Strength of connection fixed by TOBs considering out-of-plane tube wall deformation-Part 1: Tests and numerical studies

Tuoya Wulan,Peijun Wang,Chengxin Xia,Xinyu Liu,Mei Liu,Fangzhou Liu,Ou Zhao,Lulu Zhang 국제구조공학회 2022 Steel and Composite Structures, An International J Vol.42 No.1

This paper presents a study on the behavior of a bolted T-stub to square tube connection using Thread-fixed Oneside Bolts (TOBs) through tests and numerical simulations. It outlines a research work of four connections with focus on the failure modes and strengths of the connection under tensile load. It was observed that the thread anchor failure caused by shear failure of hole threads controlled the final failure of the connection in the tests. Meanwhile, the out-of-plane deformation of tube wall resulted in the contact separation between hole threads and bolt threads, which in turn reduced the shear strength of hole threads. Finite element models (FEMs) allowing for the configuration details of the TOBs fixed connection are then developed and compared with the test results. Subsequently, the failure mechanism of hole threads and stress distribution of each component are analyzed based on FEM results. It was concluded that the ultimate strength of connection was not only concerned with the shear strength of hole threads, but also was influenced by the plastic out-of-plane deformation of tube wall. These studies lay a foundation for the establishment of suitable design methods of this type of connection.

A Fast Sorting Strategy Based on a Two-way Merge Sort for Balancing the Capacitor Voltages in Modular Multilevel Converters

Fangzhou Zhao,Guochun Xiao,Min Liu,Daoshu Yang 전력전자학회 2017 JOURNAL OF POWER ELECTRONICS Vol.17 No.2

The Modular Multilevel Converter (MMC) is particularly attractive for medium and high power applications such as High-Voltage Direct Current (HVDC) systems. In order to reach a high voltage, the number of cascaded submodules (SMs) is generally very large. Thus, in the applications with hundreds or even thousands of SMs such as MMC-HVDCs, the sorting algorithm of the conventional voltage balancing strategy is extremely slow. This complicates the controller design and increases the hardware cost tremendously. This paper presents a Two-Way Merge Sort (TWMS) strategy based on the prediction of the capacitor voltages under ideal conditions. It also proposes an innovative Insertion Sort Correction for the TWMS (ISC-TWMS) to solve issues in practical engineering under non-ideal conditions. The proposed sorting methods are combined with the features of the MMC-HVDC control strategy, which significantly accelerates the sorting process and reduces the implementation efforts. In comparison with the commonly used quicksort algorithm, it saves at least two-thirds of the sorting execution time in one arm with 100 SMs, and saves more with a higher number of SMs. A 501-level MMC-HVDC simulation model in PSCAD/EMTDC has been built to verify the validity of the proposed strategies. The fast speed and high efficiency of the algorithms are demonstrated by experiments with a DSP controller (TMS320F28335).

A Fast Sorting Strategy Based on a Two-way Merge Sort for Balancing the Capacitor Voltages in Modular Multilevel Converters

Zhao, Fangzhou,Xiao, Guochun,Liu, Min,Yang, Daoshu The Korean Institute of Power Electronics 2017 JOURNAL OF POWER ELECTRONICS Vol.17 No.2

The Modular Multilevel Converter (MMC) is particularly attractive for medium and high power applications such as High-Voltage Direct Current (HVDC) systems. In order to reach a high voltage, the number of cascaded submodules (SMs) is generally very large. Thus, in the applications with hundreds or even thousands of SMs such as MMC-HVDCs, the sorting algorithm of the conventional voltage balancing strategy is extremely slow. This complicates the controller design and increases the hardware cost tremendously. This paper presents a Two-Way Merge Sort (TWMS) strategy based on the prediction of the capacitor voltages under ideal conditions. It also proposes an innovative Insertion Sort Correction for the TWMS (ISC-TWMS) to solve issues in practical engineering under non-ideal conditions. The proposed sorting methods are combined with the features of the MMC-HVDC control strategy, which significantly accelerates the sorting process and reduces the implementation efforts. In comparison with the commonly used quicksort algorithm, it saves at least two-thirds of the sorting execution time in one arm with 100 SMs, and saves more with a higher number of SMs. A 501-level MMC-HVDC simulation model in PSCAD/EMTDC has been built to verify the validity of the proposed strategies. The fast speed and high efficiency of the algorithms are demonstrated by experiments with a DSP controller (TMS320F28335).

