-33
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• 2003

This paper presents a numerical study on tip vortex cavitation inception predictions based on non-spherical bubble dynamics including splitting and jet noise emission. A brief summary of the numerical method and its validation against a laboratory experiment are presented. The behavior of bubble nuclei is studied in a tip vortex flow field at two Reynolds numbers, provided by a viscous flow solver. The bubble behavior is simulated by an axisymmetric potential flow solver with the effect of surrounding viscous flow taken into account using one way coupling. The effects of bubble nucleus size and Reynolds number are studied. An effort to model the bubble splitting at lower cavitation numbers is also described.

• Journal of Biomedical Engineering Research
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• v.18 no.3
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• pp.261-266
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• 1997

Nonevasive multifrequency microwave radiometry using coaxial waveguide antenna has been investigated for a homogeneous and four layer human body model. The coupling between coaxial waveguide antenna and a biological object was analyzed by use of the finite-difference time-domain(FDTD) method to obtain the absorbed power patterns in the media. The object studied in this paper was a homogeneous and four-layered lossy medium. The specific absorption rates(SAR) distribution which was corresponding to the temperature distribution was calculated in each region by use of the steady-state response in FDTD method. The SAR pattern of 1.2GHz was compared with that of 1.8GHz.