A Variable-Tensioned Transfer Matrix Method for Modal Analysis of Marine Risers and Its Application to Structural Damage Detection

Xingkun Zhou,Yuqing Sun,Wenhua Li 대한토목학회 2021 KSCE JOURNAL OF CIVIL ENGINEERING Vol.25 No.6

Structural damage caused by the vortex-induced vibration (VIV), harsh marine environment, and ultimate loads, etc., often alters marine risers' natural frequencies and mode shapes. A simple method for calculating variable-tensioned marine risers, especially for the risers with single and multiple damages, is proposed herein to explore the relationships between modal characteristics and structural damage. The approach' main advantage is that it is suitable for marine risers with various boundary conditions, variable tension, and different damage locations and degrees. Compared with the literature, the natural frequencies and mode shapes are re-examined using the intact marine risers. With the variation of damage degree and location along water depth, the effects of damage on natural frequency and the second derivative of mode curvature (SMC) are studied. To solve frequency and SMC's insensitivity problem to the node damage, a frequency-square-weighted superposition of the SMC index, i.e., SSMC, is developed. The relationships of SSMC with the single damage and the multiple damages are accurately modeled, and the damaged severities are precisely predicted by fitting a cubic polynomial and a quintic-binary function, respectively. In total, the proposed methods and the numerical results may be useful references to the damage detection of marine risers.

Chinese University Students’ and Teachers’ Perceptions of and Attitudes towards ELF

( Yanyan Zhang ),( Xingkun Du ) 범태평양 응용언어학회 2018 범태평양응용언어학회지 Vol.22 No.2

It has been widely acknowledged in the academic field that English is being used as a lingua franca among people from various first language backgrounds. However, the notion of English as a Lingua Franca (ELF) does not seem to have been integrated into English classrooms, especially in China, a country from the Expanding Circle. As China has the largest population of learners of English as a foreign language, the current study aims to investigate university students’ and teachers’ perceptions of and attitudes towards ELF in the Chinese context. A total of 168 non-English major students and 30 college English teachers from a top university in Mainland China participated in the study. Two questionnaires were distributed to our student and teacher participants, respectively, and a semi-structured interview was organized afterwards. It was found that neither the students nor the teachers have sufficient knowledge about ELF, despite their awareness of the lingua franca function of English. Both the students and the teachers appear to be deeply attached to “Standard English” under the influence of “native speaker norm” in English teaching contents and methods. However, the students hold highly positive attitudes towards ELF and express their willingness to learn about it in class. Therefore, it is of vital importance for English teachers to reconsider their beliefs and teaching practices and try to incorporate an ELF orientation into English teaching.

Experimental research on local buckling of BS700 high-strength steel thin-walled box-section members under axial compression

Lei Gao,Fei Shao,Linyue Bai,Xingkun Xie,Xiaohui He 대한기계학회 2022 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.36 No.5

In this study, the ultimate bearing capacity and local buckling failure mode of members were investigated, and the results were compared to the predicted values of the existing steel structures design code. The results indicated that the failure mode of the specimen was local buckling. Finite element model is verified using experimental results. FE model is capable of predicting the behaviour of specimens and it is used for further numerical analyses. Experimental results are compared with recommendations of the steel structures design code of GB50017-2017, ANSI/AISC 360-16 and Eurocode 3. It is observed that the 83.3 % of the test bearing capacity are slightly higher than the predictions of existing codes with a variance of 5 %. It is concluded that the provisions of existing codes can meet the design requirements. However, the number of tests is limited and further related experimental and FE numerical studies are required.

