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Sintering behavior and dielectric properties of BZN ceramic powders coated by CuSO4
Biao Jin,Xiao Wang,Liu-shuan Yang,Chao-jun Wan 한양대학교 세라믹연구소 2016 Journal of Ceramic Processing Research Vol.17 No.7
(Bi1.5Zn0.5)(Zn0.5Nb1.5)O7 (BZN) ceramics were synthesized by the traditional solid-state reaction method. Copper oxide isknown as a good sintering aid for microwave dielectric ceramics and to be less reactive toward silver. We have introduced theCuO into BZN by modifying BZN surface by a CuO thin layer on the calcined powder instead of mixing CuO directly withBZN powder. A CuO precursor solution of CuSO4, was used to prepare the CuO thin layer. This paper describes the effectof CuO layer on the sintering behavior, phase composition and dielectric properties of BZN ceramics. The results showed thatappropriate CuO addition could accelerate the sintering process and lower the densification temperature to 900 oC. Theoptimal concentration of CuSO4 was found to be 0.5 M. The BZN ceramic sintered at 900 oC presented good microwavedielectric properties i.e. εr = 141 and Qƒ = 426 GHz, which is much better than those of CuO doped BZN ceramic (εr = 134 andQƒ = 287 GHz).
Axial load behavior and stability strength of circular tubed steel reinforced concrete (SRC) columns
Biao Yan,Jiepeng Liu,Xuhong Zhou 국제구조공학회 2017 Steel and Composite Structures, An International J Vol.25 No.5
The tubed steel reinforced concrete (SRC) column is a composite column in which the outer steel tube is mainly used to provide confinement on the core concrete. This paper presents experimental and analytical studies on the behavior of circular tubed SRC (TSRC) columns subjected to axial compression. Eight circular TSRC columns were tested to investigate the effects of length-to-diameter ratio (L/D) of the specimens, diameter-to-thickness ratio (D/t) of the steel tubes, and use of stud shear connectors on the steel sections. Elastic-plastic analysis on the steel tubes was used to investigate the mechanism of confinement on the core concrete. The test results indicated that the tube confinement increased the strength and deformation capacity for both short and slender columns, and the effects on strength were more pronounced for short columns. A nonlinear finite element (FE) model was developed using ABAQUS, in which the nonlinear material behavior and initial geometric imperfection were included. Good agreement was achieved between the predicted results using the FE model and the test results. The test and FE results were compared with the predicted strengths calculated by Eurocode 4 and the AISC Standard. Based on the analytical results, a new design method for this composite column was proposed.
3D quasi-transient thermo-mechanical analysis for vehicle brake disc
Biao Hu,Xingyan Zhang,Yang Liu,Junjie Yan,Xiaobing Liu,Xin Wang,Richard Sun 대한기계학회 2022 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.36 No.2
An alternative numerical method is developed to predict the thermo-mechanical behavior of brake disc during braking. Steady-state aerodynamic simulation for entire vehicle with variant speeds are conducted to analyze the convective heat transfer characteristic of the disc surface. Then the transient heat transfer boundary of the disc is obtained by interpolating the steady-state simulation results. Based on that, the transient thermo-mechanical coupled simulation for brake disc is performed via finite element method. With those work, the characteristics of transient temperature field and stress field of the brake disc are analyzed. Meanwhile, the characteristic of contact pressure distribution on friction interface is also obtained. The results show that during the braking process, for any node in the friction areas of the brake disc surface, its temperature rise curve fluctuates like a sawtooth. The temperature field has a significant effect on the stress field of the brake disc, both in distribution and variation. To verify the numerical method and validate the simulation results, a full-scale vehicle brake-thermalperformance test is carried out. By comparison, the simulation results show good agreement with the experimental results. The proposed numerical method enables an efficient and economical way to predict and evaluate the thermo-mechanical behavior of the brake disc in early phase of vehicle development.
Biao Yang,Lin Zhao,Tian Tian,Yankui Qin,Changyu Liu 대한기계학회 2022 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.36 No.5
The “S” characteristics of a pump turbine may result in certain problems, such as excessive water hammer pressure, unstable no-load operation, and difficulty in synchronization. Accordingly, a new start-up strategy based on the partial opening of a ball valve is proposed, and the calculation model of the hydraulic transition process with misaligned guide vane devices (MGV) and a ball valve is established. The emergency shutdown and turbine start-up conditions are simulated and analyzed. The ball valve can more effectively reduce the maximum inlet pressure of the volute and increase the minimum inlet pressure of the draft tube during the shutdown process compared with the MGV devices. The newly proposed strategy can also effectively reduce the amplitude of pressure fluctuation at the volute and draft tube, shorten the synchronization time, and reduce the speed overshoot during the start-up process. The ball valve can effectively improve the operating quality of the unit in the S-shaped area.
Biao Ma,Weichen Lu,He Wang,Liang Yu 대한기계학회 2022 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.36 No.12
In order to realize the miniaturization and electrification of heavy vehicles, this paper innovatively puts forward a two-speed transmission device equiped with electrically controlled toothed band brakes. The dynamic models of the planetary gear and toothed band brake are derived, and the shift strategy is established to achieve the optimal dynamic performance. Moreover, the gearshift characteristics under different working parameters are studied to verify its feasibility. The results demonstrate that the toothed band brake has a short braking time and contributes to good shift performance, thus has potential for application. The effect of synchronous speed and actuator speed on shift performance is also analyzed. The increase of both speeds is beneficial to speed up the shift time, but lead to increased shift impact. The application of such a brake offers the possibility of full-electric and lightweight for electric vehicles.
Biao Han,김시진,황보미,황의택,박한철,고문현,박경원 한국전기화학회 2013 한국전기화학회지 Vol.16 No.2
We demonstrate rutile TiO2 branched nanostructure (TiO2-BN) electrodes synthesized by seeding method for enhanced lithium intercalation properties. The morphology and crystal-line nature of the TiO2-BN were clearly observed by field-emission transmission electron microscopy and fast Fourier transform pattern. The TiO2-BN electrodes showed excellent capac-ity and high rate performance. The improved lithium-ion intercalation properties of the TiO2-BN may be attributed to relatively large specific surface area and short transport distance of the branched nanostructure.
Delivering IPTV Service over a Virtual Network: A Study on Virtual Network Topology
Biao Song,Mohammad Mehedi Hassan,허의남 한국통신학회 2012 Journal of communications and networks Vol.14 No.3
In this study, we design an applicable model enabling internet protocol television (IPTV) service providers to use a virtual network (VN) for IPTV service delivery. The model addresses the guaranteed service delivery, cost effectiveness, flexible control,and scalable network infrastructure limitations of backbone or IP overlay-based content networks. There are two major challenges involved in this research: i) The design of an efficient, cost effective,and reliable virtual network topology (VNT) for IPTV service delivery and the handling of a VN allocation failure by infrastructure providers (InPs) and ii) the proper approach to reduce the cost of VNT recontruction and reallocation caused by VNT allocation failure. Therefore, in this study, we design a more reliable virtual network topology for solving a single virtual node, virtual link, or video server failure. We develop a novel optimization objective and an efficient VN construction algorithm for building the proposed topology. In addition, we address the VN allocation failure problem by proposing VNT decomposition and reconstruction algorithms. Various simulations are conducted to verify the effectiveness of the proposed VNT, as well as that of the associated construction,decomposition, and reconstruction algorithms in terms of reliability and efficiency. The simulation results are compared with the findings of existing works, and an improvement in performance is observed.