• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 1998.04a
• /
• 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.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2008.04a
• /
• pp.299-304
• /
• 2008

Dynamic characteristics of smart hull structure are investigated and active vibration control performance is evaluated. Dynamic model of smart hull structure with surface bonded Macro-fiber Composite (MFC) actuators is established by analytical method. Equations of motion of the host hull structure are derived based on Donnell-Mushtari equilibrium equations for a thin cylindrical shell. A general model for the interaction between hull structure and MFC actuator is included in the dynamic model. Modal analysis is then conducted and mode shapes and corresponding natural frequencies are investigated. After constructing of the optimal control algorithm, active vibration control performance of the proposed system is evaluated. It has been shown that structural vibration can be reduced effectively with proper control input.

• Transactions of the Korean Society for Noise and Vibration Engineering
• /
• v.18 no.8
• /
• pp.832-840
• /
• 2008

Dynamic characteristics of smart hull structure are investigated and active vibration control performance is evaluated. Dynamic model of smart hull structure with surface bonded macro-fiber composite(MFC) actuators is established by analytical method. Equations of motion of the host hull structure are derived based on Donnell-Mushtari equilibrium equations for a thin cylindrical shell. A general model for the interaction between hull structure and MFC actuator is included in the dynamic model. Modal analysis is then conducted and mode shapes and corresponding natural frequencies are investigated. After constructing of the optimal control algorithm, active vibration control performance of the proposed system is evaluated. It has been shown that structural vibration can be reduced effectively with proper control input.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2009.04a
• /
• 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.

• Transactions of the Korean Society for Noise and Vibration Engineering
• /
• v.19 no.9
• /
• 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.

• Transactions of the Korean Society for Noise and Vibration Engineering
• /
• v.16 no.4 s.109
• /
• pp.339-345
• /
• 2006

In this paper, a physically meaningful methodology which can assess the contribution of each vibration mode to various vibration response signals (displacement, velocity, acceleration) is developed. Based on these results, the problem of quantitative assessment of the relative importance of a structural system's vibrational modes is discussed. In addition, a direct method which ran assess the relative importance of each mode from uniformly sampled experimental data is also proposed.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2006.05a
• /
• pp.1159-1164
• /
• 2006

Torsional vibration is an important vibration mode when shafts, cylinders and pipes are considered. However, the modal testing of torsional vibrations is not an easy job to carry out because of the lack of proper transducers. This work presents a new torsional vibration transducer based on the magnetostrictive principle and its application to torsional modal testing. The transducer is so designed as to generate/measure only torsional vibrations excluding other vibration modes such as longitudinal and bending vibrations. The transducer is composed of ferromagnetic patches bonded to a test structure, permanent magnets, and a solenoid. Though patches and magnets are bonded to a structure, torsional vibrations are generated and measured wirelessly by a solenoid encircling a test structure. The proposed transducer works even at considerably high frequencies, say, tens of kilohertz. Furthermore, the transducer can be manufactured at a low price. To check the performance of the proposed method, the torsional modal testing on a hollow aluminum shaft was conducted. The results, such as eigenfrequencies, obtained by the proposed transducer agreed favorably with theoretical results.

• Transactions of the Korean Society for Noise and Vibration Engineering
• /
• v.16 no.8 s.113
• /
• pp.879-885
• /
• 2006

Torsional vibration is an important vibration mode when shafts, cylinders and pipes are considered. However, the modal testing of torsional vibrations is not an easy task to carry out because of the lack of proper transducers. This work presents a new torsional vibration transducer based on the magnetostrictive principle and its application to torsional modal testing. The transducer is so designed as to generate/measure only torsional vibrations excluding other vibration modes such as longitudinal and bending vibrations. The transducer is composed of ferromagnetic patches bonded to a test structure, permanent magnets, and a solenoid. Though patches and magnets are bonded to a structure, torsional vibrations are generated and measured wirelessly by a solenoid encircling a test structure. The proposed transducer works even at considerably high frequencies, say, tens of kilohertz. Furthermore, the transducer can be manufactured at a low price. To check the performance of the proposed method, the torsional modal testing on a hollow aluminum shaft was conducted. The results, such as eigenfrequencies, obtained by the proposed transducer agreed favorably with theoretical results.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2008.11a
• /
• pp.354-359
• /
• 2008

Modal characteristics of a cracked beam with a concentrated mass undergoing rotational motion are investigated in this paper. Hybrid deformation variables are employed to derive the equations of motion of a rotating cantilever beam. The flexibility due to crack, which is assumed to be open during the vibration, is calculated basing on a fracture mechanics theory. To obtain more general information, the equations of motion are transformed into a dimensionless form in which dimensionless parameters are identified. The effects of the dimensionless parameters related to the angular speed, the depth and location of a crack and the size and location of a concentrated mass on the modal characteristics of the beam are investigated numerically.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2008.04a
• /
• pp.290-293
• /
• 2008

This paper proposes a criterion to select the modes for modal truncated model of flexible rotor only supported by active magnetic bearings. The proposed approach relies on the concepts of minimum control input and output energy assuming that the system is subjected to transient disturbances. Accurate large order model for the levitated rotor is taken by finite element analysis and transformed to the modal equation. By proposed methodology, which modal states should be retained in the truncated model are investigated over the whole operational speed range by the calculation. Finally, the effectiveness is verified by checking the model error between original model and reduced model.