scholarly journals A New Identification Method for Bolt Looseness in Wind Turbine Towers

2019 ◽  
Vol 2019 ◽  
pp. 1-10 ◽  
Author(s):  
He Xianlong ◽  
She Tianli
Keyword(s):  
Wind Turbine ◽  
Phase Difference ◽  
Damping Ratio ◽  
Research Result ◽  
Vibration Characteristics ◽  
First Order ◽  
Before And After ◽  
Wind Turbine Towers ◽  
Vibration Tests ◽  
Experimental Data Analysis

Flange plates are key joining components used in wind turbine towers. Bolt looseness results in common fatigue damage in wind turbine towers. Detailed vibration tests were carried out on six wind turbine towers with loose bolts. First, the bolt looseness situation of each wind turbine tower was detected by the torque method. The vibration characteristics of each tower were then tested and analyzed in detail before maintenance. Finally, the vibration characteristics were tested and analyzed in detail after maintenance. The experimental data analysis shows that the first-order natural frequencies of the wind turbine towers before and after bolt maintenance do not change; the damping ratio does not change significantly; and the first-order vibration mode remains effectively unchanged. The phase difference between the upper and the lower plates of a flange has a significant and abrupt characteristic even when the bolt looseness ratio is 6%; however, the phase difference does not exhibit this characteristic after the flange bolts are retightened. The experimental results show that compared with other vibration characteristics, the first-order phase difference characteristic of wind turbine towers is more markedly affected by the looseness of the flange bolts; hence, this characteristic can be used as a diagnostic that reflects flange bolt looseness. Whether the flange bolts of a given tower require tightening can be identified based on whether the absolute value of the phase difference between the upper and lower plates of the flanges suddenly increases. This research result can provide a new method for the identification of bolt looseness in wind turbine towers.

Cable Reinforced Small Scale Horizontal Axial Wind Turbine

2013 ◽  
Vol 394 ◽  
pp. 309-313
Author(s):  
Yuan Ma ◽  
Pan Zeng ◽  
Hong Ya Lu ◽  
Yue Jie Xu
Keyword(s):  
Wind Turbine ◽  
Turbine Blade ◽  
Wind Turbines ◽  
Noise Level ◽  
Wind Turbine Blade ◽  
Small Scale ◽  
Optimum Location ◽  
Reinforcement Structure ◽  
First Order ◽  
Vibration Tests

In this paper, a cable reinforcement structure for small scale horizontal axial wind turbines is proposed. Shock-vibration tests were performed on the cable reinforced structure with different parameters of cable installation. The first order frequency of the blade was chosen to represent the stiffness of the blade rotor. According to the results, an optimum location of cable reinforcement exists at around 1/3 length of the wind turbine blade, and the first order frequency of the blade rotor will rise with the tension of the cable in a certain range. Further analysis showed that besides improving the reliability of the wind turbine rotors, the cable reinforcement structure also provides a possibility to use cheaper materials for blade manufacturing and also control the noise level of small scale horizontal axial wind turbines.

scholarly journals Performance Degradation in Cross-Eye Jamming Due to Amplitude/Phase Instability between Jammer Antennas

Sensors ◽  
2021 ◽  
Vol 21 (15) ◽  
pp. 5027
Author(s):  
Je-An Kim ◽  
Joon-Ho Lee
Keyword(s):  
Performance Analysis ◽  
Phase Difference ◽  
Taylor Expansion ◽  
Amplitude Ratio ◽  
Random Variables ◽  
Performance Degradation ◽  
Analytical Performance ◽  
Phase Instability ◽  
Gaussian Random Variables ◽  
First Order

Cross-eye gain in cross-eye jamming systems is highly dependent on amplitude ratio and the phase difference between jammer antennas. It is well known that cross-eye jamming is most effective for the amplitude ratio of unity and phase difference of 180 degrees. It is assumed that the instabilities in the amplitude ratio and phase difference can be modeled as zero-mean Gaussian random variables. In this paper, we not only quantitatively analyze the effect of amplitude ratio instability and phase difference instability on performance degradation in terms of reduction in cross-eye gain but also proceed with analytical performance analysis based on the first order and second-order Taylor expansion.

Wind load response of offshore wind turbine towers with fixed monopile platform

2016 ◽  
Vol 158 ◽  
pp. 122-138 ◽  
Author(s):  
M. Feyzollahzadeh ◽  
M.J. Mahmoodi ◽  
S.M. Yadavar-Nikravesh ◽  
J. Jamali
Keyword(s):  
Wind Turbine ◽  
Wind Load ◽  
Offshore Wind ◽  
Offshore Wind Turbine ◽  
Load Response ◽  
Wind Turbine Towers

Research on Damage Status of the Reinforced Concrete Ground Floor Columns

2012 ◽  
Vol 226-228 ◽  
pp. 1436-1440
Author(s):  
Li Jun Gao ◽  
Yong Sheng Zhang ◽  
Qin Li
Keyword(s):  
Reinforced Concrete ◽  
Measurement Method ◽  
Damping Ratio ◽  
Simple Calculation ◽  
Dynamic Measurement ◽  
Concrete Column ◽  
Destructive Testing ◽  
Reinforced Concrete Column ◽  
First Order ◽  
Vibration Model

In this paper, dynamic measurement method is applied to test the damage of the bottom reinforced concrete column. The comparison between the calculated first order frequency of the bottom reinforced concrete column and the measured first order frequency shows that the result is consistent. This indicates that this approach is feasible. However, in recent years, dynamic measurement method is widely used in non-destructive testing of bridges and floors. The principle of the dynamic measurement method for the detection of reinforced concrete column utilizes the measured natural frequency, vibration model and damping ratio of reinforced concrete column and such inherent dynamic characteristics of indicators to reflect the damage of reinforced concrete column. And there is no secondary injury for the column. The simplified method of structure dynamics is applied to calculate the frequency of the bottom reinforced concrete column. And the simple calculation method is verified by experiment and practice.

