• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 1998.04a
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• pp.244-249
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• 1998

The present paper improves the direct identification scheme based upon the equation error formulation with incomplete modal data. First, an indirect estimation technique is considered for estimating unmeasured elements of latent vectors by the combined use of a model and measured incomplete eigen vectors. It is used for estimating the other elements of eigen vectors, which are essential for identification but not available. Next an index is introduced here to indicate the quality of estimation with respect to the mode and the measured positions. A sensitivity formula for eigenvalues with respect to the unknown joint coefficient is also derived to select the modes appropriate for identification. An identification strategy is suggested to meet with practical problems with the help of the index and sensitivity formula. The index and the sensitivity are proved to be useful for selecting measurement positions and modes appropriate for identification A comprehensive simulation study is performed to test the proposed method.

• Transactions of the Korean Society of Mechanical Engineers
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• v.19 no.2
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• pp.363-373
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• 1995

In this study, a FE model tuning method using experimental modal data was suggested after examining all the published conventional methods. The idea of this method is introducing scale factors to maintain both the structural connectivity and the consistency in the corrected stiffness matrix which makes it always possible to interpret the stiffness elements with the corresponding physical configuration of the targeting structure. The scale factors are determined to minimize the objective function of eigen-properties. The proposed method was tested to determine the joint stiffness of a T shaped beam. The test results were also compared with the tuned stiffness obtained from a probed commercial package (SYSTUNE) and found that this method is very accurate and compatible.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2001.04a
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• pp.471-474
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• 2001

Recently, due to demands of faster speed and extra features for the chip mounters, there has been ever-demanding needs for the basic technology. Until four or five years ago, chip mounters placing 0.3sec/chip were considered to be in the high speed category, but since then it has become a borderline for categorizing high speed machines capable of placing 0.1sec/chip. In this study, in order to analyze the vibration of head generated by the dynamic behavior of x-frame, FEM model is composed and modal analysis is performed to identify the dynamic characteristics of the structure. Those results are compared with the modal test in order to verify the model. In this paper, Several other factors, such as definition of dynamic accuracy, static accuracy and tolerance of the axis settling range, that might affect the dynamic behavior the head are discussed.

• Structural Engineering and Mechanics
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• v.54 no.2
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• pp.239-256
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• 2015

An adaptive-scale damage detection strategy based on a wavelet finite element model (WFEM) for thin plate structures is established in this study. Equations of motion and corresponding lifting schemes for thin plate structures are derived with the tensor products of cubic Hermite multi-wavelets as the elemental interpolation functions. Sub-element damages are localized by using of the change ratio of modal strain energy. Subsequently, such damages are adaptively quantified by a damage quantification equation deduced from differential equations of plate structure motion. WFEM scales vary spatially and change dynamically according to actual needs. Numerical examples clearly demonstrate that the proposed strategy can progressively locate and quantify plate damages. The strategy can operate efficiently in terms of the degrees-of-freedom in WFEM and sensors in the vibration test.

• Smart Structures and Systems
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• v.4 no.2
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• pp.153-169
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• 2008

The use of pre-tensioned shape memory alloy (SMA) wires to retrofit historic masonry structures is investigated. A small wall, serving as a prototype masonry specimen, is constructed to undergo a series of shaking-table tests. It is first studied in its original state, and its dynamic characteristics (in terms of modal frequencies) are extracted from the recorded signals. The results are then compared with those obtained when an increasing number of couples of pre-stressed SMA wires are introduced in the specimen to link the bricks together. A three-dimensional finite element model of the specimen is developed and calibrated according to the modal parameters identified from each experimental test (with and without SMA wires). The calibration process is conducted by enhancing the masonry mechanical behaviour. The results and the effectiveness of the approach are presented.

• Proceedings of the Earthquake Engineering Society of Korea Conference
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• 2005.03a
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• pp.437-444
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• 2005

An equivalent linearization technique based on Rayleigh peak distribution for friction damper and brace system (FDBS) under stochastic excitation is proposed. For verification, shaking table test of a small scale 3-story building model with the FDBS is conducted for various slip moment levels. Using experimental result, equivalent linearization of the FDBS is conducted based on Rayleigh peak distribution, which is compared with measured peak distribution. For comparative study, model updating technique is applied based on identified modal properties. Finally, complex modal analysis and time history analysis for the obtained equivalent linear systems are conducted and compared with experimental result.

• Journal of the Korean Society of Clothing and Textiles
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• v.27 no.11
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• pp.1291-1299
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• 2003

In order to design the better brassiere in terms of appearance and functions, various parameters of the materials should be considered; in this study, fatigue properties and subjective sensation of wing materials and its relation to the preference for a brassiere was investigated. After the survey of commercially available products, five elastic fabrics such as cotton, Modal, polyester, nylon, and Tactel, all of which contain 10% polyurethane, were chosen as specimens. Fabric growth were determined to evaluate fatigue properties. Qmax was determined to evaluate the warm-cool feeling. For the sensory test, semantic differential scale which contains 15 adjectives were developed. Fatigue properties were very similar at the 20% elongation irrespective of the duration of tension, but at 40% and 100% elongation, man made fabric showed less growth than cellulose fabrics. The factor analysis showed four factors such as sense of warmth, smoothness, weight and elasticity. Preference of the specimens was ranked in the order of Tactel>Modal>cotton>nylon>polyester.

• Journal of the Society of Disaster Information
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• v.5 no.2
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• pp.124-137
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• 2009

The research on the effect of the prestressing force on the frequency of PSC(Prestressed Concrete beam) has been conducted theoretically and experimentally, and a few theory has been presented. However, the presented theories show no agreement in predicting the effect of the prestressing force. In this paper, the theories on the effect of the prestressing force on the frequency of PSC beam are presented and evaluated using the experimental result. To obtain the experimental result, two PSC beam specimens were manufactured, and the modal test and analysis were performed. The modal analysis results revealed that the prestressing force increased the natural frequency of the PSC beam. Comparing predicted results using existing theories show that Kim's model, which substitutes the prestressing tendon with the equivalent beam, gives the best prediction result.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2004.05a
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• pp.831-836
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• 2004

Vibration of electric-powered hand grinder comes from the parts of motor, gear, bearing, and fan. Excessive vibration can be harmful to workers. To reduce vibration of a hand grinder we analyzed the frequency components from the routing electric-powered grinder and did modal test to find the natural frequencies of the each part. It shows that the vibration is due to the resonance of the case. To remove the resonance, the case structure is modified and the bearing cap is replaced on a basis of the results from the rotor dynamic analysis using SAMCEF. As a result the vibration of the hand grinder is reduced greatly.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.16 no.3 s.108
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• pp.233-239
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• 2006

The effect of the joint condition of automotive muffler shell and baffle on radiated noise from muffler shell Is studied. Shell vibration characteristics, especially shift In natural frequency and change in of response amplitude, was identified from finite element analysis and modal tests for various joint conditions between shell and baffle. When there is heat expansion and inner pressure from the exhaust 9as in the muffler with elliptical cross section, the shell expands out, and construct gap with baffles. This gap causes more degrees of freedom of shell vibration and natural frequency shift. By welding the muffler shell to the baffles or using a dual shell muffler, the radiated noise problem could be mitigated supplying more a rigid joint and damping, respectively.