• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2006.05a
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• pp.453-457
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• 2006

This study predicts the modified structure of eigenvectors and eigenvalues due to the changes in the mass and the stiffness of the structure. The sensitivity method of natural frequency using partial differential are derived with respect to the physical parameter to calculate the structure modification. The method are applied to the 3 degree of freedom???slumped mass model by modeling the mass and stiffness, and then applies the method to a real crankshaft system. The position, direction of parameter change and modified value were predicted for modification. Finally the predicted value is used to investigate the magnitude of vibration and we found that the effect of modification results to reduce the level of magnitude vibration is satisfactory.

• Journal of the Korea Institute of Military Science and Technology
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• v.15 no.6
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• pp.827-831
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• 2012

Passengers and mounted equipments on a vehicle are exposed to the vibration when it is driven on the road. To minimize the vibration and improve the dynamic characteristics of a vehicle are important factors. Those are changed by modifying parameters of the vehicle. To save development cost and time, simulation methods using vibration model have been widely used before making the real vehicle. In this paper two aimed functions, displacement between wheels and the body and acceleration of the body, have been defined for the parameter sensitivity analysis of the large vehicle. Full Vehicle Model having 11 degrees of freedom applied to solve those issues.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.26 no.4
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• pp.739-744
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• 2002

This study predicts the modified structural eigenvectors and eigenvalues due to the change in the mass and stiffness of a structure by iterative calculation of the sensitivity coefficient using the original dynamic characteristics. The method is applied to examples of a cantilever and 3 degree of freedom lumped mass model by modifing the mass and stillness. The predicted dynamic characteristics are in good agreement with these from the structural reanalysis using the modified mass and stiffness.

• Journal of the Society of Naval Architects of Korea
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• v.41 no.3
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• pp.28-34
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• 2004

This paper presents the results of the structural analysis and optimal design of the ROV to be operated at 6000m depth in the ocean. This will be the first domestic deep-sea ROV operating with an AUV and a launcher equipped with robot arms and the current weight is about 3 ton. initial optimal dimension of the frame is determined based on the stress analysis using FEA code ANSYS and design sensitivity and optimization results. The current design is the initial design and there is a possibility to change the design according to the modification of material, equipments and array of structure.

• Journal of Korean Association for Spatial Structures
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• v.12 no.3
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• pp.97-104
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• 2012

In the design procedure of the cooling tower the form-finding of the shell is the most important process, because the shape of the shell determines the sensitivity of dynamic behaviour of the whole tower against wind excitation. In engineering practice, geometric parameters of the shell are generally determined based on natural frequency analysis. 32 cooling tower shell geometries were selected through variation of the geometric parameters of an existing cooling tower shell. They were evaluated based on the first natural frequency. From the result three representative cooling towers are selected for the analysis of the structural behaviour by means of linear FE-method. As a result, a hyperbolic rotational shell with the small radius overall will yield the shell geometry with a higher first natural frequency and thus a wind-insensitive structure.

• Computers and Concrete
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• v.12 no.6
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• pp.803-818
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• 2013

In this study, analytical and experimental modal analyses of a scaled bridge model are carried out to extract the dynamic characteristics such as natural frequency, mode shapes and damping ratios. For this purpose, a scaled bridge model is constructed in laboratory conditions. Three dimensional finite element model of the bridge is constituted and dynamic characteristics are determined, analytically. To identify the dynamic characteristics experimentally; Experimental Modal Analyses (ambient and forced vibration tests) are conducted to the bridge model. In the ambient vibration tests, natural excitations are provided and the response of the bridge model is measured. Sensitivity accelerometers are placed to collect signals from the measurements. The signals collected from the tests are processed by Operational Modal Analysis; and the dynamic characteristics of the bridge model are estimated using Enhanced Frequency Domain Decomposition and Stochastic Subspace Identification methods. In the forced vibration tests, excitation of the bridge model is induced by an impact hammer and the frequency response functions are obtained. From the finite element analyses, a total of 8 natural frequencies are attained between 28.33 and 313.5 Hz. Considering the first eight mode shapes, these modes can be classified into longitudinal, transverse and vertical modes. It is seen that the dynamic characteristics obtained from the ambient and forced vibration tests are close to each other. It can be stated that the both of Enhanced Frequency Domain Decomposition and Stochastic Subspace Identification methods are very useful to identify the dynamic characteristics of the bridge model. The first eight natural frequencies are obtained from experimental measurements between 25.00-299.5 Hz. In addition, the dynamic characteristics obtained from the finite element analyses have a good correlation with experimental frequencies and mode shapes. The MAC values obtained between 90-100% and 80-100% using experimental results and experimental-analytical results, respectively.

