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Hai Le Xuan,Quoc-Dong Hoang,Soon Geul Lee,Dat Pham Xuan,Hoang Tran Viet,Minh Pham Van,Hung Pham Van,Hung Pham Viet,PHAM DUC TUAN,Duc Anh Nguyen 대한기계학회 2022 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.36 No.2
Ballbots, which have been studied for over ten years, are under-actuated mobile robots that operate using the inverted pendulum paradigm. Controlling a ballbot poses a number of challenges, including maintaining the stable upright posture from the ground in all directions and making sure it follows the desired trajectory. External factors such as a minor change in contact surface properties or fabrication errors can affect the system's stabilization and transfer capabilities. In this study, an adaptive hierarchical sliding mode control algorithm based on an artificial neural network is developed to make the ballbot robust to external factors. The use of the proposed controller ensures system stability despite uncertainties including friction, accidental centrifugal forces and gravity that occur when the ballbot follows the reference trajectory. The system stability is guaranteed on the basis of Lyapunov theory. Control efficiency and robot stability under system uncertainties are demonstrated by numerical simulation.
Van-Hoang Tran,Thanh-Huan Nguyen,Frédéric Plourde,Khanh-Duy Cong Do,Duy-Hung Chung,Cong-Truong Dinh,Gia-Diem Pham 한국유체기계학회 2023 International journal of fluid machinery and syste Vol.16 No.2
In order to increase turbine efficiency while retaining structural integrity, modern jet engines need an effective cooling system. Pin-fin arrays play a significant role in the internal cooling system of the turbine blade. In examining the efficacy of cooling techniques using pin-fins, the other papers focus on pin-fin configurations. In contrast, the current study is a step toward optimizing cooling cascade endwalls for better maneuvering and reservation of vortices, which leads to more considerable heat transfer near the endwalls. This study examines the flow field and heat transfer of roughed endwall in the pin-fin channel, including varieties with flat endwall and extruded endwall. The heat transfer of the channel and pressure drop properties of the extruded endwall case are quantitatively assessed to contrast with those of the flat endwalls scenario for an intake Reynolds number range of 7400 to 36000. The leading and trailing surfaces of the channel are divided into five streamwise regions to understand better how well the pin-fins and endwalls transmit heat. The results show that the new endwall construction significantly increases the high heat transfer zones around the pin-fins compared to the flat endwall scenario. In the meantime, the heat transfer of the channel to the pin-fins is enhanced by the modified endwall configuration. The redesigned endwall outperformed the basic case regarding the HTEI, rising by 15.9%. It is found that the friction factor of the new design is increased due to the narrowing channel. However, due to their much higher heat transfer capacity, the HTEI of extruded endwall is up to 41.5% higher than the HTEI of the channel with flat endwalls. These results demonstrate that the heat transfer properties of pin-fins can be significantly improved by optimizing endwall design.
Hang T. Dao,George A.C. Beattie,Gillian W. Watson,Van Lam Pham,Van Liem Nguyen,Duc Khanh Le,Thi Hoa Nguyen,Viet Nguyen,Paul Holford 한국응용곤충학회 2018 Journal of Asia-Pacific Entomology Vol.21 No.1
Armoured scales (Hemiptera: Diaspididae) belong to the largest scale insect family and are among the mostinvasive insects in the world. Accurate identification of armoured scales is essential for systematic and phylogeneticstudies; biogeography; trade and plant quarantine; and pest management, particularly biological control. Several species are serious pests of citrus. Records of past field surveys conducted in Viet Nam between 1967 and2010 indicated the presence of 28 species on citrus there. Discrepancies in these records, and the retention ofspecimens of only five species in collections, led us to undertake surveys throughout the citrus-growing regionsof the country in 2013 and 2014 to verify previous records and conserve voucher specimens. The presence of 21diaspidid species was confirmed based on morphological and molecular data. The species observed werecommon but rarely abundant. Populations in commercial orchards may have been influenced by use of pesticides,but most species were recorded also in gardens and orchards where pesticide use was uncommon. Naturalenemies were abundant, but were not thoroughly documented for all the diaspidids we observed. An identificationkey to the species collected is provided. Differences between our findings and previous records from VietNam, from Yunnan and Guangxi in China, and from Indochinese countries neighbouring Viet Nam, indicate theneed for extensive surveys to fully document the diaspidid fauna on citrus in the region.
