• 한국해양공학회지
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• 제2권1호
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• pp.46-58
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• 1988

The experimental investigations on the motion characteristics of a marine riser both in air and water were performed. The static deflections and natural frequencies of the riser in air including the effect of static offset, were obtained from the experiment. These results were compared with those of theoretical prediction by using a simple asymptotic formula. In order to investigate the nonlinear motion characteristics of the riser subject to nonlinear viscous drag and large displacement, the forced oscillation tests both in air and water were performed. In the forced oscillation tests in air, it was found that the transverse motion due to geometrical nonlinearity grows when the amplitude of in-line oscillation exceeds a certain critical value, say, order of 1-2 diameters. The planar motions of the riser in water due to vortex shedding and the geometrical nonlinearity were described. Some of these results were also compared with those of theoretical analysis, which uses a numerical perturbation technique based on the derived linear asymptotic solutions, and found to be generally in good agreement.

• Geomechanics and Engineering
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• 제21권2호
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• pp.103-109
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• 2020

The inflow rate is of interest in the design of underground structures such as tunnels and buried pipes below the groundwater table. Soil permeability governing the inflow rate significantly affects the hydro-geological behavior of soils but is difficult to estimate due to its wide range of distribution, nonlinearity and anisotropy. Volume changes induced by stress can cause nonlinear stress-strain behavior, resulting in corresponding permeability changes. In this paper, the nonlinearity and anisotropy of permeability are investigated by conducting Rowe cell tests, and a nonlinear permeability model considering anisotropy was proposed. Model modification and parameter evaluation for field application were also addressed. Significance of nonlinear permeability was illustrated by carrying out numerical analysis of a tunnel. It is highlighted that the effect of nonlinear permeability is significant in soils of which volume change is considerable, and particularly appears in the short-term flow behavior.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1987년도 전기.전자공학 학술대회 논문집(I)
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• pp.565-568
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• 1987

In order to determine the standard composition of ZnO varistor with higher nonlinearity, various contents of $MnO_2$, $Co_2O_3$ were added to ZnO-1.0m/o $Bi_2O_3$ system. Also, samples that contained small amount of Sb, Si-oxides in standard composition determined before were fabricated. As a result, the standard composition of higher nonlinearity-oriented ZnO varistor was shown as ZnO-1.0 m/o $Bi_2O_3$-1.0m/o $MnO_2$-1.0m/o $Co_2O_3$ and $Sb_2O_3$ largely enhanced nonlinear exponent and nonlinear resistance, hut SiO largely enhanced nonlinear exponent only.

• 비파괴검사학회지
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• 제27권6호
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• pp.576-581
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• 2007

Ultrasonic nonlinearity has been considered as a promising method to evaluate the micro damage of material; however, its magnitude is so small that its measurement is not easy. Especially, when we use contact PZT transducer, if the contacting pressure is not kept in constant during the measurement then there exists extraneous fluctuation in the measured nonlinearity caused by the unstable contact condition, In this paper, we developed a pneumatic control system to keep the contacting pressure of transducer in constant during the measurement and analyzed the effect of contacting pressure to the ultrasonic nonlinearity measurement As a result, we found that the pressure of transducer in our measurement system should be greater than 170 kPa to measure the ultrasonic nonlinear parameter in stable with no dependency on the contacting pressure.

• Structural Engineering and Mechanics
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• 제88권3호
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• pp.209-220
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• 2023

This study investigates the effectiveness of tuned mass dampers (TMDs) in controlling vibrations in low-rise reinforced concrete buildings. It examines both linear and nonlinear behaviors of concrete structures subjected to strong ground motions from the PEER database. The research follows the ASCE 7-16 provisions to model structural nonlinearity. Additionally, the study explores the effect of varying TMD mass ratios on the performance of these systems in real-world conditions. The findings emphasize the importance of accounting for structural nonlinearity in low-rise buildings, highlighting its significant influence on the controlled response under severe seismic excitations. The study suggests including nonlinear analysis in seismic design practices and recommends customizing TMD designs to optimize vibration control. These recommendations have practical implications for enhancing the safety and effectiveness of seismic design practices for low-rise buildings.

