• Title/Summary/Keyword: Free Vibration Test

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Model test method for dynamic responses of bridge towers subjected to waves

  • Chengxun Wei;Songze Yu;Jiang Du;Wenjing Wang
    • Structural Engineering and Mechanics
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    • v.86 no.6
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    • pp.705-714
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    • 2023
  • In order to establish a dynamic model test method of bridge pylons subjected to ocean waves, the similarity method of hydroelastic model test for bridge pylons were analyzed systematically, and a model design and production method was proposed. Using this method, a dynamic test model of a bridge pylon was made, and then a free vibration test on the model structure and a dynamic response test of the model structure under wave actions were conducted in a wave flume. The results of the free vibration test show that the primary natural frequencies of the structure by the model test are close to the design frequencies of the prototype structure, indicating that the dynamic characteristics of the bridge pylon are well simulated by the model structure. The results of the dynamic response test show that wave induced base shear forces and motion responses on the model structure are consistent with the numerical results of the prototype structure. The model test results confirm that the proposed model test design method is feasible and applicable. It has application and reference significances for model testing studies of such marine bridge structures.

Experimenal Study of Dynamic Characteristics of Brace-Typed Dampers using Vibration-resistant Rubbers (방진용 고무를 이용한 가새형 감쇠기의 진동 특성에 관한 실험 연구)

  • 민경원;김진구;조한묵;이성경;호경찬
    • Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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    • 1998.04a
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    • pp.381-385
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    • 1998
  • Vibration-resistant rubbers, whose elastic and shear behaviors are similar to viscoelastic materials, are used to make brace-typed dampers to reduce the building vibration. Experimental study is carried out to find the vibration characteristics of the dampers installed in the building model. The natural frequencies and modal damping ratios are obtained from the free vibration test and Fourier analysis. Analytical model of the modal strain energy method are used to find the viscoelastic characteristics of the brace-typed dampers from the experimental results. Finally shaking table test is performed to find the response behavior of the building model under earthquake loading. The present experimental study shows that the brace-typed dampers have the behavior of viscoelastic dampers, which increase the modal damping ratios and viscoelastic characteristics.

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Free Vibration Test for Base Isolated Real Size One Bay-Two Story Steel Frame (면진된 실대형 일경간-이층 철골조 자유진동 실험)

  • 김대곤
    • Proceedings of the Earthquake Engineering Society of Korea Conference
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    • 2000.04a
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    • pp.391-398
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    • 2000
  • To evaluate the seismic performance of a base isolated building accurate analytical model should be selected. The analytical results such as reduced accelerations member forces and relative displacements of the superstructure of the base isolated building are only meaningful when the analytical model is close enough to the real structure. Real size one bay-two story steel frame and two kinds of seismic isolators(laminated elastomeric bearing and lead-rubber bearing) are designed. manufactured and constructed in the laboratory. Free vibration tests using fuse bars were conducted to evaluate the change of dynamic characteristics(period and damping) before and after base isolation of the steel frame. The experimental results of free vibration tests were also used as a bench mark for adjusting the selected analytical modeling to real base isolated steel frame.

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Free Vibration and Dynamic Response Analysis by Petrov-Galerkin Natural Element Method

  • Cho, Jin-Rae;Lee, Hong-Woo
    • Journal of Mechanical Science and Technology
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    • v.20 no.11
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    • pp.1881-1890
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    • 2006
  • In this paper, a Petrov-Galerkin natural element method (PG-NEM) based upon the natural neighbor concept is presented for the free vibration and dynamic response analyses of two-dimensional linear elastic structures. A problem domain is discretized with a finite number of nodes and the trial basis functions are defined with the help of the Voronoi diagram. Meanwhile, the test basis functions are supported by Delaunay triangles for the accurate and easy numerical integration with the conventional Gauss quadrature rule. The numerical accuracy and stability of the proposed method are verified through illustrative numerical tests.

A Study on the Dynamic Stability of Air-to-Ground Missile Using the Free Vibration Technique (자유진동기법을 이용한 공대지 미사일의 동안정성에 관한 연구)

  • 박재현;백승욱;조환기;허원욱
    • Journal of the Korea Institute of Military Science and Technology
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    • v.2 no.2
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    • pp.61-69
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    • 1999
  • A dynamic stability test was performed to determine dynamic stability derivatives for the pure pitching motion of air-to-ground missile model in the low speed wind tunnel. The free vibration technique was employed to acquire oscillation characteristics of the model for damping coefficients. Damping coefficients are obtained by the method of logarithmic decrement. Results show good damping effects and stability capability at Mach numbers 0.1 and 0.2, with the angle of attack ranging from -15 to +20 degrees.

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Topology Optimization of Plane Structures under Free Vibration with Isogeometric Analysis (등기하해석법을 이용한 자유진동 평면구조물의 위상최적화)

  • Lee, Sang-Jin;Bae, Jungeun
    • Journal of the Architectural Institute of Korea Structure & Construction
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    • v.34 no.6
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    • pp.11-18
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    • 2018
  • Isogeometric concept is introduced to find out the optimum layout of plane structure under free vibration. Eigenvalue problem is formulated and numerically solved in order to obtain natural frequencies and mode shapes of plane structures. For the exact geometric expression of the structure, the Non-Uniform Rational B-spline Surface (NURBS) basis functions is employed and it is also used to define the material density functions. A node-wise design variables is adopted to deal with the updating of material density in topology optimization (TO). The definition of modal strain energy is employed to achieve the maximization of fundamental frequency through its minimization. The verification of the proposed TO technique is performed by a series of benchmark test for plane structures.