A Parallel Algorithm of Multiple String Matching Based on Set-Partition in Multi-core Architecture

Jiahui Liu,Fangzhou Li,Guanglu Sun 보안공학연구지원센터 2016 International Journal of Security and Its Applicat Vol.10 No.4

With the coming of the big data era, the data processing in large scale comes out with a new challenge. However, string matching still plays an important role in the network security and information retrieval fields, because of the large size of pattern set with the overhead of memory and access memory time. Improving the string matching algorithm to adapt to the large scale tasks is desirable and meaningful. In this paper, we present and implement a parallel algorithm of multiple string matching based on multi-core platform. In addition, this work focuses on the partition of pattern set by using genetic algorithm through the internal relation of the patterns to reduce the memory overhead and execution performance. Compared with the classical ones, our experiments on both high and low hit-rate data demonstrate that the performance of algorithm enhances about on average by 20%-40% in general. Besides, the proposed algorithm reduces the memory cost on average by 4%-20%.

Improved Hausdorff Distance Based Pilot Protection for Multi-terminal HVDC system

Huai Qing,Qin Liang,Liu Kaipei,Xu Yi,Wang Fangzhou,Ding Hua 대한전기학회 2021 Journal of Electrical Engineering & Technology Vol.16 No.4

In order to overcome the weakness of dc line protection under high impedance fault, a traveling wave similarity based pilot protection method is proposed using improved Hausdorff Distance algorithm. The issue of asynchronous data, noise and anomalies are solved with the improved Hausdorff Distance algorithm. The instantaneous frequency based wave head detection method is used to overcome the problem of delay in protection start-up. Based on this protection scheme, external fault can be distinguished from internal faults regardless of fault impedance, fault location and fault type. Moreover, the faulty pole and fault direction are recognized via ratio of transient energy at line terminals. Taking the Zhangbei high voltage dc transmission project as an example, a four-terminal ring type dc grid model is developed in PSCAD/EMTDC platform for fault simulation and the data processing is performed in MATLAB platform. Based on the theoretical analysis and simulation study, the proposed pilot protection is verifi ed with excellent fault impedance withstanding ability and robustness against noise, abnormal data and asynchronous data.

TiO2ecarbon nanotube composites for visible photocatalysts - Influence of TiO2 crystal structure

Mu Yao Guo,Fangzhou Liu,Yu Hang Leung,Alan Man Ching Ng,Aleksandra B. Djurišić,Wai Kin Chan 한국물리학회 2013 Current Applied Physics Vol.13 No.7

We investigated the influence of the crystal structure of TiO2 and the use of different TiO2 precursors on the properties and photocatalytic activity of carbon nanotube (CNTs)etitania composites. We found that the crystal structure and properties of starting TiO2 nanomaterial significantly affected the effect of CNTs incorporation on the photocatalytic activity under simulated solar and visible light illumination (simulated solar illumination with UV-blocking filter). In case of significant photocatalytic activity under visible light illumination (anatase TiO2), likely due to the presence of native defects, composites exhibited lower activity under visible illumination only, but higher activity under simulated solar illumination. The opposite trends were observed for P25 (anatase þ rutile) and rutile TiO2, where incorporation of CNTs resulted in a significant increase of photocatalytic activity under visible illumination. Thus, control over crystal structure and native defects is essential for the development of efficient visible light activated photocatalysts.

A numerical investigation of the tensile behavior of the thread-fixed one-side bolted T-stubs at high temperature

Yang You,Le Liu,Xiaojing Huang,Peijun Wang,Fangzhou Liu 국제구조공학회 2022 Steel and Composite Structures, An International J Vol.45 No.4

The tensile behavior of the Thread-fixed One-side Bolt (TOB) at high temperatures was studied using the Finite Element Modeling (FEM) to explore the structural responses that could not be measured in tests. The accuracy of the FEM was verified using the test results from the failure mode, load-displacement curve as well as yielding load. Three typical failure modes of TOB connected T-stubs were observed, which were the Flange Yielding (FY), the Bolt Failure (BF) and the Coupling Failure mode (CF). The influence of the flange thickness tb and the temperature θ on the tensile behavior of the T-stub were discussed. The initial stiffness and the yielding load decreased with the increase of the temperature. The T-stubs almost lost their resistance when the temperature exceeded 700℃. The failure modes of T-stubs were mainly decided by the flange thickness, which relates to the anchorage of the hole threads and the bending resistance of flange. The failure mode could also be changed by the high temperature. Design equations in EN 1993-1-8 were modified and verified by the FEM results. The results showed that these equations could predict the failure mode and the yielding load at different temperatures with satisfactory accuracy.