Tribological performance of some organic fluorine-containing compounds as lubricants

Weimin Liu,Chengfeng Ye,Qunji Xue 한국트라이볼로지학회 2002 한국트라이볼로지학회 학술대회 Vol.2002 No.10

The friction and wear behaviors of fluorine-containing compounds such as perfluoropolyethers (PFPE), phosphazenes (X-1P), ionic liquids as lubricants for steel/seel, steel/ceramic, ceramic/ceramic were investigated using a SRV tester and a one-way reciprocating friction tester both in ball-on-disc configuration. It was found that the three fluorine-containing lubricants could reduce friction coefficient and wear volume effectively. The effectiveness of the three lubricants in reducing wear volume could be ranked as ionic liquids>X-1P>PFPE. Tests also showed that aryloxyphosphazene with polar substituent as a lubricant of steel/steel pair gave low wear, while aryloxyphosphazene with nonpolar group on the phenyl pendant led to high wear. The morphology and the tribo-chemical reaction of the worn surfaces were analyzed with a scanning electron microscope (SEM) and X-ray photoelectron spectroscope (XPS). XPS analyses illustrated the formation of iron fluoride in steel/steel system with the lubrication of both phosphazenes and ionic liquids.

Visual Fatigue Reduction Based on Depth Adjustment for DIBR System

( Ran Liu ),( Yingchun Tan ),( Fengchun Tian ),( Hui Xie ),( Guoqin Tai ),( Weimin Tan ),( Junling Liu ),( Xiaoyan Xu ),( Chaibou Kadri ),( Naana Abakah ) 한국인터넷정보학회 2012 KSII Transactions on Internet and Information Syst Vol.6 No.4

A depth adjustment method for visual fatigue reduction for depth-image-based rendering (DIBR) system is proposed. One important aspect of the method is that no calibration parameters are needed for adjustment. By analyzing 3D image warping, the perceived depth is expressed as a function of three adjustable parameters: virtual view number, scale factor and depth value of zero parallax setting (ZPS) plane. Adjusting these three parameters according to the proposed parameter modification algorithm when performing 3D image warping can effectively change the perceived depth of stereo pairs generated in DIBR system. As the depth adjustment is performed in simple 3D image warping equations, the proposed method is facilitative for hardware implementation. Experimental results show that the proposed depth adjustment method provides an improvement in visual comfort of stereo pairs as well as generating comfortable stereoscopic images with different perceived depths that people desire.

Fracture analysis of a welded front axle tube structure from a mini-truck

Weimin Guo,Ning Ding,Na Xu,Long Liu,Nan Li,Junbo Shi,Chi-Man Lawrence Wu 대한기계학회 2020 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.34 No.1

The failure (fracture) mechanism of a welded front axle tube structure made of C45E4 steel from a mini truck was analyzed. The fracture occurred on the right side of the right support frame with the fracture surface perpendicular to the tube axis. SEM examination showed that the fracture surface could be divided into three areas: intergranular area, cleavage area and dimple area. Crack initiation site of the failed front axle tube was at the front weld joint fixing the right support frame on the axle tube. The crack propagated in two opposite directions along the circumference of the tube and converged at the dimple area. Intergranular fracture was found to be in heat affected zone (HAZ). With higher magnification, fine dimples, intergranular and trans-granular fracture characteristics were observed in the crack initiation site. By metallurgical examination, Widmanstätten ferrites, which could decrease the toughness and strength of the weld joint, were observed in the columnar grains. The hardness of HAZ coarse grain area (623 VHN) was far higher than HAZ fine grain area (310 VHN) and base metal (225 VHN). As the weld process indicates, neither pre-weld nor post-weld treatment was carried out. A non-uniform temperature distribution around the weld joint could generate large thermal residual tensile stress in HAZ; thus, the material was very unstable. It could fracture for very small or even no external stress. Hydrogen atoms would be released during welding and microstructures with the highest hardness are the most susceptible of hydrogen assisted cracking. It is concluded that the fracture was caused by hydrogen assisted brittleness under the induction of weld residual stress. Post-weld aging treatment (PWAT) is recommended to release the residual stress generated during welding process. In this case, PWAT was carried out on the failed weld joint and Vickers hardness of HAZ coarse grain area, HAZ fine grain area and base metal decreased to 232 VHN, 205 VHN and 125 VHN, respectively. That indicates that the PWAT procedure could effectively soften the material and relieve residual stress.

