Vortex-induced vibration characteristics of multi-mode and spanwise waveform about flexible pipe subject to shear flow

Bao Jian,Chen Zheng-Shou 대한조선학회 2021 International Journal of Naval Architecture and Oc Vol.13 No.1

Numerical simulations of the Vortex-Induced Vibration (VIV) about a large-scale flexible pipe subject to shear flow were carried out in this paper. Efficiency verification was performed firstly, validating that the proposed fluid–structure interaction solution strategy is competent in predicting the VIV response. Then, the VIV characteristics related to multi-mode and spanwise hybrid waveform about the flexible pipe attributed to shear flow were investigated. When inflow velocity rises, higher vibration modes are apt to be excited, and the spanwise waveform easily convertes from a standing-wave-dominated status to a hybrid standing–traveling wave status. The multi-mode or even multiple-dominant-mode is prone to occur, that is, the dominant mode is often followed by several apparent subordinate modes with considerable vibration energy. Hence, the shedding frequencies no longer obey Strouhal law, and vibration trajectories become intricate. According to the motion analysis concerning the coupled cross-flow and in-line vibrations, as well as the corresponding wake patterns, a tight coupling interaction exists between the structural deformation and the wake flow behind the flexible pipe. In addition, the evolution of the vortex tube along the pipe span and a strong 3D effect are observed due to the slenderness of the flexible pipe and the variability of the vortex shedding attributed to the shear flow.

A Family of Non-Isolated Photovoltaic Grid Connected Inverters without Leakage Current Issues

Baojian Ji,Jianhua Wang,Feng Hong,Shengming Huang 전력전자학회 2015 JOURNAL OF POWER ELECTRONICS Vol.15 No.4

Transformerless solar inverters have a higher efficiency than those with an isolation link. However, they suffer from a leakage current issue. This paper proposes a family of single phase six-switch transformerless inverter topologies with an ac bypass circuit to solve the leakage current problem. These circuits embed two unidirectional freewheeling current units into the midpoint of a full bridge inverter, to obtain a freewheeling current path, which separates the solar panel from the grid in the freewheeling state. The freewheeling current path contains significantly fewer devices and poor performance body diodes are not involved, leading to a higher efficiency. Meanwhile, it is not necessary to add a voltage balancing control method when compared with the half bridge inverter. Simulation and experiments are provided to validate the proposed topologies.

A Dual Buck Three-Level PV Grid-Connected Inverter

Baojian Ji,Feng Hong,Jianhua Wang,Shengming Huang 전력전자학회 2015 JOURNAL OF POWER ELECTRONICS Vol.15 No.4

The use of a PV grid-connected inverter with non-isolated topology and without a transformer is good for improving conversion efficiency; however, this inverter has become increasingly complicated for eliminating leakage current. To simplify the complicated architecture of traditional three-level dual buck inverters, a new dual Buck three-level PV grid-connected inverter topology is proposed. In the proposed topology, the voltage on the grounding stray capacitor is clamped by large input capacitors and is equal to half of the bus voltage; thus, leakage current can be eliminated. Unlike in the traditional topology, the current in the proposed topology passes through few elements and does not flow through the body diodes of MOSFET switches, resulting in increased efficiency. Additionally, a multi-loop control method that includes voltage-balancing control is proposed and analyzed. Both simulation and experimental results are demonstrated to verify the proposed structure and control method.

Experimental study of enhanced oil recovery with CO2 slug+N2 flood in low permeability reservoir

Baojian Du,Linsong Cheng 한국자원공학회 2014 Geosystem engineering Vol.17 No.5

Gas injection has become a significant enhanced oil recovery (EOR) measure to develop low permeability reservoirs. CO2 injection can achieve miscible displacement, but its cost is relatively high and CO2 is corrosive. N2 injection is cheap, but it is difficult to achieve miscible displacement in the formation with a limited EOR efficiency. Based on these problems, a feasibility analysis of CO2 slug+N2 to boost the recovery in low permeability reservoirs is studied through experiment. In this paper, with slim-tube test and core flood experiment, an analysis of minimum miscibility pressure, recovery of different gas injection scheme, and sensitivity of oil displacement efficiency of CO2 slug+N2 are obtained. The results show that the scheme of CO2 slug+N2 gets low miscibility pressure and can achieve miscible displacement with high ultimate recovery approximate to the scheme of continuous injection of CO2. Besides, injection timing, slug size of injected CO2, and formation pressure recovery before CO2 slug injection greatly influence the ultimate recovery. This study is significant for the understanding of EOR mechanism of CO2 slug+N2, optimization of injection parameters, and associated numerical simulation in low permeability reservoirs.

A Family of Non-Isolated Photovoltaic Grid Connected Inverters without Leakage Current Issues

Ji, Baojian,Wang, Jianhua,Hong, Feng,Huang, Shengming The Korean Institute of Power Electronics 2015 JOURNAL OF POWER ELECTRONICS Vol.15 No.4

Transformerless solar inverters have a higher efficiency than those with an isolation link. However, they suffer from a leakage current issue. This paper proposes a family of single phase six-switch transformerless inverter topologies with an ac bypass circuit to solve the leakage current problem. These circuits embed two unidirectional freewheeling current units into the midpoint of a full bridge inverter, to obtain a freewheeling current path, which separates the solar panel from the grid in the freewheeling state. The freewheeling current path contains significantly fewer devices and poor performance body diodes are not involved, leading to a higher efficiency. Meanwhile, it is not necessary to add a voltage balancing control method when compared with the half bridge inverter. Simulation and experiments are provided to validate the proposed topologies.

