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Evaluation of cavitation erosion of a propeller blade surface made of composite materials
Nhut Pham-Thanh,Hoang Van Tho,염영진 대한기계학회 2015 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.29 No.4
Cavitation erosion strongly impacts the efficiency and strength of marine propellers. This is more important for propellers made fromdifferent types of composite materials. Thus, an investigation of cavitation erosion on the blade surface of composite ship propellers isnecessary. A small three-blade propeller was made from fiberglass combined with epoxy, polyester and gelcoat resin. This propeller wastested in a circulating water channel and revolution speed and depth were determined by conditions of cavitation number. Cavitation erosionwas observed and evaluated by images, weight loss and cavitation area. The results indicated that the cavitation erosion occurred atregions 0.4 R (Radius) and 0.7 R from the center, and cavitation also occurred randomly on pressure or suction surfaces and leading ortrailing edges. Most damaged regions propagated along the circumferential direction of the propeller. Among the blade materials, the Ge-GF blade had the best property. This material had the smallest cavitation area and the most stable cavitation area rate. The Po-GF blade hadthe worst property with strong progression of the cavitation area, and the Ep-GF blade was of medium quality with a small reduction of thedamage area rate. Besides, the depth of the damaged area of the Ge-GF blade was also lower than that of the Ep-GF and Po-GF blade.
Nhut Khai Hoan, Tran,Koo, Insoo IEEE 2017 IEEE SENSORS JOURNAL Vol.17 No.7
<P>Herein, the authors consider harvested energy powered cognitive radio networks (CRNs) in which harvested energy is stored in a rechargeable battery which has finite capacity. In addition, a practical scenario in which the amount of harvested power is finite is taken into account. Cognitive users (CUs) opportunistically access a licensed channel (or primary channel); meanwhile, it should be ensured that their confidential communications are not leaked to an eavesdropper. We investigate an optimal spectrum sensing schedule and the optimal amount of transmission energy for the CUs in each processing time slot. In particular, at the beginning of each time slot, based on the remaining energy in the battery, CU transmitter decides either: 1) to be active to sense the channel and transmit its data if the channel is found vacant or 2) to stay inactive during the current time slot in order to save energy and wait for more incoming energy for use in the next time slots. The decision is based on expected secrecy transmission rate calculated for both cases over subsequent K time slots. The proposed scheme aims to improve long-term secrecy transmission rate of CRNs in comparison with a conventional scheme where the decision for the current time slot is made to maximize current secrecy transmission rate without considering any future reward.</P>
A Wideband On-Chip Directional Coupler Using a Negative Capacitance Circuit
Doan, Nhut-Tan,Lai, Ngoc-Duy-Hien,Kim, Hyoungsoo,Yoon, Sang-Woong IEEE 2019 IEEE transactions on microwave theory and techniqu Vol.67 No.1
<P>We propose a wideband lumped element directional coupler using lossy negative capacitance (NCAP). NCAP provides a broadband resonance effect combined with passive inductors and capacitors in a circuit, enabling the coupler to exhibit wideband directivity performance. In addition, a 3-dB loss in the NCAP enhanced the bandwidth at the expense of the transmission gain, which decreased by only 0.3 dB. The proposed coupler was implemented in the IBM 7RF 180-nm CMOS technology. The size of the core chip is <TEX>$1180\,\,\mu \text {m} \times 570\,\,\mu \text{m}$</TEX>. The designed NCAP provides a capacitance of −13 pF using a supply voltage of 2.7 V and a current of 9.6 mA. The coupling was designed to be −10 dB at the center frequency of 1 GHz. The bandwidth was defined by the frequency range, which exhibited a directivity of more than 30 dB. The S-parameter measurements showed an absolute bandwidth ranging from 0.86 to 1.12 GHz, and a fractional bandwidth of 26%. In the bandwidth, the coupling had a 0.5-dB variation, the transmission loss was smaller than 2.14 dB, and the noise figures were 1.8–2.5 dB.</P>
Attitude Estimation using accelerometers with constrained external acceleration
Tri-Nhut Do,Sang Kyeong Park,Young Soo Suh 제어로봇시스템학회 2010 제어로봇시스템학회 국제학술대회 논문집 Vol.2010 No.10
An attitude algorithm from output vector of accelerometer was proposed with the assumption that the direction of external acceleration is precisely localized or relatively localized on a certain plane. Simulation and experimental results verify that the estimation performance of the proposed method is better than that of the conventional method.
Huynh Tan Nhut,Nguyen Tri Quang Hung,Tran Cong Sac,Nguyen Huynh Khanh Bang,Tran Quang Tri,Nguyen Trung Hiep,Nguyen Minh Ky 대한환경공학회 2020 Environmental Engineering Research Vol.25 No.5
This study evaluates the efficiency of domestic wastewater treatment via Sponge-Based Moving Bed Biofilm Reactor (S-MBBR). The laboratory-based treatment plan uses polyurethane sponge with a specific surface area was 260 ㎡/㎥ as a carrier. The treatment plan operated under four different organic load rate: OLR1 = 0.4 ㎏ BOD/㎥.day; OLR2 = 0.6 ㎏ BOD/㎥.day; OLR3 = 0.8 ㎏ BOD/㎥.day; and OLR4 = 1.0 ㎏ BOD/㎥.day. During 80 d of the experiment, the highest treatment efficiency was at the organic load rate of 0.4 ㎏ BOD/㎥.day, with COD, SS, TN and TP were found to be 85.0 ± 12.9%, 85.7 ± 5.3%, 68.9 ± 1.7%, and 40.3 ± 0.2%, respectively. In which, the influent SS concentration were from 117.3 to 126.0 ㎎/L, the effluent concentration were in ranged 18.0 to 34.22 ㎎/L, respectively. The values of influent and effluent COD were 298.8 ± 12.88 and 44.8 ± 3.78 ㎎/L in turn. The OLR1 influent TN, TP concentrations were respectively 47.9 ± 2.11 and 3.6 ± 0.15 ㎎/L; the effluent TN, TP concentration were 14.9 ± 0.18 and 2.2 ± 0.06 ㎎/L, respectively. The study suggests that the effluent is within the allowable limits of National technical regulation on domestic wastewater (Column B1), indicating the applicability of S-MBBR for the domestic wastewater treatment plant.