• 대한공업교육학회지
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• v.34 no.2
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• pp.331-345
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• 2009

In this research Sagnac interferometer three different types of mandrel are suggested and this fiber optic sensor is using in monitoring of electric transformer. Vibration characteristics of those mandrels were analyzed and finally more sensitivity mandrel are suggested. Three different mandrels using in fiber optic sensor are hollow cylinder with outer bump, pure hollow cylinder, hollow cylinder with inner bump. Natural frequencies and mode shapes are investigated using finite element method. Mode shape are considered at the frequency range from 2 kHz to 20 kHz. Fundamental dimensions of the hollow cylinder type's mandrel are 30 mm in outer diameter, 50 mm in length, 1 mm in cylinder thickness, $2mm{\times}2mm$ in bump size. Based on the finite element results, when the outer acoustic frequency is near 11 kHz outer bump type and hollow cylinder can get higher sensitivity. Near 17 kHz outer bump and inner bump mandrel can get higher sensitivity. Near 20 kHz hollow cylinder and inner bump mandrel is useful. This results can be applied to design of fiber optic sensor using in monitoring the electrical transformer. Several MHz of outer acoustic frequency can be easily detected using more sensitive mandrel in pursuing expand this technique.

• Structural Engineering and Mechanics
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• v.75 no.3
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• pp.377-387
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• 2020

Modern long-span floor system typically possesses low damping and low natural frequency, presenting a potential vibration sensitivity problem induced by human activities. Field test and numerical analysis methods are available to study this kind of problems, but would be inconvenient for design engineers. This paper proposes a simplified method to determine the acceleration amplitudes of long-span floor system subjected to walking or running load, which can be carried out manually. To theoretically analyze the acceleration response, the floor system is simplified as an anisotropic rectangular plate and the mode decomposition method is used. To facilitate the calculation of acceleration amplitude a_P, a coefficient α_wmn or α_Rmn is introduced, with the former depending on the geometry and support condition of floor system and the latter on the contact duration t_R and natural frequency. The proposed simplified method is easy for practical use and gives safe structural designs.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2008.11a
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• pp.61-68
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• 2008

A set of modal parameters of a stay-cable have been extracted from a moving picture captured by a digital camera supported by shaking hands. It is hard to identify the center of targets attached on the cable surface from the blurred cable motion image, because of the high speed motion of cable, low sampling frequency of camera, and the shaking effect of camera. This study proposes a multi-template matching algorithm to resolve such difficulties. In addition, a sensitivity-based system identification algorithm is introduced to extract the natural frequencies and damping ratios from the ambient cable vibration data. Three sets of vibration tests are conducted to examine the validity of the proposed algorithms. The results show that the proposed technique is pretty feasible for extracting modal parameters from the severely shaking motion pictures.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2004.05a
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• pp.864-869
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• 2004

A novel concept of feedback loop design for modal test and model updating is proposed. This method uses the closed -loop natural frequency information for parameter modification to overcome the problems associated with the conventional method employing the modal sensitivity matrix. To obtain new modal information from closed-loop system, controllers should be effective in changing modal data while guaranteeing the stability of closed-loop system. It is very hard to guarantee the stability of the closed-loop system with non-collocated sensor and actuator set. Ill this research, we proposed a controller called mode-decoupling controller that can change a target mode as much as the designer wants guaranteeing the stability of closed-loop system. This controller can be computed just using measured open-loop modeshape matrix. A simulation based on time domain input/output data is performed to check the feasibility of proposed control method.