Modeling, analysis, and experiments of a pause-and-leap jumping robot during takeoff, flight, and landing buffering

Qi Yang,Jing Zhao,Ziqiang Zhang,Bin Chang,Xingkun Liu 대한기계학회 2019 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.33 No.10

Jumping robots can overcome obstacles strongly and are suitable for complex terrain environments. However, the takeoff parameters of most jumping robots, especially pause-and-leap jumping robots, cannot be changed accurately. Moreover, the stability of the flight and landing of these robots needs to be improved. On the basis of observations of the jumping process of a locust, leg mechanisms, including one-degree-of-freedom jumping leg and series buffering leg, are designed. Then, dynamic models for takeoff, flight, and landing buffering are established and combined with Lagrange/Newton-Euler dynamic modeling methods and conservation of momentum moment. For the former, the effects of structural parameters, including position of the driving spring, absolute position of the center of mass, and stiffness coefficient of the driving spring, on takeoff velocity and acceleration can be obtained. The takeoff parameters can also be changed accurately. For the flight phase, the relationship between the relative position of the center of mass and the stability of flight is revealed. For the latter, the effects of two buffering modes on the supporting forces and energy storage capacity are analyzed. On the basis of the parameters determined by the abovementioned modeling method, a prototype is developed, and an experiment is conducted to verify the rationality of the modeling method. Experimental results show that the prototype can acquire accurate takeoff parameters and achieve stable flight and landing buffering. This study provides a useful reference for the design and control of jumping robots.

An On-line Strategy based on Rolling State Prediction for Hybrid Energy Storage System of Tram

Yu Wang,Zhongping Yang,Fei Lin,Xiaochun Fang,Xingkun An,Hongda Zhou 전력전자학회 2019 ICPE(ISPE)논문집 Vol.2019 No.5

This paper aims at a hybrid tram with the onboard battery-supercapacitor storage system. This paper proposes an on-line strategy based on rolling state prediction (ROS). A wavelet neural network (WNN) is used to predict the running state of the tram in a certain period of time in the future according to the historic data, and the dynamic programming (DP) algorithm is used to optimize the energy management strategy (EMS) during the period. The strategy aims to optimize the system efficiency and battery life. Compared with classical rule-based (RB) strategy, ROS greatly increases the system efficiency and lengthens lifespan of battery and achieves real-time optimization.

The Geochemical and Zircon Trace Element Characteristics of A-type Granitoids in Boziguoer, Baicheng County, Xinjiang

윤경무,유춘화,박정현,소흥곤,양해도,서해명,왕군,Yin, Jingwu,Liu, Chunhua,Park, Jung Hyun,Shao, Xingkun,Yang, Haitao,Xu, Haiming,Wang, Jun The Korean Society of Economic and Environmental G 2013 자원환경지질 Vol.46 No.2

