• Smart Structures and Systems
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• v.33 no.1
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• pp.27-39
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• 2024

The effectiveness of conventional tuned liquid dampers (TLDs) in controlling the wind-induced response of tall flexible structures has been indicated. However, the impaired control effect in the detuning condition or a considerably high mass cost of liquid may be incurred in ensuring the high-level serviceability. To provide an efficient TLD-based solution for wind-induced vibration control, this study proposes a serviceability-oriented optimal design method for isolated TLDs (ILDs) and derives analytical design formulae. The ILD is implemented by mounting the TLD on the linear isolators. Stochastic response analysis is performed for the ILD-equipped structure subjected to stochastic wind and white noise, and the results are considered to derive the closed-form responses. Correspondingly, an extensive parametric analysis is conducted to clarify a serviceability-oriented optimal design framework by incorporating the comfort demand. The obtained results show that the high-level serviceability demand can be satisfied by the ILD based on the proposed optimal design framework. Analytical design formulae can be preliminarily adopted to ensure the target serviceability demand while enhancing the structural displacement performance to increase the safety level. Compared with conventional TLD systems, the ILD exhibits higher effectiveness and a larger frequency bandwidth for wind-induced vibration control at a small mass ratio.

• Journal of the Korean Society of Hazard Mitigation
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• v.3 no.4 s.11
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• pp.103-109
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• 2003

A numerical analysis of cable-stayed bridge is conducted to determine optimum longitudinal modulus of elasticity which represents the boundary condition between the tower and main girder. The effect of longitudinal modulus of elasticity is investigated for different loading condition (live load, wind load, seismic load), respectively. There are significant changes in the member forces as variations of longitudinal modulus of elasticity, such as, $k_h$=e=100tonf/m/bearing (live load), $k_h$=e=1000tonf/m/bearing (seismic load), However, the wind loads do not affect member forces. The optimum longitudinal modulus of elasticity is determined from considering minimum member forces in the numerical analysis results.

• Smart Structures and Systems
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• v.31 no.5
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• pp.469-483
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• 2023

The dynamic characteristics of wind turbine blades are usually monitored by contact sensors with the disadvantages of high cost, difficult installation, easy damage to the structure, and difficult signal transmission. In view of the above problems, based on computer vision technology and the improved YOLOv5 (You Only Look Once v5) deep learning model, a non-contact dynamic characteristic monitoring method for wind turbine blade is proposed. First, the original YOLOv5l model of the CSP (Cross Stage Partial) structure is improved by introducing the CSP2_2 structure, which reduce the number of residual components to better the network training speed. On this basis, combined with the Deep sort algorithm, the accuracy of structural displacement monitoring is mended. Secondly, for the disadvantage that the deep learning sample dataset is difficult to collect, the blender software is used to model the wind turbine structure with conditions, illuminations and other practical engineering similar environments changed. In addition, incorporated with the image expansion technology, a modeling-based dataset augmentation method is proposed. Finally, the feasibility of the proposed algorithm is verified by experiments followed by the analytical procedure about the influence of YOLOv5 models, lighting conditions and angles on the recognition results. The results show that the improved YOLOv5 deep learning model not only perform well compared with many other YOLOv5 models, but also has high accuracy in vibration monitoring in different environments. The method can accurately identify the dynamic characteristics of wind turbine blades, and therefore can provide a reference for evaluating the condition of wind turbine blades.

• 한국방재학회:학술대회논문집
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• 2009.02b
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• pp.63.2-63.2
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• 2009

• Journal of the Korean Society of Hazard Mitigation
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• v.1 no.3 s.3
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• pp.103-110
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• 2001

The objective of this study is to investigate the behavior of superstructure considering several factors such as change of pile rigidity, soil characteristics, and the constraint condition of support. The results of this study are as follows: 1. Pile-rigidity computed by the rotating deformed plane method is continuously varied up to approximately 5D(D=diameter of pile) below the ground level. This result is consistent with the previous study$^{(12)}$, in which the pile deformation occurs at approximately $3{\sim}6$ times of pile diameter from the ground level. 2. For bridge structure-pile system, analytical results of internal forces and deformations show different values for modified pile rigidity and unchanged pile rigidity. 3. Detaild analysis considering modified pile rigidity is required for the long-span bridge design with structure pile system.