Individual Channel Design-based Modeling and Analysis of Three Phase Grid-tied Inverter with Unbalanced Grid Impedance

Weimin Wu,Yun Li,Jiahao Liu,Frede Blaabjerg 전력전자학회 2019 ICPE(ISPE)논문집 Vol.2019 No.5

Three-phase grid-tied inverters are usually designed to operate in symmetric grid impedance. In actual operations, due to the imbalanced loads, three-phase systems with significant single-phase loads, imbalanced power line impedance or the imbalanced short-circuit impedance of the three grid power transformer, the equivalent three-phase grid impedance is unbalanced. It is, consequently, important to develop an effective model and stability analysis method to address three-phase grid-tied inverter with unbalanced grid impedance. Traditionally, the stability of unbalanced system can be analyzed by harmonic linearization technique, however, the model derivation is complex and the controller parameters need second designing. This paper develops the system model in a multivariable frequency domain, by using the individual channel analysis and design (ICAD), simplifying the stability analysis of the unbalanced system. The detailed study on the three-phase LCL filter-based grid-tied inverter under the unbalanced grid impedance condition is presented. Simulation and experiment analysis are carried out on a 380 V/50 Hz/6 kW grid-tied inverter prototype.

Engineering Homochiral Metal-Organic Frameworks for Heterogeneous Asymmetric Catalysis and Enantioselective Separation

Liu, Yan,Xuan, Weimin,Cui, Yong WILEY-VCH Verlag 2010 ADVANCED MATERIALS Vol.22 No.37

<P>Owing to the potential applications in technological areas such as gas storage, catalysis, separation, sensing and nonlinear optics, tremendous efforts have been devoted to the development of porous metal-organic frameworks (MOFs) over the past ten years. Homochiral porous MOFs are particularly attractive candidates as heterogeneous asymmetric catalysts and enantioselective adsorbents and separators for production of optically active organic compounds due to the lack of homochiral inorganic porous materials such as zeolites. In this review, we summarize the recent research progress in homochiral MOF materials, including their synthetic strategy, distinctive structural features and latest advances in asymmetric heterogeneous catalysis and enantioselective separation.</P> <B>Graphic Abstract</B> <P>Homochiral porous metal-organic frameworks (MOFs) are particularly attractive candidates as heterogeneous asymmetric catalysts and enantioselective adsorbents and separators for production of optically active organic compounds. This review summarizes the recent research progress in homochiral MOF materials, including their synthetic strategy, distinctive structural features and applications in enantioselective catalysis and separation. <img src='wiley_img_2010/09359648-2010-22-37-ADMA201000197-content.gif' alt='wiley_img_2010/09359648-2010-22-37-ADMA201000197-content'> </P>

MPMTP-AR: Multipath Message Transport Protocol Based on Application-Level Relay

( Shaowei Liu ),( Weimin Lei ),( Wei Zhang ),( Xiaoshi Song ) 한국인터넷정보학회 2017 KSII Transactions on Internet and Information Syst Vol.11 No.3

Recent advancements in network infrastructures provide increased opportunities to support data delivery over multiple paths. Compared with multi-homing scenario, overlay network is regarded as an effective way to construct multiple paths between end devices without any change on the underlying network. Exploiting multipath characteristics has been explored for TCP with multi-homing device, but the corresponding exploration with overlay network has not been studied in detail yet. Motivated by improving quality of experience (QoE) for reliable data delivery, we propose a multipath message transport protocol based on application level relay (MPMTP-AR). MPMTP-AR proposes mechanisms and algorithms to support basic operations of multipath transmission. Dynamic feedback provides a foundation to distribute reasonable load to each path. Common source decrease (CSD) takes the load weight of the path with congestion into consideration to adjust congestion window. MPMTP-AR uses two-level sending buffer to ensure independence between paths and utilizes two-level receiving buffer to improve queuing performance. Finally, the MPMTP-AR is implemented on the Linux platform and evaluated by comprehensive experiments.

