• Journal of Mechanical Science and Technology
• /
• 제15권10호
• /
• pp.1408-1416
• /
• 2001

It is very important to well understand the dynamic characteristics of damaged structures to successfully develop or to choose a most appropriate structural damage identification method (SDIM) as the means of non-destructive testing. In this pope., the dynamic equation of motion for damaged plates is derived by introducing a damage distribution function, which may characterize the effective state of structural damages. It is found that structural damages may induce the coupling between modal coordinates. The effects of damages on the vibration characteristics of a plate depending on their locations, sizes, and magnitudes are numerically investigated in a systematic way. The numerical investigations are also given to the effects of damage-induced modal coupling on the changes in vibration characteristics and to the minimum number of natural modes required to predict sufficiently accurate vibration characteristics of damaged plates.

• 산업기술연구
• /
• 제16권
• /
• pp.239-245
• /
• 1996

Modal parameters determine the frequency response characteristics of vibration system or acoustic system. When the two systems are fully coupled, however, coupling changes the vibrational and acoustic model parameters into those of the coupled system. In this case, it is very difficult to obtain the modified model parameters and response characteristics. In this paper, coupling effect is analytically investigated on the natural frequency, mode and frequency response characteristics. The result can be applied to understand and to design the frequency response characteristics of the vehicle passenger compartment.

• Structural Engineering and Mechanics
• /
• 제50권2호
• /
• pp.137-149
• /
• 2014

In this study, modal parameters such as natural frequencies, mode shapes and damping ratios of RC frames with low strength are determined for different construction stages using ambient vibration test. For this purpose full scaled, one bay and one story RC frames are produced and tested for plane, brick in-filled and brick in-filled with plaster conditions. Measurement time, frequency span and effective mode number are determined by considering similar studies and literature. To obtain experimental dynamic characteristics, Enhanced Frequency Domain Decomposition and Stochastic Subspace Identification techniques are used together. It is shown that the ambient vibration measurements are enough to identify the most significant modes of RC frames. The results indicate that modal parameters change significantly depending on the construction stages. In addition, Infill walls increase stiffness and change the mode shapes of the RC frame. There is a good agreement between mode shapes obtained from brick in-filled and in-filled with plaster conditions. However, some differences are seen in plane frame, like expected. Dynamic characteristics should be verified using finite element analysis. Finally, inconsistency between experimental and analytical dynamic characteristics should be minimize by finite element model updating using some uncertain parameters such as material properties, boundary condition and section properties to reflect the current behavior of the RC frames.

• Nuclear Engineering and Technology
• /
• 제55권3호
• /
• pp.947-957
• /
• 2023

Curved cylindrical structures such as elbows have a non-uniform thickness distribution due to their fabrication process, and as a result have a number of complex mode shapes, including circumferential and axial nodal patterns. In nuclear power plants, material degradation is induced in pipes by flow accelerated erosion and corrosion, causing the wall thickness of carbon steel elbows to gradually thin. The corresponding frequencies of each mode shape vary according to the wall thinning state. Therefore, the thinning state can be estimated by monitoring the varying modal characteristics of the elbow. This study investigated the varying modal characteristics of artificially thinned carbon steel elbows for each thinning state using numerical simulation and experimental methods (MRIT, Multiple Reference Impact Test). The natural frequencies of specified mode shapes were extracted, and results confirmed they linearly decreased with increasing thinning. In addition, by comparing single FRF (Frequency Response Function) data with the results of MRIT, a concise and cost effective thinning estimation method was suggested.

• 대한기계학회논문집A
• /
• 제20권11호
• /
• pp.3549-3559
• /
• 1996

In this study, the effect of parameter and modal filter errors on the vibration control characteristics of flexible structures is analyzed for IMSC ( Independent Modal Space Control). If the control force is designed on the basis of the mathematical model with the parameter and modal filter errors, the closed-loop performance of the vibration control system will be degraded depending on the magnitude of the errors. An asymptotic stability condition of the system with parameter and modal filter errors has more significant effect on the stability condition of the system with parameter and modal filter errors has been drived using Lyapunov approach. It has been found that modal filter error has more significant effect on the stability of closed-loop system than parameter error does. The extent of the response deviation of the closed-loop system is also derived and evaluated using operator thchniques.

• 한국소음진동공학회:학술대회논문집
• /
• 한국소음진동공학회 1998년도 춘계학술대회논문집; 용평리조트 타워콘도, 21-22 May 1998
• /
• pp.381-385
• /
• 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.

• 한국소음진동공학회:학술대회논문집
• /
• 한국소음진동공학회 2009년도 춘계학술대회 논문집
• /
• pp.384-389
• /
• 2009

In the present paper, dynamic characteristics and vibration control performance of a cylindrical shell structure are experimentally investigated and results are presented in the air and underwater conditions. End-capped cylindrical shell structure is manufactured and Macro-Fiber Composite (MFC) actuators are attached on the inside-surface of the structure. Modal characteristics are studied in the air and under the water conditions and then equation of motion of the structure is derived from the test results. Structural vibration control performances of the proposed structure are evaluated via experiments with optimal control algorithm. Vibration control performances are presented both in the frequency and time domains.

• 한국소음진동공학회논문집
• /
• 제19권9호
• /
• pp.899-906
• /
• 2009

In the present paper, dynamic characteristics and vibration control performance of a cylindrical shell structure are experimentally investigated and results are presented in the air and underwater conditions. End-capped cylindrical shell structure is manufactured and macro-fiber composite(MFC) actuators are attached on the inside-surface of the structure. Modal characteristics are studied in the air and under the water conditions and then equation of motion of the structure is derived from the test results. Structural vibration control performances of the proposed structure are evaluated via experiments with optimal control algorithm. Vibration control performances are presented both in the frequency and time domains.

• Computers and Concrete
• /
• 제12권1호
• /
• pp.79-90
• /
• 2013

In this study, dynamic characteristics such as natural frequencies, mode shapes and damping ratios of RC frame is determined for different construction stages using Operational Modal Analyses method under ambient vibration. Full scaled, one bay and one story RC frames are selected as an application for different construction stages such as plane, brick in-filled and brick in-filled with plaster. The RC frame is vibrated by natural excitations with small impact effects and the response signals are measured using sensitive accelerometers during ambient vibration tests. Measurement time-frequency span and effective mode number are determined by considering similar studies in literature. Sensitive seismic accelerometers are used to collect signals obtained from the experimental tests. To obtain experimental dynamic characteristics, output-only system identification technique is employed namely; Enhanced Frequency Domain Decomposition technique in the frequency domain. It is demonstrated that the ambient vibration measurements are enough to identify the most significant modes of RC frames.

• 한국소음진동공학회:학술대회논문집
• /
• 한국소음진동공학회 2004년도 추계학술대회논문집
• /
• pp.840-845
• /
• 2004

Development of the linear motors is recently required to control a high-speed and high-resolution in the high-integrated and speed process industry. This paper presents vibration analyses as well as measurement standards of the newly developed linear motors through analyzing the vibration characteristics of the advanced products. Vibration experiments are conducted for identifying vibration level during operation. They are also included in the modal test to analyze dynamic characteristics. Analytic data using Finite Element Method (FEM) are compared with the results of the modal. The FEM and experiments make it possible to understand these characteristics. Further, through computer simulation for the behavior of moving part to be vibration source, the best acceleration pattern of moving part movement can be verified to achieve effective moving part positioning and reduce the vibration due to moving part movement.