Experimental characterization of ultrasonic nonlinearity in concrete under cyclic change of prestressing force using Nonlinear Resonant Ultrasonic Spectroscopy

Kim, Gyu-Jin,Park, Sun-Jong,Kwak, Hyo-Gyoung Elsevier BV 2017 Construction and Building Materials Vol.157 No.-

<P><B>Abstract</B></P> <P>In this paper, an experimental study was conducted to investigate the effect of varying prestressing force on the nonlinearity of concrete. Prestressed concrete beams, which have been rarely studied in terms of ultrasonic nonlinearity, were prepared. When the prestressing force changes, the stress condition of the concrete inside the beam is affected. This leads to the generation of micro-cracks and a change of the mechanical properties, and as such it is necessary to introduce a nonlinear ultrasonic technique that sensitively reflects microstructural change. In the experiment, a repetitive prestressing load history, which includes maximum levels of 45%, 60%, and 75% based on the compressive strength, was designed to evaluate the effects of repetitive loading and different levels of loading on the nonlinearity. A comparison with the measured results of the linear ultrasonic method was also carried out to verify the stress-dependent change of nonlinearity induced by external loads. With the experimental results, the adopted technique is found to be more sensitive to damage then conventionally used ultrasonic method. As the investigation of the methodology is effective in prestressed concrete structures, the possibility of ultrasonic nonlinearity as an indicator of prestressing force is evaluated.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Prestressing force effects on decreasing the ultrasonic nonlinearity. </LI> <LI> Cyclic loading effects on increasing the ultrasonic nonlinearity. </LI> <LI> Sensitivity comparison of NRUS with UPV on measuring the ultrasonic nonlinearity. </LI> </UL> </P>

Accurate modeling and nonlinearity compensation in the speed mode of a twisted string actuator

Lee, Hyoryong,Choi, Hyunchul,Park, Sukho Elsevier 2019 Mechanism and machine theory Vol.137 No.-

<P><B>Abstract</B></P> <P>A twisted string actuator (TSA) is an effective method that can change the rotational motion of a motor into a linear motion, as well as control the speed and stiffness of the actuator. In particular, because the speed mode of the TSA (SM-TSA) can adjust the rotation–linear motion ratio by changing the diameter and length of the twisting shaft, it is a good to increase the usability of the TSA. However, the SM-TSA has a significant limitation in that it demonstrates a nonlinear translatory motion with respect to the constant rotational motion of the motor in terms of its operating principle. To solve this problem, a more accurate modeling method of the SM-TSA should be applied to predict the nonlinearity and compensate for the nonlinearity. Herein, we analyze the tendency of the twisted strings of the SM-TSA and propose a more precise modeling method of the nonlinear SM-TSA. In addition, a nonlinearity compensation algorithm using the proposed modeling of the SM-TSA is developed to linearize the nonlinear translatory motion. Through various experiments of the SM-TSA, we validated that the proposed model exhibits the nonlinearity of the SM-TSA more precisely when compared to the previous model. Additionally, we confirmed that the nonlinearity compensation algorithm using the proposed model can perform more accurate linearization of the translatory motion of the SM-TSA.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Analysis of twisting tendency in speed mode of twisted string actuator (SM-TSA). </LI> <LI> A new simple nonlinear analytical model of SM-TSA. </LI> <LI> A nonlinearity compensation algorithm using nonlinear models of SM-TSA. </LI> <LI> Proposed analytical model could follow more accurately twisting tendency in SM-TSA. </LI> <LI> Compensated linear translatory motion of SM-TSA using proposed analytical model. </LI> </UL> </P>

