• Structural Monitoring and Maintenance
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• 제5권3호
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• pp.345-361
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• 2018

The set of processes performed to determine the dynamic characteristics of the constructed structures is named experimental modal analysis. Using experimental modal analysis and interpreting its results, structural failure can be assessed and then it would be possible to plan for their repair and maintenance. The purpose of the experimental modal analysis is to determine the resonance frequencies, mode shapes and Mode damping for the structure. Diverse methods for determining the shape of the mode by various researchers have been presented. There are pros and cons for each of these methods. This paper presents a method for determining the mode shape of the structures using the response spectrum in the experimental modal analysis. In the first part, the principles of the proposed method are described. Then, to check the accuracy of the results obtained from the proposed method, single and multiple degrees of freedom models were numerically and experimentally investigated.

• Journal of Advanced Marine Engineering and Technology
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• 제9권3호
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• pp.214-224
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• 1985

In this paper, some theoretical equations are derived to calculate natural frequencies and their modes of a portal type derrick system and developed a computer program to carry out their calculations. The ship's structures, such as funnels, upper decks, engine structures, shaft systems suffer local vibrations of the ship. The exciting forces of vibrations are induced by the bearing force and the surface force of propeller or by the main engine. For solving the vibration problem of riggings like the derrick system the natural frequency of its system must be exactly estimated as far as possible and its resonance condition must be kept out of the normal engine operating speed range. When some severe resonances are encountered after the ship's launching, it may be required a tremendous cost to amend their condition. An experimental model of the portal type derrick is made, which is composed of two posts and a truss. This experimental model is excited by an electrical-magnet, and its vibration responses are found out. The calculating results of the model by the developed computer program are compared with those of measured values of model experiment, and they show fairly good agreements.

• 한국공간구조학회논문집
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• 제2권1호
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• pp.67-73
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• 2002

Measurement of fluctuating pressure by tube system is carefully designed due to the organ-pipe resonance. It is necessary to correct the pressure before analysis. The three method for correction the distortion fluctuation pressure short tube length and the frequency response functions and insert a restrictor in the tube to increase the damping. The first method is useful when the tube length is short. In second method, the distorted signal through the tubing transformed into the frequency domain, dividing by transfer function and inverse fourier transforming back into the time domain gives the required pressure signal. In this paper three types of tubing which have different length of 100cm, 150cm, 200cm were experimented the distorted signal and correct the distortion signal

• 한국자동차공학회논문집
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• 제6권1호
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• pp.122-133
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• 1998

This paper presents the static analysis, the modal analysis and the forced vibration analysis on engine structures to find out the structure-borne noise sources by finite element method. The deformation of engine structures under the maximum combu- stion gas force was calculated through the static analysis, and the resonance possibilities were predicted by the modal analysis which ascertains mode shapes and the corresponding frequencies of engine global and its major noise sources in engine surfaces were investigated with the forced vibration analysis by means of finding the transfer mobilities on engine surfaces due to the piston impact and the velocity levels due to the combustion in consideration of oil film stiffness and damping coefficients. Finally, the direction of engine structure-borne noise reduction can be estabilished by the above-mentioned analysis procedure and the reduction effect of cost on proto-type engine build-up is expected.

• Smart Structures and Systems
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• 제4권1호
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• pp.35-46
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• 2008

In this paper the authors address the problem of comparing two different smart damping techniques using the numerical modelling of the electro-mechanical impedance for plate structures partially treated with active constrained layer damping treatments. The paper summarizes the modelling procedures including a finite element formulation capable of accounting for the observed behaviour. The example used is a smart cantilever plate structure containing a viscoelastic material (VEM) layer sandwiched between a piezoelectric constrained layer and the host vibrating plate. Comparisons are made between active constrained layer and active damping only and based on the resonance frequency amplitudes of the electrical admittance numerically evaluated at the surface of the piezoelectric model of the vibrating structure.

• Wind and Structures
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• 제8권3호
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• pp.163-178
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• 2005

Wind-induced mean and dynamic interference effects of tall buildings are studied in detail by a series of wind tunnel tests in this paper. Interference excitations of several types of upwind structures of different sizes in different upwind terrains are considered. Comprehensive interference characteristics are investigated by artificial neural networks and correlation analysis. Mechanism of the wakes vortex-induced resonance is discussed, too. Measured results show significant correlations exist in the distributions of the interference factors of different configurations and upwind terrains and, therefore, a series of relevant regression equations are proposed to simplify the complexity of the multi-parameter wind induced interference effects between two tall buildings.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2008년도 춘계학술대회논문집
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• pp.77-80
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• 2008

In this paper the electromagnetic shunt damper was newly employed for vibration suppression of the flexible structures. The electromagnetic shunt damper consists of a coil and a permanent magnet. The ends of the coil were connected to the RLC shunt circuit. The numerical solutions of resonant frequency of the shunt circuits were calculated by using Pspice. The vibration and damping characteristics of the flexible beams with the electromagnetic shunt damper were investigated by tuning the circuit parameters. Also, the effect of the magnetic intensity on the shunt damping was studied with the variation of the gap between the aluminum beam and the permanent magnet. Present results show that the magnet shunt damper can be successfully applied to reduce the vibration of the flexible structures.

• Journal of information and communication convergence engineering
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• 제16권3호
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• pp.197-202
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• 2018

This paper reveals the impact of the insertion of electromagnetic band gap (EBG) structures on the performance of circularly polarized (CP) patch-slot antenna with offset slot. Several optimizations are necessary to precise physical parameters in the aim to fix the resonance frequency at 3.2 GHz. The proposed antenna possesses lightweight, simplicity, low cost, and circular polarization ensured by two feeding sources to permit right-hand and left-hand circular polarization process (RHCP and LHCP). The measured results compared with simulation results of the proposed circularly polarized EBG antenna with offset slot show good band operations with –10 dB impedance bandwidths of 9.1% and 36.2% centered at 3.2 GHz, which cover weather radar, surface ship radar, and some communications satellites bands. Our investigation will confirm the simulation and experimental results of the EBG antenna involving new EBG structures.

• 대한자기공명의과학회:학술대회논문집
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• 대한자기공명의과학회 2001년도 제6차 학술대회 초록집
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• pp.155-161
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• 2001

Anisotropic DWI - Mapping of the Proton Diffusion "tensor". In neural ordered tissue, it is thought that water diffusion is mainly influenced by the presence of myelin sheaths and intracellular structures. Perpendicular to the fiber tracts, the cholesterol-laden myelin lipid bilayers might restrict or hinder the spins from diffusing through the normally highly permeable cytomembrane. Diffusion along the fiber is more or less determined by subcellular structures, such as the endoplasmatic reticulum, mitochondria, neuro-filaments and macromolecules. In addition to that, the entire complex of axons and stabilizing tissue (i.e., glia cells, astrocytes) is also assumed to influence diffusion due to the tortuosity of proton translation, but the uniform distribution of such cells throughout the brain might render this notion less important as initially anticipated.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2003년도 춘계학술대회 논문집
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• pp.911-914
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• 2003

The non-contact laser measurement system what can be used for the vibration analysis of structures is discussed. There are few systems using laser speckle interferometer for vibration analysis. One of these systems is the Electronic Speckle Pattern Interferometer (ESPI). With ESPI system, one can obtain the vibration mode shape qualitatively and the maximum vibration amplitude quantitatively of the structure at each resonance frequency. In this paper, the phase-shifting ESPI system with stroboscopic illumination for measuring vibration mode shapes is constructed and the operating software is programmed. The results are compared with that of commercial ESPI system.