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Chunfa Li,Enmin Feng 한국전산응용수학회 2005 Journal of applied mathematics & informatics Vol.18 No.1-2
Parameter identification problem of a three species (predator, mutualist-prey, and mutualist) ecological system with reaction-diffusion phenomenon is investigated in this paper. The mathematical model of the parameter identification problem is constructed and continuous dependence of the solution for the direct problem on the parameters identified is obtained. Finally, the existence of optimal solution and an optimality necessary condition for the parameter identification problem are given.
Magnetic Properties and Microstructure of DyAlCu-diffusion Sintered Nd-Fe-B Magnets
Chunfa Liao,Xun Zhou,Peng Jiang,Zhiyong Zeng,Lianghua Que 한국자기학회 2022 Journal of Magnetics Vol.27 No.2
The ability to improve the coercivity of sintered Nd-Fe-B diffused by Dy-Al-Cu alloy derived from electrolysis in a fluoride salt-oxide system was evaluated. The results show that with the increase in heat treatment time, the coercivity of the magnet firstly increased and then decreased. Holding at 900 ℃ for 4 h, tempering at low temperature for 3 h at 550 ℃, the coercivity of GBDPed magnet increased by 44.34 %, the remanence decreased by 1.26 %, the Dy-rich shell phase was recognizable, and the Nd-rich phase evenly distributed. Electron microscope analysis showed that when the GBDP time was longer than 4h, the diffusion of Dy from the shell phase to the matrix phase dominated, decreasing the coercivity with the increase in the diffusion time. The increase of Fe content in the grain boundary phase enhanced the exchange coupling between grains, which also reduced the coercivity of the GBDPed magnet. The infiltration of the matrix phase by excessive Dy and deterioration of (00L) texture of Nd-Fe-B resulted in the reduction of the remanence and the maximum energy product.
Chunfa Lin,Siyu Wang,Haoran Yan,Yuqiang Han,Junyi Zhu,Hao Shi 대한금속·재료학회 2021 METALS AND MATERIALS International Vol.27 No.2
A novel structure-optimized SiC fiber reinforced metal-intermetallic-laminated composite (SiCf-Ti/Al3Ti) without intermetalliccenterline defect has been fabricated by vacuum hot pressing using stacked fibers and foils as well as Ti barrierlayer. Through microstructure characterization by SEM and EBSD, the mechanisms of centerline formation and structuraloptimization were investigated detailedly. The mechanical properties and fracture behaviors of the optimized and nonoptimizedSiCf-Ti/Al3Ti composites were studied via quasi-static compression tests. The experimental results indicatedthat the intermetallic centerline region existing at the mid-plane of Al3Tilayer in non-optimized composite mainly containsnewly-formed Kirkendall voids and gathered metallic oxides. Additionally, owing to the similar moving trails of fibers,oxides and voids in molten Al during hot pressing, SiC fiber is always accompanied with centerline, which causes the poorbonding of SiCf/Al3Ti interface. Unlike that, due to the adding of Ti barrier layer, SiC fibers are separated from centerlineand metallurgically bonded with Al3Tiintermetallic in the optimized composite. The compression testing results proved thatthe optimized SiCf-Ti/Al3Ti composite possesses superior strength and toughness compared with those of the non-optimizedcomposite. Besides, the extending of cracks along centerline often leads to large-scale centerline splitting and untimelySiCf/Al3Ti interface debonding in non-optimized composite. Nevertheless, cracks formed in optimized composite tend topropagate at the interfacial zone between layers instead of cutting off Al3Tilayer along its mid-plane. Moreover, ascribedto the well-bonded SiCf/Al3Ti interface, SiC fibers play an important role in strengthening and toughening the optimizedSiCf-Ti/Al3Ti composite by fiber bridging mechanism.
OPTIMAL CONTROL OF SYSTEMS OF PARABOLIC PDES IN EXPLOITATION OF OIL
Li, Chunfa,Feng, Enmin,Liu, Jinwang 한국전산응용수학회 2003 Journal of applied mathematics & informatics Vol.13 No.1
Optimal control problem for the exploitaton of oil is investigated. The optimal control problem under consideration in this paper is governed by weak coupled parabolic PDEs and involves with pointwise state and control constraints. The properties of solution of the state equations and the continuous dependence of state functions on control functions are investigated in a suitable function space; existence of optimal solution of the optimal control problem is also proved.
LI, CHUNFA,FENG, ENMIN 한국전산응용수학회 2005 Journal of applied mathematics & informatics Vol.18 No.1
Parameter identification problem of a three species (predator, mutualist-prey, and mutualist) ecological system with reaction-diffusion phenomenon is investigated in this paper. The mathematical model of the parameter identification problem is constructed and continuous dependence of the solution for the direct problem on the parameters identified is obtained. Finally, the existence of optimal solution and an optimality necessary condition for the parameter identification problem are given.
Leiting Sun,Jianqiang Tao,Chunfa Li,Shengkai Wang,Ziqiang Tong 대한토목학회 2018 KSCE JOURNAL OF CIVIL ENGINEERING Vol.22 No.9
The purpose of this paper is to optimize the signal timing through multi-agent simulation technology. Firstly, a conceptual model of the actual intersection is described. Secondly, the social dynamics model of the vehicle and pedestrian evolution rules are established from the micro perspective, which is simulated respectively by Anylogic and Synchro on this basis. Finally, the signal timing strategies for the different vehicle priorities are discovered through the heuristic algorithm. The case study shows that: ①The actual signal timing is not reasonable. ②The optimization strategies of signal timing can improve traffic efficiency. ③By comparing the signal timing strategies of different vehicle priority, the study shows that the Anylogic is more superior to the Synchro, which provides a new way to solve the traffic congestion.