체적파 혼합기법을 이용한 재료 손상 진단 적용 가능성 연구

최정석(Jeongseok Choi),조윤호(Younho Cho) 한국비파괴검사학회 2016 한국비파괴검사학회지 Vol.36 No.1

초음파 비선형 진단을 이용한 기법의 경우 재료의 단순 결함 검출뿐만 아니라 부식, 소성변형과 같은 미세손상을 평가할 때 주로 이용된다. 1차 조화파(primary wave)와 2차 조화파(second harmonic wave)의 진폭의 비를 이용하여 비선형성을 나타내며, 이러한 비선형성의 비교 결과를 진단에 사용한다. 실험 특성상 비선형성은 재료의 비선형성뿐만 아니라 장비의 비선형성 또한 포함하게 된다. 장비 비선형성은 사용자가 측정하고자 하는 값이 아니므로 오차로 작용하여 분석을 방해한다. 본 연구에서는 오차로 작용하는 장비의 비선형성을 감소시켜 보다 정확한 진단을 위해 체적파 혼합기법을 사용하였다. 체적파 혼합기법의 가장 큰 특징은 기존의 초음파 비선형 진단보다 장비의 비선형성을 줄일 수 있다는 점이다. 본 연구에서는 체적파 혼합기법을 이론 및 실험적으로 검증하였으며, 기존의 초음파 비선형 진단기법의 결과와 체적파 혼합기법의 결과를 비교하여 장단점 및 적용 가능성 분석에 초점을 두었다. Ultrasonic nonlinear evaluation is generally utilized for detection of not only defects but also microdamage such as corrosion and plastic deformation. Nonlinearity is determined by the amplitude ratio of primary wave second harmonic wave, and the results of its comparison are used for evaluation. Owing to the experimental features, the experimental nonlinearity result contains system nonlinearity and material nonlinearity. System nonlinearity is that which is unwanted by the user; hence, it acts as an error and interrupts analysis. In this study, a bulk wave mixing technique is implemented in order to minimize the system nonlinearity and obtain the reliable analysis results. The biggest advantage of this technique is that experimental nonlinearity contains less system nonlinearity than that for the conventional nonlinear ultrasonic technique. Theoretical and experimental verifications are performed in this study. By comparing the results of the bulk wave mixing technique with those of the conventional technique, the strengths, weaknesses, and application validity of the bulk wave mixing technique are determined.

The Study of Ultrasonic Nonlinearity in Heat Treatment Material

Weibin Li(이위빈),Jaesun Lee(이재선),Younho Cho(조윤호) 대한기계학회 2009 대한기계학회 춘추학술대회 Vol.2009 No.11

Nonlinear ultarsonic is very senstive to material property change. This paper attempts to study the correlation between heat treatment and ultrasonic nonlinearity by taking the nonlinearity factors into account. The modified ultrasonic velocity formula was deriven. It turns out that nonlinearity varies with ultrasonic velocity change in the material heat treatment, the experimental results show that relative nonlinearity parameters obtained from the modified ultrasonic velocity and the rai\tio of amplitudes(second harmonic and fundamental wave)have a good agreement. Both of them prove that the heat treatment can change the material nonlinearity. Furthermore, then relative nonlinearity calculated from the modified velocity is much more sensitive, representing the relative nonlinearity change based on the modified ultrasonic velocity in this case.

Nonlinearity Detection and Compensation in Radio over Fiber Systems Using a Monitoring Channel

Kim, Sung-Man The Korea Institute of Information and Commucation 2015 Journal of information and communication convergen Vol.13 No.3

A radio over fiber (RoF) system is a kind of analog optical transmission system and considered as a strong candidate for the next-generation fronthaul link in the future mobile network. In RoF systems, nonlinearity compensation is essential to increase the link capacity. In this paper, we propose a nonlinearity detection and compensation scheme using a monitoring channel in RoF systems. A monitoring channel is added at the transmitter site and used for transmitting a reference signal in an RoF transmission. The nonlinearity in the RoF transmission is detected by comparing the received monitoring signal and the original reference signal at the receiver site. Finally, the nonlinearity is compensated at the receiver by giving the reverse function of the detected nonlinearity. Our results show that the proposed scheme can almost remove the error vector magnitude degradation induced by the nonlinearity in the RoF system.