Aero-elastic wind tunnel test of a high lighting pole

  • Luo, Yaozhi;Wang, Yucheng;Xie, Jiming;Yang, Chao;Zheng, Yanfeng
    • Wind and Structures
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    • v.25 no.1
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    • pp.1-24
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    • 2017
  • This paper presents a 1:25 multi-freedom aero-elastic model for a high lighting pole at the Zhoushan stadium. To validate the similarity characteristics of the model, a free vibration test was performed before the formal test. Beat phenomenon was found and eliminated by synthesis of vibration in the X and Y directions, and the damping ratio of the model was identified by the free decay method. The dynamic characteristics of the model were examined and compared with the real structure; the similarity results were favorable. From the test results, the major along-wind dynamic response was the first vibration component. The along-wind wind vibration coefficient was calculated by the China code and Eurocode. When the peak factor equaled 3.5, the coefficient calculated by the China code was close to the experimental result while Eurocode had a slight overestimation of the coefficient. The wind vibration coefficient during typhoon flow was analyzed, and a magnification factor was suggested in typhoon-prone areas. By analyzing the power spectrum of the dynamic cross-wind base shear force, it was found that a second-order vortex-excited resonance existed. The cross-wind response in the test was smaller than Eurocode estimation. The aerodynamic damping ratio was calculated by random decrement technique and the results showed that aerodynamic damping ratios were mostly positive at the design wind speed, which means that the wind-induced galloping phenomenon is predicted not to occur at design wind speeds.

Flexural Stiffness and Characteristics of Vibration in CFT Truss Girder (CFT 트러스 거더의 휨강성 및 진동특성)

  • Chung, Chul-Hun;Song, Na-Young;Kim, In-Gyu;Jin, Byeong-Moo
    • KSCE Journal of Civil and Environmental Engineering Research
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    • v.29 no.1A
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    • pp.19-30
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    • 2009
  • The primary objective of the present study was to attempt to quantify the effect of the existing codes for CFT composite section on initial section flexural stiffness, based on the measured vibration frequency of CFT truss girders. The formulae for the initial flexural stiffness of the composite sections in the different codes are compared with the free vibration test results. The results of the free vibration test on the CFT truss girders are in good agreement with the analysis results when used in ACI formulae. The free vibration analysis of CFT truss girders for different f/L ratios was conducted to determine how the natural frequency of the CFT truss girder is affected by different f/L ratios. The presence of the f/L ratios in CFT truss girders alters its frequencies of vibration because of the global stiffness of the CFT girders. The frequency in horizontal modes decreases as the f/L ratio increases. However, the frequency in vertical modes increases as the f/L ratio increases.

A Vibration Response Analysis of Steel Building Frame with K Shape Brace Vibrationally Controlled by Turbulent Flow Dampers sealed by Visco-elastic Material (점탄성물질 난류댐퍼를 이용한 K형 철골 브레이스 골조의 진동응답해석)

  • Lee, Ho
    • Journal of Korean Association for Spatial Structures
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    • v.6 no.2 s.20
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    • pp.61-68
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    • 2006
  • In this thesis, a full-scale K shape damper test model was constructed in which a passive vibration control system. This passive vibration control system was incorporated with the use of a newly developed turbulent flow damper sealed by viscoelastic material. A series of tests and earthquake observation has been conducted in this test model. The purpose of the present thesis is to investigate the vibration response characteristics of the building and to verify the effectiveness of the vibration control system. By the static loading test, it was recognized that incorporation of the dampers had little influence on static horizontal stiffness of the building. Free vibration tests revealed that the dampers incorporated increased the damping ratio of the building up to 3 times compared with the undamped case. The effectiveness of the developed vibration control system was confirmed based on the excitation tests and earthquake response observation.

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Vibration Control of Beam using Piezoceramic Composite Actuator LIPCA (압전 복합재료 작동기 LIPCA를 이용한 보의 진동 제어)

  • Arief, Suhariyono;Goo, Nam-Seo;Park, hoon-Cheol;Yoon, Kwang-Joon
    • Journal of the Korea Institute of Military Science and Technology
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    • v.8 no.4 s.23
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    • pp.130-135
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    • 2005
  • This paper presents application possibility of Lightweight Piezoceramic Composite Actuator(LIPCA) to suppress vibration of dynamic structures as an actuator. LIPCA is composed of a piezoelectric layer, a carbon/epoxy layer and glass/epoxy layers. When compared to the bare piezoelectric ceramic(PZT), LIPCA has advantages such as high performance, durability and reliability. In this study, performances of LIPCA have been estimated in an active vibration control system. Experiments were performed on an aluminum beam with cantilever configuration. In this test, strain gages and single LIPCA are attached on the aluminum beam with epoxy resin. Digital ON-OFF control algorithm is applied into the system to exhibit performance of LIPCA as actuator in active vibration control system. First, we performed static actuation test of bare PZT and LIPCA in order to show the superiority of LIPCA. Secondly, we carried out beam vibration control test using LIPCA. The results showed LIPCA could suppress free vibration of the aluminum beam, which means that LIPCA can be applied as an actuator to control vibration of dynamic structures.