• 한국광학회지
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• 제28권4호
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• pp.158-165
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• 2017

광 흡수체로부터 측정되는 광음향 신호의 크기가 광 흡수계수 값의 증가에 따라 증가하다가 포화되는 광음향 비선형성에 대한 기존의 분석에서는 초음파 측정기의 물리적 형태를 고려하지 않았다. 이 논문에서는 초음파 측정기의 구면 초점 형태가 광음향 비선형성에 미치는 영향을 분석하였다. 구면 초점 초음파 측정기의 공간 필터링에 의한 광음향 공명 현상을 고려하고 기존의 광음향 비선형성에 대한 연구 방법을 보완하여 구면 초점 초음파 측정기로 측정한 광음향 신호에 대한 해석식을 이론적으로 유도하였다. 이 해석식에 의한 결과는 광음향 신호가 특정한 광 흡수계수 값에서 최대값을 나타내고 최대값 이후로는 광 흡수계수 값의 증가에 따라 오히려 감소함을 보였다. 주파수 영역에서 구면 초점 초음파 측정기에 의해 측정된 광음향 신호의 공명 스펙트럼과 초음파 측정기의 주파수 전달 함수를 비교하여 이 기존의 통념과는 다른 특징을 보이는 광음향 비선형성을 이해하였다. 또한, 이 주파수 영역에서의 물리적 해석으로 인해 광음향을 발생시키는 광 흡수체 내부의 광 조도 형태도 광음향 비선형성에 영향을 미친다는 것을 알 수 있었다.

• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 2006년도 정기 학술대회 논문집
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• pp.141-148
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• 2006

Concrete in a CFT(Concrete Filled Tube) column has enhanced strength and ductility because it is triaxially confined by a steel tube. But CFT columns are designed based on linear analyses by stress block method without the confining effect or the nonlinearity of the concrete. These make the significantly difference between the analysis results and the experimental results. Thus in this study, a nonlinear CFT column model was developed considering the confining effect on the concrete in a CFT column. This developed model was verified by experimental results from other researchers and compared with the results of various specifications. With the developed model, parametric studies were performed and the developed column model showed reasonable and accurate results.

• Structural Engineering and Mechanics
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• 제31권2호
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• pp.163-180
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• 2009

In the design of tall reinforced concrete (R/C) buildings, the serviceability stiffness criteria in terms of maximum lateral displacement and inter-story drift must be satisfied to prevent large second-order P-delta effects. To accurately assess the lateral deflection and stiffness of tall R/C structures, cracked members in these structures need to be identified and their effective member flexural stiffness determined. In addition, the implementation of the geometric nonlinearity in the analysis can be significant for an accurate prediction of lateral deflection of the structure, particularly in the case of tall R/C building under lateral loading. It can therefore be important to consider the cracking effect together with the geometric nonlinearity in the analysis in order to obtain more accurate results. In the present study, a computer program based on the iterative procedure has been developed for the three dimensional analysis of reinforced concrete frames with cracked beam and column elements. Probability-based effective stiffness model is used for the effective flexural stiffness of a cracked member. In the analysis, the geometric nonlinearity due to the interaction of axial force and bending moment and the displacements of joints are also taken into account. The analytical procedure has been demonstrated through the application of R/C frame examples in which its accuracy and efficiency in comparison with experimental and other analytical results are verified. The effectiveness of the analytical procedure is also illustrated through a practical four story R/C frame example. The iterative procedure provides equally good and consistent prediction of lateral deflection and effective flexural member stiffness. The proposed analytical procedure is efficient from the viewpoints of computational effort and convergence rate.

• Smart Structures and Systems
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• 제30권6호
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• pp.639-648
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• 2022

This study aims at numerically and experimentally investigating torsional guided wave mixing with weak material nonlinearity under acoustoelastic effect in tubular structures. The acoustoelastic effect on single central frequency guided wave propagation in structures has been well-established. However, the acoustoelastic on guided wave mixing has not been fully explored. This study employs a three-dimensional (3D) finite element (FE) model to simulate the effect of stress on guided wave mixing in tubular structures. The nonlinear strain energy function and theory of incremental deformation are implemented in the 3D FE model to simulate the guided wave mixing with weak material nonlinearity under acoustoelastic effect. Experiments are carried out to measure the nonlinear features, such as combinational harmonics and second harmonics in related to different levels of applied stresses. The experimental results are compared with the 3D FE simulation. The results show that the generation combinational harmonic at sum frequency provides valuable stress information for tubular structures, and also useful for damage diagnosis. The findings of this study provide physical insights into the effect of applied stresses on the combinational harmonic generation due to wave mixing. The results are important for applying the guided wave mixing for in-situ monitoring of structures, which are subjected to different levels of loadings under operational condition.

• Wind and Structures
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• 제23권6호
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• pp.485-503
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• 2016

To investigate the nonlinear aerostatic stability of the Hutong cable-stayed rail-cum-road bridge with ultra-kilometer main span, a FEM bridge model is established. The tri-component wind loads and geometric nonlinearity are taken into consideration and discussed for the influence of nonlinear parameters and factors on bridge resistant capacity of aerostatic instability. The results show that the effect of initial wind attack-angle is significant for the aerostatic stability analysis of the bridge. The geometric nonlinearities of the bridge are of considerable importance in the analysis, especially the effect of cable sag. The instable mechanism of the Hutong Bridge with a steel truss girder is the spatial combination of vertical bending and torsion with large lateral bending displacement. The design wind velocity is much lower than the static instability wind velocity, and the structural aerostatic resistance capacity can meet the requirement.