Methodology for seismic risk assessment for tubular steel wind turbine towers: application to Canadian seismic environment

2011 ◽  
Vol 38 (3) ◽  
pp. 293-304 ◽  
Author(s):  
Elena Nuta ◽  
Constantin Christopoulos ◽  
Jeffrey A. Packer
Keyword(s):  
Seismic Hazard ◽  
Wind Turbine ◽  
Seismic Loading ◽  
Element Analysis ◽  
Design Spectrum ◽  
Wind Turbine Tower ◽  
Damage States ◽  
Wind Turbine Towers ◽  
Hazard Level ◽  
Hazard Levels

The seismic response of tubular steel wind turbine towers is of significant concern as they are increasingly being installed in seismic areas and design codes do not clearly address this aspect of design. The seismic hazard is hence assessed for the Canadian seismic environment using implicit finite element analysis and incremental dynamic analysis of a 1.65 MW wind turbine tower. Its behaviour under seismic excitation is evaluated, damage states are defined, and a framework is developed for determining the probability of damage of the tower at varying seismic hazard levels. Results of the implementation of this framework in two Canadian locations are presented herein, where the risk was found to be low for the seismic hazard level prescribed for buildings. However, the design of wind turbine towers is subject to change, and the design spectrum is highly uncertain. Thus, a methodology is outlined to thoroughly investigate the probability of reaching predetermined damage states under any seismic loading conditions for future considerations.

Remote monitoring and nondestructive evaluation of wind turbine towers

2014 ◽  
Author(s):  
Chih-Hung Chiang ◽  
Chih-Peng Yu ◽  
Keng-Tsang Hsu ◽  
Chia-Chi Cheng ◽  
Ying-Tzu Ke ◽  
...  
Keyword(s):  
Nondestructive Evaluation ◽  
Wind Turbine ◽  
Remote Monitoring ◽  
Wind Turbine Towers

scholarly journals EFEKTIVITAS MODEL PEMBELAJARAN JIGSAW PADA KETERAMPILAN MENULIS BAHASA PERANCIS

2020 ◽  
Vol 20 (1) ◽  
pp. 121-131
Author(s):  
Tri Indri Hardini ◽  
Iim Siti Karimah ◽  
Adelya Erliani
Keyword(s):  
Research Result ◽  
Writing Skills ◽  
Posttest Score ◽  
Education Students ◽  
Writing Ability ◽  
Argumentative Text ◽  
Before And After ◽  
French Education ◽  
Positive Impression ◽  
Test Result

This research aims to describe student’s writing ability before and after using Jigsaw model, the effectiveness of Jigsaw model in improving writing skills, and the opinion of students. This study applies descriptive quantitative method in form of pre-experimental design. Instruments that are used in the form of tests and questionnaires. The sample of this research is 32 characteristics writing skill of 6th  semester French Education students. Based on the research result, the researcher can conclude that the students have been able to write the argumentative text nicely. The test result showed that the average test score after using the Jigsaw model is 8.9. It means, the average posttest score is higher than the average pretest score, up to 1.7%. Meanwhile, the results of the questionnaire show that students like writing but they find so much difficulty in making a writing or a text, and most students give a positive impression for the Jigsaw model.

scholarly journals Earth-termination system for onshore wind Turbines.

2020 ◽  
Vol 11 (7-2020) ◽  
pp. 66-72
Author(s):  
Liubov A. Belova ◽  
Keyword(s):  
Wind Turbine ◽  
Wind Turbines ◽  
Lightning Strike ◽  
Lightning Protection ◽  
Protection Measures ◽  
Lightning Strikes ◽  
Grounding System ◽  
Initial Stage ◽  
Wind Turbine Towers ◽  
Surge Protection

The earth-termination system for towers of ground-based wind turbines in addition to protective and functional grounding provides lightning protection grounding, which is especially important since the wind turbine is susceptible to lightning strikes. If insufficient protective measures are taken, the risk of damage to a wind turbine due to a lightning strike increases. Therefore, a well-thought-out built-in grounding system for wind turbine towers is needed, which would function as necessary and guarantee long-term mechanical strength and corrosion resistance. The configuration of grounding systems for wind turbines is discussed in IEC 61400-24, which deals with the topic of lightning protection for wind turbines, including detailed information on the choice of lightning protection measures and surge protection. It is advisable to create a lightning protection concept at the initial stage of planning a wind turbine in order to avoid later costly repairs and retrofitting.

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