• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2001.11b
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• pp.1162-1165
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• 2001

Operational Modal Analysis also known as Output Only Modal Analysis has in the recent years been used for extracting modal parameters of civil engineering structures and is now becoming popular for mechanical structures. The advantage of the method is that no artificial excitation need to be applied to the structure or force signals to be measured. All the parameter estimation is based upon the response signals, thereby minimising the work of preparation for the test. This test case is a controlled lab set-up enabling different parameter estimation methods techniques to be used and compared to the Operational Modal Analysis. For Operational Modal Analysis two different estimation techniques are used： a non-parametric technique based on Frequency Domain Decomposition (FDD), and a parametric technique working on the raw data in time domain, a data driven Stochastic Subspace Identification (SS!) algorithm. These are compared to other methods such as traditional Modal Analysis.

• Structural Engineering and Mechanics
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• v.23 no.6
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• pp.691-711
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• 2006

This paper uses the finite element method to simultaneously consider the coupled cable-deck vibrations and the parametric vibrations of stay cables in dynamic analysis of a cable-stayed bridge. The stay cables are represented by some cable finite elements, which can consider the parametric vibration of the cables. In addition to modeling stay cables using multiple link cable elements, a procedure for removing the self-weight term of cable element is proposed. A eigenvalue analysis process using dynamic condensation method for sorting out the natural modes of the girder-tower vibrations and the Rayleigh damping considering element damping for damping matrix are also proposed for dynamic analyses of cable-stayed bridges. The possibilities of using cable elements and of using global and local vibrations to evaluate the parametric vibrations of stay cables in a cable-stayed bridge are confirmed, respectively.

• Steel and Composite Structures
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• v.23 no.6
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• pp.737-746
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• 2017

In this paper the influence of aspect ratio, height ratio and material angle on static and free vibration behaviour of orthotropic elliptic paraboloid shells is studied by using a four-node hybrid stress finite element. The formulation of the element is based on Hellinger-Reissner variational principle. The element is developed by combining a hybrid plane stress element and a hybrid plate element. A parametric study is carried out for static and free vibration response of orthotropic elliptic paraboloid shells with respect to displacements, internal forces, fundamental frequencies and mode shapes by varying the aspect and height ratios, and material angle.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 1993.10a
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• pp.21-27
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• 1993

매개변수가진에 종속되는 현의 횡방향진동을 시간영역에서 필터작업, 힐버트 변환과 순간주파수 개념을 도입하여 해석함으로서 종방향의 순간진동변위를 추정하는 방법이 제시되었다. 그리고, 실험을 통하여 이론의 타당성을 검증 하였다. 또한, 모의 실험의 결과 일반적인 현구동계에 있어서는 넓은 적용변 수의 선\ulcorner영역에서 종변위가 횡변위와 분리(decoupling) 되어서 공간적으로 길이에 따르는 선형적인 증가성과 시간적으로 조화적인 주기성을 가진다는 것을 확인함으로서 임의의 위치에서의 종변위를 파악함이 가능하였다.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2001.11b
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• pp.1055-1060
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• 2001

Springing phenomena of ships is introduced with its concept, research history and approach methodology. Being a hydroelasticity problem, non-linear vibration and stochastic process, springing was formulated and modeled in vibration point of view separating hydrodynamic force into system properties and excitation force. Both RAO and response spectrum as well as wave spectrum were presented as a case study of springing analysis for a flexible vessel with wide breadth. The effect of advance speed, heading angle and loading condition were investigated as parametric study. The results and observations showed availability of analysis for the prediction of the ship springing behavior.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2011.04a
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• pp.655-656
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• 2011

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2011.04a
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• pp.498-499
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• 2011

• Smart Structures and Systems
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• v.31 no.1
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• pp.89-100
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• 2023

This paper conducts a parametric study of a new tuned mass damper with pre-strained superelastic SMA helical springs (SMAS-TMD) on the vibration reduction effect. First, a force-displacement relation model of superelastic SMA helical spring is presented based on the multilinear constitutive model of SMA material, and the tension tests of the six SMA springs fabricated are implemented to validate the mechanical model. Then, a dynamic model of a single floor steel frame with the SMAS-TMD damper is set up to simulate the seismic responses of the frame, which are testified by the shaking table tests. The wire diameter, initial coil diameter, number of coils and pre-strain length of SMA springs are extracted to investigate their influences on the seismic response reduction of the frame. The numerical and experimental results show that, under different earthquakes, when the wire diameter, initial coil diameter and number of coils are set to the appropriate values so that the initial elastic stiffness of the SMA spring is between 0.37 and 0.58 times of classic TMD stiffness, the maximum reduction ratios of the proposed damper can reach 40% as the mass ratio is 2.34%. Meanwhile, when the pre-strain length of SMA spring is in a suitable range, the SMAS-TMD damper can also achieve very good vibration reduction performance. The vibration reduction performance of the SMAS-TMD damper is generally equal to or better than that of the classic optimal TMD, and the proposed damper effectively suppresses the detuning phenomena that often occurs in the classic TMD.

• Journal of the Korean Society for Precision Engineering
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• v.18 no.11
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• pp.107-115
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• 2001

Most of rotating machineries supported by contact bearing accompany lowering efficiency, vibration and wear. Moreover, because of vibration, which is occurred in rotating shaft, they have the limits of driving speed and precision. The rotor system has parametric variations or external disturbances such as mass unbalance variations in long operation. Therefore, it is necessary to research about magnetic bearing, which is able to support the shaft without mechanical contact and to control rotor vibration without being affected by external disturbances or parametric changes. Magnetic bearing system in the paper is composed of position sensor, digital controller, actuating amplifier and electromagnet. This paper applied the robust control method using quantitative feedback theory (QFT) to control the magnetic bearing. It also proposed design skill of optimal controller, in case the system has structured uncertainty, unstructured uncertainty and disturbance. Reduction of vibration is verified at critical rotating speed even external disturbance exists. Unbalance response, a serious problem in rotating machinery, is improved by magnetic bearing using QFT algorithm.

• Smart Structures and Systems
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• v.25 no.3
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• pp.311-322
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• 2020

This paper studies the influence of parameters of a novel SMA helical spring energy dissipation brace on the seismic resistance of a frame structure. The force-displacement relationship of the SMA springs is established mathematically based on a multilinear constitutive model of the SMA material. Four SMA helical springs are fabricated, and the force-displacement relationship curves of the SMA springs are obtained via tension tests. A numerical dynamic model of a two-floor frame with spring energy dissipation braces is constructed and evaluated via vibration table tests. Then, two spring parameters, namely, the ratio of the helical spring diameter to the wire diameter and the pre-stretch length, are selected to investigate their influences on the seismic responses of the frame structure. The simulation results demonstrate that the optimal ratio of the helical spring diameter to the wire diameter can be found to minimize the absolute acceleration and the relative displacement of the frame structure. Meanwhile, if the pre-stretch length is assigned a suitable value, excellent vibration reduction performance can be realized. Compared with the frame structure without braces, the frames with spring braces exhibit highly satisfactory seismic resistance performance under various earthquake waves. However, it is necessary to select an SMA spring with optimal parameters for realizing optimal vibration reduction performance.