• Proceedings of the Korean Vacuum Society Conference
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• 2006.08a
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• pp.156-156
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• 2006

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.18 no.10
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• pp.1203-1210
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• 2007

The multibeam surveillance radar is a state-of-art of 3D radar technology. It applies the stacked beam-on-received realized by a digital beamformer. In this paper, a method of a low target altitude extraction for multibeam surveillance radar in multipath environmental condition is proposed and investigated. The model of multipath propagation and radar generation produced from the low altitude target in multibeam surveillance radar and the nelder-mead simplex multipath reduction(NMSMR) method which enables a reliable low altitude target extraction in specular reflection situations are described. The proposed algorithm is simulated to confirm the effectiveness of proposed algorithm in accordance with a various of target altitudes and radar frequencies.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.20 no.10
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• pp.3173-3185
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• 1996

Multi-model vibration control of laminated composites plates for various fiver orientations has been carried out by making use of piezolectric materials(PZT) as sensors and actuators. Cantilever plate is used as a specimen to test multi-modal vibration supression under random exitation. Impulse technique is applied to determine the natural frequency, the damping ratio(.zeta.) and the modal damping(2.zeta..omega.) of the first bending and the trosion modes. Two independent controllers are implemented to control the two modes simultaneously and established digitally on the basis of the direct negative velocity feedback control with collocated sensor/actuator. Experimental results for various fiber orientations and feedback gains are compared with finite element analysis considering stiffnesses and dampings of piezoeletiric sensors, actuators and bonding layer.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.12 no.1
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• pp.5-11
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• 2002

Active vibration control of intelligent laminated composite plates is performed experimental1y Laminated composite place is modeled by the system identification method. For the system identification process, the laminated composite place is excited by two piezoelectric actuators with PRBS signals. At the same time, the displacement of the laminated composite plate is measured by a gap sensor. From these excited PRBS signals and the measured displacement sequence, system parameters of the laminated composite plate are estimated using a recursive prediction error method. Model of the laminated composite plate with two piezoeletric actuators is assumed to be the form of ARMAX. From the estimated ARHMAX model, a state space equation of the observable canonical form is obtained. With this state space equation, a controller and an observer for active vibration control is designed using the optimal control method. Controller and observer are implemented on a digital system. Experiments on the vibration control are Performed with changing the outer layer fiber orientation of intelligent composite plates.

• Computational Structural Engineering
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• v.10 no.2
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• pp.255-263
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• 1997

The optimum design of most structural systems used in practice requires considering design variables as discrete quantities. The present paper shows that the linear approximation method is very effective as a tool for the discrete optimum designs of unsymmetric composite laminates. The formulated design problem is subjected to a multiple in-plane loading condition due to shear and axial forces, bending and twisting moments, which is controlled by maximum strain criterion for each of the plys of a composite laminate. As an initial approach, the process of continuous variable optimization by FDM is required only once in operating discrete optimization. The nonlinear discrete optimization problem that has the discrete and continuous variables is transformed into the mixed integer programming problem by SLDP. In numerical examples, the discrete optimum solutions for the unsymmetric composite laminates consisted of six plys according to rotated stacking sequence were found, and then compared the results with the nonlinear branch and bound method to verify the efficiency of present method.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.16 no.1 s.92
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• pp.78-83
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• 2005

LTCC filters have been widely used to wireless terminals. They generally adopt the multilayer structure. Some of multilayer LTCC filters are made of symmetrical parallel-coupled lines and anti-symmetrical parallel-coupled lines to reduce the length of resonators. The equivalent circuit of parallel-coupled lines was analyzed and applied to bandpass filters using multilayer parallel-coupled line resonators. The three-pole bandpass filter with the center frequency of 2.45 GHz is designed by using the proposed equivalent circuit and the measured results have good agreement with the design results.

• Composites Research
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• v.13 no.3
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• pp.9-20
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• 2000

Free vibration characteristics of a cantilevered laminated composite beam with multiple non-propagating transverse open cracks are investigated. In the present analysis a special ply-angle distribution referred to as asymmetric stiffness configuration inducing the elastic coupling between chord-wise bending and extension is considered. The multiple open cracks are modelled as equivalent rotational springs whose spring constants are calculated based on the fracture mechanics of composite material structures. Governing equations of a composite beam with open cracks are derived via Hamilton's Principle and Timoshenko beam theory encompassing transverse shear and rotary inertia effect is adopted. The effects of various parameters such as the ply angle, fiber volume fraction, crack numbers, crack positions and crack depthes on the free vibration characteristics of the beam with multiple cracks are highlighted. The numerical results show that the existence of the multiple cracks in an anisotropic composite beam affects the free vibration characteristics in a more complex fashion compared with the beam with a single crack.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2001.04a
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• pp.96-99
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• 2001

Strength and manufacturing characteristics were evaluated in this paper. It depends on lay-up type and fiber direction when the fiber/resin composites have specific notch shapes. Unique jig and fixture were designed and used to test laminated specimens with notches. From the result of uni-direction specimen test we try to predict strength of multi-direction specimen by FEA.

• Journal of Korean Society of Steel Construction
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• v.10 no.4 s.37
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• pp.691-700
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• 1998

Based on Von Karman-Donnell kinematic assumptions for laminated shells, the nonlinear vibration behaviour of antisymmetrically or asymmetrically laminated cross-ply circular cylindrical shells with clamped and simply-supported ends are studied by a multi-mode approach. A equation is formulated and satisfies the associated compatibility equation and all boundary conditions. The displacement function is assumed to take the form of the lowest linear vibration mode and to satisfy continuity of the circumferential displacement. The nonlinear vibration equation is derived by the Galerkin's method. And nonlinear frequency is obtained by using the harmonic balance method as a function of lamination parameters, material constants, aspect ratio and amplitude of vibration. The effect of initial imperfection is also included. Results of the non-linear vibration are presented for different amplitudes of initial imperfection and four sets of boundary conditions. Present results are compared well with existing analysis results.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.18 no.9
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• pp.1090-1097
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• 2007

The multibeam surveillance radar is a state-of art of 3D radar technology. It applies the stacked beam-on-received realized by a digital beamformer. In this paper, a design concept of beamformer and a method of target altitude extraction for multibeam surveillance radar in the normal environmental condition considering no multipath situations are proposed and investigated. The extraction algorithm based on antenna sine space coordinated system in a FFT digital beamformer is described. The proposed algorithm is simulated by 1 look-up table data and confirmed to have consistent results in accordance with a variety of target altitudes and a full radar frequency range.