• Transactions of the Korean Society of Machine Tool Engineers
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• v.14 no.2
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• pp.62-68
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• 2005

The objective of this study is structural analysis and modal analysis of treadmill roller. A 3D finite element model is implemented to calculate the stress, strain and natural frequency for treadmill roller In order to analyses treadmill roller, many variables such as load condition, boundary condition, weight condition and resonance are considered. Natural frequency of treadmill is compare to motor revolution.

• Transactions of the Korean Society of Mechanical Engineers
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• v.18 no.11
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• pp.3032-3038
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• 1994

The paper discusses a combustion instability phenomena encountered in recent solid rocket motor development efforts at ADD(Agency for Defense Development). It has happened to occur as an irregular burning in development of smokeless propellant rocket motor. Through investigating the spectral analysis of accelerometer and strain gage signals which are recorded in static firing tests and acoustic modal analysis of motor inside cavity with ANSYS, the instability is found to be the second tangential mode.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.14 no.9 s.90
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• pp.819-826
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• 2004

A multi-step optimum strategy for the selection of the locations and directions of strain gauges is proposed in this paper to capture at best the modal response of blade in a series of modes on fan blades. It is consist of three steps including two pass reduction step, genetic algorithm and fine optimization to find the locations-directions of strain gauges. The optimization is based upon the maximum signal-to-noise ratio(SNR) of measured strain values with respect to the inherent system measurement noise, the mispositioning of the gauge in location and gauge failure. Optimal gauge positions for a fan blade is analyzed to prove the effectiveness of the multi-step optimum methodology and to investigate the effects of the considering parameters such as the mispositioning level, the probability of gauge failure, and the number of gauges on the optimal strain gauge position.

• International Journal of Naval Architecture and Ocean Engineering
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• v.10 no.3
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• pp.348-359
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• 2018

A series of indoor simulation tests on a large-sized shaking table was performed, which was used to simulate the earthquake ground motion for the pipe-soil interaction system to be tested. The purpose of this study is to examine the dynamic characteristic and seismic response of a length of PVC pipeline lay on a clay seabed under seismic load. The pipeline was fully instrumented to provide strain and acceleration responses in both transverse and in-line. Dynamical modal tests show that corresponding mode shapes vertically and horizontally are basically the same. But the absolute values of the natural frequencies vertically are all higher than those corresponding values in transverse. It turned out that the geometry configuration of riser affects its stiffness. Seismic response of pipeline depends significantly on the waveform, and Peak Ground Acceleration (PGA). As the seismic loading progressed, the strain response was severe around both TDZ and catenary zone. Additionally, strain responses in top and bottom positions were more severe than the result in left or right side of the pipeline in the same section.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 1996.04a
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• pp.361-369
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• 1996

The accurate prediction of modal parameters of a rotating blade is an important requirement in the assessment of the dynamics of a helicopter rotor. Indeed, predictions of flight loads and stability are normally dependent on initially predicting the undamped mode shapes. A measuring technique, known as Strain Pattern Analysis (SPA), appears to be the most successful technique for measuring the mode shapes of rotating blades. This method was developed to be used on actual aircraft so no attempt was made to measure rotating mode shapes directly in order to validate the SPA method. This report summarizes results from experimental investigations which were carried out to validate the SPA method for the prediction of aerodynamically damped modes of a rotating blade. A series of modal tests were carried out on two rotor models in which the non-rotating, undamped and aerodynamically damped rotating modes were measured directly (strain and displacement patterns). It is shown that the SPA method to be very successful in itself but there are a number of limitations in validating this technique. To provide data which could be used to confidently validate theoretical prediction codes, existing limitations should be addressed.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.28 no.4
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• pp.401-408
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• 2015

Conventional model updating methods for the structures have used global structural responses which are modal parameters obtained through vibration measurements. Although models updated by modal parameters estimate global structural responses accurately, they have difficulties to predict local responses for safety assesment of structural members. The safety of structural members in the structures has been evaluated through the stress estimation based on strain measurements. Thus, this study additionally uses measured strain responses of structural members to perform model updating besides modal parameters. In the proposed method, the objective functions are set to the differences of the global and local responses obtained from updated model and measurement and those functions are minimized by NSGA-II, one of the multi-objective optimization techniques. The strain responses predicted from updated model are used for safety assessment of the steel frame structures. The proposed method are verified by numerical and experimental studies through the impact hammer tests for a steel frame specimen.

• Smart Structures and Systems
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• v.25 no.1
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• pp.1-22
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• 2020

The modal strain energy method is one of the efficient methods for detecting damage in the structures. Due to existing some limitations in real-world structures, sensors can only be located on a limited number of degrees of freedom (DOFs) of a structure. Therefore, the mode shape values in all DOFs of structures cannot be measured. In this paper, a modified modal strain energy based index (MMSEBI) is introduced to locate damaged elements of structures when a limited number of sensors are used. The proposed MMSEBI is based on the reconstruction of mode shapes using Improved Reduction System (IRS) method. Therefore, in the first step by employing IRS method, mode shapes in slave degrees of freedom are estimated by those of master degrees of freedom. In the second step, the proposed MMSEBI is used to located damage elements. In order to evaluate the efficiency of the proposed method, two numerical examples are considered under different damage patterns considering the measurement noise. Moreover, the universal threshold based on statistical hypothesis testing principles is applied to damage index values. The results show the effectiveness of the proposed MMSEBI for the structural damage localization when comparing with the available damage index named MESBI. The results demonstrate that the presented method can be used as a practical strategy for structural damage identification, especially when a limited number of sensors are installed on the structure. Finally, the combination of MMSEBI and IRS method can provide a reliable tool to identify the location of damage accurately.

• 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.

• Journal of the Society of Naval Architects of Korea
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• v.55 no.1
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• pp.37-44
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• 2018

To understand the dynamic characteristics of the vessel with hydroelastic response, it is very important to estimate the dynamic modal parameters such as mode shapes, natural frequency, and damping ratio. These dynamic modal parameters of full scale ship are a priori unknowns, hence to be estimated directly based upon the full scale measurement data. In this paper, dynamic modal parameters were extracted by signal processing of acceleration and strain data measured from a large container ship whose loading capacity is 9400TEU. The mode shapes of the vibrating hull were identified using the proper orthogonal decomposition and the vibration response of hull was decomposed into its modal magnitudes. Natural frequencies of specific modes were derived via Fourier transform of these modal magnitude. Also, the free decay signal of the vibrating hull was obtained through the random decrement technique and the damping ratio was estimated with accuracy.

• Structural Engineering and Mechanics
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• v.46 no.2
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• pp.231-244
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• 2013

An efficient method is proposed here to identify multiple damage cases in structural systems using the concepts of flexibility matrix and strain energy of a structure. The flexibility matrix of the structure is accurately estimated from the first few mode shapes and natural frequencies. Then, the change of strain energy of a structural element, due to damage, evaluated by the columnar coefficients of the flexibility matrix is used to construct a damage indicator. This new indicator is named here as flexibility strain energy based index (FSEBI). In order to assess the performance of the proposed method for structural damage detection, two benchmark structures having a number of damage scenarios are considered. Numerical results demonstrate that the method can accurately locate the structural damage induced. It is also revealed that the magnitudes of the FSEBI depend on the damage severity.