Pham, Duc Cuong,Na, Kyung-Hwan,Pham, Van Hung,Yoon, Eui-Sung Korean Tribology Society 2009 KSTLE International Journal Vol.10 No.1
This paper reports an investigation on nanotribological properties of silicon nanochannels coated by a diamond-like carbon (DLC) film. The nanochannels were fabricated on Si (100) wafers by using photolithography and reactive ion etching (RIE) techniques. The channeled surfaces (Si channels) were then further modified by coating thin DLC film. Water contact angle of the modified and unmodified Si surfaces was examined by an anglemeter using the sessile-drop method. Nanotribological properties, namely friction and adhesion forces, of the Si channels coated with DLC (DLC-coated Si channels) were investigated in comparison with those of the flat Si, DLC-coated flat Si (flat DLC), and Si channels, using an atomic force microscope (AFM). Results showed that the DLC-coated Si channels greatly increased hydrophobicity of silicon surfaces. The DLC coating and Si channels themselves individually reduced adhesion and friction forces of the flat Si. Further, the DLC-coated Si channels exhibited the lowest values of these forces, owing to the combined effect of reduced contact area through the channeling and low surface energy of the DLC. This combined modification could prove a promising method for tribological applications at small scales.
Hung-Cuong Trinh,Van-Huy Pham,Anh H. Vo 한국인터넷정보학회 2023 KSII Transactions on Internet and Information Syst Vol.17 No.12
Ensuring reliability of a machinery system involve the prediction of remaining useful life (RUL). In most RUL prediction approaches, noise is always considered for removal. Nevertheless, noise could be properly utilized to enhance the prediction capabilities. In this paper, we proposed a novel RUL prediction approach based on noise injection and a Kalman filter ensemble of modified bagging predictors. Firstly, we proposed a new method to insert Gaussian noises into both observation and feature spaces of an original training dataset, named GN-DAFC. Secondly, we developed a modified bagging method based on Kalman filter averaging, named KBAG. Then, we developed a new ensemble method which is a Kalman filter ensemble of KBAGs, named DKBAG. Finally, we proposed a novel RUL prediction approach GN-DAFC-DKBAG in which the optimal noise-injected training dataset was determined by a GN-DAFC-based searching strategy and then inputted to a DKBAG model. Our approach is validated on the NASA C-MAPSS dataset of aero-engines. Experimental results show that our approach achieves significantly better performance than a traditional Kalman filter ensemble of single learning models (KESLM) and the original DKBAG approaches. We also found that the optimal noise-injected data could improve the prediction performance of both KESLM and DKBAG. We further compare our approach with two advanced ensemble approaches, and the results indicate that the former also has better performance than the latters. Thus, our approach of combining optimal noise injection and DKBAG provides an effective solution for RUL estimation of machinery systems.
Experiment on Nearest Level Modulation algorithm for FPGA based Modular Multilevel Converters
Tran Hung Cuong,Pham Viet Phuong,Tran Van Phuong,Tran Trong Minh 전력전자학회 2019 ICPE(ISPE)논문집 Vol.2019 No.5
Modular Multilevel Converters (MMC) have many advantages in comparison with conventional multilevel converters in application to high voltage system. However, the control system of MMC requires a large amount of I/O signal ports which cannot be generated by a single digital signal processor (DSP) with maximum I/O port of 24. This paper fucuses on the experimental results of aMMC that uses a Field Programmable Gate Array (FPGA) in which embedge the Nearest Level Modulation (NLM) method and capacitor voltage balancing algorithm. The MMC consists of 12 Sub-Modules (SM) in each phase to generate a 13-level ac output voltage. Applying the NLM method and capacitor voltage balancing algorithm have significantly reduced the switching frequency and produced an ac output voltage with very low harmonic distortion. The experimental results have verified by a laboratory-scale prototype and compared with the simulation results.
Bui Hung Thang,Pham Van Trinh,Le Dinh Quang,Nguyen Thi Huong,Phan Hong Khoi,Phan Ngoc Minh 한국물리학회 2014 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.65 No.3
Carbon nanotubes (CNTs) are some of the most valuable materials with high thermal conductivity. The thermal conductivity of individual multiwalled carbon nanotubes (MWCNTs) grown byusing chemical vapor deposition is 600 ± 100 Wm−1K−1 compared with the thermal conductivity419 Wm−1K−1 of Ag. Carbon-nanotube-based liquids – a new class of nanomaterials, have shownmany interesting properties and distinctive features offering potential in heat dissipation applicationsfor electronic devices, such as computer microprocessor, high power LED, etc. In this work,a multiwalled carbon-nanotube-based liquid was made of well-dispersed hydroxyl-functional multiwalledcarbon nanotubes (MWCNT-OH) in ethylene glycol (EG)/distilled water (DW) solutionsby using Tween-80 surfactant and an ultrasonication method. The concentration of MWCNT-OHin EG/DW solutions ranged from 0.1 to 1.2 gram/liter. The dispersion of the MWCNT-OH-basedEG/DW solutions was evaluated by using a Zeta-Sizer analyzer. The MWCNT-OH-based EG/DWsolutions were used as coolants in the liquid cooling system for the Intel Core i5 processor. Thethermal dissipation efficiency and the thermal response of the system were evaluated by directlymeasuring the temperature of the micro-processor using the Core Temp software and the temperaturesensors built inside the micro-processor. The results confirmed the advantages of CNTs inthermal dissipation systems for computer processors and other high-power electronic devices.