신장 위구르 자치구 바이청현 보즈구얼 지역의 A형 화강암체는 타림지대의 북쪽 끝과 동서쪽 방향의 알칼리 관입암대에 접하여 위치해 있다. 이 화강암체는 추휘석(aegrine)이나 아페소나이트(arfvedsonite)-석영-알칼리장석 섬장암, 또는 아페소나이트-알칼리장석 화강암, 흑운모-알칼리장석 섬장암으로 구성되며, 주요광물로는 알바이트(albite), K-장석, 석영, 아페소나이트(arfvedsonite), 추휘석, 시데로필라이트(siderophyllite) 등이 있으며 부성분 광물로는 지르콘(zircon), 파이로클로르(pyrochlore), 토라이트(thorite), 형석, 모나자이트(monazite), 바스네사이트(bastnaesite), 제노타임(xenotime), 아스트로필라이트(astrophyllite) 등이 있다. 이 알칼리 화강암체는 67.32%의 평균값을 갖는 $SiO_2$를 포함하고 평균 11.14%의 높은 $Na_2O+K_2O$(9.85~11.87%) 조성을 보이며 이 중 $K_2O$는 평균 4.73%의 조성을 보인다. $K_2O/Na_2O$의 비는 0.31~0.96 사이이며 $Al_2O_3$는12.58%부터 15.44%사이로 포함되고 총 $FeO^T$함량은 2.35~5.65%이내이다. CaO, MgO, MnO, $TiO_2$의 함량은 낮은 것으로 관찰된다. 희토류원소의 총량은 평균 $77{\times}10^{-6}$으로 비교적 높게 나타나고 경희토원소는 농축되어 있지만 중희토원소는 Eu원소의 부(-)의 이상과 함께 상대적으로 결핍되는 특징을 가진다. 또한 알칼리 화강암체의 chondrite-normalized 희토류원소의 패턴은 오른쪽으로 기울어진 갈매기형태를 보인다. Zr는 평균 $594{\times}10^{-6}$의 함량을 보이며 Zr+Nb+Ce+Y는 평균 $1362{\times}10^{-6}$의 함량을 나타낸다. 또한 이 알칼리 화강암체는 높은 HFSE(Ga, Nb, Ta, Zr, Hf)함량과 낮은 LILE(Ba, K, Sr)함량을 보인다. Nb/Ta의 비는 평균 16.5이며 Zr/Hf의 비는 평균 36.80이다. 지르콘은 경희토원소에서 결핍되고 중희토원소에서 농축되어있다. 지르콘의 chondrite-normalized 희토류원소는 Eu원소의 강한 부(-)의 이상과 함께 왼쪽으로 기울어진 갈매기형태를 보인다. 보즈구얼지역의 A타입 화강암체는 A1타입의 화강암과 유사한 특징을 나타낸다. 화강암질 마그마의 평균온도는 $832{\sim}839^{\circ}C$이며 보즈구얼 지역의 A타입 화강암체는 지각과 맨틀의 혼합양상을 보이며 고온, 무수, 낮은 산소의 퓨개시티(fugacity) 환경을 가진 판 내부의 비조산대에서 생성되었을 가능성이 있다. The Boziguoer A-type granitoids in Baicheng County, Xinjiang, belong to the northern margin of the Tarim platform as well as the neighboring EW-oriented alkaline intrusive rocks. The rocks comprise an aegirine or arfvedsonite quartz alkali feldspar syenite, an aegirine or arfvedsonite alkali feldspar granite, and a biotite alkali feldspar syenite. The major rock-forming minerals are albite, K-feldspar, quartz, arfvedsonite, aegirine, and siderophyllite. The accessory minerals are mainly zircon, pyrochlore, thorite, fluorite, monazite, bastnaesite, xenotime, and astrophyllite. The chemical composition of the alkaline granitoids show that $SiO_2$ varies from 64.55% to 72.29% with a mean value of 67.32%, $Na_2O+K_2O$ is high (9.85~11.87%) with a mean of 11.14%, $K_2O$ is 2.39%~5.47% (mean = 4.73%), the $K_2O/Na_2O$ ratios are 0.31~0.96, $Al_2O_3$ ranges from 12.58% to 15.44%, and total $FeO^T$ is between 2.35% and 5.65%. CaO, MgO, MnO, and $TiO_2$ are low. The REE content is high and the total ${\sum}REE$ is $(263{\sim}1219){\times}10^{-6}$ (mean = $776{\times}10^{-6}$), showing LREE enrichment HREE depletion with strong negative Eu anomalies. In addition, the chondrite-normalized REE patterns of the alkaline granitoids belong to the "seagull" pattern of the right-type. The Zr content is $(113{\sim}1246){\times}10^{-6}$ (mean = $594{\times}10^{-6}$), Zr+Nb+Ce+Y is between $(478{\sim}2203){\times}10^{-6}$ with a mean of $1362{\times}10^{-6}$. Furthermore, the alkaline granitoids have high HFSE (Ga, Nb, Ta, Zr, and Hf) content and low LILE (Ba, K, and Sr) content. The Nb/Ta ratio varies from 7.23 to 32.59 (mean = 16.59) and the Zr/Hf ratio is 16.69~58.04 (mean = 36.80). The zircons are depleted in LREE and enriched in HREE. The chondrite-normalized REE patterns of the zircons are of the "seagull" pattern of the left-inclined type with strong negative Eu anomaly and without a Ce anomaly. The Boziguoer A-type granitoids share similar features with A1-type granites. The average temperature of the granitic magma was estimated at $832{\sim}839^{\circ}C$. The Boziguoer A-type granitoids show crust-mantle mixing and may have formed in an anorogenic intraplate tectonic setting under high-temperature, anhydrous, and low oxygen fugacity conditions.