Hole-filling Based on Disparity Map for DIBR

( Ran Liu ),( Hui Xie ),( Fengchun Tian ),( Yingjian Wu ),( Guoqin Tai ),( Yingchun Tan ),( Weimin Tan ),( Bole Li ),( Hengxin Chen ),( Liang Ge ) 한국인터넷정보학회 2012 KSII Transactions on Internet and Information Syst Vol.6 No.10

Due to sharp depth transition, big holes may be found in the novel view that is synthesized by depth-image-based rendering (DIBR). A hole-filling method based on disparity map is proposed. One important aspect of the method is that the disparity map of destination image is used for hole-filling, instead of the depth image of reference image. Firstly, the big hole detection based on disparity map is conducted, and the start point and the end point of the hole are recorded. Then foreground pixels and background pixels are distinguished for hole-dilating according to disparity map, so that areas with matching errors can be determined and eliminated. In addition, parallaxes of pixels in the area with holes and matching errors are changed to new values. Finally, holes are filled with background pixels from reference image according to these new parallaxes. Experimental results show that the quality of the new view after hole-filling is quite well; and geometric distortions are avoided in destination image, in contrast to the virtual view generated by depth-smoothing methods and image inpainting methods. Moreover, this method is easy for hardware implementation.

Integration of Multipath Transmission into the IMS Framework

( Shaowei Liu ),( Weimin Lei ),( Wei Zhang ),( Hao Li ) 한국인터넷정보학회 2017 KSII Transactions on Internet and Information Syst Vol.11 No.8

IP multimedia subsystem (IMS) is an open standardized architecture for delivering multimedia service over IP network in a route-agnostic manner. With the increasing popularity of conversational class service, the delivery of a traffic flow with a certain bandwidth demand over a single network path is either not possible or not cost-effective. Multipath transmission is considered to be a promising solution to provide high-quality delivery service. This paper proposes a software defined service overlay network (SDSON) based multipath transmission framework for IMS, which is complementary to existing network architecture. The framework transforms original two-party session negotiation into three-party session negotiation that supports participants to negotiate multipath transmission capacity and path information by signaling message. Based on existing IETF standards, SIP and SDP are scalable to support these functions. Finally, the proposed framework is fully implemented on open source platform and examined by experiments. Experimental results show that multipath-enabled IMS is an effective way to improve the delivery performance of conversational class service.

Study of Credibility Evaluation of Dynamic Models and their Parameters

Guo, Weimin,Ye, Xiaohui,Zhong, Wuzhi,Su, Yi,Tang, Yaohua,Song, Xinli,Liu, Tao The Korean Institute of Electrical Engineers 2014 The Journal of International Council on Electrical Vol.4 No.1

The time-domain simulation plays an important role in planning, designing and operation of the power system, but mismatches between its results and the actual system response show that the credibility evaluation of dynamic models is critical in all the above aspects of power systems. This paper discusses the technologies of credibility evaluation, including hybrid dynamic simulation with PMU measurements, error analysis and the calculated indices. Moreover, a phase shift method is presented to implement hybrid dynamic simulation in PSD-FDS. Then the paper proposes a credibility evaluation scheme to provide solution for the evaluation. At last, one sample is used to validate the implementation of hybrid dynamic simulation, while the other sample illustrates the effectiveness of the credibility evaluation approach.

Study on Formation of Microstructure in Rheo-Diecastings of Semi-Solid A380 Aluminum Alloy Slurry

Zhiyong Liu,Guotao Cui,Tan Wan,Weimin Mao 대한금속·재료학회 2021 METALS AND MATERIALS International Vol.27 No.7

The formation of the microstructure in the rheo-diecastings were studied by the experiment of rheo-diecasting with semi-solidA380 Aluminum alloy slurry. The results show that the grain diameter and shape factor of primary α-Al grains decreased andincreased along the rheo-diecasting direction, respectively, making the primary α-Al grains gradually distributing uniformly. The combination of injection pressure and narrow gate of the runner and ingate was the main reason for the evolution of theprimary α-Al grains, moreover, the collision and friction among primary α-Al grains during the flling were helpful for therefnement and spheroidization of the primary α-Al grains. The residual liquid solidifed into the secondary solidifcationmicrostructure accompanied by the evolution of the primary α-Al grains. The accumulation of the fragments of the primaryα-Al grains, the secondary α2-Al nuclei or grains which formed in previous positions, the efective nucleation rate of theresidual liquid, and the collision and fraction among the secondary α2-Al grains and between the secondary α2-Al grainand the primary α-Al grains made the secondary solidifcation microstructure of the residual liquid present multiplex andcomplicate characteristics.