• Journal of the Korean Society of Hazard Mitigation
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• v.7 no.5
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• pp.99-110
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• 2007

A single slab concrete pavement has been modeled and analyzed by ABAQUS program. The stress and displacement of the JCP slab under traffic load with frictionless contact interaction between slab and base calculated by ABAQUS program have been compared with the results obtained by KENSLABS program. The results of the stresses of the two modeling show similar tendency and the difference of the two modeling is very small however the results of the displacement of the two modeling show some dissimilarity. In order to analyze the effects of material and geometric properties on the responses of slab, some varying parameters were chosen as input for the modeling. The changing parameters include the thickness and elastic modulus of the concrete slab, the thickness and elastic modulus of base and the elastic modulus of the subgrade. The contact interaction between the slab and base layer had been also studied and different friction coefficient 0, 2.5, 6.6, 7.5, 8.9 had been used to simulate the different friction interface condition. The results of the analysis showed that the responses of the concrete slab vary with the material and geometric properties of the pavement structure and the slab-base friction condition.

• Journal of the Korean Society of Hazard Mitigation
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• v.8 no.3
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• pp.165-169
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• 2008

It has been reported that most wastewater treatment plants have difficulties in nitrogen removal during winter season due to declined activity of nitrifiers in the condition of low temperature. This study was conducted in order to find out optimum operating condition for efficient nitrogen removal in low temperature. A series of operating conditions with various HRTs of each tank were simulated using the GPS-X program. The optimum HRT combination for effective nitrogen removal was 0.3 hr/0.5 hr/1.36 hr/4.84 hr(PreAx/An/Ax/Ox) with 51.4% of T-N removal efficiency and 57.3% of $NH_4^+$-N removal efficiency.

• Journal of the Korean Geotechnical Society
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• v.29 no.11
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• pp.49-60
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• 2013

The plan for major design-build projects of railway link among countries in gulf area (GCC) and freight rail construction is recently announced, but Korean companies have a hard time tendering due to special geotechnical condition in the Middle East. The major geotechnical risks during railway construction in the Middle East are related to ground improvement of soft Sabkha ground, wind-blown sand mitigation measure, dune sand compaction, and construction of large-scale cut and embankment. In this study, the characteristics of special geotechnical condition and potential geotechnical risks during railway construction in the Middle East are discussed on the basis of field observation, literature review, and field and laboratory test results.

• Journal of the Korean Society of Hazard Mitigation
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• v.8 no.1
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• pp.71-79
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• 2008

To find out the effect of the vegetation recovery and the problems of forest land, the researches of the mortality in pine stand and vegetation recovery have been carried out from the burned site. In area which is damaged by fire scar on crown and stem, rate of dead is higher. Where stand growing stocks were totally damaged by crown forest fire, most of vegetation was recovered by sprouts and planted seeds. Vegetation recovery power were depending on the condition of soil depth condition. For the artificial recovery, the damage happened by insects in the planted birches plantation. Rate of growth was somewhat different between Pinus densiflora and Pinus thunbergii in the plantation, because of individual growth rate.

• Journal of Welding and Joining
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• v.33 no.2
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• pp.40-46
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• 2015

This study was performed to investigate the effect of ultrasonic nano crystal surface modification (UNSM) on residual stress mitigation after Weld Inlay repair for butt dissimilar metal weld with Alloy 82/182 in reactor vessel In/Outlet nozzle. As-welded and Weld Inlay specimens were made in accordance with design standard of ASME Code Case N-766, and two planes of their weld specimens were peened by the optimum UNSM process condition. Peening characteristics for weld specimens after UNSM treatment were evaluated by surface roughness and Vickers hardness test. And, residual stress for weld specimens developed from before and after UNSM treatment was measured and evaluated by instrumented indentation technique. Consequently, it was revealed that the mitigation of residual stress in weld metal after Weld Inlay repair of reactor vessel In/Outlet nozzle could be possible through UNSM treatment.