Jiaqi Zeng,Wenchao Li,Min Lei,Chunfa Dong,Kui Zhou 한국섬유공학회 2023 Fibers and polymers Vol.24 No.10
Polycaprolactone (PCL) exhibits limited applicability in the application of biological tissue engineering scaffolds due to its lower surface hydrophilicity and surface energy. In this paper, PCL crystal lamellae scaffolds with different surface roughness were fabricated by immersing electrostatic direct-written PCL scaffolds in PCL/Amyl acetate (AC) solution for 15 , 30 , 60 and 120 min, respectively, using solution incubation for crystallization. The rough scaffolds were subsequently coated with polydopamine (PDA) for 4 h, 8 h, 12 h and 16 h. Surface morphology, chemical properties and water contact angle tests were performed on both types of scaffolds. To evaluate the feasibility of the modified scaffold as a bionic scaffold, L929 mouse fibroblasts were inoculated on the surface of the scaffold and cultured for 1, 3 and 7 days. When compared to the untreated scaffolds, the surface of the scaffolds treated for 15 , 30 , 60 , and 120 min, respectively exhibited a distinct PCL crystal lamellae structure, accompanied by a significant increase in surface roughness and corresponding water contact angle elevation. In the cell experiments, the 30 min treatment group demonstrated superior cellular activity compared to the other experimental groups. The water contact angle of the PDA-modified scaffolds decreased over time with extended treatment durations, ultimately reaching 0°. In the cell experiments, the 8 h treatment scaffolds exhibited a more pronounced improvement in activity compared to the other groups. Based on these results, it can be concluded that the PDA-modified PCL crystal lamellae electrostatic direct-write scaffold promotes cell proliferation and differentiation, thereby facilitating tissue regeneration.
Peng, Cheng,Mansour, Alaa M.,Wu, Chunfa,Zuccolo, Ricardo,Ji, Chunqun,Greiner, Bill,Sung, Hong Gun Techno-Press 2018 Ocean systems engineering Vol.8 No.4
Floating Production Storage and Offloading (FPSO) units have the advantages of their ability to provide storage and offloading capabilities which are not available in other types of floating production systems. In addition, FPSOs also provide a large deck area and substantial topsides payload capacity. They are in use in a variety of water depths and environments around the world. It is a good solution for offshore oil and gas development in fields where there is lack of an export pipeline system to shore. However due to their inherently high motions in waves, they are limited in the types of risers they can host. The Low Motion FPSO (LM-FPSO) is a novel design that is developed to maintain the advantages of the conventional FPSOs while offering significantly lower motion responses. The LM-FPSO design generally consists of a box-shape hull with large storage capacity, a free-hanging solid ballast tank (SBT) located certain distance below the hull keel, a few groups of tendons arranged to connect the SBT to the hull, a mooring system for station keeping, and a riser system. The addition of SBT to the floater results in a significant increase in heave, roll and pitch natural periods, mainly through the mass and added mass of the SBT, which significantly reduces motions in the wave frequency range. Model tests were performed at the Korea Research Institute of Ships & Ocean Engineering (KRISO) in the fall of 2016. An analytical model of the basin model (MOM) was created in Orcaflex and calibrated against the basin-model. Good agreement is achieved between global performance results from MOM's predictions and basin model measurements. The model test measurements have further verified the superior motion response of LM-FPSO. In this paper, numerical results are presented to demonstrate the comparison and correlation of the MOM results with model test measurements. The verification of the superior motion response through model test measurements is also presented in this paper.
Yuqiang Han,Qinghua Que,Ran Cheng,Ran Cheng,Chunfa Lin,Wenqing Han,Enhao Wang,Junyi Zhu,Haoran Yan 대한금속·재료학회 2021 METALS AND MATERIALS International Vol.27 No.10
In present work, a novel SiCfreinforced (Al3Ti + Al3Ni)-based metallic–intermetallic laminate (Ti–(Al3Ti + Al3Ni)/SiCf-MIL) composite without centerline defect was prepared using Ti, Al foils, NiTi wires and SiC fibers by vacuum hot pressingsintering method. Electron backscatter diffraction was employed to characterize the microstructure and phase constituents ofTi–(Al3Ti + Al3Ni)/SiCf-MIL composite during various stages of preparation process. The elimination mechanism of intermetalliccenterline was discussed. Besides, quasi-static compressive performance and fracture toughness of the synthesizedcomposite were investigated. The experimental results indicated that as reaction time increasing, the NiTi/Al interfacialreaction occurred prior to the Ti/Al interfacial reaction to form an Al3Ti/Al3Ni zone. Then, the oxides gathered at the frontof Ti/Al interfacial reaction layer were dispersed in the intermetallic layer rather than being pushed together to generate thecenterline due to the Al3Ti/Al3Ni zone. After reaction, there were no residual NiTi phases and intermetallic layers mainlyconsisting of Al3Tiand Al3Niphases were obtained in this composite. In addition, high angle grain boundaries in Al3Tigrains occupied a large proportion, conversely, low angle grain boundaries dominated in Al3Nigrains. Furthermore, stressconcentration appears at the interface between layers instead of along the middle plane of intermetallic layer. Moreover,both compressive strength and fracture toughness of the composite are superior in comparison with SiCfreinforced Ti–Al3Timetallic–intermetallic laminate composite (Ti–Al3Ti/SiCf-MIL) ascribed to the elimination of centerline.