A Dual Buck Three-Level PV Grid-Connected Inverter

Ji, Baojian,Hong, Feng,Wang, Jianhua,Huang, Shengming The Korean Institute of Power Electronics 2015 JOURNAL OF POWER ELECTRONICS Vol.15 No.4

The use of a PV grid-connected inverter with non-isolated topology and without a transformer is good for improving conversion efficiency; however, this inverter has become increasingly complicated for eliminating leakage current. To simplify the complicated architecture of traditional three-level dual buck inverters, a new dual Buck three-level PV grid-connected inverter topology is proposed. In the proposed topology, the voltage on the grounding stray capacitor is clamped by large input capacitors and is equal to half of the bus voltage; thus, leakage current can be eliminated. Unlike in the traditional topology, the current in the proposed topology passes through few elements and does not flow through the body diodes of MOSFET switches, resulting in increased efficiency. Additionally, a multi-loop control method that includes voltage-balancing control is proposed and analyzed. Both simulation and experimental results are demonstrated to verify the proposed structure and control method.

On the general decay stability of stochastic differential equations with unbounded delay

Xuejing Meng,Baojian Yin 대한수학회 2012 대한수학회지 Vol.49 No.3

This work focuses on the general decay stability of nonlinear stochastic differential equations with unbounded delay. A Razumikhin-type theorem is rst established to obtain the moment stability but with-out almost sure stability. Then an improved edition is presented to derive not only the moment stability but also the almost sure stability, while ex-isting Razumikhin-type theorems aim at only the moment stability. By virtue of the M-matrix techniques, we further develop the aforementioned Razumikhin-type theorems to be easily implementable. Two examples are given for illustration.

An Inherent Zero-Voltage and Zero-Current-Switching Full-Bridge Converter with No Additional Auxiliary Circuits

Jianhua Wang,Baojian Ji,Hongbo Wang,Naifu Chen,Jun You 전력전자학회 2015 JOURNAL OF POWER ELECTRONICS Vol.15 No.3

An inherent zero-voltage and zero-current-switching phase-shifted full-bridge converter with reverse-blocking insulated-gate bipolar transistor (IGBT) or non-punch-through IGBT is proposed in this paper. This converter not only ensures that the switches in the lagging leg works at zero-current switching, but also minimizes circulating conduction loss without any additional auxiliary circuits. A 1.2 kW hardware prototype is designed, fabricated, and tested to verify the proposed topology. The control loop design procedures with small-signal models are also presented. A simple, low-cost, and robust democratic current-sharing circuit is also introduced and verified in this study. The proposed converter is a suitable alternative for compact, cost-effective applications with high-voltage input.

Identification of a C-type lectin from Antheraea pernyi, which may associate with the immune response to pathogens

Cen Qian,Kunzhang Lin,Baojian Zhu,Chao-Liang Liu,Lei Wang,Ya Liu,Dan Liang,PeiWang,Guo-Qing Wei 한국응용곤충학회 2017 Journal of Asia-Pacific Entomology Vol.20 No.2

C-Type lectins (CTLs) are carbohydrate-recognition proteins and play critical roles in innate immunity. In this study, we characterized a CTL fromAntheraea pernyi, named ApCTL,which has two carbohydrate-recognition domains (CRDs). A fragment of 1017 bp cDNA of ApCTL was isolated, which constituted 927 bp open reading frame (ORF), and it encoded putative protein of 308 amino acids. The recombinant protein of ApCTL was expressed in Escherichia coli, and anti-ApCTL antibodieswere prepared. ApCTL genewas constitutively expressed in a variety of tissueswhile it showed a higher expression level in fat body than other tissues. Protein andmRNAlevels of ApCTL in fat body and hemolymph were elevated upon nuclear polyhedrosis virus (NPV) and E. coli challenges. Recombinant ApCTL increased the agglutination of E. coli in a Ca2+-dependent manner and had the bacteriolytic activity on E. coli. Our results suggested that ApCTLmay play critical roles in pathogen recognition and could be involved in the innate immunity of A. pernyi.

An Inherent Zero-Voltage and Zero-Current-Switching Full-Bridge Converter with No Additional Auxiliary Circuits

Wang, Jianhua,Ji, Baojian,Wang, Hongbo,Chen, Naifu,You, Jun The Korean Institute of Power Electronics 2015 JOURNAL OF POWER ELECTRONICS Vol.15 No.3

An inherent zero-voltage and zero-current-switching phase-shifted full-bridge converter with reverse-blocking insulated-gate bipolar transistor (IGBT) or non-punch-through IGBT is proposed in this paper. This converter not only ensures that the switches in the lagging leg works at zero-current switching, but also minimizes circulating conduction loss without any additional auxiliary circuits. A 1.2 kW hardware prototype is designed, fabricated, and tested to verify the proposed topology. The control loop design procedures with small-signal models are also presented. A simple, low-cost, and robust democratic current-sharing circuit is also introduced and verified in this study. The proposed converter is a suitable alternative for compact, cost-effective applications with high-voltage input.