열처리된 재료의 초음파 비선형성에 관한 연구

Weibin Li,이재선(Jaesun Lee),조윤호(Younho Cho) 대한기계학회 2010 大韓機械學會論文集A Vol.34 No.6

비선형 초음파는 선형 초음파와 비교하였을 때 재료의 물성 변화에 민감하게 반응한다. 이 연구의 목표는 비선형 요소를 포함하여 열처리 조건과 초음파 비선형성의 상관관계를 알아내는 것이다. 본 연구에서 기존의 방법과는 다른 수정된 초음파속도계산 식이 새롭게 제안되었다. 이것은 열처리된 재질에서 초음파 속도변화가 재료의 비선형성 때문에 발생하는 것을 찾아내었다. 실험을 통하여 수정된 초음파 속도와 1차 조화 및 2차 조화파의 진폭 비율이 서로 동일한 경향을 보이는 것을 알아냈다. 그리고 수정된 초음파속도식을 통해 계산된 상대적인 비선형계수는 기존의 방법을 이용하였을 때보다 더 민감함을 알아냈다. Ultrasonic nonlinearity is very sensitive to changes in material properties. This paper describes the study of the correlation between heat treatment and ultrasonic nonlinearity by taking nonlinear factors into consideration. A modified formula was proposed for ultrasonic velocity. This formula indicated that the changes occurring in nonlinearity during heat treatments cause changes in the ultrasonic velocity. The experimental results show that the relative nonlinearity parameters calculated from the modified ultrasonic velocities and the ratio of amplitudes of the second harmonic and fundamental wave are in good agreement. The experimental results prove that heat treatment can result in changes in material nonlinearity. Moreover, the relative nonlinearity parameter calculated from the modified velocity formula is has a large value. Since this parameter has high sensitivity to changes in nonlinearity, it can be used to represent the relative nonlinearity change calculated in this study by using the modified formula for ultrasonic velocity.

BDS 통계와 DVS 알고리즘을 이용한 수문시계열의 비선형성 분석

최강수(Choi Kang Soo),경민수(Kyoung Min Soo),김수전(Kim Soo Jun),김형수(Kim Hung Soo) 대한토목학회 2009 대한토목학회논문집 B Vol.29 No.2B

수문시계열 분석과 예측을 위하여 통상적으로 기존의 선형적인 모형들을 이용하여 왔다. 그러나 최근 자연현상이나 수문시계 열의 패턴 그리고 변동성에 비선형구조가 존재하고 있다는 것이 입증되고 있다. 따라서 기존의 선형적인 방법들에 의한 시계열 분석이나 예측은 비선형 시스템에 대해서 적절하지 않을 것이다. 최근, 시계열의 비선형성 구조를 판단하기 위해 카오스 이론을 토대로 한 상관적분으로부터 BOS(Brock-Dechert-Scheinkman) 통계 기법이 유도되었다. BDS 통계는 시스템의 비선형구조와 무작위성 구조를 구별하는데 매우 효과적으로 이용되어 오고 있다. 또한 DVS(Deterministic Versus Stochastic) 알고리즘은 카오스와 추계학적 시스템을 구별하고 예측하는데 주로 이용되어 왔다. 그러나 본 연구에서는 DVS 알고리즘에 의해 시계열의 비선형성을 판별할 수 있음을 보이고자 한다. 따라서 본 연구에서는 추계학적 시계열과 수문학적 시계열들의 비선형성을 검사 하고자 한다. ARMA 모형과 TAR(Threshold autoregressive) 모형으로부터로 발생시킨 추계학적 시계열, 미국 유타주 GSL 체적자료, 미국 플로리다 주 St. Johns 강 Cocoa 지점의 유출량 자료, 소양강 댐 일 유입량 자료 등의 수문시계열에 대해 비선형성 분석을 수행하고 그 결과를 비교하였다. 분석결과 BDS 통계가 선형 및 비선형 시계열을 구분하는데 매우 강력한 도구임을 보였고,DVS 알고리즘 또한 시계열의 비선형성을 구별하는데 효과적으로 이용될 수 있음을 보였다. Classical linear models have been generally used to analyze and forecast hydrologic time series. However, there is growing evidence of nonlinear structure in natural phenomena and hydrologic time series associated with their patterns and fluctuations. Therefore, the classical linear techniques for time series analysis and forecasting may not be appropriate for nonlinear processes. In recent, the BDS (Brock-Dechert-Scheinkman) statistic instead of conventional techniques has been used for detecting nonlinearity of time series. The BDS statistic was derived from the statistical properties of the correlation integral which is used to analyze chaotic system and has been effectively used for distinguishing nonlinear structure in dynamic system from random structures. DVS (Deterministic Versus Stochastic) algorithm has been used for detecting chaos and stochastic systems and for forecasting of chaotic system. This study showed the DVS algorithm can be also used for detecting nonlinearity of the time series. In this study, the stochastic and hydrologic time series are analyzed to detect their nonlinearity. The linear and non?linear stochastic time series generated from ARMA and TAR (Threshold Auto Regressive) models, a daily streamflow at St. Johns river near Cocoa, Florida, USA and Great Salt Lake Volume (GSL) data, Utah, USA are analyzed, daily inflow series of Soyang dam and the results are compared. The results showed the BDS statistic is a powerful tool for distinguishing between linearity and nonlinearity of the time series and DVS plot can be also effectively used for distinguishing the nonlinearity of the time series.

A normalized compensation method for voltage nonlinearity of three‑level ANPC inverter

Juyeon Lee,June-Seok Lee 전력전자학회 2024 JOURNAL OF POWER ELECTRONICS Vol.24 No.8

This paper proposes a normalized compensation method for voltage nonlinearity of the three-level active neutral point clamped (3L ANPC) inverter. The operation of the 3L ANPC inverter includes the voltage nonlinearity caused by voltage errors, which are induced by the nonlinear components of switching devices and their operations. Since this voltage nonlinearity seriously distorts the phase current, it must be compensated to improve the quality of power conversion. For the 3L ANPC inverter, however, the voltage nonlinearity varies depending on the topology and modulation scheme, as well as the power factor of the system. Although many conventional methods have been proposed, these methods do not fully deal with the factors affecting the voltage nonlinearity. In this paper, a normalized compensation method for the voltage nonlinearity considering the characteristics of the 3L ANPC inverter and the power factor of the system is proposed. Two general topologies and modulation schemes of the 3L ANPC inverter are discussed in this paper, and the voltage nonlinearity is analyzed to derive the compensation components. By executing the compensation based on these analyses, the proposed method ensures its performance remains consistent across operating conditions, and is simply implemented. The effectiveness of the proposed method is verified by experimental results.

Flutter Characteristics ofAircraft Wing Considering Control Surface and Actuator Dynamics with Friction Nonlinearity

Lee, Seung-Jun,Lee, In,Shin, Won-Ho The Korean Society for Aeronautical and Space Scie 2007 International Journal of Aeronautical and Space Sc Vol.8 No.1

Whenever the hinge axis of aircraft wing rotates, its stiffness varies. Also, there are nonlinearities in the connection of the actuator and the hinge axis, and it is necessary to inspect the coupled effects between the actuator dynamics and the hinge nonlinearity. Nonlinear aeroelastic characteristics are investigated by using the iterative V-g method. Time domain analyses are also performed by using Karpel's minimum state approximation technique. The doublet hybrid method(DHM) is used to calculate the unsteady aerodynamic forces in subsonic regions. Structural nonlinearity located in the load links of the actuator is assumed to be friction. The friction nonlinearity of an actuator is identified by using the describing function technique. The nonlinear flutter analyses have shown that the flutter characteristics significantly depends on the structural nonlinearity as well as the dynamic stiffness of an actuator. Therefore, the dynamic stiffness of an actuator as well as the nonlinear effect of hinge axis are important factors to determine the flutter stability.

Experimental characterization of ultrasonic nonlinearity in concrete under cyclic change of prestressing force

김규진,박선정,곽효경 사단법인 한국계산역학회 2017 Computers and Concrete, An International Journal Vol.19 No.5

In this paper, an experimental study was conducted to investigate the effect of varying prestressing force on the nonlinearity of concrete. Prestressed concrete beams, which have been rarely studied in terms of ultrasonic nonlinearity, were prepared and the nonlinear resonant ultrasonic method was adopted. When the prestressing force changes, the stress condition of the concrete inside the beam is affected. This leads to the generation of micro-cracks and a change of the mechanical properties, and as such it is necessary to introduce a nonlinear ultrasonic technique that sensitively reflects microstructural change. In the experiment, a repetitive prestressing load history, which includes maximum levels of 45%, 60%, and 75% based on the compressive strength, was designed to evaluate the effects of repetitive loading and different levels of loading on the nonlinearity. A comparison with the measurement results of the linear ultrasonic method was also carried out to verify the stress-dependent change of nonlinearity induced by external loads. With the experimental results, the possibility of ultrasonic nonlinearity as an indicator of prestressing force is evaluated.